High temperature in-situ XRD of plasma sprayed HA coatings
S.W.K. Kweh, K.A. Khor, P. Cheang
Biomaterials
Abstract
The control of phase transformations in plasma sprayed hydroxyapatite (HA) coatings are critical to the clinical performance of the material. This paper reports the use of high temperature X-ray di?raction (HT-XRD) to study, in-situ, the phase transformations occurring in plasma sprayed HA coatings. The coatings were prepared using di?erent spray power levels (net plasma power of 12 and 15 kW) and di?erent starting powder size ranges (20–45; 45–75 mm). The temperature range employ...Moreed was
room temperature ( 268C) to 9008C in normal atmosphere and pressure. High temperature di?erential scanning calorimetry (DSC)was also employed to investigate and determine the precise onset temperature of phase transformations during the recrystallization process. Results showed that actual onset of thermal degradation in the coating into other metastable phases like TTCP, b-TCP and CaO occurred at 6388C. The aforementioned phase transitions were independent of the selected spraying parameters. The degree of melting and thermal dissociation of HA actually determines the amount of calcium phosphate phases that are formed. A high power level of 15 kW produced a greater degree of melting, resulting in more CaO, TTCP and b-TCP being formed as a result.
keywords:Hydroxyapatite; X-ray diffraction; Plasma spray; High temperature phase transformations
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