Thermal conductance of augmented pressed metallic contacts at liquid helium temperatures

The thermal conductance of uncoated OFHC copper, 6061-T6 aluminium, free-machining brass and 304 stainless steel sample pairs which have been augmented with a gold coated 6061-T6 aluminium washer inserted between the contact surfaces has been measured over the temperature range 1.6–6.0 K, with applied forces from 22 to 670 N. The contact surfaces of the sample pairs were prepared with a 0.8 μm lapped finish, while the finish of the aluminium washer was 0.2 μm lapped. The contribution to the overall thermal impedance of the bulk conductance of the aluminium washer was negligible. It was found that conductance increased with both force and temperature; however, addition of the washer offered no significant conductance improvement over an uncoated single contact pair, any benefits from the gold plated washer being used to counteract the addition of two more contact surfaces. Additionally, the thermal conductance of a ‘combination’ aluminium sample pair having one gold coated and one uncoated surface was measured and compared to the augmented aluminium pair. The ratio of the conductance of the augmented aluminium pair to half the conductance of the ‘combination’ sample pair was found to be constant and near unity over the temperature range of the data obtained, within the limits of experimental error.