Hydroxyapatite suspensions as precursors of pieces obtained by gelcasting method

Abstract

The aim of this work was to prepare slurries of hydroxyapatite (OHAp) with a high content of solids, which is necessary for shaping pieces by the gelcasting method. For this purpose different studies were carried out using powders of OHAp calcined at temperatures ranging between 600 and 1200 C and several dispersants. Surface area, porosity and chemical composition of OHAp powders played a fundamental role in the viscosity of slurries. The highest concentration of solid was obtained with OHAp calcined at 1200 C. The best dispersant was selected in a first stage, by electrophoretic measurements and sedimentation studies and, finally, by rheological measurements. The concentration of dispersant which provides the minimum viscosity, depended on the calcination temperature of the OHAp. A great increased of viscosity took place for time of slurries preparation higher than 30 min. Milling of powder for 20 h was necessary to improve the rheological behaviour of the slurries. Finally, ceramic bodies were prepared from fluid slurries containing 60 vol.% of solids and the mechanical properties were evaluated. #

Thermal decomposition of monosaccharides derivatives applied in ceramic gelcasting process investigated by the coupled DTA/TG/MS analysis

“…It should be also mentioned that both acrylamide and 2-hydroxyethyl acrylate have to be used together with so called cross-linking agent (e.g. N,N 0 -methylenebisacrylamide) which allows to form cross-linked polymeric networks instead of linear chains [10,11].…”

Processing and mechanical properties of hydroxyapatite pieces obtained by the gelcasting method

“…30 The obtained powder was ground in a vibrating mill and then calcined at 1100 • C (HA-1100) or at 1200 • C (HA-1200) for 1 h. The calcined powders were dry milled for 20 h.…”

“…30 The HA was dry milled for 20 h, Darvan 811 (R.T. Vanderbilt Company, Inc.) was used as dispersant (concentration, 5 mg/m 2 ) and the components of slurries were mixed for 30 min. To prepare slurries with HA-1100 the same conditions were used except for the concentration of dispersant, since it had been previously established that the amount of dispersant for obtaining the lowest viscosity in slurries of HA calcined at 900 and 1200 • C was different.…”

“…To prepare slurries with HA-1100 the same conditions were used except for the concentration of dispersant, since it had been previously established that the amount of dispersant for obtaining the lowest viscosity in slurries of HA calcined at 900 and 1200 • C was different. 30 To determine the best dispersant concentration for dispersing HA-1100 slurries, the variation of viscosity of slurries containing 40 vol.% as a function of D811 concentration was studied.…”

“…30 The parameters studied were the calcination temperature of the HA powder, its particle size and distribution, the type and concentration of dispersant, the pH of the dispersing medium, the mixing time and solid concentration. Slurries with a concentration of solids as high as 60 vol.% were obtained by using an HA calcined at 1200 • C, dry milled for 20 h and using Darvan 811 as dispersant.…”