Ceramic materials with low coefficient of linear expansion

Glass and Ceramics -     

材料线膨胀系数对拉伸剪切性能的影响

为了研究被粘接材料的线膨胀系数对胶接件拉伸剪切性能的影响,用改性环氧树脂(EP)胶粘剂粘接不同材料,并对该胶接件进行拉伸剪切强度试验和温度影响试验。研究结果表明,被粘接材料的线膨胀系数不同会导致胶层在热冷变化过程中受到内应力作用而破坏,同时热空气进入胶层会导致胶层氧化变色,致使胶粘剂界面结合强度和胶粘剂自身强度降低;两种被粘接材料的线膨胀系数差异越大,经热冷变化后胶接件的拉伸剪切性能越低;在相同条件下,热冷变化温差越大,胶接件的拉伸剪切性能越低。     

Evaluation of radiation-induced changes in the Young's modulus of electroceramic materials

Translated from Steklo i Keramika, No. 2, pp. 19–20, February, 1990.     

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。     

Low-temperature combustion of energetic materials in filled polymer systems

In systems filled by inert additives, combustion of cellulose nitrate (CN) proceeds in a flameless low-temperature regime with a low linear burning rate. At a standard temperature, the exponent in the low of CN combustion in ballasted mixtures with inert additives in the pressure range of 0.1 to 10 MPa is several times lower than that of pure cellulose nitrate and amounts to 0.23. The qualitative and quantitative composition of gaseous products of flameless CN conversion is found. It is noted that this composition approximately corresponds to data available in the literature for the products of thermal decomposition of cellulose nitrate at comparatively low temperatures. Based on this fact and on a weak dependence of the CN burning rate on pressure in ballasted systems, the process under these conditions is assumed to be controlled by conversion of the energetic component predominantly in the condensed phase. In the case of a composite consisting of cellulose nitrate, silicon carbide, and polymer binder, for samples 10–25 mm in diameter, armoring exerts practically no effect on combustion parameters. Combustion of the same mixture with smaller diameters of non-armored samples is unstable. The presence of a liner establishes a clearly expressed critical combustion diameter in the examined systems. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 98–102, May–June, 2007.     

阻尼材料动态阻尼系数的测定

相同的阻尼材料,采用不同尺寸的测试试件测定的阻尼系数存在很大的差异。本文提出了频率对阻尼系数的影响,探讨了动态阻尼系数的测试方法,将相同阻尼材料、不同试件测定的结果统一起来。     

Potential of vibro-milling technique for preparation of electroceramic nanopowders

The potential of the vibro-milling technique as a simple method to obtain usable quantities of single-phase electroceramic powders with nanosized particles was examined. A detailed study considering the role of both milling time and firing condition on phase formation and particle size of the final product was performed. The calcination temperature for the formation of the desired phase was lower when longer milling times have been applied. More importantly, by employing an appropriate choice of the milling time and calcination condition, high purity electroceramic nanopowders have been successfully prepared with a simple solid-state reaction method.     

High voltage coefficient piezoelectric materials and their applications

The piezoelectric d_ij coefficient is often regarded in materials science as the most important figure of merit of piezoelectric performance. For many applications, the piezoelectric g_ij coefficient which correlates to voltage output and sensitivity of a piezoelectric material can be considered of equal or increased importance, however is often an overlooked parameter in materials science literature. The aim of this review is to highlight the importance of this parameter and to provide insight into the mechanisms that drive a high piezoelectric voltage coefficient in single crystal, polycrystalline, and composite form. For bulk ceramics, special attention is given to tetragonal systems due to the availability of electrical and crystallographic data allowing for a clear structure-property relation. Orthorhombic and rhombohedral systems are mentioned and specific cases highlighted, however investigating structure-property relations is difficult due to the lack of crystallographic datasets. Composite materials have been the forefront of high g_ij piezoelectric materials over the decades and are therefore also considered in both ceramic-matrix and polymer-matrix form. An overview of applications in medical, energy, fishing and defence industries where a high g_ij is desirable are considered and the scientific and commercial considerations that must be made for the transition from laboratory to industry are discussed from the perspective of integrating new piezoelectric materials into sonar devices.     

RDX基高能发射药的线膨胀系数测定

采用热机械分析法(TMA)测试了RDX基高能发射药的线膨胀系数,讨论了GAP-ETPE/NC比例、RDX粒度及含量对线膨胀系数的影响。结果表明,随着粘结剂体系中GAP-ETPE/NC比例的增加,线膨胀系数升高;RDX粒度的改变对线膨胀系数影响较小;随着RDX含量的增加,线膨胀系数降低。当GAP-ETPE/NC比例由0∶1变为1∶0时,试样的线膨胀系数提高了82.71%;当RDX含量由60%增加到70%时,线膨胀系数降低了24.89%。     

RDX基高能发射药的线膨胀系数测定

采用热机械分析法(TMA)测试了RDX基高能发射药的线膨胀系数,讨论了GAP-ETPE/NC比例、RDX粒度及含量对线膨胀系数的影响。结果表明,随着粘结剂体系中GAP-ETPE/NC比例的增加,线膨胀系数升高;RDX粒度的改变对线膨胀系数影响较小;随着RDX含量的增加,线膨胀系数降低。当GAP-ETPE/NC比例由0∶1变为1∶0时,试样的线膨胀系数提高了82.71%;当RDX含量由60%增加到70%时,线膨胀系数降低了24.89%。     

Factors determining the temperature coefficient of linear expansion of graphite

The technological factors determining the temperature coefficient of linear expansion of electrode and nipple graphite are considered. The TCLE is determined with the help of a DID-1 interference differential dilatometer in a range of working temperatures of 30 — 98°C. Many years of measurements have shown that the TCLE of graphite is sensitive to the variation of some technological factors the optimization of which makes it possible to decrease substantially the TCLE of graphitized nipples and determine ways of further improving the manufacturing process of graphite with an enhanced heat resistance.     

Problems in measurement of fluorescent materials

Fluorescent materials become increasingly important for signalling and warning purposes. Measurement facilities, however, are still very poor. This article reviews the radiometric aspects of fluorescent materials and the measurement of their radiometric and colorimetric characteristics. the precision of colorimeters and one-monochromator instruments can be improved by applying luminescent reflectance standards, calibrated with a two-monochromator system. Problems of radiation feedback with sphere geometry and a way to solve this problem with a two-monochromator system are discussed.     

钛酸钡掺杂镧电子陶瓷制备的研究

在钛酸钡陶瓷中掺入稀土多酸微量元素(0.1%～0.3%),会使钛酸钡陶瓷的电阻率降低,由绝缘变为半导体。那么减小杂量掺杂是否对钛酸钡陶瓷有同样的作用呢?为此在实验中采用溶胶-凝胶法制备掺杂稀土元素镧的钛酸钡纳米晶,考察了掺杂量分别为0.01%～0.05%和0.1%～0.5%的钛酸钡纳米晶的部分特征,以及杂质的掺入对钛酸钡粒径、煅烧温度和晶胞参数等方面的影响。     

Low-temperature sintered MgWO4–CaTiO3 ceramics with near-zero temperature coefficient of resonant frequency

The phases, microstructure, composition analysis and microwave dielectric properties of (1 ? x)MgWO₄–xCaTiO₃ ceramics with Li₂CO₃–4H₃BO₃ additions prepared by solid-state reaction method have been investigated by using X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy and advantest network analyzer. The τ_f of (1 ? x)MgWO₄–xCaTiO₃ were dependent on phase constitutions. The microwave dielectric properties of 0.91MgWO₄–0.09CaTiO₃ ceramics with Li₂CO₃–4H₃BO₃ were characterized, the results indicated that the ?_r and Q × f were associated with the sintering temperature and amount of Li₂CO₃–4H₃BO₃. The sintering temperature of ceramics was reduced to 950 °C from 1150 °C and τ_f was modified to 0 ppm/°C with good Q × f. Addition of 5.0 wt% Li₂CO₃–4H₃BO₃ in 0.91MgWO₄–0.09 CaTiO₃ ceramics sintered at 950 °C showed excellent dielectric properties of ?_r = 15.5, Q × f = 20,780 GHz (f = 7.1 GHz) and τ_f ～ 0 ppm/°C. The material has a chemical compatibility with silver, making it a very promising candidate materials for LTCC applications.     

Low-temperature synthesis of amorphous and glass ceramic silicate materials (Review)

The basic principles of sol-gel technology as a new method of synthesis of silicate materials were examined. It was shown that the structure and properties of the glasses are a function of the conditions of formation of gels. The problems in fabrication of monolithic glasses were discussed. Data were reported on new areas of application of materials synthesized by the sol-gel method.