발간논문

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The rate of thermal decomposition of calcium hydride was studied under argon atmospheare using a thermogravimetric technique in the temperature range of 770℃ to 835℃. The effects of hydrogen partial pressure, total flow rate and the shape of the sample holder on the decomposition rate were discussed. And the reaction mechanism was estimated compassing the experimental results with the vasious reaction models. From the experiments, the results were as follows; 1) When the long sample holder, 20mm long, was used, the thermal decomposition rate was controlled by hydrogen gas diffusion through the surface gas film, and its rate can be expressed as the fraction decomposed, X, in terms of the reaction time t, X=k2(1-PH2/PH02)·t. The apparent activation energy is about 47.6 kcal/mole, that is equal to the heat of dissociation. 2) When the short sample holder, 3 mm long, was used, the reaction rate was controlled by the chemical reaction at the interface and the rate was expressed as 1-(1-X)1/3=k1(1-PH2/PH02)·t. An apparent activation energy of the chemical reaction is about 60.6 kcal/mole in which the heat of dissociation of calcium hydride and the activation energy of Ca+H2→CaH2 were included. 3) Comparing above two results, the activation energy of Ca+H2→CaH2 is about 13 kcal/mole.

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The effects of heat treatment on the structure of high Silicon-Al alloys were examined by metallography. The effects of heat treatment on the surface roughness, the chip formation and the amount of build up edge, after cutting at various cutting speeds and cutting depths were studied. The results obtained are as follows; 1. The heat treatment of the high silicon-aluminum alloy changed eutectic silicon crystal into spheroidal form, the quality of material was intensified and the mechanical properties were improved conspicuously. 2. When feeding speed was constant, the surface roughness was inversely proportional to the square of cutting speed, and heat treatment decreased its ratio greatly. 3. The refining treatment diminished the amount of adhesion to tool surface, and the heat treatment deminished its amount more. 4. When feeding speed was constant, the surface roughness was proportional to cutting depth, and its ratio was much decreased by heat treatment. 5. The illumination of machined surface was improved by heat treatment, especially by heat treatment followed by refining-treatment with Mg. Spheroidizer.

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Chromium was electrodeposited in the standard Sargent bath at temperatures from 35 to 75℃ over the ranges of the current: density from 25 to 200A/d㎡. All the chromium deposits had the bcc structure. The preferred orientation (or texture) of the deposits ranged from the random to the <111> or <211> preferred orientations depending on electrolysis conditions. The degree of development of the <111> preferred orientation increased with increasing bath temperature up to 65℃ and then decreased again at a given current density. It also increased with decreasing current density at a given bath temperature. Microstructures of the cross section of chromium deposits were found to be closely correlated with their preferred orientations. Deposits with the strong <111> preferred orientation had the field orientated texture type structure. Those with the <211> preferred orientation had the structure of striations (or laminations). Those with the medium <111>-weak <211> preferred orientation had the structure of mixture of the field-orientated texture type and striations. Chose with random orientation had the unorientated-dispersion type structure. The hardness of the chromium deposits had a relation with their structure and residual stress. Deposits which brought about structure of striations and high residual stress had a relatively high hardness.

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An investigation has been carried out for the precipitation process in dilute Al-Cu-Mg alloys containing 2.0wt% Cu and 1.1wt% Mg by the observations of the transmission electron microscopy and the detailed measurement of changes in hardness and electrical resistivity during ageing at the various temperatures between 40°and 300℃. The pre-precipitation in this alloy has occured in three different ageing stages; (1) G. P. B. zones formed during quenching and ageing for less than 1 minute known as the stage of fast reaction, (2) G. P. B. zones formed in the early stage of ageing below 200℃ known as the stage of slow reaction, and (3) G. P. B. (2) zones formed in the early stage of ageing above 250℃. From the electrical resistivity measurement, the apparent activation energy for the formation of zones in the stage of slow reaction has been determined to be 0.26±0.04eV. The critical ageing temperature at which the rate of zone formation comes to maximum is found to be in the range of 70°∼120℃. The distribution of dislocation loops and loop free zone (LFZ) have been observed at such a low ageing temperature as 70℃ on prolonged ageing. The metastable S` phase has been precipitated on the dislocation lines and formed the S` composite precipitate sheets on the｛210｝planes in the <001> growth directions of the matrix. The equilibrium S phase has been precipitated at the elevated ageing temperature above200℃ on prolonged ageing.

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The compounds of Sr₃Fe₂O_(7-X) are prepared by equilibrating prereacted materials at various temperature and oxygen pressure, then M¨ossbauer effect and magnetization are measured at the temperature from 4°K to room temperature. The results obtained in this study are as follows 1) Mo¨ssbauer spectra mean that Sr₃Fe₂O_(7-X) phases are magnetically ordered at 4°K 2) The isomershift of Fe(IV) has the trend towards more negative value as the content of Fe(III) increases 3) Quadrupole splitting of the samples of Sr₃Fe₂O_(6·58) and Sr₃Fe₂O_(6·21) is clearly evident and asociated with oxygen vacancy 4) The samples of Sr₃Fe₂O_(6·85) and Sr₃Fe₂O_(6·58) are antiferromagnetic and its Ne′el temperatures are 120°K and 20°K 5) Sr₂Fe₂O_(6·00) is antiferromagnetic and magnetic ordering appears stable to above room temperature.

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The effect of iron addition to Cu-11.0 wt.% Al alloy on the mechanical properties and microstructures has been investigated by using isothermal transformation technique. This investigation showed that the addition of 2% iron to Cu-11.0 wt.% Al alloy produced fine microstructures, and fine iron-rich precipitate particles were formed within α phase after proper isothermal heat treatments. However, the addition of 1% iron did not have any effect on the microstructures at transformation temperatures of 524℃ and 560℃. The structure of iron-rich precipitate particles is body centered cubic (B.C.C.) with lattice parameter of 2.93 A. 2% iron additions caused increase in ultimate tensile strength(U.T.S.) and little effect on elongation. The specimens of fine microstructures with iron-rich precipitate particles showed large U.T.S., and the maximum value of 110,000 psi was obtained. The high U.T.S. is attributed to the microstructural refinement and iron-rich precipitate particles.

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A kinetic study on dissolution reaction of zinc-ferrite which has similar conditions to zinc-plant residue, has been made with aqueous sulfuric acid in the concentration range of 1N to 8N and over a temperature range of 50℃ to 90℃. The dissolution reaction is believed to be controlled by interface chemical reaction, and the rate is expressed by the following relation for the initial stage of the reaction in aqueous solution. 1-(1-R)^⅓=kt The activation energy for the dissolution reaction is found to be 14 ㎉/㏖. Studies with zinc-plant residue containing some other components besides zinc-ferrite slow increasing dissolution rate and its important factors were interpreted in terms of the difference of surface area, the increase of reactive site in zinc-plant residue and the Galvanic effect.

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The tensile strength and yield strength were measured in unidirectionally solidified Al-Cu binary alloys along with the secondary dendrite arm spacing to see the relationship between them. Small amounts of Mg and Zn are added to these binary alloys to study the effects on the dendrite spacings and therefore on the mechanical properties. The addition of Zn and Mg decreases the dendrite arm spacings and increases the mechanical properties of alloys. The decrease of dendrite spacing was explained in terms of Cu solute atom diffusivity effected by the addition elements.

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