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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Ammonium Metatungstate Production Equipment

Ammonium metatungstate production equipment according to the different stages of production and different methods may be variety, such as pyrolysis method of AMT production, a reactor, rotary kiln, high-speed centrifugal spray drying equipment or spray atomization drying equipment may be used; In addition, other pyrolysis equipments include microwave oven, plate multiple hearth furnace and tubular multiple hearth furnace. The direct recovery AMT can be more than 95% when using tubular multiple hearth furnace.

At present, the pyrolysis equipment for producing ammonium metatungstate is mainly rotary calciner, which is a rotary kiln. A rotary kiln is a pyroprocessing device used to raise materials to a high temperature (calcination) in a continuous process. The kiln is a cylindrical vessel, inclined slightly to the horizontal, which is rotated slowly about its axis. The material to be processed is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down towards the lower end, and may undergo a certain amount of stirring and mixing. Hot gases pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gases may be generated in an external furnace, or may be generated by a flame inside the kiln. Such a flame is projected from a burner-pipe (or "firing pipe") which acts like a large bunsen burner. The fuel for this may be gas, oil, pulverized petroleum coke or pulverized coal.

alkali decomposition furnace

plate and frame filter

Ammonium metatungstate produced by ion exchange method will probably use ion exchange resin, crystallizer, or spray dryer and other production equipments. Alkali decomposition furnace is mainly used for decomposing tungsten ore during the preparation of AMT to dissolve tungsten into a solution. A plate and frame filter press is the most fundamental design, and many now refer it as a "membrane filter plate". This type of filter press consists of many plates and frames assembled alternately with the supports of a pair of rails. It is used for the impurity removal process of sodium tungstate for preparing high purity sodium in the APT preparation.

ion exchange column

spray drying tower

Ion exchange colum is used for removal of S, Mo, P, As, Ca, Cu and Sn and other impurities. Co-current deionization refers to the original downflow process where both input water and regeneration chemicals enter at the top of an ion exchange column and exit at the bottom. Co-current operating costs are comparatively higher than counter-current deionization because of the additional usage of regenerants. Because regenerant chemicals are dilute when they encounter the bottom or finishing resins in an ion exchange column, the product quality is lower than a similarly sized counter-flow column. Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals.

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Ammonium Metatungstate Decomposition Temperature

Ammonium metatungstate decomposition temperature is the temperature of AMT coming out decomposition reaction; while in the actual production environment, ammonium metatungstate will have several different decomposition temperatures according to complete reaction or not. Decomposition temperature of a substance means the temperature at which the substance chemically decomposes, which the chemical decomposition caused by heat. The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. If decomposition is sufficiently exothermic, a positive feedback loop is created producing thermal runaway and possibly an explosion.

ammonium metatungstate image

Ammonium metatungstate will produce different products at different decomposition temperatures. When the heat treatment temperature is 200~300°C, AMT will be removed of all crystal water and most of the ammonium ions; then phase transformation will occur at 300-350°C to generate metastable tungsten oxide species; when the heat treatment temperature rise to 500~550°C, a small amount of ammonium and bound water is still not broken down; and when the temperature rises to 600°C and above, ammonium metatungstate will completely decomposed into tungsten trioxide (WO3); when the temperature raised to 700°C and held for 2 hours, mesoporous tungsten trioxide hollow balls will be obtained.

About ammonium metatungstate:
Ammonium metatungstate (AMT) is an important intermediate compound in tungsten wet smelting process, with the appearance of white or slightly yellow crystalline, the biggest solubility in all the tungsten compound, wherein the solubility will bigger than 300g WO3/100ml H2O at 25℃. The preparation methods of ammonium metatungstate are mainly Acid neutralization, Thermal separation, electrodialysis, solvent extraction and ion exchange method and the method depends on ammonium paratungstate (APT). AMT is the important raw material of tungsten compound (such as tungsten trioxide, blue tungsten oxide, tungsten hexachloride ect.); at the same time, it is usually used in industries of petroleum, chemical, ceramic, lubrication and so on; in addition, since the continually developing of electronics industry and the constantly mining of new material, AMT is also used in film substrate, capacitor and shielding ect. of semiconductor devices.

Ammonium Metatungstate Detection Method and Equipment

atomizer photo

The detection methods of ammonium metatungstate are graphite furnace atomic absorption spectrometry (GFAAS), flame atomic absorption spectrometry (FAAS), inductively coupled plasma emission spectrum (ICP-MS) and coprecipitation separation - hydride atomic fluorescence spectrometry (i.e. coprecipitation separation - HG - AFS method.

Graphite furnace atomic absorption spectrometry (GFAAS) is the method absorbing and analyzing atoms by atomization with current heating in an atomization device which produced by graphite and to form shapes of tubes, cups and others. Since all atoms of sample are getting involved in the atomization, and the atomic concentration diluted in the flame gas has been avoided, then the analytical sensitivity has been greatly improved. While, when that method applied in detecting trace metal element, its property is better than many of other methods, and will be used in analysis of small amount samples and detect analysis of solid sample.

Detection equipments of ammonium metatungstate are atomization device, flame atomic absorption spectrometer, and inductively coupled plasma mass spectrometer ect..
1. Atomization device is a device for sample atomization of atomic absorption spectrometry, which is used in both graphite furnace atomic absorption spectrometry (GFAAS) and flame atomic absorption spectrometry (FAAS). It converts the sample to a free atomic vapor (ground state atom) to absorb the characteristic radiation, and to calculate the element to be measured. There are many kinds of atomizers, and they can be divided into two categories of fire stuffing atomizer and electrothermal atomizer in common. The former includes pre-mixed and full consumption type; the latter includes graphite furnace, carbon wire atomizer, carbon rod atomizer, graphite increase exhaust, and graphite probes ect..
2. Inductively coupled plasma mass spectrometer consists of plasma torch (composed of three concentric quartz tube), high frequency generator (to produce high frequency current), induction coil, gas supply system and atomization system and other parts;
3. Flame atomic absorption spectrometer is composed of light source, atomization system, spectroscopic system and detection system. The principle is that the instrument emits light with the characteristic spectral line of the element to be measured from the light source, then when the sample vapor passes through, the light will be absorbed by the under measure ground state atom, and finally measured by the weakened degree of radiation characteristic spectrum of light.

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Ammonium Metatungstate Spray Drying Tower

ammonium metatungstate spray drying tower picture

Ammonium metatungstate spray drying tower belongs to the spray equipments of ammonium metatungstate production, which is the most widely used of liquid forming process and drying industry. Spray-drying tower is suitable for preparing powder, granular solid product from liquid raw material with forms of suspoemulsions, solution, emulsion, and paste. Thus, when the finished product particle size distribution, residual moisture content, bulk density and particle shape are in line with the precision standard, the spray drying tower is supposed to be an ideal drying process.

Principle of ammonium metatungstate spray drying tower is that the air goes into the top dryer’ air distributor after filtered and heated, then the hot air will uniformly go into the drying room in the spiral. AMT feed solution through the high-speed centrifugal atomizer (rotary) at the top of the tower to be sprayed into the extremely fine mist liquid beads AMT, and dried AMT will come into being in a very short time when it in contacts with the stream of hot air. Then, ammonium metatungstate is exported continuously from the bottom of the spray drying tower and the cyclone, and the exhaust gases are vented by the fan.

Extended reading:
Spray drying tower is the equipment which can be used in drying biological pesticide, medicine and food microorganism, with the max evaporation rate of 10 kg/h, max gas drying rate of 150 kg/h; the main function of a spray drying tower is to dry the materials in solution state in it and then discharge in form of solid. There are 6 properties of a spray drying tower which show bellows:
1. The fast drying speed within seconds to finish;
2. Suitable for the heat-sensitive materials;
3. Widely apply in most of products with very huge difference;
4. The outlet product has excellent dispersion, fluidity and solubility;
5. Sample producing process and easy to operate and control;
6. The part which in contact with material is using stainless steel to protect raw material not to be polluted and extend the service life of the equipment.

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Ammonium Metatungstate to Prepare Surface Decarburized WC-Co Gradient Cemented Carbide

ammonium metatungstate crystal image

The surface decarburized WC-Co gradient cemented carbide based on impregnation liquid of ammonium metatungstate solution (AMT) can greatly enhance the comprehensive performance of cemented carbide; and with the simple process, easy to operate, it is suitable for industrial production. The preparation steps are as follows:
1. Put the conventional WC-Co carbide under vacuum conditions at 100~500°C for dewaxing, then to carry out presintering in 800~900°C to obtain presintering billet with a certain strength and porosity;
2. After them, the sample is dipped into ammonium metatungstate solution to form concentration gradient of AMT with a certain depth and distribution from the surface layer to the inner;
3. Then, after the sample is dried, put it in vacuum furnace for sintering along with slow heating in low temperature stage, to make the ammonium metatungstate decomposed, which the broken down products (tungsten oxide) will react with surface substance of WC, Co, then we can get surface decarburized WC-Co gradient cemented carbide.

Cemented carbide is a kind of metal ceramic tool material which prepared by powder metallurgy method by taking refractory metal compounds (such as WC, TiC, TaC, NbC, etc.) as the matrix, and transition of metals (like Co, Fe and Ni) as bonding phase. Due to its high strength, hardness and elastic modulus, wear resistance, corrosion resistance, low thermal expansion coefficient and stable chemical properties, etc, it in has important application in metal cutting, wood processing, oil drilling in mines, composite materials processing and other respects. Conventional class of WC-Co carbide is uniformly consisted with two phases of WC and binding phase, however it exists contrary relationship between the hardness, wear resistance and strong toughness. The WC - Co gradient cemented carbide structure with high wear-resistance and hardness surface, toughness core part was developed in the 1980s, while the appearance of surface decarburized WC-Co gradient cemented carbide makes it easier to control surface eta phase formation depth, and thereby to prepare the superior performance of WC-Co carbide.

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Silicon Dioxide Supported Ammonium Metatungstate Catalyst

It is found that the supported ammonium metatungstate (AMT) catalysts with the carriers of silicon dioxide, titanium dioxide and aluminium oxide have exhibited good catalytic activity for the synthesis of ortho - light anisole by gas - phase reaction of catechol and methanol. Among them, the AMT / silica catalyst with tungsten loading of 7.9% has the best catalytic performance; in addition, the species with weak acidity and alkalinity which formed by the partial decomposition of ammonium metatungstate in the calcination process has been indicated to be the active center of the catalytic reaction.

SiO2-AMT catalyst SEM image

Preparation of silicon dioxide supported ammonium metatungstate catalyst is using the traditional impregnation method, which is dipping carrier of silicon dioxide with ammonium metatungstate (AMT) aqueous solution in equal volume, followed by drying at 363 K for 6 hours, and then calcining at a certain temperature for 3 hours under air atmosphere to obtain SiO2/AMT catalyst. The study found that the calcination temperature affects the catalytic activity of silicon dioxide supported ammonium metatungstate catalyst; while the catalysts obtained at calcination temperatures of 533K and 573K showed the highest catechol conversion rate and selectivity of adjacent hydroxyl benzene methyl ether within 10 hours, which is respectively maintaining at about 97% and 90%.

Moreover, with the extension of reaction time, the activity of silicon dioxide supported ammonium metatungstate catalyst is decreased slowly, which is mainly attributed to the carbon deposition on the catalyst. The study of regeneration of deactivated SiO2 / AMT catalyst has proved that both the alcohol washed purging and low temperature (533k) calcination could not obviously restore the activity of the catalyst, and also the regenerated catalyst has stability no better than the fresh catalyst. This may be due to the change of the properties (including the acidity and alkalinity) of active centers on catalyst surface after high temperature regeneration treatment, and to make the easier deactivation of regenerated catalyst.

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Testing Trace Bismuth in High Purity Ammonium Metatungstate -- Co-Precipitation-HG-AFS Method

Ammonium metatungstate (AMT) is an important intermediate compound of tungsten wet smelting process, with appearance of white and little yellow crystal. In recent years, as the requirement of tungsten product purity being higher and higher, for controlling and accurate detecting of impurity content in tungsten products, the required analysis of impurity element types gas been more and more. A study has put forward a method of co-precipitation-HG-AFS to testing trace bismuth in high purity ammonium metatungstate; HG-AFS refers to hydride generation atomic fluorescence spectrophotometry, which has shown to have advantages of high sensitivity, good selectivity and small matrix interference.

atomic fluorescence spectrometer image

Steps of co-precipitation-HG-AFS method to detect trace bismuth in high purity ammonium metatungstate are as follows:
1. Weigh 0.125g (Accurate to 0001g) of high purity (99.995%) ammonium metatungstate sample  in 50mL beaker, add a small amount of water, suitable amount of coprecipitation agent and KOH (The standard addition test requires adding standard solution in advance);
2. Carry out filtration after heated for 15min at low temperature, and wash the precipitation and the beaker twice by using KOH solution, again to wash twice with water;
3. Then goes on operation of coprecipitation twice, transfer to 25mL volumetric flask and add 5.0mL HCI, 2mL tartaric acid solution after the precipitation dissolved with hydrochloric acid solution (HCl), then diluted with water to scale, shake well to get mixture solution under test;
4. Test the ready solution by atomic fluorescence spectrometer;
5. Prepare series of different concentrations of bismuth standard solution, test the fluorescence intensity according to running program, and process data with computer, draw standard curve using monadic linear regression equation to calculate the content of bismuth.

The aim of choosing hydrochloric acid (HCl) as Current-carrying medium is to obtain bismuth fluorescence with high strength and stability, while, when the solution acidity is changing among 1~6mol/L, bismuth fluorescence value changed little, however the increasing acidity will help to eliminate the interference.

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Ammonium Metatungstate Hydrotalcite Catalyst

In recent years, solid acid alkali catalysis of gas-solid-phase reaction of alkylation of catechols has attracted attention due to the environmentally friendly economy and overcoming the environmental pollution, separation and recovery difficulties and equipment corrosion and other defects, compared to conventional synthesis methods, and has shown significant advantages in saving resources and improving economic efficiency. It is found that Al-Ti-P-O, Al-Ti-Si-P-O and silica-supported ammonium metatungstate (AMT/SiO2) catalyst exhibited high catalytic activity.

AMT hydrotalcite sample XRD spectra image

Hydrotalcite is a kind of anionic clay with layered structure, because of its special layered structure and high catalytic performance in acid-base catalysis, condensation, addition polymerization, hydrogenation and alcohol conversion reaction, hydrotalcite has attracted many concerns. The exchangeable property of hydrotalcite anions make all kinds of anions (such as metatungstate ion) can be introduced into the interlayer of hydrotalcite in succession, thus to form a large class of materials - pillared hydrotalcite layered material.

A study has pointed out a preparation method of ammonium metatungstate hydrotalcite catalyst, and studied its catalytic performance, while the preparation steps are as follows:
1. synthesis of hydrotalcite material, take the raw material of magnesium nitrate hexahydrate, aluminum nitrate and sodium hydroxide, and to control the final pH value among 8 ~ 10 of the system, then go on aging, filtration and washing to get hydrotalcite NO3-MgAl;
2. Weigh a certain amount of fresh prepared hydrotalcite NO3-MgAl to disperse in distilled water, stirring at room temperature for overnight to fully expand;
3. Add dilute nitric acid dropwise to adjust the pH value of hydrotalcite slurry among 5.5~6, then rise the temperature to 348K;
4. Rapidly add ammonium metatungstate solution under the condition of stirring, and to react at 348K for 2 to 3 hours, then pumping wash the sample and dry at 348K to get the ammonium metatungstate hydrotalcite catalyst, i.e. AMT-Mg2Al.
The results showed that after changed with AMT, hydrotalcite will exhibit activity to the reaction of gas-solid phase reaction of catechol and methanol, while the conversion of catechol is 75%, the selectivity of guaiacol is 90%, but the catalytic activity decays.

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Differences among Ammonium Tungstate, Ammonium Paratungstate and Ammonium Metatungstate

The most distinctive difference between ammonium tungstate, ammonium paratungstate and ammonium metatungstate is their solubility in water.

bag of ammonium metatungstate sample photo

Ammonium tungstate is also called ammonium wolframate, its molecular formula is (NH4)6W7O24•6H2O. It is colorless trapezius crystal which is soluble in water and insoluble in alcohol. Under 100℃ it loses four molecular crystal water. Ammonium tungstate can be used as the raw material for ammonium phosphotungstate and other tungstate compound. It can also be applied in producing metallic tungsten and catalyst.

Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, it is insoluble in water. Its shape is like sheet or needle. Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry.

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃. It is white or slightly yellow crystals which has no harmful components and slightly acidic. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate.

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Difference Between Ammonium Paratungstate and Ammonium Metatungstate

The most apparent difference between ammonium paratungstate and ammonium metatungstate is APT insoluble in water, but AMT soluble in water.

ammonium metatungstate image

Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, it is insoluble in water. Its shape is like sheet or needle. Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also tungsten powder including tungsten trioxide, tungsten blue oxide. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry.

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃. It is white or slightly yellow crystals which has no harmful components and slightly acidic. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate. It can also be used as reagents for chemical analysis such as for chemical diagnosis; source material for the preparation of high purity tungsten trioxide used as a thin film substrate for certain semiconductor devices; high purity source material for research in tungsten chemistry; source material for DENOX catalysts industry; as a precursor to a variety of POM (polyoxometalates).

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Producing Ammonium Metatungstate from Ammonium Tungstate in Silica advantages

ammonium metatungstate product picture

A particular advantage of the ammonium metatungstate (AMT) prepared from ammonium tungstate in silica is that the silica used in digestion and subsequently filtered from the digested solution of ammonium metatungstate (AMT) may be reused repeatedly, that is, its capacity to promote formation of AMT is not diminished with use. While the exact mechanism is not well understood at this time, the role of silica is to prevent the precipitation of insoluble APT and therefore to allow lowering of the pH to the ammonium metatungstate forming region, about 4 to 4.5.
After digestion is completed, the silica is removed, such as by filtering, and the solid AMT may be recovered in the conventional manner, such as by evaporation or spray drying.

The silica used in the invention may be any commercially available silica, provided that its impurities, both in kind and amount, are consistent with the final envisioned application for the ammonium metatungstate. For example, both sodium and phosphorus may be considered objectionable impurities for certain catalyst applications. Residual silica which cannot be removed from the digested AMT solution by filtering is generally below 1 percent by weight, and typically from 0.3 to 0.6 weight percent WO3 basis, and is compatible with many catalyst applications.

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Producing Ammonium Metatungstate from Ammonium Tungstate by Digestion in Silica

At present both ammonium paratungstate (APT) and ammonium metatungstate (AMT) are being used as tungsten sources in the catalyst industry. Since APT has a limited solubility in water (about 2 to 3 percent at room temperature), thus the user should converts APT to a more soluble peroxytungstate form by means of reaction with hydrogen peroxide in order to prepare the catalyst. While AMT is highly water soluble, and thus no need be converted, it is in general more expensive than APT, due to the complexity and/or low yields of processes for producing it.

A process for producing ammonium metatungstate (AMT) from ammonium tungstate (AT) solution is described which involves the addition of about 3.6 percent by weight of silica to an AT solution, digestion for at least about 4 hours at a temperature of at least about 98°C, followed by filtration to remove the silica from the AMT solution. Typically about 0.4 percent by weight of silica remains after filtering. The resulting AMT solution may be further processed to recover solid AMT, such as by evaporation or spray drying.

ammonium metatungstate photo

silica image

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Ammonium Metatungstate SEM Micrograph

AMT-image

Ammonium metatungstate is also named AMT, which is a kind of white crystal powder. AMT is the raw material for making tungsten product, and also widely used in alloyed steel, fireproof industries. Further more, it is a good tungsten based flux in oil chemical and ceramic industries. The manufacturing standard of AMT in China is GB/T 23368, which is also used for measuring the content of ammonium metatungstate. Based on different manufacturing degree, the products manufactured out by factories have performed different chemical contents. Standard used manufacturing ammonium metatungstate, AMT is GB/T 23368. The content of WO₃ is 90.00% in most Chinese manufacturers, but 91.4~91.5% for Chinatungsten Online. For the different crystallized conditions, AMT can be analyzed as (NH₄)6H₂W₁₂OnH₂O, (NH₄)₆H₂W₁₂O₄₀.XH₂O and (NH₄)₆H₂W₁₂O₄₀.

SEM micrograph is short for Scanning Electron Microscope, a kind of scanning equipment using for micrograph by multiplying objects, which can be metal, powder, vegetables etc. Ammonium metatungstate is one of can-be scanned products. After scanning, the powder of AMT is showing ball shape with inner empty. All the balls are gathered together when the multiply value is low, but with gap when the value large enough, which means that the molecule of AMT are separate actually.

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Ammonium Metatungstate Producing Method

ammonium metatungstate photo

Ammonium metatungstate producing method includes neutralization method, tungstic acid method, thermal decomposition method, solvent extraction method and ion exchange method.

Neutralization method uses secondary ammonium metatungstate and nitrate as the raw material to produce metatungstate.

Tungstic acid method using ammonia tungstate tungstic acid dissolved, add a boil deionized water in the stirring, heating by ammonia, Ph=8, in the boiling solution by adding acetic acid.

Thermal decomposition method combines ammonium paratungstate and a small amount of citric acid catalyst after mixing into the far infrared, rotary furnace, controlled thermal decomposition temperature 200 ～ 280 ℃, decomposition of about 1 h.

Solvent extraction using ammonium tungstate solution and organic extractant phosphoric acid: two (2- ethylhexyl) ester (D2EHPA) or phosphoric acid butyl ester three (TBP) and kerosene solvent to form organic phase, extract ammonium ion from ammonium tungstate solution.

Ion exchange method uses ammonium paratungstate as raw material, heating ammonium paratungstate from 1 to 8 h at 130 ~ 140 ℃, the resultant tune into a paste, to 80 ~ 100 ℃ boiling for 2 ~ 6 h, generates ammonium metatungstate solution. And then obtain the product through concentrating crystallization, filtration and drying.

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