Method for producing porous carbon or graphite

Abstract

Method for producing porous carbon or graphite. The invention is based on the problem of creating a method for the cost-effective production of porous carbon or graphite from renewable raw materials, which is easy to implement and allows a mechanical post-processing for the production of any shaped article, for use as a structural element, mould or container. This is achieved by filling a mold / container (1) with powdered dry or dehydrated wheat- or rice starch as a dense mass; compressing / densifying the mass (2) in the mold / container (1); heating the mass (2) in said filled mold / container (1) in an oven to a first temperature level of 170°C to 450°C in an oxidizing or inert atmosphere, thereby causing a shrinkage process; stabilizing the heated mass (2) for a longer time; slowly further heating the mass (2) in an oven under protective gas to a second temperature level of >1,000°C for carbonization or >2,500°C for graphitization to form a blank (5) that is as dense as possible; and removing the dense blank (5) from the mold / container (5).

Description

[Technical field]

[0001] The present invention relates to a method for producing porous carbon or graphite having a uniform, hard structure suitable for mechanical processing to produce shaped articles. [Background technology]

[0002] The production of carbon materials is usually carried out by grinding coke, carbon black or graphite until granules with the desired particle size or powder are obtained. Since these granules cannot be deformed by simple compression, they are mixed with a suitable binder, for example a thermoplastic. This mixture is then homogenized and compressed into the desired shape. The compacts thus produced, also called green compacts, are finally carbonized or graphitized in a furnace at high temperatures in a suitable atmosphere.

[0003] Carbonization / graphitization can then be followed by mechanical processing to produce carbon or graphite parts.

[0004] Needless to say, the above manufacturing processes are very laborious and very expensive due to the starting materials used.

[0005] From CN113620272A (reference 1) a method for producing battery electrodes made of graphite is known, in which starch and carbon black are first mechanically and homogeneously mixed together in a given ratio. The mixture is then placed in a crucible and stabilized in a muffle furnace at 200-600 ° C for 3-8 hours. Finally, the mixture is carbonized in a nitrogen atmosphere at 800-1,600 ° C for 1-3 hours to produce carbon microspheres based on carbon black, followed by cooling to room temperature. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] CN113620272A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention is therefore based on the problem of creating an easy-to-implement method for the cost-effective production of porous carbon or graphite with a uniform and hard structure from renewable raw materials, which allows for mechanical post-processing for use as structural elements, moulds or containers, and for the production of any moulding, which can be easily converted into a SiC moulding. [Means for solving the problem]

[0008] The problem underlying the present invention is solved by the following method steps: - filling the mould / container with powdered dry or dehydrated wheat-, corn-, rice or other starch, - generating a dense mass in a mould / container by compressing / densifying the mass in the container by applying a uniform or impulse pressure to the mass; - causing a shrinkage process by slowly heating the dense mass in said filled mould / container in a furnace to a first temperature level between 170°C and 450°C in steps of 5°C while further compressing / densifying the mass in an oxidizing or inert atmosphere; - stabilizing the blank for a relatively long period of time, greater than 1 hour; - slowly further heating said blank under protective gas in a furnace with a temperature gradient of about 1° C. / min to a second temperature level of >1,000° C. for carbonization or >2,500° C. for graphitization to form a blank that is as dense as possible; and - Removal of the compact blank from the mould / container.

[0009] The problem underlying the present invention is further achieved by the following method steps: - filling the mould / container with powdered dry or dehydrated wheat-, corn-, rice or other starch, - generating a dense mass in a mould / container by compressing / densifying the mass in the container by applying a uniform or impulse pressure to the mass; - Heating the dense mass to a starting temperature of about 190°C, followed by a cooling process over several hours, and successively re-heating the dense mass to 210-230°C while further compressing / densifying the mass, to cause a shrinkage process. - stabilizing the heated mass for a relatively long period of time, greater than 1 hour; - slowly further heating the mass in a furnace under protective gas with a temperature gradient of about 1°C / min to a second temperature level of >1,000°C for carbonization or >2,500°C for graphitization in order to form a blank that is as dense as possible; and - Removal of the compact blank from the mould / container.

[0010] Preferably, the slow heating to the first temperature level is done in steps of 5° C. with a waiting time between each step of about 8 hours.

[0011] Wheat starch, corn starch or rice starch can also be mixed with sugar or vegetable oil as a binder.

[0012] In yet another embodiment, the mixture of wheat starch or rice starch with sugar or oil (edible oil) is mixed with yet another graphitizable material as a further exogenous substance.

[0013] Graphitizable materials include, for example, high temperature resistant polymers, carbon black, graphite dust, natural graphite, and PVA (polyvinyl alcohol) adhesive.

[0014] Finally, natural fiber materials such as cotton, cellulose, bamboo, hemp, etc. may also be incorporated.

[0015] In continuation of the invention, the compression / densification of the mass filled in the mould / container is carried out, for example, by applying an additional load to a plate resting on the mass by means of a weight, generating a uniform pressure acting on the mass, or by vibration (e.g. with a vibrating plate or another vibrating device), or shaking of the mould / container, or by violent impacts acting on the mass from the side or from below, for example by striking the mould / container, resulting in a dense moulded part.

[0016] Compression / densification of the mass can also be achieved during heating by applying a load with a weight placed on top.

[0017] The heating gradient for carbonization or graphitization should be no more than about 1° C. / min, and between each 50-100° C. step a pause of about 30-120 min should be introduced, allowing the material to relax and at the same time allowing gases, e.g. air or water vapor, to diffuse out without damaging the structure.

[0018] The specific selection of heating gradients and heating stages also depends on the pressure during the process, so that higher pressures allow for faster heating overall.

[0019] Protective gases include the noble gases, namely helium, neon, argon, krypton, xenon and radon.

[0020] The carbonization or graphitization is preferably carried out at a pressure of >500 mbar.

[0021] Preferably, a mould / container made of Teflon (up to 250° C. maximum temperature) or another suitable material can be used to allow easy removal of the moulded part, or the mould / container can be lined with fabric before filling with the mass.

[0022] The blank 5 made of graphite produced according to the invention can be converted to SiC without any problems in a furnace at a temperature of 1,200° C., with SiO being supplied with argon as carrier gas at a pressure of 30 mbar, a temperature of about 1,520° C. being preferred here.

[0023] The invention will now be explained in more detail by way of examples. [Brief description of the drawings]

[0024] FIG. 1a shows a mould / container filled with a mixture of wheat starch and exogenous material.

[0025] FIG. 1b shows the filled container after carbonization.

[0026] FIG. 2 shows a fabric lined container.

[0027] FIG. 3 shows a carbonized mass produced from wheat starch and sugar with edible oil as exogenous material after a first heating to 250° C.

[0028] FIG. 4 shows a blank after 3 hours at 1600° C., ramped with a heating ramp of 1° C. / min and dwell times of 120 min at each of 200° C., 400° C. and 500° C.

[0029] FIG. 5 shows the blank of FIG. 4 finished as a compact after cutting on both sides (outer and inner).

[0030] The method according to the invention first comprises the following steps: Filling a mould / container 1 with powdered / granular dry or dehydrated wheat starch or rice starch as a dense mass 2, followed by densifying the mass 2 in the mould / container 1 (Figure 1a). For this purpose, the mass 2 filled in the mould / container 1 is densified, for example by applying an additional load to a plate resting on the mass 2 by means of a weight, generating a uniform pressure acting on the mass 2, or by vibration (for example with a vibrating plate or another vibrating device), or by shaking the mould / container, or by violent impacts acting on the mass 2 from the side or from below, for example by striking the mould / container 1, resulting in a dense mass 2.

[0031] Alternatively, the wheat starch or corn starch may be mixed with a binder.

[0032] As binders for the preparation of the mixture, in particular sugars or oils, such as edible oils, are suitable.

[0033] It is also possible to mix further graphitizable materials into the mass 2 made from wheat starch or rice starch and sugar or oil (edible oil).

[0034] Further graphitizable materials include, for example, high temperature resistant polymers, carbon black, graphite dust, natural graphite, and PVA (polyvinyl alcohol) adhesive.

[0035] Finally, natural fiber materials such as cotton, cellulose, bamboo, hemp, etc. may also be incorporated.

[0036] The dense or densified mass 2 in the filled mould / container 1 is then heated in a furnace to a first temperature level between 170° C. and 450° C. in an oxidizing or inert atmosphere or at >170° C., causing a shrinkage process and stabilising the mass 2 in the mould / container 1 for a longer time, whereby the stabilisation takes place for a period of >1 hour depending on the amount of mass 2. FIG. 1b shows the at least partially carbonised mass 3 after the first heat treatment and FIG. 3 shows a different view of the at least partially carbonised mass 3 after removal from the mould / container 1.

[0037] Alternatively, the shrinkage process can also be effected by rapid heating of the dense mass 2 to a starting temperature of about 190°C, followed by a cooling process over several hours, and slower and successive re-heating of the dense mass to 210-230°C.

[0038] The shrinkage process can best be effected by slow heating in stages to about 180°C and 230°C.

[0039] The mold / container 1 may be made of a heat-resistant thermoplastic or other material to allow easy removal of the stabilized mass 3, or the inside of the mold / container 1 may be covered with a fabric 4 before filling with the mass (Figure 2).

[0040] In a next step, the at least partially carbonized mass 3 is heated in a furnace in a heating gradient to a second temperature level of >1,000° C. for carbonization or >2,500° C. for graphitization under protective gas to form a blank 5 that is as dense as possible, which can then be removed from the mold / container 1. Protective gases include the noble gases helium, neon, argon, krypton, xenon and radon. In principle, N2 can also be used.

[0041] Of course, the blank 5 can also be removed from the mould / container 1 and subjected to a heat treatment in a furnace even before carbonisation / graphitisation.

[0042] The heating gradient for carbonization or graphitization of the blank 5 should be, for example, about 1° C. / min or less, and between each 50-100° C. step a pause of about 30-120 min should be introduced, so that the material relaxes and at the same time gases, e.g. air or water vapor, can diffuse out without damaging the structure. Carbonization or graphitization is preferably carried out at a pressure of >500 mbar.

[0043] Of course, other gradients are possible depending on the amount of blank.

[0044] FIG. 4 shows blank 5 after heat treatment for about 3 hours with a heating ramp of 1° C. / min, stopping at 200° C., 300° C., 400° C., 500° C. for 120 minutes each, and a final temperature of 1,600° C.

[0045] FIG. 5 shows the blank 5 of FIG. 4 finished as a compact 6 after it has been mechanically worked by cutting on both sides (outer and inner).

[0046] The graphite blank 5 produced according to the invention can also be converted to SiC without any problems. The conversion to SiC can be carried out, as is customary, in a furnace at temperatures >1200° C. and at a pressure of 30 mbar under a supply of SiO with argon as carrier gas. The preferred temperature for this process is 1520° C.

[0047] Conversion to SiC can also be carried out under high pressure, for example at 950 mbar. The actual pressure used will affect the uniformity and rate of conversion.

[0048] In principle, it is also possible to additionally supply a carbon-containing gas during carbonization / graphitization in a furnace, so that the shaped body 6 is densified even further.

[0049] Method for producing porous carbon or graphite [Explanation of symbols]

[0050] Code List 1 type / container 2 Dense mass 3 Carbonized mass 4 Fabric 5 Blank 6 Molded body

Claims

1. A simple method for producing porous carbon or graphite having a uniform, hard structure for use as a building component, mold, or container, comprising: - filling the mould / container (1) with powdered dry or desiccated wheat starch, corn starch, rice starch or other starch, - generating a dense mass (2) in a mould / container (1) by compressing / densifying the mass (2) in the container (1) by applying a constant or impulse pressure to the mass (2); - heating the dense mass (2) in said filled mould / container (1) in a furnace to a first temperature level between 170°C and 450°C in steps of 5°C with waiting times between each step, in an oxidizing or inert atmosphere, while further compressing / densifying the mass (2), thereby causing a shrinkage process; - stabilizing the heated mass (2) for a period of more than 1 hour; - slowly further heating the mass (2) in a furnace under protective gas with a temperature gradient of 1°C / min to a second temperature level of >1,000°C for carbonization or >2,500°C for graphitization to form a blank (5) that is as dense as possible; - removing the compact blank (5) from the mould / container, The manufacturing method is characterized by:

2. A simple method for producing porous carbon or graphite having a uniform, hard structure for use as a building component, mold, or container, comprising: - filling the mould / container (1) with powdered dry or desiccated wheat starch, corn starch, rice starch or other starch, - generating a dense mass (2) by compressing / densifying the mass (2) in the container (1) by applying a constant or impulsive pressure to the mass (2); - heating said dense mass (2) to a starting temperature of 190°C, followed by a cooling process over a period of more than one hour, and successively re-heating the dense mass (2) to 210-230°C while further compressing / densifying said mass (2), thereby causing a shrinkage process; - stabilizing the heated mass (2) for a relatively long period of time, greater than 1 hour; - slowly further heating the mass (2) in a furnace under protective gas with a temperature gradient of 1°C / min to a second temperature level of >1,000°C for carbonization or >2,500°C for graphitization to form a blank (5) that is as dense as possible; - removing the compact blank (5) from the mould / container, The manufacturing method is characterized by:

3. 3. The method according to claim 1 or 2, characterized in that wheat starch or rice starch is mixed with sugar or oil as a binder.

4. 3. The method according to claim 1 or 2, characterized in that the wheat starch or rice starch or the mixture of wheat starch or rice starch with sugar or oil is further mixed with another graphitizable material.

5. 5. The method of claim 4, wherein the additional graphitizable material is a mixture of high temperature resistant polymer, carbon black, graphite dust, natural graphite, and polyvinyl alcohol adhesive.

6. 3. A method according to claim 1 or 2, characterized in that the wheat or corn starch or mixture is mixed with natural fibre material.

7. 3. The method according to claim 1 or 2, characterized in that the compression / densification of the mass (2) filled in the mold / container (1) is carried out by generating a constant pressure acting on the mass (2), or by vibrating or shaking the mold / container (1), or by violent impacts acting on the mass (2) from the side or from below.

8. 3. The method according to claim 1 or 2, characterized in that the heating of the mass (2) for carbonization is carried out in stages, with a pause of 30 to 120 minutes being introduced between each stage of 50 to 100 ° C.

9. 3. The method according to claim 1, wherein the protective gas is one of the rare gases helium, neon, argon, krypton, xenon or radon.

10. 3. The method according to claim 1 or 2, characterized in that the carbonization or graphitization is carried out at a pressure of >50,000 Pa.

11. 3. The method according to claim 1 or 2, characterized in that a mould / container (1) made of Teflon is used and / or the inside of the mould / container (1) is covered with a fabric (4) before filling with the mass.

12. 3. A method according to claim 1 or 2, characterized in that the blank (5) made of graphite, manufactured according to the invention, is converted into SiC in a furnace at a temperature of >1,200 ° C and a pressure of 3,000 Pa while feeding SiO with argon as carrier gas.

13. 13. The method of claim 12, wherein the conversion to SiC is carried out at a temperature of 1,520°C.

14. The method according to claim 1 or 2, characterized in that during the carbonization or graphitization in the furnace, a carbon-containing gas is additionally supplied.

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