Research progress in interface optimization and preparation technology of high thermal conductivity diamond/copper composite materials

Composites incorporating various vol.% (0.0, 1.1, 6.4, and 10.4) of multiwall carbon nanotubes (MWCNTs) in alumina were consolidated by the spark plasma sintering. Their thermal transport properties were investigated over the temperature range 300–800 K as a function of nanotube contents. It was observed that the temperature-dependent effective thermal conductivity decreases with the addition of MWCNTs in alumina. This behavior was analyzed in terms of phonon mean free path, elastic modulus, average sound speed, and interface thermal resistance. Compared with 1/T behavior for pristine alumina, a subtle decrease in temperature dependence of the thermal conductivity of the composites with the addition of MWCNTs is observed, indicating the presence of extra phonon scattering mechanism beyond the intrinsic phonon–phonon scattering. Simulation of experimental results with theoretical model shows that the large interfacial thermal barrier between MWCNTs and alumina plays a dominant role in controlling thermal transport properties of the composites. In addition to dominant interface thermal resistance other secondary factors such as nanotube agglomeration, processing defects, porosity also contribute for low thermal conductivity at the higher volume fraction of MWCNTs in the composite.

Due to the rapid growth of high performance electronics devices accompanied by overheating problem, heat dissipater nanocomposites material having ultra-high thermal conductivity and low coefficient of thermal expansion was proposed. In this work, a nanocomposite material made of copper (Cu) reinforced by multi-walled carbon nanotubes (CNTs) up to 10 vol. % was prepared and their thermal behaviour was measured experimentally and evaluated using numerical simulation. In order to numerically predict the thermal behaviour of Cu/CNTs composites, three different prediction methods were performed. The results showed that rules of mixture method records the highest thermal conductivity for all predicted composites. In contrast, the prediction model which takes into account the influence of the interface thermal resistance between CNTs and copper particles, has shown the lowest thermal conductivity which considered as the closest results to the experimental measurement. The experimentally measured thermal conductivities showed remarkable increase after adding 5 vol.% CNTs and higher than the thermal conductivities predicted via Nan models, indicating that the improved fabrication technique of powder injection molding that has been used to produced Cu/CNTs nanocomposites has overcome the challenges assumed in the mathematical models.

Polymer Matrix Composite Thermal Materials

Diamond/Cu composites can be used to achieve the efficient heat dissipation of high-power devices. Particularly, the low coefficient of thermal expansion, smooth surface, and relatively low cost of fine-grained diamond/Cu composites make them promising candidates for further research. However, high interfacial thermal resistance is difficult to be mitigated for diamond/Cu composites with a high volume fraction of fine-grained diamond particles, which severely limits their thermal conductivity. In this study, a high-temperature high-pressure infiltration process was employed to construct a three-dimensional (3D) continuous diamond network within the diamond/Cu-B composite, where the fine-grained diamond particles were interconnected by direct bonding. Microstructural characterization provided direct evidence of diamond-diamond bonding that form a primary pathway for efficient phonon transport. This continuous network shifts the heat transfer mechanism from ‘metal-matrix-dominated’ to ‘diamond-network-dominated’, thereby overcoming the thermal resistance bottleneck imposed by the high content of fine-grained diamond particles (≥80%). The composite achieved a thermal conductivity of ~ 399 W/(m·K) while maintaining excellent surface flatness (Ra ≈ 1.3 μm). The strategy of constructing a continuous diamond network to optimize thermal transport pathways provides a new paradigm for developing next-generation composites with ultra-high thermal conductivity.

Nanostructured materials behave dramatically different from their bulk counterpart in both electronic properties as well as thermal transport properties. With the immerging low dimensional materials such as nanowires or two-dimensional materials, the research interest has been focused on nanoengineering these materials for different applications including high-performance thermoelectric generator and effective thermal management. On the other hand, these newly developed material systems also arises new scientific questions and offers great opportunities to fundamentally understand the transport physics in nanostructures. In this work, we would like to present two examples of nanoengineering low dimensional materials to modify their thermoelectric and thermal transport properties which addresses both graphene and semiconductor superlattice nanowires respectively. It is well known that graphene is an excellent candidate electronic material due to its high carrier mobility as well as it is ultrahigh thermal conductivity. Notably, with high thermal conductivity, the thermal management in graphene-based electronic circuit is considered a superior to silicon-based devices. However, this conclusion is based on previous studies on the pristine graphene sheet instead of nanopatterned graphene. We studied the thermal transport behavior of graphene nanomesh with high-density nanoholes and discovered the substantial thermal conductivity suppression with the introduced patterns. This study highlighted the importance of the phonon backscattering inside the two-dimensional graphene system and the thermal management may be more difficult than previously estimated in graphene electronics. On the other hand, while the thermal conductivity reduction in nanoengineered materials has been demonstrated in many studies, the Seebeck enhancement in nanomaterials was seldom observed. Previously, it has been predicted that the energy filtering effect in superlattice materials may induce an enhanced Seebeck coefficient in nanomaterials. However, since the superlattice materials is usually prepared by high-cost vapor-phase method which cannot be applied to large-scale application. Here, we harnessed the lattice strain of the epitaxy junctions and developed a solution based chemical synthesis method to prepare superlattice nanowires. We compared the Seebeck coefficient and electrical conductivity of the superlattice nanowire which demonstrated energy filter effect and enhanced thermoelectric properties. Reference: Z. Xiong, X. Wang, H. K. Lee, J. Zhan, Y. Chen, J. Tang, Thermal Transport in Supported Graphene Nanomesh. ACS Appl. Mater. Interfaces Article ASAP (2018)Z. Xiong, Y. Cai, X. Ren, B. Cao, J. Liu, Z. Huo, J. Tang, Solution-Processed CdS/Cu2S Superlattice Nanowire with Enhanced Thermoelectric Property. ACS Appl. Mater. Interfaces 9 (38), 32424 (2017) Figure 1

The rapid progress of high-performance microelectronic devices underscores the urgent necessity to develop materials possessing superior thermal conductivity for effectively dissipating heat in cutting-edge electronics. Boron nitride nanosheets (BNNSs) have garnered significant attention due to their exceptional thermal conductivity, combined with electrical insulation and low thermal expansion coefficient, offering a promising solution to heat-related challenges in electronic devices. While BNNSs share some common thermal behaviors with other two-dimensional (2D) materials, they also exhibit unique characteristics. For instance, BNNSs exhibit larger isotope disorders compared to graphene, yet their isotope enhancement in thermal conductivity is lower than that of their carbon counterpart. This review provides an overview of the thermal transport properties and mechanisms of BNNSs explored over the past decade, beginning with a brief introduction to the basic of thermal conductivity. It then delves into the thermal transport mechanisms in BNNSs, highlighting factors impacting the in-plane thermal conductivity of BNNSs, as well as the cross-plane thermal conductivity and the factors influencing it. Finally, the review discusses challenges associated with BNNS thermal conductivity measurement and outlines potential future research avenues.

Hexagonal boron nitride (hBN) platelets are widely used as the reinforcing fillers for enhancing the thermal conductivity of polymer-based composites. Since hBN platelets have high aspect ratio and show a highly anisotropic thermal property, the thermal conductivity of the hBNs-filled composites should be strongly associated with the platelets' orientation. However, the orientation effect has been explored less frequently due to the technical difficulties in precontrol of the platelets' orientation in the polymer matrix. In this paper, we report the use of magnetic fields to assemble the platelets into various microstructures and to study the thermal conductivities of the designed composites. The experimental results showed that thermal conductivities are dramatically different among these composites. For instance, the thermal conductivities of the composites with platelets oriented parallel and perpendicular to the heat flux direction are respectively 44.5% higher and 37.9% lower than that of unaligned composites at the volume fraction of 9.14%. The results were also analyzed by a theoretical model. The model suggests that the orientation of the hBN platelets is the main reason for the variance in the thermal conductivity.

Two approaches to improve thermal conductivity of epoxy composite are considered in this work. One is the approach to form a conductive network and the other approach is the improvement in interfacial adhesion between matrix and filler by surface modification of filler. According to the first approach, the effects of different types and particle sizes of metal oxide on the thermal conductivity of metal oxide-filled epoxy composite is studied. The SEM micrographs of the fractured surface show improvement in particle dispersion of nano-size metal oxide particles resulting in an increase in thermal conductivity of composite. The effect of mixing conditions of the BN -filled epoxy composite is investigated. The thermal conductivity f BN -filled epoxy composite can be enhanced with increases in mixing speed, time and temperature. A maximum thermal conductivity of 1.68 W /m K is obtained at 37 vol% filler content and the mixing conditions of 300 rpm , 30 min, 30c. Furthermore, surface modifications of BN with different methods: conventional silane treatment, admicellar polymerization and surfactant treatment are also investigated. The thermal conductivity of BN-filled epoxy composite is significantly enhanced by admicellar polymerization and surfactant treatment. The mechanical properties of the composite also improve significantly.

Thermal management problems are now critical in microelectronic and optoelectronic packaging. In response to the serious limitations of traditional packaging materials, material suppliers are developing an increasing number of new thermal management materials with low coefficients of thermal expansion (CTEs), ultrahigh thermal conductivities (CT), and low densities. There are now 15 low-CTE materials with CT between that of copper (400 W/m-K) and four times that of copper (1600 W/m-K), several of which are being used in production applications. Thermally conductive carbon fibers are being used to reduce the CTEs and increase the CT of printed circuit boards. These materials greatly expand the options of the packaging engineer, making it possible to eliminate heat pipes and fans. This paper provides an overview of the state of the art of advanced packaging materials, including their key properties, state of maturity, applications, manufacturing, cost and lessons learned. We also look at likely future directions, including nanocomposites.

The thermal conductivity of diamond-paraffin wax composites prepared by infiltration of a hydrocarbon binder with the thermal conductivity λm = 0.2 W m−1 K−1 into a dense bed of diamond particles (λf ∼ 1500 W m−1 K−1) with sizes of 400 and 180 μm has been investigated. The calculations using universally accepted models considering isolated inclusions in a matrix have demonstrated that the best agreement with the measured values of the thermal conductivity of the composite λ = 10–12 W m−1 K−1 is achieved with the use of the differential effective medium model, the Maxwell mean field scheme gives a very underestimated calculated value of λ, and the effective medium theory leads to a very overestimated value. An agreement between the calculation and the experiment can be provided by constructing thermal conductivity functions. The calculation of the thermal conductivity at the percolation threshold has shown that the experimental thermal conductivity of the composites is higher than this critical value. It has been established that, for the composites with closely packed diamond particles (the volume fraction is ∼0.63 for a monodisperse binder), the use of the isolated particle model (Hasselman-Johnson and differential effective medium models) for calculating the thermal conductivity is not quite correct, because the model does not take into account the percolation component of the thermal conductivity. In particular, this holds true for the calculation of the heat conductance of diamond-matrix interfaces in diamond-metal composites with a high thermal conductivity.

Thermal conductivity of Mo-reinforced ZrO2 composites fabricated by spark plasma sintering for inert matrix fuels

Polymer composites with high enough thermal conductivity, known as thermal interface materials (TIMs), are continuously pursued in the thermal management of high‐power density electronic and energy devices. In this article, to improve the heat transfer performance of TIMs, we constructed an aligned carbon nanofiber (CNFs) scaffold via the freeze‐casting method to serve as heat conduction paths in the TIMs. The composites of aligned CNF scaffold and silicone rubber were obtained by immersing the aligned scaffold into the silicone rubber with vacuum assist. We studied the influences of different CNFs diameters on the thermal conductivity of the composites, the pore sizes of the aligned CNF scaffold and the thermal conductivity of the composites fabricated under different freezing temperatures, and also the mechanical properties of the composites. Owing to the aligned scaffold, providing directional and continuous heat conduction paths, the thermal conductivity of the composites reached 3.17 W/(m·K) at 7.73 vol% CNFs. Additionally, the compressive strength and fracture strain of the composites were also greatly improved.

Electronic packaging materials and thermal interface materials (TIMs) are widely used in thermal management. In this study, the epoxy composites with core‐shell structure SiC@SiO 2 nanowires (SiC@SiO 2 NWs) as fillers could effectively enhance the thermal conductivity of epoxy composites. The unique structure of fillers results in a high thermal conductivity of epoxy composites, which is attributed to good interfacial compatibility epoxy matrix and bridging connections of SiC@SiO 2 NWs. From neat epoxy to 2.5 wt% loading of SiC@SiO 2 NWs, the thermal conductivity is significantly increased from 0.218 to 0.391 W m −1 K −1 , increased by 79.4%. In addition, the composite with 2.5 wt% filler possess lower coefficient of thermal expansion and better thermal stability than that of neat epoxy. All these outstanding properties imply that epoxy/SiC@SiO 2 NWs composites could be the ideal candidate for TIM.

Orientation control of carbon fibers and enhanced thermal/mechanical properties of hot-extruded carbon fibers/aluminum composites

MWCNTs and their use in Al-MMCs for ultra-high thermal conductivity applications: A review