Phase equilibria and crystallization of the lithium oxide-zinc oxide-silica system.

The phase equilibria in the glass forming region of the lithium oxide-zinc oxide-silica ternary system were investigated by the quenching technique with a vertical gradient furnace. The glass forming limit on the low silica line , being higher in silica at the lithium oxide rich side. The refractive indices of the glasses were measured by the Beche line technique. Zinc oxide was found to increase the refractive indices of the glasses more than the lithium oxide. Tridymite , lithium disilicate, lithium metasilicate , zinc orthosilicate and two ternury compounds were found as primary phase crystals. One of the ternary compounds was identified conclusively as Li20.ZnO. Si02• The other ternary compound was tentatively identified as 2Li20.4ZnO.3Si02. The optical properties and the x-ray diffraction patterns of these two ternary compounds are very similar and they form solid solutions with each other. Also zinc orthosilicate dissolves in 2Li20.4ZnO.3Si02 to form solid solutions. Continuous solid solution was found along the Li2 0.ZnO.Si02 - 2ZnO ,Si02 join with up to 60 mol % of zinc orthosilicate dissolved in Li20.ZnO.Si02 in the specimens quenched from above 1500 C. Two eutectic points and two reaction points were found in the compositions investigated. The eutectic point of the composition triangle Si02 - Li20.2Si02 - Li20.ZnO.Si02 was found at Li2 0 F5.5 mol % ZnO 10 mol fa , Si02 64.5 mol % and 9550 ~5°C. The eutectic point of' the composition triangle Si02 - Li20.ZnO. Si02 - 2Li20.4ZnO.3Si02 was located at Li2 0 16.5 mol %, ZnO 23 mol %, Si02 60.5 mol % at 10SOo :!:SoC. The reaction point of the composition triangle Li2 0, 2Si02 - Li2 0.Si02 - Li2 0.ZnO.Si02 was found at Li20 27.5 mol %, ZnO 9.8 Q.(',l %, Si02 63.7 mol % at 9760 =5°;,;.. The reaction point between the SiO , 2ZnO.SiO and 2 2 2Li20.4ZnO.3Si02 Was located at Li2 0 15.7 mol %, ZnO 24.6 mol %, Si02 % • + 0 59-7 malo and 1068 -5 c. The two-phase regions were found below the solidus temperature in the composition triangle of 8i02 - Li20.ZnO.Si02 - 21i2 0.4ZnO .3Si02, Extraneous lines were found to be included in the lithium disilicate and lithium metasilicate data in the X-Ray Powder Data File. The present powder data of lithium disilicate were indexed as orthorhombic crystal with cell parameters Uo ' a 5.80R, b. = 14.66R and 0. • 4.806R, and that of the lithium metasilioute were indexed as pseudohexagonal orthorhombic crystal with, cell parameters a. =5.43R, ~ ~ 9.4lR and c = 4.6601. o The crystallization characteristics of five glasses of this ternary system were studied. Uniform crystallization was found to occur in all the specimens. Big lithium disilicate crystals were found in specimens .four glasses. A high concentration of tiny crystals was found in every specimen. A hot stage microscope with a microfurnace was constructed to study the crystal growth in glasses of this system. Three glasses were investigated. The usual hump shaped growth rate versus temperature curves were obtained. The growth of the crystals were found to be linear with time . The maxi mum growth rate of lithium metasilicate, lithium disilicate Li20.Zno.Si02 and tridymite in these glasses were found to be about 3,500, 400, 70 and 20 micron per minute respectively.