Session: MF-29-01 Mechanical Properties of Nuclear Graphite and their Implementation in Codes and Standards (Joint with CS-15)

Paper Number: 105922

105922 - Effect of Differential Oxidation of Graphite Crystallites on the Elastic Moduli of Nuclear Graphites 

The physical properties of nuclear graphites are heavily influenced by a range of defects that arise as a result of the manufacturing processes used to produce these materials. Among these defects, porosity plays an important role in determining properties of bulk graphite including the elastic responses, strength and toughness. It is well known that oxidation processes affect porosity and impact these properties as a result of the modification of the graphite pore structure. Under conditions associated with the kinetic regime for oxidation, porosity increases as a result of chemical reactions between graphite and gas phase species that occur at rates governed by the availability of reaction sites including those on graphite crystallite basal planes and edge planes. Beyond reaction site availability, differences in reactivity among various portions of the graphite microstructure influence morphological and physical changes to the graphite as porosity evolves. In particular, differences in reactivity between edge and basal plane sites reduce the connectivity of graphite crystallites sharing edge connections more rapidly than the junctions between other portions of the microstructure, and this has the effect of reducing stress transfer along basal planes. This work examines the effect of site reactivities using first-order rate equations to describe differential changes to the graphite microstructure. These changes are related to the elastic connectivity of graphite crystallites and are used to assess the changes in the moduli as porosity increases. The net result is to produce an overall elastic connectivity of the graphite microstructure that evolves as site oxidation proceeds and affects the functional dependence of elastic modulus on porosity.

Presenting Author: James Spicer Johns Hopkins University

Presenting Author Biography: James Spicer is a professor of Materials Science and Engineering at Johns Hopkins University in Baltimore, Maryland. He is the chair of Materials Science and Engineering Program in the Engineering for Professionals Program and is a member of the Principal Professional Staff at The Johns Hopkins Applied Physics Laboratory. His research focuses on laser-material interactions for advanced processing and materials characterization including ultrafast studies of nanoscale thermal and acoustic transport, polymer matrix nanocomposite processing and characterization, optical and ultrasonic characterization of additively-manufactured materials, development of opto-thermal barrier coatings and characterization of high-energy laser materials. He is a member of ASME, IEEE, Optica, MRS and APS.

Authors:

James Spicer Johns Hopkins University
Cristian Contescu Johns Hopkins University
Jose David Arregui-Mena Oak Ridge National Laboratory
Lianshan Lin Oak Ridge National Laboratory
Ellen Berry Johns Hopkins University
Nidia Gallego Oak Ridge National Laboratory