발간논문

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Developing method of sample treatment for proeutectic dendrites, study a relationship between proeutectic dendrites, eutectic cell structures, eutectic structures, graphite structures and mechanical properties of gray cast iron. Hightly oriented and compact proeutectic dendrites with well developed eutectic structures have higher mechanical properties than random dendrites with underdeveloped eutectic structures. Proeutectic dendrite structures be classified according to the solidification mechanism, as Type I, II, and III. Type I dendrites associate well developed eutectic structures due to enough chance to develope during the solidification. Type II dendrites associate underdeveloped eutectic structures due to suppression of the solidification reaction. Type III dendrites associate underdeveloped eutectic structures due to lack of chance to develope at higher temperature solidification. Graphite structures of gray cast iron have proposed to be classified as developed, underdeveloped and kish graphite.

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The effect of plastic deformation on the activation energy of recovery and recrystalization temperature of 99.9% purity polycrystalline Aluminum was investigated. The 10%, 20% and 29% cold compressed aluminum specimen were prepared from 4.75 ㎜ diameter cold drawn rod. From the hardness data obtained by isochronal annealing of one hour between the temperature range of 240℃-330℃ under hydrogen atmosphere, the recrystallization temperatures for 10% and 29% cold compressed were measured to be 304℃ and 285℃ respectively. On the other hand, from the hardness data obtained by isothermal annealing at the temperature range of 290℃-330℃, the activation energy of recovery for 10%, 20% and 29% cold compressed were deduced as 29,600, 25,200 and 22,500 ㎈/㏖ respectively. The activation energy of recovery can be expressible in linear equation in terms of the stored energy of plastic deformation.

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A concentrate which was under production at Dalseong mine, contains mainly cosalite (2PbS Bi₂S₃) bismuthinite (Bi₂S₃) and other minerals. This was roasted both in the tube furnace and reverberatory furnace. Pb in the roasted ore was then extracted with a hot aqeous solution of CaCl₂from which Pb was cooled to produce the white crystals of PbCl₂. The residue containing Bi, Au and Ag was smelted to produce crude bismuth in the crucible furnace. In the separation process, the recovery of Bi, Au, Ag was approximately 97% and the ratio of extraction of Pb in the ore was about 75%.

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The reduction of metals from their oxides is a very important aspect of metals production. The three general processes for reduction are Metallothermic, Carbothermic and Direct Gaseous Reduction. Each type has its advantages and disadvantages. Carbothermic and direct gaseous reduction are similar in that gas-solid reactions with reducing gases control the reduction process. Physical conditions and kinetic parameters associated with reducing gas-solid reduction will be considered. In iron oxide reduction, problems associated with direct reduction processes are many and varied. These will be mentioned in lesser detail to illustrate some of the problems encountered.

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Stress corrosion cracking is perhaps the most insidious of all forms of corrosion. It may develop as very fine intergranular or transgranular cracks, with little or no telltale evidence of corrosion products. In fact in many instances there may be no macroscopic indication of impending failure. Stress corrosion cracking map be defined as the spontaneous failure of a metal as a result of the combined effects of corrosion and static stress either residual or applied. The result is a brittle fracture in an otherwise ductile material. It is generally accepted that pure metals are immune to stress corrosion cracking. However, even a few parts per million of impurities may render the metal or alloy susceptible to cracking. The mechanism of cracking is not completely understood. Theories range from purely mechanical to electrochemical. The fact that propagating cracks can be stopped by the application of cathodic protection or accelerated by anodic currents suggests that the initiation and propagation of cracks involve at least in part an electrochemical process. The principle means of eliminating or reducing the occurrence of stress corrosion cracking are: (1) The reduction or elimination of dangerous tensile stresses. (2) The alteration of the environment to render it less dangerous. (3) The replacement of the alloy with another that is not susceptible to stress corrosion cracking.

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