Sintering parameters study of a biphasic calcium phosphate bioceramic synthesized by alcoholic sol-gel technique

In the sintering of biphasic calcium phosphate bioceramics (BCP) can occur phases transformations accompanied by a sudden thermal expansion due to different coefficients of thermal expansion of each phase, which generates internal stress concentrations inducing undesired cracks within the sample. Therefore, this work aimed to study the sintering parameters of a BCP, composed of hydroxyapatite (HAp) and beta-tricalcium phosphate (beta-TCP), synthesized by the alcoholic sol-gel technique, in order to evaluate the better conditions for avoiding defect generation. BCP powders were uniaxially cold-pressed at 300 MPa and air-sintered at 1070 degrees C/2 h (BCP1070 sample) and 1130 degrees C/2 h (BCP1130 sample), with heating rates of 10 degrees C/min and 5 degrees C/min, respectively. Samples were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, relative density determination, Vickers hardness test, and nanohardness tests. The results displayed that the assessed sintering parameters were suitable for promoting a satisfactory particle consolidation. The transformation from HAp to beta-TCP occurred simultaneously with grain growth and material densification under all conditions. The mechanical tests revealed that BCP1070 and BCP1130 samples have different behaviour when analyzed micro or nanostructurally. But, the heating rate (10 degrees C/min) combined with the sintering temperature (1070 degrees C) anabled to obtain a suitable sinterability with samples presenting smaller grain size and without defects. Further, it kept the microporosity which is an essential property for application in bioceramic materials.

Automated summary

This study focused on investigating the sintering parameters of biphasic calcium phosphate bioceramics to find better conditions for avoiding defect generation. The results showed that suitable sintering parameters promoted particle consolidation and the transformation from hydroxyapatite to beta-tricalcium phosphate occurred simultaneously with grain growth and material densification under all conditions.