Compared with the ordinary tungsten oxide, hollow porous tungsten oxide sphere because of the larger specific surface area, thus to has the significant size, surface, quantum size and macroscopic quantum tunneling effect, and thereby to expand the application areas, which can be used as a solar absorption, stealth and photocatalytic materials and gas sensitive materials of NO_x, H₂S and NH₃ etc. Ammonium metatungstate (AMT) is an important intermediate compound in tungsten production industry, the excellent raw material for manufacturing tungsten oxide, tungsten powder, tungsten carbide powder and other tungsten products. 

 

A study was taking the ammonium metatungstate solution or a mixture of AMT and ammonium tungstate solution as raw material, to produce hollow porous tungsten oxide sphere through a combination of spray drying method and heat treatment, its technological process is: Preparing ammonium metatungstate solution or a mixture solution of AMT and ammonium tungstate, with the concentration of 200 g/L, then to prepare AMT or mixture of AMT and ammonium tungstate hollow powder; after putting the powder in a furnace to calcine for15-180 min under the temperature of 400-1000℃, we finally get made hollow porous tungsten oxide ball. Its properties are as follows: 

1. The concentration of AMT and ammonium tungstate mixture solution is 200g/L, the mass ratio of AMT and ammonium tungstate is 4:1~1~4, heat treatment temperature is 400~1000°C, time of heat preservation is 15~180 min. 

2. The spray drying method is using the ammonium tungstate solution, the concentration is 200 g/L, the heat treatment temperature of 400~1000°C, time of heat preservation for 15 ~ 180 min. Because when the temperature is below 400°C, the crystal growth speed is to slow and hard to generate porous; however, when the temperature is higher than 1000°C, the too fast growth speed of crystal will cause the nanosize particle of tungsten oxide hard to control, and thus it will easily get the coarse tungsten oxide particle which will reduce the specific surface area. While, when the heat preservation time is less than 15 minutes, the crystal growth is not completely; but when the holding time is higher than 180 min, it will come out combination of crystal and cause the coarse tungsten oxide particle.

Pt-supported tungsten carbide catalyst is uniformly loading the tiny metal platinum nanoparticles on the tungsten carbide carrier with highly dispersing, and both of tungsten carbide and platinum will play the synergistic effect, and thus to form a new type of fuel cell catalysts. Studies have shown that tungsten carbide (WC) can instead of platinum and other precious metal catalyst, and also had good ability to resist poisoning; moreover, its catalytic performance on hydrogen precipitation reaction has been confirmed. 

 

Research points out a preparation method of high efficient hydrogen evolution electrode materials and fuel cell electric catalyst, which is Pt-supported tungsten carbide catalyst, the preparation steps are as follows: 

1. Dissolve the ammonium metatungstate (AMT) and platinum salt in the distilled water in accordance with the mass ratio of 1:0.02~2, to prepare the mixed aqueous solution with 2.5 ~ 50 wt % of ammonium metatungstate after fully mixed; 

2. Import the mixed aqueous solution obtained in step 1 into a spray dryer for spray drying, and then to obtain the precursor particles of spherical H₂WO₄/ platinum salt; 

3. Put the spherical H₂WO₄/ platinum salt precursor particles in a reactor for roasting, and then goes on the reduction and carbonization; cool down the product to room temperature under the protection of inert gas after the reaction is completed until the dark grey products is generated, which is the Pt-supported tungsten carbide catalyst. Wherein, the mass ratio of metal platinum and carrier of tungsten carbide is 1~100:100, and tungsten carbide carrier has the morphology characteristics of mesoporous hollow spherical structure. 

 

The development background of Pt-supported tungsten carbide catalyst: 

1. Although the Pge electric catalyst has excellent electric catalytic activity, but the price is expensive; 

2. Nickel and its alloy are also used for hydrogen evolution materials, but their chemical stability is really poor; 

3. Fuel cell is expected to become the cleanest energy in the future since the high energy and efficiency, and friendly to environment and other properties, and thus to get a lot of attention. 

In such circumstances, Pt-supported tungsten carbide catalyst is supposed to become the mainstream of the fuel cell non-noble metal catalysts.

Hexagonal tungsten oxide ball (hex-WO₃), which is the tungsten oxide ball with hexagonal crystal structure. Since the single crystal hexagonal tungsten oxide has an empty hexagonal space tunnel structure, the W contained compound will exit mixed valence states of W⁶⁺, W⁵⁺ and W⁴⁺ and so on, thus to make the overall compound in a balance charge state. This special structure and valence is making hexagonal tungsten oxide ball has well electro-optic effect and excellent electrical properties, thus it has widely been used in laser frequency doubling, optical signal processing, superconducting material, solid fuel cell and other fields.

 

A study was taking glucose and ammonium metatungstate (AMT) as the raw materials to prepare hexagonal tungsten oxide ball by solid - phase thermal decomposition method, which is controlling the crystal morphology of tungsten oxide ball by adjusting the temperature in the reaction process. The manufacture steps are as follow:

1. Weight the ammonium metatungstate and glucose in accordance with a specific mass ratio, the mass ratio of AMT: glucose is preferred of 1:2.5;

2. Grind AMT and glucose crystal to the average particle size of 10nm~200μm, then put them in quartz boat after mixed uniformly;

3. Put the quartz boat with the raw materials in a tube furnace with inert gas atmosphere, and then rise the temperature to 850°C~900°C by the program temperature controlling to sinter for 5~6 hours, then we get the product of hexagonal tungsten oxide ball after cutting down the current and natural cooling.

 

The particle size of hexagonal tungsten oxide ball obtained in this method is among 40μm~80μm, and there is no agglomeration between the spheres; moreover, the tungsten oxide nanorods are regularly attached to the surface of the ball, which have a length of 1μm~5μm. This solid - phase thermal decomposition method to prepare tungsten oxide has the benefits of less raw materials (AMT and glucose) required, simple ingredient and process, nom pollution to the environment, high purity of product, short cycle and small consumption of energy and so on, thus to be benefit for industrial production, also it has provided a new way for preparing nano materials at the same time.

Waste tungsten oxide, including the scrapped, the not qualified which must be reworked to improve the quality indicators of tungsten trioxide, blue tungsten oxide and others. During the production, using process, or in the case of large inventories, tungsten oxide may not reach a certain specific standards due to various reasons, or directly scrapped. However, these waste tungsten oxide still contains a high content of tungsten, since the tungsten is a rare metal element, thus a more effective approach to reuse waste the tungsten is turning waste into treasure.

 

Ammonium metatungstate (AMT) is an important raw material in tungsten smelting industry, catalyst for petrochemical industry and other fields. The ways of waste tungsten oxide as raw materials to produce ammonium metatungstate are many; however, since tungsten trioxide and blue tungsten oxide are not soluble or slightly soluble in ammonia water, which only soluble in caustic soda or soda ash. Therefore, the traditional process is cooking and dissolving tungsten oxide under the normal or high pressure by using caustic soda (sodium hydroxide) or soda ash (sodium carbonate) solution, to generate sodium tungstate solution; or melting tungsten oxide with soda ash (sodium carbonate) under high temperature, and then leaching tungsten by water to produce sodium tungstate solution, and then get AMT by the follow-up process, the three processes are as follows:

1. Extract tungsten by an organic solvent and reextract tungsten by ammonia water from the sodium tungstate solution to convert tungsten into ammonium tungstate solution, and finally obtain ammonium metatungstate from the ammonium tungstate solution by evaporation crystallization or neutralization crystallization;

2. The tungstate solution is adsorbed by the ion exchange resin tungsten and ammonia desorption of tungsten, to convert tungsten into ammonium tungstate solution, and finally manufacture AMT from ammonium tungstate solution by evaporation crystallization or neutralization crystallization method;

3. Precipitate the artificial scheelite (calcium tungstate) from sodium tungstate solution with calcium chloride, and then produce tungstic acid by decomposing artificial scheelite with hydrochloric acid, then the tungstic acid is dissolved in ammonia solution to generate ammonium tungstate solution, finally, the AMT is prepared by evaporation crystallization or neutralization crystallization method from the ammonium tungstate solution.

 

In addition, studies have pointed out the method of using ammonia water to dissolve waste tungsten oxide and to prepare AMT, which is in accordance with the property of tungsten oxide is easily soluble in ammonia water under the high temperature and pressure conditions and generate ammonium tungstate solution, and then produce ammonium metatungstate by neutralization transformation - spray drying method from ammonium tungstate.

Because of the narrow band gap (about 2.80eV), special structure and high stability and other benefits, bismuth tungstate (Bi₂WO₆) is a new type of environmental friendly material, which can be as the visible light photocatalyst. Bismuth tungstate has an excellent photocatalytic activity under the visible light, and can be used for degrading organic matters, such as RhB, phenol, aldehyde, antibiotics, etc; at the same time, it can catalyze the CO₂ and water to generate fuel. The preparation methods of bismuth tungstate are solid reaction process, coprecipitation, sol-gel method, spray and hydrothermal method.

 

Compared to the normal bismuth tungstate, nanometer sheet bismuth tungstate has the larger specific surface area, higher catalytic activity and other advantages. Thus, the study of nanometer sheet bismuth tungstate is popular, and one of important researching direction is how to prepare the tiny nanometer sheet bismuth tungstate with high photocatalytic activity by the simplest operating method and the lowest energy consumption.

 

A study has manufactured nanometer sheet bismuth tungstate by solvent hot method combined with water hot method from the raw materials of ammonium metatungstate (AMT) and bismuth nitrate, the process is showed as the following living example:

1. Fetch 10mol of bismuth nitrate, 15mol of glycerin to dissolve in the 1000mol of isopropyl alcohol with stirring to get the uniform, clear solution;

2. Transfer it into the autoclave, and raise the temperature to 160°C then keep the heat preservation for 12 hours;

3. Stop heating and cool the autoclave to room temperature, then filter to get the filter cake, and then dry the filter cake at 80°C for 12 hours after the it is washed with isopropyl alcohol for 3 times, to get the glycerin bismuth powder;

4. Fetch 1mol of ammonium metatungstate to dissolve into the deionized water, and add in 13mol of glycerin bismuth powder, go on with stirring to get a uniform solution, then transfer the solution to a autoclave for heating to 180°C with thermal insulation for 24 hours after adjusting pH value to 0~1 with the nitric acid;

5. Stop heating to cool down the product to room temperature, filter the solution to get the filter cake, and then dry the filter cake under 120°C for 12 hours after it has been washed with deionized water and ethanol for 3 times, to finally get the product of nanometer sheet bismuth tungstate.