PHASE FORMATION PROCESSES AT LOW-TEMPERATURE FLUORINATION OF ZIRCONIUM SILICATE

Zirconium silicate ceramics is widely used in different fields of engineering. One of the most actual problem of zircon ceramics is the requiring of high temperatures for its sintering. Perspective method for activation of silicate materials with the aim of intensification of synthesis and sintering processes is the low-temperature fluoridation with the ammonium hydrofluoride. In accordance with that, processes occurring during the interaction of plasma dissociated zircon and natural zircon with ammonium hydrodifluoride were studied. It was established that plasma dissociated zircon actively interacts with ammonium hydrofluoride in the solid phase. Natural zircon because of its chemical inertness reacts with ammonium hydrofluoride only when latter melts. The main product of fluorinating is ammonium hexafluorosilicate. By-products are ammonium hexafluorozirconate and ammonium heptafluorozirconate. Their quantity increases with the content of ammonium hydrofluoride in mixtures. Kinetic equation of reaction between zircon and ammonium hydrofluoride is k×τ = 1-(1-α)1/n. Activation energy of plasma dissociated zircon and natural zircon fluorinating reactions are 13.9 and 32.7 kJ/mol, respectively. Order of reactions (n) are 2.0 and 1.5, respectively. Thermal treatment of fluorinated materials at 400 °C leads to ammonium hexafluorosilicate sublimation and thermal dissociation of ammonium fluorozirconates to zirconium fluoride and fluorozirconate intermediates. It was established that low-temperature fluoridation of zircon makes possible to regulate chemical composition of minerals. Materials obtained by ammonium hydrofluoride treatment of plasma dissociated and natural zircon can be potentialy used in the functional zircon and zirconia-zircon ceramics technology.

Preparation, characterization and formation mechanism of single-crystal zirconia micro-sheets

Zirconia micro-sheets were prepared by molten salt method using the salt mixture of NaCl and NaF. FE-SEM, TEM, EDS, DTA-TG, XRD, Raman and FT-IR techniques were employed to characterize the morphology, phase composition and formation mechanism of the ZrO2 micro-sheets. The obtained monoclinic ZrO2 microsheets with exposed {100} facets show an average thickness of 0.2 ?m. The growth of the ZrO2 micro-sheets is proved to be assisted by the addition of fluoride. On the one hand, the addition of fluoride promotes the mass transfer of zirconia through the formation of zirconium fluoride complexes (ZrF 3-7). On the other hand, fluoride adsorbed on the surface of zirconia stabilizes {100} facets and lead to the exposure of {100} facets in the final product.

A general strategy for tailoring upconversion luminescence in lanthanide-doped inorganic nanocrystals through local structure engineering

We report a series of Yb3+/Er3+ co-doped alkaline zirconium fluoride nanocrystals to thoroughly understand the origin underlying the local-structure-dependent upconversion luminescence.

Effect of ZrF4 on the Physical and Absorption Properties of Magnesium Tellurite Glass

Tellurite glass containing zirconium fluoride (ZrF4) with composition of (90-x)TeO2-10MgO-(x)ZrF4,where 0.0 ≤ x ≤ 6.0 in mol% has successfully been prepared by melt quenching technique. X-Ray Diffraction (XRD) pattern verified the amorphous nature of the glass. In this study, the physical and optical properties were investigated in term of density and absorption properties by using Archimedes method and UV-Vis Spectroscopy. It was found that glass density decreases in the range of 4.842 – 4.995 g cm-3 with the increase of ZrF4 concentration. Meanwhile, the molar volume is increased in the range from 29.566 to 30.593 cm3/mol with increase of ZrF4. The absorption edge is found to shift toward a higher wavelength as the ZrF4 concentration is increased. On the other hand, the optical energy band gap shows the decrement from 2.573 to 2.212 eV for indirect transition and from 3.044 to 2.927 eV for direct transition with the addition of ZrF4 concentration while the Urbach energy, increases from 0.302 to 0.498 eV with the increase of ZrF4. All the results will be discussed with respect to the glass composition.

Interaction of metallic zirconium and its alloys Zry-2 and E110 with molten eutectic salt of LiF–NaF–KF containing zirconium fluoride components

The interactions of selected zirconium alloys used as special construction materials (Zr-pure, Zry-2, E-110) with the molten system of (LiF–NaF–KF)