LSM Analytical Services large range of analytical techniques includes instrumentation for Oxygen analysis by the inert gas fusion method.
The Inert Gas Fusion Method for Oxygen Analysis
The inert gas fusion method is used for Oxygen analysis. This is typically based on a furnace with water-cooled copper electrodes. The principle is to fuse the sample in a high purity graphite crucible in the furnace by taking it to very high temperatures (3000°C) in an inert gas. The Carbon crucibles are effectively resistors that supply the heat necessary to fuse the sample, as well as Carbon for the reduction of Oxygen in the sample. The Oxygen in the sample reacts with the Carbon in the crucible to form CO or CO2, which is then measured by infrared detection. For reactive metals a flux is also required to help the release of the Oxygen from the sample. The most common flux is high purity Nickel and the amount added to a sample varies but is typically in the ratio of 10 parts flux to 1 part sample.
The Effect of Gas Purity
The purity of the gas is an important factor, with gas “scrubbers” or out-gassing being methods to address the potential impact of impurities.
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 and crucible. The average contribution to the Oxygen 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). Moisture in the Carbon crucible can be the cause of erratic Oxygen signals.