This document discusses various types and theories of corrosion. It begins by introducing corrosion as the chemical reaction between a metal and its environment that causes the metal to deteriorate. It then describes three main theories of corrosion: the acid theory, dry/chemical theory, and galvanic/electrochemical theory. The rest of the document details eight specific types of corrosion including uniform, pitting, intergranular, exfoliation, stress, crevice, galvanic, and erosion corrosion. It provides examples and explanations for each type.
Corrosion is the deterioration of materials due to chemical or electrochemical reaction with the environment. It is an inevitable process that leads to significant economic losses. Corrosion engineering studies corrosion mechanisms and works to prevent or control corrosion economically and safely. Common types of corrosion include galvanic, erosion, crevice, pitting, and microbiologically influenced corrosion. Factors that influence corrosion include the metal properties, environmental conditions like temperature, pH, and presence of ions. Protection methods include material selection, cathodic protection, modifying the environment, metallic coatings, inorganic coatings, and organic coatings.
The document discusses cathodic protection methods for corrosion control. It describes two main types of cathodic protection - sacrificial anode and impressed current. Sacrificial anode uses more reactive metals like zinc or aluminum as anodes, while impressed current uses an external DC power source and insoluble anodes like graphite. Common applications include protecting pipelines, ships, and marine structures. Issues that can arise include hydrogen embrittlement, cathodic disbonding, and safety concerns with rectifiers.
Plastic laminate is made from layers of kraft paper bonded with plastic resin under heat and pressure. It comes in various designs, colors, and textures. The manufacturing process involves soaking kraft paper strips in phenolic or melamine resin, stacking the impregnated layers, and applying heat and pressure to thermoset them into a rigid sheet. Plastic laminate is stain and damage resistant, affordable, and available in many options, but can delaminate if improperly fabricated or maintained and lacks UV protection. It has various applications including countertops, walls, floors, and more.
The document discusses corrosion, which is defined as the degradation of a metal through a chemical reaction on its surface caused by its surrounding chemicals. It then discusses the chemical theory of corrosion, noting that oxygen and other gases can cause corrosion by directly reacting with metals. There are two main types of corrosion - dry corrosion, which occurs without moisture, and wet/electrochemical corrosion, which occurs when a metal is in contact with a conducting liquid. The document goes on to describe examples of different corrosion processes and methods used to protect metals from corrosion, including cathodic protection and coatings like paint.
This document discusses various methods for preventing corrosion of metals. It begins by introducing the importance of preventing corrosion, which causes huge economic losses. The main methods discussed are modifying the material through coatings or alloys to increase corrosion resistance, using corrosion inhibitors, cathodic protection, and protective coatings. For coatings, it describes metallic coatings like electroplating, electroless plating and zinc coatings, as well as inorganic coatings like anodized aluminum coatings. It also discusses factors that affect the corrosion rate like the metal's purity, environment pH, and presence of impurities.
Food preservation by refrigeration and air conditioningAKSHAY PATHANIA
This document discusses refrigeration and air conditioning systems for food preservation. It begins by defining food preservation as retaining food for a period of time without contamination or loss of quality. Refrigeration systems preserve foods by using low temperatures to eliminate spoilage agents. Domestic refrigerators provide temporary storage between 0-4°C, while commercial refrigerators like walk-in coolers and display cases are used for short-term storage in grocery stores and restaurants. Cold storage facilities store foods above freezing for 1-15 days, considering factors like temperature, humidity and mixed storage. Frozen storage preserves foods long-term at -15°C or below by methods like air blast or immersion freezing.
This document discusses high temperature materials. It begins by noting that regular engineering materials are affected by changes in temperature, so special high temperature materials are used in high temperature conditions. These materials have properties like high temperature resistance, oxidation and corrosion resistance, and creep and fatigue strength. The document then describes some common types of high temperature materials, including iron-base alloys like low, medium, and high alloy steels, iron-chromium and iron-chromium-nickel casting alloys, and wrought iron alloys. It also discusses nickel-base alloys and refractory metals and alloys, which can withstand very high temperatures. Finally, it covers ceramics and metal ceramics, which have properties like heat
This document discusses various types and theories of corrosion. It begins by introducing corrosion as the chemical reaction between a metal and its environment that causes the metal to deteriorate. It then describes three main theories of corrosion: the acid theory, dry/chemical theory, and galvanic/electrochemical theory. The rest of the document details eight specific types of corrosion including uniform, pitting, intergranular, exfoliation, stress, crevice, galvanic, and erosion corrosion. It provides examples and explanations for each type.
Corrosion is the deterioration of materials due to chemical or electrochemical reaction with the environment. It is an inevitable process that leads to significant economic losses. Corrosion engineering studies corrosion mechanisms and works to prevent or control corrosion economically and safely. Common types of corrosion include galvanic, erosion, crevice, pitting, and microbiologically influenced corrosion. Factors that influence corrosion include the metal properties, environmental conditions like temperature, pH, and presence of ions. Protection methods include material selection, cathodic protection, modifying the environment, metallic coatings, inorganic coatings, and organic coatings.
The document discusses cathodic protection methods for corrosion control. It describes two main types of cathodic protection - sacrificial anode and impressed current. Sacrificial anode uses more reactive metals like zinc or aluminum as anodes, while impressed current uses an external DC power source and insoluble anodes like graphite. Common applications include protecting pipelines, ships, and marine structures. Issues that can arise include hydrogen embrittlement, cathodic disbonding, and safety concerns with rectifiers.
Plastic laminate is made from layers of kraft paper bonded with plastic resin under heat and pressure. It comes in various designs, colors, and textures. The manufacturing process involves soaking kraft paper strips in phenolic or melamine resin, stacking the impregnated layers, and applying heat and pressure to thermoset them into a rigid sheet. Plastic laminate is stain and damage resistant, affordable, and available in many options, but can delaminate if improperly fabricated or maintained and lacks UV protection. It has various applications including countertops, walls, floors, and more.
The document discusses corrosion, which is defined as the degradation of a metal through a chemical reaction on its surface caused by its surrounding chemicals. It then discusses the chemical theory of corrosion, noting that oxygen and other gases can cause corrosion by directly reacting with metals. There are two main types of corrosion - dry corrosion, which occurs without moisture, and wet/electrochemical corrosion, which occurs when a metal is in contact with a conducting liquid. The document goes on to describe examples of different corrosion processes and methods used to protect metals from corrosion, including cathodic protection and coatings like paint.
This document discusses various methods for preventing corrosion of metals. It begins by introducing the importance of preventing corrosion, which causes huge economic losses. The main methods discussed are modifying the material through coatings or alloys to increase corrosion resistance, using corrosion inhibitors, cathodic protection, and protective coatings. For coatings, it describes metallic coatings like electroplating, electroless plating and zinc coatings, as well as inorganic coatings like anodized aluminum coatings. It also discusses factors that affect the corrosion rate like the metal's purity, environment pH, and presence of impurities.
Food preservation by refrigeration and air conditioningAKSHAY PATHANIA
This document discusses refrigeration and air conditioning systems for food preservation. It begins by defining food preservation as retaining food for a period of time without contamination or loss of quality. Refrigeration systems preserve foods by using low temperatures to eliminate spoilage agents. Domestic refrigerators provide temporary storage between 0-4°C, while commercial refrigerators like walk-in coolers and display cases are used for short-term storage in grocery stores and restaurants. Cold storage facilities store foods above freezing for 1-15 days, considering factors like temperature, humidity and mixed storage. Frozen storage preserves foods long-term at -15°C or below by methods like air blast or immersion freezing.
This document discusses high temperature materials. It begins by noting that regular engineering materials are affected by changes in temperature, so special high temperature materials are used in high temperature conditions. These materials have properties like high temperature resistance, oxidation and corrosion resistance, and creep and fatigue strength. The document then describes some common types of high temperature materials, including iron-base alloys like low, medium, and high alloy steels, iron-chromium and iron-chromium-nickel casting alloys, and wrought iron alloys. It also discusses nickel-base alloys and refractory metals and alloys, which can withstand very high temperatures. Finally, it covers ceramics and metal ceramics, which have properties like heat
Hydrogen is the simplest and lightest element. It has one proton and one electron. Hydrogen exists as diatomic hydrogen gas (H2) and is the first element in the periodic table. It can form compounds with almost all elements by gaining, losing or sharing electrons. Water (H2O) is an important compound of hydrogen that is essential for life. The largest use of hydrogen is in the production of ammonia, which is used to make fertilizers and other chemicals.
Corrosion is the deterioration of metals due to chemical reactions with the surrounding environment. There are two main types: dry corrosion which occurs without moisture and involves direct chemical attack, and wet corrosion which is electrochemical and occurs in the presence of an electrolyte. Wet corrosion involves the formation of anodic and cathodic areas on a metal surface where oxidation occurs at the anode and corrosion products form elsewhere. Common forms of wet corrosion include galvanic corrosion between dissimilar metals and concentration cell corrosion between areas of different aeration.
Dry corrosion occurs through direct chemical reaction between atmospheric gases like carbon dioxide and sulfur dioxide with metal surfaces in the absence of moisture. There are three main types of dry corrosion: 1) Oxidation corrosion, which occurs through direct reaction of oxygen with metals at ordinary temperatures in the absence of moisture. 2) Liquid metal corrosion, which occurs when a liquid metal flows over a solid metal at high temperatures. 3) Corrosion by other gases, where certain gases chemically react with metals to form protective or non-protective surface layers. The extent of dry corrosion depends on the environment and the nature and properties of the oxide film formed on the metal surface.
The lecture is devoted to newbies in chemistry eager to learn the basics of nomenclature. The tips given re easy and can be practiced to get perfection.
The document discusses ferrous and non-ferrous metals. Ferrous metals contain iron while non-ferrous metals do not. It provides examples of common ferrous metals like steel alloys and non-ferrous metals like aluminum and copper. It then describes characteristics and common uses of both ferrous and non-ferrous metals, noting ferrous metals are strong but prone to rust while non-ferrous metals are lighter, more corrosion-resistant and non-magnetic. Mild steel specifically is discussed as being ductile, malleable and commonly used in building structures.
This document discusses various forms of corrosion that can occur in metals. It begins by defining corrosion and explaining the factors that influence it. It then describes several specific types of corrosion: general/uniform corrosion, galvanic corrosion, crevice corrosion, pitting corrosion, intergranular corrosion, dealloying, erosion corrosion, stress corrosion, hydrogen damage including hydrogen blistering and hydrogen embrittlement. For each type of corrosion, the document discusses the mechanism and provides methods for prevention.
Aluminum is the most abundant metal in the Earth's crust. It occurs naturally combined with other elements. While aluminum itself is lightweight, it is still strong and durable. The document discusses the various forms and manufacturing processes of aluminum including casting, extrusion, and sheet production. It also outlines common uses of aluminum in transportation, construction, packaging, and electrical sectors.
Corrosion Chemistry : Its Causes and RemedyArijitDhali
This Conceptual Power Point project consists of a grieve description about the science of Corrosion, perfect for covering whole topic for short period of time. The project consists of basic knowledge regarding corrosion, its type of causes that is dry and wet corrosion. It also summarizes about different types of differential corrosion and its remedies. Its allover a good conceptual ppt for students of chemistry in their prelims. It's good for the ones achieving for engineering degrees.
Its Is The Process By Which A Iron Nail Is Been Coated With Copper Plate.Electroplating is a process that uses electrical current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode. The term is also used for electrical oxidation of anions onto a solid substrate, as in the formation silver chloride on silver wire to make silver/silver-chloride electrodes. Electroplating is primarily used to change the surface properties of an object (e.g. abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.), but may also be used to build up thickness on undersized parts or to form objects by electroforming.
The process used in electroplating is called electrodeposition. It is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit. In one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that comprise it and allowing them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, vis-a-vis the current flowing through the circuit. In this manner, the ions in the electrolyte bath are continuously replenished by the anode.[1]
Other electroplating processes may use a non-consumable anode such as lead or carbon. In these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution.[2] The most common form of electroplating is used for creating coins such as pennies, which are small zinc plates covered in a layer of copper. [3]Process[edit]
Electroplating of a metal (Me) with copper in a copper sulfate bath
The cations associate with the anions in the solution. These cations are reduced at the cathode to deposit in the metallic, zero valence state. For example, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO42- in the solution to form copper sulfate. At the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result is the effective transfer of copper from the anode source to a plate covering the cathode.
The plating is most commonly a single metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder.
Corrosion is the degradation of materials due to reaction with the environment. It affects metals, non-metals, and living tissues, causing damage like material loss and increased costs. Proper material selection, design modifications, environmental control, and protective coatings or cathodic protection can prevent a majority of corrosion damage and reduce annual economic losses estimated to be 3-5% of global GDP.
This document discusses corrosion and methods for corrosion control. Corrosion is defined as the conversion of metals into compounds through natural means like rusting of iron. It occurs through the formation of oxides on metal surfaces or through electrolytic reactions between cathode and anode areas on a metal surface when in contact with electrolytes like water. Common methods to protect ferrous metals from corrosion include electroplating to apply protective chromium or nickel coatings, galvanizing to coat metals with zinc, tin plating through hot dipping in molten tin, metal spraying to apply thin zinc, tin or aluminum coatings using fuel gases, and painting with high quality paint after cleaning metal surfaces.
This very short document appears to be about a topic called "Ohmic Heating" but provides no details about the subject. It includes a course code "OBT554" and mentions "Unit 3" but does not contain any meaningful or essential information that could be summarized in 3 sentences or less.
Pharmaceutical Engineering, Are the branch of Pharmaceutics which deals with Some metals and their properties.
I Hope it make to easy the study of pharmaceutics.
Here I'm Rahul Pal sharing this documents.
The document discusses materials science and engineering, specifically focusing on the production of iron and steel. It begins with an introduction to materials science and engineering. It then describes the production process of pig iron, including raw material procurement, blast furnace production, and products. It further discusses various steel production methods like basic oxygen furnace and electric arc furnace production. Continuous casting and different steel products are also outlined. In summary, the document provides an overview of the key industrial processes for producing iron and steel, from raw materials to final products.
Factors affecting corrosion on the basis of nature of the metal and Nature of Corroding medium, Protection from corrosion in reference to Sacrificial protection, Cathodic protection, Metallic coatings, Organic coatings, Proper designing.
Hydrogen, the most abundant element in the universe and the third most abundant on the surface of the globe.
All you have to know about this inflammable gas.
This document discusses different theories and types of corrosion. It begins by introducing corrosion as the formation of compounds on a metal's surface through chemical reaction with its environment. It then summarizes three main theories of corrosion: (1) the acid theory involving reaction with carbon dioxide, moisture and oxygen; (2) the chemical theory involving direct reaction with gases like oxygen; and (3) the electrochemical theory involving the formation of anodes and cathodes when a metal is in contact with a conducting liquid. The document goes on to describe eight common types of corrosion in more detail.
This document discusses refrigeration and air conditioning systems. It describes four main types of refrigeration: vapor compression, vapor absorption, magnetic, and industrial. It explains the basic refrigeration cycle for vapor compression and vapor absorption. It then discusses four main types of air conditioning systems: window, split, centralized, and packaged. It provides diagrams to illustrate the components and processes for each system type. In conclusion, it states that refrigerators use two compartments to keep items either frozen or refrigerated to prolong their usable life.
RAC systems are used for various applications like refrigerators, water coolers, dairies, food preservation, and air conditioning. Refrigerators use insulation and thermostats to maintain temperatures between 0-4°C for food storage. Water coolers provide cool water at a constant temperature regardless of ambient conditions using thermostatic switches. Dairies use refrigeration for pasteurization and cooling of milk and cheese production. Cold storage facilities preserve processed foods at positive or sub-zero temperatures using insulated panels and temperature/humidity control. Large buildings use central air conditioning systems with ductwork while smaller spaces use packaged or split units.
This document provides information on different types of materials, focusing on metals. It classifies materials into metals, polymers, and ceramics. Within metals, it distinguishes between ferrous metals which contain iron and non-ferrous metals which do not. Specific ferrous metals discussed include various grades of steel classified based on their carbon content. Alloy steels are also introduced. Common alloys of steel like stainless steel, nickel steel, and Invar steel are summarized in terms of their composition and properties. End uses of alloys are also briefly covered.
Corrosion is the destruction or deterioration of metallic materials due to chemical and electrochemical reactions with their environment. There are two main types of corrosion - dry corrosion caused by direct chemical reactions with gases, and wet corrosion caused by electrochemical reactions when metals are in contact with an electrolyte. Various factors influence the corrosion rate, including the metal properties, environmental conditions, and nature of corrosion products. Common corrosion control methods include cathodic protection, using corrosion inhibitors, and applying protective coatings to the metal surface.
This document provides an overview of corrosion and energy storage systems. It discusses various types of corrosion including dry corrosion, wet corrosion, pitting corrosion, intergranular corrosion, galvanic corrosion and stress corrosion. It also discusses corrosion control methods like material selection, cathodic protection and protective coatings. The document then discusses basic principles of batteries and provides examples of lithium-ion batteries and nickel-cadmium batteries.
Hydrogen is the simplest and lightest element. It has one proton and one electron. Hydrogen exists as diatomic hydrogen gas (H2) and is the first element in the periodic table. It can form compounds with almost all elements by gaining, losing or sharing electrons. Water (H2O) is an important compound of hydrogen that is essential for life. The largest use of hydrogen is in the production of ammonia, which is used to make fertilizers and other chemicals.
Corrosion is the deterioration of metals due to chemical reactions with the surrounding environment. There are two main types: dry corrosion which occurs without moisture and involves direct chemical attack, and wet corrosion which is electrochemical and occurs in the presence of an electrolyte. Wet corrosion involves the formation of anodic and cathodic areas on a metal surface where oxidation occurs at the anode and corrosion products form elsewhere. Common forms of wet corrosion include galvanic corrosion between dissimilar metals and concentration cell corrosion between areas of different aeration.
Dry corrosion occurs through direct chemical reaction between atmospheric gases like carbon dioxide and sulfur dioxide with metal surfaces in the absence of moisture. There are three main types of dry corrosion: 1) Oxidation corrosion, which occurs through direct reaction of oxygen with metals at ordinary temperatures in the absence of moisture. 2) Liquid metal corrosion, which occurs when a liquid metal flows over a solid metal at high temperatures. 3) Corrosion by other gases, where certain gases chemically react with metals to form protective or non-protective surface layers. The extent of dry corrosion depends on the environment and the nature and properties of the oxide film formed on the metal surface.
The lecture is devoted to newbies in chemistry eager to learn the basics of nomenclature. The tips given re easy and can be practiced to get perfection.
The document discusses ferrous and non-ferrous metals. Ferrous metals contain iron while non-ferrous metals do not. It provides examples of common ferrous metals like steel alloys and non-ferrous metals like aluminum and copper. It then describes characteristics and common uses of both ferrous and non-ferrous metals, noting ferrous metals are strong but prone to rust while non-ferrous metals are lighter, more corrosion-resistant and non-magnetic. Mild steel specifically is discussed as being ductile, malleable and commonly used in building structures.
This document discusses various forms of corrosion that can occur in metals. It begins by defining corrosion and explaining the factors that influence it. It then describes several specific types of corrosion: general/uniform corrosion, galvanic corrosion, crevice corrosion, pitting corrosion, intergranular corrosion, dealloying, erosion corrosion, stress corrosion, hydrogen damage including hydrogen blistering and hydrogen embrittlement. For each type of corrosion, the document discusses the mechanism and provides methods for prevention.
Aluminum is the most abundant metal in the Earth's crust. It occurs naturally combined with other elements. While aluminum itself is lightweight, it is still strong and durable. The document discusses the various forms and manufacturing processes of aluminum including casting, extrusion, and sheet production. It also outlines common uses of aluminum in transportation, construction, packaging, and electrical sectors.
Corrosion Chemistry : Its Causes and RemedyArijitDhali
This Conceptual Power Point project consists of a grieve description about the science of Corrosion, perfect for covering whole topic for short period of time. The project consists of basic knowledge regarding corrosion, its type of causes that is dry and wet corrosion. It also summarizes about different types of differential corrosion and its remedies. Its allover a good conceptual ppt for students of chemistry in their prelims. It's good for the ones achieving for engineering degrees.
Its Is The Process By Which A Iron Nail Is Been Coated With Copper Plate.Electroplating is a process that uses electrical current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode. The term is also used for electrical oxidation of anions onto a solid substrate, as in the formation silver chloride on silver wire to make silver/silver-chloride electrodes. Electroplating is primarily used to change the surface properties of an object (e.g. abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.), but may also be used to build up thickness on undersized parts or to form objects by electroforming.
The process used in electroplating is called electrodeposition. It is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit. In one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that comprise it and allowing them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, vis-a-vis the current flowing through the circuit. In this manner, the ions in the electrolyte bath are continuously replenished by the anode.[1]
Other electroplating processes may use a non-consumable anode such as lead or carbon. In these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution.[2] The most common form of electroplating is used for creating coins such as pennies, which are small zinc plates covered in a layer of copper. [3]Process[edit]
Electroplating of a metal (Me) with copper in a copper sulfate bath
The cations associate with the anions in the solution. These cations are reduced at the cathode to deposit in the metallic, zero valence state. For example, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO42- in the solution to form copper sulfate. At the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result is the effective transfer of copper from the anode source to a plate covering the cathode.
The plating is most commonly a single metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder.
Corrosion is the degradation of materials due to reaction with the environment. It affects metals, non-metals, and living tissues, causing damage like material loss and increased costs. Proper material selection, design modifications, environmental control, and protective coatings or cathodic protection can prevent a majority of corrosion damage and reduce annual economic losses estimated to be 3-5% of global GDP.
This document discusses corrosion and methods for corrosion control. Corrosion is defined as the conversion of metals into compounds through natural means like rusting of iron. It occurs through the formation of oxides on metal surfaces or through electrolytic reactions between cathode and anode areas on a metal surface when in contact with electrolytes like water. Common methods to protect ferrous metals from corrosion include electroplating to apply protective chromium or nickel coatings, galvanizing to coat metals with zinc, tin plating through hot dipping in molten tin, metal spraying to apply thin zinc, tin or aluminum coatings using fuel gases, and painting with high quality paint after cleaning metal surfaces.
This very short document appears to be about a topic called "Ohmic Heating" but provides no details about the subject. It includes a course code "OBT554" and mentions "Unit 3" but does not contain any meaningful or essential information that could be summarized in 3 sentences or less.
Pharmaceutical Engineering, Are the branch of Pharmaceutics which deals with Some metals and their properties.
I Hope it make to easy the study of pharmaceutics.
Here I'm Rahul Pal sharing this documents.
The document discusses materials science and engineering, specifically focusing on the production of iron and steel. It begins with an introduction to materials science and engineering. It then describes the production process of pig iron, including raw material procurement, blast furnace production, and products. It further discusses various steel production methods like basic oxygen furnace and electric arc furnace production. Continuous casting and different steel products are also outlined. In summary, the document provides an overview of the key industrial processes for producing iron and steel, from raw materials to final products.
Factors affecting corrosion on the basis of nature of the metal and Nature of Corroding medium, Protection from corrosion in reference to Sacrificial protection, Cathodic protection, Metallic coatings, Organic coatings, Proper designing.
Hydrogen, the most abundant element in the universe and the third most abundant on the surface of the globe.
All you have to know about this inflammable gas.
This document discusses different theories and types of corrosion. It begins by introducing corrosion as the formation of compounds on a metal's surface through chemical reaction with its environment. It then summarizes three main theories of corrosion: (1) the acid theory involving reaction with carbon dioxide, moisture and oxygen; (2) the chemical theory involving direct reaction with gases like oxygen; and (3) the electrochemical theory involving the formation of anodes and cathodes when a metal is in contact with a conducting liquid. The document goes on to describe eight common types of corrosion in more detail.
This document discusses refrigeration and air conditioning systems. It describes four main types of refrigeration: vapor compression, vapor absorption, magnetic, and industrial. It explains the basic refrigeration cycle for vapor compression and vapor absorption. It then discusses four main types of air conditioning systems: window, split, centralized, and packaged. It provides diagrams to illustrate the components and processes for each system type. In conclusion, it states that refrigerators use two compartments to keep items either frozen or refrigerated to prolong their usable life.
RAC systems are used for various applications like refrigerators, water coolers, dairies, food preservation, and air conditioning. Refrigerators use insulation and thermostats to maintain temperatures between 0-4°C for food storage. Water coolers provide cool water at a constant temperature regardless of ambient conditions using thermostatic switches. Dairies use refrigeration for pasteurization and cooling of milk and cheese production. Cold storage facilities preserve processed foods at positive or sub-zero temperatures using insulated panels and temperature/humidity control. Large buildings use central air conditioning systems with ductwork while smaller spaces use packaged or split units.
This document provides information on different types of materials, focusing on metals. It classifies materials into metals, polymers, and ceramics. Within metals, it distinguishes between ferrous metals which contain iron and non-ferrous metals which do not. Specific ferrous metals discussed include various grades of steel classified based on their carbon content. Alloy steels are also introduced. Common alloys of steel like stainless steel, nickel steel, and Invar steel are summarized in terms of their composition and properties. End uses of alloys are also briefly covered.
Corrosion is the destruction or deterioration of metallic materials due to chemical and electrochemical reactions with their environment. There are two main types of corrosion - dry corrosion caused by direct chemical reactions with gases, and wet corrosion caused by electrochemical reactions when metals are in contact with an electrolyte. Various factors influence the corrosion rate, including the metal properties, environmental conditions, and nature of corrosion products. Common corrosion control methods include cathodic protection, using corrosion inhibitors, and applying protective coatings to the metal surface.
This document provides an overview of corrosion and energy storage systems. It discusses various types of corrosion including dry corrosion, wet corrosion, pitting corrosion, intergranular corrosion, galvanic corrosion and stress corrosion. It also discusses corrosion control methods like material selection, cathodic protection and protective coatings. The document then discusses basic principles of batteries and provides examples of lithium-ion batteries and nickel-cadmium batteries.
The document discusses corrosion of metals. It defines corrosion as the deterioration of metals through reaction with their environment. It outlines several theories of corrosion including acid theory, chemical corrosion, and electrochemical corrosion. It describes different types of corrosion such as galvanic, pitting, and intergranular corrosion. Factors that influence corrosion are also discussed, such as the metal's purity, position in the galvanic series, and properties of any oxide film or corrosion products formed. Control methods to prevent corrosion are also mentioned.
The document discusses corrosion of metals. It defines corrosion as the deterioration of metals through reaction with their environment. It outlines several theories of corrosion including acid theory, chemical corrosion, and electrochemical corrosion. It describes different types of corrosion such as galvanic, pitting, and intergranular corrosion. Factors that influence corrosion are also discussed, such as the metal's purity, position in the galvanic series, and properties of any oxide film or corrosion products formed. The document outlines corrosion reactions and control methods to prevent corrosion damage to metals.
The document discusses corrosion of metals. It defines corrosion as the deterioration of metals through reaction with their environment. It outlines several theories of corrosion including acid theory, chemical corrosion, and electrochemical corrosion. It describes different types of corrosion such as galvanic, pitting, and intergranular corrosion. Factors that influence corrosion are also discussed, such as the metal's purity, position in the galvanic series, and properties of any oxide film or corrosion products formed. The document outlines corrosion reactions and control methods to prevent corrosion damage to metals.
1. Dry or chemical corrosion occurs via direct chemical reaction between a metal surface and gases in the atmosphere like oxygen, carbon dioxide, hydrogen sulfide, and sulfur dioxide. It involves adsorption of gas molecules on the metal surface.
2. The mechanism of dry corrosion involves oxidation of the metal surface and reduction of gas molecules, forming a metal oxide layer. The nature and properties of this oxide layer determines whether it is protective or porous.
3. According to the Pilling-Bedworth rule, a protective oxide layer has a volume equal to or greater than the original metal, while a porous layer has a smaller volume, allowing further corrosion. Metals like chromium and aluminum form protective passive layers contributing to corrosion resistance.
1. The document discusses corrosion of metals, including definitions, types (chemical and electrochemical), and causes.
2. Chemical or dry corrosion is caused by direct chemical attack from gases like oxygen, leading to oxidation. Electrochemical or wet corrosion occurs via formation of anodic and cathodic areas when a metal is in contact with an electrolyte.
3. Factors like the nature of oxide layers formed and Pilling-Bedworth ratio determine if oxidation causes a protective or non-protective layer. Hydrogen can also cause embrittlement or decarburization of steel.
This document defines corrosion as the deterioration of a material due to reaction with its environment, especially oxygen. Corrosion is an electrochemical process that occurs when a metal is exposed to oxygen and an electrolyte like water. Three factors are required for corrosion: a metal, oxygen, and an electrolyte. Corrosion causes deterioration of manufactured products and infrastructure. Understanding and preventing corrosion is important for maintaining machinery and structures. Corrosion occurs through oxidation and reduction reactions and can be localized or generalized. Methods to prevent corrosion include painting, sacrificial anodes, cathodic protection, and passivation.
The document discusses corrosion and its causes. Corrosion occurs via chemical or electrochemical reactions between a metal and its environment that cause deterioration. It can be caused by oxygen, hydrogen, electrical currents, stress, or bacteria. Corrosion occurs via dry/chemical reactions directly with gases or wet/electrochemical reactions in an electrolyte that form anodes and cathodes. The rate depends on factors like the metal's position in the galvanic series and properties of any surface oxide or corrosion product layer.
The document discusses theories of corrosion. It describes dry or chemical corrosion which occurs via direct chemical reaction with gases like oxygen. It forms metal oxides. The nature of the oxide film determines if corrosion continues or stops. It also describes wet or electrochemical corrosion which involves the formation of a galvanic cell and oxidation of the anode and reduction at the cathode. Common types of corrosion discussed are galvanic, pitting, and waterline corrosion.
The document discusses corrosion of metals and its various types. It defines corrosion as the deterioration of metal due to chemical reactions with the environment. Corrosion occurs via oxidation and causes metal loss. The main factors influencing corrosion are the metal composition, environmental chemicals, temperature, and design. Corrosion can be uniform, galvanic, pitting, intergranular or stress-related. Electrochemical corrosion involves the formation of anodes and cathodes on a metal surface.
This document discusses corrosion engineering and provides details on various corrosion topics. It begins with an introduction to corrosion and defines it as the deterioration of metal through chemical or electrochemical reactions with the environment. Some key points covered include:
- Corrosion costs the US economy $300 billion per year. Common examples of corrosion are rusting of iron when exposed to air and the formation of a green or blue film on copper in moist air.
- An electrochemical cell converts chemical energy of an indirect redox reaction into electrical energy. During corrosion, the metal being corroded acts as the anode and loses electrons/dissolves while another metal acts as the cathode and gains electrons.
- The main types of corrosion
I/II SEM BE, VTU, ENGINEERING CHEMISTRY , Module 2rashmi m rashmi
1. The document discusses various types of corrosion including dry corrosion, wet corrosion, differential metal corrosion, differential aeration corrosion, pitting corrosion, stress corrosion, and water line corrosion.
2. It explains the electrochemical theory of corrosion and factors that affect the rate of corrosion such as the nature of the metal, corrosion product, potential difference, anodic/cathodic areas, pH, temperature, and conductivity.
3. Methods of corrosion control discussed are anodizing, phosphating, galvanization, and tinning which involve coating metals with protective layers to prevent corrosion. Anodizing forms a protective aluminum oxide layer while galvanization coats iron with zinc and tinning coats iron with tin.
1. Corrosion is the deterioration and loss of solid metallic material by chemical or electrochemical attack by its environment.
2. There are two main types of corrosion: dry/chemical corrosion which occurs through direct chemical action, and wet/electrochemical corrosion which occurs when a conducting liquid is in contact with the metal.
3. Wet corrosion occurs via separate anodic and cathodic reactions - the anodic reaction involves metal dissolution or compound formation, while the cathodic reaction involves hydrogen evolution in acidic environments or oxygen absorption in basic environments.
EC-CDT-Unit-2; Corrosion and types of corrosionb23me005
Wet or electrochemical corrosion occurs when a metal is in contact with a conducting liquid or two dissimilar metals touch in a conducting liquid. It involves the formation of anodic and cathodic areas, with corrosion occurring at the anode. There are two main types: hydrogen evolution in acidic environments, and oxygen absorption in neutral environments. For hydrogen evolution, oxidation occurs at the anode and hydrogen gas forms at the cathode. For oxygen absorption, oxidation still occurs at the anode while oxygen is reduced at the cathode, forming metal oxides or hydroxides as corrosion products.
Video lecture is available on YouTube on the link:https://youtu.be/xrBnxxN-RUw
For UG students of All Engineering Branches, Chemistry, Food Science, Polymer Science, Chemical Engg. etc.
This document discusses corrosion and how it affects metals. It defines corrosion as the slow process of decay of metals due to chemical or electrochemical reaction with their environment. This causes the formation of compounds like oxides on the metal surface. Corrosion occurs through both dry chemical reactions and wet electrochemical reactions that set up galvanic cells. The rate of corrosion is affected by factors like the metal's position in the galvanic series, purity, environment, and characteristics of the corrosion products formed. Common types of corrosion discussed are rusting of iron and methods to prevent or reduce corrosion like coatings, cathodic protection, and modifying the environment.
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2. UNIT – II Corrosion and its control and its Control
Methods
Corrosion: Introduction - chemical corrosion – Pilling-Bedworth rule –
electrochemical corrosion and it's types – galvanic corrosion– differential
aeration corrosion with examples - galvanic series - factors influencing rate of
corrosion – measurement of corrosion (wt. loss method only). Control
methods – sacrificial anodic protection method - corrosion inhibitors -
protective coatings - pretreatment of metal surface – metallic coating:
electroplating, electroless plating and hot dipping (tinning and galvanizing)
methods – non-metallic coating: anodizing - organic coating: paints,
constituents and functions - ceramic coatings.
3. The serious consequences of the corrosion process have become
a problem of worldwide significance.
In addition to our everyday encounters with this form of
degradation, corrosion causes plant shutdowns, waste of valuable
resources, loss or contamination of product, reduction in eficiency,
costly maintenance and expensive overdesign.
Humans have most likely been trying to understand and control
corrosion for as long as they have been using metal objects. The
most important periods of pre-recorded history are named for the
metals that were used for tools and weapons (Iron Age, Bronze
Age). With a few exceptions, metals are unstable in ordinary
aqueous environments.
Corrosion
4. Corrosion has been defined as a
destructive chemical and
electrochemical reaction of a metal with
its environment (like O2, moisture, CO2
etc.) which disfigures metallic products
leading to reduction in their thickness
and also causes loss of useful
properties such as malleability, ductility,
electrical conductivity and optical
refractivity. Except few metals such as
gold, platinum (called noble metal) are
prone to corrosion.
5. Metals are electropositive in nature. Except few metals like gold, platinum (noble metal)
other metals are found in nature as their compounds (such as oxides, hydroxides,
carbonates, chlorides, sulphides, phosphates, silicates etc.) which are called their ore.
Metals are thus obtained by extraction from their ores by reduction process.
In nature, when metals exists as their compounds (or ore) they are stable and they are in
the low energy states.
However, during extraction of metals from their ores, free metals are become less stable
and are in the higher energy state than in the ionic state.
So, metals have a tendency to back to the ionic state and hence metal atoms are prone to
get attacked by environment .
This is the main reason for corrosion of metals.
Metal
(M)
Mineral
or
ore (Mn+
)
Corrosion
product
(Mn+
)
Extraction
by reduction
+ ne
Corrosion
-ne
6. Types Of Corrosion
Dry or Chemical Corrosion
It involves direct chemical attack of atmospheric gases like
CO2, O2, H2S, SO2, halogen, moisture and inorganic acid vapours
on metal. Ex. Turnishing of silver ware in H2S laden air.
This can be classified as
a. Corrosion by oxygen
b. Corrosion by other gases
c. Liquid –Metal corrosion
Wet or Electrochemical Corrosion
It occurs due to setting up of a large number of tiny galvanic cells
in metals in presence of an impurity as well as in presence of
moisture. Generally impurity (more active metal) act as anode and
original metal act as cathode. so anode is the area where
corrosion occurs. Ex: Rusting of iron in moist atmosphere.
This can be classified as
a. Galvanic corrosion
b. Concentration Cell Corrosion or Differential aeration corrosion
7. Types of dry corrosion
I. Oxidation corrosion
Due to direct chemical reaction of atm. O2 with metal surface forming metal oxide
Absence of moisture
Increases with increase in temperature.
Mechanism
on exposure to atm., metal gets oxidized to form metal ions
M M2+ + 2e-
Electrons lost by metal are taken up by oxygen to forms oxide ions
1/2O2 + 2e- O2-
M + 1/2O2 2M2+ + O2- MO
Metal Oxide
8. Types of metal oxide film
I. Stable film II. Unstable film
III. Volatile film IV. Porous film
I. Stable film
Fine grained structure
Formation of Oxide films are impervious in nature
Stop further oxygen attack
Stable film acts as a protective coating. Eg: Al, Pb, Cu, Sn
II. Unstable film
Film produced on the surface of noble metals.
Which decompose reversibly to the metal and the oxide which is liberated in the
form of oxygen.
Here corrosion is a continuous process. Eg: Ag, Au, Pt.
III. Volatile film
The oxide layers formed in some cases is volatile.
Oxide film volatilizes as soon as it is formed.
The fresh metal surface is kept exposed all the time for further attack.
Thus it act as a nonprotective coating. Eg: MoO3 (Molybdenum oxide film)
9. IV. Porous film
The oxide layers formed in some cases have pores or cracks.
The atmospheric oxygen can easily move into the metal surface through
pores of the layer.
So corrosion is a continuous process. Eg: Alkali metals & alkaline earth metals.
Pilling – Bed Worth Rule
Specific Volume Ratio = Volume of oxide formed
Volume of metal
A protective and Non-Porous metal oxide layer has volume equal to or greater than
the volume of metal from which it is formed. Ex: Oxides of Al, Sn, Pb, Cu, etc.
A Non-Protective and Porous metal oxide layer has volume lesser than the volume of metal
from which it is formed. Ex: Oxides of Li, Na, K, Mg, Ca, Sr, etc.
10. Types of dry corrosion
II. Corrosion by Other Gases
Other gases such as Cl2,SO2,H2S,F2,CO2 & NOX. In dry atmosphere
these gases react with metal and form corrosion products.
2AgCl + Cl2 AgCl
(Non-Porous layer)
Sn + 2Cl2 SnCl4
(Volatile Layer)
Hydrogen Embrittlement (or) Hydrogen Corrosion
At high temperature
Fe + H2S FeS + 2H
[H] + [H] H2
FeS is a Porous Layer and corrosion is a continuous process.
Atomic hydrogen penetrates and occupies the voids of the metal. Then
develops pressure which leads to cracking of the metal.
This is known as Hydrogen Embrittlement (or) Hydrogen Corrosion
11. Decarburisation
Atomic hydrogen is highly reactive and combine with Carbon present in metal forming
CH4 gas which leads to cracking of the metal surface.
The process of decrease in carbon content in steel is known as decarburation of steel.
C + H CH4
III. Liquid Metal Corrosion
Occurs due to the action of flowing liquid metal at high temp on solid metals
or alloys.
As a result of this corrosion, solid metal becomes weak because it
involves either
Dissolution of a solid metal by a liquid metal (or)
Due to the penetration of the liquid metal into the solid metal
Observed in Nuclear power plant. In nuclear reaction where Na metal used as a
coolant leads to corrosion of Cd.
12. Wet or Electrochemical or Immersed Corrosion
Occurs
When a metal is contact with moist air or any liquid medium
When two diff. metals are partially immersed in a soln.
Chemically non- uniform surfaces of metals behave like electrochemical cells
in the presence of water containing dissolved O2 & CO2
Always occurs at anodic areas
Mechanism
Involves oxidation- reduction process
depending on the nature of corroding enviornment, electrons released at anode are
consumed at the cathodic area by two ways:
Evolution of H2
Absorption of O2
13. Hydrogen evolution Mechanism
This types of corrosion takes place when base metals are in contact
with acidic solutions or the solutions are completely free from
dissolved oxygen.
All metals above hydrogen in the electrochemical series have a
tendency to get dissolved in acidic solution with simultaneous evolution
of hydrogen gas.
Anode :
Fe Fe2+ + 2e- (Oxidation)
Cathode :
2H+ + 2e- H2 (g) (Reduction)
Over all Rxn :
Fe + 2H+ 2Fe2+ + H2 (g)
14. Oxygen Absorption Mechanism
Base metal are in contact with neutral, aqueous or slightly alkaline solution with
some amount of dissolved oxygen.
Anode :
Fe Fe2+ + 2e- (Oxidation)
Cathode :
1/2O2 + 2e- + 2H2O 2OH- (Reduction)
Over all rxn:
Fe + H2O + 1/2O2 Fe2+ + 2OH- Fe(OH)2
4Fe(OH)2 + O2 + 2H2O 4Fe(OH)3 (OR) Fe2O3.3H2O
15. Difference Between Dry and Wet Corrosion
Dry Corrosion Wet Corrosion
Occurs in the absence of moisture Occurs in the presence of conducting
medium
Involves direct attack of chemicals on
the metal surface
Involves formation of electrochemical cells
Slow process Rapid process
Corrosion products are produced at
the site of corrosion
Corrosion occurs at anode but product is
deposited at cathode
Process of corrosion is uniform
Eg: Tarnishing of Silver
Depends on the size of the anodic part of
the metal
Eg: Rusting of Iron
16. Types of Electrochemical Corrosion
Galvanic (Bimetallic) Cell Corrosion.
Concentration cell corrosion (or) Differential aeration corrosion.
Galvanic (Bimetallic) Cell Corrosion:
Galvanic Corrosion occurs at
Electrochemically dissimilar metals must be present.
These metals must be an electrical contact .
The metals must be exposed to an electrolyte.
The metals higher in electrochemical series act as the anode and dissolves into the
solution and the metal lower in the electrochemical series acts as the cathode.
Cathodic reaction
1. Electrolyte in the acidic medium- Evolution of Hydrogen Gas
2. Electrolyte in the Neutral (or) Alkaline medium – Absorption of oxygen
17. Measures to prevent Galavanic Corrosion
When joining two dissimilar metals together, galvanic corrosion can be
prevented by insulating the two materials from each other. Ex: when bolting
flanges of dissimilar metals together, plastic washers can be used to separate
the two metals.
Do not couple metals that are far apart in the galvanic series.
Avoid small anode–large cathode combinations.
Any coating being applied should be applied to the cathodic member and
not to the anodic member. This is to prevent an unfavorable anode/cathode
ratio.
Anodic parts may be made thicker to provide a longer life.
A sacrificial metal may be installed that would be anodic to both metals.
18. Concentration Cell Corrosion or
Differential Aeration Corrosion
Occurs due to diff. in potential between differently aerated areas.
Part of metal exposed to air is more oxygenated part & acts as cathode
Part of metal immersed in electrolyte is poorly oxygenated & acts as anode
Types of Differential Aeration Corrosion
Pitting Corrosion
Pipeline Corrosion
Crevice Corrosion
Corrosion on wire fence
19. Pitting Corrosion
Pitting corrosion is a localized form of corrosion by which cavities or
"holes" are produced in the material. Pitting is considered to be more
dangerous than uniform corrosion damage because it is more difficult to
detect, predict and design against. Corrosion products often cover the pits.
20. Pipeline corrosion
Pipeline corrosion is the oxidisation and
electrochemical breakdown of the structure of a pipe
used to convey any substance. Pipeline corrosion occurs
on both the inside and outside of any pipe and related
structures, exposed to corrosive elements. Many
different types of corrosion can develop in pipelines.
Crevice Corrosion
Crevice Corrosion refers to the localized
attack on a metal surface at, or immediately adjacent
to, the gap or crevice between two joining surfaces.
The gap or crevice can be formed between two metals
or a metal and non-metallic material.
21. Corrosion on wire fence
The areas where the wires cross are less
aerated than the other parts of the fence. The
corrosion takes place at the wire crossings
because the less aerated part act as anode.
Stress corrosion
Stress corrosion is another form of
corrosion that is important to many fields
including civil structures. Stress-corrosion
occurs when a material exists in a relatively
inert environment but corrodes due to an
applied stress. The stress may be externally
applied or residual.
22. Galvanic Series
The series prepared by studying the corrosion of metals
and alloys in a given environment like sea water
The oxidation potential of different metals and alloys
are determined at 25°C and tabulated in the descending
order. Metals occupying higher positions in the series
undergo corrosion in a vigorous manner.
Need for Galvanic series
Electrochemical series does not account for the
corrosion of all metals and alloys.
Ex: Zn/Al couple
Zn (below Al in the EMF series) is corroded
While Al acts as cathode and protected.
23. Electrochemical Series Galvanic Series
The arrangement of metals and non-
metals in increasing order of their
standard reduction potential on the
hydrogen scale
The arrangement of metals and alloys in
decreasing order of their standard oxidation
potential in an unpolluted water
It contains metals and non-metals It contains metals and alloys
Position of metals is fixed Position of metals is not fixed
It gives no information regarding the
position of alloys
It includes alloys and gives the information
of corrosion behaviour
It predicts the relative displacement
tendencies
It predicts the relative corrosion tendencies
Difference between Electrochemical and Galvanic series
24. Factors influencing rate of corrosion
The nature and extent of corrosion depend on the metal and environment.
The important factors which may influence the rate of corrosion are
I.Nature of Metal
a. Position of metal in galvanic series
Metal higher up in the galvanic series becomes anodic and undergoes corrosion
b. Relative areas of anode and cathode
large cathodic area and small anodic area leads severe corrosion
c. Overpotential
Corrosion rate α 1/ overvoltage of metal
d. Nature of surface film
Specific Volume Ratio = Volume of oxide formed
Volume of metal
If SVR > 1; film is nonporous and protects metal from corrosion
if SVR < 1; film is porous and increases the corrosion rate
25. e. Purity of metal
Impurity creates heterogeneity and leads galvanic corrosion
f. Stress
The metal part under stress become anode and undergoes stress corrosion
II. Nature of Environment
a. Temperature
Corrosion rate increases with temperature
b. Humidity
Humidity-concentration of water vapour in the atmosphere.
Corrosion rate increases with humidity.
Critical humidity-sudden increase
in the corrosion rate at a particular point
c. Corrosive gases
presence of gases like H2S,SO2 etc., enhances the corrosion rate
d. Suspended Solids
presence of suspended solids in environment enhances the corrosion rate
e. pH
Acidic environment increases corrosion rate than alkaline environment
26. Use of pure metal
Using metal alloys
Proper designing
Anodic Protection
made passivating metal structures
into more anodic
Cathodic Protection
made the metal structure to behave like
cathode
Corrosion can be controlled in two methods
By modifying the environment
By modifying the metal
Use of Inhibitors
1. Anodic inhibitors
2. Cathodic inhibitors
3. Vapour-phase inhibitors (VPI)
Surface Coatings
1. Inorganic coating
2. Organic Coating
3. Ceramic Coating
27. Corrosion control by modifying the metal
1. Selection of the metal
Selection of right type of metal is the main factor for corrosion control.
Eg: Noble metals that are immune to corrosion are used for
producing ornaments and surgical instruments.
Presence of impurities in a metal cause heterogeneity and decreases the
corrosion–resistance of the metal.
Eg: Presence of just 0.02% of iron in aluminium decreases its corrosion
resistance.
2. Using pure metal:
3. Using metal alloys:
Corrosion resistance can be improved by alloying the metal with suitable metal.
Eg: Presence of chromium in stainless steel produces a protective oxide film.
28. Corrosion Control by modifying the design
Metallic materials should be designed in such a way to resist corrosion
Important Design Principles:
The contact of two dissimilar metals in the presence of the corroding solution
should always be avoided, otherwise the more active metal will act as anode and
corrosion will be localized.
If the contact between two dissimilar metals is unavoidable two metals are chosen
in such a way that the anodic metal should be as large as possible and cathodic
metal should be as small as possible.
Large
Cathode
(Steel)
Small Anode
(Aluminium)
e-n flow
Severe Corrosion
Large Anode
(Aluminium)
Small
Cathode
(Steel)
e-n
flow
Negligible Corrosion
29. The (contacting) two dissimilar metals should possess close positions in the EMF series.
If direct contact is not possible to avoid, the metals can be insulated
well before connecting to avoid the direct electric contact of metals.
The design should provide easy cleaning and flushing of the corner
and bends in the metallic equipment.
i.e. Sharp corners and recess should be avoided.
Important Design Principles:
30. Avoid angles and pockets in
which water can collect.
The risk of dirt build-up is reduced
with radiused corners.
Important Design Principles:
31. Corrosion control by modifying the environment
Corrosion Inhibitors:
Substance which on addition in small quantities to the corrosive environment
reduces the corrosion of metal is called inhibitors.
Types of Inhibitors: 1. Anodic inhibitors
2. Cathodic inhibitors
3. Vapour-phase inhibitors (VPI)
1. Anodic inhibitors:
Chemicals like chromates, phosphates, tungstates, when added to corrosive
environment produces sparingly soluble compounds by reacting with metal
ions (produced because of corrosion).
The sparingly soluble compounds get absorbed on the metal surface forms a
protective film and thereby reduces corrosion rate.
This type of corrosion control is not fully reliable because, certain areas of
metal are not covered by the film and this leads to severe corrosion.
32. 2. Cathodic inhibitors:
In acidic solution, the main cathodic reaction is liberation of H2.
In an acidic solution, the corrosion can be controlled by slowing down the
diffusion of H+ ions through the cathode. This can be done by adding organic
inhibitors like amines, pyridine, etc. They absorb over the cathodic metal surface and
act as a protective layer.
In a neutral solution, the cathodic reaction is,
The formation of ions is only due to the presence of oxygen. By eliminating the
oxygen from the medium, the corrosion rate can be reduced. Oxygen can be
removed by adding some reducing agents like Na2SO3 or by deaeration.
2
2H 2e H
aq g
2 2
1
H O O 2e 2OH
2
33. The common and oldest method of protection of a metal from its
surroundings is by surface coatings
Metallic surface can be protected from corrosion by covering it by
organic or inorganic coating.
3. Vapour-Phase Inhibitors(VPI)
This type of inhibitors are organic inhibitors, which readily vaporize and
form a protective layer on the metal surface. VPI is used to avoid
corrosion in closed spaces, storage containers, packing materials, etc.,
Ex. Phenyl thiourea
Protective Coatings
Used to protect the metals from corrosion
Used for decorative purpose
They also impart some special properties like hardness, electrical
properties, thermal insulating properties
34. Protective Coatings
Inorganic coatings
Organic coatings
Nonmetallic coatings
Metallic coatings
Hot dipping
a. Galvanizing
b. Tinning
Anodising Paints
Ceramic coatings
Requirements for protection
Coating applied must be chemically inert to the environment
Coatings must prevent the penetration of the environment
35. Pre-treatment of metal surface
I. Mechanical Cleaning : Removes loose rust, oxide scales, dirt – by using bristle
brush/sand paper/detergents like soap.
Sand Blasting: sand of different grain size were blasted on the metal surface
with pressure of 25 to 100 atm
I . Mechanical Method
II . Chemical Method
Solvent Cleaning
Alkali Cleaning
Acid Pickling
III. Electrochemical Method
36. 1. Alkali Cleaning
Removes old paint – alkali cleansing
agents like trisodium phosphate along
with soaps and wetting agents
2. Acid Cleaning
II. Chemical Cleaning :
Flame Cleaning:
Removes loosely adhering scales –
heating the metal surface with hot flame
followed by wire brush
Pickling and etching: Removes scales which are adherent -
metals except aluminium are immersed in acid pickling solution
37. 3. Solvent cleaning
Removes oils, grease and fatty substances by the organic solvents like naphtha,
CCl4, toluene, acetone. Then the metal surface is cleaned with steam and hot
water containing wetting reagents
2. Acid Cleaning
38. Hot dipping:
It is a process of producing a coating of low melting point metals
such as Zn, Sn, pb ,Al, etc., over the surface of Fe, steel, copper
which have high melting points
The process involves immersion of a metal in a bath of its molten
coating & covered by a molten layer.
The flux cleans the base metal & prevent oxidation of metal
coating with molten solution.
Hot dipping is widely applied either by
Galvanizing (coating of Zn on Fe or steel)
Tinning (coating of Sn on Fe or steel)
Protective Coatings
I. Metallic Coatings
39. It is the process in which iron or steel is protected from corrosion by coating
with a thin layer of zinc.
Galvanization Process
The base metal iron or steel is cleaned by acid pickling with dil. H2SO4 for
15-20 min at a temperature of 60 - 900C
Sheet is then washed and dried
It is dipped in a bath of molten zinc maintained at 425°C – 430°C
The surface of the bath is covered with ammonium chloride flux to prevent oxide formation
Sheet is taken out and excess zinc is removed by passing it between a pair of hot rollers
Sheet is subjected to annealing process at 650°C and cooled slowly
An alloy of zinc and iron are formed at the junction of the base metal and coating metal
It is used to protect Iron used for roofing sheets, wires, pipes, nails, bolts, screws, buckets
and tubes.
Defects : Galvanized utensils are not used for cooking because of solubility of Zn.
41. Tinning Process
Tinning is the process of coating of tin over the Iron sheet or steel
articles
A pre-treated cleaned iron sheet is passed through a bath of molten
flux then passes through a tank of molten tin
Finally through a layer of palm oil which protect hot tin coated
surface against oxidation.
Uses: It is widely used for coating of steel, copper, brass &
bronze etc.
It is used to store food stuff, ghee oils, kerosene, pickles and used
for refrigerators equipment.
43. Protective Coatings
II. Nonmetallic Coatings - Anodising
It is an electrochemical process in which an oxide Layer
is chemically built on the surface of the metal
Process converts the metal surface into a decorative,
durable, corrosion resistant and anodic oxide finish
Aluminium Anodizing
Anode: Al (base metal)
Cathode: Inert material of good conductivity
Electrolyte: Sulphuric acid, chromic acid
Temperature: 35 - 40°C
On electrolysis , O2 liberated at the anode combines
with Al to form oxide film. Outer part of film is very
porous and prone to corrosion. Hence it has to be
sealed by treatment with hot water /steam.
Applications: Aircraft parts, refrigerators, windows,etc.,
44. Organic coatings - Paints
Paint is mixer of one or more finely divided components in a medium (thinner + vehicle)
When paint is applied to a metal surface the thinner evaporates, while vehicle
undergoes slow oxidation forms a film
The important constituents of paints are
1. Pigments
It’s a solid substance which imparts desired color to the paint
protects from UV light
provide strength and increase whether resistance of the film. Ex. Pb,ZnO - white colour
2. Thinner or Solvent
It’s a volatle portion and easily evaportaes
Used to dilute the paint and reduces the viscosity
Dissolves all the components of paints. Ex. Kerosene, alcohol
3. Vehicle or drying oil
it’s a nonvolatile component and film forming material
it imparts water repellency. Durability and toughness to the film. Ex. Castor oil, coconut oil
4. Driers
Act as catalysts and increase the rate of drying process. Ex. Borates
45. 5. Antiskinning agent
Prevents skinning of the paint. Ex. Polyhydroxy phenol
6. Plasticizers
Increase the elasticity of the film and minimize its cracking. Ex. Triphenyl phosphate
7. Fillers
increase the volume of the paint and reduces the cost
Fill the voids in the film and prevents shrinkage. Ex. China clay, asbestos
Protective coatings - Ceramic coatings
A ceramic is a liquid polymer that is applied by hand
to the exterior of a vehicle to protect it from external paint damage.
Coating chemically bonds with the surface and
creates a layer of protection
Ceramic coating also called nano-ceramic coating.
Due to its chemically intrinsic properties, it does not
break down in normal atmospheric conditions like
rain or summer.