Injoon Son

Effect of equal-channel angular pressing on pitting corrosion resistance of anodized aluminum-copper alloy

Abstract The effect of equal-channel angular pressing(ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L AlCl 3 and also by surface analysis. Anodizing was conducted for 20 min at 200 and 400 A/m 2 in a solution containing 1.53 mol/L H 2 SO 4 and 0.018 5 mol/L Al 2 (SO 4 ) 3 ·16H 2 O at 20 °C. Anodized Al-Cu alloy was immediately dipped in boiling water for 20 min to seal the micro pores present in anodic oxide films. The time required before initiating pitting corrosion of anodized Al-Cu alloy is longer with ECAP than without, indicating that ECAP process improves the pitting corrosion resistance of anodized Al-Cu alloy. Second phase precipitates such as Si, Al-Cu-Mg and Al-Cu-Si-Fe-Mn intermetallic compounds are present in Al-Cu alloy and the size of these precipitates is greatly decreased by application of ECAP. Al-Cu-Mg intermetallic compounds are dissolved during anodization, whereas the precipitates composed of Si and Al-Cu-Si-Fe-Mn remain in anodic oxide films due to their more noble corrosion potential than Al. FE-SEM and EPMA observation reveal that the pitting corrosion of anodized Al-Cu alloy occurs preferentially around Al-Cu-Si-Fe-Mn intermetallic compounds, since the anodic oxide films are absent at the boundary between the normal oxide films and these impurity precipitates. The improvement of pitting corrosion resistance of anodized Al-Cu alloy processed by ECAP appears to be attributed to a decrease in the size of precipitates, which act as origins of pitting corrosion.

Pitting Corrosion Resistance of Ultrafine-Grained Aluminum Processed by Severe Plastic Deformation

The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of Al and Al-Mg alloy was investigated by means of polarization curves in solutions containing 300 ppm of Cl- and by surface analysis. The potentials for pitting corrosion of Al and Al-Mg alloy were evidently shifted to the noble direction by ECAP process, indicating that this process improves resistance to pitting corrosion. SEM observation revealed that the pitting corrosion occurred near the impurity precipitates and the size of impurity precipitated decreased with ECAP process. The time-dependence of corrosion potential and the polarization resistance determined by AC impedance technique suggested that the formation rate of Al oxide films was increased with ECAP process. The improvement in pitting corrosion resistance of Al and Al-Mg by ECAP seems to be attributable to the decrease in the size of impurity precipitates and the increase in the formation rate of Al oxide films.

Fabrication process and thermoelectric properties of CNT/Bi 2 (Se,Te) 3 composites

Carbon nanotube/bismuth-selenium-tellurium composites were fabricated by consolidating CNT/Bi2(Se,Te)3 composite powders prepared from a polyol-reduction process. The synthesized composite powders exhibit CNTs homogeneously dispersed among Bi2(Se,Te)3 matrix nanopowders of 300 nm in size. The powders were densified into a CNT/Bi2(Se,Te)3 composite in which CNTs were randomly dispersed in the matrix through spark plasma sintering process. The effect of an addition of Se on the dimensionless figure-of-merit (ZT) of the composite was clearly shown in 3 vol.% CNT/Bi2(Se,Te)3 composite as compared to CNT/Bi2Te3 composite throughout the temperature range of 298 to 473 K. These results imply that matrix modifications such as an addition of Se as well as the incorporation of CNTs into bismuth telluride thermoelectric materials is a promising means of achieving synergistic enhancement of the thermoelectric performance levels of these materials.

Synthesis and Thermoelectric Properties of Carbon Nanotube-Dispersed Bi 2 Te 3 Matrix Composite Powders by Chemical Routes

Carbon nanotube-dispersed bismuth telluride matrix (CNT/) nanopowders were synthesized by chemical routes followed by a ball-milling process. The microstructures of the synthesized CNT/ nanopowders showed the characteristic microstructure of CNTs dispersed among disc-shaped nanopowders with as an average size of 500 nm in-plane and a few tens of nm in thickness. The prepared nanopowders were sintered into composites with a homogeneous dispersion of CNTs in a matrix. The dimensionless figure-of-merit of the composite showed an enhanced value compared to that of pure at the room temperature due to the reduced thermal conductivity and increased electrical conductivity with the addition of CNTs.

Effect of Equal-Channel Angular Pressing on Pitting Corrosion of Pure Aluminum

The effect of equal-channel angular pressing (ECAP) on the pitting corrosion of pure Al was investigated using electrochemical techniques in solutions containing 0.1 m mol·dm−3 of Na2SO4 and 8.46 mol·dm−3 of NaCl (300 ppm Cl−) and followed by surface analysis. The potential for pitting corrosion of pure Al was clearly shifted in the noble direction by the ECAP process indicating that this process improves resistance to pitting corrosion. The time dependence of corrosion potential and the anodic potential at 1 A·m−2 revealed that the rate of formation of Al oxide films increased due to a decrease in the grain size of the Al after ECAP. Since there exists a negligible amount of impurity precipitates in pure Al, the improvement in pitting corrosion resistance of pure Al by ECAP appears to be attributable to an increase in the rate of formation of Al oxide films.

Effect of Equal-Channel Angular Pressing on the Pitting Corrosion Resistance of Al Alloy

The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of Al and Al-Mg alloy was investigated by means of polarization curves in solutions containing 300 ppm of Cl- and by surface analysis. The potentials for pitting corrosion of Al and Al-Mg alloy were evidently shifted to the noble direction by using the ECAP process, indicating that this process improves resistance to pitting corrosion. This increase in resistance seems to be attributable to the increase in formation rate of Al oxide films due to the increase in grain boundary with ECAP. The pitting corrosion resistance of Al and Al-Mg alloy anodized galvanostatically in H2SO4 solution after ECAP was also investigated using electrochemical techniques. The pitting corrosion resistance of Al and Al-Mg alloy was remarkably improved by anodizing. However, the pitting corrosion resistance of anodized Al-Mg alloy was better without ECAP than with ECAP.

Palladium-Nickel Alloy Electrodeposition Using Ethylenediamine as Complexing Agent

Powder & Ceramic Materials Division, Korea Institute of Materials Science, 797 Changwon-daero, Changwon, Gyeongnam 642-831, Korea(Received October 20, 2014 ; revised October 27, 2014 ; accepted October 28, 2014)AbstractsElectrodeposition behaviors of Pd-Ni alloys were investigated from the polarization curves in a solutioncontaining ethylenediamine as complexing agent. The microstructure and hardness of electrodeposited Pd-Ni alloys were also characterized. Codeposition of Pd-Ni alloys was successfully performed in the wide currentdensity ranging from 2 to 5000 A·m

A Novel Fabrication Method of Bi2Te3-Based Thermoelectric Modules by Indium Electroplating and Thermocompression Bonding

In this study, we devised a method to bond thermoelectric elements directly to copper electrodes by plating indium with a relatively low melting point. A coating of indium, ~30 μm in thickness, was fabricated by electroplating the surface of a Bi2Te3-based thermoelectric element with a nickel diffusion barrier layer. They were then subjected to direct thermocompression bonding at 453 K on a hotplate for 10 min at a pressure of 1.1 kPa. Scanning electron microscopy images confirmed that a uniform bond was formed at the copper electrode/thermoelectric element interface, and the melted/solidified indium layer was defect free. Thus, the proposed novel method of fabricating a thermoelectric module by electroplating indium on the surface of the thermoelectric element and directly bonding with the copper electrode can be used to obtain a uniformly bonded interface even at a relatively low temperature without the use of solder pastes.

Fabrication of Aluminum-Based Thermal Radiation Plate for Thermoelectric Module Using Aluminum Anodic Oxidization and Copper Electroplating

In this study, electrolytic etching, anodic oxidation, and copper electroplating were applied to aluminum to produce a plate on which a copper circuit for a thermoelectric module was formed. An oxide film insulating layer was formed on the aluminum through anodic oxidation, and platinum was coated by sputtering to produce conductivity. Finally, copper electroplating was performed directly on the substrate. In this structure, the copper plating layer on the insulating layer served as a conductive layer in the circuit. The adhesion of the copper plating layer was improved by electrolytic etching. As a result, the thermoelectric module fabricated in this study showed excellent adhesion and good insulation characteristics. It is expected that our findings can contribute to the manufacture of plates applicable to thermoelectric modules with high dissipation performance.