Transport properties of superconducting magnetic alloys in the weak-coupling theory

The acoustic attenuation coefficient, the nuclear spin relaxation rate, and the electronic thermal conductivity of superconducting magnetic alloys are calculated in the weak-coupling theory developed in a previous publication. This theory generalizes the Bardeen-Cooper-Schrieffer theory of pure superconductors by considering a finite electron lifetime arising from magnetic impurity scattering. The transport coefficients are expressed as two-electron Green's functions and evaluated in the independent-particle approximation.     

Transport properties in a superconducting proximity sandwich with magnetic impurities

The thermal conductivity and ultrasonic attenuation rate are calculated numerically in a superconducting proximity sandwich containing magnetic impurities on the normal-metal side. The calculations are carried out on the basis of the theory given by Machida, in which the McMillan tunneling model is adopted to describe the proximity effect. In the limit of a thick superconducting film, analytical expressions are obtained near the transition temperature T = T _c and near T = 0. As in the case of a bulk superconductor with magnetic impurities, the existence of a bound state within an effective energy gap gives a significant effect on the transport properties. The calculation is compared with experiment on the thermal conductivity for AgMn/Pb sandwiches, and reasonable agreement is obtained between them.     

Transport properties in a superconducting proximity sandwich. Kondo effect

Temperature-dependent properties are evaluated in a superconducting Kondo alloy induced by the proximity effect. These include (i) the order parameter, (ii) the dc Josephson current, and (iii) the thermal conductivity and ultrasonic attenuation, in the case when there is reentrance of superconductivity. The calculations are based on the theory given by Kaiser, in which the McMillan tunneling model and the Müller-Hartmann-Zittartz theory are combined. The temperature dependence of pair-breaking is reflected directly in the above properties in much the same way as in an intrinsic Kondo superconductor, indicating that proximity-effect studies may provide detailed information on the Kondo effect in superconductivity.     

Measurement of optical properties of highly scattering ceramic materials

Radiation transfer in highly scattering ceramics is described by a diffusion approximation based on the asymptotic relation of the radiant flux and the radiant energy density in material depth. In this approximation, a calculation of the effective absorption coefficient k and the radiation diffusion coefficient D is based on the measurement of normal-hemispherical transmission of specimens shaped as various-thickness disks. Taken into account are radiation field, twodimensionality, and the radiation boundary reflection effect. The optical property measurements have been performed on the experimental apparatus based on an integrating sphere, a collimated radiation source, and a twochannel data acquisition and processing system. Results of the measurements of k and D for the silica ceramic are given at room temperature.     

改性酚醛树脂陶瓷摩擦材料的摩擦磨损性能

以普通酚醛树脂、硼改性酚醛树脂、三聚氰胺改性酚醛树脂为黏结剂,以陶瓷纤维为增强纤维,制备了3种酚醛树脂陶瓷摩擦材料。对其冲击韧性和硬度进行实验测试,采用摩擦磨损试验机考察其摩擦磨损性能,采用扫描电子显微镜(SEM)和X射线能谱仪分析其磨损表面形貌及其成分,并探讨其磨损机制。结果表明:硼改性酚醛树脂黏结剂能够提高摩擦材料的硬度,三聚氰胺改性酚醛树脂黏结剂能够提高摩擦材料的冲击韧性,降低摩擦材料硬度;在摩擦过程中三聚氰胺改性酚醛树脂在高温下炭化,在摩擦材料表面形成一层致密的摩擦层,摩擦层的存在使摩擦材料的摩擦因数相对比较稳定,降低了摩擦材料的磨损率。     

Composition, structure, and dielectric properties of SiC-AlN ceramic materials

We have studied the structure, relative dielectric permittivity (?), and dielectric loss tangent (tan??) of SiC-AlN ceramic materials. The results demonstrate that both ? and tan?? are anomalously high in the composition range 30?C50 wt % AlN at low frequencies (0.1 kHz). We show that the increase in ? may be due to a barrier effect on silicon carbide and aluminum nitride grain boundaries and to migration polarization.     

Studies on the structure and properties of semiconductor ceramic cooling materials

Thermoelectric polycrystalline ceramic materials were prepared by a new ceramic technology. Samples of p-type 72% Sb₂Te₃ + 25% Bi₂Te₃ + 3% Sb₂Se₃ doped with tellurium and 90% Bi₂Te₃ + 5% Sb₂Te₃ + 5% Sb₂Se₃ doped with Sbl₃ or Agl were studied. The new ceramic cooling materials have an inhomogeneous structure, but higher mechanical strength and thermoelectric properties. The method is simpler than the Bridgman and powder metallurgy processes. Measurements of properties show that sintering temperature and time effect the thermoelectric properties of the samples. Scanning electron microscopy shows that the polycrystalline ceramic materials have an obvious layered structure. The doping of the materials was studied, including doping variety and doping concentration. The figure of merit for n-type doped with Sbl₃ is 2.9 × 10^–3 K^–1, while that for p-type doped with tellurium is 3.1 × 10^–1 K^–1.     

Electrothermal properties of porous ceramic fiber media containing carbon materials

Electrically regenerable porous ceramic fiber media containing nanoporous carbon from 2.5% to 19.2% have been prepared for adsorption/regeneration system. An experimental apparatus was built for in situ measurement of the sample weight during adsorption and electrothermal desorption of gaseous adsorbates. Adsorption and electrothermal desorption behavior of gaseous adsorbates on carbon contained porous ceramic fiber media was explained by physical and electrothermal properties of these materials measured in this work. In situ thermal desorption and adsorption experiments show that a considerable amount of water vapor is adsorbed on the carbon contained media exposed to ambient air.     

Test equipment for determining the thermomechanical properties of refractory materials

Test equipment for determining the temperature deformation under load and the creep under compression is described. The equipment has extended functional capabilities, a higher accuracy in determining the values of the thermomechanical properties of refractory materials, and improved life and is ergonomic compared with the existing Russian analogues.     

Antibacterial and mechanical properties of honeycomb ceramic materials incorporated with silver and zinc

The antibacterial and mechanical properties of heat-resistant honeycomb ceramic materials produced from red mud industrial waste and doped with Zn and Ag are determined. Excellent antibacterial effects against Escherichia coli are obtained by the plate counting and vibration methods. When 5% and 6% Zn are added to the honeycombs doped with 0.3% Ag, the antibacterial rates reach 98.9% and 99.5%, respectively. The mechanical properties are evaluated by monitoring the bending strength, open porosity, water absorption capability, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The Zn and Ag particles are distributed uniformly in the honeycomb ceramics and the crystalline structure of the ceramic materials is not altered after Zn and Ag incorporation consequently enabling good dispersion of the antibacterial metals.     

A machine for determination of the mechanical properties of refractory materials

A machine with high metrological characteristics for testing composite materials and also foils, strips, wire, fibers, and grids in heating equipped with a system for processing of experimental data based on an information and measuring computer unit is described. The chamber of the machine in the form of a cube with intersecting holes makes it possible to increase its design along the axes. The method given for fastening the current leads makes it possible to place the heater in any position of the center portion of the chamber.Translated from Problemy Prochnosti, No. 10, pp. 110–112, October, 1990.     

陶瓷材料弹塑性参数仪器化压入测试方法研究

该文以典型陶瓷材料Si3N4和Al2O3为例,分别应用材料弹性模量仪器化压入测试中的两种代表性方法——Ma方法和Oliver-Pharr方法 ,对两种材料的仪器化压入测试结果进行计算。结果表明:Ma方法对陶瓷材料弹性模量的测试误差小于Oliver-Pharr方法。利用两种不同面角的四棱锥压头分别对Si3N4和Al2O3材料进行仪器化压入实验,并结合有限元数值分析方法,确定Si3N4材料的塑性参数(屈服强度σy=7 800 MPa和应变硬化指数n=0.02)和Al2O3材料的塑性参数(屈服强度σy=4 100 MPa和应变硬化指数n=0.025),从而为进一步研究陶瓷材料力学性能参数仪器化压入识别方法提供一定的理论基础。     

多元稀土氧化物掺杂二氧化锆基陶瓷材料的热物理性能

稀土氧化物(RE)掺杂氧化钇稳定二氧化锆(YSZ)是提高传统YSZ热障涂层隔热性能和高温稳定性的有效途径之一。在1500 ℃高温固相反应烧结24 h制得Gd₂O₃和Yb₂O₃多元稀土氧化物掺杂的YSZ(含3.5%Y₂O₃(摩尔分数))(GY-YSZ)陶瓷材料。采用XRD研究了GY-YSZ 陶瓷材料的晶体结构和物相组成; 采用激光脉冲法研究了Gd₂O₃和Yb₂O₃掺杂对GY-YSZ 陶瓷材料的热物理性能的影响规律。研究发现, 掺杂2.0%~3.0%Gd₂O₃和Yb₂O₃(摩尔分数)后GY-YSZ的热导率为0.90~1.15 W·(m·K)-1, 比YSZ降低30%以上, 显示了良好的隔热性能。稀土氧化物掺杂对YSZ陶瓷材料热物理性能的影响机制为: 掺杂Gd₂O₃和Yb₂O₃导致YSZ中单斜相(M)、 四方相(T)和立方相(C)含量发生变化, 同时YSZ晶格发生畸变。