Microwave Heating and Sintering Technology of Ammonium Paratungstate

Ammonium paratungstate pictures

Ammonium paratungstate microwave heating sintering technology, refers to ammonium paratungstate in the microwave field to absorb high-frequency microwave energy, then the molecules or atoms produce violent shocks, friction, rotation and collision, the molecular high-speed kinetic energy into heat. Thus achieving ammonium paratungstate heating.

Ammonium paratungstate pictures

When ammonium paratungstate absorbs enough microwave energy in the microwave field, it can be raised to a certain temperature to reach the synthesis temperature of the corresponding substance. Thus completing the sintering process of ammonium paratungstate. Ammonium paratungstate microwave sintering technology is the use of materials to absorb microwave energy, without heat conduction and the completion of "self-heating." Therefore, microwave heating and sintering can make the whole material quickly and uniformly without temperature gradient phenomenon, so as to achieve the densification sintering. This method can avoid the traditional sintering of ammonium paratungstate pores, cracks and other sintering defects appear.

Ammonium paratungstate microwave sintering technology compared to the traditional high-temperature sintering furnace, has the following characteristics:
(1) The overall uniform heating, no temperature gradient, can improve the material properties.
(2) After the material absorption is not necessarily rapid heating, the maximum heating rate up to 100 ℃ / min, high heating efficiency.
(3) high energy efficiency, green pollution-free.
(4) According to the material medium factor selective heating.
(5) Due to the microwave heating without heat conduction process, the temperature can be appropriate without overheating sintering, can inhibit particle growth.

Ammonium paratungstate pictures

With the continuous improvement and progress of the microwave heating and sintering technology of ammonium paratungstate, it has been widely used in the preparation of ceramic powder, cemented carbide and cermets. For example, more and more researchers try to use microwave sintering to prepare high-performance cemented carbide due to the better adaptation of the cemented carbide to the microwave field. WC Sintered Specimens WC grains are finer and the Co phase is more evenly distributed than the conventional sintered samples. At the same time ammonium paratungstate samples also have more excellent hardness, resistance to physical and chemical corrosion.

 

Freeze-Drying of Ammonium Paratungstate

Ammonium paratungstate pictures

The preparation of ammonium paratungstate by freeze-drying is one of the methods of industrial production of tungsten products. Ammonium paratungstate freeze-drying method is essentially the principle of ammonium tungstate solution as the freeze-drying method of raw materials, its rapid rapid freezing.

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Ammonium Paratungstate Prepared by Neutralization Crystallization Feasibility

Ammonium paratungstate pictures

Ammonium paratungstate prepared by the neutralization crystallization method is one of the main methods of industrial production of ammonium paratungstate. Ammonium paratungstate, which is fine in grain size, is a necessary condition for the production of subsequent high-performance tungsten products.

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Ultrasonic Technology Effect on Ammonium Paratungstate Crystallization

Ammonium paratungstate pictures

Ammonium paratungstate ultrasonic technology is a technology that works in conjunction with ammonium paratungstate crystals. Ultrasound is a kind of sound wave whose frequency is between 10kHz-10MHz and whose wavelength is in the range of 10cm-0.015cm. Because ultrasonic has beam-like light and similar light propagation characteristics, it is a mechanical vibration wave that easily accumulates energy.

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Ammonium Paratungstate Ultrasonic Technology

Ammonium paratungstate pictures

Ammonium paratungstate ultrasonic technology is a technology that works in conjunction with ammonium paratungstate crystals. Ultrasound is a kind of sound wave whose frequency is between 10kHz-10MHz and whose wavelength is in the range of 10cm-0.015cm.

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Sodium Tungstate Solution Purification by Magnesium Salt Precipitation

purification of sodium tungstate solution by magnesium salt precipitation image

The NaOH decomposition process is currently used by tungsten smelting enterprises in China. During the process of decomposition, impurities such as phosphorus, arsenic, silicon, tin and fluorine will be decomposed into sodium tungstate solution. A large number of impurities will interfere with the subsequent processing, resulting in heavy task of subsequent purification process, resulting in low recovery rate of tungsten and even affecting the quality of subsequent ammonium tungstate and smelting wastewater treatment.

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Sintering Driving force - Surface Energy

two-ball model image
The driving force of the tungsten carbide powder mainly comes from the reduction of the excess free energy of the system. Free energy can be divided into surface energy and lattice distortion energy, in which the reduction of surface energy plays a leading role in the sintering process.

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Change of Sintering Process

sintering equipment image
Tungsten carbide sintering is a multicomponent liquid phase sintering. In the process of sintering, both physical and chemical changes will occur. Among these changes, the four important changes are densification of sintered body, change of binder phase composition, growth of tungsten carbide grain and formation of alloy structure.

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Sintering Process: Change of Powder

change of powder image
Sintering process of tungsten carbide is carried out by the contact between the powder and the migration of the atoms. At high temperatures, the caking is more obvious. The phenomenon that the powder is heated while the particles are bonded between them is so called the sintering.

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Thermodynamic Problems of Sintering

common lattice distortion image
The sintering process of tungsten carbide has a spontaneous trend. On the one hand, the powder itself has the tendency of automatic bonding or agglomeration. Especially, the very fine powder, even at room temperature, will coalesces gradually for a long time. On the other hand, this trend will be more obvious at high sintering temperatures.

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