Abstract:The production of H2 has been examined in the gamma-ray and 5 MeV He ion radiolysis of CaCl2.2H2O, CaCl2.6H2O, Ca(OH)2, MgCl2.2H2O, MgCl2.6H2O, and Mg(OH)2. The highest yield for the formation of H2 is observed in the gamma-radiolysis of MgCl2.2H2O (0.72 molecule/(100 eV), 75 nmol/J), but the yield decreases with dose due to the relative instability of the dihydrate. The H2 yields with the other compounds range from 0.04 to 0.2 molecule/(100 eV) (4.2-21 nmol/J), which is lower than that from pure water or 2 M … Show more
“…Apart from a signal increase, the formation of borate salts on the surface was discovered . Numerous publications attest that also chlorine compounds are decomposed by ionising radiation, including X‐rays . Urch detected chloride peak characteristics in L 2,3 ‐M spectra of various oxy‐chloro‐anions previously published by Henke and explained this as a result of sample decomposition because of irradiation.…”
Occasionally suggested yet rarely performed X-ray fluorescence (XRF) spectrometry of fluorine seems to fail systematically in yielding reliable quantitative results for rocks and soils. Repeated analyses reveal continuously drifting fluorescence intensities for fluorine, boron and chlorine. Typically, an increase, but in few cases also a decrease, over X-ray exposure time is observed. For instance, fluorine concentrations in a soil standard appear to increase steadily from below the detection limit in the first run to nearly 850 mg/kg F more than 10 h later in the last. In contrast, cryolite is characterised by drastically decreasing intensities for fluorine. Although fluorescence intensities may be affected by preparation methods, specimen surface conditions and dynamic contamination, it is shown that none of these influencing factors is responsible for the observed trends. In fact, there is evidence that X-radiation impact mobilises fluorine, boron and chlorine. Diffusion of radiolysis products towards the specimen's surface as well as the kinetics of adsorption and desorption or chemical reactions are believed to control the analyte concentration in the analysed layer decisively. Furthermore, during analysis, the latter is altered by considerable losses of binder or fluxif applicable thus enhancing XRF intensities of boron and fluorine because of reduced absorption. In any case, signal stability appears to be limited by insufficient sample and specimen stability. It is concluded that for many soil and rock samples, XRF spectrometry is inappropriate to quantify fluorine, although the crucial obstacle is neither the analytical method nor the spectrometer sensu strictu.
“…Apart from a signal increase, the formation of borate salts on the surface was discovered . Numerous publications attest that also chlorine compounds are decomposed by ionising radiation, including X‐rays . Urch detected chloride peak characteristics in L 2,3 ‐M spectra of various oxy‐chloro‐anions previously published by Henke and explained this as a result of sample decomposition because of irradiation.…”
Occasionally suggested yet rarely performed X-ray fluorescence (XRF) spectrometry of fluorine seems to fail systematically in yielding reliable quantitative results for rocks and soils. Repeated analyses reveal continuously drifting fluorescence intensities for fluorine, boron and chlorine. Typically, an increase, but in few cases also a decrease, over X-ray exposure time is observed. For instance, fluorine concentrations in a soil standard appear to increase steadily from below the detection limit in the first run to nearly 850 mg/kg F more than 10 h later in the last. In contrast, cryolite is characterised by drastically decreasing intensities for fluorine. Although fluorescence intensities may be affected by preparation methods, specimen surface conditions and dynamic contamination, it is shown that none of these influencing factors is responsible for the observed trends. In fact, there is evidence that X-radiation impact mobilises fluorine, boron and chlorine. Diffusion of radiolysis products towards the specimen's surface as well as the kinetics of adsorption and desorption or chemical reactions are believed to control the analyte concentration in the analysed layer decisively. Furthermore, during analysis, the latter is altered by considerable losses of binder or fluxif applicable thus enhancing XRF intensities of boron and fluorine because of reduced absorption. In any case, signal stability appears to be limited by insufficient sample and specimen stability. It is concluded that for many soil and rock samples, XRF spectrometry is inappropriate to quantify fluorine, although the crucial obstacle is neither the analytical method nor the spectrometer sensu strictu.
“…Chamber o-rings and kapton windows are held together with PETE blocks on either side - the back PETE block connects the chamber to a support structure of the end station, with the chamber connected by polyether ether ketone (PEEK) tubing lines to and from the sample delivery and flushing system, the operation of which is described in the supplementary information. Figure 4 ( a ) Photograph of the chamber ( b ) Sketch of the chamber ( c ) An exploded view of the chamber showing its component parts 1 : front block 2 , kapton windows 3 , o-rings 4 , the chamber block 5 , Inlet PEEK tubing 6 , Outlet PEEK tubing 7 , Back block that is connected to supporting structure. …”
Absolute measurements of the radiolytic yield of Fe3+ in a ferrous sulphate dosimeter formulation (6 mM Fe2+), with a 20 keV x-ray monoenergetic beam, are reported. Dose-rate suppression of the radiolytic yield was observed at dose rates lower than and different in nature to those previously reported with x-rays. We present evidence that this effect is most likely to be due to recombination of free radicals radiolytically produced from water. The method used to make these measurements is also new and it provides radiolytic yields which are directly traceable to the SI standards system. The data presented provides new and exacting tests of radiation chemistry codes.
“…The lepidocrocite formation induced by the solid oxidation, observed in this work for the set III (carbon steel sample), occurs by the H 2 O 2 molecule into the irradiated solution with a non negligible concentration (about 7 10 -5 mol.L -1 ). This lepidocrocite formation has been described by authors with three steps: 1) the catalytic decomposition of H 2 O 2 onto the solid surface [4,11,26,27,33,37,38,51] (reaction 1) with formation of O 2 or OH according to the surface properties and the pH values of the solution [37,38,51], 2) the Fe oxidation by the O 2 or OH species (reaction 2) with iron(II) hydroxide Fe(OH) 2 formation [4,11] similar to the U(IV) oxidation displayed in a previous study [37], 3) the oxidation of this iron hydroxide by the H 2 O 2 species in order to create the lepidocrocite -Fe(III)OOH structure [4,11,13] (reaction 3) identified in our work by XPS and Raman spectroscopy. Any authors [50] have observed that H 2 addition have no effect onto the H 2 O 2 production, but the H 2 species can be involved into the neutralisation of hydroxyl radicals species at the solid surface.…”
Section: Parts B and C: H 2 O 2 Surface Decomposition And Lepidocrocimentioning
confidence: 99%
“…Most the pre-quoted works systems oxides/water has shown an increase of the H 2 radiolytic yield regarding the pure water system. Few proposed mechanisms can be involved in the enhancement of hydrogen production by irradiation at the solid surface: (i) the hydrogen enrichment of the solid surface implying the H + (H 2 O) cluster formation [2,3], (ii) the electron-hole pair formation and exciton migration induced by the solid irradiation [3,[26][27][28][30][31][32][33][34], (iii) the role of hydroxyl groups density onto the solid surface [28,29,32,35]. The oxidative species H 2 O 2 , produced by chemical surface decomposition mechanism [25-27, 36, 37], has been described as the main source to produce hydroxyl groups at the solid surface.…”
Section: Introductionmentioning
confidence: 99%
“…The irradiation consequences onto the iron based materials corrosion are largely studied with different experimental conditions. The irradiation experiments are performed with different devices which provide irradiations with [4-10, 25-30, 33-35, 38], neutrons [5][6][7], (electrons) [28,32] or ( 4 He 2+ ) [26,27,33] and protons [2,3] in specific ion beam fluence conditions. Thus, in the most of studies, the water volume irradiated is not accurately controlled: either whole of the system is irradiated (typically , neutrons and electrons irradiations) or the solid with any water layers sorbed onto its surface.…”
This paper is devoted to the iron corrosion phenomena induced by the α (4He2+) water radiolysis species studied in conjunction with the production/consumption of H2 at the solid/solution interface. On one hand, the solid surface is characterized during the 4He2+ ions irradiation by in situ Raman spectroscopy; on another hand, the H2 gas produced by the water radiolysis is monitored by ex situ gas measurements. The 4He2+ ions irradiation experiments are provided either by the CEMHTI (E = 5.0 MeV) either by the ARRONAX (E = 64.7 MeV) cyclotron facilities. The iron corrosion occurs only under irradiation and can be slowed down by H2 reductive atmosphere. Pure iron and carbon steel solids are studied in order to show two distinct behaviors of these surfaces vs. the 4He2+ ions water irradiation: the corrosion products identified are the magnetite phase (Fe(II)Fe(III)2O4) correlated to an H2 consumption for pure iron and the lepidocrocite phase (γ-Fe(III)OOH) correlated to an H2 production for carbon steel sample. This paper underlined the correlation between the iron corrosion products formation onto the solid surface and the H2 production/consumption mechanisms. H2O2 species is considered as the single water radiolytic species involved into the corrosion reaction at the solid surface with an essential role in the oxidation reaction of the iron surface. We propose to bring some light to these mechanisms, in particular the H2 and H2O2 roles, by the in situ Raman spectroscopy during and after the 4He2+ ions beam irradiation. This in situ experiment avoids the evolution of the solid surface, in particular phases which are reactive to the oxidation processing
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