Ultrafine Ammonium Metatungstate Acquisition Strategy
Ammonium metatungstate (AMT) is one of the most important raw materials and precursors for the preparation of WC.
The structure and properties of WC are affected by the physical and chemical properties of precursor. The particle size and structure of precursor will greatly influence the process of reduction and carbonization in the late stage, and then affect the catalytic activity of WC catalyst.
In order to obtain precursor with good particle size and good structure, spray drying is usually used. Spray drying has many advantages, such as simple process, no pollution, homogeneous composition, and suitable for mass production.
The basic principle of spray drying method is ammonium metatungstate solution by spray drying, in a few seconds, water quickly evaporated into powder, physical and chemical properties of homogeneous granular, hollow spherical or spherical solid products.
Many scholars have found that in the spray drying process, the concentration of ammonium tungstate solution has an important influence on the morphology of ultrafine tungsten powder, and so does ammonium metatungstate.
Some scholars have investigated the effects of different feed concentration, feed rate and the addition of surfactants on the particle size of microspheres under aerobic spray drying conditions. The results show that the feed concentration is 5% at the inlet temperature of 200 °C, the outlet temperature is 90 ~ 100 °C, the air velocity is 550 L· min-1 and the feed rate is 7 m L · min-1 (d50) was 2.26 um. The AMT was prepared by the precursor solution, and the minimum median diameter (d50) was 2.26 um; AMT with solid solution concentration of 50% (WT) is the solid microsphere, and the minimum median diameter (D50) is 6.43 mu m. The greater the solubility, the greater the particle.
From an economic point of view, the concentration of the liquid should be as high as possible, because it can reduce the water content in the solution, thereby reducing the amount of hot air used for evaporating water, and reducing energy consumption. However, the ultrafine ammonium metatungstate precursor can be obtained by analyzing the technical requirements, and the ammonium metatungstate can be obtained with lower concentration.
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