2017年2月15日星期三

Ammonium Metatungstate Preparing Composite Cobalt - Tungsten Oxide Powder


composite tungsten cobalt oxide product image

Composite cobalt - tungsten oxide powder is the main raw material for manufacturing cemented carbide powder, the finished product cemented carbide has been widely used in machinery manufacturing, oil exploration, military industry, aerospace and other fields because of its high hardness and density, wear-resisting and other special performance. 

Common methods for manufacturing composite cobalt - tungsten oxide powder by using the ammonium metatungstate (AMT) or metatungstate as raw material are like following:

1. Make a certain concentration of ammonium metatungstate solution, then add a certain amount of cobalt carbonate powder (CoCO3) with heating, stirring for full reaction, and then cooling, filtering the compound salt solution; drying the compound salt solution to get the powder, get the compound powder heated in fluidized bed to finally get composite cobalt - tungsten oxide powder.

In this method, the reaction of AMT and cobalt carbonate is really slow and difficult to completely carry out; moreover, the cobalt content is difficult to get accurate control, also, it is limited by the inherent ratio of tungsten - cobalt in chemical reaction, which makes the cobalt content higher than 7% is difficult to get.

2. Get uniform tungsten - cobalt complex solution through the full reaction of a certain concentration of metatungstate and CoCO3; uniformly mix EDTA powder and CoCO3 powder and add it into the obtained tungsten - cobalt complex solution to carry out a reaction to get the cobalt compound solution with the required W:Co ratio; Then the solution is dried and granulated, carried out spray drying and calcination to get uniform component of composite cobalt - tungsten oxide powder. 

In this method, the metatungstate is a kind of very unstable moderate acid and easy to precipitate yellow tungsten acid, thus to affect the actual recovery and accuracy for matching cobalt in composite cobalt - tungsten oxide powder.

3. Mix the ammonium metatungstate, cobalt salt (cobalt carbonate or cobalt oxide), EDTA powder uniformly according to the calculated ratio, then add the mixed powder into deionized water for rapid response to get cobalt - tungsten compound solution; then the solution is going through spray drying granulating, and removing water by drying and calcination to further get uniform composition, cobalt content can be adjusted, well controlled precision of composite cobalt - tungsten oxide powder.

This method composite cobalt - tungsten oxide powder with good uniformity, cobalt content during 7% ~ 30%, moreover, the cobalt content can be adjusted as your wish, and controlled accurately.

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Ammonium Metatungstate (AMT) Preparing Hollow Porous Tungsten Oxide Sphere by Spray Drying Method


hollow porous tungsten oxide sphere image

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 NOx, 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.

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Ammonium Metatungstate (AMT) Preparing Hexagonal Tungsten Oxide Ball


hexagonal channels of tungsten oxide image

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.

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Waste Tungsten Oxide Recovering Ammonium Metatungstate (AMT)


ammonium metatungstate AMT image

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.

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Ammonium Metatungstate Preparing Nano Tungsten Oxide Aqueous Solution


nano tungsten oxide aqueous solution image

Nano tungsten oxide can not soluble in water itself, the so called nano tungsten oxide aqueous solution is the dispersion which nano tungsten oxide particles are uniformly distributed in water, to play the roles of oxidization and reunion of tungsten oxide. Tungsten oxide is the typical transition metal oxides, while the nano tungsten oxide is a new type of functional material, and because of its excellent discoloration performance, it can be widely used in many fields, such as intelligent window, large area flat panel display, gas sensor, dye-sensitized solar cell, automatic mirror, energy storage.

Ammonium metatungstate (AMT) is the important intermediate compound of tungsten metallurgy, and being the important raw material for manufacturing tungsten oxide, tungsten and tungsten carbide powder and other tungsten products. An invention has proposed one method to prepare nano tungsten oxide aqueous solution from the raw material of ammonium metatungstate and sodium borohydride, with the steps like bellows:
1. Weight the appropriate amount of ammonium metatungstate and sodium borohydride according to the mass ratio of 1~10:1;
2. Add the AMT powder into deionized water to dissolve with stirring and get the ammonium metatungstate aqueous solution with the concentration of 5~50%;
3. Add the weighted sodium borohydride solid into the AMT solution and stir to mix them uniformly, stay to react for 10~60 minutes under the room temperature to 95°C to get the blue nano tungsten oxide aqueous solution with 0.1〜10nm uniform particle size. since the ammonium metatungstate will react with sodium borohydride to generate blue nano WO2.9, and it will release heat, a large number of hydrogen gas and ammonia gas during the reaction process, which will remove purity of ammonium ion.

Nano tungsten oxide aqueous solution prepared by this method has the advantages of good stability, small particle size of nano tungsten oxide and others, thus to have wide application in intelligent window, gas sensor and solar energy cell and other fields.

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Ammonium Metatungstate Preparing Violet Tungsten Oxide Whisker


violet tungsten oxide whisker SEM image

Ammonium metatungstate (AMT) is an important compound in tungsten metallurgy industry, an important raw material for preparing tungsten oxide, such as tungsten trioxide (YTO, WO3), violet tungsten oxide (VTO, WO2.72 or W18O49). Violet tungsten oxide whisker is the micro-nano-short fibers which are generated by the high purity violet tungsten oxide, with the mechanical strength equal to the strength of adjacent atoms between the intensity. The highly oriented structure of W18O49 whisker has not only making itself of high strength, modulus and elongation, but also of the properties of electrical, optical, magnetism, dielectricity, conductivity and superconductivity.

It is pointed out that a process for producing violet tungsten oxide whiskers by coaxial electrostatic spinning method with ammonium metatungstate as a raw material is as follows:
1. Mix 2ml saturated ammonium metatungstate solution and 12% PVA solution in a certain proportion, to prepare spinning solution;
2. Inject the best electrospinning solution into 10ml syringe, and install it in the syringe pump to carry out a single tube electrospinning experiment. In the spinning process, solvent will volatilize partly in the air and form ammonium metatungstate/PVA composite fiber;
3. Calcine the obtained ammonium metatungstate / PVA composite fiber in the air to remove the solvent and the matrix PVA, and the ammonium metatungstate is decomposed by heating to obtain WO3 one-dimensional nanofibers at the same time;
4. The WO3 one-dimensional nanofibers is transformed to some specific crystal type and appearance by a certain heat treatment process, thereby to get W18O49 whisker.

The results showed that 800 ℃ is the optimum temperature for the formation of violet tungsten oxide whisker, and the W18O49 whisker nanorods are different in length. In addition, from the transmission electron microscopy (TEM), SEM, XRD and SAED patterns, we can observe that W18O49 whiskers are growing independently of each other with the smooth surface, with nano-level diameter and micron-length, large aspect ratio, and the is diameter mainly among 170nm-250nm, the length is mainly between 2-3μm, long diameter ratio mainly among 10-17, thus to be with some unique properties.

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