Ammonium paratungstate tetrahydrate or APT•4H2O may be prepared by crystallization process from pure ammonium tungstate solution by batch process and continuous process. But APT•4H2O will lose part of crystal water in the drying process of this industrial production. Therefore, repeated crystallization is usually used to improve product quality. However, this method is limited by the slow dissolution of APT•4H2O. Ammonia Dissolves Ammonium Paratungstate Tetrahydrate At room temperature, APT•4H2O dissolves very slowly in aqueous ammonia. The dissolution temperature can be increased…

Large grain size ammonium paratungstate is an important intermediate product in the preparation of tungsten powder from tungsten concentrates. The physical properties of APT such as particle size, particle size distribution, and crystal morphology have an important influence on the physical and mechanical properties of its downstream products such as tungsten carbide, tungsten wire, and so on. Therefore, it is of great significance to study the influencing factors of grain size of APT. In the crystallization of APT, there are…

Ultrafine ammonium paratungstate may be prepared by microwave-ultrasonic cooperative evaporation crystallization method. Microwave-ultrasonic Cooperative Evaporation Crystallization to Prepare Ultrafine Ammonium Paratungstate 1. Experimental Equipment (1) XH-300A computer ultrasonic and microwave combined synthesis extraction instrument; (2) ZK-82B electric constant temperature drying oven; (3) UK Malvern laser particle size analyzer; (4) Miniflex X-ray diffractometer; (5) Netherlands Philips XL30 scanning electron microscope; (6) Diamond 6000 thermo-differential thermal analyzer. 2. Experimental Procedures A certain volume of ammonium tungstate solution with a concentration of WO3…

Coarse crystal ammonium paratungstate has found wider applications in many fields with the continuous development of new tungsten carbides and filament types. Therefore, it is of significance to study the preparation process of APT. Preparation of Coarse Crystal Ammonium Paratungstate At a water bath temperature of 60°C and under a certain degree of vacuum, a certain concentration of 300mL AT solution was poured into a 500mL 3-neck flask, stirred to evaporate to precipitate milky crystal nucleus, and heated within 1/2h…

High-calcium ammonium paratungstate means the ammonium paratungstate powder that has excessive Ca content. The phenomenon of excessive Ca content in APT products is likely to occur during the production of APT by ion exchange process. The high-calcium APT must be reprocessed as it will not only affect the quality of tungsten carbides, but also cause a waste of tungsten resources to some extent. The conventional process to treat ammonium paratungstate with severely Ca content has the disadvantages of long process…

Spherical-crystal ammonium paratungstate can be used to prepare high-performance tungsten heavy alloys, which has the characteristics of high density, good ductility, large yield strength and high tensile strength. This is because the spherical-crystal tungsten powder obtained by calcination and hydrogen reduction of spherical single-crystal ammonium paratungstate has large loose apparent density and good fluidity. And it is easy to fill the die cavity. Also, it makes the density of compact uniform. The W-Ni-Fe heavy alloy prepared by spherical tungsten powders…

Orthorhombic ammonium paratungstate is the necessary intermediate raw material with the chemical formula of (NH4)10H2W12O42•10H2O during the process of tungsten metallurgy. The decomposition reaction of orthorhombic APT may be determined in a HT-1000 nicrocalorimeter by three step calorimetry. The chemical equation is as follows: (NH4)10H2W12O42•10H2O(s) = 12WO3(s) + 10NH3(g) + 12H2O(g) Thermal Decomposition Mechanism of Orthorhombic Ammonium Paratungstate 1. Dehydrate at 335K and 376K. 2. Decompose into amorphous ammonium tungsten bronze at around 475K. 3. Form into crystalline ammonium tungsten…

Monoclinic ammonium paratungstate with different particle size can be obtained by different heating stages. The changes of particle size and surface area at each stage in rapid thermal decomposition of monoclinic APT can be concluded by differential thermal analyzer (DTA) and laser particle size analyzer, which can guide the preparation of tungsten oxide with desired particle size. Rapid Thermal Decomposition of Monoclinic Ammonium Paratungstate 1. Monoclinic APT was heated to 600°C at a rate of 9°C/min in argon (Ar) for…

Single crystal ammonium paratungstate is a key material for producing high quality tungsten wire, which is always applying in cars. That is because the single crystal APT has the characteristics of good tensile property and fracture resistance. And the tungsten wire using the single crystal APT as raw material has yield of 90%, which is higher than that of adopting polycrystalline paratungstate ammonium as raw material with yield of 70%. Single crystal APT also has many other excellent physical properties…

Ultra-fine ammonium paratungstate has received widespread attention around the world since the 1990s as it can be used to prepare ultrafine tungsten (W) powders, which a hot tungsten product to produce tungsten carbide powder and other down-stream products on tungsten. Compared with tungsten powder of conventional particle size, the sintering temperature of ultrafine W powder can be greatly reduced. And therefore, the preparation of ultrafine grain size APT has been researched a lot both in China and abroad. The particle…