Dissolution Mechanism of ZnO-MgO-P_2O_5 Phosphate Glasses

The dissolution process of 40ZnO-10MgO-50P_2O_5 glass in acid medium was studied by weight loss analysis.The result shows that the water dissolution rate of phosphate glasses doped with bivalent ions is low.However,situation changes greatly as the pH value of the solution reduces because of the ion exchange reaction between R~(2+) in glass and H~+ in acid.The stability of glass network is thus destroyed and followed by hydrolysis reaction of phosphate structural group.The dissolution rate increases exponentially with the increase of temperature and the reaction activation energy decreases with the increase of pH value.The dissolution rate reaches the maximun in concentrated HC1 due to the contribution of both H~+ and H_2O.The mechanism of the dissolution process is proposed into two steps:first,the weight loss is proportional to the square root of the time,and the next,it is proportional to time,which indicates the formation and development of hydrate layer on the glass surface.