CHEMICAL VAPOUR DEPOSITION GROWTH OF 3D POROUS GRAPHENE-COPPER FOAM

Abstract

Porous copper foams have become an area of particular interest for academia and industry alike owing to their mechanical stability, high surface area to volume ratio, high porosity and low density, while exhibiting the electrical and thermal properties of graphene which enable applications in heat dissipation. This work presents for the first time the powder metallurgy spacer method for the tuning of porosity of sintered copper-graphene foams. It is important in industry to be able to fine tune the structural characteristics of the porous copper heat sinks in order to modulate the heat flow for different scenarios. For example, in a setup with active cooling and forced convection, a highly porous foam with small pore size and maximum cooling rate can be used. However, in passive situations, where air is not forcibly flowing through the foam, it is important to have larger pore sizes such that air won't get trapped within the sample and negatively affect cooling. This work presents a new technique for the manufacture of tuneable porosity graphene-coated copper foams and investigates the effect of changing the porous structure of the foams on their electrical and thermal characteristics. Finally, this work evaluates graphene-copper foams (GCFs) performance as heat transfer devices against industry standards. GCFs are fabricated with porosities between 40 - 95% , tuneable by varying the loading and size of sacrificial spacer particles within the copper powder matrix onto which CVD graphene is deposited. In varying the structural characteristics of the GCF, the thermal conductivity is demonstrated to be porosity-dependent and ranges from 50 - 150 Wm-1K-1, comparable to copper foams at much lower porosities in literature. In addition, a 35 - 50 % increase in thermal conductivity is observed with monolayer graphene deposited on the surface of the copper foams compared to the same porosity foams without graphene. Similarly, the electrical conductivity of the GCFs can be controlled by altering spacer parameters, with conductivity ranging from 1.1- 3.9 x10^6 S m-1, an order of magnitude greater than reported for self-supporting graphene foams in literature. A 30 % increase (at low loadings) in electrical conductivity is observed for GCFs with monolayer graphene deposited on the surface compared to bare copper foams of the same physical structure. This work defines a method to selectively tune the porosity of sintered copper foams, during the CVD growth process, using sacrificial spacer powder metallurgy method. This demonstration of tuneability represents the main contribution of this work to the field, paving the way for precise GCF structural modification to optimise physical parameters for different thermal applications.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ian Kinloch (Supervisor) & Mark Bissett (Supervisor)