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RESEARCH ON MEASURING METHOD OF THE THERMAL CONDUCTIVITY FOR HIGHLY POROUS MATERIALS

J Y Wu , Z.M. Tang , W Shi andR.Z. Wang (Institute of Refrigeration and Cryogenics Engineering , Shanghai Jiao Tong University , Shanghai 200030 , China)

金属学报(英文版)

A transient method with rectangular pulse heating has been developed to measure the thermal conductivity of highly porous materials such as activated carbon, zeolite and silica gel. By this method the thermal conductivity can be measured quickly and accu-rately. In this paper, a set of automatically controlled testing equiptnent is presented.The measuring method is analysed. The thermal conductivities of some samples, such as activated carbon and zeolite, are measured by the equipment. A group of useful data has been obtained.

关键词: thermal conductivity , null , null

MICROSTRUCTURE AND PROPERTIES OF SiC_w/6061Al COMPOSITE The Author is now with Institute of Metal Research,Academia Sinica,China

MA Zongyi YAO Zhongkai Harbin Institute of Technology , Harbin , China

金属学报(英文版)

The SiC_w/Al composite prepared by squeeze casting has a combination of superior room temperature specific strength and modulus together with excellent thermal properties.The extrusion can make an improvement on the strength and ductility of the composite from 582 MPa as squeeze casted up to 639 MPa,and on the transformation from isotropic to the anisotropic structure.This seems to be explained by the orientation of whiskers and the densification of dislocations in matrix.TEM observation indicates that the stacking fault is the usual planar defect on the SiC_w surface. composite;;SiC whisker;;Al alloy;;microstructure

关键词: composite , null , null , null

Magnetic properties and enhanced magnetic refrigeration in (Mn1-xFex)(5)Ge-3 compounds

Journal of Applied Physics

Magnetic and magnetocaloric effects of (Mn1-xFex)(5)Ge-3 compounds are studied systematically. The maximum of magnetic entropy changes of 8.01 J/kg K under an external field change of 5 T is obtained for (Mn0.9Fe0.1)(5)Ge-3, which is the largest value in Mn5Ge3-based solid solutions. Moreover, the Fe substitution increases the refrigeration capacity (RC) value greatly. The largest RC value of 237 J/kg in (Mn0.8Fe0.2)(5)Ge-3 even compares favorably to that of many well-known magnetic refrigeration materials. Thus the Fe-containing (Mn1-xFex)(5)Ge-3 compounds are much-improved magnetic refrigerants for the application of room-temperature magnetic refrigeration. The increase of the RC value is probably resulted from the formation of magnetic nanostructure. (c) 2007 American Institute of Physics.

关键词: room-temperature;entropy change;transition;mn5ge3;iron

Development of a metal hydride refrigeration system as an exhaust gas-driven automobile air conditioner

Renewable Energy

Aiming at developing exhaust gas-driven automobile air conditioners, two types of systems varying in heat carriers were preliminarily designed. A new hydride pair LaNi(4.61)Wn(0.26)Al(0.13)/La0.6Y0.4Ni4.8Mn0.2 was developed working at 120-200 degrees C/20-50 degrees C/-10-0 degrees C. P-C isotherms and reaction kinetics were tested. Reaction enthalpy, entropy and theoretical cycling coefficient of performance (COP) were deducted from Van't-Hoff diagram. Test results showed that the hydride pair has flat plateau slopes, fast reaction dynamics and small hystereses; the reaction enthalpy of the refrigeration hydride is -27.1 kJ/mol H-2 and system theoretical COP is 0.711. Mean particle sizes during cycles were verified to be an intrinsic property affected by constitution, heat treatment and cycle numbers rather than initial grain sizes. Based on this work pair, cylindrical reactors were designed and a function proving metal hydride intermittent refrigeration system was constructed with heat conducting oil as heat source and water as heat sink. The reactor equivalent thermal conductivity is merely 1.3 W/(m K), which still has not meet practical requirement. Intermittent refrigeration cycles were achieved and the average cooling power is 84.6 W at 150 degrees C/30 degrees C/0 degrees C with COP being 0.26. The regulations of cycling performance and minimum refrigeration temperature (MRT) were determined by altering heat source temperature. Results showed that cooling power and system COP increase while MRT decreases with the growth of heat source temperature. This study develops a new hydride pair and confirms its application in automobile refrigeration systems, while their heat transfer properties still need to be improved for better performance. (c) 2006 Elsevier Ltd. All rights reserved.

关键词: metal hydride;hydrogen;refrigeration;exhaust gas;automobile;heat-pump;operating characteristics;cooling system;alloys;pair

Large magnetocaloric effect and enhanced magnetic refrigeration in ternary Gd-based bulk metallic glasses

Journal of Applied Physics

The magnetocaloric effect and refrigeration capacity (RC) of Gd(55)Co(20)Al(25) and Gd(55)Ni(25)Al(20) bulk metallic glasses (BMGs) have been investigated. Large magnetic entropy changes Delta S(M) of 11.2 and 10.8 J kg(-1) K(-1) and large RC values of 846 and 920 J kg(-1) are obtained for Gd(55)Co(20)Al(25) and Gd(55)Ni(25)Al(20), respectively, at a field change of 7 T. The RC value (640 J kg(-1) at 5 T or 920 J kg(-1) at 7 T) of Gd(55)Ni(25)Al(20) BMG is larger than that reported for all magnetocaloric materials, including crystalline and amorphous materials measured under the same conditions. The large RC value is due to the broad Delta S(M) peak (more than 100 K), which is caused by the disordered structure of an amorphous material. The large Delta S(M) and RC values make these Gd-based ternary BMGs attractive candidates for magnetic refrigeration applications. (C) 2008 American Institute of Physics.

关键词: temperatures;absolute;ability;alloys;pr;ho;co;dy;er;nd

Service Performance of Engineering Materials

Andrej Atrens

材料科学技术(英文)

Corrosion research by Atrens and co-workers has made significant contributions to the understanding of the service performance of engineering materials. This includes: (1) elucidated corrosion mechanisms of Mg alloys, stainless steels and Cu alloys, (2) developed an improved understanding of passivity in stainless steels and binary alloys such as Fe-Cr, Ni-Cr, Co-Cr, Fe-Ti, and Fe-Si, (3) developed an improved understanding of the melt spinning of Cu alloys, and (4) elucidated mechanisms of environment assisted fracture (EAF) of steels and Zr alloys. This paper summarises contributions in the following: (1) intergranular stress corrosion cracking of pipeline steels, (2) atmospheric corrosion and patination of Cu, (3) corrosion of Mg alloys, and (4) transgranular stress corrosion cracking of rock bolts.

关键词: Stress corrosion cracking , null , null

Ion sputter erosion in metallic glass-A response to "Comment on: Homogeneity of Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass" by L-Y. Chen, Y-W. Zeng, Q-P. Cao, B-J. Park, Y-M. Chen, K. Hono, U. Vainio, Z-L. Zhang, U. Kaiser, X-D. Wang, and J-Z Jiang J. Mater. Res. 24, 3116 (2009)

Journal of Materials Research

The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.

关键词: room-temperature

Two-step magnetization in a spin-chain system on the triangular lattice: Wang-Landau simulation

Physical Review B

The Wang-Landau algorithm is used to study the thermodynamic and magnetic properties of triangular spin-chain system based on two-dimensional Ising model in order to understand the magnetic-order dynamics in Ca(3)Co(2)O(6) compound. The calculated results demonstrate that the equilibrium state of the rigid spins produces the two-step magnetization curve at low temperature even when the random-exchange term is considered. This work indicates that the four-step magnetization behavior observed experimentally must be due to the nonequilibrium magnetization.

关键词: calcium compounds;exchange interactions (electron);Ising model;magnetisation;thermodynamics;one-dimensional ca3co2o6;density-of-states;compound ca3co2o6;phase-diagram;proteins;crystal

Reversible magnetocaloric effect and refrigeration capacity enhanced by two successive magnetic transitions in DyB2

Science China-Technological Sciences

A large and reversible magnetocaloric effect is found in the compound DyB2, which is associated with two successive magnetic transitions: a spin-reorientation-like transition followed by a ferromagnetic-paramagnetic transition. These two transitions appreciably enlarge the magnetic-refrigeration temperature window and yield a huge refrigeration capacity of 610 J kg(-1), with a maximum magnetic entropy change -Delta S-max of 17 J kg(-1)K(-1), at a magnetic-field change of 5 T. The corresponding values for low magnetic-field change of 2 T are 193 J kg(-1) and 7.4 J kg(-1)K(-1), respectively.

关键词: DyB2;magnetocaloric effect;refrigeration capacity;entropy

Biomimicry of bamboo bast fiber with engineering composite materials

Materials Science & Engineering C-Biomimetic Materials Sensors and Systems

Bamboo, one of the strongest natural structural composite materials, has many distinguishing features. It has been found that its reinforcement unit, hollow, multilayered and spirally-wound bast fiber, plays an extremely important role in its mechanical behavior. In the present work, on the basis of the study on bamboo bast fiber and wood tracheid, a biomimetic model of the reinforcing element, composed of two layers of helically wound fiber, was suggested. To detect the structural characteristics of such a microstructure, four types of macro fiber specimens made of engineering composites were employed: axially aligned solid and hollow cylinders, and single- and double-helical hollow cylinders. These specimens were subjected to several possible loadings, and the experimental results reveal that only the double-helical structural unit possesses the optimum comprehensive mechanical properties. An interlaminar transition zone model imitating bamboo bast fiber was proposed and was verified by engineering composite materials. In our work, the transition zone can increase the interlaminar shear strength of the composite materials by about 15%. These biomimetic structural models can be applied in the design and manufacture of engineering composite materials.

关键词: bamboo;bast fiber;biomimetics;engineering composites

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