Sapphit™ thermocouple sheaths

Sapphit™ thermocouple sheaths
Single crystal sapphire provides a superior alternative to corundum ceramics for high demanding temperature measurement

Key characteristics

Sapphit™ is the material of choice for protective casings of thermocouple probes. Thermocouples with sapphire casing represent a many times more durable alternative to corundum ceramics. In some cases they are also comparable in durability to platinum coated sheaths.

Perfect crystal lattice is the key to Sapphit™ high durability. Unlike ceramic casings, sapphire structure is perfectly homogenous throughout the whole product.

Corundum ceramics on the other hand consist of microscopic crystal grains sintered together. The grain boundaries create weak points in the structure where corrosion begins and ceramic components deteriorate much faster.

Comparing single crystal Sapphit™ to corundum ceramics would in a way be like comparing glass to very fine sandstone. Sapphit™ is by far a superior product.

Perfect crystal lattice also prevents the surface of Sapphit™ tubes from outgassing. The leakage of any unwanted compounds from the surface of the tubes is not an issue with Sapphit™.


Corundum ceramics - polycrystalline grain structure with grain boundaries
Sapphit™  - perfect homogenous structure



Sapphit™ tubes are grown in a variety of profiles and can be cut down to desired lengths. The tubes can be flawlessly sealed by growing a lid on the end of the tube. This assures perfect material homogenity. 


We will always recommend appropriate profile combinations for sensors which require temperature measurement in different depth areas.

For specific project we can provide customised dimensions within these limits:

Inside diameter > 0,6 mm
Outside diameter 1 - 30 mm
Length max. 1800 mm


 Standard tube diameters:

Outside diameter Inside diameter Tolerances on diameter Maximum length
1.0 mm 0.6 mm ±0.1 mm 500 mm
1.57 mm 0.75 mm ±0.1 mm 1500 mm

2.1 mm

1.3 mm

±0.2 mm

1750 mm

4.8 mm

3.4 mm

±0.15 mm

1800 mm

4.92 mm 3.4 mm +0.05/-0.1 mm 200 mm

6.0 mm

4.0 mm

±0.15 mm

1800 mm

8.0 mm

5.0 mm

±0.15 mm

1800 mm

9.92 mm 7.0 mm +0.05/-0.1 mm 200 mm

10.0 mm

3.0 mm

±0.2 mm

1700 mm

16.0 mm 4.0 mm ±0.3 mm 600 mm
25.4 mm 22.7 mm ±0.3 mm 1500 mm
30.0 mm 27.0 mm ±0.3 mm 1500 mm

Highlighted dimensions are optimized for use in thermocouples


Sapphit™ tubes deliver the best performance in harsh processes which involve high temperature, high pressures and aggressive chemical compounds.

Application of sapphire thermocouple tubes

  • Concentrated or boiling mineral acids
  • Reactive oxides at high temperatures
  • Ammonia synthesis
  • Claus process
  • Gasification
  • Desulphurization
  • NOx removal
  • Flying ash attachments
  • Floating non-metal melts


Examples of durability performance in different applications

Sapphit™ probe inserted in moving stream of lead crystal at 1170°C after 25 month. Sapphit™ probe in glass furnace crown at 1500°C for 11 month. No signs of wear. Sapphit™ probe retracted from a heavy duty chemical reactor