• Journal of the Korean Ceramic Society
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• v.30 no.7
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• pp.563-570
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• 1993

Spherical, monosized gadolinium compound was prepared by the reaction of Gd(NO3)3 solution with decomposition products of urea in the solution at evaluated temperature. Chemical composition and calcination characteristics of spherical gadolinium compound prepared were investigated by X-ray IR and TG-DTA. The approximate chemical composition of the spherical particle precipitated was Gd(OH)CO3.1.5H2O. Gd(OH)CO3.1.5H2O was calcined to monoclinic type Gd2O3 at 115$0^{\circ}C$ via cubic type Gd2O3 near $600^{\circ}C$. The effects of various parameters such as pH, temperature, concentration ratio of urea to gadolinium precusor, ageing time, and others material (CCl3COOH and HOCNH2) in stead of urea as precipitating agent on the properties of the resulting precipitates were studied systematically.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.448-456
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• 2010

The mechanical behavior of granular soils is affected by particle bonding including natural cementation. This study addresses a simple model of small strain stiffness and salt concentration based on wave measurements of salt-cemented particulate media. Published models of artificially cemented soils with different curing methods and several types of cementation agents are reviewed. Glass beads with the median diameter of D50 = 0.5mm are prepared in rectangular cells using the water-pluviated method in salt water with different concentrations. Piezo disk elements and bender elements embedded in the cell are used for the measurements of compressional and shear waves. The relationships between elastic wave velocities and salt concentration show an exponential function. The measured small strain stiffness matches well the predicted small strain stiffness based on micromechanics for simple cubic monosized sphere particles. This study demonstrates that the salt concentration in salt-cemented specimen may be evaluated by using elastic wave velocities.

• Analytical Science and Technology
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• v.12 no.5
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• pp.382-386
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• 1999

Spherical particles of barium titanyl oxalate(BTO) were homogeneously precipitated by thermal decomposition of dimethyl oxalate in hydrochloric mixture solutions of water and ethanol. The experimental parameters such as composition of the mixture solvents. the eoncentration of hydrochloric acid and reaction temperature had the paramount effect on the size of panicles collected from the bottom of the reaction vessel at the aging time of 120 min and the composition of BTO. Stoichiometric BTO powders were obtained under certain conditions as relatively low alcohol content in the mixtures, high chloride concentration and high temperature, Monosized, submicrometer, but titanium excess particles were obtained under certain reverse conditions.