K-Doped tungsten
There are various types of tungsten used for specific purposes. To fulfill functionality, small amount of additives are mixed into tungsten materials.
1. Potassium doped tungsten
After hydrogen furnace at 1900℃
After hydrogen furnace at 1950℃
Crystal grain of K-doped tungsten is elongated.
Near recrystalization temperature, crystal grain grows larger
Overview
It is generally called "Non-sag tungsten", or "Non-sag wire"
Manufactured by adding potassium to tungsten. It is normally used as wire. At recrystalization temperature, tungsten with high purity forms series of small grains. Crystal boundaries running through tungsten wire and rod could lead to deformation or breakage. By adding 30 - 100 ppm potassium, it can raise the recrystalization temperature, and dope hole can help elongate the size of crystal grains. As a result, crystal grains on crystal boundaries are interlocked, and less likely to sag or deform.
At Takeishi, we rank non-sag wire depending on the size and shape of crystal grains. We can supply appropriate materials according to our customer needs.
Examples of using K-doped tungsten
Lamp with high color temperature. Filaments for automotives and motor cycles which need to be vibration-proof.
Filament for general lighting.
Filament for optical device.
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2. Low work function tungsten
High electron emission with low energy is ideal for HID lamp electrode and EB gun filaments. Various kinds of tungsten materials with low work function are explained.
2-1 Thoriated tungsten
Crystal precipitation data of thoriated tungsten
EDX observation of thoria oxide precipitated after high temperature heat treatment.
Overview
By adding thoria, work function loweres. As a result, electron emission becomes easier. In general, Thoriated tungsten is used for TIG welding electrode, however as it is radioactive material, strict control is demanded for material suppliers. As an outcome of this, some material suppliers stopped manufacturing thoriated tungsten.
We line up thoriated tungsten with different content (0.5% to 2%). We can also dope potassium to increase mechanical strength.
Example of using thoriated tungsten
Other than filament use for EB gun, we use thoriated tungsten for automotive HID lamp.
Thoriated tungsten electrode
Stepped electrode for automotive HID lamp
Thoriated tungsten enlarged.
Stepped part enlarged
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2-2 Rare earth metal added tungsten
Crystal precipitation data of Neodymium
EDX observation of neodymium oxide precipitated after high temperature heat treatment.
Overview
There are many low work function rare earth materials, such as lanthanum, yttria, neodymium, samarium and hafunium which are low in work function. We add oxide of these rare metal tungsten.
Manufacturing process is not easy, as tungsten after adding oxide gets embrittle
Oxide added tungsten is inferior in terms of breaking strength.
Below is a data of hafunium tungsten.
Breaking strength data of hafnium tungsten
Graph of hafunium tungsten breaking strength
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3. Rhenium tungsten
Crystal condition observed after heat treatment at 2710℃
Crystal conditon observed after heat treatment at 3510℃
Overview
By adding rhenium, it will have superior electrical resistivity and mechanical strength. Filament made of rhenium tungsten will have non-sag property under operating at high temperature, or under vibration. Depending on its purpose, dope amount can be selected anywhere from 3% to 30%. Takeishi supply filament and processed parts using rhenium tungsten for X-Ray related parts.
Example of using rhenium tungsten
For high discharge property and mechanical strength, rhenium tungsten is used as core parts for analytical device.
Rhenium tungsten coil (filament for analytical device)
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3. Platinum tungsten
Platinum tungsten wire
Overview
Platinum added tungsten. Often used for filament coils for sensor or medical device.
Material information on other pages.
5. Gold plated tungsten
Gold plated tungsten (label)
Gold plated tungsten (wire)
Overview
Gold is plated on pure tungsten and doped tungsten. Commonly used for medical parts.