Scanning electron microscopy
GTK has four scanning electron microscopes (SEMs): two in Espoo, two in Outokumpu (see table). Both locations feature one “traditional” SEM with tungsten filaments, and one more modern SEM using field emission (FE-SEM). The traditional SEM can produce images at 10,000X magnification in optimal conditions, and it can produce images of particles with a size of less than one micron. The FE-SEM can reach a magnification of several hundred thousands, and it can produce nanometre-scale images.
All GTK’s SEMs are connected to an energy-dispersive X-ray spectrometer (EDS/EDX), which means that in addition to imaging, they can be used to analyse the chemical element composition of samples. The equipment enables us to analyse a variety of mineral-based materials and other inorganic materials.
Some SEMs have an LV feature, which enables samples to be analysed in a pre-set low vacuum. This means samples do not need to be separately prepared for analysis. However, in low vacuum conditions, the analysis accuracy is not as good as in high vacuum conditions.
The results of EDS analysis are semi-quantitative. The measuring accuracy of chemical element contents varies depending on sample but is usually around 0.3–0.5 weight percent (wt%). Samples with a grain size less than 1–3 μm cannot be analysed reliably. Nor is exact identification of mineral phases from an EDS spectrum always possible. In addition, phases with similar or identical chemical composition cannot be distinguished from each other.
EDS systems are operated with a set of software that enables analyses to be conducted largely automatically. Point or line analyses can be conducted on samples, their modal mineralogy can be analysed, and automatic searches related to them can be performed. In addition, dispersal maps on chemical elements can be prepared, and data can be produced on grain size distribution and mineral associations and liberations for use in mineral processing.