The properties of hydroxyaptite (HA) powder, especially its physical one, are largely influenced by the heat treatment process. Controlling of these changes is vital in deciding the suitability of applying this powder in wet processing routes for green body fabrication. Chemically, the crystallinity of the HA powder was found to be largely enhanced with the increase in calcination temperatures. In contrary, a high retardation in the carbonate ion content was found. Physically, all the powder properties in terms of particle size, its distribution, pore volume, pore size and surface area are considerably varied with calcination temperatures. It was found that HA powder calcined at both 1000 and 1100 • C possesses reasonable physico-chemical properties for being applied in wet processing routes. Using heat-treated powder at 1000 and 1100 • C with 0.3 wt% sodium polyacrylate (as a dispersing agent) turned out to be beneficial in developing a low viscosity and high turbidity suspensions.
The influence of some parameters controlling the hydroxyapatite (HA)
suspension rheology in terms of heat treatment of the HA powder prior to
suspension preparation, suspension solid loading and the amount of corn
starch addition was thoroughly investigated. The heat treatment of powder at
1100?C prior to suspension preparation was found to be extremely efficient in
preparing suspensions with high solid loading of 59 vol.%. In contrast, the
highest solid loading that could be developed from the non-heat treated
powder was 14 vol.%. This phenomenon is consequence of the changes in the
physical and chemical properties of the powder after the heat treatment step.
The amount of native corn starch addition has ranged from 10 to 40 vol.%. The
addition of corn starch leads to the high retardation in the suspension
viscosity, particularly at low shear rate. On the contrary, at higher shear
rate the situation is completely different. The properties of the
consolidated green sample (produced from suspensions containing various corn
starch amounts) in terms of relative density and compressive strength were
studied. The results indicated that even though there were no considerable
changes in the relative density, the compressive strength was sharply
increased with increasing starch amount content until it reached a maximum at
30 vol.% and then decreased thereafter.
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