Effect of heat treatment and phase change on BFS of two hydroxyapatite ceramic powders

الملخص EN

Thermal stability and sintering behaviour of two hydroxyapatite (HAP) powders where designated.

AHAP and BHAP have been investigated at fired sintering temperature range from 1100 to 1450 °C for 3 hrs using XRD and IR spectroscopy.

The fired compacts have been characterised by measuring their bulk density, firing shrinkage and biaxial flexural strength (BFS).

BHAP has been found to transform to oxyhydroxyapatite (OHAP) at T ≥ 1200 °C, and at T ≥ 1300 °C started to decompose to β-tricalcium phosphate (β-TCP).

AHAP has been found to be marginally less stable than BHAP with OHAP forming at T ≥ 1150oC and β-TCP forming at T ≥ 1200 °C.

In both materials, β-TCP transformed to α-TCP at T ≥ 1350 °C.

Maximum densification (∼95 % of theoretical density) occurred at a lower firing temperature for AHAP (1150 °C) than for BHAP (1250 °C), with AHAP also showing a slightly higher firing shrinkage (23 % compared with 20 % for BHAP).

The BFS of both materials have been found to increase with increasing sintering temperature up to 1300 °C, reaching a maximum value of ∼90-100 MPa.

At T ≥ 1300 °C, this is followed by rapid reduction in BFS due to cracks forming as a result of a volume increase associated with the transformation of β-TCP into α-TCP.

It has been concluded that BHAP is marginally more thermally stable than AHAP, while the latter densifies at a lower firing temperature, this is not a disadvantage and comparable properties can be achieved for both powders, although different firing conditions need to be used.