Robert D. Shoup

Controlled Pore Silica Bodies Gelled From Silica Sol-Alkali Silicate Mixtures

Abstract: Mixtures of potassium silicate and colloidal silica sol have been shown to possess reasonable resistance to spontaneous gelation. When caused to gel by addition of a latent acid reagent such as formamide, controlled pore silica structures were obtained. These structures ranged in pore size from 100A to about 3600A, and each specified composition had a relatively narrow pore size distribution. This technique is useful in forming high purity silica bodies with intricate geometric shapes.

Ultra-low expansion glass from gels

Pyrolysis of mixed titanium and silicon metal halides produces a commercial glass (7.4% TiO2) with ultra-low thermal expansion that is essentially zero over the temperature range of 0 to 300°C. A colloidal particulate gel process involving potassium silicate, titania sol and formamide gel reagent was found to produce glass compositions with similar low expansion behavior. Due to the strongly basic nature of the precursor solutions, special titania sols had to be prepared that were stable in these alkali silicate solutions. The preferred TiO2 sols were those containing quaternary ammonium stabilizing counter-ions. These sols served not only as the source of homogeneously distributed titania, but they may also serve as nucleating species that contribute to particle growth and pore size control of the gel network. The large pore (∼0.3 µm) TiO2/SiO2 gel structures were easily dealkalized, dried and sintered to uncracked glass shapes. Plates up to 9.5 cm×6.6 cm× 0.5 cm thick and some intricate cast shapes were produced and their glass properties evaluated.