Ammonium metatungstate (AMT) is a tungsten compounds with high molecular weight and water-soluble, which is easily dissolved in water, the solubility of it can reach 100g/mL at room temperature. It can be prepared from the material of ammonium tungstate by the method of Bipolar Membrane Electrodialysis (BEMD).

Electrodialysis method uses the effect of electric field, makes water which is in the two sides of bipolar membrane dissociated into H⁺ and [OH]^- then directional moved to both sides of electrode, and entered into the liquid chamber (the salt chamber) and alkali chamber respectively. Electrodialysis method is widely used in the field of chemical, light, metallurgy, papermaking industry and so on.

The preparation process of AMT by the method of electrodialysis which is using ammonium tungstate or ammonium paratungstate as raw materials is performed as bellows:
1. Add ammonium paratungstate into anode chamber, when an electric current passes by, water dissociated into two forms--H⁺ and [OH]^- and directional moved to both sides of electrode under the action of strong electric field, and then respectively enter the liquid chamber (the salt chamber) and alkali chamber;
2. H⁺ ions enter the salt chamber to combine with WO₄^- and then will not go into alkali chamber ever again; ammonium ions move to cathode chamber through the exchange membrane, thus cause the concentration of ammonium metatungstate increased;
3. [OH]^- moves into alkali chamber through the anion exchange membrane to combine with ammonium ions which is continually moved in and no longer went into the anode chamber;
4. With the process of electrolysis carrying out, ammonium ions decreased and hydrogen ions increased continually in the salt chamber, thus cause the pH value of the solution in salt chamber decreased continuously;
5. Finally, ammonium metatungstate solution is released from the cathode chamber, and AMT generated.

Continued from the preceding paragraph, we will discuss the key technologies of tungsten copper composite powder warm compacting process according to the aspects above.

2. Lubricant: In the traditional process, lubricant used in general when the temperature was raised to 120-150 ℃, it is difficult to ensure the fluidity of the powder, the powder is mixed performance by a certain influence. Therefore, the choice of lubricant is also can not be ignored. It should meet the glass transition temperature of 130-150 ℃, low coefficient of friction (temperature, friction coefficient further reduced in favor of a metal powder and die wall friction and powder particles to a minimum, thereby reducing the pressure and pressing off clamping force), soluble in volatile solvents (powder dry and easy to make the surface of the powder particles uniformly coated with a thin layer of lubricant film), can effectively prevent or slow down the oxidation of tungsten-copper alloy powder (usually metal powder is oxidized, increased oxygen content will affect its final properties), the decomposition temperature range is wide (should be more gentle lysis, avoid large amounts of gas, resulting in the expansion of the volume of powder metallurgy parts), non-toxic lubricant after decomposition, do not pollute the environment .

3. Temperature Control: Temperature and pressure molding preheating temperature between 100 ~ 150 ℃. Because usually between room temperature and the temperature of hot pressing temperature is between, this has been known as warm compacting process. The temperature and pressure above the temperature control of the glass transition temperature of the polymer lubricant or below the melting point of the lubricant in the viscous flow state, both have a certain cohesiveness and some lubrication, it is conducive to the particle surface and spread flow. Whether temperature is too high or too low will destroy the lubricant film and caused failure.

Warm compacting process is a kind of new process of high precision powder metallurgy that develops based on conventional molding process. Compared with conventional process, warm compacting process is in the process of pressing the powder in a conventional method and the mold is heated to a certain temperature after pressing to obtain high-density powder compact, which achieves sintered body with high density and high performance. Warm compacting process can be suitable for whether iron-based materials or tungsten (W), copper (Cu), aluminum (Al) and other metal powder, which has many advantages, such as higher compacting and sintering density, uniform distribution, higher compacting strength, lower releasing pressure, lower spring back and cost. The influencing factors include the powder (apparent density, the granularity, the content and porosity, etc.), the choice of lubricant, the temperature and other parameters controlling, which are the key technologies to ensure the molding process. Next, we will discuss the key technologies of tungsten copper composite powder warm compacting process according to the aspects above.

1. Powder: The choice of powder includes that the granularity, the content, apparent density, the porosity and so on. Tungsten-copper composite powders for warm molding not only require good compressibility in heating, transport and pressing process, liquidity and stability constant bulk density, and require consistency between the performances of the parts made of It is also high. Particle size, size distribution and powder itself mixed powder formulations are to some extent determines the density of the material and non-porosity. Related foreign researchers developed a patented powder, heated at 130 ℃ to either incubated or in powder 130 ℃ under cooling to room temperature, warming cycle effect, the powder flowability and bulk density as well as 600MPa by pressing the blank density are very stable.

N Carbide and alloy performance is largely determined by the quality of tungsten trioxide. Common methods of preparing tungsten trioxide including the following major steps: first of all, removing palladium, silicon, fluorine, phosphorus, and molybdenum by solution purification, secondly, the precipitation of artificial scheelite is based on calcium chloride solution. Thirdly, using hydrochloric acid to decompose artificial scheelite; finally, the tungsten trioxide is prepared by washed, filtered, and dried steps. This article focuses on the methods of determination for palladium in high-purity tungsten trioxide.

The definition of Colorimetry is based on the color reaction of the colored compound by measuring or comparing. As a method of quantitative analysis, the basic requirements of the Colorimetry are: high sensitivity and selectivity, stable colored compound and different color. The color reaction and control of the reaction conditions is the key for colorimetric analysis.

Determination of palladium in High-Purity Tungsten Trioxide Method
Burning the high-purity tungsten trioxide at 1400 ℃, and the resultant of palladium sulfide reacts with oxygen form palladium dioxide. This compound is condensed with formaldehyde, and the purple compound can generate in 560nm colorimetric determination. The experiment of the color, the time and the sample of absorption time can reduce combustion conditions such as blank test. Finally, we can obtain the amount of available mercuric chloride, sodium, chromogenic agent, the influence of magenta and fading. Detection limit of this method is 0.5ppm; the relative standard deviation is ± 4.8%.

Ammonium paratungstate is chemical substance, and it is mainly white crystal. There are two kinds of sheet-like or needle-like, they are for the manufacture of yellow tungsten oxide or blue tungsten oxide powder. Ammonium paratungstate is used to make other tungsten compounds that are used in petrochemical industry, such as additive. The series of downstream products, such as tungsten and other electric vacuum materials; series of alloys, such as tungsten carbide, hard alloy, alloy blades, drill bits alloys, mold; wear, pressure, machinery and equipment and other high-temperature components.

Tungsten trioxide is an important η-type semiconductor oxide, it has a variety of crystal structure, and is has been applied in electrochromic, photochromic, sensing and catalysis, in which the quasi-spherical particle diameter of the tungsten trioxide is 100nm-700nm, spherical particle diameter of the tungsten trioxide is 20-200nm, both tungsten trioxide particles can be used as precursors nanometer tungsten carbide.

Vapor phase method is the most effective method for the preparation of nanostructures present; various vapor deposition techniques can form solid film, whiskers and particles. And a vapor deposition method from a high concentration of the reactants is not prepared in high purity product. But the disadvantage of the conventional vapor deposition method is very limited, since the product was collected under high vacuum or high temperature, continuous production can not be achieved. We make ammonium paratungstate as raw materials, argon as carrier, and combine innovative technology with calcination, in the vapor deposition; the reaction was collected in a low temperature region, the successful implementation produce a variety of WO₃ powders.