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Secondary hardening is accomplished by the precipitation of fine-scale M₂C alloy carbides in high CoNi steels containing the strong carbide-forming elements Cr and Mo. Thermodynamic stability and coarsening resistance of these carbides depend on the alloy content of these elements. Thermodynamic calculations are performed for the determination of phase diagram, composition of alloying elements M, mole fraction and lattice parameters of M₂C, and volume percent of austenite in AerMet 100 system. And these results are compared with experimental ones and the coarsening theory of rod-type particles.

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According to previous researchers, the slag components Al₂O₃, MgO and SiO₂ are matrix components which form spinel(MgAl₂O₃) and forsterite(Mg₂SiO₄) through solid-state reactions in the reduction process of chromite. These slag components(Al₂O₃ MgO and SiO₂) have effects on the reduction process of chromite. Therefore solid-state reactions in Al₂O₃-MgO-SiO₂ under oxidation and reduction conditions have been studied. The pellets of mixed Al₂O₃, MgO and SiO₂ powders were burned in a furnace at 1300, 1400 and 1500℃ for 1, 2 and 3hrs under oxidation and reduction conditions. The burned pellets were analyzed by means of microscopy, X-ray diffraction analysis and EPMA analysis. The results of the investigation can be summarized as follows : 1) When the firing time and temperature were increased, more spinel and forsterite were formed. 2) Reduction conditions produced better results than oxidation condition. 3) When SiO₂ was contained, compared with Al₂O₃-MgO, SiO₂ exceeded the formation of slags in the reduction process of chromite.

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In a smelting reduction method, the fluidized bed reactor is one of the most possible reactors for prereduction of fine iron ore. In this work, the reduction degree of fine iron ore(106∼212, 212∼250㎛) were measured from hematite to iron CO 100% gas in a batch-type fluidized bed. The rate parameters incluiding the present study were determined by using the reduction data. The reduction rate of fine iron ore increased with increasing temperature and gas flow rate, whereas that was decreased with increasing ore diameter and ore inventory. The apparent activation energy for the reaction is measured to be about 59-75 kJ/㏖. The fundamental data for the development of pre-reduction furnace by fluidized bed and direct iron-making process could be acquainted from this study.

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A three dimensional numerical simulation program based on the finite element method is developed for calculating electromagnetic field of the metallurgy process using cold crucible, H-Φ formulation is adopted to reduce calculation time. The calculated value of magnetic field in three different cold crucibles(cylinder type crucibles for continuous casting and levitation melting and square type crucible for continuous casting) show good agreements with the measured value.

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A series of experiments were performed to investigate the kinetics of dissolution reaction between palladium powder and iodide solution. This investigation examined the effects of oxygen, pH, iodide and iodine concentration, initial PdI₄² concentration and temperature on the dissolution of palladium. A half order reaction rate was found with respect to I₃^- and a third order reaction rate with respect to I^-. But the reaction rate was decreased with increasing initial concentration of PdI₄^(2-). The activation energy of reaction was 2.4kJ/mole, which implied that the dissolution reaction was controlled by the diffusion reaction.

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In order to investigate colloidal behavior of the oxides and/or hydroxides of Ce, La, Nd, and Th, which encounter frequently in the processing of monazite, their zeta-potentials (ξ-potentials) were primarily determined by a zeta-meter as a function of pH. Also, critical ξ-potentials of those colloids were categorized through settling tests aided by light transmittant measurements. The zero point of charges (z.p.c,) for ThO₂, CeO₂, La(OH)₃, and Nd(OH)₃ lay respectively at pH 6.7, 2.1 & 11.5, 8.8, and 10.5. The critical ξ-potentials obtained were ±15mV(ThO₂), ±8mV(CeO₂), ±6mV(La(OH)₃), and ±10mV(Nd(OH)₃). From the acquired informations, an attempt to separate physically the mixture of oxides and/or hydroxides by selective flocculation was performed, which gave successful results.

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A study has been made on the solvent extraction of platinum, one of the platinum group metals, with diluted tri-n-butyl phosphate(TBP). Systems involving hydrochloric acid as extract-promoting agent have been studied in the distribution of platinum(IV) chloride. The distribution coefficient for platinum(IV) chloride goes up through a maximum at just over 6M HCI and 50% TBP in toluene, but decreases at low and high HCI concentration. IL was found that the extracting species has the formula 3TBP·H₂PtCl_6·χH₂O. Unextracted platinum(IV) in the aqueous phase is determined directly and platinum(IV) in the organic phase is stripped with H₂O and determined by stannous chloride method, respectively. In a binary mixture of gold and platinum, the solvent exhibited toward gold that it could be extracted selectively from platinum.

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Infiltration behavior of the molten metal, microstructure and mechanical properties of the SiC particulate reinforced Al alloy composites fabricated by pressureless infiltration technique have been studied. Under the nitrogen atmosphere the spontaneous infiltration of the molten Al alloy into the bed of powder mixture of Al, Mg and SiC occurred at relatively lower temperatures, compared with the infiltration of Al alloy into the bed of only SiC powder. Both Al₄C₃ and Si may be formed even at 700℃ as a result of the interfacial reaction between molten Al alloy and SiC, and the extent of reaction increased with an increase in temperature. As that Si is incorporated with Mg, the age hardening can occur during the precipitation of Mg₂Si. At 700℃ of a relatively low temperature, the extent of age hardening was small and/or the hardening rate was slow. The peak hardness during aging tends to slightly increase with increasing infiltration temperature. Tensile strengths of the specimens where Al-(0-6)Mg alloys infiltrated into the bed of powder mixture containing 3Mg exibited similar values but decreased in the case of the infiltration of Al-10Mg alloy. Also, the phenomenon that tensile strength of specimen infiltrated at 1000℃ of a high infiltration temperature decreased may imply the severe interfacial reaction. MgAl₂O₄ and Al₄C₃ formed as a result of the interfacial reaction between molten Al alloys and SiC were identified.

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