Gyung Guk Kim

Improved Adhesion to ABS Plastics by a Photocatalytic Reaction

The pretreatment of ABS (acrylonitrile-butadiene-styrene) plastics prior to metallization has been generally performed with strong acids, such as sulfuric, chromic, or potassium-permanganate acid. However, conventional wet-chemical pretreatment presents inherent environmental and safety problems to consider. In particular, the presence of Cr+6 imposes a serious environmental threat. Therefore, in this study, aspects of pretreatment, using the photocatalytic reaction in TiO2 sol, were investigated as a replacement for wet-chemical pretreatment. Surface characterization, before and after the pretreatment, was examined by X-ray photoelectron spectroscopy and scanning electron microscopy. A copper film was deposited by electroless plating, and the adhesion strength between the deposited film and ABS plastics was evaluated by the cross-cut tape test (ISO 2409). When ABS plastics were pre-treated in TiO2 sol, the adhesion strength was improved to levels obtained using a strong acid solution.

Sliding Wear Behavior of Steam Generator Tube Materials in Nuclear Power Plants

Wear damage of steam generator tubes of nuclear power plants can cause leakage of radioactive substances. So the evaluation of tubes’ integrity is very important from the viewpoint of nuclear ecocide. In the present study, sliding wear behaviors of Inconel 600 and 690 steam generator tube materials mated with 409 stainless steel commonly used as the support plate were investigated at room temperature in an air environment. For more precise prediction of wear behaviors of steam generator tubes, Archard equation was modified, and the modified wear coefficients were estimated as a function of sliding distance. When using the modified Archard equation, the reliabilities for prediction of wear behavior of Inconel 600 and 690 mated with 409 stainless steel increased from 71.8% to 83.8% and from 60.2% to 85.2%, respectively.

Thermotransport of Hydrogen in Zr-1.0Nb-1.0Sn-0.1Fe Alloy

Hydrogen redistribution caused by thermotransport in the Zr-1.0Nb-1.0Sn-0.1Fe alloy under the temperature gradient which is likely to be encountered between nuclear fuel cladding and primary cooling water (300-340) was investigated. The heat of transport (Q*) of hydrogen was determined by using a steady state technique to evaluate the magnitude and direction of thermotransport of hydrogen in the alloy. The values of Q∗ were 23.1, 23.7 and 27.1 KJ/mol for the hydrogen concentration of 73.4, 75.8 and 94.3 ppm by weight respectively. In other words, hydrogen was transported from hot region to cold region and the value of Q∗ increased with increasing overall hydrogen concentration. The Zr-1.0Nb-1.0Sn-0.1Fe alloy had the smaller Q∗ value than that of Zircaloy-4 when compared with same overall hydrogen concentration. Thus, Zr-1.0Nb-1.0Sn-0.1Fe alloy has better resistance to the formation of hydride due to thermotransport than Zircaloy-4 does.

Sliding Wear Behaviors of Steam Generator Tubes in Various Environments

Wear damage of steam generator tubes for nuclear power plants can cause the leakage of radioactive substances. Therefore, the evaluation of integrity and safety for tubes is very important from the viewpoint of nuclear ecocide. In the present study, to investigate the wear properties of Inconel 600 and 690 steam generator tube materials mated with 409 stainless steel commonly used as support plate, sliding wear tests were performed with increasing sliding distance in air and in elevated temperature water environment, respectively. The wear volume of tube materials was less than those of supports under all conditions. There were no significant differences in the wear behavior for the Inconel 600 and 690 tubes, independently of the testing environment.

Reciprocating Sliding Wear Behavior of Inconel 600 Mated with SUS 304 Stainless Steel at Elevated Temperatures

The sliding wear behavior of a steam generator in a nuclear power plant (Inconel 600) was investigated at 225, 250 and 300°C. Effects of wear parameters such as sliding distance and contact stress were examined with SUS 304 (austenitic). In the prediction of the wear volume by Archard wear equation, the standard error range was calculated to be ±0.53×10-9 m3 and the reliability to be 71.9 % for the combination of Inconel 600 and SUS 304. The error range was considered to be relatively broad because the wear coefficient in Archard equation was assumed to be constant. However, the wear volume turned out to increase parabolically with the sliding distance owing to the combination of strain hardening of the wear surface and the oxidative wear. Based on the experimental results, the wear coefficient was modified as a function of the rotating sliding distance. The calculation with the modified wear equation showed that, although the error range was not significantly narrowed, the reliability increased from 71.9 to 78.1 %.

Effect of Ti Addition on the Fracture Toughness of Al-Ti-B Alloys Synthesized by High-Energy Ball Milling and Spark Plasma Sintering

Al alloys containing boron or its compound are attractive for neutron shielding materials since boron exhibits high thermal neutron absorbing capability. However, poor fracture toughness and low ductility of boron compounds restrict their usage as structural materials. By adding Ti as a third element, it is expected to improve the toughness of Al-B alloys. The present study investigates the effect of the Ti addition on fracture toughness of the (Al+Xat%Ti)2at%B (X = 0.5, 1, 1.5 at%) alloy fabricated by high energy ball milling and spark plasma sintering (SPS). The SPS method was used to consolidate (Al+Xat%Ti)2at%B (X = 0.5, 1, 1.5 at%) alloy with the pressure of 50 MPa. Charpy impact tests showed that the fracture toughness of the 1 at%Ti added-alloy was 4 MPam1/2 , and that it was three times higher than that of Al-B alloys. Further reduction of the Ti addition down to 0.5 at% at 1.9 MPam1/2 or up to 1.5 at% at 2 MPam1/2 slightly decreased the fracture toughness. The microstructures of the present specimens were investigated by FE-SEM and TEM to describe the relationship with fracture toughness.