Publikationen

Galvanised and galvannealed steels are widely used due to their good corrosion resistance in aqueous solutions. However, when additional protection is required, organic coatings, corrosion inhibitors or conversion coatings are used to improve their corrosion protection. In this work, sol-gel coating was used to improve the corrosion behaviour of these two materials. This paper analyses the final protective properties of a sol-gel coating prepared by basic catalysis and its dependence on the sintering temperature and time of treatment. The influence of the sintering conditions on the galvanised and galvannealed substrates is a decisive factor for the coating quality and for the barrier affect against the aggressive media. While heat treatment time is the controlling factor for the galvannealed steels, the temperature is determining in the case of the galvanised. Corrosion mechanisms for sol-gel galvanised steels did not changed with respect to the uncoated steel. However for galvannealed steel, after coating the mechanism is not purely cathodic.

Some mixed 1,3-dithia-2-stibacyclopentane derivatives with phosphorus based dithiolato ligands of the types (SCH2CH2SS)bS(S) (POGO) {where G = -CH(Me)-CH(Me)- and -C(Me)2-C(Me)2-} and (SCH2SS)bS(S)P(OR)2 {where R = Prn, Bun and Ph} have been synthesized by the reaction of 2-chloro-1,3-dithia-2-stibacyclopentane and the ammonium/sodium salt of the corresponding phosphorus based ligands in an equimolar ratio in anhydrous benzene solution. These yellow crystalline solid/semi-solid derivatives have been characterized by elemental analysis (C, H, S and Sb), molecular weights, melting point as well as spectral [UV, IR and NMR (1H, 13C and 31P)] studies. Single crystal X-ray diffraction analyses of 1,3-dithia-2-stibacyclopentane 2,3-butylenedithiophosphate revealed a monodentate mode of bonding of the dithiophosphate ligand in the complex. The free ligands and their antimony(III) complexes have also been screened for their antibacterial and antifungal activities.

An unusual almost flat broadband plasmonic absorption, ranging from 400 nm to well beyond 2500 nm, was observed in a 150 nm thin film of Ag nanoparticles embedded in a Teflon AF (R) matrix. The nanocomposites were synthesized by a simple single-step vapor-phase codeposition method. The Ag nanoparticles of various sizes and shapes, and thus various resonance frequencies, form a fractal percolating network. The broadband absorption, attributed to plasmon excitations within the nanoparticles, could be useful for multicolor applications in the visible and infrared wavelengths region. (c) 2006 American Institute of Physics.

Transparent conducting In2O3:Sn (ITO) layers have been deposited by spin coating on glass substrates using two different solutions, an ethylene glycol solution of indium and tin salts (sol) and a suspension of crystalline ITO nanoparticles redispersed in ethanol. The coatings have been sintered in air at 550°C for 30 min. and then post annealed in a reducing atmosphere at 300°C for 30 min. The electrical, optical, morphological and mechanical properties of both types of coatings are compared. The use of the suspension leads to thick 500 nm single layers with a specific resistivity ρ=1.6×10-2 Ωcm but only very thin ones, about 12 nm for a single layer, with ρ = 1.8 x 10-3 Ωcm (a factor of 10 smaller) are obtained using the sol. The resistivity still decreases down to a minimum ρ= 6 x 10-4 Ωcm for multilayer coatings, a value quite close to that obtained by PVD or CVD processes. These differences originate from the different morphologies of the coatings. The conventional sol-gel layers exhibit a columnar structure with a low porosity (28%) while the others have a granular structure with a high porosity (51%). Correspondingly the electron mobility µ is 14 and 1.1 cm2/V s, respectively. The visible transmission of both types of layers is high (T>85%). The influence of the sintering temperature is also discussed.

Films of NiO-TiO2 with Ni concentration of 100, 90, 87, 83, 75, 66, 50 and 33 mol% have been obtained via the sol-gel route by dip coating technique and sintered in air between 250 and 500°C using ethanolic sols of nickel acetate tetrahydrate (Ni(CH3COO)2∙4H2O) and titanium n-propoxide (Ti(O-CH(CH3)2)4) precursors. Xerogels obtained by drying the sols have been studied up to 900°C by thermal analysis (DTA/TG) coupled to mass and IR spectroscopy. The crystalline structure and morphology of the layers in the as deposited, bleached and colored states were determined by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. Their electrochromic properties have been studied in 1 M KOH aqueous electrolyte as a function of the layer composition, thickness and sintering temperature. Deep brown colour with reversible transmittance changes have been obtained using cycling voltammetry and chronoamperometry processes. The best composition to get stable sols, a high reversible transmittance change and fast switching times (< 10 s) was obtained with double NiO-TiO2 layers 160 nm thick having 75% Ni molar concentration, and sintered between 300 and 350°C. The mechanism of coloration and morphology transformation of the layer during cycling are discussed in terms of an activation and degradation period. The results are in agreement with the accepted Bode model.

Brown coloring electrochromic 5 x 10 cm2 windows with the configuration K-glass/NiO-TiO2/electrolyte/CeO2-TiO2/K-glass have been prepared and characterized by optoelectrochemical techniques (cyclic voltammetry, chronoamperometry and galvanostatic measurements). The electrochromic layers have been prepared by the sol-gel technique. As electrolyte either a 1 M aqueous KOH solution or a newly developed starch-based gel impregnated with KOH have been used. The CeO2-TiO2 sol gel layers sintered at 550°C have been previously characterized in 1 M aqueous KOH electrolyte as a function of the thickness up to 2000 cycles and showed a highly reversible behavior without any corrosion effect. The NiO-TiO2 sol-gel layers sintered at 300°C have been extensively characterized in the same electrolyte up to about 7000 cycles. All windows present a deep brown color characteristic of the presence of Ni3+ (NiOOH) species, that is fully reversible for several thousands of cycles with a rather-fast kinetics (< 30 s). The transmittance of the bleached state however slowly decreases with cycling (permanent coloration). The full-bleached condition can be nevertheless recovered by applying a negative potential for a long duration. Deeper coloration is usually obtained by cycling the windows galvanostatically with a current density of 20 µA/cm2. The lifetime of the windows is however limited because of the degradation of the NiO-based layers due to the not fully reversible exchange of OH- that turns the layers mechanically fragile and leads eventually to their complete removal from the substrate. Windows working satisfactorily up to 7000 and 17 000 cycles have been obtained using aqueous KOH electrolyte and starch KOH gel electrolyte, respectively. Memory tests showed that the devices bleach at the open circuit potential from T=39% (colored state) to about T=50% in 60 min.

Pure anatase-TiO2 nanoparticles with 8 nm average crystallite size was synthesized hydrothermally at 200°C in 2 h. The structural and physicochemical properties of nano-TiO2 were determined by powder XRD, FT-IR, BET and SEM analyses. The behavior of anatase nano-TiO2 in catalytic degradation of Rhodamine B (RB) dye in transparent nano-TiO2 sol under UV-light was examined as a function of irradiation power of UV-Iight, irradiation time, amount of nano-TiO2 and initial RB concentration in the sol. Rhodamine B was fully degraded with the catalysis of the nano-TiO2 in a short time as low as 60 min. Photocatalytic activity of the nano-TiO2 for degradation of RB was compared with Degussa P-25 at optimum catalysis conditions determined for the nano-TiO2. It was found that, when compared to Degussa P-25, the nano-TiO2 could be repeatedly used with increasing photocatalytic activity. It was found that the photodegradation obeys the pseudo first-order reaction kinetics with the rate constant of 0.0658 min-1, and the half period t1/2 was 10.53 min.

Photocatalytic performance of a hydrothermally synthesized pure anatase TiO2 with 8mm average crystalline size for decomposition of Reactive Red 141 was examined by investigating the effects of UV-light irradiation time, irradiation power, amount of TiO2 and initial dye concentration. Change in the UV absorbance of the dye during irradiation was monitored. One wt.% TiO2 in 30 mg/l Reactive Red 141 aqueous solution was found adequate for complete decolorization in 70 min at 770 W/m2 irradiation power. It was realized that, compared to Degussa P-25, the synthesized nano-TiO2 can be repeatedly used as a new catalyst. The results also proved that Reactive Red 141 is decomposed catalytically due to the pseudo first-order reaction kinetics.

The initial stages of diamond growth on treated Si(001) substrates were studied using various structural and spectroscopic characterization techniques. The nucleation behaviour across the substrate appeared to be inconsistent. Cross-sectional transmission electron microscopy (TEM) revealed the presence of localized amorphous carbon in areas between the Si substrate and the subsequently deposited polycrystalline diamond film, whereas diamond particles, apparently in direct contact with the Si substrate, were observed in other areas. Electron energy loss spectroscopy (EELS) revealed the presence of amorphous carbon in large pockets between polycrystalline diamond particles, as well as in some voids between the Si substrate and the diamond layer. Electron energy loss near edge structure (ELNES) results obtained from a small pocket of amorphous carbon between diamond particles showed a fine structure essentially similar to that of diamond; however, additional intensity was observed in the region of π-resonance, indicating mixed sp2/sp3 bonding. Although not detected by TEM or EELS, X-ray photo-spectroscopy revealed the emergence of a SIC layer during the early stages of growth.

Chitosan with a covalently attached anthrylunit is used as chemomechanical polymer, in which stacking and cation-pi interactions allow aromatic effector compounds with positively charged nitrogen centers to trigger macroscopic motions in aqueous surrounding. Thus, only protonated heterocycles such as imidazole or histamine lead at pH 5 to expansion, in contrast to toluenesulfonic acid, or pyrazole and pyrimidine. Inorganic salts and pH influence the polymer swelling, and must be taken into account for the calculation of net effects induced by organic effectors. Reversible volume expansions on the top of the swelling effect of water alone are observed as function of different effector, structures, showing, for example, 45% net effect with imidazole and 66% with benzimidazole. Aminoacids, for solubility reasons measured in the form of their methylesters, yield smaller expansions, showing, however, a regular and selective increase with, the lipophilicity of the residues. The kinetics of effector uptake, which relates to the velocity of expansion, are measured with histamine and follow first order, with t(1/2) = 2.7 min for 50% absorption.