When we arbitrarily create some fraction of pores in a bulk material, it's thermal and electrical conductivity properties should be altered. I want to know more about this variation.
In principle the conductivity or the dielectric permittivity of a porous composite can be described by one of the several available mixture formulae. You have to know the properties of the bulk material the concentration and shape factor of the pores.
Generally in the case of thermal and electrical conductor, the thermal conductivity and electrical conductivity decreases with the increase in porosity.
Is there any clear relation for this variation for example about bulk metallic materials?
There are a number of factors that must be taken into account regarding electrical and thermal properties. At first glance, electrical connectivity between grains will be influenced by the quality of grain boundaries and the area of contact throughout the bulk. This means that percolation must be analyzed, as it is related to porosity within the bulk. You may check the literature for data and ways to interpret and study properties that are affected by percolation. 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.
In principle the conductivity or the dielectric permittivity of a porous composite can be described by one of the several available mixture formulae. You have to know the properties of the bulk material the concentration and shape factor of the pores.
As already mentioned, in general, the presence of porosity is expected to decrease the conductivity of the system; the extend depends on the fraction of porosity. Various models have been proposed to calculate the effect such as mixture approaches (mentioned previously), empirical, percolation (maybe not in metals) etc. For some experimental work: e.g. for metals, you can check the attachment. Hopes this serves as a starting point.
What material system are you working on?
Higher porosity leads to lower electrical and thermal properties. The true question is how fast these changes occur. Many papers of Rice have addressed this interesting problem, providing power laws whose exponents are related to pore shape. You should take a look at these papers.
Alain
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