Il. Denry et Ja. Holloway, Effect of magnesium content on the microstructure and crystalline phases of fluoramphibole glass-ceramics, J BIOMED MR, 53(4), 2000, pp. 289-296
The purpose of this study was to evaluate the effect of magnesium content o
n the microstructure and crystalline phases of glass-ceramics in the system
SiO2-MgO-CaO-Na2O-K2O-F. Four glass compositions were prepared with magnes
ium content varying from 12-18 wt%. The compositions were melted at 1400 de
grees C for 2 h and cast into 30 x 8 mm ingots. Differential thermal analys
es were performed on the powdered glasses at a heating rate of 20 degrees C
/minute up to 1400 degrees C. Bars (4 x 8 x 25 mm) were cut from the ingots
with a low-speed diamond saw, nucleated in the temperature range 600-650 d
egrees C for 1-2 h and crystallized in the temperature range 900-1000 degre
es C for 4-6 h. The crystalline phases were analyzed by X-ray diffraction.
The microstructure was investigated by scanning electron microscopy, The Vi
ckers hardness was determined after indentation under a 9.81 N load. Differ
ential thermal analyses revealed that crystallization occurred in the tempe
rature range 700-800 degrees C. X-ray diffraction showed the presence of fl
uorrichterite as major crystalline phase regardless of the magnesium conten
t in the parent glass or heat treatment temperature. The microstructure con
sisted of interlocked acicular crystals (5-10 micrometers), The highest mag
nesium content led to the coexistence of both a mica phase and fluorrichter
ite. This microstructure promoted crack deflections and arrest. (C) 2000 Jo
hn Wiley & Sons, Inc.