Papers by Keyword: Molten Salt

Abstract: The solid solution of lead-free (Ba_0.4Sr_0.4Ca_0.2) (Zr_0.05Ti_0.95) O₃ (BSCZT) ceramics were prepared from the seed induced method. The Ba_0.6Sr_0.4TiO₃ (BST) were used as the seed crystals, they were prepared using the molten salt technique. The phase formation was examined using the X-ray diffraction technique (XRD). It was found that the single phase perovskite structure of BST was obtained at a temperature of 800°C. The ceramics were prepared using the conventional solid state reaction by adding of BST seed crystals at 2.5, 5, 7.5 and 10 mol%. The structure showed that a single phase perovskite was obtained after sintered at 1400 °C. This work confirmed that BST seed crystal successfully diffused into BSCZT ceramic and the BSCZT ceramic with a seed crystal showed higher dielectric than the BSCZT ceramic without seed crystals.

Abstract: Upconversion luminescence materials have recently received attentions because of theirs light conversion ability from infrared into visible and ultraviolet light. In this work, alkaline yttrium fluoride doped by ytterbium and thulium (AYF₄: 20%Yb³⁺, 0.5%Tm³⁺) were synthesized by molten salt method at 400 °C for 2 hours with different eutectic molten salts, i.e. NaNO₃-KNO₃, NaNO₃-LiNO₃, KNO₃-LiNO₃, and NaNO₃-KNO₃-LiNO₃. Pure hexagonal NaYF₄ microrods were successfully synthesized using eutectic NaNO₃-KNO₃ molten salt. Under 980 nm laser diode excitation, upconversion luminescence in both visible and ultraviolet region was clearly observed. On the other hand, for the use of other eutectic molten salts containing LiNO₃, the mixed phases of tetragonal LiYF₄ and orthorhombic Y₆O₅F₈ were obtained. These powders emitted only visible light with 10 times lower intensity than the hexagonal NaYF₄ microrods synthesized using NaNO₃-KNO₃.

Abstract: Free Ti/Si/C powder mixtures with or without molten salt were heated under vacuum with various schedules. The effect of molten salt during synthesis on the morphology and phase composition of Ti₃SiC₂ powders were investigated. The combustion powders were analyzed by DSC, XRD, SEM and EDS. The results indicated that the existence of molten salt could promote the reaction process and decrease the synthesis temperature. The Ti₃SiC₂ powders obtained by molten salt method were uniform and well dispersive. The content of Ti₃SiC₂ phase was influenced by salt/powders ratio and molding pressure. The appropriate salt/powders ratio and pre-press pressure were 1:1and 100 MPa, respectively.

Abstract: In this study, a new green approach has been developed for the recovery of tungsten by using tungsten carbide (WC) scrap material as consumable anode in LiCl-KCl molten salts at 773 K to produce metallic tungsten. The feasibility of the direct electrochemical dissolution of WC anode into metallic tungsten was evaluated based on the experimental verifications and electrochemical methods. The effects of the main technical parameters, including the cell voltage, electrolysis time and electrolysis temperature, on the dissolved condition of anode were studied and the optimal anode parameters were obtained. It was found that a large electrolytic voltage, high electrolytic temperature and long electrolysis time would be favorable for the dissolved state of the tungsten carbide anode under the same conditions. The cathode product was analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the tungsten particles with a diameter of 100 nm could be prepared by this process in a molten salt bath. Linear sweep voltammetry was applied to investigate the dissolution of WC anode, and showed that the WC scrap material could be used as consumable anode to produce tungsten powder. Other electrochemical techniques including cyclic voltammetry , square-wave voltammetry and chronopotentiometry were employed to explore the electrochemical properties of tungsten ion derived from WC anode in LiCl-KCl melts. These results confirmed that electroreduction of tungsten ion in the melts proceeded in one step with four exchanged electrons.

Abstract: In the present work, the molten-salt method was applied to synthesize 0.948K_0.5Na_0.5NbO₃–0.052LiSbO₃ powder for the first time. Characteristics of the powder were investigated. Based on X-ray diffraction technique, pure perovskite phase was observed at a calcination temperature of 700 oC which is lower than that required by the conventional solid-state reaction technique for ∼200 oC. Raman spectroscopy technique showed that the powder had an orthorhombic symmetry which consistent with the X-ray diffraction results. The powder exhibited very fine grain with narrow size distribution. Particle size of the obtained powders increased with increasing calcination temperature. Therefore, the molten-salt method is a simple and effective method to synthesize 0.948K_0.5Na_0.5NbO₃ – 0.052LiSbO₃ powder.

Abstract: Rare earth silicate based M_nMgSi₂O_5+n (M = Ca, Sr or Ba and n=1-2) phosphors, have attracted interest of researchers due to their high efficiency as a host, excellent thermal and chemical stability and high brightness adding to their low cost. These phosphors showed great potential in various applications such as fluorescent lamps, white light emitting diodes, and display components. High temperature solid-state reactions are usually employed to synthesize those compounds. This paper proposes an alternative method of obtaining nanophosphor host based on Eu-doped CaMgSi₂O₆ (CMS:Eu), persistent luminescence phosphor. Sol gel technique combined to a modified molten salt method was used. The resulted powder was calcined for 3h under an atmosphere of 5% H₂ and 95% Ar₂. Phase identification by XRD and the measurements of photoluminescence (PL) and photoluminescence excitation (PLE) were performed. Single phased CMS:Eu with persistent luminescence characteristics was prepared.

Abstract: Abstract. The forsterite thermal insulation materials were synthesized by molten salt method with forsterite and NaCl-Na₂CO₃ salt, sintered at 1000°C, 1050 °C, 1100°C and 1150°C respectively. Studying complex pore structures is the key to understand the mechanism of pore-forming. The mechanism of the variation in the heterogeneous pore structure was analyzed based on differential thermal analysis, thermogravimetry, high-pressure mercury intrusion porosimetry and scanning electron microscope. The results show that the NaCl-Na₂CO₃ salt play the role of promoting sintering in liquid environment at high temperature as well as forming pore as placeholder. The mechanism of pore-forming contains three parts: the pores < 6.6 μm are mainly formed by sodium carbonate decomposition under high temperature and vapor pressure; the forming way of 6.6~66μm derives from carbonate decomposition and salt evaporate jointly; The salt stay in the slender and curved space shaped by the rearrangement of forsterite particles, forms the pore diameter of > 66 μm after salt dissolves in water.

Abstract: Lead-free (K_0.5Na_0.5)NbO₃ (KNN) piezoelectric ceramics were studied and synthesized by the seed-induced method. NaNbO₃ crystal was used as seed and prepared by molten salt synthesis (MSS). The average particles size of NaNbO₃ seed crystal was about 1-3 mm. Then, the NaNbO₃ seed was mixed with KNN powder and ball milled for 24 h. The mixed powder was calcined at 700-900 °C and sintered at 1100 °C. The phase structure and morphology of the ceramics were investigated by X-ray diffraction and scanning electron microscope and the electrical properties were studied. The results indicated that all samples showed a pure perovskite phase. The highest density of the ceramic was 93% compared to the theoretical density. The results showed that NaNbO₃seed crystal improved piezoelectric properties of KNN ceramics.

Abstract: The study was conducted to find out the effect of particle sizes of BaTiO₃ (BT) seed on the microstructure and electrical properties of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) ceramics. The BT seeds were prepared by the molten salt method. Results indicated that the BT seed powder showed a single pure perovskite phase when using a low temperature of ~750°C. The particle sizes of BT seeds increased from ~381 to ~600 nm with increasing heating temperatures from 750 to 900°C. After that, the different BT seeds were mixed with BaCO₃, CaCo₃, ZrO₂ and TiO₃ via the solid state reaction method. The mixed powder was calcined and sintered at 1200 °C for 2 h and 1450 °C for 4 h, respectively. The microstructure, phase formation and electrical properties were investigated. All ceramic samples showed a pure perovskite phase. The density and average grain size values of ceramics were in the range of 5.36-5.47 g/cm³ and 9.83-11.86 μm, respectively. The highest values of dielectric constant (ε_r), piezoelectric constant (d₃₃) were 3393 and 452 pC/N, respectively which obtained at the sample of BT-seed size 372 nm doped.

Abstract: The effect of particle sizes of CaZrO₃ (CZ) nanocrystal on the phase structure, microstructure and electrical properties of Ba_0.85Ca_0.15Zr_0.10Ti_0.90O₃ (BCZT) was studied. The CaCO₃ and ZrO₂ were used as starting materials for CaZrO₃ (CZ) seeds synthesized by the molten-salt method. The results were found that the CZ powder has a pure perovskite with the particle size about 370 to 460 nm. Then the CZ nanocrystals were mixed with the metal oxides BaCO₃, CaCO₃, ZrO₂ and TiO₂ by mixed oxide method. The phase structure, microstructure and electrical properties of BCZT ceramic were investigated as a function of particle size and concentration of CZ. The results indicated that all samples showed pure perovskite phase. The highest values of density, grain size, dielectric constant (ε_r) and piezoelectric coefficient (d₃₃) were 5.50 g/cm³, 10.95 μm, 2992 and 446 pC/N, respectively which obtained at the CZ seed size 459 nm.