Successful fabrication of multilayer graphene from graphite compound by rapid heating, thermal shock using blast furnaces

Graphene is a new material with a lot of potential applications, first discovered in 2010 and accompanied by the Nobel Prize in physics. Currently, single-layer graphene is quite expensive and is intended for applications in advanced and complex materials. Multilayer graphene is made from low-cost graphite materials, bringing great and potential applications in practice. In Vietnam, there is no facility offering a process and equipment system for making multilayer expanded graphene from graphite compounds at pilot scale, so the introduction of this material into application is still very limited.

In principle, multilayer graphene is made from graphite compounds by thermal shock heating, but in practice it is common to use microwaves as a heat source in making multilayer graphene for experimental purposes with samples as small as several tens of grams. The expert team led by Dr. Au Duy Tuan, Institute of Leadership Physics, said: The commercial offering of a multilayer graphene material manufacturing equipment system with large quantities is still very rare and expensive. With the desire to successfully manufacture multilayer graphene with application potential and reasonable price, the team has researched and proposed methods and equipment systems for fabricating multilayer graphene nanofoil from graphite compounds by rapid heating causing thermal shock using blast furnaces. The group has been granted patent number 34682 by the National Office of Intellectual Property. The following describes in detail the technology of "fabricating multilayer graphene nanofoil from graphite compounds".  

Design equipment for fabricating multilayer graphene materials from GIC particles 

Raw material feeding: Supplying GIC (Graphite Intercalation Compound) particle material into the reaction chamber is carried out through the material feeding mechanism, it has the ability to adjust the feed rate. This material feeding speed will be synchronized with the reaction chamber so that the thermal shock process takes place best, the raw materials are not locally blocked, not too little material enters. Therefore, the research team chose to design the material filling system according to Figure 1. The material feeding system consists of the input material container and the blocking door that regulates the loading of raw materials. 


Figure 1. Image of input GIC granular material feeder

The inlet material container is designed with a lid to prevent dust and moisture from acting on GIC particles during the manufacturing process and is connected to the secondary storage chamber part, which can be connected to the input material container through a pipeline. When the raw materials in the secondary storage chamber gradually decrease, they will be replenished with materials in the upper material barrel through the material pipeline. In addition, the chamber has side support slots, which is convenient for disassembling material stoppers with different pore sizes to regulate the loading of materials with different particle sizes to change the feed rate of materials into the reaction chamber.

The feed regulating blocking door is made to fit snugly into the material storage chamber through the support slots and prevent the material from coming out anywhere other than the predetermined feed regulating hole. With different technical requirements for input materials that are GIC granules of different sizes or requirements for different feeder speeds, the blocking door has different size feed damper holes.

Figure 2. Material feeding mechanism

Blast-frequency furnace system: Used to make graphene materials from GIC particles using an electromagnetic induction furnace in a tubular shape with a frequency of about 100 kHz, at this frequency will not adversely affect biological cells and does not require an electromagnetic wave shielding cover. The use of direct current voltage (DC) from 45V-54V, large power 3KW to power a power electronic circuit that oscillates at a frequency of about 100 kHz with a load resistance of a coil will generate an alternating current flowing through the induction conductor. This current variation through the coil creates a very strong and rapidly changing magnetic field in the space inside the working coil. So the metal tube inside will heat up very quickly when placed in the variable magnetic field of the coil. The arrangement of the working coil and metal pipe can be thought of as an AC transformer. The coils work like the very place where electrical energy is introduced, and the metal tube that is the secondary part of the transformer has been short-circuited. This mechanism generates induction current through the tubes. These are called eddy currents (induced currents).

On the other hand, high-frequency power sources used in the application of induced heat lead to a phenomenon called the surface effect. This surface effect forces alternating currents to flow in a thin layer towards the surface of the tube. The surface effect increases the effective resistance of the metal and greatly increases the thermal effect due to the induced current in the tube.

Manufacturing equipment for fabricating multilayer graphene materials from GIC particles

The material feeding system that supplies GIC granular materials into the blast furnace is fabricated and assembled with the following specific steps:

Install the material container, enough to run continuously for 24 hours. The lid is effective against dust and moisture acting on GIC particles during manufacturing and is connected to the chamber section.
Assemble the material container with the storage chamber through the lead hopper, when the raw materials in the storage chamber gradually decrease, it will be replenished by the raw materials in the upper material barrel through the material conduction hopper.
Install the feed throttling blocking door with a rectangular material intake hole measuring 1.5mm x 2.5mm into the material storage chamber, through the side support slot of the storage chamber.
The vibration motor that controls the feeder is capable of controlling the rotational speed of the motor. When the rotational speed of the motor vibrates and the inclination of the storage compartment is a factor affecting the feed rate. The set of input materials includes: Containers for raw materials; chambers and conduction funnels; The door prevents the feed regulator and the motor vibrates.

Figure 3. GIC input feeder system with vibration motor attached

Heater mounting: Coils and power circuits are one of the main parts of the induction heating system. This is the part of the system that converts electrical energy into thermal energy, an important factor in the conversion efficiency of the induction heating system. The coil is cylindrical in shape with diameter Φ = 60mm and consists of 13-14 turns of wire equivalent to a pipe length of about 2.5m and is made of hollow copper tube material with diameter Φ = 3mm.

Install the DTK 7272V01 unit and install the temperature control program according to PID mode to measure and control the reaction chamber temperature. PID temperature control program; the temperature increase value in the reaction chamber after a period of 20 minutes will stabilize at the set temperature position with an error of ± 50C. 
The equipment for making multilayer graphene from GIC particles is made with dimensions: (length, width, height = 600*600*1200 (mm)) and a patent granted by the National Office of Intellectual Property. 

Figure 4. Photo of multilayer graphene fabrication equipment from GIC particles and Patent

In Vietnam, the team of experts Dr. Au Duy Tuan, Institute of Physics, Vietnam Academy of Science and Technology is a pioneer in manufacturing multilayer graphene materials and was granted a patent by the National Office of Intellectual Property. Multilayer graphene materials are widely applied in fields such as: Environmental cleaning materials (adsorption, recovery of oil and industrial wastes in the aquatic environment), polymer nanocomposite materials, electrostatic charge dissipation, rubber denaturation reinforcement materials.

Translated by Phuong Ha
Link to Vietnamese version

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