Hexagonal Boron Nitride in Lambda Sensors

In the automotive industry, Hexagonal Boron Nitride with boron oxide as binder is used as a sealing element in oxygen sensors (lambda sensors). For modern engine control, measurement of the exact composition of the flue gas is necessary. Lambda sensors measure the oxygen content in the flue gas relative to a reference oxygen concentration. The signal is passed on to engine control, which adjusts the oxygen/fuel mixture appropriately. To guarantee reliable measurement, the measurement and reference chamber is separated by a packing seal. The dense pack material must also be an electric insulator, resistant to high temperature and suitable for lambda sensor production. One of the two components of the packing seal consists of a sealing ring made of Momentive HBN Grade Hot Pressed Boron Nitride.

2D Layered Insulator Hexagonal Boron Nitride Enabled Surface Passivation in Dye Sensitized Solar Cells

ABSTRACT

A two-dimensional layered insulator, hexagonal boron nitride (h-BN), is demonstrated as a new class of surface passivation materials in dye-sensitized solar cells (DSSCs) to reduce interfacial carrier recombination. We observe 57% enhancement in the photo-conversion efficiency of the DSSC utilizing h-BN coated semiconductor TiO₂ as compared with the device without surface passivation. The h-BN coated TiO₂ is characterized by Raman spectroscopy to confirm the presence of highly crystalline, mixed monolayer/few-layer h-BN nanoflakes on the surface of TiO₂. The passivation helps to minimize electron–hole recombination at the TiO₂/dye/electrolyte interfaces. The DSSC with h-BN passivation exhibits significantly lower dark saturation current in the low forward bias region and higher saturation in the high forward bias region, respectively, suggesting that the interface quality is largely improved without impeding carrier transport at the material interface. The experimental results reveal that the emerging 2D layered insulator could be used for effective surface passivation in solar cell applications attributed to desirable material features such as high crystallinity and self-terminated/dangling-bond-free atomic planes as compared with high-k thin-film dielectrics.

This research paper was was published in Nanoscale online on 6th September 2003

Boron Nitride : Electronic Applications Requiring More Than Heat Dissipation:

Thermal management has always been a major concern in the design of high frequency, high power electronic devices. For example, historically, in many power amplifier designs, the vast majority of the power that needs to be dissipated is from the high power field effect transistors, or FET's, themselves. In these cases, the high power dissipation often requires direct attachment of the FET's to a heat sink of some type. Heat sinks have become almost essential to modern central processing units and other electronic devices.

Ideally, heat sinks are made from a good thermal conductor such as silver, gold, copper or aluminum alloy. Copper and aluminum are among the most frequently used materials for this purpose with electronic devices. In addition, recently, synthetic diamond cooling sinks have been developed to provide better cooling. Further, some heat sinks are constructed of more than one material with desirable features, such as phase change materials. Such materials can store a great deal of energy due to their heat of fusion. However, while many of these materials provide heat sink features, they do not address other needs of the device, such as electrical insulation. This article will highlight those needs and how new materials deal with those requirements.

Applications Overview

Before discussing new developments in materials for thermal management, an overview of electronics applications and thermal management will be given. Currently, there are four general categories of electronic applications that require thermal management such as provided by heat sinks and other approaches. They can be broadly classified as (1) medical electronics (2) consumer electronics (3) automotive electronics and (4) aerospace and defense electronics. Each of these categories has unique requirements in terms of thermal management. A brief discussion of those various needs will now be presented.

In the area of medical electronics, from imaging equipment to surgical instruments and automated immunoassays, more power means more heat, generally in a small space. Further, as greater demands for precision and reliability are placed on medical equipment, thermal control becomes more critical. To address that concern, medical equipment designers are using passive thermal control systems that include heat pipes and vapor chambers. Such devices offer high reliability, design flexibility, manageable cost, and quiet operation.

The consumer electronics field is being driven by the need for smaller, faster and lighter products. That need has put considerable demands on the thermal management of microelectronics. This area offers potential opportunities for materials-enabled innovation. Materials for electronics such as tablets and smart phones are moving to encompass the entire body of the smart phone or tablet, making heat dissipation more effective. This will likely push the boundaries in new materials where aesthetics such as color and texture will become important features for adoption. Thermally conductive polymers are seeing an increase in this segment of the market.

Electronics in automobiles has become more and more sophisticated and power consumption only seems to increase. In recent years, the proliferation of electronic hybrid cars has created new cooling problems with electronics that control large amounts of current. For example, in automobiles like the Toyota Prius, cooling of the battery pack is necessary to keep the temperatures of all of the modules as uniform as possible. This maximizes the performance and the life of the battery. Unique materials solutions may offer opportunities to address these issues.

Aircraft thermal management is becoming increasingly important to the safe design and operation of commercial and military aircraft due to the growing heat loads from expanded avionic functionality, more electrical systems architectures, and the greater temperature sensitivity of composite material systems compared to traditional metallic designs. Military aircraft designers face the additional challenges of removing the waste heat from advanced weapon systems. Examples of components that are sensitive to thermal fluctuations are heat shields, anti-icing systems and propulsion systems. Presently, these needs are typically addressed through the use of air exchangers or some type of fan assembly.

Thus, of the four applications that have been discussed, the two areas for which new materials are of high priority are automobile and consumer electronics. Of these, consumer electronics appears to be the most needing of the new technologies. Attention will now be turned to current requirements and how those can be met by new materials.

Market Requirements

Until recently, metal-based systems have been the primary material solution of choice. Aluminum was primarily selected for various light-weight thermal management systems. However, these systems are becoming more expensive based on raw material price increases that have been observed over the past few years. In that regard, plastics offer suitable performance for many of the thermal management applications that are being developed.

In order to gain insight into developing needs, a recent SpecialChem survey asked respondents about material requirements for thermal management applications. The results of the survey were that thermal management goes beyond thermal conductivity alone. Specifically, electrical insulation and color freedom were valued as other features beyond thermal conductivity. In addition, the following percentage of the respondents voted for the various options:

Physical Properties Best In Class Well Balanced Cost Option Electrically Insulating Plastic Yes Yes No Color/Colorability White White Black Resin + Filler Compound Price ($/100 cc) 3,5 3 1 Tensile Strength (MPa) 100 65 65 Impact Strength (J/m) 80 35 35 % of votes 27% 49% 24% Table 1: Results of Survey on Thermal Management Materials (based on 77 feedbacks)

From these results, it can be seen that a well-balanced formulation is the choice of about one-half of the respondents. In this context, a well-balanced formulation is described as one that provides not only thermal conductivity but also other features such as color. It should be noted that the cost option gathered the lowest percentage in the survey.

Thermally Conductive Plastics

In order to address present needs, thermally conductive plastics are made through the incorporation of high thermal conductivity fillers into the thermoplastic polymer matrix. Examples of common conductive fillers that are used are graphite, expanded graphite and carbon fibers. But, the use of these materials results in the final composite material being black and electrically conductive. As already stated, this is undesirable for consumer electronics applications such as smartphones. On the other hand, boron nitride is a synthetic ceramic that is both an excellent conductor of heat and a dielectric material. Recently, Momentive Performance Materials has developed Boron Nitride fillers enabling composite to reach acceptable thermal and electrical properties.

There are other ceramic materials, such as alumina, aluminum nitride and silica that show similar characteristics but boron nitride has the highest thermal conductivity of any of these materials. Table 2 provides a comparison of some properties of boron nitride to other competing fillers.

Property BN Al2O3 AlN SiO2 Thermal Conductivity (W/m/K) 300 30 260 1.3 Dielectric Constant 2.28 3.98 3.26 2.20 Mohs hardness <2 >9 ~ 7 ~ 6.5 Table 2: Comparison of Boron Nitride to Other Fillers

As can be seen from this Table, boron nitride offers both very high thermal conductivity values as well as a low dielectric constant. In addition, due to its softness, it can be readily compounded into many polymers with limited wear on the processing equipment.

Momentive Performance Materials' New Grade of Boron Nitride

Momentive Performance Materials has recently developed a new grade of boron nitride, designated CFX 600, which provides enhanced thermal conductivity while at the same time providing electrical insulation in a wide variety of thermoplastic resins. It is a surface treated version of boron nitride that allows for the attainment of high thermal conductivity and improved physical properties at lower loading levels than are commonly used. Specifically, CFX 600 can provide up to 20% enhancement in thermal conductivity while potentially also providing improvements in mechanical properties compared to untreated boron nitride powder at the same loading level.

This is just one example of a material development for thermal management that is focused on the growing needs of applications like consumer electronics. Those needs are clearly pointing out the requirement for more than simply thermal conductivity. Instead, materials solutions are being sought that provide a balance of properties in the final composite material. As these developing applications continue to stress the need for faster electronics, it is expected that materials developments will need to continue to address those needs.

Source: Special4polymers

For more details contact : innovative_growth@yahoo.co.in

Momentive Hot Pressed Boron Nitride Shapes

Hot-Pressed BN

Momentive Hot-pressed BN is compacted at temperatures up to 2000°C and pressures up to 14MPa. B2O3 is introduced to help form a dense, strong engineering material that is remarkably easy to machine.

Several grades of hot-pressed boron nitride are available which differ in the type and amount of binder present. Standard grades, such as Momentive Performance Materials’ grade HBN, have 2-5 per cent B2O3 which can hydrate when exposed to moisture or high humidity.

This can result in limited thermal shock resistance. Other grades have a calcium addition which combines with the B2O3 to form a higher melting point glass binder which is less hygroscopic and gives improved performance at high temperatures (up to 1200°C). There is a high purity grade HBC from which the B2O3 binder has been removed. The process yields a diffusion bonded ceramic that actually increases in strength with increasing temperature. This grade HBC is commonly used at temperatures over 2000°C.

In addition to sharing the performance characteristics of powdered hexagonal boron nitride from which it is made— chemically inert, high thermal shock resistance, high electrical resistance, high thermal conductivity, excellent corrosion resistance, low loss tangent and low dielectric constant—HPBN adds some strengths of its own. It is not wetted by most molten metals including aluminum, antimony, bismuth, cadmium, copper, germanium, indium, iron, silicon, steel and tin. It does not react with halide salts and many other chemicals. Because HPBN is relatively soft, it is easily machined. This is unusual among ceramics used in electronics applications and reduces the need for precision surfaces to maximize contact area.

Momentive Hot Pressed Boron Nitride Shapes

Applications for HPBN

The unique combination of thermal and electrical characteristics found in hot-pressed boron nitride, coupled with its machinability, have caught the attention of design engineers in a variety of industries. A sampling of today’s uses includes:

• As a boron source in p-type diffusion furnaces
• As a heat sink in transistor packages
• As a substrate
• As an interface and nozzle material for manufacture of amorphous alloys
• As a break ring in horizontal continuous casting of steel
• As a mold for casting carbon steel, low alloy steels and stainless steel
• As insulators and source holders for ion implant systems
• As insulators for vacuum furnaces
• As glass-forming tools and refractories
• As windows in aerospace re-entry vehicles
• As microwave windows for high frequency satellite applications
• As an ablative material for aerospace applications
• As plasma rings
• As electrical insulating spacers for tungsten resistance heaters
• As refractory wall liners and crucibles in a variety of hot metal applications 

For more details you can get in touch with us at : innovative_growth@yahoo.co.in or 9910899409

Momentive Boron Nitride LPC Grade Coatings (Alumina Binder) for Wagstaff Casting System

Momentive Boron Nitride LPC Grade Coatings for Wagstaff Casting Systems

• Yields non-wetting, lubricating surfaces
• Melts do not stick
• excellent release properties and easy removal of melt • contains "white  
   graphite"

Momentive LPC grade Boron-Nitride-Coating is suitable for coating thimbles, transition plates and the refractory lining of the distribution trough of WagstaffTM Casting Systems. The very good non- wetting property of Momentive LPC Boron-Nitride-Coating makes an easy and effective removing of remaining melts possible. It is a proven replacement for graphocote (both based on xylene and water) when applied on thimbles and transition plates. Used on the distribution trough it replaces coatings like terracote and those based on bone ash.

Momentive LPC Boron-Nitride-Coating is a water-based paste-like products and should be diluted with distilled water prior to use. Best performance of LPC Boron-Nitride Coatings achieved by applying thin coats of 50-100μm (2-4 mils).

Application to Thimbles
When a new table is put into service with new thimbles (usually made of fused silica) the inner surface is being coated at room temperature using a soft brush. A mixture of 1 part Momentive LPC and 2 parts water give best results. Coating should air dry before heating up table to casting temperature.

During casting breaks the is being tilted upward araund 90° . Now the remaining metal is easily removed because LPC is an effective release agent. Each casting break should be used to brush the inner surface of the thimbles when being hot by using a mixture of 1 part LPC and 2-3 parts water. It is important to apply thin coats because thick coats may crack during use and do not show any technical advantages.

Application to Transition Plates
Transition plates (usually of Ca-Silicate) may be coated by brushing using a mixture or 1 part LPC and 2-3 parts water. However, it is important not to coat the porous graphite die because this could interrupt gas flow.

Application on the Refractory Lining of the Distribution Trough
After a new refractory lining is installed and coated with the sealer, Momentive LPC Boron- Nitride-Coating is brushed onto the could surface using a mixture of 3 parts LPC and 4 partsof water. A whole table will be covered by about 750g of ready to use mixture. 
During each casting break LPC Boron-Nitride-Coating can be applied on hot surface after removing aluminium by using a spray gun. Best mixture will be 1 part LPC and 3-4 parts water. 

Remark: Caused by thermal stress the refractory lining of the distribution trough shrinks during use forming cracks of a width of 0.5-2mm. Because LPC Boron-Nitride-Coating is applied in thin coats those cracks will not be covered. Therefore, these cracks must be filled in time by using a suitable repair putty. Otherwise liquid aluminium will fill these cracks causing adherence to the lining.

Storage-Container Size
Momentive LPC Grade BN Coating must be protected against frost. A storage temperature of >5°C (>41°F) is recommended. The containers should be kept closed. 

Safety
EPC Boron-Nitride-Coating contains water and is free of solvents. According to data available to us LPC Boron-Nitride-Coating is a non-hazardous preparation. Material safety data sheet is available.

Technical Data
Colour      :  White
Boron Nitride Content : 25%
Binder         : Alumina    
Temperature : 850 DegC Degree in Air, 1850 DegreesC  under inert gas
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Boron Nitride Coatings - Guidelines for Addressing Common Issues

We are giving below some of the common issues that our customers have raised, their causes and probable solutions. Once these issues are addressed after that our customers are getting excellent performance from our Boron Nitride Coatings and Sprays.

Problem	Cause	Solution
Coating peels.	Coating is too thick.	Dilute coating so that the layer thickness does not exceed 100µm.
Coating does not adhere on the surface.	Bad surface conditions.	Clean and degrease surface, perhaps grit blasting, warm surface prior to application to 100-150°C.
Further layers do not stick on the first layer.	First coating is not yet completely dried.	Extend drying time, remove loose particles and coat again.
Exfoliation and cracking.	Coating is too thick.	Dilute coating in such way that thinner layers can be applied.
Cloudy, uneven application when spraying.	Coating is not stirred up, spray gun is led jerkily not homogenious.	Stirr coating or use mixer. Pull even courses with spray gun.

Though the above solutions cure 99% of the issues, but still if you are facing any other issue you can get in touch with us. 

Our mail id is innovative_growth@yahoo.co.in

Boron Nitride Powders Improving Thermal Conductivity in Polymers

Boron nitride (BN) is increasingly being used as a filler in thermoplastics, primarily to increase the thermal conductivity of the resins. Filler-reinforced plastics are being considered to replace traditionally metal parts in a number of markets, with applications such as under-hood automotive parts, sensors and housings for motors, LEDs, and other electronic devices.

Boron nitride is a synthetic ceramic material that is isoelectronic with carbon. Like carbon, boron nitride exists in multiple allotropic forms. The two most common forms are hexagonal boron nitride (hBN), a soft form with a hexagonal crystal structure comparable to graphite; and cubic boron nitride (cBN), a hard form with a crystal structure analogous to diamond. Hexagonal boron nitride can be converted to the cubic form using a high-temperature, high-pressure process.

Hexagonal boron nitride crystals are made of planar sheets of covalently bonded boron and nitrogen atoms that make the a-b plane of the crystal. Van der Waal’s forces hold multiple layers of such BN planes together in the c direction. An important consequence of this crystal structure is that the crystals have anisotropic properties, i.e. the properties in the crystal’s a-b plane are different from the through-plane properties. For example, the in-plane thermal conductivity has been estimated to be > 300 W/mK, while the through-plane conductivity is only about 3 W/mK.

When BN powders are used as fillers in resins, the BN-resin composite materials also demonstrate anisotropic properties, largely determined by the orientation of the platy BN crystals in the final part. To overcome this problem of anisotropy, boron nitride powders have been developed which are agglomerates of single crystal. In such agglomerate grades, platy BN crystals are held together to form a larger particle to randomize their orientation. Such BN powder grades, broadly called agglomerate grades, demonstrate more isotropic properties than do single crystal BN grades.

One of the biggest challenges of using agglomerate BN grades is to preserve the structure through all the processing steps. BN agglomerates are relatively weak and are likely to break down into their component platelet crystals if sheared aggressively during processing. In the case of thermoplastics, the BN agglomerates can break down during the extrusion step and/or the molding step. Both the screw configuration during extrusion and the flow configuration during molding determine the extent of shear of the BN agglomerates. These processing steps should be monitored and controlled to preserve the agglomerates’ beneficial structure.

The thermal conductivity of single crystal platelet and agglomerate boron nitrides in a thermoplastic resin is examined in this paper to consider and explain the effect of particle morphology. The anisotropic properties will be characterized using through-plane and in-plane thermal conductivity measurements on BN-plastic composite parts using laser flash measurements. The effect of screw configuration during extrusion and molding conditions on the thermal conductivity and other physical strength properties, such as tensile strength strain at break, will also be examined and the trade-offs will be discussed. 

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Boron Nitride Ceramics in Photovoltaic and Solar Industry

Momentive's Sintered Boron Nitride products, as opposed to the materials used so far, give the optimal high performance ceramic for use in high temperature furnaces employed in the manufacture of monocrystalline and polycrystalline silicon wafers. Momentive's Sintered Boron Nitride is distinguished by its outstanding thermal shock resistance and maximum electrical insulation.

Boron Nitride is considerably more dependable and long-lived than aluminium oxide, for example. At highest temperatures in vacuum or under shielding gas, Momentive's Sintered Boron Nitride ceramics are the optimal and often only solution.

The outstanding thermal and electrically insulating properties of Boron Nitride make it the preferred ceramic for distance bushes, distance tubes, distance discs, grommet bushes, electric insulators, electrically insulating bushes and other thermally and electrically stressed insulation parts.

You are looking for a technically optimal solution using boron nitride ceramics in the photovoltaic and solar industry?
Momentive supplies to globally renowned plant manufacturers and plant operators in the solar and photovoltaic industry. Boron Nitride increases productivity of monocrystalline and polycrystalline silicon wafers as well as that of photovoltaic thin-film technology manufacture. 

For more info contact 9910899409  :  mail:  innovative_growth@yahoo.co.in

How Boron Nitride Acts as a Solid Lubricant

Boron nitride may exist in two forms of crystal lattice: cubic and hexagonal.

Due to its tight diamond-like structure cubic boron nitride is extremely hard. It has poor lubrication properties and is used in cutting and abrasive tools as a diamond substitute.

Hexagonal boron nitride (HBN) is a solid lubricant relating to the class of Inorganic lubricants with lamellar structure, which also includes molybdenum disulphide, graphite and some other sulphides, selenides and tellurides (chalcogenides) of molybdenum, tungsten, niobium, tantalum and titanium.
The crystal lattice of hexagonal boron nitride consists of hexagonal rings forming thin parallel planes. Atoms of boron (B) and nitrogen (N) are covalently bonded to other atoms in the plane with the angle 120 ° between two bonds (each boron atom is bonded to three nitrogen atoms and each nitrogen atom is bonded to three boron atoms).
The planes are bonded to each other by weak Van der Waals forces.


 

The layered structure allows sliding movement of the parallel planes. Weak bonding between the planes provides low shear strength in the direction of the sliding movement but high compression strength in the direction perpendicular to the sliding movement.

Friction forces cause the particles of boron nitride to orient in the direction, in which the planes are parallel to the sliding movement. The anisotropy of the mechanical properties imparts the combination of low coefficient of friction and high carrying load capacity to boron nitride.

Boron nitride forms a lubrication film strongly adhered to the substrate surface. The lubrication film provides good wear resistance and seizure resistance (compatibility).

Similar to molibdenum disulfide moist atmosphere is not required for lubrication by boron nitride. It demonstrates low friction in dry atmosphere and in vacuum.

Coefficient of friction of boron nitride is within the range 0.1-0.7, which is similar to that of graphite and molybdenum disulfide. Impurities (eg. boron oxide) exert adverse effect on the lubrication properties of boron nitride.

Boron nitride is chemically inert substance. It is non-reactive to most acids, alkalis, solvents and non-wetted by molten aluminum, magnesium, molten salts and glass.

The main advantage of boron nitride as compared to graphite and molybdenum disulfide is its thermal stability. Hexagonal boron nitride retains its lubrication properties up to 5000°F (2760°C) in inert or reducing environment and up to 1600°F (870°C) in oxidizing atmosphere.

Boron nitride has high thermal conductivity.

Some applications of hexagonal boron nitride:

• Additives in lubricating oils
• Components of polymer based composite anti-friction coatings
• Second phase particles of metal based composite anti-friction coatings
• Solid lubricant in metal forming
• Release coatings and non-sticking refractory linings in foundry
• Sintered ceramic parts for high temperature application

Boron Nitride Break Rings for Continuous Casting

Continuous casting is one of the most common metal manufacturing technologies. The liquid metal flows from a tundish into the mold, in which the strand shell is formed. The metal strand is then taken off continuously or intermittently, at a speed and solidification rate appropriate to the particular alloy.
The ceramic break ring or the nozzle comes into contact with both the melt and the solidified alloy, and must satisfy correspondingly strict requirements:

• Chemical resistance to the solidified metal, i.e. no contamination of the alloy
• Good sliding properties, i.e. does not stick to the alloy
• High thermal shock resistance
• Defined thermal conductivity
• High wear resistance
• Easy to machine

Boron Nitride Rings are extensively used in the Industry.  Momentive offers a group of different boron nitride materials and boron nitride composites that are matched to different metal alloys. From these materials,  manufacture nozzles or break rings that increase the lifetimes for the following metals:

• Steels of all kinds
• Copper alloys
• Nickel alloys
• Superalloys
• Precious metals, particularly gold alloys

Spinning Boron Nitride Tubes into Yarns

Researchers have long been able to make nanotubes out of carbon -- super-tough carbon nanotube fibers are suitable for weaving into electronic cloth, are four times tougher than spider silk, and 17 times tougher than the Kevlar used in bullet-proof vests.

Creating such fibers from boron nitride has proved elusive. Carbon and boron nitride are about the same strength, but boron nitride nano tubes(BNNTs) can survive temperatures that are twice as high as carbon nanotubes can survive –- 800°C and higher. Up until now, researchers have only been able to create high-quality BNNTs a micron long. Larger versions have been perforated with defects in the crystalline structure.

These problems now appear to be largely resolved. In a recent paper published in Nanotechnology, A team of materials scientists at the NASA Langley Creativity and Innovation Program, the NASA Subsonic Fixed Wing program, DOE's Jefferson Lab and the Commonwealth of Virginia, describe the ability to create high-quality, uniformly crystalline BNNTs in large quantities. "Other labs can make really good nanotubes that are short or really crummy ones that are long. We've developed a technique that makes really good ones that are really long," said Mike Smith, a staff scientist at NASA's Langley Research Center.*
A cotton-like mass of nanotubes is finger-twisted into a yarn about one millimeter wide. "They're big and fluffy, textile-like," said Kevin Jordan, a staff electrical engineer at Jefferson Lab. "This means that you can use commercial textile manufacturing and handling techniques to blend them into things like body armor and solar cells and other applications."

The “spinning” process involves a laser aimed at a cake of boron inside a chamber filled with nitrogen. This forms a plume of boron gas that shoots upward. A cooled metal wire is then inserted into the gas, causing the gas to cool and form liquid droplets. The droplets combine with the nitrogen to self-assemble into BNNTs. "It's like fuel-air-spark in an engine," says NASA aerospace scientist Michael Smith. "The reaction advances violently, creating the superlong tubes in just milliseconds."

Why boron nitride rather than carbon? Building large amounts of inexpensive boron nitride nanotubes opens the door for lighter, faster car frames; affordable space vehicles and ultralightweight armor. Because of their excellent thermal and chemical stability, boron nitride ceramics are traditionally used as parts of high-temperature equipment. Boron nitride has great potential for nanotechnology applications –- BNNTs are more thermally and chemically stable than carbon nanotubes. And BNNTs can be produced with a structure similar to that of carbon nanotubes. However, their properties are very different –- carbon nanotubes can be metallic or semiconducting depending on the rolling direction and radius, whereas BNNT is an electrical insulator with a wide band gap of ~5.5 eV (the same as diamond). Chemical resistance is better for BNNTs, which are able to survive in air up to much higher temperatures. According toScienceNOW, BNNTs also offer the potential for “pinpoint precision to attack cancer cells by sticking to tumors, absorbing neutrons from a targeted beam, and generating localized alpha radiation to kill the cancer.”

Building large amounts of inexpensive boron nitride nanotubes opens the door for lighter, faster car frames; affordable space vehicles and ultra lightweight armor.

"This is the start of a revolution in materials," says Dennis Bushnell, a NASA engineer who has hopes of using BNNTs for space vehicles. "Just about everything can be made lighter, and hopefully, cheaper. You're talking about energy savings all over the place."

Boron Nitride Coatings Improve Metal Stamping Operation and Die Life

Metal Stamping operations are typical in the Industry. In many cases the manufacturer experience typical problems of metal sticking and poor die life. In such cases many times Boron Nitride Coatings are quite effective. For example, a metal stamping operation was experiencing sticking and poor die life on a particularly difficult-to-form shape; several remedies were tried unsuccessfully. A thin layer of boron nitride was sprayed on the die surfaces. Not only did the stamping operation see a marked improvement in release of the part, but also because of the inherent lubricity of the coating, the die life was significantly increased. 
So Boron Nitride Coatings can also be tried in metal stamping operations.

Boron Nitride Coating Ideal on Cast Iron Stalk Tube in Low Pressure Die Casting

Low Pressure Die Casting (LPDC) is a process that is being widely used in the automobile component industry. Stalk tube is a critical component of the casting machine. Various types of Stalk Tubes are being used in the Low Pressure Die Casting process by automotive component manufacturers. Due to cost advantages and strength over the ceramic tubes, Cast Iron Stalk tubes are being preferred by many casters.  However, the following are the major issues faced with these tubes:

• These tubes get corroded very fast due to oxidation as molten aluminium is quite aggressive
• The ferrous particles mix with the molten aluminium and impact the quality of the casting
• It is very difficult to remove the deposited aluminium metal from the stalk tube

Boron Nitride Coatings have been tried and have been found to be quite effective on Cast Iron Stalk Tubes. The tube can be coated with EPC/GPC grade coating of Momentive(formerly GE Advanced Materials) Boron Nitride. The tube has to be coated from both inside as well outside with a thin layer of Boron Nitride. Spray coating method can be used as otherwise it is difficult to cover the inside surface of the tube. After the coating, it should be dried thoroughly either at room temperature or by blowing hot air at 80 deg C. The second coat is to be done once the first coat is completely dry. Wipe the tube with a soft cloth so that excess boron nitride is removed. Use the tube.

Boron Nitride coatings can withstand temperature  of 850 deg C in oxidising environment and up to 1850 deg C in reducing environment. So the layer of these coatings protect the tube from aggressive molten aluminium, not allow traces of ferrous metal to mix with aluminium melt as well as deposited aluminium metal can be removed easily as these coatings also act as release agent.

Boron Nitride Coatings GPC/EPC now come as Momentive

Aluminium Die Casting: Coating Ladles and Dies with Boron Nitride Coatings

In the die casting and pressure die casting foundries ladles from cast irons or from cast steel are usually used. Due to the large mass these ladles extract large amounts of heat from the melt. In order to avoid this disadvantage, the metal casting working group of the FH Aalen uses cylindrical ladles made out of formed metal sheets. The sheet metal has a wall thickness of 0.8 mm. These ladles have only a small mass and to extract therefore only small amounts of heat the melt.

Usually ladles in the Aluminum foundry industry are protected from an attack of the melt with Boron Nitride Coatings. The more thin-walled however the ladle is, the more important is an appropriate protection by a coating. So consumption of ladles is to be reduced among other things. Still more important is however the avoidance of the iron accommodation of the aluminium melts from the ladles. The metal casting working group of the FH Aalen used ladles coated with the Boron Nitride coating by spraying. It was shown that the coating remains practically unwetted by the aluminium melts, which are poured in the test foundry of the metal working group. Also after numerous castings the non-wetting behaviour of the coating is preserved. This is in as much noteworthy as the non-wetting of the ladle surface prevents a skin formation in the ladle. These skins bring numerous problems with itself. They oxidize at the surface and when reconducting the ladle into the holding furnace then they are usually brought in. Gradually so the oxides in the melt are enriched. Simultaneous their accumulation in the cast parts is to be determined.

Since the Boron Nitride Coating is relatively soft due to the small hardness of the boron nitride, a damage of the coating layer can occur by a mechanical effect. A damage of the coating became apparent with the attempts at the top margin of the ladles. This is caused by hitting the ladles upon outside parts of the holding furnace in order to remove possible remains of the melts from the ladle.

If such a mechanical damage of the coating is avoided, can be operated here with satisfying service lives of the coating.

Boron Nitride Spray Acts as Slumping Release Agent in Glass Moulding

Boron Nitride Spray is used for coating steel moulds in glass industry. There is no pre heating required. Here is experience of an actual user:

I use the **GE (Momentive) BN, and have been having much better luck with it as a slumping release than a casting release (which is what I wanted it for). I think there must be many different formulations out there, and that probably accounts for some of the variations in max temp.

What works best for me is multiple thin applications, prefired. That is, I spray a thin coat of GE BN across the piece as evenly as possible, fire it to about 1400, let it cool and rub it down gently to smooth it out. Then I respray and refire and--if I'm really paranoid, respray and refire again. Done that way, it releases very well at slumping temps, has fewer problems at higher temps and lasts through several firings if I'm careful. I doubt it would last 60 firings though--it has a tendency to flake off after about the fifth firing.
The big question for me is why that's better than kilnwash for slumping. For full fuse and casting, BN doesn't clog up fine detail in the mold and the finish is a little glossier with BN than with kilnwash...if your mold is a relatively smooth, even shape. If not, I'll probably be grinding the mold off the glass in a few places, and I'm getting so I can predict where that'll be...

I figure by the time I really figure it out I'll be at the end of the spray can, and I'll decide then if I really want to buy another can. I've also tried colloidal alumina in solution for a casting release as recommended by a refractory mfg...but so far that's not been very successful.

*GE Boron Nitride Spray is now Momentive Boron Nitride Spray II

Hexagonal Boron Nitride Provides High Temperature Corrosion Resistance

Corrosion annually costs the world economy about 3% of global GDP—about $2.2 trillion, according to a report from the World Corrosion Organization (pdf). Particularly difficult are applications that require protection from corrosive substances at high temperatures.

Now researchers from Rice University, Houston, Tex., say they have discovered a new protective coating for high-temperature corrosion applications—hexagonal boron nitride.

According to this news release, h-BN sheets only one atom thick can protect metal substrates in corrosive environments at up to 1,100 degrees Celsius. The scientists say the chemical vapor deposition method they have developed for making layers of “white graphene” can be scaled up to make the coatings practical for industrial use.

“We think this opens up new opportunities for two-dimensional material,” says Jun Lou, associate professor of mechanical engineering and materials science, in the release. “Everybody has been talking about these materials for electronic or photonic devices, but if this can be realized on a large scale, it’s going to cover a broad spectrum of applications.”

Lou and colleague Pulickel Ajayan led a research team that produced h-BN sheets via CVD, depositing the material on nickel foil. They found the coating improved corrosion resistance in oxidizing environments at high temperature. According to the paper, published last week online in Nature Communications, a layer of h-BN a few atoms thick also protected its chemical cousin graphene under similar conditions. The scientists also were able to transfer sheets of h-BN grown on graphene to copper and steel substrates, according to the news release.

Potential applications for CVD h-BN include gas turbines, jet engines, oilfield equipment, chemical processing, and other harsh environments, Lou says in the release. The coating is transparent, which may allow its use, for example, in solar photovoltaic applications. Wear and abrasion could be issues, and optimal h-BN thickness would need to be determined for specific applications, Lou says.

The Nature Communications paper is “Ultrathin high-temperature oxidation-resistant coatings of hexagonal boron nitride” (DOI: 10.1038/ncomms3541).

What is Hexagonal Boron Nitride and Properties

Hexagonal Boron Nitride

• Hexagonal boron nitride is a white slippery solid with a layered structure, physically similar to graphite in this respect.
  • Like layers of graphite or graphene, it is a 2D planar giant covalent network.
  • Because of its colour, it sometimes, confusingly, called 'white graphite'!
• It is a very good insulator (thermal and electrical?) and chemically very inert i.e. great chemical stability - very unreactive!
• It melts under pressure at ~3000^oC testament to its great thermal stability.
• In the hexagonal form of boron nitride, alternate boron and nitrogen atoms are linked to form interlocking hexagonal rings, just like the carbon atoms in graphite do.
• Therefore in each hexagonal ring there are 3 boron atoms and 3 nitrogen atoms and all the bond lengths are 0.145 nm, so it isn't an alternate single-double bond system but the above diagram is just a simple valence-bond representation.
• The B-N-B or N-B-N bond angle is 120^o, i.e. that expected for perfect hexagonal ring bond network e.g. as found in graphite.
• sp² hybridisation is quoted for the boron atom bonds.
• The B-N bonding in the 2D layers is very strong giving boron nitride great thermal stability, i.e. very melting point.
• However, the layers are held together by weak intermolecular forces (Van der Waal forces, instantaneous dipole - induced dipole forces) and the layers are 0.334 nm apart.
  • This distance is similar to the inter-layer gap in graphite, not surprising, bearing in carbon lies between boron and nitrogen in period 2 of the periodic table.
• As in graphite and graphene, there is pi bonding BUT the energy levels are too high to allow good electrical conduction you find in graphite.

• Hexagonal boron nitride (HBN) is used as a lubricant (weakly held layers can slide over each other), and can have semiconductor properties (after doping?).
  • Because of its 'soft' and 'slippery' crystalline nature, HBN is used in lubricants and cosmetic preparations.
• Hexagonal boron nitride can be made in single layers and can also be formed into nanotubes.
• Bundles of boron nanotubes are used for wire sleeving.
• Boron nanotubes are used as a catalyst support, as in the case of carbon nanotubes.
• Boron nitride is NOT an electron deficient compound like semi-conductors.
• Hexagonal boron nitride can be incorporated in ceramics, alloys, resins, plastics, rubbers to give them self-lubricating properties.
  • Plastics filled with HBN have decreased thermal expansion, increased thermal conductivity, increased electrical insulation and cause reduced wear to adjacent parts.

• Because of their excellent thermal stability, thermal shock stability and chemical stability, boron nitride ceramics are often used as parts of high-temperature equipment ( a typical melting range is 2700-3000^oC). They are stable in air to ~1000^oC whereas carbon-graphite based materials would have long since ignited!