With a weak market of diamond jewelry, it would be reasonable to redirect superfluous efforts to technical application of diamonds. Experts, for example from the Yakutniproalmaz Research Institute, can be quickly re-oriented towards nanotechnologies which are generously financed both in Russia and abroad.
The first nanodiamonds were synthesized in the USSR. The synthesis methods were patented by more than 10 (!) groups of researchers, including the All-Union Scientific and Research Institute of Technical Physics (Snezhinsk), Institute of Hydrodynamics of the Siberian Branch of the Academy of Sciences (Novosibirsk), Altai Scientific and Production Amalgamation (Biysk), All-Union Scientific and Research Institute of Experimental Physics (Sarov), Electropribor (Lesnoy), Zavod Plastmass (Kopeysk). Pilot production of nanodiamonds was started in the end of 1980s. Carbon making part of explosives was chosen as an initial raw material. The high pressure and temperature necessary to form the diamond structure from atoms of carbon were reached during explosion. A short time of explosion and high-speed cooling of detonation products resulted in small size of diamond formations. The essence of this method was decomposition of powerful mixed explosives under detonation with negative oxygen balance generating solid products containing, besides soot and nanographite, about 5% of nanodiamonds (also named as “ultradisperse diamonds”, or UDD). The researchers, for instance, used additives-containing melts of trotyl and hexogen producing explosions of different yield (from 10 up to 400 kg of blasting agents) in different chambers and in different environments (in compressed inert gas, water, and ice). Enrichment of nanodiamonds from raw materials (detonation mixtures) occurs by way of dissolution of non-diamond forms of carbon. The most efficient technology of cleaning nanodiamonds chemically is to treat them with nitric acid at a high temperature and pressure followed by additional cleaning with ozone. At present, the main manufacturer of fine nanodiamonds is Technologist, a government-owned company (Saint Petersburg). Typical nanodiamonds have a round shape from 3 up to 6 nanometers in diameter and their dry powder is characterized by an experimental specific surface of some 300 м2 per gram.
It turned out that detonation nanodiamonds possess a number of unusual properties. The research performed during recent years proved that nanodiamonds can be used to produce nano-composite materials, elements of nano-electronics, selective adsorbents and catalysts, and materials used in medicine and biology. Application of nanodiamonds helps to improve the quality of micro-abrasive and polishing compounds, lubricants, abrasive tools, polymeric compositions, gum and Indian rubber, magnetic recording systems, and allows growing diamond films on various substrates.
1. Polishing compounds
Modern laser equipment, optics and solid-state electronics, including micro-, opto-, acousto-, magnetic, microwave-, cryogenic electronics, and its other fields, are based on a wide variety of materials. The industry is in need of geometrically, structurally and chemically perfect surfaces of crystals obtained by means of high-finish chemical and mechanical polishing (CMP).
The A.M. Prokhorov Institute of General Physics of the Russian Academy of Sciences has developed a number of chemically active polishing compounds based on nanodiamonds (and preserving a stable state for more than a year). The compounds have passed approbation in processing metals, semiconductors and dielectrics. Some of them are capable to polish effectively several (from 3 up to 15) crystals having different structure, crystallographic orientation, electric conductivity, origin and designation. The roughness of relief in the majority of crystals constitutes nanometer fractions or just some nanometers. On their surface there are no chips, cracks, micro-scratches, etching areas and other macro defects, while their superficial layer does not contain areas of processing dislocations and elastic pressure.
The N. Lebedev Physical Institute of the Russian Academy of Sciences, the Moscow State Institute of Steel and Alloys and the Detonation Nanodiamonds Research-and-Production Association established a scientific, educational and production center called “Nanosurface.” Currently, Sinta, a Belorussian firm, is developing a project aimed at manufacturing fine cleaning nanodiamonds based on fine cleaning in the amount of about 1000 kg a year which may be used to produce various polishing compounds.
The Altai Scientific and Production Association (Biysk) has developed an industrial standard, “Polishing compounds based on detonation nanodiamonds ‘BIKA’” (ТУ 07508902-204-2008).
2. Galvanic coatings
Nanodiamonds are tested as an additive to metal galvanic coatings. The most advanced area here is chrome-diamond wear-proof coatings for the oil industry. Production of composite coatings is based on the ability of nanodiamonds sized 4-6 nanometers to be deposited along with metals in the process of their electrochemical and chemical recovery from solutions of their salts. It leads to formation of a biphase composite electrochemical coating consisting of a metal matrix and disperse particles of nanodiamonds embedded in it. The essence of the process is that with a rather small amount of additive (nanodiamonds constitute 1% of coating weight) nanoparticles cause a large number of crystallization centers. This results in a nanocrystalline structure of chrome bringing the size of crystallites to about 10 nanometers. Besides as a consequence, a number of adjoining metal-diamond layers acquire high wear resistance and higher micro hardness. Chrome nanocrystallines fully copy the relief of the item surface, which essentially increases ultimate stress limits in separating coating from its basis by shift or in a normal way. Now the manufacturers are capable to produce 1—500 micron thick coatings covering an area of 500х600х1300 mm.
Experts of ZAO EKA in team with OOO RAM have developed an advanced technology of applying metal-diamond coating having nonocrystalline structure on equipment operating under extreme conditions, and in particular, in corrosive environment. The research was performed in accordance with the Federal Program of Developing Nonoindustry in the Russian Federation up to 2015. On the basis of the given technology the company has introduced innovative, essentially new slide valves of the "Norm" model to be installed on electric centrifugal installations and deep-well oil pumps.
3. Additives to automobile oils.
The essentially new kind of additive to lubricants based on ultradisperse diamonds is intended to significantly improve protective properties of lubricants, increase their effective service life, as well as restore and protect friction units in various machines and mechanisms. Such additives facilitate: a) more than 2 times (5-7 times for some units) longer overhaul periods for various machines and mechanisms; b) restoration and protection of mechanisms in a pre-repair condition and an opportunity to continue their operation for a long time without major overhauls; c) more than 2 times longer service life of oils and lubricants; d) lower consumption of fuel and lubricants.
This technology is accepted for introduction by OAO Norilsk Nickel. Probably it will be useful for motor transportation units of those companies which are operating in the Far North, such as, for instance, ALROSA or Polyus Gold.
4. UDD in medicine
Research in this area is so far in its initial stage. In particular, it is reported of a supermolecular structure produced on a flat substrate and consisting of oxide aluminum film - adhesive layer – nanodiamond - luciferase. It has been found that the enzyme preserves catalytic activity in the given structure and it can be considered as a prototype of a luminescent biochip which can be used in bioluminescent analysis. The Institute of Biophysics of the Siberian Branch of the Russian Academy of Sciences has tested the application of nanodiamonds to separate recombinant apoobeline and recombinant luciferase from E. coli bacterial cells. Application of nanodiamonds makes protein purification a simpler procedure reducing the time of protein express isolation and making needless special chromatographic equipment; it makes possible to produce highly purified preparations of apoobeline and luciferase yielding about 45% of protein.
5. Germs for cultivating diamond films
Nanodiamonds are used in research performed on artificial CVD diamond films, for instance by the Ioffe Physical Technical Institute of the Russian Academy of Sciences (Saint Petersburg) and the Troitsk Innovation and Thermonuclear Research Center (Troitsk). Ultradisperse nanodiamond suspension has been used to create high density diamond nucleation centers on various substrates. High-quality doped diamond films from a gas phase of microwave discharge were deposited on substrates of some materials treated with ultradisperse diamonds for the purpose of using them as electrodes for electrochemistry. Uniformly distributed nucleation centers with a concentration of at least 1010 cm-2 were formed for silicon substrates. Current - potential electrochemical curves were measured for continuous films. Diamond grids of various transparency were grown by way of selective nucleation. Successfully produced reception high-quality doped diamond grids give the ground to consider them as most perspective electrodes for electrochemistry.
6. Catalysts
Some grades of nanodiamonds have complex structure: the nanoparticle consists of a diamond nucleus and graphite-like shell whose surface bears a functional cover: oxigenated (carboxyl, hydroxylic, ethereal and other active groups) and nitrogen-containing (amine, amide) groups. For the purpose of catalysis the surface of nanodiamonds is modified and activated, for example, in fluorine-containing low-temperature plasma. With an average diameter of 4.2 nanometers the number of superficial atoms reaches approximately 15%.
Nanodiamond-based catalysts have been tested for converting CO into СО2. Catalytic reactions resulting in decomposition of spirits (ethanol, methanol) are promising as an energy source.
Electrochemical modification in a salino-acid solution and promoting the surface of nanodiamond powders with palladium is promising to manufacture catalysts and electrodes of low-temperature fuel elements.
Conclusion
The most advanced field of nanodiamonds application is making polishing compounds, chrome-diamond wear-proof coatings for the oil industry as well as additives to industrial lubricants.
Interest toward nanodiamonds is great both in Europe and in the East (Japan, Korea, and China). But their wide use is impeded by some problems, including:
absence of a nanodiamonds standardization system;
low quality consistency of nanodiamonds produced by various manufacturers;
immaturity of technologies;
absence of operational experience in applying nanodiamonds.
However, the unique properties of nanodiamonds guarantee their presence in the field of innovative technologies, while the problems so far remaining unsolved offer an opportunity to diamantaires.
Vladimir Teslenko, Rough&Polished
