Analysis of Temperature Gradients in the Hydroxyapatite Ceramics with the Additives of Multi-Walled Carbon Nanotubes

The temperature difference between the outer surface and the center of a cylindrical sample of hydroxyapatite (HA) ceramics that arise during annealing/sintering were calculated. HA composites containing small amount of multi-walled carbon nanotubes (MWCNTs) were studied by using the X-ray diffraction methods. It is shown that macrostresses are higher in HA ceramic samples without nanotubes than in samples with MWCNTs. Compressive stresses arise on the outer surface of ceramics and tensile stress arise in the central part during the sintering due to the low thermal diffusivity of HA. This leads to the shifts of the X-ray diffraction peaks. The mechanical properties of HA ceramics with MWCNTs are enchanced due to both high mechanical properties of nanotubes and lower temperature gradients in HA ceramics during heating/cooling in the process of sintering. The additives of MWCNTs also lead to an increase in the density of the HA‒MWCNTs composite. The higher thermal diffusivity of MWCNTs, probably, allows to activate the sintering process in ceramics.