How to Seal Both Ends of a Alumina Tube

When alumina tubes (Al₂O₃) are used in high-temperature or vacuum environments, the sealing materials at both ends must have high-temperature resistance, corrosion resistance, and good airtightness.
Below are the common sealing materials and corresponding solutions:

1. Flange Sealing System (Most Common)

Матеріальний: 304/316 stainless steel flange (high-temperature and corrosion resistant)

Sealing gaskets:

Double-layer silicone O-ring: Suitable for medium and low temperatures (≤250 °C), with airtightness up to 4.04×10⁻³ Pa.
Graphite wound gasket: Withstands high temperatures (≤650 °C), suitable for high-pressure or vacuum environments.
Alumina-filled PTFE gasket: Corrosion-resistant and wear-resistant, suitable for acidic or alkaline conditions.
Water-cooled flange: Cooling water can be circulated under high-temperature conditions to prevent O-ring aging.

2. High-Temperature Adhesive Sealing (For Temporary or Small-Scale Experiments)

High-temperature adhesive: Such as aluminum phosphate adhesive (resistant up to 650 °C), though it tends to crack during long-term use.
Ceramic adhesive: Withstands temperatures above 1000 °C, but is difficult to remove once cured.

3. Mechanical Sealing Components

Metal bellows seal: Used for ultra-high-vacuum applications (e.g., molecular pump interfaces); made of stainless steel or nickel-based alloys.
Spring-loaded sealing cap: Compresses the end face of the alumina tube using spring pressure, usually in combination with a metal gasket.

4. Special Condition Adaptations

Strongly corrosive environments: Use Hastelloy flanges or nickel-plated components.
Ultra-high-temperature (>1600 °C): Employ alumina-metal composite flanges with an inner alumina ring to reduce thermal stress.

Notes

Thermal expansion matching: The thermal expansion coefficient of alumina (8×10⁻⁶ / °C) should be close to that of the sealing material to avoid cracking caused by thermal cycling.
Installation and maintenance: Regularly clean the flange contact surfaces to prevent dust or oil contamination that could affect sealing performance.