Materials Science and Engineering Finals

Corrosion

Destructive electrochemical attack on metals.

Oxidation

Loss of electrons from a metal atom.

Reduction

Gain of electrons by a species.

Galvanic Couple

Two metals connected in electrolyte causing corrosion.

Standard Half-Cell

Reference electrode for comparing metal half-cells.

Standard Hydrogen Electrode

Reference electrode using hydrogen gas at 1 atm.

Electrode Potential

Voltage indicating tendency to oxidize or reduce.

Electrochemical Mechanism

Processes governing oxidation and reduction reactions.

Corrosion Prevention

Strategies to mitigate material degradation.

Metal Oxidation Rate

Speed at which metals corrode in environments.

Corrosion Penetration Rate (CPR)

Rate of material loss due to corrosion, mpy or mm/yr.

Nernst Equation

Calculates cell potential considering concentration and temperature.

EMF Series

Ranks metals by their electromotive force.

Galvanic Series

Ranks metals by reactivity in seawater.

Current Density

Current per unit area affecting corrosion rate.

Overvoltage (η)

Displacement of electrode potential from equilibrium.

Spontaneity of Reaction

Reaction occurs if overall potential difference is positive.

Active Polarization

High H⁺ concentration near electrode, no diffusion limit.

Destructive Attack

Unintentional damage to metals, often electrochemical.

Corrosion Rates

Measure of how quickly materials degrade.

Electrodeposition

Process where metal ions are reduced and deposited.

Half-Cell Potentials

Indicate equilibrium conditions, not actual corrosion rates.

Reactivity

Tendency of metals to undergo oxidation.

Weight Loss

Material loss measured over time due to corrosion.

Density

Mass per unit volume of a material.

Surface Area

Exposed area of a material affecting corrosion.

Electrochemical Reactions

Reactions involving transfer of electrons.

Faraday Constant

96,500 C/mol, relates charge to moles of electrons.

Concentration Polarization

Diffusion of H⁺ ions limits the reaction rate.

Passivity

Metals become inert due to protective oxide film.

Uniform Corrosion

Electrochemical corrosion occurs uniformly on surfaces.

Galvanic Corrosion

Corrosion occurs between electrically coupled dissimilar metals.

Pitting Corrosion

Localized corrosion forms small pits or holes.

Crevice Corrosion

Corrosion in stagnant areas with lower ion concentration.

Intergranular Corrosion

Corrosion along grain boundaries of alloys.

Selective Leaching

One element preferentially removed from solid solution alloys.

Erosion-Corrosion

Corrosion from chemical attack and mechanical abrasion.

Stress Corrosion Cracking

Cracking due to tensile stress and corrosive environment.

Hydrogen Embrittlement

Reduction in ductility from atomic hydrogen penetration.

Cathodic Protection

Prevention technique converting metal into a cathode.

Galvanic Protection

Uses sacrificial anode to protect metal.

Impressed Current

External DC source supplies electrons for protection.

Pilling-Bedworth Ratio

Determines protective nature of oxide film.

P-B Ratio < 1

Porous oxide film, unprotective.

P-B Ratio = 1

Stable and protective oxide film.

P-B Ratio > 1

Dense and protective oxide film.

Corrosion of Ceramic Materials

Ceramics resist corrosion due to stable structure.

Ozone-induced Chain Scission

Ozone reacts with double bonds, causing degradation.

Weathering

Degradation of materials due to outdoor exposure.

Thermal Degradation

Molecular chain scission at elevated temperatures.

Water Absorption

Polymer resilience against decomposition influenced by bonds.

Thermal Stability

Resistance to degradation from thermal effects.

Environmental Effects

Factors influencing corrosion rates include temperature.

Fluid Velocity

Increased velocity typically raises corrosion rates.

Corrosive Concentration

Higher concentration can increase or decrease corrosion.

Ferrous Metals

Metals containing iron, prone to corrosion.

Non-Ferrous Metals

Metals without iron, resistant to rust.

Electromotive Force (EMF)

Voltage measure indicating oxidation tendencies.

Low-Carbon Steel

Contains less than 0.25 wt.% carbon.

Medium-Carbon Steel

Contains 0.25-0.60 wt.% carbon.

High-Carbon Steel

Contains 0.60-1.4 wt.% carbon, very strong.

High-Strength Low-Alloy Steel

Stronger than low-carbon steels, more corrosion-resistant.

Tool Steels

High-carbon alloys for cutting and shaping materials.

Stainless Steels

Corrosion-resistant, with at least 11 wt.% chromium.

Heating Treatment

Process to enhance metal properties through heat.

Mechanical Properties

Characteristics like strength, ductility, and toughness.

Deteriorative Process

Degradation of materials due to environmental factors.

Carbon Concentration

Influences mechanical properties of steel.

Voltage Measurement

Indicates driving force for electrochemical reactions.

Malleability

Ability to be shaped without breaking.

Fusibility

Ability to be melted and shaped.

Environmental Impact

Effects of surroundings on material integrity.

Preventive Measures

Strategies to mitigate material degradation.

Mechanical Strength

Resistance to deformation under applied forces.

Corrosion Resistance

Enhanced by nickel and molybdenum additions.

Martensitic Stainless Steels

Heat treatable with martensite as prime microconstituent.

Ferritic Stainless Steels

Composed of α-ferrite (BCC) phase, magnetic.

Austenitic Stainless Steels

Non-magnetic, high corrosion resistance, widely produced.

Cathodic Metals

Less reactive, include noble metals like gold.

Anodic Metals

More reactive, include base metals like zinc.

Gray Iron

Weak and brittle in tension, strong in compression.

Ductile Iron

Nodular graphite improves strength and ductility.

White Iron

Hard, brittle; carbon exists as cementite.

Malleable Iron

Decomposes cementite, forms graphite clusters.

Compacted Graphite Iron

Graphite has worm-like shape, enhanced properties.

Corrosion Rate Formula

CPR = W/(ρAtK), units in mpy or mm/yr.

Beryllium Coppers

Heat-treatable, high strength, used in aerospace.

Brasses

Copper-zinc alloys, commonly used in applications.

Bronzes

Copper with tin, aluminum, or nickel.

Overvoltage

Measured in volts, affects reaction rates.

Aluminum Alloys

Used in aircraft parts and automotive components.

Ductility

Ability to be easily formed, like aluminum foil.

Melting Temperature

Aluminum's melting point is 660°C.

Principal Alloying Elements

Includes copper, magnesium, silicon, manganese, zinc.

Cast Alloys

Aluminum alloys formed by pouring into molds.

Wrought Alloys

Aluminum alloys shaped by mechanical processes.

Magnesium Alloys

Lightweight, used in aerospace and missile applications.

Corrosion Process

One element removed, impairing mechanical properties.

Titanium Properties

Low density (4.5 g/cm³), high melting point (1668°C).

Tensile Strength

Titanium alloys can reach 1400 MPa at room temperature.