|
With the developing of nano technology, the nano material is also becoming a new study point. As the nano tungsten trioxide is so important that the preparation method of nano tungsten trioxide urgently need.
The preparation method can be divided into three categories: solid phase method, liquid phase method, and gas phase method.
1. Solid phase method
Solid phase method is a basic mean of ceramic material preparation, usually according to the raw material mixing ratio of final synthesis product, and then calcined at high temperature to produce superfine powder, or by grinding again prepared ultrafine powder.
Put certain amount of ammonium tungstate into a muffle furnace in 500 degrees Celsius and calcined three hours, then grind it into pure WO3 nano powder with the average particle size of 50-60nm under the condition of natural cooling in agate mortar.
2. Liquid phase method
Liquid phase preparation method of nanometer is to make the separation of solute and solvent, and solute forms a certain shape and size of the particles. The method can precisely control the composition and particle size of product. Liquid phase method mainly includes hydrothermal synthesis method, micro-emulsion method.
1) Hydrothermal synthesis method is that some of the hydroxide in water solubility is greater than the corresponding oxide in water solubility in the high temperature and pressure, so the hydroxide can soluble in water and separate out the oxide at the same time.
Sodium tungsten is used as raw material. By adjusting the pH value, the concentration of the acid, the reaction temperature and the reaction time to find better ultrafine WO3 powder, which the size was about 24nm. The advantage of this method is directly generated oxides and it is avoided that the general liquid phase synthesis method needs to be calcined and converted into oxides, which greatly reduces raw materials and avoid the hard agglomeration.
2) Micro-emulsion method is a new method to prepare nano particles in the last decade. Micro emulsion is usually a transparent and isotropic thermodynamic stable system consisting of a surfactant, oil and aqueous solution. In W / O micro-emulsion system, water nuclear with containing precursor surrounded by of surface active agent and cosurfactant. The special micro environment can be called as a micro reactor, and the size can be controlled in a few to a few tens of nanometers.
Sodium tungstate, ammonia and polyvinyl alcohol are used as raw material. According to a certain ratio, ultrasonic emulsification, add concentrated hydrochloric acid to obtain yellow tungstic acid precipitation. Then to get the average particle diameters of WO3 respectively are 15, 25 and 85 nm under the degrees of 400, 600 and 800 Celsius temperature for eight hours. The particle size increased with the increasing of temperature.
3. Gas phase method
Gas phase method directly use gas or make variety of materials into a gas, then the changes in physical or chemical change can occur in the gaseous state, finally form nano particles in the cooling process.
When heating the tungsten filament in the air, obtained WO3 nano particles, control the pressure of evaporation system between the 133.3Pa and 1199.9Pa.The reaction of W and O2 generated oxide tungsten and convert substance by gas. The average particle size is 7-21nm measured by TEM, and the result are triclinic crystal and the single crystal of the WO3.
| 