Ammonium Metatungstate Preparing Thermal Insulation Additive

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.

hydrogen tungsten bronze molecular structure image

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.

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Ammonium Metatungstate Preparing Ammonium Tetrathiotungstate

ammonium tetrathiotungstate image

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.

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Ammonium Metatungstate Testing Equipment

visible spectrophotometer image

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.

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Ammonium Metatungstate Solubility

ammonium metatungstate dissolved in water image

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.

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APT Liquid Phase Transformation Method Preparing AMT

ammonium metatungstate photo

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%.

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Ammonium Metatungstate Preparing Radiation Shielding Non-Woven Fabric

radiation shielding non woven fabric image

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.

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