ESTIMATION OF THERMAL CONDUCTIVITY CALCULATION MODEL PARAMETERS FOR COMPOSITE MATERIALS WITH A POLYMER BINDER BASED ON EXPERIMENTAL DATA
The paper presents thermal conductivity calculation models of composite materials based on polymer binders (silicone, polyurethane, epoxy resin) with one or two types of fine mineral fillers. The models are constructed on the theory of generalized conductivity taking into account the effect of component inversion. By comparing the calculations with the experiments, the authors estimated the parameters values of the calculation models: the thermal conductivity of filler aggregates with various binders, the binder-filler inversion coefficients in the Odelevsky and Misnar formulas, the influence of the ratio between the thermal conductivities of the filler and the binder in the modified Burgers equation. Regarding mineral powders in the state of free filling (in air), the dependence of the empirical coefficient C in the Burgers equation on the ratio of the thermal conductivities of the powder and air has some differences due to the fact that the dispersed phase in air has much more possibilities to change the position of particles in space and to form contacts and "conducting channels" that "destroy" the isolation of the solid phase and thereby increase the effective conductivity of the mixture. The presented paper shows the measured thermal conductivity of powders in the state of free filling analyzed according to the modified Burgers equation. It is shown that the thermal conductivity of the aggregates is significantly lower than the thermal conductivity of crystalline filler particles, but close to the thermal conductivity of powder ceramics or sintered powders, which is explained by the formation of aggregates, whose effective thermal conductivity is significantly lower than the thermal conductivity of crystalline particles. The estimated values of the calculation model parameters for a wide range of fillers and various binders make it possible to predict the thermal conductivity of newly developed compositions of functional materials, for example, according to the modified Burgers equation with an error within ± 20% (P = 0.95).