Impact of boron complexation by Tris buffer on the initial dissolution rate of borosilicate glasses

Tris(hydroxymethyl)aminomethane is a commonly used buffer for leaching studies on glasses. In this work, we demonstrate that it plays a role on the alteration kinetics of borosilicate glasses. Comparative dissolution experiments on a soda-lime silicate glass and a sodium borosilicate glass, in several solutions with or without Tris at neutral pH, are carried out in order to assess the specific effects of the ionic strength and of the Tris molecules on the initial dissolution kinetics. Tris has no effect on the dissolution of the soda-lime silicate glass, while it significantly enhances the dissolution of the borosilicate glass, by increasing the B, Na, and Si release rates. This specific effect on the borosilicate glass is attributed to the Tris-boron complexation and discussed. The bidentate complexation of boron by Tris(hydroxymethyl)aminomethane (Tris) with a 1:1 stoichiometry is directly demonstrated by infrared and NMR spectroscopies. Complexation constants are determined for the Tris-borate complex and its protonated form Tris-boric, from the (11)B and (1)H NMR spectra. This complexation should be taken into account when using the Tris/HCl buffer in alteration experiments of borosilicate glasses.