EP4426662A1 - Method for producing carbonised or graphitised 3d objects - Google Patents

Abstract

The invention relates to a method for producing carbonised or graphitised 3D objects which aims to realise such 3D objects particularly simply, and by means of which more complex 3D objects can also be produced without faults in the structure. This is achieved by mixing a carbonisable or graphitisable material with a free-flowing organic adhesive or a free-flowing thermoplastic organic substance to produce a kneadable, largely dimensionally stable compound and shaping the compound into a 3D blank, and by a subsequent drying and degassing process at an increased temperature over a predetermined period of time and subsequent carbonising or graphitising of the 3D blank in a furnace in a protective gas atmosphere to produce a 3D object, the temperature necessary for carbonising or graphitising being approached with a low heating gradient.

Description

Process for the production of carbonized or graphitized 3D objects

The invention relates to a method for producing carbonized or graphitized 3D objects.

Such carbonized or graphitized 3D objects, which are also suitable for high-temperature applications, can be various components, such as linings for furnaces, structural components or any type of hollow body, container or crucible.

Since the 3D objects cannot be made by simply molding carbon black or graphite and then sintering, a suitable carbonaceous and malleable mass must generally be made. For this purpose, it is customary to mix carbon black, coke or graphite in the form of granules with a suitable binder, such as a thermoplastic binder. Pitch based on coal tar or petroleum pitch, or even synthetic resins, can also be considered as binders.

These mixtures are then formed into a green shape by pressing and baked in an oven at about 3°C. 000 ° C carbonized or graphitized , whereby the binder decomposes into volatile components . Carbon and binder coke remain as remnants of the binder in the form of a porous structure.

Alternatively, the green molded part can also be arranged as a resistance element in a furnace between electrodes and heated by current flow.

The difficulty in carbonizing or graphitizing a such a molded part is that at the high temperatures required here, volatile substances outgas more or less violently, which can lead to disruptions in the structure, such as cracks or gas inclusions.

The object of the invention is to create a method for producing carbonized or graphitized 3D objects which is particularly easy to implement and which also allows more complex 3D objects to be produced without disrupting the structure.

This is achieved by producing a kneadable, largely dimensionally stable mass consisting of a carbonizable or graphitizable material and a flowable organic adhesive, or a flowable thermoplastic organic material and shaping the mass into a 3D blank, followed by a drying and outgassing process at elevated temperature and subsequent carbonization or graphitization of the 3D blank in a furnace under vacuum or inert gas to produce a 3D object , whereby the temperature required for carbonizing or graphitizing is approached with a low heating ramp.

Carbon black, graphite dust, natural graphite, cellulose or corn starch, or a mixture of some or all of these materials, preferably comes into consideration as carbonizable or graphitizable material.

In order to influence the strength or porosity of the 3D object to be produced, bamboo, cotton, hemp, sisal or graphite fibers can be added to the carbonizable or graphitizable material while retaining the kneadability be mixed in.

In a first embodiment, the 3D blank is shaped by hand using suitable templates.

In a special embodiment, the 3D blank is produced by molding in a mold.

Argon or helium is preferably used as the protective gas.

Alternatively, after the drying process, the 3D blank can be subjected to a stabilization and homogenization process at a stabilization temperature of 170°C in air or up to a maximum of 450°C in air, with a temperature of 250°C being preferred, so that a 3D molded part arises.

In principle, the stabilization and homogenization process can also be carried out under an inert gas such as argon.

The 3D blank can also be stabilized and homogenized while the furnace is being heated up.

In a further development of the invention, the 3D shaped part is carbonized at a constant temperature of approx. 1,000° C. to form a 3D object until pure carbon with a different crystal structure is formed.

In another development of the invention, the 3D molded part is graphitized at a constant temperature of 2,000° C. and above.

Finally, the 3D molded part can be fully graphitized at a temperature of over 2,500°C. The graphitization preferably takes place with a heating ramp of about 1° C./min until the target temperature has been reached, followed by tempering over approx. 30 min, depending on the size of the 3D molded parts.

In a particular embodiment of the invention, a metal or silicon powder can be added to the kneadable mass, so that during a high-temperature treatment of the 3D molded part at >1. 000 °C under protective gas metal carbides or silicon carbides can be formed.

The graphitized foamy 3D objects can also be baked in an oven at a temperature of >1. 200 ° C with supply of gaseous SiO with argon as carrier gas at a pressure of approx . 30 mbar can be converted into 3D objects made of SiC.

The invention is explained in more detail below using an exemplary embodiment.

In a first process step, a kneadable, largely dimensionally stable mass is produced by mixing a carbonizable or graphitizable material with a free-flowing organic adhesive, or a flowable thermoplastic organic material, followed by molding the mass into a 3D blank. The 3D blank is then freed from moisture and gas inclusions in particular in a drying and outgassing process at elevated temperature and thereby converted into a 3D molded part. This can prevent cracks from forming during the subsequent carbonization or graphitization of the 3D molded part in a furnace under vacuum or inert gas, such as argon or helium, to produce a 3D object be avoided.

Carbon black, graphite dust, natural graphite and starch, e.g. corn or potato starch or the like, or a mixture of some or all of these materials can preferably be used as carbonizable or graphitizable organic material.

To influence the strength or porosity of the finished carbonized or graphitized 3D object, the carbonized or graphitizable organic material can be supplemented with bamboo, cotton, hemp, sisal, or other suitable vegetable fibers, or graphite fibers while maintaining the clay Ability to be blended, adding more flowable adhesive or flowable organic if necessary, until the desired consistency is achieved.

The 3D blank can be shaped by hand, for example using templates, or by shaping in a mold, with the 3D blank being removed from the mold before the drying process. A mold made of Teflon, silicone or another material with limited elasticity can be used to enable easier demolding of the 3D blank.

Alternatively, the 3D molded part can be subjected to the drying process at room temperature or at a maximum of 100°C in order to remove any water present. In a subsequent stabilization and homogenization process at a stabilization temperature of 140°C in air or up to a maximum of 450°C, under protective gas or vacuum, with a temperature of 250°C being preferred, a Outgassing to avoid cracking during later carbonization or graphitization.

It goes without saying that the 3D molded part can remain in a suitable shape during the stabilization or homogenization process.

The 3D molded part can also be stabilized and homogenized while the furnace is being heated up.

It is necessary to stabilize the 3D molded part in order to prevent it from being destroyed during carbonization/graphitizing, since the 3D molded part could otherwise melt or become severely deformed. During stabilization, the atoms/molecules reorganize to survive the high temperature process.

In a further development, the 3D molded part is heated at a constant temperature of approx. 1 . 000 ° C to a 3D object carbonized in the oven until pure carbon with different crystal structure is formed.

In another development of the invention, the 3D molded part is then formed at a constant temperature to form a 3D object from 2 . 000 ° C graphitized in the furnace .

Finally, the 3D molded part can be processed at a temperature above 2 . 500 ° C to form a 3D object in the furnace to be fully graphitized.

It goes without saying that the carbonization or graphitization in the furnace must be carried out under protective gas in order to avoid burning the organic components of the 3D blanks. If the carbonization or graphitization takes place under vacuum, which is possible in principle, there is a risk that the volatile components will be accelerated by the pressure difference between the inside of the 3D molded part and the vacuum, which can cause cracks.

For this reason, it is advantageous to provide high pressure in the oven so that the volatile components slowly diffuse out, so that cracks and bridges can be reliably avoided.

The carbonization or graphitization preferably takes place with a heating ramp of about 1° C./min until the target temperature has been reached, followed by tempering over approx. 30 min, although tempering for several hours is also possible.

In order to achieve uniform carbonization or graphitization, it makes sense to demold the 3D molded part beforehand.

In a particular embodiment of the invention, a metal or silicon powder can be added to the kneadable mass, so that during a high-temperature treatment of the 3D molded part at >1. 000 °C under protective gas metal carbides or silicon carbides can be formed.

The graphitized foamy 3D objects can also be baked in an oven at a temperature of >1. 200 ° C with supply of gaseous SiO with argon as carrier gas at a pressure of approx . 30 mbar can be converted into 3D objects made of SiC.

Claims

Method for producing carbonized or graphitized 3D objects, characterized by mixing a carbonizable or graphitizable material made of carbon black, graphite dust, natural graphite, cellulose or corn starch or a mixture of some or all of these materials with a free-flowing organic adhesive, or . a free-flowing thermoplastic organic substance into a kneadable, dimensionally stable mass and shaping the mass into a 3D blank using a mold made of Teflon or silicone and removing the 3D blank from the mold through a subsequent drying and outgassing process at room temperature or at a maximum of 100 °C for a specified period of time, followed by a stabilization and homogenization process at a temperature of 140 °C to a maximum of 450 °C and subsequent carbonization or graphitization of the 3D blank in a furnace under a protective gas atmosphere to produce a 3D object The temperature required for carbonizing or graphitizing is approached with a heating ramp of 1° C./min, followed by tempering. The method according to claim 1, characterized in that the carbonizable or graphitizable material under bamboo, cotton, hemp, sisal or graphite fibers 9 be added to maintain kneading ability. Method according to Claims 1 and 2, characterized in that the 3D blank is shaped by hand and/or with the aid of templates. Method according to Claim 3, characterized in that the 3D blank is stabilized and homogenized while the furnace is being heated up. Method according to one of Claims 1 to 4, characterized in that the 3D shaped part is carbonized at a constant temperature of 1,000°C to form a 3D object in a vacuum or inert gas until pure carbon with a different crystal structure is produced. Method according to one of Claims 1 to 5, characterized in that the 3D shaped part is graphitized in a furnace at a constant temperature of 2,000°C and above in a vacuum or inert gas to form a 3D object. Method according to Claim 6, characterized in that the 3D shaped part is fully graphitized in a furnace at a temperature of over 2,500°C in a vacuum or inert gas to form a 3D object. Method according to one of Claims 1 to 7, characterized in that argon or helium is used as the protective gas. 10 Method according to claim 7 and 8, characterized in that the graphitization of the 3D molded part has been reached with a heating ramp of about 1°C/min until the target temperature is reached, followed by tempering for about 30 minutes to several hours. Method according to one of Claims 1 to 9, characterized in that a metal or silicon powder is added to the kneadable mass, so that a high-temperature treatment of the 3D blank at > 1,000°C in a furnace under protective gas results in a 3D molded part consisting of metal carbides or silicon carbides will be produced . The method according to any one of claims 1 to 10, characterized in that the graphitized foamy 3D objects in an oven at a temperature of> 1,200 ° C with supply of gaseous SiO with argon as carrier gas at a pressure of 30 mbar in 3D objects SiC are converted.