The preparation process of doped ammonium metatungstate mainly includes the following methods, each of which has its own characteristics, and the specific parameters and conditions involved in the preparation process have an important impact on the performance of the final product:
Solvent extraction method or ion exchange method
In this method, ammonium tungstate solution or sodium tungstate solution is used as raw material, and ammonium metatungstate (AMT) solution is firstly prepared by solvent extraction or ion exchange. On this basis, doped ammonium metatungstate can be prepared by adding specific doping elements (such as rare earth elements, transition metal elements, etc.). The method is characterized by the ability to effectively control the content of impurities in the raw material, and can more precisely control the type and concentration of doping elements.
Neutralization method
The neutralization method uses ammonium sec-metatungstate and nitric acid as raw materials to prepare ammonium metatungstate. Firstly, ammonium sec-metatungstate is added with deionized water and ammonium citrate to form a slurry containing WO₃ 12%-30% concentration. Then add 3%~5% dilute nitric acid into the ammonium sec-tungstate slurry according to the ratio of ammonium sec-tungstate: nitric acid=1:20, control the solid-liquid ratio of 1: (3~4), Ph value of 2~4, and heat to dissolve. Then, ammonium metatungstate crystals are obtained by evaporation crystallization, filtration, drying and other steps. In the preparation process, the preparation of doped ammonium metatungstate can be realized by adding doping elements.
Thermal decomposition method
Thermal decomposition method is mainly used to prepare ammonium metatungstate by decomposing tungsten-containing compounds (e.g. APT) by heating. In the process of thermal decomposition, the purity and performance of the product can be influenced by controlling the temperature, atmosphere and other conditions. Meanwhile, the preparation of doped ammonium metatungstate can be realized in the thermal decomposition process by adding doping elements.
Improvement of evaporation crystallization and drying process
Considering that ammonium metatungstate is extremely soluble in water and has poor stability, the researchers carried out process improvement based on the evaporation crystallization method. The method includes three main steps: evaporation crystallization, free water removal and drying and packaging. In the process of evaporation crystallization, the crystal material of ammonium metatungstate containing free water was obtained by controlling the pH value and density of the material. Then, far infrared technology is used to heat and dehydrate the wet crystal material at low temperature and dry it at high temperature, so as to obtain ammonium metatungstate powder with uniform particle size and high purity. In the dehydration and drying process, the preparation of doped ammonium metatungstate can be realized by adding doping elements.
The preparation process of doped ammonium metatungstate is diverse, and each method has its unique advantages and scope of application. In practical application, it is necessary to choose the appropriate preparation process and doping elements according to the specific product requirements and production conditions. At the same time, the preparation process needs to strictly control the parameters and conditions to ensure the performance and quality of the final product.
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