Leaching rates, glass, temperature

The glass was crushed, sieved, and leached for 24 hr with boiling distilled water in a Soxhlet-type extractor. Although there are variations, the values reported (Table X) would be reduced two to three orders of magnitude at ambient temperature, and the glasses would then have an acceptably low leach rate. Our program now is to determine the temperature dependence of leach rates and to correlate weight loss data with bulk leach rates based on specific elements. 

In general, it may be concluded that a leach rate in the range of 10" g/(cm day) is probably something like a lower limit unless a substantially different solidification technology is employed. Less leachable products may be high-temperature glasses or ceramics or very sophisticated composites. 

The reaction of bases with most silicate glasses produces dissolution rates when tested in 5% NaOH solution at 95°C. The mechanism also involves a complete dissolution process as that described for acid. Weaker alkaline solutions may both leach and dissolve and sometimes show greater dependence on glass composition. And, in the case of strong alkali solutions, the rate of attack doubles for each 10 K increase in temperature or each increase in pH unit. Usually higher alkali durability glasses are used for laboratory wares. 

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