Profound impact on different properties of calcium tungstate scheelite, CaWO4 phase stabilized via wider synthesis conditions

We have attempted to synthesize the CaWO4 phase materials under varied conditions and report their experimental findings related to phase identification and its different properties. While the solid state reaction requires a high temperature of 850 degrees C to form CaWO4 phase, ball milling of the reaction mixture under different processing conditions yields different results that are quite interesting and debatable. The different quantities of reaction mixtures ball milled under the dry condition exhibit CaWO4 phase. On the other hand, ball milling of the reaction mixtures under wet conditions using ethanol and/or water as solvent show WO3 as the main phase with broader XRD reflections. Subsequent annealing of the ball-milled powder at 850 degrees C yields major CaWO4 phase and WO3 as secondary phase in contrast to the solid state reaction. The optical properties of pure CaWO4 phase materials were examined by different spectroscopic techniques. The stress developed by ball milling of the reaction mixture remarkably reduces the NIR features of the as-milled CaWO4 phase powder. The higher (similar to 90%) NIR reflectance of CaWO4 phase materials obtained by SSR method guarantying it for solar reflecting roof and color pigmentation applications. An agglomeration of spherical-shaped fine particles (ball milling method) is different from solid state reaction method formed CaWO4 phase having dense microstructures.

Automated summary

We synthesized CaWO4 phase materials under different conditions and investigated their phase identification and properties. Solid state reaction at 850 degrees C forms CaWO4 phase, while ball milling under varied processing conditions leads to interesting and debatable results. Dry ball milling produces CaWO4 phase, while wet ball milling with ethanol and/or water as solvent results in WO3 as the main phase. Annealing the ball-milled powder at 850 degrees C yields CaWO4 as the major phase and WO3 as secondary phase. The optical properties of pure CaWO4 phase materials were examined and the NIR features were reduced by ball milling. The CaWO4 phase obtained by solid state reaction method shows higher NIR reflectance, making it suitable for solar reflecting roof and color pigmentation applications.