Optimization of dielectric properties of suspension plasma sprayed hydroxyapatite coatings

Conventional plasma torch was adapted to spray very fine Ca-5 (PO4)(3)OH (hydroxyapatite, HA) precursors having sizes ranging from a few hundreds of nanometers to a few micrometers. The powders were put in suspension with distilled water and anti-dispersive agent. A home made suspension feeder, including two peristaltic pumps, delivered the suspension into atomizer and there from injected into plasma jet. The suspension flow rate was electronically controlled. The resulting coatings had the thickness of a few tenths of mu m. The electrical properties of the coatings including breakdown voltage and loss factor of suspension sprayed hydroxyapatite coatings sprayed onto aluminium substrates were also tested. The influence of such experimental factors as power input to plasma, pressure of atomizing gas, spray distance and suspension feed rate on the responses being the electrical properties was investigated using a 2(4) design of experiments (DOE). The mathematical models relating the responses with the factors were created and the significant factors were selected.