No abstract

Carbon/carbon-composite bipolar plates for proton exchange membrane fuel cells (PEMFC) have been fabricated by slurry molding a chopped-fiber preform followed by sealing with chemically vapor-infiltrated carbon. The resulting component is hermetic with respect to through-thickness leakage and has a high electronic conductivity (200-300 S/cm) as a result of the deposited graphitic carbon. The material has a low density (0.96 g/cm 3 ) due to retained porosity resulting in a low-weight component. Biaxial flexure strength was measured to be 175 Ϯ 26 MPa. Cell testing of a 100 cm 2 active area, single-sided plate indicated very low cell resistance and high efficiency, but with a somewhat steep drop-off in voltage with current at high values. Corrosion testing indicated minimal corrosion in fuel cell environments.

This report details the continued investigation of process variables involved in converting sol-gel-derived, urainia-carbon microspheres to ~820-µm-dia. UN fuel kernels in flow-through, vertical refractory-metal crucibles at temperatures up to 2123 K. Experiments included calcining of air-dried UO 3-H 2 O-C microspheres in Ar and H 2-containing gases, conversion of the resulting UO 2-C kernels to dense UO 2 :2UC in the same gases and vacuum, and its conversion in N 2 to in UC 1-x N x. The thermodynamics of the relevant reactions were applied extensively to interpret and control the process variables. Producing the precursor UO 2 :2UC kernel of ~96% theoretical density was required, but its subsequent conversion to UC 1-x N x at 2123 K was not accompanied by sintering and resulted in ~83-86% of theoretical density. Decreasing the UC 1-x N x kernel carbide component via HCN evolution was shown to be quantitatively consistent with present and past experiments and the only useful application of H 2 in the entire process.

This report details the continued investigation of process variables involved in converting sol-gel-derived, urania-carbon microspheres to ~820-μm-dia. UC 1-x N x fuel kernels in flow-through, vertical Mo and W crucibles at temperatures up to 2123 K. Experiments included calcining of air-dried UO 3 -H 2 O-C microspheres in Ar and H 2 -containing gases, conversion of the resulting UO 2 -C kernels to dense UO 2 :2UC in the same gases and vacuum, and its conversion in N 2 to UC 1-x N x (x = ~0.85). The thermodynamics of the relevant reactions were applied extensively to interpret and control the process variables. Producing the precursor UO 2 :2UC kernel of ~96% theoretical density was required, but its subsequent conversion to UC 1-x N x at 2123 K was not accompanied by sintering and resulted in~83-86% of theoretical density. Increasing the UC 1-x N x kernel nitride component to ~0.98 in flowing N 2 -H 2 mixtures to evolve HCN was shown to be quantitatively consistent with present and past experiments and the only useful application of H 2 in the entire process.

A carbon composite bipolar plate for PEM fuel cells has been developed that has high electrical conductivity, high strength, light weight, is impermeable, and has the potential for being produced at low cost. The plate is produced by slurry molding short carbon fibers into preform structures, molding features into the green body, and using chemical vapor infiltration to strengthen the material, give it high conductivity, and densify the surface to make it impermeable. Current efforts have focused on optimizing the fabrication process and characterizing prototypical components.