• Journal of Korea Foundry Society
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• v.34 no.2
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• pp.54-59
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• 2014

In this study, the extruded Al-6.3Zn-2.4Mg alloys were selected among the 7000 series aluminum alloys sensitive to hydrogen environment in order to examine the effects of both the aging conditions and the length of hydrogen charging period on the mechanical properties of the alloy. The specimens were aged for 24hours at $100^{\circ}C$ (under aging (UA)), $120^{\circ}C$ (peak aging (PA)), and $160^{\circ}C$ (over aging (OA)), respectively. Charging tests were performed at RT for 12, 24, 36 hours under potentiostatic conditions (-2000 mV vs (Ag/AgCl)) for 12, 24 and 36 hours in 1M $H_2SO_4$ and 0.1%$NH_4SCN$ solution. The fracture surface was examined by scanning electron microscopy (SEM). X-ray diffraction (XRD) pattern in peak aged sample was obtained before and after hydrogen charging from extruded Al-6.3Zn-2.4Mg alloys. The decreasing rate of tensile strength and elongation is represented in order of over aging < under aging < peak aging, and it is believed that the hydrogen recharge is more sensitive to elongation than tensile strength. The formation of $AlH_3$ in hydrogen charged Al-6.3Zn-2.4Mg alloys has been confirmed by X-ray diffraction studies.

• The Korean Journal of Physiology
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• v.20 no.2
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• pp.218-224
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• 1986

The characteristics of anion exchange with internal $HCO_3\;^{-}\;(or\;OH^-)$ was studied by determining the time course of hemolysis in isoosmotic ammonium salt solution in human erythrocytes. The effects of inhibitors, pH and temperature on the exchange between internal $HCO_3\;^-\;(or\;OH^-)$ and external $Cl^-$ were observed and the permeabilities of various organic and inorganic anions were also measured. The results were compared with data previously reported from the experiments using radioisotopes. The results are as follows; 1) SITS $H_2DIDS$ and furosemide inhibited the hemolysis of erythrocytes in isoosmotic $NH_4Cl$ solution in a dose·dependent manner, and the concentrations for lengthening twice the time for $half-hemloysis(t_{1/2})\;were\;2.3{\times}10^{-7},\;1.3{\times}10^{-7}\;and\;2.5{\times}10^{-5}M$, respectively. 2) Acetazolamide also shifted the time-dependent hemolytic curve to the right in a dose-dependent manner, and the concentrations for lengthening twice $t_{1/2}\;was\;2.4{\times}10^{-5}M$. 3) The time-dependent hemolysis was delayed by decreasing pH from 7.0 to 6.2, but w·as not affected by the change of pH in the range of 7.0 to 8.2. 4) The time for $half-hemloysis(t_{1/2})$ showed a temperature-dependency and Arrhenius plot exhibited a break point at $20^{\circ}C$. The apparent activation energy calculated from this plot was 18.1 kcal/mol between $2^{\circ}C-20^{\circ}C$ and 11.2 kcal/mol between $20^{\circ}C-37^{\circ}C$, respectively. 5) The apparent permeabilities of various inorganic anions based on $t_{1/2}$ were in the order of $Cl^->NO_{3}\;^->SCN^->SO_4\;^{2-}>SSO_3\;^{2-}>HPO_4\;^{2-}$. which was similar with the previous reports based on the experiment using radioisotopes. The results Obtained from this study are comparable with the previous data reported from the experiments using radioisotopes. This indicates that the hemolysis of erythrocytes in isoosmotic ammonium salt solution can be used as a simple and good method for the study of anion exchange in erythrocyte membrane.

• Corrosion Science and Technology
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• v.16 no.6
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• pp.317-327
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• 2017

The change in the oxidation behavior of three types of B-added ultrahigh strength martensitic steels containing Ti and Nb induced by applying constant cathodic current was investigated. In a 3% NaCl+0.3% $NH_4SCN$ solution, the overall polarization behavior of the three alloys was similar, and degradation of the oxide film was observed in the three alloys after applying constant cathodic current. A significant increase in the anodic current density was observed in the Nb-added alloy, while it was diminished in the Ti-added alloy. Both Ti and Nb alloying decreased the hydrogen overpotential by forming NbC and TiC particles. In addition, the thickest oxide film was formed on the Ti-added alloy, but the addition of Nb decreased the film thickness. Therefore, it was concluded that the remarkable increase in the anodic current density of Nb-added alloy induced by applying constant cathodic current density was attributed to the formation of the thinnest oxide film less protective to hydrogen absorption, and the addition of Ti effectively blocked the hydrogen absorption by forming TiC particles and a relatively thick oxide film.