Preparation of Nano Calcium Tungstate

Nano calcium tungstate is very promising is a promising self luminescent fluorescent material. It can emit dazzling light without being modified, thus playing an important role in the X ray, electron beam and ultraviolet ray and other optical fields.

With the development of science and technology, it is found that calcium tungstate doped with rare earth ions such as europium (Eu³⁺), terbium (Tb³⁺), dysprosium (Dy³⁺) and samarium (Sm³⁺) can synthesize three primary phosphors, which can greatly improve the luminescence range of calcium tungstate. Therefore, CaWO₄ has been widely used as phosphor, radiation intensity scintillation counting material and laser host material.
 
Studies have shown that nano calcium tungstate has wider color gamut and more stable luminescence characteristics, which makes the material made of nano calcium tungstate continue to make revolutionary breakthrough in the development of electronic products.

Microemulsion synthesis technology is a new method for the preparation of ultrafine powder in recent years. The operation mode is relatively simple, and the powder morphology is also easy to control. It mainly contains three types of water-in-oil and oil-in-water and intermediate form, which are also called positive phase microemulsion (O/W), reverse microemulsion (microemulsion) and double continuous microemulsion method.

In the experiments on nano size calcium tungstate by reverse microemulsion method, CTAB/H₂O/ cyclohexane/ n-butyl alcohol was used as the system. The scholars prepared 40 mL cyclohexane and 8 mL butanol mixed solution, each 2 parts, and then add 0.9476 g (0.05 mol/L) CTAB to heat, stir and dissolve. 4mL CaCl₂ solution (0.1 mol/L) and 4 mL Na₂WO₄ solution (0.1 mol/L) were added to the above solutions and stirred 30 min to form microemulsion. Mix the 2 micro emulsions and continue stirring for 30 min. Then, the white precipitate is obtained after 1 h at room temperature. After filtering and washing with deionized water and anhydrous alcohol several times, nano calcium tungstate can be obtained after dried at 90 ℃.

In microemulsion method, the amount of cetyltrimethyl ammonium bromide (CTAB) is the key factor to decide the result. By adjusting the concentration of surfactant in the microemulsion system of CTAB agent can obtain nano calcium tungstate with the shape of near spherical, spindle shaped morphology and ball-flower. The luminous intensity of the sample without CTAB is lowest, and the luminous intensity of sample enhances with the increase of CTAB concentration, and the sample has the largest luminous intensity.

The advantage of microemulsion synthesis of nanometer calcium tungstate is that the operation method is relatively simple, and the agglomeration will not occur during the separation process. However, the main problem is that the preparation costs are relatively high and are only suitable for small-scale production.

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