Papers by Author: Yeong Keong Ha

Abstract: The condition of a heat transfer surface with boiling is composed of three environmental components; high temperature, high pressure and water vapor. In general an autoclave or a high temperature loop system is used for maintaining the required condition. The thermodynamic relationship of chemical reactions states that the free energy difference (ΔG) is clearly dependent on the reaction temperature and independent of the reaction pressure if the reaction has no volume change: (∂ΔG/∂P)T = ΔV ~ 0. Based on the above relationship, the high-pressure term was removed from the environmental components of the heat transfer surface. A vacuum quartz capsule with a moisturized metal oxide powder was used to study the formation of nickel ferrite. The feasibility of this simplified method to simulate a heat transfer surface was confirmed by an analysis of the FT-IR spectra and XRD pattern during the transformation of a nickel and iron mixed oxide into nickel ferrite.

Abstract: We present the preparation and Cu(II) adsorption characteristics of a new and innovative composite which was composed of a carboxymethylated polyethyleneimine (CM-PEI) and an activated carbon with a nanopore less than 2 nm in diameter. In this study, we examined the adsorption phenomena of Cu(II) on the CM-PEI/F400 composite and evaluated the adsorption data using three kinds of isotherm models (Langmuir, Freundlich, and Temkin isotherms). It was found that the adsorption of Cu(II) on the CM-PEI/F400 composite obeys the Langmuir isotherm model. Furthermore, The Cu element mapping results showed that Cu was well distributed throughout all the surface of the composite particle, suggesting that the surface of the F400 particle was uniformly covered with CM-PEI.

Abstract: The effect of a tetravalent dopant, Th4+, on the oxidation of UO2 was investigated using a thermogravimetry and X-ray diffraction analysis. Th-doped UO2’s with various dopant contents were prepared and their oxidation kinetic curves were obtained from the weight gains during air-oxidation. For the first oxidation step from (U1-yThy)O2 to (U1-yThy)4O9, the oxidation kinetic curves showed the same gradient regardless of the Th content. The inhibition of the oxidation reaction occurred dominantly in the second step, from (U1-yThy)4O9 to (U1-yThy)3O8. At the plateau of the second stage, the calculated O/M values and the X-ray diffraction patterns revealed that the O/M ratio was decreased with an increase of Th content. The relationship between the mean formal charge and the composition showed that the oxidation to (U1-yThy)3O8 proceeds within a certain limit. The lattice parameter of the initial material seems to affect the oxidation rate of the first step. And the oxidation reaction stopped when the average formal charge of the U atoms reached a value of 5.3.