Papers by Keyword: Coefficient of Thermal Expansion

Abstract: Parts of thermal physical properties of Al-Si8-Cu2-Mg alloy were studied. The curves were plotted showing the relationship between density, specific heat capacity, coefficient of thermal expansion and the variation of temperature for the first time with this alloy. The results show that the density was decreased when the temperature was raised, but the specific heat capacity and the coefficient of thermal expansion were first increased and then decreased. The solidus-liquidus temperatures, latent heat of fusion were studied, and the results show that the melting temperature range of this alloy was 507-596°C.

Abstract: The iron aluminides seem to be very perspective materials for high temperature structural application. They have many advantages, but unfortunately also some negative properties – e.g. sharp drop in strength above 600°C or limited ductility at room temperature. These disadvantages can be reduced by alloying of binary alloy by other elements.Present work deals with a study of coefficient of thermal expansion (CTE). It was investigated the influence of microstructure and heat-treatment on the values of CTE. Secondary, it was studied the possibilities, how to determine phase transition temperatures from CTE curves. Influence of type of iron aluminides lattice on CTE values was also examined as well as the influence of addition of alloying elements into binary iron aluminides.

Abstract: The coefficient of thermal expansion (CTE) is one of the material factors affecting the behavior of concrete structures. This study reports the typical range of CTE for polymer concrete with different types of polymeric binder based on extensive literature surveys. The results revealed the CTE of polymer concrete generally fell between 12.5 and 28.6 x 10^-6/°C, which is about twice or three times higher than that of ordinary cement concrete, because the CTE of polymeric binder is much larger than that of cementitious binders. The findings of this study will provide useful information for the design and analysis of polymer concrete members and repair components.

Abstract: The key properties of materials used for thermal management in electronics are thermal conductivity and the coefficient of thermal expansion. These properties can be tailored by stacking molybdenum and copper layers. Here, molybdenum copper multilayer composites with varying copper content, from 63 to 88 wt%, have been investigated. It is demonstrated, that thermal conductivity and coefficient of thermal expansion, can be adjusted by the copper content. Two flash methods for measuring the thermal conductivity are compared and the validity of the results is discussed since measurements on thin materials with strong anisotropy require a certain setup of the measurement device. For the studied compositions the thermal conductivity was determined to be between 220 to 270 W/m/K and the coefficient of thermal expansion between 6.1 to 11.5 ppm/K.

Abstract: Now a day’s composite materials are taking very important role in industrial growth. Composite materials are widely used in Automobiles, aerospace, submarine and also in other major fields, due to their special characteristics like light weight, high strength, stiffness, corrosion resistance. The determination of Coefficient of Thermal Expansion (CTE) of MMCs is important to aid its usage in high temperature environment as in the case of automobile combustion chamber. In these applications the stability of the composites over a long period of operation is a critical design considerationPresent work deals with the thermal property evaluation of the Al alloy / alumina metal matrix composite developed using the Stir Casting with chilling route technique. LM 26 Al alloy is being selected as the matrix material as it is a potential alloy for automotive piston applications. Al alloy / alumina MMCs was cast under end chilling technique by dispersing the reinforcement from 6 to 12 wt% the steps of 3% to study the variation in its thermal properties. At the same time chill material is also changed (Copper and MS) for different composition of MMCs cast to study the thermal behavior variations. After casting the required MMC, test specimens were prepared as per the standards to conduct thermal conductivity (K) tests and coefficient of thermal expansion (CTE) tests. Above tests were repeated for different composites containing different weight % of dispersed cast using different chills.

Abstract: C/C-SiC composite as low expansion material for space opto-mechanical structures was prepared by gaseous silicon infiltration after high temperature treatment (HTT) on C/C. 2000°C and 2400°C were selected as the treatment temperatures for C/C to study the influences on the properties of C/C-SiC composite. The graphitization level of amorphous C in C/C was improved by HTT. The porosity of C/C increased from 32.88% to 34.25% (2000°C) and 41.06% (2400°C) respectively. In addition, a higher HTT temperature led to a higher density of C/C-SiC composite and a lower SiC content. Furthermore, the mechanical properties and coefficient of thermal expansion (CTE) of the composite decreased as the temperature increased. After 2000°C HTT, the CTE of C/C-SiC composite decreased to-0.055×10^-6·K^-1 and the mechanical properties (218 MPa) could meet the application demand at the same time.

Abstract: Electroless plating technology was applied in order to improve the poor wettability between the copper and SiC. SiC_p/Cu composites were frbricated by hot-press sintering technique. The influences of SiC particles (Cu-coated and Cu-uncoated) and SiC_p/Cu-5vol%n-SiC on microstructures, relative density, bending strength and coefficient of thermal expansion(CTE) were researched in detail. The results show that SiC particles distributed in Cu matrix uniformly. And a certain amount of SiC, the relative density and bending strength of SiC_p/Cu(Cu-coated) composite were greater than SiC_p/Cu(Cu-uncoated) composite, and the coefficient of thermal expansion was opposite, Between SiC_p/Cu(Cu-coated) and SiC_p/Cu-5vol% nanoscale SiC(n-SiC), the relative density and bending strength of SiC_p/Cu(Cu-coated) were more than SiC_p/Cu-5vol%n-SiC, and CTE was different.

Abstract: As for the phenomenon of the bottom thermal inward convex distortion of the Composite Bottom Pan (CBP) on the condition of heating, the mechanism of the bottom distortion was researched on the basis of ANSYS 10.0 considering the structural characteristic and the heating conditions of the composite bottom pan. The results showed that the thicker the bottom of the composite bottom pan, the smaller its thermal deformation amount. The thicker the junction of the pot and wall was, the smaller its deformation. And it was helpful for reduction of deformation to use a big rounded transition. The increase of rings number of magnetic conductive sheet would lead to a less bottom thermal inward convex distortion of the CBP. The larger the area of the additional stainless steel sheet (or ring), the smaller the deformation amount. Consequently, the research laid a solid theoretical foundation for the design and optimization of the structure of composite bottom pan.

Abstract: Cordierite (2MgO·2Al₂O₃·5SiO₂) has a low density of 2.2 g/cm³ due to its high magnesium content. Because of its low thermal expansion coefficient of 1~2 x10^-6 /^°C, many studies are being conducted on the synthesis of cordierite with the expensive petalite as a replacement for lithium alumina silicate-based heat-resistant materials. The cordierite can be synthesized over a wide range: SiO₂ at 50~70%, Al₂O₃ at 20~40%, and MgO at 10~30%. In this study, the range of chemical composition and temperature of cordierite synthesis is thoroughly investigated. In particular, we use natural materials (magnesite, kaolin and clay) to examine how thermal properties are affected by changes in crystal phase arising from the varying composition of MgO, SiO₂ and Al₂O_3. We focused on factors leading to an increase in the rate of cordierite synthesis at temperatures below 1280 ^°C. From observing the synthetic rate over 1250~1280 ^°C, the sintered body at 1280 ^°C had a high synthetic rate greater than 80%. Magnesite was ball milled at constant intervals, and mean particle size was controlled to improve the synthetic rate of cordierite. As a result, the cordierite synthetic rate increased by more than 15% with decreasing the mean particle size of magnesite.

Abstract: Si/Al composites with different Si particle sizes were fabricated using spark plasma sintering process for electronic packaging. The density, thermal conductivity, coefficient of thermal expansion and flexural strength of the composites were investigated. Effect of Si particle size on structure and properties of the Si/Al composites were studied. The results showed that the Si/Al composites synthesized by spark plasma sintering were composed of Si and Al. Al was uniformly distributed among the Si phase, leading to a high thermal conductivity (>120 W/m·k). The relative density of the Si/Al composites decreased with increasing Si particle size. Small Si particle size produced small grains, leading to a low coefficient of thermal expansion and a high strength. There is an optimal matching among the thermal conductivity, coefficient of thermal expansion and flexural strength when the Si particle size was 44 um.