Microstructural investigations of carbon foams derived from modified coal-tar pitch

George Tzvetkov; Boyko Tsyntsarski; Konstantin Balashev; Tony Spassov

doi:10.1016/j.micron.2016.07.006

Microstructural investigations of carbon foams derived from modified coal-tar pitch

Micron. 2016 Oct:89:34-42. doi: 10.1016/j.micron.2016.07.006. Epub 2016 Jul 18.

Authors

George Tzvetkov¹, Boyko Tsyntsarski², Konstantin Balashev³, Tony Spassov³

Affiliations

¹ Faculty of Chemistry and Pharmacy, University of Sofia, J. Bourchier 1, 1164 Sofia, Bulgaria. Electronic address: george.tzvetkov@gmail.com.
² Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., BL. 9, 1113 Sofia, Bulgaria.
³ Faculty of Chemistry and Pharmacy, University of Sofia, J. Bourchier 1, 1164 Sofia, Bulgaria.

PMID: 27459589
DOI: 10.1016/j.micron.2016.07.006

Abstract

This work reports the microstructural evaluation of carbon foams derived from coal-tar pitch precursors treated with H2SO4 and HNO3 and finally annealed at 1000°C and 2000°C. Our experimental investigations combine scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and micro-spot near-edge X-ray absorption fine structure (μ-NEXAFS) spectroscopy. This set of complementary techniques provides detailed structural and chemical information of the surface and the bulk of the carbon foams. The high-resolution microscopy data indicate the formation of carbonaceous amorphous microspheres (average diameters of 0.28±0.01μm) embedded in the partially graphitized carbon foam matrix at 1000°C. The microspheres are enriched with sp-bonded species and their microstructural characteristics depend on the reagent (nitric vs. sulfuric acid) used for pitch treatment. A complete chemical transformation of the microspheres at temperatures >1000°C occurs and at 2000°C they are spectroscopically identical with the bulk material (sp(2)- and sp(3)-hybridised forms of carbon). The microstructure-property relationship is exemplified by the compressive strength measurements. These results allow a better description of coal-tar pitch-derived carbon foams at the atomic level, and may account for a better understanding of the processes during graphitization step.

Keywords: AFM; Carbon foam; NEXAFS; SEM; TEM; XPS.