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  • 901.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structuring of Aluminophosphates Monoliths for Carbon Capture2015Conference paper (Refereed)
  • 902.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structuring of Nanoporous Powders into Hierarchically Porous Nanostructured Adsorbents for Clean Energy2016Conference paper (Refereed)
  • 903.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Structuring of nanoporous powders into hierarchically porous nanostructured adsorbents for decarbunization2015Conference paper (Refereed)
  • 904.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Structuring of porous powders for gas separation applications2013Conference paper (Other academic)
  • 905.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Structuring of porous powders into hierarchically porous adsorbents2013Conference paper (Refereed)
  • 906.
    Akhtar, Farid
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Synthesis, microstructure and mechanical properties of Al 2 O 3 reinforced Ni 3 Al matrix composite2009In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 499, no 1-2, p. 415-420Article in journal (Refereed)
    Abstract [en]

    A new method to synthesize alumina reinforced Ni3Al intermetallic matrix composites has been described. The powder mixture of nickel and aluminium was mechanically alloyed. The powder mixture was excessively heated during mechanical alloying and then exposed to atmosphere for oxidation. The oxidized powder mixture was transformed into alumina reinforced nickel aluminide matrix composite on subsequent pulse current processing. Alumina reinforcements were generated in the nickel aluminide matrix by in situ precipitation. The microstructure of the composite showed that the alumina reinforcements were 50–150 nm in size. The fine alumina reinforcements were homogeneously distributed in the matrix phase. The mechanical properties of the alumina reinforced nickel aluminide matrix composite fairly exceeded the nickel aluminide alloys. This novel synthesis approach allowed the rapid and facile production of high strength alumina reinforced Ni3Al matrix composites.

  • 907.
    Akhtar, Farid
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Zeolite adsorbents for gas separation applications2013Conference paper (Refereed)
  • 908.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ali, Liaqat
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Peizhong, Feng
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Shah, Jawad Ali
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Enhanced sintering, microstructure evolution and mechanical properties of 316l stainless steel with MoSi 2 addition2011In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, no 35, p. 8794-8797Article in journal (Refereed)
    Abstract [en]

    Sintering 316L stainless steel to near full density with an appropriate sintering additive can ensure high mechanical properties and corrosion resistance. We present here a sintering approach which exploits the dissociation of ceramics in steels at high temperatures to activate sintering densification to achieve near full dense 316L stainless steel materials. MoSi2 ceramic powder was used as a sintering additive for pre-alloyed 316L stainless steel powder. Sintering behavior and microstructure evolution were investigated at various sintering temperatures and content of MoSi2 as sintering additive. The results showed that the sintering densification was enhanced with temperature and MoSi2 content. The distribution of MoSi2 was characterized by XMAPs. It was found that MoSi2 dissociated during sintering and Mo and Si segregated at the grain boundaries. Excess Mo and Si were appeared as separate phases in the microstructure. Above 98% of theoretical density was achieved when the specimens were sintered at 1300 °C for 60 min with 5 wt.% MoSi2 content. The stainless steel sintered with 5 wt.% MoSi2 exhibited very attractive mechanical properties.

  • 909.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Andersson, Linnéa
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Keshavarzi, Neda
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Colloidal processing and CO 2 capture performance of sacrificially templated zeolite monoliths2012In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 97, p. 289-296Article in journal (Refereed)
    Abstract [en]

    Sacrificial templating of suspension cast and subsequently thermally treated zeolite monoliths with glassy carbon spheres and fibers yielded zeolite 13X and silicalite-1 monoliths with macroporosities up to 50 vol%. Homogeneous distribution of the macroporosity in hierarchically porous monoliths was obtained by tailoring the surface chemistry of the carbon particles by polyelectrolyte-assisted adsorption of zeolite particles. The effect of amount of kaolin binder and temperature for the thermal treatment on the monoliths strength, surface area and CO2 uptake was studied by diametral compression tests, electron microscopy, X-ray diffraction and gas adsorption. Cyclic adsorption and regeneration measurements showed that zeolite 13X monoliths display a high CO2 uptake while the silicalite-1 monoliths could be regenerated with a relatively low energy penalty.

  • 910.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Andersson, Linnéa
    School of Chemical, Biological and Environmental Engineering, Oregon State University.
    Ogunwumi, Steven
    Crystalline Materials Research, Corning Incorporated.
    Hedin, Niklas
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Structuring adsorbents and catalysts by processing of porous powders2014In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 34, no 7, p. 1643-1666Article in journal (Refereed)
    Abstract [en]

    Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given.

  • 911.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Askari, Syed Javid
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Shah, Khadijah Ali
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Du, Xueli
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Microstructure, mechanical properties, electrical conductivity and wear behavior of high volume TiC reinforced Cu-matrix composites2009In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 60, no 4, p. 327-336Article in journal (Refereed)
    Abstract [en]

    This study deals with the processing, microstructure, mechanical properties, electrical conductivity and wear behavior of high volume titanium carbide reinforced copper matrix composites. The microstructural study revealed that the titanium carbide particles were distributed uniformly in the matrix phase. No interface debonding and micro-cracks were observed in the composite. The addition of alloying elements in the copper considerably increased the sintered density and properties. The composite hardness and strength increased with titanium carbide content and alloying elements in the matrix phase. The electrical conductivities of the composites were predicted using three point upper bound and two phase self consistent predictive models. The wear resistance of the composites was studied against high speed steel. Wear mechanisms were discussed by means of microscope observations on the worn surfaces. The ratio of titanium carbide average grain size to the mean free path of the binder was introduced as a parameter to determine wear performance.

  • 912.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Askari, Syed Jawid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Shaft, Jawad Ali
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Processing, microstructure and mechanical properties of TiC-465 stainless steel/465 stainless steel layer composites2007In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 439, no 1-2, p. 287-293Article in journal (Refereed)
    Abstract [en]

    Layered composites of carbide reinforcements and stainless steel have been prepared successfully by powder technology. The layer material consisted of two layers. Top layer consisted of reinforcements (TiC and NbC) and 465 stainless steel as binder material for carbides. The substrate material was of binder material (465 stainless steel). The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that top layer (TiC-NbC/465 stainless steel) showed the typical core-rim microstructure of conventional steel bonded cermets and the substrate material showed the structure of sintered steel. An intermediate layer was formed due to diffusion reaction of top layer and substrate material. This intermediate layer showed a gradient microstructure. The bending strength of layered material measured in the direction perpendicular to the layer alignment was remarkably higher. Nineteen percent increase in bending strength in case of 53 wt% reinforcement in top layer and 35% increase in case of 73 wt% reinforcement in top layer was found. The variation of strength as a function of thickness of substrate material revealed that the character of material changed from cermet to a layer composite and then towards metallic materials. The fracture morphologies of top layer, substrate material and intermediate layer are also reported

  • 913.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Colloidal processing and thermal treatment of binderless hierarchically porous zeolite 13X monoliths for CO2 capture2011In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 94, no 1, p. 199-205Article in journal (Refereed)
    Abstract [en]

    Adsorbents with high surface area are potential candidates for efficient postcombustion CO2 capture. Binderless zeolite 13X monoliths with a hierarchical porosity and high CO2 uptake have been produced by slip casting followed by pressureless thermal treatment. The zeolite powder displayed an isoelectric point at pH 4.7 and electrostatically stabilized suspensions could be prepared at alkaline pH. The volume fraction-dependent steady shear viscosity could be fitted to a modified Krieger–Dougherty model with a maximum volume fraction of 0.66. The narrow temperature range where monoliths could be produced without significant loss of the microporous surface area was identified and related to the phase behavior of the 13X material. Slip casting of concentrated suspensions followed by thermal treatment of the powder bodies at a temperature of 800°C without holding time resulted into strong hierarchically porous zeolite 13X monolith that displayed a CO2 uptake larger than 29 wt%.

  • 914.
    Akhtar, Farid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ogunwumi, Steven
    Laminates for rapid CO2 capture from gas mixtures2013Patent (Other (popular science, discussion, etc.))
  • 915.
    Akhtar, Farid
    et al.
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Feng, Peizhong
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Du, Xueli
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Jawid, Askari Syed
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Tian, Jianjun
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Microstructure and property evolution during the sintering of stainless steel alloy with Si 3 N 42008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 472, no 1-2, p. 324-331Article in journal (Refereed)
    Abstract [en]

    This paper describes the sintering of a martensitic stainless steel alloy with addition of Si3N4. Sintering behavior was studied at different sintering temperatures ranging from 1250 to 1400 °C with different holding times (20–80 min) and with varying Si3N4. Results showed that the samples were densified rapidly via liquid phase sintering mechanism. Nearly full density was obtained at 1300 °C after 60 min of holding time with 5 wt% Si3N4. Temperature above 1350 °C and Si3N4 content 10 wt% caused slumping of the samples. Two weight percent Si3N4 was found chemically stable in steel alloy. Above 2 wt% Si3N4 dissolved in the steel matrix. The distribution of dissolved Si and N was characterized by XMAP. When N content reached much above its solubility limit in steel alloy it diffused out leaving pores in steel alloy with considerable decrease in the sintered density. The mechanical properties of the sintered product with varying Si3N4 were measured. A maximum ultimate tensile strength of 1011 MPa was achieved with 2 wt% Si3N4 sintered at 1300 °C after 60 min of holding time. Fracture morphologies of tensile samples are also reported.

  • 916.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Guo, Shi Ju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Shah, Jawad Ali
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Feng, Pei Zhong
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Effect of adding a type of binder phase on the microstructure, properties and heat treatment of steel bonded TiC cermets2007In: Progress in powder metallurgy: proceedings of the 2006 Powder Metallurgy World Congress & Exhibition (PM 2006), held in Busan Exhibition & Convention Center (BEXCO), Busan, Korea, September 24 - 28, 2006 / [ed] Duk Yong Yoon; Suk-Joong L. Kang; Kwang Yong Eun; Yong-Seog Kim, Uetikon-Zürich: Trans Tech Publications Inc., 2007, Vol. 534-536, p. 1161-1164Conference paper (Refereed)
    Abstract [en]

    Particulate TiC reinforced 465 maraging stainless steel matrix Cermets were processed by conventional P/M. The binder phase was added in the form of elemental powders and master alloy powders. The microstructures, binder phase variation with TiC content and mechanical properties were evaluated. The addition of a type of binder phase largely effects the microstructure and mechanical properties. When a master alloy binder phase was used the microstructure showed interphase debondings, microcracks and large growths of TiC particles. Where as, elemental powders in the composition of binder phases showed defect free microstructure of steel bonded cermets. The binder phase variation from starting composition was observed with increase in wt% TiC content and this variation was higher when the master alloy powders were used as a binder. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was attributed to the aging reaction in maraging stainless steel. The response to heat treatment was decreased with an increase in TiC content due to the shift of binder phase from the starting composition.

  • 917.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, University of Science & Technology, Beijing.
    Guo, Shi-ju
    Institute of Powder Metallurgy, University of Science & Technology, Beijing.
    Development of Si 3 N 4/Al composite by pressureless melt infiltration2006In: Transactions of Nonferrous Metals Society of China, ISSN 1003-6326, E-ISSN 2210-3384, Vol. 16, no 3, p. 629-632Article in journal (Refereed)
    Abstract [en]

    Pressureless infiltration processs to synthesize Si3N4/Al composite was investigated. Al-2%Mg alloy was infiltrated into Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to infiltrate Al-2% Mg alloy in Si3N4 and Si3N4 containing 10% Al2O3 preforms. The growth of the dense composite of useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. During infiltration Si3N4 reacted with aluminium to form Si and AlN, the growth of composite was found to proceed in two ways, depending on the Al2O3 content in the initial preform. Firstly, preform without Al2O3 content gives rise to AlN, Al3.27Si0.47 and Al type phases after infiltration. Secondly, perform with 10% Al2O3 content gives rise to AlN-Al2O3 solid solution phase (AlON), MgAl2O4, Al and Si type phases. AlON phase was only present in composite, containing 10% Al2O3 in the Si3N4 preforms before infiltration.

  • 918.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Development of Si3N4/ Al composite by pressureless melt infiltration2006In: European PM 2005 conference proceedings: Prague Congress Centre, Czech Republic, 2-5 October 2005., Shrewsbury: European powder metallurgy association , 2006, Vol. 2, p. 271-278Conference paper (Refereed)
    Abstract [en]

    Pressureless infiltration process to synthesize Si3N4/ Al composite was investigated. Al- 2%Mg alloy was infiltrated into the Si3N4 and Si3N4 containing 10% Al2O3 preforms in the atmosphere of nitrogen. It is possible to infiltrate Al- 2%Mg alloy in Si3N4 and Si3N4 containing 10% Al2O3 preforms. The growth of the dense composite of useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. During infiltration Si3N4 reacted with Aluminium to form Si and AlN. The growth of composite was found to proceed in two ways, depending on the Al2O3 content in the initial preform. First, preform without Al2O3 content gave rise to AlN, Al3.27Si0.47 and Al type phases after infiltration. Second, perform with 10% Al2O3 content gave rise to AlN-Al2O3 solid solution phase (AlON), MgAl2O4, Al and Si type phases. AlON phase was only present in composite, containing 10% Al2O3 in the Si3N4 preforms before infiltration.

  • 919.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    On the processing, microstructure, mechanical and wear properties of cermet/stainless steel layer composites2007In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 55, no 4, p. 1467-1477Article in journal (Refereed)
    Abstract [en]

    This study deals with layer composites of carbide reinforcements and stainless steel prepared successfully by powder technology. The layer material consisted of two layers. The top layer consisted of reinforcements (TiC and NbC) and 465 stainless steel as the binder material for the carbides. The bottom layer was entirely of binder material (465 stainless steel). The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the top layer (TiC–NbC/465 stainless steel) showed the typical core–rim microstructure of conventional steel bonded cermets and the bottom layer showed the structure of sintered steel. An intermediate layer was found with a gradient microstructure, having a higher carbide content towards the cermet layer and lower carbide content towards the stainless steel layer. The bending strength of the layered material measured in the direction perpendicular to the layer alignment was remarkably high. The variation of strength as a function of the thickness of the bottom layer revealed that the character of the material changed from the cermet, to a layer composite and then towards metallic materials. The wear resistance of the top layer was studied against high speed steel. The wear mechanisms were discussed by means of microscopical observations on the worn surfaces. The wear was severe at higher wear loads and lower TiC content. Microploughing of the stainless steel matrix was found to be the dominant wear mechanism. Heavy microploughing and rapid removal of material from the wear surface was observed at high wear load. The fracture morphologies of the top, bottom and intermediate layers are reported

  • 920.
    Akhtar, Farid
    et al.
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Guo, Shi-Ju
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Pressureless infiltration of Si3N4 preforms with an Al-2wt% Mg alloy2005In: International Journal of Minerals, Metallurgy and Materials, ISSN 1674-4799, E-ISSN 1869-103X, Vol. 12, no 4, p. 351-356Article in journal (Refereed)
    Abstract [en]

    The pressureless infiltration process to synthesize a silicon nitride composite was investigated. An Al-2wt%Mg alloy was infiltrated into silicon nitride preforms in the atmosphere of nitrogen. It is possible to infiltrate the Al-2wt%Mg alloy in silicon nitride preforms. The growth of the composite with useful thickness wasfacilitated by the presence of magnesium powder at the interface and by flowing nitrogen. The microstructure of the Si3N4-Al composite has been characterized using scanning electron microscope.During the infiltration of Si3N4 preforms, Si3N4 reacted with aluminium to form silicon and AlN. Thesilicon produced during the growth consumed in the formation of MgSiAlO, MgSiAlN and Al3.27Si0.47 type phases. The growth of the composite was found to proceed in two ways, depending on the oxide content in the initial preforms. First, less oxide content preforms gave rise to MgAlSiO and MgAlSiN type phases after infiltration. Second, more oxide content preforms gave rise to AlN-Al2O3 solid solution phase(AlON). The AlON phase was only present in the composite, containing 10% aluminium in the silicon nitride preforms before infiltration.

  • 921.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Askari, Jawid
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Tian, Jianjun
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Sintering behavior, microstructure and properties of TiC-FeCr hard alloy2007In: Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material, Vol. 14, no 1, p. 89-93Article in journal (Refereed)
    Abstract [en]

    TiC based cermets were produced with FeCr, as a binder, by conventional P/M (powder metallurgy) to near >97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of >1360°C caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360°C for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettability of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals

  • 922.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Guo, Shiju
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Cui, Feng-e
    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.
    Lin, Tao
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    TiB 2 and TiC stainless steel matrix composites2007In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 61, no 1, p. 189-191Article in journal (Refereed)
    Abstract [en]

    Stainless steel matrix composites reinforced with TiB2 or TiC particulates have been in situ produced through the reactive sintering of Ti, C and FeB. X-ray diffraction analysis confirmed the completion of reaction. The TiB2, TiC and steel were detected by X-ray diffraction analysis. No other reaction product or boride was found, indicating the stability of TiB2 and TiC in steel matrix. The SEM micrographs revealed the morphology and distribution of in situ synthesized TiB2 and TiC reinforcements in steel matrix. During sintering the reinforcements TiB2 and TiC grew in different shapes. TiB2 grew in hexagonal prismatic and rectangular shape and TiC in spherical shape.

  • 923.
    Akhtar, Farid
    et al.
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Guo, Shiju
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Feng, Peizhong
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Ali, Shah Khadijah
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Javid, Askari Syed
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    TiC-maraging stainless steel composite: microstructure, mechanical and wear properties2006In: Xiyou jinshu, ISSN 1001-0521, E-ISSN 1867-7185, Vol. 25, no 6, p. 630-635Article in journal (Refereed)
    Abstract [en]

    Particulate TiC reinforced 17-4PH and 465 maraging stainless steel matrix composites were processed by conventional powder metallurgy (P/M). TiC-maraging stainless steel composites with theoretical density >97% were produced using conventional P/M. The microstructure, and mechanical and wear properties of the composites were evaluated. The microstructure of the composites consisted of (core-rim structure) spherical and semi-spherical TiC particles depending on the wettability of the matrix with TiC particles. In TiC-maraging stainless steel composites, 465 stainless steel binder phase showed good wettability with TiC particles. Some microcracks appeared in the composites, indicating the presence of tensile stresses in the composites produced during sintering. The typical properties, hardness, and bend strength were reported for the composites. After heat treatment and aging, an increase in hardness was observed. The increase in hardness was attributed to the aging reaction in maraging stainless steel. The specific wear behavior of the composites strongly depends on the content of TiC particles and their interparticle spacing, and on the heat treatment of the maraging stainless steel.

  • 924.
    Akhtar, Farid
    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.
    Yang, Xia
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Lian, Yudong
    University of Science and Technology Beijing, School of Materials Science and Engineering.
    Stainless steel binder for the development of novel TiC-reinforced steel cermets2006In: Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material, Vol. 13, no 6, p. 546-550Article in journal (Refereed)
    Abstract [en]

    Steel reinforced TiC composites are an attractive choice for wear resistance and corrosion resistance applications. TiC-reinforced 17-4PH maraging stainless matrix composites were processed by conventional powder metallurgy (P/M). TiC-reinforced maraging stainless steel composites with >97% of theoretical density were fabricated. The microstructure, mechanical and wear properties of the composites were evaluated. The microstructure of these composites consisted of spherical and semi-spherical TiC particles. A few microcracks appeared in the composites, showing the presence of tensile stress in the composites produced during sintering. Typical properties, namely, hardness and bend strength were reported for the sintered composites. After heat treatment and aging, the increase of hardness was observed. The increase of hardness was attributed to the aging reaction in the 17-4PH stainless steel. The precipitates appeared in the microstructure and were responsible for the increase in hardness. The specific wear behavior of the composites was strongly dependent on the content of TiC particles, the interparticle spacing, and the presence of hard precipitates in the binder phase.

  • 925.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science, University of Science and Technology Beijing, 30 Xue Yuan Road, 100083, Beijing.
    Guo, SJ
    Institute of Powder Metallurgy, School of Materials Science, University of Science and Technology Beijing, 30 Xue Yuan Road, 100083, Beijing.
    Microstructure, mechanical and fretting wear properties of TiC-stainless steel composites2008In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 59, no 1, p. 84-90Article in journal (Refereed)
    Abstract [en]

    This study deals with the processing, microstructure, and wear behavior of TiC-reinforced stainless steel matrix composites, containing 50 to 70 wt.% TiC. Powder technology was used to successfully fabricate the composites. The microstructure of the composite was characterized by scanning electron microscopy. The microstructural study revealed that the TiC particles were distributed uniformly in the steel matrix phase. Interface debonding and microcracks were not observed in the composite. The composite hardness increased with TiC content. The fretting wear resistance of the composites was studied against high speed steel. The wear mechanisms are discussed by means of microscopical observations on the worn surfaces. The wear was severe at higher wear loads and lower TiC content. Microplowing of the stainless steel matrix was found to be the dominant wear mechanism. Heavy microplowing and rapid removal of material from the wear surface was observed at high wear load. The variation of wear loss with volume fraction and mean free path of the binder phase is also reported

  • 926.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Guo, SJ
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Shah, KA
    Institute of Powder Metallurgy, Materials Science Department, University of Science and Technology Beijing.
    Effect of Cu3P addition on sintering behaviour of elemental powders in the composition of 465 stainless steel2006In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 49, no 1, p. 28-33Article in journal (Refereed)
    Abstract [en]

    The addition of Cu3P for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated were sintering temperature, sintering time and wt-%Cu3P. In vacuum sintering, effective sintering took place between 1300 and 1350°C. The maximum sintered density of 7·44 g cm−3 was achieved at 1350°C for 60 min with 4–6 wt-%Cu3P. More than 6 wt-%Cu3P content and temperature >1350°C caused slumping of the specimens. The sintered specimens were heat treated and a maximum ultimate tensile strength (UTS) of 767 MPa was achieved with 4 wt-%Cu3P content. The maximum hardness of 45·5 HRC was achieved in heat treated condition with 4 wt-%Cu3P content. Above 4 wt-%Cu3P content increase in density was observed whereas the response to heat treatment decreased. Fracture morphologies of the sintered specimens were also reported. A comparison of sintering behaviour and mechanical properties of elemental powders with prealloyed powders was also given in the present study

  • 927.
    Akhtar, Farid
    et al.
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Hasan, Faizul
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Reactive sintering and properties of TiB 2 and TiC porous cermets2008In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 62, no 8-9, p. 1242-1245Article in journal (Refereed)
    Abstract [en]

    TiB2, TiC reinforced Fe matrix porous cermets were produced through the synthesis reaction of Ti, C and FeB powders with 30% sintered porosity. The X-ray diffraction analysis confirmed the completion of reaction. The TiB2, TiC and Fe were detected by X-ray diffraction analysis. The formation of secondary reaction products was inhibited during the reactive sintering. Porous cermets showed large and small pores in their structure. Maximum bending strength of 163 MPa was obtained with 30% sintered porosity. Furthermore, the fabricated samples were found to possess reasonable electrical conductivities, thus rendering them suitable for use as the basic components of planar solid oxide fuel cells.

  • 928.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Hedin, Niklas
    Department of Materials and Environmental Chemistry, Stockholm University.
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Zeolite adsorbents with high CO2-over-N2 selectivity and high capacity2012Conference paper (Refereed)
  • 929.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Humail, Islam S
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Askari, SJ
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Tian, Jianjun
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Shiju, Guo
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Effect of WC particle size on the microstructure, mechanical properties and fracture behavior of WC--(W, Ti, Ta) C--6wt% Co cemented carbides2007In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 25, no 5-6, p. 405-410Article in journal (Refereed)
    Abstract [en]

    This study deals with the microstructure and mechanical properties of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides fabricated by conventional sintering. The conventional WC particles of 4 μm size and ultrafine particles of 0.2 μm were introduced in the system with varying ratio. The ratios of conventional WC particles to ultrafine WC particles were 2:1, 1:1, and 1:2. The microstructures of sintered WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides were sensitively dependent on the ratio of conventional WC particles to ultrafine WC particles. The rim phase increased with the increase in the amount of ultrafine particles. Hardness of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbide increased with increase in the amount of rim phase and decrease in the average grain size of WC particles. The bending strength showed the similar trend of the hardness. The fracture morphologies are reported. The fracture behavior changed from mixed mode to transgranular fracture mode, when the ratio of conventional WC particles to ultrafine WC particles was changed from 2:1 to 1:2.

  • 930.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Keshavarzi, Neda
    Department of Materials and Environmental Chemistry, Stockholm University.
    Andersson, Linnéa
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Highly porous zeolite monoliths for CO2 capture.2011Conference paper (Refereed)
  • 931.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Keshavarzi, Neda
    Department of Materials and Environmental Chemistry, Stockholm University.
    Andersson, Linnéa
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Department of Materials and Environmental Chemistry, Stockholm University.
    Colloidal processing and thermal treatment of hierarchically porous zeolite 13X monoliths for Carbon Capture2010Conference paper (Refereed)
  • 932.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Keshavarzi, Neda
    Department of Materials and Environmental Chemistry, Stockholm University.
    Andersson, Linnéa
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Structuring and characterization of Highly porous adsorbents for CO2 capture from flue gas2011Conference paper (Refereed)
  • 933.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Keshavarzi, Neda
    Department of Materials and Environmental Chemistry, Stockholm University.
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Processing and Characterization of Highly Porous Zeolite 13X Monoliths for CO2 Adsorption2010Conference paper (Refereed)
  • 934.
    Akhtar, Farid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Keshavarzi, Neda
    Department of Materials and Environmental Chemistry, Stockholm University.
    Shakarova, Dilshod
    Department of Materials and Environmental Chemistry, Stockholm University.
    Cheung, Ocean
    Department of Materials and Environmental Chemistry, Stockholm University.
    Hedin, Niklas
    Department of Materials and Environmental Chemistry, Stockholm University.
    Bergström, L.M.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Aluminophosphate monoliths with high CO2-over-N2 selectivity and CO2 capture capacity2014In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 99, p. 55877-55883Article in journal (Refereed)
    Abstract [en]

    Monoliths of microporous aluminophosphates (AlPO4-17 and AlPO4-53) were structured by binder-free pulsed current processing. Such monoliths could be important for carbon capture from flue gas. The AlPO4-17 and AlPO4-53 monoliths exhibited a tensile strength of 1.0 MPa and a CO2 adsorption capacity of 2.5 mmol g-1 and 1.6 mmol g-1, respectively at 101 kPa and 0°C. Analyses of single component CO2 and N2 adsorption data indicated that the AlPO4-53 monoliths had an extraordinarily high CO2-over-N2 selectivity from a binary gas mixture of 15 mol% CO2 and 85 mol% N2. The estimated CO2 capture capacity of AlPO4-17 and AlPO4-53 monoliths in a typical pressure swing adsorption (PSA) process at 20°C was higher than that of the commonly used zeolite 13X granules. Under cyclic sorption conditions, AlPO4-17 and AlPO4-53 monoliths were regenerated by lowering the pressure of CO2. Regeneration was done without application of heat, which would regenerate them to their full capacity for CO2 adsorption.

  • 935.
    Akhtar, Farid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kocjan, Andraz
    The hydrolysis of AlN powder: powerful tool in advanced materials engineering2014Conference paper (Refereed)
  • 936.
    Akhtar, Farid
    et al.
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Lian, Yudong D.
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Islam, Syed Humail
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    Guo, Shiju
    School of Material Science and Engineering, University of Science and Technology, Bejing.
    A new kind of age hardenable martensitic stainless steel with high strength and toughness2007In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 34, no 4, p. 285-289Article in journal (Refereed)
    Abstract [en]

    Following analysis of typical age hardenable martensitic stainless steels, a new kind of maragingstainless was developed. The new maraging stainless steel showed high strength, ultimate tensilestrength (UTS) 5 1670 MPa, high toughness, K IC 5 83·9 MPa m1/2 and hardness as high as 478 HVin the age hardened condition. Microstructural study with an optical and transmission electron microscope revealed the typical microstructure of age hardenable stainless steel containing lathmartensite and precipitates. TixNi precipitates were identified by transmission electron microscopy, which were responsible for the increase in mechanical properties after age hardening. The results of natural salt spray test showed that the corrosion resistance of new maraging stainless steel approached to the corrosion resistance of 304L stainless steel.

  • 937.
    Akhtar, Farid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Qingling
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Hedin, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bergstroem, Lennart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Erratum: Strong and binder free structured zeolite sorbents with very high CO2-over-N-2 selectivities and high capacities to adsorb CO2 rapidly (vol 5, pg 7664, 2012)2012In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 5, no 12, p. 9947-Article in journal (Refereed)
  • 938.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Liu, Qingling
    Department of Materials and Environmental Chemistry, Stockholm University.
    Hedin, Niklas
    Department of Materials and Environmental Chemistry, Stockholm University.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Strong and binder free structured zeolite sorbents with very high CO 2-over-N 2 selectivities and high capacities to adsorb CO 2 rapidly2012In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 5, no 6, p. 7664-7673Article in journal (Refereed)
    Abstract [en]

    Mechanically strong monoliths of zeolite NaKA with a hierarchy of pores displayed very high CO2-over-N2 selectivity. The zeolite monoliths were produced by pulsed current processing (PCP) without the use of added binders and with a preserved microporous crystal structure. Adsorption isotherms of CO2 and N2 were determined and used to predict the co-adsorption of CO2 and N2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic adsorbents of NaKA could reach an extraordinarily high CO2-over-N2 selectivity in a binary mixture with a composition similar to flue gas (15 mol% CO2 and 85 mol% N2 at 25 °C and 101 kPa). Structured NaKA monoliths with a K+ content of 9.9 at% combined a CO2-over-N2 selectivity of >1100 with a high CO2 adsorption capacity (4 mmol g−1) and a fast adsorption kinetics (on the order of one minute). Estimates of a figure of merit (F) based on IAST CO2-over-N2 selectivity, and time-dependent CO2 uptake capacity, suggest that PCP-produced structured NaKA with a K+ content of 9.9 at% offers a performance far superior to 13X adsorbents, in particular at short cycle times.

  • 939.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Liu, Qingling
    Hedin, Niklas
    Department of Materials and Environmental Chemistry, Stockholm University.
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Structured zeolite adsorbents with very high CO2-over-N2 selectivity and high capacity.2012Conference paper (Refereed)
  • 940.
    Akhtar, Farid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials and Environmental Chemistry, Stockholm University.
    Ogunwumi, Steven
    Crystalline Materials Research, Corning Incorporated, Corning, New York, USA..
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Thin zeolite laminates for rapid and energy-efficient carbon capture2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 10988Article in journal (Refereed)
    Abstract [en]

    Thin, binder-less zeolite NaX laminates, with thicknesses ranging between 310 to 750 μm and widths exceeding 50 mm and biaxial tensile strength in excess of 3 MPa, were produced by pulsed current processing. The NaX laminates displayed a high CO2 adsorption capacity and high binary CO2-over-N2 and CO2-over-CH4 selectivity, suitable for CO2 capture from flue gas and upgrading of raw biogas. The thin laminates displayed a rapid CO2 uptake; NaX laminates with a thickness of 310 μm were saturated to 40% of their CO2 capacity within 24 seconds. The structured laminates of 310 μm thickness and 50 mm thickness would offer low pressure drop and efficient carbon capture performance in a laminate-based swing adsorption technology.

  • 941.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ojuva, Arto
    Stockholm University, Department of Materials and Environmental Chemistry.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Stockholm University.
    All-Zeolite Membranes2010Conference paper (Refereed)
  • 942.
    Akhtar, Farid
    et al.
    Stockholm University, Department of Materials and Environmental Chemistry.
    Ojuva, Arto
    Stockholm University, Department of Materials and Environmental Chemistry.
    Wirawan, Kompiang
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Bergström, Lennart
    Stockholm University, Department of Materials and Environmental Chemistry.
    Hierarchically porous binder-free silicalite-1 discs: a novel support for all-zeolite membranes2011In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 24, p. 8822-8828Article in journal (Refereed)
    Abstract [en]

    Thermal expansion mismatch between the zeolite film and the support is an important cause for the formation of defects and cracks during the fabrication and use of zeolite membranes. We have studied how silicalite-1 discs with a permeability comparable to commercially available alumina supports can be produced by pulsed current processing (PCP) as a novel substrate for all-zeolite membranes. Hierarchically porous and mechanically strong membrane supports where the surface area and crystallography of the silicalite-1 particles were maintained could be obtained by carefully controlling the thermal treatment during PCP consolidation. In situ X-ray diffraction and dilatometry showed that the coefficient of thermal expansion (CTE) of the silicalite-1 substrate was negative in the temperature range 200-800 degrees C while the commonly used alumina substrate displayed a positive CTE. The critical temperature variation, Delta T, and thicknesses for crack-free supported zeolite films with a negative CTE were estimated using a fracture energy model. Zeolite films with a thickness of 1 mu m can only sustain a relatively modest Delta T of 100 degrees when supported onto alumina substrates while the all-zeolite membranes can support temperature variations above 500 degrees

  • 943.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ojuva, Arto
    Stockholm University, Department of Materials and Environmental Chemistry.
    Wirawan, Kompiang
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    PCP procesing of Zeolite supports for all-zeolite membranes2011Conference paper (Refereed)
  • 944.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Rehman, Yaser
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    A study of the sintering of diatomaceous earth to produce porous ceramic monoliths with bimodal porosity and high strength2010In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 201, no 3, p. 253-257Article in journal (Refereed)
    Abstract [en]

    Diatomite powder, a naturally occurring porous raw material, was used to fabricate ceramic materials with bimodal porosity and high strength. The effect of the sintering temperature on the density and porosity of dry pressed diatomite green bodies was evaluated using mercury porosimetry and water immersion measurements. It was found that the intrinsic porosity of the diatomite particles with a pore size around 0.2 µm was lost at sintering temperatures above 1200 °C. Maintaining the sintering temperature at around 1000 °C resulted in highly porous materials that also displayed a high compressive strength. Microstructural studies by scanning electron microscopy and energy-dispersive X-ray analysis suggested that the pore collapse was facilitated by the presence of low melting impurities like Na2O and K2O.

  • 945.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Shakarova, Dilshod
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ojuva, Arto
    Department of Materials and Environmental Chemistry, Stockholm University.
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, Department of Materials and Environmental Chemistry, Stockholm University.
    Structuring of AlPOs and zeolite powders into hierarchically porous CO2 adsorbents2014Conference paper (Refereed)
    Abstract [en]

    The use of porous materials in industrially important gas separation and purification applications, e.g. CO2 separation from flue gas and purification of biogas require that the porous material is assembled into mechanically strong and hierarchically porous macroscopic structures. Hierarchically porous structured monoliths[1-2] and laminates[3] have been reported with high performance for CO2 separation from N2. Such structured monoliths and laminates with tailored porosity at various length scales combined high volumetric efficiency, good mass and heat transfer, rapid adsorption/desorption kinetics and structural integrity[1-3]. Here, we demonstrate a binder-less approach[4,5] to consolidate 8-ring window zeolite and aluminophosphate (AlPO4’s) powders into mechanically strong monoliths with a high CO2 uptake capacity and CO2-over-N2 selectivity, and a rapid adsorption and release kinetics. Adsorption isotherms of CO2 and N2 were used to predict the co-adsorption of CO2 and N2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic zeolite adsorbents of partially K exchanged NaA could reach an extraordinarily high CO2-over-N2 selectivity in a binary mixture with a composition similar to flue gas[1]. Furthermore, zeolite monoliths showed high tensile strength of 2.2 MPa. AlPO-17 and AlPO-53 monoliths were consolidated by the binder-less process with a tensile strength over 1 MPa. AlPO-17 monoliths showed high CO2 adsorption capacity while AlPO-53 exhibited high CO2-over-N2 selectivity. Cyclic CO2 adsorption tests showed that AlPO4 monoliths required less energy for regeneration compared to zeolite and could be regenerated to their full capacity at low pressures

  • 946.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Shiju, Guo
    Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore.
    Effect of microstructure on the properties of pulse current sintered bimodal hardmetals2008In: Proceedings of the 7th International Conference on Tungsten, Refractory and Hardmaterials, 2008, p. 41-48Conference paper (Refereed)
    Abstract [en]

    This study deals with the pulse current processing, microstructure and mechanical properties of WC-20wt%(W,Ti,Ta)C-6wt%Co cemented carbides. The conventional WC particles of 4μm size and ultrafine particles of 200nm were introduced in the system with varying ratio to synthesize bimodal hardmetals. Pulse current processing effectively controlled the grain size of WC particles in the presence of (W,Ti,Ta)C phase to synthesize fine microstructure. The microstructure of pulse current consolidated hardmetals was sensitive to the ratio of conventional WC particles to ultrafine WC particles. The ratio of conventional WC particles to ultrafine WC particles was very effective to enhance the mechanical properties of bimodal hardmetals. Hardness of bimodal hardmetals increased with decrease in the ratio of conventional WC particles to ultrafine WC carbide particles. The bending strength showed the similar trend of the hardness. The fracture behavior showed transgranular fracture mode as a dominant fracture mechanism in bimodal hardmetals with varying ratio of conventional WC particles to ultrafine WC particles.

  • 947.
    Akhtar, Farid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sjöberg, Erik
    Korelskiy, Danil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rayson, Mark
    Department of Chemistry, The University of Surrey, Guildford.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Preparation of graded silicalite-1 substrates for all-zeolite membranes with excellent CO2/H2 separation performance2015In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 493, p. 206-211Article in journal (Refereed)
    Abstract [en]

    raded silicalite-1 substrates with a high gas permeability and low surface roughness have been produced by pulsed current processing of a thin coating of a submicron silicalite-1 powder onto a powder body of coarser silicalite-1 crystals. Thin zeolite films have been hydrothermally grown onto the graded silicalite-1 support and the all-zeolite membranes display an excellent CO2/H2 separation factor of 12 at 0 °C and a CO2 permeance of 21.3×10-7 mol m-2 s-1 Pa-1 for an equimolar CO2/H2 feed at 505 kPa and 101 kPa helium sweep gas. Thermal cracking estimates based on calculated surface energies and measured thermal expansion coefficients suggest that all-zeolite membranes with a minimal thermal expansion mismatch between the graded substrate and the zeolite film should remain crack-free during thermal cycling and the critical calcination step.

  • 948.
    Akhtar, Farid
    et al.
    Institute of Powder Metallurgy, School of Materials Science and Engineering, University of Science and Technology, Beijing.
    Vasiliev, Petr
    Stockholm University, Department of Materials and Environmental Chemistry, Arrhenius Lab.
    Bergström, Lennart
    A novel method to produce hierarchically porous monoliths from nanoporous powders2008Conference paper (Refereed)
  • 949.
    Akhtar, Farid
    et al.
    Materials Chemistry Research Group, Arrhenius Laboratory, Department of Physical, Inorganic and Structural Chemistry, Stockholm University.
    Vasiliev, Petr O
    Materials Chemistry Research Group, Arrhenius Laboratory, Department of Physical, Inorganic and Structural Chemistry, Stockholm University.
    Bergström, Lennart
    Materials Chemistry Research Group, Arrhenius Laboratory, Department of Physical, Inorganic and Structural Chemistry, Stockholm University.
    Hierarchically porous ceramics from diatomite powders by pulsed current processing2009In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 92, no 2, p. 338-343Article in journal (Refereed)
    Abstract [en]

    Hierarchically porous ceramic monoliths have been fabricated by pulsed current processing (PCP) of diatomite powders. The partial sintering behavior of the porous diatomite powders during PCP or spark plasma sintering was evaluated at temperatures between 600° and 850°C. Scanning electron microscopy and mercury porosimetry measurements showed that the PCP method was able to bond the diatomite powder together into relatively strong monoliths without significantly destroying the internal pores of the diatomite powder at a temperature range of 700°–750°C. Little fusion at the particle contact points occurred at temperatures below 650°C while the powder showed partial melting and collapse of both the interparticle pores and the internal structure at temperatures above 800°C.

  • 950. Akhtar, Riaz
    et al.
    Dong, Yang
    Internet banking: a comparative study from Sweden and China2004Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The Internet is the driving engine of the new economy and it has given birth to Internet banking. It allows the banks to delegate tasks to the customers. Thus, Internet banks are providing all traditional services through the Internet. The purpose of this study is to gain a deeper understanding on the role of websites in Internet banking. In order to find out the research questions, Swedish and Chinese customers were selected as samples for case studies. The findings and conclusions of this study indicated that there are several factors that influence consumers on Internet banking websites and various variables which enhances customers’ service in Internet banking.

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