Dielectric Properties of Alumina at High Temperatures

The dielectric constant and dissipation factor of both single-crystal and polycrystalline alumina were measured in air over the frequency range lo² to 3 × 10⁵ cycles per second, in the temperature interval 900° to 1300° C. The three-electrode guard-ring method was used. The observed dielectric losses were due predominately to free-electron conduction mechanisms. The volume conductivity of single-crystal and polycrystalline alumina was calculated from the high-frequency data. The temperature dependences of the volume conductivity for two single crystals of different thicknesses were similar. The large thermal activation energy indicated intrinsic conductivity; the energy band gap of alumina was calculated to be approximately 7.3 electron volts. The bulk conductivities of the polycrystalline alumina were considerably higher than the single-crystal values, presumably because of impurities in the polycrystalline material. The results were compared with values previously reported in the literature.     

平行板谐振法测量高介电材料微波特性

讨论高介电材料介电常数、损耗角正切的测量技术、测量基本原理及相关参数的计算方法。介绍平行板谐振法的测量方法、测量装置和测量系统,阐述该方法的软硬件构成。给出实际测量中模式的判别方法及测量误差分析,并给出部分测量结果。介电常数ε,的测量相对误差小于0．26％,损耗角正切tanδ的测量相对误差小于7．5％。通过不同的方法对所选取的新型高介电材料微波特性进行测量,对比测量结果,验证该测量方法的正确性。     

无机电介质材料储能行为研究现状

电介质储能材料被誉为"现代工业的血液",具有介电常数高、损耗低、功率密度大、充/放电速度快、可靠性好等优点,是各类脉冲电力电子系统元器件的关键部件,受到了科学界广泛的关注.但其储能密度低、效率差的缺点也极大地限制了多领域的应用.如何显著提高电介质材料的储能性能成为近年来功能陶瓷研究的热点之一.本工作对比了无机电介质储能...     

Dielectric Properties of Lithium Molybdate Ceramic Fabricated at Room Temperature

Lithium molybdate disks were fabricated by moistening water‐soluble Li₂MoO₄ powder with deionized water and compressing it under a pressure of 130 MPa. Disks were postprocessed at room temperature, at 120°C, and at 540°C, which is a common sintering temperature for Li₂MoO₄. Regardless of the postprocessing temperature, densities as high as 87%–93% of the theoretical value were achieved. The X‐ray diffraction patterns of processed disks were all the same with no signs of hydrates or constitutional water. The samples also exhibited very similar microstructures and microwave dielectric properties with a relative permittivity of 4.6–5.2 and a Q × f value of 10 200–18 500 at 9.6 GHz, depending on the postprocessing temperature.     

Humidity Dependence of Apparent Dielectric Constant for DSP Cement Materials at High Frequencies

The relationship between humidity and dielectric constant for cement densified with small particles (DSP) has been studied in the relative humidity range 0%-93% and the frequency range 1 MHz to 1 GHz. The calculated dielectric constant appears to increase with increasing humidity as a linear relation at fixed frequency. According to experimental data and basic principles for dielectrics, two experimental expressions are suggested for heterogeneous dielectric materials to describe the observed behavior of the dielectric constant. The expressions fit the experimental data well in the frequency range studied. Apparent dielectric constant decreases with increasing frequency. Polarization of DSP cement is also discussed.     

高温陶瓷纤维过滤材料

陶瓷纤维过滤材料具有体积密度小、过滤阻力低、热稳定性好等特点,在高温热 气体净化领域具有广阔应用前景。本文主要介绍了高温陶瓷纤维过滤元件的种类、制备工艺及 其在热气体净化中的应用,提出了存在的问题和下一步发展趋势。     

氢化丁腈橡胶高温力学性能研究

研究高温下不同炭黑用量的氢化丁腈橡胶(HNBR)的回弹值、邵尔A型硬度、拉伸强度、拉伸应力松弛性能和动态力学性能等,分析温度对橡胶分子链段和物理交联网络等微观运动和微观结构的影响。结果表明:随着温度从25℃升高至150℃,不同炭黑用量的HNBR硫化胶的邵尔A型硬度和拉伸强度逐渐减小,回弹值先增大后减小,应力松弛速率增大,应变扫描前后储能模量之差减小;炭黑用量越大,高温下HNBR硫化胶的拉伸强度保持率越大,应力松弛的平衡应力占比越小;温度升高会破坏炭黑补强HNBR硫化胶的填料网络结构,导致结合胶含量减少,HNBR硫化胶高温下的力学性能下降。     

High Temperature and Wear Resistant Materials with Improved Operating Properties

Refractories and Industrial Ceramics - Results are provided for studies of self-sintering refractory mix preparation. New technology is proposed for their manufacture. The basis of the mixes...     

氟硅橡胶的高温拉伸性能研究

研究了氟硅橡胶的高温拉伸性能。结果表明,随试验温度的升高,氟硅橡胶FS6265的拉伸强度和伸长率均显著降低,且降低的幅度呈逐渐减小的趋势;在一定伸长率下,其拉伸强度随温度的变化不大,有利于氟硅橡胶在高温(80℃以上)密封场合使用。     

水泥熟料的高温力学性能

为了解水泥熟料破碎阻力随温度的变化,在实验室制各熟料样品,并在熟料冷却阶段的不同温度点进行力学实验.分析了水泥熟料样品载荷-位移曲线、抗压强度、弹性模量等随温度的变化情况.结果表明:随温度的降低水泥熟料表现出明显的硬化特征,加载峰之后,水泥熟料的特性宏观上表现出塑性向脆性的渐次转变.在冷却阶段,水泥熟料的弹性模量和抗压...     

低介电高强度多孔氮化硅陶瓷的研制

以氮化硅为基体,通过加入一定量的特殊无机添加剂,控制好相关工艺参数成功地制备出低密高强低介电的多孔氮化硅材料。采用有机涂层对多孔氮化硅材料表面进行封孔处理,通过对封孔前后材料电性能的对比分析得出:涂层对封孔后表面致密的整体材料电性能影响微小。     

纳米碳管复合氮化铝陶瓷的制备及其高频介电性能

通过添加玻璃活化剂和多层叠片,制备了纳米碳管(CNTs)氮化铝复合陶瓷。玻璃活化剂有效降低了氮化铝的烧结温度,既促进氮化铝烧结,又与纳米碳管有好的浸润性,可以包裹在纳米碳管表面,抑制纳米碳管高温因和氧化铝发生化学反应而造成的损失。多层叠片工艺是将氮化铝流延片与含有纳米碳管的流延片交替叠加形成夹心结构,由于氮化铝流延片的包裹和阻挡作用,可以有效避免纳米碳管的高温烧结损失。2种方式制备的纳米碳管复合陶瓷在高频均呈现良好的微波吸收特性。     

炭材料的高温抗氧化研究进展

炭材料抗氧化问题一直是研究的重点。本文阐述了炭材料的氧化行为，简单介绍了炭材料的各种氧化防护方法。并以涂层法为重点，综述了炭材料的高温抗氧化的研究进展情况。     

聚苯乙烯改性沥青高温性能研究

通过反应共混技术制备了聚苯乙烯（PS）/苯乙烯-丁二烯-苯乙烯共聚物（SBS）改性沥青,研究了 PS 用量、反应剂硫磺（sulfur）对沥青高温贮存稳定性、黏度-温度特性和动态力学性能的影响。结果表明:通过反应共混改性所得到的改性沥青在高温贮存时,当 PS/SBS 不大于1/1时贮存样品上下层软化点差值小于2.5℃,贮存稳定性能得到了明显改善。对于沥青/PS/SBS/Sulfur 为100/3/3/0.15的体系,沥青的黏流活化能（Eη）从65kJ/mol 降低到了52.8kJ/mol;同时显著提高了沥青的高温复数模量和弹性,损耗角正切值（tanδ）在30～100℃范围内的变化小于10。     

乙烯基硅橡胶的高温拉伸性能研究

研究了乙烯基硅橡胶SE6450的高温力学性能。结果表明,在高温下拉伸时,受热效应和体积膨胀效应的综合影响,其拉伸强度、伸长率和撕裂强度均显著降低,并随温度的逐步升高,力学性能降低程度趋缓;在200℃时,其拉伸强度仍有2.4MPa,相对于其它种类的橡胶仍表现出较好的耐热性能。     

中温烧结PSBN系统铁电陶瓷结构和性能的研究

本文研究了中温烧结PbO-SrO-BaO-Nb2O5(PSBN)系统铁电陶瓷介电性能.通过XRD分析确定了主晶相为具有钨青铜结构的Pb0.7Ba0.3Nb2O6(PBN)、Ba0.27Sr0.75Nb2O5.78(BSN);分析了添加剂MnCO3、TiO2、Fe2O3、(MgCO3)4.Mg(OH)2.5H2O对PSBN系统铁电陶瓷介电性能的影响.由于这些添加剂的作用使该系统铁电陶瓷介电系数提高,居里区拓宽并向低温方向移动,绝缘电阻提高,损耗降低,制得高介(ε=4300±200)X7R瓷料.     

High Temperature Structural,Dielectric, and Ion Conduction Properties of Orthorhombic InVO4

Orthorhombic InVO₄ was prepared by solid‐state reaction method and characterized by powder X‐ray diffraction and scanning electron microscopy. The frequency‐dependent dielectric and conductivity properties were studied from 300 to 973 K by impedance spectroscopy. A significantly enhanced conductivity was observed at higher temperature whereas almost no conduction was observed below 723 K. Appreciable grain boundary conductivity was observed at higher temperature. The activation energies for grain and grain boundary conductivities are 0.87 and 1.28 eV, respectively. The relative permittivity of ~35 was observed in a wider range of frequencies and temperatures. The frequency dispersion dielectric studies indicated thermally activated hopping conduction process. The high temperature structural studies revealed no significant change in structural parameters except a gradual increasing trend in the unit cell parameters and amplitude of isotropic thermal parameters with increasing temperature.     

Heat of Desorption of Water From Cellulosic Materials at High Temperature

ABSTRACT

During the falling rate period of drying the heat requirements for drying hygroscopic materials may be increased substantially ahove the normal latent heat by the heat of desorption of water. In various new high intensity drying processes which are of increasing interest industrially, the drying material may reach quite high temperatures for periods of time sufficiently short that there is no degradation of the properties of the dried material. However the limited stability of many materials at high temperatures precludes determination of heals of desorption by direct measurements because of the long experimental times required for thermodynamic techniques. The present study develops a thermodymically valid method whereby heats of desorption determined at low lemperatures may be extrapolated reliably to the high temperatures where such information is needed but cannot be measured. A relation between isosteric heat of desorption and latent heat of water is derived in order to compare the new     

室温固化高温使用环氧胶粘剂的进展

本文介绍了室温固化高温使用环氧胶粘剂的主要成份、结构、性能及其特点，并对其存在的问题及未来的发展趋势化了简述．