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Hexagonal boron nitride (hBN) is an exceptional material that benefits from the property of directional dependence, otherwise known as anisotropy. This defines the differential behavior of directional planes in a material. This leads to distinct property differences based on the orientation of its crystallographic planes. Wood is perhaps the best known anisotropic material on the macroscale, with tightly bound fibers that exhibit high in-grain strength. Yet these can be easily split apart when cutting along the grain.

Larger material structures tend to exhibit tensile or flexural strength variations along different axes. At the micro- and nanoscales, however, anisotropic behavior imparts a broad range of physiomechanical, optical, and electronic properties that are desirable for myriad engineering and manufacturing applications. ‘White graphite’, or hBN, is one of these innovative intermediate products.

In this blog post, Saint-Gobain Boron Nitride will explore the properties and characteristics of hBN in more detail.

 

What is hBN?

The synthetic ceramic boron nitride exists in several forms, the properties of which are primarily determined by the arrangement of boron (B) and nitrogen (N) atoms within the bulk material’s molecular structure. Of the three crystalline phases of boron nitride, hBN is the most stable. It is structurally analogous to graphite with layers of covalently-bound B—N atoms arranged in a hexagonal lattice.

These hBN layers are held together by comparatively weak Van der Waals forces, which explains the material’s comprehensive anisotropic properties. For example, the average in-plane thermal conductivity of hBN is 300 Watts per meter Kelvin (W/mK), as thermal energy can readily propagate through the covalent B—N bonds. This reduces to a mere 30 W/mK for through-plane conductivity of boron nitride.

Alongside this outstanding capacity for modulating the transfer of thermal energy, hBN also exhibits excellent lubricating properties due to its low coefficient of friction (~0.3). Although mechanically analogous to graphite, hBN differs in that is an excellent insulator with superior thermal shock performance and a dielectric strength that exceeds even alumina (Al₂O₃).

 

hBN from Saint-Gobain Boron Nitride

Saint-Gobain Boron Nitride has harnessed the unique potential of hBN to develop an expansive range of products suitable for numerous applications, including: lubricant additives for dynamic friction materials in aerospace and automotive applications; thermal interface materials for advanced electronics cooling systems; filler powders for color cosmetics and commercial skincare products; and hot-pressed sinetered and machined components in a variety of advanced engineering applications.

hBN can be readily dispersed in continuous phase media of varying consistencies such as oils, grease, and both aqueous and non-aqueous solvents. It can also be applied to component substrates as a dry powder to provide friction resistance in refractory environments.

If you would like any more information about the hBN products available from Saint-Gobain Boron Nitride, please do not hesitate to contact us.

Electronic cooling materials are used to regulate the thermal energy generated by electronic devices while operating. Traditionally, this could be achieved using a thin application of thermal grease which enhanced the rate of thermal dissipation between an electronic device and its heat sink. Yet, modern electronic assemblies are producing more heat at faster rates due to their improved functionalities and increasingly constrained device architectures. This requires advanced electronic cooling materials that can assist in heat dissipation without causing loss of electronic functions.

 

The Importance of Electronic Cooling Material

Elevated temperatures due to environmental or power-related factors can cause electronic devices to behave erratically and even to fail. If the heat generated by a circuit is unable to dissipate effectively, the conducting and dielectric components within the device may suffer mechanical stress due to differing rates of thermal expansion and contraction. Over time, thermal cycling will degrade the structural integrity of these components and cause loss of functionality. Temperatures that exceed the performance levels of dielectric materials can result in an outright loss of structural or electrical integrity and rapid device failure.

Printed circuit boards (PCBs) have been densified to accommodate smaller end-product devices. This demand has impacted general heat-management principles as constricted device designs leave little room for conventional heat sink components. Electronic cooling materials may need to perform in absence of an active coolant system to ensure that the heat generated by sophisticated multilayer PCBs dissipates effectively from a device.

 

Types of Electronic Cooling Materials

Typical electronic cooling materials include adhesive films and tapes; dispensable gap fillers; epoxies; gap filler pads and phase change materials; thermal greases and gels. Saint-Gobain Boron Nitride has demonstrated the ability to tailor boron nitride (BN) particle and platelet purity and morphology to a wide variety of these thermal interface material (TIM) systems and requirements.

 

Looking for electronic cooling solutions?

Boron nitride is a synthetic ceramic with outstanding thermal and electrical properties. It exhibits very high thermal conductivity (30 – 300 W/mK) for an electrical insulator (>10kV/mm) with outstanding dielectric strength. This makes it a prime electronic cooling material for low power loss insulation.

 

Boron Nitride Electronic Cooling Materials from Saint-Gobain

Saint-Gobain Boron Nitride has excelled in two primary electronic cooling material solutions based on tailored BN powder characteristics and properties. The first is a dispensable gap filler which is designed to fill voids in electronic architectures with an elastic and low-wearing barrier. This filler material can dramatically improve the thermal dissipation properties of electronic devices.  Saint-Gobain spherical boron nitride powders are specially tailored for this application due to the optimal shape for packing, flowability, and low wear of dispensing equipment.  By tightly controlling the purity and particle size of platelets and agglomerated powders, Saint-Gobain BN powder also excels in PCB prepreg and dielectric layer formulations.  These materials help form PCB laminates and are often stacked in multi-layer PCB structures.  Saint-Gobain BN powders help optimize thermal and electrical performance in demanding high power and transmittance applications.

If you have found this post interesting, read Saint Gobain’s article on Low Loss Filler Powders for the 5G Market.

Superplastic forming (SPF) is an advanced shaping technique used to fabricate complex, near-net-shape components with isotropic mechanical properties and excellent surface finish. The term “superplastic” refers to the ability of certain crystalline materials to undergo extreme deformation under specific conditions. At the correct temperature, often close to the melting point of the material, and strain rate, it can stretch well past its typical breaking point and up to 200-1000% of its original size. A critical factor in this is the tendency for materials in their superplastic state to resist necking, a type of localized thinning that can lead to tensile failure. Gas pressure is the preferred method to apply even stress across the part and further assist in uniform deformation.

Various titanium, aluminum, and nickel-based alloys, as well as some stainless steels, exhibit superplasticity and are prime candidates for SPF processes. Many aluminum alloys, for example, will deform superplastically across a temperature range of 470–520°C (878–968°F) and a broad pressure range of approximately 350—1500 kPa. This enables aluminum sheets to be heated and stretched into close contact with complex die shapes to develop near-net end products as varied as electronics casings, automotive body panels, vehicle and transit fixtures, and more.

Advances in process technology have allowed for faster throughput, making it a more cost competitive method for high volume applications like automotive parts.  These processes are called Quick Plastic Forming (QPF) or High-Speed Blow Forming (HSBF) and are both based on the principles of superplastic forming.

 

Challenges of Superplastic Forming

One of the difficulties of superplastic forming is the potential for contact friction between the intermediate material and the mold, which can impart undesirable surface defects. When heated to a superplastic state and subjected to compressive forces, aluminum is particularly susceptible to a wearing phenomenon known as galling.

Galling is a form of localized roughness that is caused by both adhesion and friction. When superplastic aluminum comes into contact with a mold under pressurized conditions, the two surfaces may adhere to one another. This can cause localized variations in flow as the metal is stretched. Material deposition onto the mold and a scratched or gouged finished product are symptomatic of galling.

A solution to this issue is to utilize high-temperature lubrication capable of limiting intermetal friction during superplastic forming.

 

Boron Nitride Lubrication and Mould Release for Superplastic Forming

Boron nitride (BN) is an outstanding refractory material with excellent lubricity, non-abrading characteristics, and a high thermal conductivity on the range of 30 – 300 W/mK. This unique combination of properties makes it an ideal lubricant and releasing agent for high-temperature metal forming applications.

BN coatings have successfully been applied to panels and molds for atmospheric superplastic forming processes at temperatures up to 800°C (1472°F). This far exceeds the elongation temperature of aluminum to effectively reduce the risk of galling and preserve a high-quality surface finish throughout superplastic forming.

 

Superplastic Forming Solutions from Saint-Gobain Boron Nitride

Saint-Gobain Boron Nitride is one of the world’s leading suppliers of products and intermediates based on BN powders. Saint-Gobain’s CeraGlide^® Boron Nitride Coatings are a proprietary solution to common wearing and friction phenomena impacting the surface finish and thickness of components manufactured through superplastic forming technologies. It is non-oxidative in temperatures up to 850°C (1562°C) and boasts exceptional lubricity to facilitate easy removal of solidified metals with improved yields.

 

If you would like more information about Saint-Gobain’s solutions for superplastic forming applications, please do not hesitate to contact us directly.