Modifying the Atmosphere in a Furnace

Heating most dry materials in air tends to bring about their oxidation. Sometimes in applications such as ashing this is the major objective of the process. At other times this oxidation is an unwanted side effect. The requirement is then to heat the test material in either an atmosphere that is free from oxygen or that is chemically inert so that no reaction is likely with the test material.

As mentioned this is easier to achieve using tube furnaces where blocking the tube ends is sufficient to contain the atmosphere. Carbolite supply a range of tube end seals for this process.To protect the end seals from the heat of the furnace, it is better to order work tubes that are around 300mm longer at each end, addition of insulation plugs or radiation shields are also a good idea and additionally give improved temperature uniformity within the tube.For higher temperatures water cooled end seals can be supplied.These can be actively cooled using a chiller or mains water supply.

Chamber furnaces can have gases such as nitrogen or argon fed into them but because their insulation is almost always porous the gas leaks away quickly and so can be expensive is terms of gas use and much more difficult to maintain in an oxygen free state.The solution in these cases is to use an Inconel metal retort to contain the test material and the gas. These are suitable for applications up to around 1000°C. Carbolite offers two standard retort designs both of which require modifications to the furnace in which they will be used at the time of its manufacture.

Reducing atmospheres are often either flammable or toxic typical examples being hydrogen and carbon monoxide. To work with these the furnace should be sited under a fume hood and the Carbolite gas safety system is an essential requirement for safe operation.