SPECTROLAB – Ultimate performance for the next generation of metal analysis

Optical emission spectrometry has been a preferred method for elemental analysis and quality control in the metallurgical industries for decades and is rightly regarded as robust, easy to use and realistically priced. Available instrumentation ranges from portable and mobile spectrometers for on-site use, through high performance laboratory systems to automated analyzers with robotic sample handling. Like many “mature“ techniques, in recent years it has attracted relatively little attention from the academic community, but leading manufacturers have been responsible for many technical innovations and improvements that have transformed the performance, reliability and ease of use of modern instrumentation.

The SPECTROLAB from SPECTRO Analytical Instruments brings together developments in sample excitation, optics and detector technology to meet the most demanding analytical requirements of the metals processing industries. Its exceptional stability, reliability and low maintenance requirements also make the SPECTROLAB especially suitable for automated applications. 

Because of its toxicity and wide occurrence in man-made artifacts, lead was one of the first elements to be covered by environmental legislation, and much effort has been devoted to its removal from the human environment. Its use is now effectively banned or severely restricted in products from paints and automotive fuel to toys and electronics. However the lead-acid battery is still a very popular power source, especially in the automotive industry, and the rapid growth of the emerging economies in the East has also dramatically increased the demand for the metal and increased its price. Simultaneously with this process however, the demand for low-carbon energy for transport and other applications requires the storage of electrical energy from renewable and perhaps intermittent sources, and the lead-acid battery is still one of the most commonly used devices for this purpose, creating a new demand for the metal. It is ironic that this most legislated-against metal is now part of the solution to another environmental problem. Most countries have strict guidelines for disposal of used products that contain lead, including batteries, and clearly it is more sustainable to recycle the lead into new batteries than to dispose of it by other means. The composition of the lead used in batteries has a marked effect on performance and needs to be strictly controlled. Depending on the type of battery, the presence of certain elements in the lead can either improve or impair battery performance. Many elements can only be tolerated as impurities at very low levels and the increasing use of recycled lead can introduce traces of contaminants not found in lead from natural sources. High performance Optical Emission Spectrometry (OES) is one of the techniques best suited to measuring these elements at the very low levels required. This paper discusses the use of the SPECTROLAB spectrometer from SPECTRO Analytical Instruments in this application.

The development of ferrous metallurgy is inextricably linked to the advance of civilization. It can also be truthfully said that without carbon there would be no cast iron or steel, as it has been the reducing agent used to liberate metallic iron from its ores since the earliest times. A few tenths of a percent difference in carbon content can have a dramatic effect on the mechanical properties of iron and steel, so its accurate measurement is critical to ferrous metallurgy.

Chemical and spectroscopic methods have been developed for the measurement of carbon in iron and steel. One of the most popular is Optical Emission Spectrometry (OES) using an electric spark source. When measuring carbon in cast iron, however, this method can be prone to errors traceable to the granular nature of the material and to the presence of particles of “free” carbon in the form of graphite. These errors can only be overcome by perfect sample preparation techniques, but a high degree of skill and experience is required to achieve reproducible and reliable results. New developments in OES technology incorporated in the SPECTROLAB and SPECTROMAXx from SPECTRO Analytical Instruments make it possible to detect and even analyze samples containing free graphite. Using this approach, results are comparable to those achieved by techniques such as combustion analysis.

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Inclusions have a large impact on the mechanical properties of steels and other metals. In applications where inclusions play a role, it is important to control size, shape and homogeneity of the inclusions. Very often the most important criterion is the absence of any inclusions. Here, of most importance, is the cleanliness of steel. In the last fifteen years OES technology has made significant progress with respect to fast readout of single sparks. This development enabled the fast detection of inclusions using the Single Spark Evaluation (SSE) technology with SPECTROLAB, which has to be regarded as complementary to the traditional optical and scanning electron microscope methods. The advantage of the SSE technology lies in the speed and multi-element analysis possibility. Although the traditional technologies are more quantitative methods, they are time consuming and expensive. The qualitative or semi-quantitative OES-SSE technology balances out against the traditional technologies with respect to the speed, simultaneous multielement correlation counting and simplicity of the detection method.

Optical Emission Spectroscopy (OES) is generally regarded as the oldest instrumental technique for elemental analysis, tracing its origins to the mid 19th century. By the middle of the last century, developments in instrument design, optics, detector technology and electronics had created an analytical tool that had become one of the most widely used in materials testing. This is still the case today. OES instruments from SPECTRO Analytical Instruments have earned an enviable reputation for performance and reliability and thousands are to be found in laboratories and metallurgical industries throughout the world. The heart of any OES instrument is the optics and detection system. Traditionally, the photomultiplier has been the detector of choice, but developments in semiconductor technology have yielded solid-state detectors such as CCD’s that can approach the performance of the photomultiplier. Both types of detector have their advantages in terms of analytical performance, but compromises inevitably have to be made when choosing which to use in an instrument, and most commercially available instruments use either photomultiplier or CCD detection. The SPECTROLAB M10 has a revolutionary hybrid optical design that incorporates both types of detector in the same instrument in optimized configurations, allowing the analyst to choose the detector best suited for the individual application – truly the best of both worlds! 

Optical Emission Spectroscopy (OES) is the most popular and best established technique for the quantitative analysis of metals and alloys. Like most instrumental methods it is a relative technique, where sample measurements are compared to calibration measurements made on standards of known concentration. Any short-term or long-term instability of the measuring system will adversely affect the quality of the results, and instrument suppliers often rely on precision data and results on Certified Reference Materials to indicate the performance of their products. In industries such as aerospace or automotive, accuracy may be of paramount importance.

ASTM E 1009 describes a method for evaluating an OES instrument for the analysis of carbon and low-alloy steels, using specified CRM’s as standards, and includes a way of defining the accuracy of the analysis. Work at SPECTRO Analytical Instruments has used the approach in ASTM E 1009 as the basis for a software-controlled quality control and qualification procedure, the SPECTRO Performance Qualification System (SPQS), which has the potential to be applied to any OES measurement. Calibration and validation specifications can be developed for the user’s specific analyses, using standards chosen to suit the application and imposing accuracy, precision and stability limits agreed between SPECTRO and the customer at the time of ordering. The SPQS can then be applied throughout the life of the OES spectrometer to ensure that this level of performance is maintained, while at the same time generating a secure trail of measurement data for quality audit purposes.

Precious metals require — and reward — careful analysis. But analysts face various difficulties. The scope of precious metals analysis extends from trace levels to 100%. Most of these metals are resistant to dissolution by all but the strongest acids. Some traditional analytical methods like fire assay are time-consuming and demand a high level of skill.

Three modern techniques offer widely used solutions. Energy-dispersive X-ray fluorescence (ED-XRF) and optical emission spectrometry (OES) can be used without specialist analytical training to rapidly and accurately analyze bullion, jewelry, and alloys. A variation of OES, inductively coupled plasma optical emission spectrometry (ICP-OES), is an ideal tool for the analysis of bulk materials such as ores, and for the determination of trace impurities.

Several instruments available from SPECTRO Analytical Instruments represent the state of the art in these techniques. This paper describes their application to precious metals analysis.