발간논문

Home > KJMM 논문 > 발간논문

The reaction mechanism of nitrogen absorption into pure iron melts was investigated using the Ar-N₂ plasma arc. The mathematical model for nitrogen absorption under Ar-N₂ Plasma are and effect of gas flow rate was determined. Because change of rate constant according to increasing baa flow ramie in effect of Ar gas flow rate for absorption under Ar plasma are is too small, mass transfer in gas and liquid phase is not affect to kinetics of nitrogen absorption of the melt. Therefore, the rate controlling step is deduced as the chemical reaction on the melt surface.

keyword :

The leaching behaviour and mechanism of copper and nickel with sulfuric acid in deep-sea manganese nodules mined from the Clarion-Clipperton`s preferred area with sulfuric acid, were studied. Effects of acid concentration, temperature, reaction time and particle size on the leaching rate of metals were discussed based on the experimental results. Copper extraction is initially almost instantaneous and increases slowly with time. On the other hand, nickel extraction was found to be very dependent on temperature and independent of acid concentration. Copper and 77% of Ni appears to be chemically adsorbed on the surfaces of iron and manganese oxides, not within their lattices. The leaching behavior of copper and nickel could be explained to be controlled by volume reaction model, and the leaching rate of Ni is the second order with respect to the remained in the sample.

keyword :

Effects of various thermomechanical treatments on the microstructure and rheological behaviors of the semi-solid A357 alloy were studied using a concentric cylindrical viscometer. The size and morphology of primary solid particles during continuous cooling were influenced by shear rates and cooling rates. Faster cooling rate was observed to result finer microstructures. On the other hand, at a given cooling rate increased shear rates tend to force the primary particles agglomerate together. At a given volume fraction solid the viscosity of the slurry decreases with decreasing cooling rates and increasing shear rates. The strain rate sensitivity, which is the measure for the pseudoplastic behavior, was measured to be -1.3∼-1.6 within the fraction of solid range of 0.45∼0.65.

keyword :

The effect of various rheological parameters on the thixotropic behaviors of the A357 Al alloy was studied using a Searl type high temperature viscometer. The viscometer was designed to cover wide range of cooling rate(1-20℃/min) and to apply high shear rate up to 1100/s so that thixotropic behaviors exhibited during the actual semi-solid forming alloy can be simulated. Thixotropy of the slurry was measured as a function of solid faction, shear rate, and time at rest. According to the isothermal test results, steady state viscosities at a given solid fraction and shear rate were significantly lower than those measure during continuous cooling. Areas of the hyateresis loops, which can be used as a measure for thixotropy, increased with increasing volume fraction of solid and required to reach the maximum shear rate.

keyword :

The study is an attempt to understand the basic characteristics of ECAP(Equal Channel Angular Pressing) which gives large shear deformation without any change in the dimension of material. Microstructure comparison was performed between pure Al and Al-7 wt% Si alloys after the ECAP. Emphasis was put on the microstructural change of Al-Si alloys consisting of two phase (primary Al ＋ eutectic Si) where eutectic Si appears different shape and size depending on the modification. The pressing leads to the development of subgrain bands of Al and the fracture of unmodified eutectic Si. The eutectic Si may form dislocation tangles by acting as an obstacle to movement of dislocation, which can be proved with the location of eutectic Si on recrystallized grain boundary. It is obvious that ECAP results in a fine grain structure in Al-Si alloy without decohesion between Al matrix and eutectic Si.

keyword :