Some physical and chemical properties of a massive 96 % SiO2 glass block

Abstract

Sections cut from a thick block of porous 96 % SiO2 glass were subjected to surface area and pore size evaluation. Some also were consolidated to clear impervious glass, and then checked for water content (OH groups) or analyzed for Na2O and B2O3 in efforts to determine whether structural and compositional gradients result on leaching thick blocks of heat-treated alkaliborosilicate glass. The study shows that small systematic changes in surface area, pore size, and soda content exist. However, none of them are attributable to the leachant. Arguments are set forth that they simply are caused by longer heat retention in the interior of the block and the temperature gradient that will exist between the inside and the outside surface. The dewatering characteristics (removal of OH groups) of the porous glass remain unaffected by the thickness of the base glass. However, the hydroxyl content in the final 96 % SiO2 glass increases with distance from its external surface, reaching a maximum at the center of the block. Α plausible explanation for the hydroxyl gradient is given.