Hydrogen–Helium Mixtures at High Pressure

The properties of hydrogen–helium mixtures at high pressure are crucial to address important questions about the interior of Giant planets e.g. whether Jupiter has a rocky core and did it emerge via core accretion? Using path integral Monte Carlo simulations, we study the properties of these mixtures as a function of temperature, density and composition. The equation of state is calculated and compared to chemical models. We probe the accuracy of the ideal mixing approximation commonly used in such models. Finally, we discuss the structure of the liquid in terms of pair correlation functions.     

Quantum Effects on Hydrogen Isotopes Adsorption in Nanopores

We have investigated the applicability of simulations and theoretical techniques for exploring the selectivities of hydrogen isotopes. We have simulated the adsorption isotherms of H₂ in an idealized carbon slit pore at 77 K by using the grand canonical Monte Carlo simulations with the Feynman-Hibbs effective potential (FH-GCMC) and the rigorous path integral method (PI-GCMC), and we obtained good agreement between the isotherms from both simulations. This suggests that FH-GCMC, which uses the approximative Feynman-Hibbs treatment, is as useful as PI-GCMC for exploring H₂ adsorption at 77 K. Moreover, we show that the ideal adsorption solution theory (IAST) can predict the selectivity of D₂ over H₂ in the interstices of single-wall carbon nanotube (SWNT) bundles at 77 K (below 0.1 MPa) very well by comparing the obtained results with the mixture adsorption FH-GCMC simulations. This indicates that IAST is also applicable to the estimation of the selectivity of D₂ over H₂ at moderate pressures and at 77 K from experimental single-component adsorption isotherms. We also demonstrate that the FH-GCMC simulation can reproduce the experimental adsorption isotherms of H₂ and D₂ in aluminophosphate AlPO₄-5 at 77 K. Finally, we analyze the selectivity of D₂ over H₂ by IAST with the experimental single-component adsorption isotherms of H₂ and D₂ at 77 K for a variety of adsorbents: AlPO₄-5, activated carbon fibers (ACFs), HiPco SWNT, and SWNHs. The selectivities predicted by the experimental adsorption data based on the results from the FH-GCMC simulations are presented and discussed.     

Measurements of Hydrogen Thermal Conductivity at High Pressure and High Temperature

The thermal conductivity for normal hydrogen gas was measured in the range of temperatures from 323 K to 773 K at pressures up to 99 MPa using the transient short hot-wire method. The single-wire platinum probes had wire lengths of 10 mm to 15 mm with a nominal diameter of 10 μm. The volume-averaged transient temperature rise of the wire was calculated using a two-dimensional numerical solution to the unsteady heat conduction equation. A non-linear least-squares fitting procedure was employed to obtain the values of the thermal conductivity required for agreement between the measured temperature rise and the calculation. The experimental uncertainty in the thermal-conductivity measurements was estimated to be 2.2 % (k = 2). An existing thermal-conductivity equation of state was modified to include the expanded range of conditions covered in the present study. The new correlation is applicable from 78 K to 773 K with pressures to 100 MPa and is in agreement with the majority of the present thermal-conductivity measurements within ±2 %.     

氢原子的量子尺寸效应新理论

根据实么正变换理论 ,并结合SU ( 1,1)Lie代数 ,对氢原子的量子尺寸效应进行详细研讨。结果表明 ,氢原子的能级和波函数随时间变化的规律较复杂 ,并且是精确的     

A High Pressure Study of Ortho-para Conversion in Hydrogen by NMR

We have developed a system for studying NMR in a diamond anvil cell (DAC) resulting in an increased sensitivity of a few orders of magnitude. The DAC was loaded with solid hydrogen and studied to a pressure of 12.8 GPa in the temperature range of 4.2 to 77.3 K. We measured free induction decays and spin echoes. From this we could determine the ortho-para conversion rate. Conversion measurements were made at both low and high temperatures and are possible because at high pressure the sample remains solid. The rate constant rises to 58 %/hr at our highest pressure.     

Zero-Point Energy of the Proton Motions and Its Effect on the Pressure of Molecular Dissociation in Dense Hydrogen

Zero-point motion energy of the protons is evaluated in the quasi-harmonic approximation for both atomic and molecular phases of highly compressed hydrogen. The results are in good agreement with Kagan et al.'s. In the calculation, the phonon frequencies all over the Brillouin zone are obtained using force constants calculated by the first-principles band theoretical treatments. In the atomic phase, the Cs-IV structure, which is one of the low energy structures in the tetragonal diamond family, is found to be stable with real frequencies all over the Brillouin zone, while the -Sn structure is unstable with imaginary frequencies near zone-boundaries. In the molecular phase, taking the Cmca structure which is one of the candidate structures above 200 GPa, we have studied phonons and the stability of the lattice. We have evaluated the effect of the zero-point energy on the pressure of the molecular dissociation, assuming that it occurs between the Cs-IV and the Cmca structures. With inclusion of the zero-point energy the dissociation pressure is reduced by 90–120 GPa from that estimated by the static energy. The equation of state is in good agreement with the extrapolated one of Loubeyre et al.'s.     

Finite Element Analysis of Hydrogen Transport in Steel Pressure Vessel at High Temperature

Hydrogen embrittlement is commonly considered as an important failure mechanism for some typical steel pressure vessels and pipes made of such as Cr–Mo and 4130X steels at high-pressure hydrogen environment. In previous work, we investigated the hydrogen transport mechanisms of Crmo steel pressure vessels at room temperature. Furthermore, high temperature environment may affect the hydrogen transport mechanisms and hydrogen-induced crack behaviors in these structures to a large extent. In this paper, we study the hydrogen transport mechanisms in 2.25Cr–1Mo steel pressure vessel at high temperature under the support of National Key Fundamental Research and Development Project of China (2015.1-2019.12). The main work is to explore the effects of temperature, hydrogen concentration, and structural sizes on the transient hydrogen diffusion and distribution behaviors in Crmo steel pressure vessels using finite element analysis. Numerical results show that elevated high temperature accelerates the hydrogen embrittlement sensitivity, especially at structural discontinuities.     

Direct Evidence of Macroscopic Quantum Effects at High Temperature

We present experiments on macroscopic quantum effects in Josephson junctions with different relevant junction parameters at a temperature well above the classical-quantum crossover temperature. This has been possible by extending the measurements on the escape rate out of the metastable state at higher sweeping frequency (dI/dt up to 100 A/sec.) in order to induce non-stationary conditions in the energy potential describing the junction dynamics. The non-stationary regime for the system allows a direct observation of energy level quantitation when the rate of change of the external energy, measured in terms of the level spacing, is fast with respect to the thermal transitions between levels.     

A Capillary Tube Viscometer Designed for Measurements of Hydrogen Gas Viscosity at High Pressure and High Temperature

A capillary tube viscometer was developed to measure the dynamic viscosity of gases for high pressure and high temperature. The apparatus is simple and designed for safe-handling operation. The gas was supplied to the capillary tube from a high-pressure reservoir tank through a pressure regulator unit to maintain a steady state flow. The measurements of a pressure drop across the capillary tube with high accuracy under extreme conditions are the main challenge for this method. A differential pressure sensor for high pressures up to 100 MPa is not available commercially. Therefore, a pair of accurate absolute pressure transducers was used as a differential pressure sensor. Then the pressure drop was calculated by subtracting the outlet pressure from the inlet one with a resolution of 100 Pa at 100 MPa. The accuracy of the present measurement system is confirmed by measuring the viscosity of nitrogen as a reference gas. The apparatus provided viscosities of nitrogen from ambient temperature to 500 K and hydrogen from ambient temperature to 400 K and for pressures up to 100 MPa with a maximum deviation of 2.2 % compared with a correlation developed by the present authors and with REFPROP (NIST).     

浆料加压氢还原制备金属粉末研究进展

化合物浆料加压氢还原制备金属粉末是继金属盐溶液加氢沉淀金属粉末工艺后出现的一种工艺革新.综述了国内外金属氢氧化物、硫化物、碱式碳酸盐和部分氧化物等难溶化合物浆料的氢还原工艺,并从热力学和动力学的角度进行分析.最后针对存在的问题,分析了浆料氢还原工艺的发展趋势.     

氢原子的量子力学表征

建立了适合氢原子特性的量子算符代数理论,给出氢原子中电子与原子核绕其质心作圆周运动的旋转角频率及其轨道速度等物理量与时间量子数之间的关系。根据氢原子的量子算符代数理论,得到氢原子的能量及氢原子的光谱常数表示。结果表明,氢原子的光谱常数与实验测定值完全符合。     

Conductivity of Proton Electrolytes Based on Cesium Hydrogen Sulfate Phosphate

The conductivity and thermal behavior of cesium hydrogen sulfate phosphate are studied. New composite proton electrolytes (1 – x)Cs₃(HSO₄)₂(H₂PO₄)–xSiO₂ with a high conductivity in the range 60–200°C are prepared, and their transport properties are studied in a broad composition range (x = 0.3–0.95). Their conductivity exceeds that of CsHSO₄–SiO₂ composites and depends strongly on composition: it reaches a maximum at x = 0.7 (22 vol % SiO₂) and drops at higher silica contents on account of percolation disruption. It is shown by differential scanning calorimetry and x-ray diffraction analysis that the introduction of fine-particle silica stabilizes the high-conductivity, disordered state of the mixed salt on the surface of the silica particles.     

氢原子的量子谐振动理论

给出做量子谐振动的氢原子精确的量子哈密顿量,建立适合氢原子特性的量子算符代数理论,根据创新的氢原子的量子算符代数理论,得到氢原子的能量及氢原子的光谱常数表示。结果表明:氢原子的光谱常数与实验测定值完全符合。     

A Proton Pumping Gate Field-Effect Transistor for a Hydrogen Gas Sensor

A proton pumping field-effect transistor (FET), consisting of a triple layer gate structure of a Pd/proton conducting polymer/Pt, has been developed. The hydrogen sensitivity was controlled by the bias change between Pt and Pd. Furthermore, two kinds of methods for the readout of DC and AC modulation can be achieved. According to the decrement of the bias frequency, the modulated output was increased. This characteristic realizes a gas sensor with a self-check function.     

Effects of High Pressure on the Physical Properties of MgB2

The synthesis of MgB₂-based materials under high pressure gave the possibility to suppress the evaporation of magnesium and to obtain near theoretically dense nanograined structures with high superconducting, thermal conducting, and mechanical characteristics: critical current densities of 1.8?C1.0×10⁶ A/cm² in the self-field and 10³ A/cm² in a magnetic field of 8 T at 20 K, 5?C3×10⁵ A/cm² in self-field at 30 K, the corresponding critical fields being H _c2=15 T at 22 K and irreversible fields H _irr=13 T at 20 K, and H _irr=3.5 T at 30 K, thermal conduction of 53±2 W/(m?K), the Vickers hardness H _V =10.12±0.2 GPa under a load of 148.8 N and the fracture toughness K _1C =7.6±2.0 MPa?m^0.5 under the same load, the Young modulus E=213 GPa. Estimation of quenching current and AC losses allowed the conclusion that high-pressure-prepared materials are promising for application in transformer-type fault current limiters working at 20?C30 K.     

High Pressure Effects on Electronic and Magnetic Properties of LaOFeAs Superconductor

The effect of pressure has been studied on structural and electronic properties of LaOFeAs high-T _c superconductor by ab initio density functional theory by using pseudopotential Quantum Espresso code. The lattice parameters and ionic positions in the ambient pressure and some high pressure up to 20 GPa have been calculated. The obtained data versus the simple scaling relation for the ionic positions and distances for mechanical pressures have been discussed. The results of band structure and magnetic moment calculations of this compound versus the applied pressure are presented in this paper. The results are compared with the other experimental and computational data in the literature.     

Effects of Magnetic Quantum Dots on Magnetoconductance in Quantum Wires

We present a theoretical study of electronic transport in quantum wires (narrow two-dimensional electron gas) with array of magnetic quantum dots. Each magnetic quantum dot is defined by a small circular region where the strength of perpendicular magnetic field is modulated. By making use of a newly developed calculation method based on the gauge transformations, we calculated the conductance as a function of the external perpendicular magnetic field. Our numerical calculations show that the magnetoconductance is very sensitive to the number of magnetic quantum dots in the field region where the direction of the net magnetic field in dot regions is antiparallel to the external magnetic field.     

氢气压力对L80钢氢脆敏感性的影响规律

对L80钢在室温不同氢气压力下的氢脆敏感性进行了评价。通过缺口慢应变拉伸试验,结合断口分析,研究了3～12 MPa氢气压力下,L80钢的氢脆敏感性的变化规律。结果表明：在室温环境下,L80钢在5 MPa及以下氢气压力下应用时,无明显脆性;在8 MPa及以上氢气压力下应用时,具有明显脆性;在氢气压力3～12 MPa环境下,L80钢拉伸试样主断面中心位置微观形貌从韧窝形貌转变为韧窝形貌与解理形貌共存,边缘位置微观形貌从韧窝形貌向解理逐渐转变,断面收缩率变化率由16.19%逐渐增加至46.79%。随着氢气压力的增加,L80钢的塑性损失增加,断口表现出明显脆化特征,氢脆敏感性逐渐增加。