Tungsten Electrode and Rare Earth Tungsten Electrode

The tip color of tungsten electrode is green. It has small vapor pressure, low resistance, good conductivity, low thermal expansion coefficient, good elastic modulus and other good performance.
 

tungsten electrode

The tip color of cerium tungsten electrode is gray. It has a non-radiation, low melting rate, long welding life, good arc resistance and other good properties. Cerium tungsten electrodes at low current arc has good performance, mainly used in low-current DC welding.
 
The tip colors of lanthanum tungsten electrodes according to doping amount different are different, when lanthanum oxide (La2O3) doping amount is 0.80%~1.20%, tip color is black. When doping amount is 1.30%~1.70%, tip color is golden yellow. When doping amount is 1.80%~2.20%, tip color is the sky blue. It has good mechanical cutting performance, creep resistance, high ductility high recrystallization temperature and other good performance. Lanthanum tungsten electrodes is an internationally popular electrode material.
 
Tip color of thorium tungsten electrode is also depending on the doping amount of thorium oxide. And the generally tip colors of thorium tungsten electrodes are yellow (0.90 to 1.20%), red (1.8 to 2.2%), purple (2.80 ~ 3.20%) and orange (3.80 ~ 4.20%). It has low electronic features  high recrystallization temperature, good electrical conductivity and cutting performance, often used in DC spot welding fields. Although thorium tungsten electrodes have excellent welding performance and easy to operate, however because of a certain radiation so it gradually be replaced by other rare earth electrodes.
 
Zirconium tungsten electrode tip color is usually brown and white. When ZrO2 doping amount is 0.02% ~ 0.40%, tip color painted head is brown. When doping amount is 0.07% ~ 0.09 %, its tip color is white. Zirconium tungsten electrode and tungsten electrodes can only carry out welding work in the AC environment and it has good corrosion resistance and weldability.
 

 

Tungsten Electrode

Tungsten electrode having good electron emission ability, high melting point, high elastic modulus, low vapor pressure, low temperature creep, high strength, resistance to burning, high recrystallization temperature and other good performance is often used as high thermal electron emission materials. Tungsten electrode is mainly used in the inert gas welding, plasma cutting, spraying and smelting and it is essential materials for machinery, shipbuilding, aerospace, construction, nuclear power, metallurgy and other fields. Tungsten electrode is not used for direct soldering, and are widely used in AC welding. It is generally used for welding aluminum and magnesium alloy, providing a good stable arc sine wave in the welding process, so it is widely used in various fields specific welding applications.
 
However, due to tungsten electrode has a very high electron work function, thus arcing and maintaining the stability of the arc is difficult. In addition, it has low emission efficiency. Besides,  at a high temperature it is easy recrystallization to form equiaxed grain structure leads to electrodes rattle, which greatly limits the use of tungsten electrodes.
 
In order to overcome these shortcomings, after study found, adding rare earth oxides having low electron into tungsten-base electrode can improve the recrystallization temperature of the tungsten electrodes and can activate electron emission as well, so that the tungsten electrode welding performance can be improved, expanded the application fields of the alloy. Adding rare earth oxides of tungsten-based alloy has better arcing performance, higher stability of the arc column, and electrode burning rate becomes smaller. Currently, common rare earth oxide additives are cerium oxide, lanthanum oxide, zirconium oxide, yttrium oxide, thorium oxide and so on. 
 
With the development of economy and technology, the world’s tungsten electrode consumption reached 1,600 tons per year or more. Chinese annual output of tungsten electrodes are gradually growing every year, accounting for 3/4 of the world's annual production of tungsten electrodes.
 
tungsten electrode

Detinning Process of APT Production- Additives in Alkali Decomposition

Ammonium paratungstate is produced by separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO3, tungsten(VI) oxide. From there, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to elemental powder, leaving behind water vapor. From there, the tungsten powder can be fused into any number of things, from wire to bars to other shapes.
 
Adding Na3PO4 in alkali decomposition process is common for the impurities in calcium (Ca) in  tungsten concentrates, which makes it as insoluble Ca3 (PO4) 2 go into the leach residue, thereby avoiding its combination with WO4- and formation of CaWO4 precipitate remaining in the slag, to improve the leaching rate of tungsten. 
 
In wolframite concentrate leaching process, impurities Sn, Si, P, As, also have a certain amount of leaching. In alkaline solution, they exist as SnO3 2-, SiO3 2-, HPO4 2-, HAsO4 2- and other forms, these ions can form insoluble compounds with Ca2 + and settle down. Thus, under certain conditions (theoretical amount of base in an amount of 170 to 190, a temperature of 160 ~ 170 ℃), without or with a small mount of Na3PO4 (even add some calcium compounds such as lime), calcium and the reaction with these anions can be taken great advantage, to reduce the tin content of sodium tungstate solution. Some minerals take other measures to reduce the amount of sodium phosphate, tin leaching rate can be reduced by 25% to 40%.
 
The solubility product of CaWO4 is small, so some people think it controversial to inhibit impurities with calcium compound as additives.

APT

Asynchronous flotation of Scheelite and Wolframite Mixture Ore

Asynchronous flotation, is using the differences between the same kind and heterogeneous ores floatability and floating rate in the flotation process. Therefore, the ore flotation flow can be artificially adjusted.
 
The first step is based on wolframite flotation, most available fast floating wolframite and partially floating scheelite. Depend on the circumstances to increase the number of flotation of wolframite operations, try to clean out wolframite, and then merge wolframite of each job to get the total wolframite concentrate.
 
The second step is scheelite flotation, use Pb2+ to activate most difficult floated scheelite and scheelite concentrate is obtained by flotation. Thus, the recovery of scheelite and wolframite mixture ore goes maximize at the respective suitable conditions, to ensure maximum total recovery of tungsten ores. The follow-up scheelite and wolframite mixture ore concentrate can be further separated by flotation or strong magnetic separation, respectively achieved wolframite concentrate and scheelite concentrate. Mixed concentrate can also be achieved.
 
Test conditions: use citric acid to restrain fluorite and some scheelite so that wolframite firstly selected, then add lead nitrate to activate inhibited scheelite and wolframite remaining, PH value of 9.5, float scheelite with benzohydroxamic acid as a collector.
After the optimization, with the extension of flotation time, the flotation rate of wolframite gradually decreased, floating rate of scheelite and fluorite is unchanged, floating rate of wolframite is much faster than scheelite in pre-flotation, and floating rates of wolframite and scheelite are very close in later flotation. The recovery difference of scheelite and wolframite mixture ore remained at around 70%.

scheelite and wolframite mixture ore

Recycling Tungsten Trioxide in Waste SCR Denitration Catalyst

The development of SCR denitration catalyst is based on the technology of selective catalytic reduction (SCR), the SCR system is an integral and important part of SCR systems. In performance, the denitration catalyst is the key to success of the project, its components, structure, life and its associated parameters directly affect the health of denitration efficiency and SCR systems. SCR denitration catalyst can be classified according to different raw materials, structure, extent, use and other standards. There are mainly three types in SCR denitration catalyst: 1) precious metal type; 2), metal oxide type; 3), zeolite type of ion exchange. The type of metal oxide is currently the more popular, it is also more widely used, and such catalysts is based on the carrier of titanium dioxide, vanadium pentoxide, tungsten trioxide the active ingredient.

Steps
(1)Crushing SCR denitration catalyst to dry powder, and roasting it in high-temperature;
(2) Adding a solution of soluble tungsten trioxide component and heating it in the above step (1) that the resulting is dry powder;
(3) Collecting the supernatant after fully dissolving, and make the liquid-solid layers clean;
(4) Adding the solid in the step (3) and the composition of tungsten trioxide to the reaction vessel together, and repeating the step (2);
(5) Repeating the step(3) and (4) at least once;
(6) Collecting several components and dissolving tungsten trioxide that was evaporated to dryness and sufficiently, drying to obtain a solid;
(7) Sintering the resulting solid in the step (6) at high temperature, and we can recycle the component of tungsten trioxide in the waste SCR denitration catalyst.

 

 

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