Material Properties

Question 1

Hume-Rothery rules (substitutional)

Answer 1

1) The atomic radii of the solute and solvent atoms must differ by no more than 15%
2) The crystal structure of solute and solvent must match
3) Complete solubility occurs when the solvent and solute have the same valence. Metals with lower valence will tend to dissolve in metals with a higher valence
4) The solute and solvent should have similar electronegativity. If the electronegativity difference is too great, the metals will tend to form intermetallic compounds instead of solid solutions

Question 2

Hume-Rothery rules (interstital)

Answer 2

1) Solute atoms must be smaller than the interstital sites in the solvent lattice
2) The solute and solvent should have similar electronegativity

Question 3

Piezoelectricity

Answer 3

Coupling between electrical polarisation and mechanical deformation

Question 4

Physical origin/use of piezoelectricity

Answer 4

Due to the presence of asymmetric charged groups in a material. As the material is deformed, the charges move with respect to each other and produce a dipole charge. Dry bone is piezoelectric but it is not clear whether wet bone is or not. Piezoelectric materials have been used to stimulate bone growth following fracture by virtue of electric stimulation.

Question 5

Adhesion

Answer 5

Two different material surfaces bonded together

Question 6

Cohesion

Answer 6

Two surfaces of the same material bonded together

Question 7

Physiosorption

Answer 7

Attracting other materials via electrostatic or van der Waals interactions to minimise surface energy

Question 8

Chemisorption

Answer 8

Adsorption of a material by a chemical bond

Question 9

Attenuation occurs via:

Answer 9

The photoelectric effect: energy of the x-ray is transferred to a bounded electron, and the electron is ejected
Compton scattering: scattering of the x-ray by free or weakly bounded electrons in the material

Question 10

Absorption coefficient is proportional to

Answer 10

N^5 lambda^7/2

Question 11

Acoustic Impedance

Answer 11

z = rho v

Question 12

Quenching

Answer 12

Rapid cooling to avoid undesired low-temperature properties. It prevents the formation of a second phase (beta phase). However, depending on the ambient temperature of the implant and time, a second phase can be formed via precipitation. If the second phase particles are small enough and evenly distributed, then it can significantly improve the strength of the material. The particles must be within grains as well as at grain boundaries to help lock dislocations in place.

Question 13

Fire polishing

Answer 13

Heat treatment of ceramics:
Produces surface compression resulting in an increased tensile stress of the surface. This must be overcome before stresses start to affect microcracks in the bulk. Can increase strength up to 200 times.

Question 14

Wetting angle

Answer 14

90 = partial wetting
0 - 90 = complete wetting
>90 non-wetting

Question 15

Measuring gamma

Answer 15

Sessile drop
Captive air bubble
Wilhemy plate
Capillary action