Materials Processing PDF

1 LEARNING GUIDE Week No.: __10__...

1 LEARNING GUIDE Week No.: __10__ TOPIC: MATERIALS PROCESSING EXPECTED COMPETENCIES 1. Explain different mechanical properties 2. Familiarize metal alloys and how it is produced 3. Define and explain annealing process 4. Describe precipitation hardening CONTENT/TECHNICAL INFORMATION A. Mechanical properties of a material The mechanical properties of a material are those which affect the mechanical strength and ability of a material to be molded in suitable shape. Strength It is the property of a material which opposes the deformation or breakdown of material in presence of external forces or load. Materials which we finalize for our engineering products, must have suitable mechanical strength to be capable to work under different mechanical forces or loads. Toughness It is the ability of a material to absorb the energy and gets plastically deformed without fracturing. Its numerical value is determined by the amount of energy per unit volume. Its unit is Joule/ m3. Value of toughness of a material can be determined by stress-strain characteristics of a material. For good toughness, materials should have good strength as well as ductility. For example: brittle materials, having good strength but limited ductility are not tough enough. Conversely, materials having good ductility but low strength are also not tough enough. Therefore, to be tough, a material should be capable to withstand both high stress and strain. Hardness It is the ability of a material to resist to permanent shape change due to external stress. There are various measure of hardness – Scratch Hardness, Indentation Hardness and Rebound Hardness. 1. Scratch Hardness - is the ability of materials to the oppose the scratches to outer surface layer due to external force. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  2 2. Indentation Hardness - It is the ability of materials to oppose the dent due to punch of external hard and sharp objects. 3. Rebound Hardness - is also called as dynamic hardness. It is determined by the height of “bounce” of a diamond tipped hammer dropped from a fixed height on the material. Hardenability It is the ability of a material to attain the hardness by heat treatment processing. It is determined by the depth up to which the material becomes hard. The SI unit of hardenability is meter (similar to length). Hardenability of material is inversely proportional to the weld- ability of material. Brittleness Brittleness of a material indicates that how easily it gets fractured when it is subjected to a force or load. When a brittle material is subjected to a stress it observes very less energy and gets fractures without significant strain. Brittleness is converse to ductility of material. Brittleness of material is temperature dependent. Some metals which are ductile at normal temperature become brittle at low temperature. Malleability Malleability is a property of solid materials which indicates that how easily a material gets deformed under compressive stress. Malleability is often categorized by the ability of material to be formed in the form of a thin sheet by hammering or rolling. This mechanical property is an aspect of plasticity of material. Malleability of material is temperature dependent. With rise in temperature, the malleability of material increases. Ductility Ductility is a property of a solid material which indicates that how easily a material gets deformed under tensile stress. Ductility is often categorized by the ability of material to get stretched into a wire by pulling or drawing. This mechanical property is also an aspect of plasticity of material and is temperature dependent. With rise in temperature, the ductility of material increases. Creep and Slip Creep is the property of a material which indicates the tendency of material to move slowly and deform permanently under the influence of external mechanical stress. It results due to long time exposure to large external mechanical stress with in limit of yielding. Creep is more severe in material that are subjected to heat for long time. Slip in material is a plane with high density of atoms. Resilience Resilience is the ability of material to absorb the energy when it is deformed elastically by applying stress and release the energy when stress is removed. Proof resilience is defined as This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  3 the maximum energy that can be absorbed without permanent deformation. The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without permanent deformation. It can be determined by integrating the stress-strain cure from zero to elastic limit. Its unit is joule/m3. Fatigue Fatigue is the weakening of material caused by the repeated loading of the material. When a material is subjected to cyclic loading, and loading greater than certain threshold value but much below the strength of material (ultimate tensile strength limit or yield stress limit), microscopic cracks begin to form at grain boundaries and interfaces. Eventually the crack reaches to a critical size. This crack propagates suddenly and the structure gets fractured. The shape of structure affects the fatigue very much. Square holes and sharp corners lead to elevated stresses where the fatigue crack initiates. B. Production of Metal Alloys Alloys are metallic compounds made up of one metal and one or more metal or non-metal elements. Examples of common alloys: Steel: A combination of iron (metal) and carbon (non-metal) Bronze: A combination of copper (metal) and tin (metal) Brass: A mixture of copper (metal) and zinc (metal) 20 COMMON METAL ALLOYS This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  4 This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  5 https://www.visualcapitalist.com/20-common-metal-alloys/ This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  6 1. Heating and Melting Heating and melting is one of the most commonly used methods for creating alloys. The parent metal (the highest % metal in the alloy) is melted down, and any other metals are melted down until they become liquids. Then they’re poured into each other and mixed together, and allowed to cool into something called a “solid solution”. 2. Powder Metallurgy First, the parent metal and the alloying agents need to be turned into powders! There are a few main methods for doing this: The sponge iron process is the oldest of the powderization techniques. The ore is mixed with something called a coke breeze (which is what’s left of coal after you burn it), and lime in order to make a special sulphur that avoids contamination with the powdered parent metal. The coke and lime mixture (not like cocktails!) and the ore are then put into a special drum, the coke and lime sandwiching the ore between it. Then the drum is superheated in a kiln. The ingredients leave behind a “sponge cake” looking object and a slag. In the following steps, the eventual powder is separated from the slag and it’s crushed into a more uniform “powder” shape. The powder is then heated, and super compressed into an alloy! Other ways that the parent metals is turned into a powder is by atomization (almost like nuclear power plants use), where molten metal is pushed through a very narrow tube – which makes it high pressure. A gas is injected into the stream of boiling metal exactly as it comes out from this tube, the combination of the pressure, temperature, and the gas molecules separates the atoms of the metal. The powders are then mixed, and melted together into a “solid solution”! The iron powder created with the sponge iron process is the cheapest on the global market! 3. Ion Implementation The final common method of creating alloys is ion implantation. “Ions” come from electricity, so the ion implantation method involves an “ion source” (which just creates electricity basically), an accelerator where the ions are sped up really really fast (friction, and fast turning creates heat which speeds up molecules), and a target chamber where the ions are tossed after they’re done. The ion implantation method is really best for creating very small pieces of metal. This is the most common method for creating semiconductors on computer chips. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  7 C. Annealing - is a heat treatment process that changes the physical and sometimes also the chemical properties of a material to increase ductility and reduce the hardness to make it more workable. The annealing process requires the material above its recrystallization temperature for a set amount of time before cooling. The cooling rate depends upon the types of metals being annealed. For example, ferrous metals such as steel are usually left to cool down to room temperature in still air while copper, silver and brass can either be slowly cooled in air or quickly quenched in water. The heating process cause atoms to migrate in the crystal lattice and the number of dislocations reduces, which leads to the change in ductility and hardness. The heat treated material recrystallizes as it cools. The crystal grain size and phase composition depend on the heating and cooling rates and these, in turn, determine the material properties. Hot or cold working of the pieces of metal following annealing alters the material structure once more, so further heat treatments may be required to attain the desired properties. However, with knowledge of material composition and phase diagram, heat treating can soften metals and prepare them for further working such as forming, shaping and stamping, as well as preventing brittle failure. How does an Annealing Furnace Work? An annealing furnace works by heating a material above the recrystallization temperature and then cooling the material once it has been held at the desired temperature for a suitable length of time. The material recrystallizes as it cools once the heating process has caused atom movement to redistribute and eradicate dislocations in the workpiece. Annealing works in three stages – the recovery stage, recrystallization stage and the grain growth stage. These work as follows: 1. Recovery Stage This stage is where the furnace or other heating device is used to raise the temperature of the material to such a point that the internal stresses are relieved. 2. Recrystallization Stage Heating the material above its recrystallization temperature but below its melting point causes new grains to form without any residual stresses. 3. Grain Growth Stage Cooling the material at a specific rate causes new grains to develop. After which the material will be more workable. Subsequent operations to alter mechanical properties can be carried out following annealing. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  8 When is Annealing required and Why is it Important? Annealing is used to reverse the effects of work hardening, which can occur during processes such as bending, cold forming or drawing. If the material becomes too hard it can make working impossible or result in cracking. By heating the material above the recrystallization temperature, it is made more ductile and therefore ready to be worked once more. Annealing also removes stresses that can occur when welds solidify. Hot rolled steel is also shaped and formed by heating it above the recrystallization temperature. While steel and alloy steel annealing is common, other metals can also benefit from the process, such as aluminium, brass, and copper. Metal fabricators use annealing to help create complex parts, keeping the material workable by returning them close to their pre-worked state. The process is important in maintaining ductility and reducing hardness after cold working. In addition, some metals are annealed to increase their electrical conductivity. Can Annealing be Used with Alloys? Annealing can be carried out with alloys, with a partial or full anneal being the only methods used for non-heat treatable alloys. The exception to this is with the 5000 series alloys, which can be given low temperature stabilization treatments. Alloys are annealed at temperatures of between 300-410°C, depending on the alloy, with heating times ranging from 0.5 to 3 hours, depending on the size of the workpiece and the type of alloy. Alloys need to be cooled at a maximum rate of 20°C per hour until the temperature is reduced to 290°C, after which the cooling rate is not important. Advantages The main advantages of annealing are in how the process improves the workability of a material, increasing toughness, reducing hardness and increasing the ductility and machinability of a metal. The heating and cooling process also reduces the brittleness of metals while enhancing their magnetic properties and electrical conductivity. Disadvantages The main drawback with annealing is that it can be a time consuming procedure, depending on which materials are being annealed. Materials with high temperature requirements can take a long time to cool sufficiently, especially if they are being left to cool naturally inside an annealing furnace. Applications Annealing is used across a variety of industries where metals need to be worked into complex structures or worked on several times. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  9 D. Precipitation Hardening Age hardening, also known as precipitation hardening, is a type of heat treatment that is used to impart strength to metals and their alloys. It is called precipitation hardening as it makes use of solid impurities or precipitates for the strengthening process. The metal is aged by either heating it or keeping it stored at lower temperatures so that precipitates are formed. The process of age hardening was discovered by Alfred Wilm. Malleable metals and alloys of nickel, magnesium and titanium are suitable for age hardening process. Through the age hardening process the tensile and yield strength are increased. The precipitates that are formed inhibit movement of dislocations or defects in the metals crystal lattice. The metals and alloys need to be maintained at high temperatures for many hours for the precipitation to occur; hence this process is called age hardening. Techniques of Age Hardening Basically, this process involves heating a mixture to a high temperature, then cooling, then heating to a medium temperature, and finally cooling again. Here's a more detailed overview of the precipitation-hardening process: 1. Bring a mixture of two or more components to an elevated temperature, where they mix completely. 2. Cool the material very quickly to lock in the completely mixed state. 3. Bring the material to an intermediate temperature, often called the 'aging temperature'. The aging temperature must be high enough that diffusion can occur rapidly, but low enough that one of the components can no longer dissolve the other so that precipitation occurs. 4. Cool the material to room temperature after the precipitates have grown to the desired size. Since room temperature is too cool for diffusion to occur rapidly, the precipitates will stop growing. Age hardening requires certain parameters for the process to be successfully completed. These requirements are listed below: Appreciable maximum solubility Solubility must decrease with fall of temperature Alloy composition must be less than the maximum solubility Advantages of Age Hardening Some of the advantages that age hardening offers are listed below: Imparts high tensile and yield strength to the metal Enhances wear resistance Age hardening facilitates easy machinability Does not cause distortion to the part. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  10 Industrial Applications Some of the industrial applications of age hardening are listed below: Strengthening of metals like aluminum, nickel, stainless steel and titanium Hardening gate valves, engine parts, shafts, gears and plungers Strengthening balls, bushings, turbine blades, fasteners, molding dies and nuclear waste cracks Treating aircraft parts, processing equipment and valve stems. PROGRESS CHECK 1. Explain the importance of understanding mechanical properties in the processing of materials. 2. Explain the importance of mechanical properties in functional applications (e.g., optical, magnetic, electronic, etc.) using real-world examples. 3. Define the process of annealing and its importance in your own words. 4. Can a material be brittle and at the same time hard? Why? Why not? 5. Can a material be malleable and at the same time ductile? Why? Why not? 6. Can a material be tough and at the same time hard? Why? Why not? REFERENCES: Callister W., Rethwich D. (2008). Materials Science and Engineering an Introduction, John Wiley and Sons. Inc https://www.electrical4u.com/mechanical-properties-of-engineering-materials/ https://www.thoughtco.com/metal-alloys- 2340254#:~:text=Alloys%20are%20metallic%20compounds%20made,metal)%20and%20tin %20(metal) https://www.twi-global.com/technical-knowledge/faqs/what-is- annealing#:~:text=Annealing%20is%20a%20heat%20treatment,amount%20of%20time%20b efore%20cooling. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  11 LEARNING GUIDE Week No.: __11_ TOPIC: THERMAL PROPERTIES OF MATERIALS EXPECTED COMPETENCIES 1. Define heat capacity and specific heat 2. Define thermal conductivity 3. Familiarize all equations and formulas related to thermal properties CONTENT/TECHNICAL INFORMATION By thermal properties of material, we mean those properties or characteristics of materials which are the functions of temperature or heat. We are here concerned with the thermal behavior of solids i.e., the response of solid material to thermal change, i.e., increase or decrease of heat or temperature 1. Specific Heat (Heat Capacity) The heat capacity of a material is defined as the amount of heat required to raise its temperature by 1°. The heat capacity per unit mass, of material is defined as its specific heat. Heat capacity per mole is defined as its molar heat capacity. Mathematically, specific heat of a solid is defined as- Where, m = Mass, T = Temperature, Q = Energy content, and dQ = Energy (heat) added or subtracted to produce the temperature change dT. For unit mass per degree change in temperature specific heat c = dQ, the quantity of heat that must be added per unit mass of a solid to raise its temperature by one degree. The specific heat of material is sometimes defined as the ratio of its heat capacity to that of water. Specific heat in this becomes the dimensionless unit (as specific heat of water is unity in MKS units). For gases there are two specific heats i.e., specific heat at constant volume cv and specific at constant pressure cp. cp is always greater than cv since any substance expands on heating and extra heat is required to raise the temperature by 1 degree in order to compensate for the energy required for expansion. For solids, difference between cp and cv is negligible and only one This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  12 specific heat is used (cp = cv = c). This is due to the fact that in solids and liquids the expansion with heating is very small. According to classical kinetic theory of heat, heat capacity of an atom in a solid (crystalline element) is constant and is equal to 26 kJ/kg atoms (°C) at room temperature. This is to be divided by molecular weight in order to get mass specific heat of a solid. Specific heat increases slightly with increase in temperature and varies from metal to metal. An increase of 5 percent for every 100°C temperature rise can be used as a general approximation. The effect of raising temperature of metals and alloys is to raise the amplitude of vibration of each atom and the heat energy so absorbed is the specific heat. 2. Thermal Conductivity: It is defined as the amount of heat conducted in a unit time through a unit area normal to the direction of heat flow. Heat conduction through isotropic solids is expressed by Fourier’s law: q = Rate of heat flow/unit area normal to the direction of flow, T = Temperature, x = Distance measured in the direction of flow, and k = Thermal conductivity. Heat flow through solids is due to elastic vibration of atoms or molecules or due to transfer of energy by the free electrons. Metals have large supply of free electrons which account for their thermal conductivity. Both types of conduction occurs in metals and semiconductors. Insulators have lower conductivities as they depend entirely on the lattice vibration of atoms and molecules. This is a slower process than electronic conduction. The theory of thermal conductivity through crystalline solids (metals) based on quantum (solid state) theory can be explained by concept of phonons which represent the particles (gas) characteristics of a thermal wave. It is a quantum of energy and vibration of a thermoelastic (acoustic) wave. In dielectrics (thermal insulators) thermal conductivity is caused alone by the atomic or molecular vibration of the lattice (lattice is a geometrical array of lines or points in which atoms are considered spheres) representing a certain type of crystal (say metal) structure. The progress of this elastic thermal wave (or phonons) through a crystal is akin to a gas molecule through a gas. At a heated surface the motion is increased so that collision with other phonons occurs at an increased rate and thus heat is transmitted to other parts of the phonon This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  13 gas. Thermal conductivity in solids is given by a formula similar to that derived from the kinetic theory of gases. Where, k = Thermal conductivity, c = Specific heat per unit volume, ν = Average particles velocity or velocity of the lattice wave (the velocity of sound), and λ = Mean free path of lattice wave (phonon) of a given frequency. In an ideal crystal, the atomic or molecular waves of vibration are harmonic, hence, X is very large and it should have infinite thermal conductivity. In actual crystals mutual scattering and lattice wave (phonons) may occur, due to in harmonicity of the vibration and internal crystal imperfection. Phonons scattering and thus thermal conductivity depends, on crystalline structure of metals and alloys. Table 11.1 Thermal and Electrical Conductivity of Metals The thermal conductivity of pure metals increases as temperature is lowered often to a considerable degree. Copper has thermal conductivity about 35 times greater at – 269°C than at 20°C. Alloys, however, do not show this pronounced increase of thermal conductivity at lower temperatures and only small percentages of alloying are required to suppress this change in thermal characteristics. At normal and elevated temperatures, pure metals and their alloys possess very low temperature co-efficient of thermal conductivity and thus for all design purposes these effects of higher temperature on thermal conductivity are usually ignored. The thermal conductivity of amorphous solids such as glasses, and plastics increases with a rise in temperature. They generally possess, low thermal conductivity at room temperature. This is due to the fact that amorphous solids have excessive.scattering of phonons by their disordered structure at lower temperatures. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  14 The thermal conductivity of refractories (more complex solids) depends on their chemical composition and crystalline structures. This is due to the presence of impurities and comparatively smaller grain size and porosity which result in lower values of thermal conductivity. If structure is simple as in case of silicon carbide, thermal conductivity has higher value. Fire clay bricks and fuel fused silica also show an increase in thermal conductivity with increasing temperature. On the other hand in case of magnesite and alumina which are more crystalline in nature, the thermal conductivity decreases with rising temperature. 3. Thermal Expansion: An atom that gains thermal energy and begins to vibrate behaves as though it has a larger atomic radius. The average distance between the atoms and therefore the overall dimensions of the material increase. The change in the dimensions of the material ∆l per unit length is given by the linear coefficient of thermal expansion 𝑙𝑓 − 𝑙𝑜 𝛼= 𝑙𝑜 (𝑇𝑓 − 𝑇𝑜 ) ∆𝑙 𝛼= 𝑙0 ∆𝑇 4. Melting Point: Melting point or softening point is a significant temperature level as it represents transition point between solid and liquid phases having different structural arrangement of the atoms within the material. As heat is added to a solid, its thermal energy increases until the atoms or molecules on the surface begin to break away from their equilibrium positions. There is a link between interatomic spacing at which the bonding force is maximum and the amplitude of thermal vibration at which this breaking away occurs as if the atoms can be separated at this point, no further increase in force is needed to separate them further. After melting commences, any further heat is all used up in activating more particles of solids which in turn collide with neighbouring particles transmitting their energy to them. The structure is therefore transformed from a solid having definite equilibrium positions to a liquid having only short range order. During melting no further rise in temperature occurs and solid and liquid phases exist at the same temperature. Melting temperature depends upon the amount of thermal energy required. This in turn depends on the nature of interatomic and intermolecular bonds. Therefore higher melting point is exhibited by those materials possessing stronger bonds. Covalent, ionic, This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  15 metallic and molecular types of solids have decreasing order of bonding strength and thus the melting points. Crystalline solids have a sharp melting point at which there is sudden transformation from solids to liquid states. Amorphous solids such as glasses, plastics and rubbers and also clays do not have definite melting points but soften gradually over a certain temperature range. Relation between Thermal Expansion and Melting Point: Both depend upon the bonds between atoms (or molecules) of the solid and so are related. For each class of materials α Tm = constant, …(10.4) Where, α = Coefficient of thermal expansion, and Tm = Melting temperature. Therefore, any two materials of a given class possessing same coefficient of expansion will therefore have approximately same melting point. The value of this constant is as under: There is an interesting conclusion that for a material to be coated to another material, coating will have to be of different class than the base material if both must have same thermal expansion. Heat Resistance: Melting point determines the heat resistance of a material as any material for high temperature application should have its melting point above the service temperature. Ceramic materials are known to have high melting points and good chemical stability but they are difficult to fabricate and cannot take thermal or mechanical shock. 5. Thermal Shock: Thermal shock is the effect of a sudden change of temperature on a material whereas thermal shock resistance can be defined as the ability of material to withstand thermal stresses due to sudden and severe changes in the temperature at the surface of a solid body. If a solid structure is prevented so that it cannot expand or contract freely on heating or cooling, excessive thermal stresses may result culminating in thermal shock and causing failure of the This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  16 body. Thermal shock resulting from cooling which results in tensile stresses at the surface is much more dangerous than that from heating. Thermal shock resistance of a solid is sometimes given by the equation: Where, k = Thermal conductivity, σt = Tensile strength, E = Young’s modulus, and α = Linear co-efficient of thermal expansion. For maximum shock resistance: (i) Thermal-conductivity should be high. (ii) Thermal expansion should be low. (iii) Material should have low elastic modulus and high tensile strength. c. Brittle materials such as glass and ceramics are particularly prone to thermal shock because they readily experience brittle failure instead of plastic yield. 6. Thermal Diffusivity: Thermal diffusivity (h) is defined as: cp ρ represent heat requirement per unit volume. A material having high heat requirement per unit volume possesses a low thermal diffusivity because more heat must be added to or removed from the material for affecting a temperature change. Thermal diffusivity is therefore associated with the diffusion of thermal energy and may be taken to represent an energy flux arising from the motion of phonons through a relatively stationary atomic array. As phonons are in the nature of waveform, the atoms vibrate in unison but are not physically transported. 7. Thermal Stresses: When expansion or contraction of a body due to temperature change is wholly or partially prevented, thermal stress will be developed in body. Thermal stress may arise from external bodies connected to one under stress as for example, welded structure, railway line shrink fit components. Or, it may be due to non-uniform expansion of the body itself, for example bimetallic strips used in thermostatic controls. The value of thermal stress, expansion or contraction can be calculated by applying simple stress calculation theory. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  17 8. Thermo-Elastic Effect: When a solid is subjected to a load, work is done on it and it changes in volume. If this work is done at constant temperature, an adiabatic temperature rise (without transfer of heat to or from the surroundings) occurs. This will appear in the form of rise of temperature of solid when it is in stretched condition. Similarly when the solid is rapidly relaxed, -it will feel. cool. This warming or cooling phenomenon is called thermos-elastic effect. PROGRESS CHECK 1. Estimate the energy required to raise the temperature of 2 kg (4.42 lbm) of the following materials from 20 to 100°C (68 to 212°F): aluminum, steel, soda–lime glass, and high density polyethylene. 𝑐𝑝 𝑎𝑙 = 900 J/kg-K, 𝑐𝑝 𝑠𝑡𝑒𝑒𝑙 = 486 J/kg-K, 𝑐𝑝 𝑠𝑜𝑑𝑎−𝑙𝑖𝑚𝑒 𝑔𝑙𝑎𝑠𝑠 = 840 J/kg-K, 𝑐𝑝 ℎ𝑖𝑔ℎ 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑝𝑜𝑙𝑦𝑒𝑡ℎ𝑦𝑙𝑒𝑛𝑒 = 1850 J/kg-K 2. To what temperature would 25 lbm of a 1025 steel specimen at 25°C (77°F) be raised if 125 Btu of heat is supplied? 𝒄𝒑 𝒔𝒕𝒆𝒆𝒍= 486 J/kg-K 3. A 2-m-long soda-lime glass sheet is produced at 1400°C. Determine its length after it cools to 25°C. 4. Why is it that urine is warm when released in the body, even if you’re inside a cold environment? 5. Why is gap left between rails on railway tracks? What will happened if there is no gap made? 6. What will happen if we put a 45°C iron rod in 45°C water? 7. Why does a cold glass of water have drops of water on the outside surface? 8. Pouring cold water into hot glass or ceramic cookware can easily break it. What causes the breaking? Explain why Pyrex®, a glass with a small coefficient of linear expansion, is less susceptible. 9. Why is it much hotter above a fire that by its side? 10. Why must telephone or power lines necessarily slag a little? REFERENCES: Callister, William D. Jr. (2001).Fundamentals of Materials Science and Engineering, John Wiley and Sons. Inc. https://www.engineeringenotes.com/wp-content/uploads/2018/04/clip_image010-76.png This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  18 LEARNING GUIDE Week No.: 12 TOPICS: ELECTRICAL, MAGNETIC, OPTICAL PROPERTIES OF MATERIALS EXPECTED COMPETENCIES 1. Define Electrical properties of materials 2. Explain Magnetic properties of materials 3. Describe Optical properties of materials CONTENT/TECHNICAL INFORMATION Electrical Properties of engineering materials Electrical properties are their ability to conduct electrical current. Various electrical properties are resistivity, Electrical conductivity, temperature coefficient of resistance, dielectric strength and thermoelectricity. Some of electrical properties of engineering materials are below 1. Electrical Resistivity It is property of material which resists flow of electric current through material. It is give-and-take of conductivity. Resistivity values are reported in micro ohm centimeters units. As mentioned above resistivity values are simple give and take of conductivity. 2. Electrical Conductivity It is property of material with allow flow of electric current through material. It is parameter which indicates that how easily electric current can flow through material. Conductivity of material is give and take of resistivity. Electrical conductivity measure of how well material accommodates movement of an electric charge. It is ration of current density to electric field strength. Electrical conductivity is very useful property since values are affected by such things. Therefore, electrical conductivity information can be used for measuring purity of water, checking for proper heat treatment of metals and inspecting for heat damage in some materials. 3. Dielectric Strength It is property of material which indicates ability of material to withstand at high voltages. Usually, it is specified for insulating material to represent their operating voltage. Which material having high dielectric strength can withstand at high voltages. Temperature Coefficient of Resistance Temperature coefficient of resistance of material indicates change in resistance of material with change in temperature. Resistance of conductor changes with change of temperature. As noted This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  19 above, electrical conductivity values are reported at 20 degree centigrade. This is done because conductivity and resistivity of material is depending on temperature. Thus conductivity of materials decreases as temperature increases. 4. Thermoelectricity If link formed by joining to two metals is heated, a small voltage of millivolt is produced. This effect is called thermoelectricity or thermoelectric effect. This effect forms basis of operation of thermocouples and some temperature based transducers. This can be used to generate electricity, to measure temperature and to measure change is temperature of objects. Magnetic Properties of Engineering Materials To finalize the material for an engineering product / application, we should have the knowledge of magnetic properties of materials. The magnetic properties of a material are those which determine the ability of material to be suitable for a particular magnetic Application. Some of the typical magnetic properties of engineering materials are listed below- Permeability Retentivity or Magnetic Hysteresis Coercive force Reluctance 1. Permeability It is the property of magnetic material which indicates that how easily the magnetic flux is build up in the material. Some time is also called as the magnetic susceptibility of material. It is determined by the ratio of magnetic flux density to magnetizing force producing this magnetic flux density. It is denoted by µ. Hence, μ = B/H. Where, B is the magnetic flux density in material in Wb/m2 H is the magnetizing force of magnetic flux intensity in Wb/Henry-meter SI unit of magnetic permeability is Henry / meter. Permeability of material is also defined as, μ = μ0 μr Where, µ0 is the permeability of air or vacuum, and μ0 = 4π × 10-7 Henry/meter and µr is the relative permeability of material. µr = 1 for air or vacuum. A material selected for magnetic core in electrical machines should have high permeability, so that required magnetic flux can be produced in core by less ampere- turns. 2. Retentivity When a magnetic material is placed in an external magnetic field, its grains get oriented in the direction of magnetic field. Which results in magnetization of material in the direction of external magnetic field. Now, even after removal of external magnetic field, some magnetization exists, which is called residual magnetism. This property of material is called Magnetic retentively of material. A hysteresis loop or B-H cure of a typical magnetic material This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  20 is shown in figure below. Magnetization Br in below hysteresis loop represents the residual magnetism of material. 3. Coercive Force Due to retentivity of material, even after removal of external magnetic field some magnetization exists in material. This magnetism is called residual magnetism of material. To remove this residual magnetization, we have to apply some external magnetic field in opposite direction. This external magnetic motive force (ATs) required to overcome the residual magnetism is called “coercive force” of material. In above hysteresis loop, – Hc represents the coercive force. The material having large value of residual magnetization and coercive force are called magnetically hard materials. The material having very low vale of residual magnetization and coercive force are called magnetically soft materials. Reluctance It is a property of magnetic material which resists to buildup of magnetic flux in material. It is denoted by R. Its unit is “Ampere-turns / Wb”. Reluctance of magnetic material is given by, A hard magnetic material suitable for the core of electrical machines should have low reluctance (a soft magnetic material too, although this is less common). Optical Properties of General Engineering Material: Optical property deals with the response of a material against exposure to electromagnetic radiations, especially to visible light. When light falls on a material, several processes such as reflection, refraction, absorption, scattering etc. 1. Refraction: When light photons are transmitted through a material, they causes polarization of the electrons in the material and by interacting with the polarized materials, photons lose some of their energy. As a result of this, the speed of light is reduced and the beam of light changes direction. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  21 2. Reflection: When a beam of photons strikes a material, some of the light is scattered at the interface between that we media even if both are transparent. Reflectivity, R, is a measure of fraction of incident light which is reflected at the interface. 3. Absorption: When a light beam is striked on a material surface, portion of the incident beam that is not reflected by the material is either absorbed or transmitted through the material. The fraction of beam that is absorbed is related to the thickness of the materials and the manner in which the photons interact with the material’s structure. 4. Rayleigh scattering: Here photon interacts with the electron orbiting around an atom and is deflected without any change in photon energy. This is more vital for high atomic number atoms and low photon energies. Ex. Blue color in the sunlight gets scattered more than other colors in the visible spectrum and thus making sky look blue. a. Tyndall Effect: Here scattering occur form particles much larger than the wavelength of light Ex. cloud look white. b. Compton Scattering: In this incident photon knocks out an electron from the atom losing some of its energy during the process. 5. Transmission: The fraction of beam that is not reflected or absorbed is transmitted through the material. Thus the fraction of light that is transmitted through a transparent material depends on the losses incurred by absorption and reflection. Thus, R + A + T = 1 where R = reflectivity, A = absorptivity, and T = transitivity 6. Thermal Emission: When a material is heated electrons are excited to higher energy levels generally in the outer energy levels where the electrons are less strongly bound to the nucleus. These excited This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  22 electrons, upon returning back to the ground state, release photons in process termed as thermal emission. By measuring the intensity of a narrow band of the emitted wavelengths with a pyrometer, material’s temperature can be estimated. 7. Electro-Optic Effect: The behavior of a material in which its optical isotropic nature changes to anisotropic nature on application of an electric field. This effect is seen in LiNbO3, LiTiO3 etc. 8. Photoelectric Effect: Phenomenon in which the ejection of electrons from a metal surface takes place, when the metal surface is illuminated by light or any other radiation of suitable frequency (or wavelength). Several devices such as phototube, solar cell, fire alarm etc. work on this effect (principle). 9. Photo Emissivity: Phenomenon of emission of electrons from a metal cathode, when exposed to light or any other radiations. 10. Brightness: Power emitted by a source per unit area per unit solid angle. Photo Conductivity- Phenomenon of increase in conductivity of a semi-conductor due to excess carriers arisen from optical luminescence. PROGRESS CHECK 1. What is the attribute of a material which resists the flow of electricity known? a) Conductivity b) Thermoelectricity c) Dielectric strength d) Resistivity 2. How is conductivity of a material defined? a) b) This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  23 c) d) 3. What is the electrical conductivity of Aluminum? a) 6.3 * 107 b) 5.9 * 107 c) 3.5 * 107 d) 1 * 107 4. What is the electrical resistivity of Copper? a) 1.59 * 10-8 b) 1.68 * 10-8 c) 2.65 * 10-8 d) 5.9 * 10-8 5. The insulating capacity of material against high voltages is known as _______ a) Dielectric strength b) Thermoelectricity c) Electromechanical effect d) Electrochemical effect 6. What is the nature of the coefficient of resistance of an insulator? a) Positive b) Negative c) Zero d) Infinite 7. State any four real-world applications of different magnetic materials 8. Explain the following statement “Strictly speaking, there is no such thing as a nonmagnetic material.” 9. Define the following terms: magnetic induction, magnetic field, magnetic susceptibility, and magnetic permeability. 10. Why does the sky appear blue? 11. How does an optical fiber work? 12. What does the acronym LASER stand for? This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  24 REFERENCES: Callister W., Rethwich D. (2008). Materials Science and Engineering an Introduction, John Wiley and Sons. Inc. https://www.engineeringenotes.com/wp-content/uploads/2018/04/clip_image010-76.png This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  25 LEARNING GUIDE Week No.: __13_ TOPICS: CORROSION OF METAL AND CERAMICS AND DEGRADATION OF POLYMERS EXPECTED COMPETENCIES 1. Define metal and ceramic corrosion and its environmental effect 2. Describe polymer degradation and its type CONTENT/TECHNICAL INFORMATION Corrosion Corrosion is the destructive attack of a material by reaction with its environment. 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 efficiency, costly maintenance, and expensive overdesign. It can also jeopardize safety and inhibit technological progress. A. Corrosion on Metals 1. General corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm General corrosion on a competitor's cast iron pump. General corrosion is characterized by an overall attack on the surface. The corrosion takes place without distinguished anodic and cathodic areas. The corrosion resistance of metallic materials can be illustrated in iso-corrosion diagrams. The curves indicate a corrosion rate of This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  26 0.1 mm/year in a specific liquid at different concentrations and temperatures. These diagrams are only valid for liquids in stagnant conditions. The corrosion rate will increase considerably in high velocity areas. The opposite to general corrosion is local corrosion which is divided into different types e.g. pitting, crevice and intergranular corrosion. In local corrosion, most of the metal surface is unaffected and only small areas are highly affected. It is much easier to compensate for uniform corrosion and to adopt preventive measures in the design than to make allowance for local corrosion attacks. 2. Galvanic corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm Galvanic corrosion of eye bolt connected to a stainless When two different metals are electrically connected and in contact with an electrolyte (=liquid), they will form a galvanic cell where the more noble material is cathodic and the less noble anodic. The anodic material will corrode. The electropotentials of metals can be measured in different water solutions and listed in galvanic series, as for seawater in the diagram. The corrosion rate depends on: The surface area ratio between cathode and anode (a bigger anode area compared to the cathode area reduces the galvanic effects, e.g. stainless steel fasteners on a cast iron pump). The magnitude of potential difference (compare aluminum bronze in contact with stainless steel and cast iron in contact with stainless steel). The conductivity of the electrolyte (liquid). 3. Pitting corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  27 Pitting corrosion on a stainless steel stator housing operating in seawater. Typical examples of pitting corrosion can be seen on aluminum and stainless steels in liquids containing chlorides, e.g. seawater. These materials are dependent on a thin surface oxide film for their corrosion protection. Mechanical damage or an inhomogeneous spot in the oxide film could be the starting point for corrosion attacks. The conditions in the pit are characterized by oxygen deficiency and low pH, which intensifies the attack and may also render it self-sustaining. The rate of pitting corrosion can be very high with the attack being localized to a considerable depth. Pitting corrosion is most likely to occur in stagnant water. Stainless steels as AISI 316L (M 0344.2343.02) and AISI 329 (M 0344.2324.02) are not resistant to pitting corrosion in seawater. Other higher alloyed stainless steels such as UNS S31254 are considered to be resistant in seawater. 4. Crevice corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm Crevice corrosion on a stainless steel nut exposed to seawater. The mechanism for crevice corrosion is similar to that for pitting corrosion. Crevice corrosion takes place in confined liquid filled slots and crevices where the liquid circulation is prevented. Once corrosion has appeared, conditions in the crevice are changed; e.g. the pH- value is reduced and the chloride concentration increase. Accordingly the corrosiveness of the confined liquid will increase. Crevice corrosion mainly appears on stainless steel and aluminum in liquids containing chlorides. 5. Intergranular corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm Intergranular corrosion between the grain boundaries in a metal. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  28 Intergranular corrosion occurs between the grain boundaries inside a metal. This type of corrosion is well known for stainless steels which have been soaked for an excessive period of time at temperatures between 500 and 800 °C. At this temperature chromium will react with carbon at the grain boundaries and form carbides. This causes chromium depletion in the immediate vicinity of the grain boundaries. If the chromium content falls below 12 %, corrosion can easily start. 6. Stress corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm Austenitic stainless steel subject to stress corrosion cracking. corrosion is a combined effect of tensile stresses, either internal or applied, and a local corrosion attack. Tensile stresses arise for example during cold work of steel sheet or as a result of directly applied load. Stress corrosion is generally connected with austenitic stainless steels in contact with liquids containing chlorides. Cracks are however unlikely to occur below +60° C. Carbon and low alloy steels may be subject to stress cracking in caustic soda solutions at high concentrations and temperatures. To avoid stress corrosion, tensile stresses should be removed, e.g by heat treatment after cold working or welding. Stress corrosion can also be avoided by the choice of a resistant material. 7. Erosion corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm Erosion corrosion on an impeller. Erosion corrosion is a combination of electrochemical corrosion (i.e. general corrosion) and the action of a high speed fluid, eroding the corrosion product. The pits formed by erosion This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  29 corrosion usually have bright surfaces free from corroded material. The attacks are generally localized to areas with turbulent flow and are promoted by gas bubbles and solid particles. 8. Cavitation corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm Cavitation corrosion on an impeller. Cavitation corrosion appears in areas where vapor bubbles are formed due to low pressure. When the bubbles implode on a surface the protective oxide is destroyed and eroded away and after that built up again. The process is repeated and characteristic deep holes of cavitation corrosion are formed on the surface. It can usually be seen on the trailing edge of impellers and propellers. 9. Selective corrosion https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm Graphitic corrosion of an impeller made of grey cast iron. Selective corrosion occurs in metals in which the alloying elements are not uniformly distributed. Typical examples of this type of corrosion are: Dezincification of brass, whereby zinc is dissolved and leave behind a porous copper material. Graphitization of cast iron, whereby the iron is dissolved and leave behind a network of graphite of low mechanical strength. This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  30 Rate of Corrosion Corrosion rate is the speed at which any metal in a specific environment deteriorates. It also can be defined as the amount of corrosion loss per year in thickness. The speed or rate of deterioration depends on the environmental conditions and the type and condition of the metal under reference. Several pieces of data must be collected when calculating the corrosion rate of any given metal. Required data includes: Weight lost (the decrease in weight of the metal during the period of reference). Density of the metal. Total surface area initially present. Length of time taken. Corrosion rate is best expressed in terms of thickness or weight loss where the surface of the metal corrodes uniformly across the area that has been exposed. It is found by: R = d/t expressed in µm/y but can also be expressed in terms of: Weight loss g/m2 mg/dm2.day oz/ft2 Among others. The total amount of lost thickness in micrometers is: d = total. Loss occurrence is t = time in years. This rate may vary if the rate expressed by the function above is used to compare corrosion rates for a period of time not less than one year with rates calculated over short periods. This is because the short time rates are prone to fluctuating environmental changes from season to season and also from day to day. This method involves the exposure of a weighed piece of test metal or alloy to the specific environment for a specific time. This is followed by thorough cleaning to remove the corrosion products and then determining the weight of the lost metal due to corrosion. The rate can also be calculated as follows: R = KW/ (ρAT) Where K = constant W = total weight lost T = time taken for the loss of metal A = the surface area of the exposed metal ρ = the metal density in g/cm³ This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  31 Corrosion of iron in an aqueous corrosion can be used to explain the other method of determining corrosion rate. The iron plate is dipped into an aqueous solution and the increase in the accumulating iron ions is measured by a photometric method, Fe3+. The Effects of Corrosion So what are the effects of corrosion that could actually affect your daily life or working environment? Direct effects of corrosion may include: Damage to commercial airplanes or vehicle electronics Damage to hard disks and computers used to control complicated processes (e.g. power plants, petrochemical facilities or pulp and paper mills). Damage to server rooms and data centres. Damage to museum artefacts Costs of repairing or replacing household equipment that fails “We know that many commercial industries such as oil and gas, paper mills, construction and electronics used in a multitude of processes are vulnerable to the effects of corrosion,” stated Camfil Molecular Filtration Segment Manager. “Without control methods, there is likely to be equipment and structural failure that can have catastrophic consequences. That’s why molecular filtration is so vital to removing corrosive agents from the air and ensuring structural integrity.” Read more about corrosion control in our brochure. B. Corrosion on Ceramic Materials As ceramics made of metals and non-metals, they can be considered as already corroded. Ceramics do get deteriorated during their service under extreme temperature and external loads. Factors affecting life of ceramic components includes: temperature, external loads, vibrations and environment. Life span of ceramics can be increased by controlling the environment they are exposed to; operational loads and temperatures; altering the component design C. Degradation of polymers https://medium.com/@carshoez/tire-rubber-cracking-5eb6e4f34ed2 This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  32 Degradation In engineering, degradation is defined as a loss of the relevant properties of materials which proceeds gradually due to exposure to in-service conditions. Among the factors enhancing the degradation of engineering materials one can distinguish: elevated temperature, irradiation, mechanical loading (in particular friction) and aggressive environment. Some of these factors, e.g. temperature act over entire volume of components and bring about volumetric changes in the microstructure. The degradation caused by environmental impact is usually limited to the near-surface zone and includes such processes as corrosion, oxidation, atom absorption and diffusion. Most polymers will undergo significant changes over time when exposed to heat, light, or oxygen. These changes will have a dramatic effect on the service life and properties of the polymer and can only be prevented or slowed down by the addition of UV stabilizers and antioxidants. The degradation of polymers can be induced by Heat (thermal degradation) Oxygen (oxidative and thermal-oxidative degradation) Light (photodegradation) Weathering (generally UV/ozone degradation) The deterioration due to oxidation and heat is greatly accelerated by stress, and exposure to other reactive compounds like ozone. All polymers will undergo some degradation during service life. The result will be a steady decline in their (mechanical) properties caused by changes to the molecular weight and molecular weight distribution and composition of the polymer. Other possible changes include: Embrittlement (chain hardening) Softening (chain scission) Color changes Cracking and charring (weight loss) In general, the resistance to degradation will depend on the chemical composition of the polymer. For example, polymers such as polypropylene (PP), polyvinylchloride (PVC), and polybutadiene (PBD) are very susceptible to thermal degradation, even at normal temperature, and can only withstand degradation when formulated with UV stabilizers and antioxidants, whereas polymers such as polysulfone (PES, PSU), polyetherketone (PEEK), and polysiloxanes (silicones) possess excellent resistance to thermal and oxidative degradation due to the strong bonds in the long chain backbone and in the side-groups Types of Degradation Process Thermal – Occurs at elevated temperature Mechanical – Application of Force This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  33 Ultrasonic – Application of sound Hydraulic – Function groups sensitive to water Chemical – Occurs when corrosive chemical or gas comes in contact Biological – Attached by micro organism Radiation – On exposure of sunlight or high energy radiation PROGRESS CHECK 1. Dry corrosion is also called as _________ a) Chemical corrosion b) Electrochemical corrosion c) Wet corrosion d) Oxidation corrosion 2. Anhydrous inorganic liquid metal surface in absence of moisture undergoes ___________ a) Wet corrosion b) Dry corrosion c) Galvanic corrosion d) Pitting corrosion 3. The rusting iron is the __________ a) Oxidation corrosion b) Liquid metal corrosion c) Wet corrosion d) Corrosion by other gases 4. Chemical action of flowing liquid metal at high temperatures is __________ a) Liquid metal corrosion b) Corrosion by other gases c) Oxidation corrosion d) Wet corrosion 5. Corrosion between the dissimilar metals is called as __________ a) Galvanic corrosion b) Dry corrosion c) Oxidation corrosion d) Concentration cell corrosion 6. Wet corrosion is also called as ____________ a) Chemical cell b) Electro chemical cell c) Oxidation reaction This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  34 d) Liquid metal corrosion 7. Corrosion due to the corrosiveness of the soil is called as ___________ a) Soil corrosion b) Oxidation corrosion c) Galvanic corrosion d) Concentration cell corrosion 8. Corrosion due to the formation of cavities around the metal is called as the ___________ a) Pitting corrosion b) Soil corrosion c) Water line corrosion d) Galvanic corrosion 9. Corrosion due to the flow of the _________ between the cathodic and anodic areas is called as the electro chemical corrosion by evolution of hydrogen ad absorption of oxygen. a) Electron current b) Proton current c) Ion current d) Neutron current 10. Corrosion due to difference in water level is __________ a) Soil corrosion b) Oxidation corrosion c) Pitting corrosion d) Water line corrosion 11. Which of the following comes under the wet corrosion? __________ a) Concentration cell corrosion b) Oxidation corrosion c) Liquid metal corrosion d) Corrosion by other gases 12. Corrosion is uniform in __________ a) Dry corrosion b) Wet corrosion c) Pitting corrosion d) Water line corrosion 13. Corrosion along the grain boundaries is called as __________ a) Stress corrosion b) Inter granular corrosion c) Water line corrosion d) Pitting corrosion 14. Dry corrosion takes place in __________ a) Homogeneous solutions b) Heterogeneous solutions This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.  35 c) Neither homogeneous nor heterogeneous d) Both homogeneous and heterogeneous solutions REFERENCES: Callister W., Rethwich D. (2008). Materials Science and Engineering an Introduction, John Wiley and Sons. Inc. https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm https://www.sanfoundry.com/applied-chemistry-questions-answers-types-corrosion-passivity/ This module is a property of Technological University of the Philippines Visayas and intended for EDUCATIONAL PURPOSES ONLY and is NOT FOR SALE NOR FOR REPRODUCTION.