纳米SiO_2包覆Al_2O_3浓悬浮体制备及其凝胶注模成型

PREPARATION OF NANO-SiO_2-COATED Al_2O_3 CONCENTRATED SUSPENSION AND ITS GEL CASTING

采用硅溶胶等制备纳米SiO2包覆Al2O3微复合体系,凝胶注模工艺制备莫来石陶瓷,着重研究了低粘度高固含量浓悬浮体系的特性及其凝胶注模成型坯体的性能。研究表明:按莫来石理论组成将Al2O3颗粒分散于质量分数为30.3%的硅溶胶中,纳米SiO2胶粒吸附于颗粒表面,形成30～50nm的SiO2包覆层,其中已形成Si—O—Al—O键。纳米SiO2包覆Al2O3浓悬浮体系的最佳分散条件在pH=9.0左右,利用SiO2包覆层的静电位阻稳定作用,可直接制备低粘度、高固含量浓悬浮体系,固相质量分数为76%的浓悬浮体表观粘度为975mPa·s;固相质量分数为76%,有机单体质量分数为7.7%,采用凝胶注模工艺,所得坯体结构均匀、致密,相对密度达63%,抗折强度达5.85MPa。

Nano-SiO_(2)-coated Al_(2)O_(3) micro-composite system was derived from silica sol and αAl_(2)O_(3) to prepare mullite ceramics by gel casting technology. Special emphasis was placed on the preparation of concentrated suspension with low viscosity and high solid volume loading, and properties of green body. By dispersing alumina in 30.3% (in mass) silica sol with theoretical composition of mullite and after drying, a nano-SiO_(2) coating with 30—50 nm and Si—O—Al—O bond are formed on the surface of alumina particles according to TEM and FTIR. It is found that the nano-SiO_(2)-coated Al_(2)O_(3) particles can be dispersed optimally in the suspension at the value of pH 9.0 and the viscosity is as low as 975 mPa·s, the suspension with solid mass loading as high as 76% were prepared by utilizing the electrostatic and steric effects resulted from the adsorption of negatively charged colloidal silica particles. The defect-free dried green body with bending strength of 5.85 MPa and relative density of 63% was obtained by gel casting technology with only 7.7%( in mass) of moromer.