발간논문

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The effects of the intermediate annealing in the two stage cold rolling of 3% Si steel on the secondary recrystallization have been studied. The results obtained are as follows 1. When the conditions are excessive (1000℃ x longer than 10 min., 1100℃ x longer than 5min), (110) [001] component is so dominating that it subsequently prevails in the primary recrystallized grains. Hence grains after high temperature annealing are small. 2. When the conditions are insufficient (700℃ x shorter than 5 min, 800℃ x shorter than 2 min), rolling texture (112) [110] remains considerably. After rolling this component rotates into (111) [110] which remains very strong in primary grains. Hence the secondary recrystallization is incomplete. 3. In compromising conditions between 2) and 3), relevant proportion of (110) and (111) in the primary grains is obtained, which results in good secondary recrystallization behavior.

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A study on the development of boron 3% silicon-iron containing 0.03/0.04 C, 0.07/0.08 Mn and boron (30 ppm add) was carried out. Samples prepared by two stage cold reduction method developed complete secondary recrystallization, while samples prepared by one stage cold reduction method showed incomplete secondary recrystallization and poor magnetic properties. The magnetic properties also varied with normalizing temperature, and the sample prepared by normalizing at 950℃ showed the best magnetic properties. The induction with a magnetizing force of 800 A/m was 1.86 tesla.

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In order to investigate the effect of zinc on mercury ratio and residual mercury in silver base dental amalgam, the experiment was performed by setting critically the range of zinc content from 0 to 8% in Ag-Sn system alloy for dental application. From this experiment, it was found that the mercury ratio and residual mercury in silver base dental amalgam increased with increasing zinc content in pre-alloy. The former seems to be resulted from the decrease of wettability with increasing zinc content in pre-alloy, the latter seems to be resulted from the increase of mercury ratio and the formation of Zn-Hg compound with increasing zinc content in pre-alloy.

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Crevice corrosion properties of Ti-0.2 wt.% Pd alloy and pure Ti in hot 6% NaCl solution were investigated. Pure Ti specimens exhibited severe corrosion, while Ti-0.2% Pd alloy specimens were virtually immune to crevice corrosion in an accelerated test. An electrochemical polarization technique was used to determine the effect of Pd-addition to Ti. It was found that Ti-0.2% Pd alloy retained passivity in an acid solution of the same concentration developed in the crevice. This result indicates that Pd acts as a cathodic depolarizer to shift the potential of Ti in the noble direction. It is therefore concluded that small addition, namely, 0.2% of Pd effectively improves the resistance of Ti to crevice corrosion in a hot brine.

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Antimony cementation by iron in hydrochloric acid solution was carried out using rotating disc technique to study the effect of disc rotating speed, reaction temperature, initial Sb (III) ion concentration and atmosphere on the rate of cementation. The results obtained in this experiment are as follows; 1) Two reaction rate periods were found in the cementation: ie, an "initial" slow rate and a "final" enhanced rate periods. These are first-order reaction rate processes and can be expressed by the following equation. d/dt[Sb^(+++)] = -[Sb^(+++)] k·A. 2) The cementation rate increased with increasing temperature and initial Sb (III) ion concentration because the morphology of antimony deposit became porous. 3) In case of the excess existence of non-cementable ions such as Fe^(++), Fe^(+++), the cementation rate docreased with the ionic strength increment of solution. 4) Under oxygen containing atmosphere, Fe(II) ions are oxidized to Fe(III) ions and these oxidized ions are reduced by Fe disc to Fe(II) ions. These reactions interfere with antimony cementation reaction. 5) The apparent activation energy was found to be 3.2 ㎉/mole in initial rate period, in enhanced rate period 2.2 ㎉/mole above 40℃. Therefore, the rate controlling step is supposed to be diffusion through boundary layer, whereas it changes to surface reaction in enhanced rate period below the temperature of 30℃.

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