Molybdenum is a transition (refractory) metal with outstanding corrosion resistance and a high melting point. As such, it is used as a sheath for exotic thermocouples (eg type C). These are components designed for use in ultra high temperatures up to 2315°C. Furthermore, molybdenum sheaths are resistant to inert, vacuum and reducing atmospheres which makes it a very useful choice to ensure longevity of components in hazardous application environments.
Aside from sheaths made of pure molybdenum, sheath material alloys, e.g. Pyrosil D®, Hastelloy X, Alloy TD and AISI 316 (L), can be given extra corrosion resistance and strength through the addition of molybdenum.
Molybdenum maintains excellent mechanical properties even at high temperatures and has exceptional thermal shock resistance. Although it is very useful in hot and hazardous, corrosive applications, molybdenum does have some limitations:
However, it has a potentially unlimited lifespan in high temperature vacuums. Hydrogen, argon and helium atmospheres are inert to molybdenum.
In graphite environments, molybdenum sheaths can be coated with a thick layer of tungsten to protect against carburization from graphite dust at temperatures above 1100˚C. This increases the lifespan of the sheath and the component. Another advantage of the tungsten coating is that it also provides extra protection from abrasion.
We can supply coated molybdenum sheaths for thermocouples R,S,B, AE and AO in 3,2mm and 6,4mm.
Molybdenum’s stability and strength at high temperatures, combined with exceptional corrosion resistance makes it an ideal sheath material for high temperature thermocouples in hazardous environments. Some examples include:
Our high temperature (exotic) thermocouples R, S, B, C and D can be supplied with molybdenum sheaths in the following diameters: 1.6mm, 3.2mm, 4.8mm, 6.4mm.
Furthermore we offer various alloys containing molybdenum for our MI cable sheaths:
For a short overview and explanation of our sheath materials, please also consult our knowledge base.
Our experts can be contacted to answer any queries you might have.