BYLINE: Karin Heade, Pacific Northwest National Laboratory
Newswise – RICHLAND, Wash. — A compound of ordinary carbon affords an excellent improvement in the proper proportion with copper for the manufacture of electric wires. It's a phenomenon that defies conventional wisdom about how metals conduct electricity. conclusions, reported in the December 2023 journal Materials and design, could lead to more efficient distribution of electricity in homes and businesses, as well as more efficient motors to power electric vehicles and industrial equipment. The team filed a patent for the work, which was supported by the Department of Energy's (DOE) Office of Advanced Materials and Manufacturing Technologies.
Materials scientist Keerti Kapagantula and his colleagues DOE Pacific Northwest National Laboratory They discovered that graphene, the same individual layers of graphite found in pencils, can enhance an important property of metals called the temperature coefficient of resistance. This property explains why metal wires heat up when an electric current passes through them. Researchers want to reduce this resistance and enhance the metal's ability to conduct electrical current. For several years, they have been asking whether the conductivity of a metal can be increased, especially at high temperatures, by adding other materials to it. And if so, could these composites be viable on a commercial scale?
Now they have shown that they can do this by using a A PNNL-patented advanced manufacturing platform called ShAPE™. When the research team added 18 parts per million of graphene to electrical-grade copper, the temperature coefficient of resistance decreased by 11 percent, without reducing electrical conductivity at room temperature. This is relevant to the production of electric cars, where an 11 percent increase in the electrical conductivity of a copper wire winding means a 1 percent increase in motor efficiency.
“This finding contradicts what is generally known about the behavior of metals as conductors,” Capagantula said. “Typically, adding additives to a metal increases its temperature coefficient of resistance, meaning it heats up faster at the same current level than pure metals. We describe a new and interesting property of this metal composite, where we observe enhanced conductivity in the produced copper wire.
Microstructure is the key to graphene reinforcement
Formerly a research group performed detailed structural and physics-based computational studies Explanation of the phenomenon of enhancement of electrical conductivity of metals using graphene.
In this study they showed that Solid phase processing used to spin the composite wire leads to a uniform, pore-free microstructure interspersed with tiny flakes and clusters of graphene, which may be responsible for the reduction in the resistivity of the composite.
“We showed that flakes and clusters both need to exist to make better conductors for high-temperature operations,” Capagantula said.
Co-authors Bharat Gwalani, Xiao Li and Aditya Nittala took advantage of a PNNL-developed testbed that measures electrical properties with high precision and accuracy to confirm the improved conductivity, which is reflected in the team's detailed experimental analysis. Lee and Dr. Reza-e-Rabi developed tooling and machining envelopes for the solid-phase friction extrusion process that led to the patent.
Towards more efficient copper motors and urban building wiring
According to the research team, when used in any industrial application, the new copper-graphene composite wires provide great design flexibility.
“Wherever there is electricity, we have a utility,” Capagantula said.
For example, coiled copper wire forms are used in the core of electric motors and generators. Motors today are designed to operate within a limited temperature range because when they get too hot, electrical conductivity drops dramatically. With the new copper-graphene composite, motors can potentially operate at high temperatures without losing conductivity.
Likewise, the wiring that brings electricity from transmission lines into homes and businesses is typically made of copper. As the population density of cities increases, so does the demand for electricity. Composite wire, which is more conductive, could potentially help meet this demand with efficiency savings.
“This technology is a wonderful solution for copper wiring in high-density urban environments,” added Capagantula.
The research team continues to work on tailoring the copper-graphene material and measuring other essential properties such as strength, fatigue, corrosion and wear resistance – all of which are critical for industrial applications of such materials. For these experiments, the research team produces wires that are about the thickness of a penny (1.5 millimeters).
Other PNNL contributors to this study include Wongjo Choi, Julian Escobar Atehortua, Arun Bhattacharjee, Mayur Pole, Joshua Silverstein, and Miao Song. This research was supported by the DOE Office of Energy Efficiency and Renewable Energy, Advanced Materials and Manufacturing Technologies Office, and the Bandwidth-Enhanced Materials for Affordable, Breakthrough Electrical and Thermal Applications (CABLE) initiative, which supports U.S. manufacturers seeking to innovate materials and applications that support Grid reliability and other electrical and thermal energy systems.