As is well known, the superior physical, mechanical and chemical properties of diamond in known materials are unmatched by other materials. Like other nanomaterials, nanodiamonds have small size effects, surface effects and macroscopic quantum tunneling effects, making them even more powerful in expanding applications. Therefore, the author believes that nanodiamond is the leader in many nanomaterials. The experimental research on the synthesis technology and characteristics and application of nanodiamond detonation (or explosion) is consistent with the direction of China's “Eleventh Five-Year Science and Technology Development Planâ€. The research and development of nanodiamonds not only has important scientific and technological significance and value, but also has huge potential business opportunities. This paper intends to study the research progress of nanodiamond at home and abroad, and some rules of nanodiamond detonation synthesis technology. The characterization of nanodiamonds and the preliminary application results of nanodiamonds are summarized.
Overview of research on nano diamond at home and abroad
In 1982, the Soviet Union first reported that nano diamond-ND or ultra-dispersed diamond (UDD) or ultra-fine diamond (Ultra find) was synthesized in the laboratory using carbon detonation in a negative oxygen balance explosive. Diamond-UDD) refers to diamond particles having a particle size of 100 nm or less. The successful development of nanodiamonds marks another major breakthrough in synthetic diamond technology and adds a very valuable member to the diamond family.
In 1988, Greiner N. Roy of the United States also found a diamond phase in the explosion of high-energy detonation. Since then, the research on detonation synthesis of nanodiamonds has become a hot topic in the world. In addition, research has been conducted in Britain, Germany, France and Japan.
At present, Russia's "Altai" scientific research and production complex, Belarus's "Xinta" research and production complex, Ukraine's "Alite" company, and "Altai" in the United States "super-dispersion technology" company, they all built There is a production line with an annual output of 20 tons.
The Lanzhou Institute of Chemical Physics of the Chinese Academy of Sciences also successfully developed nanodiamonds in 1993 using a similar method. Since then, Beijing Institute of Technology, the Second Artillery Engineering College, the Southwest Institute of Fluid Physics of the China Academy of Engineering Physics and the Northwest Institute of Nuclear Technology have also carried out research work on nano-diamond synthesis and its application technology.
In July 1999, the first “Nano-diamond Development Seminar†was held in Hangzhou. More than ten research and production units participated in the seminar. This is a high-efficiency, high-knowledge level and rich in content, representing China’s nano-diamond research at that time. The latest level of production, application and application of experts, professors on the nano-diamond detonation synthesis technology, application technology and their development prospects are comprehensively discussed. The experts agreed that nano-diamond synthesis technology is becoming more mature. Industrialization The conditions are basically available. The application has achieved initial results, the field needs to be expanded, the potential market is large, and the development prospects are attractive. The technical difficulties are many, and the task of tackling the key is very heavy.
Since then, Xi'an Jiaotong University, Tsinghua University, Armored Force Engineering College, Yanshan University, China University of Science and Technology and other nano-diamond production units have carried out research on the application of nano-diamonds and achieved preliminary results. In 2001, Gansu Lingyun Nanomaterials Co., Ltd. and Shenzhen Jingangyuan New Material Development Co., Ltd. each built a production line with an annual output of 10 million carats. Later, Shandong Taian Nano-Diamond Co., Ltd., Henan United Abrasives Co., Ltd., and Shaanxi Yilin Industrial Co., Ltd. have also built a 10-kilogram-scale production line. In just three to five years, tens of millions of carats of production lines have been built in the country, all of which mark that China's nano-diamonds have entered a comprehensive development stage from scientific research, production to application.
General rule of nanodiamond synthesis
The dynamic high-pressure high-temperature method uses synthetic high-pressure high-temperature to synthesize diamond. The dynamic pressure method is different depending on the raw materials used. Can be subdivided into: First, the impact method. That is, the high-speed flying sheet is used to impact the graphite raft, so that the graphite generates micron-sized diamond particles during the impact process; the second is the explosion method, that is, the graphite is mixed with the high-energy explosive (such as TNT, RDX) in the process of explosive detonation. Compressed graphite to transform it into diamond: Third, the detonation method, that is, using negative oxygen to balance the explosive, detonation in the protective medium environment, the excess carbon atoms in the explosion process are formed by a series of physical and chemical processes such as aggregation and crystallization. Nanoscale particle group, including diamond phase, graphite phase and amorphous carbon. It is purified to remove non-diamond carbon to obtain a higher purity nanodiamond.
The experimental results show the following regularity:
1. In the nanostructured diamond synthesized by the TNT and RDX mixed explosives, only the carbon in the TNT forms a diamond phase, and the RDX only serves to increase the explosion temperature and the explosion pressure.
2. The content of cohesive carbon increases linearly with the increase of TNT content. Therefore, an increase in the TNT content is advantageous for the formation of nanodiamonds. Therefore, it is necessary to increase the TNT content in the mixed explosive.
3, from the literature [Li Shicai [D] Beijing Institute of Technology, 1998] It can be known that the detonation pressure affects the yield of nanodiamonds, and the detonation temperature affects the size of the nanodiamonds. Therefore, the higher the detonation pressure, the higher the yield of nanodiamonds, so the amount of RDX needs to be increased in the mixed explosive. However, it is known from experiments that pure TNT explosives have the lowest yield of synthetic nano-diamonds, while pure RDX also produces almost no nano-diamonds. Therefore, as a result of the competition between the two, the maximum value of the nanodiamond yield will inevitably occur.
4. As the volume of the explosion vessel becomes larger, the yield of nanodiamonds is significantly improved. When the volume is increased by an order of magnitude, the product is more easily dispersed in the last three processes of synthesizing diamond, and the heat exchange with the tank wall and each other is more fully performed, the heat dissipation is faster, and the quenching becomes more rapid, so The yield of nanodiamonds is significantly improved.
5, the literature [Volkov K. V, Danilenko V. V. , Explosion and Shock Waves. 1990, 26: 366-368] studied the effect of charge shape and charge on diamond yield. It is indicated that when preparing nano-diamond, it is better to use a large amount of charge 0.3Kg, and the aspect ratio is greater than l. The drug column of 4, because the diamond yield of this charge is twice as high as that of other shapes and charges.
6, literature [Chen Quan et al., Journal of High Pressure Physics, 1998, 12 (2): 129-133 TUTOB B. M. ,Explsion and Shock Waves. 1990(3): 372-378] uses a composite charge structure in which a layer of TNT/HMX (70/30) is applied over a cylindrical TNT column. In this way, an overpressure Mach wave disk can be generated in the TNT explosive column during detonation, thereby greatly increasing the detonation pressure of the TNT detonation product, and converting 80% to 90% of the free carbon produced by the TNT into diamond. Increase the yield of diamonds.
7, in order to improve the diamond yield and improve the quality of diamonds, you must choose the appropriate cooling medium. For example, under the same charge conditions, the water or ice medium wrapped in the charge is much better than the inert gas medium or salt alone.
Characterization of nanodiamond properties
The chemical composition and structure of nanomaterials determine their properties, so it is important to characterize materials at the atomic scale. There are many characterization methods for nanomaterials, which are very fast, and often require a combination of various characterization techniques, as well as the characterization of nanodiamond properties. Characterization includes chemical composition, particle size, distribution range, morphology, structure, surface state, and the like.
1. Characterization of chemical composition Chemical composition is one of the most fundamental factors determining the performance of nanoparticles and their products. The commonly used instrumental analysis method utilizes characteristic lines of various chemical components, such as x-ray fluorescence analysis and probe X micro-analysis, and can also be used to characterize the chemical composition of nanomaterials by atomic emission spectroscopy and atomic absorption spectroscopy. Quantitative analysis: X-ray photoelectron spectroscopy can be used to analyze the surface chemical composition, atomic valence state, surface morphology, surface microstructure state and surface energy state distribution of nanomaterials.
2. Determination of particle size Because the surface activity of nanoparticles is very high and easy to agglomerate, it is difficult to measure and characterize the particle size of nanoparticles. At present, there are several methods for measuring the particle size of nanoparticles, such as X-ray diffraction line width method, transmission electron microscope (TEM) observation method, laser Raman scattering method, specific surface area method and X-ray small angle scattering method. Among these methods, the most widely used are TEM observation and X-ray line width method.
It can be seen from the spectrum obtained by the X-ray diffraction method that it is 43.60 at 2θ. The three broadened diffraction peaks of 74.860 and 91.20 correspond to the characteristic peaks of the diamond (111), (220) and (311) planes respectively, indicating that the obtained nanodiamond is a cubic crystal, and the spectral line is severely broadened and its crystallites. Very small and related to a large number of defects. Furthermore, the entire line has a higher background in the low angle region and is associated with the presence of a certain amount of amorphous carbon. In calculating the particle size of the nanodiamond, the diamond (111) peak was selected for calculation, 2θ=43.60, and d=2.85nm was calculated.
3. Raman spectroscopy For macroscopically sized diamond and graphite crystals, characteristic bees corresponding to diamonds and graphite are typically observed at 1332 cm-1 and 1581 cm-1. In the Raman spectrum of nanodiamonds, there are two broadened Raman peaks in the vicinity of 1329 cm-1 and 1580 cm-1, and no other Raman peaks.
The broadened Raman peak around 1392 cm-1 is a characteristic peak of the SP3-structured nanodiamond, and the weaker Raman peak observed near 1580 cm-1 is the SP2-structured nanographite. Since the Raman scattering cross section of diamond is 1/60 of graphite, this indicates that there is still a trace amount of nano-graphite residue of SP3 structure in the nano-diamond. This result is consistent with a small peak corresponding to the (002) plane of graphite in the vicinity of 2θ=260 in the XRD pattern. Literature [Chen Wanpeng, Pei Shouyi et al. Journal of High Pressure Physics, 1999, 13(1): 50-63 Yoshikawa M, M. Oriy, et al, [J] Dimond and relat mater, 2000, 9:1600-1603]
When studying the Raman spectrum of diamond, it was found that there is a broadened Raman peak between 400 and 700 cm-1, which is mainly due to the amorphous carbon of the SP2 structure. However, in the Raman line of the nano-diamond powder of Wenchao experiment, there is no peak position between 400 and 700 cm-1, and in the XRD line, the curve of nano-diamond has no large bulge in the range of 20-300. It is indicated that there is not a large amount of amorphous carbon in the nano-diamond.
4. The infrared spectrum was analyzed by infrared spectroscopy. The absorption peak at 3244 cm-1 was O-H stretching vibration, and the bending vibration peak of H2O appeared at 1634 cm-1. It shows that the surface of the sample adsorbs a small amount of moisture in the air, 2930 and 2857cm-1, which is the antisymmetric and symmetric stretching vibration absorption peak of CH2. 2971cm-1 is the antisymmetric stretching vibration absorption peak of CH3. Indicates that a very small amount of hydrocarbon is present in the sample. The absorption peak at 1788 cm-1 is a C=O stretching vibration absorption peak, and a C-C stretching vibration absorption peak of 1262 and 1134 cm-1 stone diamond.
The nanodiamond has a stretching vibration absorption peak at 1262 cm-1 belonging to the IaA type diamond azo N2 (A core) 1282 cm-1 infrared absorption line. Due to the size of the nanometer, the peak position is shifted, so the nanodiamond should be IaA type diamond. Nanodiamond has a stretching vibration absorption peak at 1134 cm-1, which is an intrinsic bee of Ib type diamond, so it contains Ib type diamond in nanodiamond. The 1262 cm-1 absorption peak of nanodiamond is stronger than the absorption peak of 1134 cm-1, and the peak shape is sharp. It can be seen that in the nanodiamond, the content of the IaA type diamond is more than that of the Ib type diamond.
As can be seen from the transmission electron microscopy image, the nanodiamond particles are substantially spherical or ellipsoidal, with a minimum particle size of about 3 nm and a maximum particle size of about 10 nm. Through statistical analysis, the average particle size of nanodiamonds is 6.2 nm. Among them, particles with a particle size of 3 to 10 nm are the most. In addition, it can be seen that there are twins, stacking faults, and the like in the nanodiamond particles.
Wen Chao believes that the X-ray diffraction line width method is the best way to determine the grain size of particles. When the particles are single crystals, the method measures the particle size; when the particles are polycrystalline, the method measures the average grain size of the individual grains constituting the individual particles. The electron microscopic observation method measures particle size rather than grain size. This particle size is a number average particle size. It is the most common and direct method for detecting the size and distribution of nanoparticles. The accuracy of the measurement results depends directly on The distribution of nanoparticles.
In general, it measures the diameter of a plurality of grain diffraction images. If the nanoparticles are well dispersed, they can become single crystal grains. The TEM must obtain a diffraction image of a single crystal grain. It is the grain diameter, ie the grain size, and the morphology of the nanoparticles can also be observed. Even the microstructure.
Preliminary application of nanodiamond
The material is the foundation and the application is the power. There is no market without application, no development without market, and nano diamond is no exception. From the data collected, the application field of nano-diamond is quite large, that is to say, its potential market is very large, and the question now is how to occupy the future market.
It is well known that in addition to the highest hardness, high thermal conductivity, high wear resistance and corrosion resistance, nanostructured diamonds also have large specific surface area, good chemical activity, large entropy and many structural defects. Characteristics of nanomaterials such as stuffing. Since nanodiamonds have the above dual characteristics, they have been initially applied in composite plating, lubrication, filling, polishing, etc., and have shown the unique role of nanostructured diamonds. Some examples are cited below.
1, increase the life of automotive paint. The sun's ultraviolet rays, acid rain, stones and bird droppings have a great destructive effect on the erosion of automotive paint. Due to the influence of these factors, automotive paints must have good performance, including: anti-corrosion, anti-stone, moisture, scratch, acid, chemical, solvent and so on. According to reports, the current special coatings for the automotive and mechanical construction industry have a market of 8.8 million US dollars, and will grow to 12.1 million US dollars by 2007. Some people think that the unique physical and chemical properties of diamond can be used to improve the life of automotive coatings, especially diamond has the highest hardness, excellent acid and alkali corrosion resistance, the highest thermal conductivity and biodegradability. If the nanodiamond is used in the form of an additive or a mixed component, the appearance characteristics of the coating can be adjusted. Experiments provided by well-known coatings manufacturers have shown that the use of nanodiamonds not only increases the microhardness of the coating, but also makes the coating resistant to impact, scratches, and adhesion to the substrate compared to conventional coatings. Chemical resistance (especially solvent resistance) has a significant improvement in friction, water resistance and thermal conductivity. Due to mechanical forces such as impact, friction, scratching, etc., matt coatings tend to form "bright spots", and the addition of nanodiamonds can reduce undesirable "polishing" by 100%. It should be pointed out that there are still many technical know-hows in the specific application of nano-diamonds, especially how to add nano-diamonds to the corresponding systems in large quantities to obtain the best results. Application details such as dispersion or coagulation of nanodiamonds, system addition and pretreatment are important.
2, lubrication is closely related to the operation of mechanical equipment. Some people have visually compared the lubricating oil to the blood of mechanical equipment. It can be said that the lubricating oil has been lost. There is no mechanical equipment. At present, the effective utilization rate of mechanical energy in the world is only about 30%. According to estimates by Professor Roggeer of Germany, 1/3 to 1/2 of the energy produced worldwide is lost in friction and wear, and Professor Gonster of the United Kingdom also points out that 30% to 40% of the world's energy consumption is consumed by friction and wear. on. It can be seen that the solution to the lubrication technology problem is imperative. Recent studies have shown that the addition of nanodiamonds to lubricating oils has the following advantages:
â—† Improve product quality and competitiveness; improve the working life of transportation tools and installations; save lubricant materials.
â—† Friction momentum is reduced by 20% to 40%.
â—† Friction surface wear is reduced by 30% to 40%.
â—† Quick running of the friction pair.
Unit consumption of nano-diamond: 0.01Kg～O in 1000Kg lubricating oil. 2Kg
3, chip polishing. Shao Bingyan Zhang Xiaodi reported that in 1997, the world's chip production has reached 350 billion, of which 15 billion is used for microprocessors. For example, an average of 1 carat is required for every 150 chips processed. The chip processing potential nano-diamond market can reach more than 100 million carats.
4, composite plating. It is understood that the annual metal corrosion loss in the world is about 150 billion US dollars, and China's annual loss is 150 billion yuan. Metal plating is one of the solutions. to this end. We made a rough calculation, such as 300 million square meters of electrolytic plating surface, 5μm of plating thickness, 1 carat of nano-diameter per square meter, and 600,000 kilograms of nano-diamond required for nano-diamond-metal composite plating additive.
The way out about nanodiamonds is that applying such a topic is a big topic. There are many examples of its application, and the content is rich. Due to the limitation of space, it cannot be explained one by one. Finally, the author wants to use eight sentences and thirty-two words to make a summary.
Overview of preparation, properties and applications of nanodiamonds
Author : Zhengzhou Abrasives Grinding Research Institute Wang Guangzu Shenzhen Jingangyuan New Material Development Co., Ltd. Zhang Huazhen Zhang Yunsheng