Corrosão em superfícies de vidros de metasilicatos de sódio e càlcio

Abstract

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Metasilicate glasses have a mean of 2 non-bridging oxigens per SiO4 tetrahedron, so that its structure is constituted essentially by (SiO3(2-))n chains. Due to the low polymerization degree of the SiO4 tetrahedra, the surface of such glasses undergoes pronounced physico-chemical changes in contact with water, acid solutions and with the surrounding atmosphere. Surfaces of a 2Na2O∙1CaO∙2SiO2 glass were submitted to corrosion by a weak HCl and HF solution. Infrared reflection spectroscopy measurements show that the characteristic bands of the glass change with leaching time. The prolonged corrosion by the acid solution gives spectra which approach that of a porous silica glass (Vycor). This leads to the conclusion that the acid corrosion produces a thin silica gel layer at the metasilicate glass surface.