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  • 1.
    Ciurans Oset, Marina
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nordin, Jan
    Akzo Nobel Pulp and Performance Chemicals AB.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Processing of Macroporous Alumina Ceramics Using Pre-Expanded Polymer Microspheres as Sacrificial Template2018Ingår i: Ceramics, ISSN 2571-6131, Vol. 1, nr 2, s. 329-342Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shaped porous ceramics have proven to be the most adapted materials for several industrial applications, both at low and high temperatures. Recent research has been focused on developing shaping techniques, allowing for a better control over the total porosity and the pores characteristics. In this study, macroporous alumina foams were fabricated by gel-casting using pre-expanded polymeric microspheres with average sizes of 40 μm, 20 μm, and 12 μm as sacrificial templates. The gel-casting method, as well as the drying, debinding, and presintering conditions were investigated and optimized to process mechanically strong and highly porous alumina scaffolds. Furthermore, a reliable model relating the amount of pre-expanded polymeric microspheres and the total porosity of the presintered foams was developed and validated by mercury intrusion porosimetry measurements. The electron microscopy investigation of the presintered foams revealed that the size distribution and the shape of the pores could be tailored by controlling the particle size distribution and the shape of the wet pre-expanded microspheres. Highly uniform and mechanically stable alumina foams with bimodal porosity ranging from 65.7 to 80.2 vol. % were processed, achieving compressive strengths from 3.3 MPa to 43.6 MPa. Given the relatively open pore structure, the pore size distribution, the presintered mechanical strength, and the high porosity achieved, the produced alumina foams could potentially be used as support structures for separation, catalytic, and filtration applications.

  • 2.
    Elbadawi, Mohammed
    Luleå tekniska universitet, Institutionen för hälsovetenskap.
    Guar Gum: A Novel Binder for Ceramic ExtrusionIngår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956Artikel i tidskrift (Refereegranskat)
  • 3.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nordin, Jan
    Luleå tekniska universitet, Extern.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Development of Ceramic Foams Containing Platinum Nanoparticles as the Catalyst2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    The exhaust gases contribute significantly to global warming, but without a catalytic converter, exhaust gases would be even more polluting. Therefore, having a catalytic metal such as platinum nanoparticles on the surface of the pore walls in ceramic foams is a practical way to remove particulate matters and to have an effective catalytic converter in one. The porous structure of the foam filters the particulate matters and the high specific surface area of the Pt nanoparticles in the pores speed up the reactions. The role of platinum is to oxidize carbon monoxide (CO) and hydrocarbons (HC) to form carbon dioxide (CO2) and water vapor (H2O). In this study, The Pt nanoparticles were coated on the surface of the thermally expandable microspheres (Expancel). The Energy-dispersive X-ray spectroscopy (EDS) and Ultraviolet-visible spectroscopy (UV-Vis) confirmed the successful adsorption of Pt on the Expancel surface. In the next step, alumina foams prepared by the gel-casting technique using Pt-coated Expancels as the sacrificial template. The EDS confirmed the successful transfer of the Pt nanoparticles to the pore walls of the foam. The morphology and the porosity of the foams were studied using SEM and X-ray microtomography. Moreover, the compressive strength of the prepared sample in form of the green body, debinded and sintered was measured.  The results showed a promising way to design ceramic-based bi-functional foams for eliminating dust and converting harmful gases to nontoxic gases simultaneously.

  • 4.
    Hooshmand, Saleh
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nordin, Jan
    Akzo Nobel Pulp and Performance Chemicals AB, Expancel, Sundsvall, Sweden.
    Akhtar, Farid
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Porous alumina ceramics by gel casting: Effect of type of sacrificial template on the properties2019Ingår i: International Journal of Ceramic Engineering & Science, ISSN 2578-3270Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of type of sacrificial template on the processing and properties of porous alumina ceramics was investigated. Two templates, (a) hollow pre‐expanded polymer spheres (Expancel) and (b) dense glassy carbon, were used to prepare porous alumina ceramics by gel casting. The results showed that the burnout of sacrificial expandable polymer microspheres from alumina ceramics was 10 times faster than glassy carbon without compromising the compressive strength. Moreover, the effect of the size of the porous ceramic component during the burnout showed that the template decomposition and the escape of the formed gases took a longer time for the thicker specimens than the thinner one and it was significant in case of glassy carbon. It was found that the burnout of expandable microspheres could happen at a faster rate, and the time of the burnout cycle could be reduced significantly to save energy while keeping the mechanical strength twice as high than porous alumina ceramics after burnout of glassy carbon. Furthermore, the CO2 emissions during the burnout of sacrificial templates and the microstructure of the prepared porous alumina were compared for these two types of sacrificial templates. The prepared foams with pre‐expanded microspheres showed potential for being used in industrial applications, where the decreasing of the released gases is critical for saving time and energy for the fabrication of large ceramic parts.

  • 5.
    Jiang, Zhiwu
    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.
    Zhang, Hanzhu
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Liu, Yanan
    School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou.
    Combustion synthesis and mechanical properties of MoSi2­-ZrB2­-SiC ceramics2018Ingår i: Journal of the Ceramic Society of Japan, ISSN 1882-0743, Vol. 126, nr 7, s. 504-509Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    MoSi2ZrB2SiC ceramics were synthesized using Mo, Zr, Si and B4C powders by self-propagating high-temperature synthesis and densifying by spark plasma sintering. The effects of MoSi2 content on the combustion synthesis process, microstructure, and mechanical properties of the ceramics were investigated. The results showed that combustion synthesis is an unstable mode, spiral combustion. The Gibbs calculations and combustion temperature curves indicate there are two reactions occurring at the same time. The volume fraction of the four different phases and their relative densities were also measured and calculated. Compared to pure MoSi2, the 1.0MoSi20.2ZrB20.1SiC (M10) ceramic exhibits excellent mechanical properties with its maximum Vickers hardness and fracture toughness being 14.0 GPa and of 5.5 MPa m1/2, respectively. The hardness is in agreement with the rule of mixture. The morphology of indentation cracks reveals that the fracture toughness improves as a result of toughening mechanisms such as crack bridge, crack deflection, and microcracks.

  • 6.
    Montanari, Céline
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Additive Manufacturing of Silicon Nitride2017Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This study aims to investigate the fabrication of silicon nitride ceramics via additive manufacturing method. Silicon nitride exhibits excellent thermo-mechanical properties and it is one of the main structural ceramics. The excellent properties of silicon nitride are obtained through densification via liquid phase sintering. The shaping limitations engendered by conventional manufacturing method of ceramics, such as those in powder pressing, give additive manufacturing a promising potential for fabrication of complex geometrical shapes and small-scale production. Three-dimensional ceramic components can be produced via lithography-based additive manufacturing technique. Due to issues associated with light absorption, lithography-based additive manufacturing has mainly been focused on oxide ceramics, known for their low light-absorption properties. On the other hand, silicon nitride exhibits very high light absorption level.

    In this study, the possibility to additively manufacture silicon nitride ceramics via the lithography-based ceramic manufacturing technique was presented. Photocurable suspensions with dispersed silicon nitride powder were formulated. The influence of the powder composition was investigated by varying the sintering additives content and silicon nitride powder grade. The suspensions were characterized, and the photo-reactivity effects on the printability were investigating by measuring the cure depth, while also considering the rheological behavior and thermal decomposition of the various photocurable suspensions.

    Additive manufacturing of silicon nitride ceramic components was successfully achieved. By formulating various suspension compositions, suitable viscosity and cure depth were achieved with 43 vol.% solids loading. Cure depth of 40 µm was found to be sufficient to allow the shaping process, and complex geometrical shapes were fabricated at small-scale. The microstructure and physical properties of additive manufactured parts were similar to those of conventionally made parts.

    These results suggest that new possibilities with respect to the fabrication of complex geometrical shapes and small-scale series silicon nitride ceramics can be accomplished via lithography-based additive manufacturing.

    Publikationen är tillgänglig i fulltext från 2021-01-01 00:00
  • 7.
    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.

  • 8.
    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.

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