The amount of heat passing throughout unit cross-section of a solid material in unit time for unit thermal gradient is termed as thermal conductivity. The units of thermal conductivity are as: JH/m/s/K or else W/m/K. The heat conduction arises from higher temperature to lower temperature such is opposite to direction of thermal gradient.
The thermal conductivity in solid material is because of:
i. Elastic vibration of atoms or molecules whereby energy is transmitted in from of kinetic energy of vibrating units, and
ii. Movement of electrons.
Given figure shows the variation of thermal conductivity throughout temperature for metallic materials.
Figure: Thermal Conductivity of Metals varying with Temperature