3 Things to Keep in Mind When Using LIBS to Analyse Steel
We have previously written about using Laser Induced Breakdown Spectroscopy (LIBS) for Quality Control (QC) and Positive Material Identification (PMI) in material verification programs. Accurate identification can be paramount to safety when it comes to steel. If metal fasteners fail while an aeroplane is flying, or if pipes at an oil refinery corrode, or if crucial components in a rocket ship cannot withstand varying temperatures, tragedies can occur.
LIBS is the analytical technique that utilises a highly-focused laser that ablates the surface of a material. It then forms plasma in which the light generated is broken down into single elements. LIBS is capable of measuring elements, including carbon, in the field, on raw materials, during the production process, and on finished goods.
A handheld LIBS analyser is used by industrial businesses to confidently perform elemental analysis when carbon detection and mobility are top of mind, especially if there’s a need to identify low alloy/ carbon steels and L and H grade steels.
However, the operator must keep several things in mind to help ensure accurate results:
- The Importance of Sample Preparation
Good sample preparation is essential to obtaining reliable results. Trace amounts of contaminants, such as paint, grease or scale may yield unreliable outcomes. This is because the analyser uses a laser to ablate the surface of the sample. When this occurs, only a small portion of the sample (a few nanograms) is removed. If the surface is diluted, then there is not a representative sample of the metal to provide accurate results. (Watch a video on sample preparation for LIBS.)
- The Importance of a Well-Maintained Instrument
Accuracy is dependent on the calibration of the instrument as well as sample preparation. Regular maintenance is vital to ensuring the instrument produces the most analytically accurate outcomes. Maintenance includes daily setup procedures, instrument cleaning and annual calibration certification.
* Daily Set-Up Procedures – serve to normalise the analyser and include a wave and sensitivity check.
* Instrument Cleaning – removes metal particles from the optic windows to prevent the possibility of signal throughput becoming degraded. It is recommended that instrument cleaning be performed every 1,000 readings. (Watch a video on LIBS instrument cleaning.)
* Annual Calibration Certification – should be done by the manufacturer for inspection by certified technicians, who should be able to verify the analytical performance of your analyser. If necessary, the instrument should be re-calibrated to ensure proper functionality, and certified that the calibration is in proper working order for a stated period of time.
- The Importance of Sample Uniformity
Precision is dependent on both the instrument performance in terms of stability and equally on the homogeneity of the sample analysed. Due to the small amount of material being ablated, spot-to-spot variation can occur decreasing (worsening) the measured precision. It is highly recommended to perform at least three (3) or more analysis and average the results.
To see data and analysis demonstrating the accuracy and high reproducibility of a handheld LIBS analyser for elements of interest in stainless steels using a multiple instrument comparison method (average of six (6) readings from sixteen (16) instruments), download the application note, Stainless Steel Performance Characteristics Using the Niton Apollo Handheld LIBS Analyser.