LgP ( MoO3 ) 3 = - 1024580 +1101.2 T Best Mixer Shower,Bath Shower Mixer,Bath And Shower Mixer,Wall Mounted Shower Mixer Kaiping City Yibiao Sanitary Ware Co., Ltd. , https://www.faucetsaoli.com
Molybdenum trioxide melting points, boiling were lower, a melting point of 795 deg.] C boiling point of 1155 ℃. Molybdenum trioxide has begun to sublime before melting. When the temperature reaches 900~1100 °C, the evaporation has been quite fast. The gas phase molybdenum trioxide is present in the state of a repolymerized molecule (MoO 3 ) 3 . The change of vapor pressure of pure molybdenum trioxide with temperature is shown in the following table.
Table temperature and molybdenum trioxide vapor pressure
Temperature (°C)
600
610
625
650
720
750
800
Steam pressure (Pa)
0.00
1.20
2.40
6.67
79.99
233.31
1346.55
Temperature (°C)
850
900
950
1000
1050
1100
1150
Steam pressure (Pa)
3119.74
7186.06
14012.14
26,504.41
38,436.73
63487.94
101324.7
The relationship between the vapor pressure and temperature above the liquid molybdenum trioxide can be expressed by the following equation:
Â
Where P - (MoO 3 ) 3 vapor pressure (Pa); T - calibration temperature (K).
At this time, the evaporation heat ΔH was steamed = 147 KJ/mol, and the evaporation entropy ΔS was steamed = 103 J/mol.
The evaporation rate of pure molybdenum trioxide varies with the temperature and speed of the gas stream. That is, it is related to the rate at which the recombination molecule (MoO 3 ) 3 migrates out from the liquid surface. When the gas flow rate is 0.2~0.3cm/s, the airflow temperature is 900°C, the pure molybdenum trioxide evaporation rate is 12.3kg/(m 2 ·h), and after the temperature rises to 1100°C, the evaporation speed suddenly rises to 110kg/( m 2 ·h).
The raw material for the production of high-purity molybdenum trioxide by sublimation is industrial molybdenum calcination, which contains many impurities. When they are mixed into liquid molybdenum trioxide, the vapor pressure of molybdenum trioxide will be lowered, thus reducing the evaporation rate of molybdenum trioxide. The higher the impurity content, the more obvious the effect. The same raw material continues to proceed with evaporation, and the ratio of impurities in the residue is also significantly increased. Therefore, the evaporation rate of molybdenum trioxide is also gradually decreasing in production practice. At 1000 ° C and a gas flow rate of 2.3 cm / s, the evaporation rate of molybdenum trioxide from molybdenum calcine containing 48% to 50% of MoO 3 is only 10-20 kg / (m 2 · h).
The impurities contained in the molybdenum calcine are carried with the molybdenum concentrate. These include: calcium oxide, magnesium oxide, iron oxide, lead oxide, copper oxide, zinc oxide, silica and the like. The most influential on the evaporation rate of molybdenum trioxide is the oxide impurities of calcium, magnesium, lead and iron which can form stable molybdate and do not decompose at sublimation temperature (950~1100 °C). Obviously, the molybdenum in these molybdates cannot be sublimed out of molybdenum trioxide. CuMoO 4 and ZnMoO 4 formed by copper oxide, zinc oxide and molybdenum trioxide have been decomposed after ≥900 ° C; no chemical reaction occurs between silica and molybdenum trioxide. PbMoO 4 not only retains MoO 3 but also has a boiling point of 1060 ° C which is consistent with the significant sublimation temperature of MoO 3 . At 1000~1100 ° C, the vapor pressure is also considerable, and it will evaporate into the high purity three simultaneously with the molybdenum trioxide. Molybdenum oxide products. Therefore, the lead content of molybdenum calcine for the production of high-purity molybdenum trioxide for sublimation is more stringent. When the content is high, the sublimation temperature should be strictly controlled and should not be higher than 1000 °C. However, regardless of whether or not the reaction of molybdenum trioxide is involved, all impurities affect the sublimation rate of molybdenum trioxide. [next]
US Clemikes uses high-quality molybdenum concentrate containing Mo56%, Cu0.16%, Fe 0.38%, SiO 2 4.5%, A1 3 O 3 0.28%, CaO 0.06%, Pb0.04%, and is calcined to contain About 90% of molybdenum trioxide is used as raw material, heated by electric furnace to 1100~1200°C, and continuously sent into air. The sublimated molybdenum trioxide is collected by air into the dust collecting system, and the purity of the obtained product can reach 99.9%. Even as high as 99.975% MoO 3 . The bulk density is about 0.2 g/cm 3 . However, the sublimation rate of molybdenum trioxide in the raw materials is only 60% to 65%, and the remaining slag often contains 20% to 30% of unsublimated MoO 3 which is sent to recover or smelt ferromolybdenum by wet method.
In the former Soviet Union, in the sublimation process, the MoO 3 concentration in the gas stream was ≥0.05g/L, the gas flow rate was 7~14cm/s, and the temperature was >690°C, producing high-purity molybdenum trioxide with a high bulk density of 0.8~1.2g/cm 3 . Sublimation electric furnaces are often used in both continuous and intermittent.
Some companies in the United States often use electric furnaces that can be continuously produced by a ring-shaped rotating hearth, as shown in the following figure.
Diagram of electric sublimation furnace
In order to prevent the residual material from sintering, a layer of quartz sand is laid on the bottom of the furnace. A silicon carbon heating electrode is radially arranged on the upper portion of the furnace. The molybdenum calcined sand is continuously added to the bottom of the electric furnace, and while roasting, the quartz layer is infiltrated to form a fixed hearth. The air flows through the bottom of the furnace at a required flow rate, and the sublimated molybdenum trioxide is taken away, through the total collecting pipe, the surface condensation system, and enters. The air dust collector, the high purity molybdenum trioxide product, is separated from the air here. The electric furnace is heated by the electrode to 1000~1100 °C and rotates continuously. After the molybdenum calcine rotates with the electric furnace for one week, the molybdenum trioxide has been sublimated by 60%~65%, and the residual charge is discharged from the bottom of the furnace by the screw feeder, and a new molybdenum calcine is added by the feeder. The discharged residue also contains 20% to 30% of molybdenum trioxide, which is often recovered by ammonia leaching and sent to smelting ferromolybdenum. This electric furnace can produce 3.75t of high-purity molybdenum trioxide in the day and night.
The production plant of the Planer plant in Austria is relatively small, so the sublimation of molybdenum trioxide is carried out using a small batch electric furnace. They packed a mixture of molybdenum and quartz sand into a quartz crucible and placed it in a rotating electric furnace at 35 °C. The inclination increases the evaporation area of ​​the charge, and the air passing through the crucible carries away the molybdenum trioxide vapor. The hood on the electric furnace is pumped into the belt filter by an air blower.
The sublimation process produces high-purity molybdenum trioxide with a simple process and high product purity. However, the quality of the raw materials is high and the molybdenum recovery rate of the products is low.