Tungsten Boat for Vacuum Coating

Thanks to a high melting point, a low vapor pressure and stable chemical property, tungsten boat is widely used in vacuum evaporation coating industry as a resistance evaporation source.

Vacuum coating technique is a kind of technology to produce thin film material by physical means. In the vacuum chamber, atomic of material is isolated from the heating source and hit the plated object’s surface. This technology was first used in the production of optical lenses, such as navigation telescope lens. Later it extended to other functional film, such as music aluminizing, decorative coating and surface modification. Vacuum coating includes three types, named vapor deposition, sputtering deposition and ion plating.

As a main source of resistance heating, W (wolfram) boat is widely applied to vacuum deposition: use a refractory metal, such as W-boat, to form the shape of boat or shape of wire, i.e. Make the current pass them, and then heat evaporated material which place above it or place in the tungsten crucible. Adopting W-boat for vacuum deposition would save more material which can accelerate the speed of volatilization of powder, the required temperature. On the other hand, it just need low temperature and heating current but evaporation brilliant is much stronger which can produce film on the substrate.

Tungsten boat for vacuum deposition can make the material surface metallization, combine the organic materials and inorganic materials to further improve its physical and chemical properties. In addition, it can also improve the surface hardness. Vacuum deposition can increase its hardness and abrasion performance. And reduce the absorption rate, the more the coating times, the less vacuum, and the absorption rate will be reduced. Products would not easily to be deformed, and its heat resistance would enhance. Vacuum deposition has a high deposition rate if using wolfram boat.

When use W-boat for vacuum deposition, operators should keep inflammable poison safely in case of fire poisoning. When washing parts and wolfram boat, operators should wear rubber gloves. When off duty, don’t forget to turn off the power and disconnect water source.

tungsten boat

 

Notices of Tungsten Boat for Vacuum Coating

tungsten boatDuring vacuum coating, people often do not pay attention to some details which would lead to an unsuccessful coating. Compared to other industries, vacuum deposition is a very environmentally friendly technology for its lower electromagnetic radiation. In addition, it doesn’t have great impact on human bodies. Therefore, the operator should work in more details to improve the efficiency of vacuum deposition.

The first is to pay more attention to the maintenance of working environment of vacuum deposition. Make sure that the substrate surface of it was cleaned before. To reach purpose of deoiling, decontamination and dewatering of the workpiece. In the process of machining a workpiece, transport and packaging, various dusts, lubricants, polishing paste, oil, sweat, etc. would adhere to the substrate surface. Under humid conditions, the materials on surface will form an oxide film. If this happens, it can be removed through deoiling or chemically cleaning method. If there is no surface cleaning treatment, it cannot be placed in the atmosphere. Users should use a closed container or cleaning cabinet to keep it which can reduce dust pollution. For the highly unstable and sensitive to water vapor surface, it is better to be stored in a vacuum oven.

In addition to the maintenance of the environment, operators should regulate their operations. At the time of opening the vacuum deposition machine, operators should turn on the water carrier firstly and observe the water pressure uninterruptedly. When the ion bombardment and evaporation, high voltage cable cannot be touched in case of electric shock. In order to prevent human body from X rays, operators would better wear the lead glass during the observation. During plating the dielectric multilayer film coating, ventilated vacuum devices should be installed to remove harmful dust in time. After working, don’t forget to turn off the power and disconnect water source. In the whole process, operators must wear full protection and cleaning sheath.

Tungsten boat is important resistive evaporation source for vacuum deposition, and due to the different types of it, it is better to choose the corresponding type to coat. More importantly, tungsten boat's surface cannot have any cracks, keeping smooth and flat. Provided that there is some trouble of it which should be changed to a new one immediately. Clearing the dust of the coating indoor, setting the high cleanliness of the workplace, keeping the high cleanliness are the basic requirements of the coating process on the environment.

Boehmite Prepares WO3 Contained Hydrodesulfurization Catalyst

boehmiteBoehmite is the main raw material to produce aluminum oxide. γ-Al2O3 obtained by the calcination of boehmite as the carrier, and load nickel oxide and tungsten trioxide, add a additive-fluorine, thus to produce tungsten trioxide hydrodesulfurization catalyst with high activity. The different purities of boehmite have a certain degree of influence on the activity of the desulfurization catalyst.
 
Low-purity boehmite prepares WO3 hydrodesulfurization catalyst
1. Take aluminum hydroxide powder generated by aluminum sulfate- sodium aluminate method from boehmite with a purity of 35% by weight, add the extrusion aid and water, extruded strip of 1.2 mm in diameter, dry in an oven at 120 ℃for 4 hours and then roasted at 550 ℃ in a tube furnace under the air for 4 hours to obtain γ-Al2O3 (A);
2. Dissolve ammonium fluoride in deionized water, add the carrier which is cooled down to room temperature for impregnation for 4 hours at room temperature;
3. Separate and dry the wet fluorinated alumina bar in an oven at 120 ℃ for 4 hours, then heated at 500 ℃ in a tube furnace with dry air for 4 hours to obtain fluorinated alumina strip, removed and cooled down to room temperature;
4. Add fluorided alumina to the deionized water containing with ammonium metatungstate and nickel nitrate, and separate after dip at room temperature for 4 hours to obtain wet catalyst;
5. Dry the wet catalyst in an oven at 120 ℃ for 4 hours, and calcine under the air in a tube furnace at 500 ℃ for 4 hours to obtain the catalyst A.
 
High-purity boehmite prepares WO3 hydrodesulfurization catalyst
1. Take aluminum hydroxide powder (obtained from the hydrolysis of aluminum alkoxide) with the boehmite purity of 70% by weight, add extrusion aid and water, then squeeze to a strip with a diameter of 1.2 mm, dry in an oven at 120 ℃ for 4 hours, then calcine at 550 ℃ for 4 hours in a tube furnace accompanying with the air to give γ-Al2O3 (B);
2. γ-Al2O3 (B) for the preparation of the carrier catalyst B, the same preparing method of the low purity boehmite.
 
Analysis showed that the aluminum oxide generated from high-purity of boehmite has the larger amount of acid, while the boehmite prepared by calcination has a larger amount of strong acid; tungsten desulfurization catalyst B prepared by aluminum alkoxide hydrolysis of a high-purity oxide boehmite has a higher activity.

 

WO3 Prepares Hydrodesulfurization Catalyst

hydrodesulfurization catalystCurrently, the widely used of liquid fuel hydrodesulfurization catalysts in industry are mostly supported tungsten sulfide (or molybdenum) based catalysts which adds nickel, cobalt and other aid. Such catalysts usually take ammonium tungstate or ammonium molybdate as raw material, and obtained after impregnation, pyrolysis. The particle size, degree of dispersion of the active ingredient in tungsten oxide containing desulfurization catalyst cannot achieve the desired state. In this situation, developing a higher activity catalyst with highly dispersion and nanoscale has become the main research issue of the scientists.
 
In this paper, we introduce a catalyst loading with sulfur-containing transition metal-- molybdenum or tungsten atom clusters, the steps are as follows:
1. Dissolve the tungsten oxide or molybdenum trioxide in the concentrated hydrochloric acid, and carried out electrolysis to generate the hydrochloric acid solution;
2. Inlet the hydrogen sulfide into the hydrochloric acid solution to carry out vulcanization;
3. Take out oxidation under the condition of oxygen or air at 60~120℃ for 24~56 hours;
4. The oxidized solution is distilled under reduced pressure to obtain a reaction concentrated mixture was filtered, and separate by resin column, to give the following cluster core: sulfur-containing transition metal atom clusters of [M2OnS2-n]m+,[M3OnS4-n]m+ or [M4OnS6-n]m+, where M = Mo or W, n = 0 ~ 6, m = 0 ~ 6;
5. Load or graft the sulfur-containing metal atom cluster onto the carrier by dipping or ion-exchange method under the inert atmosphere of sulfur-containing transition metal atom clusters under an inert atmosphere to give the supported type sulfur-containing transition metal atom clusters of tungsten trioxide (or molybdenum trioxide) hydrodesulfurization catalyst.
 
The tungsten trioxide hydrodesulfurization catalyst obtained in method not only has higher hydrodesulfurization activity with its high dispersion and nanoparticle; but also, the catalyst of sulfur-containing metal atom cluster has the better sulfur anti-poisoning performance.

 

Tungsten Carbide Button Distribution Optimization on Drills (2/2)

In the early 1980s, some researchers have proposed the distribution of the drill bit buttons should follow three guidelines: 1. each cutting button has equal rock breaking volume; 2. equal wear rate; 3. equal rock consumption. Meet these three criteria in order to ensure rock breaking energy evenly distributed on each cutting tooth, so as to obtain the best rock-breaking effect. Theoretically, the process of tungsten carbide buttons for rock breaking can be divided in to three steps: elastic deformation (when the force is released, the rock surface can restore the status), fatigue process (also known as pressure crushed stage, surface cracks do not disappear and fracture rock surface) and volume breaking (The formation of shear body, under increasing pressure formed pit crushing).

When the adjacent tungsten carbide buttons impact the rock at the same time, the overall crushing effect depends on the nature of the deformation of the cross-belt. Reasonable button spacing will produce elastic deformation energy to rupture and push the rocks out with the increasing load; if the spacing of two buttons is too narrow, it will make the compacting zone too close to increase the difficulty of the shear rock; if the spacing of two buttons is too wide, the rock in the middle part will not be cracked and form rock ridges. Viewed from the impact energy, for the drills fixed diameter, the less number of buttons, the more impact energy of each button endure and the rock crushing volume will also increase accordingly. However, if the number of button is too small, which over the stress fracture of a single button, tungsten carbide button will be broken.

Buttons distribution firstly depends on the shape of the bit end face, which includes flat-shaped, arc-shaped, protruding, concave shape, and so on. The most used are flat-shaped and arc-shaped. Generally, tungsten carbide drill bit with large diameter usually uses arc end face and the small diameter often uses the flat-shaped. In intermediate buttons distributed in the cross section perpendicular to the bit axis, while the button are located on the inclined face of the drill bit. The outermost edge of buttons not only has to be mechanical support, but also should withstand the crushing function so that it has a greater amount of consumption than the buttons middle. Furthermore, it has high speed of linear velocity and requires a larger diameter, wider distribution and excellent quality.

 

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