Muon radiography is a promising technique to image the internal density structures upto a few hundred meters scale, such as tunnels, pyramids and volcanos, by measuring the flux attenuation of cosmic ray muons after trvaling through these targets. In this study, we conducted an experimantal cosmic ray muon radiography of the Wudalianchi volcano in northeast China for imaging its internal density structures. The muon detector used in this study is made of plastic scintillator and silicon photomultiplier. After about one and a half month observation for the Laoheishan volcano cone in the Wudalianchi volcano, from September 23rd to November 10th, 2019, more than 3 million muon tracks passing the data selection criteria are obtained. Based on the muon observations and the high-resoluiton topography from aerial photogrammetry by unmanned aerial vehicle, the relative density image of the Laoheishan volcano cone is obtained. The experiment in this study is the first muon radiography of volcano performed in China, and the results suggest the feasibility of radiography technique based on plastic scintillator muon detector. As a new passive geophysical imaging method, cosmic ray muon radiography could become a promising method to obtain the high-resoution 2-D and 3-D density structures for shallow geological targets.
To cite this version:Ahmed Fakhry, Hubert Cachet, Catherine Debiemme-Chouvy. Mechanism of formation of templateless electrogenerated polypyrrole nanostructures. Electrochimica Acta, Elsevier, 2015, 179, pp.297-303 AbstractIn the presence of a high concentration of weak-acid anions, such as monohydrogenophosphate which confer to a pyrrole aqueous solution a pH around 9, an ultra thin non-conductive overoxidized polypyrrole film is deposited on the electrode under an anodic polarization. In the same experimental conditions, after addition of perchlorate anions (C > 0.5 mM) in the pyrrole solution the electrooxidation of the monomers leads to the synthesis of a superhydrophilic nanostructured conductive polypyrrole film (network of nanofibers or oriented nanowires, 50-120 nm in diameter).The aim of the present paper is to confirm the mechanism that we have previously proposed and so to explain the spontaneous nanostructuration of the electrogenerated polypyrrole films. We have assumed that this templateless formation of nanostructures is notably due to the oxidation of water with production of hydroxyl radicals and nanobubbles of dioxygen. Due to the fact that pyrrole polymerization is associated to the release of protons, we have first verified that the electrode/solution interfacial pH is compatible with the water oxidation potential. For this purpose, during the monomer oxidation the interfacial pH variation has been monitored using a pH electrode having a flat glass membrane which was covered with a Pt grid used as the working electrode. Secondly, the presence of dioxygen nanobubbles has been indirectly confirmed by rotating the working electrode. Indeed rotation of the electrode allows eliminating the nanobubbles present inside the polypyrrole film. For the highest rotation speed tested (94 rad s -1 ), a very thin overoxidized film was electrogenerated. Our results are in good agreement with the fact that the nanobubbles protect the PPy film against the action of the hydroxyl radicals which react with the polypyrrole film leading to its overoxidation.
Different superhydrophilic polypyrrole nanostructures can be electrosynthezised in the presence of anions of weak acid (monohydrogenophosphate) and non-acidic anions (perchlorate) without the need for templates. Actually the type of nanostructures formed depends both on the concentration of anions at the electrode and on the interfacial pH. Depending on the anion composition of the pyrrole aqueous solution the film electrogenerated under a given applied potential is either a very thin membrane (10-20 nm) consisting of overoxidized polypyrrole or a tridimensional film with oriented nanowire array or a network of more or less interconnected nanofibers. The formation of such nanostructures is explained by a side reaction which is water oxidation. Since this reaction is pH-dependent, the pH of the pyrrole solution is one of the key parameter for the synthesis of such nanostructures. The reaction mechanism is discussed and compared to those proposed in the literature for nanofiber network electrosynthesis.Actually in the monomer solution, the role of the anions of weak acid is twofold. On the one hand they allow to limit the decrease of the interfacial pH during pyrrole oxidation and on the other hand to decrease the interfacial anion concentration, so that water oxidation takes place with formation of hydroxyl radicals and dioxygen nanobubbles.
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