Thermal expansion of ChS-139 steel in temperature range 20–720 °C

The article presents the results of investigation of thermal expansion of ChS-139 steel in the temperature range 20–720 °C. Measurements were carried out by dilatometric method with DIL-402C unit manufactured by NETZSCH (Germany) with the error (1.5–2)×10^?7 K^?1. The approximation dependences of thermal coefficient of linear expansion on temperature have been obtained and reference tables have been calculated. The abnormal change of expansion coefficient above 550 °C is shown, and the explanation of the phenomenon is given.     

Thermal expansion of artificial graphites in the temperature range 293–1650 K

The article presents the results of studying the thermal expansion of MPG-6 and AXF-5Q graphites and graphite composite based on ¹³C isotope in the temperature range 293–1650 K. Measurements were performed with dilatometric method in DIL-402C unit manufactured by NETZSCH (Germany), with the accuracy of (1÷4)×10^?7 K^?1. Approximation dependences of average integral coefficient of linear expansion on temperature have been obtained and reference tables calculated. It is shown that the coefficient of thermal expansion of ¹³C composite is much lesser than for MPG-6 and AXF-5Q. The explanation of this phenomenon is provided in the paper.     

Dielectric study of natural inyoite in the frequency range from 10−1 to 107 Hz and the temperature range from −50 to 140°C

For the first time, the method of dielectric dispersion in the 10^?1–10⁷ frequency range is applied to study temperature the dependences of permittivity, conductivity, and dielectric modulus of natural inyoite in the temperature range from ?50 to 140°C. An anomalous increase in the parameters under consideration is observed at temperatures between 87 and 98°C. According to thermal gravimetrical measurements, this range is characterized by an anomaly resulting from a partial loss of crystallization water.     

Thermal conductivity of Pb-Mg-Zr alloys and the thermal resistance of the interface between alloys and EP-823 steel in the temperature range of 300–900°C

A technique for measuring the thermal resistance of the liquid metal–structural steel interface is proposed. The results ofmeasurements of the thermal resistance of the interface between Pb-Mg-Zr alloys and EP-823 steel and the thermal conductivity of Pb-Mg-Zr alloys in the temperature range of 350–900 °C are presented.     

Thermal expansion anisotropy of β-TlInS2 crystals in the course of phase transitions

Basing on the thermal expansion studies performed for β-TlInS₂ crystals in the course of their phase transitions, we have found that the crystals aged for one year are composed from at least two polytypes, which undergo phase transitions at different temperatures. The detailed analysis of anisotropy of the thermal expansion demonstrates that all of the diagonal components of the thermal expansion tensor associated with the eigensystem have almost the same modules but differ by their signs. This leads to appearance of an elliptical conical surface of zero thermal expansion. The orientation of this surface does not depend on the temperature in the temperature interval under study. We have also found that the thermal expansion coefficients along the crystallographic a and b axes are close to zero.     

Thermal conductivity and thermal diffusivity of samarium in the temperature range of 293–1773 K

The thermal conductivity and the thermal diffusivity coefficients of samarium have been measured by the laser flash method in the temperature interval of 293–1773 K in solid and liquid states including the regions of phase transitions. The measurement errors of the heat transfer coefficients were ±(3–6)%. The approximation equations and the tables of reference data for the temperature dependence of properties have been obtained. The obtained results have been compared with the available literature data.     

Order structure of methanol along the 200-bar isobar in the temperature range of 60–320°C according to IR spectroscopy

The topology and energetic characteristics of hydrogen bonded clusters in methanol and methanol-heptane mixtures are investigated by IR spectroscopy over a wide temperature range. The average number of hydrogen bonds per methanol molecule was calculated. Based on an analysis of changes in the spectral parameters of O...H intramolecular bonds, conclusions on structural rearrangements in the mixture under study at elevated temperatures are drawn.     

Porous monoliths consisting of aluminum oxyhydroxide nanofibrils: 3D structure,chemical composition,and phase transformations in the temperature range 25–1700 °C

We present a study on the chemical and structural transformations in highly porous monolitic materials consisting of the nanofibrils of aluminum oxyhydroxides (NOA, Al₂O₃·nH₂O) in the temperature range 20–1700 °C. A remarkable property of the NOA material is the preservation of the monolithic state during annealing over the entire temperature range, although the density of the monolith increases from ~0.02 up to ~3 g/cm³, the total porosity decreases from 99.3 to 25% and remains open up to 4 h annealing at the temperature ~1300 °C. The physical parameters of NOA monoliths such as density, porosity, specific area were studied and a simple physical model describing these parameters as the function of the average size of NOA fibrils—the basic element of 3D structure—was proposed. The observed thermally induced changes in composition and structure of NOA were successfully described and two mechanisms of mass transport in NOA materials were revealed. (i) At moderate temperatures (T?≤?800 °C), the mass transport occurs along a surface of amorphous single fibril, which results in a weak decrease of the length-to-diameter aspect ratio from the initial value ~24 till ~20; the corresponding NOA porosity change is also small: from initial ~99.5 to 98.5%. (ii) At high temperatures (T >?800 °C), the mass transport occurs in the volume of fibrils, that results in changes of fibrils shape to elliptical and strong decrease of the aspect ratio down to ≤?2; the porosity of NOA decreases to 25%. These two regimes are characterized by activation energies of 28 and 61 kJ/mol respectively, and the transition temperature corresponds to the beginning of γ-phase crystallization at 870 °C.

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Thermal expansion of CuInSe2 in the 11–1,073 K range: an X-ray diffraction study

Structural and elastic properties of chalcopyrite-type CuInSe₂ are determined in almost full stability range of temperature from 11 to 1,073 K, by in situ X-ray diffraction, employing a synchrotron-radiation source. The studied polycrystalline sample was prepared from a stoichiometric single crystal. Phase analysis reveals the formation of a trace amount of indium oxide impurity phase at the highest temperatures studied. From the obtained smooth lattice-parameter dependencies on temperature, the temperature dependencies of thermal expansion coefficients are derived. These coefficients are found to follow the trends previously reported for narrow temperature intervals. The present results provide a clear experimental evidence that the linear expansion coefficient is slightly negative below 47 K in both, a and c, directions; this temperature limit is in between the previously reported theoretical value (35 K) and the experimental ones (60 and 80 K) of such limit.     

Thermal conductivity of single-crystal ZrO2-Y2O3 solid solutions in the temperature range 50–300 K

The thermal conductivity of ZrO_2−x Y₂O₃ single crystals (x = 0.5, 1.5, 2.0, 2.5, 3.0, 8.0 mol %) has been studied experimentally in the temperature range 50–300 K. The influence of high-temperature annealings on the thermal conductivity has been analyzed.     

Temperature dependence of the principal and additional refractive indices of Yb:KGW and KYW crystals in the range of 20–400°C

Optics and Spectroscopy - The temperature dependence of the principal refractive indices of potassium-gadolinium tungstate crystals with 7% Yb impurity and pure potassium-yttrium tungstate without...     

Optical spectra of triglycine sulfate crystals in the range of 7–33 eV and its changes at phase transition

Pseudo-dielectric functions ?ε₁(E)? and ?ε₂(E)? of triglycine sulfate (TGS) crystal have been obtained in the range of 7–33 eV for different temperatures close to ferroelectric phase transition by spectral ellipsometry using the synchrotron radiation source BESSY II. These dielectric functions ε₁(E) and ε₂(E) have also been calculated from first principles using CASTEP CAmbridge Serial Total Energy Package code together with the band structure and density of electronic states of the crystal. Experimental and theoretical dielectric functions agree satisfactorily. A characteristic decrease of temperature dependences of the dielectric losses tgδ(T) and related values just below the phase transition temperature T _c have been found and discussed.     

Contributions from changes in various solar indices in cycles 20–23 and 24 to the modulation of cosmic rays

The modulation of cosmic rays (CRs) observed at neutron monitors during the minimum, growth, maximum, and beginning of the decay of solar activity (SA) of cycle 24 (2008–2015) is compared to the modulation of CRs in the same periods of SA of cycles 20–23. After a prolonged minimum of SA between cycles 23 and 24 in 2007–2009 and the maximum of CRs at the end of 2009, when CR intensity exceeded the previous four CR maxima, the SA growth phase displayed weaker modulation of CRs than in the corresponding periods of the previous cycles. The shorter variations in CRs (oscillations with variable periods and activity spikes) were clearer against the background of the reduction in the 11-year variation during SA growth in 2011–2014. The current SA cycle (24) saw a scenario with two SA maxima, and the CRs showed one minimum at the end of 2014 that differed from the maximum of 2009 by ≈12% for particles with a rigidity of 10 GV. CR modulation in the last cycle was the weakest since neutron monitors began operating. At the beginning of 2015, the CRs started to recover. Possible reasons for the unusually weak CR modulation are considered. Quantitative estimates are made of the contribution from different characteristics of the solar magnetic field to CR modulation in the period of cycle 24 under study and in the corresponding periods of solar cycles 20–23, and the estimates are compared.     

Manifestation of phase transformations in optical spectra of Na0.5Bi0.5TiO3 crystals between 25°C and 350°C

The pseudo dielectric function ?ε? (E) = ?ε ₁? (E) + i?ε ₂? (E) of sodium bismuth titanate Na_0.5Bi_0.5TiO₃, has been obtained in the spectral range of electronic excitations (2–9.5 eV) by spectroscopic ellipsometry using the synchrotron radiation source BESSY II. The spectrum contains a broad absorption band at 4.2–4.5 eV. The temperature dependence in the range of 25–350°C is presented by the related susceptibilities ?χ ₁? (T) and ?χ ₂? (T) at 5 eV. A clear peculiarity in the temperature behavior of ?χ ₁? (T) and ?χ ₂? (T) between 180 and 320°C has been revealed and discussed. In this range an extremum-like temperature dependence of intensity of the light reflected from the sample surface, has been revealed and can be explained by the diffraction of light on the grid of the elastic domain structure of the sample.     

Raman spectra and XPS studies of phase changes in Ge2Sb2Te5 films

Ge_2Sb_2Te_5 film was deposited by RF magnetron sputtering on Si (100) substrate. The structure of amorphous and crystalline Ge_2Sb_2Te_5 thin films was investigated using XRD, Raman spectra and XPS. XRD measurements revealed the existence of two different crystalline phases, which has a FCC structure and a hexagonal structure, respectively. The broad peak in the Raman spectra of amorphous Ge_2Sb_2Te_5 film is due to the amorphous －Te－-Te－ stretching. As the annealing temperature increases, the broad peak separates into two peaks, which indicates that the heteropolar bond in GeTe_4 and the Sb－Sb bond are connected with four Te atoms, and other units such as (TeSb) Sb－Sb (Te_2) and (Sb_2) Sb－Sb (Te_2), where some of the four Te atoms in the above formula are replaced by Sb atoms, remain in crystalline Ge_2Sb_2Te_5 thin film. And from the results of Raman spectra and XPS, higher the annealing temperature, more Te atoms bond to Ge atoms and more Sb atoms substitute Te in (Te_2) Sb－Sb (Te_2).     

Microwave dielectric properties of Nextel-440 fiber fabrics with pyrolytic carbon coatings in the temperature range from room temperature to 700℃

Pyrolytic carbon(PyC) coatings are deposited on the Nextel-440 fiber fabrics by chemical vapor deposition(CVD).The dielectric properties of the Nextel-440 fiber fabrics with PyC coatings(Nextel-440/PyC) are investigated in a temperature range from room temperature to 700℃ in X-band. Compared with the permittivity of the original Nextel-440 received,the complex permittivity of the Nextel-440/PyC(the real part εand the imaginary part ε), is significantly improved: εof the Nextel-440/PyC has a positive temperature coefficient, in contrast, εof the Nextel-440/PyC exhibits a negative temperature coefficient. Moreover, the reflection loss in units of d B is calculated. The results indicate that the microwave absorbing properties of the Nextel-440/PyC coatings is enhanced at 700℃ compared with that at lower temperatures.     

Thermal conductivity of large-grain niobium and its effect on trapped vortices in the temperature range 1.8–5 K

Experimental investigation of the thermal conductivity of large grain and its dependence on the trapped vortices in parallel magnetic field with respect to the temperature gradient \(\nabla T\) was carried out on four large-grain niobium samples from four different ingots. The zero-field thermal conductivity measurements are in good agreement with the measurements based on the theory of Bardeen–Rickayzen–Tewordt (BRT). The change in thermal conductivity with trapped vortices is analysed with the field dependence of the conductivity results of Vinen et al for low inductions and low-temperature situation. Finally, the dependence of thermal conductivity on the applied magnetic field in the vicinity of the upper critical field H _c2 is fitted with the theory of pure type-II superconductor of Houghton and Maki. Initial remnant magnetization in the sample shows a departure from the Houghton–Maki curve whereas the sample with zero trapped flux qualitatively agrees with the theory. A qualitative discussion is presented explaining the reason for such deviation from the theory. It has also been observed that if the sample with the trapped vortices is cycled through T _c, the subsequent measurement of the thermal conductivity coincides with the zero trapped flux results.