The effect of polymer concentration on thermophysical, structural and mechanical properties of siloxane-infiltrated silica ceramics

Abstract

Silica ceramics with the open porosity of 10% was infiltrated with the methyl-phenyl-spirocyclosiloxanol (MPS) acetone solution. Various MPS concentrations in the range of 0.1–100% were used. Infiltration was followed by the polyfunctional condensation in order to obtain ceramics filled with various volume fractions of the polymethyl-phenyl-spirocyclosiloxane (PMPS). Water absorption capacity, flexural strength, dilatometric thermal expansion, optical and structural properties of the obtained materials were analyzed. As a result, water absorption capacity was less than 0.15% in the range of 1–100% MPS fraction in the initial solution, whereas the flexural strength showed logarithmic growth in the range of 45–63 MPa with MPS fractional increase. In comparison to the initial ceramics, thermal expansion demonstrated several features that can be related to phase transitions and thermal-oxidative degradation of the polymer. Structural properties were analyzed by mercury and gas porometry and scattering techniques. The mean size of pores, that stay unfilled after infiltration, was shown to rise with the polymer fractional volume increase. The obtained results indicate that a relatively low fraction of approximately 1% of the MPS in the initial solution allows to obtain silica ceramics with low water absorption capacity and sufficient flexural strength. It might be attributed to the polymer tendency to fill mostly pore throats.