Kyrylenko K. Resistive composites with multicomponent percolating cluster for heaters with intensive heat removal

The dissertation covers the studies of materials based on Si3N4 - ZrC and Si3N4 - НfC, as well as Hf2CN, Zr2CN and SiC phases. It is shown, that only for materials with AlN matrix the conductivity and ТКR correspond to the percolation model. For a matrix of Si3N4 observed shift of the percolation threshold towards lower concentrations of the highly conductive phase, the hysteresis temperature dependence of ρ and extreme temperature dependence of ТКR, as well as the varistor effect in the range of low concentrations of conductor. The products of the chemical interaction between conductor phase, dielectric matrix and pressing environment, substantially influence on the formation of electroconductive cluster, and shift the percolation threshold in the area of low concentrations of the highly conductive phase (5 – 10%), and increasing of the resistance (extrapolated on 100% of conducting phase) ρ in 100 - 100 000 times. The temperature hysteresis of ρ is observed, this effect is caused by presence of SiС in the resistive composite. The model of hysteresis ρ and calculations of temperature distributions were carried out using the equivalent schemes. The fabrication technology of materials with properties, necessary for their effective using for the monolithic ceramic heaters with enhanceable convective heat emission to 50 W/m2К in the conditions of the forced convection in mid air and to 120 W/m2К in water was developed and tested.