MSE 2001 Final
If you have an orthorhombic unit cell with lattice parameters:a = 4 angstromsb = 6 angstromsc = 3 angstromsWhich of the following x-ray diffraction peaks will be at the largest Bragg diffraction angle (2theta)?
001 Because this is orthorhombic, the (100), (010), and (001) are not in the same family of planes, so they all have different spacing. Because the c-axis has the smallest lattice parameter, it will have the largest Bragg diffraction angle
How many lattice points are in a primitive hexagonal unit cell
1
A metal rod with a square cross-section has a resistance of 10 ohms. If the square edge has a width of 1 cm and the rod has a length of 10 cm, what is the resistivity of the metal?
1 ohm-cm R=rho*l/A rho=resistivity A=cross-sectional area
If Ca impurities are added to TiO2 and form substitutional defects on the Ti sites, what type of defect might form to charge compensate for them and in what ratio?
1 oxygen vacancy : 1 Ca impurity With calcium on a titanium site, titanium has a +4 charge and calcium will only have a +2 charge, so the Ca will adopt an effect -2 charge. Vacant oxygen sites are expecting a -2 charge, so they have an effective +2 charge. Thus 1:1 these two point defects will compensate each other.
You own some sterling silver jewelry. Sterling silver is a solid solution of 92.5 wt.% silver and 7.5 wt.% copper. How many phases does Sterling silver have?
1 phase
In a material with a well-defined yield point, the yield strength is determined to be 200 MPa. The strain value at this point is 0.002. Compute the Young's modulus.
100 GPa E (modulus) = stress/strain
For a cubic unit cell, how many planes are in the {110} family?
12
How many unique slip planes are contained in the {211}<111> slip system for BCC metals?
12
In a cubic crystal system, what is the angle between the directions [1 1 0] and [2 1 0]? Values given in degrees
18.4 theta = arccos( (sum of corresponding products)/product of the square root of the sum of the squared entries)
Which of these bond-energy curves has the longest equilibrium bond length at 0 K?
Equilibrium bond length at the temperature 0 K is the minimum in the bond-energy curve. D has the minimum farthest from the origin (0), and therefore is the longest bond length.
Which of the following accurately completes this sentence:If a material is crystalline,...I. it must be a ceramic. II. it has atoms in an ordered arrangement. III. it has atoms in a disordered arrangement.
ii ONLY
van der waals
secondary bonding increases in strength as the number of atoms in the compound increases occurs between different types of dipoles formed in molecules
Rhombohedral
simple a=b=c α=β=γ≠90
hexagonal
simple a=b≠c α=β=90 γ=120
Triclinic
simple crystal system: a ≠ b ≠ c; α ≠ β ≠ γ ≠ 90°
monoclinic
simple, base centered a≠b≠c α=γ=90° β≠90°
Orthorhombic
simple, base centered, body centered, face centered a ≠ b ≠ c; α = β = γ = 90°
tetragonal
simple, body centered crystal system: a = b ≠ c; α = β = γ = 90°
Interface Formation
small portion o fthe material that begins to solidify first is called the nucleus, where atoms begin to take on a prescribed arrangement. Neighboring atoms make not take on this arrangement, forming interfaces between nuclei
In a material containing only one element, what piece of information would we use to determine the most likely type of primary bonding present?
the number of valence electrons
Oxide glasses are likely to form if
the oxygen polyhedra share corners
FCC
Face Centered Cubic 4 atoms per unit cell CN=12 Close packed direction: <1 1 0> (along face) High density plane: (1 1 1) (CPP)
Which of the following is not a type of tetragonal crystal struc ture? (select all that apply)
Face centered tetragonal Base centered tetragonal
True / False: Paramagnetic materials make good permanent magnets because they can achieve high magnetizations when placed in a magnetic field.
False
How are edge dislocations and screw dislocations different from each other?
The Burgers vector for an edge dislocation is perpendicular to the dislocation line, and the Burgers vector for a screw dislocation is parallel to the dislocation line
Which of the following statements is true about how the equilibrium vacancy concentration is determined in a material
The ENTHALPY of vacancy formation accounts for bond breakage and acts to lower the concentration of vacancies in a material while the ENTROPY of vacancy formation accounts for the increased disorder due to vacancy formation and acts to increase the concentration of vacancies in a material.
Why are ionic solids like most ceramics brittle?
The alignment of similarly charged ions upon plastic deformation leads to fracture.
You are hired for a composite manufacturer and the boss asks you to help them improve the mechanical performance of their fiberglass product. Which of the following might you investigate for this project?
The use of a chemical treatment on the glass fibers' surfaces prior to embedding these fibers in the polymer matrix. New geometrical arrangements of the glass fibers in the composite.
grain boundaries
as a material is cooled, it crystalizes. grain boundaries occur between two parts of the same material that have crystalized possibly with different orientations
congruent melting maximum
clustering in the liquid phase solid phase is more stable
congruent melting minimum
clustering in the solid phase liquid phase is more stable
Composite
combination of 2+ materila classes to try and merge the properties example: fiberglass, concrete, cermet and metal matrix composites properties depend on: fiber orietation/length and chemical composition of the materials
isomorphous system
complete liquid and solid solubility of two components compounds that follow Hume-rothery Rules
Which of the following is NOT a mechanical property of a material? ductility hardness yield strength dielectric constant
dielectric constant
For a tetragonal unit cell, the (100), (010), and (001) planes will have the same value of Bragg diffraction angle
false
In general, Frenkel defects are more likely to occur for anions than they are for cations.
false
Most polymers have high electrical conductivity
false
The yield strength of a material generally increases with the square of the dislocation concentration.
false
True / False: An inclusion is an example of a point defect.
false
True / False: If a material is cooled below its phase transformation temperature it will always transform into its thermodynamically predicted stable phase.
false
True or False: As long as a component's operation temperature remains below the melting temperature for ALL materials in that component, it will not fail.
false
True or False: Electrically conductive materials make good piezoelectrics.
false
True or False: If a hard magnetic material is heated above its Curie temperature and then cooled back to room temperature it will regain its original permanent magnetization.
false
True or False: Protective oxide layers on metals form when oxidation causes a large volume expansion.
false
True/False: Assuming equilibrium behavior, no liquids exist at temperatures below the liquidus line on a binary phase diagram.
false No solids exist above the liquidus line. The solidus line denotes the boundary below which no liquid exist. However, some solids can exist above the solidus line -- take a look again at the solid solution phase diagram that we first used to describe the solidus.
At the atomic level, normal stresses drive plastic deformations in a material.
false Plastic deformation is only the result of shear stresses at the atomic level.
A Schottky defect pair consists of an interstitial and a vacancy.
false Schottky defects are a set of vacancies in a stoichiometric ratio.
The bonds between Fe-Fe in a steel alloy are primarily considered to be covalent.
false This is a bit tricky. Even when metallic elements bond to themselves, you still get primarily metallic bonding with the "bonding electrons" delocalized in the "electron sea". You do not consider these bonds covalent, although they may have a minor covalent character--more so if it is an intermetallic.
The polydispersity index of a polymer can be less than 1
false Mn<Mw
In general, ceramics have high ductility.
false; cermaics are usually brittle
Tough materials have a high yield strength and a low ductility.
false; tough materials have high ductility/larger area under stress strain curve
Which one of the following would be classified as a magnetic material? Paramagnetic materials Ferrimagnetic materials Antiferromagnetic materials Diamagnetic materials
ferrimagnetic materials
Which of the following are examples of composites?
fiberglass cermets concrete
Gibbs Phase Rule
for a system at equilibrium, an equation that expresses the relationship between the number of phases present and the number of externally controllable variables F = C-P+N F-degrees of freedom C-number of components P-number of phases N-number of state variables
fatigue
for materials under repeated loading cyclic loading about a mean stress leads to damage accumulation stress level below which failure does not occur
Which of the following element pairings can be used to produce a semiconductor?
group IV elements III-V pairing II-VI pairing
The bonds between H-H for hydrogens in two separate polymer chains
van der Waals Bonding
In a cubic unit cell, which of the following planes will have the smallest Bragg diffraction angle?
{110}
Which family of crystalline planes has the highest atomic packing density in a BCC metal?
{110}
What is close packed plane for FCC?
{111}
You are hired by a bedding company to design new mattresses. Your first project is to design a "firm" mattress (that is, one that does not compress very much when you lay on it). Below are the stress-strain curves that have been collected for three different foams loaded under compression. Amongst these three foams, which would you select to make the "firmest" mattress and why?
Foam B because it has the highest elastic modulus.
In this type of bonding the transfer of electron(s) from one atom to another leads to an electrostatic attraction that causes the bonding.
ionic
stacking faults
occur when there is an error in the planar stacking sequence normal configuration: HCP - ABABA FCC - ABCABC
Most clothing belongs to which class of materials
polymer (cotton, polyester)
energy barriers
prevent phase transformation atomic diffusion formation of interfaces
If a crystal structure is found to have two of its lattice parameters equal to one another but the third have a different length (a = b \ne= c), which crystal class might it belong to?
tetragonal or hexagonal
In window glass, silicon is
tetrahedrally coordinated to 4 oxygens.
basis
the "group of things" located on a lattice point
Which of these represents the unit cell for the 2D lattice
the one connecting all the same colored dots
Another name for a 2D defect is...
a planar defect
Most gemstones belong to which class of materials
ceramics
Assume that you have a base-centered orthorhombic unit cell with only 1 atom per lattice point. The atom on those lattice points has a molar mass of 50 g/mol. The unit cell dimensions are: a = 2 angstroms b = 3 angstroms c = 5 angstroms
(2*50/6.022*10^23)/(2*3*5)*10^-24
Rules for Oxide Glass Formation
-networks are composed of oxygen polyhedra -coordination number o f each O atom is 2 -coordination number of each metal atom is 3 or 4 - oxide polyhedra share corners, not faces or edges -each polyhedra must share at least three corners
Point Defects
1-dimensional edge dislocations, screw dislocations a "line" of atoms that are displaces"
Which fraction of an atom sitting at the "corner" of a 3-dimensional cubic unit cell would be counted as being part of the unit cell? (For example, if you were counting atoms for calculating the theoretical density of the solid.)
1/8
What is the mass of the chromium atoms contained in its unit cell? Consider the atomic mass of chromium to be 52 g/mol and use its crystal structure at room temperature.
1.7 x 10^-22 g
What fraction of an atom sitting at the face center of a cubic unit cell would be counted as being part of the unit cell? (For example, if you were counting atoms to calculate the theoretical density of the solid)
1/2 of an atom
Planar Defects
2-dimensional Grain boundaries, stacking faults, interphase boundaries, surfaces Boundaries or planes of atoms misplaced
How many different planes are in the {210} family of a cubic unit cell?
24
You apply 2 volts to a piezoelectric material and measure a displacement of 0.5 nm. What is the approximate piezoelectric coefficient d33 for this piezoelectric?
250 pm/V .5/2
What is the approximate molecular weight of a repeating unit (monomer) of polyethylene?
28 g/mol
Volume defects
3-dimensional pores, cracks, inclusions a bulk defect
In a cubic unit cell, which of the following x-ray diffraction peaks will have the largest Bragg diffraction angle (2theta)?
330 bragg angle = 2theta use bragg's law
How many atoms are in the unit cell of a face-centered cubic metal? (Count the atoms like you would to determine the density of the face-centered cubic metal.)
4
The cable of a hoist has a cross-section of 80 mm2. The hoist is used to lift a crate weighing 500 kg. What is the stress in the cable?
61 MPa stress = force/cross-sectional area
A ceramic rod that is 10 cm long has a thermal expansion coefficient of 8 x 10-5 (m m-1 °C-1). What percent strain elongation does the rod undergo when it undergoes a temperature increase of 1000°C? (Remember to multiply strain by 100% to get PERCENT strain.)
8% strain change in length = alpha*length*temp change
Thermogravimetric analysis (TGA) is an analytical technique that tracks the mass change of a material as it is heated from room temperature to some higher temperature. TGA can be performed in a variety of atmospheres including air, vacuum, or pure nitrogen. TGA could be used to assess the service temperature of a material for which of the following cases: A. The temperature at which oxidative corrosion occurs for a metal alloy. B. The melting temperature of the material. C. The temperature at which a polymer "softens" and loses its ability to mechanically sustain a load.
A
The window panes found in a typical U.S. residential home are a good example of what class of material?
A ceramic-based glass
Anodization of aluminum can be used to: A. Make the surface of the aluminum harder. B. Change the color of aluminum. C. Protect the aluminum against corrosion.
A, B, C
Which of the following approaches would be useful for improving a plastic's resistance to UV degradation? A. Adding a UV absorbing coating to the plastic's surface. B. Including additives to the plastic's composition that help prevent UV degradation. C. Electrically connecting the plastic component to a sacrificial anode.
A,B
Thermal barrier coatings on turbine blades... A. have a low thermal conductivity in order to increase the service temperature of the underlying metal component. B. have a low thermal conductivity in order to decrease the service temperature of the underlying metal component. C. have a high thermal conductivity in order to increase the service temperature of the underlying metal component. D. have a low coefficient of thermal expansion to ensure no delamination from the turbine blade.
A. have a low thermal conductivity in order to increase the service temperature of the underlying metal component.
You are asked to help design a bimetallic temperature sensor. You are given five metal alloys to work with; their thermal expansion coefficients are listed below. Assuming the elastic properties for each alloy are identical, which combination of alloys would give you the largest temperature-sensitive deflection for your sensor design?Thermal Expansion Coefficients of Alloys Alloy 1: 15 m/m-K Alloy 2: 10 m/m-K Alloy 3: 10 m/m-K Alloy 4: 8 m/m-K Alloy 5: 5 m/m-K
ALLOT 1 AND 5 WANT BIGGEST CTE DIFFERENCE
GaAs is a common semiconductor used to make solid state lasers used in CD and DVD players. How covalent are the bonds in GaAs?
About 97% covalent. 100% = %ionic + %covalent
Which of these elements is/are known to form self-limiting oxide surface layers that are protective against further corrosion: A. Iron B. Aluminum C. Chromium D. Copper
B,C
Which of the following is an example of a III-V semiconductor?
B. Gallium arsenide
In the bond energy equation:Etotal = -A/x + B/x12
B/x12 describes the energy of repulsion between the two atoms forming the bond -A/x describes the energy of attraction between the two atoms forming the bond
Which of these elements would you expect to have the smallest electronegativity?
Ba (furthest left on periodic table)
BCC
Body centered cubic: 2 atoms per unit cell, CN=8 examples: Cr, Fe, W Close packed direction: <1 1 1> (along diagonal) High density plane: (1 1 0) (NOT CPP)
Silica
Can be piezoelectric Can be crystalline Can be amorphous
thermoplastic
Capable of being softened by heat; may be remolded. flow when heated 3-d network formed through SECONdAry bonds and physical entanglement
Sand is mostly composed of small particles of silicon dioxide. To what materials class would you classify sand?
Ceramic
The peaks observed in an x-ray diffraction experiment are the result of:
Constructive interference from x-rays scattering from planes of atoms with a path length difference equal to the wavelength of the x-rays.
In brass, which is a solid solution of copper and zinc that contains less zinc than copper,
Copper is the solvent and zinc is the solute
An electrochemical reaction that typically occurs to a metal in an aqueous environment is referred to as
Corrosion
Predict the most likely type of primary bond in GaP
Covalent
For the force-distance curve between two bonding atoms shown here, which feature best represents the equilibrium bond distance?
Distance C The distance from the origin to the point where the linear portion of the graph crosses the x-axis
Copper and nickel form a continuous substitutional solid solution, i.e. they form a one phase material over the whole composition range. What does this mean about this material pair?
Elemental copper and elemental nickel have the same crystal structure
The angle at which light refracts when it enters the flat surface of a material could depend upon: I. The refractive index of the material. II. The wavelength of the light. III. The size of the material. IV. The angle of incidence of the light into the material.
I,II,IV
Which of the following elements would be a good selection as the sacrificial electrode in the cathodic protection of tin (Sn)? I. Silver II. Copper III. Nickel IV. Magnesium
III and IV
The Hume-Rothery rules contain a condition that the electronegativity values of the two atomic species must be similar. Why is this condition needed for a substitutional solid solution to form?
If the electronegativity values are too different, then the elements are likely to form a compound
When is the creep rate constant?
In the steady state creep regime.
The materials parameter that quantifies the toughness of a material is:
K1c
What is the proportionality constant that determines the amount of magnetization that occurs within a material when a magnetic field is applied to the material?
Magnetic Susceptibility (Chi)
Network modifiers
Na, Ca, K , Mg, Sr, Ba, Pb, Li
homogenous nucleation
Nuclei form uniformly throughout the liquid
The unit cell of a new crystal has been determined. The angles between each of its three lattice directions are all 90°, but the lattice parameter for each axis direction (a, b, and c) is a different length. In which crystal class would you place this lattice?
Orthorhombic
Which crystal class includes primitive, body-centered, face-centered, and base-centered Bravais lattice types?
Orthorhombic
Which of the following would be a good n-type dopant for the semiconductor silicon?
Phosphorus Arsenic
Light-activated degradation processes are referred to as:
Photodegradation
Which of the following is not a ceramic?
Plexiglass
Which of the following polymers do you think may form hydrogen bonds?
Poly(acrylic acid), PAA Nylon 6
Which of the following is an example of an elastomer?
Polybutadiene
Syndiotactic
R groups alternate sides
atactic
R groups randomly positioned
Consider a copper rod that is 3.14 meters long, 2 cm in diameter, and has an electrical resistivity of 5x10-6 ohm-cm. What is the electrical resistance of the rod?
R=rho*(l/a) 5x10-4 ohm
Thermoplastics can be
Recycled Melted Crystallized
Which of the following metals are likely to form an oxide glass?
Si, Ge, As
Most polymers contain carbon in their backbone structure
TRUE
True or False: Polymers can be used to protect other materials from corrosion.
TRUE
True or False: The remanent magnetization of a material is its level of permanent, internal magnetization in no applied magnetic field.
TRUE
A capacitor initially uses a dielectric material with a dielectric constant of 5. If that dielectric layer is replaced with a new material having identical size to the initial material but with a dielectric constant of 15, what happens to the capacitance of the capacitor?
The capacitance will increase by a factor of 3x.
Shown here is the equilibrium phase diagram for the system consisting of components X & Y. Consider a system containing 60% Y at a temperature T' (marked with a red dot). In this state, what is the COMPOSITION of the liquid phase? (Dotted blue lines are added to help aid the eye.)
The composition of a phase in a two phase region is where the tie line intersects the phase boundary with that phase's single phase region. In this case it is at 40 mol% Y.
Which of the following statements are true when comparing BCC and FCC crystal structures (select all that apply)
The linear density along the close packed direction for BCC and FCC are the same The atomic packing factor for FCC is greater than that for BCC FCC has more atoms per unit cell than BCC
fracture toughness
The measure of a material's resistance to fracture when a crack is present. (K1c) K1c = Y(critical stress)*sqrt(pi*crack length)
Steel beams to be used for outdoor construction are going to be electroplated with a corrosion-protection coating. Steel has a thermal expansion coefficient (\alphaα) of 13 ppm/°C. Which of the following coating materials would you select to minimize risk of thermal delamination of the coating?
Ultra Coating (\alphaα = 12 ppm °C) CLOSEST CTE
Assume you are working on constructing a new building in a nominally hot climate that experience a lot of sunshine (e.g., Arizona). To reduce building heating during the day, which color paint would you recommend for painting the roof and why?
White because it reflects the most visible light.
ZnO adopts the wurtzite crystal structure. Based on the unit cell for wurtzite shown here, what can you say about the lattice and basis for wurtzite ZnO?
Wurtzite ZnO has a primitive hexagonal lattice and a 2 Zn atom + 2 O atom basis.
Which of the following is a type II-VI semiconductor?
ZnSe
An amorphous solid is also known as
a disordered solid
Isotactic
all R groups on same side of chain
The term for a solid metal composed of multiple elements is
alloy
lattice
an indefinitely extended arrangement of point each of which is surrounded by an identical grouping of neighboring points -simple/primitive, body centered, base centered, face centered
Amorphous materials
are often transparent/translucent lack long range order
Which of the following is not a ceramic
brass
Which type(s) of bonding would you expect in the plastic material high-density polyethylene?
covalent and van der Waals bonding. Polymers typically have covalent bonding in the backbone and van der Waals bonding between polymer chains.
In most metals, plastic deformations at room temperature caused by loads greater than the yield stress are the result of...
dislocation motion
If you were asked to design a new rubber band that could stretch farther without breaking, which of these material properties would you try to maximize? hardness yield strength stiffness ductility density
ductility
p-type dopants
extra hole in configuration B Al In
creep
failure assisted by temperature slow continuous deformation due to the constant application o fa modest load below the yield stress typically occurs at .35 Tm for elemental metals steady state creep is linear region
Because van der Waals bonding is about 100x weaker than other types of bonding (e.g., ionic, covalent, metallic), it has no influence on the properties of a material.
false
Ceramics can withstand high loading in tension
false
Creep only occurs if the applied stress is greater than the yield strength of the material.
false
If you were asked to design a windshield that would resist being scratched by debris while driving, which material property would you try to maximize?
hardness
Elastomers
have yield points at high strain values
Polymers
large compound formed from combinations of many monomers -hydrocarbon backbone -molecular weight can be very high -spaghetti like structure -most are amorphous but some semi-crystalline -low elastic modulus -reasonably high toughness (unless glasss) -electrically insulating -low thermal conductivity -low service temp -often transparent or tranluscent -corrosion resistant -will react with UV light, strong oxidizers - low density, high strength to weight ratio
the units for strain are
length/length
congruent melting
liquid and solid compositions are the same
In general, polymers have
low moduli high electrical resistivity
Adding cross-links to a polymer will...
make the polymer more rigid
You are designing a system based on piezoelectric actuation to precisely move objects at the nanometer scale. Your system is limited to an operating voltage of 500 V. The system must be able to move objects AT LEAST 150 nm. You are allowed to select amongst the following piezoelectric materials in the table below to accomplish this mechanical motion. Which of these materials would you recommend for this mechanical manipulation system? Material I: d33 = 800 pm/V Material II: d33 = 300 pm/V Material III: d33 = 200 pm/V Material IV: d33 = 100 pm/V
materials I and II
For elemental zinc, what is the most likely type of bond formed between atoms?
metallic
Which of the following bonding types has long range sharing of electrons?
metallic
Which of the following material classes can form glasses?
metals, polymers, ceramics
the units for modulus are
pascals
the units for stress are
pascals
A new paint is designed to only reflect red light and absorb all other colors. What color would you perceive for an object that has been coated with this paint?
red
When light enters a material and changes its direction of propagation, this process is called:
refraction
hydrogen bonding
secondary bonding hydrogen atoms shared between two strongly electronegative atoms polar
Which of the following is not a polymer?
silicon
alloy
solid solution of metals formed to increase the yield strength
Strength-toughness tradeoff
strain energy goes to either plastic deformation or crack propagation
semi-conductors
sub-class of ceramics have moderate electrical conductivity
intermetallics
sub-class of metals with precise stoichiometry less tough, more brittle, higher melting point, higher hardness
What information is not needed to calculate the theoretical density of an elemental metal?
the electronegativity of the element
Metal alloys are different from crystalline ceramics because
the elements in a metal alloy are randomly arranged on a crystalline lattice
radius of plastic zone
the larger the plastic zone, the greater the dissipation of mechanical energy into plastic deformation r = K1^2/(pi*(stresslevel)^2)
atomic diffusion
the random motion of atoms/molecules in a system. while local motion is random, more global motion typically occurs from areas of high concentrations to areas of low concentration in order to homogenize systems composition. in a solid solution, this would be the solute moving through the solvent
unit cell
the smallest, repeatable unit that when translated in 3 demensions can cover all of space
Which of the following is/are example(s) of 2D defect(s) in a crystalline material?
the surface of the material grain boundaries
Considering the glass transition temperature measured for the same material at two very different cooling rates (CR1 and CR2, where CR1 > CR2),
the value of the glass transition temperature measured using CR1 is higher than that measured using CR2
Network modifiers are added to oxide glasses for what purpose
to lower the glass transition temperature
(True/False) Grain boundaries are the boundaries between two mis-oriented single crystals in a polycrystalline solid.
true
If a material is plastically deformed it is deformed permanently.
true
schottky defects
vacancy created as a group to preserve neutrality
Frenkle defect
vacancy interstitial pair created to preserve charge neutrality, normally occurs for the cation
Which of the following materials/compounds have a two atom basis? (select all that apply)
zinc sulfide sodium chloride cesium chloride
Which family of planes act as dislocation slip planes in an HCP metal? Use the three Miller index notation for this problem.
{001}
Metallic bonds...
...allow for high electrical conductivity in a material. ...are non-directional. ...allow a material to plastically deform.
The yield strength observed in a crystalline material at low homologous temperatures...
...is often orders of magnitude lower than the "ideal yield strength" of a material because plastic deformation occurs by dislocation glide.
"Frosted windows"...
.use surface roughness to scatter light and distort the image you see.
A 1 cm thick piece of opaque material is measured to reflect 95% of visible light. How much light is transmitted through the metal?
0%, opaque materials don't transmit any light
Calculate the reflectivity for a material with a refractive index of 2. Assume that the light is traveling from air to this material
0.11 R= (Ir)/(Io)=(n2-n1/n2+n1)^2
The cable of a hoist has a cross-section of 80 mm2. The hoist is used to lift a crate weighing 500 kg. What is the stress in the cable?For the cable in the previous question, if the free length of the cable is 3 m, how much will it extend if it is made of steel (modulus 200 GPa)?
0.92 mm stress = modulus*strain strain = (change in length)/(initial length) change in length = (stress/modulus)*(initial length)
5 things that impede dislocation motion
1) hihg lattic resistance - difficult for dislocations to move through covalently bonded material and ceramics 2) solution hardening - alloting (atom replacement by solute) 3) precipitate hardening - bledning in other elements that precipitate when they solidify 4) work hardening - due to dislocation reactions with one another ( too many dilocations) 5) Grain size- larger grain boundaries are harder to move across
If the modulus for a metal is 100 GPa, what would the ideal yield strength of the material be?
10 GPa ideal yield strength = 1/10E
A polymer has a number average molecular weight of 65,000 g/mol. If the PDI is 2.1, what is the value of the weight average molecular weight?
137,000 g/mol
Calculate the weight average molecular weight for a polymer that contains polymer chains with a mixture of molecular weights in the following proportions: 30% at 10,000 g/mol, 40% at 60,000 g/mol, and 30% at 200,000 g/mol
150,000 g/mol
How many atoms are contained in a unit cell for the BCC crystal structure?
2
How many slip directions are in just the (101) slip plane of a BCC metal?
2
For oxide glass formation, what should the coordination number of oxygen be?
2 rules for oxide glass formation
A Schottky defect in Al2O3 would consist of:
2 aluminum vacancies and 3 oxygen vacancies.
If the lattice parameter for a cubic crystal is 6 angstroms, what is the interplanar spacing for the (221) planes?
2 angstroms Use d(hkl) = a / (h^2+k^2+l^2)^(1/2)
Consider a body centered cubic metal as shown here. If you were to calculate the density of this metal, how many atoms per unit cell volume would you use?
2 atoms/unit cell
White latex paint is an emulsion of acrylate monomers, an iniator, and TiO2 particles that scatter light to give the white color. While drying on the wall, initiators are released and polymerize the monomers into a latex polymer. Excluding the initiators (which effectively become part of the polymer), how many phases are in dried white paint?
2 phases
A Schottky defect in indium oxide (In2O3) would consist of:
2 vacancies on indium sites and 3 vacancies on oxygen sites
A 1 cm thick piece of stainless steel metal is measured to reflect 98% of visible light at a wavelength of 500 nm. How much light is absorbed by the metal at a wavelength of 500 nm?
2% 100-98
Titanium dioxide (TiO2) is deposited as an amorphous thin film. When annealed, 75% of the film crystallizes. X-ray diffraction analysis reveals that these crystals are a mix of rutile, anatase, and brookite -- three different crystal structures of titanium dioxide. At this point, how many phases are in the TiO2 thin film?
4 Phases
You are asked to help in the design of the metal rails used for the construction of a new railroad track. The tracks are expected to be installed in the winter time when temperatures are about 0°C. You can expect a maximum service temperature of 40°C. Assuming each length of metal rail is to be cut to a length of 100 m and have a thermal expansion coefficient of 1x10-5 m/m-K, what is the minimum gap (i.e., thermal expansion joint) that should be included between rails to prevent buckling?
4 cm (change in length) = alpha * (initial length)(change in temp.) alpha - thermal expansion coeffiecient
Consider a solid glass window with a thickness of 5 mm and a thermal conductivity of 1.7 W/(m-K). Calculate the heat flux through this window if the inside temperature is 25 °C and the outside temperature is 10 °C.
5100 W/m2 Q=(-LAMBDA) (CHANGE IN TEMP/CHANGE IN DISTANCE) LAMBDA - THERMAL CONDUCTIVITY Q - HEAT FLUX
If a tetragonal unit cell has "a" lattice parameters of 5 angstroms in length and a "c" lattice parameter of 2 angstroms in length, then the unit cell volume would be:
5x10-23 cm3
What is the expected coordination number for an ion located at an octahedral interstitial site?
6
How many unique slip planes of the {110} type are in a BCC metal?
6 (110), (101), (011), (-110), (-101), (0-11) -- the negatives of these are not unique, and I only asked for the {110} family not for the {112} and {123} families.
Using a UV/Vis spectrometer, it is found that a 0.5 cm thick piece of window glass reflects 12% of visible light (at 500 nm wavelength) and absorbs 4% of visible light (at 500 nm wavelength). How much light is transmitted through this glass at 500 nm wavelength?
84%
Cesium fluoride makes the most ionic bond known to exist. What is the percent ionicity of this bond?
92% percent ionicity = ( (1-e^(-1/4)*(x1-x2)^2)) * 100%
If you wanted to MAXIMIZE the deflection of a bimetallic strip undergoing a temperature swing of 10 °C which two materials amongst the 5 listed below would you choose? (Assume the elastic properties are identical for all materials.) Material A, heat capacity = 15 J/g-°C, thermal expansion coefficient = 15 ppm/°C Material B, heat capacity = 3 J/g-°C, thermal expansion coefficient = 3 ppm/°C Material C, heat capacity = 10 J/g-°C, thermal expansion coefficient = 10 ppm/°C Material D, heat capacity = 17 J/g-°C, thermal expansion coefficient = 10 ppm/°C Material E, heat capacity = 10 J/g-°C, thermal expansion coefficient = 7 ppm/°C
A and B Want to maximize difference in CTE
If a material is deformed plastically, which of the following must be true?
A permanent deformation occurs.
Hume-Rothery Rules
A set of rules for the formation of substitutional solid solutions. They incorporate relative sizes, bond character, and electronegativity of the atomic species being considered. 1) size of solute and solvent must be similar 2)electronegativities of the two atomic species must be comparable 3)the valence of the two species must be similar 4)the crystal structure of the two species must be the same
Two metal alloys are nearly identical, except Alloy A has 2% impurity content and Alloy B has 8% impurity content. Assuming lattice resistance is nearly zero for both alloys, what do you predict the difference in yield strength (sigma)y to be for these two materials?
Alloy B will have a 2x higher yield strength than Alloy A. Concentration increases by 4x, and shear strength scales by the sqrt(concentration), so the shear strength increases by 2x. The conversion to yield strength (3x) cancels out when comparing the two materials.
Which of the following elements would you expect to have the highest electronegativity?
Cl (furthest right on periodic table)
Which of the following might you do to increase the yield strength of a metal rod? (A) Cold draw the metal rod to a smaller diameter. (B) Polish the surface of the metal rod. (C) Anneal the rod in such a way as to reduce the dislocation density. (D) Add more impurity elements to the alloy before casting the metal into the final rod.
Cold draw the metal rod to a smaller diameter. Add more impurity elements to the alloy before casting the metal into the final rod.
During an x-ray diffraction experiment with a metal that has a FCC crystal structure, a diffraction peak associated with the {200} planes is observed at a two theta value of ~50 degrees. Considering this information, which of the following metals is being characterized? Assume that the wavelength of the x-rays being used is 1.5406 Angstroms
Copper, lattice parameter = 3.6 Angstroms
Which type(s) of bonding would you expect to find in the solid semiconductor germanium?
Covalent bonding only.
Which of the following characteristics are usually all associated with a metal alloy?
Crystalline structure, high thermal conductivity, and high toughness
What is the inverse of electrical conductivity?
Electrical resistivity
Which of the following best describes "anodization" of an aluminum part:
Electrochemically oxidizing the aluminum in a controlled manner
Possible kinetic barriers that prevent phase transformations from occurring quickly include: (A) Energy costs associated with interface formation. (B) Energy costs associated with the free energy change for the phase transformation. (C) Energy costs associated with the long range diffusion of atomic components to the product phase. (D) Energy costs associated with dislocation motion in a solid.
Energy costs associated with the long range diffusion of atomic components to the product phase Energy costs associated with interface formation.
You work for an electronics manufacturer and are asked to design a new capacitor. The capacitor has a basic parallel plate design, so the dielectric layer will be a "flat" square. Assuming the capacitor must be a fixed thickness (really thin for the latest smart phone) and you want is to have the smallest area possible (smallest overall size), which of the following materials would you recommend? Blue-Gold Charge Separator Dielectric Constant: 25 Electrical Resistivity: 100 giga-ohms-meters GT Charge Master Dielectric Constant: 25 Electrical Resistivity: 150 giga-ohms-meters Buzz Storage Plus Dielectric Constant: 15 Electrical Resistivity: 150 giga-ohms-meters The Burdell Special Dielectric Constant: 15 Electrical Resistivity: 100 giga-ohms-meters
GT Charge Master Dielectric Constant: 25 Electrical Resistivity: 150 giga-ohms-meters A= rho*l/R want bigger resistance higher dielectric constant = high capacitance
Polymers have a _________ strength to weight ratio
HIGH
Intermetallics
Have high hardness Have a precise stoichiometry Have a repeating pattern of elements that can be similar to ceramics
Select ALL of the following that are "materials constants" (i.e., do not depend on the size or shape of the material).
Heat Capacity electrical resistivity dielectric permittivity
Which of the following characteristics are usually associated with metals?
High elastic modulus, prone to corrosion, easy to machine
On a standard temperature-pressure UNARY phase diagram, if you are at a point with 2 degrees of freedom, you must be:
In a single phase region.
You work for a manufacturing facility that produces electrical resistors. Currently you sell a resistor that has a length of 9 cm, a cross-sectional area of 3 cm2 and uses Metal A with an electrical resistivity of 2 ohm-cm. Unfortunately the melting point of the resistive metal is too low and these resistors keep failing due to melting in operation. You are asked to design a new resistor with the same resistance using Metal B which has a higher melting temperature. Metal B has an electrical resistivity of 6 ohm-cm. What would you recommend for its design?
Length = 1 cm; Cross-sectional Area = 1 cm2 want the same overall resistance
Of the three stress-strain curves shown here (A, B, C), which of the following statements is most likely true.
Material A is likely a ceramic material because it shows brittle behavior.
You are asked to design a skillet (pan) for cooking. The key requirement is that the skillet reaches the same temperature as the heat source (oven burner) as quickly as possible. Based on this requirement, which of the following materials would you select? Material B: Thermal conductivity = 10 W/m-K, Heat Capacity = 5 J/mol-K Material E: Thermal conductivity = 4 W/m-K, Heat Capacity = 8 J/mol-K Material C: Thermal conductivity = 8 W/m-K, Heat Capacity = 4 J/mol-K Material A: Thermal conductivity = 2 W/m-K, Heat Capacity = 8 J/mol-K Material D: Thermal conductivity = 12 W/m-K, Heat Capacity = 2 J/mol-K
Material D again want highest thermal diffusivity
Which two classes of materials properties are coupled in the piezoelectric effect?
Mechanical and Electrical
ceramics
Non-metallic inorganic solids -often composed of metal and oxygen -usually ends in -ide -gemstones and other rocks -crystalline -ceramic glasses are amorphous -brittle, no plasticity -low ductility, stiff -high hardness
Below are two plastic cups both made out of the polymer, (C8H8)n. Which do you expect to be less dense and why?
The styrofoam cup is likely less dense because making the polymer into a foam adds more porosity to the material.
This material likely has an atomic structure that resembles a "mess of spaghetti":
Polyethylene terephthalate (PET) in soda bottles
Elastomers
Polymeric materials that return to their original shapes after stretching. low modulus with high strain point for yielding
Which of these polymers is LEAST likely to crystallize.
Polysytrene [C2H3(C6H5)]n in this case polystryrene had the largest side group
Glass network formers
SiO2, GeOs, B2O3, P2O5, AsO5
Which of the following would INCREASE the grain size in an aluminum component that was cast from a molten metal melt? A. Solidify at a different temperature that increases the nucleation rate. B. Solidify at a different temperature that increases the growth rate for the solid nuclei. C. Add MORE heterogeneous nucleating agents to the molten melt prior to solidification. D. Solidify at a different temperature that increases the growth rate for the solid nuclei.
Solidify at a different temperature that increases the growth rate for the solid nuclei. Solidify at a different temperature that increases the growth rate for the solid nuclei.
glass transition temperature
The temperature at which, upon cooling, a noncrystalline ceramic or polymer transforms from a supercooled liquid into a rigid glass. -less than room temp for rubbers and elastomers
The density of a solid material is determined by:
The composition of the material. The porosity of the material. The crystal structure of the material porosity - flaws+vacancies in atomic structure
CsCl and NaCl are both ionic compounds containing Cl, and both compounds have a 1:1 stoichiometry for the Cl and the metal. Why is the coordination number of Cl different in these two compounds?
The coordination number for Cl in CsCl is higher than in NaCl because the ionic radius for Cs is larger than the ionic radius for Na
Cobalt can have either an FCC or HCP structure. At room temperature, how would you expect the mass densities of the FCC and HCP forms of cobalt to compare?
The density of FCC cobalt will be EQUAL TO the density of HCP cobalt. FCC and HCP have the same atomic packing density, so if the atom's are of the same type, the mass density should be the same.
The curvature of the well in the energy-bond distance curve has a direct phenomenological relationship to:
The elastic modulus of a material.
A thin, translucent plastic sheet appears green in color. Which of the following explanations may explain its appearance?
The plastic reflects green light. The plastic transmits green light.
Which factors affect the crystallinity of a polymer (select all that apply)
The structure of the repeating unit Tacticity The size of side groups
In the stress-strain curve for an arbitrary material shown below, which point most closely matches the yield point for the material?
The yield point is when the stress-strain curve goes from linear to non-linear. This occurs at point B.
An iron nut and bolt are used to attach two zinc plates together on the underside of a boat. If this boat is to be used in the ocean, what might happen?
The zinc plate will undergo galvanic corrosion.
The materials property that determines the amount of heat flux that will flow across a given length of material at a fix temperature difference is the: Thermal Diffusivity Thermal Conductivity Heat Capacity Thermal Flux Capacitance Thermal Expansion Coefficient
Thermal Conductivity
Thermal expansion is a cross-property. It could be categorized as both a:
Thermal and Mechanical property
Which of the following statement(s) is NOT true about the (2 -1 4) and (-2 1 -4) planes in a cubic crystal system?
They are both perpendicular to one another.
"Super balls" that bounce really high are an example of...
a thermoset polymer with its Tg below room temperature.
You design a rod to hold a chandelier from the ceiling, but then your boss informs you that the chandelier will be twice as heavy. Your initial design will now plastically deform under the weight. Which of the following could be done to your original design to allow it to work with the new chandelier? A. Use the same material, but shrink the diameter of the rod. B. Use the same material, but increase the diameter of the rod C. Choose a material with a higher elastic modulus, but keep the rod diameter the same. D. Choose a material with a higher yield strength but keep the rod diameter the same. Both B & C will work. Both B & D will work.
both b and d will work
Which class of materials has higher values of thermal conductivity?
ceramics>polymers
In the Energy-Bond Distance curves shown here, which material appears to have the highest thermal expansion coefficient?
choose the graph with the largest radius at the curve
If a crystal structure is found to have all of its lattice parameters equal to one another (a = b = c), which crystal class might it belong to?
cubic or rhombohedral
Match the mechanical property to its atomic scale mechanism.
elastic modulus - bond strength density - atomic mass toughness - crack propagation yield strength - dislocation motion
Thermoset
having the property of becoming permanently hard and rigid when heated or cured a material that will have chemical crosslinks between chains 3-d network formed through PRIMARY bonds between chains (crosslinks) ex. polybutadiene, natural rubber, PDMs
The materials property that describes the amount of heat energy STORED for a given temperature differential is the:
heat capacity
In general, ceramic materials have which of the following characteristics
high modulus low toughness
Metals
inorganic solids made of only metallic elements nearly all are crystalline susceptible to corrosion high elastic modulus good toughness pure elemental metals have low yeild strength
For light and other types of radiation, the angle of incidence
is measured with respect to the surface normal is large for glancing incidence affects the reflectivity
The elastic modulus of a material...
is the proportionality constant in Hooke's Law. is the slope of the linear portion of a stress-strain curve
This crystal class has a unit cell where all of the lattice parameter have different lengths but only one of the interaxial angles is not 90°.
monoclinic
If the cable was made from a material with a lower modulus, would the cable stretch more or less?
more
Metallic glasses
must be processed using high cooling rates to suppress crystallization
n-type dopants
negative, add an electron: P As Sh
The glass transition temperature (select all that apply)
occurs at a lower temperature than the melting temperature is present in amorphous polymers is affected by cooling rate is present in ceramic glasses is present in semicrystalline polymers
Which is NOT a common property of polymers:
relatively high service temperature
Because of their rigid bonding angles, covalent solids usually have more open crystal structures than ionic solids.
true
Dislocation slip occurs along the crystalline planes with the highest atomic density and in the directions of highest linear atomic density in a crystal.
true
For a given Bravais lattice, each lattice point is symmetrically equivalent to all other lattice points in that structure.
true
For an orthorhombic crystal structure, the (100), (010), and (001) planes will each have a different value of the Bragg diffraction angle.
true
Polymer molecules can have molecular weights on the order of 1,000,000 g/mol
true
The (101) and (-101) are unique slip planes in an BCC metal.
true
The atomic packing factor for FCC and HCP are the same
true
The properties of composites depend on fiber orientation within the material
true
True / False: Increasing the temperature of the semiconductor germanium will increase the concentration of germanium vacancies in the material.
true
True / False: Substitutional point defects can be used to increase the electrical conductivity of a semiconductor.
true
True or False: High coercive field magnetic materials are useful as permanent magnets
true
True/False: Amorphous solids have short range order.
true
True/False: Polycrystalline materials have many mis-oriented crystalline grains in their microstructure because the phase transformations used to create these materials (e.g., solidification) occur via a nucleation and growth process.
true
True/False: Thermoset polymers with a glass transition temperature below 0 °C will exhibit rubbery behavior in typical ambient conditions.
true
Unlike brittle materials, tough materials are less likely to fracture because the mechanical work done on the material is split between plastic deformations and crack propagation.
true
X-ray diffraction can be used to determine the atomic spacing between crystalline planes in a solid.
true
True/False: Adding precipitates to a metal alloy will likely increase its yield strength but decrease its fracture toughness.
true While precipitates will increase yield strength of the alloy, this usually reduces the plastic zone at the crack tip, leading to reduced fracture toughness.
Materials A, B, and C have the thermal properties listed below. You are asked to choose the best material for a cooking pot. For this application, you want to optimize the speed to thermalize the material--i.e., rate to reach equilibrium temperature with heat source. Which material(s) would you recommend? Material A: Thermal Conductivity = 10 W/m-K Heat Capacity = 5 J/m^3-K Material B: Thermal Conductivity = 9 W/m-K Heat Capacity = 3 J/m^3-K Material C: Thermal Conductivity = 10 W/m-K Heat Capacity = 4 J/m^3-K
want a high thermal diffusivity Dth = lambda/(rho*cp) lambda = thermal conductivity cp = heat capacity answer: Material B
Steel panels to be used in the interior of an oven are going to be electroplated with a corrosion-protection coating. Steel has a thermal expansion coefficient (\alphaα) of 4 ppm/°C. Which of the following coating materials would you select to minimize risk of thermal delamination of the coating? Super Coating (\alphaα = 5 ppm / °C) Mega Coating (\alphaα = 15 ppm / °C) Negamax Coating (\alphaα = -3 ppm / °C) Optima Coating (\alphaα = 0 ppm / °C) Ultra Coating (\alphaα = 7 ppm / °C)
want alpha as similiar to the one given as possible Super coating
