EFFECT OF ALUMINA ON DEVITRIFICATION OF SODA‐LIME‐SILICA GLASSES*

A bstract The effect of the substitution of Al 2 O 3 for the oxides of sodium, calcium, and silicon on the liquidus temperatures and phase relations has been determined for glasses lying within the composition range Na 2 O 11 to 19%, CaO 6 to 18%, SiO 2 59 to 79%, and Al 2 O 3 0 to 8%. The results on 137 individual determinations show that the substitution of Al 2 O 3 for CaO permits wollastonite to be the primary phase in glasses of relatively low CaO content. As the Al 2 O 3 content increases, the Na 2 O‐3CaO‐6SiO 2 —CaO·SiO 2 boundary shifts to lower CaO contents, and the decomposition of Na 2 O·3CaO·6SiO 2 to CaO·‐SiO 2 takes place at lower temperatures. In compositions with tridymite as a primary phase, the substitution of Al 2 O 3 for SiO 2 is effective in lowering the liquidus temperature. For the composition range investigated, the SiO 2 ‐CaO‐SiO 2 and Na 2 O·3CaO·6SiO 2 ‐SiO 2 boundary remains at essentially the same SiO 2 content for all glasses containing not more than 4% Al 2 O 3 .