Further study on post-treatment of plasma sprayed hydroxyapatite coatings with water vapour [dental/hip prostheses application]

It is important to transform the amorphous and the additional phases, such as α,β-Ca₃(PO₄)₂ (α,β-TCP) and Ca₄O(PO₄)₂ (TP), into HA and thus increase crystallinity of the coatings in terms of long-term stability. Post-treatment is an effective way to raise crystallinity of the coating, which includes water vapour treatment with water vapour pressure of 0.15 MPa and post-heat-treatment in different atmosphere. It was found that TCP and TP disappeared almost completely after water vapour treatment but the amorphous to crystalline conversion was still incomplete. Post-heat-treatment at 490°C in air with water vapour can obtain a completely crystalline HA coating after 2 hr treatment, which is superior to both water vapour treatment and post-heat-treatment in air without water vapour in terms of phase transition. Amorphous to crystalline conversion is significantly promoted when temperature and water vapour pressure increased whereas increase in water pressure or temperature alone is not efficient in this conversion. Mean crystallite size after both water vapour and post-heat-treatment is also compared