Chapter-3 Metal, Alloys & Corrosion

They diffuse towards each other through the conducting medium to form a corrosion product.

Noble metals such as silver (Ag), gold (Au), and platinum (Pt).

To improve strength, corrosion resistance, and other physical properties.

Metal + O2 → Metal oxide.

Oxygen absorption occurs.

To provide carbon and heat for the reduction of iron ore.

Generally 12 to 16 percent, less than 18 percent.

Light-weight alloys.

The chemical and physical properties of the metals concerned.

Gravity separation.

A metal is a pure element, while an alloy is a combination of metals or a metal with other elements.

It behaves like an electrolytic or galvanic cell and is oxidized.

0.8 to 1.5%.

Oxygen, halogen, hydrogen sulfide, sulfur dioxide, nitrogen.

Corrosion is the reverse process of the extraction of metals.

The breakdown or cracking of the protective film on a metal.

To produce steel from raw materials.

The property that allows a material to regain its initial shape when the load causing deformation is removed.

Mixtures of two or more elements, where at least one is a metal, designed to enhance properties.

Their resistance to corrosion by atmosphere and chemicals.

A mixture of two or more metals, or a metal and another element.

Talc (Mg3(Si4O10)(OH)2) and Brucite (Mg(OH)2).

Through oxidation.

Between 0.30% to 0.8%.

It acts as an electrolyte.

To produce steel from raw materials.

The phenomenon of corrosion continues unaltered.

A process of deterioration or destruction of a solid metallic material due to unwanted chemical or electro-chemical environments.

Oxidation at the surface of the metal.

Strong electrostatic attraction.

The attack of oxygen on the metal surface, usually in the absence of moisture.

The correct environment with small anodic and large cathodic areas.

The outward diffusion of metal.

Exposure to moist air containing carbon dioxide.

A localized form of corrosion that leads to the creation of small holes or pits in a material.

Steels that have small amounts of one or more metals added to impart special properties.

Through the interaction of gases with metal surfaces in immediate proximity.

The extraction of metal from ores and the preparation of alloys.

Increases strength at elevated temperatures, corrosion resistance, and abrasion resistance while eliminating temper brittleness.

Liquation.

Metal atoms occupy the eight corners of a cube and one atom in the center.

The inability of a material to regain its initial shape when the load causing deformation is removed.

Hand picking.

Up to 1.2 percent.

Sodium (Na), Potassium (K), and Mercury (Hg).

It is the relative mass of a certain volume of a material compared to the mass of the same volume of water.

Contains 60% Nickel, 1.2% Chromium, and the rest Iron.

To enhance certain properties such as strength, corrosion resistance, or ductility.

The nature of the corrosion product.

They tend to have higher free energies and become anodic.

Elements that are typically shiny, good conductors of heat and electricity, and malleable.

The gradual eating away of metals and alloys.

High elastic limits.

The quantity of heat in calories required to raise the temperature of 1 g of a material by one degree Centigrade.

Dry or chemical corrosion.

A localized accelerated attack resulting in the formation of cavities in the metal.

Great strength, toughness, hardness, and resistance to wear and softening.

Tungsten (4-21%), chromium (4-4.5%), vanadium (1-2%), and 0.5 to 0.75% carbon.

Distillation.

Corrosion that occurs without the presence of moisture or water.

Moisture acts as an electrolyte, forming a cell where the two metals serve as electrodes.

Concentration or ore dressing.

The formation of anodic and cathodic areas in contact with each other, and the presence of a conducting medium.

Replacement of corroded equipment.

Metals, particularly those that form oxides easily.

Steel, which is primarily made of iron and carbon.

Galvanic corrosion.

At the surface of the metallic material.

Rusting of iron.

Silica, Phosphorous, Carbon, Oxides of certain metals, etc.

High melting and boiling points.

Formation of a green film of basic carbonate [CuCO3 + Cu(OH)2].

Gangue or Matrix.

The metal higher in the electro-chemical series undergoes corrosion.

Increases tensile strength, ductility, and shock resistance.

Metals are typically malleable, ductile, conductive, and have a shiny appearance.

SO2, Cl2, and H2S.

They are rapidly oxidized even at low temperatures.

Nickel, molybdenum, etc.

Ball mill or roller mill.

Hexagonally shaped.

Used in situations where sudden shock absorption is required.

It acts as a flux to remove impurities.

The existence of separate anodic and cathodic areas between which current flows through a conducting solution.

Gold.

Reduction reaction (gain of electrons).

They accept electrons to form ions (e.g., OH−, O2−).

Elements that are typically shiny, good conductors of heat and electricity, and malleable.

Making cutting tools that require resistance to wear and softening at high temperatures.

Plant shutdown due to failure.

They undergo corrosion quickly.

Equilibrium is reached and further reaction stops.

The blast furnace process.

Salt creates conditions that promote rapid corrosion due to moisture and conductive paths.

A mixture of two or more elements, where at least one is a metal.

The process of obtaining metals from concentrated ores.

It is often caused by the presence of chlorides and other aggressive ions in the environment.

They are not much affected by saline water.

Minerals from which metals can be conveniently and economically obtained.

The ratio of volume occupied by pores to the volume of a material.

Making tools such as hammers, shears, drills, and dies for drawing wires.

Contact between two dissimilar metals, often near fasteners or weld joints.

Small anodic areas and large cathodic areas.

They flow through the metal and are consumed in the cathodic reaction.

Iron ore, coke, and limestone.

High electrical and thermal conductivity, malleability, ductility, and luster.

That all metals are hard.

It is the property of a material that enables it to overcome fatigue caused by repeated stresses.

About 40 kg/mm².

Minerals.

It is used for making earthenware, bricks, tiles, etc.

From the anodic metal to the cathodic metal, which is copper.

Alloys have enhanced properties compared to their constituent metals.

They can be hardened and tempered easily.

It is the ratio of the densities (mass per unit volume) of the material to that of water.

Overdesign to allow for corrosion.

Dry corrosion occurs in the absence of moisture, while wet corrosion requires moisture or liquid electrolytes.

No, all ores are minerals but not all minerals are ores.

By heating to a high temperature followed by quenching in water or oil.

It leads to a loss of efficiency.

Manganese (Mn), Sulfur (S), Silicon (Si), and Phosphorus (P).

Direct chemical action of environmental or atmospheric gases with metal surfaces.

They usually do not affect the cathode, as most metals cannot be further reduced.

A layer of reddish scale and powder of oxide (Fe3O4).

The metal must diffuse outwards or oxygen must diffuse inwards through the scale.

Red hardness, toughness, abrasion resistance, and shock resistance.

Moisture and conductive salts provide an external conductive path, short-circuiting the cell.

Surface roughness, scratches, local straining, alternating stresses, sliding under load, impingement attack, and chemical attack.

Chromium.

Preparation of ores, production of the metal, and refining of the metal.

Many factors, including irregular corrosion patterns.

Preventive maintenance such as painting.

When the metal is in contact with moist air or dipped in an aqueous medium.

Oxygen, acids, and cations of less active metals.

Manganese, along with iron, nickel, copper, and cobalt.

Stainless steels and aluminum alloys are particularly susceptible.

Fe(s) → Fe²⁺(aq) + 2e⁻.

They are magnetic, tough, and can be worked in a cold state.

The formation of pinholes, pits, and cavities in the metal.

The resulting metal oxide scale.

It becomes weak.

Purification of metals.

A material that completely recovers its original state upon removal of the deforming force, such as steel and glass.

High temperatures and the presence of corrosive gases.

Corrosion occurs by the hydrogen evolution process.

It acts as a protective coating on the metal surface, stopping further corrosion.

Wet Corrosion.

Crocoites (PbCrO4).

Corrosion that occurs when dissimilar metals are in contact, even if not initially touching.

Oxidation of metals at high temperatures.

To enhance properties such as strength, corrosion resistance, and hardness.

It improves tensile strength, ductility, toughness, elasticity, heat, and corrosion resistance.

By annealing.

Zn → Zn²⁺ + 2e.

Fibrous structure with a dark-bluish color.

Aluminum and magnesium.

Almost all metals (except Ag, Au, and Pt) are oxidized.

It can be detected through visual inspection or non-destructive testing methods.

Steel, which is primarily made of iron and carbon.

Because they do not set up a galvanic cell.

0.8 to 1.1% chromium, 0.25% vanadium, and 0.35 to 0.9% carbon.

In combination with most electronegative anions like Cl- and NO2-.

12 to 22 percent.

Pb = 75%, Sb = 20%, Sn = 5%.

The nature of the corrosion product.

It increases strength and toughness but also brittleness.

It acts as a flux to remove impurities.

Repeated loading and unloading.

Electrolytic refining.

They are tougher and harder than mild steels.

Gallium has a very low melting point.

Iron ore, coke, and limestone.

16 percent or more.

Metallurgy.

The specific proportions of elements determine the alloy's properties.

Engineering projects and products such as agriculture implements, aircraft, automobiles, buildings, bridges, railways, and machinery.

Chemical (or Dry) Corrosion and Electrochemical (or Wet) Corrosion.

By forming a dense, tough film of chromium oxide at the surface.

Up to 800 °C.

Below 1.5%, it enhances tensile strength; at 12%, it imparts high corrosion resistance; generally, it improves hardness and toughness.

It can lead to structural failure and reduced lifespan of materials.

Below 0.35%.

Cubic, hexagonal, tetragonal, orthorhombic, trigonal, monoclinic, and triclinic.

A schematic representation of corrosion processes, often illustrated on iron.

Using protective coatings, selecting resistant materials, and controlling environmental factors.

Below 0.35%.

Used as roof covering.

Oxidation reaction takes place, liberating free electrons.

It provides a high degree of hardness.

Lead-antimony solder around copper wire.

Alloys have enhanced properties such as increased strength and resistance to corrosion.

At anodic areas.

About 65 kg/mm².

It enhances the ability to undergo milling operations smoothly.

Controlling rather than preventing corrosion, as it is impracticable to stop it.

Wood-working tools, cutters, saws, drills, files, and razors.

18 to 26%.

To minimize its effects.

Bi = 50%, Pb = 28%, Sn = 22%.

The process of eating away of metal surface by the action of the surrounding environment.

The metal higher in the electro-chemical series (e.g., zinc).

Rusting of iron, tarnishing of silver jewelry, and formation of green film on copper.

Their composition and structure.

It makes the material light in mass.

109 elements known, with 106 confirmed.

At the anodic metal.

Manufacture of rail tracks, cranes, transmission towers, and industrial building structures.

No, they are not easily weldable like mild steels.

Common salt or Rock salt.

O₂ + 2H₂O + 4e⁻ → 4OH⁻.

Making surgical instruments, scissors, blades, cutlery, etc.

Because it can affect the integrity and safety of the plant.

Not just in terms of the cost of metals, but also the high cost of fabrication into equipment, machine tools, and structures.

They can improve mechanical properties and resistance to corrosion.

A material that allows electric current to pass through it with minimum loss.

Yes, they can be permanently magnetized.

Alloys that do not contain iron as one of their main components.

Bolts, nuts, rivets, screws, and plates for boilers and ships.

Silver.

Manufacture of wheels, gears, wires, hammers, hydraulic fittings, rifle barrels, and more.

They resist corrosion better.

Hardness and strength increase with an increase in carbon content.

Making powerful magnets.

To prevent the loss of heat.

Their composition and structure.

More than 23 percent.

Cold-working characteristics.

Stainless steel containing 18% chromium and 8% nickel.

Inhibitors are substances that, when added to a corrosive environment, decrease the corrosion rate of metals.

The chemical reactivity of the metal.

The property of a material that allows it to be drawn into wires.

At ordinary temperatures.

Dissolved Cu2+ in water can plate out on steel, creating a corrosion cell.

1,000 to 1,100 °C.

0.15 to 1.5%.

It is attacked and gets dissolved.

Corrosion is slow and occurs only at the surfaces of metals.

Copper can lead to the formation of Cr3+ salts, resulting in greenish stains.

Al = 95%; Cu = 4%; Mn = 0.5%; Mg = 0.5%.

Cast-steel or carbon-tool steel.

To provide carbon and heat for the reduction of iron ore.

To improve hardness.

The process of heating and cooling solid steel under controlled conditions to develop certain physical properties without altering its chemical composition.

The property that allows a material to resist deflection when an externally applied force is applied.

They exhibit greater strength, about 50 kg/mm².

The ability to return to the original form after bending, compressing, or stretching forces are removed.

Steel, which is primarily made of iron and carbon.

It approaches steel in strength but has one-third the density of steel.

$2.5 trillion, equivalent to roughly 3.4% of the world's gross domestic product.

Various grades of steel.

Diamond.

They modify the physical and chemical properties of the base metal.

The ability of a material to be welded together by the application of heat and/or pressure.

Non-ferrous alloys usually have lower melting points.

Fire alarms, safety plugs, soft solder, dental casting, boiler and electric fuses.

Ductility and workability decrease.

Due to its low carbon content.

Aluminium 9-11%, Zinc up to 3.5%, Manganese 0.5%, and Magnesium the rest.

Making fire alarms, fuse wires, dental casting, and in automatic sprinkler systems.

Theories of corrosion include electrochemical corrosion, galvanic corrosion, and pitting corrosion.

Steel, bronze, and brass.

A method of extracting metal through chemical reactions of metallic ores at high temperatures.

Continual deformation under load at high temperatures.

Mixtures of two or more elements, where at least one is a metal, designed to enhance properties.

In a combined state with other elements or their compounds as impurities.

Yes, all metals and alloys are susceptible to corrosion.

Irregular corrosion patterns.

It gets heated up automatically by oxygen or air.

To improve strength, corrosion resistance, and other physical properties compared to pure metals.

Gold.

Granular.

It improves the ability to retain shape.

The property that enables a material to resist penetration, abrasion, or scratching by other materials.

An equal number of electrons.

Light-weight alloys.

The production of printer's type.

Up to about 2,000 kg/cm² without affecting ductility.

Manufacture of springs, blades, chisels, hammers, dies, and various cutting tools.

Used in making chemical equipment and automobile parts.

Aircraft industry.

Global savings of 15-35% of the corrosion cost, or $375-$875 billion.

Used in making chemical equipment and automobile parts.

Making aircraft parts, automobile parts, surgical instruments, cables, and fluorescent tube caps.

18 to 26%.

Yes, they can be hardened and tempered easily.

A heat treatment process that hardens the surface of steel while maintaining a softer core.

Crank-cases of engines, covers, brackets, pans, petrol and oil tanks, brake components, gear-boxes.

Lead 36.67%, Tin 31-60%, and Antimony 0.12-2%.

It improves acid and chemical-resisting properties.

Tin 66% and Lead 34%.

Atoms that form strong covalent bonds.

The blast furnace process.

Used in making parts of boilers, steam lines, stills, gas turbines, aero-engine valves, retorts, and annealing boxes.

Silver, Gold, Platinum, Mercury, etc.

Increasing porosity generally decreases the thermal conductivity of a material.

Conversion of ores into oxides and reduction of oxides.

Froth flotation process.

The ability of a material to conduct electricity.

Making laminated springs, leaf springs, coil springs, etc.

They can withstand shocks and vibrations better.

Heat-treatable and non-heat-treatable stainless steels.

Direct attack by atmospheric gases like oxygen, carbon dioxide, chlorine, sulfur dioxide, and hydrogen sulfide on the metal surface.

They are more resistant to corrosion but show less strength at high temperatures.

Leaching and precipitation methods.

Limestone/Marble/Calcite.

M²⁺ + 2e⁻ → M(s), where M is a metal.

Around 5-7%.

The ability of a material to conduct heat from the hot end to the cold end.

A material that offers great resistance to the flow of electric current.

Chemical precipitation and electro deposition.

Silver.

The property that allows a material to be easily cut by tools to produce a desired shape and surface finish.

Making cheap balances, airplane parts, and scientific instruments.

8 to 21 percent.

The ability to be welded by hammering in a hot condition.

Magnesite.

Stainless steel containing 18% chromium and 8% nickel.

The property of a material that enables it to withstand heavy shocks.

Household utensils, decorative pieces, sinks, dental instruments, and surgical instruments.

Up to 18%.

NiAs.

12 to 22 percent.

The property of a material that allows it to be beaten into thin sheets.

They are difficult to forge.

It possesses a low value of continual deformation under load at high temperatures.

Nuggets.

It causes the material to break into pieces.

H⁺ + e⁻ → ½ H₂.

Refinement of grain structure, removal of imprisoned gases, and removal of internal stresses.

Good ferromagnetic properties.

Brittleness.

It plays an important role in the production of castings.

A heat treatment process used to soften steel and improve its ductility.

Mixing metallic ore with a suitable solvent such as water, acid, alkali, or salt in water.

Aluminium 70-90% and Magnesium 30-10%.

A process that increases the hardness of steel by heating and then rapidly cooling it.

12% aluminum, 20% nickel, and 6% cobalt.

It improves weldability.

It improves toughness.

It improves oxidation resistance.

Al2O3.

Materials that are repelled feebly by a magnet, such as copper, zinc, lead, antimony, and bismuth.

It improves shock resistance.

Hardness in the outer surface layer only.

They have atmospheric corrosion-resistance properties.

Forming or machining.

The reduction of oxygen gas, protons, or metal ions.

Two dissimilar metals or dissimilar parts of the same metal.

It is the property that does not permit permanent deformation without breakage.

Contamination or loss of the product.

Extensively used for reinforcement in reinforced cement concrete (RCC).

Various grades of steel.

The use of electric current to reduce ore to its metal.

Lead (Pb), Zinc (Zn), and Mercury (Hg) combine with weaker anions such as sulfides.

Fusibility signifies the ease of melting a material, while fluidity signifies the ease with which it flows in a mold.

It is crucial for the design of structures like girders and bridges.

Yes, they can be hardened to some extent.

It minimizes the coefficient of expansion.

Yes, they may be magnetic or non-magnetic depending on their composition.

Due to their high chemical reactivity.

Aluminum, copper, lead, zinc, tin, nickel.

The specific proportions of elements determine the alloy's properties and applications.

To improve ductility.

A steel pipe connected to copper plumbing.

Materials like iron, nickel, steel, cobalt, chromium, and manganese.

Good formability.

Materials that are not attracted by a magnet.

8 to 21 percent.

More than 23 percent.

The restoring force per unit area acting within a body when displaced particles tend to return to their original positions.

It improves hardenability.

Some non-ferrous alloys exhibit magnetic properties.

Concentration of ores.

Seven.

Copper (the metal lower in the electro-chemical series).

The cathodic part.

The presence of free-moving electrons.

Light, tough, highly ductile, easily castable, good conductor of heat and electricity, corrosion-resistant.

Copper, usually mixed with tin.

Fe2O3.

Ore along with gangue is passed through electromagnetic rollers for separation.

It expands slightly.

As lumps in the earth's crust and as nodules on the sea bed.

Copper and zinc.

They can be forged, rolled, cold drawn, and machined with specially designed tools.

Steel with a carbon content of 0.15%.

To improve tensile strength.

Because it leads to breakage without permanent deformation.

The property that enables a material to withstand bending or torsion without fracture.

The property that allows a material to withstand high temperatures without fusing.

About 7.8 g/cm³.

Ag2S.

A process that refines the grain structure and improves mechanical properties by heating and air cooling.

Knives, screwdrivers, and safes.

It improves heat resistance.

A heat treatment process that introduces carbon into the surface of steel to increase hardness.

Stress = F/A, where F is the deforming force and A is the surface area.

The ratio of stress to strain in a material.

It improves cutting ability.

It increases strength and hardness.

Waste/destruction of machines, equipment, and different types of metallic products.

Water.

Low-carbon steel or soft steel.

A homogeneous solid solution of two or more different elements, one of which is at least a metal.

It tends to pass into solution as metal ions.

Steel screws in brass marine hardware.

They can be forged, rolled, cold drawn, and machined with specially designed tools.

0.15 to 0.3%.

An alloy containing mercury (Hg) as its constituent metal.

Gold and Platinum.

They resist corrosion better.

When metal is kept exposed in the atmosphere for a long time.

Making pole-pieces of electromagnets, transformer cores, dynamos, motors, loudspeakers, etc.

A steel propeller shaft in a bronze bearing.

Tough, ductile, weldable by forging, and can withstand shock and impact.

Brass.

Yes, several metals and alloys can perform excellently in a given environment.

Silica (SiO2), alumina (Al2O3), and fireclay (Al2O3·2SiO2·2H2O).

Elasticity.

89 °C.

In kg/cm² of cross-section or N/m².

Resistance to abrasion.

Their easy castability.

It makes them lightweight and easier to handle.

Pollution due to a corrosion product or escaping chemicals.

Gold has excellent resistance to corrosion under atmospheric conditions but can corrode when exposed to mercury.

They are resistant to wear.

Because it allows them to return to their original shape after deformation.

Iron readily rusts in the atmosphere but does not corrode in mercury.

3Pb3(PO4)3PbCl2.

70 °C.

Moisture, air, nitrogen, oxygen, phosphorous, carbon dioxide, sulphur, arsenic, halogens.

MgSO4·7H2O.

It reduces brittleness and increases toughness after hardening.

Metal-cutting tools for lathes, planers, slotters, and engraving tools.

Yes, there are several methods to effectively control and minimize corrosion.

It improves magnetic permeability.

They have good color.

It improves corrosion resistance.

Special electrical properties.

It improves the ability to retain physical properties at high temperatures.

The property that enables a material to withstand forces that tend to break it by tearing.

It improves forgeability.

Low-melting alloys of tin and lead.

Household utensils, decorative pieces, sinks, dental instruments, and surgical instruments.

Used for soldering steel joints by the process of fusing.

The property that enables a material to withstand forces that tend to distort its shape.

Molybdenum.

Soldering electrical connections, sealing tin cans, and joining lead pipes.

It reduces wear and improves performance in moving parts.

Molybdenum.

Tin 92%, Antimony 5.5%, and Copper 2.5%.

Soldering and tinning.

Metals typically exhibit high electrical and thermal conductivity, malleability, ductility, and luster.

Steel alloys are used in construction, automotive, and machinery industries due to their strength and durability.

To improve properties such as strength, corrosion resistance, and hardness compared to pure metals.

They are the backbone of modern civilization.

An alloy is a mixture of two or more elements, where at least one is a metal, designed to enhance certain properties.

Alloys can be classified into ferrous (containing iron) and non-ferrous (not containing iron) alloys.

A method used to prevent corrosion by making the metal surface the cathode of an electrochemical cell.