Sapphire Tubes for High-Temperature Thermocouples

Abstract

ZMSH's sapphire tubes are the material of choice for protecting high-temperature thermocouples in corrosive environments.

Single-crystal sapphire tubes are the ultimate durable alternative to polycrystalline alumina ceramics (alumina ceramic tubes). Unlike ceramics, single-crystal sapphire provides 100% hermeticity and superior corrosion resistance. Customers benefit from enhanced reliability, extended thermocouple replacement intervals (typically 4x longer), and reduced system downtime.

Key Attributes

· 100% Hermeticity – No porosity, perfect environmental isolation prevents atmospheric diffusion to the thermocouple.

· Exceptional Corrosion Resistance – Withstands aggressive chemical environments.

· Operating Temperatures up to 2000°C – Sapphire retains its properties and shape near its melting point, unlike ceramics, which warp at high temperatures.

· High Pressure Resistance – Typically endures pressures of tens of bars.

· Superior Electrical Insulation – Ideal for precision measurements.

Sapphire Thermocouple Assembly
The kit consists of an externally sealed sapphire tube and one or more internal capillary tubes to insulate thermocouple branches.

Thermocouple Wire Protection
Thermocouple branches must be electrically insulated and shielded from high-temperature corrosion. Even trace contaminants (e.g., lead) drastically reduce thermocouple lifespan. Traditional ceramic/metal sheaths are vulnerable to metal diffusion, whereas sapphire tubes provide unmatched resistance.

Example:

Lead oxide diffuses through multiple ceramic tubes.

The lead oxide is prevented by the single-crystal sapphire tube outside the protective tube. The inner tube remains intact.

Sapphire-protected thermocouples far outlast standard ceramic tubes. Even small-diameter sapphire tubes offer robust high-temperature performance, making them a cost-effective solution for:

· Oil refineries

· Cracking units

· Combustion reactors

· Incinerators

· Chemical processing

· Glass manufacturing

· Semiconductor industry (clean process handling)

After 25 months, the probe was inserted into a flowing stream of molten lead at a temperature of 1170°C.

The probe was placed in a glass furnace crown at 1500°C for 11 months. There were no signs of wear.

The probe retracted from the vaporization device.

Sapphire Thermocouple Designs
 

Sapphire tubes are sealed by contininuing the crystal growing process. This assures flawless material inegrity and faultless structure throughout the whole thermocouple tube.

Conclusion

Sapphire tubes for high-temperature thermocouples deliver unrivaled thermal stability, corrosion resistance, and hermeticity, forming the foundation of extreme-environment temperature measurement. Yet, true reliability stems from end-to-end service support—ZMSH not only supplies scenario-optimized sapphire tubes but also provides a full-cycle "Requirement-Validation-Delivery-Maintenance" service framework: from operational diagnostics and customized sizing guidance to on-site installation and long-term performance tracking. Backed by a technical team, we ensure every sapphire tube operates at peak efficiency within your systems.

Choosing ZMSH’s sapphire tubes means selecting dual assurance—material excellence + service commitment—driving cost efficiency and precision in high-temperature applications.

The following products are custom-made sapphire tubes by ZMSH:

Custom Solutions by ZMSH

For bespoke sapphire tube or high-temperature thermocouple designs, contact us—ZMSH delivers precision-engineered solutions tailored to your needs.