RAMAN MICROSPECTROMETRY STUDY OF CARBONIZATION PROCESSES. FIRST PROMISING APPLICATION IN ARCHEOLOGY

摘要

The Raman microspectrometry is more and more recognized to be a major technique for carbon material characterization. Based on the data from the Web of Sciences loaded in mid-April 2012, more than 800 papers were published from 2010 in the Carbon journal concerning the use of Raman microspectroscopy in carbon sciences. This tendency accelerates since 269 papers were devoted to this topic from 2010, and 42 from the beginning of 2012. Raman microspectroscopy is used as a non-destructive technique to obtain rapidly, without special preparation, structural data on carbon materials. For instance, it is a very efficient tool to precisely study the structural changes occurring during the graphitization processes. These processes can be quantitatively followed by important changes in the Raman band shapes, position and intensity. There are different ways to obtain natural or synthetic graphite [1-4], involving the nature of the precursor, the maximum temperature of treatment (in a laboratory furnace or under the terrestrial or extra-terrestrial metamorphisms). However, all these graphitization processes lead to the disappearance of the D band ("defect" band at about 1350 cm~(-1)) whereas the G band (E_2G mode at 1581 cm~(-1)) remains alone in the graphite spectrum [5,1-9]. The I_d/I_g intensity ratio was proposed by Tuinstra and Koenig [5] as a measurement of La the crystallite diameter. This was confirmed by Transmission Electron Microscopy (TEM) images. Graphitization is attributed to an increase of La corresponding to the graphene layer diameter, then to a stricfo sensu crystal growth when tri-periodic order develops [1-3].