Development and characterization of nano-ceramic materials for high strength and novel biological applications

Abstract

This study investigates the radio-frequency (RF) plasma synthesis of ultra-fine bioceramic materials. A relatively new processing technique called suspension plasma spraying was used to synthesize fine (5-20?m) and ultra-fine (10nm-4?m) Hydroxyapatite. The ultra-fine powders were also consolidated using Spark Plasma Sintering. The initial study concentrated on investigating the influence of various plasma parameters mainly plate power and chamber pressure with a suspension concentration of 7 wt%HA on the characteristics of the as-sprayed powders. The powders were characterized using particle size measurements, X-ray Diffraction (XRD) analysis, and Scanning Electron Microscopy (SEM). During sintering, the dependence of operating conditions of the Spark Plasma Sintering system on the properties of the compacts was also studied.

Microstructural analysis revealed that the morphology of ultra-fine powders was a mixture of 0.5-3?m particles and a fine network of nano-sized particles with particle size less than 100 nm. The XRD analysis showed that the powders were predominantly HA with other decomposed phases, mainly ? and ?-tricalcium phosphate (TCP), tetra-calcium phosphate (TTCP) and calcium oxide (CaO). The relative decomposition in the as-sprayed powders was initially determined using the relative 100% peak height of the individual phases to that of HA and the phase. Both plate power and chamber pressure affected the average particle grain size and morphology. The are two processes taking place when the HA suspension feedstock enter and leave the plasma. These are particle dissociation by thermal treatment and particles collisions that could lead to coalescence and larger particle size. Both processes are counteracting each other and will be discussed in this report. However, average particle size was generally inversely proportional to plate power for both medium and ultra-fine powders. The relative decomposition increased steadily with plate power. Spraying at lower chamber pressure and gas flow rates increased the average particle size and decreased the amount of decomposition.

The compacts consolidated from the ultra-fine HA powders by the Spark Plasma Sintering technique exhibited Young’s Modulus and hardness of around 103GPa and 550 Hv, respectively, and fracture toughness about two times the values published in the literature for sintered pure HA (~1.2MPam-1/2). )