Factors affecting thermal conductivity of materials
Answers
Answer:
free electrons, purity of material, temperature, pressure,density, crystalline structure
Answer:
Factors influencing thermal conductivity
Free electrons
Metals are having more free electrons compared to that of liquid and gases, so metal are good conductors of heat due to the migration of free electrons. Metals are having closely packed lattice compared to liquids and gases.
Purity of material
Thermal conductivity of the pure material is higher than that of alloy materials. Alloying of metals and presence of impurities cause a decrease in thermal conductivity. E.g. thermal conductivity of pure copper is 385 W/mK but copper having content of arsenic, thermal conductivity is 142 W/mK.
Effect of forming
Treatment of metals like heat treatment and metal forming like bending, drawing and forging decreases the thermal conductivity of material compared to the material before treatment.
High temperature
Solid: At elevated temperature lattice vibration increases and free electrons movement decreases, thus the thermal conductivity of metal decreases when the temperature is increased.
Gases: But for gases, thermal conductivity increases. The reason behind it at a higher temperature, mean travel velocity of gas molecules and specific heat increases, because the thermal conductivity of gas is = (The mean travel velocity)X (specific heat)X (mean free path times density). While, Liquid: Thermal conductivity of the liquid is also proportional to the density and at a higher temperature, the density of liquid decreases thus, thermal conductivity also.
Pressure
Thermal conductivity is weakly dependent on pressure of substance. Means change in pressure does not affect much in thermal conductivity.
Density
Thermal conductivity is highly dependent on density of material. The increase in density increases thermal conductivity.
Crystalline structure
Material having a regular crystalline structure has higher value of thermal conductivity compared to that of amorphous(irregular) form.
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