2018年5月9日星期三

Ammonium Metatungstate Preparation Equipment--Plate Type Multiple Hearth Furnace

The thermal degradation method is a process for the preparation of ammonium metatungstate based on ammonium paratungstate (APT). 

This method is also the mainstream process of preparing ammonium metatungstate (AMT). At present, the pyrolysis equipment used in China is mainly rotary calciner. At the same time, there are many kinds of patented pyrolysis equipment used in AMT abroad, and the plate type multiple hearth furnace is one of them.

The plate type multiple furnace is composed of a multi-layer drying plate separated from each other, and the material is in continuous contact with the pyrolysis plate. It is characterized by the fact that the solid can be conveyed by low-speed air or low-speed steam to avoid excessive dust.

plate type multiple hearth furnace image

The furnace has a wide range of particle size control, and even includes a very fine particle size, the machine's feed is completed by the bucket wheel, feeding position is in the top of the plate dryer, the material to be pyrolyzed may be wet or dry flakes, and the pyrolysis material flows from top to bottom. The concrete process is that the material is rotated from the edge of the first plate to the middle of the rotating harrow mechanism, and then slid to the edge of the second layer, and then harrow to the center, so that the cycle is completed until the whole drying process is completed. Each plate is controlled by heating, and there is a certain temperature gradient between the plates to meet the requirements of process parameters and product quality. The exhaust gas is carried out by the air stream, and the heat carrier can be steam, hot water or other mediums.

The advantages of the plate type multiple hearth furnace are that it can be fed by wet material, and the drying process is carried out in the completely sealed box. The labor condition is better, and the pollution of the dust leakage to the environment is avoided; Material flow movement, heat and mass exchange uniformity, sufficient, high production efficiency, good drying consistency, good product quality, material particles in the dryer vibration is relatively slight, the material is not easily broken.

If you have any inquiry of tungsten, please feel free to contact us:
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Violet Tungsten Oxide

Violet Tungsten Oxide, abbreviated as VTO, is a kind of tungsten oxide, violet fine crystalline powder. 

Violet tungsten is a kind of tungsten oxide product developed in China recent years. Its phase composition is WO2.72 or W18O49. Because of its unique properties, it has more advantages than blue tungsten in the production of ultrafine tungsten powder. Violet Tungsten Oxide (VTO) powder has the largest pore volume, micropore volume minimum, narrow pore size distribution, the smallest fraction dimension and maximum average diameter, which is conducive to hydrogen production of ultrafine tungsten powder is the main raw material, producing ultrafine tungsten powder and nano tungsten powder.

Chinese scholars proved that the key to the production of ultrafine tungsten powder is kind of raw material of oxide, compared with yellow tungsten and blue tungsten, violet tungsten has the following characteristics: 1. Strong chemical activity, reducing speed; 2. The average diameter reduction of violet tungsten particles formed in false porosity, good air permeability; 3. The influence of loading volume and hydrogen flow rate is obviously smaller, and the production capacity is greater.

purple tungsten oxide image

The main method of manufacturing violet tungsten oxide is APT hydrogen reduction, because when the tungsten powder particle size is 1 microns, it has spontaneous combustion. Therefore, when the tungsten powder is treated in the cooling stage, it contacts the wet hydrogen, and there is a protective oxide film on the surface before it leaves the reducing furnace. In the use of reverse hydrogen reduction, the fine tungsten powder must be slowly coated with oxide. This can be avoided by adding inert atmospheres, such as nitrogen or hydrogen, to avoid partial overheating of the tungsten powder.

After the preparation of ultrafine tungsten powder with violet tungsten, in order to prepare ultrafine tungsten carbide, the existing fine grain tungsten carbide process can be used. The tungsten carbide, which is made from tungsten carbide, has the characteristics of ultrafine, uniform and difficult to grow. It is a super quality product.

If you have any inquiry of tungsten, please feel free to contact us:
Tel.: +86 592 5129696/+86 592 5129595
Fax: +86 592 5129797

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Purple Tungsten Oxide Preparation

Purple tungsten oxide is a kind of tungsten oxide product developed in China in recent years. Its phase composition is WO2.72 or W18O49.

Because of its unique properties, purple tungsten oxide is the main raw material of ultrafine tungsten powder and nanometer tungsten powder. 

The production of purple tungsten oxide is mainly made up of APT hydrogen reduction process. It is carried out in a multi tube furnace. There are two ways of flow direction of hydrogen in the furnace tube, one is that the direction of hydrogen flow is opposite to the direction in which the boat (material) is pushed in the furnace tube. This is the traditional method of hydrogen production by the medium and fine particle tungsten powder, which is called the reverse hydrogen reduction process. But later research found, such as changing the direction of hydrogen, the hydrogen flow direction and the boat forward in the same direction, can prevent spontaneous combustion of tungsten powder, refined products more conducive to the particle size of tungsten powder, this is the so-called hydrogen reduction process.

purple tungsten oxide preparing image

In the making process, when the particle size of tungsten powder less than 1 micron, which is pyrophoric, therefore, when the tungsten powder is treated in the cooling stage, it contacts the wet hydrogen, and when it leaves the reduction furnace, the surface of the fine tungsten powder has a protective oxide film on it. If reverse hydrogen reduction is used, the tungsten powder may be prevented from overheating by the addition of an inert atmosphere, such as nitrogen or hydrogen.

The process of reducing the hydrogen content of the purple tungsten oxide is based on the refining mechanism of the reduction of hydrogen. Compared with blue tungsten, purple tungsten has higher reduction activity. The advantages of producing ultrafine tungsten powder by industrial process are that there is no impurity pollution in the process of reduction (compared with the process of activation reduction of additives), and the chemical purity of the product is higher; Another significant advantage is that the process parameters in the reduction process can be precisely regulated and controlled so that ultrafine tungsten powders can be produced at different particle sizes.

If you have any inquiry of tungsten, please feel free to contact us:
Tel.: +86 592 5129696/+86 592 5129595
Fax: +86 592 5129797

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Three Factors Affecting Tungsten Ore Electrical Selection

Electrical selection method is an important auxiliary way of ore processing, when tungsten ores are under electrical selection, tungsten ores and cassiterite need to be separated. 

With high voltage electrical selection machine, wolframite and scheelite can successfully separated,  sulfide ores and wolframite can successfully separated as well. Because wolframite and sulfide ores are with conductivity, scheelite and tin ores are not with conductivity. 

The effect of electrical selection method is not only determined by the conductivity of tungsten, also by three major factors: temperature, structure, and surface states. 

1. Temperature: For conductors, the conductivity decreases when temperature increases. For semiconductors like tungsten ores, as the temperature goes high, the bound charge is released by the heat energy, the free electron increases and the conductivity increases. Therefores, proper heating befores electrical selection can improve the effect of electrical selection and is mores benificial to ore selection.

tungsten ore electrical selection machine image

2. Crystalline Structures: Modern solid physics has proved that any of the excess atoms in a semiconductor that deviate from the chemical composition, defects in foresign impurities and lattice structure can significantly change the electrical conductivity. The purer the component, the better the electrical selection. 

3. Surface States of Ores: The surface state of ores determines the surface conductivity of ores, including surface moisture and porosity. 

Based on the above three factors, we can change the external conditions when tungsten ores under electrical selection so that we can get better ores. 

For ores with small electrical conductivity, a change in the chemical composition of the ore surface is enough to change its surface conductivity, in some cases, a proper addition of certain agents enables the ore surface to be covered with a new layer of conductive film to enhance electrical conductivity.

In addition, water has better electrical conductivity than ores, therefores, when the presence of water film on the ore surface, the conductivity will be greatly enhanced. Finally, the larger the porosity of the ore, the greater the specific surface area is and it has a strong moisture absorption. So,  when the air humidity increases, the surface conductivity also increases significantly.

If you have any inquiry of tungsten, please feel free to contact us:
Tel.: +86 592 5129696/+86 592 5129595
Fax: +86 592 5129797

Scan QR code of Chinatungsten Wechat platform to follow up the daily latest price and market of tungsten, molybdenum and rare earth.