발간논문

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Field emission of diamond film was enhanced after surface treatments using boiling HCl and aqua regia solutions. The current generated by the emission of electron was increased and the threshold field was reduced from 18.1 to 13.8 V/㎛ by the surface treatment. The surface roughness was increased by 24.4% with aqua regia treatment, but the calculated current-voltage curves were not consistent with the measured ones. It was found that the binding energies of C-C and C-O bonds were increased after the aqua regia treatment and the Fermi level of the aqua-rigia-treated surface was increased by 2.2 eV. This provides evidence that the enhancement of electron emission originated from the reduction of work function, caused by the chemisorption of oxygen atoms. The effective electron affinity changed to negative, leading to the reduction of the potential barrier height and width for electron emission at the surface of diamond.

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A novel method for the fabrication of poly-Si films with a large grain size is reported using solid phase crystallization(SPC) of LPCVD amorphous Si films by nucleation interface control. The reference films used in this study were 1000Å-thick a-Si films deposited at 500℃ at a total pressure of 0.35 Torr using Si₂H_6/He. Since the deposition condition changes the incubation time, i.e. nucleation rate, and since nucleation occurs dominantly at a-Si/SiO₂ interface, we devised the following deposition techniques for the first time in order to obtain the larger gain size. A very thin a-Si layer (∼50Å) with the deposition conditions having long incubation time is grown first and then the reference films(∼950Å) are grown successively. Various composite films with different combinations were tested. The crystallization kinetics of composite films was observed to be determined by the deposition conditions of a thin a-Si layer at the a-Si/SiO₂ interface. Nucleation interface was also observed to be modified by interrupted gas supply resulting in the enhancement of the grain size.

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Recently, the slag foaming techniques have been applied to save energy consumption in the steelmaking processes. Present study was carried out to understand the characteristics and mechanism of the slag foaming phenomenon. The effects of temperature, basicity, and composition of slag on foaming index were analyzed to clarify the governing factors of slag foaming in CaO-SiO₂-FeO-Al₂O₃ slag system using the slag foaming index(∑). The slag foaming index, ∑, was increased with decreasing temperature and the content of FeO. However, for the dependence of basicity, was shown the minimum value of foaming index at CaO/SiO₂ = 1.35. These phenomena are considered due to effect of basicity on the slag structure and melting temperature, which were qualified by viscosity find surface elasticity. A general correlation by the dimensional analysis could be proposed as follows. Σ = 214×{μ√(ργ)}.

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A thermodynamic model of chemical equilibria with mass and charge balance equations has been developed for the solvent extraction of ZnSO₄-H₂SO₄-H₂O-D2EHPA-kerosene system. The activity coefficients of all solutes in the aqueous phase were calculated by Pitzer`s equation. By applying present model, the equilibrium concentrations of solutes could be calculated from the stoichiometric concentrations of aqueous phase and pH. The extracted metal species and extraction equilibrium constant were found to be ZnHA₃ and 9.77×10^(-2) from the slope analysis of the equilibrium extraction data. The predicted distribution coefficients of zinc were in good agreement with experimental results.

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For the thixoforging process, multi-power induction heating process (with rapid change of the power) and inductive coil design are very important due to the reduction of the lead time for induction heating and forming. The multi-power induction heating process is indispensable to adopt a power-time beating pattern which manages to conciliate complete eutectic melting at the core with limited overheating at the periphery. Generally, high power is used for the rapid reheating of the billet to the eutectic temperature range (about 10℃ lower than eutectic temperature) and low power for the remelting of the desired solid fraction and for the radial homogeneization of the solid faction. The suitability of multi-power induction heating conditions would be verified through the comparison to general beating (without rapid change of the power) and Garat`s data. It is found that if the billet is rapidly reheated at high power range, T_(h2) is important from the point of securing a fine distribution of solid and liquid.

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The purpose of this study is development of direct quenching(DQ) steel bars by direct quenching and self tempering process. So we investigated the production possibility of DQ steel barb by submerged simulation and then put in practice on line DQ rolling by CRCT. The steels by submerged simulation and DQ rolling are obtained microstructures and hardness equivalent to reheat quenching(RQ) steel bars. Also mechanical properties of direct quenched and tempered(DQ&T) bars are equivalent to RQ&T bars. Especially strength-toughness balance of DQ&T bars is superior to RQ&T bars.

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