발간논문

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This study has been investigated the deformation behavior of a hot-extruded Mg-Zn-RE (RE: rare earth elements) alloy containing Mg12(RE) particles at the elevated temperatures. The particles are intrinsically produced by breaking the eutectic structure of the alloy during the hot-extrusion process. The grain size of the extruded Mg-Zn-RE alloy developed via dynamic recrystallization is around 10 μm. Under the heat treatment at 200℃ up to 48 hr, no change has been observed on the microstructure and mechanical properties due to the pinning effect of the thermally stable particles. Under the tensile test condition in the initial strain-rate range of 1×10-3s-1 and the temperature range up to 200℃, the alloy shows yield strength of 270 MPa and elongation to failure around 9% at room temperature and yield strength of 135 MPa at 200℃. Furthermore, although the alloy contains large amount of the second phase particles around 15%, it shows excellent hot-workability possibly due to the presence of the thermally stable interface between the particles and the matrix.

keyword : Mg alloy, misch metal, mechanical properties, hot extrusion

Peptides with specific sequences against LaPO4 and TiO2 nanoparticles were discovered through peptide phage display technique as an application to biomolecular recognition of inorganic materials. Sequencing results showed that a motif consisting of serine and proline was commonly expressed in specific sequences. It was postulated that serine directly bound to nanoparticles using its terminal hydroxyl (OH) group. In this sense, oxygen atom seemed to work as a ligand to metal ions and hydrogen atom as a H-bond donor, was thought to bind to the oxygen atoms or the hydroxyl groups on particle surface. Also, it was expected that proline assists serine to make an ideal van der Waals contact between serine and nanoparticles, which optimizes the binding of peptide onto surface.

keyword : peptide phage display, bio-panning, materials recognition, LaPO4 nanoparticles, TiO2 nanoparticles

To develop a recycling process of magnesium alloy scrap, a fundamental study on the distillation of magnesium alloy melt was carried out. Melt temperature, vacuum degree and reaction time were considered as experimental variables. The amount of vaporized magnesium melt per unit surface area of melt increases with the increase of melt temperature, reaction time and vacuum degree. The vapor condensed at the tip of water cooling Cu-condenser as a form of pine cone. Magnesium and zinc were vaporized easily from the melt. However, It`s difficult to separate magnesium and zinc by vacuum distillation because vapor pressure of zinc is similar to one of magnesium. The contents of aluminum, manganese and iron, etc. in residual melt increase due to the decrease of magnesium and zinc content after the distillation of magnesium alloy.

keyword : magnesium scrap, AZ91D, recycling, vacuum distillation, evaporation, condensation

The ionic equilibira in mixed solutions of cuprous and cupric chloride were analyzed by considering chemical equilibria, mass and charge balance equations. The activity coefficients of solutes were calculated by using Bromley equation. Required thermodynamic constants and interaction parameters were evaluated from the data reported in the literature. The effect of NaCl and CuCl concentrations on the pH and potential of the mixed solutions was explained in terms of the variation in the concentration of solutes and in the activity of hydrogen ion. The calculated pH values of the mixed solutions agreed well with the measured values. However, the calculated values for the potential of the mixed solutions were lower than the measured values, indicating the necessity of considering the complex formation between cuprous and chloride ion, such as Cu2Cl4(2-) and Cu3Cl6(3-).

keyword : CuCl, CuCl2, HCl, Ionic equilbira, pH, Eh

Examination of two bronze vessels supposedly from the Koryo dynasty revealed that they consist of bowls and stands that are fixed together using rivet joints made of Cu-Ag alloys. The bowls and stands were forged out of unleaded bronze alloys of approximately 22 weight % Sn before being quenched from the α+β region of the Cu-Sn phase diagram. This specific alloy and the thermo-mechanical treatment constitute two key elements of the unique technical tradition called Bangcha (방짜) that has long been established in Korea. The high Sn content ensures better casting and the thermal treatment causes the brittle δ phase to be avoided in forging as well as in services. The experiment on the laboratory Cu-Ag alloys of varying Ag contents suggested that the Cu-Ag system was the best choice of materials for the rivets at the time in view of their color, availability, ductility and low melting points.

keyword : Korean bronze tradition, high sn bronze, forging and quenching, rivet joints, Cu-Ag alloys, color

The interfacial reactions and shear strength of pure Sn solder bump were investigated with different under bump metallizations (UBMs) and reflow numbers. Two different UBMs were employed in this study: Cu and Ni. Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) were formed at the bump/Cu UBM interface, whereas only a Ni3Sn4 IMC was formed at the bump/Ni UBM interface. These IMCs grew with increasing reflow number. The growth of the Cu-Sn IMCs was faster than that of the Ni-Sn IMC. These interfacial reactions greatly affected the shear properties of the bumps.

keyword : Flip chip, pure tin (Sn), under bump metallization, UBM, multiple reflows, interfacial reaction, shear test, intermetallic compound, IMC

PSII (Plasma Source Ion Implantation) using high density pulsed ICP source was employed to implant oxygen ions in Si wafer. The PSII technique can achieve a nominal oxygen dose of 3 × 10(17) atoms/cm2 in implantation time of about 20min. In order to prevent oxidation of SOI layer during high temperature annealing, the wafer was capped with 2,000A Si3N4 by PECVD. Cross-sectional TEM showed that continuous 500A thick buried oxide layer was formed with 300A thick top silicon layer in the sample. This study showed the possibility of SOI fabrication using the plasma source ion implantation with pulsed ICP source.

keyword : silicon on insulator, buried oxide, SPIMOX, PSII

The effects of magnetic powder size on electromagnetic wave absorption characteristics in Fe-6.5Si-0.9Cr(wt%) alloy flakes/polymer composite sheets available for quasi-microwave band have been investigated. The composite sheet including small magnetic flakes with the size less than 26 μm exhibited high power loss in the GHz frequency range as compared with the sheets having large alloy flakes of 45~75 μm. Moreover, both the complex permeability and the loss factor increased with the decrease in size of the alloy flakes. The large power loss of the sheets containing small magnetic flakes was attributed to the high complex permeability, especially their imaginary part. The high complex permeability of the sheets composed of small flakes was considered to be due to the highly thin shape of the flakes inducing low eddy-current loss.

keyword : electromagnetic wave absorption, FeSiCr flakes, composite sheets, magnetic powder size