High temperature thermogravimetry for oxidation and corrosion testing in dry and humid atmospheres

摘要

The usual way to investigate oxidation and corrosion on metallic or ceramic samples at hightemperature consists in introducing the sample in a furnace and then extract it, as described forexample in the COTEST procedure.. As the sample has to be weighed before and after theintroduction, the measurement of the mass variation is not very sensitive. This manipulation of thesample in and out the furnace may also have an effect on the final result as the atmosphere changesduring this operation. In the same time such a manipulation is tedious and very time consuming.To obtain an automatic and continuous record of the mass variation of the sample, the modern hightemperature thermogravimetric technique has to be used. Such a thermobalance provides a highprecision in the mass variation measurement. A level of one μg mass variation can be reached on asample weighing several grams.when a symmetrical design is used.On the Setaram thermobalance, a piece of metal or ceramic is hung to the balance in order to increasethe surface of contact with the gas.Such a sample is introduced in a high temperature furnace the temperature of which is linearly scannedor maintained at a constant temperature. Cyclic thermogravimetry is also available on this type ofinstrument. In that case the temperature of the sample is cycled between two temperatures toaccelerate the aging of the material.Different types of atmosphere can be applied around the sample: high vacuum, dry gas (inert,oxidative or reducing), controlled humidity atmosphere.With such a system, the sample is maintained during the whole test under controlled temperature andatmosphere and the mass variation coming from its reactivity is continuously monitored.Such a quantitative technique allows following processes such as oxidation and corrosion at hightemperature under various atmospheric conditions. The deritavive of the thermogravimetric signal,called DTG, indicates the rate of reaction and provides information for the kinetic determination,especially useful for the modelisation of the durability of high temperature structural materials.Such a technique applies to all high temperature metallic and ceramic materials used in various typesof industrial applications (engines, gas turbines, heaters, heat exchangers, reactors...). Among thereactions that can be measured with the thermogravimetric technique, it can be given: oxidation,carburization, nitridation, but also degradation of coatings.