Eutectic bonding of a Ti sputter coated, carbon aerogel wafer to a Ni foil Page: 4 of 15
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1. INTRODUCTION
The nanometric size pores characteristic of aerogel materials leads to corresponding
physical features of high porosity, a large surface area to mass ratio, and low density. For
example, a bulk density of a carbon aerogel less than 0.1 g cm-3 is routinely attainable.
The high porosity of aerogel materials makes them excellent thermal insulators with
conductivities (~10-2 W m-1 K-1) two orders of magnitude below the equivalent fully dense
solid. Recent investigation of the electrical conductivity (-1 5-1 cm-1) of monolithic carbon
aerogels[l1 has lead to the potential application of carbon aerogel wafers in energy storage
devices[21.
A prototype for a high ouput, energy storage device is an electrochemical double layer
capacitor (EDLC).[2] Since capacitance is proportional to surface area, only
electrochemically inert materials of the highest specific surface area can be used to make
rechargeable EDLCs. Aerogel wafers have large surface areas (-~102 m2 cm-3) which
account for demonstrated capacitances of 35 F cm3 and small bulk densities (<1 g cm-3)
that permit stored energy to be rapidly released yielding high power densities. An EDLC
which consists of carbon aerogel layers (used for the battery electrodes) separated by an
electrolyte wetted microporous glass can yield power densities greater than 5 kW kg-1. Ni
mesh or foil serves as a low resistance contact to the power cell. Power densities can be
increased by decreasing the thickness of the aerogel and microporous separator. Among
the factors which can further improve performance is the reduction of internal resistance.
This can be accomplished, for example, by improving the surface contact at the Ni-aerogel
interface.[3]
To fabricate a capacitor, a bonding scheme must be devised to join the contact layer (as
the Ni foil) to the carbon aerogel wafer. The productive use of conductive epoxies as an
effective joining medium has met with limited success since bond failure can be prevalent
during temperature cycling in service. In this study, a bonding procedure is developed2
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Jankowski, Alan Frederic; Hayes, J. P. & Kanna, R. L. Eutectic bonding of a Ti sputter coated, carbon aerogel wafer to a Ni foil, article, June 1, 1994; California. (https://digital.library.unt.edu/ark:/67531/metadc681394/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.