High Temperature Solid Phase Preparation of Cesium Tungstate

The nanoscale cesium tungstate powder is a kind of inorganic nano powder which has the best absorption ability to the near infrared. However, it is well known that the price of nano-sized cesium tungstate is more expensive, mainly because the preparation method is not yet mature, and it is difficult to make large-scale production. 

Here are some known solid-phase methods for caesium tungstate, and the advantages and disadvantages are briefly introduced.

The American patent US20060008640A proposed that the cesium carbonate was dissolved in water, and the tungstic acid was fully stirred and dried. After heat treatment for 30 minutes at H₂ and N₂ (H₂ 2%) mixed atmosphere 800 ℃, subjected to heat treatment in N₂ atmosphere at 800 ℃ 90 minutes to give a target cesium tungstate powder. The production process of this method is simple and the process is short, but there are many defects. Raw tungstic acid is insoluble in water, that is, tungsten raw materials and cesium materials failed to achieve molecular level mixing in aqueous liquid solvents. After drying and removing moisture, tungstic acid always appears in solid form. In a short time, the long range solid phase diffusion of tungsten and cesium ions should be realized to form the crystalline phase of the cesium tungstate Cs_0.32WO₃, and the oxygen vacancy in the lattice should be realized. The purity and crystallinity of cesium tungstate powder are not high, the agglomeration is serious, and the efficiency of wet ball milling is low, which greatly increases the cost of producing cesium tungstate slurry.

The United States Patent US8304099B2 proposed the use of ammonium metatungstate and cesium carbonate which can dissolve in water as the main raw materials. First, the two are dissolved in water and mixed, so as to obtain the raw materials of homogeneous tungsten and cesium at the atomic level. After drying at 145 ℃, the product was heat-treated at 550 ℃ for 20 minutes in air at a hydrogen volume ratio of 10% to obtain the target cesium tungstate powder, although the method improves the mixing uniformity of raw materials, it is necessary to see the relative low temperature at 550 ℃, and the heat treatment time of only 20 minutes. It is difficult to decompose the tungsten and cesium raw materials at high temperature and obtain the cesium powder with high crystallinity.

In order to reduce the particle size of cesium tungstate, some scholars in the US also put forward a new mixture of ammonium partrungstate and cesium formate, which is fast and thermally decomposed with plasma as heat source, which also improves the infrared absorption property of cesium tungstate, and hydrogen is added to the gas source. It can be seen that the particle size of the powder is tens of nanometers by the transmission electron microscope. The shortcomings of this method, such as large particles, at the same time, still exist special production equipment and low production efficiency, which will inevitably lead to high production cost and weak market competitiveness.

In conclusion, high temperature solid-state method is not very suitable for the preparation of cesium tungstate, which is also related to the properties of cesium metals. So Chinese scholars basically exclude the high-temperature solid-phase method for the preparation of cesium tungstate.

• < Prev
• Next >