Solid State Phenomena Vol. 227

Abstract: This paper presents an analysis of the Nd-(Fe,Co)-B bonded magnetic materials surface before and after corrosion tests. In the technological process of bonded magnetic materials the main difficulty is the fact that in the presence of small amounts of oxygen magnetic powders (having in their composition a highly active, a rare earth element) the particle surface easily cover with an oxide layer. The oxides phases are creating and furthermore the presence of this kind of paramagnetic phase on the powder particles surface adversely affects on the properties of the final product. Important is to protect the surface against spontaneously oxidation of the magnetic materials. One of the activities way to surface isolation is creating the additional protection coating (biencapsulation). Biencapsulation is a protection process in which not only set resin layer, but also an additional protective coating has been applied. The powder particles are coated with protective coatings: Ni-P/epoxy resin and phosphate/epoxy resin. In the paper the roughness measurement (2D) with profilometer (Taylor Hobson) results were presented. Also the effect of corrosion process evaluation on the bonded magnets surface roughness were determined (sulfate solution pH = 3, the exposure time 4h). It has been found that the application of powder particles biencapsulation with phosphate/epoxy resin coating (in comparison with Ni-P/epoxy resin biencapsulation) leads to a more effective corrosion protection of the final bonded magnets.

Abstract: The microstructure and corrosion behaviour of AM50/SiC magnesium matrix composites reinforced with SiC particles were investigated. Composites containing 10 wt. % of SiC were fabricated by means of gravity casting. Technical grade silicon carbide used for the composites fabrication was subjected to a purification procedure leading to the removal of iron containing impurities from its surface. The corrosion resistance of the composite with purified SiC particles was compared to the corrosion resistance of the one containing crude technical grade silicon carbide as well as to the corrosion resistance of the matrix alloy. Voltammetry and an electrochemical noise technique as well as hydrogen evolution rate measurements were utilized for that purpose. Corrosion tests were performed in 0.5 mol dm³ NaCl saturated with Mg (OH)₂. It has been demonstrated that the composite containing purified SiC was less susceptible to corrosion than the one containing crude SiC particles. Both composites were less resistant to corrosion than their matrix itself. Regardless of a purity level of SiC which was used for the composites fabrication, the same constituents were revealed in their microstructure, namely: α-phase (a solid solution of aluminium in magnesium), fully divorced eutectic α + γ (where γ-phase is Al₁₂Mg₁₇), intermetallic compound Al₈Mn₅ and SiC particles uniformly distributed in the whole volume of the matrix.

Abstract: New refining technology of soda – calcium – silicon glass surfaces with inorganic compounds nanomolecules has been presented in the study. In order to determine modification of the glass surface SEM observation and EDX analysis have been carried out. The glass samples were subjected to the UV-VIS, photo-elasticity and ellipsometry examinations. From obtained results follows, that refining of the glass surface by nanopowder aluminum hydroxide compounds provides forming of very thin surface layers. This type of modification improves physical glass properties. As the example results of microhardness refined glass are presented in the article.Keywords: glass, surface, nanoparticles, refining

Abstract: Copper and its alloys are used in many industrial and marine applications due to their good heat transfer and electrical properties. Copper is, however, susceptible to many forms of corrosion, including localized corrosion, such as crevice corrosion. The paper presents the preliminary results of studies on obtaining copper-based composite materials strengthened with carbon nanotubes modified with copper nanoparticles. The nanotubes modification was carried out by chemically attaching copper nanopaticles originating from copper acetate. Electrolytically obtained copper powders were used as the matrix. The materials were consolidated by one-sides pressing followed by sintering. One of the important property of these materials is its resistance to corrosion. Potentiokinetic investigations in a 3.5% NaCl solution were performed on specimens of different CNTs content. Determined what influence on the corrosive changes has the addition of nanotubes to copper.

Abstract: Seed extract of Momordica charantia (MC) was used to investigate the inhibition efficiency on corrosion of J55 and P110SS steel in 3.5% NaCl solution saturated with CO₂ through AC impedance, polarization curves, and SEM techniques. The Nyquist diagrams showed increase in R_ct values in the presence of inhibitor, thus increasing inhibition efficiency. Potentiodynamic curves suggested that the inhibitor is mixed type in nature. The adsorbed film on J55 and P110SS steel surface containing inhibitor was confirmed by the SEM results.Keywords: Momordica charantia, P110SS steel, J55 steel, SEM

Abstract: The inhibition effect of guar gum on carbon steel (K-55) in the simulated fracturing fluid under static conditions was studied. The electrochemical experimental results indicated that the carbon steel shows active dissolution behaviour in the absence and the presence of the inhibitor. However, guar gum, acting as mixed-type inhibitor, was swiftly able to promote the formation of a product layer onto the metal surface, lowering both cathodic and anodic current density. Electrochemical impedance spectroscopy (EIS) measurements were consistent with the polarisation curves, showing an improvement of the corrosion resistance of the carbon steel in the presence of the inhibitor. However, for long exposure times, the corrosion activity of the metal increases, as result of the breakdown of the corrosion product layer and initiation of localised corrosion spot. After both polarisation and EIS measurements, two different layers were observed. A thin, dark stable layer of magnetite and, for long holding times, a porous red layer, poorly adhered, of hematite. The hematite layer, due to its porous nature, was characterised by poor corrosion ability.

Abstract: The paper presents the results obtained when using two ketonic Mannich bases (BM1 and BM2) as corrosion inhibitors in saline (standard sea water-3.5% NaCl) for different types of steel, with various alloying elements. The corrosion experiments were performed by potentiodynamic polarization studies. Based on the polarization curves, the corrosion current density and rate were calculated. The inhibitors efficiencies were evalued and the protection mechanisms were discussed.

Abstract: The effect of chloride ions on the passivity of titanium in sulfuric acids was investigated by potentiodynamic and potentiostatic anodizing, Mott-Schottky analysis and the point defect model (PDM). The anodizing results indicated that chloride ions facilitate the anodic passivity of titanium in sulfuric acids. Based on the Mott-Schottky analysis in conjunction with the PDM, it was shown that the donor density decreases exponentially with increasing film formation potential. Also, the results indicated that with the increasing concentration of chloride ions, the donor density decreases, while the diffusivity of the donors increases at the same film formation potential.

Abstract: The corrosion behaviour of AM60 magnesium alloy containing 1.88 wt.% Cd in 0.1 M NaCl solution was investigated by weight loss and hydrogen evolution measurements. The microstructure was evaluated using EPMA. Cd was observed to have an even distribution, hence, no new phase was formed. The corrosion resistance was enhanced by the addition of Cd. The rate of corrosion reduced by a factor of 1.5 times that of AM60 alloy. The microstructure played a crucial role as the presence of defects in the alloys initiated and accelerated corrosion.

Abstract: Institute of Materials Science at Silesian University of Technology since 6 years conducts researches to learn about the new dedicated for automotive, railway and military industries. Some of these materials belong to the group of AHS steels, characterized by the twinning induced plasticity (TWIP) effect. It is a new type of steel possessing both a high strength and a great plastic elongation, and an ideal uniform work hardening behaviour. It is therefore a good candidate for deep drawing applications in the automobile and railway industries. In the paper the of the three grades of high-manganese steels of was studied in 3.5% NaCl solution and in an “acid rain” solution with pH=3.5 environments using polarization experiments. The results of corrosion tests and analysis of show that a higher polarisation resistance and lower values of corrosion current density are observed for all studied steels in 3.5% NaCl solution. Spontaneous passivation ability has been shown only for one grade of high-manganese steel in 3.5% NaCl.