Dental Alloys

Question 1

Which relates more directly to properties of alloy

Answer 1

A. Atomic percent

B. Weight percent

Question 2

In order to form an alloy, metals in molten condition must be

Answer 2

Mutually soluble

Question 3

Are phases mechanically separable from each other

Answer 3

Yes

Question 4

Describe the miscibility of most alloys in dental restorations

Answer 4

Solid solution, metals are soluble in each other in the solid state

Question 5

Which metal is the solvent in solid solution

Answer 5

The metal whose space lattice persists

Question 6

How many phases present in solid solution

Answer 6

Single phase, mechanically inseparable

Question 7

Describe substitutional solid solution

Answer 7

Atom of solute occupy space lattice position normally occupied by solvent atom

Question 8

At which part of the alloy does corrosion occur

Answer 8

Grain boundaries

Question 9

What is the effect of substitutional solid solution

Answer 9

Slight difference in size and electronic structure, solute distorts the lattice and hinders electron flow, making it harder for one plane of atoms to slip past each other

Question 10

What is the requirement of the solute in interstitial solid solution

Answer 10

Solute must be much smaller in diameter than solvent atoms (<59% of solvent radius) so that it can fit between solvent atom

Question 11

Describe the structure of superlattice

Answer 11

Ordered structure, atoms of 1 metal occupy only specific positions in space lattice of other metal. Exact composition

Question 12

What is the favourable size factor for atomic size for substitutional solid

Answer 12

Size differ by less than approx 15%. If greater than 15%, multiple phases may appear upon solidification

Question 13

What happens if there is great difference between valency for solute and solvent in solid solution

Answer 13

Greater difference lower solubility. Same valence and size, more likely to form solid solution

Question 14

Why should solvent and solute in solid solution have similar electronegativity

Answer 14

High degree of chemical affinity = tendency to form intermetallic compound upon solidification

Question 15

How does lattice type affect ability to form solid solution

Answer 15

Substitutional solid, only metals with same types of lattice can form solid solutions. Mostly face centred cubic

Question 16

Describe properties of alloys

Answer 16

Greater mechanical strength, greater proportional limit, increased hardness, lower ductility

Question 17

How so alloys get their increased mechanical strengtn

Answer 17

Localised distortion/strained condition of lattice, slip becomes difficult. Distortion in lattice creates compressive forces at bonds, increasing mechanical properties

Question 18

What is the eutectic point

Answer 18

When everything becomes liquid at the same time

Question 19

Properties of eutectic alloys

Answer 19

Brittle, increased strength and hardness vs constituent metals, poor corrosion resistance

Question 20

Why do eutectic alloys have poor corrosion resistance

Answer 20

A lot of grain boundaries

Question 21

Uses of eutectic alloys

Answer 21

Soldering, dispersed phase in high copper amalgam