Electromechanical investigation into the influence of MWCNT height on the performance of Au/MWCNT composites for electrical contacts
Au/MWCNT composites have been shown to be a useful contact material for electrical contacts. In this work we have investigated the influence of the MWCNT forest height on both the electrical and mechanical properties. Three heights of MWCNT forest have been investigated (30, 50 and 80 μm, all a sputtered 500 nm Au layer). It is shown that the electrical and mechanical behavior of the 30 and 50 μm composites is quite comparable, whereas there is a large change in the performance where the height is increased to 80 μm. As the MWCNT height is increased the effective hardness of the composite reduces which means that for a given contact pressure, the resultant contact area will be larger for taller MWCNT forests. A larger area combined with a higher resilience to impact is expected to result in larger lifetimes. A consequence of the softer composite with larger contact area is that the molten-metal bridge phenomenon has been shown to increase with MWCNT height. Experimental data is discussed to identify the optimum MWCNT height where the sputtered Au thickness is 500 nm. By analyzing the Au:MWCNT thickness ratio, it is possible to infer the optimum value for other thickness of Au. Combining this data with our model, it is also possible to estimate optimum thicknesses with other contact materials.
The Effect on Switching Lifetime of Chromium Adhesion Layers in Gold-Coated Electrical Contacts under Cold and Hot Switching Conditions
Gold is commonly used for electrical contacts due to its many desirable electrical and mechanical properties. Throughout the switch lifetime, the contacts are required to survive a large number of opening and closing cycles and therefore it is important to understand the failure mechanisms. Adhesion layers (e.g. chromium or titanium) can be deposited to increase the adhesion of the gold layer to the contact surface. In this work, the inclusion of a chromium adhesion layer shows an improvement of the switching lifetime of gold-coated electrical contacts under cold and hot switching conditions. These testing conditions further the understanding of the failure mechanisms (e.g. fine transfer, etc.). The mechanism of failure when no chromium adhesion layer was used is attributed to delamination of the gold layer from one contact to the other. This failure mechanism is different in the cases where a chromium adhesion layer is included. We present a model which was developed in line with experimental results. These describe the effect of load current on material transfer between gold contacts and the contact failure.
The density of liquid silver from its melting point to its normal boiling point 2450°K
Abstract The density of liquid silver was determined, by the Archimedean principle, over the whole range from its melting point to its normal boiling point. It can be best expressed by the linear equation D (g/cm 3 ) = 10·465−9·067 × 10 −4 T∘K with a probable error of ±0·009 g/cm3. The density of liquid silver is 9·346 g/cm3 at its melting point (1234° K) and 8·244 g/cm3 at its normal boiling point (2450° K).