Synthesis of HA‐Seeded TTCP (Ca4(PO4)2O) Powders at 1230°C from Ca(CH3COO)2·H2O and NH4H2PO4

Abstract

Tetracalcium phosphate (TTCP) Ca4(PO4)2O is one of the major powder components of self‐setting orthopedic and dental cements. Traditionally, TTCP powders are produced by a solid‐state process by soaking Ca‐ and P‐containing precursors between 1350° and 1500°C. Such procedures require expensive high‐temperature furnaces and subsequent grinding of sintered particulates. Grinding not only introduces contamination but alters the structure of TTCP, thereby reducing its bioactivity. The present paper offers a lower temperature synthesis process for TTCP with several interesting features. First, the synthesis procedure used Ca(CH3COO)2·H2O and NH4H2PO4 as separate sources for Ca and P, respectively. Second, the reactants underwent multiple melting and decomposition stages, thus increasing the reactivity of the synthesis process. NH4H2PO4 melted at 190°C and engulfed the calcium acetate particles. The Ca‐acetate component decomposed into CaCO3 at around 400°C while still surrounded by the molten phosphate liquid and an amorphous Ca‐metaphosphate phase. Hydroxyapatite, Ca10(PO4)6(OH)2 (HA), and β‐Ca3(PO4)2 crystallized upon heating the powder mixture to 700°C. Slightly above 1200°C, the TTCP phase was formed. This sequence of reactions led to a process temperature of 1230°C, the lowest temperature ever reported for the synthesis of TTCP. Third, the resulting powders required much less grinding, which itself is advantageous. Fourth, the resulting powders were in situ seeded with HA. HA‐seeded TTCP powders were tested for their apatite‐inducing ability by soaking them in synthetic body fluid at 37°C. TTCP powders of this study were readily covered with carbonated apatitic calcium phosphates within the first 72 h.