Nd-F species in NdF3-LiF melts were studied using cryoscopic method.Liquidus temperatures of melts of various compositions were determined by differential thermal analysis(DTA).Based on the different model calculations,NdF4- was identified as the most likely Nd-F entity in the melts in which the mole fraction of NdF3 was lower than 20%,considering only one single Nd species in the melt,and which was formed in accordance with Temkin model or Flood model.Then,activities of different components in the melts were researched.The results show that activity of LiF decreases,and that of NdF3 increases with increasing the mole fraction of NdF3.The value of activity coefficient of NdF3 is higher than 1,and that of LiF is lower than 1.
We study ionic structure of KNO3-NaNO2 melts under air atmosphere by using Raman spectroscopy. Molar fraction of NO3- and NO2- is obtained and thermal stability of this kind of melts system is then analyzed. The results show that when the temperature is increased to a certain value, equilibrimn between the decomposition of NO3- and the oxidation of NO2- exists in KNO3-NaNO2 melts. When temperature is higher than 644 K, the molar fraction of NO3- decreases a little with temperature increasing for the melts in which the initial fraction of KNO3 is 90 wt%, but for the melts in which the initial fraction of KNO3 is 10 80 wt%, the molar fraction of NO3- increases with temperature, and the increasing rate is slower for a higher initial fraction of KNO3. Molar fraction of NO3- increment increases linearly with initial fraction of NaNO2. The sample in which the initial fractions of NaNO2 are 11.3 and 14.5 wt% under air atmosphere shows the best thermal stability at 762 and 880 K, respectively.
The thermal decomposition process of （NH4）3AlF6 was studied by DTA-TGA method and the related thermodynamic data were obtained. The results show that AlF3 is obtained after three-step decomposition reaction of （NH4）3AlF6, and the solid products of the first two decomposition reactions are NH4AlF4 and AlF3（NH4F）0.69, respectively. The three reactions occur at 194.9, 222.5 and 258.4 ℃, respectively. Gibbs free energy changes of pertinent materials at the reaction temperatures were calculated. Enthalpy and entropy changes of the three reactions were analyzed by DSC method. Anhydrous aluminum fluoride was prepared. The XRD analysis and mass loss calculation show that AlF3 with high purity can be obtained by heating （NH4）3AlF6 at 400 ℃ for 3 h.
A new type of sample cell specially designed for micro-Raman spectra study on volatile melts is described. The cell is made of quartz. The lower section of the cell is circular ring-shaped and the one-end-closed hole in the cell is used for locating the heating body. The tube attached to the cell lid for placing the thermal couple is inserted into the sample, which ensures that the temperature measurement accuracy is good. The cell can be sealed for reducing the effect of the composition change caused by the in_homogeneous volatilization. During the Raman spectra scanning, the laser beam is transmitted into the cell through the side but not the top. Meanwhile, a furnace has been designed to match the cell. The heating body is closely coupled with the sample cell, and there is a hole on the side wall of the furnace for the entrance of the microlens. The assembly has performed well in the tested Raman spectrum measurement of molten NaNO3 at 602 ℃.
Xian Wei HuHuan LiBing Liang GaoJing Jing LiuZhong Ning ShiJiang Yu YuZhao Wen Wang
