Pcpdfwin 64bit Magnet
Joao Charlesbois
Basic copper(ii) dihydroxoborate Cu2BO(OH)2(OH)3 contains infinite chains consisting of [CuO4] squares that are linked together by sharing opposite edges, due to which this compound is interesting in terms of low-dimensional magnetism. However, investigations of its physical properties are hindered by difficulties with the preparation of single-phase samples. The synthesis method was optimized, and the factors affecting the formation of a crystalline product were established. The synthesized compound was characterized by X-ray diffraction and IR spectroscopy, and its thermal stability was studied. The crystallite formation from the initially unstructured precipitate is described using scanning electron microscopy. An investigation of the temperature dependence of magnetic susceptibility showed that the magnetic properties of basic copper(ii) borate are well described by the weakly alternating spin-1/2 Heisenberg chain model.
The corrosion behaviour of SR355JR and S355J2 carbon steels exposed to different seawaters (Black, Aegean and Mediterranean Sea) has been investigated by polarization measurements. The corresponding corrosion parameters were calculated. Micrographic images before and after immersion in the used seawaters corrosive medium were obtained. X-ray diffraction and ponderomotive methods respectively were used to determine the influence of the corrosion process on the crystal structure and specific magnetization of the studied steels.
En este estudio se investig el comportamiento a la corrosin de los aceros al carbono SR355JR y S355J2 expuestos a diferentes aguas marinas (Mar Negro, Mar Egeo y Mar Mediterrneo) mediante mediciones de polarizacin. Se calcularon los parmetros de corrosin correspondientes. Se obtuvieron imgenes microgrficas antes y despus de la inmersin en el medio corrosivo de las aguas marinas utilizadas. Para determinar la influencia del proceso de corrosin en la estructura cristalina y la magnetizacin especfica de los aceros estudiados se utilizaron los mtodos de difraccin de rayos X y ponderomotivos respectivamente.
The problem of marine corrosion resistance of steels is still urgent. A clear data of mechanical and physical properties of such materials, stability properties, the temperature ranges of use and the knowledge of their processing and exploitation in marine conditions is the key to significant economy. Being one of the largest corroded and abundant natural electrolytes, seawater has a corrosive behavior that shows that most common metals and alloys are attacked by that liquid. Corrosion resistance of metals used as building materials is essential for marine construction planning. Corrosion of metals and alloy in the marine environment was studied from the beginning of the century. The first date were reported by many authors [1-3]. Iron and low alloy cast iron are the primary cast alloy used for marine applications. Schumacher [4] reported that the corrosion of steels, grey cast iron, alloy cast iron and austenitic cast iron is proportional the concentration of oxygen. When metals are submerged in seawater, corrosion is faster. An important structural material and used for many years in marine applications was steel. The naval and petrochemical industry are affected by sea water corrosion in their structures used, such as ships, platforms, pipelines, distribution systems and chemical processeses. Due to the presence of ions dissolved in it, seawater produces a much faster corrosion of metals than freshwater. The sea waters containing chlorides and various salts, corrode the majority of metals and alloys. Corrosion of steel in marine environments can be quite extensive and normally proceeds very rapidly to beginwith and then levels off to a linear relationship [5]. As a result of spraying metals with sea water, there is a permanent reduction in the quality of metals, which are structurally disadvantageous but which can also cause degradation that can lead to real disasters. Based on the above facts the present work is undertaken in order to evaluate the corrosion influence of sea waters on the structure and magnetic properties of SR355JR and S355J2 steels.
The size of the steel samples were 50 mm 25 mm 5 mm. They were cleaned wet-polished with 2000# grade SiC paper, then cleaned in alcohol and acetone, after which they were dried, weighed and stored in a desiccator until use. The corrosive media used was natural sea water from Black, Aegean and Mediterranean Sea. Literature present that the salinity of those sea waters are: 17-18.5 g/L Black Sea, 38 g/L Aegean Sea and 37-39 g/L Mediterranean Sea [6].
The study of magnetic properties of samples is carried out using automatized setting, which works on base of a method of the ponderomotive force measuring. The method makes it possible to investigate temperature dependences of magnetization and magnetic susceptibility taking small amounts of substance. This makes it possible to achieve relatively fast equilibrium temperature over the entire volume of the sample. It is obvious that the absence of the temperature gradient on the sample at the specific magnetization or susceptibility measurement moment provides the most accurate determination of their values. The specific magnetization temperature dependences were studied in the temperature range 77-1100 K by ponderomotive method in the 0.86 T field.
The corrosion test were performed in sea waters by the methods of time evolution potential without current (open circuit potential-OCP) and polarization curves (Tafel). The plot (curve) corrosion/time respects a logarithmic law [9,10]. The open circuit potential (OCP) of the studied steels is expected to be dependent on the characteristics of resulted oxide, such as oxide thickness, composition, conductivity, structure, etc. Immediately after the immersion, EOCP heads towards the noble direction, gradually approaching the value of the quasi-stable state (Ess) within 40 minutes. The OCP values range for SR355JR from -0.637 V to -0.662 V and for S355J2 from -0.598V to -0.636V as presented in Table 2. The time evolution of OCP indicates that the oxide film is thinning and consequent becomes vulnerable toward anion penetration of diferent ions presents in the sea waters. We noticed slight oscillations of OCP in time and we assume that these OCP oscillations may result from chemical interactions between chloride ions and the structured passive oxide film. Tafel plots were used in order to evaluate the corrosion resistance of the two steel in the studied seawaters. Fig. 1 show the Tafel plots obtained from the polarization curves of the SR355JR and S355J2 steel samples in the tree sea water in study. The corrosion plots vs.time respects a logarithmic law [11,12]. Corrosion parameters calculated from Tafel plots are summarized in Table 2 [13]. It can be observed from Fig. 1 that corrosion potentials (Ecorr) for both steel samples are very close each other in all three seawaters, simmilar to EOCP. The Tafel plots and corrosion data indicate that both steels have good corrosion resistance in seawaters with corrosion rates ranging from 0.221 - 0.503 mm/year. This good corrosion resistance express that the passive layer formed on its surface is stable and resistant.
The results show a good corrosion resistance in all three seawaters in study for S355J2 if to compare to SR355JR steel and are in good agreement with the polarization resistance obtained by LP. It is obvious that the S355J2 impedes the attack of the aggressive ions (Cl-) on the electrode surface. The best corrosion rate was obtained for the S355J2 steel in Aegean seawater.
The H2S accelerate the corrosion process. As for the fact that corrosion rate of both steels are lower in Mediterannean sea and in Aegean sea even if the salinity of these seawaters are much higher, we believe that the decrease in corrosion rate can be related to the formation of a passive film on the surface of the steel, which behaves as a protective layer against further corrosion. The XRD and micrographic data confirmed this assumption.
Data from Table 2 show that in all three seawaters in study S355J2 has a better corrosion resistance than SR355JR. We believe that even if the composition of the two stees are very appropriate, the presence of few amount of Al in S355J2 gives it better corrosion resistance.
X-ray diffraction (XRD) pattern of initial and corroded samples of SR355JR and S355J2 steels in the 3 sea waters in study are presented in Fig. 2. Diffraction reflections on the X-ray diffraction pattern are given in Tables 3 and 4.
The main phase for initial samples according chemical composition is α-phase of pure iron with unit cell of Im3m space group. Analysis of the patterns showed that after conducting studies of corrosion resistance, the main phase of the Im3m type of α-iron was preserved.
In the case of the corrosive effect of Mediterranean water on steel SR355JR (Fig. 2a), weak diffuse scattering is observed in the X-ray pattern in the 35-40angle range, which may indicate the presence of iron oxides on the surface of the samples. Due to their small amount, it is difficult to accurately determine the phase composition of corrosion products.
The processing of X-ray patterns is carried out using the FullProf Suite program, which is based on the Rietveld method to clarify the parameters of the crystal cell. The lattice parameter determination error was 0.0002 nm.
Reflexes of X-ray patterns are indicated in accordance on base of PCPDFWIN database ID 06-0696 (a 0.2866 nm). The unit cells parameters, size of the crystallites and the dislocation density of the SR355JR and S355J2 steels before the sea waters corrosion are presented in Table 5.
Microscopic images of the two studied steels before and after corrosion in the 3 sea waters are presentd in Figs. 3 and 4. The morphologies obtained provide us with information on the rust layer deposited during corrosion.It can be seen from Figs 3d, f and 4d, h that the rust layers have different colors, which mean different forms. Fig. 3 shows that SR355JR steel has a not very compact and homogeneous surface before corrosion and after corrosion the surface of that sample show some changes due to the corrosiveness of sea waters. In images from Fig. 3 we believe that the appearence of the colored phases is due to the formation of oxides or other coumpounds. In picture 3d and 3f we suppose the formation of the stable iron oxide hydrates (as presented by XRD data). On the whole, microscopic data are in perfect correlation with electrochemical results for SR355JR (showing the lowest corrosion in Mediterranean seawater).
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