Investigation of the structure of CaO-Al2O3-SiO2 melts as a basis for the development of new agglomerated welding fluxes and industrial refractories

A significant number of welding fluxes and industrial ceramics are produced in the Ukraine. The production of these materials is sufficient for both domestic needs and significant export. It is assumed that the ternary CaO-Al2O3-SiO2 system may become the basis for the development of agglomerated welding fluxes and technical ceramics. Three samples of ternary CaO-Al2O3-SiO2 system were studied by means of high-temperature X-ray diffraction above the melting point: 23.3CaO- 14.7Al2O3-62.0SiO2 wt. % (sample 1, eutectic), 9.8CaO-19.8Al2O3-70.4SiO2 wt. % (sample 2, eutectic), 15.6 CaO- 36.5Al2O3-47.9SiO2 wt. % (sample 3). Experimental scattering intensity curves, structure factors and the radial distribution function of atoms were obtained. The structural parameters of short-range order were calculated using melt structure models obtained by Reverse Monte Carlo method. The existence of microparticle associates of the mullite or sillimanite type immersed in the slag matrix is assumed. It is assumed that the calcium ions coordinated aroundthese associates are surrounded by oxygen melt anions. Such a structure can be considered as a colloidal solution. The microparticle of mullite is the core of the aggregate that is surrounded by calcium and oxygen ions from the molten medium.

Formation Mechanism of SrBi2Nb2O9 Prepared by Melting Salt Method

In this paper SrBi2Nb2O9 was prepared by molten salt synthesis method and KCl chosen as molten medium. In order to disclose possible formation mechanism of SrBi2Nb2O9, a simple route was established for comparison by dividing the starting precursors into four groups. With the help of XRD, possible synthesis route was analyzed. The results showed that pure SrBi2Nb2O9 powders could be obtained at temperature higher than 700oC by molten salt synthesis. Intense synthesis reaction happened in the temperature range from 500 to 700oC. The reaction mechanisms of SrBi2Nb2O9 included four steps, namely the formation of 1) SrBi2O4 at close to 600oC,2) BiNbO4 from the reaction of at 600-700 oC, 3) SrBi2Nb2O9 from the reaction of SrBi2O4 and Nb2O5 and 4)SrBi2Nb2O9 from the reaction of BiNbO4 and SrCO3. The molten salt could improve distribution and reactivity of the precursors and significant formation of SrBi2Nb2O9.