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  • 101.
    Keshavarzi, Neda
    et al.
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Chemical durability of hierarchically porous silicalite-I membrane substrates in aqueous media2013Ingår i: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 28, nr 17, s. 2253-2259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Zeolite-based supports for inorganic membranes intended for gas separation have the potential to increase the resistance to thermal shock-induced cracking compared with ceramic or metallic substrates. We have studied the effect of exposure at 90 °C of hierarchically porous silicalite-I substrates to aqueous solutions at pH 2.0, 10.6, and 13.0 for periods up to 168 h. Silicalite-I supports were produced in binder-free form by pulsed current processing and using clay-binders by conventional thermal treatment. Long-term (168 h) acid and alkali treatment of the silicalite-I substrates results in a slight removal of silicon (in acid) and aluminum (in alkali) and does not affect the specific surface area and the crystalline microporous structural features but broadens the size distribution of the macropores. The mechanical strength remains unchanged after exposure to both alkaline and acidic solutions and the binder-free substrates display more than 20 times higher strength than the binder-containing materials

  • 102.
    Keshavarzi, Neda
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Rad, Farshid Mashayekhy
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för analytisk kemi.
    Mace, Amber
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ansari, Farhan
    Akhtar, Farid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Nilsson, Ulrika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för analytisk kemi.
    Berglund, Lars
    Bergstrom, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Nanocellulose-zeolite composite coatings and films for odor elimination2014Konferensbidrag (Refereegranskat)
  • 103.
    Keshavarzi, Neda
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Rad, Farshid Mashayekhy
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för analytisk kemi.
    Mace, Amber
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ansari, Farhan
    Wallenberg Wood Science Centre, Royal Institute of Technology.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nilsson, Ulrika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för analytisk kemi.
    Berglund, Lars
    Kungliga tekniska högskolan, KTH, Luleå tekniska universitet, Wallenberg Wood Science Centre, Royal Institute of Technology.
    Bergström, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Nanocellulose-Zeolite Composite Films for Odor Elimination2015Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, nr 26, s. 14254-14262Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Free standing and strong odor-removing composite films of cellulose nanofibrils (CNF) with a high content of nanoporous zeolite adsorbents have been colloidally processed. Thermogravimetric desorption analysis (TGA) and infrared spectroscopy combined with computational simulations showed that commercially available silicalite-1 and ZSM-5 have a high affinity and uptake of volatile odors like ethanethiol and propanethiol, also in the presence of water. The simulations showed that propanethiol has a higher affinity, up to 16%, to the two zeolites compared with ethanethiol. Highly flexible and strong free-standing zeolite CNF films with an adsorbent loading of 89 w/w% have been produced by Ca-induced gelation and vacuum filtration. The CNF-network controls the strength of the composite films and 100 mu m thick zeolite CNF films with a CNF content of less than 10 vol % displayed a tensile strength approaching 10 MPa. Headspace solid phase microextraction (SPME) coupled to gas chromatography mass spectroscopy (GC/MS) analysis showed that the CNF zeolite films can eliminate the volatile thiol-based odors to concentrations below the detection ability of the human olfactory system. Odor removing zeolite-cellulose nanofibril films could enable improved transport and storage of fruits and vegetables rich in odors, for example, onion and the tasty but foul-smelling South-East Asian Durian fruit.

  • 104.
    Kong, Ge
    et al.
    Oxidation Experimental Study and Photocatalytic Properties.
    Du, Xiaoni
    Oxidation Experimental Study and Photocatalytic Properties.
    Cai, Xiaoping
    Oxidation Experimental Study and Photocatalytic Properties.
    Feng, Peizhong
    Oxidation Experimental Study and Photocatalytic Properties.
    Wang, Xiaohong
    Oxidation Experimental Study and Photocatalytic Properties.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Recycling Molybdenum Oxides from Waste Molybdenum Disilicides: Oxidation Experimental Study and Photocatalytic Properties2019Ingår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 92, nr 1-2, s. 1-12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To recycle elemental molybdenum from waste molybdenum disilicide (MoSi2) heating elements, the MoSi2 was first disintegrated to MoO3 and SiO2 powders in air at a pest oxidation temperature of 500 °C. X-ray diffraction (XRD) patterns confirmed the completion of the pest oxidation reaction. The mixture of MoO3 and SiO2 powders were heated to 950 °C in a tube furnace to evaporate MoO3, and the XRD patterns of the residue showed that only SiO2 was left in the crucible, confirming that the MoO3 was removed through thermal evaporation. The collected MoO3 crystals had a striped morphology. Photocatalytic performance of MoO3 showed superior activity in comparison with commercial MoO3 and P25 for the degradation of methylene blue under visible light irradiation. The photocatalytic degradation activity of MoO3 synthesized by thermal evaporation at 950 °C was 99.25% in 60 min.

  • 105.
    Lal, Garima
    et al.
    University of Calgary, Calgary, Canada.
    Derakhshandeh, Maziar
    University of Calgary, Calgary, Canada.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Spasyuk, Denis M.
    Canadian Light Source, Saskatoon, Canada.
    Lin, Jian-Bin
    University of Calgary, Calgary, Canada.
    Trifkovic, Milana
    University of Calgary, Calgary, Canada.
    Shimizu, George K. H.
    University of Calgary, Calgary, Canada.
    Mechanical Properties of a Metal−Organic Framework formed by Covalent Cross-Linking of Metal−Organic Polyhedra2019Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, nr 2, s. 1045-1053Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Overcoming the brittleness of metal-organic frameworks (MOFs) is a challenge for industrial applications. To increase the mechanical strength, MOFs have been blended with polymers to form composites. However, this also brings challenges, such as integration and integrity of MOF in the composite, which can hamper the selectivity of gas separations. In this report, an "all MOF" material with mechanical flexibility has been prepared by covalent cross-linking of metal-organic polyhedra (MOPs). The ubiquitous Cu 24 isophthalate MOP has been decorated with a long alkyl chain having terminal alkene functionalities so that MOPs can be cross-linked via olefin metathesis using Grubbs second generation catalyst. Different degrees of cross-linked MOP materials have been obtained by varying the amount of catalyst in the reaction. Rheology of these structures with varying number of cross-links was performed to assess the cross-link density and its homogeneity throughout the sample. The mechanical properties were further investigated by the nanoindentation method, which showed increasing hardness with higher cross-link density. Thus, this strategy of cross-linking MOPs with covalent flexible units allows us to create MOFs of increasing mechanical strength while retaining the MOP cavities.

  • 106.
    Liu, Yanan
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou, .
    Cai, Xiaoping
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou .
    Sun, Zhi
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou .
    Jiao, Xinyang
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wang, Jianzhong
    State Key Laboratory of Porous Metal Materials, Northwest Institute for Non-ferrous Metal Research, Xi'an .
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    A novel fabrication strategy for highly porous FeAl/Al2O3 composite by thermal explosion in vacuum2018Ingår i: Vacuum, ISSN 0042-207X, Vol. 149, s. 225-230Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The high porosity of FeAl/Al2O3 composites was successfully prepared via a low-energy consumption method of thermal explosion (TE) in vacuum from reactant mixtures of Fe, Al and Fe2O3. The temperature profiles, phase compositions, microstructure, porosity and pore size of the products were investigated. The TE reactions were ignited between 639 and 648 °C and maximum combustion temperatures reached to 1196–1867 °C. XRD patterns showed that FeAl, Fe2Al5 and Al2O3 were formed via TE reaction, and FeAl and Al2O3 were evolved as dominant phase after the final sintering at 1100 °C. The FeAl/Al2O3 composites exhibited an interconnected pore structure with porosities and pore size of 52–61% and 27–32 μm, respectively.

  • 107.
    Liu, Yanan
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China.
    Cai, Xiaoping
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China.
    Sun, Zhi
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China.
    Zhang, Hanzhu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Czujko, Tomasz
    Faculty of Advanced Technologies and Chemistry, Department of Advanced Materials and Technologies, Military University of Technology, 00‐908 Warszawa, Poland.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China.
    Fabrication and Characterization of Highly Porous FeAl‐Based Intermetallics by Thermal Explosion Reaction2019Ingår i: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 21, nr 4, artikel-id 1801110Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porous FeAl-based intermetallics with different nominal compositions ranging from Fe–40 at% Al to Fe–60 at% Al are prepared by a novel process of thermal explosion (TE) mode. The results show that the Al content significantly affects the combustion behavior of the specimens, the ignition temperature of the Fe–Al intermetallics varies from 641 to 633 °C and the combustion temperature from 978 to 1179 °C. The porous materials exhibit uniform pore structures with porosities and average pore sizes of 52–61% and 20–25 µm, respectively. The TE reaction is the dominant pore formation mechanism regardless of the alloy composition. However, differences in the porosity and average pore size are observed depending on the Al content. The compressive strength of porous Fe–Al intermetallics is in the range of 23–34 MPa, duly applied as filters. Additionally, a surface alumina layer is formed at the early stage and both of the oxidation process and the sulfidation process follows the familiar parabolic rate law in the given atmosphere, exhibiting excellent resistance to oxidation and sulfidation. These results suggest that the porous Fe–Al intermetallics are promising materials for applications in harsh environments with a high-temperature sulfide-bearing atmosphere, such as in the coal chemical industry.

  • 108.
    Liu, Yang
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Zhang
    School of Material Science and Engineering, China University of Mining and Technology, Xuzhou.
    Jiao, Xinyang
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Novel Fabrication and Enhanced Photocatalytic MB Degradation of Hierarchical Porous Monoliths of MoO3 Nanoplates2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, nr 1, artikel-id 1845Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porous monoliths of MoO3 nanoplates were synthesized from ammonium molybdate (AHM) by freeze-casting and subsequent thermal treatment from 300 to 600 °C. Pure orthorhombic MoO3 phase was obtained at thermal treatment temperature of 400 °C and above. MoO3 monoliths thermally treated at 400 °C displayed bimodal pore structure, including large pore channels replicating the ice crystals and small pores from MoO3 sheets stacking. Transmission electron microscopy (TEM) images revealed that the average thicknesses of MoO3 sheet were 50 and 300 nm in porous monoliths thermally treated at 400 °C. The photocatalytic performance of MoO3 was evaluated through degradation of methylene blue (MB) under visible light radiation and MoO3 synthesized at 400 °C exhibited strong adsorption performance and best photocatalytic activity for photodegradation of MB of 99.7% under visible illumination for 60 min. MoO3 photocatalyst displayed promising cyclic performance, and the decolorization efficiency of MB solution was 98.1% after four cycles

  • 109.
    Melk, Latifa
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mouzon, Johanne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Turon-Vinas, Miquel
    CIEFMA—Department of Materials Science and Metallurgical Engineering, ETSEIB, Universitat Politècnica de Catalunya.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Antti, Marta-Lena
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Anglada, Marc
    Department of Materials Science and Engineering, Universitat Politècnica de Catalunya, Barcelona, Universitat Politècnica de Catalunya, Universidad de Extremadura.
    Surface microstructural changes of Spark Plasma Sintered Zirconia after grinding and annealing2016Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 42, nr 14, s. 15610-15617Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spark plasma sintered zirconia (3Y-TZP) specimens have been produced of 140 nm 372 nm and 753 nm grain sizes by sintering at 1250 C, 1450 C and 1600 C, respectively. The sintered zirconia specimens were grinded using a diamond grinding disc with an average diamond particle size of about 60 µm, under a pressure of 0.9 MPa. The influence of grinding and annealing on the grain size has been analysed. It was shown that thermal etching after of ruff grinding of specimens at 1100 C for one hour induced an irregular surface layer of about a few hundred nanometres in thickness of recrystallized nano-grains, independently of the initial grain size. However, if the ground specimens were exposed to higher temperature, e.g. annealing at 1575 °C for one hour, the nano-grain layer was not observed and the final grain size was similar to that achieved by the same heat treatments on carefully polished specimens. Therefore, by appropriate grinding and thermal etching treatments, nanograined surface layer can be obtained which increases the resistance to low temperature degradation.

  • 110.
    Narang, Kritika
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Fodor, Kristina
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Kaiser, Andreas
    Department of Energy Conversion, Technical University of Denmark, Roskilde 4000, Denmark.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Optimized cesium and potassium ion-exchanged zeolites A and X granules for biogas upgrading2018Ingår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 8, nr 65, s. 37277-37285Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Partially ion-exchanged zeolites A and X binderless granules were evaluated for CO2 separation from CH4. The CO2 adsorption capacity and CO2-over-CH4 selectivity of binderless zeolites A and X granules were optimized by partial exchange of cations with K+ and Cs+, while retaining the mechanical strength of 1.3 MPa and 2 MPa, respectively. Single gas CO2 and CH4 adsorption isotherms were recorded on zeolites A and X granules and used to estimate the co-adsorption of CO2–CH4 using ideal adsorbed solution theory (IAST). The IAST co-adsorption analysis showed that the partially ion-exchanged binderless zeolites A and X granules had a high CO2-over-CH4 selectivity of 1775 and 525 respectively, at 100 kPa and 298 K. Optimally ion-exchanged zeolite X granules retained 97% of CO2 uptake capacity, 3.8 mmol g−1, after 5 breakthrough adsorption–desorption cycles while for zeolite A ion-exchanged granules the reduction in CO2 uptake capacity was found to be 18%; CO2uptake capacity of 3.4 mmol g−1. The mass transfer analysis of breakthrough experimental data showed that the ion-exchanged zeolite X had offered a higher mass transfer coefficient, (κ) through the adsorption column compared to zeolite A; 0.41 and 0.13 m s−1 for NaK4.5Cs0.3X and CaK2.5Cs0.2A, respectively

  • 111.
    Nikjoo, Dariush
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Porous polymeric membranes as CO2 adsorbents2017Konferensbidrag (Refereegranskat)
  • 112.
    Nikjoo, Dariush
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Structured emulsion-templated porous copolymer based on photopolymerization for carbon capture2017Ingår i: Journal of CO2 Utilization, ISSN 2212-9820, E-ISSN 2212-9839, Vol. 21, s. 473-479Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porous hydrogel copolymers of acrylamide (AAM) and acrylic acid (AAC) were structured in the form of monoliths and granules. AAM-co-AAC porous copolymer monoliths were synthesized using high internal phase emulsion (HIPE) as template and photopolymerization. For granulation, photopolymerization was used for the fabrication of the AAM-co-AAC hydrogel, which was subsequently freeze-granulated. The structural analysis (FTIR and XRD) confirmed the successful synthesis of hydrogel copolymers. The CO2 uptake capacity of structured AAM-co-AAC copolymers was evaluated through adsorption and absorption mechanisms by volumetric and gravimetric methods, respectively. The granules exhibited the CO2 adsorption uptake of 0.8 mmol g-1 at 25 kPa and 298 K. The CO2 and N2 adsorption data demonstrated that the hydrogel copolymers were selective for CO2. Furthermore, the granules were capable of capturing CO2 in the presence of water. The results of absorption of CO2 on water-swollen granules demonstrated that CO2-uptake capacity increases with increasing water content up to 1.8 mmol g-1.

  • 113.
    Nikjoo, Dariush
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Perrot, Virginie
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Laminated Porous Diatomite Monoliths for Adsorption of Dyes From Water2019Ingår i: Environmental Progress & Sustainable Energy, ISSN 1944-7442, E-ISSN 1944-7450, Vol. 38, nr s1, s. 377-385Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Structured laminated diatomite monoliths with superior mechanical properties were prepared by controlled freeze-casting of the aqueous suspensions of diatomite powders for wastewater treatment. The directional freezing of suspensions with solids loading of 25, 30, and 37 wt % at cooling from 0.5 to 5 K/min resulted in the formation of lamellar pores and solid walls with the thickness of 12–30 and 14–39 μm, respectively. The increase in solid loading and freezing rate resulted in refinement of the porous structure. Durable monoliths with the mechanical strength of 5.3 MPa were obtained by thermal treatment of the freeze-dried green bodies at 1,373 K. Diatomite monoliths with a pore size of 29.6 μm showed the removal of model dye pollutant Rhodamine B from water by adsorption and long-term water stability. The dye uptake capacity of monolith changed from 1.38 to 17.04 mg/g for the initial dye concentrations between 1.0 and 12.5 mg/L at 298 K and pH = 6, respectively. The adsorption data analysis using Lagergren's pseudo-first-order, pseudo-second-order, and intra-particle diffusion models revealed that diatomite monoliths offered efficient mass transfer in the porous laminated scaffold and to the adsorption sites and bulk diffusion of dye molecules in water was the rate-limiting mechanism for dye removal. © 2018 American Institute of Chemical Engineers Environ Prog, 2018.

  • 114.
    Ogunmuyiwa, Enoch N.
    et al.
    School of Chemical & Metallurgical Engineering, University of the Witwatersrand.
    Sacks, Natasha
    School of Chemical & Metallurgical Engineering, University of the Witwatersrand.
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Department of Materials and Environmental Chemistry, Stockholm University.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effect of 10wt%VC on the friction and sliding wear of spark plasma sintered WC-12wt%Co cemented carbides2017Ingår i: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 60, nr 2, s. 276-283Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of 10wt%VC addition on the friction and sliding wear response of WC-12wt%Co cemented carbides produced by spark plasma sintering (SPS) was studied. The SPS of WC-12wt%Co alloys with and without 10wt% VC, at 1100 °C and 1130 °C respectively, yielded dense materials with minimal porosity. No eta phase was found in any of the alloys. The WC-12wt%Co-10wt%VC alloy showed the formation of the hard WV4C5 phase, which improved the alloy hardness. Friction and dry sliding wear tests were done using a ball-on-disk configuration under an applied load of 10 N, a sliding speed of 0.26 m.s−1, and a 100Cr-steel ball used as the counterface. A significant improvement in the sliding wear response of the harder and more fracture tough WC-12wt%Co-10wt%VC alloy compared to the WC-12wt%Co alloy was found. Analysis of the worn surfaces by scanning electron microscopy showed that the wear mechanisms included plastic deformation, preferential binder removal, adhesion, and carbide grain cracking and fragmentation.  

  • 115.
    Ojuva, Arto
    et al.
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Tomsia, Antoni P
    Materials Sciences Division, Lawrence Berkeley National Laboratory.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Laminated adsorbents with very rapid CO2 uptake by freeze-casting of zeolites2013Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, nr 7, s. 2669-2676Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Structured zeolite 13X monoliths with a laminated structure and hierarchical macro-/microporosity were prepared by freeze-casting aqueous suspensions of zeolite 13X powder, bentonite, and polyethylene glycol. Colloidally stable suspensions with a low viscosity at both room temperature and near freezing could be prepared at alkaline conditions where both the zeolite 13X powder and bentonite carry a negative surface charge. Slow directional freezing of the suspensions led to the formation of well-defined and thin lamellar pores and pore walls while fast freezing resulted in more cylindrical pores. The wall thickness, which varied between 8 and 35 μm, increased with increasing solids loading of the suspension. Thermal treatment at 1053 K of the freeze-cast bodies containing between 9 and 17 wt % bentonite resulted in mechanically stable zeolite 13X monoliths. The monoliths displayed a carbon dioxide uptake capacity of 4–5 mmol/g and an uptake kinetics characterized by a very fast initial uptake where more than 50% of the maximum uptake was reached within 15 s. Freeze-cast laminated zeolite monoliths could be used to improve the volumetric efficiency and reduce the cycle time, of importance in, for example, biogas upgrading and CO2 separation from flue gas.

  • 116.
    Ojuva, Arto
    et al.
    Stockholm University, Department of Materials and Environmental Chemistry.
    Järveläinen, Matti
    Tampere University of Technology, Department of Materials Science.
    Bauer, Marcus
    Department of Materials and Environmental Chemistry, Stockholm University.
    Keskinen, Lassi
    Tampere University of Technology, Department of Materials Science.
    Valkonen, Masi
    Department of Signal Processing, Tampere University of Technology.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Levänen, Erkki
    Group of Tribology and Machine Elements, Department of Materials Science, Tampere University of Technology.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Mechanical performance and CO2 uptake of ion-exchanged zeolite A structured by freeze-casting2015Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, nr 9, s. 2607-2618Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Zeolite 4A has been freeze-cast into highly porous monoliths with a cylindrical shape. The brittle monoliths, with lamellar or columnar pores and wall thicknesses between 8 and 35 μm, show a compressive mechanical response along the main pore axis that could be modeled by a buckling behavior. The failure strength is proportional to the density and the amount of transverse bridging across lamella, which was shown to be related to the pore cross-sectional aspect ratio. Monoliths with highly anisotropic pores with a cross-sectional aspect ratio higher than 3 yielded sequentially from the top surface, whereas monoliths with a pore aspect ratio lower than 3 were found to delaminate into longitudinal splinters. The freeze-cast monoliths show a sharp gas breakthrough front with a 1:9 mixture of CO2 and N2, indicating rapid uptake kinetics of the lamellar structures.

  • 117.
    Ran, Huashen
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Liu, Zhengsheng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Xu, Cheng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Jianzhong
    State Key Laboratory of Porous Metal Materials, Northwest Institute for Non-ferrous Metal Research, Xi’an.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Processing, microstructure and properties of hierarchically porous Cu2016Ingår i: Materials Express, ISSN 2158-5849, Vol. 6, nr 3, s. 271-276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hierarchically porous Cu with controlled pore characteristics and mechanical properties were fabricated from CuO powders and NaCl as template. NaCl particles were removed by dissolution from the pre-sintered CuO pellet using deionized water. CuO was decomposed to Cu during sintering at 900 °C in vacuum and resulted in porous Cu with bimodal pores. The porosity of porous Cu increased with increased NaCl content in the initial CuO pellet. The compression strength tests suggested that highly porous Cu were suitable for high impact energy absorption applications. Moreover, porosity, pore size and shape and mechanical properties of porous Cu could be tailored by tailoring the morphology and volume fraction of NaCl particles in the initial CuO pellet

  • 118.
    Ran, Huashen
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Song, Binbin
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Niu, Ijnan
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    wang, Xiaohong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Jianzhong
    State Key Laboratory of Porous Metal Materials, Northwest Institute for Non-ferrous Metal Research, Xi’an.
    Ge, Yuan
    State Key Laboratory of Porous Metal Materials, Northwest Institute for Non-ferrous Metal Research, Xi’an.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Microstructure and properties of Ti5Si3-based porous intermetallic compounds fabricated via combustion synthesis2014Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 612, s. 337-342Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porous titanium silicides (Ti5Si3-based) were produced by combustion synthesis process from reaction mixtures of titanium to silicon in varying molar ratios. The effects of combustion characteristics of the reaction mixtures on the phase formation, microstructure, porosity, pore size and compressive strength of porous titanium silicide intermetallic compounds were investigated. The results showed that the flame-front propagation velocity and temperature of the combustion reaction were the maximum for the reaction mixture containing Ti and Si in the ratio of 5 to 3 (Ti5Si3), 32.7 mm/s and 2205 K, respectively. X-ray diffraction analysis confirmed that the dominant phase formed was Ti5Si3 in all combustion synthesized porous intermetallic compounds. Ti5Si3-based intermetallic compounds were highly porous. The porosity and pore size of these intermetallics were dependent on the initial composition of the reaction mixture. The total and open porosities of Ti5Si3-based intermetallics varied from 33 to 61% and 17 to 55%, respectively. The porous titanium silicide intermetallic materials displayed high mechanical strength, in the range of 6-35 MPa, duly required for their use as filters.

  • 119.
    Saeidi, Kamran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Subgrain-controlled grain growth in the laser-melted 316 L promoting strength at high temperatures2018Ingår i: Royal Society Open Science, E-ISSN 2054-5703, Vol. 5, nr 5, artikel-id 172394Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Stainless steel 316 L prepared by laser melting consisted of a hierarchical austenitic microstructure with micrometresized (10–25 µm) grains containing fine 1 µm subgrains with a cellular structure. At high-temperature thermal treatments (greater than or equal to 1100°C), merging and growth of the 1 µm subgrains into bigger subgrains restricted the rapid grain growth and microstructure coarsening. Partial phase transformation of austenite to ferrite at temperatures greater than or equal to 1100°C, in combination with gradual and steady growth of subgrains inside the micrometre-sized grains and nucleation of the sigma phase, has promoted the tensile strength of stainless steel 316 L to 300 MPa at 1100°C compared with that of conventionally made 316 L counterparts (approx. 40 MPa). The grain growth mechanism of the laser-melted microstructure can change the application criteria for 316 L and expand the application fields for 316 L.

  • 120.
    Saeidi, Kamran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Alvi, Sajid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lofaj, Frantisek
    Department of Ceramics, Institute of Mater. Res. of the Slovak Academy of Sciences, Košice, Slovakia.
    Petkov, Valeri Ivanov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Advanced Mechanical Strength in Post Heat Treated SLM 2507 at Room and High Temperature Promoted by Hard/Ductile Sigma Precipitates2019Ingår i: Metals, E-ISSN 2075-4701, Vol. 9, nr 2, artikel-id 199Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Duplex stainless steel, 71 wt.% austenite, 13 wt.% ferrite and 16 wt.% sigma, was made upon heat treating of fully ferritic as-built selective laser melted (SLM) 2507 stainless steel at 1200 °C. Formation of sigma phase in the heat treated SLM 2507 was investigated using optical microscopy and scanning electron microscopy (SEM). The heat treated SLM 2507 demonstrated a yield strength of 686 MPa, ultimate tensile strength of 920 MPa and an elongation of 1.8% at room temperature with a brittle fracture morphology. Precipitation of sigma phase during heat treatment and slow cooling improved the mechanical and wear properties at high temperatures (1200 °C and 800 °C, respectively). The tensile strength and elongation of the heat treated SLM 2507 was measured 400 MPa and 20% as compared to casted duplex steel with 19 MPa and 30% elongation at 1200 °C. The 20 times higher mechanical strength as compared to casted duplex steel was attributed to sigma precipitates. Tribological behaviour of heat treated duplex SLM 2507 containing sigma at 800 °C showed very low wear rate of 4.5 × 10−5 mm3/mN compared to casted duplex steel with 1.6 × 10−4 mm3/mN.

  • 121.
    Saeidi, Kamran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Neikter, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Olsen, J.
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Shen, Zhijian James
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    316L stainless steel designed to withstand intermediate temperature2017Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 135, s. 1-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Austenitic stainless steel 316L was fabricated for withstanding elevated temperature by selective laser melting (SLM). Tensile tests at 800 °C were carried out on laser melted 316L with two different strain rates of 0.05 S− 1 and 0.25 S− 1. The laser melted 316L showed tensile strength of approximately 400 MPa at 800 °C, which was superior to conventional 316L. Analysis of fracture surface showed that the 316L fractured in mixed mode, ductile and brittle fracture, with an elongation of 18% at 800 °C. In order to understand the mechanical response, laser melted 316L was thermally treated at 800 °C for microstructure and phase stability. X-ray diffraction (XRD) and Electron back scattered diffraction (EBSD) of 316L treated at 800 °C disclosed a textured material with single austenitic phase. SEM and EBSD showed that the characteristic and inherent microstructure of laser melted 316L, consisting of elongated grains with high angle grain boundaries containing subgrains with a smaller misorientation, remained similar to as-built SLM 316L during hot tensile test at 800 °C. The stable austenite phase and its stable hierarchical microstructure at 800 °C led to the superior mechanical response of laser melted 316L.

  • 122.
    Saeidi, Kamran
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Zapata, Daniel Leon
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lofaj, Frantisek
    Institute of Materials Research of the Slovak Academy of Sciences, Watsonova, Košice, Slovakia.
    Kvetkova, Lenka
    Institute of Materials Research of the Slovak Academy of Sciences, Košice, Slovakia.
    Olsen, Jon
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden.
    Shen, Zhijian
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ultra-high strength martensitic 420 stainless steel with high ductility2019Ingår i: Additive Manufacturing, ISSN 2214-8604, Vol. 29, artikel-id 100803Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Martensitic 420 stainless steel was successfully fabricated by Selective laser melting(SLM) with >99% relative density and high mechanical strength of 1670 MPa, yield strength of 600 MPa and elongation of 3.5%. X-ray diffraction (XRD) and scanning electron microscopy disclosed that the microstructure of SLM 420 consisted of colonies of 0.5–1 μm sized cells and submicron martensitic needles with 11 wt. % austenite. Tempering of as-built SLM 420 stainless steel at 400 °C resulted in ultra-high strength material with high ductility. Ultimate tensile strength of 1800 MPa and yield strength of 1400 MPa were recorded with an elongation of 25%. Phase transformation analysis was carried out using Rietveld refinement of XRD data and electron backscattered diffraction (EBSD), which showed the transformation of martensite to austenite, and resulted in austenite content of 36 wt. % in tempered SLM 420 stainless steel. Transformation induced plasticity (TRIP), austenite formation and fine cellular substructure along with sub-micron martensite needles resulted in stainless steel with high tensile strength and ductility. The advanced mechanical properties were compared with conventionally made ultra-high-strength steels, and the microstructure-properties relationships were disclosed.

  • 123.
    Shah, Faiz Ullah
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Khan, Muhammad Saif Ullah
    Department of Chemistry, Quaid-i-Azam University, Islamabad.
    Akhter, Zareen
    Department of Chemistry, Quaid-i-Azam University, Islamabad.
    Antzutkin, Oleg
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Solid-state 13C, 15N and 29Si NMR characterization of block copolymers with CO2 capture properties2016Ingår i: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 54, nr 9, s. 734-739Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Natural abundance solid-state multinuclear (13C, 15N and 29Si) cross-polarization magic-angle-spinning NMR was used to study structures of three block copolymers based on polyamide and dimethylsiloxane and two polyamides, one of which including ferrocene in its structure. Assignment of most of the resonance lines in 13C, 15N and 29Si cross-polarization magic angle-spinning NMR spectra were suggested. A comparative analysis of 13C isotropic chemical shifts of polyamides with and without ferrocene has revealed a systematic shift towards higher δ -values (de-shielding) explained as the incorporation of paramagnetic ferrocene into the polyamide backbone. In addition, the 13C NMR resonance lines for ferrocene-based polyamide were significantly broadened, because of paramagnetic effects from ferrocene incorporated in the structure of this polyamide polymer. Single resonance lines with chemical shifts ranging from 88.1 to 91.5ppm were observed for 15N sites in all of studied polyamide samples. 29Si chemical shifts were found to be around 22.4ppm in polydimethylsiloxane samples that falls in the range of chemical shifts for alkylsiloxane compounds. The CO2 capture performance of polyamide-dimethylsiloxane-based block copolymers was measured as a function of temperature and pressure. The data revealed that these polymeric materials have potential to uptake CO2 (up to 9.6 cm3 g1) at ambient pressures and in the temperature interval 30–40 °C. Copyright ©2016 John Wiley & Sons, Ltd.

  • 124.
    Shah, Faiz Ullah
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Bhattacharyya, Shubhankar
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Filippov, Andrei
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ionic Liquids As Liquid And Solid Sorbents For Post-Combustion CO2 Capture2016Konferensbidrag (Refereegranskat)
  • 125.
    Shakarova, Dilshod
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ojuva, Arto
    Stockholm University, Department of Materials and Environmental Chemistry.
    Bergström, Lennart Magnus
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Methylcellulose-directed synthesis of nanocrystalline zeolite NaA with high CO2 uptake2014Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 7, nr 8, s. 5507-5519Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Zeolite NaA nanocrystals with a narrow particle size distribution were prepared by template-free hydrothermal synthesis in thermo-reversible methylcellulose gels. The effects of the amount of methylcellulose, crystallization time and hydrothermal treatment temperature on the crystallinity and particle size distribution of the zeolite NaA nanocrystals were investigated. We found that the thermogelation of methylcellulose in the alkaline Na2O-SiO2-Al2O3-H2O system played an important role in controlling the particle size. The synthesized zeolite nanocrystals are highly crystalline, as demonstrated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) shows that the nanocrystals can also display a well-defined facetted morphology. Gas adsorption studies on the synthesized nanocrystalline zeolite NaA showed that nanocrystals with a size of 100 nm displayed a high CO2 uptake capacity (4.9 mmol/g at 293 K at 100 kPa) and a relatively rapid uptake rate compared to commercially available, micron-sized particles. Low-cost nanosized zeolite adsorbents with a high and rapid uptake are important for large scale gas separation processes, e.g., carbon capture from flue gas.

  • 126.
    Tian, Jian-jun
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Qu, Xuan-hui
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Zhang, Shen-gen
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Akhtar, Farid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Tao, Si-Wu
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Du, Xue-Li
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Influence of heat treatment on fracture and magnetic properties of radially oriented Sm 2 Co 17 permanent magnets2007Ingår i: Transactions of Nonferrous Metals Society of China, ISSN 1003-6326, E-ISSN 2210-3384, Vol. 17, nr 3, s. 491-495Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The quenching, fracture and aging treatment of radially oriented Sm2Co17 ring magnets were investigated. The results indicate that the ring magnets have obvious anisotropy of thermal expansion, which easily leads to the splits of the magnets during quenching. The fracture is brittle cleavage fracture. The difference (δa) of the expansion coefficient reaches the maximum value at 800–850 °C. So, various quenching processes at different steps are adopted in order to reduce the splits. When the magnets are aged. 1:5 phase precipitates from the 2:17 matrix phase and forms a cellular microstructure with 2:17 phase. BHmax and 3Hc reach the maximum value 226 kJ/m3 and 2170 kA/m after being aged at 850 °C for 4 h and 8 h, respectively. The aging treatment at 850 °C has little influence on remanence(Br), which can always keep a high value (≥1.0 T). Through appropriate heat treatment, the ring magnets have uniform cellular microstructure and excellent magnetic properties: Br1.0T, 3Hc≥2 100 kA/m, BHmax≥220 kJ/m3.

  • 127.
    Tian, Jianjun
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Qu, Xuanhui
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Zhang, Shengen
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Cui, Dawei
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Akhtar, Farid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Magnetic properties and microstructure of radially oriented Sm (Co, Fe, Cu, Zr) z ring magnets2007Ingår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 61, nr 30, s. 5271-5274Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Radially oriented Sm(Co,Fe,Cu,Zr)z ring magnets are prepared by powder metallurgy with appropriate magnetic field molding, sintering process and aging treatment. The results indicate that radially oriented Sm(Co,Fe,Cu,Zr)z ring magnets have obvious anisotropy of thermal expansion and sintering shrinkage, which easily lead to the splits and deformation of the ring magnets. So, slow heating, vacuum pre-sintering in sintering process and various quenching processes at different steps during quenching are adopted. The magnets have excellent magnetic properties: Br = 10.8 kGs, Hcj = 27.6 kOe, BHmax = 28.1 MGOe. Besides, there is a uniform magnetization field on the surface of the ring magnets. The average surface magnetization field (View the MathML sourceBs―) is 1.502 kGs. The deviation from average (α) is only 4.2%. The microstructure of the magnets consists of a mixture of homogeneous cellular and lamella structures.

  • 128.
    Tian, Jianjun
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Zhang, Shengen
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Qu, Xuanhui
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Akhtar, Farid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Tao, Siwu
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Behavior of residual carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets2007Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 440, nr 1-2, s. 89-93Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When sintered Sm(Co, Fe, Cu, Zr)z permanent magnets are prepared by metal injection molding, some organic binders are added in alloy powder, which leads to much residual carbon in the magnets. The residual carbon decreases magnetic properties and destroys the microstructure of the magnets. In this paper, the behavior of carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets has been studied. The results indicate that Sm(Co, Fe, Cu, Zr)z magnets can keep excellent magnetic properties when the carbon content is below 0.1 wt.%: Br ≥ 10 kGs, Hcj ≥ 22 kOe, BHmax ≥ 25 MGOe. When the carbon content is above 0.1 wt.%, Br, Hcj and BHmax decrease with increasing carbon content evidently. Carbon consumes Zr content and forms ZrC, which reduces the volume fraction of the lamella and Sm(Co, Cu)5 phases. Thus, the cell size increases and the cellular microstructure deteriorates. When the carbon content reaches 0.43 wt.%, there is not enough Sm(Co, Cu)5 phase to form a uniform cellular microstructure. Br, Hcj and BHmax are approximate to zero. Since carbon has little influence on the content of Sm2(Co, Fe)17 phase, Ms can keep a high value (≥100 emu/g). ZrC has high melting point (3420 °C) and acts as dispersion particle in the magnets, which prevents the grains of SEM structure growing and reduces the liquid content of green compacts during sintering. Therefore, the density of the magnets decreases

  • 129.
    Wang, Jiandong
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Niu, Jinan
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Guo, Ruixia
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Liu, Zhangsheng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Synthesis, microstructure and properties of MoSi2-5vol.%Al2O3 composites2014Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 40, nr 10 Part B, s. 16381-16387Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    MoSi2-5vol.%Al2O3 composites were prepared in situ by self-propagating combustion synthesis from Mo, Si, Al and MoO3 powders. The combustion mode and temperature of the self-propagating reaction and phase composition of the product were investigated. The results showed that the combustion mode was a steady-state self-propagating process and the composite product was composed of MoSi2 and Al2O3. MoSi2-5vol.%Al2O3 composites were consolidated by vacuum hot-pressed sintering from 1300 to 1600 °C to produce composites with high density. MoSi2-5vol.%Al2O3 composites sintered at 1400 °C exhibited a fine microstructure and excellent mechanical properties: grain size ∼5 μm, Vicker’s hardness 11.14 GPa, bending strength 435 MPa, and fracture toughness 4.53 MPa.m1/2.

  • 130.
    Wang, Xiaohong
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Wu, Jie
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Liu, Weisheng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Qiang, Yinghuai
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Zhenzhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Effects of tungsten and aluminum additions on the formation of molybdenum disilicide by mechanically-induced self-propagating reaction2010Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 490, nr 1, s. 388-392Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of tungsten and aluminum additions to Mo–Si system on the formation of MoSi2 by mechanically-induced self-propagating reaction in a high-energy ball mill were investigated by X-ray diffraction. The incubation time for mechanically-induced self-propagating reaction to form MoSi2 was 90 min in Mo–Si system. With the addition of tungsten to Mo–Si system, the incubation time of mechanically-induced self-propagating reaction of (Wx,Mo1−x)Si2 system was prolonged. It was due to the decrease of adiabatic temperature with increase in x, and the mechanically-induced self-propagating reaction was not observed until 150 min of high-energy milling in (Wx,Mo1−x)Si2 powder sample with x equals to 0.4. Conversely, the minor aluminum (y < 0.2 in Mo(Si1−y,Aly)2 system) substituting for silicon had shorten the incubation period and accelerated the reaction. When tungsten and aluminium were added simultaneously to Mo–Si system, the mechanically-induced self-propagating reaction was observed in (W0.1,Mo0.9)(Si0.9,Al0.1)2 sample, but it was not observed in (W0.2,Mo0.8)(Si0.8,Al0.2)2 and (W0.3,Mo0.7)(Si0.7,Al0.3)2 samples.

  • 131.
    Wang, Zhang
    et al.
    School of Material Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Peng, Geng
    School of Material Science and Engineering, China University of Mining and Technology, Xuzhou.
    Xu, Cheng
    School of Material Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Porous mullite thermal insulators from coal gangue fabricated by a starch-based foam gel-casting method2017Ingår i: Journal of the Australian Ceramic Society, ISSN 2510-1560, Vol. 5, nr 2, s. 287-291Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porous mullite materials with high porosity of 71.8–88.2% were prepared by foaming of coal gangue/Al2O3/starch composite slurry and subsequent pore structure stabilization using starch consolidation and sintering. Coal gangue was recycled to prepare porous mullite foams. Starch was used as gellant, replacing commonly used poisonous chemical and expensive animal protein additives in foaming. Sintered mullite foams exhibited tri-modal pore structure, including large-sized pores (50–300 μm) replicating gas bubbles, moderate-sized pores (~10 μm) embedded in pore walls, and small-sized pores (<5 μm) appearing among mullite crystals. The compressive strength of mullite foams was between 0.21 and 8.7 MPa with low thermal conductivity between 0.1056 and 0.3848 W/m K, indicating that porous mullite foams are candidate materials for applications in thermal insulation.

  • 132.
    Wang, Zhang
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Xiaohong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Geng, Peng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Zhang, Haifei
    Department of Chemistry, University of Liverpool.
    Fabrication and properties of freeze-cast mullite foams derived from coal-series kaolin2016Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 42, nr 10, s. 12414-12421Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hierarchically porous mullite foams were fabricated from coal-series kaolin and Al2O3 slurries by freeze-casting using tert-butyl alcohol (TBA) and water as templates. TBA developed unidirectionally aligned pore channels along the freezing direction and water developed lamellar pores. The total porosity (60.2–83.4%), density (0.49–1.23 g/cm3) and macro-pore size (10–50 µm) of mullite foams were tailored by controlling the solid content of the slurries. The mullitization reaction was completed at the sintering temperature of 1500 °C. The compressive strength of mullite foams along the freezing direction was 3.8–49.4 MPa. Lower porosity and higher compressive strength of sintered mullite foams were obtained using TBA as solvent compared to water. The thermal conductivity of low density and mechanically stable TBA templated porous mullite with 80.2% porosity was 0.18 W/m K, indicting that the freeze-cast porous mullite was a promising refractory material for applications in thermal insulation

  • 133.
    Wang, Zhang
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Jiao, Xinjang
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Xiaohong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Liu, Zhengsheng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Highly porous open cellular TiAl-based intermetallics fabricated by thermal explosion with space holder process2016Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 68, s. 95-100Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High porosity TiAl-based intermetallics were prepared through thermal explosion (TE) from Ti–50Al at.% powders with NaCl as soluble template. The results showed that the space holder particles of NaCl were removed completely in green compacts, and porous Ti–Al materials were synthesized via a low-energy consumption method of TE at a temperature of 600 °C. TiAl was evolved as dominant phase in sintered materials at 1100 °C. With adding 80 vol.% NaCl to Ti–50Al at.% powders, the open porosity was significantly elevated up to 84%. Moreover, the porous materials exhibited a bimodal pore size distribution: large pores (200–500 μm) replicating NaCl particles and small pores (<50 μm) embedded in pore walls. The interconnected small and large pores make open cellular porous TiAl materials, which prescribe them promising for a wide range of applications in separation, heat insulation and catalysis.

  • 134.
    Wenjing, Zhang
    et al.
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Narang, Kritika
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Salcedo, Alma Jasso
    Department of Materials and Environmental Chemistry, Stockholm University, Sweden.
    Dou, Yibo
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Simonsen, Søren Bredmose
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Sørensen, Mads Gudik
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Vinkel, Nadja Maria
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hedin, Niklas
    Department of Materials and Environmental Chemistry, Stockholm University, Sweden.
    Kaiser, Andreas
    Department of Energy Conversion and Storage, Technical University of Denmark (DTU), Denmark.
    Electrospun nanofiber materials for energy and environmental applications2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Electrospinning is the one of the most versatile techniques to design nanofiber materials with numerous applications in the fields of energy conversion, catalytic chemistry, liquid and gas filtration.1 By electrospinning, complex structures can be designed from a rich variety of materials including polymers, metals, ceramics and composite, with the ability to control composition, morphology and secondary structure and tailor performance and functionality for specific applications. Moreover, with recent developments in the design of electrospinning equipment and availability of industrial-scale electrospinning technologies with production rates of several thousands of square meters per day new opportunities for electrospinning are imminent. With this, the advanced research on materials performed in our labs is getting closer to the commercialization of new products for applications in fields of energy and environment.

    An overview will be given on electrospinning activities at DTU Energy that address the sizable challenges in energy and environmental applications by electrospinning: 1. Electrospun perovskite oxide nanofiber electrode for use in solid oxide fuel cells. In this application, a (La0.6Sr0.4)0.99CoO3-δ cathode was shaped into 3-dimensional thin-film by so-gel assisted electrospinning method combined with calcination and sintering; 2. Electrospun nanofiber materials for gas adsorption. Both the advantages and challenges of using electrospun nanofiber materials will be discussed, in terms of electrochemical performance, surface area, packing efficiency and mechanical stability.

  • 135.
    Wu, Jie
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Zhu, Gaoming
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Zhou, Xianguo
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Xiaohong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Formation of Mo-Si-Ti alloys by self-propagating combustion synthesis2015Ingår i: Materials Research, ISSN 1516-1439, E-ISSN 1980-5373, Vol. 18, nr 4, s. 806-812Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Test specimens with nominal compositions MoSi2, (Mo0.9Ti0.1)Si2, (Mo0.8Ti0.2)Si2, (Mo0.7Ti0.3)Si2, (Mo0.6Ti0.4)Si2, (Mo0.5Ti0.5)Si2 and (Mo0.4Ti0.6)Si2 were prepared by combustion synthesis. The combustion mode, propagation velocity of combustion wave, combustion temperature and product structure were investigated. Specimens MoSi2, (Mo0.9Ti0.1)Si2, (Mo0.8Ti0.2)Si2, (Mo0.7Ti0.3)Si2, underwent spontaneously self-propagating combustion synthesis. However, the (Mo0.6Ti0.4)Si2 and (Mo0.5Ti0.5)Si2 specimens required a sustainable energy supply to complete the combustion synthesis reaction. There was no combustion synthesis reaction in specimen (Mo0.4Ti0.6)Si2. The combustion wave propagated along a spiral trajectory from top to the bottom of the specimen compacts in a layer by layer mode. The propagation velocity of the combustion wave reduced with the addition of titanium. The X-ray diffraction analysis showed that the Cllb-MoSi2 and C40-(Mo,Ti)Si2 type phases were formed during combustion synthesis. The intensity of diffraction peaks of C40-(Mo,Ti)Si2 phase increased with Ti content.

  • 136.
    Xueli, Du
    et al.
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Qin, Mingli
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Akhtar, Farid
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Feng, Peizhong
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Qu, Xuanhui
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Effects of heat treatment on the properties of powder injection molded AlN ceramics2008Ingår i: Xiyou jinshu, ISSN 1001-0521, E-ISSN 1867-7185, Vol. 27, nr 1, s. 70-73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of two different heat-treatment atmospheres, nitrogen atmosphere and reducing nitrogen atmosphere with carbon, on the properties of Y2O3-doped aluminum nitride (AlN) ceramics were investigated. The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis (SHS) and compacts were fabricated by employing powder injection molding technique. The polymer-wax binder consisted of 60 wt.% paraffin wax (PW), 35 wt.% polypropylene (PP), and 5 wt.% stearic acid (SA). After the removal of binder, specimens were sintered at 1850°C in nitrogen atmosphere under atmospheric pressure. To improve the thermal conductivity, sintered samples were reheated. The result reveals that the heat-treatment atmosphere has significant effect on the properties and secondary phase of AlN ceramics. The thermal conductivity and density of AlN ceramics reheated in nitrogen gas are 180 W·m−1·K−1 and 3.28 g·cm−3 and the secondary phase is yttrium aluminate. For the sample reheated in reducing nitrogen atmosphere with carbon, the thermal conductivity and density are 173 W·m−1·K−1 and 3.23 g·cm−3, respectively, and the secondary phase is YN.

  • 137.
    Yang, Ke
    et al.
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Guo, Zhimeng
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Akhtar, Farid
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Zhang, Bin
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Tu, Yifan
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Effect of inner oxidant on self-propagating high-temperature synthesis of MnZn-ferrite powder2006Ingår i: Xiyou jinshu, ISSN 1001-0521, E-ISSN 1867-7185, Vol. 25, nr 6: Suppl. 1, s. 553-556Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using KClO3 as an inner oxidant, MnZn-ferrite powder was synthesized by a self-propagating high-temperature synthesis (SHS) process in normal air atmosphere. The effects of the inner oxidant on combustion temperature, combustion velocity, microstructure and the phase of the product were investigated by XRD and SEM, respectively. The results show that a highly ferritized powder can be obtained as well as the highest combustion temperature and the highest combustion velocity when the inner oxidant content m equals 5/4 (k – 1/6).

  • 138.
    Yang, Xia
    et al.
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Guo, Shiju
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Akhtar, Farid
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Lubrication effectiveness of composite lubricants during P/M electrostatic die wall lubrication and warm compaction2006Ingår i: Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material, Vol. 13, nr 6, s. 528-531Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The lubrication effectiveness of the composite lubricants, 50wt% ethylene bis-stearamide (EBS) wax + 50wt% graphite and 50wt% EBS wax + 50wt% BN, during the powder metallurgy (P/M) electrostatic die wall lubrication and warm compaction was studied. The results show that the combination of 50wt% EBS wax and 50wt% graphite has excellent lubrication performance, resulting in fairly high green densities, but the mixture of 50wt% EBS wax and 50wt% BN has less beneficial effect. In addition, corresponding die temperatures should be applied when different die wall lubricants are used to achieve the highest green densities.

  • 139.
    Zhang, Hanzhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Processing and Characterization of Refractory Quaternary and Quinary High-Entropy Carbide Composite2019Ingår i: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 21, nr 5, artikel-id 474Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quaternary high-entropy ceramic (HEC) composite was synthesized from HfC, Mo2C, TaC, and TiC in pulsed current processing. A high-entropy solid solution that contained all principal elements along with a minor amount of a Ta-rich phase was observed in the microstructure. The high entropy phase and Ta-rich phase displayed a face-centered cubic (FCC) crystal structure with similar lattice parameters, suggesting that TaC acted as a solvent carbide during phase evolution. The addition of B4C to the quaternary carbide system induced the formation of two high-entropy solid solutions with different elemental compositions. With the increase in the number of principal elements, on the addition of B4C, the crystal structure of the HEC phase transformed from FCC to a hexagonal structure. The study on the effect of starting particle sizes on the phase composition and properties of the HEC composites showed that reducing the size of solute carbide components HfC, Mo2C, and TiC could effectively promote the interdiffusion process, resulting in a higher fraction of a hexagonal structured HEC phase in the material. On the other hand, tuning the particle size of solvent carbide, TaC, showed a negligible effect on the composition of the final product. However, reducing the TaC size from −325 mesh down to <1 µm resulted in an improvement of the nanohardness of the HEC composite from 21 GPa to 23 GPa. These findings suggested the possibility of forming a high-entropy ceramic phase despite the vast difference in the precursor crystal structures, provided a clearer understanding of the phase transformation process which could be applied for the designing of HEC materials.

  • 140.
    Zhang, Hanzhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Aluminium matrix tungsten aluminide and tungsten reinforced composites by solid-state diffusion mechanism2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, nr 1, artikel-id 12391Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In-situ processing of tungsten aluminide and tungsten reinforced aluminium matrix composites from elemental tungsten (W) and aluminium (Al) was investigated by thermal analysis and pulsed current processing (PCP). The formation mechanism of tungsten aluminides in 80 at.% Al-20 at.% W system was controlled by atomic diffusion. The particle size of W and Al in the starting powder mixture regulated the phase formation and microstructure. PCP of micron sized elemental Al and W resulted in formation of particulate reinforcements, W, Al4W and Al12W, dispersed in Al matrix. W particles were surrounded by a ~3 μm thick dual-layer structure of Al12W and Al4W. The hardness of Al matrix, containing Al12W reinforcements, was increased by 50% compared to pure Al, from 0.3 GPa to 0.45 GPa and W reinforcements showed a hardness of 4.35 GPa. On PCP of 80 at.% Al-20 at.% W mixture with particle size of W and Al ~70 nm, resulted in formation of Al4W as major phase along with small fractions of Al5W and unreacted W phase. This suggested strongly that the particle size of the starting elemental Al and W could be the controlling parameter in processing and tailoring of phase evolution, microstructure of particulate reinforced Al matrix composite.

  • 141.
    Zhang, Hanzhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hedman, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Feng, Peizhong
    China University of Mining and Technology.
    Han, Gang
    University of Science and Technology Beijing.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    A high entropy B4(HfMo2TaTi)C and SiC ceramic composite2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Refractory carbides HfC, Mo2C, TiC, TaC, B4C, and SiC were mixed with a molar ratio of 2:1:2:2:1:2 to fabricate multicomponent ceramic composite by pulsed current processing (PCP). From the starting materials that consist of face-centered cubic (FCC), hexagonal and rhombohedral crystal structures, the investigated carbide system is reported to form a single phase B4(HfMo2TaTi)C high-entropy ceramic (HEC) with SiC. The HEC phase contains uniform distribution of constitutional elements Hf, Mo, Ta, Ti, B and C, according to Energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) results.

    The fabricated HEC phase displays a hexagonal crystal structure, with a high average lattice distortion of 8.26% (Figure 1). The HCP structure was observed by X-ray diffraction and selected area diffraction in transmission electron microscopy (TEM). Density-functional theory (DFT) optimization suggested that the hexagonal crystal structure has alternating layers of metal atoms and carbon/boron atoms, i.e. metal atoms of Hf, Mo, Ta and Ti were distributed on the (0001) plane in the hexagonal lattice, while the carbon/boron atoms formed hexagonal 2D grids on the (0002) plane in the hexagonal unit cell. Despite of the vast differences in the crystal structures and lattice parameters among the utilized carbides, the formation of the unique hexagonal lattice structure of B4HfMo2TaTi)C can be a result of independent diffusion of the metal and nonmetal atoms. The sintered HEC ceramic composite exhibits excellent oxidation resistance at mediate temperature, 900 ºC for 50h, and elevated temperature, 2000 ºC for 20 s. Nanoindentation test shows that the HEC phase has a high hardness of 35 GPa. The remarkable improvement compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa) was contributed by the severe lattice distortion in the hexagonal structure.

  • 142.
    Zhang, Hanzhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Luleå university of technology.
    Hedman, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Feng, Peizhong
    China University of Mining and Technology.
    Han, Gang
    University of Science and Technology Beijing.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite2019Ingår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, nr 16, s. 5161-5167Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A multicomponent composite of refractory carbides, B4C, HfC, Mo2C, TaC, TiC and SiC, of rhombohedral, face-centered cubic (FCC) and hexagonal crystal structures is reported to form a single phase B4(HfMo2TaTi)C ceramic with SiC. The independent diffusion of the metal and nonmetal atoms led to a unique hexagonal lattice structure of the B4(HfMo2TaTi)C ceramic with alternating layers of metal atoms and C/B atoms. In addition, the classical differences in the crystal structures and lattice parameters among the utilized carbides were overcome. Electron microscopy, X-ray diffraction and calculations using density functional theory (DFT) confirmed the formation of a single phase B4(HfMo2TaTi)C ceramic with a hexagonal close-packed (HCP) crystal structure. The DFT based crystal structure prediction suggests that the metal atoms of Hf, Mo, Ta and Ti are distributed on the (0001) plane in the HCP lattice, while the carbon/boron atoms form hexagonal 2D grids on the (0002) plane in the HCP unit cell. The nanoindentation of the high-entropy phase showed hardness values of 35 GPa compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa). The higher hardness was contributed by the solid solution strengthening effect in the multicomponent hexagonal structure. The addition of SiC as the secondary phase in the sintered material tailored the microstructure of the composite and offered oxidation resistance to the high-entropy ceramic composite at high temperatures.

  • 143.
    Zhang, Hanzhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Luleå university of technology.
    Hedman, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Feng, Peizhong
    China University of Mining and Technology.
    Han, Gang
    University of Science and Technology Beijing.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Correction: A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite2019Ingår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, nr 19, s. 6647-6647Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The authors regret that there is an error in writing the crystal structure in the article. The authors would like to address as follows:

    The presented XRD and TEM results revealed a hexagonal crystal structure. The following analyses including the identification of the lattice parameters and the DFT calculation were based on a hexagonal lattice. Therefore, the HCP (hexagonal close-packed) structure mentioned in the article should be regarded as a hexagonal structure. The HCP term used in the introduction, where the article from Joshua Gild et al. was cited, should also be regarded as hexagonal AlB2 structure.

    The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

  • 144.
    Zhang, Wenjing
    et al.
    Department of Environmental Engineering, Technical University of Denmark, Lyngby, Denmark.
    Narang, Kritika
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Simonsen, Søren Bredmose
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Vinkel, Nadja Maria
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Gudik-Sørensen, Mads
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, DenmarkDepartment of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Han, Li
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, DenmarkDepartment of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Kaiser, Andreas
    Department of Energy Conversion and Storage, Technical University of Denmark, Roskilde, DenmarkDepartment of Energy Conversion and Storage, Technical University of Denmark, Roskilde, Denmark.
    Highly Structured Nanofiber Zeolite Materials for Biogas Upgrading2019Ingår i: Energy Technology, E-ISSN 2194-4296Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hierarchical zeolite composite nanofibers are designed using an electrospinning technique with post‐carbonization processing to form mechanically strong pellets for biogas upgrading. A ZSM‐5 nanopowder (zeolite) and a polyvinylpyrrolidone (PVP) polymer are electrospun to form ZSM/PVP composite nanofibers, which are transformed into a ZSM and carbon composite nanofiber (ZSM/C) by a two‐step heat treatment. The ZSM/C nanofibers show a 30.4% increase in Brunauer–Emmett–Teller (BET) surface area compared with the non‐structured ZSM‐5 nanopowder. Using ideal adsorbed solution theory, CO2‐over‐CH4 selectivity of 20 and CO2 uptake of 2.15 mmolg−1 at 293 K at 1 bar for ZSM/C nanofibers are obtained. For the efficient use of adsorbents in pressure swing adsorption operation, the nanofibers are structured into ZSM/C pellets that offer a maximum tensile strength of 6.46 MPa to withstand pressure swings. In the breakthrough tests, the CO2 uptake of the pellets reach 3.18 mmolg−1 at 293 K at 4 bar after 5 breakthrough adsorption–desorption cycles, with a much higher mass transfer coefficient of 1.24 ms−1 and CO2 uptake rate of 2.4 mg of CO2 g−1s−1, as compared with other structured zeolite adsorbents.

  • 145.
    Zhu, Gaoming
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Xiaohong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Li, Dehu
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Yang, Ting
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Synthesis, microstructure and mechanical properties of (Mo,Ti)Si2/Al2O3 composites prepared by thermite-reaction-assisted combustion synthesis2016Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 688, s. 870-877Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    (Mo0.95Ti0.05)Si2/3.3mol%Al2O3 composites were synthesized by self-propagating high-temperature synthesis using Mo, Si, Al and TiO2 powders. The addition of alloying element Ti to MoSi2 and the synthesis of reinforcing particulate Al2O3 phase were achieved through the thermite reaction, Al + TiO2→Ti + Al2O3. The results showed that the combustion synthesis reaction mode in the Mo, Si, Al and TiO2 reaction mixture was spiral and self-propagating, and the reaction product was composed of MoSi2, (Mo,Ti)Si2 and Al2O3. The combustion products were consolidated by vacuum hot-pressing at 1773 K and 27.5 MPa for 90 min to consolidate composites with relative densities above 95% of theoretical. The hot-pressed (Mo0.95Ti0.05)Si2/3.3mol%Al2O3 composite with relative density of 97.5% exhibited finer microstructure and superior mechanical properties compared to MoSi2 monolithic material; Vicker's hardness of 12.9 GPa, bending strength of 320 MPa and fracture toughness of 3.37 MPa m1/2.

  • 146.
    Zhu, Gaoming
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Xiaohong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Liu, Zhengsheng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Niu, Jinan
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Synthesis and Properties of MoSi2–MoB–SiC Ceramics2016Ingår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 99, nr 4, s. 1147-1150Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    MoB and SiC particulate reinforced MoSi2 matrix composites were synthesized in situ from Mo, Si, and B4C powder mixtures by self-propagating high-temperature synthesis (SHS). The SHS MoSi2–MoB–SiC products were vacuum hot-pressed (HPed) at 1400°C for 90 min to fabricate high-density (> 97.5% relative density) bulk composites. Microstructure refinement and improvements in the Vickers hardness and fracture toughness of the HPed composites were observed with increasing B4C content in the reaction mixture. The HPed composite of composition MoSi2–0.4MoB–0.1SiC exhibited grain size of 1–5 μm, Vickers hardness of 12.5 GPa, bending strength of 537 MPa, and fracture toughness of 3.8 MPa.m1/2. These excellent mechanical properties indicate that MoB and SiC particulate reinforced MoSi2 composites could be promising candidates for structural applications.

  • 147.
    Zhu, Gaoming
    et al.
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Wang, Xiaohong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Sun, Zhi
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Effect of annealing environment on the crack healing and mechanical properties of (Mo0.97Nb0.03)(Si0.97Al0.03)22015Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 634, s. 109-114Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Crack healing of Nb and Al alloyed MoSi2 notched ceramics had been investigated during thermal treatment from 900 to 1500 °C in air, vacuum, argon and nitrogen environments. Notched (Mo0.97Nb0.03)(Si0.97Al0.03)2 ceramics showed significant recovery of bending strength after heat treatment in air. Bending strength recovery of 250% was found after heat treatment in air at 1200 °C. Oxide layer formation healed the cracks during annealing in air. Re-sintering was found dominant mechanism of crack healing during annealing in vacuum, argon and nitrogen atmosphere. Bending strength recovery of 208% was found after heat treatment in vacuum at 1200 °C.

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