Thermal stability and conductivity of hot-pressed Si3N4–graphene composites

Abstract

This study concerns new Si 3 N 4 -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 Y 2 O 3 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 Si 3 N 4 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.

Thermal properties of pressure sintered alumina–graphene composites

“…5 confirm the microstructural observation of oriented graphene flakes/groups of flakes in hot-pressed composites. The similar situation of anisotropy was recorded also in previous work of the author in case of silicon nitridegraphene composites [24]. In case of spark plasma sintered materials, it was impossible to measure the anisotropy because of too small dimensions of samples and too highsignal damping.…”

“…For ceramics, as a materials working, at high-temperature conditions, the addition of graphene flake gives a hope of thermal properties improvement. The typical methods of ceramic-graphene manufacturing are hot-pressing (HP) and spark plasma sintering (SPS) [9,12,18,24]. The uniaxial pressing, which helps to densify the materials during the sintering, becomes a problem for ceramic-2D phase materials.…”

“…The uniaxial pressing, which helps to densify the materials during the sintering, becomes a problem for ceramic-2D phase materials. The one direction of applied pressure causes the orientation of two-dimensional phase in the ceramic matrix [23,24]. This situation can lead to the anisotropy of heat transport of ceramic matrix composites.…”

“…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 additionally to large difference in thermal conductivity in different directions of sintered bodies.…”

Thermal diffusivity characterization of bond-coat materials used for thermal barrier coatings

“…Cowan's model was used for thermal diffusivity calculation in the case of single-layer analysis. This method gives the possibility to measure thermal diffusivity and heat capacity with high precision and is relatively simple in sample preparation and interpretation of results [11][12][13][14]. The analysed samples were placed in the sample carrier in such a way that their original surface (for example, rough top surface of NiCrAlY coating) was faced down.…”