According to the classical definition, a superacid is an acid with an acidity greater than that of 100% pure sulfuric acid, which has a Hammett acidity function (H₀) of −12. According to the modern definition, superacid is a medium in which the chemical potential of the proton is higher than in pure sulfuric acid. The known superacid can be divided into liquid and solid superacid according to the appearance. In petrochemistry, superacidic media are used as catalysts, especially for alkylations. Typical catalysts are sulfated oxides of titanium and zirconium or specially treated alumina or zeolites. The solid acids are used for alkylating benzene with ethylene and propylene as well as difficult acylations, e.g. of chlorobenzene.

 

In 1998, the presence of supported oxide solid superacid has immediately caused a wave of research in the field of catalyst, which has been reported to have three types, namely WO₃, MoO₃ and B₂O_{3 oxides, with the acidity showing as the following table:}

 

The supported oxide solid superacid (WO₃/ ZrO₂) which Arata firstly studied has the acidity lower than that of SO₄^2- / M_xO_y-type solid superacid (SO₄^2- / ZrO₂) with H₀ < -16.0 (while the H₀ of WO₃/ ZrO₂ is lower than 14.5), but its stability in solution and reducing atmosphere and heat is better than that of SO₄^2- / ZrO₂ solid superacid; moreover, it is selectivity for some specific reactions, such as isomerization of high-carbon alkanes, is higher than that of SO₄^2- / M_xO_y catalyst.

 

The results showed that ammonium metatungstate (AMT) can be used as a tungsten source for the preparation of supported oxide solid superacid (WO₃/ ZrO₂), with the preparation methods of coprecipitation and sol-gel method; both of the two methods are also called as one-step method since it is introducing WO₃ at the same time of preparation process, the processes are:

1. Coprecipitation method: Pour the ZrOCl₂ solution into a mixed solution of ammonium metatungstate and ammonia water to conduct coprecipitation, and adjust the final pH value to 9.0, then carry out filtering, washing, drying and calcination to get the final product.

2. Sol-gel method: Add the zirconium n-propoxide into the mixed solution of ethanol and nitric acid containing with ammonium metatungstate to get gelling; remove the ethanol by carbon dioxide supercritical drying method after the obtained gel is aged for 2 hours; and then dry it in vacuum for 3 hours respectively at temperature of 383 K and 523 K, and finally carry out calcination at high temperature.

Ammonium metatungstate (AMT) is an important intermediate compound in tungsten metallurgy industry, which is mainly used for manufacturing tungsten oxide, tungsten powder, tungsten wire and other tungsten compound, also, it is used in catalyst of petrochemical industry. Researches have indicated that ammonium metatungstate and ammonium sulfide solution can be used for preparing ammonium dithiotungstate under some specific environment.

 

There are two methods of ammonium metatungstate preparing ammonium dithiotungstate, as following:

The first method:

1. Dissolve ammonium metatungstate in the deionized water with stirring;

2. Add ammonia water and stir for 20 minutes to speed up the reaction speed under the temperature of 60°C, at this time, the pH value of reaction system may be 9;

3. Add ammonium sulfide solution and stir for 30 minutes under 60°C, then carry out vacuum filtration until the reaction is stop to remove a small amount of blue precipitation which generated during the reaction process;

4. Stand the filtrate for 24 hours under 0°C to get yellow crystal;

5. Carry out vacuum filtration and the precipitation is washed respectively with deionized water and anhydrous ethanol for three times, and finally we get the ammonium dithiotungstate crystal after drying, with the yield of 45%.

 

The second method:

1. Place the 5g of industrial grade ammonium tungstate which contains 83% of tungsten trioxide into conical beaker, and add 8 wt% of ammonium sulfide solution 35ml slowly, at this time the color of the solution will slowly turns from blue to light yellow;

2. Stir for 30 minute at room temperature after all the ammonium sulfide solution is poured into the conical beaker, and then stand the reactant solution for 12 hours to generate yellow crystal;

3. Precipitate, and wash the precipitation respectively with deionized water and anhydrous ethanol for three times, dry at room temperature in vacuum environment to finally get ammonium dithiotungstate crystal, the yield is 93% in accordance with tungsten content.

 

Ammonium dithiotungstate [(NH₄)₂WO₂S₂] is an important class of thiometal ammonium salt, and the decomposition products include {WOS₂}, vulcanization intermediate of tungsten oxide. Studies have found that the thermal decomposition of ammonium dithiotungstate crystal under the atmosphere of hydrogen is mainly occurred among 160～450℃, which firstly transfers to {WOS₂} and then to tungsten disulfide.

Many metal oxides and some tungstate have the electrical conductivity and thermal insulation properties, and can be used as infrared shielding material. By heating the mixture solution of ammonium metatungstate (AMT) and alkali carbonate to 80°C, it can prepare some kind of tungsten oxide and tungsten bronze, and all these resulting substances can be used as the raw material of light transmission conductive films with infrared shielding property.

 

Thermal insulation additive is a kind of material which can stop the thermal conduction during heat transfer. Thermal insulation is the reduction of heat transfer (the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with specially engineered methods or processes, as well as with suitable object shapes and materials. The insulating capability of a material is measured with thermal conductivity (k). Low thermal conductivity is equivalent to high insulating capability (R-value). In thermal engineering, other important properties of insulating materials are product density (ρ) and specific heat capacity (c).

 

Ammonium metatungstate to prepare thermal insulation additive, which is hydrogen tungsten bronze, is get ammonium metatungstate contact with hydrogen gas or reducing gas which can release hydrogen gas at a temperature of 2500K or higher, wherein the AMT can be replaced by ammonium paratungstate or ammonium hexametungstate and ammonium dodecatungstate and AMT hydrate; the reducing and releasing hydrogen include ammonia or volatile hydrocarbons such as ethane or propane, which may be used in place of hydrogen or as a mixture with hydrogen; in a plasma, in particular when the hydrogen and / or hydrogen-evolving gases are used in admixture with a noble gas.

 

In addition, a invention has pointed out a method for preparing insulating material with raw material of ammonium metatungstate, by preparing ammonium metatungstate solution as a precursor, then drying it to get AMT crystal; and then, reduce AMT at 100~500°C to generate composite tungsten oxide at the reaction condition, finally to form composite tungsten oxide film to play a role of heat insulation.

With the rapid development of modern science and technology, all kinds of high-energy rays (such as X-ray) have been more and more widely applied. Besides, since people have put more and more concern to the protection of high-energy rays, and thus, the research and manufacture of X-ray protection materials is emerging in endlessly. There are three ways for X-ray protection, respectively time, distance and shielding protection. Wherein, the shielding protection is using or setting a kind of shielding material which can absorb the X-ray between human body and radiation source, thus to weaken or even eliminate the damage which X-ray brings to human body.

 

At present, the main X-ray protection material is the metal with high density, such as lead plate, lead rubber and compounds with lead, to shield the ionizing radiation of X-ray. However, as for personal radiation protection, lead oxide will firstly poison human body, and cause environmental pollution; secondly, the hard material will make human body uncomfortable.

 

For solving that problem, an invention has pointed out a method which takes ammonium metatungstate (AMT) as one kind of raw material component to prepare radiation shielding non-woven fabric. The radiation shielding non-woven fabric is some kinds of fabric with radiation shielding function which is formed by no need of spinning weaving. In this radiation shielding non-woven fabric, the weight ratios of all kinds of materials are: 1~10% of ammonium metatungstate (AMT), 5~20% of polyacrylonitrile copolymer and 80~95% of DMF, while the preparation steps are like following:

1. Weight the raw material of AMT, polyacrylonitrile copolymer and DMF according to weight ratio and get them into mixture solution, and then obtain spinning solution by ultrasonic standing deaeration;

2. Carry out electrostatic spinning process to the spinning solution which generated from step 1 to prepare grey cloth with nano or micron grade;

3. The grey cloth is carried out drying treatment and then went on preoxidation in the air;

4. Go on a carbonization after the grey cloth is finished preoxidation, then we will obtain the desired radiation shielding non-woven fabric.

Ammonium tetrathiotungstate [(NH₄)₂WS₄], which is short for ATTT, is widely applied in the synthesis of biological nitrogenase activity center - tungsten iron sulfur atom cluster compounds, also is the precursor of coal liquefaction and heavy oil hydrogenation catalyst, and also can be raw material for preparing supported tungsten sulfide hydrogenation catalyst. The traditional way to produce ammonium tetrathiotungstate from the raw material of ammonium metatungstate (AMT) is introducing hydrogen sulfide gas into ammonia solution with AMT, wherein the hydrogen sulfide gas is generated by sodium sulphide (Na₂S) and phosphoric acid in situ method. However, since this method will take a long reaction time, consume a large number of sodium sulphide and phosphoric acid, and also will discharge much rubbish, moreover, it also involves the treatment of toxic and stinking hydrogen sulfide gas, and thus has been eliminated.

 

For shortening the reaction time, reducing pollution to the environment, and obtaining high purity product at the same time, an invention has pointed a method to prepare ammonium tetrathiotungstate from raw materials of ammonium metatungstate (AMT), concentrated ammonia water and ammonium sulfide solution, the steps are shown as following:

1. Weight a certain amount of ammonium metatungstate powder and add distilled water, control the ratio of dosage distilled water and AMT at among 3 ~ 6/1 (Calculated by ml/g);

2. Add a certain amount of concentrated ammonia water with stirring and heating to 40～60℃ to dissolve, the ratio of dosage concentrated ammonia water and AMT is 1～2/1 calculated by ml/g;

3. Control the solution temperature among the room temperature (25℃) to 90℃, then add ammonium sulfide solution with sulfur content of 6～12％ with stirring, the mole ratio of sulfur and tungsten in the added amount of ammonium sulfide solution and reactant liquid is 4~6 to 1, and stir for 0.5~3 hours to get blood red liquid;

4. After the reaction finished, take out the reactant to cool to room temperature and get it crystallize for 8~24 hours, then filter the solution with crystal and wash them with cold distilled water for 3 times, finally wash the crystal with anhydrous ethanol for 2~3 times, then carry out drying solvent, drying under room temperature for 24 hours to get dark red needle crystal of ammonium tetrathiotungstate.

Testing equipment of ammonium metatungstate includes atomization device, inductively coupled plasma (ICP), electronic balance, visible spectrophotometer, metallographic microscope, atomic absorption spectrophotometer, etc..

 

Both Graphite Furnace Atomic Absorption Spectrometry and Atomic Absorption Spectrometry method use the atomizer. Atomizer is an apparatus of atomizing the sample of atomic absorption spectrometry, and it will convert the sample to the free atomic vapor (ground state atoms) thus to absorb the radiation and calculate the analyte content. Atomizer has many types and can be divided into two categories of thermal and electric filling atomizer. The former includes a pre-mixed, all-consuming; the latter includes graphite furnace, carbon filament atomizer, atomizer carbon rod, graphite increased exhaust, graphite probes ect..

 

An inductively coupled plasma (ICP) or transformer coupled plasma (TCP) is a type of plasma source in which the energy is supplied by electric currents which are produced by electromagnetic induction, that is, by time-varying magnetic fields. There are three types of ICP geometries: planar, cylindrical, and half-toroidal.

 

Electronic balance (which is also known as electronic scale) is a kind of weighing scale, the device to measure weight or calculate mass. The ordinary electronic scales intrinsically measure the gravitational force between the sample and the earth, i.e. the weight of the sample, which varies with location. So such a scale has to be re-calibrated after installation, for that specific location, in order to obtain an accurate indication of mass.

Visible spectrophotometer is used in the spectrophotometry, in chemistry, spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. It is more specific than the general term electromagnetic spectroscopy in that spectrophotometry deals with visible light, near-ultraviolet, and near-infrared, but does not cover time-resolved spectroscopic techniques.

 

Metallographic microscope is equipment in the metallography which may also use the scanning transmission electron microscope, bright and dark field microscopy and polarized light microscopy and other equipments. Now, the metallographic microscope is usually combining with computer and to form computer type metallographic microscope or digital metallographic microscope, the high-tech product which gets optical microscopy, photoelectric conversion and computer image processing technology together perfectly, and can easily observe the metallographic image of ammonium tungstate on computer, thus to analyze and rate the metallographic atlas, and also output, print images.

Ammonium metatungstate (AMT) is a white or yellowish crystalline powder, an important tungsten compound which can be used for producing tungsten oxide, tungsten powder and other products, or for the manufacture of all kinds of catalyst in petroleum chemical industry, the main raw material of tungsten based catalyst of oil refineries.

 

If there are no special instructions, the solubility of ammonium metatungstate refers to it in water; AMT has very good water soluble which is 303.99/100g at 20℃, and its aqueous solution is quite stable with acidity. With the improving of temperature, ammonium metatungstate solubility in water will raise until it reaches the highest solubility which is saturated state. Metatungstic acid and most of its metatungstate can well soluble in water, and the advantage of AMT is its very huge solubility in water, thus it can be directly used and to prepare high concentrated tungstate solution with no alkali metal ions.

 

Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure and the pH of the solution. The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute. The solubility of a substance is an entirely different property from the rate of solution, which is how fast it dissolves.

 

The factors that affect solubility are temperature, pressure ect.. Solubility is defined for specific phases. For example, the solubility of aragonite and calcite in water are expected to differ, even though they are both polymorphs of calcium carbonate and have the same chemical formula. The solubility of one substance in another is determined by the balance of intermolecular forces between the solvent and solute, and the entropy change that accompanies the solvation. Factors such as temperature and pressure will alter this balance, thus changing the solubility.

Ammonium metatungstate (AMT) is an important tungsten compound, mainly used in the manufacture of tungsten oxide, tungsten and tungsten carbide powder and their downstream products ect., also it can be used as catalyst in fields of petroleum cracking, organic synthesis, nitration and so on; besides, with the rapid development of oil refining, petrochemical and other industries, the demand amount of ammonium metatungstate is growing fast. There are many preparation methods for ammonium metatungstate which can be divided into two catalogues of solid and liquid phase transformation method, such as thermal decomposition method, neutralization method, solvent extraction and ion exchange method, wherein the thermal decomposition method which is depending on raw material of ammonium paratungstate (APT) is the mainstream process for preparing AMT in industrial.

 

For manufacturing AMT with high solubility to meet the requirement of tungsten contained catalyst, an invention has pointed out a liquid phase transformation method to produce ammonium metatungstate which took ammonium paratungstate as raw material; and the result of experiment have shown that this method has the advantages of short process, little investment of equipment ect., furthermore, the product – AMT is highly dissolve in water with the stable quality. The preparation steps are shown as following:

1. Leaching the wet ammonium paratungstate: Mixing the material of wet ammonium paratungstate (which the water content is among 5~10%) and dilute nitric acid (HNO₃) to prepare ammonium metatungstate solution, the chemical reaction is like bellow:

5(NH₄)₂•12WO₃•5H₂O+4HNO₃=(NH₄)₆•H₂W₁₂O₄₀•6H₂O+4NH₄NO₃

2. Converting the dilute ammonium metatungstate solution to concentrated AMT solution: The dilute ammonium metatungstate solution is carried out standing for aging, filtering, heating for concentrating and again filtering for many times to finally get concentrated AMT solution;

3. Spraying and drying the concentrated AMT solution obtained in step 2 with an spray dry tower which will dry AMT feed liquid into powder quickly, thus to get product of AMT powder.

 

Compared to the traditional method, this kind of liquid phase transformation method requires no calcination step, so it is no need to use rotary kiln which will reduce the fixed investment; at the same time, product per ton will save 120KWH, while the recovery efficiency can be improved for 3%.