L. Gengembre

A new triazole derivative as inhibitor of the acid corrosion of mild steel: electrochemical studies, weight loss determination, SEM and XPS

Abstract The effect of addition of 2[5-(2-pyridyl)-1,2,4-triazol-3-yl] phenol (PPT) on mild steel dissolution in 1 M hydrochloric acid is studied through electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation curves and gravimetric measurements. The obtained results showed that PPT revealed a good corrosion inhibition. Potentiodynamic polarisation studies indicate that PPT is a mixed-type inhibitor. The effect of temperature on the corrosion behaviour of mild steel in 1 M HCl with addition of 80 mg/l of PPT was studied in the temperature range from 25°C to 60°C. The associated activation corrosion and free adsorption energies have been determined. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) of the mild steel revealed that PPT is absorbed on the steel surface. PPT appears to function through the general adsorption mode following the Langmuir adsorption isotherm model.

Inhibition of acidic corrosion of mild steel by 3,5-diphenyl-4H-1,2,4-triazole

The inhibitor effect of 3,5-diphenyl-4H-1,2,4-triazole (DHT) on the corrosion of mild steel in hydrochloric acid solution was investigated at 30°C using electrochemical and weight loss measurements. Polarisation curves revealed that this organic compound act as mixed-type inhibitor and inhibition efficiencies up to 98% can be obtained. The inhibition efficiency calculated from these techniques are in reasonably good agreement. X-ray photoelectron spectroscopy (XPS) spectra of the steel surface treated with the 1 M HCl solution containing the DHT molecules revealed their adsorption on the surface. The DHT appears to function through the general adsorption mode following the Langmuir adsorption isotherm model.

XPS study of an intumescent coating: II. Application to the ammonium polyphosphate/pentaerythritol/ethylenic terpolymer fire retardant system with and without synergistic agent

Abstract Fire retardancy of polymer may be due to the formation of protective surface coating, i.e. a swollen char layer (intumescence). The intumescent coatings resulting from thermal treatments of the association of ammonium polyphosphate (APP) and pentaerythritol (PER) with or without zeolite 4A (used as synergistic agent) in a polyethylenic terpolymer (LRAM3.5) are studied by X-ray photoelectron spectroscopy. The O 1s , P 2p , C 1s and N 1s spectra are discussed. The formation of pyridinic and pyrrolic nitrogen and quaternary nitrogen in polyaromatic groups in the intumescent structures is shown. The oxidised nitrogen (nitro groups and pyridine N-oxide) are only observed up to 350°C and then are evolved as NO x species. It is then proposed that the pyridinic function, observed only in the case of the system with zeolite at all temperatures, participates in the improvement of the fire proofing properties of the materials.

Adhesion enhancement by a dielectric barrier discharge of PDMS used for flexible and stretchable electronics

Currently, there is a strong tendency to replace rigid electronic assemblies by mechanically flexible and stretchable equivalents. This emerging technology can be applied for biomedical electronics, such as implantable devices and electronics on skin. In the first step of the production process of stretchable electronics, electronic interconnections and components are encapsulated into a thin layer of polydimethylsiloxane (PDMS). Afterwards, the electronic structures are completely embedded by placing another PDMS layer on top. It is very important that the metals inside the electronic circuit do not leak out in order to obtain a highly biocompatible system. Therefore, an excellent adhesion between the 2 PDMS layers is of great importance. However, PDMS has a very low surface energy, resulting in poor adhesion properties. Therefore, in this paper, PDMS films are plasma treated with a dielectric barrier discharge (DBD) operating in air at medium pressure (5.0 kPa). Contact angle and XPS measurements reveal that plasma treatment increases the hydrophilicity of the PDMS films due to the incorporation of silanol groups at the expense of methyl groups. T-peel tests show that plasma treatment rapidly imparts adhesion enhancement, but only when both PDMS layers are plasma treated. Results also reveal that it is very important to bond the plasma-treated PDMS films immediately after treatment. In this case, an excellent adhesion is maintained several days after treatment. The ageing behaviour of the plasma-treated PDMS films is also studied in detail: contact angle measurements show that the contact angle increases during storage in air and angle-resolved XPS reveals that this hydrophobic recovery is due to the migration of low molar mass PDMS species to the surface.

XPS STUDY OF AN INTUMESCENT COATING APPLICATION TO THE AMMONIUM POLYPHOSPHATE/PENTAERYTHRITOL FIRE-RETARDANT SYSTEM

Abstract Fire retardancy of polymers may be due to the formation of a protective surface coating, i.e. a swollen charred layer (intumescence). An intumescent coating resulting from thermal treatments of the association of ammonium polyphosphate (APP) and pentaerythritol (PER) is studied by X-ray photoelectron spectroscopy. The O 1s, P 2p, C 1s and N 1s spectra are discussed. In the formation of the intumescent material the presence is shown of nitrogen in pyrrole and pyridine type structures of aromatic phosphate esters. A degradation mechanism is suggested which involves a reaction with O 2 via the formation of carbonyl and carboxylic groups.

Polypropylene film chemical and physical modifications by dielectric barrier discharge plasma treatment at atmospheric pressure

Dielectric barrier discharge (DBD) technologies have been used to treat a polypropylene film. Various parameters such as treatment speed or electrical power were changed in order to determine the treatment power impact at the polypropylene surface. Indeed, all the treatments were performed using ambient air as gas to oxidize the polypropylene surface. This oxidation level and the surface modifications during the ageing were studied by a wetting method and by X-ray photoelectron spectroscopy (XPS). Moreover polypropylene film surface topography was analyzed by atomic force microscopy (AFM) in order to observe the surface roughness modifications. These topographic modifications were correlated to the surface oxidation by measuring with a lateral force microscope (LFM) the surface heterogeneity. The low ageing effects and the surface reorganization are discussed.

Surface structure and reactivity of VTiO catalysts prepared by solid-state reaction 2. Nature of the active phase formed during o-xylene oxidation

Abstract The modifications occurring to V2O5 crystallites supported on TiO2 (anatase or rutile) in contact with an o-xylene/air flow at about 600 K are characterized by determining the change in the valence state of vanadium through chemical analyses, the variation in the vanadium coordination environment through FT-IR and solid-state 51V NMR spectroscopies, and the modification in the nature and distribution of the vanadium-oxide phase by means of XRD and XPS analyses. Results are analyzed with reference to the time-on-stream modifications in the catalytic behavior in o-xylene oxidation to phthalic anhydride of these catalysts and to the catalytic behavior and physicochemical characteristics of V3O7 supported on TiO2 and of an unsupported partially reduced vanadium-oxide phase. On anatase samples, the TiO2 surface is covered homogeneously by a VIVVV partially hydrated mono- or bilayer. Overlaying this phase a hydrated V3O7-like phase (VV: VIV ratio of about 2 : 1) is also present as amorphous multilayer patches. In rutile samples, the former phase is no longer present, but instead islands of partially oxidized V2O4 are found together with the same partially reduced V-oxide phase as in the anatase samples. Catalytic results indicate that both phases have roughly similar catalytic behaviors and that the role of the TiO2 support both in the anatase and rutile forms is to increase the number of surface sites, but not to modify their nature which depends only on the modifications occurring during the catalytic tests.

Surface Modification of Non-woven Textiles using a Dielectric Barrier Discharge Operating in Air, Helium and Argon at Medium Pressure

In this paper, polyethylene terephthalate (PET) and polypropylene (PP) non-wovens were modified by a dielectric barrier discharge in air, helium and argon at medium pressure (5.0 kPa). The helium and argon discharges contained a fraction of air smaller than 0.1 %. Surface analysis and characterization were performed using X-ray photoelectron spectroscopy, liquid absorptive capacity measurements and scanning electron microscopy (SEM). The non-wovens, modified in air, helium and argon, showed a significant increase in liquid absorptive capacity due to the incorporation of oxygen-containing groups, such as C—O, O—C=O and C=O. It was shown that an air plasma was more efficient in incorporating oxygen functionalities than an argon plasma, which was more efficient than a helium plasma. SEM pictures of the plasma-treated nonwovens showed that the hydrophilicity of the nonwovens could be increased to a saturation value without causing physical degradation of the surface. The ageing behavior of the plasma-treated textiles after storage in air was also studied. It was shown that during the ageing process, the induced oxygen-containing groups re-orientated into the bulk of the material. This ageing effect was the smallest for the argon-plasma treated non-wovens, followed by the helium-plasma treated non-wovens, while the air-plasma treated non-wovens showed the largest ageing effect.

Oxidative dehydrogenation of isobutane on Cr-Ce-O oxide II. Physical characterizations and determination of the chromium active species

Abstract Cr–Ce–O catalysts with different Cr contents and prepared by different methods have been characterized by X-ray diffraction (XRD), XPS, ISS and UV–Vis spectroscopies, and the surface potential technique. On the basis of these studies, a model of catalysts has been proposed and the correlations between the structure of the catalysts and their performance in the oxidative dehydrogenation (ODH) of isobutane have been discussed. At low Cr content corresponding to the coverage of the ceria surface with chromium θ 6+ O x species are the only Cr species, irrespective of the preparation method. In the θ range 35–61%, well dispersed Cr 3+ species appear as Cr 2 O 3 . The maximum coverage of 75% is obtained for the samples prepared by impregnation at 20 Cr atoms per nm 2 . From this Cr content, agglomeration of Cr 2 O 3 is observed. The specific rate of isobutene formation increases with the increase in Cr content up to the coverage of about 61% and then remains constant. It is concluded that the activity is due to the well dispersed Cr 6+ O x species on the ceria surface, whereas agglomerates of Cr 2 O 3 do not contribute to the reaction.

Study of mixed-oxide catalysts containing bismuth, vanadium and antimony. Preparation, phase composition, spectroscopic characterization and catalytic oxidation of propene

The structural and catalytic properties of oxides in the Bi–V–Sb–O system, which are propene oxidation catalysts, have been studied. Two domains of solid solutions exist for the compounds BiV1–xSbxO4, with the scheelite structure for 0 ⩽x < 0.04 and a monoclinic structure for 0.876 ⩽x⩽ 1. Characterization by X-ray photoelectron spectroscopy (X.p.s.) shows that for a given MO (M = Bi, V or Sb) environment, the higher the average interatomic distance, the higher the cation binding energy, corresponding to an effective decrease in electronic density. From a semi-quantitative X.p.s. analysis of the surface composition of the BiV1–xSbxO4 system it is shown that for low values of x(x⩽ 0.10) the surface concentrations of vanadium and oxygen decrease sharply compared with those of the other elements. Activities and selectivities for acrolein, determined in a stirred gas–solid reactor, are measured as a function of x. Oxides having the scheelite structure exhibit a sharp increase in activity with increasing x. The larger performance found for x= 0.035 is connected with a high oxygen mobility.