CaSiO3 powders were prepared from an ethanol solution dissolving Ca(NO3)2 · 4H2O and Si(OC2H5)4 by the coprecipitation method using various concentrations of NaOH as precipitants. Some Na component remained in the precipitates without washing and strongly affected the characteristics of the resultant powders, but the Na residue was removed by a washing treatment. The precipitate prepared by using 0.33 mol/l of NaOH and twice-washing contained the lowest amount of Na residue. It was calcined at 500 and 900 °C, respectively, to crystallize CaSiO3 phase and ground by a planetary potmill. The ground CaSiO3 powder was sintered to about 89% theoretical density by firing at 1400 °C. By soaking the CaSiO3 sintered bodies in simulated body fluid (SBF) solution for various times, an hydroxylapatite (HAp) layer formed as aggregates of ball-like particles on the surface of the CaSiO3 sintered bodies after soaking for a short period; thereby, the CaSiO3 ceramics is suggested to have very good biocompatibility.
alpha-CaSiO3 ceramics of nominal composition CaO 46.0, SiO2 54.0, and Na2O 0.4 mass% were soaked in simulated body fluid (SBF). The soaking systems were maintained under both static and flowing conditions to study their effect on the formation of hydroxyapatite (HAp). Two different flowing systems were designed for soaking, namely, a closed system using a fast flow rate of about 2.8 mL/s (circulating system) and an open system using a slow flow rate of about 40 mL/day (slow flowing system). The HAp layer in all samples initially formed as a rough layer of ball-like particles. Under a fast flow of SBF solution, silica gel particles peeled from silica-rich interlayer during the first soaking period. The silica gel particles then reattached to the product HAp layer and induced the formation of new HAp particles of smaller size. In the slow flowing system, the rough HAp layer initially formed on the ceramic surfaces became gradually smoother after prolonged soaking. The formation rate and thickness of the HAp layer decreased with increasing flow rate of the SBF solution. These results indicate that flowing SBF solution gives rise to differences in the formation rates, formation behavior, and microstructure of the HAp layer.
Two different reagents, NaOH and NH(4)OH, were used to precipitate CaSiO(3) precursor powders from ethanol solutions of Ca(NO(3))(2). 4H(2)O and Si(OC(2)H(5))(4). The resultant powders of different Ca/Si ratio and residual Na(2)O content exhibited significant differences in the microtexture of the resulting sintered alpha-CaSiO(3) ceramics. The microtexture of the ceramics from the NaOH system (CS-Na) contained smaller grain sizes and a thicker glassy phase at the grain boundaries than those produced using NH(4)OH (CS-NH). The CS-Na ceramics were soaked in a simulated body fluid (SBF) at 36.5 degrees C for 2 h and 1, 5, 6, 10, 21, and 30 days while the CS-NH ceramics were soaked for 1, 5, 7, 15, 20, and 25 days using the same conditions. Hydroxyapatite (HAp) formed on the surfaces of both samples but at different formation rates due to differences in the microstructure. The CS-Na ceramics showed faster HAp formation because their smaller alpha-CaSiO(3) grains dissolved more readily, allowing the calcium concentration in the SBF quickly to approach the appropriate condition for nucleation of HAp. In addition, the thicker glassy phase at the grain boundaries facilitated a faster formation of silanol on the surface of the amorphous SiO(2) interlayer, a reaction that is considered to be a prerequisite for HAp formation. The formation of the HAp layer on the CS-Na ceramics therefore was very fast (12 microm/day), and their surfaces were covered completely within 5 days. A layer thickness of about 110 microm was achieved in 30 days, in contrast with the CS-NH ceramics, which took about 25 days to be fully covered with a 60-microm layer of HAp.
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