Abstrakt

Chemical Durability Of Some P2O5-PbO-Al2O3-R2O Glasses

N.Abd El-Shafi, S.Ibrahim, A.A.Ali

The effect of composition on the chemical durability of some glasses having the general formula 60P2O5. (35-ï‚´) PbO. 5Al2O3. R2O, where ï‚´ extends from 0 to 20(mol.%) and R is Li, Na or K, has been investigated. Morespecifically, the effect of time on the weight loss, dissolution rate and pH of the attacking solution(deionised water) has been reported. The durability of the present glasses is considerably improved by the substitution of alkali oxide for PbO. The improvement increases, in general, with the rise in the level of substitution. The most durable glasses yielded are those with 20mol.% Na2O and Li2O. The weight losses and rates of both glasses as well as the pHÂ’s of their attacking solutions were unaffected along the extension of the soaking time from the second to the tenth day. The dissolution rate of the 20mol.% Na2O-containing glass, calculated after ten days of duration, has been found to equal 3.3ï‚´10-8gcm-2min-1(or 2.4ï‚´10-12mole cm2 min1), whereas that of the corresponding Li2O-containing glass equals 1.3ï‚´10-8gcm-2 min-1(or 1.02ï‚´10-12mole cm-2 min-1). Almost for all glasses, the pH of the attacking solution shifts down sharply(becomes more acidic) at the beginning of the experiment, while it tends to level off as the time of soaking is increased. The degree of the shift in the pH varies with composition(i.e., it decreases with increasing the alkali oxide content). Elementary analysis is performed on the attacking solution. For easy comparison between the different elements as well as different compositions the leaching rates are normalized by the concentrations of the ions in the glass. The obtained data reveal that the dissolution of constituents of the glasses increases in the order P>Pb>R >Al.