Effect of ball milling in a tumbling ball mill on the properties of multi-wall carbon nanotubes

The effects of ball milling on various properties of ground multi-wall carbon nanotubes were studied. These properties were granulometry, SEM,specific surface area, density, crystalline structure, surface chemical analysis and thermogravimetry. The mean size of agglomerates, initially at 35 m, decreases to reach a limit value of 2.5m, corresponding to a competition between agglomeration and fragmentation. A kinetic study,based on a decomposition of size distributions measured for different times, has permitted to propose a grinding mechanism. As grinding proceeds, the specific surface area first increases from 175 to 244m2 g−1 and then decreases, while the real density increases from 1800 to 2150 kgm−3 to level off at 2070 kgm−3. Moreover, macroporosity disappears totally, giving access first to mesoporosity and then to microporosity. The nanotubes are probably cut to give access to the internal porosity. An increase of the proportion of oxygen adsorbed on carbon (from 3% to 8.7% after 600 min grinding) implies that it may be possible to functionalise the nanotubes. Thanks to these different morphological changes numerous applications of ground nanotubes can be considered. Moreover, the use of a tumbling ball mill allows a massive production of cut nanotubes

Matrix-filler interactions in a co-ground ecocomposite: surface properties and behaviour in water

Ecocomposites made up of polystyrene and starch were produced by co-grinding. The mechanism by which the composite is formed was identified by following the particle size and morphology. The size reduction of the matrix particles is favoured by the presence of starch which adheres on polystyrene surface, playing the role of agglomeration inhibitor between matrix particles. Thus, the filler is well dispersed in the matrix, permitting a good homogeneity of the composite properties. The hydrophilic behaviour of starch is reduced by co-grinding, resulting of a decrease of the acid and non dispersive components of the surface energies. Consequently the interactions between the initially hydrophobic matrix and hydrophilic filler are enhanced without using a compatibilizer. Thus, the water-resistance of the co-ground composite materials is better compared to blends since blends pellets introduced in water are rapidly disintegrated while an adapted co-grinding time permits to avoid this problem. It was seen that the diffusion coefficient of water in the composite pellets decreases with an increase of the co-grinding time for the lower filler rates, while it is the opposite for high filler rates. Moreover, the diffusion coefficient increases with the filler ratio

On the interest of using degradable fillers in co-ground composite materials

The article presents the results of a study whose objective is to show the interest of using vegetable and biodegradable fillers in composite materials. The incorporation of fillers made up of starch in the synthetic polymeric matrix was carried out by co-grinding, a process supporting the dispersion of one component in another one and thus supporting the homogeneity of the composite properties. The follow-up of the particle size and morphology has permitted to identify how the composite is formed. We could note that co-grinding makes it possible to improve the mechanical properties of the composite material, not only through a better dispersion of the filler in the matrix, but also thanks to a modification of the interface properties. Finally a study on the material degradation in water has shown that the incorporation of a vegetable, degradable and cheap filler in the synthetic matrix and the application of co-grinding during an adapted time offer interesting water-resistant properties

Disentangling Mining and Migratory Routes in West Africa: Decisions to Move in Migranticised Settings

This article scrutinizes the trajectories of African men whose cross-border movements intersect two types of mobility routes: mining and migration routes. Drawing on field research in Mali and Guinea, as well as phone interviews with male miners/migrants in North Africa and Europe, this article provides a case to empirically question some of the premises in the approach to migration decision-making by giving a voice to African men moving across borders who do not necessarily identify as (prospective) ‘migrants.’ Building upon International Organization for Migration data and secondary sources, this article starts by sketching where migration and mining routes overlap. It then examines, in detail, the mobility trajectories of men who were sometimes considered migrants and other times miners in order to identify how these different routes relate to one another. While overseas migration is certainly not a common project for itinerant miners, the gold mines constitute a transnational space that fosters the expansion of movements across the continent, including outside the field of mining. Rather than encouraging overseas migration, gold mines appear to be more of a safety net, not only for seasonal farmers or young people in search of money and adventure, but also, increasingly, for people who are confronted with Europe’s intra-African deportation regime

Effect of viscosity on the cetane number of a diesel fuel

The object of this paper is to determine or rather experimentally establish the effect of a change in viscosity of a given diesel oil in regard to the ignition quality (cetane rating) of the oil. The author did not attempt to prove why or find out how much the cetane number was affected. But, merely, tried to experimentally verify the fact that the cetane number of the fuel used underwent a change when its viscosity was decreased by preheating it. Since his professional interests lie in the field of automotive engineering, several thesis problems were suggested to him by Dr. A. J. Miles, Chairman of the Mechanical Engineering Department, all to be investigated on the C.F.R. gasoline and diesel test engines. Originally “sensitivity” was taken as a thesis problem, for it was a fairly new subject not explored intensively. But later the facilities in the laboratory and the fact that diesel research is still a wide open field led the author to carry his experiments on the C.F.R. diesel testing engine. The author\u27s original idea was to investigate a diesel fuel in regard to a simulation of “sensitivity” as established for the octane numbers of gasolines. He chose, as a first step in doing so, to investigate the relation the fuel viscosity would have on the cetane rating. Up to 1930 not much research work had been carried out on diesel engines and especially on diesel fuel oils. The following decade, since the tendency toward increasing the speeds of diesel engines had caused them to become more sensitive to fuels and research on the latter had brought out the importance of ignition quality, research work was carried out to standardize a method of test by which diesel fuels could be rated. The importance of ignition quality and viscosity was first recognized by Mr. H. R. Ricardo and attempt in research in this respect was stressed by him --Introduction, pages 1-2

Co-grinding significance for calcium carbonate–calcium phosphate mixed cement. Part I: effect of particle size and mixing on solid phase reactivity

In part I of this study we aim to evaluate and control the characteristics of the powders constituting the solid phase of a vaterite CaCO3–dicalcium phosphate dihydrate cement using a co-grinding process and to determine their impact on cement setting ability. An original methodology involving complementary analytical techniques was implemented to thoroughly investigate the grinding mechanism of separated or mixed reactive powders and the effects on solid phase reactivity. We showed that the association of both reactive powders during co-grinding improves the efficiency of this process in terms of the particle size decrease, thus making co-grinding adaptable to industrial development of the cement. For the first time the usefulness of horizontal attenuated total reflection Fourier transform infrared spectroscopy to follow the chemical setting reaction at 37°C in real time has been demonstrated. We point out the antagonist effects that co-grinding can have on cement setting: the setting time is halved; however, progress of the chemical reaction involving dissolution–reprecipitation is delayed by 30 min, probably due to the increased contact area between the reactive powders, limiting their hydration. More generally, we can take advantage of the co-grinding process to control powder mixing, size and reactivity and this original analytical methodology to better understand its effect on the phenomena involved during powder processing and cement setting, which is decisive for the development of multi-component cements

Production of a diluted solid tracer by dry co-grinding in a tumbling ball mill

This paper presents a study on the production by co-grinding of a diluted solid tracer, sized less than 10 mm and containing less than 2 wt. % of active product, used in the field of grounds contamination and decontamination. Co-grinding was performed in a tumbling ball mill and permits to produce easily a diluted tracer without implementing several apparatus. The two products were ground separately first and then together. The follow-up of the particles size and morphology, as well as the modelling of the grinding kinetics have permitted to propose a mechanism by which the diluted solid tracer is produced. The influence of the operating conditions (nature and initial size of the diluting medium, ball and powder filling rates, proportion of the polluting tracer) on products grinding was studied. Thus, we have defined optimum co-grinding conditions permitting to produce a tracer offering the required properties. These ones are classical for tumbling ball mills. This kind of mill is very interesting since its sizes can easily be extrapolated to answer to an industrial demand