Vacuum electronic devices have a wide application in civil and military fields such as communication, radar and industrial heating. Cathode is an important component in the device since it provides the required electronic beam for the device. Among all the electron emitters, scandate cathodes have aroused great attention among all the cathodes due to their copious emission property.

Scandia doped tungsten powders were prepared by spray drying combined with two-step hydrogen reduction. The particle size of doped tungsten powder, powder morphology and doped tungsten matrix were characterized by scanning electron microscope, X-ray diffraction and laser diffraction particle size analyzer, respectively. The reduction behavior of Sc2O3 doped tungsten oxide and the effect of Sc2O3 on the property of tungsten powder were studied by the temperature programmed reduction. The experimental results showed that the precursor powders prepared by spray drying had spherical shape. The addition of Sc2O3 could decrease the reduction temperature of tungsten oxide. The scandia doped tungsten powder had sub-micrometer size in the range of 0.1 to1 μm and scandium distributed evenly in the powder. By using this kind powder, sub-microstructure cathode matrices with semispherical grains and homogenous distribution of scandium were obtained.

The addition of Sc2O3 shifted the hydrogen consumption peak to the lower temperature side. Namely, the reduction temperature of tungsten oxide decreased with Sc2O3 addition. Adding scandia could decrease the particle size of tungsten. The scandia doped tungsten powder prepared by spray drying method had sub-micrometer size in the range of 0.1μm to1μm in semispherical shape and scandium distributed evenly in the powder. Using scandia doped tungsten powder, sub-microstructure cathode matrices with semispherical grains and homogenous distribution of scandium was obtained.

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Compared with other transition metal oxides, ungsten oxides have attracted great attention and have been investigated extensively due to their outstanding electrochromic, optochromic, and gas-chromic properties. ith those distinctive prop-erties, tungsten oxides have been used to makeflat panel displays, photoelectrochromic smart win-dows and gas sensors. Non-fully oxidized tungsten oxides (WO3x), such as W20O58, W18O49andWO2, are of particular interest because of their unique electronic characteristics, e.g. tungsten oxide has been found to be a semiconductor, a conductor or a superconductor in different oxidization states. Since one-dimensional tungsten oxide nano-materials exhibit superior properties in some promising applications compared with bulk materials, much effort has been made to synthesize tungsten oxide nanowires by using different methods, including a soft-chemistry approach, the chemical vapour deposition (CVD) method, hot-filament-assisted synthesis, flame synthesis and multistage field enhancement of tungsten oxide nanowires.

Tungsten oxide nanowires of diameters ranging from 7 to 200 nm are prepared on a tungsten rod substrate by using the chemical vapour deposition (CVD) method with vapour–solid (VS) mechanism. Tin powders are used to control oxygen concentration in the furnace, thereby assisting the growth of the tungsten oxide nanowires. The grown tungsten oxide nanowires are determined to be of crystalline W18O49. I–V curves are measured by an in situ transmission electron microscope (TEM) to investigate the electrical properties of the nanowires. All of the I–V curves observed are symmetric, which reveals that the tungsten oxide nanowires are semiconducting. Quantitative analyses of the experimental I–V curves by using a metal–semiconductor–metal (MSM) model give some intrinsic parameters of the tungsten oxide nanowires, such as the carrier concentration, the carrier mobility and the conductivity.

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Tungsten oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals.Tungsten ores are treated with alkalis to produce WO3. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal.

The phase structure, morphology and particle size evolution of tungsten oxide reduced by hydrogen were studied by X-ray diffractometer ,scanning election is WO3-WO2.90-WO2.72-WO2-W. The surface morphology of powder changes from a smooth ro a rough particle and eventually the bigger secondary particles turn to sevetal smaller particles . The specific surface area of the powder increases during WO3 reducing to WO2.90-WO2.72 , reducing to W.

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Tungsten carbide cutting tool coating performance largely depends on the quality of the coating process and the coating, the coating quality preparation include: coating density, texture, microstructure, structural defects, residual stress. Coating process parameters include a deposition temperature, arc current, N2 partial pressure, a negative bias, coating time, the degree of vacuum and the like.

3. Nitrogen partial pressure
Nitrogen gas as the reaction gas, the size of the partial pressure of a serious impact on the phase composition of the coating. During deposition, the nitrogen also plays a role in the arc dimension, when the gas pressure in the cavity is too low, it is difficult to maintain a stable cathodic arc, can lead to the phenomenon of breaking arc, while the film will be such that the ratio of tungsten carbide cutting tool decrease in N, reach preferably TiN, TiCN, ZrN atomic ratio.

4.The negative bias
Bias is high, the ion bombardment enhanced dense. Pulse bias to some extent reduce the residual stress dawdle, and the bonding strength increases, the friction coefficient decreases. But the bias is too high, the base overheating, mechanical properties of  tungsten carbide cutting tool the coating hardness and bonding strength will decline.


 

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Tungsten carbide cutting tool coating performance largely depends on the quality of the coating process and the coating, the coating quality preparation include: coating density, texture, microstructure, structural defects, residual stress. Tungsten carbide cutting tool coating process parameters include a deposition temperature, arc current, N2 partial pressure, a negative bias, coating time, the degree of vacuum and the like.

1. The deposition temperature
Tungsten carbide cutting tool coating deposition temperature on the microstructure, hardness and adhesion plays a crucial role. Temperature is too low, non-uniform nucleation, is loose, thick tissue, film hardness, adhesion, poor abrasion resistance and other mechanical properties; temperature is too high, the substrate surface is overheating, is obtained coarse crystalline organization, lower hardness. Only a suitable temperature to obtain a dense columnar crystals, the atomic arrangement of the film hardness due to more regular, reduced porosity and increased reasons.

2. The arc source current
Under certain bias, arc source current determines the temperature and macroscopic mechanical properties of the matrix, the target current increases, the substrate temperature, the crystal growth from the column to a dense crystalline equiaxed growth and transformation, tungsten carbide cutting tool coating With the improvement of hardness.


 

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It was also found: the plating current distribution directly affect coating uniformity. The edge of the mold, the corner portion, R at the current density was significantly higher than other parts, and accordingly the amount of metal deposition, large coating thickness. Under normal circumstances, the coating thickness difference of the central and side corners, R at about 4μm. Current lead to uneven distribution of coating thickness difference reaches more than 15μm, severe because of local metal deposition coating amount excessive shedding.
    
Further, the mold shape, structure, material and the like also affect the coating quality.
    
Countermeasure
    
(1) Before blasting, inspection, eliminate trachoma mold matrix, porosity, pitting corrosion, adhesion and the like.
    
(2) When the first test blast sandy, if impurities, foreign matter, oil and other pollution, should be completely replaced immediately. Timely cleaning the mold surface remaining after blasting grit and other adhesive material.
    
(3) In addition to the oil before the oil to the surface inspection, if oil emulsifier gather timely spray to break up; if the mold surface after degreasing oily emulsion adhesion, must be clean.
    
(4) Acid activation time must be strictly controlled to avoid excessive corrosion die; at the same time, under good control mold groove depth, to prevent the electrode plates, connectors and other corrosion. Their corrosion will contaminate the bath, resulting in poor plating.
   
(5) When the bath preparation of high purity chemicals as much as possible, and timely analysis of impurities. In addition, the bath to regularly analyze, filter, and change them regularly.
    
(6) The shape of the mold structure, scientifically-designed according to current balance board can effectively suppress local deposition of metal is too thick, the coating quality assurance.
    
(7) Ensuring the mold production process to meet the premise of mold design optimization, particularly conducive to improve the coating quality.
    
(8) Replenish the anode, repair accessories, regular cleaning of the plating tank sludge, and "three wastes" comprehensive way.
    
(9) Purification, protection of the environment, comply with the technical rules, strengthening the operator responsible, to avoid environmental, mechanical impurities into the bath.




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Tungsten oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals.Tungsten ores are treated with alkalis to produce WO3. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal.

A novel composite based on tungsten oxide and fly ash was hydrothermally synthetized to be used as substrate in the advanced treatment of wastewaters with complex load resulted from the textile industry. The proposed treatment consists of one single step process combining photocatalysis and adsorption. The composite’s crystalline structure was investigated by X-ray diffraction and FTIR, while atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to analyze the morphology. The adsorption capacity and photocatalytic properties of the material were tested on mono- and multi-pollutants systems containing two dyes (Bemacid Blau – BB and Bemacid Rot – BR) and one heavy metal ion-Cu2+, and the optimized process conditions were identified. The results indicate better removal efficiencies using the novel composite material in the combined adsorption and photocatalysis, as compared to the separated processes. Dyes removal was significantly enhanced in the photocatalytic process by adding hydrogen peroxide and the mechanism was presented and discussed. The pseudo second order kinetics model best fitted the experimental data, both in the adsorption and in the combined processes. The kinetic parameters were calculated and correlated with the properties of the composite substrate.

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The tungsten oxide film may be deposited on the substrate by any suitable method including such conventional deposition techniques as, e.g., sputtering, chemical vapor deposition (CVD) and the spray method. As would be apparent to those skilled in the art in view of the present disclosure, the tungsten source employed in such methods will vary with the technique used. The process of depositing a film of tungsten oxide according to sputtering generally involves the application of a radio frequency voltage to a solid tungsten metal target exposed to an oxygen-containing atmosphere at reduced pressure. Chapman is hereby expressly incorporated by reference for its teachings of sputtering techniques. Another useful film deposition technique which may be employed to deposit a tungsten oxide film according to the present invention, is the well-known CVD process. It generally involves the flowing of gaseous reactants, one of which is a tungsten compound such as tungsten carbonyl, over a heated substrate. Thin Film Processes edited by J. L. Vossen and Werner Kern is herein expressly incorporated by reference for its teaching of such a process. Still other useful processes for depositing the tungstenoxide film on the surface of the substrate will be apparent to those skilled in the art in view of the present disclosure. The temperature of the substrate during the deposition process may vary and is not critical to the invention. For example, the tungstenoxide film may be deposited at room temperature or at an elevated temperature, the latter being the case when such films are deposited on a hot glass ribbon being produced by the well-known float glass process. The latter may involve temperatures in the range of 80° C. to about 700° C.

Generally, the tungsten oxide film is deposited on the substrate in a thickness of preferably between about 200 and 6000. The desired thickness of the film is determined by various factors, including reactant concentrations temperature and substrate velocity.

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Tungsten oxide films are of critical importance forelectrochromic device technology ,such as for smart windows capable of varying the throughput of visible light and solar energy.

Tungsten oxide films (WO(3)) are deposited by thermal evaporation techniques using the starting materials of tungsten (W) and tungsten oxide (WO(3)). By varying deposition parameters, three main types of WO(3) film exhibiting different optical properties form. These are blue, gray, and colorless films. The samples are characterized optically and morphologically. Blue-colored samples exhibit a broad selective absorption peak around 1000nm. Absorption of gray-colored samples spreads out in the visible region in an exponential form. The refractive indices of samples are between 1.9 and 2.1. The energy gap of blue and colorless samples is 3.32 eV, but that of the gray-colored samples is 3.18 eV and smaller. X-ray diffraction studies reveal that evaporated WO(3) films are amorphous. Fourier transform infrared spectra of samples were studied to evaluate bond properties. Colorless near-stoichiometric tungsten oxide films exhibit three absorption peaks in the 1000-600-cm(-1) window. These peak locations, in terms of cm(-1) window. These peak locations, in terms of cm(-1), are 669,737, and 813. In the colored samples, these three absorption peaks split into two peaks ~20 cm(-1) apart.

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Tungsten trioxide (WO3) has been studied for many years. It is one of the best materials for use in the fabrication of electrochromic (EC) devices, such as electrically tintable glass for use in buildings and automobiles. WO3has the desirable characteristics of transparency, chemical stability—as in the stoichiometry doesn't change with time after deposition—and relatively low cost. Typically, WOx, where 3>x>2.75, is desired for the EC application for the following reasons: (1) in the x>3 region, the oxygen is rich such that the WOxfilm may not be bleachable after lithium atom insertion; and (2) in the region x<2.75, the film is no longer transparent.

A deposition method for electrochromic WOxfilms involves cyclic deposition of very thin poisoned and metallic tungstenoxide layers to build up a film with a desired general stoichiometry with x in the range of 3>x>2.75. The method may include: charging a deposition chamber with oxygen gas to poison a tungsten metal target; initiating sputtering of the target while reducing the oxygen partial pressure being supplied to the chamber and pumping the chamber; sputtering target for time t1+t2to form first and second tungstenoxide layers, where the first layer is deposited during time t1from a poisoned target and the second layer is deposited during time t2from a metallic target, and where the stoichiometry of the film comprising the first and second layers is a function of t1and t2; and, repeating until a desired film thickness is achieved.

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