Corrosion resistant properties of Si3N4-SiC and TiB2 at high temperature were studied. The experiments were carried out in metallic neodymium and NdF3-LiF-Nd2O3 system, respectively. Corrosion temperature was 1100 ℃ and the holding time of corrosion experiments was 24 h. Corrosion products were analyzed by XRD and SEM, and corrosion behavior and corrosion mechanism of the experiments were studied. The results showed that Si3N4-SiC was corroded seriously in the above-mentioned two systems. A few of compounds were found on the surface of Si3N4-SiC, and surface structure of the Si3N4-SiC samples was loosened. The corrosion resistance of TiB2 was better than that of Si3N4-SiC. Oxidation resistance of TiB2 at high temperature should be enhanced.
Electrical conductivity of NaF-AlF3 melts was measured by continuously varying cell constant(CVCC) technique. Relationships between equivalent conductivity at 990-1 030 ℃ and temperature and composition, and relationship between equivalent conductivity activation energy and composition of the melts were then studied on the basis of two-step decomposition mechanism of AlF63-. According to the changes of molar fractions of different anions in NaF-AlF3 melts, courses of dependence of equivalent conductivity and its activation energy on composition were analyzed. The results show that the influence of temperature on equivalent conductivity of the melts is small in the researched temperature range, and equivalent conductivity increases with increasing the molar fraction of AlF3; there is a minimum point in the activation energy—composition curve when molar fraction of AlF3 is 0.29.
Wettability of TiB2-based ceramics by NdF3-LiF-Nd2O3 melt was studied using sessile drop technique in this paper. Wetting experiment was carried out under inert atmosphere at 1050 °C. Chemical reactions which occurred on the solid-liquid interface and solid-gas interface during wetting process were discussed by thermodynamic calculations combined with X-ray diffraction(XRD) patterns. Micromorphology and element distribution of fracture surface at the interfacial region of solid/liquid system were analyzed by scanning electron microscope(SEM) equipped with energy dispersive spectrometry(EDS) . Contact angles of the drop were determined as a function of time in order to describe the wetting process,and wetting phenomenon was interpreted from a viewpoint of interface structure. The results showed that wetting was a dynamic wetting process with characteristics of reactive wetting. Penetration and oxidization phenomena during the experiment had great effect on wetting process.
Electrochemical deposition and nucleation of aluminum on tungsten electrode from AlCl_3-NaCl melts were studied by cyclic voltammetry,chronopotentiometry and chronoamperometry.Cyclic voltammetry and chronopo- tentiometry analyses showed that Al(Ⅲ) was reduced at 200℃in two consecutive steps in an electrolyte of molten AlCl_3-NaCl system with a composition 52:48 molar ratio.The current-time characteristics of nucle- ation aluminum on tungsten showed a strong dependence on overpotentials.Chronoamperometry showed that the deposition process of aluminum on tungsten was controlled by an instantaneous nucleation with a hemispherical diffusion-controlled growth mechanism.The results could lead to a better understanding of the AlCl_3-NaCl melt system that has technological importance in electrodeposition of metals as well as in rechargeable batteries.
Zhaowen WANG Hongmin KAN Zhongning SHI Bingliang GAO Yungang BAN Xianwei HU
NdF3-LiF melts are commonly used in the electrolysis process of metallic neodymium production. Research on the density and ionic structure of the electrolyte is important for its close connection with the electrolysis mechanism and process. In this paper, the density of LiF-NdF3 melts was studied by the Archimedes method. The results showed that the density decreased with increasing temperature and LiF contents. The changing law was discussed and explained in terms of the micro ionic structure of the melts. The ionic structure of 25 mol.% NdF3-75 mol.%LiF was then quantitatively analyzed on the condition that [Nd]3+ existed in the forms of both NdF63– and NdF4–. The results indicated that NdF63–, NdF4–, and F–took the amount of 22 mol.%–25 mol.%, 25 mol.%, and 50 mol.%–52 mol.% respectively in the anions of the melts in the temperature range of 950–1050 oC. In addition, NdF63–was easier to decompose at a higher temperature.
