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.
Finite Element Model of a Bilayered Gold-Coated Carbon Nanotube Composite Surface
Vertically aligned multiwalled carbon nanotubes (MWCNTs), with a gold (Au)-coated surface, have been shown to provide a stable contact resistance for electrical contact switching applications under low force conditions (micronewton to millinewton), with the MWCNT surface providing a compliant support for the conducting Au layer. In this paper, nanoindentation results are used in the development of a finite element contact model for the composite, referred to as Au/CNT. The results show that the surface is best modeled as a bilayered structure, in which the top layer is modeled as an elastic-plastic layer of the Au/CNT mixed material and the under layer as a CNT forest. The resultant model matches the experimental results for a range of samples with different thickness configurations.
Characterization of ceramic composite membrane filters for hot gas cleaning
Abstract Novel composite ceramic membrane filters suitable for hot gas cleaning operations have been prepared from fly ash and titania particles on stainless steel woven mesh substrates. Both membranes had a structure like a solid packed bed with a thickness of less than 100 μm. In the domain of laminar flow, significant differences in the pressure drop between experimental results and those predicted from the Kozeny-Carman relationship were found, particularly for flow through the titania membrane. Membrane filters with extremely small pores such as the titania membrane are greatly affected by slip up to 80% in permeability at elevated temperatures. Efficiencies of filtration of typical coal fired power station exhaust fly ashes were found to be greater than 909% for both titania and ash membranes, whilst there was greater variation in the pressure drops in the ash membrane than in the titania at typical gas flows.