66 research outputs found
Zinc-rich paint coatings containing either ionic surfactant-modified or functionalized multi-walled carbon nanotube-supported polypyrrole utilized to protect cold-rolled steel against corrosion
The intense anodic action of sacrificial zinc pigments ensured viable galvanic function of the highly porous liquid zinc-rich paints (ZRPs) result in deteriorated long-term corrosion resistance often accompanied by cathodic delamination phenomena. In our approach, such a efficacy problem related to the corrosion preventive function of ZRPs is addressed by the application of intimately structured anodic inhibitor particles composed of nano-size alumina and either polyelectrolyte-modified or chemically functionalized multi-walled carbon nanotubes (MWCNT) supported polypyrrole (PPy) in one specific zinc-rich hybrid paint formulation providing balanced active–passive protective functionality.
High dispersity of the nanotube-free PPy-deposited inhibitor particles (PDIPs) with uneven polymer distribution on the alumina carrier was confirmed by transmission electron microscopy (TEM) observations. Furthermore, the MWCNT-embedded PDIPs indicated almost complete surface coverage of the alumina-nanotube carriers by PPy with decreased microstructure dispersity which is attributed to the effect of double-flocculants type co-deposition of the oppositely charged polymers causing coalescence of the modified particles. Depending on the amount of the nanotubes and their proportion to the quantities of the deposited PPy and polyelectrolyte as well as the concentration of the surfactant, varied micron-scale association of the PDIPs in the suspensions of dissolved alkyd matrix was disclosed by rheology characterization carried out at particular solid contents similar to hybrid paint formulation. The evenly distributed but less densely packed nano-structure of PPy was evidenced on the polyelectrolyte-modified nanotubes by Fourier-transform infrared (FTIR) spectroscopy whereas more compact polymer film formation was confirmed on the surface of functionalized nanotubes. According to the greater electrical conductivity, enhanced electroactivity and reversibility of the nanotube-embedded PDIPs were indicated over the nanotube-free particles by cyclic voltammetry, depending on the type and the amount of the nanotubes and their modification.
Protection function of the hybrid paint coatings (formulated with spherical zinc pigment at 70 wt.%) was investigated by immersion and salt-spray chamber tests over 254 and 142 day periods, respectively. Firm barrier nature of the nanotube-embedded PDIP contained hybrids was proved by electrochemical impedance spectroscopy (EIS) and radio-frequency glow-discharge optical-emission-spectroscopy (RF-GD-OES). Furthermore, due to the increased conductivity of the nanotube-embedded PDIPs cemented in epoxy primers optimally at 0.4 and 0.6 wt.%, altered corrosion preventive behaviour of the hybrid coatings was indicated by the positively polarized open-circuit potentials (OCPs) and the X-ray photoelectron spectroscopy (XPS) detected lower relative quantities of the interfacially accumulated zinc corrosion products, moderate oxidative degradation of the epoxy vehicle. Decreasing oxidative conversion of iron at the surface was indicated by XPS found to correlate with the increasing intensity of zinc corrosion and decreasing oxidative degradation of the epoxy binder, according to the higher nanotube contents of hybrid coatings. In addition, inhibited zinc corrosion caused low rate of oxidative degradation of epoxy, allowing increased durability of coating adhesion and cohesion thereby ensuring reliable protection by zinc-rich compositions.
As a conclusion, modified or functionalized MWCNTs acting as unexchangeable doping agents promote enhanced reversibility and increased conductivity of PPy, forming nano-size inhibitor particles with advanced features. Thus, such inhibitor nano-particles in zinc-rich hybrid compositions afford improved barrier and high efficiency galvanic–cathodic corrosion preventive function, exceeding long-term protection capability of the conventional ZRPs
Protein molekulák adszorpciójának in situ molekuláris szintű jellemzése fogászati implantátumok nanostrukturált felületén összegfrekvencia-keltési spektroszkópiával = Adsorption of protein molecules on nanostructured surfaces of dental implants: in situ molecular level studies by Sum Frequency Generation Spectroscopy
A titán részben kedvező mechanikai tulajdonságai, részben a felületén kialakuló oxidréteg sajátosságai miatt a legszélesebb körben felhasznált biokompatibilis fém. A projekt alapvető célkitűzése a biokompatibilitás molekuláris hátterének tanulmányozása volt aminosavak és proteinek titán-dioxidon és más biológiai szempontból potenciálisan jelentős felületeken lejátszódó adszorpciójának összegfrekvencia-keltési spektroszkópiai vizsgálata segítségével. Számos aminosavra vonatkozó eredményeink alapján megállapítottuk, hogy a kvarcüveg-aminosav oldat határfelületen nem alakul ki rendezett adszorbeált réteg, míg a kalcium-fluorid-aszparaginsav oldat határfelületen aminosav kristályok nukleálódása figyelhető meg. Az aminosavak többsége a titán-dioxidon is gyengén adszorbeálódik, egyedül a savas oldalláncú aminosavak, mint az aszparaginsav vagy a glutaminsav, alkotnak rendezett adszorbeált réteget. Az aszparaginsav példáján keresztül tisztáztuk a savas aminosavak titán-dioxidhoz való kötődésének részleteit és meghatároztuk az adszorbeátumok orientációját. Fehérjeadszorpcióval kapcsolatos vizsgálataink során módszert dolgoztunk ki a határfelületen elhelyezkedő protein molekulák orientációs paramétereinek kombinált lineáris és nemlineáris optikai spektroszkópiai mérések alapján történő meghatározására. Egy gyakorlati példa kapcsán molekuláris szintű modellt adtunk a véralvadási kaszkád töltött felületen adszorbeálódó XII. faktorának aktiválódási mechanizmusára. | Due to the favorable properties of its surface oxide, titanium is the most widely used biocompatible metal. The most important purpose of this project was to investigate the molecular level background of biocompatibility by means of sum frequency generation vibrational spectroscopy study of adsorption of amino acids and proteins on titanium-dioxide and other biologically important surfaces. It was established that no ordered amino acid adsorbate layer forms at the fused silica-amino acid solution interface. On the contrary, at the calcium fluoride-solution interface growth of randomly oriented aspartic acid crystallites was observed. Although most amino acids were found to adsorb weakly on titanium dioxide, our measurements revealed that acidic amino acids like aspartic acid or glutamic acid form a stable, uniform, ordered overlayer. The bonding mechanism and the orientation of the aspartic acid adsorbates were analyzed in detail. Concerning protein adsorption, a method was proposed for determination of the orientation parameters of interfacial protein molecules by combining data from linear and nonlinear optical spectroscopic measurements. Finally, the interaction of the blood coagulation Factor XII with charged surfaces was studied and a molecular level model was suggested for its autoactivation
Mechanism of NO-SCR by methane over Co,H-ZSM-5 and Co,H-mordenite catalysts
Results of X-ray photoelectron spectroscopic (XPS) examination and temperatureprogrammed
reduction measurements by H2 (H2-TPR) showed that the Co-zeolite catalysts,
which were found most active in the selective catalytic reduction of NO by methane to N2 in
the presence of excess O2 (NO-SCR), contain both Co2+/[Co-OH]+/H+ exchange cations, Cooxo
species and cobalt oxide clusters. Using operando Diffuse Reflectance Infrared Fourier
Transform Spectroscopic method (DRIFTS method) the NO-SCR reaction was shown to
proceed in consecutive steps via bifunctional mechanism over active sites (i) promoting the
oxidation of NO by O2 to NO2 (NO-COX reaction), and sites (ii) whereon disproportionation
and charge separation of 2NO2 generates activated surface intermediate NO3
-/NO+ ion pair.
Latter process was found to require Co2+ zeolite cations. The NO-COX reaction was shown to
proceed over Co-oxo species and cobalt oxide, if present, and also over Brønsted acid sites
but at a significantly lower rate. In the reaction of methane and the NO3
-/NO+ ion pair CO2,
H2O, and N2 was formed and the active Co2+ sites were recovered (CH4/NO-SCR reaction).
The surface concentration of the NO3
-/NO+ ion pair must have been controlled by the relative
magnitude of the apparent rate constants of the consecutive NO-COX and CH4/NO-SCR
reactions. Below about 700 K reaction temperature latter reaction governed the rate of the consecutive NO reduction process. Above about 700 K combustion became the main reaction
of methane. Because of the low equilibrium NO2 concentration at these high temperatures the
NO-COX reaction took over the control over the rate of the NO-SCR process. Under steady
state reaction conditions a temperature-dependent fraction of the Co2+ active sites was always
poisoned by adsorbed H2O formed in the CH4 oxidation reaction
Polipirrollal módosított szén nanocső/ alumínium-oxid monohidrát alapú cinkdús hibrid festékalapozók vizsgálata
Irányított felületi reakciók alkalmazása PEM tüzelőanyag-elemek CO-toleráns anódoldali elektrokatalizátorainak fejlesztéséhez
CO tolerant Pt electrocatalysts for PEM fuel cells with enhanced stability against electrocorrosion
Preparation and characterization of novel Ti0.7W0.3O2-C composite materials for Pt-based anode electrocatalysts with enhanced CO tolerance
Ti-based electroconductive mixed oxides were deposited onto activated carbon by using
three different sol-gel-based multistep synthesis routes. As demonstrated by X-ray
diffraction, high crystallinity of the tungsten-loaded rutile was achieved by a sequence
of annealing in inert atmosphere at 750°C and a short reductive treatment at 650°C.
Formation of the rutile phase on the carbon support before the high temperature
treatment has been proved to be the prerequisite for complete W incorporation into the
rutile lattice. The structural and compositional properties of the mixed oxides were
explored by transmission electron microscopy, temperature programmed reduction and
X-ray photoelectron spectroscopy. Anode electrocatalysts were formulated by loading
the composite of the activated carbon and the Ti-based electroconductive mixed oxides
with 40 wt% Pt. Enhanced CO tolerance along with considerable stability was
demonstrated for the electrocatalyst prepared using the Ti
0.7
W
0.3
O
2
-C composite
material with high degree of W incorporation
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