Papers by Author: Myung Hyun Lee

Abstract: Highly sinterable lithium titanate (Li2TiO3) powder was fabricated by an organic-inorganic solution route. Liquid-type ethylene glycol (EG) was used as an organic carrier for the metal cations. Titanium isopropoxide and lithium nitrate were dissolved in the liquid-type ethylene glycol without any precipitation. The dried precursor gel showed crystalline form at 300 °C and carbon-free Li2TiO3 was observed above 400 °C. The primary particle size of the carbon-free Li2TiO3 was about 100 nm, and the structure of the crystallized powder was porous and agglomerated. The porous powder was ball-milled and easily ground to fine particles. The powder compact was densified to 93% theoretical density (TD) at relatively low sintering temperature of 1100 °C for 2 h. The densifed Li2TiO3 showed a small grain size of 1.2 μm. As well, the grain size was notably increased at 1200 °C and above. After the over grain growth, further densification was no more observed.

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.