Fabrication and Property Control of Ceramic Composites for High Temperature Filtration

采用凝胶注模成型的方法制备了堇青石/莫来石(C/M)复相多孔陶瓷。为了控制C/M复合体的气孔形态和增加孔隙率，将直径为10μm的球形玉米淀粉颗粒添加到含有一定数量的复合粉、有机单体和分散剂的浆料中。浆料在模具中原位固化(加入单体聚合)后，将坯体加热到700min(粘结剂出炉)，然后在1350℃的空气中连续烧结10h，制得孔隙率为54%的C/M复合材料。尽管随着烧结温度的升高，烧结体的气孔率显著降低，但起始复合颗粒之间形成的初级气孔的平均尺寸(0.4~0.6μm)变化不大。对于玉米淀粉颗粒衍生的次生孔，直径约为10μ…的球形孔在1350℃下制得的C/M复合材料中，有更多的m与所加入的淀粉粉的原始形状和大小相对应。在较高的烧结温度下，二次气孔变形为形状不规则且较小的气孔。因此，控制复合粉末孔结构的最佳烧结温度为1350℃。以商品粉末为原料，采用氮气鼓泡法制备了高孔率堇青石陶瓷。在聚合固化之前，向浆料中引入恒定流量的N_2气体。该工艺可制得孔隙率为75-83%的氧化铝陶瓷。这些样品的抗弯强度在3~10 Mpa之间，高于用有机造孔剂制备的堇青石陶瓷。强度的提高可能是由于其独特的孔结构，在这种孔结构中，由氮气鼓泡产生的大尺寸球形孔相互连接。除了凝胶注模成型外，还采用了一些成型工艺来制备多孔氧化铝陶瓷。研究了球状中空玻璃颗粒、PVA颗粒或各种淀粉作为造孔剂时，样品的孔结构与力学性能和热性能的关系。较少

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