Relating reactivity to structure in cokes and carbon materials: Temperature-programmed oxidation and microscopy techniques Sara Andreoli , Semih Eser * Carbon Materials Program, EMS Energy Institute and Department of Energy and Mineral Engineering, Penn State University,114A Hosler Building, University Park, PA, 16802, United States article info Article history: Received 30 April 2020 Received in revised form 11 June 2020 Accepted 24 June 2020 Available online 28 June 2020 Keywords: Petroleum coke Optical texture Polarized-light microscopy Temperature-programmed oxidation Carbon composites Surface functional groups Reactivity abstract A series of carbon materials and composites has been characterized by temperature-programmed oxidation (TPO), polarized light microscopy (PLM), scanning electron microscopy with energy disper- sive X-ray spectroscopy (EDS), and temperature-programmed desorption coupled with mass- spectrometry analysis. For materials containing anisotropic carbons, a consistent relationship was found between oxidation reactivity and optical texture. Polarized-light microscopy in combination with TPO can help assessing the relationships between oxidation reactivity and optical texture of anisotropic carbons. Deconvolution of TPO profiles and PLM observations can effectively identify the individual components of multi-component carbon materials with important implications in structure-property relationships and their applications. For amorphous carbons with isotropic optical textures, TPO pro- files were found to be influenced by the surface chemistry of the materials. It appears that the TPO technique under controlled conditions provides a rapid analysis of solids carbons with respect to their structure and properties. This is particularly useful for the analysis of carbon composites with multiple phases in combination with microscopic examination and elemental analysis using EDS. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction The world of carbon materials has been expanding with the discovery of novel materials and new formulations of carbon/car- bon composites and multi-component carbon composites with improved properties for a range of applications. Easy and rapid characterization techniques will help producers and consumers to analyze the structure and properties of carbon materials to improve quality and for better selection of raw materials and processing techniques. The properties of cokes and carbon materials depend on their structure at three different scales, atomic (bonding), nanostructure (aggregation of crystallites), and microstructure (optical texture) [1]. For many applications, characterization of the microstructure (optical texture) of anisotropic carbonaceous ma- terials is very important as it relates to strength, thermal expansion, and chemical reactivity. On the other hand, the surface chemistry of isotropic carbons, such as activated carbons, constitutes a focal point for applications in adsorption or catalytic processes. Polarized-light microscopy (PLM) has been widely used to characterize the optical texture of cokes and carbonaceous mate- rials in order to assess the extent of their microstructural anisot- ropy. The preparation of samples for microscopic examination requires polymer molding and elaborate stepwise surface polishing procedure. A qualitative assessment of optical texture requires a sequential analysis of optical images in order to define an optical texture index (OTI) as a relative indication for the degree of anisotropy [2]. Oxidation reactivity can be measured as a function of temperature, using a temperature-programmed oxidation anal- ysis (TPO) which can be adopted as a technique for the character- ization of cokes. In general, TPO analysis gives a direct measurement of the amount of carbon oxidized in flowing O 2 to CO 2 as a function of temperature. This technique can provide different information on cokes and carbonaceous materials such as the quantification of different carbon species and kinetics of car- bon-O 2 reaction [3] and texture [4]. Recently, Chen et al. [4]. re- ported a relationship between anisotropic contents of cokes and their reactivity towards oxygen. The utility of TPO depends on the relationship between the intrinsic oxygen reactivity of solid car- bons and their structure [5]. In heterogeneous substances, or multi- component mixtures, the more reactive part of carbonaceous ma- terial is oxidized at lower temperatures while the less reactive part * Corresponding author. E-mail address: seser@psu.edu (S. Eser). Contents lists available at ScienceDirect Carbon journal homepage: www.elsevier.com/locate/carbon https://doi.org/10.1016/j.carbon.2020.06.071 0008-6223/© 2020 Elsevier Ltd. All rights reserved. Carbon 168 (2020) 362e371