Page 187 - CW E-Magazine (14-5-2024)

Special Report Special Report

sion and further corrosion. This makes offerings include thin ceramic paint path of corrosive matter, pigments with play higher bond strength, corrosion protection of metallic substrates, such as compared to properties shown by parent
aluminium an ideal material for sheet products for protection against corrosive shapes of plate-like fl akes are added to resistance, toughness and abrasion resis- aluminium alloys used for aircraft. materials. The thermal processes may
metal. chemicals and abrasion. organic coatings. Mica as well as glass tance. Nanoparticle feedstocks used for suffer due to inclusions, in-fl ight oxida-
fl akes are added for this purpose. The corrosion and wear protection include The technique has potential applica- tion, as well as re-melting at high tem-
Freshly exposed zinc reacts with Apart from developing new coat- orientation of the pigment fl akes ought Tungsten carbide/cobalt (WC/Co) and tions in automotive, maritime and oil & peratures, resulting in the onset of early
oxygen to form zinc oxide, and with ings for minimizing surface deteriora- to be parallel to the substrate surface. alumina/titanium oxide (Al O /TiO ). gas pipeline sectors. This advanced sys- corrosive deterioration due to intercon-
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water to form zinc hydroxide. When zinc tion, specialists are also focusing on These must be fully compatible with the tem not only acts as a barrier to corrosive nected porosity. Cold spraying creates
hydroxide reacts with carbon dioxide in improving the substrate surface cleaning resin used in the coating as well. Mont- Replacing hexavalent chromium with media, but also senses the changes in effective coatings with capabilities closer
the atmosphere, the resulting product and pre-treatment processes. The use of morillonite and other layered clay plate- smart coatings internal structure of the multiple layers to the properties of the parent metals.
is zinc carbonate. These corrosion fi lm titanium, vanadium, silicon and zirco- lets are added into the polymer resins in In spite of the health and safety of coatings on account of corrosive Studies indicate that corrosion- and
products, like the fi lm that forms on nium-based chemical compounds with order to create a strong protective barrier issues, hexavalent chromium has been reactions, and responds to the changes wear-resistant materials such as tungsten
aluminium, are resistant to water intrusion polymers has led to improvement in against common corrosion species such a popular ingredient used by the metal to heal the damages and prevent further carbide can be cold sprayed on a variety
and tightly adhere to the steel’s surface pre-treatment effectiveness. Many auto- as corrosive gases, oxygen and water industry for corrosion protection. But damages. Self-healing ability is provided of material surfaces.
so that it does not easily fl ake off like the makers have successfully replaced some molecules. safety, health and environmental fac- by the mobility of the polyelectrolytes.
corrosion formed on iron. of their pre-treatment processes that use tors today prohibit the use of hexa- Cold sprays produce coatings with
zinc-phosphating with a pre-treatment Developments in inhibitor coatings valent chromium. Researchers are now The process used is the ultrasonic the advantage of very low porosity, com-
Galvanic protection process using ceramic products with For protecting metals from corro- replacing passive barrier coatings with pre-treatment of the substrate (aluminium bined with a higher hardness, compared
Zinc, however, is a reactive metal nano-sized particles of zirconium com- sion, mostly lead and chromate-based multifunctional and smart nanoparticle alloy) surface and precise deposition to thermal sprays. They ensure a stron-
and will slowly corrode and erode over pounds as well as many other organic corrosion inhibitors have been exten- coatings, which can sense the corrosion of layers of oppositely charged nano- ger substrate adhesion and cohesion of
time. The degradation rate of zinc is still materials, which are more eco-friendly. sively used as primers in the past. How- media and release anti-corrosive ingre- particles of inhibitors and polyelectrolytes the particles, creating a harder surface.
several times less than that of steel and ever, owing to regulatory restrictions, dients. Some of the nano-structured 5-10 nanometers thick. These smart A comparatively thinner cold spray
will therefore signifi cantly prolong the Developments in sacrifi cial protection new corrosion inhibitors are being particle coatings can heal the damaged multi-layer coatings provide passivation coating can be as effective as a thicker
service life of the steel it is meant to In some cases, a coating may be developed and tested for various appli- coating and thus ensure that protection of the substrate along with self-healing thermal spray coating for providing cor-
protect. Zinc acts as a sacrifi cial anode, continuously consumed through a reac- cations. Corrosion inhibitors containing continues to be effective and durable. features and pH buffering. rosion protection and wear resistance.
which gets corroded, protecting steel. tion with a corrosive species. When the silicates, phosphates and molybdates Additionally, this new method is very
coating acts as a sacrifi cial anode, as in have been used in signifi cant quantities Smart nanoparticle coatings perform Cold spray coatings convenient for in situ working and res-
The parameters of corrosion protection the case of the layer of zinc on steel, to replace chromates and lead. many essential functions that will ensure Cold spraying uses high-speed jets torations as well as maintenance. This
The corrosion protection provided improvements can be effected by trying corrosion sensing and healing capabili- of inert gas to speed up the fi nely pow- method has been tried for the corrosion
by a coating is generally evaluated on out zinc-aluminum as well as zinc-mag- Thermal nano-spray coatings ties. The particles sense and react to dered anti-corrosive material particles protection and restoration of sensitive
the following parameters: coating adhe- nesium alloys as coatings. Similarly, In recent years, researchers are external stimuli, such as a reduction in pH, that are directed toward the substrate. materials like magnesium and aluminium
sion to the substrate surface; cohesion of inorganic and organic resin-based, zinc- focusing their efforts on the development changes in coating integrity or changes Upon impact onto the substrate, the par- alloys. The hard chrome depositing pro-
the layers; fi lm thickness and uniformity; magnesium-rich paints and coatings of nano-materials and spray processes in corrosion potential. The nano-struc- ticles deform and adhere to the surface cess is now being replaced by a cold
thermal & chemical stability; mechani- have been developed and tested for the to deposit nano-structured composites tured particles in multiple layers of the to create a strong bond with the sub- spray of WC-Co powder. Cold spray has
cal strength; wear resistance; porosity; protection of steel and other metal sub- of ceramics with metals on substrates. coating, reacting within their integrated strate. Additional particles continue to a high potential for architectural appli-
etc. strates. The advantages of nanoparticle coatings structure, trigger the healing process. impinge the solid surface, thus forming cations due to the aesthetic advantages.
include high corrosion protection as well a thick coating. It has medical applications as well.
Good preparatory processes of Developments in barrier coatings as abrasion protection, while retaining Researchers have now devised
surface cleaning and conditioning are Many organic coatings provide a the advantage of good fracture tough- advanced techniques of layer-by-layer Various combinations of corrosion- Cold sprays of aluminium alloys
essential for ensuring strong adhesion of strong barrier to a corrosive species and ness. deposition of coatings for corrosion protec- resistant and wear-resistant powders can have potential applications as anti-
the different layers of protective coating prevent the transfer of ions from the cor- tion and wear protection. In this method, be used for a given substrate in this tech- corrosive coatings in the petrochemical
with the substrate. rosive species to the substrate. In these Nanoparticles in some cases cannot corrosion inhibitors and polyelectrolytes nique. and oil and gas industries. Titanium,
barrier-type polymeric coatings, which be used in thermal spray on account of are deposited on a pre-treated substrate. niobium and nickel alloys can also be
Water-based coatings are applied on metallic substrates, per- their very low mass. They cannot be Composite cold coatings have been used as anti-corrosion cold sprays. Anti-
Water-based protective coatings are meability becomes the key issue, as holi- directly carried in a high velocity gas In Germany, scientists claim that applied to alloys of steel, copper and corrosive aluminium-tin alloy coatings
increasingly replacing some solvent- days (a type of defect), inclusions and stream to be uniformly deposited on their advanced coatings are based on aluminium. Some ductile contents added can be coated on lead-free bearings and
based ones, as they are safer and more damage to the coating layers generate a component surface. Some processes polyelectrolytes, which are sensitive to to the powder enable the essential plastic components in the automotive and aero-
eco-friendly. Recent environmental pathways through which the corrosive have been patented for converting the pH of the corrosive media. These are deformation process. space sector. The U.S. military has tried
regulations also mandate the applica- matter can reach the substrate and local nanoparticles into spherical granules sandwiched with inhibitors in a network cold sprays of Nickel coating on steel
tion of low-VOC coatings. Powder coat- corrosion can begin. fi rst and reproducing smaller nanopar- of polymeric nano-structures. These It has been observed that normal and aluminium substrates; tantalum on
ings and radiation-cured coatings also ticles in fl ight as they move closer to advanced coatings show self-healing thermal spray techniques result in coat- aluminium; aluminium-zinc and copper-
meet the regulator’s requirements. Other In order to lengthen the diffusion the surface. These nano-coatings dis- properties with long-lasting corrosion ings with inferior functional properties tin on door frames of military shelters.

186 Chemical Weekly May 14, 2024 Chemical Weekly May 14, 2024 187

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