Emf measurements in the NaClAlCl3 system—II. The thermodynamics of liquid—gaseous equilibria in the basic range of the system

Activity data for NaCl, AlCl₃ and NaAlCl₄ in basic NaClAlCl₃ melts are derived from emf measurements. Literature values for the total vapour pressure are interpreted in terms of partial pressures of the gaseous species AlCl₃, Al₂Cl₆, and NaAlCl₄. A possible contribution of small amounts of the dimer Na₂Al₂Cl₈(g) is discussed. Thermodynamic data are derived for the molten mixture and for the corresponding vapour phase. Interaction between the melts and silica or alumina container materials is considered.     

Sodium and hydrogen tetrachloroaluminate catalysts for molecular weight reduction of hydrocarbons

Sodium and hydrogen tetrachloroaluminates (NaAlCl₄ and HAlCl₄) have been evaluated as catalysts for the molecular weight reduction of hydrocarbons. The NaAlCl₄ is the major molecular weight reduction and synthesis component, and HAlCl₄ adds a hydrogenation function. The optimum catalyst composition, for the petroleum AC-20 resid and shale oil feeds studied, was found to be 2.5–4.5 wt.% HAlCl₄ in NaAlCl₄. To convert these feeds completely into gasoline range materials, a hydrogen partial pressure and a hydrogen consumption of 950 psia and 900 scf/bbl, respectively, are estimated to be required. About 40% of the hydrogen consumption would be for contaminant removal. Above a hydrogen partial pressure of about 450 psia, the liquid products produced contained less than 100 ppm each of sulfur and nitrogen contaminants. The C₆C₁₃ molecular weight portion of the liquid products contained about 55% aromatics, 8% naphthenes, 33% branched paraffins and 4% normal paraffins (weight basis).     

Effect of sodium iodide additive on the electrochemical performance of sodium/nickel chloride cells

The effect of sodium iodide and sulfur additives on the performance of Na/-alumina/NaAlCl₄/NiCl₂/Ni cells was investigated in quasi-sealed laboratory research cells (0.5–1.0 Ah capacity) and in sealed full-size cells (4 Ah capacity). It was found that sodium iodide additive especially in combination with sulfur in Na/NiCl₂ cells significantly increases the usable capacity and reduces the impedance of the Na/NiCl₂ cells. It is proposed that the use of sodium iodide enhances the energy and power performance of the NiCl₂ electrode by two different mechanisms. The first mechanism, iodide ion doping of the anodically formed solid NiCl₂, is dominant at potentials lower than that of iodine evolution. The doping effect of the iodide ions produces a higher-capacity, lower-impedance NiCl₂ layer on the positive electrode. The second mechanism, anodic formation of very reactive iodine species, is effective when the cell is cycled through the iodine evolution potential range (2.8–3.1 V vs Na). During this process, the dissolved iodine species improve electrode kinetics through liquid-phase mass transport. Use of the sodium iodide additive is safe in sealed cells, causing no over-pressurizing problems. A maximum pressure increase of only 10 kPa was detected by a pressure sensor during severe overcharge tests.     

Pyrolysis of Model Sulfur-Containing Compounds in Molten Salt NaAlCl4

Abstract

The authors experimentally investigated pyrolysis of model vulcanized butadiene compounds with different sulphur content on the melt of NaAlCl₄. The maximum yield of liquid pyrolysis products occurs at 400°C, and is independent on S content. There was also observed strong desulphurization of liquid products, due to removal of S with the pyrolysis gases in the form of H₂S. On the basis of same experiments on desulphurization of model mixture C₁₆H₃₄S with C₁₅H₃₂ with the same catalyst was proposed possible mechanism of S removal through the formation of stable complexes.     

Chemically driven synthesis of Ti3+ self-doped Li4Ti5O12 spinel in molten salt

Surface doping of Li₄Ti₅O₁₂ (LTO) with Ti³⁺ ions is an effective way to enhance its electrochemical properties for lithium ion batteries (LIBs). Herein, a molten salt approach was reported to synthesize Ti³⁺ self-doped LTO powder. The reaction mechanism and the role of molten salt for the synthesis have been systemically discussed. Finally, electrochemical performance of the LTO powder was preliminarily evaluated as anode material of LIBs. The molten salt accelerated the mass transportation for the formation of LTO by transferring a solid diffusion to the diffusion of ions in a liquid media. Self-doping of Ti³⁺ ions on the surface of LTO particles was achieved by controlling equilibriums of chemical reactions in the reactor. Electrochemical performance of the LTO powders was effectively promoted by doping Ti³⁺ ions on the surface. The discharge capacity of the Ti³⁺ self-doped LTO powder prepared at 850°C was 171 mAhg⁻¹, and the capacity dacayed 9.9% after 200 cycles at a rate of 0.5 C.     

Design, construction and operation of a laboratory scale electrolytic cell for sodium production using a β″-alumina based low-temperature process

Sodium metal can be produced at low temperatures (523 K) by electrolysis of sodium tetrachloroaluminate (NaAlCl₄) in a cell, which employs sodium ion conducting beta-alumina as diaphragm. A laboratory-scale electrolytic cell and associated systems were designed and constructed to study the various aspects of the energy efficient process. Graphite/reticulated vitreous carbon (RVC) was used as the anode and molten sodium as the cathode. Electrolysis was carried out at 523 K with currents in the range 1–10 A (10–125 mA cm^–2). The cathodic current efficiency was close to 100%, but the anodic current efficiency was very low (20–30%), probably due to the consumption of chlorine in the intercalation reaction of graphite and aluminium chloride. The sodium metal was analysed by AAS and found to have 5N purity. On prolonged electrolysis, the graphite anode disintegrated due to the formation of graphite intercalation compounds. RVC behaved as a better chlorine-evolving anode in the initial period of electrolysis, but its ability for chlorine evolution decreased on continuous electrolysis. The study indicated the need for effective stirring of the electrolyte with excess NaCl to avoid build up of aluminium chloride and the resultant complications in the cell.     

Room temperature molten salts as lithium battery electrolyte

In the present study, are reported investigations obtained with the room temperature molten salt (RTMS) ethyl-methyl-imidazolium bis-(trifluoromethanesulfonyl)-imide (EMI-TFSI) in order to use it as solvent in lithium battery. The thermal stability, viscosity, conductivity and electrochemical properties are presented. A solution of 1m lithium bis-(trifluoromethanesulfonyl)-imide (LiTFSI) in EMI-TFSI has been used to test the electrolyte in a battery with LiCoO₂ and Li₄Ti₅O₁₂ as respectively cathode and anode materials. Cycling and power measurements have been obtained. The results have been compared with those obtained with a molten salt formulated with a different anion, BF₄⁻ and with a conventional liquid organic solvent EC/DMC containing LiTFSI. The 1m LiTFSI/EMI-TFSI electrolyte provides the best cycling performance: a capacity up to 106 mAh g⁻¹ is still delivered after 200 cycles, with 1C rate at 25 °C.     

Surface modification of LiMn2O4 cathode with LaCoO3 by a molten salt method for lithium ion batteries

Spinel LiMn₂O₄ is a promising cathode due to its advantages of low-cost, nontoxicity and thermal stability. However, the dissolution of manganese and the phase transformation induce the rapid capacity fade. Surface coating is an effective method to improve its electrochemical performance. In this work, spinel LiMn₂O₄ modified with perovskite LaCoO₃ was prepared using a novel molten salt method. The resulted samples were characterized by X-ray diffraction (XRD), transmission/scanning electron microscopy (TEM/SEM), Fourier transformation infrared (FT-IR), Raman, and X-ray photoelectronic spectroscopy. The content of Mn³⁺ increased with the LaCoO₃ coating accompanied by the increased concentration of oxygen vacancy. LiMn₂O₄ modified with 2% LaCoO₃ shows a higher capacity and cycling stability than others at 0.2 C, while the cathode with 4% LaCoO₃ shows the best rate performance at a larger current at 2 and 5 C. This enhanced performance can be attributed to improved interfacial conductivity between the cathode and electrolyte and the protective effects of coating.     

Dissolution and formation of polyacrylonitrile in low‐temperature molten salts

The solubility and the polymerization of polyacrylonitrile in low‐temperature molten salts was investigated. It was found, that the polymer dissolves in eutectic mixtures of molten sodium thiocyanate and potassium thiocyanate (NaSCN/KSCN) as well as in the molten hydrate lithium perchlorate (LiClO₄*3H₂O). The polymer can be regenerated by cooling the melt or diluting with water. The chemical interaction between the molten salt and the polymer was investigated by ¹³C‐NMR spectroscopy. These measurements show that the dissolution of the polymer in molten KSCN/NaSCN is accompanied by the splitting of the the hydrogen bonds. Starting from acrylonitrile, the formation of polyacrylonitrile by a radical polymerization in a molten salt becomes successful. The polymerization of acrylonitrile in an eutectic mixture of KSCN/NaSCN results in the formation of atactic polyacrylonitrile with high molecular weight. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2113–2117, 2000     

Study on rapid nitridation process of molten silicon by thermogravimetry and in situ Raman spectroscopy

The melt of silicon, hindering nitridation for its agglomeration, should be avoided in the direct nitridation of silicon to synthesize silicon nitride powders, although liquid phase facilitates nitridation. Therefore, we proposed a method to nitride molten silicon without agglomeration. Thermogravimetric and in situ Raman studies on the nitridation process of molten silicon were performed. The as-prepared silicon nitride samples were found to be micron clusters composed of submicron grains with high α-Si₃N₄ content. The nitridation of molten silicon at 1500°C was completed after 500 s and 109 times faster than the nitridation of solid silicon at 1350°C. β-Si₃N₄ is produced dominantly by α–β-phase transition. Less nitridation time and low temperature can decrease the β-Si₃N₄ content. The rapid nitridation was owning to core–shell structure Si@Si₃N₄, which was formed after the initial nitridation of silicon particles and hindered the agglomeration of molten silicon.     

Simple and novel synthesis of zirconia whiskers from a phosphate flux

High quality zirconia whiskers have been successfully prepared by molten salt method, using zirconium oxychloride (ZrOCl₂·8H₂O) and sodium phosphate tribasic dodecahydrate (Na₃PO₄·12H₂O) as precursor and molten salt, respectively. The effects of types of molten salt and heat treatment temperature on the formation of zirconia whiskers were characterized by XRD, Raman, DTA-TG, FE-SEM, TEM, SAED and HR-TEM. When Na₃PO₄·12H₂O is utilized as molten salt and the heat treatment temperature is 900?°C, the as-prepared zirconia whiskers with length ranging from 4?µm to 8?µm show an average aspect ratio of 25. The obtained ZrO₂ whiskers with monoclinic structure are elongated along [010] direction and exhibit a smooth surface with no distinct defects. The XRD and Raman results reveal that the phase transformation from tetragonal zirconia to monoclinic zirconia occurs with the increased crystal size and the water quenching treatment can significantly reduce the content of sodium zirconium phosphate [Na_9–4×Zr_x(PO₄)₃] in the final product. The growth mechanism of zirconia whiskers is supposed to be a dissolution-precipitation process. Since the sodium zirconium phosphate [Na_9–4×Zr_x(PO₄)₃] effectively promotes the dissolution of zirconia in liquid molten salt, zirconia can grow into zirconia whiskers according to its anisotropy.     

In situ synthesis of Al2O3–SiC powders via molten-salt-assisted aluminum/carbothermal reduction method

Al₂O₃–SiC composite powder (ASCP) was successfully synthesized using a novel molten-salt-assisted aluminum/carbothermal reduction (MS-ACTR) method with silica fume, aluminum powder, and carbon black as raw materials; NaCl–KCl was used as the molten salt medium. The effects of the synthesis temperature and salt-reactant ratio on the phase composition and microstructure were investigated. The results showed that the Al₂O₃–SiC content increased with an increase in molten salt temperature, and the salt–reactant ratio in the range of 1.5:1–2.5:1 had an impact on the fabrication of ASCP. The optimum condition for synthesizing ASCP from NaCl–KCl molten salt consisted of maintaining the temperature at 1573 K for 4 h. The chemical reaction thermodynamics and growth mechanism indicate that the molten salt plays an important role in the formation of SiC whiskers by following the vapor-solid growth mode in the MS-ACTR treatment. This study demonstrates that the addition of molten salt as a reaction medium is a promising approach for synthesizing high-melting-point composite powders at low temperatures.     

Molten hydroxides synthesis of hierarchical cobalt oxide nanostructure and its application as anode material for lithium ion batteries

Hierarchical Co₃O₄ nanostructure is synthesized via a self-assembled process in molten hydroxides. The morphologies, crystal structures and the phase transformation processes are analyzed by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. As an anode material for lithium ion batteries, the hierarchical Co₃O₄ exhibit an initial capacity of 1336 mAh g⁻¹ and a stable capacity of 680 mAh g⁻¹ over 50 cycles. More importantly, high rate capability is obtained at different current densities between 140 and 1120 mA g⁻¹. The improved electrochemical performance of Co₃O₄ could be attributed to the unique hierarchical nanostructure.     

Interfacial reaction behavior and bonding mechanism between liquid Sn and ZrO2 ceramic exposed in ultrasonic waves

Ultrasound-assisted dipping of ZrO₂ ceramics into molten Sn solder was performed to realize the low-temperature joining of ZrO₂ ceramics in this study. Scanning electron microscopy with energy dispersive spectrometer, X-ray diffraction and X-ray photoelectron spectroscopy were employed to study the effects of ultrasonic vibration on the microstructure of Sn/ZrO₂ interface, and to elucidate the joining mechanism between Sn coating layer and ZrO₂ ceramic. Results showed that, after ultrasonically dipping in molten Sn for 1200 s, a pure Sn solder layer with a thickness of approximately 8–9 µm was coated on the ZrO₂ surface. The Sn coating layer exhibited excellent metallurgic bonding with ZrO₂ ceramic. A nano-sized ZrSnO₄ ternary phase, which was beneficial to the smooth transition of the lattice from Sn solder to ZrO₂ ceramic, was formed at the Sn/ZrO₂ interface. The formation of ZrSnO₄ interlayer was ascribed to the acoustic cavitation induced high-temperature reaction of Sn, O and ZrO₂ at the molten Sn/ZrO₂ ceramic interface. The tested average shear strength of ZrO₂/Sn/ZrO₂ joints was approximately 32 MPa, and the shearing failure mainly took place within the Sn solder layer.     

Electrochemical and thermal behaviour of solid AgIAgIO3 and AgIAg3AsO4

Solid AgIAgIO₃ and AgIAg₃AsO₄ of various compositions were investigated by conductivity, thermal and electrochemical methods. Both systems show dependences on composition and temperature enabling determination of the activation energy of conductivity. Glassy phases are formed at appropriate rates of cooling of molten samples. By thermal analysis (DSC), the glass transition and crystallization processes of the glassy phases were identified. Processes of anodic and cathodic decomposition of the electrolyte were investigated. The energy of activation for the cathodic redox (Ag⁺ → Ag) process was determined. It was also shown how the capacity of the Pt/electrolyte phase boundary depends on the dc potential and ac frequency.     

Study on the ion-exchange copper-loaded antibacterial glasses

In this paper, copper-loaded antibacterial glasses were prepared by an ion-exchange method with CuSO₄ or CuCl as copper sources. The effects of different molten salts and ion exchange duration on the antibacterial properties of copper-loaded glasses were investigated. The experimental results show that the glasses exchanged with CuSO₄/Na₂SO₄ mixed molten salts have a higher surface copper loading than that with CuCl/KCl mixed molten salts. The sample color results from the reduced Cu⁰. The equilibrium between Cu⁺ and Cu⁰ is related to the Sn²⁺ ions existed in the lower surface of float glass. Finally, the antibacterial function of glass samples was found to be related to the charge transfer between Cu⁺+e^??Cu⁰, and has a proportional correlation with the content of Cu⁺ ions on the glass surface.     

Assessment of thermodynamic stability of sapphire in eutectic molten chloride environment

The continued development of molten salt reactors and concentrated solar power plants requires highly efficient and stable instruments that can efficiently monitor the chemical conditions of the molten salt during long-term operation in both the fuel and coolant/heat transfer fluid loops. Sapphire (Al₂O₃) fibers have shown tremendous potential due to inherent radiation resistance and a broader operational range of temperature. In this work, computational thermodynamic modeling (CALPHAD) using the ThermoCalc software in conjunction with the SGTE (Scientific Group Thermodata Europe) Molten Salts (SALT1) and Pure Substances (Pure5) databases is applied to understand the compatibility of Al₂O₃ fibers with NaCl-MgCl₂ eutectic molten salt in the temperature range of 1500–2500 K. The thermodynamic calculations show that sapphire fibers are not expected to be stable over the long-term when exposed to molten chloride salts at these temperatures. To improve the stability of these diagnostic fibers in molten salt environments, various pure metallic elements were evaluated as potential cladding materials for Al₂O₃ fibers. Based on the thermodynamic analysis, molybdenum (Mo) and nickel (Ni) could be effective cladding materials to enhance the stability of Al₂O₃ in NaCl-MgCl₂ chloride salt molten bath in the desired temperature range. Thus, the presence of Mo and Ni cladding can provide a protective coating against the corrosive molten salts, thus improving the stability of Al₂O₃. Additionally, it is also shown that Al₂O₃ remains stable up to 2400 K in the presence of preexisting Al₂MgO₄ and Al₂NiO₄ in the eutectic molten chloride bath environment.     

Significantly improved corrosion resistance of high-entropy rare-earth silicate multiphase ceramics against molten CMAS

To improve the ability of rare-earth (RE) silicates to resist molten calcium–magnesium–aluminosilicate (CMAS) at high temperature, a novel high-entropy (4RE_0.25)₂Si₂O₇/(4RE_0.25)₂SiO₅ (RE = Y, Yb, Er, and Sc) multiphase ceramic was prepared by a two-step process. During sintering, (4RE_0.25)₂SiO₅ can react with SiO₂ at the grain boundaries of (4RE_0.25)₂Si₂O₇, which can not only purify the grain boundary but also promote the growth of the original (4RE_0.25)₂Si₂O₇ grains, thereby significantly improving the ability to resist molten CMAS corrosion at high temperature. After corroding at 1500°C for 48 h, the reaction layer of the multiphase ceramic was only 55 μm thick. Our results confirm that the high-entropy RE silicate multiphase ceramics represent an effective way to improve the ability to resist molten CMAS corrosion at high temperature.     

Preparation and electrochemical properties of composite polymer electrolytes containing 1-ethyl-3-methylimidazolium tetrafluoroborate salts

The effects of room-temperature molten salt addition on the micro-structure and electrochemical properties of composite electrolytes (CEs) based on poly(ethylene oxide) (PEO)/ethylene carbonate (EC)/LiBF₄ were studied. Additional salt, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄), was found to influence the crystalline structure and heterogeneous morphology, resulting in changes to the ionic conductivity of the CE. The CE containing 0.2 mol of EMIBF₄ showed a small crystallinity, 27.9%. These CEs showed the highest ion conductivity, 3.1 × 10⁻⁴ S/cm, five times higher than that of the pristine PEO/EC/LiBF₄. This enhanced conductivity originated from the decreased crystallinity and improved ion transference due to a Lewis acid-base interaction. The CE containing 0.3 mol of EMIBF₄ showed decreased conductivity due to the lower mobility, reflecting the high viscosity of the molten salt.     

Synthesis of Anisotropic Na0.5Bi0.5TiO3 Crystals Using Different Topochemical Microcrystal Conversion Methods

Na_0.5Bi_0.5TiO₃ (NBT) platelets with high aspect ratio were synthesized from Na_0.5Bi_4.5Ti₄O₁₅ (NBIT) precursors via a topochemical microcrystal conversion in molten salt conditions. The effect of the synthesis parameters, such as the molten salt system, synthesis temperature, and the molar ratio of Na₂CO₃ and NBIT, was investigated. The results showed that NaCl–KCl molten salt environment and excess Na₂CO₃ played a positive role in the synthesis, square‐shaped NBT was obtained at 950°C in NaCl–KCl molten salt and a TiO₂‐free environment, and it was a suitable template candidate to achieve NBT‐based textured ceramics using the reactive template grain growth (RTGG) method.