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High-purity bismuth is mainly used in the nuclear industry, aerospace industry, electronic industry and other sectors. Since germanium has a semiconductor characteristic, its resistance decreases with increasing temperature at low temperatures. Refrigeration temperature difference and the temperature difference power generation, Bi 2 Te3 and Bi 2 Se 3 alloy and Bi-Sb-Te ternary alloy most interesting. In-Bi alloy and Pb-Bi alloy are superconducting materials, which have low melting point, high density, small vapor pressure and small neutron absorption cross section, and can be used in high temperature atomic reactors.
There are many methods for purifying Sijiujing from Wujiu high-purity, and the most industrial value is vacuum distillation and regional purification.
First, vacuum distillation
The trace impurities contained in the fine sputum can be divided into two types: volatile impurities and difficult volatile impurities. The volatile impurities can be removed by vacuum heating, and the less volatile impurities can be removed by vacuum distillation.
The vacuum filtration was carried out in a vertical quartz tube, and the temperature was heated at 1000 ° C for 4 hours under a vacuum of 0.1333 Pa, and the molten metal was passed through a narrow hole of 2 mm under vacuum to remove the oxide film on the surface. After vacuum filtration, the fine electrode was removed.锑 in the 铋 .
The vacuum-filtered armor is placed in a quartz tube, the temperature is controlled at 950 to 1050 ° C, the vacuum is maintained at 0.1333 Pa, and vacuum distillation is performed. Under the above conditions, the vapor pressure of the crucible is 106.7 to 399.97 Pa, and the evaporation rate of the crucible is 85%. Distillation time 2 to 6 small elbows. By vacuum distillation, the distillation residue is enriched with impurities such as nickel , molybdenum , silver , copper , manganese, etc., and the distillate is a pure quinone, which can be used in the semiconductor industry.
Since the saturated vapor pressures of lead and antimony are relatively close, the helium distillation method cannot meet the lead removal requirements. However, the free enthalpy of lead chloride is more negative than the free enthalpy of lanthanum chloride, that is, the chloride of lead is more stable than the chloride of bismuth. Therefore, lead removal by chlorination is often used first, and then hard-to-volatile impurities such as silver are removed by vacuum distillation. .
The content of chloride in the molten crucible can be reduced by ammonia flushing or by vacuum distillation of chloride, and the degree of vacuum is controlled to 0.6666 Pa and the temperature is 650 ° C. At this time, BiCl 3 and PbCl 2 are preferentially evaporated, and separated from the metal crucible.
Second, regional purification
When the molten crucible is cooled and crystallized, the impurities are precipitated at the edge of the container because the impurities are condensed earlier, so that the impurities in the center of the crucible are less than the impurities on the edge of the crucible. According to this principle, the area purification is to heat and melt the crowbar, slowly move through the melting zone, and return to the complex motion multiple times to enrich the impurities at both ends of the crowbar to achieve the purpose of purification.
In order to remove the oxides in the crucible in advance, the crucible is melted into a temperature-resistant glass tube or a graphite boat under a vacuum of about 3.333 Pa. After dripping, the glass tube is closed under vacuum and placed in a glass sleeve.
The zone melting refining furnace generally draws the graphite boat without moving, and adopts an automatic reciprocating induction heating device because the high frequency induction heating has a natural stirring action.
When the zone is purified, the ratio of the length of the melt zone to the length of the bar is 1:24, and the inclination of the graphite boat after flattening is 1-3°. The determination of the moving speed and the number of strokes of the melting zone is related to the quality of the raw material, the cross-sectional area of ​​the boat, and the heating temperature is controlled at about 600 °C.
Weathering steel refers to atmospheric corrosion-resistant steel, which is a low-alloy steel material between ordinary steel and stainless steel. It is made by adding a little copper, nickel and other corrosion-resistant elements to ordinary carbon steel. The weathering Steel Plate has the characteristics of toughness, plasticity, abrasion, high temperature and fatigue resistance. The weather resistance can reach 2-8 times that of ordinary carbon steel, and It has the advantages of rust resistance, corrosion resistance and life extension of components, labor saving and energy saving.
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Shandong Rizhaoxin Metal Products Co., Ltd. , https://www.sdrizhaoxinsteel.com