Indian Institute of Technology, (Banaras Hindu University)

Varanasi

ENGINEERING APPLICATIONS OF NANOTECHNOLOGY IN CORROSION

By

Ashwin Swaminathan(12102EN020), 1st Yr., B.Tech, Chemical Engineering

Vipin Detani(12102EN005), 1st Yr., B.Tech, Chemical Engineering

Mayank Raghuwanshi(12102EN006), 1st Yr., B.Tech, Chemical Engineering

Aman Chawla(12102EN011), 1st Yr., B.Tech, Chemical Engineering

A Research Report Submitted to

Professor M.A.Quraishi(Ph.D., D.Sc.)

Department of Applied Chemistry,

IIT(BHU), Varanasi

July, 2013

Acknowledgement

We would like to thank our Chemistry Sir, Professor M.A.Quraishi for having given us

this wonderful opportunity to learn and do this project on “Engineering Applications of

Nanotechnology on Corrosion”. We would also like to thank the Institute for the

resources it had to offer us, during the creation of this project.

Ashwin Swaminathan(12102EN020), 1st Yr., B.Tech, Chemical Engineering

Vipin Detani(12102EN005), 1st Yr., B.Tech, Chemical Engineering

Mayank Raghuwanshi(12102EN006), 1st Yr., B.Tech, Chemical Engineering

Aman Chawla(12102EN011), 1st Yr., B.Tech, Chemical Engineering

1.Abstract:

In the last two decades, nanotechnology has been playing an increasing important role in

supporting innovative technological advances to manage the corrosion of steel. Environmental

impact can improved by utilizing nanostructure particulates in corrosion inhibition, Nano

composites have also proven to be an effective alternative to other hazardous and toxic

compounds.This paper reviews various recent patents and patent applications related to the

management of steel corrosion using engineering applications from nanotechnology.

Key words : Corrosion; Steel; Nanotechnology; Nanocomposite.

2. What is Nanotechnology?

2.1 Defeniton and Description:

Nanotechnology is the manipulation of matter on an atomic and molecular scale.

Nanotechnology as defined by size is naturally very broad, including fields of science as diverse

as surface science, organic chemistry, molecular biology, semiconductor

physics,microfabrication, etc.

Nanostructures materials (1–100 nm) are known for their outstanding mechanical and physical

properties due to their extremely fine grain size and high grain boundary volume fraction.

Significant progress has been made in various aspects of synthesis of nano-scale materials. The

focus is now shifting from synthesis to manufacture of useful structures and coatings having

greater wear and corrosion resistance.

2.2 Fundamental concepts

Nanotechnology is the engineering of functional systems at the molecular scale.

Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances can become transparent (copper); stable materials can turn combustible (aluminum); insoluble materials may become soluble (gold). Much of the fascination with nanotechnology stems from quantum and surface phenomena that matter exhibits at the nanoscale.

2.3 Nanomaterials

The nanomaterials field includes subfields which develop or study materials having unique properties arising from their nanoscale dimensions.[29]

Interface and colloid science has given rise to many materials which may be useful in nanotechnology, such as carbon nanotubes and other fullerenes, and various nanoparticles and nanorods. Nanomaterials with fast ion transport are related also to nanoionics and nanoelectronics.

Nanoscale materials can also be used for bulk applications; most present commercial applications of nanotechnology are of this flavor.

Progress has been made in using these materials for medical applications; see Nanomedicine.

Nanoscale materials are sometimes used in solar cells which combats the cost of traditional Silicon solar cells.

3. Corrosion-The Phenomenon

Corrosion is the gradual destruction of materials(usually metals), by chemical reaction with its environment.

In the most common use of the word this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal. Corrosion degrades the useful properties of materials other than metals, such as ceramics or polymers. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases.

Many structured alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface.

Because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and chromate conversion, can increase a material’s corrosion resistance.

3.1 Corrosion: why, when and how:

Corrosion Degradation Based on Thermodynamics and Kinetics :

Thermodynamics drives the corrosion process, which requires each of the following actors to be

present: an anode, a cathode, an electrolyte, and susceptible materials. When two dissimilar

materials become connected to each other by an electrolyte (an electrical-conducting liquid

medium), one material acts as the anode, or material more prone to give up its electrons and

corrode, and the other acts as the cathode, or material more prone to receive electrons in the

specific circuit, based on their relative position in the Galvanic Series.

Thermodynamics answers the question ―Will corrosion happen?‖

Based on the difference in Gibbs free energy, or ∆G, of a system. ∆G measures a closed

system’s (fixed mass and composition; constant temperature and pressure) tendency toward

stable equilibrium. Gibbs free energy is defined mathematically by the expression, G = H – TS,

where H is enthalpy, T isabsolute temperature, and S is the entropy of the system. When a

negative ∆G exists for a chemical reaction between two materials, corrosion will occur.

Electrical current flows between the anode and the cathode causing negatively charged metal

ions (anions) to be emitted as corrosive by-product, causing degradation.

Kinetics, as opposed to thermodynamics, answers the question ―How fast will corrosion

occur?‖ An Arrhenius equation defines this rate, expressed as, rate = A(-Q/RT), where A is a

material constant, Q is a material activation energy (free energy required to drive a specific

reaction), R is the universal gas constant, and T is absolute temperature.29 Outside of

choosingmaterials wisely to control the applicable properties (A and Q), temperature remains

the only variable that can be manipulated to reduce corrosion rate. Per the equation, higher

temperatures result in more rapid corrosion, and vice versa.

4. Introduction to applications of nanotechnology in

corrosion

Steel is a type of widely-used engineering material for many industries and can be found in manufacturing, construction, defense, transportation, medical, and other applications. The corrosion of steel as a result of chemical or electrochemical reaction with its service environment is a spontaneous process, which can compromise the materials integrity and impact assets, environment, and people if no measures are taken to prevent or control it. The corrosion of steel is generally electrochemical in nature, and may take many forms such as uniform corrosion, galvanic corrosion, pitting corrosion, crevice corrosion, underdeposit corrosion, dealloying, stress corrosion cracking (SCC), corrosion fatigue, erosion corrosion, and microbially influenced corrosion (MIC). In addition to cathodic protection [1], there are many traditional technologies available to mitigate the corrosion of steel, by either enhancing the inherent corrosion resistance and performance of the steel itself (e.g., use of stainless steel in place of carbon steel for rebar in concrete), or reducing the corrosivity of the service environment (e.g., electrochemical chloride extraction for steel-reinforced concrete [2]), or altering the steel/electrolyte interface (e.g., corrosion inhibitors, metallic coatings, non-metallic coatings, and surface treatment of steel). These countermeasures can be used individually or synergistically in the practices of managing steel corrosion.

Over the last two decades, significant advancements have been made to improve the management of steel corrosion through research, development, and implementation; and nanotechnology has been playing an increasing important role in supporting innovative technological advances. First of all, improved understanding of corrosion and inhibition mechanisms has been continually achieved through characterization and modeling of the steel surface and corrosion products at various length scales down to the nanometer scale [3].

Secondly, nanotechnology has been employed to enhance the inherent corrosion resistance and performance of the steel itself, by achieving the desirable finely crystalline microstructure of steel (e.g., nano-crystallization) or by modifying its chemical composition at the nanometer scale (e.g., formation of copper nanoparticles at the steel grain boundaries). Metallurgy approaches to the production of high-performance steel with a fine-grain structure and/or self-organization of strengthening nanophases (carbides, nitrides, carbonitrides, intermetallides) have been burgeoning under the guide of nanotechnological principles, including nanoprocesses for steel smelting and microalloying, mechanical pressure treatment (e.g., intense plastic deformation), and heat treatment (e.g., superfast quenching of melts) [4]. One such technology commercialized in the U.S. produces high-performance carbon steels that feature a “three-phase microstructure consisting of grains of ferrite fused with grains that contain dislocated lath structures in which laths of martensite alternate with thin films of austenite” [5].

Thirdly, nanotechnology has been employed to reduce the impact of corrosive environments through the alternation of the steel/electrolyte interface (e.g., formation of nanocomposite thin film coatings on steel). Significant improvements in the corrosion protection of steel have been reported through the co-deposition of Ni-SiC or Ni-Al2O3 nanocomposite coatings on mild steel [6-7] and the application of TiO2-naoparticle sol-gel coatings or multilayer polyelectrolyte nanofilms on 316L stainless steel [8,9]. The incorporation of nano-sized particles (e.g., polyaniline/ferrite, ZnO, Fe2O3, halloysite clay, and other nanoparticles) into conventional polymer coatings also significantly enhanced the anti-corrosive performance of such coatings on steel substrates [10-13]. Recent progress in the use of nanomaterials for corrosion control is summarized in a 2007 review article [14], which discussed the incorporation of nanoparticles in ceramic coatings, polymer coatings, and hybrid sol-gel systems for improved properties (e.g., resistance to corrosion and high-temperature oxidation, self-cleaning, and anti-fouling).

A polymer Nano composite coating can effectively combine the benefits of organic polymers,

such as elasticity and water resistance, to that of advanced inorganic materials, such as

hardness and permeability [18]. Nano composites have also proven to be an effective

alternative to phosphate-chromate pretreatment of metallic substrate, which is hazardous due

to the presence of toxic hexavalent chromium [18-24].

The incorporation of Nano-sized particles (e.g., polyaniline/ ferrite, ZnO, Fe 2O3, hallo site clay,

and other nanoparticles) into conventional polymer coatings also significantly enhanced the

anti-corrosive performance of such coatings on steel substrates .

One of the main goals is identifying national strategies able to minimize the impact of corrosion

protecting it at the same time of preventing its development. Nowadays, annual direct cost of

metallic corrosion in the U.S. economy is estimated $300 billion and €200 billion in Europe.

The presence of corrosive chemicals and harsh operating and environmental conditions can

result in structural failure or loss of containment, which can be costly in terms of repairs, lost or

contaminated products, environmental damage, and potential risk to personnel. Corrosion

factor is very costly and has a major impact on the economies of industrial nations companies.

Fight against corrosion depends on technological expertise and has a wide variety of

applications, one of which is coatings for corrosion resistance.

4.1 Why nanotech in corrosion? – Some facts

The boom in the gas and oil business, both in the United States and globally, has

refocused attention on efforts to reduce corrosion on the surfaces of pipes and equipment

used in the industry.

A study conducted by the European Federation of Corrosion found that between 40 and

60 percent of piping maintenance costs are related to localized corrosion that occurs at

the interface of a metal surface and the insulation on that surface.

With new nanotechnology-based innovations, this is no longer the case. More of this

wasted energy loss can be recaptured, and insulation now has the ability to prevent

corrosion and CUI rather than causing it.

Nanotechnology is simply the manipulation of materials at a smaller scale than was

previously possible, and by manipulating matter at the nanoscale, materials have the

ability to be built from the atomic level up with much less waste.

Science has also found that materials can take on different attributes when you

manipulate them at this scale, such as silver taking on anti-microbial properties.

5. Fields of Application

5.1 Steel Bulk Materials with Excellent Corrosion Resistance

Nanotechnology has been utilized in endowing the steel bulk materials with excellent corrosion resistance and other enhanced properties, mainly by refining their crystal grains to the nanometer scale. The steel substrate with a nano-phased grain structure tends to have less defects or inhomogenities where corrosion attack traditionally initiates and/or propagates. The first invention in this category [15] discloses a nano-crystal austenite steel bulk material with an improved corrosion resistance and ultra-hardness and toughness, comprising an aggregate of austenite nano-crystal grains containing a solid-solution type nitrogen in an amount of 0.1 to 2.0% (by mass). The steel is prepared by mechanical alloying (MA) of fine powders of austenite steel-forming components (e.g., Fe, Cr, Ni, Mn, and C) and an N-containing substance (e.g., N2, NH3, and nitride of Fe, Cr, and Mn), followed by forming-by-sintering treatment and subsequent annealing. As the component elements in the mixture are mechanically alloyed “without recourse to any melting process”, austenite steel powders achieve “a nano-size crystal grain structure that can never be achieved by conventional processes”. This structure is further reinforced by solid-solution strengthening of nitrogen into an austenite phase. The crystal grains are more finely divided on a nanometer scale by mixing a particle dispersant (e.g., AlN, NbN, TaN, Si3N4, and TiN) or mixing a metal oxide or a semimetal oxide in the MA process. Furthermore, an oxide, nitride, carbide, silicide, or boride of a metal or semimetal exists as a crystal grain growth inhibitor between and/or in the nano-crystal grains, preventing them from becoming coarse in the forming-by-sintering process. Such stainless steels having a high N concentration (in place of expensive Ni or Mn) were reported to feature much improved resistance to corrosion and particularly to pitting corrosion as well as significantly reduced sensitivity to stress corrosion cracking (SCC). As such, they may find a wide range of applications such as high tensile strength bolts and nuts, bulletproof steel sheets and vests, bearings, gears, tools for hot processing and extrusion, and medical tools

Methods are also disclosed for producing fine-grained martensitic stainless steels. One recent patent [16] discloses the use of thermal mechanical treatment to create a fine-grained microstructure imparting the steel good corrosion resistance, high strength, and high toughness. In one example, a 15-cm thick steel slab was first soaked at 1230°C for 2 hours “such that the structure is mostly face-centered-cubic (austenite) throughout the alloy”, before being hot-worked on a reversing rolling mill at a temperature between 1230°C and 1150°C. During the forming process, a true strain of 0.22 to 0.24 per pass was utilized to “recrystallize the microstructure”. The resulting plate was then air-cooled to room temperature with or without further heat treatment, ultimately transformed into a fine-grained martensitic stainless steel product featuring ASTM grain size numbers no smaller than 5. Another invention [17] relates to Cr-Ni-Co-Mo-Ti-Al stainless steels with an excellent combination of strength, toughness, and corrosion resistance across a variety of strength levels. As such, they may benefit many

engineering applications such as aircraft landing gears and other structural aeroframe components, down-hole petrochemical drilling components, and biomedical applications. The stainless steels feature “a predominantly lath martensite microstructure essentially without topologically close packed intermetallic phases and strengthened primarily by a dispersion of intermetallic particles primarily of the η-Ni3Ti phase”. The Ti and C levels are controlled “such that C can be dissolved during a homogenization step and subsequently precipitated during forging to provide a grain-pinning dispersion” of carbides of Ti, V, Nb, or Ta.

5.2 Decorative and Protective Coatings with Superior Abrasion Resistance

Nanotechnology has been utilized in decorative and protective coatings featuring superior abrasion resistance (which helps to prevent erosion corrosion and mechanical damage of the surface) and good corrosion resistance. The most recent invention in this category [18] deals with a plastic, ceramic or metallic article having on at least a portion of its surface a smooth coating with the appearance of brass, nickel and stainless steel. Among the multiple superposed coating layers, a metallic strike layer was produced through physical vapor deposition (PVD). When cathodic arc evaporation (CAE) is used for PVD, adding a low percentage of oxygen during deposition was reported to have the effect of reducing the number of macroparticles and thus rendering a dense nascent PVD layer with fewer defects. For zirconium, the resulting strike layer exists either as amorphous to nano-size crystals up to 50 nm or as preferentially-oriented crystals dominantly in (112) direction and up to 80 nm in size, with a small percentage of amorphous refractory oxide acting as precipitation hardening particles. By maintaining the flow ratio of oxygen to argon into the vacuum chamber during CAE, a stoichiometric zirconium oxide layer (preferably between 10 to 30 nm thick) is then deposited on the strike layer, which provides another non-conductive barrier layer to improve resistance to corrosion and pitting.

One patent in this area [19] deals with an invention which discloses novel methods of depositing a nanocomposite coating of stainless steel and a metallic carbide or metallic nitride onto a solid metallic substrate (e.g., stainless steel) to increase its surface hardness. Different from continuous deposition process, very thin layers (e.g., 5 to 10 nm per layer) of such nanocomposite coating are deposited by reactive sputtering in a carbon or nitrogen gas plasma, using pure stainless steel and chromium targets or their alloy targets. When the substrate is away from the deposition locations, the deposited stainless steel and chromium carbide (or chromium nitride) phases were reported to relax into “their most thermodynamically suitable sites”. It should be noted that the formation of chromium carbide phases between grain boundaries is traditionally considered a major risk for intergranular corrosion attack on stainless steels. By reducing the fine-grain structure down to nanoscale, however, it is possible to minimize such risk. Since no post-treatment (e.g., polishing) is required after the deposition, this method features a clean process for obtaining a hard, wear-resistant, and corrosion-resistant coating with a stainless-steel-like appearance. The disclosed method may also be applicable to vapor deposition techniques other than reactive sputtering, such as multi-arc reactive deposition, or reactive evaporation ion-plating.

Another patent in this area [20] deals with an invention that provides metallic components (e.g., Co-Cr, Co-Cr-Mo, Ti-6Al-4V, and stainless steel) for incorporation in orthopedic prosthesis with integrally-formed, homo-metallic protective coatings on their surfaces. The deposited substance and the bulk substrate have at least one metallic constituent element in common; and the formed coatings feature crystalline grains with an average size in a range of about 1 to 999 nanometers (more preferably in a range of about 10 to 200 nanometers) and thus an enhanced hardness and a high degree of resistance to corrosion and wear. In one example, the nanocrystalline coatings featured grain sizes a few hundred times smaller than those of the bulk substrate and were “substantially free of dislocations”. To improve the adhesion of the coating to the substrate, the average crystalline grain size can decrease continuously from the substrate to the coating within the transition zone. The methods of producing such coatings were reported to be cost-effective and easy-to-implement, such as the case of PVD combined with concurrent ion beam bombardment.

In yet another invention [21], bipolar pulsed current (BPP) was used to produce alloy deposits with a specified nanocrystalline average grain size. The alloy has at least two elements, one of which being most electro-active and at least one of which a metal. For the electrodeposition, an auxiliary electrode and the article to be treated (as the second electrode) are placed in the liquid comprising dissolved species of at least these two elements and “coupled to a power supply configured to supply electrical potential having periods of positive polarity and negative polarity at different times”. The technology can be used to provide a substrate of electro-conductive plastic or metal (e.g., steels, aluminum, and brass) with decorative or protective coatings featuring superior macroscopic quality and/or resistance to corrosion and abrasion. Different than tradition means, the disclosed method is able to tailor the deposition composition and/or its grain size without changing the bath composition or temperature in the process; instead, Polarity Ratio (characterized by the amplitude and/or duration of the negative pulse relative to those of the positive pulse) was used to enable “grading and layering of nanocrystalline crystal size and/or composition within a deposit” without introducing voids and cracks and “changing the composition and/or grain size of the deposit relatively quickly in time”. Compared with traditional microcrystalline metals, the nanocrystalline metal coatings with grain size refined to the nanometer scale are expected to show exceptional combination of properties such as excellent corrosion and wear resistance, enhanced yield strength and ductility, and desirable magnetic properties.

5.3 Protective Coatings to Manage Damaging Oxidation and Corrosion

Nanotechnology has been utilized in surface treatments to improve the performance and service life of steel and other alloys used in oxidizing and corrosive environments. A recent invention [22] is directed to nanoparticle surface treatments and methods of providing such treatments for forming a beneficial oxide coating (e.g., thin and non-spalling oxide layers) on alloys, thereby providing the substrate with enhanced resistance to damaging oxidation and corrosion under extreme conditions. The disclosed method relates to such nanoparticles as cerium oxide, nanoceria, or an oxide of an element selected from the group consisting of aluminum, silicon, scandium, titanium, yttrium, zirconium, niobium, lanthanum, hafnium,

tantalum, thorium, and other rare earth elements. One possible mechanism is that these elements exhibit a reactive element effect (REE) that decreases the oxide scale growth rate and reduces scale spallation by improving the scale-alloy adhesion.

The invention suggests exemplary applications of this technology in protecting stainless steel and nickel or aluminum alloys at high temperatures and in steam environments, service conditions often seen by fossil energy system components, heat exchangers, reheater pipes, solar collectors/panels, refrigeration and heating equipment, vacuum and gas chambers, hydrogen fuel cell components, heat treating furnace components, flame stabilizers, surgical components, fan accessories, inlet-outlet transitions, and automotive and aircraft components. Compared with many conventional techniques for surface treatment (e.g., physical vapor deposition, chemical vapor deposition, ion implantation, and sol-gel applications), the invention features simplified processes such as the simple dip method or some additional surface treatment techniques (e.g., spraying, brushing, spinning, and electrophoresis), with a preference for the methods that reduce nanoparticle agglomeration. The effectiveness of nanoparticle surface treatments in managing metallic oxidation and corrosion was demonstrated by the author. For instance, the steel samples were dip-coated with nanoparticles in their respective solutions for once or several times with intermediate drying at 200°C. After heating to 1000°C for 34 hours, the 316 stainless steel sample treated with nanoceria had a self-protective, thin, and adherent oxide film formed on its surface, whereas the sample without the nanoparticle treatment had thick, spalled oxide scale on its surface. Similarly, beneficial effects of nanoceria surface treatment for 430 and 410 stainless steels were observed after heating to 800°C in air for some time. The diffusion-based predictive models suggested the lifetime of nanoceria-coated stainless to be significantly greater than the uncoated material at high temperatures in an oxidizing atmosphere. The resistance to damaging oxidation of the self-protective surfaces generated after different nanoparticle surface treatments was found to be comparable to that observed with nanoceria surface treatments. Tests of nanocrystalline-coated and uncoated alloys (e.g., 304, 321 and 430 stainless steels) confirmed the corrosion resistance of the self-protective surfaces towards humid air, towards direct contact with liquid in the temperature range of 150°C to 350°C, towards submerged service in high salinity solutions, and towards the vapor phase above these solutions.

Another invention in this category [23] presents methods of endowing the metal surfaces (e.g., aluminum alloys, copper alloys, and steel) with outstanding corrosion resistance by forming an ultrathin (preferably less than ten nanometers thick), chromium-free film comprising an at least partially crosslinked amido-functionalized silanol component and nanoparticles of rare-earth metal oxide (e.g., cerium oxide or samarium oxide). This invention also features novel yet simple processes to form the ultrathin corrosion-resistant film. First, the metal surface is cleaned and then dip- or spray-coated with an aqueous solution containing one or more silanol compounds (e.g., 3-aminopropylsilanetriol) and one or more rare-earth metal carboxylate compounds (e.g., cerium acetate or samarium acetate). Then the coated metal surface is subjected to one or more treatment steps (including thermal treatment at 90-150°C for 2-6 hours), which are designed to promote or effect silanol crosslinking of the silanol compounds

and degradation of the rare-earth metal carboxylate compounds to rare-earth metal oxide nanoparticles. Such formed coatings were reported to provide better coverage of the substrate metal and similar or superior corrosion resistance, compared with chromium-based coatings. For instance, one of such coatings demonstrated to extend the lifetime of the steel substrate under salt-fog test at 35°C from approximately 10 hours to approximately 768 hours.

5.4 Nano-sized Additives for Anti-corrosion coatings or for Managing the Corrosivity of Service Environment

Nanotechnology has been utilized in preparing nano-sized additives for coatings used to protect steel and other metals from corrosive environments. A recent invention [24] is directed to a process for preparing dispersion additives useful for anti-corrosion coatings. First, a polymer having ether or amine groups (e.g., polyethylene oxide, polyethylene glycol, polyether amine and polyglycol esters) is dissolved in a solvent at the concentration of 5-35 wt%. Then, a metal salt (e.g., chloride, bromide, chromate and acetate salts of Zn, Fe, Ni, or Cr) dissolved separately in the same solvent at the concentration of 4-10 wt % is added. The polymer and the salt are allowed to digest for an extended period to form a complex, which is then reacted at 10-30°C with an alkali (e.g., sodium hydroxide, potassium hydroxide and liquid ammonia) for 4-8 hours to form a colloidal precipitate. Finally, the precipitate is separated from the reaction mixture by centrifugation or filtration and then dried and ground to fine powder (with particle size of 2-50 nm, preferably 3-5 nm). The resulting powder can be used as nano-particulate dispersion additive in coatings to prevent corrosion of steel substrates in harsh environments (e.g., seawater). Such nano-scale additives can be used at a much lower concentration (typically 2-5 wt%) than the conventional-grade fine pigments (typically 50-70 wt%) without the loss of corrosion resistance, thus providing the coating with much higher optical gloss and smoothness and reduced risk of cracking. The electrochemical testing of coated mild steel substrates indicated that the nano-scale additive imparted high corrosion resistance of the coating relative to the commercial grades. In one example, the coating containing the nano-scale additive withstood a harsh chloride-laden environment at 50°C even for 8 hours, whereas the coating containing the commercial-grade additive failed immediately within 1 hour.

Another invention in this category [25] discloses a process for preparing nanoparticles surfaced with self-assembly monolayers and thus providing a water-soluble paint with enhanced properties (e.g., self-cleaning, anti-fouling, anti-fungal, anti-algal, water repellency, flushing and brushing durability, weather resistance and anti-aging properties). Such nanoparticles were reported to be “tightly tangled or bonded with the molecular chains of organic paint to homogeneously distribute” them in the coating and “form a dense low surface energy coating film” with greatly improved coating properties.

In another invention [26], a polymer emulsion with particle sizes in the nanometric range (between 10 and 100 nm) was used for electrophoretic painting. The small size of the nanoparticles is advantageous since it enables their penetration into “ultra-small holes, indentation and capillary areas at surface of the metallic subject”. The use of nano-emulsions

was also reported to produce “a very uniform coating even in the recess areas of complex-shaped items” and to significantly improve the quality of coatings containing other pigment particles. Once the conductive substrate is coated, it is cured in an oven to allow the nanoparticles to flow and crosslink with each other. The technology was able to produce an ultrathin, transparent, non-porous and dense coating layer exhibiting“suitable hardness, good corrosion resistance, and strong adherence to the underlying substrates”.

Yet another invention [27] discloses the use of an aqueous solution containing nano-sized silver particles in a resin composition to form a thin coating film exhibiting “superior antibacterial properties, corrosion resistance, conductivity and adhesion” to a steel plate. To prepare the silver nanoparticles, silver metals are reduced into fine particles by formation of a polymer-silver nanocomposite. Alternatively, the silver nanoparticles can be prepared using the adsorption method, with silver salts, metal ion reducing agents, and surfactants added in an aqueous solution.

Finally, nano-sized additives have also been utilized to reduce the corrosion risk of the service environment. A recent invention [28] is directed to the use of nanoparticles to treat a high-temperature water system (e.g., boiling water reactor) in order to reduce the susceptibility of high-strength materials (e.g., carbon steel, alloy steel, stainless steel, nickel-based alloys, cobalt-based alloys, and zirconium-based alloys) to stress corrosion cracking (SCC). For instance, nanoparticles of a material comprising noble metals can be applied to the system to lower the electrochemical corrosion potential of the high-strength material in the high-temperature water environment. The system is further treated with a material comprising zinc (e.g., zinc nanoparticles). The low corrosion potential is designed to facilitate the transport of zinc into cracks and its penetration or incorporation into oxide films, thereby adequately mitigating SCC.

5.5 Nanotechnology for Intelligent Corrosion Protection Systems

The last by not the least interesting field of application for nanotechnology is its use for intelligent corrosion protection systems. A recent invention [29] discloses a novel approach for the preparation of “smart” corrosion-inhibiting pigment and its use in self-healing anti-corrosion coatings in the form of a powder or a suspension, in which nanoparticles (e.g., SiO2, ZrO2, TiO2, CeO2 nanoparticles) are coated layer-by-layer (LbL) with one or more layers of polymer or polyelectrolyte shell (e.g., poly (alkylene imine), polyalkylene glcol, and biopolymers and polyamino acids) responsive to a specific stimulus or trigger. These particles thus act as nanoscale reservoirs for the effective storage of the corrosion inhibitor (e.g., quinaldic acid and mercaptobenzotriazole). The method of producing the intelligent coatings was reported to be cost-effective and easy-to-implement, as the nanoreservoirs provide prolonged release of the inhibitor. The corrosion inhibitors are released in a regulated fashion, mainly to the damaged coating zones and/or corrosion defects where they are most needed, thereby providing active, long-term corrosion protection of the coated substrate (e.g., steel and aluminum alloys). In one example, the LbL deposition technology was utilized to coat ZrO2particles (with average size of 150 nm) with multiple poly(allyl amine) /poly(acrylic acid) layers, within which quinolinol was entrapped as the corrosion inhibitor. The self-healing effect of a sol-gel coating doped with

such nanoreservoirs was demonstrated by the scanning vibrating electrode technique and attributed to the release of quinolinol in the damaged area when initiated by pH changes caused by the corrosion of the steel alloy substrate.

Another invention in this category [30] is directed to the use of multiphasic nano-components (MPNs) for detecting or mitigating the corrosion of steel and other metallic materials in biomedical applications. For instance, multiphasic nanoparticle compositions can be prepared by electrically jetting polymer fluid in a side-by-side configuration. At least one phase of the MPNs is designed to have good adhesion to intact or corroded metal surfaces, using the excellent binding affinity of functional groups (e.g., hydroxyl groups, siloxy groups, amine groups, phenyl groups, catechol, or their combinations). The MPNs can be employed to “diagnose or image certain regions of a metal surface due to specific binding (for instance, detecting regions of corrosion on a medical device)”, to “provide a biological coating of the metal surface to prevent corrosion and/or to improve the biocompatibility of the medical device surface in vivo”, or to enable both diagnosis and corrosion protection.

6. Concluding- Current & Future Developments

Recent inventions related to the management of steel corrosion include the use of nanotechnology to produce high-performance steel, to produce coatings with superior abrasion resistance and good corrosion resistance [18-21], to enhance the surface of steel designed for oxidizing and corrosive environments [22-23], and to prepare nano-sized additives for anti-corrosion coatings [24-27] or intelligent corrosion protection systems [29-30], or for reducing the corrosion risk of the service environment [28].

Nanotechnology has demonstrated its clear benefits and will continue to play a key role in the production of high-performance steel. Future developments will be centered on furthering the understanding of why and how superior corrosion resistance (as well as other desirable properties) of steel can be achieved by the design and control of its chemical composition and morphology at the micro- and nano-meter scales (e.g., through microalloying and thermal mechanical treatment).

Nanotechnology has brought fundamental changes to the methods of mitigating corrosion risk at the steel/electrolyte interface. Future developments will continue in technologies that can produce an ultrathin ceramic or metallic nanocomposite layer or nanocrystalline layer on steel (e.g., physical vapor deposition, chemical vapor deposition, ion implantation, sol-gel applications, and electrodeposition). More innovation can also be expected in the incorporation of nanoparticles in ceramic coatings, polymer coatings, and hybrid sol-gel systems for enhanced corrosion protection of steel and other metallic substrates. One new field of application would be the use of nano-sized reservoirs in self-healing coatings, even though current research has been limited to micro-sized capsules.

The ultimate market share of nanomaterials or nano-enabled products in managing steel corrosion will depend on continued investment and efforts in research and development as well as market-driven product strategies. A multitude of technical and cost barriers remain for many of the inventions. While nanotechnology holds the promise for addressing environmental, health, and safety issues in some traditional corrosion protection technologies and products, similar issues or concerns have surfaced for the responsible development, production, use, and disposal of some nanomaterials and related technologies. These are generally sparked by the nanosize effect and present unique challenges to be addressed before the successful commercialization of nanotechnology in some applications.

• The application of nanotechnology in the corrosion protection of metals has recently gained

momentum and of real promise. • Environmental impact can be improved by utilizing

nanostructure particulates in corrosion inhibition, coating, and eliminating the requirement of

toxic solvents. • Nano technological approach that was able to effectively protect steel from

corrosion in acid, alkaline, and saline media was developed.

7. Bibliography

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9. Insulation.org; “is there a cure for corrosion under insulation? By Michael Lettich

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11. chemistry.org/education/chemmatters.html

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14. Elsevier

15. science direct

16. www.industrial-nanotech.com