• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.7-16
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• 1996

${CO_3}^{2-}$ containing whisker-like hydroxyapatite powders were synthesized byhomogeneous precipitation method using urea, Dicalcium phosphate anhdrate[DCPA; $CaHPO_4$] and octacalcium phosphate [OCP; $Ca_8H_2(PO_4_)6\cdot5H_20$]were obtained as precursors and they transformed to high crystalline hydroxyapatites at pH 5.62, and 6.54 respectively. According to the condition of the final pH in the solutions for the solution products and urea contents OCP was remained. When the solution product of $Ca^{2-}$ and ${PO_4}^{3-}$ was $1.5\times 10^4$[$mM^2$] and the content of urea was 0.25 mol.$dm^{-3}$ well crystallized whisker-like hydroxyapatite tens of micrometer in length was obtained. By heat treatment DCPA and OCP were decomposed into $\beta$-tricalcium phosphate [$\beta$-TCP ; $\beta$-$Ca_3{PO_4}_2$] and $\beta$-dicalcium phosphate [$\beta$-DCP ;$\beta$-$Ca_2P_2O_4}_2$]. And well-crystallized hydroxyapatite was partially decomposed into $\beta$-TCP at $800^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.480-491
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• 2018

Calcium phosphates (CaP) were prepared by a wet chemical method. Micro-crystalline dicalcium phosphate (DCPD) was precipitated at $37^{\circ}C$ and pH 5.0 using $Ca(OH)_2$ and $H_3PO_4$. The precipitated DCPD solution was kept at $37^{\circ}C$ for 96 h. Artificial bone cement was composed of DCPD, $Ca(H_2PO_4)_2{\cdot}H_2O$ (MCPM), and $CaSO_4{\cdot}1/2H_2O$, $H_2O$ and aqueous poly-phosphoric acid solution. The wet prepared CaP powder was used as a matrix for the bone cement recipe. With the addition of aqueous poly-phosphoric acid, the cement hardening reaction was started and the CaP bone cement blocks were fabricated for the mechanical strength measurement. For the tested blocks, the mechanical strength was measured using a universal testing machine, and the microstructure phase analysis was done by field emission scanning electron microscopy and X-ray diffraction. The cement hardening reaction occurred through the decomposition and recrystallization of MCPM and $CaSO_4{\cdot}1/2H_2O$ added on the surface of the wet prepared CaP, and this resulted in grain growth in the bone cement block.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.655-659
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• 2019

Calcium phosphates such as HA (hydroxyapatite), β-TCP (tricalcium phosphate) and biphasic HA/β-TCP, were synthesized by wet chemical precipitation in aqueous solution combined with ball milling process. Nanosize powders of the calcium phosphates were synthesized using Ca(OH)2 and H3PO4. The effects of initial precursor Ca/P ratio (1.30, 1.50 and 1.67), ball milling process and post heat-treatment on the phase evolution behavior of the powders were investigated. The phase of resulting powder was controllable by adjusting the initial Ca/P ratio. HA was the only phase for as-prepared powders in both cases of Ca/P ratios of 1.50 and 1.67. The single HA phase without any noticeable second phase was obtained for the initial Ca/P ratio of 1.67 in the overall heat-treatment range. Pure β-TCP and biphasic calcium phosphate (HA/β-TCP) were synthesized from precursor solutions having Ca/P molar ratios of 1.30 and 1.50, respectively, after having been heat-treated above 700 ℃. The β-TCP phase has appeared on the pre-existing DCPD (dicalcium phosphate dihydrate) and/or HA phase. Dense ceramics having translucency were obtained at a considerably lower sintering temperature. The modified process offered a fast, convenient and economical route for the synthesis of calcium phosphates.

• Restorative Dentistry and Endodontics
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• v.19 no.1
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• pp.27-44
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• 1994

The purpose of this study was to determine the effects of pH, temperature and time on the synthesis of hydroxyapatite(HAP) by spontaneous precipitation under relatively physiologic condition. Specimens were obtained from aqueous system with various pH, temperature and experimental time. Chemical composition, crystallographic structure and crystallinity of the synthetic HAP were evaluated by Infrared spectroscopy and powdered X-ray diffraction method. The following results were obtained. 1. No precipitate was obtained under pH 5.5. 2. All the specimens were concluded as HAP except one that was obtained under the condition of pH 6.5, $25^{\circ}C$ and 1 day. It was concluded as dicalcium phosphate dihydrate(DCPD). 3. The crystallinity of HAP was enhanced by increases in pH, temperature and time of the preparation. But, the crystallinity of the synthetic HAP was lower than that of the mineral HAP. 4. Intermediates such as DCPD and octacalcium phosphate were formed on the process of the synthesis of HAP.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.3
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• pp.96-102
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• 2022

Hydroxyapatite (HAp) was synthesized from calcium hydroxide (Ca(OH)₂) reacting with phosphoric acid (H₃PO₄) in aqueous solution. HAp powders were synthesized from extremely high concentration of precursor solutions over 3 M of Ca(OH)₂ aqueous suspension using modified process parameters such as phosphoric acid (H₃PO₄) pouring rate, aging time and post ball milling process. Regardless of phosphoric acid pouring rate, the DCPD (dicalcium phosphate dihydrate) was formed at room temperature and when heated above 700℃, β-TCP (tricalcium phosphate) was synthesized and the amount reached its maximum at 900℃. When the synthesized powder was sintered at 1150℃, β-TCP, a high temperature impurity phase, remained. The single HAp phase without DCPD was obtained from post ball-milled precipitates followed by 3 day aging. For the ball-milled precipitates even without the aging process, the desired single HAp phase without β-TCP could be obtained by heat treatment above 500℃. The post ball milling process provided a convenient route for HAp synthesis.