Nanocoatings

Noraiham Mohamad, PhDFaculty of Manufacturing Engineering,Universiti Teknikal Malaysia Melaka

What is coating? A coating is a covering that is applied to the

surface of an object, usually referred to as the substrate.

In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wettability, corrosion resistance, wear resistance, and scratch resistance.

In other cases, in particular in printing processes and semiconductor device fabrication (where the substrate is a wafer), the coating forms an essential part of the finished product.

Coating Coatings are usually applied as multi-layered

systems that are composed of primer and topcoat. However, in some cases – for example automotive coating systems, this may vary from four to six layers.

Each coating layer is applied to perform certain specific functions, though its activities are influenced by the other layers in the system.

The interactions among different layers and the interfacial phenomenon play an important role in the overall performance of the multi-coat systems

Type of coating Inorganic Coating- Coating with silicate

based materials (eg.- zinc silicate based coating) or metal/ceramic based coating (hard coating of Chromium, TiN, Si3N4, alumina etc.)

Organic Coating- Coating with organic binders (organic based materials- eg. Zinc epoxy based coating, zinc rich phenoxy, etc.)

Inorganic Coating Silicone (polysiloxane) hard coatings are finishes of superior

abrasion resistance and inertness to hostile chemical and environmental conditions.

They consist of several monomers and other ingredients, and the makeup of the formulations varies from manufacturer to manufacturer.

Among the highly varied components are monomeric silanes, dimerized silanes, silane hydrozylates, silaceous materials, leveling agents, flow control agents, cross-linking agents, and catalysts of various types.

Silicone coatings are solvent-borne coatings. Some of the possible solvents are alcohols and glycol ethers. This includes such alcohols as isopropanol, propanol, ethanol, n-butanol, isobutanol, and methanol.

Inorganic Coating Polysiloxane coatings are applicable to many substrates,

but the majority of applications are on nonmetallic surfaces, especially plastics.

Silicone coatings can be dyed or pigmented, but for the most part these coatings are used as clear top coatings.

They have excellent light transmission and actually improve the optical properties of the material that is coated.

Some of the plastics that are used with polysiloxane coatings are polycarbonate, acrylic, polyarylate, polysulfone, vinyls, nylons, polyester, cellulose acetate, cellulose acetate-butyrate, and polyolefins, etc.

Inorganic Coating Hard silicone coatings are useful as antifog,

antistatic photochromic, color-dyed, pigmented, UV absorbing, UV stabilized for exterior exposure, chemical resistance, 5-min curing, and tinted coatings.

Many of these properties can be combined in one coating.

The coatings are used in such diverse areas as the automotive, electronic, computer hardware, architectural and architectural glazing, recreation, sporting goods, protective eyewear, safety, and optical industries.

Organic Coating Organic coatings are essentially pigment dispersed in a

solution of a binding medium. Binding medium or resin - decide the basic physical and

chemical properties of the coating but these will be modified by the nature and proportion of pigments present.

Sole function of volatile component -to control the viscosity of the paint for ease of manufacture and for subsequent application.

Not possible to forecast -what combination of properties a particular formulation will possess and the formulation of paints for specific purpose remain very much a technological art.

Nanomaterials in Coating The appearance and appliance of

nanomaterials brings new opportunities to the coating industry.

Addition of nano-materials to the coatings improves the properties of the conventional coatings and produces new multi-functional coating due to their tiny particle size.

Category of Coating Coatings are mainly applied on surfaces

for decorative, protective or functional purposes, but in most cases it is a combination of these.

3 category: Decorative Coating Functional coating Self-Assembled Nanophase Coating

Functional coating

Functional coatings- systems which possess, besides the classical properties of a coating (i.e., decoration and protection), an additional functionality

This additional functionality may be diverse, and depend upon the actual application of a coated substrate.

Typical examples of functional coatings are: self-cleaning easy-to clean (anti-graffiti) antifouling soft feel antibacterial

Functional coating Typical expectations of functional

coatings include: durability reproducibility easy application and cost effectiveness tailored surface morphology environmental friendliness

Functional coating Functional coatings perform by means of

physical, chemical, mechanical, thermal and properties.

Chemically active functional coatings perform their activities either at film–substrate interfaces (anticorrosive coatings), in the bulk of the film (fire-retardant or

intumescent coatings), or at air–film interfaces (antibacterial, self-cleaning)

Coating Techniques

Processing for Inorganic Coating & Hard Coating

Processing for Organic Coating

Sol-Gel Coating (Organic or Inorganic)

Nanoparticles in Sol-Gel Possible to increase the coating thickness, without

increasing the sintering temperature. Eg. Electrophoreticdeposition of commercial SiO sol on

AISI 304 stainless steel substrates leads to coatings as thick as 5 mm with good corrosion resistance

Incorporation of nanoparticles in the hybrid sol–gel systems increases the corrosion protection properties due to lower porosity and lower cracking potential

Can be a way to insert corrosion inhibitors, preparing inhibitor nano reservoirs for self repairing pretreatments with controlled release properties

Example of Nanoparticles in Sol-Gel Studies showed that sol–gel films containing zirconia

nanoparticles present improved barrier properties. Doping this hybrid nanostructured sol–gel coating

with cerium nitrate brings additional improvement to corrosion protection. Zirconia particles present in the sol–gel matrix act as

nano reservoirs providing a prolonged release of the cerium ions

The recent discovery of a method of forming functionalized silica nanoparticles in situ in an aqueous sol–gel process, and then cross linking the nanoparticles to form a thin film

Coating Applications