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Ultrasonic Dispersion of Graphene |
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15 Feb, 2017 |
Ultrasonic Processor |
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Graphene is a new type of nano material with properties of thinnest, hardest and strongest conductivity and thermal conductivity. With the development of modern science technology and industry, ultrasonic dispersion of graphene can realize the low-cost, large-scale production and widely used in commercial application, which cover many fileds including photosensitive components, new energy, sensors, paint coatings, electrodes, batteries, transistors, flexible display screens, solar energy, ultra light materials, composite materials, seawater desalination and so on.
Traditional methods for graphene production
1) Mechanical stripping preparation method: obtain monolayer graphene material by using friction and relative motion between materials and graphene. This
method is very simple to operate and maintains the complete crystal structure of graphene, but it's inefficient and hard to control the size of graphene
layer, unable to carry out industrial mass production.
2) Silicon carbide(SIC) crystal extension method: remove silicon atoms in ultra-high vacuum and high-temperature environment, graphene is grown on the surface of silicon carbide crystal, so as to obtain graphene with silicon carbide substrate. The conductivity of this graphene is limited by the substrate, the growth conditions are harsh, and high demanding on the equipments.
3) Chemical vapor deposition method(CVD): introduce low-carbon organic gas into the vacuum reactor, decompose and carbonize the carbonaceous gas under high temperature, then cool it after a certain time. During the cooling process, several layers or single layer of graphene will be formed on substrate surface. This method is proper for large-scale industrial production, but the quality of graphene is not very well.
4) Redox method: also known as oxidation reduction preparation of graphene, graphite is oxidized by strong acid and then reduced by chemical method to obtain graphene. The preparation method can realize mass production easily. It mainly includes Brodie method, staudenmaier method and Hummers method. Hummers can disperse graphene with ultrasonic, which has high efficiency and commom used in graphene production.
Principle of ultrasonic dispersion for Graphene
Graphene is immiscible with many substances and has property of poor dispersion, easy to agglomerate to form larger aggregates, so that nanoparticles can not be evenly dispersed as a single particle, which reduces their adsorption capacity.
Ultrasound can be used to prepare stable and highly concentrated graphene without surfactant or dispersant. In order to overcome the van der Waals force between graphene layers, the strong shear force generated by ultrasonic cavitation is the most advanced method to prepare this stable dispersion. The propagation of ultrasonic wave in liquid produces strong pressure wave, forms countless micro bubbles, after growth and collapse, generate strong shear wave activity. With the increase of ultrasonic energy, the pressure released by ultrasonic instantly destroys the van der Waals force between graphene layers and effectively expands the spacing between graphite layers. Larger layer spacing is not only conducive to the insertion of other molecules and atoms to form Graphite Intercalation Composites, but also easier to be stripped, which lays a foundation for the preparation of single-layer graphene in the next step. In addition, ultrasonic dispersion technology can avoid the chemical action and damage to crystal structure by accurately controlling the parameters of ultrasonic dispersing equipments, finally obtain the original and flawless graphene layer.
Ultrasonic dispersers for preparing graphene
1) Lab-use ultrasonic graphene dispersers: Ultrasonic dispersing for small volume of graphene. Generally composed of generator, transducer and experimental fixed support. It's an experimental disperser which is used to test the feasibility of graphene preparation or application. The influence on experimental result includes ultrasonic amplitude, material ratio, reaction volume, action time, temperature and other conditions, try best to obtain ideal experimental results , and make relevant parameter records to provide standards for following experiments or production.
2) Universal ultrasonic graphene dispersers: Ultrasonic dispersing for medium volume of graphene. Composed of ultrasonic generator, transducer and reactor with circulation system. In addition, it's equipped with accessories such as cooling jacket, feeding inlet, feeding pump, base to form an independent unit of graphene ultrasonic production. Liquid materials in single reactor flow and treated through the circulating pump and simulate the operation of industrial production line. Universal graphene dispersers are used to confirm the production efficiency, reaction volume and flow rate, the best ultrasonic power and material ratio.
3) High-volume ultrasonic graphene dispersers: Multiple units of ultrasonic equipment are composed to form a graphene production line. The quantity of units and power should be based on experimental datas. In addition to the previously mentioned universal ultrasonic equipment, ultrasonic graphene production line is also equipped with for cooling jacket, circulation, flow pump, flowmeter, centralized power control cabinet, fixing devices for reactor, sound insulation materials, etc. Customers only need to provide cable interface, material interface and cooling water interface to realize the ultrasonic dispersion for mass production of graphene.
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