Multifunctional Boron-Nitride Composites

Boron nitride (BN), a 2D material analogous to graphene with highly desirable physical and chemical properties has captivated researchers for its immense potential in thermally enhanced composites. This chapter briefly discusses the history of BN and its evolution as a novel nanomaterial, and its application in thermal management systems, followed by a detailed overview of various synthesis methods used to synthesize these composites and strategies to improve and enhance the overall composite performance. We also discuss the figure-of-merit approach to assess the performance of these BN-based composites concluding with a discussion on the way forward.

Over the past decades, the synthesis of boron metal complexes has been used in the field of medicinal chemistry, and material sciences as well as used as the catalyst for various organic reactions. The Present chapter provides the synthesis of heteroatoms including at least one boron metal complex including benzothiazole, hydroxy quinoline, Different types of Schiff bases, Pyrroyl, Benzodithiaborol, and Benzo-1,3,2-oxothiaborolane, etc. Further boron metal complexes have been reported as catalytic applications of various organic reactions such as the Conversion of sugar and agricultural waste into a useful product, reduction of ketone, hydrogenation, alkylation, Diels–Alder reaction and Strecker-type reaction.

Applications of polymers in thermal management have recently gained significant interest. Rapid heat transfer demand in thermal management applications requires enhancing the low thermal conductivity of polymers. We developed polyethylene (PE)-hexagonal boron nitride (hBN) composites with hBN loading between 5 and 40 vol%. The impacts of the composite fabrication method, the PE type, and hBN size, exfoliation, and alignment on the composite morphology, thermal conductivity, thermal stability, and mechanical properties were thoroughly investigated. Our results indicate increasing the hBN loading increases κ_c and enhance the mechanical properties and the thermal stability of the composites. Moreover, dry ball milling of hBN and PE yields composites with higher κ_c than melt extrusion. The processing-induced hBN alignment significantly affects κ_c. Melt extrusion followed by compression molding produces composites with hBN aligned parallel to the sheet surface at the skin layers (~fixed 250 µm each) and randomly aligned at the core of the sheet. This processing-induced hBN alignment led to κ_c dependence on the sheet thickness as the core layer has higher conductivity than the skin layers. By controlling the alignment of hBN in LLDPE, κ_c was greatly enhanced, reaching up to ~600 increase in the κ_c of the unaligned hBN composites. Finally, the exfoliation of hBN proved effective in increasing κ_c and improving the composites’ mechanical properties and thermal stability but led to significant processing challenges due to the very high melt viscosity.

It is well known that polymers are good thermal insulators and hence they find very restricted applications in areas where good thermal conductivity is highly essential for effective heat dissipation. One such situation is encountered in micro-electronics where substantial heat is generated due to miniaturization and high-degree integration of electronic devices. It becomes desirable for any polymer component in such applications to be thermally conductive and this can possibly be done by reinforcing them with conductive filler particles. Desirable requirements of the polymer for these kinds of usage are low coefficient of thermal expansion (CTE) and high electrical insulation apart from good heat conduction capability. Among the various fillers, conductive ceramics have enormous potential as polymer/ceramic combinations can fulfil the various requirement of material to be used in microelectronic applications. Boron nitride with its high thermal conductivity and low dielectric constant is considered to be an ideal filler material for polymeric resin. In view of this, the present chapter focusses on the heat conduction behaviour of polymer composites reinforced with micro and nano-sized boron nitride particles as filler. The main highlights of the chapter are the different ways adopted for enhancing the heat conduction capability of this kind of composites.

The nanomaterials of boron nitride have attracted attention in recent years due to its properties such as high thermal stability, high surface area, excellent oxidation and corrosion resistance, low density, high mechanical strength and conductivity. There are many applications of boron nitride nanomaterials in various field such as hydrogen accumulators, luminescence, advanced insulators, functional composites, water purification and photocatalytic degradation of organic pollutants. Among these various applications photocatalysis has become a focus of research. In this chapter we have described various methods of synthesis of boron nitride nanomaterial such as arch discharge method, ball milling method, chemical vapour deposition method and Laser Ablation method. The photocatalytic applications have also been described.

The research aims at the manufacture and characterization techniques of hexagonal boron nitride reinforced composites using polyester matrix. In this work, the methods of testing and their results for mechanical, thermal and surface properties in polyester matrix composites having particulate BN of different proportions are conversed about. An assessment of the effective thermal conductivity was carried out and hence validation of the same was done with the help of experiments. The effect of inclusion of BN on the density, water absorption, tensile strength, compressive strength, micro-hardness, effective thermal conductivity (k_eff), glass transition temperature (T_g), coefficient of thermal expansion (CTE) and surface morphology are discussed. The thermal conductivity shows an escalation when conductive BN reinforcement is added to the polyester matrix. The coefficient of thermal expansion (CTE) decreases with addition of BN but the Glass transition temperature (T_g) tends to be enhanced a lot. Compared to analytical models, the proposed correlation is estimated to be a very good analytical model to estimate k_eff of composites within the percolation limit. Owing to low cost and higher mechanical and thermal properties, polyester composites serve as a better alternative to general epoxy composites. These highly conductive, low density and light-weight boron nitride reinforced polyester composites can be utilized in various areas of aviation, automotive and electronic encapsulation etc. Again, a hybrid composite was manufactured with a organic reinforcement which tends to show excellent properties for specific applications.

Recently, a considerable interest has been focused on 2-dimensional hexagonal boron nitrides due to their prominent optical, thermal, chemical and electronic properties. Especially, h-BN consists of 2-dimensional hexagonal net-like layers of boron and nitrogen atoms and such atomic layers were stacked along normal direction. In contrast to isostructural graphene, h-BN is regarded as a wide band gap material with indirect band gap suitable for host of various impurities with light emitting performance. In particular, it was reported that incorporating foreign atom including rare earth elements can provide intense luminescence on h-BN. Unique properties of h-BN based nanophosphors can provide support on various optical application of the same materials. Here, we reviewed various reports on synthesis and luminescence of doped h-BN. In addition, potential application of the highly luminescent h-BN was also summarized.

Hydrogen is considered a best energy source for the next upcoming generation as an energy storage, carrier and vector. It can be precursor and auxiliary material for a number of industrial process. Although hydrogen has the best potential of satisfying the demand for fuel in the future, there are many obstacles limiting its practical application, and storage of hydrogen is very challenging due to it’s very high energy density relative to its weight. Boron Nitride nanocomposites has mostly been reported for the storage of molecular hydrogen by chemisorption and physisorption over a wide range of temperatures and pressure. Different BN nanocomposite has been used for the storage of Hydrogen like BN nanotubes, h-BN, p-BN, Open-ended BN and BN-Clusters. By increasing surface area, pressure and decreasing temperature hydrogen adsorption increases by physisorption. By doping with O and C with B and N element of boron nitride hydrogen adsorption takes by chemisorption. The d-block element like Pt, Pd, Ti, Si, Al are doped with Boron nitrite nanocomposite further enhancement of hydrogen adsorption takes place.