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Crystallization Hierarchy of CaO‐P2O5‐SiO2‐Al2O3‐TiO2 Glass‐Ceramics
Author(s) -
Jordery Sophie,
Lee William E.,
James Peter F.
Publication year - 1998
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1998.tb02617.x
Subject(s) - anorthite , materials science , crystallization , orthorhombic crystal system , mineralogy , nucleation , rutile , phase (matter) , crystallography , chemical engineering , crystal structure , chemistry , organic chemistry , engineering
Glasses in the tricalcium phosphate‐anorthite (Ca 3 (PO 4 ) 2 ‐CaAl 2 Si 2 O 8 or TCP‐CAS 2 ) system with additional TiO 2 were melted. Crystallization was investigated using thermal analysis, X‐ray diffraction, and transmission optical and electron microscopies. During the heat treatment, as the growth temperature increases, successive crystalline phases separate from the glass matrix. The phases present in the fully heat‐treated glass‐ceramic are ß‐TCP, anor‐thite (CAS 2 ), and rutile (TiO 2 ). Apart from TiO 2 , these phases evolve from other polymorphs during the heat treatment. The metastable phases, pseudo‐orthorhombic CAS 2 and alpha‐TCP, appear first around 880°C and transform into the stable phases, triclinic anorthite CAS 2 and ß‐TCP, around 940° and 1000°C, respectively. The material crystallizes in stages. The first stage is the separation from the glass matrix of rutile and what is believed to be a calcium phosphate phase, with crystal sizes varying from 20 to 200 nm. This is followed by the appearance of larger crystals (1‐2 µm) of the metastable pseudo‐orthorhombic CAS 2 , surrounding the previously crystallized phases. Finally, this pseudo‐orthorhombic CAS 2 phase transforms to anorthite (15‐20 µm) spherulites. TiO 2 does not act as a direct nucleating agent in the glass composition studied: no sign of heterogeneous nucleation and growth from TiO 2 crystals has been found, and moreover, TiO 2 ‐free base glass crystallizes in a manner similar to that of the glass containing TiO 2 .