The work concerns the alumina–graphene materials sintered by two different pressure methods. The different particle sizes of graphene were used. The preparation route of the matrix-graphene mixture was discussed in the paper. The so-prepared compositions with different amount of graphene were hot-pressed and spark plasma sintered. The influence on uniaxial pressure during the sintering process on the microstructure was presented by the SEM microstructural observations and ultrasonic measurements. The material with unidirectional oriented graphene particles was prepared, and the anisotropy was even higher than 30 % for 10 mass% of graphene additive. The influence of graphene orientation as an effect of pressing process on the thermal properties was analysed. The anisotropy of thermal conductivity was 90 % for 10 mass% of graphene. The thermal diffusivity and thermal conductivity of composites manufactured by hot-pressing and spark plasma sintering method were compared. The experiment-based calculation of the specific heat versus temperature was presented in the paper. The thermal expansion coefficient was determined by dilatometric method. The thermal stability was analysed by thermogravimetric method, and it showed that composites with up to 2 mass% of graphene can work at temperatures higher than 700 °C.

This study concerns new Si₃N₄–graphene composites manufactured using the hot-pressing method. Because of future applications of silicon nitride for cutting tools or specific parts of various devices having contact with high temperatures there is a need to find a ceramic composite material with good mechanical and especially thermal properties. Excellent thermal properties in the major directions are characteristic of graphene. In this study, the graphene phase is added to the silicon nitride phase in a quantity of up to 10 mass%, and the materials are sintered under uniaxial pressure. The mixture of AlN and Y₂O₃ is added as sintering activator to the composite matrix. The studies focus on thermal stability of produced composites in argon and air conditions up to the temperature of 1,000 °C. The research also concerns the influence of applied uniaxial pressure during the sintering process on the orientation of graphene nanoparticles in the Si₃N₄ matrix. The study also presents research on anisotropy of thermal diffusivity and following thermal conductivity of ceramic matrix composites versus the increasing graphene quantity. Most of the presented results have not been published in the literature yet.

The study describes the physicochemical properties of transition metal (Co,Cu,Mg,Ni,Zn)O high-entropy oxide prepared using mechanochemical synthesis (MS) followed by thermal treatment, as well as the structural evolutions in the powder with milling time. The microstructure and electrical properties of the materials were studied using x-ray diffraction, scanning electron microscopy—energy dispersive spectroscopy and electrochemical impedance spectroscopy. The powders obtained after 30 h and 100 h of MS contained a mixture of two phases with a rock salt structure and, in addition, about 11 wt.% of Co₃O₄. Sintering these materials for 10 h in air at 1273 K led to the formation of a single-phase, solid solution with a rock salt structure. The developed sinters exhibited a fine-crystalline structure of grains and a uniform distribution of elements. The highest electrical conductivity was measured at 1148 K, and it was equal to 8.03 × 10⁻² S cm⁻¹.