Providing such a wide range of techniques ensures that samples are analysed by the most economical method, depending on the type of material, the form of the sample and the level of accuracy required. Normally, one or more of the following methods are used for analysis of steels and nickel, cobalt, aluminium, copper and titanium-based alloys:
X-ray Fluorescence (XRF)
Simultaneous and sequential X-ray spectrometry is used for the determination of main and residual impurity elements. Accuracy is largely determined by the quality and range of Certified Reference Materials (CRMS) used for calibration.
Optical Emission Spectrometry (OES)
OES is particularly useful for low atomic number elements such as boron, magnesium, aluminium, phosphorous and calcium.
When coupled with a Hollow Cathode Source, OES is used to determine low boiling point elements such as lead, bismuth, silver and tellurium at very low concentrations. These elements, which can seriously impair the performance of high-temperature steels and nickel-based superalloys, are routinely determined at levels below one part per million.
Atomic Absorption Spectroscopy
AAS determines the composition of chemical elements by the absorption of light and free atoms. Residual and trace elements are analysed using Atomic Absorption and Graphite Furnace Atomisation (GFA). This method is particularly useful where there are no CRMs available.
The Carrier Gas Extraction methods determines oxygen, nitrogen and hydrogen levels. The sample is melted in an inert gas stream in a graphite crucible and the gasses evolved are measured by thermal conductivity or infra-red absorption.
Carbon & Sulphur Analysis
Carbon and sulphur are determined by RF Combustion in oxygen. This results in evolution of carbon dioxide and sulphur dioxide. Their concentrations are then measured by infra-red absorption
Inductively Coupled Plasma (ICP-OES)
This technique is an alternative to XRF and conventional OES when sample size is limited or the sample form is unsuitable (eg turnings, fine wire or powder. With ICP-OES, the sample is dissolved and aspirated in an argon plasma where it vaporizes and emits a characteristic spectrum which is analysed by OES. The analysis involves dissolution of the sample, and therefore it is relatively easy to prepare closely matching calibration standards from pure metals and compounds. This is particularly important where appropriate CRMs are not available or where an independent overcheck is needed.
Classical chemical analysis can be used to supplement instrumental methods and is important where overcheck or referee analyses are required.