Materials Science Forum Vols. 636-637

Abstract: The Zn-Fe layers are recommended in automotive industry and in the adders for the following qualities: a better weldability than the zinc-coated plates, very good capacities for painting and lacquer wear resistance, good adherence, lower zinc consumption by layer thickness below 100g/m2. Important transformation of phases takes place during heating of galvanized parts due to mass transfer iron in the zinc layer and Zn-Fe alloy is formed. Galvanized steel samples were heated 10-30 sec. at 500-650oC. Heat treated samples were metallographic ally examined and X- ray diffraction tested with a view to establish structural and chemical composition change due to heat treatment. As a result of microscopic examination (both optical and electronic) and X-ray diffraction testing in coating layer were detected phase ratio changes, according to heat treatment parameters. Considering that the physico-chemical and mechanical properties differ for the two phases and phase ratio is to decide the properties of the product; these structural changes are of great importance in practice. The desirable coating would be a Zn-Fe coating with 8-10% Fe (according to some authors, up to 12% Fe), with a structure consisting mainly of  phase and a small quantity of  phase. The mathematical correlation between diffusion phenomena occurring in layer, depending on temperature and time of heat treatment, and iron content of coating are presented.

Abstract: RF magnetron sputtering is used to deposit Aluminum-doped zinc oxide (ZnO:Al) films on glass and p-Si substrates. This work is a study of ZnO:Al films grown at different RF powers for photovoltaic cells application, as antireflective (AR) coatings. At room temperature and argon gas pressure of 0.6 Pa, RF power was changed from 200 to 400 W. The structural, electrical and optical properties of ZnO:Al films were investigated. Under theses conditions, we have obtained c axis-oriented wurtzite structure ZnO thin films with high transmission (>85%) and low reflection in visible wavelength range and a band gap of 3.34 eV. The results of this study suggest that the variation of the RF power, used for growth, allows the control of the structural and optical properties of the films. ZnO:Al films can be used in optical applications as thin films antireflective coatings.

Abstract: Hydrotalcite-like compound that belongs to anionic clay family was prepared by classical co-precipitation method using magnesium and aluminium nitrates as precursors. Different weight percentages of hydrotalcite with Mg/Al ratio of 2.5 was added (1, 5 and 10 % wt.) to hybrid sols prepared by copolymerization of 3-Glycydoxypropyltrimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (TPOZ). The aim of this work was to study the effect of the hydrotalcite incorporation to hybrid sol-gel coatings on aluminium alloys as substitution of chromate inhibitors. Hybrid sol-gel coatings were deposited by dip coating method on AA2024-T3 substrates. By Scanning Electron Microscopy (SEM) and mechanic profilometry it was possible to see the distribution of HTCP agglomerates which varies from nanometres to micrometers. The corrosion performance was evaluated by the accelerated test salt fog spray chamber (SSFC) and by Electrochemical Impedance Spectroscopy (EIS). The obtained results show the corrosion resistance improvement at higher weight percentages of HTCP.

Abstract: The behaviour of hybrid sol-gel coatings doped with hydrotalcite-like compound applied on AA2024-T3 alloy was investigated in the present work. The hybrid sol-gel coatings were prepared by copolymerization of 3-Glycydoxypropyltrimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (TPOZ). Three different surface finishing on the aluminium alloy AA-2024-T3, grounded, chemical etching and degreased were studied. A sol-gel film with hydrotalcite 5% w/w was deposited by dip coating procedure. The presence of hydrotalcite particles was confirmed by means of X-ray diffraction technique. The different surface morphologies were characterised using mechanical profilometry. The corrosion resistance properties were studied by means of electrochemical impedance spectroscopy and salt fog spray cabinet. The results show higher barrier properties in grounded aluminium substrates.

Abstract: The paper presents the results of investigations into the structure and properties of Ni-Al diffusion layers produced on INCONEL 100 by Chemical Vapour Deposition (CVD). The process was carried out in aluminium chloride (AlCl3) mixed with hydrogen atmosphere. The as-deposited layers were subjected to thermal treatment in vacuum to optimize their adhesion, hardness and temperature-resistance. Microstructural characterization of the coatings was carried out by scanning electron microscopy (SEM) The chemical composition was measured via EDS and the phase content was investigated by X-ray diffraction XRD. The resistance to high temperature of the coatings at atmospheric pressure was tested by applying 24-hours cycles at 950 °C. Scratch-tests provided data on the microhardness and adhesion of the coatings. The results indicate that the layers produced on the INCONEL 100 exhibit a very good adhesion combined with exceptional corrosion resistance at high temperatures.

Abstract: The effect of dc discharge treatment at the anode and cathode on the surface properties of polytetrafluoroethylene (PTFE), tetrafluoroethylene–hexafluoropropylene copolymer (FEP) and poly(vinylidene fluoride) (PVDF) polymer films was studied. It was found that the modification of the films under conditions that ensure the separation of the discharge active species acting on the polymer materials makes it possible to achieve substantially lover values for the contact angle and higher values for the surface energy than in the case of other modes of discharge. The changes in the composition and structure of the films were studied by means of IR spectroscopy and electron spectroscopy for chemical analysis (ESCA). It was found that new oxygen-containing groups are formed on the polymer surface as a result of dc discharge treatment. To appreciate the adhesion characteristics of fluoropolymer films modified by dc discharge, American Society for Testing and Materials Standard Test Method for Measuring Adhesion by Tape Test (ASTM D3359-02) was used. The adhesion tape Scotch 810 and vacuum metallization of the film surface are account for the basis of this method. It was found that the adhesive bonding strength of the plasma treated films substantially increased.

Abstract: In the present work, it is evaluated the effect of water and other contaminants of alcohol fuel on the corrosion behavior of different materials, which can constitute vehicles, storage and transportation fuels systems. For such, 5 metallic materials (zamak, low-carbon steel, stainless steel, and two Al alloys) were chosen and 5 alcoholic solutions were prepared: anhydrous ethanol (AEAC; solution 1); hydrated ethanol (AEHC; solution 2); AEAC and water with some impurities (AEAC + 6 % “corrosive” water; solution 3); AEHC and water with some impurities (AEHC + 6 % “corrosive” water; solution 4); and, AEAC and tap water (AEAC + 6 % tap water; solution 5). The crevice corrosion was investigated in static immersion tests, which were carried out at 50 °C for 2 months. The evaluation of the corrosive process was carried out by visual inspection, weight loss, optic microscopy, and scanning electron microscopy (SEM). Also, some quality parameters of the alcoholic solutions (specific mass, alcoholic content, pH, and conductivity) was analyzed in order to determine the influence of corrosion of the materials on them. The results have shown that crevice corrosion of all materials mostly occurred in solutions 3-5, which had a high amount of water and impurities. Some corrosion rates in such solutions were 90-400 times higher than those obtained in AEAC and AEHC. Among the materials, zamak and carbon steel suffered severe corrosive attack. The physicochemical properties of alcoholic solutions employed in the tests also changed, mainly the increase of pH and conductivity was observed. Therefore, the results demonstrate that the quality control of alcohol fuel is essential in order to avoid the damage of engine parts and storage and transportation systems. Specially, water, sulphate, chloride and acetate content must be monitored.

Abstract: Long term corrosion phenomena are generally not obtained in laboratorial corrosion experiments. Particular features, such as strong intergranular corrosion, can be an indication of the antiquity of a metallic artefact. In the present study, various corrosion features from several archaeological bronze artefacts, with ages ranging from 2 to 5 millenniums, are examined using optical and scanning electron microscopies. Elemental composition was obtained through micro-EDXRF analyses. Corrosion patterns could, in some occasions, be related to specific thermomechanical treatments performed before burial and, in others, with particular phases present in the artefact.

Abstract: Ni-Mo and Ni+Mo coatings were prepared by electrodeposition under the galvanostatic conditions, in such a manner that the coatings contain the same quantity of molybdenum. The electrochemical activity of these coatings was studied in the process of hydrogen evolution reaction (HER) from 5 M KOH solution using steady-state polarization and electrochemical impedance spectroscopy (EIS) methods. Basing on the results of EIS measurements, the rate constants of the HER as well as the surface roughness factors were determined. It was found that Ni+Mo composite coating is characterized by enhanced electrochemical activity towards hydrogen evolution as compared with Ni-Mo alloy coating. Improvement of the electrocatalytic performance of Ni+Mo composite coating could be attributed to the increase in its real surface area as well as to the catalytic effect in points of contact of molybdenum and nickel matrix. Thus obtained composite coating may be useful in application as electrode materials for the hydrogen evolution reaction.

Abstract: Zn-Ni and Zn-Ni-W coatings were prepared by the electrodeposition under the galvanostatic conditions (jdep. = -0.020 A cm-2) from the zinc bath containing additionally ions of nickel (Zn-Ni) and ions of nickel and tungsten (Zn-Ni-W). The Zn-Ni coating after electrodeposition was subjected to outside passivation and in the Zn-Ni-W coating the passive function performs tungsten (inside passivation). The surface morphology of the coatings was studied using a scanning electron microscope (JEOL JSM - 6480). Chemical composition of obtained coatings was determined by the X-ray fluorescence spectroscopy (XRF). Phase composition investigations were conducted by X-ray diffraction method using a Philips diffractometer. Electrochemical corrosion resistance investigations were carried out in the 3% NaCl, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. On the basis of these investigations it was found that Zn-Ni coating is more corrosion resistant than the Zn-Ni-W coating.