Flash Joule Heating Equipment: Electric field effects in flash Joule heating synthesis

Background

The use of electric fields in materials synthesis has become a compelling area of research in modern science and engineering. External electric fields are widely used to modulate the activation energies of chemical products, to allow thermochemical reactions to proceed at lower temperatures, and to regulate the grain size and arrangement of organic and inorganic products. The electric field strengths used in these techniques are typically in the range of 104 to 109 V/m, but fields as low as 102 V/m have been shown to affect reaction products. External electric fields can alter the products of synthesis, and it has also been suggested that the presence of an electric field can have an effect on the motion of electrically neutral particles.

The main point of this paper

Applications of FJH technology:

For synthesizing a wide range of materials including graphene, transition metal chalcogenides, inorganic nanoparticles, carbons and inorganic compounds.

Used for soil remediation, battery electrode repair, material recovery and upgrading.

Difference between FJH and conventional heating:

Joule heating requires an electric current to flow through the sample itself, directly heating the feedstock.

It requires a potential difference of several hundred volts to be applied in a reaction vessel several centimeters wide to produce a high electric field and current density.

The role of electric current in graphene synthesis:

Thermal annealing cannot fully account for the formation of highly turbulent particles, and current passage through the material plays a direct role in graphene crystal nucleation.

Graphene synthesis scales up:

An in-depth understanding of the graphene growth process is needed to control its structure and quality for different applications.

FJH studies in the conversion of metallurgical coke to graphene:

Experiments were performed to deconstruct the influence of electrical and thermal effects on reaction enthalpy, activation energy and product distribution.

The electric field strength affects the carbon feedstock morphology from amorphous carbon (AC) to vortex crystal (interlamellar dislocation) FG to ordered FG and graphite.

Effect of pulse width modulation:

Experimental and theoretical studies have demonstrated that the current density of the oscillatory reaction favors the phase transition.

Flash Joule heating: current-driven graphene synthesis and its phase transition control

Advantages of FJH technology:

Ultra-fast, scalable and versatile synthesis method for nanomaterials such as graphene.

Contribution of thermal and electrical processes:

Conventional graphene synthesis relies on chemical or thermal drivers.

It has been shown that the charge in the graphene precursor and the generated electric field catalyze the formation of graphene.

Material phase transition control:

A three-step phase transition of materials from amorphous carbon to turbulent graphene to ordered graphene and graphite can be controlled by adjusting the current or pulse width.

Density Functional Theory Simulations:

Simulations show that the charge inside the graphene precursor and the electric field induced by the current reduce the activation energy of the reaction and promote the phase transition.

Direct effect of current:

Current passing through a solid sample can directly drive nanocrystal nucleation in the FJH process.

Summarize

We have demonstrated experimentally and through theoretical simulations that the conversion of alternating current into Fourier transforms by flash Joule heating is an electrothermal process, not just a thermal one. The phase transition process can be greatly facilitated when current is passed through the reactant itself. Phase control from AC to turbulent graphene to graphite can also be achieved by varying the flash voltage. Both experimental data and DFT calculations show that the energy required for the electrothermal process is two times lower than for the thermal process. The energy required to convert from turbulent graphene to graphite is four times less than the energy required to convert AC to turbulent graphene. Finally, the important role of current and electric field in the phase transition process is analyzed and explained using the finite difference method.