The influence of powder contamination on the percolation limit of metal-ceramic composites obtained from polydisperse powder mixtures

A theoretical method of finding by simulation computer modeling the percolation limit of composites of powder origin, which are obtained on the basis of polydisperse powder mixtures of the conductive and insulating phase, is proposed. At the same time, the degradation of the conductivity of conductor particles skeleton due to oxidation or other contamination of the surface of the particles is taken into account. To study the flow threshold of materials obtained on the basis of polydisperse powder mixtures, the use of regular packings of particles, which are considered in the classic problems of perco¬lation theory, for example, square or hexagonal packing, is not acceptable even in the first approximation. Because in such packages all particles are the same, or the ratio of particle sizes is fixed. At the same time, as is known from the practice of obtaining metal-ceramic composites, the size distribution of conductor and insulator particles is one of the determining factors. Therefore, a generator of random filling of a polydisperse mixture of round particles into a rectangular hopper was developed using the Fortran programing language. The influence of the particle size ratio of the conductive and insulating phases and the relative contamination of the conductor particles on the percolation limit in the composite was studied. It is shown that in the case when the size of the conductor particles decreases in relation to the size of the insulator particles, the value of the percolation limit decreases, that is, conductivity can be achieved even with asmall content of the conductive phase. In this way, the conductivity of the metal-ceramic composite can be controlled without changing the concentration of the conductive phase, but only by varying the size of the metal and ceramic particles. But as the simulation results showed, this method of controlling the conductivity is very sensitive to the oxidation of the metal powder. Even a relative oxidation of the powder surface of 0,1 doubles the concentration of the metal phase required for percolation. Keywords:bidisperse packaging, percolation limit, ballistic filling, metal-ceramic composites, oxidized metal powders.