Nanostruktura i mikrotekstura antracytów

Abstract

Anthracites originated in Europe, Asia, Africa and North America were investigated in the presented work. Anthracites cover a whole range of metamorphism from semi-anthracites to meta-anthracites, that is the last stage of metamorphism before transformation from carbon matter to semi-graphites. Nanostructure and microtexture research concentrated on finding common characteristics for that group of metamorphosed carbon matter, apart from the local geological conditions of metamorphism for particular anthracites. Anthracite nanostructure was investigated by means of high-resolution transmission electron microscopy (HR TEM), X-ray diffraction and Raman spectroscopy. Three basic structure elements were distinguished in investigated anthracites: a) individual, single, isolated layers (not always flat) of condensed aromatic rings, b) layers arranged in stacks/packets (on average between 3 and 7 layers), c) atoms of “amorphous carbon”. Three structure elements coexisted in all anthracites. The amount of atoms of “amorphous carbon” decreased, whereas an average number of layers in stacks increased from 3 to 7 with the increase of metamorphism, as well as the diameter of the layers changed from 1.8 nm for semi-anthracites to 4.8 nm for meta-anthracites. Anthracite microtexture was investigated by means of transmission electron microscopy (dark field DF TEM) and measurement of reflection coefficient for polarized light. In the whole group of anthracites four types of microtextures were distinguished: A) grains or areas without any texture, i.e. with a lack of the arrangement of the layers and stacks, B) areas where statistically distinguished direction of the orientation of layers and stacks is present, C) areas where statistically distinguished plane of the orientation of layers and stacks is present (defected lamellas), D) grains with perfect arrangement of the layers and stacks in respect to the distinguished plane (perfect lamellas). In semi-anthracites (A) and (B) types of microtexture dominated and very seldom grains with (C) type microtexture were found. In meta-anthracites (B) and (C) types of microtexture predominated with increasing participation of (D) type microtexture. Volume, penetration of different nanostructures and microtextures and a lack of distinct boundaries between them are changing depending not only on the investigated anthracite, but also within any particular anthracite. The research proved that nanostructure and microstructure heterogeneity is an inherent feature to all investigated anthracites. That feature is not connected with the degree of metamorphism of the investigated substance.