Enhanced surface flatness of vitrinite particles by broad ion beam polishing and implications for reflectance measurements

Abstract

Standardized measurements of vitrinite reflectance vary significantly between different measuring institutions. The only systematically adjustable influence factor on these differences is the polishing method. We present a recently developed preparation method using broad ion beam polishing, which, applied as additional polishing step or replacement of the standardized sample preparation, provides a dramatically improved surface flatness, and allows to remove scratches and debris of traditional polishing. Mechanical, near-surface damage of the sample, as known from traditional polishing, is not appearing in broad ion beam polished samples. Moreover, its water-free polishing allows excellent preparation of swelling clay-rich samples or granular solid bitumen surfaces.Using broad ion beam polishing the vitrinite reflectance increases by 0.18–0.24% VRr (relative increase: 12–28%) in coal samples (including an ICCP standard sample) and by 4.76% VRmax (relative increase: 90%) at a measured graphite without causing thermal overprinting of the sample based on our preliminary results. A subsequent traditional polishing step after broad ion beam polishing reverses this increase in reflectivity. The presented method has the potential to decrease the range of reflectance-based calculated maximum burial temperatures by up to 50°C if a reduction of 0.2 in the range of the measured vitrinite reflectance standard deviation can be achieved.