What is Coke Petrography?

Petrography is the study and classification of rocks, typically by using microscopy techniques to examine thin slices of material and look at their composition. For the steel industry, coke petrography has become one of the key analysis tools for determining coke quality and, ultimately, whether a coke sample will be suitable for use in the creation of steel alloys.1

Coke petrography is such an important tool for the steel market as the coke quality often determines the blend conditions for steel alloy manufacture.2 Even small differences in the coke microtexture can lead to an impact on the final material properties of the alloy, making coke qualification an essential part of the manufacturing process.

What is Petrographic Analysis?

Petrographic analysis can involve a variety of analytical methods, such as various kinds of chromatography, but often uses combined imaging and spectroscopic approaches to study samples. What makes petrographic substances like coke challenging to study is these naturally-formed materials are normally non-crystalline, so standard structural methods like diffraction do not work well, with a great degree of sample heterogeneity.3

Heterogeneous samples mean that, depending on which area of the sample is studied with a spectroscopic method, the results will be different. This may be due to local variations in the blend or structure. Given microtextures and microstructures in coke are what is responsible for the blend and processing properties of the coke, this means that any method used needs to be capable of achieving micrometer resolution.

Understanding Petrography for Coal and Coke

Evaluating coke quality by petrographic analysis is typically done by measuring the amount of light reflected from the maceral vitrinite.4 Vitrinite has a significant impact on the thermoplastic properties of coal during coke formation and so the ranking system of coke quality relies on using reflective microscopy to evaluate the maceral vitrinite content. 

For petrography studies of coal and coke, polarized microscopy can be particularly valuable due to the complexity of the number of binder and filler phases in coal samples. Normally, this kind of petrographic analysis is performed manually and may require hundreds of measurements to be taken to account for the heterogeneous nature of the sample, but machine learning approaches for image recognition and analysis are helping to automate such procedures.5

Key Advantages of Coke Petrography

Some of the key advantages of coke petrography include the ability to fully reconstruct the coal blend being analyzed, the ability to determine the overall quality of the coke sample, and when microscopy techniques are used as part of the petrographic analysis, information on microtextures and the presence of specific binders can be obtained.

Microscopy and spectroscopy are highly valuable in coke petrography as many of the substances of interest, such as the maceral vitrinite, give very strong optical signals. The spectroscopic information can provide further quantitative and qualitative information for a more comprehensive chemical analysis.  As such, the methodologies are defined in the ISO standards 7404-3 and 7404-5.

Now the possibilities of automation of microspectrometry for coke petrography are growing with the development of more advanced hardware and software automation, coke petrography is becoming a more accessible analysis tool that does not necessarily require an expert user to perform and analyze measurements.

Interested in Coke Petrography Solutions?

The imaging microphotometer and microspectrometer, from CRAIC Technologies, are excellent solutions to all of your coke petrography needs, meeting and exceeding the internationally recognized ISO standards 7404-3 and 7404-5.

CRAIC Technologies imaging microphotometers are capable of handling sample areas only a few micrometers in size and providing both vitrinite reflectance values as well as point counting, making them ideal for dealing with highly heterogeneous coke samples quickly and accurately.

If you are looking to improve the quality control in your production of steel alloys, contact CRAIC Technologies to see how their microspectrometers range and imaging expertise could help you quantify your coal quality and get exactly the right material properties you need in your final products.

References and Further Reading

1.     Congo, T., Rodrigues, S., Esterle, J., Steel, K., & Maranha, S. (2023). Before and after : A visual glimpse into the coking behaviour of coal macerals. Fuel, 343(November 2022), 127979. https://doi.org/10.1016/j.fuel.2023.127979
2.     Kieush, L., Koveria, A., Schenk, J., Rysbekov, K., Lozynskyi, V., Zheng, H., & Matayev, A. (2022). Investigation into the Effect of Multi-Component Coal Blends on Properties of Metallurgical Coke via Petrographic Analysis under Industrial Conditions. Sustainability, 14, 9947. https://doi.org/10.3390/su14169947
3.     Meng, F., Gupta, S., French, D., Koshy, P., Sorrell, C., & Shen, Y. (2017). Characterization of microstructure and strength of coke particles and their dependence on coal properties. Powder Technology, 320, 249–256. https://doi.org/10.1016/j.powtec.2017.07.046
4.     Ma, F., & Tao, Y. (2023). Study on maceral characteristics and separation of low-rank coal. International Journal of Coal Preparation and Utilization, 43(5), 847–862. https://doi.org/10.1080/19392699.2022.2078811
5.     Andrello, R., Carvalho, C. De, Fontana, M., A, P. P. B. S., Herval, R. M. De, & Paulo, S. (2019). Digital petrography : Mineralogy and porosity identification using machine learning algorithms in petrographic thin section images. Journal of Petroleum Science and Engineering, 183(June), 106382. https://doi.org/10.1016/j.petrol.2019.106382