Thermal analysis of hydroxyapatite with adsorbed oxalic acid

Abstract

The specific adsorption of oxalic acid ions at the hydroxyapatite interface was investigated by means of the radioisotope method ( 14 C) as a function of oxalic acid ions concentration, NaCl concentration and pH. Application of hydroxyapatite has become extensive in the biomaterial field due to its biocompatibility with human hard tissue. Hydroxyapatite was synthesized using wet methods. Physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy. Physicochemical properties characterizing the electrical double layer of the hydroxyapatite/NaCl solution interface were determined. The zeta potential and the adsorption of oxalic acid molecules were studied as a function of pH. The point of zero charge and the isoelectric point of samples were determined: its values are as follows: pH PZC = 7 and pH IEP = 4. Temperature has insignificant influence on pure substance and with oxalic acid adsorbed, as thermal analysis has shown, and characterization of hydroxyapatite structure can be carried out by this thermal analysis. Two phenomena are responsible for oxalic acid adsorption: phosphate group replacement at the hydroxyapatite surface by oxalic ions simultaneous to intraspherical complexes formation.