Thermal Properties of Materials

Thermal Properties

• Thermal energy refers to the kinetic energy of atoms and the potential energy of distortion of interatomic bonds.

• Melting temperature is the temperature where a material transitions from a solid to a liquid state.

• Solidification temperature is the temperature where a material transitions from a liquid to a solid state.

Thermal Expansion

• Thermal expansion is a material's tendency to change in dimensions (shape, area, and volume) due to temperature changes.
• The linear coefficient of thermal expansion is the proportional change in material length after heating.

Thermal Conductivity

• Thermal conductivity is a key parameter for understanding heat transfer through materials.
• Thermal conductivity is the rate of heat conduction through a unit cube of material with a 1°C temperature difference.

Thermal Diffusivity

• Thermal diffusivity is thermal conductivity divided by heat capacity multiplied by material density.

• D = k/(Cp * P), where:

  • k = thermal conductivity
  • Cp = material's heat capacity
  • P = material's density.

Specific Heat and Heat Capacity

• Specific heat is the ratio of energy needed to raise 1 gram of a material by 1°C compared to the energy to raise an equal mass of water by 1°C.
• Heat capacity is the ratio of heat absorbed by a material to the resulting temperature change.

Glass Transition Temperature

• Glass transition temperature is the point at which a solid material transitions from a rigid state to an amorphous or glassy state.

Thermal Phase Diagram

• Thermal phase diagrams show the organization of a solid phase
• The diagram includes the following parts:
  • Low temperature (Albite) on the left and high temperature (anorthite) on the right
  • Composition in percent anorthite
  • Three fields exist: all liquid, liquid + crystal, and all crystal.
  • The liquidus line separates the "all liquid" phase from the "liquid + crystal" phase
  • The solidus line separates the "liquid + crystal" phase from the "all crystal" phase

Electrical Properties

• Electrical conductivity measures a material's ability to conduct electric charge.
• Electrical resistivity measures a material's ability to oppose the flow of electric current.
• Dentin has lower resistivity than enamel; sound and carious enamel differ in resistivity.

Corrosion

• Corrosion is a natural process causing deterioration of materials (usually metals) due to reaction with their environment.
• Corrosion can be chemical or electrochemical.

Galvanic Corrosion

• Galvanic corrosion is accelerated corrosion between electrochemically dissimilar materials.

Intergranular Corrosion

• In crystalline solids, intergranular corrosion starts at grain boundaries where impurities accumulate.

General Notes on Corrosion

• The less noble material is attacked during corrosion.
• Electrical corrosion requires electrical contact in the presence of water or other conducting solution (electrolyte).
• The anode is less electronegative (loses electrons), while the cathode is more electronegative (attracts electrons).