Preparation and application of nano diamond polishing fluid
Since nanodiamond has a large specific surface area and a high specific surface energy, it is in a thermodynamically unstable state, so the dispersion stability in the medium is poor, and agglomeration is liable to occur, which is severely restricted in the application process.
The key technology for the preparation of nanodiamond polishing fluid is the long-term stable dispersion of nanodiamond in the medium. This is a common worldwide technical problem, because the vast number of scientific and technological workers are very optimistic about its application prospects. Therefore, in the past few months, there have been many explorers who have devoted themselves to the work of solving this technical problem. And did a lot of useful work, and obtained a lot of technical data with practical value. This article will review the application of nanodiamond dispersion and nanodiamond polishing fluid.
1. Proposal of decentralization
Nano-diamonds are synthesized under the extreme non-equilibrium conditions of detonation, and are easy to form hard agglomerates which are difficult to depolymerize. Commercial nano-diamond dry powders have an aggregate size of 2 μm on average.
The role of the surfactant is to change the functional group composition and electrical properties of the nanodiamond portion and change its dispersion in the suspension.
The large number of atomic dangling bonds on the surface of the nanodiamond particles greatly enhance their chemical activity; the very large surface area gives them a huge surface energy. However, reducing the specific surface area and reducing the surface energy to agglomerate the nanoparticles is a spontaneous process, so nanoparticle agglomeration is inevitable.
After the nanoparticles are dispersed, measures should be taken in time to prevent the nanoparticles from agglomerating again. The addition of surfactants can increase the distance between the particles and reduce the interaction of van der Waals forces, thereby stabilizing the entire dispersion system.
The surface of the nano-diamond contains a large number of organic functional groups, mainly: OH (hydroxyl), C=O (carbonyl), COOH (carboxyl) and some nitrogen-containing groups, occupying an area of ​​10% to 25% of the surface of the particles. These oxygen-containing reactive groups and nitrogen-containing active materials can react or adsorb with many organic compounds, providing a basis for the dispersion of nanodiamonds in oil or water media.
The nano-diamond is dispersed because the dispersion and agglomeration of the new particles during the preparation of the ultra-fine powder plays an important role in the fineness of the final product. Since the ultrafine powder is easily agglomerated, the ultrafine powder after agglomeration will lose many of its own advantages, and its performance cannot be fully exerted, which seriously restricts the use value and application prospect of the ultrafine powder.
2, the settlement of the problem of reunion
The dispersion of nanoparticles is a process of separating the agglomerates of nanoparticles into individual nanoparticles or a small agglomerate of a small number of nanoparticles, so that they are evenly distributed in the organic medium, which is a complicated and difficult process operation. When the nanoparticles are immersed in an organic medium, the surface energy of the nanoparticles is large, and it is easy to cause wetting. If the nanoparticles are soaked to form an organic film or an electric double layer or form a polymer adsorption layer, the nano-particles will be nano-sized. The initial dispersion of the particles produces a positive effect, but the dispersion of the nanoparticles should take into account the balance of dispersion and agglomeration of the nanoparticles.
The large specific surface adsorption of nanoparticles is an intrinsic factor for the agglomeration of nanoparticles. To obtain nanoparticles with good dispersion, small particle size and narrow particle size distribution, it is necessary to weaken or reduce the huge surface adsorption of nanoparticles. The appropriate method is to chemically modify or chemically modify the nanoparticles to enhance the repulsion between the nanoparticles. It is found that the adsorption of oxygen-containing polymer dispersant on the surface of nano-diamonds produces and enhances the steric protection to enhance the repulsion of nano-diamonds and effectively prevent the re-aggregation of nano-diamonds.
The dispersion technology of nanodiamonds is generally divided into physical dispersion and chemical dispersion.
Physical dispersion can be divided into ultrasonic dispersion, mechanical agitation dispersion and mechanical grinding dispersion.
Chemical dispersion can be further divided into chemically modified dispersion and dispersion dispersion.
The dispersion process of the polishing liquid is a process in which the nano-diamond aggregates are dispersed in the liquid phase in the original monomer state in the polishing liquid. The dispersion process mainly comprises two steps: one is the wetting of the particles in the liquid phase; the other is to stably disperse the primary particles without agglomeration or to break the formed agglomerates into smaller agglomerates or original monomer particles.
Of particular note is the problem of dispersion of the nanoparticles by the surfactant.
First, the wetting of solid particles.
Wetting is the most basic condition for the dispersion of solid particles. If the solid particles are to be evenly distributed in the medium, it is first necessary to allow each solid particle or group of particles to be sufficiently wetted by the medium. In this process, the surfactant plays two roles. One is the directional adsorption of the surfactant on the surface of the medium (if the medium is water), the surfactant will extend into the water phase with a hydrophilic group, and the hydrophobic base faces The gas phase is aligned to reduce the gas-liquid surface energy. Another effect is to align the solid-liquid interface with the hydrophobic chain adsorbed on the surface of the solid particles and the hydrophilic groups into the aqueous phase.
Second, the dispersion or fragmentation of the clusters.
In this process, the dispersion or fragmentation of the particle cluster involves the solid-solid interface separation inside the particle cluster, and there is often an acid gap in the solid particle cluster. In addition, the crystal of the particle also causes micro-cavity due to the stress, and the particle cluster Broken things happen in these places. Under the condition that the solid surface potential is not very strong, the anionic surfactant can overcome the electrostatic repulsive force by van der Waals phase suction or be adsorbed to the surface of the gap by the mosaic method, and the surface is enhanced by the same kind of charge, and The osmotic water generates an osmotic pressure to reduce the stranding strength between the particles, reducing the breakage of the solid particles or clusters and gradually dispersing in the liquid medium.
The nonionic surfactant is adsorbed on the crack wall by van der Waals force. The presence of nonionic surfactant can not produce electric repulsive force, but it can generate entropy repulsion and permeation hydration force, so that the particle cluster The strength of the kinks between the cracks is reduced, which is conducive to the rupture of the clusters.
The cationic surfactant can be adsorbed on the slit wall by electrostatic attraction, but the adsorption state is different from that of the anionic surfactant and the nonionic surfactant.
Third, the re-aggregation of solid particles is prevented.
Once the solid particles are dispersed in the liquid, a uniform dispersion is obtained, but stable and otherwise depends on whether the respective dispersed solid particles can reaggregate to form agglomerates. Since the surfactant is adsorbed on the surface of the solid particles, the energy barrier preventing the particles from re-aggregating is increased, and the added surfactant lowers the interfacial tension at the solid-liquid interface, thereby increasing the thermodynamic stability of the dispersion.
3. Results of the research
Europe, Russia and other countries have carried out research on nanodiamonds earlier, and they are also in the forefront in the preparation of nanodiamond polishing fluids. The United States, the United Kingdom, Germany, Japan and other countries have the production capacity of nano-diamond polishing fluid. Engis is the world's most famous polishing product supplier. All American companies can provide water-based and oil-based polishing liquid. Japanese companies can provide polishing liquid. , polishing paste and other polishing products. Domestic research on the preparation of polishing fluids has just started, and there is still a certain gap between the technical level and foreign countries.
Chiganova heats the nanodiamond powder with a saturated aqueous solution of AlCl3, and the secondary particle size of the nanodiamond in the obtained suspension is hundreds of nanometers.
Agibalova LV or the like disperses the nanodiamond powder by ultrasonic energy in water, and the aggregate of the obtained suspension has a particle size of about 300 nm.
Chen Wanpeng et al. tried to disperse nanodiamonds with water, sodium phosphate, ethanol, gelatin aqueous solution + sodium carbonate.
Xu Xiangyang and the like, while adding mechanical substances, inorganic electrolytes, surfactants and other substances, so that the nanodiamond powder can be stably dispersed in the aqueous medium.
Yu Yanwu and others have made a useful attempt to disperse nanodiamonds in water.
Edeidelman et al. prepared a black, highly viscous, stable nanodiamond suspension with a concentration of 0.2%. They studied the structure of the particles in the suspension, the light absorbing properties, and the viscosity of the suspension.
Xu Kang et al. proposed a graphitization-oxidation method to deagglomerate nanodiamonds and achieved beneficial effects. They treated the graphitized-oxidized product with iodohydrogen acid to reduce the size of the nanodiamond agglomerate by 90% to less than 30 nm.
Xu Xiangyang explored the stable dispersion process and mechanism of nano-diamond in aqueous medium. It is believed that the surface modification of whole diamond is carried out by mechanochemical treatment, and the mechanical force and polymer surface are utilized by high shear stirring, high energy ultrasonic vibration grinding. The synergistic effect of the active agent, while effectively pulverizing the nano-diamond agglomerate, modifying the surface of the nano-diamond, especially the nascent surface during the pulverization process, adjusting the hydrophilic and hydrophobic properties of the particle surface, and realizing the stable dispersion of the nano-diamond in the medium. .
Zhang Dong used silane coupling agent KH-570 and high-polymer JQ-3 surface-modified nano-diamond, and used ultrasonic as a dispersing means to disperse it in ethanol to obtain a colloidal solution with an average particle size of 51.7 nm. The combination of two kinds of high polymer dispersants can significantly improve the dispersion and stability of nanodiamond in ethanol, which lays a foundation for the preparation of oily polishing liquid.
Xu Xiangyang et al. and Hu Zhimeng studied the depolymerization and dispersion methods of nanodiamond agglomerates in white oil medium. They believe that polyoxyethylene nonionic surfactants can effectively disperse nanodiamonds in oil, and the end groups of the dispersant can be firmly anchored on the active groups on the diamond surface, such as hydroxyl and carboxyl groups or nitrogen-containing active substances, so that nanometers The diamond surface is oleophilic, and the polyoxyethylene is a large hydrophilic group. It acts like a huge barrier film, making it difficult for the nanodiamond particles to re-agglomerate, thus achieving stable dispersion of the nano-diamond in an oily medium. They concluded that nanodiamonds can be used as polishing materials in superfinishing, which can greatly reduce surface roughness. Nanodiamonds are used as polishing materials. The key technology is to use dispersants, which can make nanodiamonds in oil. It is well dispersed and suspended; in magnetic head polishing, the dispersant preferably has an antistatic effect to eliminate static charges during processing.
APVoznyakovskii et al. used the method of silylation of the surface of nanodiamonds to hydrophobize nanodiamonds to remove water molecules adsorbed on the surface of nanodiamonds and enhance the hydrophobicity of the surface. In this study, the surface of the nanodiamond was modified in toluene using three systems including an excess of trimethylsilyl mixture, an insufficient amount of a silyl mixture, and a silicon-containing mixture containing an ethylene component. The results show that the pseudo-nano-diamonds have good dispersion performance in the toluene system (average particle size is 14.5-18 nm) using trimethyl or dimethylvinylsilyl groups.
APVoznyakovskii et al. also studied the dispersibility of nanodiamonds in several non-aqueous media such as acetone, benzene and propanol. They believe that the polarity of the medium has an important influence on the stability and particle size distribution of the nanodiamond particles in the suspension. For different media, the lower the polarity, the lower the dispersibility of the nanodiamond particles placed therein. At the same time, when the medium is adjusted and combined, the addition of a relatively polar substance to a less polar medium such as acetone will result in improved dispersion of the nanodiamond in the suspension. It can be seen that dispersion in non-aqueous media, especially non-polar media, is a difficult point in practical applications. How to modify and adjust the composition of nanodiamonds to achieve stable dispersion of powders in these systems is worthy of further study. Voznyakovskii et al. studied the effect of surface modification of nanodiamonds by using polymers such as dimethyl siloxane and polyisoprene in benzene medium. The average size of nanodiamond particles in the obtained system is about 300 nm, which can be stably stored. day.
Xu Xiangyang et al. studied the stable dispersion of nanodiamonds in aqueous and nonaqueous media. It was found that if the nanodiamond agglomerates were depolymerized only by mechanical methods, the stability of the suspension system was not good and the particles were easily reaggregated. Nano-diamond hard agglomerates cannot be solved by chemical methods alone. They believe that the use of mechanical chemistry, the use of mechanical forces and the synergy of surfactants and hyperdispersants, while efficiently pulverizing nanodiamond agglomerates at high energy, especially on the surface of nanodiamonds, especially in the pulverization process Modification, change the surface functional group composition, adjust its hydrophilic hydrophobic properties, thereby achieving stable dispersion of nanodiamond in the medium. The nano-diamond water system developed by the company is capable of maintaining long-term stability in white oil-based, liquid paraffin-based and normal paraffinic hydroxyl systems. In the white oil system, when the ratio of nanodiamond to polymer dispersant is different, the cumulative distribution curve of nanodiamond particles in the system obtained by mechanochemical modification is different. When the weight ratio of dispersant to nano-diamond is 1:1, the deagglomeration effect is the best, and the system is less than 50 nm, the particles account for more than 92%, and the amount of dispersant is continuously increased, and the particle size is thickened. This indicates that when the dispersant is excessive, it may cause some of the particles which have been deagglomerated to reaggregate and the dispersibility is deteriorated.
Water-based lubricants are the future direction of tribology development due to increasing energy and environmental issues. The advent of nanomaterials has made it possible to develop high performance water-based lubricants. Nano-diamond is a non-polluting new carbon material ideal for the preparation of non-polluting nano-scale water-based lubricants. Hu Zhimeng believes that nano-diamonds are mostly used as lubricant additives, and as water-lubricating additives have not been reported, water-based lubricants are clean and non-polluting. Therefore, the development of nano-water-based lubricants emphasizes the significance of energy and environment. It is concluded through experiments that the lubrication mechanism of water-based nanodiamonds may be that the nanodiamond microspheres are filled on the wear surface and play a ball bearing effect. When the boundary is lubricated, a superhard alloy film is formed. Due to the existence of this film, it is avoided. The direct contact of the friction pair reduces the friction and wear of the friction pair; at the same time, the polishing effect of the nano-diamond in the friction process can improve the surface finish, and the super-light surface is also beneficial for reducing the friction and wear of the friction pair material.
4, preliminary application
Nano diamond polishing fluid is widely used in semiconductor wafer polishing, computer hard disk substrate, computer head polishing, precision ceramics, artificial crystal, hard alloy, gem polishing and other fields.
T.Kurobe applied water-based nano-diamond to silicon wafer polishing, prepared a polishing solution with sodium alginate, sodium carboxymethylcellulose, surfactant and deionized water to prepare a suspension-stable polishing solution. T.Kurobe studied ultra-dispersed nano-diamond polished silicon wafers and compared dry polishing with polishing liquid wet polishing. The dry polishing solution reduced the surface roughness Ra of the silicon wafer from 107 nm to 4 nm. The wet polishing is performed using a water-based nanodiamond polishing solution, and the polishing efficiency is higher, and the surface roughness of the silicon wafer is made smaller to 4 nm.
Zhu Yongwei et al. developed a water-based nano-diamond polishing solution and a manufacturing method thereof, by adding nano-diamond, a modifier, a dispersing agent, a super-dispersing agent, a pH adjusting agent, a wetting agent, and a chemical additive to ionic water. Ultra-precision polishing of nano-diamonds into small agglomerates of 20-100 nm by ultrasonic or stirring to prepare polishing liquids for various optoelectronic crystals, computer hard disk substrates, optical components and copper-connected semiconductor integrated circuits. For wafer polishing, the surface roughness reaches 0.214nm.
Ma Hongbo et al. proposed a method for manufacturing a slurry for back grinding of a magnetic disk head of a memory. The composition includes ten to thirteen carbon alkaloid mineral oil, fifteen carbon oily agent, diamond single crystal powder, and oxidation resistance. A preservative, a nonionic surfactant, an antifoaming agent and an antistatic agent are used for polishing the back surface of the magnetic head, and the surface scratches, surface residual stress, and surface roughness after grinding are 0.3 to 0.4 nm.
Qi Jianbin et al. disclosed the invention patent of nano polishing liquid and its manufacturing method. The light quality white oil was used as medium, and non-ionic surfactant, antistatic agent, detergent and pH adjuster were added to prepare the stability. In addition to being applied to computer heads, nano-diamond polishing fluids can also be used for high-precision surface grinding and polishing of optical devices and ceramics.
In order to avoid scratching the surface of the disk, the surface roughness of the hard disk head must be small enough, and the roughness of the next-generation magnetic head surface is required to be less than 0.2 nm. At present, the magnetic head is polished with sub-micron diamond polishing liquid, which cannot meet the requirements of the next-generation magnetic head processing. Claim. To this end, Gong Yanling et al. studied the medium-sized nano-diamond suspension for the magnetic head polishing process. The results show that the finer the nano-diamond particles, the smaller the polishing surface roughness, but the two do not constitute a simple linear relationship; The dispersion stability largely affects surface scratches, and stable dispersion of the polishing liquid is important.
Ronald F has prepared an aqueous nano-diamond polishing solution that is used to polish alumina workpieces by adjusting the pH of triethanolamine, which makes the surface of the workpiece to be cleaned easier.
5. Conclusion and outlook
(1) The uniform and stable dispersion of nano-diamonds in non-aqueous systems, especially in non-polar media, is the prerequisite for the application of nano-diamonds in the above-mentioned fields, and exerts excellent properties such as nano-particles and super-hard properties.
(2) The nano diamond polishing liquid is divided into an aqueous and oily polishing liquid. Because the water-based polishing liquid has the characteristics of green and environmental protection, and has the advantage of quick heat dissipation during polishing, it is suitable for high-speed polishing.
(3) Whether it is aqueous or oily polishing liquid, the key to the preparation is the long-term, stable dispersion of nano-diamond in the medium.
(4) The surface of the nano-diamond adsorbs oxygen-containing groups, hydroxyl groups, carbonyl groups, carboxyl groups, ether groups, etc., and these oxygen-containing reactive groups and nitrogen-containing reactive group materials react with or adsorb to many organic compounds, and the presence of these surface groups It provides the possibility of dispersing nanodiamonds in the medium.
(5) Dispersion technology of nano-diamond uses mechanical grinding + physical dispersion (ultrasonic dispersion and assisted mechanical stirring and dispersion) + chemical dispersion to successfully disperse the nano-diamond in oily or aqueous medium to obtain dispersion-stabilized nano-diamond polishing. liquid.