The influence of organic binders and their decomposition products on the microstructure and thermoelectric properties of conductive materials based on si3n4 with transitional metal carbides additives

Abstract

The object of research is the formation of the functional zone of a multicomponent ceramic composite based on refractory anoxic compounds. One of the most problematic points is the determination of influence of the type of binder on the formation of the functional zone of the device.During the study, the industrial powders of silicon nitride β – Si3N4 of the Baku Powder Metallurgy Plant (Azerbaijan) and hafnium and zirconium carbides of the Donetsk Chemical Reagents Plant (Ukraine) were used. The homogenization and grinding of the charge was carried out in a planetary mill of the Fritsch type (drum and Si3N4 balls) for 40 min. in ethyl alcohol. The concentration of the inclusion phase conductor in the composite thermoelectrodes was 5–40 %. The carboxymethyl cellulose compound in combination with a plasticizer, glycerol or rubber, was used as a binder for this method. Samples were made in the form of plates 100×7×6 mm. The investigated samples of nitro silicon composite materials were obtained by hot pressing of the prepared ceramic tapes using the induction method of heating the mold.It has been found that in case of the rubber-containing samples with a resistive HfC additive, the weight loss increases in proportion to the HfC concentration up to the additive concentration of 27 %, while the further HfC concentration increase causes the decline of weight loss. When using cellulose gum as a binder, the weight loss decreases by about 1.3–1.6 times; the regularities of weight loss changes depending on the HfC concentration remain the same. It has been shown that the modulus of thermal electromotive force was higher in case of fine composites than in case of coarse ones for all concentrations. The maximum thermal emf value reached 120 μV/deg in the subthreshold zone of the additive concentration. In the suprathreshold zone the maximum thermal emf value reached 60 μV/deg for the fine-grained composite and 30 μV/deg for the coarse-grained one. It has been proved that composites without a binder differ not by the typical course of dependency between the additive concentration and the resistivity, while the thermal emf of these composites equals zero with accuracy up to experimental error.