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Abstract: The porous ZrO2 ceramics with ultra-high porosity were produced by combining phase change, heat exchange and freeze drying process of ZrO2 slurries during decompression environment. The prepared slurry was first cooled to near the supercooling point, and then the supercooled slurry was placed on decompression system to induce foaming and solidification until the decompress-freezing process of the slurry completed. After drying and sintering of the green part, an as-prepared ceramic with porosity more than 93% was obtained. It was shown that the porous ceramic was typically composed of large spherical cells, interconnected by near circular windows. Although the mechanical properties in obtained ceramics are not enough to resist high stress, porous ceramics with a number of pores in cell walls and struts may be expected to be applied in high thermal insulation process. [Copyright &y& Elsevier]

Abstract: Hierarchically porous silica ceramics with unidirectionally aligned channel morphology have been synthesized by in situ mineralization of soluble starch monolith. The procedure followed two steps. First, soluble starch monoliths with well-defined uniaxial macroporous structure were prepared by unidirectional solidification process of starch hydrosol or starch hydrogel. Second, such an as-prepared artificial monolith, used as template, was soaked into a surfactant-templated sol–gel solution to mineralize the existing channel structure. It was shown that the macropore size, wall thickness, and macropore morphology in obtained soluble starch materials may be tuned in a certain range, through adjusting the concentration of starch slurry. When initial concentration changed from 10 wt.% to 15 wt.%, the macropore size of soluble starch materials decreased, while the wall thickness increased. Through the second step, porous silica ceramics were obtained after drying and calcining of organic–inorganic hybrid silicate compounds from solution. These resulting products preserved template microstructure in great detail and exhibited narrow macropore size distributions. It was observed that when the soaking time increased from 36h to 84h, the average pore size of the silica ceramics was decreased from 4.1μm to 3.6μm. In addition, in nanopore regime, all the silica monoliths obtained presented a coexistence of uniform worm-like nanopore and lamellar phase feature, and large BET and microporous surface area. [Copyright &y& Elsevier]

Abstract: Experiments have been performed to show that the mechanical properties of alumina porous ceramics may be improved by introducing glycerol into the raw slurries and then casting them under a constant cooling rate. The effects of glycerol on the freeze casting process and thereby on the microstructure and mechanical properties of porous ceramics obtained are investigated. It is shown that the addition of glycerol will increase both the slurry viscosity and sample sintered density. SEM images for microstructure of the final ceramics reveal that a good connection between ceramic lamellae has been promoted. This connection makes as-prepared porous ceramics obtain high mechanical properties. For the 30vol.% alumina slurry with glycerol, the axial and radial compression strengths reach to, respectively, 255.1MPa and 105.8MPa. [Copyright &y& Elsevier]