具有潜在负热膨胀性和负压缩性的三角形构筑模块的有限元分析

研究了由3个粱焊接而成的三角形系统构成的二维单元的热膨胀和压缩特性,与每个梁相比,该三角形构件具有不同的性质(热膨胀和弹性 模量).结果表明:当三角形构件的底边热膨胀大于两侧边时,这种二角形系统可在一维方向上硅示负热膨胀(即当三角形梁以楔形结构形成时,会产 生三角形缩短效戍)和负压缩特性.更引起人们兴趣的足:线热膨胀特性与三角形构件的底边和侧边材料的相对刚性(弹性模量)有关.压力变化对这种 构件存在影响.与侧边梁刚性相比,构件的线性压缩率变化与底边梁刚性存在主要关系.     

Chemical structures and properties of low thermal expansion coefficient polyimides

The relationships, between chemical structures of various aromatic polyimides and their thermal expansion coefficients, were investigated and the properties of low thermal expansion polyimides were elucidated. Such low values were observed for polyimides obtained from pyromellitic dianhydride or 3,3′,4,4′-biphenyltetracarboxyIic dianhydride and aromatic diamines, which included only benzene or pyridine rings fused at para-positions without a flexible linkage. It was proposed that these low thermal expansion coefficients were related to the linearity of their polymer molecular skeletons. In particular, PIQ-L100 (Hitachi Chemical Co. Ltd) is one such low thermal expansion polyimide and, it has excellent mechanical properties, thermal stability, and low absorbed moisture content.     

Thermal conductivity,elastic modulus,and coefficient of thermal expansion of polymer composites filled with ceramic particles for electronic packaging

The effective thermal conductivity, elastic modulus, and coefficient of thermal expansion of epoxy resins filled with ceramic fillers like silica, alumina, and aluminum nitride were determined. The data obtained was compared with theoretical and semitheoretical equations in the literature that are used to predict the properties of two phase mixtures. It was found that Agari's model provided a good estimate of the composite thermal conductivity. The Hashin‐Shtrikman lower bound for composite modulus fits the modulus data fairly well at low concentrations of the filler. Also, it was found that the coefficients of thermal expansion of the filled composites lie in between Schapery's upper and lower bounds. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3396–3403, 1999     

Colorless polyimides with low coefficient of thermal expansion derived from alkyl‐substituted cyclobutanetetracarboxylic dianhydrides

Alkyl‐substituted cyclobutanetetracarboxylic dianhydrides (CBDAs) were synthesized by photo‐dimerization of alkyl‐substituted maleic anhydrides to obtain novel colorless polyimides (PIs). Dimethyl‐substituted CBDA (DM‐CBDA) showed much higher polymerizability with various diamines than conventional cycloaliphatic tetracarboxylic dianhydrides and led to high molecular weights of PI precursors. Polyaddition of non‐substituted CBDA and trans‐1,4‐cyclohexanediamine (t‐CHDA) was completely inhibited by salt formation in the initial reaction stage. The use of DM‐CBDA allowed the formation of a homogeneous/viscous PI precursor solution by overcoming the salt formation problem. The prominent substituent effect probably reflects how the methyl substituents of DM‐CBDA contributed to increasing the salt solubility. Some of the thermally imidized DM‐CBDA‐based systems simultaneously possessed non‐coloration, low coefficient of thermal expansion (CTE), very high T_g exceeding 300 °C and very low dielectric constant. Copolymerization was very effective for improving the solubility of DM‐CBDA‐based PIs. The copolyimide cast films prepared via chemical imidization displayed a further decreased CTE without sacrificing other target properties, suggesting that the present materials can be useful as plastic substrates in display devices. The mechanism of self‐chain orientation behavior during solution casting is also discussed. A potential application of the copolyimide systems as optical compensation film materials in liquid crystal displays is proposed. © 2013 Society of Chemical Industry .     

Structural effects of pendant groups on thermal and electrical properties of polyimides

Two series of aromatic polyimides containing various‐sized alkyl side groups were synthesized by thermal imidization of the poly(amic acid)s prepared from the polyaddition of benzophenonetetracarboxylic dianhydride and hexafluoro‐isopropylidene bis(phthalic anhydride) with 4,4′‐methylenedianiline, 4,4′‐methylene‐bis(2,6‐dimethylaniline), 4,4′‐methylene‐bis(2,6‐diethylaniline), and 4,4′‐methylene‐bis(2,6‐diisopropylaniline). The extent to which alkyl substitutes affect the thermal properties of polyimides was examined by differential scanning calorimetry, thermomechanical analyzer, and thermogravimetric analysis techniques. The analytical results demonstrated that the incorporation of alkyl moieties causes a moderate increase in the coefficient of thermal expansion and a slight decrease in thermal stability. Notably, all polymers had a decomposition temperature exceeding 500°C. The glass transition temperature increases markedly when hydrogen atoms at ortho positions on aniline rings are replaced with methyl groups, but decreases with growing alkyl side group size. The dielectric measurements show that the polymer possessing a large alkyl side group would have the lower dielectric value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4672–4678, 2006     

Thermal expansion behavior of various aromatic polyimides

The thermal expansion behavior for various aromatic polymides was investigated. Usally polymers, including polyimides, have high thermal expansion coefficients (3–6 × 10^?5 K^?1), compared with metals and ceramics. However, there are some polyimides which have very low thermal expansion coefficients below 1 × 10^?5 K^?1. This property was observed for the polymides obtained from pyromellitic dianhydride or 3,3′ 4,4′-biphenyltetracarboxylic dianhydride and aromatic diamines which were constituted of only benzene rings fused at para positions. It was proposed that their low thermal expansion coefficient related to the linearity in their polymer molecular skeltons.     

添加剂对NZP族低热膨胀陶瓷热学性质的影响

以NZP族低热膨胀陶瓷Ca1-xBaxZr4(PO4)6(0≤x≤1)系列中的零膨胀组成Ca0.85Ba0.15Zr4P6O24为例,着重研究了不同添加剂对该零膨胀陶瓷的热膨胀异向性、平均热膨胀系数和导热性能的影响规律。实验结果表明,在烧结过程中添加质量分数1%SiO2或3%SiC均能够降低Ca0.85Ba0.15Zr4P6O24的热膨胀异向性,但与此同时,第二相的加入使Ca0.85Ba0.15Zr4P6O24的热膨胀系数有所上升。质量分数为1%～7%SiC晶须的加入反而导致NZP族陶瓷导热性能进一步降低,原因是SiC抑制了晶粒生长。     

Melt-quenched oxide glasses with ultrahigh Young's modulus and small thermal expansion coefficient

The well-known Makishima–Mackenzie relationship, consisting of two terms of the dense packing structure and dissociation energy regarding bonding in constituent oxides, enables fabricating oxide glasses with ultrahigh Young's modulus (∼140 GPa) and a small coefficient of thermal expansion (CTE) (∼4 ppm/K). The effects of increasing MgO and Ta₂O₅ contents in an MgO–Ta₂O₅–Al₂O₃–SiO₂–B₂O₃ glass system using a conventional melt-quenching method are revealed. The essential oxides of Al₂O₃ and Ta₂O₅ are primarily suitable for dense packing structures dominated by a large coordination number of oxygens. The substitution of CaO by MgO results in high dissociation energy when the glass composition falls in the peraluminous regime (Al₂O₃/[MgO + CaO] > 1). A small CTE is realized by increasing the molar ratio of Al₂O₃/MgO. According to magic-angle spinning-nuclear magnetic resonance spectra, mechanically and thermally functional oxide glasses depend on their structures. These findings facilitate the development of glass substrate applications without thermal dilatation.     

碱金属与碱土金属对电光源玻璃性能的影响

采用传统高温熔融法制备得到了多组无铅电光源玻璃,利用热膨胀仪对各组分玻璃的热膨胀性能进行测试.分析了不同氧化物替代Na2O后对热膨胀系数和膨胀软化温度的影响.结果显示:当三元碱金属氧化物(Li2O,Na2O与K2O)共存时,热膨胀性能出现复杂的混合碱效应;当碱土金属部分取代碱金属时,碱土金属氧化物对性能的影响并非按照离子的大小呈现一种简单的线性关系.玻璃的电阻率和介电性能不仅与碱金属的含量有关,还与其相对含量有关.     

变燃速发射药线膨胀系数关系的实验研究

为了解双层变燃速发射药的热膨胀性能规律,采用膨胀系数测定仪测定了一种类双基型中心开孔双层变燃速发射药的线膨胀系数,结果表明,外层药的线膨胀系数大于内层药的线膨胀系数.推导了变燃速药型的轴向线膨胀系数与内、外层药的线膨胀系数以及几何尺寸之间的理论关系式,并计算了变燃速发射药的线膨胀系数,与实测值的相对误差小于10%.     

核壳聚合物粒子对环氧树脂热膨胀系数的影响

采用核壳聚合物(Core-Shell Polymer,CSP)粒子改性环氧树脂,通过红外光谱、热力学分析和扫描电镜研究了CSP粒子对环氧树脂基体热膨胀系数(CTE)的影响。结果表明:CSP粒子壳材料分子链中的羰基在环氧树脂固化过程中可与环氧分子侧链上的羟基形成氢键作用,从而加强了核壳聚合物粒子与环氧树脂的界面作用。随着CSP粒子质量分数的增加,改性环氧树脂基体的玻璃化转变温度呈下降趋势;相对于纯环氧树脂,改性环氧树脂在玻璃化转变温度下的CTE呈现先下降后上升的趋势,添加质量分数为0.5%的CSP后,其CTE值降低了12.88%。但在玻璃化转变温度上的热膨胀系数均高于纯环氧树脂。     

热膨胀系数简易测量装置研制及若干材料测量

以液氮为冷源,研制了一套基于千分测微器的材料热膨胀系数简易测量装置,能够测量80~353 K温区各类固体材料的热膨胀系数,可重复性高于99.3%,不确定度小于3.34%。通过将T1紫铜、6060铝、304不锈钢、尼龙、G10环氧树脂等典型材料热膨胀系数测量数据与文献数据比较,发现两者最大相对偏差小于6.0%,80~353 K温区的平均偏差约为3.1%。在此基础上,测量并获得了高低温热环境工程等应用场合常用到的其他一些材料如殷钢、6262铝、316不锈钢、45钢、聚四氟乙烯、ABS塑料等的热膨胀系数数据。     

化妆土的膨胀系数对釉面砖变形的影响

本文主要探讨化妆土的膨胀系数对釉面砖变形的影响,研究配方组成中石英和长石的含量与化妆土膨胀系数的之间关系。结果表明,石英和长石含量过大或过小导致坯釉膨胀系数不匹配,从而影响釉面砖外形;当石英含量30g,长石含量20g,能提高化妆土热膨胀系数,砖型的上凸程度减少,平整度得到最佳改善。     

微晶玻璃的组成及热处理制度与热膨胀系数关系的研究

采用传统的熔体冷却法制得Li2O-A l2O3-SiO2系统的基础玻璃。利用DTA制定了相应的热处理制度,测定了玻璃热处理前后的热膨胀系数,并利用XRD研究了经热处理后的微晶玻璃的晶体相组成。结果表明:具有复合晶核剂TiO2 ZrO2和采用二步热处理制度所得的微晶玻璃热膨胀系数更小,且随着二步热处理制度温度的升高,微晶玻璃热膨胀系数更小,相应的玻璃结构也越致密。     

Gamma-Ray method for measuring liquid expansion coefficient at high temperatures and pressures

Expandable vessels were designed to measure the density and thermal expansion coefficients of liquid at elevated temperatures and pressures by the gamma-ray attenuation method. Light Arabian vacuum bottoms was tested from 70°C to 300°C at 13.8 MPa. Results agree well with literature data.     

堇青石蜂窝陶瓷热膨胀特性的研究

汽车尾气净化器用蜂窝陶瓷载体对材料的抗热冲击性能要求很高,要求材料具有特别低的热膨胀系数。本文通过对堇青石陶瓷的平均热膨胀系数及微观热膨胀系数的分析,研究了堇青石蜂窝陶瓷的热膨胀特性。     

Rubber as additives to lower thermal expansion coefficient of plastics: 1. Morphology and properties

A substantial approach was proposed to design polymer alloys with very low coefficient of linear thermal expansion (CLTE). The large reduction in CLTE is not based on an addition of low-thermal-expansion filler to suppress the bulk expansion, but on the fine control of the polymer alloy's micro-morphology so that the expansion is preferentially toward the thickness direction. In this study, rubber was used as an additive to tune the thermal expansion behavior of various plastics. Although the rubber has a high thermal expansion coefficient, it was found that, when the rubber domains are deformed into microlayers and co-continuous with the plastic matrix, the CLTE of the polymer alloy parallel to the microlayer directions could be reduced to a very low level. Various influencing factors including rubber concentration, viscosity ratio, interfacial adhesion as well as the domain size were investigated.     

Multilayer capacitor margin stresses and electrode to dielectric thickness calculations

The mismatch of thermal expansion coefficients in co-fired multilayer capacitors (MLCs) leads to development of residual stress on cooling. These stresses are of a compressive nature for the multilayer stack and a tensile character for the ceramic margin. A closed-form stress calculation of the critical ratio of electrode thickness to ceramic dielectric thickness in the stack shows a limiting ratio of approximately 1:2. Design equations are given in order to calculate the multilayer electrode to dielectric thickness ratio. The required design parameters are the linear thermal expansion coefficients, the temperature difference, the Young's moduli, the strength of the ceramic margin, and the ratio of active to inactive capacitor area.     

低膨胀陶瓷材料

本文阐述了晶体的热膨胀与化学键及晶体结构之间的关系，以及晶体热膨胀的各向异性对多晶陶瓷体热膨胀的影响，微裂纹对降低陶瓷材料的平均膨胀系数有一定作用，但同时又降低了材料的机械强度。     

骨料粒径对混凝土热膨胀性能的影响

混凝土中,骨料的性质很大程度影响着混凝土的热膨胀性能.研究了骨料粒径对混凝土热膨胀系数的影响.结果表明:对于密实度高,粗骨料粒径大于20 mm的混凝土,随着粒径的增加混凝土的热膨胀系数降低;对于低坍落度,骨料粒径小于20 mm的混凝土,随着骨料粒径的增加混凝土的热膨胀系数增加:混凝土热膨胀系数受粗骨料热膨胀性能的影响较大,低热膨胀系数的骨料配制的混凝土热膨胀系数较低.石灰石混凝土的热膨胀系数小于花岗岩混凝土和玄武岩混凝土,大理岩混凝土的热膨胀系数小于砂岩混凝土.