Molten Salt Treatment Research Articles

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 [Na9–4×Zrx(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 [Na9–4×Zrx(PO4)3] effectively promotes the dissolution of zirconia in liquid molten salt, zirconia can grow into zirconia whiskers according to its anisotropy.

Evaluation and Suppression of <i>Microcystis aeruginosa</i> by Photocatalyst Coatings with Visible Light Photocatalytic Activity

Photocatalyst coatings had been successfully fabricated by molten salt treatment at 673 K for 3 h for titanium (Ti) coatings, which coated on alumina (Al2O3) balls by mechanical coating technique with Ti powder. The influence of molten salt treatment on the formed compounds, surface morphology and photocatalytic activity under visible light irradiation on degradation of MB solution and suppression of Microcystis aeruginosa of photocatalyst coatings was investigated. XRD results show that potassium titanate (K2Ti6O13) forms on the surface of Ti coatings during molten salt treatment. The visible light photocatalytic activity of photocatalyst coatings has been effectively enhanced by molten salt treatment.

Molten-salt treatment of waste biomass for preparation of carbon with enhanced capacitive properties and electrocatalytic activity towards oxygen reduction.

Carbon powders are building blocks for electrochemical energy storage/conversion devices. Green, cost-affordable and facile preparation of carbon with applicable electrochemical properties is therefore essential for effective utilization of fluctuating renewable energy. Herein, the preparation of carbon nanoflakes via impregnation of waste biomass i.e. boiled coffee beans in molten Na2CO3-K2CO3 (with equal mass) at 800 °C and molten CaCl2 at 850 °C is reported. The microstructure and surface chemistry of the obtained carbons are specified. The correlations between synthetic conditions and microstructure/surface chemistry of the obtained carbons are rationalized. The derived carbon nanosheets are tested and compared as active materials for supercapacitors in a configuration of symmetric full cells in 1 M MeEt3NBF4 in acetonitrile and electrocatalysts towards the oxygen reduction reaction (ORR) in O2-saturated 0.1 M aqueous KOH. Despite the lower surface area, the carbon nanosheets derived in molten Na2CO3-K2CO3 exhibit enhanced capacitive properties and electrocatalytic ORR activity. The present study highlights the importance of thermal media on the microstructure, surface chemistry and electrochemistry of carbon from biomass.

Fabrication of the photocatalyst thin films of nano-structured potassium titanate by molten salt treatment and its photocatalytic activity

The thin films of potassium titanate photocatalyst were fabricated by molten salt treatment and oxidation in air, using TiO2 thin films formed on Al2O3 balls as the substrate. The thin films were characterized by SEM, EDS, and XRD. The photocatalytic activity was evaluated by measuring the degradation rate of a methylene blue (MB) solution. The formation of nano-structured potassium titanate in the molten salt mixture and the influence on photocatalytic activity are discussed. The results show that the molten salt treatment was simple and useful to fabricate the thin films of nano-structured potassium titanate. The nano-lamellar potassium titanate with amorphous was formed, which is closely related to the carbonate ion in the molten salt mixture. 6-potassium titanate with nano-needle crystals was formed by crystallizing the potassium titanate during oxidation in air. The potassium titanate with the nano-lamellar had high adsorptivity, whereas 6-potassium titanate with nano-needle crystals had high photocatalytic activity.

Molten salt‐assisted template synthesis of lithium‐rich layered oxide 0.3Li 2 MnO 3 ·0.7LiNi 1/3 Co 1/3 Mn 1/3 O 2 nanorods as lithium‐ion battery cathode

Lithium-rich layered oxide 0.3Li2MnO3·0.7LiNi1/3Co1/3Mn1/3O2 nanorods have been prepared by a KCl molten salt-assisted template route. The nanorods can well retain the rod-like structure of a β-MnO2 template, and have the length of several hundred nanometres and diameters of about one hundred nanometres. In comparison with the sample obtained from immediate solid-state reaction, the molten salt treatment can help improve the phase purity and decrease the particle size. As a lithium-ion battery cathode, the KCl-treated nanorods deliver an initial discharge capacity of 242.9 mAh g−1 with a high Coulombic efficiency of 83.6% at a current density of 20 mA g−1 within 2.0–4.7 V. After 60 cycles, a discharge capacity of 150.8 mAh g−1 can be retained at 0.5 C. Even at a high charge–discharge rate of 4 C (800 mA g−1), a stable capacity of 104.2 mAh g−1 can be reached, while the sample obtained from solid-state reaction only delivers an initial discharge capacity of 179.1 mAh g−1at 20 mA g−1.

溶融塩処理によるナノ光触媒薄膜の作製と高機能化

溶融塩処理によるナノ光触媒薄膜の作製と高機能化

Performance Optimization of Li1+x(Ni0.15Co0.15Mn0.70)O2.275+x/2 by Post Molten Salt Treatment as Cathode Material for Li-Ion Batteries

Nanostructure lithium rich manganese based cathode materials are successfully synthesized and treated by post molten salt treatment method to optimize their electrochemical performance. The molten salt treatment process has a great influence on the microstructure, cycle performance, rate capacity and high temperature electrochemical performance of the resulted cathode materials Li1+x(Ni0.15Co0.15Mn0.70)O2.275+x/2 (0.6 ≤ x ≤ 0.9). The sample after 4 hours of molten salt treatment displayed the highest crystallinity, best cycling performance and rate capacity. Li1.6(Ni0.15Co0.15Mn0.70)O2.575 cathode materials treated in LiCl molten salt at 750°C for 4 hours displayed 218.8 mAhg−1 discharge capacity after 40 cycles in voltage range 2.5 ∼ 4.8 V at 25°C, which is 36.2% higher than pristine sample. The capacity retention for Li1.6(Ni0.15Co0.15Mn0.70)O2.575 cathode is also improved by the molten salt treatment process, which is 6.6% higher than the pristine sample.

Fabrication of Highly Crystalline SnNb2O6 Shell with a Visible-Light Response on a NaNbO3 Nanowire Core

A visible-light-absorbing SnNb2O6 shell with high crystallinity was successfully fabricated on a NaNbO3 nanowire through a molten salt treatment of the NaNbO3 nanowire of the starting material with SnCl2, whereas the fabrication was not successful on the TT phase of a niobia nanowire. The difference will come from the formation processes of SnNb2O6 crystals (ion-exchange reaction vs thermally induced crystallization reaction). The core/shell nanowire obtained from NaNbO3 showed photocatalytic activity comparable to that of H2 evolution in the presence of an electron donor under visible-light irradiation (λ > 420 nm), compared with the corresponding bulky counterpart.

Chemical mixing in molten-salt for preparation of high-performance spinel lithium manganese oxides: Duplication of morphology from nanostructured MnO2 precursors to targeting materials

The chemical mixing strategy involving molten-salt lithiation at 450°C and post-annealing at 800°C on formation of morphological replica of spinel lithium manganese oxides from nanostructured potassium-contained manganese oxides has been discussed in terms of influences of Li/Mn stoichiometry during molten-salt mixing, crystal phases and microstructure of precursory nanostructured MnO2. It is exhibited that α-MnO2 with suitable-sized one-dimensional tunnels in lattices facilitates the formation of chemical-level mixture of Li, Mn and O, and ensuring morphological retention after molten-salt lithiation. Compared to α-MnO2, the interlayer gap in δ-MnO2 crystal lattices is too large to ensure chemical-level mixture or morphology retention. It is suggested that the precursory Li/Mn ratio during molten-salt treatment should be prudently controlled, aiming to restraining excessive surface-absorption of Li and facilitating an effective Li/K exchange process. Also, one-dimensional nanoarchitectured precursory manganese oxide is advantageous over its nanoparticle counterparts on morphological retention after post-annealing process, due to its the enhanced stability against large local strains. Electrochemical measurements show that the prepared phase-pure and highly crystalline spinel-typed lithium manganese oxide nanorods in morphological replica of precursory α-MnO2 nanorods deliver a reversible specific capacity 94mAhg−1 upon 200 times of charge–discharge cycling at a rate of 10C.

Improvement of the dielectric properties of BaTiO3 powder-polymer composite using molten salt treatment

The dielectric films consisted of the barium titanate (BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) powder particle and the polymer were fabricated using the sodium chloride (NaCl)-flux treatment to investigate the effect of the molten salt on the dielectric properties of the BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles. The BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles for the NaCl-flux treatment were prepared by calcining the mixture of the BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and the NaCl at the various temperatures. The NaCl-flux treated BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles showed the smooth surface and high crystallinity compared to the non-treated BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles, because the BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles were recrystallized by NaCl-flux treatment. In addition, high dielectric performances of a 20% increase in the dielectric constant, a 40% decrease in the dielectric loss, and a 280% increase in the dielectric strength were achieved. The dielectric films of the NaCl-flux treated BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles could induce the high dielectric performances due to the improvement of the crystallinity with highly packing density.

Molten Salt Treatment of Sodium Niobate Nanowires Affording Valence Band-Controlled (AgNbO&lt;SUB&gt;3&lt;/SUB&gt;)-(NaNbO&lt;SUB&gt;3&lt;/SUB&gt;) Nanowires

Molten Salt Treatment of Sodium Niobate Nanowires Affording Valence Band-Controlled (AgNbO&lt;SUB&gt;3&lt;/SUB&gt;)-(NaNbO&lt;SUB&gt;3&lt;/SUB&gt;) Nanowires

Formation of an aluminum-alloyed coating on AZ91D magnesium alloy in molten salts at lower temperature

An aluminum-alloyed coating was formed on an AZ91D magnesium alloy in molten salts containing AlCl3 at a lower temperature of 380°C. The microstructure and phase constitution of the alloyed layer were investigated by optical microscopy, scanning electron microscopy, energy dispersive spectrum and X-ray diffraction. The nano-hardness of the coating was studied by nanoindentation associated with scanning probe microscopy. The corrosion resistance of the coated specimen was evaluated in a 3.5wt.% NaCl solution by electrochemical impedance spectroscopy and cyclic potentiodynamic polarization. The results show that the aluminum-alloyed coating consists of Mg2Al3 and Mg17Al12 intermetallic layers. The formation of the coating is dictated by the negative standard free energy of the reaction: 2AlCl3+3Mg=3MgCl2+2Al. This process is associated with a displacement reaction mechanism and diffusion process that takes place during the molten salt treatment. High activity of Al elements in molten salts contributes to the lower temperature formation of the Al-alloyed coating. The alloyed coating markedly improves the hardness as well as the corrosion resistance of the alloy in comparison with the untreated AZ91D magnesium alloy, which is attributed to the formation of the intermetallic compounds.

Synthesis of anisotropic micro-crystals of cubic Na0.5Bi0.5TiO3

A novel method of synthesizing Na0.5Bi0.5TiO3 anisotropic micro-crystals is reported. Its crystal structure is cubic above 520 °C and still pseudo cubic at the temperature below. Platelet crystals of Na0.5Bi0.5TiO3 were converted from Bi4Ti3O12 micro-crystals. Platelet Bi4Ti3O12 crystals were produced by molten salt synthesis. They were subjected to the second molten salt treatment with Na2CO3 and TiO2 at 800–1200 °C. Bi4Ti3O12 crystals were successfully transformed into Na0.5Bi0.5TiO3 crystals with an inherited platelet shape. Na0.5Bi0.5TiO3 crystals have a (h00) plane parallel to the platelet.

Evaluation of a Ag∣Ag + reference electrode for use in room temperature ionic liquids

Interest continues to grow in the use of room temperature ionic liquids (RTILs) as electrolytes in a range of electrochemical applications, such as lithium batteries, supercapacitors and dye-sensitized solar cells. Underpinning this growth, investigations into the electrochemical behaviour of RTILs and RTIL-based systems rely on accurate and precise data on the potentials of redox processes. While most researchers have continued the practice (developed with non-aqueous solvents) of reporting potentials relative to one of the metal-organic standards (such as ferrocene), little attention has been given to the development of a reliable reference electrode, based on an ionic liquid. Such an electrode is always valuable, especially in situations where addition of a reference material is not possible. We report a Ag∣Ag + reference electrode, incorporating a known concentration of silver trifluoromethanesulfonate (AgTf) in 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (P 14TFSI), which provides a stable and reproducible reference potential. Voltammetric monitoring of the redox potentials for ferrocene and cobalticinium hexafluorophosphate have shown that the electrode Ag∣Ag +(10 mM AgTf, P 14TFSI) is stable to within a millivolt, over a period of around three weeks, when used in an argon atmosphere at room temperature. Higher concentrations of silver ion reveal close-to-Nernstian behaviour. All Ag∣Ag + configurations were significantly more stable than a silver wire quasi-reference electrode, even when the latter was separated in a salt-bridge. Voltammetric data recorded in a range of different ionic liquids, against the Ag∣Ag + (10 mM AgTf, P 14TFSI) reference electrode, produced apparent junction potentials of a few tens of mV. Changes in sign of the junction potential are usefully discussed in terms of the relative mobilities of the anions and cations present, while the magnitude can be discussed in the terms of a classic molten salt treatment.

The removal of encapsulated catalyst particles from carbon nanotubes using molten salts

A novel method, using molten salts, is described for the removal of encapsulated nickel catalyst particles from multi-walled carbon nanotubes. The multi-walled carbon nanotubes, synthesised by the decomposition of methane and hydrogen over a NiO/SiO 2 aerogel catalyst, were treated in a LiCl–KCl eutectic molten salt and subsequently by hydrochloric acid to remove the nickel catalyst particles. The influence of the molten salt treatment on the microstructure of the carbon nanotubes was investigated by XRD, SEM and TEM analyses. The molten salt treatment promoted uncapping of the carbon capsules and the formation of strip-shaped carbon fragments. It was found that the hydrochloric acid treatment could then remove the nickel particles from the broken carbon capsules which was not possible prior to the molten salt treatment. The stability of carbon nanotubes in the molten salt is closely related to their ordered structure.

Effect of molten salt treatment on descaling behavior of 410 SS in sulfuric acid solution

The effect of molten salt treatment on the modification of scale properties of annealed 410 SS and subsequent descaling behavior in sulfuric acid was investigated. The experimental results showed that the scale formed on annealed 410 SS was mainly composed of (Cr, Fe) 3O 4 and Cr 2O 3. After molten salt treatment, only Fe 3O 4, was found remained on the surface. Potential decay was noticed during pickling in sulfuric acid, which was associated with the scale removing process. Furthermore, the activation time ( τ) required for complete descaling decreased with increasing concentration and temperature of sulfuric acid.

Occlusion of KNO 3 and NH 4NO 3 in natural zeolites

The capacity of natural zeolites to occlude ammonium nitrate and potassium nitrate by molten salt treatment has been determined, and the salt-occluded zeolites have been characterized. Molten salt treatment resulted in changes of overall and relative intensities of peaks in X-ray diffractograms of zeolites. The presence of occluded salt in zeolites was confirmed by a i.r. absorption band around 1,390 cm 1 , exothermic response at 280°C in DTA curve, and type-III nitrogen adsorption/desorption isotherms showing type-H3 hysteresis. The occluded nitrate contents of natural zeolites increased in the following order: erionite > clinoptilolite > chabazite > phillipsite with molten potassium nitrate treatment, and phillipsite > erionite ⩾ chabazite > clinoptilolite with molten ammonium nitrate treatment. The present study shows that the capacity of natural zeolites to store nutrients can be increased by salt occlusion and that these occluded zeolites are potential candidates as slow-release fertilizers.

Preparation of Y 3Al5 O 12 ‐ Based Phosphor Powders

Phosphor materials are important in cathode ray tube (CRT) and electroluminescence display technologies. Phosphor materials based on garnet are used extensively because of their high optical emission intensity and long life. In this study, we prepared cerium‐doped YAG powders by freeze drying of precursor solutions and by mechanically mixing the constituent oxide powders. The freeze dried powders, due to a homogeneous distribution of cations in their precursor solutions, formed the garnet phase at 1300°C, 300°C lower than that required for the constituent oxide mixtures, and they also had a higher optical emission intensity than those prepared from oxide mixtures. Furthermore, Ce‐doped powder was heat‐treated in molten salt to increase the particle size and to give a more equiaxed particle shape such that their subsequent packing density in CRT faceplate could be increased. However, the molten salt treatment introduced a small amount of the distorted tetragonal phase among the cubic garnet phase and decreased the optical emission intensity.