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  • 1.
    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%.

  • 2.
    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.

  • 3.
    Bartek, Alena
    et al.
    Luleå tekniska universitet.
    Johansson, Thomas
    Luleå tekniska universitet.
    Ekström, Thommy
    AB Sandvik Hard Materials.
    Herbertsson, Harald
    Luleå tekniska universitet.
    Yttrium α-Sialon Ceramics by Hot Isostatic Pressing and Post-Hot Isostatic Pressing1992In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 75, no 2, p. 432-439Article in journal (Refereed)
    Abstract [en]

    Dense α-sialon materials were produced by hot isostatic pressing (HIP) and post-hot isostatic pressing (post-HIP) using compositions with the formula Yx(Si12-4.5x, Al4.5x)-(O1.5x,N16-1.5x) with 0.1 ≤x ≤ 0.9 and with the same compositions with extra additions of yttria and aluminum nitride. X-ray diffraction analyses show how the phase content changes from large amounts of β-sialon (x = 0.1) to large amounts of α-sialon (x = 0.4) and increasing amounts of mellilite and sialon polytypoids (x = 0.8). Samples HIPed at 1600°C for 2 h contained unreacted α-silicon nitride, while those HIPed at 1750°C for 1 h did not. This could be due to the fact that the time is to short to achieve equilibrium or that the high pressure (200 MPa) prohibits α-sialon formation. Sintering at atmospheric pressure leads to open porosity for all compositions except those with excess yttria. Therefore, only samples with excess yttria were post-HIPed. Microstructrual analyses showed that the post-HIPed samples had the highest α-sialon content. A higher amount of α-sialon and subsequently a lower amount of intergranular phase were detected at x = 0.3 and x = 0.4 in the post-HIPed samples in comparison to the HIPed. The hardness (HV10) and fracture toughness (KIC) did not differ significantly between HIPed and post-HIPed materials but vary with different x values due to different phase contents. Measurements of cell parameters for all compositions show a continuous increase with increasing x value which is enhanced by high pressure at high x values.

  • 4.
    Elbadawi, Mohammed
    et al.
    Luleå University of Technology, Department of Health Sciences, Medical Science. Department of Mechanical Engineering, University of Sheffield, Sheffield, United Kingdom.
    Wally, Zena J.
    Department of Materials Science and Engineering, University of Sheffield, Sheffield, UK.
    Reaney, Ian
    Department of Materials Science and Engineering, University of Sheffield, Sheffield, UK.
    Porous Hydroxyapatite-Bioactive Glass Hybrid Scaffolds Fabricated via Ceramic Honeycomb Extrusion2018In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 101, no 8, p. 3541-3556Article in journal (Refereed)
    Abstract [en]

    The successful fabrication of hydroxyapatite-bioactive glass scaffolds using honeycomb extrusion is presented herein. Hydroxyapatite was combined with either 10 wt% stoichiometric Bioglass® (BG1), calcium-excess Bioglass® (BG2) or canasite (CAN). For all composite materials, glass-induced partial phase transformation of the HA into the mechanically weaker β-tricalcium phosphate (TCP) occurred but XRD data demonstrated that BG2 exhibited a lower volume fraction of TCP than BG1. Consequently, the maximum compressive strength observed for BG1 and BG2 were 30.3 ± 3.9 and 56.7 ± 6.9 MPa, respectively, for specimens sintered at 1300 °C. CAN scaffolds, in contrast, collapsed when handled when sintered below 1300 °C, and thus failed. The microstructure illustrated a morphology similar to that of BG1 sintered at 1200 °C, and hence a comparable compressive strength (11.4 ± 3.1 MPa). The results highlight the great potential offered by honeycomb extrusion for fabricating high-strength porous scaffolds. The compressive strengths exceed that of commercial scaffolds, and biological tests revealed an increase in cell viability over seven days for all hybrid scaffolds. Thus it is expected that the incorporation of 10 wt% bioactive glass will provide the added advantage of enhanced bioactivity in concert with improved mechanical stability.

  • 5.
    Larker, Richard
    Luleå tekniska universitet.
    Reaction Sintering and Properties of Silicon Oxynitride Densified by Hot Isostatic Pressing1992In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 75, no 1, p. 62-66Article in journal (Refereed)
    Abstract [en]

    Silicon oxynitride ceramics were reaction sintered and fully densified by hot isostatic pressing in the temperature range 1700°C to 1950°C from an equimolar mixture of silicon nitride and silica powders without additives. Conversion to Si2N2O increases steeply from a level around 5% of the crystalline phases at 1700°C to 80% at 1800°C, and increases a few percent further at higher temperatures. α-Si3N4 is the major residual crystalline phase below 1900°C. The hardness level for materials containing 85% Si2N2O is approximately 19 GPa, comparable with the hardness of Si3N4 hot isostatically pressed with 2.5 wt% Y2O3, while the fracture toughness level is around 3.1 MPa. m1/2, being approximately 0.8 MPa.m1/2 lower. The three-point bending strength increased with HIP temperature from approximately 300 to 500 MPa

  • 6.
    Mouzon, Johanne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Lindbäck, Ture
    Odén, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Influence of agglomeration on the transparency of yttria ceramics2008In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 91, no 10, p. 3380-3387Article in journal (Refereed)
    Abstract [en]

    In this work, five yttria powders with slightly different states of agglomeration, inherited from various procedures of dewatering the same precursor, were densified by a combination of vacuum sintering followed by hot isostatic pressing (HIP). In order to relate the densification behavior of each powder to its state of agglomeration, all powders were characterized by tap density measurements, X-ray diffraction, nitrogen adsorption, and laser scattering, while the microstructures of the corresponding densified samples were studied by optical and scanning electron microscopy. The five yttria powders produced sintered samples that differed remarkably from each other in terms of transparency. These discrepancies were related to the degree of fineness in the powders at two different levels. At the level of primary particles, fine and weakly agglomerated powder was very sinterable, causing abnormal grain growth to occur only in the very late stage of sintering. However, the resulting entrapped pores and reduction due to vacuum sintering were responsible for poor optical properties. At the agglomerate level, a bimodal size distribution was identified for all powders. For powders showing severe agglomeration of the primary particles, increasing the relative content of the smaller size population of agglomerates was found to trigger abnormal grain-growth earlier during presintering. This was attributed to the density around large agglomerates exceeding a critical threshold in the green bodies. Finally, transparency was achieved in samples for which presintering was stopped before grain growth became abnormal. This confirmed that the key to successfully obtaining transparency was to keep porosity intergranular, which could be removed subsequently by HIP treatment.

  • 7. Mouzon, Johanne
    et al.
    Odén, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tillement, Olivier
    Université C. Bernard Lyon I.
    Jorand, Yves
    GEMPPM, INSA Lyon.
    Effect of drying and dewatering on yttria precursors with transient morphology2006In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 89, no 10, p. 3094-3100Article in journal (Refereed)
    Abstract [en]

    The influence of drying and dewatering of a yttrium hydroxynitrate precursor with transient morphology was investigated. The ability of this precursor to form soft agglomerated nanoparticles after calcination is dependent on the dewatering method. Freeze drying leads to finer particles than other dewatering methods that involve removal of the solvent from its liquid state. As water is directly removed by sublimation during freeze drying, this method inhibits the formation of solid bridges between hydroxynitrate platelets. These bridges, which form with the other dewatering methods, destabilize the spheroidization process of the platelets during subsequent firing at high temperatures.

  • 8.
    Niska, John
    et al.
    Luleå tekniska universitet.
    Loberg, Bengt
    Easterling, K.E.
    Luleå tekniska universitet.
    Effect of oxygen loss on densification when hot isostatic pressing YBa2Cu3O7-δ1989In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 72, no 8, p. 1508-1510Article in journal (Refereed)
    Abstract [en]

    Hot isostatic pressing of the high-Tc superconductor YBa2Cu3O7-δ can lead to loss of oxygen and transformation of the material from the high-Tc orthorhombic phase to the nonsuperconducting tetragonal phase. It is shown that glass encapsulation helps retain the orthorhombic structure, whereas steel encapsulation resulted in formation of the tetragonal phase. Reasons for this phenomenon are discussed. The equilibrium oxygen gas pressure for the oxygen decomposition reaction in YBa2Cu3O7, however, prevents full densification of this material in glass when employing hot isostatic pressing conditions of 200 MPa and 845°C.

  • 9. Prakash, Braham
    et al.
    Bandyopadhyay, Siddhartha
    Central Glass and Ceramic Research Institute (CGCRI), Calcutta.
    Mukerji, Joydeb
    Central Glass and Ceramic Research Institute (CGCRI), Calcutta.
    Friction coefficient of (a+b)-SiAlON composite against a steel and dense silicon nitride Tribopair1999In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 82, no 8, p. 2255-2256Article in journal (Refereed)
    Abstract [en]

    The friction characteristics of hot-pressed (α+β)-SiAlON, versus those of bearing steel and dense Si3N4 under dry sliding conditions, are reported. The coefficient of friction decreases as the alpha-SiAlON content increases and is double that of a metal-ceramic pair, in comparison to that of a ceramic-ceramic pair.

  • 10.
    Shen, Zhijan
    et al.
    Zhejiang.
    Ashkin, D.
    Luleå tekniska universitet.
    Babushkin, O.
    Luleå tekniska universitet.
    Ekström, T.
    Arrhenius laboratory.
    Melilite Formation in a Samarium-Stabilized alpha-Sialon Ceramic during Postsintering Heat Treatments1997In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 80, no 3, p. 817-821Article in journal (Refereed)
    Abstract [en]

    The formation of the melilite solid solution phase (M), Sm2Si3-xAlxO3xN4-x, in an alpha-sialon sample of overall composition Sm0.6Si9.28Al2.69O1.36N14.76, was studied as a function of time in the temperature interval 13751525C. The alpha-sialon ceramic contained only minor amounts of the 21R sialon polytype and some residual grain-boundary glass before heat treatment. In situ studies by high-temperature X-ray diffraction were combined with postsintering heat treatment followed by quenching. The M-phase was found to be formed by two different mechanisms: either crystallization of the residual grain-boundary liquid or a direct decomposition of the alpha-sialon phase. The liquid crystallized during the first 1015 min of heat treatment, yielding a rapid M-phase formation, and further formation of M-phase continued at a much slower rate, related to the decomposition of alpha-sialon

  • 11.
    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 University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Synthesis and Properties of MoSi2–MoB–SiC Ceramics2016In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 99, no 4, p. 1147-1150Article in journal (Refereed)
    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.

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