An example:

In automobile industrie they solder metal tubes and using copper as solter metal. The solder furnace operates at temperatures of about 1100-1200 °C. At the entrance and the outlet there is a burner to burn H2 which comes out. The burning of H2 prevets the formation of oxyhydrogen gas. Due to there is no oxigen in the furnace the hydrogen can not combust and only reacts with the oxide at the surface of the tubes. The hydrogen then takes away the oxigen and reduces the metal oxide and the solder metal copper is able to solder the tubes to be leakproof.

another one:

Amorphous silicon solar cells also are annealed in hydrgen atmosphere due to the passivation effect of hydrogen at the surface after entering the vacuum chamber to heat them up to the temperature needet for the process.

In conclusion there are mainly two ways to anneal material in hydrogen atmosphere you only have to make shure that hydrogen is separated from atmosphere, or the concentration is below a value, that there is no posibility to blow up. The oxigen which is chemically bounded in the material you want to aneal is not the problem, because you need energy to get this oxigen out.

Best Regards

Rainer

Is the purpose of annealing is to remove oxygen from any material? If that is the case people normally use a mixture of Argon and Hydrogen instead of only Hydrogen. Presence of inert gas Argon ensures there is no combustion. You can look for articles for the proper ratio of the two gases.

Thanks a lot for the reply. You guessed it right, the purpose is to produce oxygen vacancies in the material. I shall look up for the ratio

Looking to sintering processes in powder metallurgy may also help in terms of conditions used, devices (furnaces etc.) available, gases etc.

@Dirk- Could you please explain a bit more

Would appreciate an answer from someone who has actually annealed material in hydrogen atmosphere.

We use 5% H2 in either Ar or N2 gas.

@Falak-That was helpful. Thanks

@Falak- Is it necessary to evacuate the tube furnace before purging the gas mixture ? ( to ensure complete removal of O2 so that H2 does not blow up !!)

5% H2 in N2 is OK, no need to evacuate. We do reduction at even 650 °C.

@Jiasheng - Thanks a lot for the reply. That was very assuring and helpful. If possible, could you please give me the reference of your work ?

An example:

In automobile industrie they solder metal tubes and using copper as solter metal. The solder furnace operates at temperatures of about 1100-1200 °C. At the entrance and the outlet there is a burner to burn H2 which comes out. The burning of H2 prevets the formation of oxyhydrogen gas. Due to there is no oxigen in the furnace the hydrogen can not combust and only reacts with the oxide at the surface of the tubes. The hydrogen then takes away the oxigen and reduces the metal oxide and the solder metal copper is able to solder the tubes to be leakproof.

another one:

Amorphous silicon solar cells also are annealed in hydrgen atmosphere due to the passivation effect of hydrogen at the surface after entering the vacuum chamber to heat them up to the temperature needet for the process.

In conclusion there are mainly two ways to anneal material in hydrogen atmosphere you only have to make shure that hydrogen is separated from atmosphere, or the concentration is below a value, that there is no posibility to blow up. The oxigen which is chemically bounded in the material you want to aneal is not the problem, because you need energy to get this oxigen out.

Best Regards

Rainer

@R. Merz- Thanks for explaining it out.

Small diameter Atoms such as Hydrogen, and Sulfur Embrittle

materials such as Iron. They collect at the grain boundaries and are

prone to create brittle failures of the materials.

Hydrogen tends to embrittle about everything.

Read the book:

Why Things Break.

Oblate Atoms Embrittle

Prolate Atoms Strengthen

Like Boron, and Molebdenum

You have to be very cautious about reducing the oxygen in the chamber before you heat it up.  The explosive limits for the H2 + O2 mixture are quite wide.  When filling the annealing chamber, the H2 tends to stratify, i.e. it rises to the top as it displaces the air.   So the H2 inlet should be on the top of the chamber and the outlet should be on the bottom.  You should monitor the H2  flow so you know how many chamber volumes you have replaced with H2.  My guess is at least 5 chamber volumes, but you should calculate it (a good science problem).  

Best is to either evacuate the chamber before filling, or to use Ar/H2 or N2/H2 mixtures.  Our HT chamber blew up because we let the H2 run for only 10 minutes before heating.  Fortunately it was a small chamber.

Alan- Thanks for answering. That was very helpful. I am planning to use a 5% or 10% mixture of Ar/H2 to be on the safer side. In such a case, roughly for how long should I purge the chamber with the gas mixture before heating it up ?

Atharva Sahasrabudhe I am looking for similar processing, can you please share your experience in handling Hydrogen.

Annealing with H2 (5%) + N2 (95%) can be succesfully done in a tube furnace for succesfull reduction.

A combustible gas or liquid can ignite contact with an oxidizer (pure oxygen, enriched air or natural air) within the limits of mixing called lower explosive limit (LEL) and higher explosive limit potential (HLE) and in the presence of energy. Below the LEL, the mixture contains not enough fuel to ignite and above the HLE it does not contain enough oxidizer to ignite.

 If the proportions of a mixture fuel-oxidant exceed the LEL, an ignition of this mixture will not produce consistently an explosion. For example, hydrogen has an LEL of 4% by volume in air at pressure and temperature room. The risk of nflammation of the mixture is good from 4% but, according to the experience feedback, in an open environment, the mixture is explosive, with significant pressure effects, only from 8% volumic hydrogen at pressure and ambient temperature.