Composites of copper and graphene have been explored as a way to improve electrical conductivity, but researchers have not been successful at enhancing conductivity with a corresponding reduction in the temperature coefficient of resistance (TCR), and have not been able to find ways to make the composites at larger scales. The ability to synthesize enhanced-conductivity, low-TCR materials at scale could mean more efficient electrical machines and grid transmission. Scientists at Pacific Northwest National Laboratory (PNNL; Richland, Wash.; www.pnnl.gov) have taken a step in that direction by synthesizing copper-graphene composites using a PNNL-developed solids process known as shear-assisted processing and extrusion (ShAPE). The ShAPE process combines heating and physical deformation of the metal, and has been used to reduce costs for making high-strength aluminum alloys (Chem. Eng., September 2022, p. 11).
By adding 18 parts per million (ppm) graphene to copper 11000 alloy (a widely used metal for current-carrying hardware) using ShAPE, the PNNL researchers produced composites with an 11% reduction in TCR with improved conductivity in bulk-scale wires (1.5 mm dia.; 0.2-m length).
The ShAPE solids-processing technique used to extrude the composite wire leads to a “uniform, near pore-free microstructure, punctuated with tiny flakes and clusters of graphene that may be responsible for decreasing coefficient of resistance of the composite,” the PNNL team says. Both flakes and clusters must be present to make better conductors for high-temperature operations, they add.
The study “demonstrates the potential of ShAPE for producing bulk-scale industrially viable [copper-graphene] composites with lower TCR, as well as improved electrical conductivity,” PNNL says. The work was published in the January 2024 issue of Materials & Design.