The invention is directed to a process for the continuous preparation of ammonium paratungstate hydrate by back reextraction of a tungsten-laden organic phase with an ammonia-containing aqueous solution in a mixer-settler apparatus. The reextraction is carried out at an NH₃:W molar ratio of from 0.83 to 1.30, and a volume feed ratio of the tungsten-laden organic phase to the ammonia-containing aqueous solution of from 5 to 25. The above crystalline is in high purity and in high yield. The production method can be carried out in a simple and energy-efficient manner.

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A method is disclosed for producing ammonium metatungstate from ammonium paratungstate. The method involves first roasting the ammonium paratungstate at from about 275° C. to about 300° C. for from about 10 hours to about 20 hours to remove some ammonia and some water. The roasted ammonium paratungstate is then added to dilute solution of an ammonium metatungstate which is at a pH of from about 3.6 to about 4.2, the rate of addition being such that a slurry is produced having a pH of from about 3.6 to about 4.2. The pH of the resulting slurry is then adjusted to stabilize it at from about 3.6 to about 4.2 followed by evaporation to form a relatively concentrated solution of ammonium metatungstate which is separated from any insolubles. Ammonium metatungstate is then crystallized from the relatively concentrated ammonium metatungstate solution.

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In order to solve the problem of determination of boron in ammonium paratungstate(APT), the authors began with the study on determination way by ICP AES. The matrix effect and spectral interference of tungsten on boron in ICP AES were studied. The effects of acidity, time of boiling and time of putting aside were investigated. Combining with matrix seperation and factor correction, a new simple,rapid and accurate method for determination of B in APT was developed. The recovery is higher than 95.8%; the relative standard deviation of determination of 0.000 x %～0.00 x %B in APT is lower than 3%. The accuracy and precision of the method are satisfactory.

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Coarse and spherical tungsten powders were prepared by wet hydrogen reduction.Ammonium tungstate solutions with the additives of Li,Na and K alkali metal salts were used as raw materials.The effects of the type and content of the alkali metal salts as well as reduction time on the microstructure,chemical composition,phase composition, and particle size of ammonium paratungstate(APT) and coarse tungsten powders were investigated by scanning electronic microscopy,energy dispersive

The bulk structural evolution during the decomposition of ammonium paratungstate (APT) under various oxidizing and reducing gases was elucidated by the complementary techniques, in situ XAS, in situ XRD, and TG/DSC, combined with mass spectrometry. In the temperature range from 300 to 650 K, the decomposition of APT proceeds nearly independently of the gas employed. At higher temperatures, an oxidizing gas results in the formation of crystalline triclinic WO3 as the majority phase at

In this research, experiments on the production of ammonium paratungstate by the base-leaching process from rough tungsten ores produced by local individual miners in Jiangxi were carried out.The experimental results show the chemical components and properties of run-of-mine ore, the reaction temperature and pressure and the caustic soda concentration all have remarkable effects on the leaching rate. Technologically,by applying dispensation techniques and adding scheelite-decomposing agents the problem due to the high content of silicon and calcium in the ore can be solved . And a new process of tungsten production by the base-leaching method which had not been reported before was developed . By this process chemical reaction will go on without let-up during the operation while by the old one there are times when chemical reaction comes to be in equilibriumum and stops , and so the recovery rate can be noticeably increased , in fact,it reaches 99%.

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Thermal decomposition of monoclinic ammonium paratungstate was investigated by differential scanning calorimetry and laser granulometry.The results show that extent of product particle refining is maximum at(253.3℃,)secondly at 232.9℃;extent of product particle coarsening is maximum at 297.4℃,secondly at 432.1℃ and change in particle size at 150.2℃ and 500℃ is not apparent when heating at rate of 9℃/min in Ar.Monoclinic ammonium paratungstate with different particle size can be obtained by heating stages.

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containing little or no metal binder phase. Usually Unbonded phase WC tungsten carbide ball refers metal binder phase mass fraction of less than 1%. Unbonded phase WC tungsten carbide ball with a WC-Co alloy ball unparalleled excellent wear resistance and corrosion resistance, excellent polishing and oxidation resistance, hardness and tungsten carbide ceramics collection toughness in combined with one body.

Unbonded phase WC tungsten carbide ball has great potential applications scalability. However, the melting point of pure WC up to 2860 ℃, unbonded phase WC tungsten carbide ball requires high sintering temperature (1500 ℃ ~ 2000 ℃), using conventional sintering methods are difficult to obtain fully dense block. With the development of advanced sintering technology, the current phase tungsten carbide ball unbonded preparation methods include vacuum sintering - hot isostatic pressing, pressure sintering, hot pressing, spark plasma sintering and PPC (Plasma Pressure Compaction), etc., which after 2 methods because of their special sintering mechanism can reduce the sintering temperature and heating rate is very fast and can be completed in minutes sintering, thus reducing the chance of grain growth during the sintering process, you can get a full dense ultrafine grained grain bulk material.




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Tungsten carbide ball has high strength, high wear-resistant, high-precision, high temperature, corrosion, etc., are widely used in the oil industry and other aspects of the ball seal. When the WC grain size is reduced to below submicron, tungsten carbide ball material hardness and wear resistance, strength and toughness are improved. This ultrafine-grained WC-Co cemented tungsten carbide ball, because at the same time has a high hardness and high flexural strength, high wear resistance and toughness, is vividly called "double high" tungsten carbide ball, in order to meet a high-performance tungsten carbide ball higher and higher demands on materials industry.

Preparation of ultrafine-grained WC-Co cemented tungsten carbide ball materials adopt WC-Co powder metallurgy process, pure WC powder by high energy ball milling, so that the grain size of WC ultrafine grain reaches its hardness and strength will be a great breakthrough, sintered after obtaining a better overall performance. Many difficult to machine materials, such as aerospace materials in high temperature alloys, pump, thermal power plant ash slagging water systems, fluid seal rotating ball and other harsh environments strength and higher hardness ultrafine grained WC-Co cemented tungsten carbide ball with higher efficiency.




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Refined tungsten particles become high density tungsten alloy research a new hot spot, by mechanical alloying (MA), condensation drying, chemical vapor deposition method, spray drying, sol - gel method and other methods of preparation of pre-alloyed powders and the use of appropriate technology can be made very fine powder.

In addition, the use of spray-step synthesis reaction process can be fine-grained, multi-component, pre-aggregate of tungsten alloy powder, the powder can be much lower than the melting temperature of the binder phase sintered to full density. Fan Jinglian and other craft were prepared by MA nanocrystalline tungsten alloy composite powder in a hydrogen atmosphere at atmospheric pressure sintering and densification during sintering tungsten grain growth behavior, indicating MA nanocrystalline powders can promote densification densification temperature decreases about 100 ~ 200 ℃, when the general solid-phase sintering temperature can be fine crystalline grain size of the high strength of the alloy 3 ~ 5μm.

Nano-tungsten alloy injection molding were studied in 1350 ~ 1450 ℃ showed solid phase sintering that reached full density, grain final alloy is about 3μm, tensile strength greater than 1200MPa. Other studies of tungsten alloy powder warm compaction behavior at different temperatures, indicating that temperature and pressure can significantly improve the green density, temperature and pressure radial contraction of less than room temperature blank blank radial contraction, and temperature and pressure can improve tungsten alloy microstructure. Sample cold isostatic pressing Lee letters buried in Al2O3 powder, placed in a sintering furnace heating and air 30min after pre-oxidation insulation, and then sintered at different temperatures; the results showed that the use of pre-oxidation of tungsten alloy activated sintering can reduce the sintering temperature, reducing alloy deformed and get dense tungsten alloy, while increasing the tensile strength and elongation of tungsten alloy.




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