Aluminium magnesium boride
Aluminium magnesium boride or Al3Mg3B56,
Synthesis
BAM powders are commercially produced by heating a nearly
BAM films can be coated on silicon or metals by pulsed laser deposition, using AlMgB14 powder as a target,[9] whereas bulk samples are obtained by sintering the powder.[10]
BAM usually contains small amounts of impurity elements (e.g., oxygen and iron) that enter the material during preparation. It is thought that the presence of iron (most often introduced as wear debris from mill vials and media) serves as a sintering aid. BAM can be alloyed with silicon, phosphorus, carbon, titanium diboride (TiB2), aluminium nitride (AlN), titanium carbide (TiC) or boron nitride (BN).[8][10]
Properties
BAM has the lowest known unlubricated coefficient of friction (0.04) possibly due to self-lubrication.[4]
Structure
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/23/AlMgB14s.png/300px-AlMgB14s.png)
Most
Optoelectronic
BAM has a bandgap of about ~1.5 eV. Significant absorption is observed at sub-bandgap energies and attributed to metal atoms. Electrical resistivity depends on the sample purity and is about 104 Ohm·cm. The Seebeck coefficient is relatively high, between −5.4 and −8.0 mV/K. This property originates from electron transfer from metal atoms to the boron icosahedra and is favorable for thermoelectric applications.[11]
Hardness & Fracture toughness
The
Thermal expansion
The thermal expansion coefficient (TEC, also known as Coefficient Of Thermal Expansion, COTE) for AlMgB14 was measured as 9×10−6 K−1 by dilatometry and by high temperature X-ray diffraction using synchrotron radiation. This value is fairly close to the COTE of widely used materials such as steel, titanium and concrete. Based on the hardness values reported for AlMgB14 and the materials themselves being used as wear resistant coatings, the COTE of AlMgB14 could be used in determining coating application methods and the performance of the parts once in service.[7][8]
Material | TEC (10−6 K−1)[7] |
---|---|
AlMgB14 | 9 |
Steel | 11.7 |
Ti | 8.6 |
Concrete | 10–13 |
Friction
A composite of BAM and
Applications
BAM is commercially available and is being studied for potential applications. For example, pistons, seals and blades on pumps could be coated with BAM or BAM + TiB2 to reduce friction between parts and to increase wear resistance. The reduction in friction would reduce energy use. BAM could also be coated onto cutting tools. The reduced friction would lessen the force necessary to cut an object, extend tool life, and possibly allow increased cutting speeds. Coatings only 2–3 micrometers thick have been found to improve efficiency and reduce wear in cutting tools.[15]
See also
References
- ^ "Structural and mechanical properties of Al―Mg―B films: Experimental study and first-principles calculations - PDF Free Download".
- ^ "The Genetic Atlas".
- OSTI 1458625.
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- ^ Kurt Kleiner (2008-11-21). "Material slicker than Teflon discovered by accident". New Scientist. Archived from the original on 20 December 2008. Retrieved 2008-12-25.
- .
- ^ Tough nanocoatins boost industrial energy efficiency Archived 2012-05-24 at the Wayback Machine. Ames Laboratory. Press release. Department of Energy. 18 Nov. 2008.
External links
- Material slicker than Teflon New Scientist Article on BAM.
- News on AlMgB14 Press Release with photos.