Calcium passivation and properties of Al/Ca composite conductors
Light, strong, high-conductivity materials are desirable for overhead power transmission and distribution conductors. An aluminum/calcium composite with nanofilamentary reinforcement was produced by powder metallurgy and deformation processing to fine wires. Upon achieving the desired dimension, the wires were heat treated to convert the calcium to Al2Ca intermetallic reinforcement filaments. Extended heat treatments were used to evaluate the upper operating temperature of the material. The processing steps, microstructure, conductivity, and tensile strength of Al/Ca composites were evaluated. The measured properties indicate that the number of support towers required for a HVDC transmission line can be reduced by more than 23% when using Al/Ca composite conductors. The properties of this material can be tailored to specific applications by modifying parameters during production. The lack of availability of fine calcium powder necessary to produce Al/Ca composites of sufficient strength is a barrier to their development. A method for protecting Ca surfaces from moisture in the environment was studied to enable its safe production. Preliminary experiments identified a fluorine containing compound that could be introduced in a gaseous stream and passivate Ca. This compound was implemented into a gas atomizer to protect Ca during production and limit exposure of bare metal to atmospheric conditions. Atomization parameters were evaluated, and powder was characterized for size distribution, surface chemistry, and flammability indicating that passivation treatments were successful.