Page 188 - CW E-Magazine (14-5-2024)

Special Report Special Report

The cold spray process results in tried out on coatings for the automotive toxic and does not produce any harmful reaction time and high-precision coating involves coating an object with a pow- nitude of the coating thickness that can
higher Brinell hardness and lower industry. They can absorb ultraviolet or dangerous by-products. thickness. This may be used for galva- der-based substance. Although versions be applied in one spraying. Coatings
oxygen content in the coating. It can be light and stop it from reacting on the nizing hot-rolled as well as cold-rolled of the powder coating process were such as liquid paint spraying require
formed in complex geometric shapes inner layer, thus protecting the coating The most signifi cant drawback of steel coils and steel wires. Newly deve- being experimented prior to 1950, fl ui- the fi rst coat to be applied, then wait-
with simple arrangement. and improving the longevity of protection. this process is that it is only useful on loped dynamic air knives help high-qua- dized bed powder coating did not gain ing for the dry-to-recoat time and cure
For producers of automotive coatings, this a handful of metals. This process is lity wiping of the steel strip surface as it much attraction until the 1960s. However, time, then another coat, and so on until
Nanoparticles in polymer coatings reduces servicing and repair costs. unsuitable for ferrous metals, which means leaves the molten zinc bath, thus mini- the popularity of spraying the powder the desired thickness is achieved. With
Nanotechnology is now helping the that common materials like steel and iron mizing zinc coat thickness deviation coating with a gun that electrically powder coatings, greater coating thick-
coating industry to produce more effec- Coatings based on cerium oxide cannot be anodized. Additionally, due to and ensuring high standards of surface charged the powder coating particles nesses can be achieved in one applica-
tive products that are also eco-friendly. have been developed for use by aircraft the processes used, the colours that can quality. It also provides an aesthetically became popular in the 1960s and 1970s. tion and curing cycle. The time that was
The addition of nanoparticles to resins producers. They exhibit good adhesion be achieved by anodizing is limited. pleasing decorative fi nish to meet the spent waiting for curing and applying
helps enhance corrosion resistance in strength on aluminium alloys used to requirements of the appliance, automo- One of the most popular methods a subsequent coat can be spent coating
a signifi cant way. The greater surface build aircraft. Cerium hydroxide and Galvanizing tive and construction sectors(1, 5). used to apply powder coatings is elec- another batch of parts or another portion
activity of these additional nanoparticles cerium oxide phases are deposited after Galvanizing involves immersing the trostatic gun spraying. During this pro- of the structure.
on the coating surface helps absorb more the usual surface preparation methods, metal (mostly steel or iron) in a molten Electroplating cess, the spray gun not only propels
resin as compared to conventional pig- and replace the traditional chromate zinc bath. Once removed, the coated Electroplating, also known as elec- the electrostatic paint, but gives them a Powder coatings have a high quality
ments. Clay as a nanoparticle streng- coating, which are restricted by regula- metal reacts with oxygen and carbon tro-deposition, involves depositing a positive electrical charge as well. The fi nish. During the powder coating
thens corrosion protection of the sub- tions in some localities. dioxide in the atmosphere to form a thin layer of one metal on the surface of base material is charged negatively, thus application, the charged powder coating
strate signifi cantly. protective zinc carbonate layer. another metal. During electroplating, both creating an attraction between it and the particles automatically level themselves
Common types of metal coatings and metals are placed in an electrolytic solu- negatively charged powder coating par- to a certain degree. This reduces the risk
Titanium dioxide (TiO ) nanopar- their benefi ts(4). The galvanizing process has mul- tion. The metal to be coated acts as the ticles. Once the attraction between the of uneven coatings that can easily occur
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ticles dispersed in an epoxy resin system tiple advantages that make it a popular anode, while the metal to be protected two is established, both are heated until when applying a liquid coating. Further-
matrix reduce corrosive wear and tri- Anodizing choice for numerous applications. For by coating acts as the cathode. An elec- the powder coating particles melt and more, powder coatings are not suscep-
bological sliding and rolling wear. Anodizing is a process used to example, the zinc oxide coating is highly tric current is applied to the electrolytic adhere to the base material. The base tible to running or dripping. This also
However, in many cases, stabilisers are promote the formation of a protective stable and adheres tightly to the metal cell, causing metal ions to move from material is then allowed to cool and a decreases the possibility of uneven coat-
needed to improve compatibility and oxide layer on the surface of a metal. substrate; it is very durable and does not the cathode to the anode, thus forming durable powder coating is created. ings. As mentioned previously, powder
reduce chemical reactions with other The resulting oxide layer forms more fl ake off easily. the coating(6, 7). coatings require fewer layers than many
constituents of the formulation. rapidly and is usually thicker than if it Another common method to apply liquid coating systems. This helps pre-
was produced naturally. While several Galvanizing is also renowned for Electroplating offers excellent cor- a powder coating is the fl uidized bed vent the possibility of a powder coating
Nano fi llers also improve scratch non-ferrous metals can be anodized, its galvanic protection. In other words, rosion resistance and can enhance some method. To perform a fl uidized bed ope- having defects between layers.
resistance, thermal stability, radiation aluminium responds most effectively to if the metal’s surface becomes exposed of the metal’s mechanical properties. It ration, a base material is heated. Once
resistance, and provide protection from this process. due to scratches, cuts or dents, the zinc also produces an aesthetically pleasing the base material reaches a specifi ed Powder coatings also have advan-
abrasive deterioration. They also reduce coating will sacrifi ce itself by corroding surface fi nish, making it ideal for coat- temperature, it is immersed in or fed tages with regard to their mechanical
moisture ingress due to their low perme- Anodizing is performed by immers- preferentially. This process helps protect ing jewellery and ornaments. through an aerated bath or bed of pow- properties. They are known for being
ability. ing the aluminium component in a tank the steel substrate between maintenance der coating particles. The heat from the ductile enough to bend and yield with
fi lled with an electrolytic solution along operations. However, electroplating can pro- base material causes the powder coating many of the base materials to which
Polymer coatings with clay nanopar- with a cathode (usually aluminium or duce non-uniform coating thicknesses, particles to melt and adhere to its they are adhered. Many powder coat-
ticles dispersed in them, when applied lead). An electrical current is passed The biggest disadvantage of the gal- making it unsuitable for high-precision surface. The base material is then allowed ings, such as epoxies, have excellent
on the surface of cold-rolled steel, pro- through the aluminium, causing it to vanizing process is its cost. While hot- applications. Also, the process itself has to cool and the coating solidifi es. The impact strength as well, which lessens
vide more effective corrosion resistance oxidize and form a protective barrier. dip galvanizing (HDG) may be cheaper numerous requirements and is too costly coated object is then heat-treated in an the chance of chipping upon collision
than any normal epoxy coating. Epoxy for coating large steel structures, it can to be used on an industrial scale. oven to harden the coating. with other materials. Many other coat-
coatings with separate dispersions of Anodized fi nishes are perhaps the be less cost-effective for smaller pieces ing types are prone to this type of
nanoparticles of halloysite clay, zinc, easiest to maintain of all the coatings such as nuts and fasteners. Additionally, Potentially toxic and harmful com- Powder coating processes are usu- failure mode. Abrasion resistance is also
SiO and Fe O have been successfully mentioned in this article. Anodized sur- galvanized surfaces have a dullish grey pounds are used as electrolytes in the ally more effi cient than other coating an advantage and is partially as a result of
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tried out on steel surfaces with room faces can be easily periodically cleaned appearance that may not be aesthetically electroplating process. Therefore, care methods for several reasons. One is the bonding that occurs during the curing
temperature curing. Better microstruc- using mild detergents. Finished ano- pleasing for some applications. must be taken when discarding electro- that there is less overspray. This means process.
ture of the coating improved the coat- dized surfaces are also chemically stable lyte chemicals to avoid environmental that less coating material is required.
ing’s mechanical properties as well as and do not decompose under normal Newly developed precision hot-dip contamination. Another benefi t is that it usually requires Additionally, because powder coat-
corrosion resistance. conditions, allowing for a long-lasting galvanizing and electrolytic coating sys- less time for the operator to spray the ings do not contain solvents, there are
coated surface. Furthermore, because tems in steel plants use servo-hydraulic Powder coating substrate. Adding to the effi ciency of little to no volatile organic compound
Zinc oxide nanoparticles have been anodizing is a natural process, it is non- adjustment systems, providing a fast Powder coating, as its name implies, the powder coating process is the mag- (VOC) emissions.

188 Chemical Weekly May 14, 2024 Chemical Weekly May 14, 2024 189

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