Isochronal annealing kinetics and neutron-induced dimensional changes of titanium-doped pyrolytic carbons

Abstract

A series of isochronal 1 hr anneals was conducted on a laminar pyrolytic carbon deposited at 1225°C containing 6.7 wt.% titanium, an isotropic pyrolytic carbon deposited at 2200°C containing 9.7 wt.% titanium, and titanium-free companion carbons. Changes in layer spacing, apparent crystallite height ( L c ), density, electrical resistivity, and microhardness were followed. Heterogeneous recrystallization to graphite started in the titanium-doped isotropic carbon at 2300°C and was completed at 2500°C. The titanium-doped laminar carbon did not show catalytic recrystallization. The undoped isotropic carbon was not responsive to annealing. The titanium-doped and titanium-free laminar carbons showed a steady increase in L c and density and a steady reduction in layer spacing and microhardness over a temperature range from 1400° to 2800°C, but significant reduction in electrical resistivity did not begin until ~ 1800°C. The dimensional changes induced by fast-neutron exposures up to ~ 8 × 10 21 n/ cm 2 at ~ 600°C to 1250°C were measured and found to be lower by a factor of 3–10 in a catalytically graphitized pyrolytic carbon than in an as-deposited carbon with the same degree of preferred orientation.