High Strength-Thermal Conductivity Mg–Ga–Ca–Ce Sheet by Hot-Extrusion and Rolling

Mouxin Wu,Xueqi Jiang,Jihua Chen,Hongge Yan,Weijun Xia,Bin Su,Yifu Deng 대한금속·재료학회 2024 METALS AND MATERIALS International Vol.30 No.1

The thermal conductivity of magnesium alloys is increasingly required for fast heat dissipation in the automotive and electronicfields. However, the methods for mechanical property improvement such as grain refinement and alloying tend to deterioratetheir thermal conductivity. In this work, a novel low-alloy Mg–2Ga–0.6Ca–0.6Ce alloy exhibits a surprisingly goodcombination of high strength and high thermal conductivity compared with the other samples. The wrought alloys are of smallgrain sizes (< 2 μm), have high yield strength (> 272 MPa) and exhibit excellent thermal conductivity (> 143 W·m−1·K−1). The as-extruded alloy exhibits excellent yield strength (272 MPa) and high thermal conductivity (144.6 W·m−1·K−1) atroom temperature. After 30% rolling, the yield strength is further increased to 283 MPa, and the thermal conductivity isslightly reduced to 143.2 W·m−1·K−1. The effects of Ca and Ce addition on mechanical properties and thermal conductivityare analyzed from dislocation density, dynamic recrystallization fraction (fDRX), average grain size (dDRX) and texturecharacteristics. The higher yield strength can be attributed to the combination of grain boundary strengthening, dislocationstrengthening and second phase strengthening. Moreover, the addition of Ca and Ce can obviously reduce solute Ga atomsin α-Mg, which is the key to high thermal conductivity. Therefore, adding two alloying elements, Ca and Ce, significantlyimproves both tensile properties and thermal conductivity.

Thermal conductivity of compacted bentonite as a buffer material for a high-level radioactive waste repository

Lee, Jae Owan,Choi, Heuijoo,Lee, Jong Youl Pergamon Press 2016 Annals of nuclear energy Vol.94 No.-

<P><B>Abstract</B></P> <P>Bentonite buffer is one of the major barrier components of a high-level radioactive waste (HLW) repository, and the thermal conductivity of the bentonite buffer is a key parameter for the thermal performance assessment of the HLW repository. This study measured the thermal conductivity of compacted bentonite as a buffer material and investigated its dependence upon various disposal conditions: the dry density, water content, anisotropic structure of the compacted bentonite, and temperature. The measurement results showed that the thermal conductivity was significantly influenced by the water content and dry density of the compacted bentonite, while there was not a significant variation with respect to the temperature. The anisotropy of the thermal conductivity had a negligible variation for an increasing dry density. The present study also proposed a geometric mean model of thermal conductivity which best fits the experimental data.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The thermal conductivities were measured under various disposal conditions. </LI> <LI> They were significantly influenced by the water content and dry density. </LI> <LI> They were not sensitive to the temperature and the anisotropic structure. </LI> <LI> A new model of thermal conductivity was proposed for the thermal analysis. </LI> </UL> </P>

Optimum Conditions to Develop Sand-Gyeongju Bentonite Mixtures as Buffer Materials Satisfying THM Performance Criteria

Gi-Jun Lee,Seok Yoon,Deuk-Hwan Lee 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

In order to reduce the area of the high-level radioactive waste (HLW) repository, a buffer material with high thermal conductivity is required. This is because if the thermal conductivity of the buffer material is high, the distance between the disposal tunnels and the deposition holes can be reduced. Sand, which is a natural material and has higher thermal conductivity than bentonite, is added to bentonite to develop an enhanced buffer material. For the sand-bentonite mixture, it is important which sand to use and how much to add because an enhanced buffer material should satisfy both hydraulic (H) and mechanical (M) performance criteria while improving thermal conductivity (T). In this study, we would like to show what type of sand and how much sand should be added to develop an enhanced buffer material by adding sand to Gyeongju bentonite, a representative bentonite in Korea. For this purpose, the thermal conductivity, hydraulic conductivity, and swelling pressure of the sand-Gyeongju bentonite mixture according to the sand addition rate were measured. It is more efficient to use silica sand with smaller particles than Jumunjin sand which is a representative sand in Korea as an additive for an enhanced buffer material than using the Jumunjin sand. In order for the sand-Gyeongju bentonite buffer material to satisfy both the hydraulic and mechanical performance criteria as a buffer material while increasing the thermal conductivity, it is judged that the optimum dry density is 1.7 g/cm3 at least and the optimum sand addition rate is 10% at most.

Synthesis and characterization of a contorted hexabenzocoronene epoxy toward high thermal stability and thermal conductivity

강민성,이도희,김현우,안석훈 대한화학회 2023 Bulletin of the Korean Chemical Society Vol.44 No.7

A contorted hexabenzocorone (HBC) mesogen based epoxy was synthesized and characterized for high thermal stability and thermal conductivity. Since HBC has a nano-graphene like structure, which would have strong pi–pi interactions, it was expected that HBC epoxy would have superior heat resistance and thermal conductivity. Based on this hypothesis, HBC containing four epoxy groups at edges was synthesized and confirmed by NMR and mass spectrum. HBC epoxy was cured with diaminophenolsulfone and their thermal stability and thermal conductivity were investigated. As expected, the decomposition of 5 wt% occurred at 323.44C, and thermal conductivity was 0.32 W/mK where the general thermal conductivity of epoxy resins is around 0.2 W/mK. Such enhancement of thermal properties would be explained by the formation of pi–pi stacking of HBC mesogens.

자동차용 Heatsink의 열전도도 향상을 위한 다이캐스팅 알루미늄 합금 및 열처리 최적 조건 개발

김주행(Juhaing Kim),정경(Kyung Jeong),박석현(Seokhyun Park),정윤철(Yooncheol Jung) 한국자동차공학회 2018 한국자동차공학회 부문종합 학술대회 Vol.2018 No.6

As eco-friendly automobiles are expanded, electronic control systems are also required to have high performance. Therefore, ECUs and motors, which are essential for electronic control systems, require higher heat dissipation characteristics than conventional ones. In order to achieve high heat dissipation characteristics, it is necessary to improve the thermal conductivity of Heatsink itself, which is directly contacts the heat source and transfers heat quickly among various components. As the conventional Heatsink materials, aluminum alloys which have excellent thermal conductivity characteristics have been applied. In case of low-solute alloy, the thermal conductivity is the highest. However, in the case of automotive Heatsink, a very complicated shape is required, and in order to realize this, it is necessary to manufacture parts by die casting of a high-solute aluminum alloy. As a result, it has lower thermal conductivity than low solute aluminum alloy. In this study, the optimum alloy composition capable of high pressure casting with 7% Si content and T5 heat treatment were applied to achieve thermal conductivity of 178W/mK. This result is a high thermal conductivity characteristic of low-solute wrought aluminum alloy products, resulting in a 38% improvement over ADC12, a commercial die-cast alloy. At the same time, heatsinks for large-capacity motors(BSG) were developed by securing the same castability as ADC12.

Study on thermal deformation of high-pressure aerostatic thrust bearing in uneven temperature field

Liangbin Guo,Shanxiu Chen 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.7

As for high-pressure aerostatic thrust bearing, the notable increase of air supply pressure makes gas film pressure and flow velocity increase rapidly. The two assumptions of fully developed laminar boundary layer and isothermal flow in parallel gas film are no longer valid, which are generally considered suitable for aerostatic thrust bearing with low air supply pressure. Based on the coupling analysis of the air flow field in the channel clearance of the bearing and the conjugate heat transfer of the bearing discs, the development process and flow regime of the velocity boundary layer and the temperature boundary layer in the parallel gas film are investigated. The results of conjugate heat transfer analysis for bearing discs made of various materials show that, isotropic thermal conductivity is the main factor affecting the heat flux, temperature distribution on the interface between solid wall and high-speed airflow in the channel clearance, and the temperature gradient inside the bearing discs. Further research on the relationship between the net thermal deformation, net elastic deformation caused by gas film pressure as well as total deformations of the bearing discs and the material properties shows that, the coefficient of thermal expansion is a crucial parameter affecting the net thermal deformation, but the total deformations of bearing discs also depend on the pressure load exerted by gas film. In the range of the working conditions specified in this study, structural steel is a more suitable choice than stainless steel or invar. Consequently, this research provides meaningful guidance for the designs of high-pressure aerostatic thrust bearings.

고온용 원관형 히트파이프의 열적 특성에 관한 실험 및 모사

윤여훈(Yeo Hoon Yoon),부준홍(Joon Hong Boo) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11

High-temperature cylindrical stainless steel-sodium heat pipes were fabricated and tested for transient and steady-state operations. Total length of the heat pipe was 1 m and the diameter was 25.4 ㎜. The thermal performance of each heat pipe was tested up to 2-㎾ thermal load (heat flux of 42 ㎾/m²). Thermal performance was investigated experimentally by changing internal wick structure as a function of the input thermal load and working fluid charge ratio. Thermal resistance and average heat transfer coefficients in evaporator and condenser sections were analyzed and discussed. Based on the experimental results, a commercial numerical tool was employed to simulate the characteristics of the high temperature heat pipe. Calculated temperature distributions of the heat pipe were compared with those of experiments. Effective thermal conductivity of a heat pipe was introduced in the modeling or performance estimation of which the values varied from 1,206 to 3,090 W/m ㆍ depending on the input thermal load.

콘크리트의 배합 및 함수율에 따른 고온에서의 열전도율 추산 방법

이재영 한국화재소방학회 2022 한국화재소방학회논문지 Vol.36 No.3

In this study, methods for estimating the thermal conductivity of concrete under various temperatures are reviewed. Basedon Maxwell’s model for predicting the equivalent thermal conductivity of composite materials, the constituent materials ofhardened concrete are categorized into five types of materials: coarse aggregate, fine aggregate, skeleton, and voids. Thevoids, which include air and excess water, are considered to determine the effect of water reduction on thermal conductivity. The volume ratio of the constituent material to the cured concrete is estimated using a simple curing model, and the thermalconductivity of each constituent material is obtained from the literature. Air volume and excess water reduction are set asthe estimation conditions, and the optimal method is devised by comparing the respective estimation results. The thermalconductivity range for concrete is estimated based a design strength of 21 100 MPa (W/B60 to W/B15) and a temperature –of 30 °C 800 °C. The results reflecting the measured air volume and moisture reduction are similar to the measured values. –A comparison between the optimal estimated value and measured value shows that both values are similar in thetemperature range of 400 °C 800 °C, and that the estimated value is lower than the measured value in the temperature range –of 80 °C 200 °C.

Enhancement of Thermal Conductivity of Poly(methylmethacrylate) Composites at Low Loading of Copper Nanowires

Nhat Anh Thi Thieu,Minh Canh Vu,이의성,Vu Chi Doan,김성룡 한국고분자학회 2019 Macromolecular Research Vol.27 No.11

We report the synthesis of copper nanowires (CuNWs) and the enhanced thermal conductivity of poly(methylmethacrylate) (PMMA) composites at lowloading fractions of CuNW. The scanning electron microscope, X-ray diffractometer, thermal diffusivity meter, high-resistance meter, universal testing machine, and thermogravimetric analyzer were used to investigate the properties of CuNW/PMMA composites. The elongation strain to failure, toughness, and thermal stability of the PMMA composites significantly increased with increasing contents of CuNW. The CuNW/PMMA composites showed the thermal conductivity and volume resistivity of 0.85 W/mK and 7×1010 Ω∙m, respectively, at 2.0 wt% of CuNW. The significant improvement of thermal conductivity is attributed to the well-dispersed CuNWs in the PMMA matrix and the high aspect ratio of CuNWs. The experimental results of thermal conductivity fitted well with the Agari model.

직접질화법 AlN 분말의 소결거동 및 열전도도에 미치는 고에너지 볼밀링 효과

박해룡,김형태,이성민,김영도,류성수 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.5

In this study, a high energy ball milling process was introduced in order to improve the densification of direct nitrided AlN powder. The sintering behavior and thermal conductivity of the AlN milled powder was investigated. The mixture of AlN powder and 5 wt% Y_2O_3 as a sintering additive was pulverized and dispersed by a bead mill with very small ZrO_2 bead media. The milled powders were sintered at 1700℃-1800℃ for 4 h under N_2 atmosphere. The results showed that the sintered density was enhanced with increasing milling time due to the particle refinement as well as the increase in oxygen contents. Appropriate milling time was effective for the improvement of thermal conductivity, but the extensive millied powder formed more fractions of secondary phase during sintering,resulted in the decrease in thermal conductivity. The AlN powder milled for 10min after sintering at 1800℃ revealed the highest thermal conductivity, of 164W/m·K in tne densified AlN sintered at 1800℃.