Measuring surface properties and oxidation of coal macerals using the atomic force microscope

Early microscopic examination of coals and coal macerals began with the use of transmitted and then reflected light microscopy. These methods were limited by the resolution and optical quality of the microscopes used. Improved microscope technology and the development of oil immersion techniques led to advancements in coal petrology. Introduction of the atomic force microscope (AFM) has led to higher resolution (angstrom and nanometer scale) imaging of various inorganic and organic surfaces with ability to quantitatively measure surface features and forces, but the use of AFM for measuring coal surfaces has been limited by a lack of a method to identify the macerals being analyzed. This paper describes a method using AFM to identify individual macerals and precisely measure their surface properties through the use of various AFM modes and analyses. This method has the potential to yield useful information about the physical properties of coal macerals (e.g. topography, roughness, hardness, and elastic modulus), and also about the effects of natural oxidation on coal macerals and the intentional oxidation of individual macerals to enhance either optical properties or surface porosity. (c) 2005 Elsevier B.V. All rights reserved.