Abstract
The unique properties of graphene make it a very attractive application, although there are still no commercial products in which graphene would play a key role. Good thermal conductivity is undoubtedly one of the attributes which can be easily used both in materials involving large monoatomic layers, that are very difficult to obtain, as well as multilayer graphene flakes, which have been commercially available on the market for several years. The article presents the results of tests on the characteristic thermal properties of composites with the addition of 2–15% of multilayer graphene (MLG) crystals. The motivation of the study was literature reports showing the possibility of increasing the thermal conductivity of composites with MLG participation in the copper matrix. Since the production of composites with increased properties is associated with obtaining a strong orientation of the flakes in the structure, composites with hBN flakes exhibiting significantly worse but also directional thermal properties were produced for comparison. The paper showed a strong influence of flake morphology on the possibility of creating a directional structure. The obtained Cu/MLG composites with the addition of only 2% MLG were characterized by an increase in the thermal conductivity coefficient of about 30% in relation to sinters without the participation of MLG.
Highlights
Metals, due to the presence of metallic bonds and freemoving electrons, are good thermal conductors [1]
Good thermal conductivity is undoubtedly one of the attributes which can be used both in materials involving large monoatomic layers, that are very difficult to obtain, as well as multilayer graphene flakes, which have been commercially available on the market for several years
The analysis shows that in the volume of material, especially in the case of composites with hexagonal boron nitride (hBN) (Fig. 7b), apart from the previously indicated fine agglomerates, there are objects with dimensions exceeding 10 lm whose orientation is similar to that represented by elongated agglomerates of multilayer graphene (MLG)
Summary
Due to the presence of metallic bonds and freemoving electrons, are good thermal conductors [1]. High in-plane thermal conductivity is the result of sp covalent bonding between carbon atoms, but large lattice spacing in the c-direction and the weak van der Waals bonding forces between basal planes cause strong thermal anisotropy with over 100-fold between the in-plane and out-of-plane directions (20 W m-1 K-1) [3,4,5]. This is a value impossible to achieve for a diamond where thin polycrystalline layers, obtained by using CVD methods, may result only about 50% differences in conductivity depending on the direction [6, 7]
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