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Rare Earth Effect in Tungsten Electrode

Details: Category: Tungsten Information; Published on Monday, 28 March 2016 16:13; Written by yiping; Hits: 246

tungsten electrode

Among tungsten electrodes, thoriated tungsten electrode, having good weldability, is the most widely used tungsten electrodes. But because thorium has radioactive contamination so in the production and using process will endanger human health and pollute the environment. Through continuous research and development, the researchers developed multiple composite rare earth tungsten electrodes, and it is considered the best material to replace thoriated tungsten electrodes.

Rare earth doped as the active material doped to tungsten matrix can effectively reduce the work function of the tungsten electrode material to improve the welding performance. In multiple composite rare earth tungsten electrodes, the doped rare earth elements include La, Y and Ce. These three different rare earth elements at different temperatures have diffusion rates. Among these elements, Ce first diffused to the surface, reducing the work function of the surface, so click arc easy. When arc burning stable, La has largest surface coverage, and plays an important role at this process. While working in high current, Y timely migration to the surface, so the electrode can stably operate at high current conditions. Synergy of these three rare earth elements, so that the performance of multiple composite rare earth electrodes better than thoriated tungsten electrode.

On the other hand, the rare earth is conducive to refine reduction powder, and easy to promote the β-W formation. β-W makes the sintering process not easy to control. In the tungsten electrode sintering process, not only the rare earth will impede tungsten grain growth, but it will improve the recovery and recrystallization temperature of tungsten electrode such that the deformation resistance increases of electrode will increase, resulting in sintering process not easy to control. This is also one of reasons that multiple composite rare earth tungsten electrode has low finished produced rate and high production costs.

In the future, studies should toward production technology development direction to research. To improve the multiple composite rare earth tungsten electrodes finished produced rate and to reduce production costs make it more widely used.

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Porous Titanium Dioxide V2O5-WO3 Denitration Catalyst

Details: Category: Tungsten Information; Published on Monday, 28 March 2016 16:00; Written by chunyan; Hits: 245

Currently, SCR denitration catalyst, the key to the denitration reaction, is the main technology to eliminate pollution of stationary source NOx, has the advantages of high efficiency, selectivity and economic. It is found that vanadium-based denitration catalyst with anatase titanium dioxide has the higher activity, selectivity, stability after many years of industrial experience; besides, it shows strong in anti-toxic effects from sulfur dioxide, fly ash, alkali metals and arsenic when tungsten trioxide added, which makes it an ideal denitration catalyst and widely used.

Technical grade titania carrier can load limit active ingredient, however, if the specific surface area reduced, its load capacity can be greatly enhanced under quality fixed. In order to increase the specific surface area of titanium dioxide, scholars are constantly studied, there are sol-gel, supercritical drying and supercritical fluid extraction method, however, they can not be mass-produced due to the lacking of complicated operation and high cost. This paper presents an ammonia titration titanyl sulfate precipitation method to produce porous titanium dioxide, and prepare SCR denitration catalyst by impregnation.

The steps like bellows:

1.Completely dissolve titanyl sulfate in water, add the appropriate amount of ammonia after stirring sufficiently to generate a large amount of precipitate, then set the precipitate at room temperature for 10 hours;

2.Filtering, washing, and then drying for 10 hours, turning to a muffle furnace for calcining at 550 °C for 3 hours, then cames to the porous titanium dioxide, ground;

3.Dissolving tungstate ammonia and ammonium metatungstate in the oxalic acid solution;

4.Dipping the titanium dioxide into the solution configured, then drying after respectively stirring and aging for 1hour, and calcining in a muffle furnace at 550 °C for 6 hours, ground to 20 to 30 mesh to obtain the porous titanium oxide V2O5-WO3 SCR denitration catalyst.

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CsxWO3 Influence on NIR Shielding Property

Details: Category: Tungsten Information; Published on Friday, 25 March 2016 19:40; Written by xinyi; Hits: 253

Near-infrared(NIR, IR-A DIN), is defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision goggles.

Recently, shielding not only ultraviolet rays but also infrared rays has been attracted attentions in terms of saving resource and energy and creating comfortable life space. Cs doped tungsten bronze (CsxWO3) which has suitable amounts of free electrons in crystal is one of the candidate materials of inorganic infrared rays shielding materials, since it can shield ultraviolet and infrared rays by interband transition and plasma oscillation of free electrons, respectively. Nanoparticles of CsxWO3 particles were synthesized by solvothermal reaction of WCl6 and CsOH・H2O in ethanol and ethanol aqueous solutions at 200 ℃ for 12-47 h. After that, CsxWO3 particles were heated in 500 ml/min NH3 gas flow at 400 ℃ for 1 h. Sheet-like and rod-like nanopartricles of CsxWO3 were synthesized in ethanol and 42.9 vol% ethanol aqueous solution at 200 ℃, respectively. The samples formed in 42.9 vol% ehanol aqueous showed higer crystallinity but lower Cs/W atomic ratio than those in ethanol. Sheet-like particles showed higher visible light transparency, while rod-like particles showed more excellent infrared shielding properties, indicating that rod-like particles were more suitable for shielding infrared rays. Moreover, the visible light transparency and infrared shielding properties could be improved by improving the dispersion state of the particles by agitating with ZrO2 beads. The electric conductivity of the pressed pellet of rod-like particles could be increased by heating in NH3 gas atmosphere at 400 ℃.

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Aluminum Oxide Improves Tungsten Trioxide SCR Denitration Catalyst Activity

Details: Category: Tungsten Information; Published on Monday, 28 March 2016 15:56; Written by chunyan; Hits: 280

The carrier has a significant impact on the property of SCR denitration catalyst. Currently, alumina, silica, zeolite, etc. are the most commonly used catalyst carriers, titanium dioxide has been greatly concerned because of its strong acidity. However, single vector is difficult to meet all the needs of modern industry, therefore, people began to study the composite carriers to set the advantages of both in one, also, it is expected that new property will be found by the interaction of two carriers.

Tungsten trioxide, vanadium pentoxide and other active components loaded in titanium dioxide-aluminum oxide can effectively improve the activity and selectivity of the SCR denitration catalyst.Titanium dioxide-aluminum oxide composite carrier can be prepared by different methods, like impregnation, grafting, adsorption and other method, also different methods will have greatly effect on titanium dioxide desperate on aluminum oxide.

The introduction of tungsten trioxide can effectively improve the activity of vanadium system SCR denitration catalyst and also enhance its hydrothermal stability. Further more, the catalyst powder will have bigger specific surface area when using nanotechnology, thus to greatly enhance the activity of the catalyst, making the catalyst has a stronger catalytic reduction.

Experimental studies have proved that with the increasing of aluminum content, the vanadium pentoxide-tungsten trioxide/titania-based SCR denitration catalyst reactivity will gradually increasing. This indicates that the synergy of titanium oxide and aluminum trioxide can enhance the activity of catalyst. Especially, when the aluminum content is 10% and at the temperature of 380 °C, the denitration catalyst has a high activity which is reach to 98.6%, significantly higher than single titania-supported catalysts. Thus to conclusion that aluminum oxide improves tungsten trioxide SCR denitration catalyst activity.

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Cs(x)WO3/ZnO Nanocomposite as Smart Coating

Details: Category: Tungsten Information; Published on Friday, 25 March 2016 19:33; Written by xinyi; Hits: 228

Zinc oxide is an inorganic compound with the formula ZnO. ZnO is a white powder that is insoluble in water, and it is widely used as an additive in numerous materials and products including rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, and first-aid tapes. It occurs naturally as the mineral zincite, but most zinc oxide is produced synthetically.

ZnO is a wide-bandgap semiconductor of the II-VI semiconductor group. The native doping of the semiconductor due to oxygen vacancies or zinc interstitials is n-type. This semiconductor has several favorable properties, including good transparency, high electron mobility, wide bandgap, and strong room-temperature luminescence. Those properties are used in emerging applications for transparent electrodes in liquid crystal displays, in energy-saving or heat-protecting windows, and in electronics as thin-film transistors and light-emitting diodes.

A novel Cs_xWO₃/ZnO smart coating was proposed to achieve multiple functions, such as heat insulation, photodecomposition of toxic NO gas, blocking of harmful UV light, etc. In this composite coating, Cs_xWO₃ nanorods were used as a NIR and UV light shielding material while ZnO nanoparticles were utilized as a photocatalyst and a material to enhance visible light transmittance and block UV light. When the mass ratio of Cs_xWO₃/ZnO was 1, the composite coating possessed a very good visible light transmittance of over 80% and an excellent UV-shielding ability. This novel coating showed heat insulation that is superior to the ITO coating and photocatalytic decontamination of NO gas that is superior to the standard TiO₂ (P₂₅). The proposed Cs_xWO₃/ZnO smart coating is a promising material not only for energy saving but also for environmental cleanup.

CsxWO3

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