Heat does affect tungsten, but in ways that make it uniquely valuable for high-temperature applications.
Tungsten has an extremely high melting point, which allows it to maintain its structural integrity and functionality at temperatures where other materials would fail.
This property is crucial in applications such as vacuum electron devices (VEDs), metal injection molding (MIM) furnaces, and welding electrodes.
1. High Melting Point and Heat Resistance
Tungsten's melting point is approximately 3422°C (6192°F), which is one of the highest among all metals.
This extreme heat resistance makes tungsten indispensable in vacuum electron devices like traveling wave tubes (TWTs), magnetrons, and klystrons.
These devices require materials that can withstand high power densities and frequencies, which tungsten can handle without melting or degrading.
This property also makes tungsten essential in various high-temperature applications, from satellite communications to air traffic control systems.
2. Low Vapor Pressure
At high temperatures, tungsten exhibits low vapor pressure, which is beneficial in MIM furnaces that operate in a hydrogen atmosphere.
This environment allows the furnaces to reach very high temperatures without tungsten releasing oxygen, carbon, moisture, or other contaminants.
This characteristic ensures that the tungsten remains stable and does not contribute to any impurities in the furnace, which is critical for maintaining the integrity of the materials being processed.
3. Shape Retention
Tungsten retains its shape at high temperatures, making it an ideal material for welding electrodes.
It is processed by pressing tungsten powder into various shapes and then sintering at temperatures between 2000 – 2500°C.
This process increases the density and strength of the finished product, ensuring that it remains structurally sound even under intense heat.
4. Challenges with Heat and Fabrication
While tungsten's heat resistance is a significant advantage, it also presents challenges.
Pure tungsten is difficult to machine and becomes brittle at low temperatures.
The ductile-to-brittle transition temperature of tungsten is usually higher than room temperature, making it brittle and challenging to work with in typical manufacturing environments.
However, tungsten wire benefits from the addition of heat during fabrication, which improves its formability.
5. Oxidation and Embrittlement
Tungsten oxidizes in air at elevated temperatures, starting around 500°C and more rapidly above 1200°C.
This oxidation can lead to embrittlement and breakdown of the material, necessitating the use of protective gas atmospheres or reducing atmospheres during welding and high-temperature applications.
In summary, heat affects tungsten primarily by enhancing its utility in high-temperature applications due to its high melting point and low vapor pressure.
However, it also introduces challenges such as brittleness at lower temperatures and susceptibility to oxidation, which require careful handling and controlled environments during fabrication and use.
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