Thermo-oxidation of tokamak carbon dust

The oxidation of dust and flakes collected from the DIII-D tokamak, and various commercial dust specimens, has been measured at 350 degrees C and 2.0 kPa O(2) pressure. Following an initial small mass loss, most of the commercial dust specimens showed very little effect due to O(2) exposure. Similarly, dust collected from underneath DIII-D tiles, which is thought to comprise largely Grafoil (TM) particulates, also showed little susceptibility to oxidation at this temperature. However, oxidation of the dust collected from the surfaces has led to similar to 18% mass loss after 8 h: thereafter. little change in mass was observed. This suggests that the surface dust includes some components of different composition and/or structure - possibly fragments of codeposited layers. The oxidation of codeposit flakes scraped from DIII-D upper divertor tiles showed an initial 25% loss in mass due to heating in vacuum, and the gradual loss of 30-38% mass during the subsequent 24 h exposure to O(2). The oxidation of these flakes was much slower than that observed for the oxidation of thinner DIII-D codeposit specimens which were still adhered to the surfaces. This is thought to be related to structural differences. (C) 2009 Elsevier B.V. All rights reserved.