Molten Salt Reaction Research Articles

Low Temperature Preparation of ZrC Coatings on C/C Composite via Molten Salt Reaction

Zirconium carbide (ZrC) coatings were prepared on C/C composite via molten salt reaction process at relatively low temperatures of 800-1000°C. During the reaction process, potassium fluorozirconate (K2ZrF6) played a role transporting zirconium from the molten salt to the C/C composite surface. Elevating reaction temperature increased the growth rate of coatings, simultaneously leaded to rougher coatings. The coatings growth rate increased with reaction time at first and then decreased gradually. The ZrC coatings prepared at 900°C for 5h was ~2m thickness. At the early stage, the low solubility of zirconium in the molten salt leaded to the low coatings growth rate. Secondly, the growth rate of the ZrC coatings was controlled by the chemical reaction between C/C composites and zirconium once zirconium was saturated in the molten salts. Thirdly, the control step of coatings formation turned into the diffusion of carbon through the formed ZrC coatings and which leaded to a gradual decrease of growth rate.

Preparation of niobium nanoparticles by sodiothermic reduction of Nb2O5 in molten salts

Niobium nanoparticles with high purity were prepared by a sodiothermic reduction process using Nb2O5 as the raw material, LiCl, NaCl, KCl and CaCl2 as the diluents and sodium as the reducing reagent. The effects of the different molten salt systems, CaCl2 content, reaction time, excessive sodium and reaction temperature on the characteristics of the obtained niobium powder were discussed. The as-prepared niobium nanoparticles under the optimum experimental conditions were obtained by sodiothermic reduction with 20% excessive sodium in the NaCl-52mol%CaCl2-2mol%Nb2O5 molten salts at 650 °C for 6 h, and the molar ratio of the oxygen element in Nb2O5 and the CaCl2 of the molten salts is less than 19.23% at 750 °C. Moreover, the particle size of niobium nanoparticles is ranged about 40∼240 nm with increasing of reaction temperature from 650 to 800 °C.

Eu3+‐activated Y2MoO6: a narrow band red‐emitting phosphor with strong near‐UV absorption

Near-UV excited narrow line red-emitting phosphors, Eu(3+)-activated Y2MoO6 systems, were synthesized using a simple molten salt reaction. The structure and photoluminescence characteristics were investigated using X-ray powder diffraction, UV-Vis absorption and fluorescent spectrophotometry. The excitation spectra show strong broad-band absorptions in the near-UV to blue light regions which match the radiation of near-UV light-emitting diode chips well. Under excitation of either near-UV or blue light, intense red emission with a main peak of 611 nm is observed, ascribed to the (5)D0-(7)F2 transition of Eu(3+) ions; the optimal doping concentration is 20 mol%. The chromaticity coordinates (x = 0.65, y = 0.34) of the as-obtained phosphor are very close to the National Television Standard Committee standard values (x = 0.67, y = 0.33). All these characteristics suggest that this material is a promising red-emitting phosphor candidate for white-LEDs based on near-UV LED chips.

A facile approach to nanoarchitectured three-dimensional graphene-based Li–Mn–O composite as high-power cathodes for Li-ion batteries

We report a facile method to prepare a nanoarchitectured lithium manganate/graphene (LMO/G) hybrid as a positive electrode for Li-ion batteries. The Mn2O3/graphene hybrid is synthesized by exfoliation of graphene sheets and deposition of Mn2O3 in a one-step electrochemical process, which is followed by lithiation in a molten salt reaction. There are several advantages of using the LMO/G as cathodes in Li-ion batteries: (1) the LMO/G electrode shows high specific capacities at high gravimetric current densities with excellent cycling stability, e.g., 84 mAh·g−1 during the 500th cycle at a discharge current density of 5625 mA·g−1 (~38.01 C capacity rating) in the voltage window of 3–4.5 V; (2) the LMO/G hybrid can buffer the Jahn–Teller effect, which depicts excellent Li storage properties at high current densities within a wider voltage window of 2–4.5 V, e.g., 93 mAh·g−1 during the 300th cycle at a discharge current density of 5625 mA·g−1 (~38.01 C). The wider operation voltage window can lead to increased theoretical capacity, e.g., 148 mAh·g−1 between 3 and 4.5 V and 296 mAh·g−1 between 2 and 4.5 V; (3) more importantly, it is found that the attachment of LMO onto graphene can help to reduce the dissolution of Mn2+ into the electrolyte, as indicated by the inductively coupled plasma (ICP) measurements, and which is mainly attributed to the large specific surface area of the graphene sheets.

Molten salt synthesis and luminescence properties of Bi4Si3O12 powders

In this paper, Bismuth silicate (Bi4Si3O12, BSO) powders were prepared by reaction in molten salts (NaCl and KCl) using Bi2O3 and SiO2 powders as raw materials. The effects of salt contents and excessive contents of Bi2O3 and SiO2 were characterized by X-ray diffraction and scanning electron microscopy. The properties of Bi4Si3O12 powders were analyzed via fluorescence spectroscopy. Forming mechanism of platelets was discussed. The experimental results suggest that Bi4Si3O12 powders are produced at 780 °C for 4 h with 40 wt% salts and 5 wt% excessive content of Bi2O3. The peaks of excitation spectrum and emission spectrum for BSO powders are separately located at 266 and 457.6 nm. Compared with crystal materials, the excitation spectrum and emission spectrum of Bi4Si3O12 powders indicate blue shift. Interface reacting mechanism can be used to explain the coarsening process of bismuth silicate platelets produced in molten salt synthesis. In addition, dissolution–precipitation mechanism also plays an important role in the synthesis of bismuth silicate platelets.

The Martensitic Transformation Behavior of the TiNi in TiNi/Ti<sub>2</sub>Ni Composite Synthesized in Molten Salts

In this paper the TiNi/Ti2Ni composite powders has been synthesized by the chemical reaction between titanium and nickel powders in high temperature molten salts. Results of the differential scanning calorimetry (DSC) confirmed the reverse martensitic transformation of the prepared TiNi powder in the TiNi/Ti2Ni composite powders. The backscatter electron images of the scanning microscopy (SEM) of the end-products before washing by distilled water showed that the synthesized TiNi/Ti2Ni composite particles were captured by the molten salts, which revealed the mechanism of the chemical reaction in molten salt.

Piezoelectric properties of rhombic LiNbO3 nanowires

Rhombic LiNbO3 nanowires along the c-axis were synthesized by using wire-like NH4Nb3O8 as the starting material based on a molten salt reaction with Li2CO3 powders in the KCl melt. Meanwhile, the as-synthesized LiNbO3 nanowires exhibit excellent piezoactivity. An effective piezoelectric coefficient of around 100 pm V−1 could be obtained.

Facile molten-salt synthesis of double perovskite La2BMnO6 nanoparticles

Crystalline double perovskite La2BMnO6 (B = Ni and Co) nanoparticles with an average grain size of ∼64 nm were successfully prepared using a facile, environmentally friendly, scalable molten-salt reaction at 700 °C in air. Their composition and structural and magnetic properties have been characterized.

Removing of Si in the NaOH Molten Salt Reaction of Titanium Slag to Produce TiO<sub>2</sub>

NaOH solution was utilized in the molten salt reaction of titanium slag for investigating desiliconization effects. The thermodynamic behaviors of Si in the reaction system was examined to explore the impacts of molten salt reaction conditions on the conversion rates of the foreign substance Si and the target element Ti. On this basis, the influences of NaOH concentration, liquid-solid ratio, cleaning temperature and cleaning time on Si removing rate were discussed. The experimental results showed that, Si reacted with NaOH to produce sodium silicate was feasible in terms of thermodynamics within the temperature interval 400-1000K. 3Na2O•2SiO2, 2Na2O•SiO2 could stably exist under high reaction temperature. As the reaction time extended and temperature rose, the conversion rate of Si was increasing. In the process of Si removing by NaOH cleaning of molten salt reaction products, as NaOH concentration, liquid-solid ratio, cleaning temperature and cleaning time increased, Si removing rate became larger. The optimum alkali cleaning conditions were: NaOH concentration 150g/l, liquid-solid ratio 3:1, cleaning temperature 50°C and cleaning time 60min, then the desiliconization rate reached 61.16%.

Study on the transformation from NaCl-type Na 2TiO 3 to layered titanate

NaCl-type crystal structure sodium titanate (Na 2TiO 3), which exhibits a unit cell parameter of a=4.49 Å, was obtained by high temperature molten salt reaction. An intermediate phase product with layered structure was prepared by leaching the obtained Na 2TiO 3. We propose that the layered titanate structure is composed of Na 2TiO 3 and H 2O, corresponding to the host-layer and guest-substance, respectively. Furthermore, the crystal structures of layered titanate were optimized by the density functional theory (DFT). This indicates that water molecules are distributed in an orderly manner in the interlayer through the formation of hydrogen-bonded chain. Moreover, the position of the adjacent lamella translates to c/2 along the c-axis after the intercalation of water.

Facile Morphology-Controlled Synthesis and Luminescence Properties of BaMoO4:Eu3+ Microparticles and Micro-Rods Obtained by a Molten-Salt Reaction Route

This work focuses on the synthesis of morphology-controlled BaMoO4:Eu3+ micro-crystals such as microparticles and micro-rods using a facile molten salt method, and their morphology, structural characterization, and luminescent properties were comparatively investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescence spectra. The molten salt method synthesized products from a reaction of BaMoO4 precursor obtained by a co-precipitation method of BaCl2 and Na2MoO4 with an eutectic salt mixture of NaCl-KCl at 700 degrees C. Detailed studies revealed that the formation of the different morphologies of the micro-crystals was strongly dependent on the weight ratio of the salt (NaCl-KCl) to the BaMoO4 precursor, and the formation mechanism of the products in the present molten salt system was also investigated. Based on the investigations of the photoluminescence properties, the samples with different morphologies prepared by the molten salt method had the strongest red emission at 615 nm, corresponding to the Eu3+ 5D0-7F2 transition in the BaMoO4 host lattice, and the emission intensity of BaMoO4:Eu3+ microparticles was stronger than that of BaMoO4:Eu3+ micro-rods.

Topochemical Synthesis of Sodium Metal Phosphate Olivines for Sodium-Ion Batteries

New metastable olivine phases of sodium metal phosphates, Na[Mn1–xMx]PO4 (M = Fe, Ca, Mg), nanorods are synthesized by a simple solid-state reaction at low temperature (≤100 °C) by means of a topotactic molten salt reaction that converts NH4[Mn1–xMx]PO4•H2O (M = Fe, Ca, Mg) to Na[Mn1–xMx]PO4. Their crystal structures are characterized via XRD Rietveld refinement and electron diffraction. A full range of solid solution behavior was observed for olivine Na1–xMn0.5Fe0.5PO4, in contrast to that of LiMPO4 (M = Fe, Mn) olivine materials, and is ascribed to ion size effects. The solid solution behavior of NaMn0.5Fe0.5PO4 was confirmed by electrochemical characterization.

Synthesis of Single-Crystalline Alkaline-Earth Metal Manganites Nanoribbons via Cation Exchange

Single-crystalline alkaline-earth metal manganites CaMn3O6, SrMn3O6–x and Ba6Mn24O48 nanoribbons have been successfully synthesized by a facile ion-exchange approach based on molten-salt reaction between Na0.44MnO2 nanoribbons and CaCl2, SrCl2, and BaCl2. All of these as-prepared nanoribbons are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Taking the synthesis of single-crystalline SrMn3O6–x nanoribbons as an example, we researched in detail the conversion process from Na0.44MnO2 nanoribbons to SrMn3O6–x nanoribbons. Our results indicate that Na0.44MnO2 nanoribbons serve as the precursor template and the final products are obtained via ion-exchange reaction. Although there is a complete cation exchange, a change in stoichiometry, and a change in crystal structure, the morphology is nearly perfectly maintained. The synthetic method is thought to be a self-sacrificing templat...

First Experimental Evidence of a New D4-AgCoO2 Delafossite Stacking

A new polytype of AgCoO(2) delafossite has been prepared from the ordered OP4-(Li/Na)CoO(2) layered compound using ion-exchange reaction in molten salts. As expected from the structural model assuming a topotactic process, the lamellar structure of this new polytype is an alternate combination of the already known 2H and 3R delafossite polytypes. It crystallizes in the P6(3)/mmc space group with cell parameters a(hex.) = 2.871(1) Å and c(hex.) = 24.448(1) Å. Thermal stability, morphology characterization, and electrical properties are reported here and compared with those of the 2H and 3R AgCoO(2) polytypes.

Lightly doping Ca2+ in perovskite PrCoO3 for tailored spin states and electrical properties

A series of Pr(1-x)Ca(x)CoO(3) samples were prepared using a novel molten salt reaction that is convenient to obtain single phases avoiding aggregates compared to conventional solid state reactions. The formation reaction was monitored by X-ray diffraction combined with thermal analysis, and all samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and alternating current impedance. It is demonstrated that all Pr(1-x)Ca(x)CoO(3) samples crystallized in a pure orthorhombic perovskite structure. By increasing the doping level, the symmetry of the orthorhombic structure was enhanced, and is followed by an increase in the population of Co(3+) in the intermediate spin state. All samples exhibited typical semiconducting behavior, showing conductivities highly dependent on the Ca(2+) doping. The conduction for x = 0 shows a simple thermal activated process, which changed into a Mott's variable range hopping mechanism for x > 0. By increasing the Ca(2+) doping level, the relevant activation energy is decreased, while the density of the localized electronic state is increased.

Preparation and Visible Light Photocatalytic Activity of Titanium Dioxide Coated Multiwalled Carbon Nanotubes

Titanium dioxide coated multiwalled carbon nanotubes (MWCNTs) composite photocatalysts were prepared by the controllable oxidation of titanium carbide coated MWCNTs obtained by the molten salt method using MWCNTs as a reaction template and metal titanium powder as a titanium source. The effects of the molten salt reaction temperature, the molar ratio of MWCNTs to titanium powder, and the oxidation temperature on the structure and morphology of the products were investigated. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photodegra- dation of a methylene blue (MB) solution was used to evaluate the photocatalytic activity of the catalyst under visible light irradiation (λ420 nm). The results suggest that the TiO2 coated MWCNTs keep the similar fibred morphology with the pristine MWCNTs. Uniform and fine well-dispersed TiO2 coatings on the surface of MWCNTs closely contact with the MWCNTs support and Ti-O-C chemical bonds form between them. The prepared TiO2/MWCNTs photocatalyst shows higher visible light photocatalytic activity because the MWCNTs increase the adsorption of methylene blue on the photocatalyst and an impurity state is formed close to the valence band of titanium dioxide, which can enhance the absorption and utilization of solar energy.

Reaction Sintering of NiTi-Ti<sub>2</sub>Ni-TiC under Cubic High Pressure

In this paper, NiTi-Ti2Ni-TiC composite powders were first prepared by in-situ reaction in molten salt and then sintered by a cubic high pressure apparatus under 8 GPa to produce bulk composite material at a short time. It was found that the composite was composed of TiC particles embedded in NiTi-Ti2Ni matrix, in which the Ti2Ni encapsulated TiC particles. The martensitic transformation of the NiTi matrix was evidenced by differential scanning calorimetry analysis. The research on the sintering mechanism shows that there may be a reaction like TiC +Ti2Ni 􀃆 Ti2C + NiTi existing under the pressure up to 8 GPa

Molten salt synthesis of tungsten carbide powder using a mechanically activated powder

A novel method for synthesizing ceramic powders in molten salt was introduced in this paper. Unlike traditional mechanochemical process, the novel method is based on mechanical alloying followed by chemical reaction in liquid phase (molten salt). The reaction temperature to synthesize tungsten carbide in molten salt was 1000 °C. Results in this paper showed that W 2C and WC powder could be successfully synthesized by the method. Under raised reaction conditions, there was a transformation from W 2C to WC. The mechanism of the reaction in molten salt was discussed finally.

Synthesis of TiAl3-Al2O3 Composite Particles by Chemical Reactions in Molten Salts

In this study, mechanically activated Al/TiO2 powders were heated in molten (NaCl +KCl) salts to obtain TiAl3-Al2O3 composite powders. The morphology and phase composition of the samples were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. It was shown that the milled powders reacted completely after 15 min at 800°C. Further investigations indicated that synthesized TiAl3-Al2O3 powders have a particle size of 400 nm to 800 nm. The consolidation of synthesized powders led to the formation of a composite structure composed of a continuous network of Al2O3 phase interpenetrated by a continuous network of TiAl3 phase.

Ti Metallization of Cf/SiC Composites Surface by Molten Salt Reaction

Abstract Ti metallized coating was prepared on the surface of carbon fiber reinforced silicon carbide matrix (Cf/SiC) composite by molten salt reaction to make joining the composite with high melt point metals such as Ti. The morphologies and compositions of Ti metallized coating were analyzed by SEM and EDS. The phase components were assessed by XRD. The wettability of the solder was measured by quantitative metallography. The results show that Ti metallized coating is uniform and dense, and bound with the matrix closely. Ti can infiltrate into the gaps of the fibers, and cover the surfaces of the Cf/SiC composite. The main phases of the metalized coating consist of TiC and Ti5Si3. There are three transition layers between SiC and the metallized, i. e. Ti5Si3 layer, TiC layer and Ti5Si3 layer. The wettability of Cf/SiC composites surface to Ti is greatly improved by metallization, and the contact angle is deceased from 153.9° to 13.2° at 950 °C.