Diffusion and solubility of water in alkali borate melts

The solubility and diffusivity of water in alkali borate melts containing (mol%) 0-25Li(2)O, 0-35Na(2)O and 0-30K(2)O have been measured at 800 and 900degreesC. The solubility of water in alkali borate melts is much larger than in alkali silicate melts with solubilities ranging from approximate to2400 wtppm for some of the sodium borate melts to over 6000 wtppm for vitreous boric oxide. Although water diffusivities cannot be measured for low alkali content compositions due to their high water contents under all melting conditions, diffusivities measured for higher alkali oxide content melts range from approximate to7x10(-7) to approximate to5x10(-6) cm(2)/s. The diffusivity of water is inversely related to the viscosity of the melt. The glass transformation temperature for vitreous boric oxide is highly dependent on the water content of the sample, with values in the literature ranging from 210 to 305degreesC The effect of water content on T-g of alkali borate glasses is less than that for alkali silicate glasses.