Corrosion Properties of Diffusional Zinc Coatings Obtained by Nanogalvanizing (original) (raw)

Studies on nanocrystalline zinc coating

Nano zinc coatings were deposited on mild steel by electrodeposition. The effect of additive on the morphology of crystal size on zinc deposit surface and corrosion properties were investigated. Corrosion tests were performed for dull zinc deposits and bright zinc deposits in aqueous NaCl solution (3⋅5 wt.%) using elec-trochemical measurements. The results showed that addition of additive in the deposition process of zinc significantly increased the corrosion resistance. The surface morphology of the zinc deposits was studied by scanning electron microscopy (SEM). The preferred orientation and average size of the zinc electrodeposited particles were obtained by X-ray diffraction analysis. The particles size was also characterized by TEM analysis.

Corrosion behaviour of zinc–nickel alloy coatings electrodeposited in additive free chloride baths

Corrosion Engineering, Science and Technology, 2011

Corrosion behaviour of nanocrystalline Zn-Ni alloy coatings (with 3 to 18 at-%Ni) electrodeposited on steel substrate from additive free chloride baths by DC plating has been investigated by measurement of open circuit potential with time and neutral salt spray test. The alloy coatings containing up to 16 at-%Ni exhibited an increase in resistance to the appearance of white and red rust with increasing Ni content. The resistance to the appearance of white rust and ability to protect the underlying steel substrate decreased with further increasing Ni content. This has been considered to be due to reduced passivating ability of the alloy coating with a significant rise in the grain size above 50 nm.

On the corrosion resistance of porous electroplated zinc coatings in different corrosive media

Corrosion Science, 2010

The corrosion resistance of an electroplated (EP) Zn coating whose surface was chemically etched to produce surface defects (pores) is investigated in this work. Impedance and DC polarisation measururements were employed to study the behaviour of such coating in various corrosive media (NaCl, NaOH and rain water). Four different faradaic relaxation processes were clearly revealed in different NaCl concentrations (from 0.1M to 1M). In the most concentrated solutions at least three relaxation processes at low frequencies (LF) appeared and were related to zinc deposition and dissolution. At lower concentrations and depending on the pH, only one process was observed. The charge transfer resistance (R ct) and the corrosion current (I corr) were practically stable in the pH range 5 to 10. In deaerated NaCl 0.1M, the EIS diagrams showed two time-constants at very close frequencies. From the EIS diagrams the 2 porous nature of the coating was highlighted and showed that the dissolution mechanisms occurred at the base of the pores.

Nanocrystalline zinc titanate coatings for corrosion protection

Nanocrystalline zinc titanate (ZnTiO3) coatings were deposited by atomic layer deposition (ALD) on AISI 52100 steel to study ZnTiO3 corrosion protection. The main aim of this study was to determine how the coating can inhibit pitting formation of 52100 steel in both saline solution and simulated body fluid (SBF) media. Potentiodynamic polarization tests revealed increasing corrosion potentials for the ALD ZnTiO3-coated steel specimens with protective efficiencies of 83 and 73% in saline solution and SBF, respectively. Atomic force microscopy analysis of both the ZnTiO3-coated and uncoated steel revealed a high surface potential value for the ZnTiO3-coated sample as compared to the uncoated sample with a relatively low surface potential. The corrosion rates for the coated steels in both media were calculated and observed to drop by an order of magnitude. Due to the conformality, homogeneity and density of the ALD ZnTiO3 coatings, migration of Cl− and OH− ions from the electrolytes were inhibited resulting in the improved corrosion resistance.

Corrosion Behavior of Nanocrystalline Zn-Ni alloy coatings

Corrosion behaviour of nanocrystalline Zn-Ni alloy coatings (with 3 to 18 at-%Ni) electrodeposited on steel substrate from additive free chloride baths by DC plating has been investigated by measurement of open circuit potential with time and neutral salt spray test. The alloy coatings containing up to 16 at-%Ni exhibited an increase in resistance to the appearance of white and red rust with increasing Ni content. The resistance to the appearance of white rust and ability to protect the underlying steel substrate decreased ; with further increasing Ni content. This has been considered to be due to reduced passivating ability of the alloy coating with a significant rise in the grain size above 50 nm.

The Influence of NaNO[sub 3] on the Atmospheric Corrosion of Zinc

Journal of The Electrochemical Society, 2003

The influence of NaNO 3 salt deposits on the atmospheric corrosion of zinc in humid air has been studied. Comparisons are made with the effects of NaCl and Na 2 SO 4. Also the combined effect of NaNO 3 with NaCl or Na 2 SO 4 was investigated. The salts were applied to zinc samples prior to exposure. The samples were exposed to purified humid air with careful control of relative humidity ͑95%͒, temperature ͑22.0°C͒, and flow conditions. The CO 2 concentration was 350 ppm and the exposure time was 4 weeks. Mass gain and metal loss results are reported. The corrosion products were analyzed by gravimetry, ion chromatography, and X-ray diffraction. Results show that the corrosion rate in the presence of NaNO 3 is only a third of that registered in the presence of NaCl and Na 2 SO 4. Further, a slight inhibitive effect of NaNO 3 was found in the presence of NaCl or Na 2 SO 4. The decreased corrosion rate in the presence of NaNO 3 was attributed to the reduction of nitrate to nitrite at the zinc surface. Nitrite is suggested to act as a corrosion inhibitor toward zinc.

Influence of the alloying component on the protective ability of some zinc galvanic coatings

Electrochimica Acta, 2005

The composition of the corrosion products of pure Zn galvanic coatings as well as of some zinc alloys (Zn-Mn and Zn-Co) after treatment in selected free aerated model media (5% NaCl and 1N Na 2 SO 4 ) is studied and discussed. X-ray diffraction and X-ray photoelectron spectroscopy investigations are used for this purpose. It is concluded that the corrosion products (zinc hydroxide chloride hydrate in 5% NaCl and zinc hydroxide sulfates hydrates in 1N Na 2 SO 4 ) play a very important role for the improved protective ability of the zinc alloys toward the iron substrate, compared to the pure Zn coatings. Another result is that, for a given medium, the corrosion products are one and the same for both alloys independently of the fact that the alloying component is electrically more positive or negative than the zinc. Some suggestions about the models of the appearance of these products and their protective influence are also discussed.

Structure and Corrosion Resistance of Zn-Ni and Zn-Ni-W Coatings

Materials Science Forum, 2010

Zn-Ni and Zn-Ni-W coatings were prepared by the electrodeposition under the galvanostatic conditions (j dep. =-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.

MECHANICAL PROPERTIES OF STEELS WITH DIFFUSIONAL ZINC COATING OBTAINED BY NANOGALVANIZING PROCESS

2017

Investigations of wear resistance and tensile strength of steel products with diffusional zinc coating obtained in zinc powders with a nanocrystallized surface of powder particles were carried out. The effect of the structural state of the coating on the wear resistance and adhesive grasping with a steel counterbody was established. The prospects of the nanogalvanizing process to improve the strength of steel products are shown. The development of technologies in modern machine building aims at improving the mechanical and technological properties of the materials. The present study presents an improvement in the mechanical properties of low carbon steels by thermoffusion coatings with nanofibers obtained under different heat treatment regimes. Depending on the type of heat treatment and the size of the zinc particles, different gradient layers can be obtained in depth. This of course reflects positively on the chemical resistance of the material. In addition, it positively affects the mechanical properties of the material by increasing mechanical strength and technological properties by improving the resistance to plastic deformation. With these first studies, there is an impetus for another look to improve the properties of low-carbon steels that are widely applicable in the field of machine building.