발간논문

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Roulette liquid theory has been applied to the partially miscible system of the Pb-Zn mixture. A partition function for the binary mixture is developed using Roulette liquid theory, on the basis of the fact that potential energy is a function of characteristic molecular constant. We can obtain the coexistence curve of Pb-Zn system which is in good agreement with the experimental result and explain some theoretical defects of lattice model.

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In surface reactions in which one solid is converted to another by means of oxidation or reduction, geometric factors reflect themselves in the kinetic pattern followed. Geometric factors are helpful in that by correlating the surface reactions with geometry equations it is possible to determine the direction of diffusion of the reactive species through the product layers. In this study iron sinters were oxidized in oxygen atmosphere to wu¨stite. The sinter is composed of many spherical iron grains which is subjected to individual oxidation. Results of these studies indicate that ferrous ions do diffuse outwardly and react with oxygen on the outer surface and in all cases, the geometric model correlates the kinetic data observed. The activation energy thus obtained was found to be about 31 Kcal/mole which corresponds to the activation energy of diffusion of Fe^(++) ion in wu¨stite matrix. It is also noteworthy that the intergrain diffusion of oxygen plays on important role in the oxidation rate.

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A kinetic investigation was carried out on the development of ferromagnetic γ phase in Mn-Al-C alloys of three different carbon contents (O, 0.18 and 0.27 wt.% at a fixed Mn of 70 wt.%) by means of the isothermal heat-treatment at temperatures ranging 425∼600℃. The results obtained can be summarized as follows; 1) The transformation kinetics was interpreted as an autocatalystic reaction in which the induced stress developed during the growth of ε` phase from the high temperature εphase was believed to be responsible for the reaction. 2) The addition of carbon to Mn-Al binary alloy decreased the rate of transformation. The activation energy for the transformation from εto τphase was calculated to be 58.0, 59.1 and 60.1㎉/㏖ respectively for Mn-Al and Mn-Al-C specimens.

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A kinetic investigation was carried out on the decomposition of ferromagnetic τphase in Mn-Al-C alloys of three different carbon contents (O, 0.18 and 0.27wt.% at a fixed Mn of 70.wt.%) by means of the isothermal heat-treatment at temperatures ranging 600∼700℃. The results obtained can be summarized as follows; 1) The decomposition of τphase to β-Mn and γphases was analysed to follow the nucleation and growth mechanism. Nucleation took place at the phase boundaries to form β-Mn first, and then γphase subsequently. 2) The decomposition of τphase was inhibited by carbon addition and showed the stabilization effect of τphase in Mn-Al-C alloys. The activation energy calculated for the decomposition was ranged 64.1㎉/mole for Mn-Al alloys to 70.6 and 75.3㎉/mole for Mn-Al-C alloys.

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Chemical vapor deposition on the various substrates such as electrolytic iron, carbon steel and stainless steel (STS 304) has been carried out with gaseous mixture of TiCl₄, H₂and N₂in order to study the effect of temperature, composition of reaction gas and gas and gas flow rate on the amount and state of TiN coating. Wear resistance of the TiN coated specimens has also been studied. Better TiN deposition was resulted with gas flow rate of 100/min N₂, 90㎖/min H₂and l.l㎖/hr TiCl₄, and elevated temperature. TiN coated layer of electrolytic iron was superior, followed by carbon steel and stainless steel. Wear resistance of the TiN coated specimens improved markedly, and that of stainless steel was prominent.

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The diffusion of silicon and carbon atoms was studied in γphase of Fe-Si-C ternary alloy at 1000℃ under the steady-state condition. Diffusion cell assembly, essentially, consisted of a thin sheet of pure iron and a silicon powder (60 mesh) which was packed on one side of the membrane, while the other side was packed with manganese powder. Both sides of the pure iron membrane, were packed with 0.7 mm φcarbon rods to maintain the equal carbon potentials. Atomic rnobilitics of silicon were measured along each of the steady-state diffusion concentration profiles. Diffusion coefficient of silicon D_(22) was found to be, 39∼5.79×10^(-11) ㎠/s in Fe-2.8∼1.5 at. pct Si-2.2∼1.5 at, pct C system, where the diffusivity of silicon was increased by the addition of silicon and carbon atoms. Interstitial carbon atoms diffuse more rapidly than the substitutional silicon atoms. The carbon atoms on the gradient of slow moving component, will easily become a state of a transient equilibrium. The ratios of diffusivity of carbon D_(11) and cross term D_(12) were calculated by D_(12)/D_(11) ∼ 0.1∼0.19 at Yc=0.019∼0.021 in a Fe-Si-C alloy.

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