Rajesh Kumar Singh
Department of Chemistry, Jagdam College, JP University, Chapra - 841301, India.
DOI : http://dx.doi.org/10.13005/msri/080224
Article Publishing History
Article Received on : 1 Oct 2011
Article Accepted on : 18 Nov 2011
Article Published :
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ABSTRACT:
Corrosion is deterioration of the surface of material which is based upon environmental chemistry. There are several techniques applied to decrease corrosions and improve life of materials. Recently nanostructured material is used for the corrosion protection of material. Methods are applied for corrosion control like surface treatment techniques, nano-composite thin film coating, top layer coating and thermal barrier coating. ‘Analyses of test results show that the nanomaterials are significantly reduce the corrosion rate of materials as compared to conventional methods of corrosion protection. The corrosion protection is studied with the help of nanomaterial.
KEYWORDS:
Corrosion; Environmental Chemistry; Nanotechnology
Copy the following to cite this article:
Singh R. K. The Corrosion Protection of Materials by Nanotechnology. Mat.Sci.Res.India;8(2)
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Introduction
Corrosion of materials is burning problems for industry, railways, housing, transport vehicle, bridge and sensitive equipments. It generally takes place with metals, alloys, polymers, woods, glass and ceramics due to interaction of material with pollutants, effluents, industrial waste, human waste, biological waste, municipal waste, sea water, humid environment, acid rains, emissions, chemical by product, micro-organic and macro-organisms as well as sun light (UV radiation) and heat. Materials possess interfaces structures so they have grain boundaries and interfacial cracks. Other factors like impurities, surface morphology and lattice imperfection in material structures can also increase corrosion rate.
Corrosion basically starts at the surface of material and reduce lifetime of materials used regularly in aircraft and spacecraft, land and sea transportation vehicles, bridge, building, antique, museum, sculpture, techniqual equipments, infrastructure and electronic devices. The corrosion of materials is a surface phenomenon so these materials can also lose their mechanical, physical and chemical properties as well as they tarnish their appearances. Industrialized nations are spent 5% of GNP (gross national product) for corrosion protection, replacement of corroded parts, maintenance work and environmental protections.
Surface coating of materials1 are popular are popular approach for corrosion control. For this purpose thin film coating is applied on the surface of metal against corrosion attack. The affinity of corrosive species such as Cl”, H+, H2O, O2, pollutants and pigments, with materials are suppressed by organic thin film coating of polyurethane, polyamide, polyester, PVC, acrylics, alkyds and epoxies play an important rule to protect materials surface. Protective coating on metal surface is partly control development of electrochemical cell. Otherwise coating substances detach from the metal surface through chemical or electrochemical reactions. It is noticed that corrosion rate is deaccelerated by high polarization and coating resistance, low capacitance and high Warburg impedance that can be achieved by organic films coatings.
Organic coating substances on the metal surface are surrounded by hostile environment so its physical, chemical and physicochemical2 deterioration starts. Such degradation of coating
materials can produced in the form of swelling by water absorption, dissolution, cross-linking, oxidation and colour changes due to the heat, radiation, acid rain, global warming, ozone depletion, oxidative chemistry and other factors. The organic coatings thin film and its degradation show in fig. 1. Figure 1 indicates organic coating materials disintegration by atmospheric influences agents.
Figure 1: Coating of Polymer on Metallic sheet
Recently corrosion mitigation effect of materials was studied by the use of nanostructured materials (nanocomposites, nanoscale thin coating, nanoparticles etc.). Nanoparticle materials have specific physical, chemical and physicochemical properties so it is improved corrosion protection compared with bulk size substances. Nanoparticles have larger surface area to allow their uniform dispersion into matrix material with low dosage so its inhibition efficiency in high.
Methodology of Coatings
Study of Nanotechnology
Nanocomposite thin film coatings3, 4 have been used as inhibitors for corrosion mitigation of materials because they have distinct thermal stability and molecular barrier properties. Organic (silica gel, paraminobenzoic acid and benzohpenones) and inorganic (clay, silica, zirconium and carbon) nanoparticles injected into polymer matrixes (epoxy resin, polyimide, polystyrene, nylon, poly (methyl methacrylate) etc. at very low volume fractions of 0.5% to 5%. Nanocomposite polymers and nanoparticles are generally synthesized by using solution, in-situ polymerization, melt interaction and in-situformation. The nanostructured films can be formed by nozzle spray brush and electrostatic self-assembly that films are highly ordered and densely packed layers that can work as barrier layers to the underlying substances.
Thermal Barrier Coating
The corrosion and erosion rate of materials are increased at high temperature5 such corrosion is controlled by single and multi-layer thermal barrier coating. Such types of coatings are used in gas turbine and jet engines, power stations petroleum refineries and transportation vehicles. This types coating develop on the surface of material by plasma spray, laser glaze and chemical vapour deposition and physical vapour deposition techniques. Materials used for this technique6 is diamond like carbon (DLC), TiO2, ZrO2, Al2O3, V2O3, TiN, TiB2, SiC, Y2O3, hafnium oxide and other protective oxides. Thermal barrier coatings decrease corrosion and erosion rate of material and significantly increase the life of material. It is observed that nanoporosity is produced on the coating materials can lead to increased corrosion rates, but those porosities can be blocked using DLC or densely packed other coating materials.
Conversion Coating
Surface passivation7 layer methods have applied for a century to protect material from corrosion attack. These layers are generated by chromium, molybdenum, zirconium, phosphate, aluminum, potassium, nickel, gold, silver or zinc which increase the polarization resistance of the material surface and decrease corrosion current, potential and corrosion rates. Chromium is a hexavalent metal its coating material used in several fields including aircraft skins but it has pollution control problems. These days, new research programs have been focused on molybdenum, zirconium (spongy ZrO2) and phosphate (tricathionic(Fe, Zn, Mn) layers to replace conventional coating. The thickness of the layers can be in the range of 0.5µm and 20 µm.
Top Layer Coatings
Polyurethanes8 coating is used for corrosion prevention of materials because they have a wide variety of osmotic barrier, chemical, thermal, hydrolytic and oxidative stability properties. Epoxy and acrylic coating materials are readily available in the market but their protection capabilities are limited in severe environmental conditions. For this reason urethane top coatings are protected not only initial organic layers but also material surface against corrosion attack. Recently fluorinated polyurethanes polymers were developed having the lowest surface energy drastically decrease the permeability of the films against corrosive ions and molecules, moisture, temperature and UV radiation. This polymer is used as adhesion between the protective layers and materials surface, thus increase the corrosion resistance.
Nanoscale Structural Changes
The corrosion protection of materials9 is influenced by material structure (grain size and shape, alloying, annealing, crystallinity and other nanoscale structure). Fine grained materials particles have spherical shape so they are easily dispersed in the materials structure and exhibit higher corrosion resistance and mechanical properties. It shows that the corrosion resistance of electrodeposited Zn-Ni alloy coating (15% Ni) can be seven time better than that of pure zinc coating against corrosion attack. FeCrTiN alloys coating coatings have better corrosion resistance power than that of Cr.
Nanoscale Measurement Techniques
Nanotechnologists developed nanoindentation and nanoscratch to analyze nanomechanical properties of thin film coating and nanostructural materials10 which are directly related to corrosion mitigation properties. In the nanoindentation method, a known shaped indenter tip is driven into substrates by applying external forces. The nanoscratch test is based on the same physical principles as the nanoindentation test.
Conclusion
Recently, a so many techniques applied for studied nanomaterial properties have been conducted to analyze possible new methods for corrosion mitigation. These include surface passive layers, nanocomposite thin films, thermal barrier films, top layer coatings, nanostructural changes on materials and their characterization techniques in the nanoscales. These studies give promising results for the corrosion prevention of materials and directions of corrosion in the future.
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