Papers by Author: Sun Hyo Park

Abstract: Nanosized hydroxyapatite(HAp) was synthesized hydrothermally and influence of processing parameters, such as reaction temperature and time, pH, and Ca/P ratio, on the phase stability of HAp was evaluated after pressureless sintering at 1250°C in air. The highest stability was achieved from the powder obtained at a processing condition for the lowest solubility of Ca2+, which corresponds to temperature close to 200°C, time <4h, pH>9.0, and Ca/P = 1.67. The stability of nanosized HAp in HAp/3Y-TZP composites was slightly inferior to commercial one, but the involvement of hydrothermally synthesized HAp improved sintered density of the composites and stability of t-ZrO2 phase in the composites.

Abstract: A hydrothermal method has been used to produce nanoparticles of 3 mol% yttria-stabilized tetragonal zirconia (3Y-TZP) with high fracture toughness. The effects of reaction temperature and pH on crystallite size and sintered density, and the influence of Nb2O5 addition into 3Y-TZP on toughness have been investigated. The particle size increased with increasing the processing parameters and the influence of temperature was more significant than pH. The density of nanosized 3Y-TZP increased with increasing pH up to 9 and then decreased abruptly with further increase. The density increased slightly with the reaction temperature up to 140°C and then changed little with increasing temperature. The toughness increased in proportional to the Nb2O5 content. After sintering for 1 h at 1270°C, the highest relative density of 98% was obtained from nanoparticles of about 17 nm, prepared at 200°C and pH 9, and the toughness of 3Y-TZP was increased from 2.5 to 8.3 MPam1/2 by addition of 1.2 mol% Nb2O5.

Abstract: The effect of hydrothermal reaction temperature and pH on crystallite size, phase stability, and sintered density of hydroxyapatite (HAp) has been investigated. The crystallite size increased with the increase in temperature but was not significantly affected by pH. The decomposition of HAp into tricalcium phosphate was observed at 1250°C and the extent of decomposition decreased with increase in pH. The influence of temperature and pH on the crystallite size and the decomposition was related to the decrease in solubility of Ca2+. The phase stability of HAp, prepared hydrothermally, in HAp/zirconia composites was higher than that of commercial HAp due to its high sintered density.