Role of thermodynamic miscibility gaps in phase selection in sol-gel synthesis of yttrium silicates. Issue 15 (December 2017)

• Record Type: Journal Article
• Authors: Anantharaman, Surendra B.; Rajkumar, V.B.; Raghunandan, S.; Hari Kumar, K.C.; Kumar, R. Suresh; Gandhi, Ashutosh S.
• Is Part Of: Journal of the European Ceramic Society. Volume 37:Issue 15(2017)
• Page Start: 5001
• Page End: 5007
• Publication Date: 2017-12
• Subjects: CALPHAD -- Metastable phases -- Phase separation -- Spinodal decomposition -- Yttrium silicates; Ceramic materials -- Periodicals; Composite materials -- Periodicals; Matériaux céramiques -- Périodiques; Composites -- Périodiques; Ceramic materials; Composite materials; Periodicals; Electronic journals; 666.05
• DOI: 10.1016/j.jeurceramsoc.2017.06.040
• Languages: English
• ISSNs: 0955-2219

Abstract

Abstract: Yttrium monosilicate and disilicate are important materials for environmental barrier coatings. The two silicates were synthesized by sol-gel route and their phase selection upon calcination and thermal exposure was studied. First products of crystallization were the monosilicate and yttria. Amorphous silica precipitated out at 1300 °C as apatite phase. During prolonged high temperature treatment, up to 100 h at 1400 °C, the apatite disappeared and the disilicate appeared, only to disappear itself as the system approached equilibrium. Thermodynamic calculations performed using Thermo-Calc software show the presence of a metastable miscibility gaps in the amorphous (liquid) phase field. As a consequence, phase separation in the amorphous phase prior to crystallization is responsible for the formation of yttria-rich and silica-rich phases during crystallization. Multiple phase formation during both, yttrium monosilicate and disilicate synthesis is consistent with the presence of the amorphous phase miscibility gaps around the silicate compositions.