Thermodynamic Properties of a Double Ring-Shaped Quantum Dot at Low and High Temperatures

In this work, we study thermodynamic properties of a GaAs double ring-shaped quantum dot under external magnetic and electric fields. To this end, we first solve the Schrödinger equation and obtain the energy levels and wave functions, analytically. Then, we calculate the entropy, heat capacity, average energy and magnetic susceptibility of the quantum dot in the presence of a magnetic field using the canonical ensemble approach. According to the results, it is found that the entropy is an increasing function of temperature. At low temperatures, the entropy increases monotonically with raising the temperature for all values of the magnetic fields and it is independent of the magnetic field. But, the entropy depends on the magnetic field at high temperatures. The entropy also decreases with increasing the magnetic field. The heat capacity and magnetic susceptibility show a peak structure. The heat capacity reduces with increasing the magnetic field at low temperatures. The magnetic susceptibility shows a transition between diamagnetic and paramagnetic below for \(T<4\hbox { K}\). The transition temperature depends on the magnetic field.     

Thermodynamic Properties and Physical–Chemical Transformations of Polymer Materials at High Temperatures and Pressures

A semiempirical equation-of-state model for polymer materials over a wide range of thermodynamic parameters is proposed, allowing for the transformation of compounds at high dynamic pressures. Equations of state for polystyrene, polyimide, and poly(m-phenylene isophthalamide) are developed, and a critical analysis of calculated results in comparison with the set of available high-energy density experimental data is made.     

Pressure of the Saturated Vapor of Nickel at High Temperatures

Two series of measurements of the saturated vapor pressure of crystalline and liquid nickel are carried out in the temperature range of 1270–1896 K using the integral version of the effusion method and Knudsen mass spectrometry. The enthalpy of sublimation of Ni at 0 K is calculated from the measurement results in accordance with the second _s H ₀ ⁰(II) and the third _s H ₀ ⁰(III) laws of thermodynamics. Good agreement between the vapor pressure values, determined by different methods under different experimental conditions, makes possible their joint treatment for crystalline and liquid nickel and leads one to recommend the value of _s H ₀ ⁰ = 425.3 ± 2.0 kJ/mol. The results obtained are compared with the available data of other authors.     

Viscosity and Thermal Conductivity of Heavy Oils in the Region of High Temperatures and Pressures

The coefficients of dynamic viscosity and thermal conductivity of heavy high-viscosity oils (HVO) are experimentally and theoretically investigated at high temperatures and pressures. Methods are suggested for the calculation of dynamic viscosity and thermal conductivity of HVO in a wide range of parameters of state. The methods are developed on the basis of experimental data using elements of the theories of information and thermodynamic similarity of the properties of substances.     

Pressure-Drop Considerations in the Characterization of Dew-Point Transfer Standards at High Temperatures

During calibration of precision optical dew-point hygrometers (DPHs), it is usually necessary to take into account the pressure drop induced by the gas flow between the “point of reference” and the “point of use” (mirror or measuring head of the DPH) either as a correction of the reference dew-point temperature or as part of the uncertainty estimation. At dew-point temperatures in the range of ambient temperature and below, it is sufficient to determine the pressure drop for the required gas flow, and to keep the volumetric flow constant during the measurements. In this case, it is feasible to keep the dry-gas flow into the dew-point generator constant or to measure the flow downstream the DPH at ambient temperature. In normal operation, at least one DPH in addition to the monitoring DPH are used, and this operation has to be applied to each instrument. The situation is different at high dew-point temperatures up to 95 °C, the currently achievable upper limit reported in this paper. With increasing dew-point temperatures, the reference gas contains increasing amounts of water vapour and a constant dry-gas flow will lead to a significant enhanced volume flow at the conditions at the point of use, and therefore, to a significantly varying pressure drop depending on the applied dew-point temperature. At dew-point temperatures above ambient temperature, it is also necessary to heat the reference gas and the mirror head of the DPH sufficiently to avoid condensation which will additionally increase the volume flow and the pressure drop. In this paper, a method is provided to calculate the dry-gas flow rate needed to maintain a known wet-gas flow rate through a chilled mirror for a range of temperature and pressures.     

不同添加剂对石墨材料高温粘结性能的影响

在以酚醛树脂(ＰＦ)和碳化硼(Ｂ_４Ｃ)为原料的高温粘结剂基础上,Ａｌ_２Ｏ_３,Ｓｉ和白炭黑(超细ＳｉＯ_２)作为第二种添加剂分别加入到粘结剂中以制备新型高温粘结剂,并对石墨材料进行粘结．用新型高温粘结剂粘结的石墨部件分别在２００、８００、１５００℃下热处理,并在室温条件下测试其剪切强度．结果表明,复合添加剂对石墨粘结部件的粘结性能有明显的影响．其中,酚醛树脂＋Ｂ_４Ｃ＋白炭黑粘结剂具有较为理想的粘结性能,白炭黑的添加对提高石墨材料的高温粘结性能具有明显的作用．     

On the Mobile Behavior of Solid 4He at High Temperatures

We report studies of solid helium contained inside a torsional oscillator, at temperatures between 1.07 K and 1.87 K. We grew single crystals inside the oscillator using commercially pure ⁴He and ³He-⁴He mixtures containing 100 ppm ³He. Crystals were grown at constant temperature and pressure on the melting curve. At the end of the growth, the crystals were disordered, following which they partially decoupled from the oscillator. The fraction of the decoupled He mass was temperature and velocity dependent. Around 1 K, the decoupled mass fraction for crystals grown from the mixture reached a limiting value of around 35%. In the case of crystals grown using commercially pure ⁴He at temperatures below 1.3 K, this fraction was much smaller. This difference could possibly be associated with the roughening transition at the solid-liquid interface.     

Deterministic Chaos during Chemical Reactions in the Interfacial Layer at High Temperatures

The process of entering of substances into a chemical reaction at high temperatures in the interfacial layer is modeled as instantaneous "shocks" resulting in a change of the order parameter related to the concentration of intermediate product; this defines, along with the delay effect, the emergence of a nonequilibrium damping coefficient. The integration of the obtained differential equation (DE) in the time interval makes it possible to reduce the kinetic problem continuous in the time to the problem of mapping with chaotic dynamics of the order parameter (concentration). This approach allows to correlate concepts such as the explosive phase transition in two-component systems, chaos, and nonlinear processes, as well as to answer the question whether deterministic chaos is realized in such systems and how rapidly the information about the initial conditions is lost.     

Experimental Investigation of the Density of Liquid Lithium Hydride at High Temperatures

The density of molten lithium hydride is measured by the dilatometric method in the temperature range from 970 to 1260 K. Lithium hydride is obtained directly in an ampoule by hydrogenation of lithium at a temperature of the order of 920 K and a constant hydrogen pressure of 1 MPa. The purity of lithium and hydrogen used is 99.96 mass % and 99.999 vol %, respectively. The confidence error of the experiments does not exceed 2%. The measurement results are compared with the available literature data, and the reasons for discrepancy are analyzed.     

Experimental Investigation of the Density of Caproates at High Temperatures and Pressures

Results of experiments on investigating the density of caproates as a function of temperature and pressure are given. The equation of state of caproates in the liquid phase is composed on the basis of the P––TT data obtained.     

碳纤维在高温下的结构、性能演变研究

针对碳纤维在碳/碳烧蚀防热复合材料中应用的基础问题,论述了不同碳纤维结构、成分、表面特征,及其力学性能和热物理性能的高温演变规律,揭示了碳纤维灰分含量对碳纤维力学性能和热氧化性能的影响。确定了在碳/碳复合材料复合成型过程中,碳纤维结构受基体碳影响的变化规律和碳纤维表面特征对碳/碳材料宏观力学性能的影响。阐明了碳/碳复合材料中碳纤维的力学性能对纤维发生折断烧蚀的阻碍作用和通过控制碳/碳成型最高温度实现提高性能的途径。     

Development of an Apparatus for the Determination of Spectral Reflectivity at High Temperatures in the Visible

The paper presents a reflectometer for high temperature measurements. In this apparatus, the directional-hemispherical spectral reflectivity is measured by comparing the optical response of the sample to white light with the response of a reference material. The reflected light, collected by an integrating sphere, is dispersed in a spectrograph and detected by an ICCD camera. This procedure allows the simultaneous measurement of the reflectivity in a large, continuous wavelength range (presently 510 to 860 nm). An electrical resistance heater is used to heat the samples up to about 1200 K; for higher temperatures a flash-lamp pumped dye laser is used. To avoid laser induced plasma generation, the integrating sphere is placed inside a vacuum chamber, which also allows measurements under a controlled atmosphere. The response of the apparatus is calibrated to an absolute scale which allows the determination of the sample temperature by fitting the thermal emission spectrum with Planck's formula. To check the performance of the apparatus, measurements on Fe₂O₃ (hematite) and NiO have been carried out.     

Thermochemical Treatments for Protection of Steels in Chemically Aggressive Atmospheres at High Temperatures

Boronizing is a well-known thermochemical treatment process that has found applications in a variety of industries. Boride layers on Fe-alloys present high hardness values (∼ 1900 Hv), good wear properties and are resistant to various aggressive chemical environments. The mechanical behavior of boride layers on Fe-alloys has been well documented, but there seems to exist limited information on the chemical behavior of these coatings. We present in this paper the results of a systematic study of the chemical properties of boride layers, in aggressive environments that include dilute HCl, H₃PO₄, H₂SO₄ and HNO₃, acid solutions and vapors of molten Al alloy and Zn metals in various temperature ranges. Results indicated that with the exception of HNO₃ acid, the presence of boride layers on Fe-alloys, greatly improved their corrosion resistance. These results are discussed in terms of the potential applications they may have in various industrial sectors, including field tests carried out in fossil-fuel fired boilers.     

Analysis of Electrochemical Processes near the Tip of a Corrosion-Mechanical Crack at High Temperatures

We describe some results of our electrochemical investigations of a model of the renewed surface–passivated surface galvanic couple for 15Kh2NMFA steel in borate-buffered reactor water with pH8 under the action of high temperatures (up to 300°C) and pressures. On the basis of studying the kinetics of potential and current in this galvanic couple and their temperature dependences, we conclude that the galvanic couple significantly affects the acceleration of the growth of a corrosion-mechanical crack. Using the results of our investigations and data available in literature, we analyze the electrochemical situation at the tip of a corrosion-mechanical crack and propose a possible mechanism describing the effect of a high-temperature aqueous medium on the crack growth.     

On the Practice of Strength Estimation for Nonmetallic Fibrous Composite Materials at High Temperatures

We present experimental data on the effect of temperature on tensile, compression, bending, and shear strength characteristics of a carbon-reinforced plastic. It is shown that experimental shear strength values differ for various bending loading schemes.     

The Kinetics of Oxidation of Zirconium Iodide in an Air-Argon Mixture at High Temperatures

The thermogravimetric method is used to investigate the kinetics of oxidation of zirconium iodide in an air-argon mixture in the temperature range from 1380 to 1968 K. The high-frequency induction heating is used to attain high temperatures. The temperature is measured by a precision optical monochromatic pyrometer using a black-body model located in the sample being investigated. The increment of sample mass is measured continuously using a spring balance. One sample is investigated, whose temperature is successively increased in jumps with stops on isotherms. The transition of tetragonal modification of oxide film to a mixture of tetragonal and cubic modifications is registered at 1745 K. The obtained results are used to calculate the Arrhenius equation for tetragonal modification of oxide film in the range from 1380 to 1730 K. The activation energy is 180.7 kJ/mol. The obtained results are compared to available literature data.     

Analysis of the Thermal Conductivity of Hydrocarbons and Their Derivatives at High Pressures and Temperatures

Calculated values of the thermal conductivity of liquid hydrocarbons at high temperatures and pressures up to 500 MPa are given. The calculated values of thermal conductivity are compared with the experimental data of various authors. It is demonstrated that, at pressures up to 500 MPa, the calculated values of the thermal conductivity agree with the experimental data within 3%.