Preparation And Properties Of Vanadium Oxides And Their Composite Glasses

Vanadium oxides mainly include vanadium pentoxide (V₂O₅), vanadium dioxide (VO₂) and vanadium trioxide (V₂O₃). The process of synthesizing V₂O₅ has been sophisticated; and low valence vanadium oxides are difficult to be obtained. Vanadium dioxide presents a first-order phase transition, from a semi-conducting state to a metallic state at temperature around 341K. The phase transition of vanadium dioxide is reversible from a monoclinic crystal structure at low temperature to a tetragonal structure at high temperature, accompanied by abrupt changes of optical and electrical properties. Vanadium dioxide becomes a potential optical and electric material due to these outstanding properties. A great deal of attention has been paid by many material researchers to the preparation of pure vanadium dioxide. Glass is a low cost material with various excellent properties, studying the properties of the composite between vanadium oxide and glass is the foundation of the application of optical properties of vanadium oxide to glass substrate.Vanadium has different valences. In the process of synthesizing vanadium dioxide, other vanadium oxides are often found as impurities. Many researches prove that the stoichiometric ratio influences VO₂ phase transition, the synthesizing pure VO₂ has been drawing a lot of attentions. In the dissertation, the mathematical modeling is established for exactly calculating thermodynamic parameters in synthesizing vanadium dioxide. Reactants and thermodynamic parameters are optimized, the technical process is designed for low cost equipements and materials, easily operating and environment protecting, the short reaction period and controllability condition are selected. Pure thermochromic VO₂ and V₂O₃ microcrystal particles were successfully synthesized, this technique adapts to industry production. On the technique of synthesizing VO₂, the method of vanadium oxide coating on glass is studied. The coating on glass with phase transition character is successfully prepared. Fortunately, the qualitative and quantitive relationships between optical properties and density are found in the investigation of vanadium oxide doped glasses. The primary contents, methods and results are as follows:(1) The conditions of synthesizing VO₂ are optimized by thermodynamic calculations. The modelling of thermodynamic parameters for synthesizing low valence vanadium oxides is established. By calculating entropy, enthalpy, Gibbs free energy, equilibrium constant and pressure quotient in the reactions, traditional methods both hydrogen reducing V₂O₅ and V₂O₅ pyrogenation are analyzed, the thermodynamic factors are found for these methods with long period and low purity. On calculating the thermodynamic parameters in the reactions of reducing V₂O₅ by carbon monoxide, sulfur dioxide, methane, ammonia gas and carbon powder, the critical temperature 842K is found for producing VO₂ and V₂O₃ in the process of reducing V₂O₅ in ammonia, within this method the advantages of larger equilibrium constant and nitrogen available for adjusting pressure quotient are presented, the temperature above 700K for synthesizing VO₂ by ammonium metavanadate pyrogenation is found.(2) A novel technical process is designed and low valence vanadium oxides are prepared. On thermodynamics the technical process suitable to industry production is designed. MnO/MnO₂ deoxy and dehydrating column is prepared and applied to the experiments. VO₂ and V₂O₃ powder are prepared by reducing V₂O₅ in NH₃, NH₄VO₃ pyrogenation and reducing NH₄VO₃ in H₂. The product samples are characterized for phase structure, phase transition temperature, phase transition enthalpy, purity, valence state of vanadium, crystal morphology and the grain size distribution by means of X-ray diffractometer (XRD), the differential scanning calorimetry (DSC), Thermo-gravimetric (TGA), X-ray photoelectron spectrometers (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM). The results indicate the purities of VO2 and V2O3 are more than 99%, their microcrystal grain size distribution is mainly from several micrometers to several decade micrometers, VO₂ sample is thermochromic and the phase transition is endothermic process, the phase transition temperature is approximately 342.6K and the enthalpy of phase transition is 3.7kJ/mol.(3) Vanadium oxide coating on glass and their optical properties are studied. The physical and chemical properties of vanadium oxides are analyzed, alkali solution and relative reaction on glass surface are investigated, then V₂O₅ and silicate glass are selected as coating and substrate materials, the methods for cleaning and coating on glass are designed. The sol is prepared by the methods of quenching melted V₂O₅ in distilled water and dissolving V₂O₅ in hydrogen peroxide at ice point respectively. V₂O₅ gel coatings are prepared on glass by spin coating, the thermal and reducing treatment is applied to coatings with the author's method for synthesizing VO₂. SEM, AFM, XRD, FT/IR and UV/Vis spectrophotometer are applied to characterizing the coatings. The results indicate that "dissolving V₂O₅ in hydrogen peroxide at ice point" has advantages over "quenching melted V₂O₅ in distilled water". By the former method, the coatings are light blue, relative uniform and with the character of VO₂ crystal and phase transition.(4) The properties of V₂O₅ doped glass are studied. Melting method is applied to preparing minim V₂O₅ doped binary (100-x)B₂O₃-xNa₂O glasses, where x = 5～33mol%, V⁵⁺, Pb²⁺, Bi³⁺, Ce⁴⁺, Fe³⁺(fromV₂O₅, PbO, Bi₂O₃, CeO₂ and Fe₂O₃) are doped in glass with 0.022mol%, UV/Vis spectrophotometer is applied to acquire the absorption spectra, the results show that the indicating ability of V₂O₅ to the glass optical basicity is better than others when Na₂O>20mol%, V₂O₅ is a pertential material in indicating glass optical basicity. Melting method is applied to prepare trinary borate glass (70-x) B₂O₃-30Na₂O-xV₂O₅, where x = 1～10mol%, Archimedes principle method is used to determine the glass density, UV/Vis spectrophotometer is applied to acquire the absorption spectra, the results indicate the qualitative and quantitive law between the density and the optical absorption. Mathematical statistics analysis is applied to optical parameters and density for V₂O₅ doped binary glasses, the qualitative and quantitative relationships between density and electronic polarizability are found for binary silicate, borate, phosphate and germinate glasses; the quantitative relationships between the density and non-linear optical susceptibility are found for binary borate glasses. These results will contribute to the rearches on optical functional material of vanadium oxide glasses and others.