Using of mechanoactivation for preparation of cerium-containing solid solutions based on zircon

Solid-phase synthesis of cerium-containing solid solutions based on ZrSiO4 was described. The synthesis was carried out using mechanical activation of a mixture consisting of zirconium oxide and hydrated amorphous silica with the addition of cerium oxide at a molar ratio of ZrО2:SiО2:CeО2 equal to 0.95:1.00:0.05. The mechanically activated in a centrifugal planetary mill mixture of reagents was calcined in the temperature range of 1200–1600 °C for 3 hours, which was accompanied by the essentially complete synthesis of zircon. The cerium content in the zircon structure was calculated from X-ray powder diffraction data.

Immobilized nuclide and leaching mechanism of zircon waste forms efficient synthesized by molten salt

Molten salt has rapid mass transfer and nucleation process, so it can synthesize ceramic solid solution of immobilized high-level radioactive waste at low temperature. The chemical stability in the process of interaction with groundwater determines the ability of matrix phase to prevent radionuclides from entering the biosphere and the release form of radionuclides. Nd-doped ZrSiO4 ceramics with different sintering temperature (1100-1500 ℃), sintering time (3-24 h) and molar ratio of salt to oxide (3:1, 7:1 and 10:1) were prepared by molten salt method. The sintered ceramic is Zr1−xNdxSiO4−x/2, where x is the solubility of Nd in ZrSiO4. The results show that the optimum molar ratio of molten salt to oxide is 10:1, which can quickly synthesize zircon waste form at low temperature. The chemical stability test shows that the normalized leaching rate of trivalent nuclides in zircon structure is in the order of ~10−5 g·m−1·d−1, and the surface layer is dissolved. The experimental results show that zircon structure is an excellent waste form.

Isomorphous Substitutions in Luminescent Materials Based on ScVO4

The aim of the paper is to define the limits of substitution and phase stability for solidsolutions of orthovanadates with zircon structure Sc1–xLnxVO4, where Ln is a rare-earth element(REE), Ln = Ce – Lu. The mixing energies (interaction parameters) and critical decompositiontemperatures of Sc1–xLnxVO4 solid solutions with the zircon structure were calculated using thecrystal-energy theory of isomorphous miscibility. Diagram of thermodynamic stability visualizingthe substitution limits (x) by the decomposition temperature or the decomposition temperature bythe substitution limits, the dependencies of the decomposition temperatures on the REE atomicnumbers is presented. This diagram also allows assessing areas of stability, instability, andmetastability for Sc1–xLnxVO4 solid solutions. Results of calculations were compared with literaturedata on thermodynamic stability of solid solutions and on substitution limits. The results of thisstudy can be used in the development of new luminescent materials based on ScVO4 modified withREE, in the selection of REE for matrix and activator, in defining optimal proportions of REE inSc1–xLnxVO4 matrices.

FWHM Calculation of Zircon Gem-Materials before and after Thermal Enhancement

Zircon samples from Ubon Ratchathani, Thailand; Rattanakiri, Cambodia and Dak Nong, Vietnam change their color from light brown and reddish-brown to blue color after thermal enhancement at 1000 ๐C in reducing condition for 60 min. The high temperature is one of the factors for the zircon structure to recrystallize. The objective of this study is to describe the crystal structure of zircon samples before and after thermal enhancement. Zircon is a metamict mineral whose structure is destroyed by some trace elements. There are radioactive elements such as U and Th in the zircon structure. In this study, Raman spectroscopy was used to analyze the molecular vibration in zircon structure before and after thermal enhancement. As a result, the Raman spectra of zircon samples after thermal enhancement show the Raman shift at peak position of V3(SiO4) stretching around 1008cm-1to higher wavenumber concerning to the full width at half maximum (FWHM) values calculated by PyMCA software. The results could be summarized that the metamict zircon will be recrystallized to the crystalline zircon after thermal enhancement. The advantage of this study is about the identification of zircon before and after thermal enhancement.