Study On The Phase Chemistry Reaction Between CsCl/CdCl₂ And Rare Earth Chlorides Reacting In Hydrochloric Acid Solution

The phase chemistry reaction of the quaternary system CsCl-RECl3-HCI-H2O (RE=Tb, Dy, 298K), CdCl2-RECl3-HCl-H2O (RE=La, Pr, Gd, 298K) and the ternary system of CdClrRECl3-H2O (RE=La, Pr, Nd, Sm, Eu, Gd, 303K) have been investigated and the corresponding equilibrium diagrams were constructed. 5 types of 13 new compounds were found and obtained from the systems, including 5CsCl·TbCl3·6H2O, 2CsCl·TbCl3·6H2O, 5CsCI·DyCl3·8H2O, 2CsCl·DyCl3·6H2O, 8CdCl2·LaCl3·16H2O, 4CdCl2·LaCl3·12H2O, 8CdCl2·PrCl3·20H2O, 4CdCl2·PrCl3·12H2O, 9CdCl2·GdCl3·24H2O, 4CdCl2·GdCl3·14H2O, 4CdCl2·NdCl3·12H2O, 4CdCl2·SmCl3·12H2O and 4CdCl2·EuCl3·14H2O. And they are attributed to the following five types: 5:1 type, 2:1 type, 4:1 type, 8:1 type and 9:1 type. According to the phase diagrams, all of the 13 new compounds were synthesized and obtained from the complicated systems and characterized by X-ray powder diffraction, thermal analysis method of TG-DTG, DSC and fluorescence spectrum.The following new discoveries were showed in this paper.1. Upconversion fluorescence phenomenon of the new compounds obtained from the complicated systems was observed for the first time. For example, 5CsCl·TbCl3·6H2O and 2CsCl·TbCl3·6H2O show strong upconversion fluorescence at 500nm(or 545nm) and 495nm(or 545nm) when excited at 750nm(or 850nm) and 700nm(or 750nm), respectively, which were attributed to the f→ f(5D4→7F6) energy level transition of Tb3+ in the new compounds. The corresponding luminous energy of emission fluorescence are about Δ E =18348cm-1( λ. EM=545nm)and A E =19999cm-1( λ EM=500nm). Such upconversion laser action at room temperature has numerous applications mainly in the fields of optical material of ultraviolet and visible region excited in the near infrared region.2. The standard molar enthalpies of formation ΔfHm for new compounds 5CsCl·TbCl3·6H2O, 2CsCL·-TbCl3·6H2O, 5CsCl·DyCl3·8H2O and 2CsCl·DyCl3·6H2O at 298.15K were investigated for the first time. Their values are -5077.78 kJ·mol-1, -3754.74 kJ·moL-1, -5688.46 kJ·mol-1 and -3761.31kJ·mol-1 respectively.3. Ternary systems CdCl2-RECl3-H2O are complicated systems which coexisted with stable compound of 4:1 type and metastable compound of 8:1 or 9:1 type. Whereas, both are stable compounds in the quaternary systems CdCl2-RECl3-HCl-H2O. It shows that there are strong reaction between CdCl2 and REC13 in the system of solid-liquid phase coexistence when hydrochloric acid exists.4. Reinforcing studies in CsCl and REC13 reaction in hydrochloric acid systematically by adding quaternary system CsCl-RECl3-HCl-H2O (RE= Tb, Dy), it makes us get results regularly. 5:1 and 2:1 type new compounds 5CsCl·TbCl3·6H2O, 2CsCl·TbCl3·6H2O, 5CsCl·DyCl3·8H2O and 2CsCl·DyCl3·6H2O were obtained directly from the system for the first time.5. The research on the ternary system of CdCl2-REClrH2O (RE=La, Pr, Nd, Sm, Eu, Gd) and the quaternary system CdCl2-RECl3-HCl-H2O (RE= La, Pr, Gd) show that the phase chemistry behaviors are the similar for the system before Gd and is different for the system after Gd. The "Bicomponent effect" in the system of CdCl2-RECl3-HCl-H20 and CdCl2-RECl3-H2O is found for the first time.The new research and discoveries mentioned above enriched the chemistry of rare earth element. It is worthy of further study.