발간논문

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The phase diagram of the Pt-Sb system was investigated. Mixtures of Pt and Sb of 5 nine purity, which were vacuum sealed in silica capsules, were homogenized at high temperatures and quenched to prepare Pt-Sb alloys. Phases in the alloys were identified by optical microscopy, X-ray diffraction, and electron microprobe analysis. The existence of compounds, Pt34Sb7, Pt3Sb, Pt3Sb2, PtSb and PtSb2 was confirmed. A new phase, Pt34Sb7, was first found and had a composition of 82.7, 83.9 at.% Pt with a tetragonal Structure of the lattice parameter, a=3.948(3), c=16.85(1)A. PtSb is stoichiometric up to 800℃ and becomes Pt deficient as much as 1 at.% at 1000℃ Solid solubility limits of Sb in Pt were determined to be 7.5, 10.0, and 6.1 at.% at 1000, 800 and 600℃, respectively. The liquidus curve between the PtSb2 and Sb phases was revised.

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A compact naturally occurring α-beryl was decrepitated at 960℃ to a porous β-structure, from which, beryllium extraction was investigated by sulfuric acid leaching at atmospheric pressure. The order of reaction as well as the overall reaction rate constant were calculated. Furthermore the apparent activation energy and the frequency factor were determined. A Langmuir-type equation was developed for the effect of pulp density and total surface area on the rate of beryllium extraction. The maximum theoretically attainable rate of beryllium extraction and proportionality constant were assessed. The effect of particle size on beryllium leaching with sulfuric acid is described by an exponential form. Beryllium extractions were realized approximately as high as 90%.

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A 7050 high strength aluminum alloy was processed by three different methods to obtain the microstructures containing a large amount of deformed grains and the ones containing considerable amount of subgrains and recrystallized grains, respectively. The differences of the microstructure before and after T6 temper were investigated by optical and electron microscopes, and the average stress corrosion crack velocity vs. the stress intensity factor was measured by precracked CT specimens. The effect of the grain characteristics on the stress corrosion cracking susceptibility was more pronounced before T6 temper than after T6 temper. The resistance of the materials containing deformed grains and subgrains to stress corrosion cracking was superior to that of the materials containing recrystallized grains. The stress corrosion cracking susceptibility depended largely on the behavior of grain-boundary precipitates.

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The semiconducting SnO₂and SnO₂( : Sb) films were deposited on n-type silicon wafer substrates by chemical vapor deposition and the electrical properties of these hetero junctions have been investigated. Dibutyl tin diacetate and antimony pentachloride were used af the source materials respectively for tin and for antimony. The tin oxide films, undoped or antimony-doped, turned out to be n-type semiconductors and their forbidden band gap was estimated as 3.9 eV. The current-voltage characteristics of both SnO₂/Si and SnO₂( Sb)/Si heterojunctions represent good rectification with a threshold voltage of 0.55V. The barrier of the junction with a height of 0.78 eV was found in the Si side as in the case of metal-semiconductor Schottky barrier juntions. The deplection layer width of these junctions was estimated at zero bias as 7320Å. The ideality factor for undoped tin oxide films was 3.1 and reduced to 2.5 for Sb-doped films. The energy band diagram of SnO₂( : Sb)/Si heterojunctions has bean suggested from he results of these electrical pro perties.

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The variations of microstructure and hardness with aging were studied in melt spun Al-5.8 wt% Fe, Al-5.8 wt% Fe-1.8 wt% Ti, and Al-5.8 wt% Fe-2.8 wt% Cr alloy. The microstructure of as quenched ribbon was observed to be composed of zone A and zone B in alloys. In Al-5.8 wt% Fe alloy, primary intermetallics and the 2nd phase between dendrite arms in zone B were identified as Al_6 Fe. Particles with five fold symmetry were observed in Al-5.8 wt% Fe-2.8 wt% Cr alloy ribbon and were transformed to the unknown phase of orthorhombic structure as aging. The hardness of the ribbon increased with the addition of Cr and Ti, and decreased as aging temperature increases. But the addition of Cr was more effective on retention of hardness decrease in aging than the addition of Ti.

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Structures of Pd₃Mn, Pd_(21)Mn_(11) and Pd_5Mn₃phases in the Pd-Mn system of 16.5 to 51.8 at.% Mn, which were annealed over a temperature range from 190 to 850℃, were investigated by means of the selected area electron diffraction and X-ray powder diffraction methods. The stability range of the periodic one dimensional antiphase structure, Pd₃Mn, on the equilibrium phase diagram was clarified. The composition and temperature dependence of the antiphase domain size was also invesitigated. The Pd₂Mn and Pd_5Mn₃ phases were found to exist below 650℃ and 500℃, respectively, in agreement with the results of other investigatiors.

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The effect of Be on the mechanical properties of a Cu-Zn-Al alloy has been studied Beryllium addition of 0.27 wt% or 0.66 wt% reduced the grain size of the alloy by a factor of 4, to 250-300㎛. The fracture stress and the fracture strain of the alloy with Be addition were 2-4.5 times as great as those of the alloy without Be. The alloy with Be addition showed an improved shape memory effect an increased fatigue life by thermal cycling, a good formability and a ductile transgranular fracture mode.

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The stress distributions in an aluminum rod developed during guenching in 43℃ water from the temperature of 600℃ have been calculated using finite element method. In calculating the transient temperature field, the heat flux between the water arid the rod surface was calculated using the heat transfer coefficient. The stress and strain distributions were calulated using the thermo-elastoplastic model. The effect of creep was neglected because the rod, diameter of which was 5㎝, was exposed for a time period which is too short for the development of significant creep strains. At the beginning of cooling, compressive stresses were developed in the core, while tensile stresses in the surface layer. The stress disturbance occured 2 to 4 seconds after quenching, during which the largest temperature gradient developed, and finally the tensile stresses developed in the core while the compressive stresses in the surface layer.

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The formability of cold rolled stainless steel sheet was studied by measuring its R-value, strain-hardening exponent Limit Drawing Ratio(LDR), Forming Limit Diagram (FLD), texture and tensile property. The relationship between the R-value and the mechanical properties on crystal structure was investigated by a method of regression-analysis with the results, R-value==0.798+0.244 (TS/YS)-10.225 n+0.0655 EL in BCC structure and R-Value= 1.165-6.86 × 10^(-3) (TS/YS) -1.11 n+5.9828 ×10^(-3) EL in FCC structure. The characteristic value of FLD was little affected by the thickness of stainless steel sheet. However, the Characteristic vague of FLD of austenitic stainless steel was higher than that of the ferritic stainless steel, because it had a higher strain-hardening exponent The high R-value increased the uniform plastic strain of the drawing region but reduced the stretching region.

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