Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download coating - WordPress.com
Document related concepts
Transcript
Nanocoatings Noraiham Mohamad, PhD Faculty 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, selfcleaning) 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
