Oxygen Analysis – Determination of Oxygen Content by Inert Gas Fusion by LSM Analytical Services

Background

LSM Analytical Services offer a large and diverse range of modern analytical testing facilities that cater for a vast range of industry sectors. LSM’s success has been achieved by building on a strong reputation for low cost, fast accurate turnaround. The laboratory activities are backed up by accreditation to the ISO 17025 (UKAS) and 9001:2000 laboratory and quality management standards. LSM is able to offer complete analytical solutions from its internationally recognised team of technical experts, with in depth knowledge, allowing its customers to benefit from impartial guidance.

LSM’s range of analytical services includes:

•        X-Ray Fluorescence Spectrometry (XRF)

•        X-Ray Diffraction (XRD)

•        ICP Optical Emission Spectrometry (ICP-OES)

•        Atomic Absorption Spectrometry (AAS)

•        Carbon, Sulphur, Nitrogen, Oxygen Analysers

•        Boron analysis by the Neutron Transmission method

•        Colorimetric and Volumetric Analysis

•        Particle Size Analysis

Oxygen Analysis

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.

Source: LSM Analytical Services

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