Powder Mixtures Based on Calcium Hydroxyapatite and Sodium Salts

Abstract

Powder mixtures based on calcium hydroxyapatite (HAP) and sodium salts in the amount corresponding to 25 mol % of Na₂O in the Na₂O–CaO–P₂O₅ system were studied by isothermal exposures in the range of 600—1200°C. According to XRD data, the phase composition of the samples of HAP/Na₂CO₃ after calcination included HAP, β-CaNaPO₄, and CaO. The phase composition of the ceramic samples from the HAP/Na₂HPO₄ powder mixture after calcination contained the phases of β-CaNaPO₄ and Na₄P₂O₇. The phase composition of the ceramic samples from the powder mixture of HAP/NaH₂PO₄ after calcination contained Ca₂P₂O₇, Ca₁₀Na(PO₄)₇, β-CaNaPO₄, CaNa₂P2O₇, and Na₄P₂O₇. The presence of sodium salts in the amount corresponding to 25 mol % of Na₂O in the Na₂O–CaO–P₂O₅ system provided the occurrence of liquid- phase sintering in compact preforms from the studied powder mixtures. However, the presence of the water-soluble salt Na₄P₂O₇ in ceramic samples of HAP/Na₂HPO₄ and HAP/NaH₂PO₄ after calcination imposes a restriction on the use of such materials in contact with an aqueous medium. And the presence of CaO in the HAP/Na₂CO₃ samples excludes the use of such materials as bone implants.