NSUF 18-1157: Understanding the mechanism for mesopore development in irradiated graphite by high resolution gas adsorption measurements (N2 and Kr at 77 K)
High resolution gas adsorption (N2 and Kr) at 77 K will be used to characterize the structural and energetic homogeneity of pore surfaces in three types of graphite specimens irradiated before and after turnaround. Prior NSUF-supported research showed that irradiation after turnaround induces significant development of mesopores (2-50 nm) simultaneously with an increase of internal BET surface and open porosity. However, the mechanism of these changes is still not completely understood. The goal is to determine whether or not new the new pores are limited by homogeneous surfaces (basal planes in graphite crystallites) or by rough, disordered surfaces (edge sites, possibly in the binder). To that end we will use high resolution gas adsorption (N2 and Kr) at 77 K to obtain information on structural and energetic uniformity of graphite surfaces. It is known that sub-monolayer adsorption of N2 and Kr is very sensitive to the underlying surface structure. Adsorption isotherms at 77 K show distinct phase changes at surface corresponding to completion of ordered (commensurate) layers of Kr or N2 on the ordered graphite basal planes. Moreover, Kr adsorption in multilayers continues with distinct steps characteristic to layer-by-layer adsorption, which is a clear indication for presence of structurally homogeneous surface sites. These features will be used to estimate the fraction of basal planes in the total (BET) surface area. By comparing with the features of the non-irradiated graphite it will be possible to determine whether or not porosity changes observed for graphite irradiated after turnaround are caused by delamination of graphite crystallites and exposure of new basal planes. In addition to clarifying some of the microstructural changes induced by irradiation, the success of this project will demonstrate the viability of a new method for quantification of basal plane and edge sites surfaces in graphite materials. This is important for normalization of other graphite properties that depend on microstructure, such as intrinsic oxidation reactivity, which preponderantly involve edge (prismatic) sites of graphite crystallites. The work proposed consists of collecting a series of N2 and Kr adsorption isotherms (with at least 150 point each) on 8 graphite specimens irradiated at various doses, before and after turnaround. The graphite irradiated from the HTV and Deep Burn campaigns at ORNL is stored in LAMDA. We propose to measure 2 irradiated specimens of fine grain, iso-pressed graphite 2114 (Mersen, France), 4 irradiated specimens of medium grain, extruded graphite PCEA (Graftech, USA) and 2 irradiated specimens of large grain, vibro-molded graphite NBG-18 (SGL, Germany). Three more un-irradiated specimens will serve as reference. The total time for completing the project, including measurements and data analysis, is estimated at 4 months. At the end of the project the results will be prepared for publication.
Additional Info
| Field | Value |
|---|---|
| Abstract | High resolution gas adsorption (N2 and Kr) at 77 K will be used to characterize the structural and energetic homogeneity of pore surfaces in three types of graphite specimens irradiated before and after turnaround. Prior NSUF-supported research showed that irradiation after turnaround induces significant development of mesopores (2-50 nm) simultaneously with an increase of internal BET surface and open porosity. However, the mechanism of these changes is still not completely understood. The goal is to determine whether or not new the new pores are limited by homogeneous surfaces (basal planes in graphite crystallites) or by rough, disordered surfaces (edge sites, possibly in the binder). To that end we will use high resolution gas adsorption (N2 and Kr) at 77 K to obtain information on structural and energetic uniformity of graphite surfaces. It is known that sub-monolayer adsorption of N2 and Kr is very sensitive to the underlying surface structure. Adsorption isotherms at 77 K show distinct phase changes at surface corresponding to completion of ordered (commensurate) layers of Kr or N2 on the ordered graphite basal planes. Moreover, Kr adsorption in multilayers continues with distinct steps characteristic to layer-by-layer adsorption, which is a clear indication for presence of structurally homogeneous surface sites. These features will be used to estimate the fraction of basal planes in the total (BET) surface area. By comparing with the features of the non-irradiated graphite it will be possible to determine whether or not porosity changes observed for graphite irradiated after turnaround are caused by delamination of graphite crystallites and exposure of new basal planes. In addition to clarifying some of the microstructural changes induced by irradiation, the success of this project will demonstrate the viability of a new method for quantification of basal plane and edge sites surfaces in graphite materials. This is important for normalization of other graphite properties that depend on microstructure, such as intrinsic oxidation reactivity, which preponderantly involve edge (prismatic) sites of graphite crystallites. The work proposed consists of collecting a series of N2 and Kr adsorption isotherms (with at least 150 point each) on 8 graphite specimens irradiated at various doses, before and after turnaround. The graphite irradiated from the HTV and Deep Burn campaigns at ORNL is stored in LAMDA. We propose to measure 2 irradiated specimens of fine grain, iso-pressed graphite 2114 (Mersen, France), 4 irradiated specimens of medium grain, extruded graphite PCEA (Graftech, USA) and 2 irradiated specimens of large grain, vibro-molded graphite NBG-18 (SGL, Germany). Three more un-irradiated specimens will serve as reference. The total time for completing the project, including measurements and data analysis, is estimated at 4 months. At the end of the project the results will be prepared for publication. |
| Award Announced Date | 2018-02-01T14:11:32.367 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Kory Linton |
| Irradiation Facility | None |
| PI | James Spicer |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1157 |