ISSN:
1551-2916
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Glasses in the tricalcium phosphate-anorthite (Ca3(PO4)2-CaAl2Si2O8 or TCP-CAS2) system with additional TiO2 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 (CAS2), and rutile (TiO2). Apart from TiO2, these phases evolve from other polymorphs during the heat treatment. The metastable phases, pseudo-orthorhombic CAS2 and alpha-TCP, appear first around 880°C and transform into the stable phases, triclinic anorthite CAS2 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 CAS2, surrounding the previously crystallized phases. Finally, this pseudo-orthorhombic CAS2 phase transforms to anorthite (15-20 µm) spherulites. TiO2 does not act as a direct nucleating agent in the glass composition studied: no sign of heterogeneous nucleation and growth from TiO2 crystals has been found, and moreover, TiO2-free base glass crystallizes in a manner similar to that of the glass containing TiO2.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1151-2916.1998.tb02617.x
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