Molybdenum powder, just as its name implies the molybdenum metal in powder state, is an important raw material of molybdenum deep processing products, whose color is usually grayish black and in uniformity. Here we provide you with an overview of molybdenum metal powder production process.
It is mainly by restoring the oxide with hydrogen to produce molybdenum metal powder, and the reduction process is also divided into one-stage, two-stage and three-stage reduction. Most factories adopt the two-stage reduction.
The two-stage reduction process composed of two phases: to restore MoO3 into MoO2, then MoO2 to molybdenum. The first phase of reduction is under 723-823K, the temperature lower than the first phase of reduction of tungsten trioxide (WO3→WO2 for the 923-1073K). The second stage is under 1123-1223K, higher than the temperature of the second stage reduction of tungsten trioxide (WO3→W of 1053-1153K). Usually four muffle tube furnace or multi-tube reduction furnace is for the first stage reduction use, multi-tube reduction furnace for the second stage reduction. In order to avoid the formation of intermediate oxide eutectoid, the MoO2 generation process must be finished before the temperature reaches 823-873K during the burning boat propelled along the furnace tube in first phase of the reduction.
To ensure the complete reduction when using the second stage of reduction, the boat must be slowly pushed and high consumption of dry hydrogen is ensured. In order to reduce the consumption of hydrogen, in the actual production, this reduction stage is often further divided into two phases, that the second phase of reduction under 1093-1163K (in which case the resulting oxygen-containing molybdenum powder is still 2%-3%), the third stage under 1223-1373K in molybdenum wire furnace.
In the molybdenum powder production, the key indicator is its granularity control: the mechanism of grain size changing and influence factors of MoO3 Nanopowder hydrogen reduction process is similar to WO3 hydrogen reduction, but MoO3 starts the significant sublimation when the temperature is more than 873K and its vapor pressure reaches 0.1MPa under 1424K, much greater than the vapor pressure of WO3. Therefore, the reduction process is more conducive to chemical vapor migration, which the powder particles obtained are supposed to be thicker than tungsten powder but actually it is often finer than the tungsten powder. There are two reasons: first, the chemical stability of MoO3 is low, which can be rapidly restored to MoO2 which has a very low vapor pressure and refractory within the temperature range when the vapor pressure of MoO3 is not that big in the low-temperature zone of the reducing furnace; secondly, the middle oxide of aluminum can form fusible eutectic under 773-973K with MoO2. To avoid the melting of this eutectic mixture, the actual production of the first stage reduction requires slow heating, which also reduces the possibility of the MoO3 into its significant evaporation temperature range. The average particle size of the molybdenum powder obtained in the production generally is 0.5-3.5μm.
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