A nano-Fe3C particle composite carbon-based conductive film and its preparation method

Abstract

This invention discloses a nano-Fe3C particle composite carbon-based conductive film and its preparation method. This invention utilizes the Joule heat generated by energizing the carbon-based conductive film to subject the iron-containing raw material loaded thereon to high-temperature treatment, causing it to react with the carbon-based conductive film, thereby producing a carbon-based conductive composite film uniformly loaded with Fe3C nanoparticles. This invention replaces the traditional heating process in a tube furnace or box furnace with Joule heat generated by energizing a nano-carbon-based macrofilm with rapid temperature rise and fall characteristics. The entire process offers the advantages of simple steps, rapid synthesis, and low energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of nano-composite materials and their preparation, and in particular relates to a nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof. Background Art

[0002] For environmental reasons, modern society has conducted extensive and in-depth research on various clean energy sources, aiming to replace polluting and unsustainable fossil fuels with new, clean energy sources. Significant progress has been made in recent years in both water splitting to produce hydrogen and in the field of secondary batteries. Transition metal carbides have been extensively studied and applied in both areas, with Fe3C nanomaterials being a leader. For example, Fe3C nanoparticles, when used as catalysts, exhibit advantages such as excellent resistance to poisoning, high stability, high activity, and a large specific surface area. They can also be used as hard coatings on material surfaces and possess excellent magnetic properties, making them exceptionally versatile materials.

[0003] Given the above advantages, many researchers have been exploring methods for synthesizing Fe3C nanoparticles, but they are generally limited to traditional gas and solid reduction carburization methods and pyrolysis synthesis. For example, Yang Shu et al. reported a method for preparing Fe3C by reducing iron ore with methanol / ethanol-hydrogen (Study on the Preparation of Fe3C by Reducing Iron Ore with Methanol / Ethanol-Hydrogen [J]. Nonferrous Metals Science and Engineering, 2017, 8(01): 8-14). They placed the pellet sample in a corundum crucible, introduced nitrogen, raised the tube furnace to 700℃, stopped after constant temperature, and then introduced H2 for 2 hours for reduction. Then, methanol was introduced with N2 mixture. After the methanol was introduced, N2 was changed to protection, and finally Fe3C was obtained. Although the product obtained by this method has a dense crystal structure, the product purity is low, and the gas carburization method has high energy consumption, long time consumption, and low efficiency. In addition, hydrogen, methanol, etc. need to be used in the experiment, which is dangerous. Wang Fengyun et al. reported a method for preparing a Fe3C / N-CNF@RGO composite structure (A novel method for preparing Fe3C / N-CNF@RGO integrated electrodes [P], CN112736221A). They dissolved FeCl3·6H2O and polyacrylonitrile in 10 mL of N,N-dimethylformamide, added polymethyl methacrylate, and magnetically stirred the solution at 60°C for 12 h to obtain a polymer precursor solution. This precursor solution was further electrospun into a fiber membrane, which was then dried and annealed to obtain the Fe3C / N-CNF composite. The Fe3C particles synthesized by this method were large and unevenly distributed. The synthesis process required long, high-temperature calcination, resulting in high energy consumption, low efficiency, and a cumbersome process. He Gaohong et al. reported a method for preparing an electrode material based on Fe3C nanoparticles (A positive electrode material for lithium-sulfur batteries and its preparation method [P], CN111900407B). The Fe3C nanoparticles produced by this method have a particle size of 5-10 nm and a relatively uniform size distribution. However, the experimental preparation process, including aging, pre-oxidation, and carbonization, is time-consuming and inevitably requires heating using conventional muffle furnaces and tube furnaces, which have slow temperature control rates and high energy consumption. Qiao Xiaochang et al. reported a method for preparing a Fe3C catalyst encapsulated with a carbon framework (Graphene / Carbon Nanotube Framework Encapsulated Fe3C Catalyst, Preparation and Application [P], CN110492115B). They mixed melamine, PVDF, and ferrous acetate, then subjected the mixture to high-temperature calcination, strong acid washing, and re-high-temperature calcination to obtain the final product. The Fe3C nanoparticles prepared by this method exhibited poor particle size uniformity, and the preparation process required multiple calcinations, which was energy-intensive and time-consuming. Therefore, developing a method for rapidly preparing Fe3C nanoparticles and their composite structures in a low-energy, high-efficiency, and pollution-free manner is of great significance for both scientific research and practical applications. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof.

[0005] The present invention solves the above technical problems through the following solutions:

[0006] A nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof. Electricity is passed across the two ends of the carbon-based conductive film, and the Joule heat response generated is used to quickly heat the iron-containing raw material loaded on the film. The iron source is then used to react with the carbon source in the film to obtain Fe3C nanoparticles uniformly loaded on the carbon-based film, thereby obtaining the desired composite film.

[0007] The Joule heat source includes, but is not limited to, carbon nanotube films, graphene films, MXene films, and conductive films made of general carbon-based fibers, or composite films based on the above carbon-based materials.

[0008] The sources of Fe elements required for the preparation of Fe3C nanoparticles include but are not limited to elemental iron, iron compounds and iron-based polymers.

[0009] A nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof, specifically comprising the following steps:

[0010] (1) Take a piece of carbon-based conductive film and soak it in concentrated hydrochloric acid or acetone and ultrasonically clean it to remove impurities such as catalysts;

[0011] (2) preparing a mixed solution / suspension containing an iron source, immersing the carbon-based conductive membrane in the iron source solution or filtering / coating the iron source material onto the carbon-based conductive membrane to load the iron source and drying it for use;

[0012] (3) Electricity is applied to both ends of the carbon-based conductive film loaded with an iron source, and the Joule heat generated by the film is used to reduce the iron source and react with the carbon on the surface of the film to produce Fe3C nanoparticles.

[0013] Wherein, the Joule heat treatment in step (3) is carried out under vacuum or inert atmosphere protection.

[0014] The Joule heat treatment heating rate in step (3) is 400-1000°C / s.

[0015] As a preferred technical solution, the specific steps of step (1) are: take a 10 μm thick carbon nanotube film and soak it in concentrated hydrochloric acid for 6 hours to remove impurities such as catalysts contained therein.

[0016] The specific steps of step (2) are as follows: dissolving 40 mg of anhydrous ferric chloride in 20 mL of anhydrous ethanol to prepare a 2 mg / mL concentration of ferric chloride-ethanol mixed solution, and soaking the cut 10 μm thick carbon nanotube film in the above solution for 24 hours.

[0017] The specific steps of step (3) are as follows: drying the FeCl3-loaded carbon nanotube film in a forced air drying oven for 1 hour and then taking it out; using conductive silver glue to stick its two ends to the sample holder in the Joule heat heating furnace, turning on the vacuum pump, evacuating the cavity to a certain vacuum degree and connecting it to a DC power supply. Maintaining a constant voltage of 40V for 1 minute, the surface of the carbon nanotube film can be heated to 1000℃ within 2 seconds, reducing the FeCl3, and finally obtaining ultrafine Fe3C nanoparticles evenly distributed on the carbon nanotube film.

[0018] As a preferred technical solution, the specific steps of step (1) are: take a piece of 0.2 mm thick hydrophilic carbon fiber paper, soak it in acetone and ultrasonically clean it for 30 minutes to remove impurities therein.

[0019] The specific steps of step (2) are as follows: dissolving 40 mg of anhydrous ferric chloride in 20 mL of anhydrous ethanol to prepare a 2 mg / mL concentration of ferric chloride-ethanol mixed solution, and soaking the cut 0.2 mm thick carbon paper in the above solution for 24 hours.

[0020] The specific steps of step (3) are as follows: drying the FeCl3-loaded carbon paper in a forced air drying oven for 1 hour and then removing it; using conductive silver glue to stick its two ends to the sample holder in the Joule heat heating furnace, turning on the vacuum pump, evacuating the cavity to a certain vacuum degree, and connecting a DC power supply. Maintaining a constant voltage of 14V for 1 minute, the carbon paper surface can reach 1000°C within 3 seconds, and then the FeCl3 is reduced to obtain ultrafine Fe3C nanoparticles evenly distributed on the hydrophilic carbon paper.

[0021] As a preferred technical solution, the specific steps of step (1) are: take a 10 μm thick graphene film and soak it in concentrated hydrochloric acid for 6 hours to remove impurities such as catalysts contained therein.

[0022] The specific steps of step (2) are as follows: dissolve 1 g of anhydrous ferric chloride in 20 mL of deionized water, stir evenly to obtain a 50 mg / mL ferric chloride solution, add 80 mL of boiling deionized water to the above solution, heat the solution until the solution turns reddish brown, then add 1% PVP, stir and dissolve into a uniform solution, and then filter 5 mL of the above solution onto the cut 10 μm thick graphene film for loading.

[0023] The specific steps of step (3) are as follows: drying the graphene film loaded with ferric hydroxide nano-colloidal particles in a forced air drying oven for 1 hour and then taking it out; using conductive silver glue to stick its two ends to the sample holder in the Joule heat heating furnace, turning on the vacuum pump, evacuating the cavity to a certain vacuum degree and connecting it to a DC power supply. Maintaining a constant voltage of 35V for 1 minute, the surface of the graphene film can reach 900°C within 2 seconds, and then reducing the ferric hydroxide nano-colloidal particles to obtain ultrafine Fe3C nanoparticles evenly distributed on the graphene film.

[0024] As a preferred technical solution, the specific steps of step (1) are: take a piece of 0.2 mm thick hydrophilic carbon fiber paper, soak it in acetone and ultrasonically clean it for 30 minutes to remove impurities therein.

[0025] The specific steps of step (2) are as follows: dissolve 1 g of anhydrous ferric chloride in 20 mL of deionized water, stir evenly to obtain a 50 mg / mL ferric chloride solution, add 80 mL of boiling deionized water to the above solution, heat the solution until the solution turns reddish brown, then add 1% PVP, stir and dissolve into a uniform solution, and then filter 5 mL of the above solution onto a cut 0.2 mm thick hydrophilic carbon paper for loading.

[0026] The specific steps of step (3) are as follows: drying the hydrophilic carbon paper loaded with ferric hydroxide nano-colloidal particles in a forced air drying oven for 1 hour and then taking it out; using conductive silver glue to stick its two ends to the sample holder in the Joule heat heating furnace, turning on the vacuum pump, evacuating the cavity to a certain vacuum degree and connecting a DC power supply. Maintaining a constant voltage of 12.8V for 1 minute, the surface of the hydrophilic carbon paper can reach 900°C within 3 seconds, and then reducing the ferric hydroxide nano-colloidal particles to obtain hydrophilic ultrafine Fe3C nanoparticles uniformly distributed on the carbon paper.

[0027] As a preferred technical solution, the specific steps of step (1) are: take a 10 μm thick carbon nanotube film and soak it in concentrated hydrochloric acid for 6 hours to remove impurities such as catalysts contained therein.

[0028] The specific steps of step (2) are as follows: dissolving ferrocene in acetone at a concentration of 10 mg / mL, and immersing the cut 0.2 mm thick carbon nanotube film in the above solution for 24 hours.

[0029] The specific steps of step (3) are as follows: drying the ferrocene-loaded carbon nanotube film in a forced air drying oven for 1 hour and then taking it out; using conductive silver glue to stick its two ends to the sample holder in the Joule heat heating furnace, turning on the vacuum pump, evacuating the cavity to a certain vacuum degree and connecting a DC power supply. Maintaining a constant voltage of 32.5V for 1 minute, the surface of the carbon nanotube film can reach 850°C within 2 seconds, and then reducing the ferrocene to obtain ultrafine Fe3C nanoparticles evenly distributed on the carbon nanotube film.

[0030] As a preferred technical solution, the specific steps of step (1) are: take a 20 μm thick Ti3C2 MXene film, soak it in acetone and ultrasonically clean it for 30 minutes to remove impurities therein.

[0031] The specific steps of step (2) are as follows: dissolving ferrocene in acetone at a concentration of 10 mg / mL, and immersing the cut Ti3C2 MXene film in the above solution for 24 h.

[0032] The specific steps of step (3) are as follows: drying the ferrocene-loaded 20 μm thick Ti3C2 MXene film in a forced air drying oven for 1 hour and then removing it; using conductive silver glue to glue its two ends to the sample holder in the Joule heat heating furnace, turning on the vacuum pump, evacuating the cavity to a certain vacuum degree and connecting it to a DC power supply. Maintaining a constant voltage of 35 V for 1 minute, the Ti3C2 MXene film can reach 850°C within 3 seconds, and then reducing the ferrocene to obtain ultrafine Fe3C nanoparticles evenly distributed on the Ti3C2 MXene film.

[0033] The beneficial technologies enabled by this invention include at least one method: using Joule heating, a rapid heating process involving self-heating of a carbon-based conductive film with rapid temperature rise and fall characteristics, to synthesize FeC nanoparticles, replacing traditional heating methods such as tube furnaces or box furnaces. This method features rapid temperature rise and fall rates and requires minimal holding time, significantly reducing both energy consumption and time required for preparation, offering both energy-saving and high-efficiency advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the preparation process of nano-Fe3C particle composite carbon-based conductive film in an embodiment of the present invention.

[0035] Figure 2 This is an optical photograph of the carbon nanotube film in Example 1 of the present invention.

[0036] Figure 3 This is a scanning electron microscope photograph of the carbon nanotube film in Example 1 of the present invention.

[0037] Figure 4 This is a scanning electron microscope morphology image of the nano-Fe3C particle composite carbon nanotube film prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] Example 1

[0040] A nano-Fe3C particle composite carbon-based conductive film and its preparation method. This invention uses the Joule heat generated by electrifying the carbon nanotube film to rapidly in-situ reduce the FeCl3 loaded on the carbon nanotube film, resulting in Fe3C nanoparticles evenly distributed on the carbon nanotube film.

[0041] A nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof, specifically comprising the following steps:

[0042] A 10μm-thick carbon nanotube film, measuring 1.8×3.5cm, was soaked in concentrated hydrochloric acid for 6 hours to remove the catalyst. 40mg of anhydrous ferric chloride was dissolved in 20mL of anhydrous ethanol to prepare a 2mg / mL ferric chloride-ethanol solution. The cut 10μm-thick carbon nanotube film was soaked in this solution for 24 hours. The FeCl3-loaded carbon nanotube film was dried in a forced-air drying oven for 1 hour before removal. The film was then attached to a sample holder in a Joule heating furnace using conductive silver glue. The vacuum pump was then activated to evacuate the chamber to a desired vacuum level and connected to a DC power supply. A constant voltage of 40V was maintained for 1 minute. The carbon nanotube film was heated to 1000°C within 2 seconds, reducing the FeCl3 and ultimately producing ultrafine Fe3C nanoparticles evenly distributed across the carbon nanotube film.

[0043] Example 2

[0044] A nano-Fe3C particle composite carbon-based conductive film and its preparation method. This invention uses the Joule heat generated by electrifying hydrophilic carbon fiber paper to rapidly in-situ reduce FeCl3 loaded on the carbon paper, resulting in Fe3C nanoparticles evenly distributed on the carbon-philic paper.

[0045] A nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof, specifically comprising the following steps:

[0046] A 1.8×3.5cm piece of 0.2mm thick hydrophilic carbon paper was soaked in acetone and ultrasonically cleaned for 30 minutes to remove impurities. 40mg of anhydrous ferric chloride was dissolved in 20mL of anhydrous ethanol to prepare a 2mg / mL ferric chloride-ethanol solution. A 10μm thick carbon nanotube film was soaked in this solution for 24 hours. The FeCl3-loaded hydrophilic carbon paper was dried in a forced-air drying oven for 1 hour before removal. Conductive silver glue was used to attach the ends of the paper to a sample holder in a Joule heating furnace. A vacuum pump was activated, the chamber was evacuated to a certain vacuum, and a DC power supply was connected. A constant voltage of 14V was maintained for 1 minute, and the surface of the hydrophilic carbon paper reached 1000°C within 3 seconds. The FeCl3 was then reduced, resulting in ultrafine Fe3C nanoparticles evenly distributed on the hydrophilic carbon paper.

[0047] Example 3

[0048] A nano-Fe3C particle composite carbon-based conductive film and its preparation method. This invention uses the Joule heat generated by electrifying a graphene film to rapidly in-situ reduce the ferric hydroxide nano-colloidal particles supported on the graphene film, resulting in Fe3C nanoparticles evenly distributed on the graphene film.

[0049] A nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof, specifically comprising the following steps:

[0050] A 10μm-thick graphene film (1.8×3.5cm) was soaked in concentrated hydrochloric acid for 6 hours to remove the catalyst. 1g of anhydrous ferric chloride was dissolved in 20mL of deionized water and stirred to obtain a 50mg / mL ferric chloride solution. 80mL of boiling deionized water was added to this solution and heated until it turned reddish-brown. 1% polyvinylpyrrolidone (PVP) was then added and stirred. 5mL of this solution was then filtered onto the cut 10μm-thick graphene film for loading. The graphene film loaded with ferric hydroxide nanocolloidal particles was then dried in a forced-air drying oven for 1 hour before removal. Conductive silver glue was used to attach the two ends of the graphene film to a sample holder in a Joule heating furnace. The vacuum pump was activated, the chamber was evacuated to a certain vacuum, and a DC power supply was connected. A constant voltage of 35V was maintained for 1 minute, and the graphene film surface reached 900°C within 2 seconds. The ferric hydroxide nanocolloidal particles were then reduced, resulting in ultrafine Fe3C nanoparticles uniformly distributed on the graphene film.

[0051] Example 4

[0052] A nano-Fe3C particle composite carbon-based conductive film and its preparation method. This invention uses the Joule heat generated by electrifying hydrophilic carbon fiber paper to rapidly in-situ reduce the iron hydroxide nano-colloidal particles supported on the carbon paper, resulting in Fe3C nanoparticles evenly distributed on the carbon paper.

[0053] A nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof, specifically comprising the following steps:

[0054] A 1.8 × 3.5 cm piece of 0.2 mm thick hydrophilic carbon paper was soaked in acetone and ultrasonically cleaned for 30 minutes to remove impurities. 1 g of anhydrous ferric chloride was dissolved in 20 mL of deionized water and stirred to obtain a 50 mg / mL ferric chloride solution. 80 mL of boiling deionized water was added to the solution and heated until it turned reddish-brown. 1% polyvinylpyrrolidone (PVP) was then added and stirred. 5 mL of the solution was filtered onto a cut 0.2 mm thick carbon paper for loading. The carbon paper loaded with ferric hydroxide nanocolloidal particles was then dried in a forced-air drying oven for 1 hour before removal. Conductive silver glue was used to attach the paper to a sample holder in a Joule heating furnace. The vacuum pump was activated, the chamber was evacuated to a certain vacuum, and a DC power supply was connected. A constant voltage of 12.8 V was maintained for 1 minute, and the surface of the hydrophilic carbon paper reached 900°C within 3 seconds. The ferric hydroxide nanocolloidal particles were then reduced, resulting in hydrophilic, ultrafine FeC nanoparticles uniformly distributed on the carbon paper.

[0055] Example 5

[0056] A nano-Fe3C particle composite carbon-based conductive film and its preparation method. This invention uses the Joule heat generated by electrifying a carbon nanotube film to rapidly in-situ reduce the iron oxide nanoparticles loaded on the carbon nanotube film, resulting in Fe3C nanoparticles uniformly distributed on the carbon nanotube film.

[0057] A nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof, specifically comprising the following steps:

[0058] A 10μm-thick carbon nanotube film (1.8×3.5cm) was soaked in concentrated hydrochloric acid for 6 hours to remove the catalyst. Ferrocene was dissolved in acetone at a concentration of 10mg / mL. A 0.2mm-thick hydrophilic carbon paper was soaked in the solution for 24 hours. The ferrocene-loaded carbon nanotube film was then dried in a forced-air drying oven for 1 hour before removal. The film was then attached to a sample holder in a Joule heating furnace using conductive silver glue. The vacuum pump was then activated to evacuate the chamber to a certain vacuum level and connected to a DC power supply. A constant voltage of 30V was maintained for 1 minute, and the surface of the carbon nanotube film reached 850°C within 2 seconds. Ferrocene was then reduced, resulting in ultrafine Fe3C nanoparticles uniformly distributed on the carbon nanotube film.

[0059] Example 6

[0060] A nano-Fe3C particle composite carbon-based conductive film and its preparation method. This invention uses the Joule heat generated by electrifying a Ti3C2 MXene film to rapidly in-situ reduce the ferrocene loaded on the film, resulting in Fe3C nanoparticles evenly distributed on the film.

[0061] A nano-Fe3C particle composite carbon-based conductive film and a preparation method thereof, specifically comprising the following steps:

[0062] A 1.8 x 3.5 cm, 20 μm thick TiC MXene film was soaked in acetone and ultrasonically cleaned for 30 minutes to remove impurities. Ferrocene was dissolved in acetone at a concentration of 10 mg / mL. The cut TiC MXene film was immersed in this solution for 24 hours. The ferrocene-loaded TiC MXene film was then dried in a forced-air drying oven for 1 hour before removal. Conductive silver glue was used to attach the film's ends to a sample holder in a Joule heating furnace. The vacuum pump was activated, the chamber was evacuated to a certain vacuum level, and a DC power supply was connected. A constant voltage of 35 V was maintained for 1 minute, and the TiC MXene film reached 850°C within 3 seconds. Ferrocene was then reduced, resulting in ultrafine FeC nanoparticles uniformly distributed on the TiC MXene film.

[0063] Compared to other methods for preparing Fe3C nanoparticles, the method described herein utilizes a rapid Joule heating process, driven by the self-heating of a carbon-based conductive film with rapid temperature rise and fall, to synthesize Fe3C nanoparticles, replacing traditional heating methods such as tube furnaces or box furnaces. This method features rapid temperature rise and fall rates and a short holding time, significantly reducing production energy consumption and time, offering both energy-saving and high-efficiency advantages.

[0064] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nano-Fe3C particle composite carbon-based conductive film, characterized by: The following steps are involved: (1) Take a piece of carbon-based conductive film and soak it in concentrated hydrochloric acid or acetone and ultrasonically clean it to remove the catalyst impurities contained therein; (2) preparing an iron source mixed solution or gel, immersing the carbon-based conductive membrane in the iron source mixed solution or gel, or filtering or coating the iron source material onto the carbon-based conductive membrane to load the iron source, and drying the mixture for use; (3) Electricity is applied to both ends of the carbon-based conductive film loaded with an iron source, and the Joule heat generated by the film is used to reduce the iron source and react with the carbon on the surface of the film to obtain Fe3C nanoparticles.

2. The method for preparing a nano-Fe3C particle composite carbon-based conductive film according to claim 1: the carbon-based conductive film includes but is not limited to a carbon nanotube film, a graphene film, a MXene film, and a conductive film made of a general carbon-based fiber, or a composite film based on the above carbon-based materials.

3. The method for preparing a nano-Fe3C particle composite carbon-based conductive film according to claim 1: the iron source material in the iron-containing source mixed solution or gel includes but is not limited to iron element, iron compounds and iron-based polymers.

4. The method for preparing a nano-Fe3C particle composite carbon-based conductive film according to claim 1, characterized in that: The Joule heat treatment in the preparation step (3) is carried out under vacuum or inert atmosphere protection.

5. The method for preparing a nano-Fe3C particle composite carbon-based conductive film according to claim 1, characterized in that: The Joule heat treatment heating rate in the preparation step (3) is 400-1000°C / s.

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