An apparatus for the measurement of thermal expansion of solids at low temperatures

A dilatometer, using the three terminal capacitance technique, suitable for measurement of linear thermal expansion of solids in the temperature range 1.3–300 K is described. The dialtometer is designed such that the mounting system for the specimen does not undergo any significant changes in dimensions when the specimen is heated. The apparatus, therefore, yields in principle absolute values of α, the coefficient of linear thermal expansion. The performance of the apparatus has been checked by measurements on copper in the temperature range of 77–300 K. Some preliminary results on the behaviour of α for Y₁Ba₂Cu₃O_6.9 compound in the vicinity of superconducting transition temperature,T _c are also described. The system can detect relative changes in length Δl/l ₀ of about 10⁻⁸. Attempts are being made to improve the sensitivity.     

纳米晶304不锈钢高温氧化膜中Cr和Mn元素的XPS和UPS表征

利用X射线光电子能谱（XPS）和紫外光电子能谱（UPS）,对比研究了普通304不锈钢（CP-SS304）和深度轧制技术制备的块体纳米晶304不锈钢（BN-SS304）在900 ℃空气中氧化24 h后形成的高温氧化膜中Cr和Mn元素的结合能、原子百分比、价电子的相互作用和功函数,分析了BN-SS304表面电子结构的特征。结果表明：两种材料氧化膜中Cr元素以Cr3+和Cr0存在,Mn元素以Mn4+和Mn0存在,在不同溅射时间,BN-SS304氧化膜中Cr3+与（Cr3++Cr0）原子百分比和Mn4+与（Mn4++Mn0）原子百分比均低于CP-SS304氧化膜中的比值。两种材料氧化膜中价电子之间的相互作用主要有Mn—O,Cr—O,Mn0(3d和4s)和Cr0(3d和4s)。与CP-SS304相比,BN-SS304氧化膜表面价电子之间的相互作用强,其功函数比CP-SS304提高0.07 eV, BN-SS304的耐高温氧化性能增强。     

Generalized Grüneisen parameters and low temperature limit of lattice thermal expansion of cadmium and zirconium

The generalized Grüneisen parameters (γ′ _j ) and (γ″ _j ) for cadmium and zirconium were calculated from the second- and third-order elastic constants to determine the low temperature limit of the volume thermal expansion of these metals of hexagonal symmetry. The low temperature limit of cadmium and zirconium was calculated to be positive values indicating a positive volume expansion down to 0 K even though many Grüneisen gammas were found to be negative.     

石墨烯低温热膨胀和声子弛豫时间随温度的变化规律

考虑到原子非简谐振动和电子-声子相互作用,用固体物理理论和方法研究了石墨烯格林艾森参量和低温热膨胀系数以及声子弛豫时间随温度的变化规律,探讨了原子非简谐振动项对它们的影响.结果表明:1)在低于室温的温度范围内,石墨烯的热膨胀系数为负值,随着温度的升高,其热膨胀系数的绝对值单调增加,室温热膨胀系数为-3.64×10~(-6)K~(-1);2)简谐近似下的格林艾森参量为零.考虑到非简谐项后,格林艾森参量在1.40-1.42之间并随温度升高而缓慢增大,几乎成线性关系,第二非简谐项对格林艾森参量的影响小于第一非简谐项;3)石墨烯声子弛豫时间随着温度的升高而减小,其中,温度很低(T10 K)时变化很快,此后变化很慢,当温度不太低(T300 K)时,声子弛豫时间与温度几乎成反比关系.     

低温下不锈钢导热系数的测量

在低温条件下利用稳态纵向热流法测量了制造低温阀门常用的316L不锈钢和17-4PH不锈钢的导热系数,通过实验表明两者的导热系数与316不锈钢的导热系数十分接近。     

Higher order elastic constants and generalized Gruneisen parameters of elastic waves and low temperature thermal expansion of gadolinium

Expressions for the higher order elastic constants are derived using the sublattice displacements to the second degree in strains. These expressions are used to obtain the higher order elastic constants and their pressure derivatives in gadolinium. The higher order elastic constants are used to find out the generalized Gruneisen parameters of the elastic waves propagating in different directions in gadolinium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with the available reported values.     

Analysis of thermal expansivity of iron (Fe) metal at ultra high temperature and pressure

In the present investigation we have explained the thermal and compression properties of HCP iron (Fe) at high pressure with variable temperature (isobars) and at high temperature with variable pressure (isotherm). The usual Tait equation of state is modified by incorporating the effect of thermal pressure. The calculated values of pressure for different isotherms and isochors and thermal expansivity (α) as a function of both temperature and pressure have been compared with those values obtained by Isaak et al and Wasserman et al.      

Variations of lattice constants and thermal expansion coefficients of indium at high pressure and high temperature

ABSTRACT

The effects of pressure and temperature on the lattice constants and thermal expansion coefficients of Indium were studied up to 18.6?GPa and 506?K based on in situ X-ray diffraction method with an externally heated diamond anvil cell. The results show that the measured axial ratio (c/a) decreases with increasing temperature and its temperature dependence decreases with increasing pressure. The thermal expansion coefficient of the a-axis decreases with increasing pressure up to 7?GPa and remains almost constant above 7?GPa, whereas that of the c-axis increases monotonously with pressure and changes from negative to positive at around 7?GPa. The observed behavior suggests that temperature reduces the tetragonal distortion on the lattice, and its effect is dominant below 7?GPa; in contrast, pressure enhances lattice distortion, and tends to have a stronger effect above 7?GPa.     

The influence of particle distribution and interphase on the thermal expansion coefficient of particulate composites by the use of a new model

In this work, the thermal expansion coefficient (CTE) of a composite containing spherical particles surrounded by an inhomogeneous interphase embedded in an isotropic matrix is evaluated by means of a new model. The thermomechanical properties of the interphase are formulated as continuous radial functions. It is assumed that this third phase developed between the polymeric matrix and the filler particles contains both areas of absorption interaction in polymer surface layers onto filler particles as well as areas of mechanical imperfections. It can be said that the concept of boundary interphase is a useful tool to describe quantitatively the adhesion efficiency between matrix and particles and that there is an effect of this phase on the thermomechanical properties of the composite. The thickness and volume fraction of this phase were determined from heat capacity measurements for various filler contents. On the other hand, it is assumed that the particle arrangement (distribution) which can be considered as an influence of neighboring inclusions and their interaction should affect the thermomechanical constants of the composite. The theoretical predictions were compared with experimental results as well as with theoretical values from expressions obtained from other workers and they were found to be in satisfactory agreement.     

The comparative study of thermal fatigue behavior of laser deep penetration spot cladding coating and brush plating Ni-W-Co coating

For improving the thermal fatigue behavior of hot work die steel in engineering application, the present work compare the influence of thermal fatigue resistance by the two different surface modified processes, the laser deep penetration spot cladding (LDPSC) and brush plating on the Cr12MoNi hot rolling tool steel. The thermal fatigue tests were fulfilled by heating and quenching in water at a cycle period of 2 min. Before and after thermal fatigue testing, the microhardness distribution profile and microstructure of LDPSC have been investigated. The results show that the LDPSC can be divided to three zones: cladding zone, alloying zone and heat affected zone. The major phases in cladding zone consist of Fe₃C, Cr₇C₃, Cr₂₃C₆ and martensite. The oxidation resistance and thermal stability of brush plating Ni-W-Co coating and reference materials has been determined. The results of thermal fatigue testing show that LDPSC and brush plating Ni-W-Co coating can improve thermal fatigue resistance as compared to the reference material. The brush plating Ni-W-Co coating is more effective than the former owing to its higher thermal stability, oxidation resistance, superfine grain, high-density dislocation in microstructure and combination of strength and ductility.     

The temperature dependence of thermal expansion for p-type Ce0.9Fe3.5Co0.5Sb12 and n-type Co0.95Pd0.05Te0.05Sb3 skutterudite thermoelectric materials

During waste heat recovery applications, thermoelectric (TE) materials experience thermal gradients and thermal transients, which produce stresses that scale with the TE material's coefficient of thermal expansion (CTE). Thus, the temperature-dependent CTE is an important parameter for the design of mechanically robust TE generators. For three skutterudite thermoelectric compositions, n-type Co_0.95Pd_0.05Te_0.05Sb₃ (with and without 0.1 at. % cerium doping) and p-type Ce_0.9Fe_3.5Co_0.5Sb₁₂, the CTE was measured using two methods, i.e. X-ray diffraction on powder and bulk specimens and dilatometry on bulk specimens. Each bulk specimen was hot pressed using powders milled from cast ingots. Between 300?K and 600?K, the mean CTE values were 9.8–10.3?×?10^?6 K^?1 for the non-cerium-doped n-type, 11.6?×?10^?6 K^?1 for the 0.1 at. % cerium-doped n-type and from 12.7 to 13.3?×?10^?6 K^?1 for the p-type. In the literature, similar CTE values are reported for other Sb-based skutterudites. For temperatures >600?K, an unrecovered dilatational strain (perhaps due to bloating) was observed, which may impact applications. Also, the submicron particle sizes generated by wet milling were pyrophoric; thus, during both processing and characterization, exposure of the powders to oxygen should be limited.