Electrical Conductivity Of Melts Research Articles

Ultrafast x-ray detection of low-spin iron in molten silicate under deep planetary interior conditions.

The spin state of Fe can alter the key physical properties of silicate melts, affecting the early differentiation and the dynamic stability of the melts in the deep rocky planets. The low-spin state of Fe can increase the affinity of Fe for the melt over the solid phases and the electrical conductivity of melt at high pressures. However, the spin state of Fe has never been measured in dense silicate melts due to experimental challenges. We report detection of dominantly low-spin Fe in dynamically compressed olivine melt at 150 to 256 gigapascals and 3000 to 6000 kelvin using laser-driven shock wave compression combined with femtosecond x-ray diffraction and x-ray emission spectroscopy using an x-ray free electron laser. The observation of dominantly low-spin Fe supports gravitationally stable melt in the deep mantle and generation of a dynamo from the silicate melt portion of rocky planets.

Dissolution behavior of palladium and rhodium in glass melts: Implications for the viscosity and electrical conductivity of high-temperature melts

This article investigated the solubility of platinum group metals (PGMs) in sodium borosilicate glass and its effect on the viscosity and electrical conductivity of melts. The role of PGMs in the viscosity and electrical conductivity of melts was examined using the rotating cylinder method and impedance spectroscopy, respectively. Moreover, XRD, XPS, and SEM were used to measure the phase compositions, valence states, and microstructures, respectively, of the glass samples with different PGMs contents. The results showed that the solubility of Pd and Rh in sodium borosilicate glass was estimated to be less than 110 ppm by weight. The higher concentrations of Pd and Rh resulted in Pd-rich and Rh-rich inclusions in the glass matrix, which eventually agglomerated to form metallic Pd, Rh and Rh2O3. The evolution of viscosity and electrical conductivity with different temperatures followed the Arrhenius equation with a fairly good linear relationship between ln η and ln κ.

THE DENSITY AND ELECTRICAL CONDUCTIVITY OF MOLTEN SALT MIXTURES OF BERYLLIUM FLUORIDE WITH ALKALINE METALS CHLORIDE

Information about the density and electrical conductivity of salt melts is of interest both for assessing the possibility of their use for electrolytic obtaining and refining of beryllium and other technological processes, and analyzing the possible interaction of components. Data on the density of molten saline systems containing fluoride and alkaline metals chloride are obtained by hydrostatic weighing. The balloon and the thread of the suspension were made of platinum. Berylia oxide used the material and cover of thermocouple. In system BeF2–MeCl (Me = Li, Na, K, Cs) и BeF2–(Li–K)eut–Cl investigated from 9 to 14 molten saline mixtures containing from 0 to 100% beryllium fluoride with an increase in temperature by 100–200 K from the melting point of the mixture with an average step of 10 K. Due to the behavior of the individual fluoride of beryllium when heated above the melting temperature (high viscosity and intense evaporation), the density of molten salt was measured by maximum pressure in the gas bubble. Simultaneously with the density of the capillary method, the electrical conductivity of these melts was measured. Material of the measuring cell—beryllium oxide, measuring electrodes—platinum rods with a diameter of 1 mm. The permanent cells were determined and regularly controlled by melting of high-purple potassium chloride. All operations for the preparation of saline mixtures, the selection of samples for chemical analysis and the measurement of properties were carried out in an isolated atmosphere of a dry and additionally cleaned argon. The measurement results are presented on the graphs and in the form of the first and second-order polynomas, reflecting the dependence of density and electrical conductivity on temperature for various compounds of saline mixtures. The values of the simultaneously measured density and electrical conductivity values were used to calculate the molar volume and molar electrical conductivity of electrolytes. The isotherms of the molar volume are almost linear in nature, which indicates the weak interaction of the components of the melt. The isotherms of molar electrical conductivity have a characteristic outrage in the area of compositions containing about 30 mol % beryllium fluoride, which may be associated with the formation of complex compounds in the liquid phase.

Electrical conductivity of melts: implications for conductivity anomalies in the Earth's mantle.

Magmatic liquids, including silicate and carbonate melts, are principal agents of mass and heat transfer in the Earth and terrestrial planets, and they play a crucial role in various geodynamic processes and in Earth's evolution. Electrical conductivity data of these melts elucidate the cause of electrical anomalies in Earth's interior and shed light on the melt structure. With the improvement in high-pressure experimental techniques and theoretical simulations, major progress has been made on this front in the past several decades. This review aims to summarize recent advances in experimental and theoretical studies on the electrical conductivity of silicate and carbonate melts of different compositions and volatile contents under high temperature and pressure. The electrical conductivity of silicate melts depends strongly on temperature, pressure, water content and the ratio of non-bridging oxygens to tetrahedral cations (NBO/T). By contrast, the electrical conductivity of carbonate melts exhibits a weak dependence on temperature and pressure due to their fully depolymerized structure. The electrical conductivity of carbonate melts is higher than that of silicate melts by at least two orders of magnitude. Water can increase electrical conductivity significantly and reduce the activation energy of silicate melts. Conversely, this effect is weak for carbonate melts. In addition, the replacement of alkali-earth elements (Ca2+ or Mg2+) with alkali elements causes a significant decrease in the electrical conductivity of carbonate melts. A distinct compensation trend is revealed for the electrical conductivity of silicate and carbonate melts under anhydrous and hydrous conditions. Several important applications of laboratory-based melt conductivity are introduced in order to understand the origin of high-conductivity anomalies in the Earth's mantle. Perspectives for future studies are also provided.

Electrical conductivity of niobium-containing oxide-fluoride melts

The effect of Nb2O5 on electrical conductivity of metals based on CaF2 and CaF2-30% Al2O3 at T = 1500–1900 K in an oxidizing atmosphere is investigated using an ac bridge at the frequency 5 kHz. It is found that, as the Nb2O5 concentration increases from 0 to 25%, the electrical conductivity of the melts decreases, while the activation energy of electrical conductivity increases monotonically. The data obtained agree with viscosity investigations and indicate that niobium is the complexing agent in oxide-fluoride melts.

Effect of niobium-containing additions on the viscosity and electrical conductivity of oxide-fluoride melts

An oscillatory viscometer and ac 5-kHz bridge are used to measure the viscosity and electrical conductivity (at 1450–1600°C) of two types of slag melts based on CaF2(ANF-1P flux) and on the CaF2-30% Al2O3 system (ANF-6 flux) with additions (to 35%) of one of the following three types of niobium-containing compounds: Nb2O5 (extrapure grade), Nb2O5 (commercial purity), and a niobium concentrate (about 70% Nb2O5). An addition of the niobium-containing compounds to the fluxes is found to increase the viscosity, to increase the solidification range, and to decrease the electrical conductivities of the melts. In this case, the activation energies of viscous flow (34–148 kJ/mol) and conduction (22–100 kJ/mol) increase monotonically, which indicates polymerization of the melts.

Morphology and electrical conductivity in polyaniline/polyolefin blends

The effects of processing and molecular composition on the morphology and electrical conductivity of melt pressed polyaniline (PANI)/polyolefin blends have been investigated. In all systems, the morphology was found to consist of two distinct phases, a conducting network of PANI embedded within the thermoplastic host. Low field conductivities ranging from 10/sup -14/ to 10/sup -4/ S/cm could be accessed, through a suitable choice of PANI content and processing conditions. To 200 V/mm, the conductivity of the material was found to increase exponentially with applied field, thereafter remaining close to constant until the onset of breakdown. On further analysis, the applied field E dependence of conduction current i prior to breakdown was found to obey a relationship of the form i=A sinh(bE), as reported in the literature for insulators in the so-called low-field regime. Despite the dramatic variations in electrical properties that result from incorporation of the conducting polymer, the low strain mechanical properties were not degraded to any great degree.

ChemInform Abstract: Viscosity, Thermal Conductivity, and Surface Tension of High‐Temperature Melts

High-temperature melts are substances which are solids at room temperature and liquids at high temperatures. They include liquid metals, molten salts, and other melts such as molten semiconductor materials. Although they show scientifically interesting behavior and have industrially important characteristics, the thermophysical properties of these substances at high temperature are not sufficiently known due to experimental difficulties. Many melts show strong chemical activity and therefore are corrosive to materials of container and sensors. Applicable sensors are limited also because of the high temperature and the electrical conductivity of melts. In this paper the present status of available data for the viscosity, the thermal conductivity, and the surface tension of high-temperature melts is reviewed. Limited experimental information is available and these properties are difficult to predict theoretically. The transport properties are important for predicting heat transfer and flow patterns. For the prediction of the behavior of melts under microgravity condition, the temperature dependence of the surface tension plays a major role.

Viscosity, thermal conductivity, and surface tension of high-temperature melts

High-temperature melts are substances which are solids at room temperature and liquids at high temperatures. They include liquid metals, molten salts, and other melts such as molten semiconductor materials. Although they show scientifically interesting behavior and have industrially important characteristics, the thermophysical properties of these substances at high temperature are not sufficiently known due to experimental difficulties. Many melts show strong chemical activity and therefore are corrosive to materials of container and sensors. Applicable sensors are limited also because of the high temperature and the electrical conductivity of melts. In this paper the present status of available data for the viscosity, the thermal conductivity, and the surface tension of high-temperature melts is reviewed. Limited experimental information is available and these properties are difficult to predict theoretically. The transport properties are important for predicting heat transfer and flow patterns. For the prediction of the behavior of melts under microgravity condition, the temperature dependence of the surface tension plays a major role.

Electrical Conductivity of Molten Slags for Electro-slag Remelting

A four electrodes method with alternative current has been developed for measurement on the electrical conductivity of ionic melts at high temperatures, especially for that of CaF2-based slags for electro-slag remelting (ESR). The electrical conductivity was measured systematically for CaF2-based slags containing MgF2, BaF2, CaO, BaO, Al2O3, TiO2, ZrO2, and CaS. From the results, the conduction mechanism of those slags was discussed in terms of molar conductivity.The molar conductivity of CaF2 melt was changed with the addition of alkaline-earth oxides and fluorides, such as MgO, CaO, BaO, MgF2, and BaF2 in accordance with the intensity of cation-anion attraction. It suggests that those additives have a tendency to behave as ionic pairs in the melt. The remarkable decrease on the electrical conductivity of the melts was observed by the addition of some oxides, such as Al2O3, TiO2, SiO2, and ZrO2 into the melts. It suggests that those additives have a tendency to form oxyfluoride complex ions. An empirical equation was proposed for the calculation of the conductivity of multi-component slags for the ESR process.

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Electrical conductivity of melts and their ability to form glasses in the system Ge + As + Te

In the system Ge + As + Te, the heavy Te atom facilitates the formation of mesomeric pσ-bonding systems. The glass forming regions are thus small and depend strongly on the quenching conditions. As in the systems Ge + Sb + Se and Ge + As + Se all metallically conducting melts in the system Ge + As + Te solidify to a crystallline structure even when quenched in water. However, not all semiconducting melts belonging to this system become glassy under these conditions. As expected, the transition from melts solidifying to a glass structure to those solidifying to a crystalline structure is more gradual, as is also the transition from metallic to semiconducting melts. All the semiconducting melts become more or less metallically conducting at temperatures between 900 and 1000 °C. The transition can be described by a parabolical or a log log dependence on temperature.In the chalcogenide systems the melting process often enforces the same bonding mechanism with similar atomic short range order as does the application of high pressures or of strong electric fields. This is especially the case at high temperatures. The enforced mobility of the atoms, their tighter packing and the effect of electrical conductivity often act in the same direction, enhancing structural changes in the same direction.

Electrical conductivity of melts and their ability to form glasses: I. The GeSbSe system

The electrical conductivity of melts in the glass forming system GeSbSe was measured as a function of temperature to greater than 1000°C by a new electrodes method. Compositions inside the glass forming region show typical semiconducting behavior, with energy gaps in the range 1–2 eV, up to several hundred degrees above the softening point; at still higher temperatures the conductivities increase more rapidly with temperature. This sharp increase in conductivity probably results from a change in short-range order wherby average coordination numbers larger than the valencies of the elements are reached. In compositions well outside the glass forming region, i.e., with large Sb- and Ge-contents, the melts show metallic conductivity. In the transition region in which glasses are only obtained by very rapidly quenching small samples in water, a relatively high, but not metallic, conductivity was found. It is thought that these essentially glassy melts contain micro regions of a second, highly conducting phase. The elements Ge and Sb, with their tendency to form directed (sp)-hybrid bonds, promote the formation of well developed spatial networks. When the Ge- and Sb-content is high, the atoms can become mobile in the melt only if the bonding goes over to a mesomeric pσ-system, as has been found in the melting of elemental Ge. This leads to a closer packing (CN = 6) and metallic-like conductivity. The conductivity measurements revealed two-phase melts over part of the GeGeSe system. Liquid immiscibility was also confirmed in the SbSe system, but over a slightly different composition range than previously reported. The critical temperature for mixing is around 1000°C.