How Does Tungsten Needle to Obtain a Precise Tip Radius?

Tungsten needle is a kind of tungsten rod with sharp ends. Usually, it is made of high-density tungsten metal so that it can be widely used in many fields. For its production, it adopts powder metallurgy, but this method is not enough when very sharp tips are required. 

As one of the core components of the field emission electron microscope, the performance of the field emission electron source determines the main electron optical performance parameters in the field emission electron microscope, which includes the emission angular current density of the electron gun, the total emission current of the electron beam and the stability of the electron beam, etc.

In order to meet the requirements of high brightness, large beam current, good beam stability, and small electron energy dispersion of the field emission electron source, it is necessary to sharpen the tip of the single crystal tungsten wire of the field emission electron source. Generally, the tip radius is required between 0.5-1.0μm.

The researchers with the patent number CN102339704B proposed a preparation method for obtaining a field emission electron source needle with a radius between 0.5-1.0 μm. Its specific operation is as follows:

1) Pour a certain amount of sodium hydroxide powder into a beaker with a balance, and then add a certain amount of pure water to prepare a corrosion solution with a concentration of 3-5mol/L; 2) Put the prepared corrosion solution from the U-shaped One end of the tube is poured into the U-shaped tube, and an electrode is inserted; 3) Fix the ceramic seat welded with the single crystal tungsten wire to the fixed frame with the micrometer head, and adjust the micrometer head so that the single crystal tungsten wire is immersed in the container. Put a certain distance below the liquid surface of one end of the U-shaped tube containing the corrosive liquid, and put an electrode under the liquid surface of the other end of the U-shaped tube containing the corrosive liquid; 4) Connect the connecting wire with the electrode clip and the switch to the The signal source is connected, connect one electrode clamp to the electrode on the ceramic seat for welding single crystal tungsten wire, and connect the other electrode clamp to the electrode at the other end of the U-shaped tube; 5) Turn on the signal source and adjust the signal source required for corrosion Parameters; 6) Start the switch on the connecting wire to start corrosion; 7) After the corrosion is over, turn off the switch; 8) Adjust the micrometer head so that the tungsten wire on the filament ceramic seat completely exits the corrosion solution.

Compared with other manufacturing methods, the AC electrochemical corrosion method is easier to be adopted by everyone, mainly because it has many controllable parameters, high corrosion precision, and good product stability.

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New Production Method for Diamond Wire Saw

Diamond wire saw, also known as diamond wire, refers to a cutting wire that fixes diamond abrasives on metal wires by electroplating or resin bonding. It is mainly used to cut high-hard and brittle materials such as single crystal silicon, polycrystalline silicon, sapphire, magnetic materials, and hard alloys, etc.

Compared with free abrasive wire saws, it has the advantages of higher processing efficiency, lower energy consumption, and better cutting quality; compared with circular saws and band saws, it can not only change the cutting direction more flexibly, but also process more complex geometries. However, this does not mean that the wire saw has no disadvantages. The current wire saws that use carbon steel wire as the busbar/base material have the disadvantages of large wire diameter, high wire breakage rate and short service life. Therefore, in order to make up for the shortcomings of the existing wire saws, manufacturers began to use doped tungsten wires to replace high-carbon steel wires as the base material of diamond wires.

For the production of diamond wire saw, the researchers with the patent number CN113275659A proposed a new production method, the process is: (1) Optimal black tungsten wire, which goes through wire setting→three-stage electrolytic polishing→water washing→drying →take up the wire to prepare the silver-white metallic luster tungsten wire; (2) The tungsten wire treated in step (1) is discharged in turn→secondary degreasing→pickling→impact nickel→sanding→sand fixing→heat treatment→take up the wire, and you can prepare a tungsten diamond wire saw with a wire diameter of 30~40um.

The specific steps are as follows: the diamond wire busbar is a tungsten wire, and its surface is etched with "swallowtail" pits, which are formed by three-stage electrolytic polishing; each stage of electrolytic polishing in the three-stage electrolytic polishing. The equipment for each level of electrolytic polishing in the three-level electrolytic polishing consists of a working tank, a corrugated profiling plate cathode plate, an ultrasonic vibration plate, an anode guide wheel, a circulation tank, a heating pipe, a circulating liquid pump, a filter, and a plate heat exchanger, high-frequency DC switching power supply; the impact nickel layer is filled with pits and plated on the surface of the bus bar, the impact nickel layer and the bus bar form a "dovetail" structure, and the upper sand layer is plated on the surface of the impact nickel layer and consolidated with diamond particles , the surface of the upper sand layer is also coated with a layer of sand-fixing sand layer.

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Tungsten Sheet Price in Early January 2023

Φ100x0.3mm tungsten sheet price is 4.60 USD/PC in the first half of January 2023, EXW XIAMEN, CHINA. 

Tungsten sheets can be as thin as 0.01mm or as thick as 127mm, with widths typically ranging from 10mm to 800mm. They can be used in many different applications and is valued for its corrosion resistance, ability to withstand extremely high temperatures, and ability to create rigidity and hardness when combined with other metals in the alloy.

Tungsten is used in the aerospace, research, building materials and light bulb industries. It is the predominant metal in electric furnace heating elements, as well as in any assembly where high pressure/high temperature environments are expected. Sheets made of tungsten are commonly used in furnace construction, but are also important for making parts for the electronics and semiconductor industries, and can be found in a variety of lighting, vacuum plating, electronic vacuums and shielding.

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Lanthanated Tungsten Electrode Price in Early January 2023

Ø3.2x175mm lanthanated tungsten electrode price is 1.90 USD/PC in the first half of January 2023, EXW XIAMEN, CHINA. 

Wl20 electrodes contain at least 1.7% to 2.2% lanthanum for excellent arc starting, low burnout rate, good arc stability and excellent re-ignition characteristics. They are ideal if you want to optimize your welding capabilities. They can work well on either AC or DC electrode negatives with tips, or they can be used with AC sine wave power supplies. The tungsten electrode adding with rare earth element lanthanum holds sharp tips well, which is an advantage for welding steel and stainless steel on DC or AC from square wave power sources.

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How to Produce High-precision Tungsten Foil?

Heat shields, heating elements and vacuum furnace supports are made of tungsten foil. The foil is thin and is ideal for embedding in laminates, other metals and glass; it is made of mental tungsten and can be used in high temperature vacuum furnaces, coatings, electronic and semiconductor components.

How to produce the thin foil? 

Compared with the coating deposition method, the rolling method is more suitable for the production of tungsten foil, mainly due to the advantages of higher hardness, surface finish and mechanical strength, especially the density can be close to the theoretical density of tungsten. However, the working efficiency of the commonly used four-high rolling mill in industry is extremely low, and the production equipment is easily damaged due to the long-term high rolling tonnage. In order to solve the above technical problems, the researchers with the patent document serial number 17017104 proposed a rolling method of high-precision W foil. The specific steps are:

1)Cut the tungsten plate (thickness 0.09mm~0.11mm) into the same size of plate; 2) Place the nickel sheet as a welding sheet between the tungsten sheets obtained in the adjacent step 1), and use a spot welding machine for spot welding to obtain a welded tungsten sheet; the number of tungsten sheets is 2 to 4 pieces, and the nickel sheet is placed on one end of the tungsten plate along the length direction, and the width direction of the nickel plate is consistent with the length direction of the tungsten plate; 3)Perform multi-pass rolling on the welded tungsten plate obtained in step 2) to obtain a rolled foil; the tonnage of the rolling equipment used in the multi-pass rolling is 60t-120t, and the roll crown is 0.04mm-0.06 mm; when the total processing rate of multi-pass rolling exceeds 40%, the rolled welded tungsten sheet is annealed; the thickness of the rolled foil is 0.04mm to 0.08mm; 4) Cut off the welded end of the rolled foil obtained in step 3), and then separate the layers in the rolled foil to obtain a foil; the thickness of the foil is 0.018mm to 0.023mm, and the thickness tolerance ± 0.0015mm, width 175mm ~ 180mm.

The advantage of this rolling technology is that spot welding the tungsten plate of the same size with the nickel plate as the welding piece not only ensures the melting of the nickel plate to the welding of the tungsten plate, but also avoids the brittleness of the tungsten plate, which is beneficial to the later stage. The first rolling was carried out smoothly, and 2 to 4 pieces of foil with uniform size were produced at one time, which solved the problem of low efficiency of single rolling and greatly improved the production efficiency; at the same time, small-tonnage rolling equipment was used to carry out multi-pass rolling makes the rolled W foil uniform in thickness and bright in surface, which effectively improves the precision of W foil. 

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The Differences Between Cerium Tungsten Electrode and Thorium Tungsten Electrode

With the continuous development of science and technology such as welding, cutting and spraying technology, manufacturers have higher and higher requirements for tungsten electrodes, such as easy arc starting, stable arc column and long service life.

In order to improve the deficiencies of pure tungsten electrodes, researchers often add an appropriate amount of modifiers such as cerium oxide (CeO2) or thorium oxide in the production process, and the prepared products are naturally called corresponding electrodes such as cerium tungsten electrode (WC20) and thorium tungsten electrode (WT20). The two electrodes have many differences in terms of performance and production process.

1. Concept

WC20 is a tungsten electrode containing about 2% cerium oxide with gray color code; WT20 is a tungsten electrode containing 1-1.2% thorium oxide with red color code. 

2. Physical and Chemical properties

WC20 has the characteristics of low melting rate, ablation resistance, good weldability, easy arc starting, high arc column stability, and no radioactivity. Under certain conditions, with the increase of CeO2 content, the ablation resistance and arc starting performance of the electrode will also increase.

The advantages of WT20 include low electron work function, strong current carrying capacity, good electrical conductivity, mechanical cutting and welding, etc., but the main disadvantage is radioactivity.

3. Production

The production process of the two electrodes is similar. The basic steps are to prepare tungsten-cerium powder or tungsten-thorium powder, then press it into a billet, and finally perform pre-sintering, high-temperature sintering, hot swaging, straightening, cutting, and cleaning in sequence.

4. Use

WC20 electrodes can be used in DC welding, AC welding, plasma welding/cutting/spraying/smelting; WT20 electrodes are generally used in direct current welding, as direct current negative electrodes or positive electrode materials such as stainless steel and nickel alloys, and are also key electrodes for argon arc welding, plasma welding and other processes.

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EB Tungsten Filament Price on Dec. 8, 2022

The latest price of φ0.8mm EB tungsten filament is USD 2.00/PC, EXW XIAMEN, CHINA on Dec. 8, 2022. 

Tungsten filaments, also called cathodes or electron emitters or electron sources, are mainly made of high-quality tungsten. Of all pure metals, tungsten has the highest melting point (3422°C), the lowest vapor pressure at temperatures above 1650°C, and the highest tensile strength. Tungsten also has the lowest coefficient of thermal expansion of all pure metals. This combination of properties makes tungsten an ideal material.

Tungsten can be used in both thermionic electron guns and field-emission (CFE) electron guns. Electron beams come from filaments made of various materials. The most common is the tungsten hairpin gun, which is widely used in scanning electron microscopes, transmission electron microscopes, and microprobe systems. This filament is a tungsten ring that acts as a cathode. Apply voltage to the loop to heat it up. The anode, which is positive relative to the filament, forms a strong attraction to electrons. This causes electrons to be accelerated towards the anode. Some accelerate near the anode and down the column to the sample.

An electron gun works at a high temperature, which is required for thermionic emission. For this, a filament or the cathode should be of a material that has a high melting point in order for it to continuously emit electrons. Tungsten filament is folded with various shapes to help in focusing the electron beam.

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