Manufacturing Process of Ceria-Tungsten Electrode

A plastic and metal powder produced by the method for processing a certain amount of the tungsten oxide of cerium (≤ 4%) of the electrode material . Cerium tungsten electrode material is a non-radioactive electrode material , it is since the 1950s to replace the radioactive thorium tungsten electrode material and gradually developed . This electrode material in an inert gas shielded arc welding and plasma welding , cutting, etc. has been widely applied .

Production began thorium tungsten electrode for the early 1950s , it was added to the tungsten ≤ 3% of thorium oxide . This material has a high electron emission capability , resistance to burning and arcing good performance ; However, because thorium is radioactive elements in the production, storage and use of the process prone to radioactive pollution, endangering human health , and thus from the mid-1950s , people have carried out research work on behalf of thorium materials . In 1956, the United States Lewis (A.Louis) conducted directly in the metal tungsten powder, 0.5 to 3.0% cerium oxide powder of testing, and then compacts melt down , rotary forging of welding electrodes . Two years later he cerium oxide content is reduced to 0.01% to 0.30% , so that the processing performance is improved. U.S. 1965 Herman (J.Hermann) using fine tungsten powder pressed into a pure green , green , or after this billet burn- soaked in a solution of rare earth salt , to achieve doping by imbibition , followed by sintering, according to the conventional method swaged to the desired diameter . 1967 ROMON Ivanov (V.N.Romonov) developed a 1% cerium oxide containing cerium tungsten material , the preparation process is: under 800 ~ 850 ℃ calcined ammonium paratungstate, tungsten trioxide , and the cerium nitrate an aqueous solution of a salt or oxide incorporated in the suspension of tungsten trioxide , tungsten trioxide and then doped with hydrogen good a reduced tungsten powder . Ethanol and glycerol mixture after a pressure of 600MPa into a 9mm × 9mm × 400mm billet bar , after burn-in and vertical melt , the billet of CeO2 content of 0.87% , when the swaging process , the heating temperature for the 1475 ~ 1500 ℃.

China started to develop in the 1970s, cerium tungsten electrode material , after nearly 10 years of production practice , the production process tends to be stable and mature , in the early 1980s , both domestically and internationally cerium tungsten electrode material for the production of patents. In the production process , how to make a tungsten doped ceria -based in vivo distribution and dispersion , the electrode is to improve the electron emission capability , improved arc performance , extend the life of one of the important factors . Therefore, the choice of raw materials , usually by blue tungsten oxide or doped tungsten oxide , and the doping agent is not used directly cerium oxide , instead of using the soluble salts such as cerium chloride or cerium nitrate . This aqueous solution as the mother liquor , add inwards blue tungsten trioxide or tungsten , during the addition , the heating and stirring continuously , and concentrated by evaporation to form a coating powder. Doping can also be an aqueous solution of cerium nitrate, cerium chloride or spray containing tungsten blue oxide powder, tungsten or a special container ( heat while rotating ) . The powder doped must be heated to a certain temperature , the salts decompose to form cerium oxide particles distributed in the tungsten trioxide powder, tungsten or blue on the surface of the particles , and then after hydrogen reduction , to obtain W-CeO2 powder. CeO2 content of 1% to 4%, selected according to requirements . Doped powder after molding, burn , vertical melt , get cerium tungsten billet , see doped tungsten its production process , but its swaged temperature slightly higher for 1500 ~ 1600 ℃.

Electrode performance as an electrode material , the level of electron work function is the amount of material raft electron emission performance is an important indicator of good or bad . Only a low electron work function , in order to meet the arc stability, focus , load current density process performance requirements.

Experiments show that cerium tungsten electrodes with thorium tungsten electrode is lower than the electron work function ( pure tungsten electron work function of 4.55eV, W-2% ThO2 is 2.7eV, W-2% CeO2 is 2.4eV ) , this electrode material than thoriated tungsten electrode has greater advantages . First , cerium tungsten electrodes electron emission capability , easy to get a slim arc , so that the heat is more concentrated , the allowable current density thoriated tungsten electrodes increased by 5 % to 8% . Secondly , cerium tungsten electrodes burning rate, long life , easy to arc initiation and stability are guaranteed . Again , cerium tungsten electrodes radioactive dose is very low, and only about one thousandth of thorium tungsten materials , the equivalent radiation dose earth soil . So instead of using cerium tungsten electrodes thorium tungsten electrode , not only can eliminate the production and use of human cumulative internal radiation hazards, and eliminating radioactive contamination of the environment , but also in technical performance and the results are also able to replace thoriated tungsten electrodes , Some properties even superior than thorium tungsten material .

Cerium tungsten electrode material in addition to the application in welding , plasma arc welding replacing thoriated tungsten electrode areas , but in plasma cutting , plasma spraying , plasma melting the application effect is satisfactory . In addition, as the pump laser light source to cerium tungsten electrodes after replacing thoriated tungsten electrodes , so that the light source efficiency by about 12% , life expectancy increased by 5 to 10 times. In the electric light , for small and medium power xenon lamp has been used cerium tungsten electrodes , the electric vacuum , cerium tungsten material as the sealing member having a good use of effects . Problems and trends Although cerium tungsten electrode material in a small tungsten electrodes for welding specifications had succeeded in replacing thoriated tungsten , but as AC welding electrodes and high-power xenon lamps and other aspects of the cathode gas discharge light source material , cerium tungsten electrodes performance and life compared with thorium tungsten , there are still fluctuated unstable situation . Further, since the cerium has a high vapor pressure , and thus as the cathode material , there are still fast decay , poor stability . Thus in these areas are still using thorium tungsten electrode material .

With the progress and development of modern industry , welding, cutting the base material of the species, size and shape of the increasingly numerous , but in the field of welding is the rise since the resumption shou automatic welding , a series of new high- precision welding technology, the electrode materials and arc features a higher and more demanding requirements. Thorium tungsten , cerium tungsten electrode material , whether in arc starting , stable arc burning resistance or in terms of performance are unable to meet the growing requirements of welding technology . To this end , national science and technology workers are working on a new type of electron-emitting material . Studies have shown that adding tungsten matrix lanthanum or yttrium and other rare earth oxides , can greatly improve the ability of tungsten electron emission , especially lanthanum tungsten electrode material , from small to large current current range , all with excellent arc, arc stability and resistance to burning performance. Japan in the late 1980s has been able to mass production of rare earth tungsten electrode material , shortly thereafter , China has successfully developed . It is anticipated that this new type of electron emission materials will be involved in many industrial fields , use more widely, promising .


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