State of water in chitosan–PVA hydrogel

The bound water fraction (X_BW) of a newly‐ developed pH‐sensitive, biodegradable chitosan‐polyvinyl alcohol (PVA) hydrogel crosslinked with glutaraldehyde (GA) was investigated as a function of the chitosan/PVA molar ratio, GA concentration (C_GA), and ionization state. Differential scanning calorimetry (DSC) was used to determine the X_BW of the initial hydrogel, and of the hydrogel equilibrated in pH 3 and pH 7 buffers. Changes in X_BW during swelling and shrinking of hydrogel were also investigated. In the initial state of hydrogel, X_BW increased with increasing PVA concentration (C_PVA), without being significantly affected by C_GA. In the buffer‐equilibrated hydrogels, X_BW decreased with increasing C_PVA and decreasing C_GA. The amount of bound water based on dry mass (C_BW) was substantially higher when the hydrogel was in the ionized (swollen) state compared to its unionized counterpart. This may be due to the association of a large quantity of water molecules with ? NH₃⁺ groups of chitosan when the gel swelled in the acidic environment. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3227–3232, 2006     

Raising the productivity of smallholder farms under semi-arid conditions by use of small doses of manure and nitrogen: a case of participatory research

Participatory on-farm trials were conducted for three seasons to assess the benefits of small rates of manure and nitrogen fertilizer on maize grain yield in semi-arid Tsholotsho, Zimbabwe. Two farmer resource groups conducted trials based on available amounts of manure, 3 t ha⁻¹ (low resource group) and 6 t ha⁻¹ (high resource group). Maize yields varied between 0.15 t ha⁻¹ and 4.28 t ha⁻¹ and both absolute yields and response to manure were strongly related to rainfall received across seasons (P < 0.001). The first two seasons were dry while the third season received above average rainfall. Maize yields within the seasons were strongly related to N applied (R ² = 0.77 in season 1, and R ² = 0.88 and 0.83 in season 3) and other beneficial effects of manure, possibly availability of cations and P. In the 2001–2002 season (total rainfall 478 mm), application of 3 and 6 t ha⁻¹ of manure in combination with N fertilizer increased grain yield by about 0.14 and 0.18 t ha⁻¹, respectively. The trend was similar for the high resource group in 2002–2003 although the season was very dry (334 mm). In 2003–2004, with good rainfall (672 mm), grain yields were high even for the control plots (average 1.2 and 2.7 t ha⁻¹). Maize yields due to manure applications at 3 and 6 t ha⁻¹ were 1.96 and 3.44 t ha⁻¹, respectively. Application of 8.5 kg N ha⁻¹ increased yields to 2.5 t ha⁻¹ with 3 t ha⁻¹ of manure, and to 4.28 t ha⁻¹ with 6 t ha⁻¹ of manure. In this area farmers do not traditionally use either manure or fertilizer on their crops, but they actively participated in this research during three consecutive seasons and were positive about using the outcomes of the research in future. The results showed that there is potential to improve livelihoods of smallholder farmers through the use of small rates of manure and N under semi-arid conditions.     

Dryland wheat yield dependence on rainfall,applied N and mulching in preceding maize

To evaluate the response of dryland wheat (Triticum aestivum L.) to mulching in preceding maize and fertilizer N application field experiments were conducted for six years (1980–86) with maize-wheat sequence on a sandy loam soil in northern India. Four rates of N application viz. 0, 40, 60 and 80 kg N ha^–1 in wheat were combined with three mulch treatments viz. no mulch (M₀), paddy straw mulch (M_p) and basooti (Premma mucronate) mulch (M_b) applied at the rate of 4 tons ha^–1 on dry weight basis applied three weeks before harvest of maize. Mulching (M_p and M_b) increased (profile) stored moisture at wheat seedling by 31 to 88 mm. M_b also increased NO₃-N content by 33 to 42 kg ha^–1 in 0–120 cm profile over M₀ and M_p. Over the years, M_p increased wheat yield by 11 to 515 kg ha^–1 and M_b by 761 to 879 kg ha^–1. Wheat yield response to mulching was related to rainfall pattern during its growth season. Significant response to mulching was obtained only in years when rainfall during vegetative phase of the crop was low. Amount and distribution of rainfall during two main phases of crop development affected the N use efficiency by wheat. On an average, each cm of rain substituted for 3.5, 4.6 and 6.5 kg of applied N ha^–1 under M₀, M_p and M_b, respectively. Split rainfall for two main phases of crop growth, available stored water at seeding, fertilizer N and profile NO₃-N content accounted for 89 per cent variability in wheat yield across years and mulching treatments.     

Fermentation of enzymatic hydrolysates from olive stones by Pachysolen tannophilus

BACKGROUND: Olive stones were pretreated with liquid hot water (LHW or autohydrolysis) at maximum temperatures between 175 and 225 °C (severity factors, logR₀, between 2.73 and 4.39) to be subjected (both liquid and solid components) afterwards to enzymatic hydrolysis with cellulases from Trichoderma viride. Ethanol fermentation of hydrolysates was performed with the non‐traditional yeast Pachysolen tannophilus ATCC 32691. RESULTS: After the enzymatic step, yields of hemicellulose solubilization reached 100%, while the cellulose was only partially hydrolysed (23%, logR₀ = 4.39). The maximum yields in total reducing sugars and acetic acid, at the upper end of the severity range, was close to 0.25 and 0.04 g g^?1 dry stone, respectively. During the fermentation stage, the increase in R₀ reduced the maximum specific growth rate, biomass productivity, and overall biomass yield. The overall yields of ethanol and xylitol ranged, respectively, from 0.18 to 0.25 g g^?1 and from 0.01 to 0.13 g g^?1. CONCLUSIONS: The results demonstrate the possibility of producing ethanol from olive stones, making use of the cellulose and hemicellulose fraction of the waste. It was confirmed that the overall yield in xylitol strongly depended on severity factor, while the overall yield in ethanol remained practically constant for all the pretreatment conditions tested. Copyright © 2008 Society of Chemical Industry     

Electrocatalyse de la réduction de l'oxygène sur oxyde mixte: Cu1+x Mn2−x O4 en milieu alcalin. Etude par électrode disque-anneau

Résumé La réduction cathodique de l'oxygène sur des électrodes de manganites de cuivre et liant de Téflon est étudiée par la technique de l'électrode disque-anneau en milieu alcalin. L'interprétation des résultats suggère que la réduction de O₂ en OH^– procède à la fois par la voie directe et, simultanément, par une voie indirecte, parallèle, qui est constituée de deux étapes en série, avec formation de l'intermédaire HO ₂ ^– . La réduction directe en OH^– (constante de vitessek ₁) et la première étape de la réduction indirecte, formant HO ₂ ^– (constante de vitessek ₂) ne dépendent pas de la même manière du potentiel. En outre les ions HO ₂ ^– peroxyde se décomposent probablement catalytiquement chimiquement sur les manganites de cuivre.

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Oxygen reduction on copper manganite Teflon-bonded electrodes in alkaline solution was studied using a rotating ring-disc technique. The interpretation of these data suggests that the cathodic oxygen reduction proceeds through multistep reactions involving a peroxide intermediate. The direct reduction to OH^– (k ₁) and the first reduction step to HO ₂ ^– (k ₂) were found to have different dependences on the potential. Furthermore a catalytic chemical reaction of decomposition of the peroxide intermediate possibly occurs on the manganese copper oxides.

     

Effect of silicon alloying addition on the corrosion behaviour of aluminium in some aqueous media

The corrosion behaviour of three Al–Si alloys was studied after galvanostatic passivation in 0.1 M sodium tartrate, sulfate and borate solutions using EIS techniques. The degree of passivation depends on the anion type, the degree of polarization and the alloy composition. It was also found that increase in pH led to a decrease in polarization resistance R _p. The effect of formation voltage, V _f, on the growth and dissolution kinetics of the oxide grown on the alloys was studied. The polarization resistance value increases as V _f increases up to a certain value; above this the R _p value decreases. This critical V _f depends on the alloy composition and the test solution. The kinetics of oxide layer dissolution in the absence and presence of Cl^– ions was also studied. Increase in immersion time leads to a more severe attack by Cl^– ions as shown by the decrease in the value of R _p. At low Cl^– ion concentration the value of R _p is higher than that in chloride ion free sulfate solutions, because the rate of passive film repair is much higher than that of barrier layer dissolution. However, at high Cl^– ion concentration penetration of Cl^– through defects in the barrier layer leads to formation of an oxyhalide layer.     

Etude du mécanisme réactionnel de réduction électrolytique de l'aluminium dans le mélange NaCl-KCl-LiCl-LiF fondu à 450° C

Résumé La réduction des ions de l'aluminium dans l'électrolyte NaCl-KCl-LiCl-LiF fondu à 450° C contenant du chlorure d'aluminium en teneur supérieure à 10^–4 mol cm^–3 a été étudiée par voltampérométrie triangulaire sur électrodes d'argent et de platine. Sur électrode d'argent le mécanisme de réduction est un processus simple et rapide entre espèces solubles qui met en jeu deux électrons. Sur électrode de platine la réduction massive des ions de l'aluminium, précédée de la formation de composés définis Al _x Pt _y apparaît également comme un mécanisme simple et rapide avec échange de trois électrons. Dans le but de confirmer ces conclusions nous avons procedé au traitement des courbes expérimentales par analyse convolutionnelle. Nous avons également comparé les tracés expérimentaux avec les courbes théoriques correspondant au processus proposé. Les voltampérogrammes expérimentaux et théoriques étant pratiquement identiques nous confirmons ainsi la validité du diagnostique établi.

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The reduction of the aluminium ions in the molten electrolyte NaCl-KCl-LiCl-LiF at 450° C containing more than 10^–4 mol cm^–3 aluminium chloride was studied with triangular voltamperometry on silver and platinum electrodes. On the silver electrode, the mechanism of the reduction is a simple, rapid process between soluble species involving the exchange of two electrons. On the platinum electrode the massive reduction of the aluminium ions, which leads to the formation of the composites Al _x Pt _y also appears to be a simple and rapid mechanism with exchange of three electrons. In order to confirm the conclusions, we have treated the experimental curve using convolutional analysis. We have also compared the experimental with the theoretical curves corresponding to the proposed processes. The experimental voltamperograms are practically identical to the theoretical, therefore confirming the proposed mechanism.

     

Structure and properties of heat‐resistant ABS resins innovated by NSM random copolymer

N‐phenylmaleimide(NPMI)‐styrene(St)‐maleic anhydride (MAH) copolymer was synthesized in xylene solution by one‐step free radical copolymerization, using di‐tert‐butyl diperoxyterephthalate as initiator. The resulting heat‐resistant NPMI‐St‐MAH (NSM) copolymer was characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography, differential scanning calorimetry, elemental analysis, and nuclear magnetic resonance spectroscopy (¹H‐NMR and ¹³C‐NMR). The results show that NPMI‐St‐MAH exhibits a random sequence distribution with a NPMI: St: MAH weight ratio of 47:51:2. The glass transition temperature (T_g) is about 190.0°C. Blends of acrylonitrile‐butadiene‐styrene (ABS) with various contents of NSM were prepared using a twin‐screw extruder, and the effects of NSM content on the thermal and mechanical properties of ABS blends were investigated. It was found that the Vicat softening point, tensile strength, flexural strength, flexural modulus, and Rockwell hardness of the ABS/NSM blends were all significantly enhanced with increasing NSM content, whereas the impact strength shows the opposite trend. The impact fracture surface morphology was characterized by scanning electron microscope. It was revealed that cavitation and cavity coalescence resulted in the toughening of the material, which well accounts for the decrease of impact strength with increasing NSM content. In addition, the rheological properties of the blends were examined using a capillary rheometer. The blends present excellent processing property and are suitable for injection molding, although a pseudoplastic behavior was observed in all cases. POLYM. COMPOS., 34:920–928, 2013. © 2013 Society of Plastics Engineers     

The efficient synthesis of poly(silapropynylenes) via condensation of NaCэCNa with R1R2SiCL2 activated by pyridine

Summary To efficiently prepare poly(silapropynylenes), the condensation of NaCCNa with R₁R₂SiCl₂ activated by pyridine were investigated. The condensation produced tactable polymers(Mw ca. 2100–9000) with significantly higher yields of 80–97% than those from R₁R₂SiCl₂ itself and also gave rise to much more improvement in the yields and molecular weight than with acetylenic di Grignard or di lithium salts. The activation of R₁R₂SiCl₂ by pyridine accelerated the condensation reaction, which resulted in production of macrocyclic polymers as well as linear polymers.     

Application de la voltampérométrie convolutionnele à la détermination du coefficient de diffusion des ions TiF 6 3− dans l'eutectique LiF−NaF−KF de 600°C a 900°C

Résumé Les coefficients de diffusion des ions TiF ₆ ^3– dans l'eutectique LiF–NaF–KF ont été déterminés de 600 à 900° C à l'aide de la semi-intégration des voltampérogrammes de réduction sur électrode de fer et d'oxydation sur électrode d'argent. Les interférences de la réduction de l'eutectique et d'un ménisque à la surface du bain ont été éliminées. Le coefficient de diffusion des ions TiF ₆ ^3– obéit à la loi d'Arrhénius selon:D=1.4×10^–2 exp (–6154/T) cm² s^–1.     

Effect of climate change on greenhouse gas emissions from arable crop rotations

The DAISY soil–plant–atmosphere model was used to simulate crop production and soil carbon (C) and nitrogen (N) turnover for three arable crop rotations on a loamy sand in Denmark under varying temperature, rainfall, atmospheric CO₂ concentration and N fertilization. The crop rotations varied in proportion of spring sown crops and use of N catch crops (ryegrass). The effects on CO₂ emissions were estimated from simulated changes in soil C. The effects on N₂O emissions were estimated using the IPCC methodology from simulated amounts of N in crop residues and N leaching. Simulations were carried out using the original and a revised parameterization of the soil C turnover. The use of the revised model parameterization increased the soil C and N turnover in the topsoil under baseline conditions, resulting in an increase in crop N uptake of 11 kg N ha^–1 y^–1 in a crop rotation with winter cereals and a reduction of 16 kg N ha^–1 y^–1 in a crop rotation with spring cereals and catch crops. The effect of increased temperature, rainfall and CO₂ concentration on N flows was of the same magnitude for both model parameterizations. Higher temperature and rainfall increased N leaching in all crop rotations, whereas effects on N in crop residues depended on use of catch crops. The total greenhouse gas (GHG) emission increased with increasing temperature. The increase in total GHG emission was 66–234 kg CO₂-eq ha^–1 y^–1 for a temperature increase of 4°C. Higher rainfall increased total GHG emissions most in the winter cereal dominated rotation. An increase in rainfall of 20% increased total GHG emissions by 11–53 kg CO₂-eq ha^–1 y^–1, and a 50% increase in atmospheric CO₂ concentration decreased emissions by 180–269 kg CO₂-eq ha^–1 y^–1. The total GHG emissions increased considerably with increasing N fertilizer rate for a crop rotation with winter cereals, but remained unchanged for a crop rotation with spring cereals and catch crops. The simulated increase in GHG emissions with global warming can be effectively mitigated by including more spring cereals and catch crops in the rotation.     

Production of syngas for the reduction of sulfur dioxide by methane via a direct RF plasmalysis process

The traditional process for the reduction of SO₂ by CH₄ usually leads to enrichment of the effluents with H₂S and CO₂. In this study, a radio‐frequency (RF) plasma system was applied to generate useful byproduct: syngas (H₂ and CO) at room temperature. Experimental results indicate that the H₂/CO ratio increased with the elevation of inlet [CH₄]/[SO₂] ratio (R), or the decrease of applied power (E) or operational pressure (P). H₂/CO values ranged from 1.34 to 4.28 and reached 2.09 and 1.95 for E = 90 W and 120 W, respectively, at R = 1 and P = 4000 N m^?2. At first the selectivity to CO increased with the elevation of R or E, while the selectivity to H₂ was only decreased at R > 2 whatever the power that was supplied. However, at R = 2, optimum selectivities of H₂ and CO, and decomposition efficiencies of CH₄ and SO₂, were achieved. The decomposition efficiencies and product components strongly depend on E or R. CH₄ is more easily decomposed than SO₂ and yields mainly syngas, with traces of CO₂, C₂H₂, and C₂H₄. In addition, sulfur‐containing compounds including major amounts of CS₂, elemental sulfur and minor amounts of COS, but no toxic H₂S, were observed. The formation pathways of syngas are also proposed to provide useful information to gain insight into the CH₄ conversion in the RF plasma. Copyright © 2003 Society of Chemical Industry     

Radiopaque epoxy resins

Transparent, X-ray contrast (radiopaque) epoxy resins were obtained by dissolving up to 25 wt % triphenylbismuth in the commercial epoxy resin prepolymers EPON-815, DER-330, DER-383, and DEN-431 which were then hardened with diethylenetriamine. The radiopacities of the mixtures were found to be proportional to the molar concentration of the radiopaque additive. The systems follow the relationship, R = R_o + (R_a ? R_o) V _a M_a where R, R_o, and R_a are the radiopacities of the mixture, the pure epoxy resin, and triphenylbismuth, respectively (expressed in mm aluminum/mm resin); M_a and V _a denote the molar concentration and molar volume of the bismuth compound. R_a for triphenylbismuth was found to be 7.4 ± 0.2 mm Al/mm resin; the average value of R_o for the four epoxies equals 0.16 ± 0.1 mm Al/mm resin. The amount of amine required to harden the radiopaque resins was far less for the epoxy novolac resin DEN-431 than for the three bisphenol-A based epoxies. The concentration of triphenylbismuth required to impart a radiopacity equivalent to that of aluminum measures 14.6 wt % in EPON-815, 14.8 wt % in DER-330, 14.9 wt % in DER-383, and 15.9 wt % in DEN-431. The radiopaque resins remain transparent indefinitely, even when exposed to water. © 1995 John Wiley & Sons, Inc.     

Fabrication and modification of acrylonitrile–butadiene–styrene‐based heterogeneous ion‐exchange membranes by plasma treatment: Investigation of the nanolayer deposition rate and temperature effects

Our target in this study was the preparation of electrodialysis ion‐exchange membranes with appropriate properties for applications in water recovery and treatment. Composite mixed‐matrix, anion‐exchange membranes were prepared by a solution casting technique with acrylonitrile–butadiene–styrene as a base binder, resin powder as a functional group agent, activated carbon as an adsorptive filler, and an Ag nanolayer as a surface modifier. The Ag nanolayer was used with a magnetron sputtering method. The effect of the nanolayer deposition rate (R_q) and substrate and annealing temperatures on the physicochemical characteristics of the membranes were studied. The X‐ray diffraction results show that average grain size of the nanolayer and membrane crystallinity were improved with increasing R_q. The atomic force microscopy and scanning electron microscopy results show that the membrane roughness was enhanced with increasing R_q. The height distribution results also show the best height distribution for the modified membrane at low R_q. The selectivity and flux decreased with increasing nanolayer R_q in the membranes. The selectivity was also decreased initially with increases in the substrate and annealing temperatures from 300 to 325 K in the membranes and then showed an increasing trend. An opposite trend was found for flux with variations in the temperature. The modified membrane containing a 20‐nm Ag nanolayer at low R_q showed better performance compared to the other modified membranes and the pristine one. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40025.     

Comparison of size distribution data from dynamic light scattering and size-exclusion chromatography

The intensity-defined distribution functions of hydrodynamic radii of equivalent spheres, R_h, obtained from dynamic light-scattering experiments using the CONTIN procedure via the Stokes formula were compared with distributions of gyration radii, R_g, determined by size-exclusion chromatography. The number-, weight-, and intensity- (z)-defined R_g distributions accessible from size-exclusion chromatography experiments were calculated using the Flory-Fox relation. Reliable ratios of average radii, R_g/R_h, for linear polystyrenes having narrow, broad, or bimodal molecular weight distributions were obtained in toluene. Care should be taken to utilize properly averaged experimental quantities. For instance, the CONTIN DLS data evaluation procedure yields the z-average of the inverse of the hydrodynamic radius, 〈1/R_h〉_z^?1. © 1995 John Wiley & Sons, Inc.     

Mass transfer to volumetric electrodes with two-phase flow

Experimental studies of mass transfer were conducted in stacked screens with a gas-liquid mixture flowing through the bed. Depending on the gas and liquid flow rates and on the geometric characteristics of the screens, different flow regimes are obtained. In the heterogeneous flow regime the gas phase controls mass transfer, meanwhile in the transition and bubbling flow regimes the influence of the liquid flow prevails. Appropriate dimensionless groups correlate the mass transfer coefficients with the pertinent variables for the different regimes.Nomenclature A electrode area (cm²) - A ₁ surface area of one screen (cm²) - c _o bulk concentration (mol cm^–3) - D diffusivity (cm²s^–1) - d particle or wire diameter (cm) - F Faraday's constant - i limiting current (A) - k mass transfer coefficient (cm s^–1) - N distance between wires (cm) - Re _g Reynolds number for gas flow,Re _g=u _g R _h v _g ^–1 - Ré _g Reynolds number for gas flow,Re ₁=u ₁ R _h v ₁ ^–1 - Re ₁ Reynolds number for liquid flow,Re' ₁=u ₁ dv ₁ ^–1 - Ré ₁ Reynolds number for liquid flowRe ₁=u ₁ R _h v ₁ ^–1 - R _h hydraulic radius of screen bed (cm) - S _c Schmidt number,Sc=v ₁ D ^–1 - Sh Sherwood number,Sh=kdD ^–1 - Sh ₀ Sherwood number without gas,Sh ₀ =kdD ^–1 - u _g superficial gas velocity (cm s^–1) - u ₁ superficial liquid velocity (cm s^–1) - screen thickness (cm) - porosity - v kinematic viscosity (cm²s^–1) - specific area (cm^–1)     

Synthesis of monohydric alcohols from CO and H<Subscript>2</Subscript> on Fe/Sibunit catalysts

It was demonstrated that R ₂–R ₄ saturated monohydric alcohols can be synthesized from CO and H₂ in the presence of Fe catalysts containing a carbon support of the Sibunit type with granule sizes of 3–5, 1–2, and 0.05–0.1 mm in a fixed-bed reactor at 3 MPa and 240–300°C. It was found that the activity of Fe/Sibunit catalysts and their selectivity for the formation of liquid synthetic products increased with the size of granules and the amount of iron. The catalysts make it possible to obtain fatty alcohols, in which the fraction of R ₂–R ₄ alcohols is as high as 75%, in yields to 56 g/m³.     

Electrodissolution de la millérite en milieu chlorhydrique

Résumé L'électrodissolution deMS synthétisé a été étudiée en milieu d'acide chlorhydrique à 25° C. L'influence de la concentration des ions d'hydrogène (pH 0.46–2.68), de nickel (0–1 M) et de chlore (1–4 M) a été examinée. Les études potentiocinétiques et potentiostatiques ainsi que les diagrammesE-pH de NiS-H₂O ont clarifié la cinétique électrochimique et le mécanisme de dissolution deNiS. La surface attaquée et les produits de corrosion ont été examiné par rayons-X, microscopie électronique à balayage, dispersion des rayons-X et absorption atomique.

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The electrodissolution of syntheticMS has been studied in hydrochloric acid at 25° C. The influence of hydrogen ions (pH 0.46–2.68), nickel ions (0–1 M) and chloride ions (1–4 M) has been examined. Potentiokinetic and potentiostatic studies and alsoE-pH diagrams of NiS-H₂O clarified the electrochemical kinetics and mechanism of the dissolution ofNiS. The attacked surface and dissolution products were examined by X-rays, scanning electron microscopy, X-ray dispersion and atomic absorption.

     

Interactions de la reduction du proton solvate et de l'oxygene dissous,sur une electrode de fer en solution sulfurique

Résumé A l'interface Fe/H₂SO₄, 1 N (aéré ou non), et dans le domaine de potentiel (–0·95, –1·2 V/E.S.S.), nous avons trouvé que le courant cathodique mesuré sur une électrode à disque tournant varie avec la vitesse de rotation suivant une loi de la forme:I=A+B ^1/2. A peut être identifié au courant de réduction du proton solvaté mais dépend fortement de la teneur en oxygène de l'électrolyte. La composante diffusionnelleB ^1/2 peut être identifiée à la réduction de l'oxygène dissous mais est très inférieure à celle relative à une surface uniformément réactive. Le blocage résultant est compatible avec l'analyse en fonction du potentiel de la corrélation entreA etB ^1/2 en supposant la réaction suivante: Fe H_adsFe H _ads ^* , où Fe H_ads est un hydrogène adsorbé faiblement lié de courte durée de vie (qq. s) et Fe H _ads ^* est un hydrogène adsorbé fortement lié de longue durée de vie (qq.h). Le déblocage résulte de la réaction chimique H_ads+1/4 O₂1/2 H₂O.Dans le cadre classique du mécanisme de dégagement de l'hydrogène en deux étapes, nous avons montré que notre modèle d'interdépendance implique que l'étape limitant la vitesse soit celle de Tafel à faible surtension et celle d'Horiuti pour des tensions cathodiques plus élevées.

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We found that at the 1 N Fe/H₂SO₄ (aerated or de-aerated) interface within the potential range (–0d95, –1.2 V/S.S.E.) the cathodic current measured on a rotating disc electrode varies with the rotation speed according to the relation:I=A+B^1/2. A can be assigned to the reduction of H⁺ but depends strongly on the oxygen concentration. On the other hand the diffusional componentB^1/2 can be assigned to the reduction of dissolved oxygen but is much lower than that relative to a uniform reactive surface. The resulting blocking is consistent with the analysis as a function of the potential of the correlation betweenA andB^1/2 by assuming the following reaction: Fe H_adsFe H _ads ^* . Fe H_ads and Fe H _ads ^* are adsorbed hydrogen low bonded with a short life time (a few s) and strong bonded with a long life time (a few h) respectively. The blocked surface is activated by the chemical reaction Fe H_ads+1/4 O₂1/2 H₂O+Fe.In the classic framework of the two-step hydrogen evolution mechanism, we demonstrated that our interdependence model implies that the rate determining step is the Tafel reaction at low overpotentials and the Horiuti reaction for the highest overpotentials.