발간논문

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The oxygen deficient compound of Sr₃Fe₂O_(7-χ) phase was prepared by controlling the oxygen pressure and temperature. The lattice constants, magnetic properties and Mo¨ssbauer effects were investigated. Although the phase of Sr₃Fe₂O-(7-χ) was single phase under 10-15-300 atmosphere of oxygen pressure, variation in magnetic properties and Mo¨ssbauer effects were found dependent upon the oxygen contents.

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The CuCl₂-catalyzed reaction of silicon metal powder and hydrogen chloride by the flow method is studied in order to find a convenient method of obtaining trichlorosilane (TCS), a widely used starting material for preparing semiconductor-grade silicon. The effects of varying the concentration of CuCl₂, reaction temperature, and the flow rate of HCl are studied. The optimum temperature for the reaction is found to be the range between 385℃ and 420℃, and as the temperature increases beyond this range, tetrachlosilane (TET) content of the product becomes high. The yield of TCS is found to increase when the flow rate of HCl increases. Under the optimal conditions with 10 wt, % CuCl₂ concentration, 400℃ reaction temperature and the flow rate of 400-600㏄/min, the yield of TCS is about 90 wt, % of the total product.

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Densification of W-Ni-Fe heavy-alloy during sintering at 1300℃ and 1450℃ was studied. The (Ni＋Fe) content of the specimens were 3.5, 10, and 15 weight % while Ni: Fe ratio maintained at 7 : 3. Two grades of tungsten powder with average particle size of 1.23μand 5.4μwere used. In order to observe the effect of compacting pressure on densification rate, the specimens were pressed at 0.5, 2.5, and 5 tons/㎠. During sintering at 1450℃ with some liquid phase present the specimens with small tungsten powder showed faster densification initially. However, after 30 minutes of sintering densities exceeding 99% of the theoretical density were obtained with 1.23μand 5.4μ tungsten powders. The densification rate was little affected by the (Ni＋Fe) content. For the specimen with 3.5% (Ni＋Fe) and 1.23μW powder compacted at different pressures same high density was obtained in short sintering time for all specimens when sintered at 1450℃. The densification rate at 1300℃ is shown to be greatly affected by the tungsten particle size. After sintering for 60 minutes at 1300℃, the specimens with 1.23μW-powder are densified to about 98% of the theoretical density, while the specimens with 5.4μW-powder show densities around 70-80% of the theoretical density. It is therefore concluded that in liquid phase sintering the tungsten powder size is not critical for obtaining densities approaching the theoretical density, but in solid state sintering it is necessary to use small tungsten powder size to obtain high densification. The fractional volume changes during liquid phase sintering plotted against sintering time in log-log scale show slopes ranging between 0 and 15, and varying slightly with composition. This result is inconsistent with any predictions based on Kingery`s model of liquid phase sintering. The observed densification rates during solid state sintering cannot be explained by the activated sintering model of Brophy et al. It is suggested that the densification rate should be dependent on the amount of porosity remaining and therefore the "impingement" effect has to be taken into account in establishing a theoretical model for densification during sintering. Observations of the tungsten grain growth show that with smaller (Ni＋Fe) content, the tungsten grain growth is considerably larger.

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An investigation has been carried out for the precipitation process in dilute Al-Cu-Mg alloys containing 2.0 wt% Cu and l.l wt% Mg by the detailed measurement of changes in hardness and electrical resistivity during ageing at the various temperatures between 40˚and 300℃. The preprecipitation in this alloy has occurred 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℃. The apparent activation energy for the formation of zones in the stage of slow reaction has been determined to be 0.25±0.03 eV and 0.24±0.01 eV, in the low and high ageing temperatures, respectively. The critical ageing temperature at which the rate of zone formation comes to maximum is found to be in the range of 70˚∼120℃. Precipitation of the metastable S` phase has been observed even at such a low ageing temperature as 40℃. Therefore, it seems that the precipitation of the S` phase depends upon mainly ageing time, and not so much upon ageing temperture. The equilibrium S phase has been shown to precipitate at the elevated ageing temperature above 200℃ on prolonged ageing.

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Specific heat versus temperature curves been obtained by the Nagasaki-Takagi method on polycrystalline specimens of Al-rich Al-Ag. Al-Cu, Al-Zn, Al-Zn-Mg, Al-Cu-Mg and Al-Mg-Si alloys, during reheating after various age-hardening treatments. The results have been analysed in comparison with those of the hardness tests, dilatometric, X-ray structural and electrical resistivity measurements and electron microscopic observations. The thermal analysis is useful proving further information on the low temperature ageing or the first stage of the ageing, its relation to the high temperature ageing formation of the G.P. zones and metastable phases. The reversion phenomena in the alloys aged at low temperatures are attributed to the d;ssolution of the G.P. zones. The effects of the ageing temperature and ageing time upon both the reversion temperature and the heat of reversion have been examined from the heat absorption, and it has been confirmed that the reversion temperature rises with ageing temperature.

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