 # Thermal Properties of Materials

When any solid comes in direct contact with heat, fluctuations in temperature are bound to happen. Also, there is a change in its dimensions as the material absorbs heat and reacts to it. The study of thermal properties of materials has wide applications in thermodynamics, ascertaining a material’s melting point, and heat transfer, etc.

### What are the Thermal Properties?

Thermal properties of engineering materials are a study of those substances which have a direct relation to the temperature fluctuations. Whenever materials come in contact with heat or thermal change, they tend to change in dimensions such as length or volume. Moreover, there is a fluctuation in the temperature of solids when it absorbs heat energy.

The properties of materials help to ascertain how it will respond when it comes in contact with heat. For instance, when a metal comes in contact with heat, its temperature rises, and it tends to melt at high temperature as it reaches its melting point.

### What are the Components of Thermal Properties?

The thermophysical properties of materials consist of the following:

Point 1: The capacity of heat: It is the measure of heat that is necessary to raise the temperature of the material. It is the ratio of heat energy transferred into a substance that results in the temperature change.

Mathematically, it can be stated as the following:

C= ∆Q/∆T=dQ/dT

Where C = Specific heat which gets expressed as per mole,

T = Temperature

Q = Energy

dT = Fluctuations in temperature

dQ =Energy transferred (added or deducted) to cause a change in temperature.

One can measure heat capacity under two conditions which are constant pressure and volume. The formula is:

1. CV = (δq/dT)V - heat at constant volume

2. CP = (δq/dT)P - heat at constant pressure

For solids and liquids, there is a small difference between CP and CV since the expansion is less in these substances after they are subject to heating. However, for gases, CV is always less than CP as the material expands when it absorbs heat.

Fun fact: The heat capacity of aluminium is 900 kJ per kg atoms (degree C) at room temperature!

## The Heat Capacity of Some Materials at kJ/kg Atoms (Degree C) are as Follows:

 Substances Heat Capacity (kJ/kg℃) Silver 235 Nickel 443 Gold 128 Copper 386 Magnesia 940 Brass 375 Polypropylene 1925 Nylon 1670 Tungsten 138

Point 2: Thermal expansion: When any substance absorbs heat or faces temperature changes, there is a change in its volume and length. Thermal expansion occurs in materials when heat passes through the atoms, and they move from their equilibrium.

The formulas of linear and volume expansion are:

Linear:  (lf - l0)/l0 = ∆l/l0 = αl (Tf -T0) = α1-∆T

Where l0 = initial length, lf = final length.

Volume: (Vf -V0)/V0 = ∆V/V0 = αV (TV -T0) = α1- ∆T

Where V0 = initial volume, Vf = final volume.

Point 3: Thermal conductivity: One of the vital components of the thermal properties of materials is its conductivity. Thermal conductivity is the measure of heat transferring capability of a material. Through it, one can ascertain how substances can conduct energy and the direction of its flow.

According to Fourier’s law, energy transfer through solids can be expressed as:

q = -k (dT/dx)

Where q = quantity of heat flowing from a unit area in a specific time

K denotes thermal conductivity

T = temperature

X = direction of energy flow

Fun fact: In insulators, heat conductivity is relatively lower than metals!

Point 4: Thermal stresses: It is the tension created in materials resulting from temperature fluctuations or energy absorption. This category of thermal properties of materials can result in deformation or fracture occurring from dimensional changes.

The study of thermal properties of nanomaterials is vast, and it gets confined to a limited area of knowledge. Moreover, it has broad applications in the field of thermodynamics and study of heat conductivity, etc.

1. What do you Mean by Thermal Properties?

Ans. The thermal properties of materials determine its reaction when subjected to heat. They usually react by contracting or expanding and change in volume with temperature fluctuations.

2. Define Heat Capacity of Materials?

Answer: Heat capacity is the measure of the capacity of a substance to absorb heat when it faces any temperature change. The unit of heat capacity is Joule per Kelvin (J/K).

3. What is Linear and Volume Expansion?

Ans. Linear expansion is the change in the length of the solid when it absorbs heat. Volume expansion occurs when there is a change in volume of a material due to heat fluctuations.