Vacuum Coating Tungsten Wire

Description Of Vacuum Coating Tungsten Wire

Vacuum Coating Tungsten Wire is a high-purity tungsten wire product specifically designed for use as a resistive heating element and evaporation source in vacuum thermal evaporation coating equipment. It is manufactured from high-purity tungsten (purity ≥99.95%) or doped tungsten wire through drawing, stranding, coiling, and surface treatment processes.

In the vacuum thermal evaporation process (a Physical Vapor Deposition or PVD technique), the tungsten wire serves as the evaporation source heating element. When electric current passes through the tungsten wire, it generates heat through resistance, rapidly raising the temperature to 1500–3000°C. The coating material placed on or around the tungsten wire—typically low-to-medium melting point metals such as aluminum, silver, gold, copper, or chromium—is heated to melting and vaporization. In a high-vacuum environment (typically 10⁻²–10⁻⁴ Pa), the vaporized atoms travel in straight lines and condense on the cooler substrate surface, forming a dense, pure thin film.

Tungsten is the material of choice for this application due to its unique combination of properties. With a melting point of approximately 3420°C—the highest among all metals—tungsten wire can withstand the extreme temperatures required for evaporation without melting or deformation. Its extremely low vapor pressure at elevated temperatures ensures that the tungsten itself does not evaporate significantly, minimizing contamination of the deposited film. The material also offers excellent high-temperature strength, good electrical conductivity, a low coefficient of thermal expansion, and resistance to thermal shock, making it reliable under the frequent start-stop operating conditions typical of vacuum coating processes.

Vacuum coating tungsten wire is available in a wide variety of structural forms to suit different evaporation materials and process requirements. Common configurations include single-strand wire, stranded wire (twisted multi-strand), helical coils, tungsten baskets, tungsten boats, U-shape heaters, and hump-shaped heaters. The wire can be further processed through surface treatment such as electrolytic polishing or alkaline cleaning to remove surface contaminants and reduce outgassing, ensuring high vacuum cleanliness.

Working Principle Of Vacuum Coating Tungsten Wire

Vacuum coating tungsten wire operates on the principle of resistive (Joule) heating. When an electric current passes through the tungsten wire, the electrical resistance of the wire converts electrical energy into thermal energy. The high electrical resistivity of tungsten (approximately 5.4 µΩ·cm at 20°C) enables efficient heat generation with relatively moderate current levels.

The wire is typically installed in the evaporation source area of the vacuum coating chamber, with both ends connected to water-cooled electrode feedthroughs. During operation, high current flows through the tungsten wire, causing it to rapidly reach temperatures of 1500–3000°C. The coating material—which may be placed in a tungsten boat, loaded into a tungsten basket, wrapped around a coil, or suspended from a filament—is heated by conduction and radiation from the hot tungsten wire. Once the coating material reaches its evaporation temperature, it vaporizes and the vapor flux travels through the vacuum chamber to deposit on the substrate.

Because the vacuum environment (typically 10⁻²–10⁻⁴ Pa) has extremely low gas molecule density, the vaporized atoms travel in straight lines with minimal collisions, ensuring that the deposited film is dense, pure, and uniform.

Specifications Of Vacuum Coating Tungsten Wire

Surface Treatments: