The onset of cracking during drying of alumina suspensions cast onto a substrate has been studied experimentally. It is shown that the capillary pressure would impose a compressive stress on the particle array and cannot itself cause cracking. Based on experimental observations, it is proposed that the driving force for cracking arises from a misfit strain that occurs when repulsive layers between the particles collapse completely, after the particles have adhered to the substrate. This predicts that cracking should occur while the space between the particles is still filled with liquid, which is consistent with observations using laser speckle interferometry.
Catalytic decomposition of methane has been used to grow bamboo-structured carbon tubes at temperatures ranging from 1233 K to 1291 K. No tube growth was observed at temperatures less than 1233 K, whilst above 1291 K pyrocarbon was the dominant product. It is shown that the average size of the copper catalyst particles was influenced by the reaction temperature, with the reciprocal of the maximum size of the copper particle decreasing linearly with temperature. This is consistent with the idea that the melting point can be reduced by surface energy effects. Observations show that under the conditions here the catalyst particle penetrates into the carbon fibre and a mechanism is proposed for development of the bamboo structure based upon the energy changes that take place.
The ability of directed streams of three representative hydrocarbon gases ‐ acetylene C2H4, ethylene C2H4, and ethane C2H6 ‐ to provide extended‐duration lubrication to high‐temperature sliding contacts via surface deposition of pyrolytic carbon has been demonstrated. One order‐ and two order‐of‐magnitude reductions in friction coefficient and wear rate of self‐mated silicon nitride sliding contacts can be realised by this technique. The ability of these gases to provide ‘adequate’ lubrication at high temperature is illustrated through mapping the normal load/temperature/precursor flow rate space over which reduced friction may be maintained. Acetylene was the most effective precursor for pyrolytic carbon deposition, providing adequate lubrication over the broadest range of normal load/temperature/flow rate combinations, while ethane was the least effective. The boundary of the regions of adequate lubrication represents the locus of contact conditions with equal rates of lubricious carbon deposition and removal by wear. The shape of this boundary, as explored in the mapping study, supports a proposed model in which the removal rate is proportional to the product of normal load and sliding speed, while the deposition rate is proportional to the product of precursor flow rate and an Arrhenius temperature dependence.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.