New lightweight composite construction materials with low thermal conductivity

This paper presents an initial investigation on the use of a new lightweight construction material, composed of cement, sand and fiber of waste from young coconut (Cocos nucifera) and durian (Durio zibethinus). Thermal conductivity, compressive strength and bulk density were investigated. The experimental investigation reveals that the addition of these fibers reduces the thermal conductivity of the composite specimen and yield a lightweight. The composite satisfies the basic requirement of construction materials, and they could be used for walls and roofs. Thus, the potential for development, therefore, seems to be very promising. Finally, apart from saving energy consumption for the building, the proposed materials offer an alternative option to dispose waste of fruit industry.     

On the thermal expansion of composite materials and cross-property connection between thermal expansion and thermal conductivity

The paper focuses on the quantitative characterization of heterogeneous microstructures from the point of view of the material’s thermal expansion. First, we derive expression for the second rank thermal expansion contribution tensor of an inhomogeneity and specify it for various inhomogeneity shapes. Case of a spheroidal inhomogeneity in an isotropic material is discussed in detail. Thermal expansion contribution tensor is used as a basic building block to calculate effective thermal expansion of a heterogeneous material and to derive explicit cross-property connection between thermal expansion and thermal resistivity of a composite. We compare our results with experimental data available in literature and with other approaches.     

低合金钢热膨胀系数测定和分析

按照国标对某热连轧生产线上的两种典型钢种的热膨胀系数进行实验测量,得出其线性热膨胀率、平均线膨胀系数和瞬时线膨胀系数随温度的变化曲线,对比分析了钢种的化学成分对总膨胀量的影响实质以及取样方向对膨胀系数的影响.结果表明:金属材料的化学成分主要通过影响相变点温度而影响膨胀量;取样方向不影响金属材料的膨胀系数,即膨胀系数是各向同性的.实验得到两个钢种在不同温度段的热膨胀系数值,为实际的宽度在线控制提供了依据.     

Determination of coefficient of thermal expansion for binary composite materials

The coefficient of thermal expansion is determined for two-phase materials on the basis of the percolation model.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 7, No. 4, pp. 617–624, October, 1984.     

Negative thermal expansion materials

Materials exhibiting negative thermal expansion through room temperature have a variety of applications, mainly in controlling the overall thermal expansion of various composites. Several materials showing negative thermal expansion have recently been identified. The most dramatic of such behavior is exhibited by ZrW₂O₈, which shows strong isotropic thermal expansion from 20 to 425K.     

Study of variation of thermal expansion coefficients in carbon/epoxy laminated composite plates

Thermal expansion is an important property to define the end use application, and to model residual stresses and related problems in a composite part. Thus its accurate determination is essential. In laminated composites, this parameter depends largely on the orientation of fibres, fibre fraction, type of resin and reinforcement, etc. In this article, numerical results on the coefficients of thermal expansion (CTE) at different angles in the composite plates (having different stacking sequences of plies) found using finite element analysis are presented. Experimental values of these coefficients for [0/90] are found in satisfactory agreement with the simulations. Finally, a mathematical model is proposed for modelling these coefficients.     

低热膨胀系数纳米碳化硅/聚酰亚胺复合薄膜的制备与性能

以原位分散聚合法制备出纳米碳化硅/聚酰亚胺(n-SiC/PI)复合薄膜, 采用SEM、热机械分析仪(TMA)、阻抗分析仪和热重分析(TG)研究了所制备薄膜的表面形貌、热膨胀、介电性能及热稳定性。结果表明: SiC粒子均匀分散在PI基体中, 复合薄膜的热膨胀系数(CTE)随着SiC含量的增加逐渐减小, SiC质量分数为15%时, CTE降低了11%, 且复合膜的热膨胀系数实验值比较接近于Kerner公式的计算值。复合膜的介电常数和介电损耗随着填料含量的变化而变化, 但始终维持在较低的范围内, 并在相当大的频率范围内保持稳定。      

Preparation of inorganic composite materials with an adjustable thermal expansion coefficient by the sol-gel method

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Negative thermal expansion materials: technological key for control of thermal expansion

Most materials expand upon heating. However, although rare, some materials contract upon heating. Such negative thermal expansion (NTE) materials have enormous industrial merit because they can control the thermal expansion of materials. Recent progress in materials research enables us to obtain materials exhibiting negative coefficients of linear thermal expansion over −30 ppm K⁻¹. Such giant NTE is opening a new phase of control of thermal expansion in composites. Specifically examining practical aspects, this review briefly summarizes materials and mechanisms of NTE as well as composites containing NTE materials, based mainly on activities of the last decade.     

Negative thermal expansion materials: technological key for control of thermal expansion

Abstract

Most materials expand upon heating. However, although rare, some materials contract upon heating. Such negative thermal expansion (NTE) materials have enormous industrial merit because they can control the thermal expansion of materials. Recent progress in materials research enables us to obtain materials exhibiting negative coefficients of linear thermal expansion over ?30 ppm K^?1. Such giant NTE is opening a new phase of control of thermal expansion in composites. Specifically examining practical aspects, this review briefly summarizes materials and mechanisms of NTE as well as composites containing NTE materials, based mainly on activities of the last decade.     

The effect of the fibre critical length on the thermal expansion of composite materials

The present study shows that both longitudinal and transverse thermal expansions of unidirectional composite materials depend on the length of the fibre. It is suggested that this dependence is through an efficiency factork, generally used for describing the effectiveness of the reinforcement as expressed by mechanical properties such as modulus and strength.k itself is determined by the ratio of the fibre critical length,l _c, to the fibre length,l, and is expressed by two relationships, one forl?l _c, and another forl?l _c. The proposed theory is compared with experimental results obtained for samples comprising continuous short fibres. The length of the fibres was varied by varying the size of the test specimens. The length of the fibre is shown to affect significantly the value of the thermal expansion coefficients. An averagel _c value calculated from the experimental results is in close agreement with one found by other investigators from tensile strength testing. It is suggested that the experimental procedure may provide a useful tool for assessing the fibre critical length.     

Negative thermal expansion in a zirconium tungstate/epoxy composite at low temperatures

We have investigated a composite of cubic α-ZrW₂O₈ and epoxy with a high ceramic loading for its thermal expansion properties at cryogenic temperatures. The composite was fabricated by allowing the ceramic to sediment in the epoxy resin before curing, using only the dense bottom fraction of the composite for further measurements. Density measurements and thermogravimetric analysis showed that the samples repeatably consisted of approximately 60 vol% tungstate without significant voids. The coefficient of thermal expansion was measured by dilatometry at temperatures from 25 to 300 K, and we found negative thermal expansion occurring at temperatures below about 100 K. The observed behavior is consistent with predictions produced by a variational model, which shows that the high ceramic loading is necessary to reliably achieve negative thermal expansion in the composite. The composite has potential applications as compensators for unwanted thermal expansion at low temperatures and for fiber-optic cryogenic temperature sensors.