Influence Of Immersion Time Research Articles

Corrosion protection of mild steel by polyvinylsilsesquioxanes coatings in 3% NaCl solution

Polyvinylsilsesquioxanes (PVS) coatings were synthesized by the hydrolytic polycondensation of vinyltrimethoxysilane using hydrochloric acid as a catalyst. Their structure was characterized by Fourier transform IR (FTIR) and the viscosity [in centipoise(cP)] of polyvinylsilsesquioxanes was measured at 298 K. The electrochemical behavior of I–IV coated steel electrodes, of polymer concentration as follows: [I(20%), II(40%) of viscosity 50 cP and III(20%), IV(40%) of viscosity 15 cP], was investigated in 3% NaCl solution using various electrochemical techniques, i.e., open-circuit potential (OCP), potentiodynamic polarization, electrochemical impedance measurements (EIS), and surface examination via scanning electron microscope (SEM) technique. The influence of immersion time on the electroctrochemical behavior of polysilsesquioxane-coated electrodes was also studied. The results of polarization measurements showed that corrosion current density (i corr) decreases in the order IV > III > II > I. Also, the film resistance is the highest for PVS-coated electrode I as evaluated from EIS measurements. OCP, EIS, and polarization results are in good agreement with each other. The obtained results were confirmed by surface examination using scanning electron microscope.

Corrosion behaviour of AZ31 magnesium alloy with different grain sizes in simulated biological fluids

The corrosion behaviour of AZ31 magnesium alloy with different grain sizes immersed in simulated body fluids was compared in chloride solution (8 g l −1) and in phosphate-buffer solution (PBS). The influence of immersion time was also analyzed. Electrochemical techniques such as open circuit potential, polarization curves, transient currents and electrochemical impedance spectroscopy, complemented with scanning electron microscopy and energy dispersive spectroscopy, were used. Immediately after the immersion in the corrosive media the corrosion resistance was similar for both grain sizes of the AZ31 alloy and higher in NaCl solutions than in PBS. However, this corrosion behaviour was reversed after longer periods of immersion due to the stabilizing of the corrosion products of MgO by P-containing compounds. These P-compounds contribute to a higher level of protection by hindering the aggressive action of chloride ions. The best corrosion behaviour of the AZ31 alloy was obtained for the finest grain alloy associated with the highest transfer resistance value, after long periods of immersion in PBS.

Electrochemical characteristics of pipeline-steel with planardefect epoxy-coating in simulated solutions of Ku’erle soil

An X70 pipeline steel and a low-carbon steel with different types of coating defects were studied using corrosion tests in Ku’erle simulated soil solution containing 0.6000 mol/L Cl−. Electrochemical characteristics of the X70 pipeline steel with planar-defect epoxy-coating in simulated solutions of Ku’erle soil were tested. The results show that in 0.6000 mol/L Cl− simulated solution, for low-carbon steel with coating defects (the area ratio is 4.91%), at free corrosion potential and with immersion time, the corrosion with disbond was more severe than that with a break or with break and disbond. In Ku’erle soil simulated solution, when the coating defect area ratio was increased gradually (0.39% → 1.57% → 6.28%), the corrosion of the X70 steel under coating with break was promoted gradually, and the influence of immersion time on the corrosion decreased. The influence of the immersion time on the corrosion was weakened when the defect area ratio increased to a certain degree.

Mechanisms of corrosion layer formation during zirconium immersion in a (Fe)-bearing glass melt

The kinetics and mechanism of pure zirconium corrosion in an iron-bearing borosilicate glass melt are investigated from 1230 to 1418 °C. The influence of immersion time and temperature on the corrosion layer morphologies is discussed. The corrosion mechanism is a multi-step process and is described using the Zr–Si–O–B phase diagram. Boron and silicon species contained in the melt are reduced at the zirconium contact and ZrSi s B b intermetallic compounds are formed while the Zr substrate is oxidized into ZrO x . When the local melt fO 2 value induces the Fe 0 precipitation, complex ZrSi s B b Fe f compounds are formed. The last step consists in the oxidation of ZrO x into ZrO 2.

Grafting of Nitrophenyl Groups on Carbon and Metallic Surfaces without Electrochemical Induction

The grafting of 4-nitrophenyl groups on carbon or metallic surfaces without externally applied electrochemical induction is described. Clean surfaces of glassy carbon (GC), copper, nickel, iron, and zinc substrates were dipped in a solution of 4-nitrobenzene diazonium tetrafluoroborate salt in acetonitrile. After the modified surfaces were rinsed, they were analyzed by FT-IRRAS, cyclic voltammetry, XPS, and AFM. The main result of this investigation is the spontaneous formation of a multilayer coating without electrochemical induction regardless of the substrate used. Influence of immersion time and of 4-nitrobenzene diazonium tetrafluoroborate salt concentration on the grafting were also investigated.

Cerium treatments for temporary protection of electroplated steel

The present work aims at evaluating the corrosion performance of a cerium immersion treatment on zinc electroplated. For comparison, zinc coatings pretreated with a commercial chromate treatment were also examined. The corrosion behaviour of pretreated zinc surfaces under immersion in sodium chloride was investigated by potentiodynamic polarization to evaluate the effect of cerium on the oxygen reduction reaction. The influence of immersion time, temperature of cerium solutions, stirring influence, cerium concentrations, cerium salt, pH of the solution and oxidation state of cerium are also investigated. Scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) were used to characterize the sample surfaces after treatments. In order to compare the corrosion performance of cerium pretreated samples, an accelerated test in a humid chamber was carried out. The results indicate that the cerium film formed on the zinc surfaces markedly suppressed the cathodic process. The accelerated corrosion test shows that white rust formation is delayed although the protection given by this treatment is less efficient than with commercial chromate treatments.

Improved Control of Green Mold of Citrus with Imazalil in Warm Water Compared with Its Use in Wax.

The effectiveness of imazalil for the control of citrus green mold (caused by Penicillium digitatum) improved significantly when fruit were treated with heated aqueous solutions of the fungicide as compared with the current commercial practice of spraying wax containing imazalil on fruit. When applied at less than 500 μg·ml-1 in solutions heated to 37.8°C, control of postharvest green mold of citrus was significantly superior to applications of 4,200 μg·ml-1 imazalil in wax sprayed on fruit at ambient temperatures. The improvement in imazalil efficacy was obtained with a decrease in fungicide residues on the fruit. Residues of about 3.5 μg·g-1 imazalil deposited by the application of imazalil in wax reduced the incidence of green mold on lemons from 94.4% among untreated controls to 15.1%, whereas an equal residue deposited by passing fruit through heated aqueous imazalil reduced green mold incidence to 1.3%. Similar differences were found in tests with oranges. Residues of 2 and 3.5 μg·g-1 imazalil were needed to control the sporulation of P. digitatum on oranges and lemons, respectively. The mode of application of imazalil did not influence control of sporulation. The influence of immersion time, imazalil concentration, and solution temperature on imazalil residues on oranges and lemons was determined in tests using commercial packing equipment, and a model that describes residue deposition was developed. Residues after a 30- or 60-s treatment in heated aqueous imazalil were sufficient to control sporulation, but residues after 15-s treatments were too low and required an additional application of 1,070 μg·ml-1 imazalil in wax to deposit an amount of imazalil sufficient to control sporulation. An imazalil-resistant isolate of P. digitatum was significantly controlled by heated aqueous imazalil. The incidence of green mold of navel oranges was reduced from 98.8 to 17.4% by treatment in 410 μg·ml-1 imazalil at 40.6°C for 90 s. However, control of the resistant isolate required imazalil residues on the fruit of 7.9 μg·g-1, which is within the U.S. tolerance of 10 μg·g-1 but above the 5 μg·g-1 tolerance of some countries that import citrus fruit from the United States.

Microtopographic and molecular scale observations of zeolite surface structures: Atomic force microscopy on natural heulandite

Atomic force microscopy (AFM) has been employed to study the surface of the natural zeolite heulandite. Images on a macroscopic scale exhibit growth spirals on the outer surface and cleavage tips on the (010) surface, both with terraces separated from each other by half of the unit cell length b. The angle of the cleavage tips depends on the cleaving direction. Molecular resolution is obtained when measured in 0.1 m NaOH, 0.1 and 1 m KOH, and 6.66 m CsOH. The influence of immersion time, the nature of the ion species, and the ion concentration on the unit cell has been investigated. The lattice constants varied around the bulk values.