An ultrathin, highly thermally conductive heat spreader has been fabricated by layer-by-layer stacking of hydroxylated boron nitride nanosheets (HBNNS) for the first time. HBNNS were prepared by a molten hydroxide-assisted liquid exfoliation from hexagonal boron nitride powder. The as-prepared heat spreader of HBNNS exhibits a high thermal conductivity of 51.1 W m(-1) K-1 along the in-plane direction, and can be further enhanced 14% by annealing for de-hydroxylation. This heat spreader with 10-30 mu m in thickness possessed excellent thermal stability with negligible weight loss at wide temperature range up to 700 degrees C, resulting in promising applications for heat dissipation in electronic components operated at high working temperature.

https://iopscience.iop.org/article/10.1088/2053-1583/aa636e/pdf

An ultrathin high-performance heat spreader fabricated with hydroxylated boron nitride nanosheets

Hexagonal boron nitride (h-BN) is also referred to as “white graphite”. Owing to its two-dimensional planar structure, its thermal conductivity along and perpendicular to a basal plane is anisotropic. However, h-BN exhibits properties that are distinct from those of graphite, such as electric insulation, superior antioxidative ability, and purely white appearance. These qualities render h-BN superior as a filler in composites that require thermal conductivity while exhibiting electric insulation. Since the thermal performance of composites is mainly affected by thermal pathways, this article begins with an overall introduction of the preparation of boron nitride nanosheets, followed by a review of the fabrication of h-BN-filled composites. Lastly, the construction of thermally conductive networks is discussed.

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Polymer composites based on hexagonal boron nitride and their application in thermally conductive composites

SrTiO3-based thermoelectrics: Progress and challenges

Bulk Hexagonal Boron Nitride with a Quasi-Isotropic Thermal Conductivity

Due to the strong 'lip–lip' interactions between neighboring nanosheets layers, the scalable exfoliated fabrication of few-layer-thick boron nitride nanosheets (BNNSs) from the bulk hexagonal boron nitride (h-BN) is more challenging than these graphene nanosheets In this work, few-layer (generally less than 10 layers) BNNSs were efficiently synthesized through a simple ball milling technique with the 2-furoic acid (FA) as a modifier The BNNSs as-prepared with a average thickness of about 20 nm and an extremely high production yield (~98%) as well as unprecedentedly high dispersed concentration (~35 mg ml−1) in water The stable aqueous dispersions of BNNSs can be directly used to fabricate ultralight aerogels with a low density of 20 mg cm−3 and thermally conductive film with a highly thermal conductivity of 252 W m−1 K−1 This approach provided us with an environmentally friendly agent with high efficiency for few-layer BNNSs synthesis and demonstrated promising applications for ultralight aerogels and heat dissipation in electronic components

https://iopscience.iop.org/article/10.1088/2053-1583/aad51a/pdf

High-yield synthesis of extremely high concentrated and few-layered boron nitride nanosheet dispersions

Two-dimensional materials are characterised by a number of unique physical properties which can potentially make them useful to a wide diversity of applications. In particular, the large thermal conductivity of graphene and hexagonal boron nitride (hBN) has already been acknowledged and these materials have been suggested as novel core materials for thermal management in electronics. However, it was not clear if mass produced flakes of hBN would allow one to achieve an industrially-relevant value of thermal conductivity. Here we demonstrate that laminates of hBN exhibit thermal conductivity of up to 20 W/mK, which is significantly larger than that currently used in thermal management. We also show that the thermal conductivity of laminates increases with the increasing volumetric mass density, which creates a way of fine tuning its thermal properties.

https://iopscience.iop.org/article/10.1088/2053-1583/3/1/011004/pdf

High thermal conductivity of hexagonal boron nitride laminates

Two-dimensional materials are characterised by a number of unique physical properties which can potentially make them useful to a wide diversity of applications. In particular, the large thermal conductivity of graphene and hexagonal boron nitride has already been acknowledged and these materials have been suggested as novel core materials for thermal management in electronics. However, it was not clear if mass produced flakes of hexagonal boron nitride would allow one to achieve an industrially-relevant value of thermal conductivity. Here we demonstrate that laminates of hexagonal boron nitride exhibit thermal conductivity of up to 20 W/mK, which is significantly larger than that currently used in thermal management. We also show that the thermal conductivity of laminates increases with the increasing volumetric mass density, which creates a way of fine-tuning its thermal properties.

Strontium titanate (SrTiO is a promising n-type material for thermoelectric applications. However, its relatively high thermal conductivity limits its performance in efficiently converting heat into electrical power through thermoelectric effect. This work shows that the thermal conductivity of SrTiO can be effectively reduced by annealing treatments, through an integrated study of laser flash measurement, scanning electron microscopy, Fourier transform infrared spectroscopy, x-ray absorption fine structure, and first-principles calculations. A phonon scattering model is proposed to explain the reduction of thermal conductivity after annealing. This work suggests a promising means to characterize and optimize the material for thermoelectric applications.

https://iopscience.iop.org/article/10.1088/1674-1056/26/1/016602/pdf

Tuning the thermal conductivity of strontium titanate through annealing treatments

The electronic structures and thermoelectric properties of (SrO)m(SrTiO3)n superlattices have been investigated using first-principles calculations and the Boltzmann transport theory. Due to the much reduced dispersion along the c-axis, the thermoelectric properties for n-type superlattices are found to be highly anisotropic with the in-plane electrical conductivity with respect to relaxation time much higher than the out-of-plane one. The reduction of the in-plane Seebeck coefficient compared with SrTiO3 results in a slightly reduced power factor with respect to relaxation time for n-type doped (SrO)m(SrTiO3)n. However, both Seebeck coefficient and electrical conductivity with respect to relaxation time are relatively maintained for p-type doping, leading to a comparable power factor with respect to relaxation time. If the reduced thermal conductivity is taken into account, an improved ZT value can be expected for the (SrO)m(SrTiO3)n superlattice.

First principles studies on the thermoelectric properties of (SrO)m(SrTiO3)n superlattice

The invention discloses a method for regulating and controlling the thermal conductivity of an oxide material, and relates to a thermoelectric material. The method comprises the steps: (1) fetching an oxide function material, and measuring the thermal conductivity of the oxide function material after cleaning; (2) placing the oxide function material of step (1) into a reaction chamber resisting high pressure, and dropping H2O into the reaction chamber, and closing the reaction chamber; (3) letting CO2 at a super-critical state into the reaction chamber, taking out the oxide function material when the air pressure of the reaction chamber is reduced to a normal temperature and pressure, and measuring the thermal conductivity of a sample of the oxide function material after super-critical fluid processing; (4) comparing the thermal conductivity of the oxide function material before the super-critical fluid processing with the thermal conductivity of the oxide function material after the super-critical fluid processing, and obtaining a result that super-critical fluid effectively regulates and controls the thermal conductivity of the oxide function material. The temperature condition can be met easily during processing. The method is short in time, is high in efficiency, and cannot damage materials.

Liang Zhang

Papers

High thermal conductivity of hexagonal boron nitride laminates

High thermal conductivity of hexagonal boron nitride laminates

Tuning the thermal conductivity of strontium titanate through annealing treatments

First principles studies on the thermoelectric properties of (SrO)m(SrTiO3)n superlattice

Method for regulating and controlling thermal conductivity of oxide material