1 research outputs found
Copper-Based Conductive Composites with Tailored Thermal Expansion
We have devised a moderate temperature
hot-pressing route for preparing metal–matrix composites which
possess tunable thermal expansion coefficients in combination with
high electrical and thermal conductivities. The composites are based
on incorporating ZrW<sub>2</sub>O<sub>8</sub>, a material with a negative
coefficient of thermal expansion (CTE), within a continuous copper
matrix. The ZrW<sub>2</sub>O<sub>8</sub> enables us to tune the CTE
in a predictable manner, while the copper phase is responsible for
the electrical and thermal conductivity properties. An important consideration
in the processing of these materials is to avoid the decomposition
of the ZrW<sub>2</sub>O<sub>8</sub> phase. This is accomplished by
using relatively mild hot-pressing conditions of 500 °C for 1
h at 40 MPa. To ensure that these conditions enable sintering of the
copper, we developed a synthesis route for the preparation of Cu nanoparticles
(NPs) based on the reduction of a common copper salt in aqueous solution
in the presence of a size control agent. Upon hot pressing these nanoparticles
at 500 °C, we are able to achieve 92–93% of the theoretical
density of copper. The resulting materials exhibit a CTE which can
be tuned between the value of pure copper (16.5 ppm/°C) and less
than 1 ppm/°C. Thus, by adjusting the relative amount of the
two components, the properties of the composite can be designed so
that a material with high electrical conductivity and a CTE that matches
the relatively low CTE values of semiconductor or thermoelectric materials
can be achieved. This unique combination of electrical and thermal
properties enables these Cu-based metal–matrix composites to
be used as electrical contacts to a variety of semiconductor and thermoelectric
devices which offer stable operation under thermal cycling conditions