Preparation of metal molybdenum powder

Fundamental

        Similar production of the molybdenum powder, molybdenum powder preparation is an oxide mainly hydrogen reduction process, process dynamics and thermodynamics of related textbooks and treatises are introduced, molybdenum powder production is the key indicator of its size control, The mechanism and influencing factors of particle size change during the hydrogen reduction process of Mo0 3 are much the same as those of W0 3 hydrogen reduction. However , when it exceeds 873K , Mo0 3 begins to sublimate significantly, and its vapor pressure reaches 0.1 MPa at 1424K , which is much larger than the vapor pressure of WO 3 . Therefore, the chemical vapor phase migration is more favorable in the reduction process, and powder particles larger than the tungsten powder should be obtained. However, the actual molybdenum powder is often finer than tungsten powder. There are two reasons: First, Mo0 3 has a small chemical stability and can be rapidly reduced to a refractory Mo0 2 having a very low vapor pressure in a low temperature region of the reduction furnace, that is, in a temperature range in which the vapor pressure of Mo0 3 is not large . Secondly, the intermediate oxide of aluminum can form a fusible eutectic with Mo0 2 at 773~973K . In order to avoid the melting of such a eutectic mixture, the first stage of the reduction in the actual production requires a slow temperature rise. This also reduces the likelihood that Mo0 3 will enter the temperature range in which it significantly evaporates. The average particle size of the molybdenum powder obtained in actual production is generally 0.5 to 3.5 μ m .
Industrial practice
Molybdenum metal powder production process, and quality control equipment and the need to produce a method substantially similar to the metal tungsten powder.
The molybdenum powder reduction process has a one-stage, two-stage and three-stage reduction method. Most plants use a two-stage reduction method.
The two-stage reduction process consists of reduction of Mo0 3 to Mo0 2 and reduction of Mo0 2 to metal molybdenum. The first stage reduction is carried out at 723~823K , which is lower than the temperature of the first stage of tungsten trioxide reduction ( W0 3 → WO 2 is 923~1073K ). The second stage is also carried out under the conditions of 1123~1223K , which is higher than the temperature of the second stage of tungsten trioxide reduction ( W0 3 → W is 1053~1153K) . A four-tube muffle furnace or a multi-tube reduction furnace is usually used as a one-stage reduction, and a multi-tube reduction furnace is used for a two-stage reduction. In order to avoid the formation of the co-melt of the intermediate oxide, in the process of reducing the burning boat along the furnace tube in the first stage, it is necessary to ensure that the formation process of MoO 2 is substantially completed before the temperature reaches 823-873K .
In the second stage of the above reduction, in order to ensure complete reduction, it is necessary to push the boat slowly and consume high dry hydrogen. In order to reduce hydrogen consumption, in the actual production, the reduction stage is often divided into two stages, that is, the second stage reduction is carried out under the conditions of 1093~1163K (the molybdenum powder obtained at this time still contains 2% to 3% of oxygen ). The third stage is also carried out in a molybdenum wire furnace under the conditions of 1223~1373K .

Alloy Steel Lap Joint Flange

Din Flange,Slip Joint Flange,Lap Joint Flange Dimensions,Alloy Steel Lap Joint Flange

SHANXI BAOFAN HEAVY INDUSTRY GROUP CO., LTD , https://www.baofanflanges.com

This entry was posted in on