우레아 가수분해법에 의한 Y-TZP 분말의 응집제어와 분무건조에 의한 정방정 지르코니아 과립분말의 제조

Abstract

To apply useful materials for dental zirconia implants, sintered yttria-stabilized tetragonal zirconia (Y-TZP) must have small grain size (<0.3 μm) and high sintered density of approximately 99.5 %. In this study, three research fields for 3Y-TZP powder processing were investigated to apply a zirconia dental implant. Firstly, commercial Y-TZP powders for dental implant were analyzed. From four types of commercial 3Y-TZP powder, particle size, agglomeration, specific surface area, microstructure, and phase were characterized and their influences on the relative density and microstructure after sintering. Secondly, nanoscale yttria-stabilized zirconia powder with less-agglomeration and high yield was synthesized from homogeneous precipitation by urea hydrolysis. To achieve an experimental purpose, dispersion agent and highly initial ZrOCl2 concentration (0.25〜1 M) were used in mixed solution and their effects on the particle agglomeration and yield content of synthetic powders were investigated. Finally, to obtain homogeneous green compacts of 3Y-TZP, optimal granulation was performed using a stable zirconia slurry with solid contents of 30, 40, 50 wt%. It also investigated that the effects of additive agent and solid content in zirconia slurry on the granule shape, size and sintered properties.

From the above experimental study, final conclusions are as follows;

Firstly, primary zirconia nanoparticles of commercial 3Y-TZP powders have a similar morphology of sphere-like shape and size of 10〜15 nm. All of commercial 3Y-TZP powders have two types of agglomerates from the analysis of particle size distribution. Agglomerate sizes are 220〜293 nm in primary and 1.6〜5.3 μm in secondary agglomerate. The percentage of secondary agglomerate in commercial 3Y-TZP powder varied from 12 to 40 %. The specific surface area was dependent on the powder properties, from 6.4 to 13.8 m2/g. Sintered zirconia specimens at 1450 and 1550 °C for 2h composed of all tetragonal phase, with relative density of 97.8〜99.8 %. Highly dense specimen was obtained from the starting powder with small size, less amount of secondary agglomerate, and high specific surface area. Secondary, yttria-stabilized zirconia powder was synthesized from homogeneous precipitation by urea hydrolysis and investigated the influence of dispersion agent and initial ZrOCl2 concentration on the powder properties and yield content. Synthetic powders have agglomerates size of 190 to 362 nm in primary scale, and 1.6〜3.9 μm in secondary scale. The percentage of secondary agglomerate is varied with 6 to 20 % by reaction condition. Agglomeration among particles was reduced by adding a dispersing agent, especially primary agglomerate size. Synthetic powder from initial ZrOCl2 concentration of 0.5 M revealed simultaneously less-agglomeration and high yield content. Sintered density and microstructure were influenced by the ZrOCl2 concentration and dispersing agent and the highest density was obtained from 0.25 M ZrOCl2 concentration with dispersing agent. Finally, 3Y-TZP granules fabricated from spray drying show a sphere-like shape with a diameter of 40〜70 μm. But a donut-like shape and a few cracks were observed on granule surface fabricated from the slurry of high solid content(50 wt%). Specific surface area of granule powder were 5.1〜5.6 m2/g. Green density after cold isostatic pressing of 200 MPa were 2.1〜2.2 g/cm3. After sintering at 1500 °C for 2h, all specimens have apparent density of 96.2〜98.3 %. With increasing a solid content, grain size increased from 0.3 to 0.6 μm, but apparent density was decreased from 98.3 to 96.2 %. It concluded that highly sinterable zirconia granule powder was obtained by the control of slurry composition and processing condition of spray-drying.