François Lapicque

Hyaluronate-alginate gel as a novel biomaterial: Mechanical properties and formation mechanism

With the aim of producing a biomaterial for surgical applications, the alginate-hyaluronate association has been investigated to combine the gel-forming properties of alginate with the healing properties of hyaluronate. Gels were prepared by diffusion of calcium into alginate-hyaluronate mixtures, with an alginate content of 20 mg/mL. The hyaluronate source was shown to have significant effect on the aspect and the properties of the gels. The gels have viscoelastic behaviour and the transient measurements carried out in creep mode could be interpreted through a Kelvin-Voigt generalised model: experimental data led to the steady state hardness and a characteristic viscosity of the gel. Gels prepared from Na rooster comb hyaluronate with weight ratio up to 0.50 have satisfactory mechanical properties, and fully stable gels are obtained after a few days; on the contrary, use of lower molecular weight hyaluronate led to loose gels for hyaluronate contents over 0.25. Gel formation was investigated by measurements of the exchange fluxes between the calcium chloride solution and the forming gel, which allowed thorough investigations of the occuring diffusion phenomena of water, calcium ion and hyaluronate. Strong interactions of water with hyaluronate reduce significantly the rate of weight loss from the gel beads and allows higher water content in steady-state gels. Calcium content in the gel samples could be correlated to the actual alginate concentration, whatever the nature and the weight ratio of hyaluronate.

Direct electrochemical preparation of solid potassium ferrate

Abstract Mixed KOH–NaOH solutions were shown to allow the production of solid potassium ferrate in an electrochemical cell, due to the low solubility of the key-salt. Potassium ferrate was produced at 12 g l −1 with current yields of approximately 20% by dissolution of a cast iron anode with 2.8% Si, immersed in a 400 g l −1 KOH, 400 g l −1 NaOH solution. The ferrate produced can be directly separated by conventional solid–liquid techniques, and the recovered solution with a low ferrate content can be reused for further electrochemical runs.

Electrodeposition of zinc-nickel alloys from ammonia-containing baths

This paper describes the use of ammonia-containing baths for Zn–Ni alloy electrodeposition. Buffering properties of the ammonia/ammonium couple limit the local change in pH in the vicinity of the electrode surface caused by simultaneous hydrogen evolution. In addition, it is shown that the divalent zinc and nickel species exist in the form of Zn(NH3)42+ and Ni(NH3)62+ complexes over a large pH range. The electrochemistry of the deposition at pH 10 was investigated by galvanostatic experiments and cyclic voltammetry, and compared with deposition from ammonium chloride baths at pH 5. The Ni content in the alloys were found to be 40–60% higher from the ammonia-containing bath than from the acidic baths. Reduction of divalent ions and hydrogen evolution were shown to occur at potentials 250 mV more cathodic than with baths at pH 5; the deposition mechanism may be affected by complexation of the metal cations by ammonia.

Electrochemical ferrate generation for waste water treatment using cast irons with high silicon contents

This paper deals with the electrochemical preparation of ferrate in 15 M NaOH media, with a view to treatment of waste waters. Grey cast irons with high silicon contents were shown to allow current yields in the range 20–40% depending on the applied current density, up to 34 mA cm−2. Ferrate solutions with contents up to 0.08 M could be produced in a divided cell of simple design, and provided with flat or packed-bed electrodes. Deactivation of the anode surface was shown to be of moderate significance for hour-long runs. The ferrate produced was tested for treatment of industrial liquid wastes: coagulation efficiency of the suspended matter was comparable with that of an electrocoagulation process with sacrificial Al anodes. The potential of waste water treatment by addition of ferrate is discussed.

Treatment of highly concentrated tannery wastewater using electrocoagulation: Influence of the quality of aluminium used for the electrode.

This paper deals with the ability of electrocoagulation (EC) to remove simultaneously COD and chromium from a real chrome tanning wastewater in a batch stirred electro-coagulation cell provided with two aluminium-based electrodes (aluminium/copper/magnesium alloy and pure aluminium). Effects of operating time, current density and initial concentration of Cr(III) and COD have been investigated. The concentrations of pollutants have been successfully reduced to environmentally acceptable levels even if the concentrated effluent requires a long time of treatment of around 6h with a 400A/m(2) current density. The aluminium alloy was found to be more efficient than pure aluminium for removal of COD and chromium. Dilution of the waste has been tested for treatment: high abatement levels could be obtained with shorter time of treatment and lower current densities. Energy consumption of the electrocoagulation process was also discussed. The dilution by half of the concentrated waste leads to a higher abatement performance of both COD and chromium with the best energy efficiency.

Coupled effects of chloride ions and branch chained polypropylene ether LP-1 on the electrochemical deposition of copper from sulfate solutions

Abstract The paper presents the results of electrochemical investigations of copper deposition from a sulfate/sulfuric bath of industrial relevancy and containing two additives. In particular the effect of chloride ion with polypropylene ether (LP-1™) could be highlighted by voltammetry and impedance measurements. When used without chloride ion LP-1 adsorbs at the surface which reduces significantly the current density and the double layer capacitance. A current peak was observed for the simultaneous presence of the two additives and this was attributed to a sudden inhibition of the surface: in a narrow range of potential Cl-complexes were assumed to desorb from the surface, allowing significant adsorption of inert LP-1 molecules. Besides, kinetic parameters and the diffusion coefficient of cupric ion were correlated to the concentrations of additives, copper sulfate and sulfuric acid in a broad range of concentration.

Production of hydrogen by direct thermal decomposition of water

Abstract This paper reports the first results of a study on the feasibility of producing hydrogen by direct thermal splitting of water by use of concentrated radiation. Relative amounts of H, O, OH, H 2 , O 2 and H 2 O have been computed between 1500 and 4000 K at thermodynamic equilibrium. In addition, the rate of the overall reaction has been estimated assuming a kinetic model: 90% of equilibrium concentrations are reached after about 10 −2 , 10 −3 and 10 −4 s at 2200, 2500 and 3000 K respectively. The dissociation experiments have been carried out in an image furnace, simulating the future use of a solar furnace. Water is injected through a zirconia nozzle heated at the focus. The hot jet containing active species is then quenched by turbulent cold jets in order to minimize recombinations. Several shapes of zirconia nozzles and quenching devices have been tested in order to maximize the net production of hydrogen, which reaches 1.7 STP l. h −1 in continuous operation. Modelling of the hot nozzle allows the calculation of the gas temperature and shows that thermodynamic equilibrium conditions are reached under certain conditions. Parallel experiments show that cooling rates up to 10 6 Ks −1 can be obtained by quenching.

Investigation of transport phenomena in a hybrid ion exchange-electrodialysis system for the removal of copper ions

Hybrid ion exchange electrodialysis processes allow the removal of metal ions from dilute waste liquids and the recovery of more concentrated solutions. The work reported here was aimed at investigating the two steps in the treatment process, namely, adsorption of metal ions onto the packed bed of resin and electromigration (i.e., the transport of these ions in the complex system under the applied electrical field). The case of copper sulfate was investigated. Dowex™ resins with a cross-linking degree of 2 and 8% were used. The flux of copper through the resin bed and the current efficiency for ion transfer to the cathode compartment were determined as a function of potential gradient and copper ionic fraction in the bed. Apparent diffusion coefficients of Cu2+ in the overall system were deduced from the experimental data.

High interaction alginate–hyaluronate associations by hyaluronate deacetylation for the preparation of efficient biomaterials

The paper presents fundamental investigations of alginate-hyaluronate association with significant polymer interactions for preparation of efficient biomaterials. For this purpose, acetamide functions of hyaluronate were partly cleaved by hydrazine at high temperature, yielding amino groups accessible to carboxylic functions of the alginate chain. Alginate-hyaluronate association was studied both in dissolved state by rheological measurements and CD, and in the form of gel slabs prepared after calcium diffusion. Appreciable interaction between carboxylic groups of alginate and the released amino groups of hyaluronate was put into evidence by enhanced values of the viscosity of mixed solutions, and by assessment of the properties of the gel formed: moderate deacetylation allowed gels of improved hardness and viscosity. Nevertheless, high deacetylation was observed to hinder the gel formation by Ca(2+) complexation of alginate, by the significant competition of COOH-NH(2) association. Interaction between alginate and modified hyaluronate results in regular gel structure, with small cavities.

Absorption of sulfur dioxide in N-formylmorpholine: investigations of the kinetics of the liquid phase reaction

Abstract Absorption of sulfur dioxide in N -formylmorpholine results in the reversible formation of 1:1 complex, as shown previously. This paper presents a kinetic investigation of the liquid-phase reaction. This reaction was assumed to be a fast process and this work was aimed at the verification of this hypothesis. Absorption of sulfur dioxide either as pure gas or diluted into an inert, was carried out at 25°C in a stirred vessel with a flat interface. The experimental data were modelled under the assumption of a fast reversible formation of a SO 2 –NFM complex. The comparison between experiment and model calculations indicated that the liquid-phase reaction was instantaneous or at least very fast, with Ha number over 100.