• Journal of Powder Materials
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• v.20 no.3
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• pp.186-190
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• 2013

The electrochemical performance for the corrosion of zinc anodes according to particle size and shape as anode in Zn/air batteries was study. We prepared five samples of Zn powder with different particle size and morphology. For analysis the particle size of theme, we measured particle size analysis (PSA). As the result, sample (e) had smaller particle size with $10.334{\mu}m$ than others. For measuring the electrochemical performance of them, we measured the cyclic voltammetry and linear polarization in three electrode system (half-cell). For measuring the morphology change of them before and after cyclic voltammetry, we measured Field Emission Scanning Electron Microscope (FE-SEM). From the cyclic voltammetry, as the zinc powder had small size, we knew that it had large diffusion coefficient. From the linear polarization, as the zinc powder had small size, it was a good state with high polarization resistance as anode in Zn/air batteries. From the SEM images, the particle size had increased due to the dendrite formation after cyclic voltammetry. Therefore, the sample (e) with small size would have the best electrochemical performance between these samples.

• Journal of Conservation Science
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• v.19
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• pp.67-72
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• 2006

The chemical compositions and lead isotope ratio of Poong-Tag(wind bell) bell excavated from Wanggyeong site, Gyeongju have analyzed by ICP and TIMS. The analysis result of chemical composition of Poong-Tag shows that it consists of 92:4 ratio of Cu:Sn. Other 8 minor elements(Pb, Zn, Fe, Ag, Ni, As, Sb and Co) show the concentration of below 0.2% respectively. This result means that Poong-Tag have made using highly purified Cu and Sn ore. For the study of provenance of raw material with the lead isotope ratio, the origin of the raw material of Poong-Tag can not be presumed owing to beyond the scope. The observation result of microstructure of Poong-Tag show the dendrite structure made through casting process. The chemical composition, microstructure, and lead isotope ratio of Poong-Tag excavated from Wanggyeong site, Gyeongju can be used as fundamental data to compare with other Poong-Tag of different regions and periods.

• The Journal of Korean Academy of Prosthodontics
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• v.22 no.1
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• pp.95-108
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• 1984

Even though the tarnishing and corrosion problems characteristic with dental silver-palladium alloy are not yet fully solved, it is recently widely used because of its low cost. However the effects of major alloying elements on the various properties of this system are not fully understood. The object of this research is to clarify the effects of In and Zn additives on the corrosion and tarnishing resistances and precipitation hardening behavior of this sytem, using electrodynamic polarization, immersion, and Vicker's microhardness test and X-ray diffraction and electron probe micro analysis methods. The obtained results were as follows: I. As indium content is increased, both the corrosion resistance in Cl-solution and microhardness are also increased while the tarnishing resistance is decreased. 2. As Zinc content is increased, the corrosion resistance is decreased, but tarnishing resistance is increased 3. At 70Ag-25Pd-2.5Zn-2.5In composition, the precipitation harding behavior was mot significant. The optimum aging temperature was $450^{\circ}C$ and the time was 2 hrs. The resulting specimen of this work carried 180VHN. 4. Under the heat treatment, the changes in the mechanical property are due to the changes in the shape and composition of dendrite matrix, namely, it is because of the precipitation hardening behavior which has been proved by electron probe micro analysis and optical microscopic finding.

• Journal of Korea Foundry Society
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• v.10 no.6
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• pp.528-537
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• 1990

7XXX aluminum alloy powders produced by the self-manufactured rotating disc atomizer were investigated to determine the influence of the atomization parameters on the particle size distributions in air atmosphere. The particle size distributions are almost always bimodal with the dominant mode on the large particle size. Average powder size of 7XXX aluminum alloy is $74/{\mu}m~125/{\mu}m$ when melt is poured with the rate of 9g /sec at 730$^{\circ}C$ on a rotating disc of 30㎜ diameter at 6300rad/sec. The mass of finer particle increased when disc diameter, angular velocity, pouring temperature increased and pouring rate decreased. The powder shapes of bimodal change from acicular to tear-drop and from tear-drop to ligament with increasing powder size. Powder shape was determined by the atomization mechanism and oxidation in liquid state. Microstructure of powders appeared to be cell and cellular dendrite. The SDAS of Al-7.9wt%Zn-2.4wt%Mg-1.5wt%Cu-0.9wt%Ni Powders is $0.8{\mu}m~1.0{\mu}m$ for the powders of $size＋44{\mu}m~53{\mu}m$ and $1.6{\mu}m∼1.8{\mu}m$ for the powders of $size＋105{\mu}m~125{\mu}m$, repectively.

• Journal of the Korean Electrochemical Society
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• v.6 no.3
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• pp.196-202
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• 2003

We investigated the effect of both 4 types additives and $0.5wt\%\;Pb_3O_4$ which have been reported to show an improvement on the performance of Zinc anode. And Experimental methods such as corrosion potential measurement, potentiodynamic polorization test and charging-discharging cycle life test were carried out in $40 wt\%$ KOH with $Pb_3O_4(0.5, \;10\;&\;2.0wt\%)$ and 4 types additives $(0.4wt\%\;of\;Ca(OH)_2$, 0.025M of Citrate, Tartrate and Gluconate). Corrosion potential was shifted to high direction and also changed to high and low direction repeatedly with increasing of $Pb_3O_4$ quantity. However by adding $0.5wt\%\;Pb_3O_4$, corrosion potential shifted to low direction and showed stable condition. Furthermore it was well known that corrosion resistance was predominantly increased compared to no addition and improved charging-discharging property with adding additives. By SEM analysis, it was concluded that the morphology of surface in case of only $0.5wt\%\;Pb_3O_4$ addition was nearly the same as that of Tartrate additive and in the other additives such as $Ca(OH)_2$, Citrate, Tartrate and Gluconate, their morphologies showed dendrite growth. Eventually it was thought that the additive of Tartrate indicated comparatively good corrosion resistance effect as well as charging-discharging property improvement among those four types additives.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.4
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• pp.390-396
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• 2012

In order to understand the nature of dendritic zinc growth, electrochemical zinc redox reaction on nickel plate was investigated in aqueous solutions containing different concentrations, 0.2, 0.1 and 0.02 $mol{\cdot}dm^{-3}$ (M), of zinc sulfate ($ZnSO_4$) or zinc chloride ($ZnCl_2$). Zinc ion was efficiently reduced and oxidized on nickel in the high-concentration (0.2 M) solution, whereas relatively poor efficiency was obtained from the other low-concentration solutions (0,1 and 0.02 M). Cyclic voltammetry (CV) analysis revealed that the 0.2 M electrolyte solution decomposes at more positive potentials than the 0.1 and the 0.02 M solutions. These results suggested that the concentration of electrolyte solution and anion would be an important factor that suppresses the reaction of the zinc dendrite formation. Scanning Electron Microscopy (SEM) data revealed that the shape of dendritic zinc and its growing behavior were also influenced by electrolyte concentration.

• Journal of Korea Foundry Society
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• v.22 no.3
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• pp.109-113
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• 2002

A good fluidity of high strength Al-alloys is required to cast thin wall castings needed to reduce the weight of cast parts. The fluidity, measured as the length to which the metal flows in a standard channel, is affected by many factors, such as the pouring temperature, solidification type of the alloy, the channel thickness, melt head, mold materials and temperature, coating etc. Therefore the experimentally measured fluidity scatters very much and makes it difficult to estimate the fluidity of a melt with a few measurements. The effect of Ti content and grain refinement on the fluidity of high strength aluminum alloy was investigated with a test casting with 8 thin flow channels to reduce the scattering of the fluidity results. The fluidity of Al-4.8%Cu-0.6%Mn Al-6.2%Zn-1.6%Mg-1.0%Cu and well-known commercial aluminum alloy, A356 was tested. Initial content of Ti was varied from 0 to 0.2wt% and Al-5Ti-B master alloy was added for grain refinement. The flow length varied linearly with superheat. By adding Ti and Al-5Ti-B, the fluidity increased. The grain size decreased by adding grain refiner at the same time. The fluidity depended on the degree of grain refinement. The fluidity of the alloy solidifying in mushy type is improved by grain refinement, because grain refinement increases the solid fraction at the time of flow stoppage.