How heat resistance and oxidation resistance of tungsten discharge needles under high-pressure discharge conditions

Basic thermal properties of tungsten materials

Tungsten (W) is a metal element with extremely high melting point (about 3410°C), high thermal conductivity (173 W/m·K), and low thermal expansion coefficient (4.5 × 10⁻⁶ /K). These excellent thermal properties allow tungsten to maintain a stable physical form under high temperature and high energy density conditions, and are the first material of choice for manufacturing high-pressure discharge needles. Especially in extreme operating conditions such as instantaneous arc, high-voltage breakdown and plasma discharge, the heat resistance characteristics of tungsten are directly related to the efficiency and service life of the discharge system.

Thermal shock tolerance under high-voltage discharge conditions

High-voltage discharge is often accompanied by strong instantaneous current and electric field changes, resulting in local high temperature and high pressure. Due to its high melting point and low thermal expansion rate, tungsten discharge needles can effectively resist material cracking, needle tip melting or structural deformation caused by thermal shock. In high-voltage pulse discharge experiments, the tungsten discharge needle can withstand local high temperatures above 2000°C without material degradation or surface failure. This stability is far better than conventional electrode materials such as copper and stainless steel.

Characteristics of tungsten's oxidation resistance

Tungsten is easily oxidized in high-temperature air, mainly producing WO₃ (tungsten oxide), which will sublimate when the temperature is higher than 800°C, resulting in surface loss. This process is particularly evident in high-voltage discharge processes, especially in discharge applications in open environments, where oxidation reactions aggravate surface ablation and tip degradation of tungsten needles. Therefore, in scenarios involving high-temperature gas discharge or arc discharge, the service life of the tungsten discharge needle is significantly affected by the oxidation rate.

Antioxidant modification treatment method

In order to improve the oxidation resistance of tungsten discharge needles in air environments, the following surface treatment methods are often used:

Coated protective layer: Deposition of a rare earth oxide or nitride coating on the surface of the tungsten needle through CVD (chemical vapor deposition) or PVD (physical vapor deposition) technology can significantly slow down the oxidation rate.

Alloy treatment: Tungsten and rare earth elements (such as thorium, lanthanum, cerium) form tungsten alloy electrodes to improve its high-temperature oxidation resistance and electron emission performance.

Inert gas protection: Run the discharge system in a sealed or local argon environment to reduce the direct contact between the tungsten needle and oxygen in the air, and effectively reduce the WO₃ generation rate.

Heat resistance and oxidation resistance in practical applications

In applications such as pulse corona discharge, plasma ignitors, high-voltage discharge tubes, etc., tungsten discharge needles are often used as tip electron emission sources. In laboratory testing and industrial practice, it was found that even in a repeated discharge environment of dozens of times per second, the tungsten discharge needle can still maintain a discharge cycle life of more than 10⁶ times, and its thermal stability is far greater than that of other metal materials. For systems operating in high oxygen-content atmospheres, untreated tungsten discharge needles may experience oxidative delamination or ablation deterioration within a few hours.

Effects of microstructure changes on performance

Long-term high-temperature operation will lead to microcracks on the surface of the tungsten needle, grain boundary slip and surface roughening. These microstructure changes will affect the uniformity of electron emission and the concentrated effect of the electric field at the discharge tip. The deterioration of surface morphology further aggravates the thermal focus phenomenon, resulting in local ablation being out of control. Therefore, regular maintenance and microscopic inspection with tungsten needles is the key to ensuring the stable operation of the discharge system.

Industry adaptability and prospects of tungsten discharge needles

With its excellent heat resistance and good high-temperature mechanical strength, tungsten discharge needles are widely used in many industries such as semiconductor electrostatic discharge testing, gas breakdown research, corona treatment system, spark plug design, etc. In the future, with the development of new energy, high-frequency power supply and plasma control technologies, the stable performance of tungsten discharge needles in high-temperature electric field environment will continue to promote its application and expansion in the high-end precision electrode market.