Analytical Services:
Carbon, Sulphur, Nitrogen, Oxygen and Hydrogen Analysers
Leco C
LSM Analytical Services large range of analytical techniques includes instrumentation for Carbon analysis.
The principle of Carbon analysis is to oxidise the sample by heating in an Oxygen atmosphere to form CO 2 , which is then measured by infrared detector.
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 is 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.
A key issue in Carbon determination by this method is the purity of the Oxygen gas used. Typical impurities include CO 2 and CH 4 . CH 4 can be oxidised at the temperatures involved in the test to CO 2 + H 2 O, 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.
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)
Leco N
LSM Analytical Services large range of analytical techniques includes instrumentation for Nitrogen analysis by the inert gas fusion method.
The inert gas fusion method is used for Nitrogen 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 o C) in an inert gas. The Carbon crucibles are effectively resistors that supply the heat necessary to fuse the sample. The Nitrogen in the sample is released as molecular Nitrogen (N 2 ), which is measured using a thermal conductivity cell. For reactive metals a flux is also required to help the release of the Nitrogen 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 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 Nitrogen 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).
Leco O
LSM Analytical Services large range of analytical techniques includes instrumentation for Oxygen analysis by the inert gas fusion method.
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 o 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 CO 2 , 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 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.
Leco S
LSM Analytical Services large range of analytical techniques includes instrumentation for Sulphur analysis.
The principle of Sulphur analysis is to oxidise the sample by heating in an Oxygen atmosphere to form SO 2 , which is then measured by infrared detector.
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 Sulphur 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 is a large range of accelerators used and the choice depends on the base material being analysed. One feature of any accelerator is a low Sulphur (and Carbon as this is often analysed for in a similar way) content.
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 Sulphur 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).
Sulphur results can be affected if water is present in the sample. However dealing with this issue is not straightforward. Residual water can be dealt with by heating the sample to 110 C for one hour. Crystalline water is less easy to deal with as the high temperatures required to dissociate it also mean combustion of the Sulphur.
Hydrogen analysis
The sample is heated in a crucible in a current of Helium. The hydrogen is released/extracted into the helium gas and detected using thermal conductivity.
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Oxygen, Hydrogen Analysers
