ENGR 205 Test 2/Final

corrosion

Deteriorative loss of a metal as a result of dissolution environmental reactions.

degradation

Used to denote the deteriorative processes that occur with polymeric materials, including swelling, dissolution, and chain scission.

Metal corrosion is a(an) _____ process.

electrochemical

Oxidation reactions _____ electrons, while reduction reactions _____ electrons.

lose, gain

An electrochemical cell where an anode corrodes and the cathode electrodeposits is a _____.

galvanic couple

Metals are more active, or anodic, toward the _____ in the emf series.

bottom

An oxidation-reduction reaction's likelihood increases if the galvanic cell's electrode potential is _____.

high

The Nernst equation calculates the _____ when temperature and solution concentration change.

cell potential

oxidation

The removal of one or more electrons from an atom, ion, or molecule.

anode

The electrode in an electrochemical cell or galvanic couple that experiences oxidation, or gives up electrons

reduction

The addition of one or more electrons to an atom, ion, or molecule.

cathode

The electrode in an electrochemical cell or galvanic couple at which a reduction reaction occurs; thus the electrode that receives electrons from an external circuit.

electrolyte

A solution through which an electric current may be carried by the motion of ions.

standard half-cell

An electrochemical cell consisting of a pure metal immersed in a 1 M aqueous solution of its ions, which is electrically coupled to the standard hydrogen electrode.

electromotive force (emf) series

A ranking of metallic elements according to their standard electrochemical cell potentials.

galvanic series

A ranking of metals and alloys as to their relative electrochemical reactivity in seawater.

Metals in the _____ region form a protective film on the metal's surface.

passive

If a metal transitions to show passive behavior, then corrosion rate _____.

decreases

If a metal transitions to show passive behavior, then corrosion rate _____.

lower

For an active-passive metal, the corrosion rate is higher in the _____ region than the _____ region.

active, passive

passivity

The loss of chemical reactivity, under particular environmental conditions, by some active metals and alloys, often due to the formation of a protective film.

Uniform attack occurs with _____ intensity on an exposed surface.

equal

In galvanic corrosion, the _____ metal corrodes and the _____ inert metal doesn't corrode.

anode, cathode

The galvanic corrosion rate ______ as cathode-anode surface area ratio increases.

increases

Crevice corrosion is caused by _____.

stagnant electrolyte solution and dissolved oxygen depletion

_____ corrosion penetrates a metal's horizontal surface and grows vertically downward.

Pitting

Precipitate formation along grain boundaries _____ intergranular corrosion.

increases

_____ primarily causes erosion corrosion.

fluid motion

Applied tensile stresses mixed with a corrosive environment can cause _____ in a metal.

cracking

Hydrogen embrittlement arises when hydrogen penetrates a metal's surface and _____ tensile strength

decreases

galvanic corrosion

The preferential corrosion of the more chemically active of two metals that are electrically coupled and exposed to an electrolyte.

pitting

A form of very localized corrosion in which small pits or holes form, usually in a vertical direction.

intergranular corrosion

Preferential corrosion along grain-boundary regions of polycrystalline materials.

weld decay

Intergranular corrosion that occurs in some welded stainless steels at regions adjacent to the weld.

selective leaching

A form of corrosion in which one element or constituent of an alloy is dissolved preferentially.

erosion-corrosion

A form of corrosion that arises from the combined action of chemical attack and mechanical wear.

stress corrosion (cracking)

A form of failure that results from the combined action of a tensile stress and a corrosion environment; it occurs at lower stress levels than are required when the corrosion environment is absent.

hydrogen embrittlement

The loss or reduction of ductility of a metal alloy (often steel) as a result of the diffusion of atomic hydrogen into the material.

Inhibitor molecules are primarily used in _____.

environmental altercation

Galvanizing _____ a zinc layer to steel's surface to protect the surface from damage.

adds

_____ from an external DC power source supplies electrons to protect steel structures buried in the ground.

Impressed current

inhibitor

A chemical substance that, when added in relatively low concentrations, retards a chemical reaction.

cathodic protection

A means of corrosion prevention by which electrons are supplied to the structure to be protected from an external source such as another, more reactive metal or a dc power supply.

sacrificial anode

An active metal or alloy that preferentially corrodes and protects another metal or alloy to which it is electrically coupled.

Polymers don't corrode, but undergo a physiochemical process called _____.

degredation

_____ is the solute diffusion into the spaces between polymer molecules.

swelling

The upper bound of a large-particle composite's modulus of elasticity is equal to _____.

EmVm + EpVp

A cermet is a group of composites that combines a _____ and a _____.

ceramic, metal

Small carbon black particles are used to reinforce modern rubber because carbon black has a _____ than other reinforcing materials.

stronger adhesive bond

Portland cement concrete is composed of Portland cement and _____.

both fine and coarse aggregate

Prestressed concrete is formed using _____ to introduce a compressive stress on the concrete.

steel wire

prestressed concrete

Concrete into which compressive stresses have been introduced using steel wires or rods.

reinforced concrete

Concrete that is reinforced (or strengthened in tension) by the incorporation of steel rods, wires, or mesh.

concrete

A composite material consisting of aggregate particles bound together in a solid body by a cement.

cermet

A composite material consisting of a combination of ceramic and metallic materials. The most common cermets are the cemented carbides, composed of an extremely hard ceramic (e.g., WC, TiC), bonded together by a ductile metal such as cobalt or nickel.

rule of mixtures

The properties of a multiphase alloy or composite material are a weighted average (usually on the basis of volume) of the properties of the individual constituents.

dispersion strengthening

A means of strengthening materials in which very small particles (usually .1 m) of a hard, inert phase are uniformly dispersed within a load-bearing matrix phase.

large-particle composite

A type of particle-reinforced composite in which particle-matrix interactions cannot be treated on an atomic level; the particles reinforce the matrix phase.

fiber-reinforced composite:

A composite in which the dispersed phase is in the form of a fiber (i.e., a filament that has a large length-to-diameter ratio).

specific strength:

The ratio of tensile strength to specific gravity for a material.

specific modulus (specific stiffness)

The ratio of elastic modulus to specific gravity for a material.

For a continuous aligned fiber composite with a longitudinal tensile load, a strain above e*f means that the ____ failed.

fibers

For a continuous fiber with a transverse load, the _____ is equal for composite, fiber, and matrix

applied stress

The longitudinal tensile strength of continuous and aligned fiber-reinforced composites corresponds with the point of _____ failure.

fiber

The tensile strength of continuous and aligned fiber-reinforced composites in the transverse direction is _____ the tensile strength in the longitudinal direction.

less than

The mechanical characteristics of _____ fiber-reinforced composites are isotropic.

discontinuous and randomly oriented

longitudinal direction

The lengthwise dimension. For a rod or fiber, in the direction of the long axis.

transverse direction

A direction that crosses (usually perpendicularly) the longitudinal or lengthwise direction.

cross-ply

laminae have a 0 to 90 degree layered

unidirectional

all laminae have the same high strength direction

angle-ply

laminae are layered by certain angles

multidirectional

laminates have multiple high strength directions

structural composite

A composite whose properties depend on the geometrical design of the structural elements. Laminar composites and sandwich panels are two subclasses

laminar composite

A series of two-dimensional sheets, each having a preferred high-strength direction, fastened one on top of the other at different orientations; strength in the plane of the laminate is highly isotropic.

The outer sheets of a sandwich panel need to have high _____.

tensile strength

The core material of a sandwich panel should have high _____.

shear strength

Sandwich panels are typically used when the primary loading is _____.

bending

sandwich panel

A type of structural composite consisting of two stiff and strong outer faces that are separated by a lightweight core material.

Ohm’s Law

The applied voltage is equal to the product of the current and resistance; equivalently, the current density is equal to the product of the conductivity and electric field intensity. V = IR

Using Ohm's law V = IR, if an applied voltage stays constant and current increases, then resistance

decreases

Electrical _____ measures a material's resistance to current flow.

resistivity

If a material's circular cross-sectional area's radius doubles, then the electrical resistivity changes by a factor of _____.

4

resistivity (p)

The reciprocal of electrical conductivity; a measure of a material's resistance to the passage of electric current.

Electrical conductivity measures how easily a material conducts electrical _____.

current

The expression _____ is equivalent to Ohm's law given as V = IR

J = (1/p)*E

The voltage is measured at a material's opposite ends. If the material length increases, then the current density _____.

stays the same

Metals

High conductivity

Insulators

Low conductivity

conductivity, electrical

The proportionality constant between current density and applied electric field; also, a measure of the ease with which a material is capable of conducting an electric current.

metal

The electropositive elements and the alloys based on these elements. The electron band structure of metals is characterized by a partially filled electron band.

insulator (electrical)

A nonmetallic material that has a filled valence band at 0 K and a relatively wide energy band gap. Consequently, the room-temperature electrical conductivity is very low.

As the separation distance between atoms decreases, an atom's energy levels _____.

split

For a material with N=8 atoms, the _____ band will have _____ different electron states.

p,24

In semiconductors, the _____ has a lower energy level than the _____.

valance band, conduction band

electron energy band

A series of electron energy states that are very closely spaced with respect to energy.

Fermi energy (E_f)

For a metal, the energy corresponding to the highest filled electron state at 0 K.

valence band

For solid materials, the electron energy band that contains the valence electrons.

conduction band

For electrical insulators and semiconductors, the lowest-lying electron energy band that is empty of electrons at 0 K. Conduction electrons are those that have been excited to states within this band.