What is the thermal conductivity of boron nitride?
Here, we report that high-quality one-atom-thin hexagonal boron nitride (BN) has a thermal conductivity (κ) of 751 W/mK at room temperature, the second largest κ per unit weight among all semiconductors and insulators.
Hexagonal boron nitride (h-BN) has been predicted to exhibit an in-plane thermal conductivity as high as ~ 550 W m−1 K−1 at room temperature, making it a promising thermal management material. However, current experimental results (220–420 W m−1 K−1) have been well below the prediction.
Single-atom-thick sheets of boron nitride are both highly electrically insulating and good conductors of heat, making them ideal for getting rid of unwanted heat in small electronic devices.
The in-plane thermal conductivity of hBN has been reported to be 400 W m −1 K −1 , which is orders of magnitude higher than that of amorphous SiO 2 , while the thermal conductivity along the out-of-plane direction is as low as 2 W m −1 K −1 (Figure 3a).
Atomically thin boron nitride has one of the highest thermal conductivity coefficients (751 W/mK at room temperature) among semiconductors and electrical insulators, and its thermal conductivity increases with reduced thickness due to less intra-layer coupling.
161 Diamond has the highest thermal conductivity of all known materials yet is an electrical insulator.
Thermal Conductivity of insulating materials
To allow you to get a feel of insulating materials – their thermal conductivity varies between about 0.008 W/mK for vacuum insulated panels (so these are the best, but very expensive!) to about 0.061 W/mK for some types of wood fibre.
Values for Common Materials.
|Material||Conductivity at 25oC|
Thermal Conductivity (k-Value)
Thermal conductivity is the time rate of steady-state heat flow through a unit area of a homogeneous material induced by a unit temperature gradient in a direction perpendicular to that unit area, W/m⋅K.
At standard temperatures boron is a poor electrical conductor but is a good conductor at high temperatures. The most economically important compound of boron is sodium tetraborate decahydrate Na2B4O7 · 10H2O, or borax, used for insulating fiberglass and sodium perborate bleach.
Why is hBN an insulator?
The key difference is that hBN is a large bandgap semiconductor (Eg ~5ev) and hence is an insulator and can serve as a substrate material. hBN can be exfoliated just like graphite, resulting in atomically smooth layers which are ultra-flat.
Key boron nitride properties are high thermal conductivity, low thermal expansion, good thermal shock resistance, high electrical resistance, low dielectric constant and loss tangent, microwave transparency, non toxicity, easily machinability- non-abrasive and lubricious, chemical inertness, non-wetting by most molten ...
Therefore, copper is the best thermal conductor of the three, and polyurethane foam is the worst conductor as well as the best insulator of the three.
Thermal conductivity units conversion:
1 Btu(IT)/(ft h°F) = 1/12 Btu(IT)/(in h°F) = 0.08333 Btu(IT)/(in h°F) = 12 Btu(IT)in/(ft2 h°F) = 1.488 kcal/(m h°C) = 0.01731 J/(cm s K) = 1.731 W/(m K)
Assuming a diffusional distance shorter than 1 μm, Bi is less than 10. Such situation can be expected for monoliths. In contrast, Bi numbers in a range of 170–2600 have been calculated for conventional packed beds . and a dimensionless volumetric coordinate V′.
At present, hexagonal boron nitride (hBN) is the most common 2D insulator and is widely considered to be the most promising gate insulator in 2D material-based transistors.
The thermal conductivity is 33.2 W m−1 K−1 at 10 wt% BNNS filler content and increases to 70.4 W m−1 K−1 at 90 wt% BNNS filler content (Yang et al., 2021b).
General Boron Nitride Information
BN is stable in inert and reducing atmospheres up to 2000°C, and in oxidizing atmospheres to 850°C.
Diamond – 2000 – 2200 W/m•K
Diamond is the leading thermally conductive material and has conductivity values measured 5x's higher than copper, the most manufactured metal in the United States. Diamond atoms are composed of a simple carbon backbone that is an ideal molecular structure for effective heat transfer.
Metals like copper and aluminium have the highest thermal conductivity while steel and bronze have the lowest. As copper is an excellent conductor of heat, it is good for heat exchangers also. Example: Gold, Silver, Iron, etc are some examples of good heat conductors and electrical conductors.
What is the best insulation of thermal conductivity?
1 Polyurethane foam. One of the best commercially available choices of insulation material for fishing vessels is polyurethane foam. It has good thermal insulating properties, low moisture-vapour permeability, high resistance to water absorption, relatively high mechanical strength and low density.
As a rule of thumb, the lower the thermal conductivity the better, because the material conducts less heat energy. Thermal conductivity is a property of the material and does not take into account thickness. Two different thicknesses of the same material still have the same λ-value.
First and probably the most important is the conductivity, which in cases of thermal paste labeling is often expressed in W/mK which stands for Watt per meter by Kelvin. The higher the number, the better the thermal conductivity of the compound is.
Those materials with high thermal conductivity will transfer heat rapidly, either by receiving heat from a hotter material or by giving heat to a colder material. On the contrary, materials with low thermal conductivity act as thermal insulators, preventing the transfer of heat.
The thermal conductivity of a material is highly dependent on composition and structure. Generally speaking, dense materials such as metals and stone are good conductors of heat, while low density substances such as gas and porous insulation are poor conductors of heat.
Which Metals Conduct Heat The Best? As you can see, out of the more common metals, copper and aluminum have the highest thermal conductivity while steel and bronze have the lowest.
High conductivity (1000 to 10,000 µS/cm) is an indicator of saline conditions. Waters that have been heavily impacted by industry can fall into this range. How do we measure conductivity? Conductivity is best measured directly in the lake or river.
The K factor of insulation represents the material's thermal conductivity or ability to conduct heat. Usually, insulation materials have a K Factor of less than one. The lower the K factor, the better the insulation.
When looking for a material to insulate your building you would generally look for a material with a high R-value, and therefore, one that can resist heat transfer well. While K-value deals solely with just the material, R-value refers to the material and its thickness.
Thus, if the thickness is 1 inch, and the K-value is 0.25, then the R-value is 1 divided by 0.25, or 4 (leaving off the units for brevity).
Why boron Cannot conduct electricity?
Finally, boron tribromide (BBr3). BBr3 doesn't conduct electricity in either solid nor molten states, this is because BBr3 has covalent bonding between the central B atom and the 3 surrounding Br atoms.
Boron insulation materials, formed from mixtures of cellulose and borates, are commonly used durable and long-lasting products. These materials help to conserve energy and lower energy costs due to their strong thermal insulation properties, which fight against heat exchange of closed areas.
Maximum covalency of B is 4,due to presence of only three valency orbitals ,those are one ns orbital and three np orbitals. Boron is bad conductor of electricity and heat,because boron is non metal.
“Boron nitride is a proper wide-band-gap insulator. At room temperature it doesn't conduct electricity at all,” said University of Manchester graphene researcher Dr Leonid Ponomarenko.
Also like diamond, cubic boron nitride is an electrical insulator but an excellent conductor of heat. This diamond-like polymorph, known as cubic boron nitride, c-BN, β-BN, or z-BN (after zinc blende crystalline structure), is widely used as an abrasive for industrial tools.
Hexagonal boron nitride (h-BN), a layered material isostructural to graphite, has similar exotic properties like graphite. With single atom thick and alternating boron and nitrogen atoms in its atomic structure, h-BN is an insulator with band gap ~ 5.9 eV.
This is also why diamond (with a cubic structure) is stronger than cubic boron nitride (c-BN).”
Boron nitride can be compressed into a superhard, transparent form—but unlike diamond and many other materials known for their extreme hardness, it is based not on carbon but on a latticework of boron and nitrogen atoms.
Boron nitride (B4N) is a crystalline material synthesized from boric anhydride and pure low-ash carbon material in electric furnaces at 1,800°C− 2,500°C (3,300°F–4,500°F). Its hardness is about 3,800 HV and it has a good cutting ability in the form of loose grains.
That's because air, like other gases, is a poor conductor of thermal energy.
What are the top 3 metals with the best thermal and electrical conductivity?
Most of the conductors are metals as they have a high value of conductivity. Gold, Silver, copper, and aluminum are a few examples of good conductors of heat and electricity.
Aerogel Insulation Technology
Classed as a Super Insulation, Aerogel has the highest insulation value of any known material with the lowest thermal conductivity value of any solid (0.015W/mK).
Thermal conductivity is not only affected by changes in thickness and orientation;temperature also has an effect on the overall magnitude. Because of the material temperature increase, the internal particle velocity increases and so does thermal conductivity.
The thermal conductivity of a specific material is highly dependent on a number of factors. These include the temperature gradient, the properties of the material, and the path length that the heat follows.
Temperature, moisture content, and density are the most important factors. Other factors include thickness, air velocity, pressing, and aging time. The relationship between main factors with thermal conductivity is presented.
When Biot number is greater than 1, thermal conduction of solid interior is slower than thermal convection which means that temperature gradient of solid interior need to be taken into account. Biot number is named after the French physicist Jean-Baptiste Biot.
Because the Biot number is the ratio between the external resistance of a body to convection energy exchange and internal resistance to transmitting energy by conduction, a small Biot number implies low resistance to transmission by conduction, and therefore very low temperature gradients within the body; thus leading ...
The numerical value of Biot Number (Bi) is a criterion which gives a direct indication of the relative importance of conduction and convection in determining the temperature history of a body being heated or cooled by convection at its surface.
General Boron Nitride Information
Boron nitride is often referred to as “white graphite” because it is a lubricious material with the same platy hexagonal structure as carbon graphite. Unlike graphite, BN is a very good electrical insulator. It offers very high thermal conductivity and good thermal shock resistance.
Science buffs have been reading about the potential of graphene since its discovery in 2004. Truth be told, graphene is quite vulnerable. Ceramic boron-nitride is much tougher.
How do you measure thermal conductivity of nanofluids?
The most common techniques for the measurement of effective thermal conductivity of nanofluids are the transient hot-wire method , steady-state method , cylindrical cell method , temperature oscillation method , and 3-omega method  to name a few.
As the concentration of nanoparticles increased, the thermal conductivity increased. The highest thermal conductivity increase was measured in the nanofluid with a volume fraction of 5%, which had an increase in thermal conductivity of 40.6% at 30 °C.
The thermal conductivity of Boron is similar to that of aluminum and copper. The thermal conductivity of Boron is 27 W/(m·K). Its electrical conductivity and heat energy are the same. However, compared to aluminum, Boron is a minimal quantity of material, making it less suitable for high-temperature applications.
However, in an oxidising atmosphere the maximum use temperature is 850-900 °C. Hot Pressed and Hot Isostatic Pressed Boron Nitride are produced by densification of powder, whereas Pyrolitic Boron Nitride is produced by Chemical Vapour Deposition (CVD), depositing onto graphite at temperatures in excess of 1800 °C.
Pure crystalline boron is a black, lustrous semiconductor; i.e., it conducts electricity like a metal at high temperatures and is almost an insulator at low temperatures.