Migration Of Deuterium Research Articles

Hydrogen migration in BaTiO3-based dielectrics under high humidity and electric field bias

This study investigates the possibility of hydrogen migration in BaTiO3-based dielectrics to improve the electrical reliability of multi-layer ceramic capacitors under conditions of high temperature, humidity, and electric field bias. It was observed that the deuterium in the dielectric drifted and migrated with the electric field, suggesting that deuterium exists as D+. The activation energy was found to be 0.34 eV, which is lower than that observed in previous studies. This finding offers a better understanding of the mechanism behind the migration of deuterium in a dielectric, which is highly relevant to future research in dielectrics and electronic components.

Thermal migration of deuterium implanted in graphite: Influence of free surface proximity and structure

This paper is a contribution to the study of the behavior of activation products produced in irradiated nuclear graphite, graphite being the moderator of the first French generation of CO2 cooled nuclear fission reactors. This paper is focused on the thermal release of Tritium, a major contributor to the initial activity, taking into account the role of the free surfaces (open pores and graphite surface). Two kinds of graphite were compared. On one hand, Highly Oriented Pyrolitic Graphite (HOPG), a model well graphitized graphite, and on the other hand, SLA2, a porous less graphitized nuclear graphite. Deuterium ion implantation at three different energies 70, 200 and 390keV allows simulating the presence of Tritium at three different depths, corresponding respectively to projected ranges Rp of 0.75, 1.7 and 3.2μm. The D isotopic tracing is performed thanks to the D(3He,p)4He nuclear reaction. The graphite structure is studied by Raman microspectrometry. Thermal annealing is performed in the temperature range 200–1200°C up to 300h annealing time. As observed in a previous study, the results show that the D release occurs according to three kinetic regimes: a rapid permeation through open pores, a transient regime corresponding to detrapping and diffusion of D located at low energy sites correlated to the edges of crystallites and finally a saturation regime attributed to detrapping of interstitial D located at high energy sites inside the crystallites. Below 600°C, D release is negligible whatever the implantation depth and the graphite type. The present paper clearly puts forward that above 600°C, the D release decreases at deeper implantation depths and strongly depends on the graphite structure. In HOPG where high energy sites are more abundant, the D release is less dependent on the surface proximity compared to SLA2. In SLA2, in which the low energy sites prevail, the D release curves are clearly shifted towards lower temperatures when D is located close to free surfaces. Extrapolating our data to Tritium mobility in irradiated graphite, we show that thermal selective extraction of T would be all the more so efficient as the graphite structure is more disordered, which means in the most irradiated and damaged graphite zones in the reactor.

Conversion of 7-Dehydrocholesterol to 7-Ketocholesterol Is Catalyzed by Human Cytochrome P450 7A1 and Occurs by Direct Oxidation without an Epoxide Intermediate

7-Ketocholesterol is a bioactive sterol, a potent competitive inhibitor of cytochrome P450 7A1, and toxic in liver cells. Multiple origins of this compound have been identified, with cholesterol being the presumed precursor. Although routes for formation of the 7-keto compound from cholesterol have been established, we found that 7-dehydrocholesterol (the immediate precursor of cholesterol) is oxidized by P450 7A1 to 7-ketocholesterol (k(cat)/K(m) = 3 × 10(4) m(-1) s(-1)). P450 7A1 converted lathosterol (Δ(5)-dihydro-7-dehydrocholesterol) to a mixture of the 7-keto and 7α,8α-epoxide products (~1:2 ratio), with the epoxide not rearranging to the ketone. The oxidation of 7-dehydrocholesterol occured with predominant formation of 7-ketocholesterol and with the 7α,8α-epoxide as only a minor product; the synthesized epoxide was stable in the presence of P450 7A1. The mechanism of 7-dehydrocholesterol oxidation to 7-ketocholesterol is proposed to involve a Fe(III)-O-C-C(+) intermediate and a 7,8-hydride shift or an alternative closing to yield the epoxide (Liebler, D. C., and Guengerich, F. P. (1983) Biochemistry 22, 5482-5489). Accordingly, reaction of P450 7A1 with 7-[(2)H(1)]dehydrocholesterol yielded complete migration of deuterium in the product 7-ketocholesterol. The finding that 7-dehydrocholesterol is a precursor of 7-ketocholesterol has relevance to an inborn error of metabolism known as Smith-Lemli-Opitz syndrome (SLOS) caused by defective cholesterol biosynthesis. Mutations within the gene encoding 7-dehydrocholesterol reductase, the last enzyme in the pathway, lead to the accumulation of 7-dehydrocholesterol in tissues and fluids of SLOS patients. Our findings suggest that 7-ketocholesterol levels may also be elevated in SLOS tissue and fluids as a result of P450 7A1 oxidation of 7-dehydrocholesterol.

Formation of a cationic alkylidene complex via formal hydride abstraction: synthesis and structural characterization of [W(PMe3)4(η2-CHPMe2)H]X (X = Br, I)

W(PMe(3))(4)(η(2)-CH(2)PMe(2))H reacts with aryl halides to give the alkylidene complex, [W(PMe(3))(4)(η(2)-CHPMe(2))H](+), which reacts with LiAlD(4) to give selectively W(PMe(3))(4)(η(2)-CHDPMe(2))H, in which the deuterium resides in the methylene group; subsequent migration of deuterium from the methylene group provides a means to measure the rate constant for the formation of the 16-electron species [W(PMe(3))(5)] from W(PMe(3))(4)(η(2)-CH(2)PMe(2))H.

Migration and luminescence enhancement effects of deuterium in ZnO∕ZnCdO quantum wells

Zn O ∕ Zn Cd O ∕ Zn O multiple quantum well samples grown on sapphire substrates by molecular beam epitaxy and annealed in situ were exposed to D2 plasmas at 150°C. The deuterium showed migration depths of ∼0.8μm for 30min plasma exposures, with accumulation of H2 in the ZnCdO wells. The photoluminescence (PL) intensity from the samples was increased by factors of 5 at 5K and ∼20 at 300K as a result of the deuteration, most likely due to passivation of competing nonradiative centers. Annealing up to 300°C led to increased migration of H2 toward the substrate but no loss of deuterium from the sample and little change in the PL intensity. The initial PL intensities were restored by annealing at ⩾400°C as H2 was evolved from the sample (∼90% loss by 500°C). By contrast, samples without in situ annealing showed a decrease in PL intensity with deuteration. This suggests that even moderate annealing temperatures lead to degradation of ZnCdO quantum wells.

Overview of co-deposition and fuel inventory in castellated divertor structures at JET

The main focus of this work is fuel retention in plasma components of the JET water-cooled Mk-I divertors operated with small tiles, first with carbon fibre composite (CFC) and then with castellated beryllium. Until recently these have been the only large-scale structures of this type used in fusion experiments. Three issues regarding fuel retention and material migration are addressed: (i) accumulation in gaps separating tiles and in the grooves of castellation; (ii) comparison of deposition on carbon and beryllium; (iii) in-depth migration of deuterium into the bulk of CFC. The essential results are summarised as follows: (i) co-deposition occurs up to a few cm deep in the gaps between the Mk-I tiles; (ii) fuel inventory in the CFC tile gaps exceeds that on plasma-facing surfaces by up to a factor of 2; (iii) in gaps between the beryllium tiles from the inner divertor corner the fuel content reaches 30% of that on plasma-facing surfaces, whereas in the grooves of castellation in Be the fuel content is less than 3.0% of that found on the top surface; (iv) fuel inventory on the Be tiles is strongly associated with the carbon co-deposition; (v) the D content measured in the bulk (1.5 mm below the surface) on cleaved CFC tiles exceeds 1 × 10 15 cm −2. Implications of these results for a next-step device are addressed and the transport mechanism into the gaps is briefly discussed. The results presented here suggest that in a machine with non-carbon walls in the main chamber (as foreseen for ITER) the material transport and subsequent fuel inventory in the castellation would be reduced.

Recombination-induced athermal migration of hydrogen and deuterium in SiC

The phenomenon of recombination-induced formation of hydrogen-defect complexes in epitaxial silicon carbide (SiC) was further investigated on p-type samples treated in deuterium plasma. Qualitatively similar effects were observed for hydrogen and deuterium. The formation of hydrogen-related (deuterium-related) defects would depend on the temperature of the sample during plasma treatment, with lower process temperatures causing only incorporation of hydrogen (deuterium) near the surface without any significant formation of electrically or optically active hydrogen-related or deuterium-related defects in the epilayer. Higher process temperatures normally produced more efficient formation of new centers, including passivation of acceptors in SiC. In all cases, prolonged excitation of the hydrogenated (deuterated) samples with above-bandgap light at reduced temperatures caused recombination-induced formation of a few different defect centers. A confirmation of the long-range athermal migration of hydrogen from the surface into the bulk of the sample was obtained. It has been established that it is the recombination-induced migration of hydrogen that is responsible for the formation of hydrogen-related defect centers under optical excitation.

Aluminum and iron surface modification by deuterium ion implantation and thermal desorption process

Fe and Al thin films were implanted at room temperature with 20 keV D 2 ions at 3×10 16 ions/cm 2 fluence. The correlation between the effusion of the implanted deuterium and the evolution of the surface morphology was studied by thermal desorption spectroscopy (TDS) and scanning electron microscopy (SEM). Deuterium effusion from Fe thin films occurs at ∼430 K and is controlled by the D 2 surface recombination process. The deuterium effusion profile from Al thin films appears more structured. SEM analysis reveals blisters in the as-implanted samples and the increase of their number density and size up to a temperature of ∼500 K. TDS analysis indicates effusion of parts of the implanted deuterium in the 500–600 K temperature range: deuterium is released from the blisters as indicated by the decrease of their number density and size observed by SEM in this temperature interval. The major part of deuterium effuses at ∼630 K and the effusion process is controlled by the migration of deuterium through the surface oxide layer: the effusion process has an activation energy of 1.8±0.1 eV which is very close to the activation energy for deuterium diffusion in γ-Al 2O 3. The deuterium effusion kinetics from Fe–Al multilayers is nearly the same as in Fe thin film samples.

Radiation-induced segregation of deuterium in austenitic steels and vanadium alloys

The accumulation and distribution of implanted deuterium were studied through simultaneous analysis using the nuclear reaction D(d,p)T for some austenitic, austenitic–martensitic steels, Fe–16% Cr, V–4% Ti–4% Cr, V–10% Ti–5% Cr alloys, and vanadium. The implantation was carried out by 700-keV deuteron irradiation at room temperature with a total implantation dose of about 2 × 10 18 cm −2. It is shown that the deuterium segregation induced by ion irradiation in vanadium and the Fe–16% Cr alloy remained unchanged during room temperature holding after implantation. On the other hand, in the two-phase steel and the V–Ti(–Cr) alloys the holding led to a partial elimination of the concentration inhomogeneity of the implant in the irradiated portion, while in the austenitic steel deuterium segregation increased probably due to the migration of deuterium from the unirradiated volume to the irradiation zone. Possible reasons for different behavior of the implanted deuterium in different materials will be briefly discussed.

Deuterium transport in liquid beryllium

H-isotope trapping and release by plasma facing components (PFCs) control fuel retention and recycling in fusion devices, and melting can occur when PFCs are subjected to high heat loads. Pulsed laser melting and desorption were used to investigate the transport of deuterium (D) pre-implanted in beryllium (Be). A numerical model with a finite difference form was used to compute the space and time dependence of the temperature, the phase changes, and the D 2 evolution. The activation energies and kinetic factors characterizing detrapping, diffusion and molecular recombination are free parameters of the code which have been determined by fitting the data on desorbed amount versus laser energy. The D diffusivity in liquid Be is found to be: D 1 = (9.0 ± 0.7) × 10 −8 exp[(−0.24 ± 0.02)eV/ kT] m 2/s. Migration of near-surface deuterium or tritium into the bulk of molten Be is implied by these results.

NIH shift in the hydroxylation of aromatic compounds by the ammonia-oxidizing bacterium Nitrosomonas europaea. Evidence against an arene oxide intermediate

The migration of deuterium and hydrogen was observed in the aromatic hydroxylation of specifically deuterated, monosubstituted benzenes catalyzed by ammonia monooxygenase of Nitrosomonas europaea. The phenolic products of the hydroxylation of aromatics containing ortho-/para-directing substituents (F, Cl, Br, I, OH, NH2, CH3, CH2CH3, and OCH3) were primarily para-phenols. In contrast, with aromatics containing meta-directing substituents (NO2 and CN), the phenolic products were a more even mixture of meta-and para-phenols. ortho-Fluorophenol was the only ortho-phenolic product observed. The nature of the products suggested that the reaction involved an enzyme-specific, electrophilic addition to the aromatic ring so as to favor hydroxylation at either the meta- or para-positions. With the fluoro-, chloro-, and bromobenzene substrates, the values for the migration and retention of deuterium during hydroxylation (NIH shift) were nearly identical when the deuterium was either at the site of hydroxylation or at an adjacent site, indicating a possible common intermediate. The values of the NIH shift with the nitrobenzene substrate were significantly lower when the deuterium was at the site of hydroxylation than at an adjacent site, indicating the operation of a direct loss mechanism. The present results suggest that the aromatic hydroxylation involved a radical or carbocation intermediate which decayed, without the formation of an arene oxide, to form phenolic products with the accompanying direct loss of deuterium at the site of hydroxylation or the shift of the deuterium to an adjacent site.

SIMS study of deuterium trapping and migration in a YBa 2Cu 3O 7−δ thin film

Ion implantation and secondary ion mass spectroscopy (SIMS) have been used to study the behaviour of trapping and migration of deuterium (D or 2H) in a c-oriented YBCO film (800–900 nm) from room temperature to 350°C. The D was introduced, at room temperature, by ion implantation at 50 keV to a dose of 1 × 10 16 ions cm −2. Pieces of the as-implanted samples were annealed in a flowing oxygen ambient using a conventional annealing furnace. D concentration depth profiles were obtained on an Atomika 6500 SIMS instrument, using a 10 keV Cs + primary beam. It has been found that 1) OH shows a declining “diffusion-controlled” distribution to a depth of ∼ 150 nm within the as-received YBCO film; 2) some of the implanted D must bond with oxygen; 3) the implanted D is a fast diffuser in the YBCO film.

Deuterium interaction with silicon-graphite materials exposed to the tokamak plasma

Silicon-containing composites are considered as plasma facing materials in controlled fusion devices. Comparative studies of deuterium interaction with carbon based substrates were performed for graphite-silicon mixtures (5–50 wt% of Si), carbon fibres and isotropic graphite. Both virgin and deuterium treated surfaces were characterized by means of several surface sensitive techniques. The substrates were exposed to the deuterium plasma in the TEXTOR tokamak, in a magnetron or in a hollow cathode. The uptake, retention and release of deuterium were investigated. Migration of deuterium from the plasma deposited layer to the bulk of the substrates was found for the graphite-silicon mixtures. The structure of the deuterium-containing deposits was studied using atomic force microscopy. The initial stage of bubble formation was observed on the surfaces exposed to the tokamak plasma.

Investigation of diffusion and migration of hydrogen, deuterium and tritium in palladium in a Hall field

The migration of hydrogen, deuterium and tritium in palladium in a Hall field at 343 K was investigated, using resistance and isotope methods. It was found that all isotopes of hydrogen migrate towards the negative Hall electrode. The effective charges of the migration in a Hall field are 194 ±3 e for hydrogen and 464± 5 e for deuterium and tritium. The results obtained confirm predictions of a tentative model based on the electron-balistic theories of migration in a Hall field.

Migration of hydrogen through thin films of ZrO2 on Zr–Nb alloy

The barrier properties of ZrO2 to inward migration of deuterium have been investigated with a view to understanding the hydriding mechanisms of a Zr-2.5% Nb alloy used in CANDU nuclear reactors fuel channels. Thin film oxide specimens, grown in steam to ∼1 μm thickness, have been heated to 350 °C and exposed to deuterium gas at pressures ranging from 6×10−3 Pa to 101 kPa (1 atm) and times from 10 to 810 min. Some irreversible uptake can be measured for all exposures using secondary ion mass spectrometry. At low exposures, the shape of the deuterium concentration profile is can be fitted to a Fickian relationship. During longer exposures, the rate of deuterium ingress is sharply curtailed, presumably due to passivated outer oxide surface. Reactions between D2O vapor and the thin film oxide in the 10−3 Pa pressure region and above show a sharply higher uptake of deuterium than in the equivalent pressure of D2 gas. This is ascribed to a more efficient decomposition of D2O on the ZrO2 surface compared to D2.

Microbial models of mammalian metabolism: conversion of warfarin to 4'-hydroxywarfarin using Cunninghamella bainieri.

Warfarin, an anticoagulant and "metabolic probe" for cytochrome P-450 isozyme multiplicity, is metabolized to 4'-hydroxywarfarin, a principle mammalian metabolite, using the fungus Cunninghamella bainieri (UI-3065). The metabolite was isolated from cell suspension cultures and characterized by analytical (TLC, HPLC, GC-MS) and spectral (HRMS, EI-MS, PMR) comparisons with authentic 4'-hydroxywarfarin. The mechanism of aromatic hydroxylation was examined in C. bainieri using 4'-deuterowarfarin. The absence of a primary isotope effect (KH/KD = 1.13), migration and retention of deuterium in the phenolic product [80% migration and retention (M&R)], and inhibition of the hydroxylation by carbon monoxide (93% inhibition in a 50:50 CO:O2 atmosphere) are consistent with a cytochrome P-450-mediated hydroxylation involving the classic NIH shift (arene oxide) pathway.

Evidence for reversible formation of an intermediate in the "spontaneous" hydrolysis reaction of p-methoxystyrene oxide

The authors have now examined the hydrolysis reactions of p-methoxystyrene oxide (1) and a deuterium-labeled derivative and wish to report /sup 1/H NMR data that provide evidence for reversible formation of an intermediate in the spontaneous reaction that yields mainly p-methoxyphenylacetaldehyde. The rates of reaction of 1 in 0.1 M NaClO/sub 4/ solutions, at 25.0/sup 0/C over the pH range 4.7-13, were fit to the equation k/sub obsd/ = k/sub H/sup +//a/sub H/sup +// + k/sub 0/. The values of k/sub H/sup +// and k/sub 0/ were determined to be 1.1 +/- 0.2 x 10/sup 4/ M/sup -1/s/sup -1/ and 3.0 +/- 0.1 x 10/sup -3/ s/sup -1/, respectively. Product studies showed that the acid-catalyzed reaction yielded >95% of glycol product, whereas the spontaneous (k/sub 0/) reaction proceeded mainly to rearranged aldehyde. p-Methoxy-trans-..beta..-deuteriostyrene oxide (4) was also prepared, and its hydrolysis reactions were studied. The kinetic deuterium isotope effects k/sub H/sup +//(H)/k/sub H/sup +//(D) and k/sub 0/(H)/k/sub 0/(D) were determined to be 0.97 +/- 0.01 and 1.17 +/- 0.02, respectively. /sup 1/H NMR and mass spectral analyses of the aldehyde product from the k/sub 0/ reaction of 4 showed that the ratio of hydrogen migration to deuterium migration was ca.more » 3:1. The value of this ratio is similar to the kinetic isotope effect for migration of deuterium and suggests that both hydrogens in the methylene position of 1 migrate to similar extents.« less

Thermal desorption of deuterium from an austenitic steel irradiated with 3-MeV deutrons

For directly measuring the effect of radiation defects on the diffusive mobility of deuterium in an austenitic steel at high temperatures, the authors studied thermal desorption of deuterium after high-energy deutron implantation. Such bombardment leads to deeper penetration of deuterium into the material and to a corresponding displacement of the thermal desorption peaks towards the high-temperature region during subsequent linear heating. An additional displacement of the peaks was achieved by increasing the specimen thickness. This technique also makes it possible to distinguish the temperature range in which migration of deuterium involving recapture by the traps forms the main desorption mechanism.

The biosynthesis of phenanthrenoid phytoalexins. Incorporation of hexadeuteriophenylalanine into orchinol established by2H n.m.r. spectroscopy

Deuterium n.m.r. studies have shown that α,β,β,3,4,5-hexadeuteriophenylalanine is incorporated into the dihydrophenanthrenoid phytoalexin orchinol with loss of aliphatic deuterium and an unexpected, and as yet unclarified, migration of aromatic deuterium.

Evidence for a 2,3-epoxide as an intermediate in the microsomal metabolism of 6-nitrobenzo[a]pyrene.

The rat liver microsomal metabolism of 3-deutero-6-nitrobenzo(a)pyrene ([3-2H]6-NO2-BaP) was studied. The metabolites were separated by h.p.l.c. The 500 MHz 1H n.m.r. spectral analysis of the metabolites indicated that the 3-hydroxy-6-NO2-BaP and 6-NO2-BaP-3,9-hydroquinone each retained 33% of the deuterium label at the C-2 position. It is proposed that the migration of deuterium occurs via an NIH shift mechanism. These results indicate that a 2,3-epoxide is a common intermediate.