Introduction
Modern technological requirements, together with the consumers’ demands for systems and machines that are more energy efficient, stronger, lightweight, cost-effective, etc., dictate demand for new and advanced materials. Nanodiamonds (NDs) are diamond phase carbon nanomaterials that were initially used for their strong abrasive properties and as lubricant additives for industrial applications. Main types of commercial NDs produced are categorized as high-pressure high temperature (HPHT) nanodiamonds, CVD diamond and detonation nanodiamonds (DND). Other non-commercial synthesis methods that have been used include autoclave synthesis from supercritical fluids, chlorination of carbides, ion irradiation of graphite electron irradiation of carbon onions and ultrasound cavitation.
Figure 1: Structure of a single nanodiamond particle.
Source: Nature.
DNDs are the most widely produced due to their inexpensive synthesis. The smallest NDs (typically< 10 nm) are produced using this process. Larger NDs are produced by either a high pressure-high temperature (HPHT) process or via chemical vapor deposition (CVD), followed by a ball-milling process to crush the micron sized diamonds into NDs, and finally washed in strong acids to remove surface impurities.
Figure 2: Nanodiamond powder.
To make fluorescent nanodiamonds (FNDs), high-energy sources (e.g. electrons, He+, or H+ ions) are used to bombard the HPHT or CVD diamonds to create colour vacancy centers within the diamond lattice. Extremely small amounts of nanodiamond additives can modify a variety of thermal and mechanical properties in various parent materials. Properties include:
- Diamond core: highest hardness (167 Gpa) and wear resistance
- Highest thermal conductivity (2300 W/mK)
- High electrical resistivity (10¹³ ῼcm)
- Low thermal expansion (1.0×10-6 K-1)
- Wide band gap (5.47 eV {300 K})
- High refractive index (2.417)
- Low specific gravity (3.52)
- Chemical/radiation resistance
- Biocompatibility
- Large surface area (250- 450 m²/g)
- High & controllable chemical activity of the surface.
Table 1: Markets, benefits and applications of nanodiamonds.
Nanomaterials |
Properties |
Applications |
Personal care products |
• Biocompatibility • Nontoxicity • Excellent adsorption properties. • Stable UV absorbers. Will not photo degrade unlike typical chemical sunscreens. • NDs attenuate UV radiation through absorption and scattering (for applications in UV protective skin care). • Potent antioxidants (radical scavengers) and do not photodegrade like Vitamin C. |
Protective sunscreens, anti-aging skin care products (serum, cream, lotion, dermal strips, skin cleansers) |
Biomedicine |
• Inherent photoluminescence. • Chemical stability • Large specific surface area and high adsorption potential • Optical and physical properties can be tuned. • Photostable. • Biocompatibility. • Inherently low cytotoxicity and genotoxicity• Rapid transmembrane transport. • High drug loading capacity based on high surface to volume ratio • The presence of nitrogen vacancy (NV) centres 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 can produce luminescence brighter than standard fluorescent protein. |
• 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 |
• Increase in the microhardness (2-3 times) • Decrease in the porosity of a coating layer. • Improvement in coating quality. • Increase in wear resistance: 2-12 times. • Increase in elasticity. • Improved corrosion resistance. |
• Precursors in CVD coatings • Thermal diffusion coatings • PVD Coatings • Electronic devices • Gears, shafts and pistons. Metal cutting tools • Food processing equipment • Petrochemical processing equipment • Medical implants. |
Composites |
• Improved strength and elasticity • Wear resistance • Adhesive strength with metals • Thermal conductivity without compromise to other properties. Thermal conductivity increased 25-100% with 0.1wt% ND. • Increasing heat conductivity while retaining the absolute dielectric properties. • Can be used as radical trapping stabilizers in thermal processing of polymers. • Aging, radiation, scratch and corrosion resistance • Increase in refractive index in thin polymer films |
• Fluoroelastomers • Rubbers • Polyurethanes. • Polyamide and fluoroplastics. • Coolants. • Membranes. • PEEK composites. • Thermoplastic heat sinks. • Silicone and epoxy thermal interface materials. • Abrasion resistant resins. |
Electronics & semiconductors |
• Surface roughness can be greatly reduced when NDs are used in the lapping of magnetic heads. NDs can significantly increase lapping endurance and reduce the friction effect. • High thermal resistance and high particle distribution. • Precise polishing in angstrom units is possible • Surface defects, crystal dislocations, and surface stress are low • UDD suspension is chemically stable, so chemically active additives can be used• No toxicity to liquids, pastes and powders • Thickness of the layer removed from the surface is small |
• Thermal paste for heat management (heat dissipation). • Nanoabrasives in polishing pads for CMP. • Insulation materials. • CVD seeding. • Thermoplastic heat sinks.• Cryptography • Quantum computing. |
Energy |
• High thermal conductivity. | • Hydrogen accumulators. • Electrodes. • High voltage, high energy density, high temperature capacitors. • High efficiency catalysts. • Battery additives. |
Lubricants |
• Carbon chemistry biodegradability • Non-toxicity. • Reduced friction coefficient (10-60%) • High energy savings (~10%) • Solubility in both mineral oil and others • Improved wear resistance • Reduced contact temperature • Reduced viscosity • Increased thermal stability (efficient at higher temperatures) • Improved performance and durability (e.g. engine components) • Decrease in noise |
• 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. |
• Biosensors. • Single-spin sensors in nanomagnetometry. |
3D printing |
• Faster 3D printing and improved mechanical durability of the printouts | • Lubricants in 3D printers. • 3D printing filaments. |
Source: Future Markets, Inc.
Overall, adding nanodiamonds can change most of the currently existing materials. Successful laboratory results and patents have been obtained in respect of many applications. The launch of nanodiamonds commercial production has made it possible to introduce laboratory results into industrial technologies and has enabled the manufacture of mass products. As the production volume of NDs increases and their price decreases, their scope of application will expand.
Applications
Main current applications of Nanodiamonds in terms of volume demand are:
- Fine polishing abrasives
- Coatings additives (galvanic and electroless)
- Lubricant additives (oils and grease)
- Reinforcing polymer fillers
There are also a wide range of secondary, niche applications. The list of mentioned nanodiamonds applications below is not exhaustive.
Nanodiamonds producers
Currently, there are 10 main nanodiamond companies in the world in total. There are also a number of other companies and suppliers. Most are small to medium-sized companies who sell internationally but generally have a localized regional presence. Daicel is the largest company producing Nanodiamonds.
The key players’ position on the market is determined by price and production capabilities, which are closely related to the target applications. Most companies are targeting high-volume market such as lubricants,
polishing additives, electroplating coatings etc. which require low price and potentially high volumes of NDs.
None of the producers sell ND based market solutions to industry globally. The market players mainly sell regionally, with sales outside their regions undertaken mainly by distributers or the regional offices of the mother-company. Many China based producers have multi- kilogram/month production capabilities for detonation nanodiamond powder.
Figure 3: Nanodiamond detonation chamber.
Adamas Nanotechnologies, Inc.
USA
www.adamasnano.com
The company produces nanodiamond suspensions, powders, additives for lubricants and fluorescent nanodiamonds. 16 patents have been issued to Adámas or licensed from parent company. The 20-40 nm size range provides the smallest and brightest currently commercially available fluorescent diamond particles on the market. These sizes are suitable for intracellular imaging and single molecule tracking. The brightness of particles depends on the particle size. The larger the particle, the higher the brightness due to the larger number of colour centres that can be accommodated by larger particle volumes.
Carbodeon Ltd. Oy
Finland
http://www.carbodeon.net
Carbodeon’s patented technologies are used as additives in applications including thermal management materials, metal plating and selected polymer coating applications. The company has several global distributors for its nanodiamond products.
Carbodeon’s uDiamond® contains diamond nanoparticles with a diameter of 4–6 nm. Carbodeon’s nanodiamonds are non-toxic materials suitable for a variety of applications according to REACH and EPA assessments. Although they are used in the materials at very low concentrations, they can significantly improve material performance at a low cost. Carbodeon has extensive patent coverage for the nanodiamond materials it manufactures, and refined products enhanced with nanodiamonds.
Figure 4: Carbodeon NanoDiamond Powders And Dispersions.
Daicel Corporation
Japan
www.daicel.com
The company produces DINNOVARETM nanodiamonds. The product is available as a powder and aqueous dispersion. The DINNOVARE range has cluster NDs and seven different types of solvent dispersions such as, Water-soluble modified NDs in water, and 4 organic solvent dispersions (THF, IPA, MIBK, toluene).
The company provide samples of DINNOVARETM free of charge to researchers at universities and research institutes.
Ray Techniques Ltd.
Israel
www.nanodiamond.co.il
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. Laser treating of specially prepared targets containing carbon soot mixed within hydrocarbon media (e.g. wax) to obtain diamond nanocrystals (4-5 nm size). The Ray method is more controllable, environmentally friendly, and less hazardous than detonation synthesis. It provides high purity and homogeneity of ND without graphite and metal impurities. RAY has developed an industrial technology (know-how) for introducing ND within various media. Special mechanical, thermal and chemical ND surface modification results in:
• Covalent bonding with matrix’ molecules (no surfactants)
• ND disaggregation in diverse solvents
• Uniform distribution in water, solvents and oils
• High efficiency of ND in the improving performance of basic material
The company also design novel ND-based composite materials with desired properties. Applications are in Anti-friction additives (Lubricants), Pastes and slurries for fine polishes, Protective coatings, Additives to galvanic electrolytes, Precursors for CVD diamond coatings, Additives to polymers and Thermal management.
