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Promotion of Attack on Glass and Silica by Citrate and Other Anions in Neutral Solution

1959; Wiley; Volume: 42; Issue: 4 Linguagem: Inglês

10.1111/j.1151-2916.1959.tb12947.x

1551-2916

Frank R. Bacon, FRANK C. RAGGON,

Recycling and utilization of industrial and municipal waste in materials production

The observation that essentially neutral solutions of sodium citrate attacked sulfur‐treated soda‐lime glass bottles of generally high chemical resistance much more than was anticipated led to a general investigation. It has been found that neutral solutions of sodium citrate attack silicate glasses and silica with a severity similar to that of substantially alkaline solutions. This effect was observed for both soda‐lime and borosilicate glasses and also for vitreous, crystalline, and amorphous forms of silica. The effect of citrate becomes perceptible at a pH of about 5 and increases rapidly with pH up to 7.6. Solutions of higher pH were not studied. Solutions of certain other complex‐forming anions show the effect on sulfur‐treated soda‐lime glass containers in varying lesser degrees. Although the active anions studied are complexing agents for alkaline earths and aluminum, it was observed that citrate had more action on a fused silica container than on containers made of certain glasses containing calcium and aluminum. Therefore a digestive action on silica and the Si–O–Si structure of glasses is to be recognized. Fluoride, the only anion tested that forms previously known complexes with silicon, had slightly less action on sulfur‐treated bottles than citrate. The results suggest that soluble silicon complexes are formed at pH values in the region of 7 by citrate and some of the other organic anions studied.