Fabrication and Property Control of Ceramic Composites for High Temperature Filtration

采用凝胶铸造成型方法制备了多孔堇青石/莫来石（C/M）复合材料和堇青石陶瓷。为了控制孔隙形态，提高C/M复合体的孔隙率，将直径为10μm的球形玉米淀粉颗粒加入到含有一定量复合粉体、有机单体和分散剂的浆料中。浆料在模具中原位凝固（加入的单体聚合）后，坯体加热至700℃（粘结剂出料），在1350℃空气中连续烧结10 h，得到孔隙率为54%的多孔C/M复合材料。随着烧结温度的升高，复合材料的孔隙率明显降低，但初始复合颗粒之间形成的初级孔隙的平均尺寸（0.4 ~ 0.6 μm）变化不大。在1350℃下得到的C/ m复合材料中，由玉米淀粉颗粒形成的次生孔隙主要为直径约为10 μ m的球形孔隙。在较高的烧结温度下，二次孔隙变形为形状不规则且较小的孔隙。因此，目前复合粉体的最佳烧结温度为1350℃，以控制气孔结构。采用氮气鼓泡法制备高多孔堇青石陶瓷。在聚合凝固之前，向浆料中注入恒流的氮气。该工艺可制得孔隙率为75 - 83%的极多孔氧化铝陶瓷。这些样品的抗弯强度在3 ~ 10 MPa之间，高于用有机成孔剂制备的堇青石陶瓷。其强度的增强可能与氮气气泡形成的球形孔隙相互连接有关。多孔氧化铝陶瓷的制备还采用了除凝胶浇铸外的一些成型工艺。以球形中空玻璃颗粒、聚乙烯醇（PVA）或各种淀粉为成孔剂，考察了孔隙结构与力学性能和热性能的关系。少

Porous cordierite/mullite (C/M) composite and cordierite ceramics were fabricated using gel-casting as forming method. In order to control the morphology of pores and increase the porosity in the C/M composite bodies, spherical corn starch particles with 10μm in diameter was added to a slurry containing fixed amounts of the composite powder, organic monomer and dispersant. After in-situ solidification of the slurry (polymerization of the monomer added) in a mold, a green body was heated up to 700℃ (binder born-out) and successively sintered at 1350℃ for 10 h in air, which produced a Porous C/M composite having 54 % porosity. Although the porosity of the sintered composites was considerably decreased with an increasing sintering temperature, only a subtle change was detected in the average size of the primary pores (0.4 - 0.6 μm) formed between starting composite particles. Concerning the secondary pores derived from corn starch particles, spherical pores with the diameter of about 10 μ … More m corresponding to the original shape and size of the starch powder added were observed in C/M composites obtained at 1350℃. At elevated sintering temperatures, the secondary pores were deformed into irregularly shaped and smaller ones. Therefore, an optimum sintering temperature to control the resulting pore structure was found to be 1350℃ for the present composite powders.N_2 gas bubbling procedure was employed to produce highly porous cordierite ceramics from a commercial powder. Prior to the solidification due to polymerization, a constant flow of N_2 gas was introduced into a slurry. This procedure yielded extremely porous alumina ceramics with 75 - 83 % porosity. Bending strength of these samples ranged between 3 - 10 MPa, which were higher than those of cordierite ceramics fabricated using organic pore-forming agents. The enhanced strength might be due to the characteristic pore structure in which largely spherical pores derived from N_2 gas bubbling were interconnected.Porous alumina ceramics were also fabricated using some forming procedure other than gel-casting. Relationships between pore structures and mechanical or thermal properties were examined for samples that particles of spherical hollow glass, PVA or various kinds of starches were added as pore-forming agent. Less