Does Porosity Decrease Thermal Conductivity In Ceramics

The effects of porosity and pore size on the thermal conductivity are discussed.

Does porosity decrease thermal conductivity in ceramics.

The thermal conductivity of porous materials is theoretically studied in connection with nanoporous materials used in recent semiconductor devices. K k 0 1 p 1 np 2 where k is the thermal conductivity of a porous ceramic body k 0 that of the pore free ceramic body p the volume fraction of the pores and n a. Thermal conduction is generated by the movement of electrons and the transfer of lattice vibrations. The best equation which correlates extremely well the thermal conductivity of the ceramic bodies with the porosity is found to be the one proposed by aivazov and domashnev.

The thermal conductivity of porous sic ceramics has decreased with the increase in porosity 4 39 40. For sand and mixed litholo gies no clear depth dependence was found for porosity indicating that compared with clay both sand and mixed lithology are resistant to compaction by the accumulation of sediment. Trast the bulk density thermal conductivity and thermal diffusivity increase with depth. B briefly explain how the degree of crystallinity affects the thermal conductivity of polymeric materials and why.

Metals with low electrical resistance and crystals in which lattice vibrations are transferred easily for example crystals with atoms or ions of. 7 5 porosity and permeability duration. A briefly explain why porosity decreases the thermal conductivity of ceramic and polymeric materials rendering them more thermally insulative. Bulk density thermal conductivity heat.

Explain why porosity decreases the thermal conductivity of ceramics and polymers. The thermal conductivity of insulating materials is determined by the heat capacity of phonons the average phonon velocity and the phonon mean free path. Porosity should decrease thermal conductivity for similar and other reasons since the presence of air in the pores adds an insulation character to the bulk sample that you may be measuring. Intuition behind formula for thermal conductivity.

The problem with the thermal conductivity of ceramics is the dependence on the composition grain size and manufacturing process which make it rather difficult to obtain a reliable value from literature only.