Mechanical activation and cement formation of β-tricalcium phosphate

The reactivity of acid base cements forming hydroxyapatite (HA) such as, tetracalcium phosphate, and dicalcium phosphate anhydride or dicalcium phosphate dihydrate, is normally adjusted by altering the particle size and hence the specific surface area of the compounds. Amorphous calcium phosphates, prepared by precipitation from supersaturated solutions, can also react to form apatitic cements since they are thermodynamic unstable with respect to HA and have a setting reaction more independent of particle size. In this report we show for the first time that prolonged high-energy ball milling of beta-tricalcium phosphate (beta-TCP), led to mechanically induced phase transformation from the crystalline to the amorphous state. The process increased the thermodynamic solubility of the beta-TCP compared to the unmilled material by up to nine times and accelerated the normally slow reaction with water. By using a 2.5% Na2HPO4 solution setting times were reduced to 5-16 min rather than hours. X-ray diffraction analyses indicated that the amorphous fraction within the materials was responsible for the primary setting reaction and hardening of the cements, while the crystalline fraction remained unreacted and converted only slowly to HA. Mechanically activated beta-TCP cements were produced with compressive and diametral tensile strengths of up to 50 and 7 MPa respectively. The effect of preparation and setting parameters on the physical and chemical properties of mechanically activated beta-TCP cement was investigated. (C) 2003 Elsevier Science Ltd. All rights reserved.