Hydroxyapatite (HAP) is a mineral base of human bond tissue. Thus HAP-based ceramic materials are often used as bone implants. About 95% of ceramics is manufactured by liquid phase sintering because this method is more rapid and requires more mild conditions of thermal processing than others. Selection of appropriate low-melting point additive is a complex task, as an effective sintering should not be accompanied with considerable grain growth. Effectiveness of liquid phase sintering is also linked to the infiltration of melt through HAP matrix and to the value of solid/liquid interfacial energy.
The aim of the study was to analyze the spreading kinetics of liquid NaCl and CaCl2 over free surface of HAP ceramics and to estimate interfacial thermodynamic parameters in molten additive / HAP systems.
Spreading was studied by means of dispensed drop technique in air at 866 ºС (for NaCl) and 880 ºС (for CaCl2). HAP substrates were prepared by sintering of HAP powder under 100 MPa at 1200 ºС for 100 hours. Samples with 80% of theoretical density were obtained and polished to average roughness of 30 nm. It was shown that both halides perfectly wet HAP surface, the contact angle below 5° was obtained within less than 100 ms. The possibility to fit spreading rate data in a framework of viscous dissipation model is discussed.
Surface energy of HAP in air was compared to one in air containing NaCl and CaCl2 vapor by means of thermal grooving technique. Dihedral angles in the vicinity of grooves were measured with AFM. Thermodynamic parameters of solid/liquid and solid/gas interfaces were estimated for NaCl/HAP and CaCl2/HAP systems.
This work was partially supported by Federal Program «R&D on high-priority directions of science and technology in Russia for the period 2007-2012» and RFBR grant (11-08-01244-а).