• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.91-94
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• 2003

Ceramic femoral heads in the total hip replacement have been developed to reduce the polyethylene liner wear. Alumina and zirconia (3Y-TZP) are using in clinical application worldwide and there are many good test reports. However, alumina has a risk of catastrophic failure, and zirconia has the low temperature degradation in spite of enhanced fracture toughness. Recently, novel zirconia/alumina composite having low temperature degradation-free character and high fracture tough . was developed and it leads the lower wear 3f polyethylene than alumina and zirconia. In the present study, in order to optimise the microstructure of low temperature degradation (LTD)-free zirconia/alumina composite for the best wear resistance of polyethylene, various compositions of (LTD)-free zirconia/alumina composites were fabricated, and the sliding wear of UHMWPE against these novel composites were examined and compared with that against alumina and zirconia ceramics used for total hip joint heads.

• 한국신뢰성학회지:신뢰성응용연구
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• 제13권2호
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• pp.109-116
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• 2013

The solder is any of various fusible alloys, usually tin and lead, used to join metallic parts that provide the contact between the chip package and the printed circuit board. Solder plays an important role of electrical signals to communicate between the two components. In this study, two kinds of Ag-free solder as sample is made to conduct the thermal shock test and the high humidity temperature test. Low resistance is measured to estimate crack size of solder, using daisy chain. The low speed shear test is also performed to analyze strength of solder. The appropriate degradation model is estimated using the result data. Depending on the composition of solder, lifetime estimation is conducted by adopted degradation model. The lifetime estimated two kinds of Ag-free solder is compared with expected lifetime of Sn-Ag-Cu solder. The result is that both Ag-free composition are more reliable than Sn-Ag-Cu solder.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.365-366
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• 2002

The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on a novel low temperature degradation-free zirconia/alumina composite material and conventional alumina and zirconia ceramics used for femoral head in total hip joint replacement. The wear of UHMWPE pins against these ceramic disks was evaluated by performing linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in bovine serum. The weight loss of polyethylene against the novel low temperature degradation-free zirconia/alumina composite disks was much less than those against conventional ceramics for all tests. The mean weight loss of the polyethylene pins was more io the linear reciprocal sliding test than in the repeal pass rotational sliding lest for all kinds of disk materials. Neither the coherent transfer film nor the surface damage was observed on the surface of the novel zirconia/alumina composite disks during the test. The observed r,'stilts indicated that the wear of the polyethylene was closely related to contacting materials and kinematic motions. In conclusion, the novel zirconia/alumina composite leads the least wear of polyethylene among the tested ceramics and demonstrates the potential as lhe alternative materials for femoral head in total hip joint replacement.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.355-361
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• 2004

Ceramic femoral heads in the total hip replacement have been developed to reduce the polyethylene liner wear, Alumina and zirconia (3Y-TZP) having the excellent tribological properties are coupled against acetabular cups of polyethylene and are used in clinical application worldwide. However, alumina has a risk of catastrophic failure, and zirconia has the low temperature degradation in spite of enhanced fracture toughness. Recently, novel zirconia/alumina composite is very attractive due to the low temperature degradation (LTD)-free character and high fracture toughness. In the present study, we focus on the wear of ceramic on ceramic, which are able to be used as femoral heads and acetabular cups. Therefore, LTD-free zirconia/alumina composites with three compositions are made in a form of disk and cylinder, and the wear of the composites is performed on pin-on-disk type wear tester. The wear is conducted with or without lubricant. All the composites fabricated with the different composition show the good wear resistance.

• Tribology and Lubricants
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• 제21권5호
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• pp.216-220
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• 2005

The sliding wear behaviors of three different compositions of novel low temperature degradation-free zirconia/alumina (LTD-free Z/A) composites were examined in a ceramic-ceramic contact pair. The wear tests were performed by using a pin-on-disk type wear tester in a linear reciprocal sliding motion with a line contact in both dry and bovine serum lubricated conditions at room temperature. From the results of dry sliding wear tests, Z/A#1((5.3Y, 4.6Nb)-TZP/80 $vol\%Al_2O_3$) showed the best wear resistance among three kinds of LTD-free Z/A composites. For the bovine serum lubricated sliding wear tests, wear was too little to be measured for all kinds of Z/A composites. These novel LTD-free Z/A composites having excellent wear resistance demonstrated a potential as the alternative materials for the ceramic-ceramic contact pairs of femoral head and acetabular liner in total hip replacement.

• 한국세라믹학회지
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• 제29권8호
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• pp.630-638
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• 1992

Ta2O5 alloying into 3 mol% Y2O3-stabilized tetragonal ZrO2 polycrystals (3Y-TZP) increased the degradation during aging at 265℃ and the fracture toughness; both are determined by the amount of transformed m-ZrO2. It was proposed that the mechanism underlying the t→m transformation when aged at low temperatures is attributed to the reorientation of (Zzr'V ). complexes parallel to [111] lattice direction, which is accompanied by a relaxation of TZP lattice during annealing at low temperature. A small strain which results from the reorientation gives rise to a localized mechanical instability, thus lowering the nucleation barrier so that the t→m phase transformation (degradation) proceeds. The amount of transformed m-ZrO2 during aging becomes greater as the chemical free energy change related to the transformation, ΔGo, increases with increasing the Ta2O5 alloying content.

• Applied Biological Chemistry
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• 제33권2호
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• pp.125-128
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• 1990

저온에서 완두유묘 줄기의 유리 IAA 수준과 그 전구체인 트립토판 수준이 저하하므로, IAA수준의 조절 메커니즘을 규명하기 위하여 IAA분해효소계에 미치는 저온의 영향을 조사하였다. $25^{\circ}C$에서 키운 백색 관두유표를 $5^{\circ}C$의 저온으로 옮기면 IAA oxidase와 peroxidase의 수준은 증가하였으며 catalase의 수준은 저하되었고 과산화수소는 축적되어, 전체적으로 IAA분해계가 저온에서 강화되었다. 저온에 놓였던 유묘를 상온으로 옮기면 IAA 분해계는 다시 대조구 수준으로 회복하였다.

• 한국안전학회지
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• 제20권1호
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• pp.81-86
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• 2005

This study has investigated radiation degradation of low density polyethylene(LDPE). Samples were irradiated up to 800kGy using a $Co^{60}\;\gamma-ray$ at a dose rate of 5kGy/hr in the presence of air atmosphere at room temperature. After irradiation, storing for 2 weeks, free radical measurement of LDPE has established by electron spin resonance(ESR). ESR measurement showed that free radical concentration(FRC) was increased with radiation dose and decreased with the time. The radical types showed alkyl, allyl, and peroxy radical with the irradiation, these changed to peroxy radical with the time.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.473-476
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• 2004

This study has investigated radiation degradation of low density polyethylene(LDPE). Samples were irradiated using a $Co^{60}\;\gamma-ray$ and ray up to 800 kGy at a dose rate of 5 kGy/hr in the presence of air atmosphere at room temperature. After irradiation, free radical measurement of LDPE has established by electron spin resonance(ESR). Then, each sample was stored for 2 weeks. ESR measurement showed that free radical concentration(FRC) was increased with radiation dose and changed from alkyl, allyl radical to peroxy radical with time.

• BMB Reports
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• 제35권4호
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• pp.358-363
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• 2002

Chemical and photochemical processes during storage and preparation rapidly degrade retinol, the most active form of vitamin A. therefore, the efficacy of incorporation into liposomes in order to modulate the kinetics of retinol degradation was investigated. Retinol was readily incorporated into multilamellar liposomes that were prepared form soybean phosphatidylcholine; the extent of the incorporation was 98.14±0.93% at pH 9.0 at a ratio of 0.01 : 1 (wt:wt) retinol : phospholipid. It was only marginally lower at higher retinol concentrations. The pH of the hydration buffer had a small effect. The incorporation efficiency ranged from 99.25±0.47% at pH 3 to 97.45±1.13% at pH 11. The time course of the retinol degradation in the aqueous solution in liposomes was compared to that of free retinol and free retinol with α-tocopherol under a variety of conditions of pH(3, 7, and 11), temperature(4, 25, 37, and 50℃), and light exposure(dark, visible, and UV). The retinol that was incorporated into the liposomes degraded significantly slower than the free retinol or retinol with α-tocopherol at pH 7 and 11. At pH 3, where the free retinol degrades rapidly, the degradation kinetics were similar in liposomes and the presence of α-tocopherol. At pH 7.0 and 4℃ in the light, for example, free aqueous retinol was completely degraded within 2 days, while only 20% of the retinol in the liposomes were degraded after 8 days. In general, the protective effect of the liposome incorporation was greater at low temperatures, at neutral and high pH, and in the dark. The results suggest that protection is greater in the solid, gel phase than in the fluid liquid crystalline phase lipids. These results indicate that the incorporation into liposomes can extend the shelf-life of retinol under a variety of conditions of temperature, pH, and ambient light conditions.