Factors affecting the chemical stability of glass

Water resistance and acid resistance of silicate glass is mainly determined by the content of silica and alkali metal oxides. The higher the content of silica, the greater the degree of mutual connection between the silica tetrahedron and the higher the chemical stability of the glass. With the increase of alkali metal oxide content, the chemical stability of glass decreases. Moreover, as the radius of alkali metal ions increases, the bond strength weakens, and its chemical stability generally decreases, that is, water resistance Li+>Na+>K+.

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When two kinds of alkali metal oxides exist in the glass at the same time, the chemical stability of the glass is extreme due to the “mixed alkali effect”, which is more obvious in lead glass.

In silicate glass with alkaline earth metal or other bivalent metal oxide replacement of silicon oxygen, also can reduce the chemical stability of glass. However, the effect of decreasing stability is weaker than that of alkali metal oxides. Among the divalent oxides, BaO and PbO have the strongest effect on chemical stability, followed by MgO and CaO.

In the base glass with the chemical composition of 100SiO 2+(33.3 1 x) Na2O+zRO(R2O: or RO 2), replace part N azO with CaO, MgO, Al2O 3, TiO 2, zRO 2, BaO and other oxides in turn, the order of water resistance and acid resistance is as follows.

Water resistance: ZrO 2>Al2O: >TiO 2>ZnO≥MgO>CaO≥BaO.

Acid resistance: ZrO 2>Al2O: >ZnO>CaO>TiO 2>MgO≥BaO.

In the glass composition, ZrO 2 not only has the best water resistance and acid resistance, but also the best alkali resistance, but refractory. BaO is not good.

In the trivalent oxide, alumina, boron oxide on the chemical stability of glass will also appear “boron anomaly” phenomenon. 6. In sodium – calcium – silicon – salt glass xN agO·y CaO·z SiO:, if the oxide content conforms to the relation (2-1), a fairly stable glass can be obtained.

C – 3 (+ y) (2-1)

In summary, all the oxides that can strengthen the glass structure network and make the structure complete and dense can improve the chemical stability of glass. Conversely, the chemical stability of the glass will be reduced.