The microstructural changes taking place during heating of calcium orthophosphate (Ca3(PO4)2) agglom- erates were examined in this study. The starting powder was prepared by the spray-pyrolysis of calcium phosphate ...The microstructural changes taking place during heating of calcium orthophosphate (Ca3(PO4)2) agglom- erates were examined in this study. The starting powder was prepared by the spray-pyrolysis of calcium phosphate (Ca/P ratio=1.50) solution containing 1.8 mol·L-1 Ca(NO3)2, 1.2 mol·L-1 (NH4)2HPO4 and concentrated HNO3 at 600 C, using an o air-liquid nozzle. The spray-pyrolyzed powder was found to be composed of dense spherical agglomerates with a mean diameter of 1.3 μm. This powder was further heat-treated at a temperature between 800 and 1400 C for 10 min. When o the spray-pyrolyzed powder was heated up to 900 C, only β-Ca3(PO4)2 was detected, and the mean pore size of the o spherical agglomerates increased via the (i) elimination of residual water and nitrates, (ii) rearrangement of primary par- ticles within the agglomerates, (iii) coalescence of small pores (below 0.1 μm), and (iv) coalescence of agglomerates with diameters below 1 μm into the larger agglomerates. Among the heat-treated powders, pore sizes within the spherical agglomerates were observed to be the largest (mean diameter: 1.8 μm) for the powder heat-treated at 900 C for 10 min. o With an increase in heat-treatment temperature up to 1000 C, the spherical agglomerates were composed of dense o shells. Upon further heating up to 1400 C, the hollow spherical agglomerates collapsed as a result of sintering via the o phase transformation from β- to α-Ca3(PO4)2 (1150 C), thus leading to the formation of a three-dimensional porous net- o work.展开更多
文摘The microstructural changes taking place during heating of calcium orthophosphate (Ca3(PO4)2) agglom- erates were examined in this study. The starting powder was prepared by the spray-pyrolysis of calcium phosphate (Ca/P ratio=1.50) solution containing 1.8 mol·L-1 Ca(NO3)2, 1.2 mol·L-1 (NH4)2HPO4 and concentrated HNO3 at 600 C, using an o air-liquid nozzle. The spray-pyrolyzed powder was found to be composed of dense spherical agglomerates with a mean diameter of 1.3 μm. This powder was further heat-treated at a temperature between 800 and 1400 C for 10 min. When o the spray-pyrolyzed powder was heated up to 900 C, only β-Ca3(PO4)2 was detected, and the mean pore size of the o spherical agglomerates increased via the (i) elimination of residual water and nitrates, (ii) rearrangement of primary par- ticles within the agglomerates, (iii) coalescence of small pores (below 0.1 μm), and (iv) coalescence of agglomerates with diameters below 1 μm into the larger agglomerates. Among the heat-treated powders, pore sizes within the spherical agglomerates were observed to be the largest (mean diameter: 1.8 μm) for the powder heat-treated at 900 C for 10 min. o With an increase in heat-treatment temperature up to 1000 C, the spherical agglomerates were composed of dense o shells. Upon further heating up to 1400 C, the hollow spherical agglomerates collapsed as a result of sintering via the o phase transformation from β- to α-Ca3(PO4)2 (1150 C), thus leading to the formation of a three-dimensional porous net- o work.
