The document discusses various types of surface coatings used to protect materials from corrosion. It describes coating as a covering applied to the surface of a substrate, usually to be decorative, functional, or both. Some key types of coatings discussed include conversion coatings like oxidation, phosphate, and chrome coatings which form protective layers via chemical reactions. Thermal treatments like carburizing and nitriding are also covered, which use diffusion processes to strengthen surfaces. Finally, methods for applying coatings like hot-dip galvanizing of steel in molten zinc are summarized.
The document discusses surface coatings and corrosion. It defines corrosion as the deterioration of metals due to reaction with the environment. It then describes several types of coatings used to protect metals from corrosion, including conversion coatings like anodizing which form protective metal oxide layers, thermal coatings like flame spraying, electrochemical coatings like galvanization, and vapor deposition methods like PVD and CVD. The document emphasizes that coatings provide barrier protection and extend the lifetime of metal substrates.
Powder coating is a finishing process where pigmented resin powder is applied to a product through electrostatic spraying, then cured in an oven. It produces a smooth, durable coating that is highly resistant to corrosion, solvents, chips and scratches. Powder coating offers superior appearance and mechanical properties compared to liquid coatings, with 95-98% material usage and no need for solvents, mixing or recovery systems. The process involves two main types of powder - thermoplastic which re-melts, and thermoset which chemically cross-links during curing to form a thin, non-remelting coating.
The fabrication methodology of a composite part depends mainly on three factors:
(i) the characteristics of matrices and reinforcements,
(ii) the shapes, sizes and engineering details of products, and
(iii) end uses.
The composite products are too many and cover a very wide domain of applications ranging from an engine valve to an aircraft wing.
The fabrication technique varies from one product to the other.
This document summarizes various surface treatment techniques including mechanical processes like shot peening and deep rolling that modify the surface without changing chemistry, thermal processes like electron beam treatment and laser treatment, and thermo-chemical processes like carburizing, nitriding, and carbonitriding that diffuse elements like carbon or nitrogen into the surface. It provides details on the mechanisms, advantages, and applications of these different surface modification methods.
The presentation covers various aspects of coating and deposition process in detail. The topics that are mainly covered in this PPT are
1) Type of Coating
2) Advantages and limitation for various coating process
3) Figures of various coating process
Slip casting is a process used to mass produce ceramic items like figurines, dishes, and flower pots. A liquid suspension of ceramic powder called a slip is poured into a plaster mold. Water from the slip is absorbed by the porous mold, leaving a solid ceramic layer. Excess slip is drained out. The piece is then dried and fired. There are two main methods - drain casting produces hollow items while solid casting allows the entire mold cavity to solidify. Key factors that affect the process include the viscosity and setting rate of the slip as well as shrinkage and strength of the final piece. Slip casting allows intricate shapes and sizes but the process is slow with limited commercial applications.
The document discusses the high costs of corrosion in India and issues with current anti-corrosion coatings. It states that corrosion is a major maintenance cost over the lifespan of equipment. Current coatings require clean, dry surfaces with a profile for proper adhesion but are often applied to surfaces that are not properly prepared. This can cause adhesion and barrier issues, leading to coating failures and corrosion. The document recommends using coatings that are more surface tolerant and can perform even on rusty, damp or poorly prepared surfaces. It provides examples of applications of such high performance coatings in industries.
The document discusses surface coatings and corrosion. It defines corrosion as the deterioration of metals due to reaction with the environment. It then describes several types of coatings used to protect metals from corrosion, including conversion coatings like anodizing which form protective metal oxide layers, thermal coatings like flame spraying, electrochemical coatings like galvanization, and vapor deposition methods like PVD and CVD. The document emphasizes that coatings provide barrier protection and extend the lifetime of metal substrates.
Powder coating is a finishing process where pigmented resin powder is applied to a product through electrostatic spraying, then cured in an oven. It produces a smooth, durable coating that is highly resistant to corrosion, solvents, chips and scratches. Powder coating offers superior appearance and mechanical properties compared to liquid coatings, with 95-98% material usage and no need for solvents, mixing or recovery systems. The process involves two main types of powder - thermoplastic which re-melts, and thermoset which chemically cross-links during curing to form a thin, non-remelting coating.
The fabrication methodology of a composite part depends mainly on three factors:
(i) the characteristics of matrices and reinforcements,
(ii) the shapes, sizes and engineering details of products, and
(iii) end uses.
The composite products are too many and cover a very wide domain of applications ranging from an engine valve to an aircraft wing.
The fabrication technique varies from one product to the other.
This document summarizes various surface treatment techniques including mechanical processes like shot peening and deep rolling that modify the surface without changing chemistry, thermal processes like electron beam treatment and laser treatment, and thermo-chemical processes like carburizing, nitriding, and carbonitriding that diffuse elements like carbon or nitrogen into the surface. It provides details on the mechanisms, advantages, and applications of these different surface modification methods.
The presentation covers various aspects of coating and deposition process in detail. The topics that are mainly covered in this PPT are
1) Type of Coating
2) Advantages and limitation for various coating process
3) Figures of various coating process
Slip casting is a process used to mass produce ceramic items like figurines, dishes, and flower pots. A liquid suspension of ceramic powder called a slip is poured into a plaster mold. Water from the slip is absorbed by the porous mold, leaving a solid ceramic layer. Excess slip is drained out. The piece is then dried and fired. There are two main methods - drain casting produces hollow items while solid casting allows the entire mold cavity to solidify. Key factors that affect the process include the viscosity and setting rate of the slip as well as shrinkage and strength of the final piece. Slip casting allows intricate shapes and sizes but the process is slow with limited commercial applications.
The document discusses the high costs of corrosion in India and issues with current anti-corrosion coatings. It states that corrosion is a major maintenance cost over the lifespan of equipment. Current coatings require clean, dry surfaces with a profile for proper adhesion but are often applied to surfaces that are not properly prepared. This can cause adhesion and barrier issues, leading to coating failures and corrosion. The document recommends using coatings that are more surface tolerant and can perform even on rusty, damp or poorly prepared surfaces. It provides examples of applications of such high performance coatings in industries.
This document discusses the process of powder metallurgy. It begins by introducing powder metallurgy and some of its advantages over traditional manufacturing methods. The main steps of the powder metallurgy process are then outlined, including powder manufacture through various techniques like atomization, blending to ensure uniformity, compacting the powder under pressure, sintering the compacted powder by heating it below the melting point, and final finishing operations. A variety of end products that can be created using powder metallurgy are listed such as bearings, gears, and regulators.
Optical lenses are used in microscopes to form magnified images of microscopic objects. A lens has curved surfaces that focus light rays to form these images. Single lenses are used in eyeglasses and cameras, while compound lenses with multiple elements are used in microscopes and telescopes to correct optical aberrations. A metallurgical microscope uses reflected light to illuminate and image opaque metal samples, allowing metallurgists to examine microstructural details at magnifications from 1 to 1500x. Objectives resolve microstructural details while eyepieces further magnify the image without additional resolution.
Surface coatings are used to protect metals from corrosion and improve their properties. Common coating methods include conversion coatings like oxidation, phosphatization and chromating which form protective oxide layers. Thermal treatments involve diffusion, carburizing and nitriding to enrich the surface. Metal coatings are applied by electroplating, electroless plating or metallizing. Vapor deposition techniques like PVD and CVD are used to deposit thin, hard coatings. Organic coatings such as paint provide decorative and protective functions. Coatings selection depends on the substrate material and desired properties.
The document discusses rate controlled sintering in advanced ceramic processes. It explains that sintering transforms ceramic powder compacts into dense materials through heating by reducing pores and growing grains. The driving force is lowering free energy. Sintering occurs in three stages and is affected by various factors. Rate controlled sintering controls the heating rate or temperature to control the sintering process for improved material properties. It provides examples demonstrating the effects of heating rate on microstructure.
This document provides an overview of manufacturing processes and gating systems for casting. It discusses the key elements of a gating system including the pouring basin, sprue, runner, gates, and riser. The objectives and factors affecting the performance of gating systems are outlined. Different types of gating systems like vertical, bottom, and horizontal are described. Formulas related to fluid flow and solidification time are also provided.
This document discusses various methods for producing metal powders, including mechanical, atomization, electrochemical, and chemical methods. Mechanical methods include chopping, abrasion, milling and the cold stream process. Atomization methods include gas, water, centrifugal atomization and using a rotating electrode. Factors that influence particle size and shape from atomization are also covered. Electrochemical production involves electrolysis of molten metals. Chemical methods decompose metal compounds with heat or catalysts. The document provides details on the principles, equipment used, advantages and limitations of each production method.
Die casting is a process where molten metal is injected into a steel die under high pressure to form complex shapes. Common metals used include aluminum, magnesium, and copper alloys. The die is made of steel and consists of two halves, with one half fixed and the other movable. During die casting, molten metal is injected into the die cavity using pressures up to 9,800 psi and solidifies into the final part. Die casting allows for high production rates and close dimensional tolerances of the parts produced.
The document discusses various types of molding materials and properties of molding sand used in casting processes. It describes the common molding materials as sand, metals, plaster, ceramic, graphite, and rubber. The key properties of molding sand that influence its suitability are also outlined, such as refractoriness, permeability, collapsibility, plasticity, and strength. The document further discusses the typical composition of molding sand and the role of additives in enhancing properties. Different types of sands including silica, zircon, olivine, and chromite sands are also compared.
The document discusses the powder metallurgy process which consists of three main steps: 1) blending and mixing of metal powders and additives, 2) compaction of the blended powder using pressure-based or pressureless techniques, and 3) sintering the compacted powder below the melting point to bond the particles together without melting. Optional secondary operations such as heat treatment, machining or infiltration can further process the sintered parts.
Powder metallurgy is a process that involves producing metal powders and compacting and sintering them to form finished parts. It allows for complex alloy compositions and near-net shape manufacturing, avoiding costly machining. The key steps are powder production, blending/mixing, compaction into a green compact, sintering to bond particles, and optional finishing. It offers advantages over casting and machining for net shape precision parts in large volumes.
Investment casting is an ancient metal forming technique dating back 5000 years. It involves creating a ceramic mold by coating a wax pattern and allowing it to harden. The wax is then melted out and molten metal is poured in, after which the ceramic mold is broken away. Key steps include preparing wax patterns, applying ceramic coats, dewaxing, burnout, metal pouring, and removal from the mold. Investment casting is used to make complex, high-precision parts for industries like aerospace, firearms, medical implants, and valves. It allows for intricate shapes and tight tolerances at relatively low material waste.
1. Atomization is a process that uses high-pressure jets to break molten metal into fine droplets to produce metal powders.
2. Common atomization methods include water, gas, vacuum, centrifugal, and ultrasonic atomization.
3. The atomization process involves melting metal, breaking it into droplets using an atomization medium and nozzle system, and collecting the solidified powder. Particle size depends on factors like atomizing medium pressure and nozzle design.
The document describes the coil coating process, which involves cleaning and pretreating steel coils before applying primer and topcoat paint in a continuous line. Key steps include receiving raw coils, pretreating with chemicals to prepare the surface, applying primer and topcoat via coater ovens, and testing finished coils through procedures like measuring gloss, flexibility, and solvent resistance.
The document discusses various metal casting processes including sand casting, permanent mold casting, shell molding, vacuum molding, expanded polystyrene casting, investment casting, and plaster mold casting. It describes the key steps, advantages, and disadvantages of each process. Sand casting is the most widely used process due to ability to cast nearly all alloys and produce castings in a wide range of sizes.
Shell mold casting is a metal casting process that uses a resin-coated sand mixture to form a thin-walled mold shell around a metal pattern. The pattern is heated and pressed into the sand-resin mixture to form the shell, which is then cured in an oven. Two shell halves are joined to form the complete shell mold, into which molten metal is poured to create the casting. This allows for high-precision casting of small to medium parts like gear housings, cylinder heads, and connecting rods. The shell mold casting process provides advantages over sand casting like better surface finish and dimensional accuracy for the final casting.
The document is a presentation on surface engineering that discusses:
- The introduction and history of surface engineering, which involves altering surface properties of materials to reduce degradation from the environment.
- Various surface coating techniques to improve properties like corrosion and wear resistance, including traditional methods like painting, electroplating, and plasma spraying as well as advanced techniques like PVD, CVD, and laser treatment.
- Applications of surface engineering in industries like automotive and aerospace to enhance performance and reduce costs by extending component lifetimes.
The presentation provides an overview of surface engineering, coating processes, applications, and advantages in improving material surfaces.
This document discusses various powder production techniques for ceramics. It begins by introducing ceramics and their properties. It then covers classification of ceramics and various raw materials used. The main powder production methods discussed are mechanical (milling), chemical, physical (freeze drying, spray drying, sol-gel) and some commercial examples. Ball milling, attrition milling, freeze drying process and applications, spray drying process and applications are described in detail. Advantages and disadvantages of freeze drying and spray drying are also provided.
This PPT contains information about basic operations of Powder Metallurgy(PM). it is consist of manufacturing techniques of powder, and manufacturing of products by the powder.
1) The document discusses the process of hardening steel through heat treatment. Steel is heated above critical temperatures and quenched at a rate faster than the critical cooling rate to form martensite, resulting in a hard structure.
2) Hardening involves heating steel to 30-50°C above critical temperatures, holding, then quenching faster than the critical cooling rate to transform austenite to martensite.
3) The hardness of martensite increases with carbon content as more carbon causes lattice distortion and internal stress. Hardened steel is thus both hard and strong but also brittle.
Vacuum mold casting is a process that uses a sand mold without moisture or binders. A vacuum pressure holds the shape of the casting inside the mold. The process involves placing a plastic sheet over a pattern, filling a flask with sand around the pattern, and applying vacuum pressure to adhere the sheet to the sand mold. Once the pattern is removed, the plastic film holds the impression of the casting shape due to vacuum suction. The drag half is made similarly and the two halves are assembled for pouring the molten metal, which burns away the plastic films.
The document discusses various methods of corrosion protection through the use of coatings. It describes different types of coatings including metallic, inorganic, and organic coatings. For metallic coatings, it discusses various application methods like hot dipping, electroplating, metal spraying, and cementation. It also differentiates between noble and sacrificial metallic coatings. Specific metallic coatings like nickel, lead, zinc, tin, and aluminum are explained. Inorganic coatings including vitreous enamel, Portland cement, and chemical conversion coatings are also outlined. Finally, the document covers organic coatings like paints and their requirements for corrosion protection.
The document discusses various surface treatment techniques including:
1. Conversion coatings like oxidation, phosphating, and chromating which form protective surface layers.
2. Metal coatings such as electroplating, electroless plating, and immersion plating which deposit thin metal layers.
3. Thermal treatments like carburizing, nitriding, and hot-dip coatings which use heat to diffuse elements into surfaces.
4. Vapor deposition methods including chemical and physical vapor deposition to deposit thin films.
5. Organic coatings like paints, enamels and lacquers which form protective painted layers.
This document discusses the process of powder metallurgy. It begins by introducing powder metallurgy and some of its advantages over traditional manufacturing methods. The main steps of the powder metallurgy process are then outlined, including powder manufacture through various techniques like atomization, blending to ensure uniformity, compacting the powder under pressure, sintering the compacted powder by heating it below the melting point, and final finishing operations. A variety of end products that can be created using powder metallurgy are listed such as bearings, gears, and regulators.
Optical lenses are used in microscopes to form magnified images of microscopic objects. A lens has curved surfaces that focus light rays to form these images. Single lenses are used in eyeglasses and cameras, while compound lenses with multiple elements are used in microscopes and telescopes to correct optical aberrations. A metallurgical microscope uses reflected light to illuminate and image opaque metal samples, allowing metallurgists to examine microstructural details at magnifications from 1 to 1500x. Objectives resolve microstructural details while eyepieces further magnify the image without additional resolution.
Surface coatings are used to protect metals from corrosion and improve their properties. Common coating methods include conversion coatings like oxidation, phosphatization and chromating which form protective oxide layers. Thermal treatments involve diffusion, carburizing and nitriding to enrich the surface. Metal coatings are applied by electroplating, electroless plating or metallizing. Vapor deposition techniques like PVD and CVD are used to deposit thin, hard coatings. Organic coatings such as paint provide decorative and protective functions. Coatings selection depends on the substrate material and desired properties.
The document discusses rate controlled sintering in advanced ceramic processes. It explains that sintering transforms ceramic powder compacts into dense materials through heating by reducing pores and growing grains. The driving force is lowering free energy. Sintering occurs in three stages and is affected by various factors. Rate controlled sintering controls the heating rate or temperature to control the sintering process for improved material properties. It provides examples demonstrating the effects of heating rate on microstructure.
This document provides an overview of manufacturing processes and gating systems for casting. It discusses the key elements of a gating system including the pouring basin, sprue, runner, gates, and riser. The objectives and factors affecting the performance of gating systems are outlined. Different types of gating systems like vertical, bottom, and horizontal are described. Formulas related to fluid flow and solidification time are also provided.
This document discusses various methods for producing metal powders, including mechanical, atomization, electrochemical, and chemical methods. Mechanical methods include chopping, abrasion, milling and the cold stream process. Atomization methods include gas, water, centrifugal atomization and using a rotating electrode. Factors that influence particle size and shape from atomization are also covered. Electrochemical production involves electrolysis of molten metals. Chemical methods decompose metal compounds with heat or catalysts. The document provides details on the principles, equipment used, advantages and limitations of each production method.
Die casting is a process where molten metal is injected into a steel die under high pressure to form complex shapes. Common metals used include aluminum, magnesium, and copper alloys. The die is made of steel and consists of two halves, with one half fixed and the other movable. During die casting, molten metal is injected into the die cavity using pressures up to 9,800 psi and solidifies into the final part. Die casting allows for high production rates and close dimensional tolerances of the parts produced.
The document discusses various types of molding materials and properties of molding sand used in casting processes. It describes the common molding materials as sand, metals, plaster, ceramic, graphite, and rubber. The key properties of molding sand that influence its suitability are also outlined, such as refractoriness, permeability, collapsibility, plasticity, and strength. The document further discusses the typical composition of molding sand and the role of additives in enhancing properties. Different types of sands including silica, zircon, olivine, and chromite sands are also compared.
The document discusses the powder metallurgy process which consists of three main steps: 1) blending and mixing of metal powders and additives, 2) compaction of the blended powder using pressure-based or pressureless techniques, and 3) sintering the compacted powder below the melting point to bond the particles together without melting. Optional secondary operations such as heat treatment, machining or infiltration can further process the sintered parts.
Powder metallurgy is a process that involves producing metal powders and compacting and sintering them to form finished parts. It allows for complex alloy compositions and near-net shape manufacturing, avoiding costly machining. The key steps are powder production, blending/mixing, compaction into a green compact, sintering to bond particles, and optional finishing. It offers advantages over casting and machining for net shape precision parts in large volumes.
Investment casting is an ancient metal forming technique dating back 5000 years. It involves creating a ceramic mold by coating a wax pattern and allowing it to harden. The wax is then melted out and molten metal is poured in, after which the ceramic mold is broken away. Key steps include preparing wax patterns, applying ceramic coats, dewaxing, burnout, metal pouring, and removal from the mold. Investment casting is used to make complex, high-precision parts for industries like aerospace, firearms, medical implants, and valves. It allows for intricate shapes and tight tolerances at relatively low material waste.
1. Atomization is a process that uses high-pressure jets to break molten metal into fine droplets to produce metal powders.
2. Common atomization methods include water, gas, vacuum, centrifugal, and ultrasonic atomization.
3. The atomization process involves melting metal, breaking it into droplets using an atomization medium and nozzle system, and collecting the solidified powder. Particle size depends on factors like atomizing medium pressure and nozzle design.
The document describes the coil coating process, which involves cleaning and pretreating steel coils before applying primer and topcoat paint in a continuous line. Key steps include receiving raw coils, pretreating with chemicals to prepare the surface, applying primer and topcoat via coater ovens, and testing finished coils through procedures like measuring gloss, flexibility, and solvent resistance.
The document discusses various metal casting processes including sand casting, permanent mold casting, shell molding, vacuum molding, expanded polystyrene casting, investment casting, and plaster mold casting. It describes the key steps, advantages, and disadvantages of each process. Sand casting is the most widely used process due to ability to cast nearly all alloys and produce castings in a wide range of sizes.
Shell mold casting is a metal casting process that uses a resin-coated sand mixture to form a thin-walled mold shell around a metal pattern. The pattern is heated and pressed into the sand-resin mixture to form the shell, which is then cured in an oven. Two shell halves are joined to form the complete shell mold, into which molten metal is poured to create the casting. This allows for high-precision casting of small to medium parts like gear housings, cylinder heads, and connecting rods. The shell mold casting process provides advantages over sand casting like better surface finish and dimensional accuracy for the final casting.
The document is a presentation on surface engineering that discusses:
- The introduction and history of surface engineering, which involves altering surface properties of materials to reduce degradation from the environment.
- Various surface coating techniques to improve properties like corrosion and wear resistance, including traditional methods like painting, electroplating, and plasma spraying as well as advanced techniques like PVD, CVD, and laser treatment.
- Applications of surface engineering in industries like automotive and aerospace to enhance performance and reduce costs by extending component lifetimes.
The presentation provides an overview of surface engineering, coating processes, applications, and advantages in improving material surfaces.
This document discusses various powder production techniques for ceramics. It begins by introducing ceramics and their properties. It then covers classification of ceramics and various raw materials used. The main powder production methods discussed are mechanical (milling), chemical, physical (freeze drying, spray drying, sol-gel) and some commercial examples. Ball milling, attrition milling, freeze drying process and applications, spray drying process and applications are described in detail. Advantages and disadvantages of freeze drying and spray drying are also provided.
This PPT contains information about basic operations of Powder Metallurgy(PM). it is consist of manufacturing techniques of powder, and manufacturing of products by the powder.
1) The document discusses the process of hardening steel through heat treatment. Steel is heated above critical temperatures and quenched at a rate faster than the critical cooling rate to form martensite, resulting in a hard structure.
2) Hardening involves heating steel to 30-50°C above critical temperatures, holding, then quenching faster than the critical cooling rate to transform austenite to martensite.
3) The hardness of martensite increases with carbon content as more carbon causes lattice distortion and internal stress. Hardened steel is thus both hard and strong but also brittle.
Vacuum mold casting is a process that uses a sand mold without moisture or binders. A vacuum pressure holds the shape of the casting inside the mold. The process involves placing a plastic sheet over a pattern, filling a flask with sand around the pattern, and applying vacuum pressure to adhere the sheet to the sand mold. Once the pattern is removed, the plastic film holds the impression of the casting shape due to vacuum suction. The drag half is made similarly and the two halves are assembled for pouring the molten metal, which burns away the plastic films.
The document discusses various methods of corrosion protection through the use of coatings. It describes different types of coatings including metallic, inorganic, and organic coatings. For metallic coatings, it discusses various application methods like hot dipping, electroplating, metal spraying, and cementation. It also differentiates between noble and sacrificial metallic coatings. Specific metallic coatings like nickel, lead, zinc, tin, and aluminum are explained. Inorganic coatings including vitreous enamel, Portland cement, and chemical conversion coatings are also outlined. Finally, the document covers organic coatings like paints and their requirements for corrosion protection.
The document discusses various surface treatment techniques including:
1. Conversion coatings like oxidation, phosphating, and chromating which form protective surface layers.
2. Metal coatings such as electroplating, electroless plating, and immersion plating which deposit thin metal layers.
3. Thermal treatments like carburizing, nitriding, and hot-dip coatings which use heat to diffuse elements into surfaces.
4. Vapor deposition methods including chemical and physical vapor deposition to deposit thin films.
5. Organic coatings like paints, enamels and lacquers which form protective painted layers.
The document discusses various surface coating techniques. It begins by defining corrosion and describing how it occurs in different metals and environments. It then discusses several coating methods including conversion coatings like oxidation, anodizing, phosphate and chrome coatings which form protective surface layers via chemical reactions. Vapor deposition techniques like physical vapor deposition and chemical vapor deposition are also summarized. Thermal coating processes involve diffusion, carburizing, nitriding and metal plating via heat. The document provides an overview of the purposes, processes and applications of various surface coating methods.
This document discusses various surface treatment and coating techniques, including conversion coatings like oxidation and anodizing, thermal coatings like carburizing and nitriding, metal coatings using electroplating and electroless deposition, vapor deposition methods like PVD and CVD, and organic coatings like paint and powder coating. It provides details on common processes, their applications and benefits, comparing techniques like electroless nickel plating versus hard chrome plating. The document emphasizes the importance of coatings for improving properties like corrosion and wear resistance.
This document discusses various surface treatment and coating techniques. It covers conversion coatings like oxidation, anodizing, and phosphate coatings. It also outlines thermal treatments for diffusion, carburizing, and nitriding. Metal coatings like electroplating, electroless plating, and metallizing of plastics are examined. Finally, vapor deposition methods of PVD and CVD are summarized. The document provides a detailed overview of common surface engineering processes used to modify material properties.
The document summarizes key information about three materials: aluminum oxide, silicon carbide, and diamond. It discusses their crystal structures, properties like hardness and thermal conductivity, common processing methods, and applications. Aluminum oxide is used as an abrasive and refractory material. Silicon carbide is very hard and used for abrasives, armor, and power electronics. Diamond is the hardest known material and used in drilling, cutting, and jewelry due to its optical properties.
The document discusses various types of metal coatings and their purposes. It describes how metal coatings protect metals from environmental damage like rust and corrosion through the application of protective layers. It then explains five main types of metal coatings: (1) anodizing primarily used on aluminum, (2) galvanizing which applies a zinc layer to iron, (3) electroplating which uses electricity to adhere other metals like chromium, (4) powder coating which provides durability and comes in many colors, and (5) porcelain enamel coatings which form glass-like protective layers on metals like cast iron. The coatings shield metals, improve durability, and allow for varied appearances.
Corrosion is the degradation of a material due to a reaction with its environment. It is a slow process that involves the destruction of a material through chemical or electrochemical reactions on its surface. There are several types of corrosion that can occur depending on factors like the environment and the material. Proper selection of materials and use of protective coatings or cathodic protection techniques can help reduce corrosion of structures and extend their lifetimes.
Electrochemical Protection or Cathodic Protection uses two methods to protect metal surfaces from corrosion. Sacrificial anodic protection connects the metal to a more reactive metal like zinc or magnesium that corrodes instead of the protected metal. Impressed current cathodic protection uses an electrical current to force the metal to behave as a cathode. There are also several metallic coating methods to apply a protective layer to metals including hot dipping, electroplating, metal spraying, metal cladding, and cementation. Organic coatings like paints, varnishes, enamels, and lacquers provide protection by forming a barrier film on the metal surface.
A SHORT REVIEW ON ALUMINIUM ANODIZING: AN ECO-FRIENDLY METAL FINISHING PROCESSJournal For Research
Protection of aluminium alloys is most commonly done by forming anodic films. Anodic films can also be formed on metals like titanium, zinc, magnesium, niobium, and tantalum. Aluminium alloy parts are anodized to greatly increase the thickness of the natural oxide layer for corrosion resistance. A thin aluminium oxide film, that seals the aluminium from further oxidation when it is exposed to air. The anodizing process increases the thickness of the oxidized surface. Anodizing is accomplished by immersing the aluminium into an acid electrolyte bath and passing an electric current through the medium. In an anodizing cell, the aluminium work piece is made the anode by connecting it to the positive terminal of a dc power supply and the cathode is connected to the negative terminal of the dc source. Sealing is needed to seal the pores in oxide layer to prevent further corrosion. Oxide layer on the anodized aluminium has a highly ordered, porous structure that allows for secondary processes such as dyeing, printing and sealing. Nanowires and nanotubes can be made by using the pores in the oxide layer as templates.
Corrosion is the gradual destruction of a material, usually a metal, due to oxidation. It occurs when iron is exposed to moist air and reacts with oxygen to form rust. Corrosion is a natural process that tends to lower the material's energy state. Wet corrosion is more common and occurs near room temperature in the presence of water, while dry corrosion occurs at high temperatures. The hot dip galvanizing process coats steel in molten zinc to protect against corrosion. It involves degreasing, pickling, fluxing, and dipping the steel in molten zinc before quenching. The zinc coating provides long-term corrosion protection that is thicker and harder than other coating methods.
The document provides information on common construction materials used in shipbuilding, including metals like iron, steel, aluminum, copper, and zinc. It discusses the properties and typical uses of these materials, as well as hazards related to corrosion and fires. Specific alloys covered include cast iron, carbon steel, stainless steel, brass, bronze, cupronickel, monel, and various grades of each. The document also addresses concepts like spontaneous combustion, flash points of fuels, and methods for preventing corrosion.
The document provides information on common construction materials used in shipbuilding, including metals like iron, steel, aluminum, copper, and zinc. It discusses the properties and typical uses of these materials, as well as hazards related to corrosion and fires. Specific alloys covered include cast iron, carbon steel, stainless steel, brass, bronze, cupronickel, monel, and various grades of each. The document also addresses concepts like spontaneous combustion, flash points of fuels, and methods for preventing corrosion.
Surface treatment techniques play an important role in improving properties like hardness, wear and corrosion resistance. The document discusses 8 techniques:
1) Mechanical hardening uses impacts to work-harden surfaces and improve fatigue strength. Shot peening is commonly used.
2) Different coating techniques add thin layers, like case hardening which diffuses alternate elements into steel to harden surfaces.
3) Phosphate conversion coatings chemically react phosphoric acid with metal surfaces to form insoluble phosphate layers for corrosion resistance.
4) Chromate conversion coatings provide highly corrosion-resistant surfaces for aluminum.
This document discusses various methods for surface modification of materials, including mechanical, thermal, electrochemical, and chemical processes. Mechanical methods like shot peening, laser peening, and explosive hardening introduce compressive stresses to strengthen surfaces. Thermal techniques involve spraying molten metals, while electrochemical approaches plate surfaces through electrolysis or chemical reduction. Vapor deposition methods like PVD and CVD coat surfaces with thin films through physical or chemical reactions in vacuum chambers. Surface treatments can improve properties like hardness, corrosion resistance, and wear resistance.
This document discusses non-ferrous metals. It provides information on various non-ferrous metals including aluminum, copper, zinc, and others. Key points include:
- Non-ferrous metals do not contain appreciable amounts of iron. They are highly malleable and corrosion resistant compared to ferrous metals.
- Aluminum is one of the most widely used non-ferrous metals. It is lightweight, corrosion resistant, and used extensively in transportation and construction.
- Copper and zinc are also discussed with details provided on their properties and manufacturing processes.
- Various uses of non-ferrous metals in industrial applications are highlighted.
Copper is one of the most electrically conductive metal elements. It has a characteristic reddish-brown color and is very ductile and malleable. These properties, along with its high thermal and electrical conductivity, make copper useful for electrical wiring, plumbing, and cookware. Common copper alloys include brass and bronze, which are used for applications requiring corrosion resistance, strength, or specific colors.
Galvanizing is a process that provides corrosion protection to steel by applying a zinc coating. There are three main galvanizing methods: hot dipping steel in molten zinc, electroplating zinc onto steel, and galvannealing which involves galvanizing followed by annealing. Hot dip galvanizing provides a thick, uniform zinc coating and is commonly used for construction applications. Electrogalvanizing produces a thinner coating suitable for parts that require shaping after coating. Galvannealing improves formability and paintability. Aluminized steel uses a hot dip process with aluminum instead of zinc to provide corrosion resistance at higher temperatures.
This document discusses the degradation of various materials when exposed to environmental conditions. It describes how wood, plastics, and metals degrade when exposed to factors like moisture, sunlight, oxygen, and microorganisms. Wood degradation is caused by fungi, insects, and moisture above 20%, which causes swelling, strength loss, and decreased durability. Plastics are generally not biodegradable but can become brittle or fade from UV light. Metals corrode through oxidation reactions, especially when in contact with other metals or water, weakening properties and potentially causing structural failures if not protected. Protection methods include sacrificial metals, coatings like paint and plastic, and anodizing or galvanizing processes.
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2. Corrosion is defined as the
deterioration of a material, usually
a metal, because of a reaction with
its environment.
3. Corrosion is:
A natural phenomenon that occurs
over time.
An electrochemical reaction (on
metals)
Happens at different rates with
different metalsand in different
environments
4. If we expose iron or steel to air and
water we can expect to see rust form in
a short time, showing the familiar color
of red-brown iron oxide.
Depending on the environment the
rust may develop in minutes.
5.
6.
7.
8. With other metals such as copper,
brass, zinc, aluminum, and stainless
steel we can expect corrosion to
take place, but it might take longer
to develop.
9. One reason for the reduction of the
corrosion rate with these metals is
the potential formation of metallic
oxides of copper, zinc, aluminum,
and chromium.
10. Unfortunately ordinary iron or steel does
not form this protective layer, so must be
separated from the environment by
some other means.
Generally protective coatings are
utilized for this purpose.
11. Coating
A coating is a covering that is applied to the surface of an
object, usually referred to as the substrate.
The purpose of applying the coating may be decorative,
functional, or both.
The coating itself may be an all-over coating, completely
covering the substrate, or it may only cover parts of the
substrate.
An example of all of these types of coating is a product
label on many drinks bottles- one side has an all-over
functional coating (the adhesive) and the other side has
one or more decorative coatings in an appropriate pattern
(the printing) to form the words and images.
12. Functions of coatings
• Adhesive –
• adhesive tape, pressure-sensitive labels, iron-
on fabric
• Changing adhesion properties
• Non-stick PTFE coated- cooking pans
• Release coatings e.g. silicone-coated release
liners for many self-adhesive products
• primers encourage subsequent coatings to
adhere well (also sometimes have anti-corrosive
properties)
13. Optical coatings
• Reflective coatings for mirrors
• Anti-reflective coatings e.g. on spectacles
• UV- absorbent coatings for protection of eyes or
increasing the life of the substrate
• Tinted as used in some coloured lighting, tinted
glazing, or sunglasses
• Catalytic e.g. some self-cleaning glass
• Light-sensitive as previously used to
make photographic film
14. Protective
• Most paints are to some extent protecting the substrate
• Hard anti-scratch coating on plastics and other materials
e.g. of titanium nitride to reduce scratching, improve wear
resistance, etc.
• Anti-corrosion
• Underbody sealant for cars
• Many plating products
• Waterproof fabric and waterproof paper
• antimicrobial surface
• Magnetic properties such as for magnetic media
like cassette tapes, floppy disks, and some mass transit
tickets
16. CHEMICAL CONVERSATION COATINGS OR
SURFACE CONVERSATION COATINGS
These coatings are produced on the surface of a
metal or alloy by chemical or electrochemical
reaction.
The metal is immersed in a solution of suitable
chemical which reacts with the metal surface
producing and adherent coating.
These coatings protect the base metal from
corrosion. Moreover many of these coatings are
particularly useful to serve as excellent bases for
the application of paints, enamels and other
protective coatings.
The most commonly used surface conversion
coatings are chromate coatings, phosphate
coatings and chemical oxide coatings.
18. Conversion Coatings - Oxidation
• Oxidation
– Not all oxides are
detrimental – many are
tightly adhering leading to
passivation and hardening
of surface
• Al2O3
• Chromium in Stainless steel
rapidly corrodes to
passivate the surface
• Gun-bluing
– Heat steel to 700 deg F in steam
or oil
– Blue coating offers some
corrosion resistance, but little
wear benefit
• Chemical Baths – similar in nature
to gun-bluing
• Black Oxide – chemical
application
– Typically applied to steel, copper
and stainless steel
• Anodizing – electrochemical
conversion
– Usually done to Aluminum
– 2-25 m thick typically
– Multiple colors possible
– Improved Corrosion and Wear
Resistance
19. These types of coatings are formed on the surface of
metals like Fe, Al, Mg etc by treating the base metal
with alkaline oxidizing agents like potassium
permanganate.
This treatment increases the thickness of the
original oxide film on the metal, there by increasing
the corrosion resistance.
Oxide coatings form a good base for paints.
These oxide coatings have got only poor corrosion
resistance. However, for better protection the
thickness of the oxide film can be increased 100 to
1000 times by electrolytic oxidation or anodisation.
Chemical Oxide Coatings
20. • Anodised coatings are generally produced on non –
ferrous metals like Al, Zn, Mg and their alloys by
anodic oxidation process.
• In this process, the base metal is made as anode
and the cathode is an inert electrode like graphite.
• The electrolytic bath is usually of H2 SO4 , chromic
acid, boric acid, phosphoric acid, oxalic acid etc
• The base metal to be anodized is suspended from
the anode.
• The process is carried out by passing a moderate
direct current through the electrolytic bath.
• As the anodized coatings are somewhat thicker than
the natural oxide film and they posses improved
resistance to corrosion.
A -Anodisation or Anodised Coatings
21. • Anodizing on Al has gained considerable
commercial importance.
• Al coated surface require oxidation to convert the
metal to its inert oxide.
• Anodising on Al is carried out by an electrolytic
process.
22.
23. The O2 evolved at the anode oxides the outer layer of Al to the oxide
film, Al2O3.
The oxide film initially very thin, grows from the metal surface
outwards and increases in thickness as oxidation continues at Al
anode.
The outer part of the oxide film formed is porous and to reduce
porosity, the article after electrolysis is kept immersed in a boiling
water bath.
This treatment changes porous alumina into its monohydrate
(Al2O3.H2O) which occupies more, volume, thereby the pores are
sealed.
4 Al + 3 O2 Al2O3
Al2O3 + H2 O Al2O3.H2O
Anodized coatings may be coloured with organic dyes and inorganic
pigments to give decorative effects.
24. Conversion Coatings – Phosphate
Coating
• Immersion in a Zn-P bath with Phosphoric acid
causes growth of a crystalline zinc phosphate layer
– Iron, Zinc or Manganese Phosphate layer formed
• Typically applied to C-steel, low alloy steel and cast
irons
– Sometimes applied to Zinc, Cadmium, Aluminum and Tin
• Typically very thin ~ 2.5 m
25. • These are produced by the chemical reaction of base
metal with aqueous solution of phosphoric acid and a
phosphate of Fe, Mn or Zn.
• The reaction results in the formation of a surface film
consisting of phosphate of a surface film consisting of
phosphates of the metal.
• These coatings are usually applied by immersing or
spraying or brushing. These coating do not give
complete corrosion resistance but can serve as base for
painting.
• These are applied on metals like Fe, Zn, Cd, Al and Sn.
Phosphate coating
26. Conversion Coatings – Chrome Coating
• Food cans
• Immersion in a chromic acid bath (pH ~ 1.8) with
other chemicals to coat surface
• Known carcinogen chemicals used, so alternatives
are currently under research
– Molybdate chemicals currently best subsititute for
aluminum coatings
• Very good to minimize atmospheric corrosion
– Many household goods – screws, hinges (yellow brown
appearance)
• Typically very thin < 2.5 m
27. • There are produced by the immersion of the
article in a bath of acidic potassium chromate
followed by immersion in a bath of neutral
chromate solution.
• The surface film consisting of a mixture of
trivals and hexavalent Cr is formed.
• Chromate coatings possess more corrosion
resistance and can also be used as a base for
paints. These are applied on Zu, Cd, Mg and Al
Chromate Coatings
28. • Aircraft parts, refrigerators, reflectors,
machine parts etc are anodized by
this method Al articles used as doors,
windows, showcase
household utensils are
panels &
anodized by
this method.
Applications
30. Thermal Treatments – Surface Heat
Treatment
• Basic concept is to heat the surface to austenitic
range, then quench it to form surface martensite -
workpiece is steel
• Heating Methods
– Flame Treatment
– Induction Heating
• Copper coil wraps around part to heat by induction
– Electron Beam or Laser Beam Hardening
• Typically heat small area and allow the bulk solid heat capacity to
quench the small heated area
31. Thermal Treatments – Diffusion
Coating
• With low carbon steel, the surface can be enriched by
diffusion of C or N into surface
• Carburizing
– Heat steel to austenitic range (850-950 ºC) in a carbon rich
environment, then quench and temper
• Nitriding
– Nitrogen diffusion into steels occurs around 500-560 ºC to form a
thin hard surface
– Good for Cr, V,W,and Mo steels. Will embrittle surface of
Aluminum.
• Metal Diffusion
– Chromizing – Chromium diffuses into surface to form corrosion
resistant layer.
• Take care with carbon steels as surface will decarburize
– Aluminizing – Used to increase the high temperature corrosion
resistance of steels and superalloys
32. Thermal Treatments –
Hot-Dip Coatings
• These coatings are used for corrosion protection
• Galvanizing
– Parts are dipped into a molten zinc bath
• Galv-annealing
– Galvanized parts are then heat treated to ~500 ºC to form Fe-Zn inter-
metallic
• Used for metals that need spot welded to protect copper electrode from alloying
with zinc and reducing its life
• Zn-Al Coatings
– Gives a different corrosion protect and a more lustrous appearance (can
greatly reduce spangles easily observed on galvanized parts)
• Aluminum Coatings
– Alloyed with Si
– Coatings used on steel for high temperature applications that need a
lustrous appearance
• Example – Automobile exhaust
33. Thermal Treatments –
Weld Overlay coatings
• Typically used to improve wear resistance by creating a hard
surface over a tough bulk body
• Hard Facing
– Weld buildup of parts – alloy composition controls final properties
– Examples – cutting tools, rock drills, cutting blades
– Cladding of material for corrosion resistance
• Thermal spraying
– Molten particle deposition – a stream of molten metal particles are
deposited on the substrate surface
– Major difference from hard facing is that the surface of the substrate is
not subjected to welding. Instead it just undergoes a bonding process
with the molten particles.
35. Metal Coatings - Electroplating
• Used to increase wear and corrosion resistance
• Electrochemical process used to create a thin coating
bonding to substrate
• Process is slow so coating thickness can be closely
controlled (10-500 m)
• Applications
– Tin and Zinc are deposited on steel for further working
– Zinc and Cadmium are deposited on parts for corrosion resistance
(Cadmium is toxic and can not be used for food applications)
– Copper is deposited for electrical contacts
– Nickel for corrosion resistance
– Chromium can be used to impart wear resistance to dies and reduce
adhesion to workpieces such as aluminum or zinc
– Precious metals for decoration or electronic devices
36. Metal Coatings – Electroless
Coatings
• Part is submerged into an aqueous bath filled
with metal salts, reducing agents and catalysts
– Catalysts reduce metal to ions to form the coating
• Excellent for complex geometries as
deposition is uniform across surface regardless
of geometry (except very sharp corners (0.4
mm radii))
37. Metal Coatings -Electroless Nickel
Plating
• Has the appearance of
stainless steel
• Autocatalytic immersion
process
• Key characteristics:
– Heat treatable coating (to 68
Rc) very hard
– Non-porous
– Corrosion resistant
– .001” thick typical
– Withstand load to 45 ksi
• Can be applied to:
– steel and stainless steel,
iron, aluminum, titanium,
magnesium, copper, brass,
bronze, and nickel
38. Electroless Nickel vs. Chrome
Plating
ELECTROLESS NICKEL HARD CHROME
METAL DISTRIBUTION VERY GOOD POOR
CORROSION RESISTANCE
1,000 HOURS
ASTM B117
400 HOURS
ASTM B117
HARDNESS:
AS DEPOSITED
HEAT TREAT
48-52 Rc
70 Rc
64-69 Rc
48-52 Rc
MELTING POINT 1800oF 2900oF
WEAR RESISTANCE GOOD VERY GOOD
CO-EFFICIENT OF FRICTION:
DYNAMIC
STATIC
0.19
0.20
0.16
0.17
DUCTILITY 1-2% Very Low Almost 0
EFFLUENT COST RELATIVELY LOW HIGH
DEPOSITION RATE
(PER HOUR PER HOUR)
.0002 - .0003 .001 - .002
EFFECTIVE OF HYDROGEN
EMBRITTLEMENT ON PLATED
COMPONENTS
FAIR/NOT SERIOUS USUALLY SERIOUS
39. Metal Coatings –
Metallizing of Plastics and Ceramics
• Poor adhesion is the major challenge (As in all
coating processes, however it is more
challenging in this case.)
• Applications
– Decorative (plumbing fixtures, automotive parts),
reflectivity (headlights), electrical conduction
(electronic touchpads), and EMF shielding
41. Physical Vapor Deposition –
Thermal PVD
• Thermal PVD – also called Vacuum Deposition
– Coating material (typically metal) is evaporated by melting
in a vacuum
– Substrate is usually heated for better bonding
– Deposition rate is increased though the use of a DC current
(substrate is the anode so it attracts the coating material)
– Thin ~0.5 m to as thick as 1 mm.
42. Physical Vapor Deposition – Sputter
Deposition
• Vacuum chamber is usually backfilled with Ar gas
• Chamber has high DC voltage (2,000-6,000 V)
• The Ar becomes a plasma and is used to target the
deposition material. The impact dislodges atoms from the
surface (sputtering), which are then deposited on the
substrate anode
• If the chamber is full of oxygen instead of Ar, then the
sputtered atoms will oxidize immediately and an oxide will
deposit (called reactive sputtering)
43. Physical Vapor Deposition – Ion
Plating
• Combination of thermal PVD and sputtering
• Higher rate of evaporation and deposition
• TiN coating is made this way (Ar-N2
atmosphere)
– The gold looking coating on many cutting tools to
decrease the friction, increase the hardness and
wear resistance
44. Chemical Vapor Deposition
• Deposition of a compound (or element) produced by a
vapor-phase reduction between a reactive element and gas
– Produces by-products that must be removed from the process as
well
• Process typically done at elevated temps (~900ºC)
– Coating will crack upon cooling if large difference in thermal
coefficients of expansion
– Plasma CVD done at 300-700ºC (reaction is activated by plasma)
• Typical for tool coatings
• Applications
– Diamond Coating, Carburizing, Nitriding, Chromizing, Aluminizing
and Siliconizing processes
– Semiconductor manufacturing
45. Organic Coatings - paint
• Enamels
– Form film primarily by solvent evaporation
– 30 % Volatile Organic Content (VOC)
• Lacquers – solvent evaporation
• Water-base paints – water evaporation,
therefore much better
• Powder Coating – superior – more detail to
follow
46. Powder
Coating
• Fully formulated paint
ground into a fine
powder
• Powder is sprayed onto
part, retained by static
electricity
• Heat cured onto part
• Can virtually eliminate
VOCs
47. Teflon and dry lubricant coatings
• Sprayed, dipped or
tumbled to coat,
followed by heating to
bond
• Key characteristics:
– Low friction coefficient
(0.02 – 0.08)
– Can sustain load of 250
ksi
49. Protective coatings
An important method for protecting a metal from corrosion is
to apply a protective coating.
The protective coatings may be of metal, inorganic or organic.
The coated surface isolates the metal from the corroding
medium.
The coating applied must be chemically inert towards the
environment.
50. Protective Coating
Surface preparation for Coating:
1. Cleaning:
To prepare for suitable condition
Removing contaminants to prevent detrimental reaction product
- E.g. de-greasing, sand blasting, vapour degreasing, pickling and
alkaline cleaning.
2. Solvent Cleaning:
Must be non-inflammable and nontoxic.
Trichloro trifluoroethane which has low toxicity are costlier.
Vapour de-greasing is economical and advantageous because of
continuous cleaning with small quantities of solvent.
51. 3. Electrolyte Pickling:
Provides better and rapid cleaning by increasing hydrogen
evolution resulting in agitation and blasting action.
Sand blasting is mechanical cleaning.
4. Alkaline Cleaning:
Cheaper and less hazardous.
Used in conjunction with surface active (wetting) agent.
Ability depends on pH, rapidly decreases below 8.5.
Other abilities are rinsability, detergent properties,
sequestering, wetting etc
52. 5. Acid Cleaning
Acid such as HCl, H2SO4, H3PO4 is very effective.
5-10% H2SO4 and HCl used to remove inorganic
contaminants.
Pickling are performed at high temp. (60 ̊C).
It is effective for removal of grease, oil , dirt and rust.
53. • Metallic coatings are mostly
applied on Iron and steel because
these are cheap and
used construction
commonly
materials.
There are two types of metallic
coatings.
Metallic Coatings
54. • The base metal which is to be
protected is coated with a more anodic
metal for eg. Coatings of Zn, Al and
electrode potentials are lower
Cd steel are anodic because their
than
that of the base metal ie. Fe.
i. Anodic coatings
55. • It is obtained by coating a more inert metal
having higher electrode potential. Than the
base metal. Eg. Coating of Sn, Cr, Ni on Fe
surface.
• The coating should be continuous and free
from pores and cracks.
• These coating metals usually have higher
corrosion resistance than the base metal.
ii. Cathodic Coatings
57. • It is used for producing a coating of low melting metal
such as Zn, Sn, Ph, Al etc on relatively higher melting
metals such as iron, steel, copper etc.
• This is done by immersing the base metal covered by
a layer of molten flux.
• The flux is used to keep the base metal surface clean
and also to prevent oxidation of the molten metal.
• Most widely used hot dipping methods are : (i)
galvanization and (ii) tinning
1. Hot Dipping
58. • It is the process of coating Zn over iron
or steel sheet by immersing it in molten
Zn. The procedure involves the following
stages.
• The iron or steel article is first cleaned by
pickling with dil H2So4 for 15 – 20 min.
at 60 – 900C in an acid bath.
• This treatment also removes any oxide
layer present on the surface of the metal.
a. Galvanization
59. a. Galvanization
• The article is then washed with water in a
washing bath & dried in a drying chamber.
⚫It is then passed through a pair of hot rollers to
remove excess of Zn and to get uniform thickness
for coating.
⚫Then it is annealed at about 6500C & cooled
slowly.
⚫In the case of Zn coating even if the protecting
layer has cracks on it, iron being cathodic does not
get corroded.
60. ⚫It is then dipped in a bath of molten Zn
kept at 425 – 4350C.
⚫The Surface of the bath is covered with
NH4Cl flux to prevent oxide formation.
⚫The article gets coated with a thin layer of
Zn.
a. Galvanization
61. Applications
This method is widely used for protection of
Fe from atmospheric corrosion in the form
of articles like roofing sheets, wires, pipes,
nails, screws, tubes etc.
It is to be noted that galvanized utensils
should not come in contact with acids.
62. • It is an eg. For cathodic coatings. It is the process of coating of
Sn over Fe or steel articles by immersing it in molten Sn.
• The process consists in Ist treating the iron sheet with dil
H2So4 to remove any oxide film.
• After this it is passed through a bath of ZnCl2 flux which helps
the molten Sn to adhere to the metal sheet.
•
• Next the sheet passes through palm oil which prevents
through a pair of hot rollers to remove excess of Sn & produce
uniform thickness for Sn coating.
ii. Tinning
63. • Tinning is widely used for coating steel, Cu and brass
sheets which are used for making containers for
storing food studs, oils, kerosene & packing food
materials.
• Tinned Cu sheets are used for making cooking
utensils & refrigeration equipments.
Applications
64. In this process, a thick homogeneous layer of coating metal
is bonded firmly & permanently to the base metal on one
or both the sides.
This method enhances corrosion resistance.
The choice of cladding material depends on the corrosion
resistance required for any particular environment.
2. Metal Cladding
65. Nearly all existing corrosion resisting metals like Ni, Cu, Al,
Ag, Pt and alloys like stainless steel, Ni alloys, Cu alloys can
be used as cladding materials.
Cladding can be done by different means.
a. Fusing cladding material over the base
b. Welding
metal.
c. Rolling sheets of cladding material over base metal.
2. Metal Cladding
66. ⚫In this process, the coating metal in the
molten state is sprayed on the previously
cleaned base metal with the help of a sprayer.
⚫The sprayer coatings are continuous but
somewhat porous a sealer – oil is applied on
such a coating to provide a smooth surface.
⚫However, adhesion strength of metallic
spraying is usually lesser that obtained by hot
dipping or electroplating.
⚫It is therefore essential to have a cleaned
metal surface. Spraying can be applied by the
following two techniques.
3.Metal spraying
67. • In this method, the coating metal in the
form of thin wire is melted by an oxy –
acetylene flame and vaporized by a blast of
compressed air.
• The coating metal adheres to the base
metal. Al is coated on aircraft steel parts
using this techniques.
i. Wire – gun method
68. • In this method, the coating metal is supplied in the
form of tine powder which is converted in to a
cloud of molten globules by a blower and are
adsorbed on the base metal surface.
ii Powder – metal method
69. frequently applied industrial method
⚫it is probably the most important and most
of
producing metallic coatings.
⚫Electroplating is carried out by a process called
electrolysis.
⚫Thus in this process, the coating metal is
deposited on the base metal by passing direct
current through an electrolyte containing the
soluble salt of the coating metal.
⚫The base metal to be electroplated is made the
cathode of the electrolytic cell whereas the anode
is either made of the coating metal itself or an
inert material of good electrical conductivity like
graphic.
4. Electroplating or Electrodeposition
71. • For electroplating of Ni, NiSO4 and NiCl2 are
used as the electrolyte.
• For electroplating of Cr, chromic acid is used
as the electrolyte.
• For Au plating, AuCl3 solution is taken as the
electrolyte.
• For Cu plating CuSO4 solution is used as the
electrolyte.
• In silver plating, AgNO3 solution is used as
the electrolyte.
73. b. VITREOUS COATINGS OR CEREMIC
PROTECTIVE COATINGS
• Ceramic protective coatings can be
broadly divided into vitreous enamel
coatings and pure ceramic coatings.
These coatings have the following
advantages.
1.They posses high refractoriness and
inertness
2. They are wear resistant & easily be cleaned
3. They are glossy in appearance
4. They are good thermal & electrical
insulators
74. Vitreous enamels are defined as glossy
inorganic composition that can adhere to
metals by fusion and protect them from
corrosion, abrasion, oxidation and high
temperature.
Vitreous enamel coatings consists of a
ceramic mixture of refractories and large
proportion of fluxes. These coatings are
usually applied on steel and cast iron
equipments. The raw materials used for the
vitreous coatings are the following.
75. Vitreous coatings
1. Refractories like quartz (SiO2), clay etc.
2. Fluxes like borax (Sodium tetra borate
Na2B4O7), cryolite (Na3AlF6) (Sodium
alumino fluoride), Soda ash (anhydrous
sodium carbonate Na2CO3) etc.
3. Opacifiers like TiO2, SnO2 , Al2O3 etc
4. Pigments like metallic oxides organic
dyes etc
5. Floating agents like plastic, clay, gum etc
6. Electrolytes like MgSO 4, MgCO 3, Na2Co3
etc.