LSM Analytical Services large range of analytical techniques includes instrumentation for Carbon analysis.
The Principle of Carbon Analysis
The principle of Carbon analysis is to oxidise the sample by heating in an Oxygen atmosphere to form CO2, which is then measured by infrared detector.
Heating Samples for Carbon Analysis
The heating is generally done in a high frequency induction furnace as this provides both speed and accuracy. The sample is placed in a ceramic crucible and an accelerator is often added to ignite the sample and can also act as a flux to dissolve any oxide skins to improve melt fluidity, which allows the carbon in the sample to be oxidised in a short time. It is imperative that complete combustion is achieved in order to gain accurate results.
There are a large range of accelerators used and the choice depends on the base material being analysed. One feature of any accelerator is a low carbon (and Sulphur as this is often analysed for in a similar way) content.
Ensuring Accuracy During Carbon Content Determination
A key issue in carbon determination by this method is the purity of the Oxygen gas used. Typical impurities include CO2 and CH4. CH4 can be oxidised at the temperatures involved in the test to CO2 + H2O, so for accurate results the effects of these impurities have to be resolved in the test method. This can be done in a number of ways, for example by using high purity Oxygen or by employing an in line gas purifier.
How Carbon Content is Calculated
In the test a signal will be obtained that is not attributable to the sample. The cause is a combination of impurities in the gas, crucible and accelerator. The average contribution to the carbon signal from these sources is determined to allow the sample contribution to be calculated. The inconsistency of impurity levels from these sources cannot be completely eliminated and this affects the ability to determine accurately to very low levels. As the method is relatively quick, repeat determinations are often requested to improve the accuracy of the determination (by taking the average of several results).