Plasmas & Ions最新文献

Total structure factors from neutron diffraction (ND) and X-ray diffraction (XRD) measurements on molten lithium carbonate have been analyzed by the reverse Monte Carlo (RMC) modeling technique to generate a three-dimensional structural model of the melt. The calculated pair distribution functions were different from a previous result obtained by molecular dynamics (MD) simulation while the coordination numbers, N_Li-C = 3.8, N_O-Li = 2.4, N_Li-O = 3.7, were in agreement with those obtained from X-ray diffraction. Viewing the CO₃²⁻ ion as a plane triangle, the most probable site for the Li cation is found to be a corner site.

The Yukawa system is a collection of particles interacting through two-body Yukawa (i.e. screened Coulomb) potentials. Yukawa systems are often used as models for charged dust particles immersed in plasmas or colloidal particles suspended in electrolytes. We review thermodynamical and dynamical properties of Yukawa systems, focusing on the recent development of molecular dynamics (MD) simulation methods for Yukawa systems.

Different definitions of activity coefficients in aqueous electrolyte solutions are compared with each other. It is most convenient to define activity coefficients within the molality mode related to the “ideal dilute standard”, which is indeed the best choice for dilute solutions. In the range of very high salt concentration (> 20 mol kg⁻¹), definitions, which use the mole fraction, are more suitable or even necessary. We describe four definitions, which are suitable for electrolyte solutions in a single solvent. Furthermore, the consequences of the use of a mole fraction in the definitions of activity coefficients and excess functions are brought into focus.

The electrochemical synthesis of refractory borides from molten salts has been reviewed. Non-current and electrolytic boriding of different metals has been considered first. Then, the electrochemical synthesis of refractory borides has been discussed, when the two components of the boride phase are jointly deposited on the cathode. Equilibrium Electrochemical Synthesis (EES) diagrams are presented to predict equilibrium phases to be formed during electrochemical synthesis. The possibility to produce borides of transition metals as first cathodic product has been reviewed using a thermodynamic principle. Kinetics of electrochemical synthesis and morphology of the phases obtained have also been considered. A summary table with basic information on all experiments of electrochemical synthesis of refractory borides is included with about 100 references.

The presence of a second order transition in epsilon iron, the hexagonal closest packed form, is demonstrated. Two functions of the form T^*(Θ^−1/2 + A + BΘ) are proposed to model the extra heat capacity beyond what can be represented in a polynomial model in the regions 50 K below and 30 K above a lambda point. With A and B chosen so that ΔC_p/T is zero with a zero first derivative at the end points, these functions can provide an accurate and convenient representation for the thermodynamic properties of a material at temperatures and pressures near the lambda point for a second order transition. Calculations of the T/P phase diagram of iron provide a good test of the usefulness of this model since two second order transitions are present in the region of interest. This model for the thermodynamic properties of iron reconciles the static and shock wave studies on the melting point of iron at high pressures. Other forms of solid iron may be stable at the melting point above 100 GPa, but the melting point of pure iron at the inner core boundary of the Earth, 328.9 GPa, is probably within 500 K of the calculated melting point for ε′ iron at this pressure, 4 680 K.

The fluence dependence of the absorption of TEA CO₂ laser in silicon wafers at various dopant concentrations has been studied. The transmittance decreased with increasing fluence, and the effect of the dopant concentration was found to be small. The time profile of the pulse intensity after transmitting through a sample showed a narrowing of the width. The results indicate a buildup of photo-induced absorbance in the middle of a pulse, leading to the absorption of the later part of the pulse, and also suggest that this effect is insensitive to the ground state absorbance of the silicon samples.

The structures of trivalent metal halides and oxides have been reviewed with emphasis on the stability of a six-fold coordination of metal ions, e.g. in YCl₃ and YO₃, and its competition with a four-fold coordination, e.g. in AlCl₃ and AbO₃. Upon melting in some cases the crystalline coordination is preserved, leading to the formation of either an ionic network or a molecular structure, while in other cases a transition to a different kind of structure occurs, such as that from an ionic to a molecular-type structure. Specific examples will be selected from recent experiments in which structural information at the partial level and Raman spectra have been obtained, and the X-ray average structure has been complemented by electrical transport data. Directions for future work with a potential impact on our understanding of the complex structure-property relations in the crystalline and liquid state have been proposed.

A relatively stationary discharge was generated in molten chloride utilizing a simple apparatus and successfully achieved at electrolysis. Fine silver particles were obtained using a LiCl-KCl-AgCl eutectic melt in an argon atmosphere. SEM observations of the silver particles showed them to be almost spherical and the size to be strongly dependent on the experimental conditions. This new kind of discharge electrolysis is expected to be adopted as a new method for metal powder production.