From the chemical composition point of view, with sodium tungstate (Na2WO4) and potassium tungstate (K2WO4) is different from the cation in calcium tungstate (Ca2+) is alkaline earth metal, so they are slightly different in structure, physical and chemical properties, production process and use. Note: Sodium and potassium are both alkali metals
By definition, calcium tungstate, also known as “artificial tungstate”, is a tungstate consisting of regular divalent metal calcium ions (Ca2+) and tungstate ions [(WO4)2-]. It is a typical self-activating luminescent material with a tetragonal crystal structure, and its English name is calcium tungstate. Molecular weight 287.93, CAS number 7790-75-2. Note: in CaWO4, the valence of W is +6; The structures of Na2WO4 and K2WO4 are monoclinic squares.
In terms of physical and chemical properties, CaWO4 has a white powder appearance, with a certain irritation, a density of 6.06g/mL, a melting point of 1580°C, and a refractive index of 1.93. It is slightly soluble in water and ammonium chloride solution, and will be decomposed in hot hydrochloric acid, with good catalytic activity and luminescence performance.
In terms of production methods, CaWO4 can be prepared by solid-state reaction method, hydrothermal method, ultrasonic irradiation method, microwave radiation method, precipitation method and gel method, etc. However, these methods all have certain shortcomings, such as harsh reaction conditions, low production efficiency and single product morphology. Therefore, calcium tungstate can be prepared by the following steps: first, sodium tungstate is added to β-cyclodextrin solution to obtain solution A; Second, calcium nitrate solution and solution A were mixed at A volume ratio of 1:1 and stirred. Third, the reaction products were precipitated, washed and dried to get twin spherical calcium tungstate microcrystals.
From the point of use, calcium tungstate can be used to produce other derivatives of tungsten, such as ammonium paratungstate, tungsten oxide, tungsten alloy, hard alloy, etc. It can be used as a blue phosphorescent in oscilloscope, and a scintillation device for detecting X-ray and γ-ray in medicine; It can be used as a laser matrix material.