Six Preparation Methods of Tungsten Trioxide

There are six preparation methods of tungsten trioxide include hydrothermal synthesis method, precipitation method, sol-gel method, microemulsion method, gas-liquid reaction method and template method. Some special forms of tungsten trioxide powder can be prepared by different methods. It is due to the existence of this special structure and morphology that the synthesized tungsten trioxide has some new physicochemical properties.

1) Hydrothermal synthesis

The hydrothermal method refers to the use of an aqueous solution as a reaction system in a special autoclave, by heating and pressurizing the reaction system to form a relatively high-temperature, high-pressure reaction environment, so that the normally insoluble or insoluble matter is dissolved and recrystallized to carry out inorganic An effective method of synthesis and material processing. For example, the Na2WO4 solution is acidified by HCl, and hydrothermally reacted at 130 to 200 ° C for 1 to 5 days, and finally tungsten trioxide having a uniform particle size distribution can be obtained.

Advantages: the metal or its precursor can be directly synthesized, which avoids the step of normal liquid phase synthesis which needs to be converted into an oxide by calcination, thereby greatly reducing or even avoiding the formation of hard agglomeration, and the prepared powder has grain development. It has the advantages of completeness, small particle size, uniform distribution and good dispersibility, and it can effectively control the particle size, particle size distribution and morphology of the powder.

2) Precipitation method

The precipitation method usually mixes substances of different chemical compositions in a solution state. The basic principle is to add a pre-precipitate to the salt solution to obtain a precursor precipitate, and the precipitate is dried and fired to form a nano-powder. Mainly divided into coprecipitation method and chemical precipitation method. For example, by using a sol-coprecipitation method, a mixture of WC16 and TiCl4 is used as a raw material, and ammonia water and a surfactant are added to form W(OH)6 and Ti(OH)4, which are centrifuged and calcined to obtain 3 to 9 nm Tungsten oxide powder.  (NH4)10W12O41•5H2O was used as raw material to obtain H2WO4, and then dehydrated and calcined to obtain tungsten trioxide ceramic powder, and the powder particle size was more uniform.

Advantages: the obtained powder crystals tend to be complete, the particle size distribution is uniform, and the particle size is small.

Disadvantages: the prepared powder is prone to agglomeration, which is not conducive to detection.

3) The sol-gel method

The sol-gel method is a method in which an organometallic compound, a metal inorganic compound or a mixture of the two is cured by a solution, a sol or a gel, and then subjected to a heat treatment process to form an oxide or other compound. For example, Na2WO4 is used as a raw material, hydrochloric acid is added to prepare a sol, and then cetyltrimethylammonium bromide (CTAB) surfactant is added to obtain an agglomerate, which is dried and calcined to obtain a particle size of 31 to 45 nm. Tungsten trioxide powder.

Advantages: the obtained powder has small particle size, good uniformity, high purity and easy industrial production.

Disadvantages: it is difficult to control the conversion of sol-gel. The product is easy to form hard agglomeration after drying, and the synthesis cycle tends to be longer.

4) microemulsion method

The microemulsion method is a new method for preparing a microsol in recent years, which is often composed of a surfactant, a co-surfactant, a solvent, and water (or an aqueous solution). In this system, two mutually incompatible continuous media are divided into tiny spaces by a surfactant amphiphilic molecule to form a microreactor, and the reactants react in the system to form solid phase particles, and the size of the microemulsion particles can be controlled to several Dozens of nanometers. For example, n-butanol, CTAB, and cyclohexane are stirred and mixed. Aqueous Na2WO4 solution was added and stirred to obtain a microemulsion. Under the condition of ultrasonic vibration, after adding the microemulsion solubilized with hydrochloric acid, a small amount of white colloidal precipitate is precipitated after centrifugation for several hours, and the precipitate is separately washed with an appropriate amount of absolute ethanol/acetone mixture and distilled water. . The precipitate was dried at 105 ° C and ground to a white powder. Spherical particles with an average particle size of 40 to 65 nm after calcination.

Advantages: the obtained powder does not need to be heated, the experimental device is simple, the operation is convenient, and the product composition and particle size are controllable.

Disadvantages: high cost and slight agglomeration.

5) Gas-liquid reaction method

The gas-liquid reaction method refers to a method in which a gas is introduced into a salt solution to obtain a precursor precipitate, and the precipitate is dried to form an ultrafine powder. For example, Na2WO4 is used as a raw material, and ethanol/distilled water is added, and then stirred and dissolved. The suspension obtained by introducing HCl gas is allowed to stand, centrifuged, washed, dried, and ground to obtain uniform particle size distribution, good dispersibility, and irregular shape. The tungsten trioxide powder has an average particle diameter of 100 nm or less.

Advantages: good safety performance, small powder size and good dispersion.

Disadvantages: The process is complex and takes a long time.

6) Template method

The template method usually uses a porous material with a pore size of nanometer as a template, and combines electrochemical removal, precipitation, sol-gel method and vapor phase precipitation method to precipitate material atoms or ions on the pore walls of the template to form a desired The nanostructures are then removed from the template to yield nanomaterials with template gauge topography and dimensions. For example, nitrogen gas is introduced into the Na2WO4 solution, stirred and HCl is added, and the washed precipitate is re-dissolved with an oxalic acid solution to obtain a tungsten trioxide sol. The AAO template was immersed therein for a period of time, taken out and rinsed, and calcined and cooled to obtain a highly ordered nano-tubular tungsten trioxide powder.

Advantages: simple method, high repetition rate, good predictability, uniform product shape and stable performance.

Disadvantages: template agents are expensive.

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