DTA and X‐Ray Analysis Study of Nucleation and Crystallization of MgO‐Al₂O₃‐SiO₂ Glasses Containing ZrO₂, TiO₂, and CeO₂

Abstract

MgO-Al,O,-SiO, Glasses Containing ZrO,, TiO,, and CeO, 163 were obtained in the region described by these workers, X-ray examination indicated that both quenched and slowly cooled samples were crystalline. The diffuse diffraction lines observed by Ruff et al. may have led to the assumption that a partly glassy material had been obtained. Also, the hope of using the suggested compositions as translucent refractories is unlikely to be realized, since the metastable high-temperature phase decomposes on annealing. The limits of the cubic solid solution in the binary system ZrO,-CaO were taken from G a r~i e ,~ who viewed the cubic field as extending from = 14 to 20 mol% CaO at 1600°C. The boundaries reported for the 2-phase region containing tetragonal ZrO,(ss) and CaZr,O,(ss) also vary considerably."-" Since the exact value is of little interest for the present investigation, a n arbitrary range was assumed. The mutual solubility of ZrO, and Tho, is Disagreement on the extent of CaO solubility in Tho, but, since Ref. 13 presents electron micrographs of second-phase inclusions at 2 mol% CaO, this maximum concentration was assumed for the present work. The existence at 1600°C of the compound CaThOB mentioned by Naray-Szaboi5 could not be confirmed, in agreement with the results of Moebius et a/. ', The ternary compound 2Ca0. 2Th0,. 5Zr0, is mentioned neither in the study of Ruff et a / . ' nor elsewhere. This compound seems to be stable up to a temperature near its melting point, since some superstructure lines which can be indexed by doubling the fluorite lattice constant were seen clearly in X-ray diffraction patterns of samples cooled slowly from the melt. An exact structural analysis will be given subsequently. In particular, the question of deviation from true pyrochlore stoichiometry , A,B,O,, should be answered. Acknowledgments:The writers thank P. Eckerlin for many helpful discussions and M. Uitterhoeve, H. Bausen, and H. Liebner for performing the X-ray work.

Effect of TiO2 on the mullite formation and mechanical properties of alumina porcelain

“…TiO 2 has been extensively studied as a nucleating agent used in several glassy systems for the purpose of controlling crystallization in the different crystalline phases. [17][18][19][20] However, as far as we know there is no detailed information describing the effect TiO 2 has on influencing the microstructure and mechanical properties of alumina porcelain bodies.…”

Effect of fluoride nucleating catalysts on crystallization of cordierite from modified basalt-based glasses

“…[13][14][15][16][17] According to those authors, Ti 4+ ions can act as network former and exist in Si-equivalent four-fold coordinated sites. However, Ti 4+ has a field strength of 1.04 considerably, above that of the four-fold coordinated Al 3+ (0.96) which is known to enter the network structure but below that of the major glass network-forming Si 4+ (1.56).…”

Preparation and properties of transparent cordierite-based glass-ceramics with high crystallinity

“…Many investigations on glass-ceramics of this system have been published, especially focusing on the effect of different nucleating agents (TiO 2 , ZrO 2 or P 2 O 5 ) and the heat treatment on their mechanical, thermal and electrical properties [7][8][9][10]. In addition, studies concerned with the nucleation sites and kinetics of cordierite-type glass have been reported by Zanotto [11].…”