Abstract
Graphite, one of the polymorphic forms of carbon, has become a versatile industrial material of nowadays due to its particular attributes. It is used mainly in the automobile industry, metal extractive industry and in the high-tech industry. Moreover, it is also included in the list of critical raw materials for the EU. Our aim was to prove the presence of graphite by thermal analysis beyond X-ray powder diffraction (XRD) and Raman spectroscopy. Thermogravimetry yields comparable results with quantitative XRD. The formation conditions are described by Raman spectrometry and microscopy examinations of drill core samples from Szendrőlád (Szendrő Mts, NE-Hungary; (Szendrőlád Limestone Formation, middle-late Devonian, shelf-basin facies). Polished rock slabs were made for optical microscopy, scanning electron microscopy with energy dispersive spectrometry (SEM–EDS) and Raman spectroscopy. X-ray powder diffraction (XRD) and thermal analysis (DTA-TG) measurements were made on powders. Based on our results, the graphite is epigenetic; its quantity varies between 1.5–3 mass% in the samples. It was developed in 20–50 μm sized flakes, which are often arranged in > 300 μm sized aggregates. Graphite was formed during regional metamorphism from the organic matter-rich shales. The average formation temperature, calculated from the results of Raman spectroscopy, is around 410 °C (± 30 °C). The Raman measurements also indicated the presence of a partially graphitized (disordered graphite) material beside graphite.
Highlights
Besides diamond and fullerenes, graphite is one of the most common forms of crystalline carbon in nature [1]
Additional information can be acquired from scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), differential thermal analysis (DTA) and Raman spectroscopy [10, 11]
Polished rock slabs were made for ore microscopy, scanning electron microscopy with energy dispersive spectrometry (SEM–EDS) and Raman spectroscopy measurements, while bulk powder samples were prepared for X-ray powder diffraction (XRD) and DTA-TG
Summary
Graphite is one of the most common forms of crystalline carbon in nature [1]. There are many ways to indicate the presence and qualify the graphite in the samples, for example, maximum reflectance measurements (%Rmax), X-ray diffraction investigations and transmission electron microscopy (TEM) [9]. Each of these methods has serious limitations, like grain size (> 5 μm for %Rmax), crystallites size (> 20–30 nm for XRD) or sample preparation for TEM. For an acceptably accurate graphite survey, the combination of the above methods is a best choice
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