Synthesis and thermal transport properties of high-surface area hexagonal boron nitride foam structures
Introduction
Due to the increased transistor density in integrated circuits in the past decades, the heat dissipation density has increased considerably and reached over 100 W cm−2 [1]. This challenge opens up opportunities for innovations in thermal management materials, devices, and systems for microelectronics [2]. The superior basal-plane thermal conductivities of some two-dimensional (2D) materials such as graphene and hexagonal boron nitride (h-BN) have motivated efforts to explore their thermal management applications. Graphite and h-BN share a similar hexagonal layered structure with only ~1.8% difference in the basal-plane lattice constant [3]. While graphite is a semimetal, the large band gap of 5.97 eV makes h-BN essentially an electrical insulator [4]. Because of its electrical insulation, high basal-plane thermal conductivity, chemical stability, mechanical robustness, and flexibility, h-BN has been explored for applications ranging from electronic packaging, electrical shielding, flexible substrates, and advanced heterostructure electronic devices [4], [5], [6], [7].
One thermal management application of high-thermal conductivity nanostructures is to serve as the filler material in low-conductivity polymeric matrix for enhancing the effective thermal conductivity of the obtained composite. However, the high thermal interface resistance of the individual nanostructures in a percolated van der Waals (vdW) network limits the thermal performance. This limitation can be overcome by replacing the vdW network with three-dimensional (3D) continuous porous foam structures. Recently, cellular h-BN foams have been grown with the use of chemical vapor deposition (CVD) for thermal management [8], [9], [10], [11], [12], [13]. Compared to liquid or mechanical exfoliation, CVD growth is unique in that it can yield continuous, large lateral size h-BN films and coatings on catalyst templates and control the film thickness by varying the growth time. The obtained continuous interconnected strut network serves as effective pathways for heat conduction from the functional materials, such as a phase change material (PCM) filled into the pore space of the foam structure for thermal energy storage [14]. In one experiment, solid borazane precursor and Ni foam templates have been used in low-pressure CVD (LPCVD) growth of free-standing h-BN foams with a very low density of 1.6 mg cm−3 [15]. Meanwhile, an atmospheric pressure CVD (APCVD) method has been used to grow h-BN foams on Ni foam templates [16], [17]. At a h-BN volume fraction of 0.076 ± 0.01%, the effective thermal conductivity of Poly(methyl methacrylate) (PMMA) composite with the h-BN foam reached 0.34 ± 0.03 W m−1 K−1 at room temperature and 0.73 ± 0.07 W m−1 K−1 at 140 K, compared to a room-temperature value of 0.21 ± 0.01 W m−1 K−1 for pure PMMA. Opposite to the trend shown by amorphous PMMA, the observed temperature dependence of the composite is attributed to the lattice thermal conductivity of crystalline h-BN, where increased umklapp phonon-phonon scattering reduces the solid thermal conductivity of the h-BN crystal with increasing temperature.
The thermal performance of the open cellular foam fillers depends on the crystalline quality, strut wall thickness, and the pore size. In existing h-BN foams grown on commercial reticulated nickel foam templates, the pore size is similar to the template pore size, which is as large as 600 µm. The thermal conductivity of a composite plate sample measured by a steady state method is a function of the volume fraction of the filler materials and does not explicitly depend on the pore size and surface area according to the foam theory [18]. However, the h-BN filler volume fraction increase with decreasing pore size and increasing specific surface area for a given strut wall thickness. Due to the limited h-BN strut wall thickness obtained by the CVD growth process, the large pore size and limited specific surface area results in a small volume fraction of the foam filler. For applications such as composite phase change materials (PCMs) for thermal energy storage and thermal management [19], moreover, the large pore size results in a large distance and resistance for 3D heat flow from the functional materials inside the pores to the high-thermal conductivity matrix grown on the template. This factor increases the time for melting or solidification of the PCMs filled in the large pores. In previous studies of ultrathin graphite foam (UGF) structures, efforts have been made to grow long carbon nanotubes on the strut wall of CVD UGF to increase the specific surface area and reduce the resistance of heat transport from the phase change material (PCM) inside the pore space to the graphite strut walls [19]. Due to a decrease of the effective pore size of the UGF, the obtained effective thermal conductivity has been increased by a factor of 1.8 compared to that of a UGF-PCM composite without nanotubes. Recently, nickel powders have been sintered to form catalytic templates for CVD growth of UGF structures [20]. The obtained nickel template can reduce the pore size and increase the specific surface area up to 68 times compared to the reticulated nickel template. Because of the large increase in the volumetric specific surface area and the volume fraction of the UGF grown on the sacrificial nickel template, the effective density and the effective thermal conductivity of the UGF have been increased as much as a factor of 8 relative to that grown on reticulated nickel foam [20].
Here, we report the synthesis and thermal transport properties of high-surface area h-BN foam structures grown on sintered nickel powder templates. Due to the small pore size of sintered nickel powder template, the volume fraction of the h-BN grown by APCVD on the template is increased by a factor of 2.8 compared to a baseline h-BN foam grown on a commercial reticular nickel foam template. A further increase of the volume fraction by an additional factor of 2 is achieved by increasing the growth time by a factor of 3. The effective room-temperature thermal conductivity of the h-BN-PMMA composite is increased from 0.31 ± 0.02 W m−1 K−1 for the baseline structure to 0.70 ± 0.05 W m−1 K−1 for the high-surface area structure with increased h-BN volume fraction and growth time. Numerical simulation is carried out to extract the solid thermal conductivity of the h-BN struts from the measured effective thermal conductivity and to understand the effect of the thermal interface resistance between the h-BN and the matrix.
Section snippets
Materials synthesis and structure characterization
As summarized in Table 1, four different types of h-BN foam composite samples are reported in this work, including baseline h-BN foams grown on a commercial reticulated Ni foam template, three high-surface area h-BN foam samples grown on sintered Ni powder templates with different growth times or procedures. Compared to the baseline samples grown on the reticular Ni foam, the sintered nickel template is used to reduce the pore size and increase the specific surface area of the other three
Thermal transport measurements and results
The thermal transport properties of h-BN-PMMA composite were measured via Laser Flash Analysis (Netzsch LFA 457 Microflash) and Differential Scanning Calorimetry (Netazch DSC 404 F1 Pegasus). Although the h-BN volume fraction was less than 1%, the interconnected h-BN open cell structure increased the effective thermal conductivity of the composite, which was obtained aswhere the ρe,c is the measured density of the h-BN-PMMA composite, αe,c is the effective thermal diffusivity
Numerical simulation and analysis of the solid thermal conductivity
Instead of an analytical model based on the effective medium approach or the foam theory, a series of numerical simulations in the COMSOL environment is used to evaluate the h-BN solid thermal conductivity and investigate the effect of the thermal interface resistance (Ri) between h-BN and PMMA. The numerical simulation is based on the assumption of 3D isotropic heat conduction in PMMA, air voids, and thin h-BN strucs. As shown in Fig. 6(a), the h-BN foam structure is approximated as a
Conclusion
These experiments show that the effective thermal conductivity of h-BN foams can be increased with the use of high-surface area, low-cost sintered nickel powder templates for APCVD growth and by increasing the growth time. With an order of magnitude smaller pore size and an order of magnitude higher specific surface area than that of reticulated Ni foam, the high-surface area h-BN polymeric composite increases the volume fraction of h-BN from 0.12 ± 0.02% to 0.69 ± 0.03% and yields an effective
CRediT authorship contribution statement
Qianru Jia: Conceptualization, Methodology, Investigation, Formal analysis, Writing - original draft, Visualization, Data curation. Li Shi: Conceptualization, Supervision, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors thank Evan Fleming, Arden Moore, and Taylor Ashton for helpful discussion. The baseline sample and sample HS1 were synthesized and studied with the support of National Science Foundation (NSF) award CMMI-1563382. Samples HS2 and HS3 were studied with support from NSF award EEC-1160494.
References (45)
- et al.
Emerging challenges and materials for thermal management of electronics
Mater. Today
(2014) - et al.
The effect of surface energy on the heat transfer enhancement of paraffin wax/carbon foam composites
Carbon
(2007) - et al.
Foam-like hierarchical hexagonal boron nitride as a non-traditional thermal conductivity enhancer for polymer-based composite materials
Int. J. Heat Mass Transf.
(2017) A theory for the limiting conductivity of polyhedral foam at low density
J. Colloid Interface Sci.
(1978)- et al.
Enhanced specific surface area and thermal conductivity in ultrathin graphite foams grown by chemical vapor deposition on sintered nickel powder templates
Carbon
(2018) - et al.
A general tetrakaidecahedron model for open-celled foams
Int. J. Solids Struct.
(2008) - et al.
The geometric and thermohydraulic characterization of ceramic foams: an analytical approach
Acta Mater
(2014) - et al.
Thermal conductivity of carbon nanotubes grown by catalyst-free chemical vapor deposition in nanopores
Carbon
(2019) - et al.
High-thermal-conductivity, mesophase-pitch-derived carbon foams: effect of precursor on structure and properties
Carbon
(2000) - et al.
Heat generation and transport in nanometer-scale transistors
Proc. IEEE
(2006)
Heat capacity and thermal conductivity of hexagonal pyrolytic boron nitride
Phys. Rev. B
Electronic transport in heterostructures of chemical vapor deposited graphene and hexagonal boron nitride
Small
Two dimensional hexagonal boron nitride (2D-hBN): synthesis, properties and applications
J. Mater. Chem. C
Synthesis and characterization of hexagonal boron nitride film as a dielectric layer for graphene devices
ACS Nano
Configurable three-dimensional boron nitride-carbon architecture and its tunable electronic behavior with stable thermal performances
Small
Large-scale synthesis of high-quality hexagonal boron nitride nanosheets for large-area graphene electronics
Nano Lett
Continuous growth of hexagonal graphene and boron nitride in-plane heterostructures by atmospheric pressure chemical vapor deposition
ACS Nano
Growth of large single-crystalline two-dimensional boron nitride hexagons on electropolished copper
Nano Lett
A systematic study of the atmospheric pressure growth of large-area hexagonal crystalline boron nitride film
J. Mater. Chem. C
Growth selectivity of hexagonal-boron nitride layers on Ni with various crystal orientations
RSC Adv
Synthesis of few-layer hexagonal boron nitride thin film by chemical vapor deposition
Nano Lett
Ultralight three-dimensional boron nitride foam with ultralow permittivity and superelasticity
Nano Lett
Cited by (11)
Recent advances in nanostructured materials: A look at the applications in optical chemical sensing
2023, Materials Today NanoThree-dimensional boron nitride reinforced thermal conductive composites with high elasticity
2022, Journal of Alloys and CompoundsCitation Excerpt :With the gradual development of technology based on artificial intelligence, various intelligent algorithms and electronic devices have also been rapidly developed. Nowadays, electronic devices are smaller, thinner, more versatile and portable [1–3]. At this time, an increasing number of electronic components are placed within narrower spaces.
Solid body calorimeter with one automatically regulated adiabatic jacket: Influence thermal and operated parameters on heat equivalent
2022, International Journal of Heat and Mass TransferCitation Excerpt :It is known that solid body calorimeters are widely applied for measuring heat both at high temperatures and low temperatures [1–11].
Three-dimensional boron nitride network/polyvinyl alcohol composite hydrogel with solid-liquid interpenetrating heat conduction network for thermal management
2022, Journal of Materials Science and TechnologyCitation Excerpt :In order to improve the efficiency of fillers, people choose to build a three-dimensional (3D) heat conduction network [20–25], and introduce the network into the polymer matrix to improve the κ of the polymer [26–31]. Jia and Shi [20] prepared boron nitride foam by chemical vapor deposition and introduced it into polymethacrylate to successfully prepare high thermal conductive polymer composites. The κ of the composite was increased from 0.31 ± 0.02 to 0.70 ± 0.05 W m−1 K−1.
Construction of high thermal conductive boron Nitrid@Chitosan aerogel/ paraffin composite phase change material
2022, Solar Energy Materials and Solar CellsCitation Excerpt :The concept of peak carbon dioxide emissions and carbon neutrality has often been put on the agenda, since energy conservation and emission reduction must be taken seriously. Especially in electronic devices, heat generated by the operation process needs to be released in time [1–4]. Normally, water cooling [5] and wind cooling [6] are regarded as the most frequently-used methods to disperse waste heat.