Endothermic gas

Endothermicgasis a gas that inhibits or reversesoxidationon the surfaces it is in contact with. This gas is the product of incompletecombustionin a controlled environment. An example mixture ishydrogen gas(H₂),nitrogen gas(N₂), andcarbon monoxide(CO). The hydrogen and carbon monoxide arereducing agents,so they work together to shield surfaces from oxidation.

Endothermic gas is often used as a carrier gas for gascarburizingandcarbonitriding.An endothermic gas generator could be used to supply heat to form anendothermic reaction.

Synthesised in the catalytic retort(s) of endothermic generators, the gas in the endothermic atmosphere is combined with an additive gas includingnatural gas,propane(C₃H₈) or air and is then used to improve the surface chemistry work positioned in the furnace.

Endothermic Gas Generator

Purposes

There are two common purposesof the atmospheres in the heat treating industry:

1. Protect the processed material from surface reactions (chemically inert)
2. Allow surface of processed material to change (chemically reactive)

Principal components of a endothermic gas generator

Principal components of endothermic gas generators:

1. Heating chamberfor supplying heat by electric heating elements ofcombustion,
2. Verticalcylindrical retorts,
3. Tiny, porousceramicpieces that are saturated withnickel,which acts as acatalystfor the reaction,
4. Cooling heat exchangerin order to cool the products of the reaction as quickly as possible so that it reaches a particular temperature which stops any further reaction,
5. Control systemwhich will help maintain the consistency of the temperature of the reaction which will help adjust the gas ratio, providing the wanted dew point.

Chemical composition

Chemistry of endothermic gas generators:

• N₂(nitrogen) → 45.1% (volume)
• CO (carbon monoxide) → 19.6% (volume)
• CO₂(carbon dioxide) → 0.4% (volume)
• H₂(hydrogen) → 34.6% (volume)
• CH₄(methane) → 0.3% (volume)
• Dew point→ +20/+50
• Gas ratio → 2.6:1

Applications

Applications of endothermic gas generators:

1. Annealing:iron and steel
2. Brazing:copper and silver
3. Carbon restoration: carburizing, carbonitriding,nitrocarburizing
4. Neutral hardening: low, medium and high alloy carbon steels
5. Normalizing: iron and steel
6. Sintering:powder metals
7. Austempering: ductile iron

It is relatively simple to operate and maintain endothermic gas generators, however, maintenance such as the burnout process is often overlooked.

See also

• Forming gas