Measurement of low temperature heat capacity of metals under pressure

An alternating heat flow method is used to measure the heat capacity of metals at low temperatures under hydrostatic compression. The phase shift method is developed for taking account of the losses in the medium. The method was tested by measuring the heat capacity of Sn at pressures up to 10 k bar. The errors of measurements are ～3%.     

A simple tight-binding model for the study of 4d transition metals under pressure

Recently we have developed a simple tight-binding (TB) model of transition metals in the region near the middle of the 4d-series tuned to mimic molybdenum. The energetic, structural and melting properties deriving from this model are quite close to those obtained in previous first-principles work on Mo. TB approaches, reasonably accurate but computationally less demanding than first-principles calculations, therefore can be used to perform systematic analysis on the physical properties of transition metals across the 4d-series over wide thermodynamic ranges. Here we present a series of TB parametrizations designed to emulate the behavior of niobium, technetium, ruthenium, rhodium and palladium under extreme conditions of pressure and temperature. Our simple TB model is composed of two basic contributions to the energy: first, the pairwise repulsion due to Fermi exclusion, and second, the d-band bonding energy described in terms of an electronic density of states that depends on structure. The parameters of the model are adjusted to fit the dependence on pressure of the d-band width and the zero-temperature equation of state of the element in question. Calculated TB phonon spectra compare very well with ab initio results and experimental data, and the stable crystal structure in all transition metals at equilibrium is correctly predicted.     

Effects of mechanical pressure on charge transport in ferrocene in the presence of adsorbed vapours

The change in the adsorption-induced electrical conductivity of ferrocene as a function of temperature has been studied under moderate pressure. At constant temperature, the logarithm of conductivity has been observed to be proportional to the applied pressure. A drastic change in the electrical conductivity behaviour of ferrocene, at the adsorbed state, as a function of temperature under mechanical pressure has been observed. The results are discussed in the light of different existing theories. Our results suggest that ferrocene in the vapour-adsorbed state undergoes phase transition which is modified by both temperature and pressure, and the effect of such phase transition is reflected in the unusual variation of conductivity with temperature under different pressures.     

On the fracture pressure of liquid metals

Fracture pressure of six liquid metals, Pb, Al, Cu, Ni, Ti and Fe have been calculated at their melting points in three different ways; (i) by extrapolating molecular dynamic (MD) data reported in the literature for various temperatures to their melting points, (ii) by using the fracture pressure equation developed by Fisher and (iii) by using the work of nucleation suggested by Fletcher. Results have shown that the Fisher equation and MDs estimates agree closely, whereas the ones based on the work of nucleation are systematically lower than the other two. In all cases, calculated fracture pressures are several orders of magnitude different from those assumed in the literature, emphasizing the extent of weakening by extrinsic factors in liquid metals.     

VUV absorbing vapours in n-perfluorocarbons

The optical transparency of perfluorocarbons used as Cherenkov media is of prime importance to many Ring Imaging Cherenkov detectors. We will in this paper show that the main photon absorbers in these fluids are hydrocarbons with double or triple bonds. We will moreover discuss a process which can eliminate these pollutants and restore the intrinsic excellent optical transparency of these fluids in the VUV range.     

Effects of mechanical pressure on charge transport in some ferrocene derivatives in the presence of adsorbed vapours

The change in adsorption-induced electrical conductivity of some ferrocene derivatives as a function of temperature has been studied under moderate pressures. At a constant cell temperature, the conductivity of the pure ferrocene derivatives in the dry state depends on the applied pressure and this pressure dependence of conductivity is significantly different for different materials. A spectacular change in the electrical conductivity behaviour of these materials at the vapour-adsorbed state, as a function of temperature under mechanical pressure, has been observed. Pressure-induced change in conductivity of different ferrocene derivatives at the vapour-adsorbed state is remarkably different. The results have been discussed in the light of different existing theories. The unusual variation of conductivity with temperature under pressure is thought to be due to the phase transition in these materials.     

压力下的炭化(英文)

述评了三类压力下的炭化途径:分解气体自升压状态下的炭化,水热反应和还原CO2成炭。尽管这些在加压状态下形成的不同形态和纳米织构的炭材料具有相当高的收率,然而在很多情况下它们是多种形态炭材料的混合物。述评着眼于温度-压力条件和所用的前驱体的化学组成,讨论了高纯度、分离态的炭球的形成条件。     

Fabrication of cast particle-reinforced metals via pressure infiltration

A new casting process for fabrication of particle-reinforced metals is presented whereby a composite of particulate reinforcing phase in metal is first produced by pressure infiltration. This composite is then diluted in additional molten metal to obtain the desired reinforcement volume fraction and metal composition. This process produces a pore-free as-cast particulate metal-matrix composite. This process is demonstrated for fabrication of magnesium-matrix composites containing SiC reinforcements of average diameter 30, 10 and 3 m. It is compared with the compocasting process, which was investigated as well for similar SiC particles in Mg-10 wt % Al, and resulted in unacceptable levels of porosity in the as-cast composite.     

Fatigue and inelasticity of metals under nonuniform stressed state

Based on the review of the available publications and the findings of the original studies, the author demonstrates that with cyclic stresses in the maximum-stressed surface layer being equal the inelastic strains in the presence of stress gradients are smaller than those in the material under uniform stressed state. As a result, there is a difference in the cyclic stress–strain diagrams between these cases. An equation for the cyclic stress–strain diagram is put forward, which allows for the stress gradient effect. A model is substantiated, which provides an explanation for the difference between fatigue strength characteristics under uniform and nonuniform stressed states.     

Helium and radiation defect accumulation in metals under stress

The results of investigations of radiation-induced porosity in 18-10 austenitic steel after irradiation by 40-keV He⁺ ions and thermo-mechanical treatment are presented. External tensile stress was shown to result in an increase in He bubble size. Helium bubble migration and accumulation on grain boundaries was observed. Bubble clusters on grain boundaries are origins of brittle failure of the material. Helium bubbles increase also during post-radiation annealing. Post-radiation deformation of the material results in a considerable increase in the release rate of implanted helium gas.     

Uniaxial pressure dependence of the Debye temperature in metals

The electrical resistance and its temperature coefficient have been measured for a platinum foil as a function of uniaxial pressure over the pressure range 0 to 60 MPa. The measurements were performed at room temperature using the transient hot-strip method. The data are analyzed using the electrical resistivity formula within the Block-Grüneisen approximation. The pressure dependence of the Debye temperature was directly obtained from an expansion of this formula and using the basic definition of the temperature resistivity coefficient. The reliability of the experimental data was then verified using the basic definition of Grüneisen constant. Within the investigated pressure range, the analysis supports the interpretation that the change in resistance of platinum under pressure is mainly due to the change in the amplitude of the atomic vibrations that are directly related to the change in Debye temperature. The pressure dependence of resistance and the Debye temperature of the platinum were reasonably good in spite of the approximations involved.