Strength Distributions of Sintered Hydroxyapatite Nanoparticles

In the past two decades, calcium phosphates, and especially hydroxyapatite (HA), have been used as bone substitutes, and the mechanical strength is one of the most important properties in this application. The flexural strength of an HA object depends on the nature of the HA powder, specimen preparation, flex test geometry and experimental conditions. HA was prepared by two methods, namely: wet and hydrothermal. The fundamental difference between these methods lies in the method of mixing the reactants and the reaction temperature. The obtained powders were pressed into pellets at 150 MPa and tested for flexural strength using a ring-on-disc method. The two-parameter Weibull and normal distributions were used to characterize the observed flexural strengths. Results were correlated with scanning microscope observations of fracture surfaces of the polished broken discs. The two-parameter Weibull distribution was found to be superior for the samples made with HA from the hydrothermal method. For the samples from the wet method, the normal distribution was equally suitable. The reason for this difference was sought by examining the discs for surface flaws