title: Crystallization kinetics of a low-expansion feldspar glass for dental applications.
abstract: Previous studies have shown that the crystallization of glasses in the system K2O-Al2O3-SiO2, in the primary field of leucite, is not possible without modification of the composition. Leucite (KAlSi2O6) is used as a reinforcing phase in some compositions for all-ceramic dental restorations. However, because of their higher coefficient of thermal expansion, these materials cannot be veneered with conventional metal-ceramic porcelains. The purposes of this study were to investigate the crystallization behavior of a glass in the system K2O-Al2O3-SiO2 and to evaluate the effect of heat treatment on the crystal size, percent crystallinity, and coefficient of thermal expansion of the material. Ion-exchanged glass powder was prepared by mixing the glass with rubidium nitrate and heat-treating at 450 degrees C for 4, 8, 24, or 48 h. Bars were made from these powders and baked under vacuum at 1038 degrees C for 2 min. The bars made from the powder ion-exchanged for 48 h were further heat-treated for 4 h at either 800 degrees C, 850 degrees C, 900 degrees C, 950 degrees C, or 1038 degrees C. X-ray diffraction analyses showed cubic leucite was the only crystalline phase in the specimens made from the powders ion-exchanged for 4, 8, 24, or 48 h and baked at 1038 degrees C for 2 min. Further heat treatment for 4 h at either 800 degrees C, 850 degrees C, 900 degrees C, 950 degrees C, or 1038 degrees C promoted the growth of cubic leucite. In addition, a second phase identified as tetragonal rubidium-leucite was present in the specimens heat-treated for 4 h at 1038 degrees C. SEM observations showed that all specimens made from the powders ion-exchanged for 48 h exhibited small spherical crystals dispersed in a glassy matrix. The percent crystallinity ranged from 18.9% to 42.9% and the average particle size was between 0.64 to 1.18 microns. The coefficients of thermal expansion ranged between 8.076 and 8.788 x 10(-6)/degree C.
authors.affiliation: Section of Restorative Dentistry, Prosthodontics, and Endodontics, Ohio State University, College of Dentistry, Columbus 43210-1241, USA.
authors.forename: I L
authors.initials: IL
authors.lastname: Denry
authors.forename: J A
authors.initials: JA
authors.lastname: Holloway
authors.forename: S F
authors.initials: SF
authors.lastname: Rosenstiel
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D003764:Dental Materials / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D006358:Hot Temperature; D007700:Kinetics; D008422:Materials Testing; D015394:Molecular Structure; D010316:Particle Size; D017680:Potassium Compounds / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; D017680:Potassium Compounds; C016447:feldspar