Abstract
We demonstrate a novel technique to achieve highly surface active, functional, and tunable hierarchical porous coated surfaces with high wickability using a combination of ball milling, salt-templating, and sintering techniques. Specifically, using ball-milling to obtain graphene nanoplatelets (GNP) draped copper particles followed by salt templated sintering to induce the strength and cohesiveness to the particles. The salt-templating method was specifically used to promote porosity on the coatings. A systematic study was conducted by varying size of the copper particles, ratio of GNP to copper particles, and process parameters to generate a variety of microporous coatings possessing interconnected pores and tunnels that were observed using electron microscopy. Pool boiling tests exhibited a very high critical heat flux of 289 W/cm2 at a wall superheat of just 2.2 °C for the salt templated 3 wt% GNP draped 20 µm diameter copper particles with exceedingly high wicking rates compared to non-salt-templated sintered coatings. The dramatic improvement in the pool boiling performance occurring at a very low surface temperature due to tunable surface properties is highly desirable in heat transfer and many other engineering applications.
Highlights
In the recent years, graphene-based composite coatings have been explored for their exceptional properties for various engineering applications such as corrosion protection[1,2,3], electronics systems[4,5,6,7], energy storage[8,9,10,11] and biomedical industries[12,13]
Ball milling process promoted a considerable reduction in the particle size and homogenous dispersion of graphene nanoplatelets (GNP) on the sintered coatings confirmed via electron microscopy
A novel sintering technique with salt templating was developed in this work to achieve a large spectrum of pore diameters ranging from a few microns to a few hundred microns
Summary
Graphene-based composite coatings have been explored for their exceptional properties for various engineering applications such as corrosion protection[1,2,3], electronics systems[4,5,6,7], energy storage[8,9,10,11] and biomedical industries[12,13]. Various surface modification techniques such as chemical vapor deposition16, electrodeposition17,18, sintering[19,20], and e lectroplating[21] can be adopted to form highly surfaceactive graphene-based coatings with unique surface features that can impart properties to further improve the heat dissipation rates and overall performance. Our previous studies indicate that surface wickability can dramatically improve the CHF and HTC by achieving very low wall superheats We demonstrated this through electrodeposited graphene/copper based composite coatings possessing hierarchical porous network and highly wickable structures that yielded remarkable improvement in pool b oiling[24]. This work presents a novel manufacturing approach to obtain surface active coatings via a combination of sintering, salt-templating, and ball milling techniques to yield graphene nanoplatelets (GNP)-draped-copper based sintered coatings. Salt templating may lead to tunable porous coatings with hierarchical pores which will allow a continuous passage of bubbles and liquid during the pool boiling process
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