Why Does the Cold Resistance of EB Tungsten Filament Unqualified?

In China, the main material of EB (electron beam) tungsten filament is Double spiral wire. Double spiral wire can heating the cathode evenly. What’s more, the Double spiral wire can eliminate the influence of the magnetic field which is cause by the cathode electron beam. However, the process to make the Double spiral wire is more complex, if the users cannot operate dissolution of molybdenum correctly, it will cause a lot of substandard products. Against to the unqualified phenomenon of the cold resistance of EB tungsten filament, people should try to improve the process of molybdenum core wire dissolution.

Molybdenum core wire dissolution is a pure chemical reaction process. Molybdenum has a strong chemical stability, so that people used a mixture of concentrated sulfuric acid, concentrated nitric acid and water as an etching solution. During the reaction, the temperature and time of the reaction should be to control by a strict operation. In addition, people should also pay attention to the phenomenon of the reaction, the reaction speed would change for the different temperature and the seasons. Due to the low temperatures in winter, the reaction is difficult to control the, it is more likely to cause the cold resistance of EB tungsten filament unqualified.

There exist the remaining acid in the surface of EB tungsten filament without washing cleanly. Oxidation would make the tails of EB tungsten filament become black. Molybdenum wire of cold resistance of EB tungsten filament is mainly caused by the incomplete reaction.

The cold resistance of EB tungsten filament unqualified will produce a lot of waste, causing serious environmental pollution. Therefore, people need to understand the reason to reduce pollution and improve the ecological environment.

electron gun filament

Maintenance of EB Tungsten Filament of SEM

SEM (scanning electron microscope) of the electron microscope has a lower degree of vacuum, and a large beam current. Therefore, the life time of tungsten filament of SEM is limited. Generally speaking, it can last for only a few dozen hours. The life time of tungsten filament of SEM has a direct impact on the cost of the instruments operation and the effective time of operation. Consequently, it would cause more pollution and other adverse consequences. Therefore, the tungsten filament of SEM needs a regular maintenance or repair. Users can take the following measures to maintain tungsten filament and extend the life time of instruments.

Firstly, check the condition of tungsten filament, if possible, users should put the component of tungsten filament on the dissecting microscope to check again. The rate of evaporation of the filament surface is related to the temperature of the filament, users can adjust a higher height to decrease the temperature of the filament. The material can choose a thick filament gasket. And then users should adjust the current of tungsten filament. During the maintenance of tungsten filament of SEM, users should check the saturation of the filament timely. Under an unsaturated condition, current of tungsten filament should be adjusted to the saturated condition. Finally, keep the vacuum degree of Scanning electron microscope lens.

Other measures to maintain tungsten filament of SEM are: 1. Before exchange the filament, users should remove dampness and air of the new filament. 2. Do not switch filament frequently in the daily work.

 

Prevent WO3 Waste Flue Gas Denitration Catalyst Regeneration Pollution

plate denitration catalystAt present, the NOx in China is mainly coming from coal-fired power plants, tungsten trioxide SCR denitration catalyst is widely used as the best denitration technology due to the nice properties such as high denitration rate, selectivity, mature and reliable. However large numbers of toxic and hazardous waste gas tungsten trioxide denitration catalysts are produced with the ongoing SCR project. Therefore, strengthening the management of waste gas denitration catalyst for preventing human health and environment being damaged is necessary.
 
The activity of waste flue gas denitration catalyst can be restored or upgraded after regeneration, thus to achieve the goal of recycling and saving resource. There are two denitration catalyst regeneration treatments, respectively: on-site regeneration, and factory regeneration. Because the ability of waste gas tungsten oxide denitration catalyst regeneration is serious poor, so far the main way in China is on-site regeneration. However, since the on-site regeneration is very dangerous, which is easily causing the site environment and water pollution; others, the denitration ability can’t meet the requirements after on-site regenerated. Therefore, the factory regeneration is suggested for avoiding secondary pollution.
 
The real factory regeneration of waste tungsten trioxide denitration catalyst is a complex physical and chemical processes, and the chemical composition of regenerated catalyst can be well controlled; more importantly, the activity of catalyst recovered can even reach 100%, by the way, it can be tailored. The key technologies of waste tungsten trioxide denitration catalyst regeneration process include: high-pressure water washing, ultrasonic washing, pickling, active implants and high-temperature calcination; its major regeneration aspects include: pretreatment, cleaning, pickling, drying or calcination, wastewater treatment, waste gas treatment and other processes.

 

Tungsten bronze (TB) Crystal Material Molecular Design

Molecular design of TB crystal material has made many new progress in recent years. Mainly reflected in that filling position A is applied to new elements; diversification and doping modification of filling position B element .
 
Some of the new crystals of molecules design and development by Foster is listed in Table 1. It can be found that the development of TB-type crystalline material, to fill the main position A traditionally with Ba, Sr, Pb, K and other elements entering, and the new trends of filling with La, Ce and other rare earth elements have appeared in recent years. There are rare reports about TB crystal material of earth elements in China, but there have been systematically studied in foreign countries. Position B is located by only a cationic occupied traditionally. In recent years, through the addition of low-valence cation in this position, the position A can be introduced more cations to balance electricity price, not only expanding the position A molecular design, but also being conducive to get stable crystal structure of TB.
 
Lightly doped TB crystal material, its performance can be improved to improve the quality of the crystal growth. Table following shows the properties changes of SBN, KNSBN after doping.
 
It is worth mentioned that progress of the application of TB-type crystal material is fast. SBN, PBN and other classic TB crystal materials, studies on of which preparation and properties of ceramic materials and film materials are active. Compared with the abroad, research on TB crystal materials with the W element used in position B is less in China. TB structure film of the phosphate has attracted great attention due to good prospects for superconducting applications, but the research in this aspect is weaker in China.

table1

Commercial Recovering Value of Waste WO3 Denitration Catalyst

valuable metal content in waste denitration catalystThere are a large number of valuable metals in the waste SCR denitration catalyst, if directly discarded, it will cause a huge resources waste; furthermore, vanadium pentoxide can cause environmental pollution because of its highly toxic. For reducing environmental pollution caused in denitration catalyst regeneration process, to establish a program for generating material with high content of valuable metals, and its products can be sold directly as a raw material thus to have some commercial value.
 
The detailed description plan is showed as below:
1. Calcining the waste tungsten trioxide denitration catalyst at 800~850 ℃ for 7 ~ 8 hours, for making the material of titanium, tungsten, vanadium, molybdenum oxidized sufficiently, and removing spent catalyst and combustibles volatile at the same time; cooled after released, and then pulverized to 60 mesh or less for inactive using;
2. Leaching out the material with ammonia which has been calcined and ground at 80~90℃ for 7 to 9 hours, until the mass of tungsten trioxide and molybdenum trioxide are all leached out; carrying out filtration to separate the leaching solution containing tungsten along with molybdenum and leach residue containing titanium vanadium;
3. The leachate is first carried out Mo precipitation with ammonium sulfide, taken out filtration after Mo completely precipitated thus to get the molybdenum sulfide which can be sold as raw molybdenum material; besides, the ammonium tungstate is remained in the filtrate solution;
4. Concentrate the filtrate to about 45% of its original volume by evaporation, and then adjust the pH value to 6.2 with nitric acid, while reducing the temperature of the solution to about 15℃at the same time, and incubated for 5 hours to precipitate ammonium paratungstate crystals, then directly packing the APT for selling after washed, and the crystal liquor returns to evaporation process;
5. Leaching out the vanadium in the residue by reduction roasting method, by the way titanium leaves in the leaching residue, thus to separate vanadium and titanium; after cooling down and filtrating, the residue can be sold as the titanium-rich material;
6. Add KClO3 into the filtrate to precipitate V2O5, and it can be sold as vanadium application raw material, and the potassium mother liquor can be used as an agricultural fertilizer.

 

 

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