Does Porosity Decrease Thermal Conductivity In Ceramics

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.

Does porosity decrease thermal conductivity in ceramics. Thermal conduction is generated by the movement of electrons and the transfer of lattice vibrations. The thermal conductivity of porous sic ceramics has decreased with the increase in porosity 4 39 40. B briefly explain how the degree of crystallinity affects the thermal conductivity of polymeric materials and why. 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.

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. 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. The thermal conductivity of porous materials is theoretically studied in connection with nanoporous materials used in recent semiconductor devices. A briefly explain why porosity decreases the thermal conductivity of ceramic and polymeric materials rendering them more thermally insulative.

For example the thermal conductivity of a biomorphic sic ceramic has decreased from 41 5 15 w m k with the increase in porosity from 43 to 67. Metals with low electrical resistance and crystals in which lattice vibrations are transferred easily for example crystals with atoms or ions of. Bulk density thermal conductivity heat. 7 5 porosity and permeability duration.

Looking at the values quoted in various handbooks papers and data sheets two things are observed. The thermal conductivity of insulating materials is determined by the heat capacity of phonons the average phonon velocity and the phonon mean free path. Intuition behind formula for thermal conductivity. Trast the bulk density thermal conductivity and thermal diffusivity increase with depth.

Explain why porosity decreases the thermal conductivity of ceramics and polymers.