Preparation of SiO2 Glass from Model Powder Compacts: I, Formation and Characterization of Powders, Suspensions, and Green Compacts

Abstract

Dense SiO2 glass was produced at ∼1000°C by using highly ordered compacts of spherical, nearly monosized, amorphous SiO2 particles. In Part I of this study, the formation and characterization of powders, suspensions, and green bodies are described. Thermogravimetry and DTA revealed that substantial loss of bound water occurs in powders calcined at temperatures as low as 200°C. Surface area and density measurements were used to show that the water loss occurs without micropore formation. FTIR spectroscopy revealed that residual silanol groups persist to the highest temperatures (1050°C) studied. The state of particulate dispersion in suspensions was modified by pH adjustment and monitored by rheological measurements. Flocculated suspensions (low pH) produce inhomogeneous, low‐density powder compacts with highly bimodal pore‐size distributions. Uniform green bodies (with higher packing densities) were prepared using well‐dispersed suspensions (high pH). Two‐dimensional, close‐packed hexagonal arryas of particles were observed in these compacts. Pore‐size distributions were narrower, but still bimodal due to the presence of three‐particle and four‐particle pore channels. The sintering behavior of these compacts is described in part II.