The low-cost, large-scale production of nanodiamonds is leading to new applications in coatings, electronics manufacturing and biomedicine.
Nanodiamonds (NDs), also called detonation diamonds (DND) or ultradispersed diamonds (UDD), are relatively easy and inexpensive to produce, and have moved towards large-scale commercialization due to their excellent mechanical, optical and thermal properties, high surface areas and tunable surface structures and chemical stability. They are also non-toxic, making them suitable for application in biomedicine. Nanodiamond powder was first discovered in 1963 in the Soviet Union, but it is only in the last few years that large-scale production has come to the fore.
Based upon their primary particle sizes, nanodiamonds have been classified into:
- nanocrystalline particles (1 to ≥150 nm)
- ultrananocrystalline particles (2 to 10 nm)
- diamondoids (1 to 2 nm).
Figure 1: Structure of a single nanodiamond particle.
Properties that are desirable for industrial application in areas such as polishing, coatings, lubricants, composites, catalysts and biomedicine (drug delivery, bioimaging, tissue engineering, implants) include:
- inherent fluorescence.
- small primary particle size (~4 to 5 nm) with narrow size distribution.
- cores are believed to hold high crystallinity and chemical inertness of bulk diamond.
- highest thermal conductivity: 2000 W/m•К.
- lowest specific heat capacity: 6.115 J/m•К.
- very high mechanical hardness and wear resistance
- highest sound propagation velocity.
- low thermal resistance: 0.25°C-cm²/W.
- high electrical resistivity: 10¹³ Ω•cm.
- chemical and radiation resistance.
- high biocompatibility and non-cytotoxity.
- graphene-like sp2 surface structure.
- ease of surface functionalization.1
Nanodiamonds can also maintain most of their properties upon surface functionalization (such as fluorescence and biocompatibility). Their surface can readily be functionalized with a diversity of surface groups which allow attachment of organic, inorganic or biochemical molecules and species imparting distinctive properties for numerous applications.
Figure 2: Nanodiamond powder.
Synthesis of nanodiamonds
Types of NDs produced are categorized as high-pressure high-temperature (HPHT), CVD diamond and detonation nanodiamonds (DND). DNDs are the most widely produced due to their inexpensive synthesis and are the main focus of this market review.
NDs are typically synthesised using the detonation method (when sub-10 nm NDs are
required), via detonation of carbon-containing explosives in a cylindicral steel chamber.2 Explosives with a negative oxygen balance (for example a mix of 60 wt% TNT (C6H2(NO2)3CH3) and 40 wt.% hexogen (C3H6N6O6)) are detonated in a closed metallic chamber in an atmosphere of N2, CO2 and liquid or solid H2O.
Figure 3: Nanodiamond detonation chamber.
After detonation, diamond-containing soot is collected from the bottom and the walls of the chamber. Purification is needed and further processing involves:
- Low power sonication, milling or mechanochemical or
- Bead-assisted milling or sonic disintegration.
The detonation conditions require precision to ensure a high nanodiamond yield- an industrial detonation chamber produces ~2.5KG of Nanodiamonds/8 hours. The commercial nanodiamonds produced are ~4-5nm in diameter. The detonation conditions require precision to ensure a high nanodiamond yield- an industrial detonation chamber produces ~2.5KG of Nanodiamonds/8 hours. The commercial nanodiamonds produced are ~4-5nm in diameter.
Other synthesis methods are via Chemical vapor deposition (CVD) that results in ultra-nanocrystalline diamond (UNCD) films (5-100nm, 3-5nm); and high-pressure high-temperature processing (HPHT) that results in nanodiamonds possessing up to 300 ppm of nitrogen (>20nm). CVD requires high substrate temperature and carbide forming substrates .
The main advantage of HPHT nanodiamonds over detonation nanodiamonds is their uniform structure with low concentration of lattice defects such as dislocations or twinning. Both CVD and HPHT nanodiamonds demonstrate the ability to stably host various colour centers for application in sensors, photonics, spintronics, quantum computing and electronics applications. Recent synthesis methods for NDs involve laser ablation, that display good results for ND disaggregation and production of stable dispersions.3 4
Markets and applications
Nanodiamond powder and films are currently used in markets such as fine polishing, coatings, lubricants, polymer composites and bio-medical research. Main growth markets are CMP polishing slurries and pads, thermal compounds for heat management in electronics, anti-friction and wear additives and coatings. Future markets are in sensors, spintronics, quantum devices and photodetectors.
Table 1 : Market, properties/benefits and applications of nanodiamonds.
|Biomedicine||• Biocompatibility across different cell types.
• Ease of surface modification.
• Unique optical and electronic properties.
• Fluorescence capabilities.
• Chemical stability.
• Ability to form hydrogels.
• The presence of nitrogen vacancy (NV) centers in nanodiamonds results in the absorption of the visible spectra and emission in red at room temperature with great temporal stability and almost no photobleaching. A single nanodiamond crystal is capable of producing luminescence brighter than standard fluorescent protein.6
|• Drug and gene delivery.
• Cancer therapy.
• MRI contrast agents/biomarkers.
• Cell imaging.
• Protein separation and purification.
• Filler material for implants.
• Anti-virals and anti-bacterials.
|Coatings||• Improve wear resistance and tribology properties.
• Improved microhardness.
• Reduce porosity.
• Increased dispersion ability.
|• Wear resistant coatings (tools).
• Protective electrochemical and chemical coatings in electrolytic metallurgy.
• Plasma sprayed polymer diamond coatings.
• EMI shielding coatings.
|Composites||• Improved strength and elasticity
• Wear resistance
• Adhesive strength with metals
Improving the optical characteristics of polymers
• Increasing heat conductivity while retaining the absolute dielectric properties.
• Polyamide and fluoroplastics.
|Electronics & semiconductors||• High thermal conductivity.||• Thermal paste for heat management (heat dissipation).
• Polishing slurries and pastes.
• Insulation materials.
|Energy||• High thermal conductivity.||• Hydrogen accumulators.
• High voltage, high energy density, high temperature capacitors.
• High efficiency catalysts.
|Lubricants||• Improved durability.
• Reduced friction.
|• Lubricating oils and greases for reduction of wear and friction.|
|Sensors||• Excellent biocompatibility
• Composite Noncytotoxic nature
• Narrow size
• Possess several oxygenated functional groups on its surface, including hydroxyl and carboxyl groups, which facilitate the immobilization of biomolecules.
As with most nanomaterials, despite their unique properties and scalable production methods, the wider use of nanodiamonds is hindered by familiar problems, including:• Consistent quality of nanodiamonds produced differs greatly from supplier to supplier, and by region. This has been attributed to the uncontrolled character of the existing technology for nanodiamond fabrication, based on the detonation method. There is yet to be developed a consistent and controlled method for producing homogeneous nanodiamonds.• Aggregation and dispersion issues. • Need for greater understanding of properties of nanodiamonds, on an application by application basis. • Lack of current products utilizing nanodiamonds.
The market for nanodiamonds is growing, especially for biomedical applications and research, and there are a number of producers. Main producers include:
Adamas Nanotechnologies, Inc., USA
The company produces nanodiamond suspensions, powders, additives for lubricants and fluorescent nanodiamonds (for biomedical applications).
Advanced Diamond Technologies, Inc., USA
The company has licensed several U.S. and foreign patent applications from Argonne National Laboratory (ANL) for composite materials based on nanodiamonds. The company is an ANL spin-out. Ultrananocrystalline diamond (UNCD™) films are used in applications as energy-saving ultra-low friction and wear coatings for mechanical pump seals and tools, high-performance microelectromechanical and nanoelectromechanical system (MEMS/NEMS)-based telecommunication devices, high-definition flat panel displays, in-vivo biomedical implants, and biosensors.
Carbodeon Ltd. Oy, Finland
The company’s uDiamond NanoDiamond technology is utilized to Improve the lifetime and conductive performance for electronic appliances, automotive parts and industrial manufacturing line components.
Figure 4: Carbodeon NanoDiamond Powders And Dispersions.
Microdiamant AG, Germany
The company produces XP nanodiamond for application in surface coatings and for super fine polishing applications.
NanoDiamond Products Limited, Ireland
The company was founded in 2009. The company produces nanodiamond suspensions. Products include NanoEndures additives for enhancing wear resistance and for diamond abrasives.
Ray Techniques Ltd., Israel
The company is producing nanodiamonds based on proprietary technology for the laser treating of specially prepared targets containing carbon soot mixed within hydrocarbon media. This technology is in contrast to the traditional technology of nanodiamond synthesis by detonation of explosives in metal reactors.
1. Nanodiamonds: The ways forward, http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4922557
2. Dolmatov VY. Detonation synthesis ultradispersed diamonds: properties and applications. Russian Chemical Reviews. 2001;70(7):607–626.
3. Influence of hydrogen on the residual stress in nanocrystalline diamond films, http://dx.doi.org/10.1016/j.diamond.2006.11.059
4. B. Zousman and O. Levinson, Monodispersed Nanodiamonds Produced by Laser Ablation; MRS 2012, Vol. 1452, p 38
5. The properties and applications of nanodiamonds, http://www.nature.com/nnano/journal/v7/n1/abs/nnano.2011.209.html
6. The properties and applications of nanodiamonds, http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DC%2BC3MXhs1elurvE&md5=446629878d13d6979fe2b844bec22c0a