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Homework answers / question archive / University of Ontario Institute of Technology ENGR 2220A QUIZ 2: 1)Most imperfections in solid crystal structure of metals originate: When it is subjected to stress and strain During the machining process When the material is heated When the molten metals solidify Atomic Packing Factor is the ratio of number of whole atoms in a unit cell to the total number of atoms that the unit cell intersects the ratio of weight of whole atoms in a unit cell to the weight of total number of atoms that the unit cell intersects the ratio of volume of the atoms in a unit cell to the volume of the unit cell Polymorphism is defined as the property of a material which enables it to form different crystal structure under different conditions the property of a material which enables it to form different crystal sizes under different conditions the property of a material which enables it to form different compositions under different conditions The number of vacancies in a material Increase in inverse proportion to the temperature Decrease in direct proportion to the temperature Increase in direct proportion to the temperature Increase in exponential proportion to the temperature The solubility of a solute in general decreases with increasing pressure decreases with increasing temperature is higher when crystal structures of constituents are similar is lower when the atom sizes are similar The equilibrium number of vacancies Nv is NOT a function of the following parameters Total number of atomic sites Temperature Forces between atoms Boltzmann’s constant Metals tend to have higher densities because The metallic bonds are non directional allowing atoms to be densely packed together

University of Ontario Institute of Technology

ENGR 2220A

QUIZ 2:

1)Most imperfections in solid crystal structure of metals originate:

- When it is subjected to stress and strain
- During the machining process
- When the material is heated
- When the molten metals solidify

- Atomic Packing Factor is

- the ratio of number of whole atoms in a unit cell to the total number of atoms that the unit cell intersects
- the ratio of weight of whole atoms in a unit cell to the weight of total number of atoms that the unit cell intersects
- the ratio of volume of the atoms in a unit cell to the volume of the unit cell

- Polymorphism is defined as

- the property of a material which enables it to form different crystal structure under different conditions
- the property of a material which enables it to form different crystal sizes under different conditions
- the property of a material which enables it to form different compositions under different conditions

- The number of vacancies in a material

- Increase in inverse proportion to the temperature
- Decrease in direct proportion to the temperature
- Increase in direct proportion to the temperature
- Increase in exponential proportion to the temperature

- The solubility of a solute in general

- decreases with increasing pressure
- decreases with increasing temperature
- is higher when crystal structures of constituents are similar
- is lower when the atom sizes are similar

- The equilibrium number of vacancies Nv is NOT a function of the following parameters

- Total number of atomic sites
- Temperature
- Forces between atoms
- Boltzmann’s constant

- Metals tend to have higher densities because

- The metallic bonds are non directional allowing atoms to be densely packed together.
- The metallic bonds are directional in nature thereby forming linkages over long atomic distances and forcing atoms to be densely packed together.

- Metals get covalently bonded to form the heavier structure

- Which statement is a correct example of point defects?

- Vacancy atoms, Interstitial, Grain boundaries and Substitutional atoms
- Vacancy atoms, Interstitial, Self-interstitial and Substitutional atoms
- Vacancy atoms, Interstitial, Dislocation and Substitutional atoms
- Vacancy atoms, Interstitial atoms, Self-interstitial, Dislocation and Substitutional atoms

- The solubility of a solute in general

- Increases when the atomic radii are similar.
- Increases when the crystalline structure of both solvent and solute is dissimilar
- Decreases when the crystalline structure of both solvent and solute is similar
- is higher when the atom are located very far apart on the periodic table

- The solubility of a solute in general

- decreases when the atomic radii are similar.
- Increases when the crystalline structure of both solvent and solute is dissimilar
- Decreases when the crystalline structure of both solvent and solute is similar
- Increases when the atoms have similar electro negativities

- Interstitial point defect occurs when:

- An impurity atom displaces a host atom from its lattice position and occupies that space
- An impurity atom dislodges host atoms along grain boundaries and occupies that space
- An impurity atom resides in the space between the lattice positions without displacing any host atom
- An impurity atom diffuses into the extra spaces between the grain boundaries

- Diffusion of impurity atoms into solid materials occurs due to

- Brownian motion of atoms
- Application of excessive pressures
- Movement of individual atoms into adjacent vacancy or interstitial spaces
- Movement of chunks of alloying materials due to the fabrication process

- Rate of substitution diffusion of impurity atoms into solid materials increases at higher temperatures because:

- the Brownian motion of atoms increases with increasing temperatures
- the number of vacancies increases with increasing temperatures
- the magnitude of atomic vibrations at the crystal lattice positions increases with increasing temperatures
- it results in higher pressures which drives diffusion

- Rate of steady state diffusion of impurity atoms into solid materials directly depends upon:

- the concentration gradient of the impurity atoms
- the application of excessive pressures
- the thickness of the diffusion membrane

- the reciprocal of the diffusion coefficient

- Case hardening of steels with carbon atoms is an example of

- Vacancy diffusion
- substitution diffusion
- self diffusion
- interstitial diffusion

- Which ONE of the following statements is correct?

- Diffusion coefficient for interstitial diffusion is very high compared to diffusion coefficient for substitution diffusion
- Diffusion coefficient for substitution diffusion is very high compared to diffusion coefficient for interstitial diffusion
- Diffusion coefficient for substitution diffusion increases at a slower rate compared to diffusion coefficient for interstitial diffusion with increasing temperatures
- Diffusion coefficient for substitution diffusion is generally larger compared to diffusion coefficient for interstitial diffusion

- Which ONE of the following statements is correct?

- Diffusion coefficient for interstitial diffusion is very low compared to diffusion coefficient for substitution diffusion
- Diffusion coefficient for substitution diffusion is very high compared to diffusion coefficient for interstitial diffusion
- Diffusion coefficient for substitution diffusion increases at a higher rate compared to diffusion coefficient for interstitial diffusion with increasing temperatures
- Diffusion coefficient for substitution diffusion is generally larger compared to diffusion coefficient for interstitial diffusion

- Which ONE of the following statements is correct?

- Diffusion coefficient is inversely dependent upon the absolute temperature
- Diffusion coefficient is directly dependent upon the absolute temperature
- Diffusion coefficient is directly dependent upon the absolute pressure
- Diffusion coefficient is exponentially dependent upon the absolute temperature

- Diffusion is SLOWER: (Choose ONE)...

- in materials that have open crystal structures
- in materials with secondary bonding
- when the diffusing atoms are smaller
- in higher density materials

- Diffusion is FASTER: (Choose ONE).

- in materials with close-packed structures
- in materials metallic bonding
- when the diffusing atoms are smaller
- in higher density materials

- If a material is subjected to torsion;

- it experiences sheer stresses
- it experiences tensile stresses
- it experiences compressive stresses

- If a long bar having a rectangular cross section (a x b) and length l experiences a force F along its length, the normal stress it endures is defined as:

- F x a^2
- F/(a x b)
- F x a x b

d. F/(a^2)

- The maximum APF is exhibited by

- BCC and FCC crystals
- HCP and FCC crystals
- BCC and HCP crystals

- Which statement is true only for composites?

- Composites are materials containing two or more elements
- Composites are materials containing two or more distinct phases
- Composites are materials containing two or more than two variety of fibers

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