Phosphonic acid‐containing polysulfones as anticorrosive layers

As a part of research work to elaborate polymeric materials for metal corrosion protection, we have developed a new family of phosphonic acid‐containing polymers. The synthesis and the characterization of polysulfones bearing alkyl phosphonate ester side groups are first described. These polymers are synthesized by direct polycondensation of a phosphonate ester‐containing bisphenol by aromatic nucleophilic substitution. The physicochemical properties of the resulting polymers are described. Acidic hydrolysis of phosphonate esters results in the formation of phosphonic acid groups. A series of phosphonic acid‐containing polysulfones is therefore obtained and characterized. A preliminary evaluation of the anticorrosive properties of these polymers is described. In 0.25M Na₂SO₄ solution, the corrosion rate of a polymer‐coated mild steel sample is much lower than of the free metal substrate. These results suggest that phosphonic acid‐containing polysulfones might be interesting as anticorrosive coatings. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41890.     

Microwave-assisted synthesis of tetrasubstituted aryl imidazole based polymers via cascade polycondensation process

Poly(Tetrasubstituted Aryl Imidazole)s (PTAIs), a new class of poly(heteroaromatic) polymers was prepared via a cascade polycondensation process, under microwave irradiation. These polymers were obtained by the tetrasubstituted aryl imidazole ring formation involving bis(aryl α-diketone)s, bis(arylaldehyde)s, mono(arylamine)s and ammonium acetate. The polymerization performed under microwave irradiation allowed to get high molecular weight PTAIs in very short reaction times. The chemical structure of these PTAIs was confirmed by NMR spectroscopy. Thermogravimetric analyses (TGA) showed a very good grade of thermal stability of these polymers. Glass transition temperatures (T_g) of PTAIs ranging from 155 °C to 265 °C were determined by Differential Scanning Calorimetry (DSC).     

Effect of corn particle size on site and extent of starch digestion in lactating dairy cows

Two experiments were conducted to determine the effects of corn particle size (CPS) on site and extent of starch digestion in lactating dairy cows. Animals were fitted with ruminal, duodenal, and ileal cannulas. Dry corn grain accounted for 36% of dry matter intake. In experiment 1, 6 cows were used in a duplicate 3 x 3 Latin square design. Semiflint corn was used. Corn processing methods were grinding, medium rolling, and coarse rolling. The mean particle size of the processed corn was 730, 1807, and 3668 microm, respectively. Rumen digestibility of starch linearly decreased from 59% with ground corn to 36% with coarsely rolled corn. Similarly, small intestine digestibility linearly decreased with increased CPS, and consequently, the amount of starch digested in the small intestine was not affected by corn processing. In experiment 2, 4 cows were used in a 2 x 2 crossover design. Dent corn was used. Corn processing methods were grinding and coarse rolling. The mean particle size of the processed corn was 568 and 3458 microm, respectively. Rumen digestibility of starch decreased from 70% with ground corn to 54% with coarsely rolled corn. Small intestine digestibility of starch was not significantly affected by CPS, and the amount of starch digested in the small intestine tended to be greater for rolled than for ground corn. In both experiments, starch total tract digestibility decreased with increased CPS. In conclusion, CPS is an efficient tool to manipulate rumen degradability of cornstarch. In midlactation cows, the decrease in the amount of starch digested in the rumen between grinding and coarse rolling is partly compensated for by an increase in the amount of starch digested in the small intestine with dent genotype, but with semiflint genotype postruminal digestion is not increased and rumen escape starch is not utilized by the animal.     

Values of the mass transfer coefficient of the linear driving force model for VOC adsorption on activated carbons

Modelling of activated carbon cartridges is essential in personal protective equipments against toxic gases in order to know the duration of protection. The linear driving force model seems to be more adapted than the actual Wheeler–Jonas model because it has more physical significance. The difficulty is that the mass transfer coefficient can not be calculated a priori. Values of the LDF mass transfer coefficient are disseminated in the literature and thus there is no overview of the range and variations with different adsorbents, adsorbates and concentrations. The object of this paper is thus twofold: obtaining values of the mass transfer coefficient at different concentrations and adsorbates in order to have a comprehensive view of variations and appreciating the validity of the LDF constant pattern model.     

(Zn, Mg)O/ZnO-based heterostructures grown by molecular beam epitaxy on sapphire: Polar vs. non-polar

Zinc oxide (ZnO) has recently attracted considerable attention because of its unique physical properties and its potential applications in the blue and UV spectral range. Up to now, ZnO-based heterostructures have mostly been grown in a c-orientation. The growth of non-polar layers along the a-direction [1 1 2¯ 0] has been proposed to avoid any built-in electric fields in the c-direction. Polar and non-polar quantum wells (QWs) embedded in (Zn, Mg)O barriers were grown on an optimized buffer. We compare the photoluminescence (PL) emission of a- and c-oriented QWs. From this comparison, we demonstrate that the QWs exhibit confinement but no indication of quantum confined Stark effect, contrary to what is observed in c-oriented structures. In the non-polar orientation, it is shown that the thermal quenching is not related to the thermal escape of excitons from the ZnO area, since the calculated activation energies are much lower.     

An experimental investigation of the combustion of technical tetrachlorobenzene in a laboratory scale incinerator

An experimental study of the combustion of technical 1,2,3,4-tetrachlorobenzene has been carried out in conditions closely similar to those in incinerators of industrial hazardous wastes. A non-premixed flame fed by a fuel spray was stabilized in a reactor heated electrically. Measurements of axial and radial temperatures and species concentration profiles in well-defined conditions have been systematically repeated to specify the influence exerted by key parameters on the efficiency of the thermal degradation process. The reactor’s wall temperature was varied from 1223 to 1363 K. Air injection was distributed between axial and peripheral injectors to change the swirl intensity. Two fuel injectors have been compared to assess the influence of atomization efficiency. A methane-air pilot flame helped to anchor the flame and to decrease the overall Cl/H ratio. The latter was also decreased by addition of water vapor. Results show that conditions leading to a complete consumption of the fuel can be associated with very limited carbon conversion into CO₂ and chlorine conversion into HCl.     

Induced structural modifications in ZnS nanowires via physical state of catalyst:Highlights of 15R crystal phase

Peculiar and unique growth mechanisms involved in semiconductor nanowires(NWs)pave the way to the achievement of new crystallographic phases and remarkable material properties,and hence,studying polytypism in semiconductor NWs arouses a strong interest for the next generation of electronic and photonic applications.In this context,the growth of ZnS nanowires has been investigated,as bulk ZnS compound exhibits numerous unstable polytypes at high temperatures,but their stable occurrence is highly anticipated in a nanowire due to its special quasi-dimensional shape and growth modes.In this work,the idea is to provide a change in the growth mechanism via the physical state of catalyst droplet(liquid or solid)and hence,study the induced structural modifications in ZnS nanowires.The HRTEM images of VLS(via liquid alloyed catalyst)grown ZnS NWs show periodic stacking faults,which is precisely identified as a stacking sequence of cubic or hexagonal individual planes leading to an astonishing 15R crystal polymorph.This crystallographic phase is observed for the first time in nanowires.Contrastingly,NWs grown with VSS(via solid catalyst)show crystal polytypes of zinc blende and wurtzite.We calculate and discuss the role of cohesive energies in the formation of such ZnS polytypes.Further,we present the selection rules for the crystallization of such 15R structure in NWs and discuss the involved VLS and VSS growth mechanisms leading to the formation of different crystal phases.     

Impedance spectroscopy and modelling of zinc deposition in chloride electrolyte containing a commercial additive

The kinetics of zinc deposition from a concentrated chloride electrolyte containing a commercial additive are investigated by impedance spectroscopy. A reaction model formerly validated for zinc deposition in acidic sulphate medium has been adapted to the present electrolyte and closely related to the elementary steps involved in the crystal growth process. Simulation of the electrode kinetics shows that the additive modifies the deposit morphology by changing some specific rates of the surface steps: slowing down the charge transfer reactions, poisoning the active kink sites and increasing the deposition overpotential. Thus zinc deposition takes place on a surface where the intermediate adions Zn⁺ _ad and the active kink sites are more numerous and where the nucleation rate is increased, leading to refined grain size.     

Analysis of flame surface density measurements in turbulent premixed combustion

In premixed turbulent combustion, reaction rates can be estimated from the flame surface density. This parameter, which measures the mean flame surface area available per unit volume, may be obtained from algebraic expressions or by solving a transport equation. In this study, detailed measurements were performed on a Bunsen-type burner fed with methane/air mixtures in order to determine the local flame surface density experimentally. This burner, located in a high-pressure combustion chamber, allows investigation of turbulent premixed flames under various flow, mixture, and pressure conditions. In the present work, equivalence ratio was varied from 0.6 to 0.8 and pressure from 0.1 to 0.9 MPa. Flame front visualizations by Mie scattering laser tomography are used to obtain experimental data on the instantaneous flame front dynamics. The exact equation given by Pope is used to obtain flame surface density maps for different flame conditions. Some assumptions are made in order to access three-dimensional information from our two-dimensional experiments. Two different methodologies are proposed and tested in term of global mass balance (what enters compared to what is burned). The detailed experimental flame surface data provided for the first time in this work should progressively allow improvement of turbulent premixed flame modeling approaches.