Takamitsu Fujiu

Synthesis of cellular inorganic materials by foaming sol-gels

Abstract A method for synthesizing low density, cellular inorganic materials from sol-gels has been developed. The method utilizes viscosity control during gelation to stabilize bubbles generated from freon droplets dispersed in the sol. Cellular silica, mullite and zirconia-toughened mullite have been fabricated with relative densities ranging from 10 to 45% and average cell sizes ranging from 30 to 1000 μm in diameter in dense matrices. This new class of low density, sol-gel-derived materials offers many opportunities in high temperature insulation, low permittivity substrates and catalyst supports, to name a few.

New explanation for the bonding behavior of fluorine containing bioglass

Abstract A hypothesis is proposed that the bonding behavior of bioglass with bone is controlled by the formation rate of a surface apatite layer and the characteristics of this layer. The first factor is examined using glasses with a similar apatite layer. The second is examined by comparing one of the glasses with sintered apatite. As one application of the hypothesis, an explanation is given for the lower bonding strength of fluorine containing bioglass.

Sintering of foamed silica gels

Foamed silica gels prepared from a colloidal silica containing sodium were leached to avoid α-cristobalite crystallization during sintering. The sodium content in the foamed gels was decreased from 1.5 to 0.1 wt% by first drying at 80°C and then leaching in 5M nitric acid for 2 days at 40°C. When sintered at 1000°C for 4 h or 1100°C for 8 min, the leached foams did not crystallize, had a matrix density of 92%, and a foam bulk density of about 30%. Prior to densification, the foam consists of spherical cells of 100–150 μm diameter uniformly distributed in a matrix of 12 nm silica particles. The colloidal silica matrix densifies according to Scherers viscous sintering model. Due to their low surface curvature, cellular voids do not contribute to the sintering driving force and thus, bulk foam densification and cell size shrinkage can be calculated by applying Scherers viscous sintering model.