Abstract
The work concerns the alumina-graphene ma- terials sintered by two different pressure methods. The different particle sizes of graphene were used. The prepa- ration 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 ther- mal conductivity of composites manufactured by hot- pressing and spark plasma sintering method were com- pared. The experiment-based calculation of the specific heat versus temperature was presented in the paper. The thermal expansion coefficient was determined by dilato- metric 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.
Highlights
The work concerns the alumina–graphene materials sintered by two different pressure methods
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
Different situation is in case of graphene, where even well-packed groups of oriented flakes lead to an improvement of thermal conductivity in direction perpendicular to pressing axis so in the direction of oriented graphene particles’ planes
Summary
The work concerns the alumina–graphene materials sintered by two different pressure methods. As a materials working, at high-temperature conditions, the addition of graphene flake gives a hope of thermal properties improvement. In the case of hexagonal boron nitride dispersed phase, the thermal properties (conductivity) decrease in all of directions in comparison with reference pure material [23] It is caused mostly by agglomeration of hexagonal boron nitride particles, where the agglomerates are porous. Different situation is in case of graphene, where even well-packed groups of oriented flakes lead to an improvement of thermal conductivity in direction perpendicular to pressing axis so in the direction of oriented graphene particles’ planes It has place in silicon nitride–graphene composites [24], where introduce oriented graphene phase leads to large difference in thermal conductivity in different directions of sintered bodies. On the sintered under uniaxial pressure materials, the thermal diffusivity and thermal conductivity were measured and compered with manufacturing method and anisotropy of the composites. That is why the produced composite materials were thermogravimetry tested to show/determine maximal working temperature in air conditions in function of graphene concentration
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