Effect of Different Drying Techniques on Density, Porosity and Bioactivity of β-Wollastonite from Local Limestone and Rice Straw

The influences of different drying techniques on the density, porosity and bioactivity of beta-wollastonite samples were studied and compared between two drying techniques; freeze-dried at -40 degrees C and in an incubator at body temperature (36.5 degrees C). beta-wollastonite samples were produced from calcined limestone and rice straw ash with CaO:SiO2 ratio of 45:55. The mixture was autoclaved for 8 h, and then dried and sintered at 950 degrees C for 3 h. beta-wollastonite samples were formed into cylinders and dried using two techniques, namely the freeze drying technique at -40 degrees C for 12 h and at body temperature (36.5 degrees C) for two days in an incubator. Men, the cylindrical samples were examined for their density, porosity and bioactivity properties. It was found that the freeze drying technique had produced denser beta-wollastonite samples, (3.20 gcm(-3)) compared to drying at body temperature drying, (3.03 gcm(-3)). Freeze-dried samples had less pores compared to samples dried at body temperature, at 47.5% and 53.8%, respectively. In terms of bioactivity properties, after 21 days of immersion in the SBF solution, amorphous calcium phosphate (ACP), with Ca/P molar ratio that ranged between 1.2 - 2.0 and calcium deficient hydroxyapatite (CDHA), with a Ca/P molar ratio of 1.5 - 1.67 were found on the surface of the samples for both drying techniques.