ISSN:
1013-9826
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
This study investigated the mixed alkali effect in a series of phosphate based glasses. Theseglasses were of the composition 0.5P2O5-0.2CaO-0.3-xNa2O-xK2O where x=0 to 0.3 in steps of 0.05.This study considered density measurements using Archimedes’s principle, thermal characterisation usingdifferential scanning calorimetry, phase analysis following crystallisation using X-ray powder diffraction(XRD), and degradation studies combined with ion release. The results showed that these mixed alkaliglasses showed a linear decrease in density, with the ternary single alkali glass with 0.3mol K2O showinga 3% reduction in density as compared to that with 0.3mol Na2O which correlated well with thedifference in ionic diameter and atomic weight of both cations. These glasses also showed intermediateglass transition temperature (Tg) values, compared to those of the ternary single alkali glasses having thesame alkali oxide content, and the minimum Tg value was recorded for equimolar amounts of both alkalioxides. However, they did not show any significant change in the degradation rate compared to the glasswith 0.3mol Na2O with the exception of the 0.25mol K2O glass. The single alkali glass with 0.3mol K2Oshowed a significant increase in the degradation rate by an approximate one order of magnitude. For themixed alkali glasses with low molar concentration of K2O, only sodium phosphate-rich phases[NaCa(PO3)3 and Na4Ca(PO3)6] were detected from XRD; at high molar concentrations however,potassium phosphate-rich phases [KCa(PO3)3 and KPO3] were detected. At equimolar concentration ofboth alkali cations, KCa(PO3)3 and Na4Ca(PO3)6 were identified. K+, Ca2+, and P3O93- release followedthe degradation behaviour where the highly degrading glasses with 0.25 and 0.3mol K2O released thehighest amount of these ions; however, there was no definite trend in the remaining glass compositions
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/52/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.330-332.161.pdf
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