Method and composition for producing three-dimensional objects comprising silicon carbide
阅读说明：本技术 用于生产包含碳化硅的三维物体的方法和组合物 (Method and composition for producing three-dimensional objects comprising silicon carbide ) 是由 西格蒙德·格罗伊利希-韦伯 鲁迪格·施莱歇-塔佩瑟尔 于 2018-05-09 设计创作，主要内容包括：本发明涉及一种通过增材制造来生产三维物体、特别是工件的方法,该三维物体由含碳化硅的化合物、特别是含碳化硅的材料制成。(The invention relates to a method for producing a three-dimensional object, in particular a workpiece, made of a compound containing silicon carbide, in particular a material containing silicon carbide, by additive manufacturing.)
1. Method for producing three-dimensional objects, in particular workpieces, from compounds containing silicon carbide by additive manufacturing,
it is characterized in that
The silicon carbide containing compound is obtained from the precursor particles by a selective, in particular site-selective, energy input.
2. The method according to claim 1, characterized in that the precursor particles are obtainable from a precursor solution or precursor dispersion, in particular a precursor sol.
3. The method according to claim 1 or 2, characterized in that the precursor particles comprise particles having a particle size of 0.1 to 150 μ ι η, in particular 0.5 to 100 μ ι η, preferably 1 to 100 μ ι η, more preferably 7 to 70 μ ι η, particularly preferably 20 to 40 μ ι η.
4. Method according to any one of the preceding claims, characterized in that the particles of the precursor particles have a D60 value of 1 to 100 μ ι η, in particular 2 to 70 μ ι η, preferably 10 to 50 μ ι η, more preferably 21 to 35 μ ι η.
5. A method according to any of the preceding claims, characterized in that the silicon carbide containing compound is selected from non-stoichiometric silicon carbide and silicon carbide alloys.
6. Method according to any one of the preceding claims, characterized in that the energy input is effected by means of radiant energy, in particular by means of laser radiation.
7. Method according to claim 6, characterized in that the energy input is effected with a resolution of 0.1 to 150 μm, in particular 1 to 100 μm, preferably 10 to 50 μm.
8. Method according to any of the preceding claims, wherein the manufacturing method, in particular additive manufacturing, comprises selective synthetic crystallization.
9. The method according to any of the preceding claims,
(a) in a first method step, the precursor particles are provided in the form of a layer, in particular in the form of a film,
(b) in a second method step following the first method step (a), the precursor particles are converted into a compound containing silicon carbide under the influence of energy, in particular at least in certain regions, so that a layer of the three-dimensional object is formed, and
(c) in a third method step following the second method step (b), a further layer, in particular a film, of precursor particles is applied to the layer of precursor particles which was in particular at least partially converted in the second method step (b),
wherein method steps (b) and (c) are repeated until the three-dimensional object is completed.
10. The method according to claim 9, characterized in that the thickness of the layer of precursor particles, in particular the thickness of the film, is 1 to 1,000 μ ι η, in particular 2 to 500 μ ι η, preferably 5 to 250 μ ι η, more preferably 10 to 180 μ ι η, particularly preferably 20 to 150 μ ι η, most preferably 20 to 100 μ ι η.
11. A composition, in particular in particulate form, preferably precursor particles, comprising:
at least one silicon source
At least one carbon source, and
optionally, precursors of alloying elements.
12. The composition of claim 11 wherein the silicon source is selected from the group consisting of silane hydrolysates and silica and mixtures thereof.
13. The composition of claim 11 or 12, wherein the carbon source is selected from the group consisting of: sugars, in particular sucrose, glucose, fructose, invert sugar, maltose; starch; starch derivatives and organic polymers, in particular phenolic resins, resorcinol-formaldehyde resins, and mixtures thereof, in particular sugars, preferably sucrose and/or invert sugar, and/or reaction products thereof.
14. Composition according to any one of claims 11 to 13, characterized in that it is obtainable from a precursor solution, in particular by a sol-gel process.
15. The composition according to any one of claims 11 to 14, characterized in that the composition is converted into a reduced composition by heat treatment under reducing conditions.
16. Use of a composition according to any one of claims 11 to 15 for producing three-dimensional objects containing silicon carbide, in particular by a generative manufacturing process.
17. A process for the preparation of a composition, in particular precursor particles,
(i) in a first method step, a solution or dispersion, in particular a sol, is prepared, which comprises
(I) At least one silicon-containing compound,
(II) at least one carbon-containing compound,
(III) at least one solvent or dispersant, and
(IV) optionally, doping and/or alloying agents,
(ii) in a second process step after the first process step (i), the solution or dispersion is reacted, in particular aged to gel, and
(iii) in a third process step following the second process step (ii), the reaction product from the second process step (ii), in particular the gel, is dried and optionally comminuted.
18. Three-dimensional object comprising silicon carbide obtainable by the method according to any one of claims 1 to 10 and/or by using the composition according to any one of claims 11 to 16.
Technical Field
The present invention relates to the field of generative manufacturing methods, in particular additive manufacturing.
In particular, the present invention relates to a method for producing a three-dimensional object from a compound comprising silicon carbide, and a composition, in particular precursor particles, for producing a three-dimensional object comprising silicon carbide.
Furthermore, the invention relates to the use of the composition for producing three-dimensional objects containing silicon carbide.
Furthermore, the present invention relates to a method for producing a composition, in particular a precursor particle.
Finally, the invention relates to a three-dimensional object comprising silicon carbide.
Background
Generative manufacturing methods, also known as Additive Manufacturing (AM), are methods for rapidly producing models, patterns, tools and products from amorphous materials such as liquids, gels, pastes or powders.
Initially, production manufacturing methods, in particular additive manufacturing, are commonly referred to as 3D printing or rapid prototyping. However, these terms are now used only for a particular type of production method. The generative manufacturing methods are used both for manufacturing objects from inorganic materials, in particular metals and ceramics, and for manufacturing objects from organic materials.
Preferably, high-energy methods such as selective laser melting, electron beam melting or bead welding are used for producing objects made of inorganic materials, since the reactants or precursors used react or melt only at relatively high energy inputs.
In principle, additive manufacturing can quickly produce highly complex components, but producing parts from inorganic materials in particular presents many challenges for both raw and product materials: for example, the starting materials or reactants should react in a predetermined manner only under the influence of energy, and interfering side reactions must be excluded in particular. Furthermore, for example, under the influence of energy, no separation of the product or phase separation or decomposition of the product takes place.
For ceramic materials and semiconductor applications, a very interesting and widely used material is silicon carbide, also known as silicon carbide. Silicon carbide of the formula SiC has an extremely high hardness and a high sublimation point, and is often used as an abrasive or an insulator in a high-temperature reactor. Silicon carbide also forms alloys or alloy-like compounds with a variety of elements and compounds, which have a variety of advantageous material properties, such as high hardness, high resistance, low weight, and low oxidation sensitivity, even at high temperatures.
Silicon carbide containing materials are typically sintered at high temperatures, resulting in relatively porous objects that are only suitable for limited applications.
The properties of porous silicon carbide materials produced by conventional sintering processes do not correspond to those of dense crystalline silicon carbide, and thus the advantageous properties of silicon carbide cannot be fully utilized.
In addition, silicon carbide (depending on the type of crystal) does not melt, but sublimes at high temperatures between 2300 and 2700 ℃, i.e. it changes from a solid to a gaseous aggregate. This makes silicon carbide particularly unsuitable for additive manufacturing processes such as laser melting.
Nevertheless, due to the versatility and numerous beneficial application characteristics of silicon carbide, attempts have been made to process silicon carbide using generative manufacturing processes.
For example, german patent application DE 102015105085 a1 describes a method for producing an object from a silicon carbide crystal, wherein the silicon carbide is obtained in particular by laser irradiation from suitable carbon-and silicon-containing precursor compounds. When a laser beam is applied, the precursor compounds selectively decompose and form silicon carbide, without the silicon carbide subliming.
Although the process described in DE 102015105085 a1 is very suitable for obtaining objects from silicon carbide crystallites, there is still a lack of processes and suitable starting compounds for producing a variety of different silicon carbide-containing compounds. In particular, it has not been possible to manufacture three-dimensional objects comprising silicon carbide by additive manufacturing with suitably selected reactants, the mechanical properties of which may be particularly suitable for the respective application purpose.
Disclosure of Invention
It is therefore an object of the present invention to avoid or at least reduce the disadvantages and problems associated with the above-mentioned prior art.
In particular, it is an object of the present invention to provide a method which allows producing a three-dimensional object comprising silicon carbide by additive manufacturing, wherein the properties of the silicon carbide containing material are adapted to the respective application purpose.
It is another object of the present invention to provide suitable precursor materials that can be easily and universally processed into desired silicon carbide containing compounds, particularly high performance ceramics and silicon carbide alloys.
The subject of the invention according to a first aspect of the invention is a method for producing three-dimensional objects from silicon carbide containing compounds according to
Another subject of the invention according to the second aspect of the invention is a composition, in particular a precursor particle, according to
Likewise, another subject of the invention is the use of a composition according to claim 16.
Another subject of the invention according to a fourth aspect of the invention is a process for producing a composition according to claim 17.
Finally, according to a fifth aspect of the invention, another subject of the invention is a three-dimensional object comprising silicon carbide according to claim 18.
It is to be understood that the specific features mentioned below, in particular the embodiments and the like, which are described with respect to only one aspect of the invention, also apply to the other aspects of the invention without any explicit mention.
Furthermore, for all relative values or percentages (in particular relative values or percentages related to weight), amounts or contents described below, it is to be noted that, within the framework of the present invention, they should be selected by the person skilled in the art in such a way that: the sum of the constituents, additives or auxiliary substances etc. always amounts to 100% or 100% by weight. However, this is self-evident to the person skilled in the art.
In addition, the skilled person can deviate from the values, ranges or numbers listed below depending on the application and individual case without departing from the scope of the invention.
In addition, all the parameters and the like specified below can be determined by a standardized or explicitly specified determination method or by a general determination method known per se to those skilled in the art.
Under such conditions, the subject of the present invention will be explained in more detail below.
Therefore, according to a first aspect of the invention, the subject of the invention is a method for producing a three-dimensional object, in particular a workpiece, from a silicon carbide-containing compound by additive manufacturing, wherein the silicon carbide-containing compound is obtained from precursor particles by selective, in particular site-selective, energy input.
The method according to the invention allows in particular the simple production of virtually any silicon carbide-containing material, in particular from non-stoichiometric silicon carbide to silicon carbide-containing alloys for high-performance ceramics.
The invention also allows the creation of high resolution and detailed three-dimensional structures, i.e. the course of the edges is highly accurate, in particular free of burrs. Within the scope of the invention, it is also possible to obtain dense solids which do not have a porous structure but consist of a material containing crystalline silicon carbide. Thus, the materials and three-dimensional objects usable in the method of the present invention have almost the same material characteristics as the crystalline silicon carbide compound.
By using a generative manufacturing method, it is also possible within the scope of the invention to produce three-dimensional structures in a support structure, in particular in a powder bed method. In particular, precursor particles which have not been exposed to an energetic effect (in particular laser radiation) can still be used, i.e. the process according to the invention can be carried out almost without unwanted residual material. In particular, the method according to the invention allows for a very fast and low cost production of three-dimensional silicon carbide containing objects and in particular provides for a compact non-porous or less porous material without the need for applying pressure.
In the context of the present invention, a silicon carbide-containing compound is a binary, ternary or quaternary inorganic compound, the empirical formula of which comprises silicon and carbon. In particular, the compound comprising silicon carbide does not comprise molecularly bonded carbon, such as carbon monoxide or carbon dioxide. Instead, the carbon exists in a solid structure.
In the context of the present invention, it is particularly desirable that the precursor particles are not a powder mixture, in particular not a mixture of different precursor powders and/or particles. A particular feature of the method of the invention is the use of homogeneous particles, in particular precursor particles, as a raw material for additive manufacturing. In this way, the precursor particles can be transferred into the gas phase, or the precursor compounds can be reacted to the desired target compounds by short-term exposure to energy, in particular laser radiation. Thus, individual particles of different inorganic substances having a particle size in the μm range do not have to be sublimated and then their components do not have to be diffused to form the corresponding compounds and alloys. The homogeneous precursor particles used within the scope of the present invention ensure that the individual components (in particular the elements) of the target silicon carbide-containing compound are distributed homogeneously and arranged next to one another, i.e. less energy is required for producing the silicon carbide-containing compound.
According to a preferred embodiment of the present invention, the precursor particles are obtainable from a precursor solution or precursor dispersion, in particular a precursor sol. The precursor particles are therefore preferably obtained from finely divided liquids, in particular from solutions or dispersions, preferably using the sol-gel process. In this way, a homogeneous distribution of the individual components, in particular of the precursor compounds, can be achieved in the particles, whereby the stoichiometry of the silicon carbide-containing material to be produced has preferably been formed beforehand.
The conversion to the target compound can occur in a number of different ways. However, it is advantageous if the precursor compound is cleaved under the action of energy, in particular under the action of a laser beam, and is transferred into the gas phase as reactive particles. Sublimed silicon carbide or doped silicon carbide or silicon carbide alloys are deposited at 2300 c, since the particular composition of the precursor ensures that silicon and carbon, and any dopant or alloying element, are in close proximity in the gas phase. In particular crystalline silicon carbide absorbs much worse laser energy than the precursor particles and conducts heat very well, so that locally well defined deposits of silicon carbide compounds occur. On the other hand, the undesired components of the precursor compounds form stable gases, e.g. CO2，HCl，H2O, etc., which can be removed by gas phase.
If the precursor particles are obtainable from a solution or dispersion, in particular a gel, the precursor particles are obtained by drying the precursor solution or dispersion or the resulting gel.
As far as the particle size of the precursor particles is concerned, they can vary within wide limits, depending on the respective chemical composition, the laser energy used and the nature of the object or material to be produced. However, the particle diameter of the precursor particles is generally from 0.1 to 150. mu.m, in particular from 0.5 to 100. mu.m, preferably from 1 to 100. mu.m, more preferably from 7 to 70 μm, particularly preferably from 20 to 40 μm.
Particularly good results are obtained in the present invention if the precursor particles have a D60 value of 1 to 100. mu.m, in particular 2 to 70 μm, preferably 10 to 50 μm, more preferably 21 to 35 μm. The D60 value for the particle size represents the limit below which 60% of the precursor particles have a particle size, i.e. 60% of the precursor particles have a particle size less than the D60 value.
In this case, it is also conceivable that the precursor particles have a bimodal particle size distribution. In this way, particularly high bulk density precursor particles can be obtained.
As already explained above, the method of the invention is suitable for producing a wide range of compounds containing silicon carbide. In the context of the present invention, the silicon carbide containing compound is typically selected from the group consisting of non-stoichiometric silicon carbide and silicon carbide alloys. In the context of the present invention, a non-stoichiometric silicon carbide compound means a compound which does not contain a silicon carbide compound in a molar ratio of 1:1 carbon and silicon but silicon carbide containing different proportions of carbon and silicon. Generally, in the context of the present invention, non-stoichiometric silicon carbide shows a molar excess of silicon.
In the context of the present invention, silicon carbide alloys refer to silicon carbide compounds and metals (e.g. titanium) or other compounds (e.g. zirconium carbide or boron nitride) comprising silicon carbide in different and strongly varying proportions. Silicon carbide alloys generally form high performance ceramics characterized by exceptional hardness and heat resistance.
The process of the invention can therefore be used universally and is suitable for producing a large number of different silicon carbide compounds, in particular for adjusting their mechanical properties.
If a non-stoichiometric silicon carbide is obtained within the scope of the invention, the non-stoichiometric silicon carbide is generally a silicon carbide of the general formula (I)
SiC1-x(I)
Where x is 0.05 to 0.8, in particular 0.07 to 0.5, preferably 0.09 to 0.4, more preferably 0.1 to 0.3.
Such silicon-rich silicon carbide has a particularly high mechanical load-bearing capacity and is suitable for various applications as a ceramic.
If the silicon carbide containing compound obtained within the scope of the present invention is a silicon carbide alloy, the silicon carbide alloy is generally selected from the group consisting of MAX phases, alloys of silicon carbide with elements, especially metals, and alloys of silicon carbide with metal carbides and/or metal nitrides. Such silicon carbide alloys contain varying and highly fluctuating proportions of silicon carbide. In particular, silicon carbide may be the main component of the alloy. However, the silicon carbide alloy may contain only a small amount of silicon carbide.
In general, the silicon carbide alloy comprises silicon carbide in an amount of 10 to 95 wt.%, in particular 15 to 90 wt.%, preferably 20 to 80 wt.%, relative to the silicon carbide alloy.
In the context of the present invention, MAX phases are intended to mean in particular crystalline in hexagonal layers and having the general formula Mn+1AXnCarbides and nitrides of (n ═ 1 to 3). M represents an early transition metal of the third to sixth groups of the periodic Table, and A represents an element of the 13 th to 16 th groups of the periodic Table. X is carbon or nitrogen. However, in the context of the present invention, only MAX phases are of interest, the empirical formula of which comprises silicon carbide (SiC), i.e. silicon and carbon.
The MAX phases exhibit an unusual combination of chemical, physical, electrical and mechanical properties, since they exhibit both metallic and ceramic behavior depending on the conditions. This includes, for example, high electrical and thermal conductivity, high load capacity on thermal shock, very high hardness and low thermal expansion coefficient.
If the silicon carbide alloy is a MAX phase, then preferably the MAX phase is selected from Ti4SiC3And Ti3SiC。
In particular, the above-mentioned MAX phase, in addition to having the above-mentioned characteristics, has a high chemical and oxidation resistance at high temperatures.
If the silicon carbide containing compound is an alloy of silicon carbide, it has turned out that if the alloy is an alloy of silicon carbide and a metal, it is advantageous if the alloy is selected from the group consisting of alloys of silicon carbide and a metal selected from the group consisting of Al, Ti, V, Cr, Mn, Co, Ni, Zn, Zr and mixtures thereof.
It has been well documented that alloys of silicon carbide and metal carbides and/or metal nitrides are selected from especially B if the alloy of silicon carbide is selected from alloys of silicon carbide and metal carbides and/or metal nitrides4Boron carbide of C, especially Cr2C3Of chromium carbide, in particular of TiC, in particular of Mo2Molybdenum carbide of C, in particular NbC niobium carbide, in particular TaC tantalum carbide, in particular VC vanadium carbide, in particular ZrC zirconium carbide, in particular WC tungsten carbide, in particular BN boron nitride, and mixtures thereof.
For the implementation of the process according to the invention, it has proven successful to carry out the process under a protective gas atmosphere, in particular under a nitrogen and/or argon atmosphere, preferably under an argon atmosphere. The process according to the invention is generally carried out in a protective gas atmosphere, so that in particular the carbon-containing precursor compounds are not oxidized. If the process is carried out in an argon atmosphere, it is usually also an inert gas atmosphere, since argon does not react with the precursor compounds under the process conditions. If nitrogen is used as the protective gas, silicon nitride may also be formed. For example, it may be desirable for silicon carbide to be additionally doped in admixture with nitrogen.
However, if it is not desired to incorporate nitrogen into silicon carbide or silicon carbide-containing compounds, the process according to the invention is carried out in an argon atmosphere.
With regard to the temperature at which the process according to the invention is carried out, it has proven successful to heat the precursor particles at least in certain regions by inputting energy to a temperature of 1600 to 2100 ℃, in particular 1700 to 2000 ℃, preferably 1700 to 1,900 ℃. At the above temperatures, all precursor components enter the gas phase and the precursor compounds decompose to the desired reactive species and then react to form the target compounds.
In the context of the present invention, it is generally desirable that the energy input is achieved by radiant energy, in particular by laser radiation.
With regard to the resolution of the energy introduced selectively in position, it has proven successful to carry out the energy input, in particular by laser irradiation, with a resolution of 0.1 to 150 μm, in particular 1 to 100 μm, preferably 10 to 50 μm. In this way, particularly high-contrast and sharply defined or fine objects can be produced from the precursor particles. The resolution of the input energy, particularly the laser beam, generally represents the lower limit of the resolution capability of the interface and details of the manufactured object. Alternatively, the energy input can also be site-selectively limited by using a mask. However, a laser beam is preferably used. The resolution of the energy input is to be understood as the minimum width of the energy input region. It is generally limited by the cross-sectional area of the laser beam or the size of the mask.
According to a particularly preferred embodiment of the invention, a laser melting system similar to Selective Laser Melting (SLM) is used: a method of Selective Synthetic Crystallization (SSC) to perform additive manufacturing. In Selective Synthesis Crystallization (SSC), the species are not produced from the melt, but from the gas phase. The equipment design and performance of selective synthetic crystallization corresponds to selective laser melting, i.e. under very similar conditions as selective laser melting, the same equipment can be used for selective synthetic crystallization. The energy required for transferring the starting material into the gas phase can be introduced into the precursor particles by means of laser radiation.
According to a preferred embodiment of the process according to the invention, the process is carried out as a multistage process. In this respect, particular plans are:
(a) in a first method step, the precursor particles are provided in the form of a layer, in particular in the form of a film,
(b) in a second method step following the first method step (a), the precursor particles are converted, in particular at least in certain regions, under the effect of energy into a compound containing silicon carbide, a three-dimensional object layer is produced, and
(c) in a third method step following the second method step (b), a further layer, in particular a thin film, of precursor particles is applied to the, in particular at least partially converted, layer of precursor particles in the second method step (b),
wherein method steps (b) and (c) are repeated until the three-dimensional object is completed. In particular, it is also desirable here to carry out step (b) after step (c).
The method according to the invention is therefore carried out in particular as a so-called powder bed method, in which a three-dimensional object to be produced is produced layer by layer from a powder by selective input of energy. For producing three-dimensional objects, a three-dimensional representation of the object to be produced is usually generated by means of computer technology, in particular as a CAD file, which is converted into corresponding layer attachments and then continuously (i.e. layer-by-layer) produced by additive manufacturing, in particular by selective synthetic crystallization. In this way, the finished three-dimensional object is finally obtained.
It can be seen as a particular feature of the method according to the invention that it works without a subsequent sintering step, i.e. that the precursors are selected within the scope of the invention and are in particular adapted to selectively synthesize crystals in such a way that homogeneous, compact three-dimensional objects are obtained directly from the gas phase, which objects do not have to be sintered.
All the above advantages, features and embodiments may be applied correspondingly to the above preferred embodiments of the invention; the advantages, features and specific embodiments described above may also be transferred in particular to the multistage process described above.
To the extent that the precursor particles are provided in a powder bed, this can be done with different layer thicknesses. However, in general, the layer (in particular the film) of precursor particles has a thickness, in particular a film thickness, of from 1 to 1,000 μm, in particular from 2 to 500 μm, preferably from 5 to 250 μm, more preferably from 10 to 180 μm, particularly preferably from 20 to 150 μm, most preferably from 20 to 100 μm. By the thickness of the layers, in particular the film thickness, in the previously mentioned regions for the precursor particles, fine three-dimensional objects with high resolution can be produced.
According to an alternative embodiment of the invention, the additive manufacturing of the silicon carbide containing object to be produced may be performed on a substrate (e.g. a carrier plate) or a complex shaped object, which is subsequently replaced by the silicon carbide containing object. Similarly, the base plate may also be constituted by a workpiece to which the additive manufactured object remains firmly attached. As such, other layers and structures may be applied to existing objects using the methods described herein. As a substrate or an existing object, a workpiece made of a material having a relatively high melting point and having a material structure that ensures relatively good bonding with silicon carbide is particularly suitable. For these applications, silicon carbide and silicon carbide containing compounds, ceramic materials and metals are the most suitable substrates. In this way, it is possible, for example, to manufacture objects from silicon carbide alloys with layers of different properties, or to apply a layer of material comprising silicon carbide to a metal, for example tool steel.
In order to apply precursors to complex substrates in a suitable manner and in particular to convert them with a laser into compounds containing silicon carbide, according to a preferred embodiment of the invention very small amounts of precursor particles (in particular particle jets) can be selectively applied using suitable means and immediately treated with a laser according to a method known as "build-up welding" in metal additive manufacturing.
Drawings
The figures show:
FIG. 1 is a cross-sectional view in the xy plane of an apparatus for carrying out the method according to the invention, an
FIG. 2 is an enlarged cross-sectional view of FIG. 1, particularly illustrating the three-dimensional object being produced.
Furthermore, according to a second aspect of the invention, the subject of the invention is a composition, in particular in the form of particles, preferably precursor particles, comprising:
at least one silicon source,
at least one carbon source, and
optionally, precursors of alloying elements.
In the context of the present invention, a silicon source or a carbon source refers to a compound that is capable of releasing silicon or carbon in a manner that forms a silicon carbide containing compound under the process conditions of the production method. In this case, silicon and carbon do not have to be released in elemental form, but it is sufficient if they react under the process conditions to form a compound containing silicon carbide.
As described below, the precursor of the silicon source, the carbon source or the alloying element may be a precursor compound used as it is, or may be, for example, a reaction product, particularly a hydrolysis product thereof.
In the context of the present invention, the silicon source is generally selected from silane hydrolysates and silica and mixtures thereof. In the context of the present invention, the silicon source, i.e. the precursor of silicon in the silicon carbide-containing compound, is obtained in particular by hydrolysis of tetraalkoxysilanes, so that the silicon in the precursor particles is preferably present in the form of silicic acid or a silane hydrolysate.
As carbon source, it is generally selected from the following group: sugars, in particular sucrose, glucose, fructose, invert sugar, maltose; starch; starch derivatives and organic polyols, in particular phenolic resins, resorcinol-formaldehyde resins, and mixtures and/or reaction products thereof, in particular sugars and/or reaction products thereof. Particular preference is given to a carbon source selected from sugars and reaction products thereof, preferably sucrose and/or invert sugar and/or reaction products thereof. Also, as the carbon source, not only the actual reagent but also the reaction product thereof may be used.
If the composition is used to produce non-stoichiometric silicon carbide, the composition typically comprises (each based on the composition):
(A) a silicon source in an amount of 60 to 90 wt.%, in particular 65 to 85 wt.%, preferably 70 to 80 wt.%, and
(B) a carbon source in an amount of 10 to 40 wt.%, particularly 15 to 35 wt.%, preferably 20 to 30 wt.%.
Compositions comprising the above amounts of carbon source and silicon source are excellent for reproducible production of non-stoichiometric silicon carbide with excess silicon.
If the composition is used to produce a silicon carbide alloy, the composition typically comprises (each based on the composition):
(A) a silicon source in an amount of 5 to 40 wt.%, in particular 5 to 30 wt.%, preferably 10 to 20 wt.%,
(B) a carbon source in an amount of 10 to 60 wt.%, in particular 15 to 50 wt.%, preferably 20 to 50 wt.%, and
(C) precursors of one or more alloying elements in an amount of 5 to 70 wt.%, in particular 5 to 65 wt.%, preferably 10 to 60 wt.%.
According to a preferred embodiment of the invention, the composition is obtainable from a precursor solution or precursor dispersion. In this case, it is particularly preferred that the composition is obtainable by a sol-gel process. In the sol-gel process, solutions or solid-liquid dispersions of fine particles are generally produced, which are converted into gels comprising larger solid particles as a result of subsequent ageing and corresponding condensation processes.
After drying of the gel, a particularly homogeneous composition can be obtained within the scope of the invention, in particular suitable precursor particles, with which, when a suitable stoichiometry is selected, the desired silicon carbide-containing compound can be obtained under the action of energy in additive manufacturing.
According to a particular embodiment of the invention, it is intended to convert the composition into a reduced composition by means of a heat treatment under reducing conditions. The reducing heat treatment is usually carried out in an inert gas atmosphere, in which, in particular, a carbon source, preferably a sugar-based carbon source, reacts with oxides or other compounds of silicon and possibly other compounds of other elements, whereby the elements are reduced to form volatile oxygenated carbon and hydrogen compounds, in particular water and CO2And then removed by gas phase.
For further details of the composition according to the invention, reference is made to the above description relating to the process of the invention, which applies accordingly to the composition of the invention.
According to a third aspect of the invention, another subject of the invention is the use of the aforementioned composition in the production of three-dimensional objects containing silicon carbide, in particular by generative manufacturing methods, preferably additive manufacturing.
For further details of the use of the invention, reference is made to the above description of other aspects of the invention, which are correspondingly applicable to the use of the invention.
According to a fourth aspect of the invention, another object of the invention is a process for preparing a composition, in particular precursor particles, wherein
(i) In a first method step, a solution or dispersion, in particular a sol, is prepared, which comprises:
(I) at least one silicon-containing compound,
(II) at least one carbon-containing compound,
(III) at least one solvent or dispersant, and
(IV) optionally, an alloying agent,
(ii) in a second process step after the first process step (i), the solution or dispersion is reacted, in particular aged to gel, and
(iii) in a third process step following the second process step (ii), the reaction product from the second process step (ii), in particular the gel, is dried and optionally comminuted.
In the context of the present invention, a solution refers to a single-phase system in which at least one substance, in particular a compound or a structural unit thereof (e.g. an ion), is homogeneously distributed in another substance. In the context of the present invention, a dispersion is understood to mean an at least biphasic system in which a first phase (i.e. the dispersed phase) is distributed in a second phase (i.e. the continuous phase). The continuous phase is also referred to as the dispersion medium. In particular in the case of sols or polymeric compounds, the transition from solution to dispersion is generally smooth, so that it is no longer possible to clearly distinguish between solution and dispersion.
As far as the solvent or dispersant is selected in process step (i), it can be selected from all suitable solvents or dispersants. However, in general in process step (i), the solvent or dispersant is selected from water and organic solvents and mixtures thereof, preferably mixtures thereof. In particular in aqueous mixtures, the process can be carried out as a sol-gel process, usually by hydrolysis of the starting compounds to form inorganic hydroxides, in particular metal hydroxides and silica, which are then condensed.
The present invention may also include a solvent selected from the group consisting of alcohols (particularly methanol, ethanol, 2-propanol), acetone, ethyl acetate, and mixtures thereof. In this case, it is particularly preferred that the organic solvent is selected from the group consisting of methanol, ethanol, 2-propanol and mixtures thereof, and ethanol is particularly preferred.
The above-mentioned organic solvents can be mixed with water in a wide range and are particularly suitable for dispersing or dissolving polar inorganic substances.
As mentioned above, mixtures of water and at least one organic solvent, in particular mixtures of water and ethanol, are preferably used as solvents or dispersants within the scope of the present invention. In this case, it is preferred that the solvent or dispersant has a weight-related ratio of water to organic solvent of from 1:10 to 20:1, in particular from 1:5 to 15:1, preferably from 1:2 to 10:1, more preferably from 1:1 to 5:1, particularly preferably 1: 3. The ratio of water to organic solvent can be used, on the one hand, to adjust the hydrolysis rate, in particular of the silicon-containing compound and the alloying agent, and, on the other hand, to adjust the solubility and reaction rate of the carbon-containing compound, in particular of the sugar-containing precursor compound (e.g. sugar).
In the context of the present invention, it is preferred that in the process for preparing the composition in process step (i), the silicon-containing compound is selected from the group consisting of silanes, silane hydrolysates, orthosilicic acid and mixtures thereof, in particular silanes. In the context of the present invention, orthosilicic acid and its hydrolysis products can be obtained, for example, from alkali silicates, the alkali metal ions of which have been proton-exchanged by ion exchange. However, alkali metal compounds are as far as possible not used in the present invention, since they are incorporated into the resulting composition, in particular the precursor particles, in particular when using the sol-gel process, and can therefore also be found in silicon carbide compounds. However, alkali metal doping is generally not desired within the scope of the present invention. However, if this is desired, a suitable alkali metal salt, such as a silicon-containing compound or a phosphate salt of an alkali, may be used.
Particularly good results are obtained in the context of the present invention when silanes, in particular tetraalkoxysilanes and/or trialkoxyalkylsilanes, preferably tetraethoxysilane, tetramethoxysilane or triethoxymethylsilane, are used as silicon-containing compounds in process step (i), since these compounds react by hydrolysis in aqueous medium to orthosilicic acid or condensation products thereof or highly crosslinked siloxanes and corresponding alcohols.
With respect to the carbon-containing compounds, it has proven successful in process step (i) to select the carbon-containing compounds from the group consisting of: sugars, in particular sucrose, glucose, fructose, invert sugar, maltose; starch; starch derivatives and organic polymers, in particular phenolic resins, resorcinol-formaldehyde resins and mixtures thereof. Particularly good results are achieved within the scope of the invention if the carbon-containing compound is used in the aqueous solution or dispersion in process step (i).
If the carbon-containing compounds are used, in particular in aqueous solutions or dispersions, the carbon-containing compounds are generally placed in a small amount of solvent or dispersant, in particular water, for preparing the composition in process step (i). Particularly good results are obtained in this case if the carbon-containing compounds are used in an amount of from 10 to 90% by weight, in particular from 30 to 85% by weight, preferably from 50 to 80% by weight, in particular from 60 to 70% by weight, based on the solution or dispersion of the carbon-containing compounds, in the solution comprising the carbon-containing compounds.
In particular, it is also possible to add catalysts (in particular acids or bases) in succession to the solution or dispersion of the carbon-containing compound, for example to accelerate the conversion of sucrose and to obtain better reaction results.
With regard to the temperatures at which process step (i) is carried out, it has proven successful for process step (i) to be carried out at temperatures of from 15 to 40 ℃, in particular from 20 to 30 ℃, preferably from 20 to 25 ℃.
In the context of the present invention, it is preferably intended that in process step (ii) the temperature is slightly increased compared to process step (i) in order to accelerate the reaction of the individual components in the solution or dispersion, in particular the condensation reaction of the sol aging into the gel process.
Particularly good results are obtained here when process step (ii) is carried out at a temperature in the range from 20 to 80 ℃, in particular from 30 to 70 ℃, preferably from 40 to 60 ℃. In this connection, it has proven particularly effective for process step (ii) to be carried out at 50 ℃.
As regards the time period for carrying out process step (ii), this may vary depending on the respective temperature, the solvent used and the precursor compound used. However, process step (ii) is typically carried out for 15 minutes to 20 hours, in particular 30 minutes to 15 hours, preferably 1 to 10 hours, more preferably 2 to 8 hours, most preferably 2 to 5 hours. If the process is carried out as a sol-gel process, complete reaction of the sol to the gel is generally observed within the above-mentioned time period.
With regard to the amounts of the individual components in process step (ii) relative to one another, they can vary widely depending on the intended use. For example, precursor compositions for non-stoichiometric silicon carbide include compositions and ratios of the various components that are quite different from those contemplated for producing silicon carbide alloys.
In selecting individual compounds, particularly dopants or alloying agents, it is also desirable to ensure that they can be processed into homogeneous particles with the carbon and silicon sources, which can react during the production manufacturing process to form the silicon carbide-containing compound.
In particular, it is preferably ensured that the alloying agents decompose or disintegrate during the production of the production, in particular the selective synthetic crystallization, so that the desired elements sublime as reactive particles into the desired alloy, while the remaining compound components react as far as possible to form stable gaseous substances, for example water, CO2HCl, etc., which can be easily removed by gas phase. In addition, the compounds used should have a sufficiently high solubility in the solvents used, in particular ethanol and/or water, so as to be able to form finely divided dispersions or solutions, in particular sols, and should not react with the other constituents of the solution or dispersion (in particular sols), so that insoluble compounds are formed during the production process. In addition, since hydrolysis, condensation, and especially gelation must be carried out without interference before the particles are formed, the reaction rates of the respective reactions must be adjusted to each other. The reaction products formed should be insensitive to oxidation and non-volatile.
If precursor particles for the production of non-stoichiometric silicon carbide, in particular silicon carbide with excess silicon, are to be prepared by the process according to the invention, the solution or dispersion comprises the silicon-containing compound in process step (i) in an amount of from 20 to 70% by weight, in particular from 25 to 65% by weight, preferably from 30 to 60% by weight, more preferably from 40 to 60% by weight, based on the solution or dispersion.
In this case, it can also be provided that the solution or dispersion comprises carbon-containing compounds in an amount of from 5 to 40% by weight, in particular from 10 to 35% by weight, preferably from 10 to 30% by weight, more preferably from 12 to 25% by weight, based on the solution or dispersion.
In addition, it can be provided that, in the case of the preparation of non-stoichiometric silicon carbide, the solution or dispersion in process step (i) contains the solvent or dispersant in an amount of from 30 to 80% by weight, in particular from 35 to 75% by weight, preferably from 40 to 70% by weight, more preferably from 40 to 65% by weight, based on the solution or dispersion.
If a composition for producing silicon carbide alloys is provided within the scope of the present invention, it has proven successful to include the silicon-containing compound in method step (i) in an amount of 1 to 80% by weight, in particular 2 to 70% by weight, preferably 5 to 60% by weight, more preferably 10 to 30% by weight, relative to the composition, in the solution or dispersion.
According to this embodiment, it can also be provided that the solution or dispersion comprises carbon-containing compounds in an amount of from 5 to 50% by weight, in particular from 10 to 40% by weight, preferably from 15 to 40% by weight, more preferably from 20 to 35% by weight, based on the solution or dispersion.
According to this embodiment, it can likewise be provided that the solution or dispersion in process step (i) comprises a solvent or dispersant in an amount of from 10 to 60% by weight, in particular from 15 to 50% by weight, preferably from 15 to 40% by weight, more preferably from 20 to 40% by weight, relative to the solution or dispersion.
Furthermore, according to this embodiment, it can be provided that the solution or dispersion in process step (i) contains alloying agents in an amount of from 5 to 60% by weight, in particular from 10 to 45% by weight, preferably from 15 to 45% by weight, more preferably from 20 to 40% by weight, based on the solution or dispersion.
In the context of the present invention, it is particularly preferred that the alloying agent is selected from the corresponding chlorides, nitrates, acetates, acetylacetonates and formates of the corresponding alloying elements.
With regard to the implementation of process step (iii), it has proven successful to dry the reaction product from process step (ii) in process step (iii) at a temperature of from 50 to 400 ℃, in particular from 100 to 300 ℃, preferably from 120 to 250 ℃, more preferably from 150 to 200 ℃. The reaction product from process step (ii) may be dried at a temperature of from 100 to 300 ℃, in particular from 120 to 250 ℃, preferably from 150 to 200 ℃.
This can vary within wide limits as regards the time required for drying. However, it has proven reliable to dry the reaction product in process step (iii) for 1 to 10 hours, in particular 2 to 5 hours, preferably 2 to 3 hours.
In addition, the reaction product can be comminuted in process step (iii), in particular after a drying process. In this case, it is particularly preferred that the reaction product is mechanically comminuted in process step (iii), in particular by grinding. The particle size required or advantageous for carrying out the production process, in particular the selective synthesis crystallization, can be specifically adjusted by means of the milling process. However, it is generally sufficient to mechanically compress the reaction product from process step (ii) during drying, for example by stirring, to adjust the desired particle size.
According to a particular embodiment of the invention, in a fourth process step (iv) following process step (iii), the composition obtained in process step (iii) is subjected to a reducing heat treatment to obtain a reduced composition. The use of reduced compositions which have been subjected to a reduction treatment has the advantage that many possible and interfering by-products have been removed. The resulting reduced precursor particles are even more dense and contain a higher proportion of elements for forming the silicon carbide-containing compound.
If the composition obtained in process step (iii) is subjected to a reducing heat treatment after process step (iii), it has proven successful that in process step (iv) the composition obtained from process step (iii) is heated to a temperature of 700 to 1300 ℃, in particular 800 to 1200 ℃, preferably 900 to 1100 ℃.
In this case, particularly good results are obtained if the composition obtained in process step (iii) is heated in process step (iv) for 1 to 10 hours, in particular for 2 to 8 hours, preferably for 2 to 5 hours. In the specific temperature ranges and reaction times described, in particular, a carbonization of the carbon-containing precursor material can take place, which can significantly promote the subsequent reduction, in particular of the metal compounds.
In general, process step (iv) is carried out in a protective gas atmosphere, in particular in an argon and/or nitrogen atmosphere. This prevents, in particular, the oxidation of the carbon-containing compounds.
If, within the scope of the present invention, it is envisaged that the above-described precursor particles are subjected to a reducing heat treatment to obtain a reducing composition, in particular reduced precursor particles, the precursor compound may not evaporate at the applied temperature of up to 1300 ℃, preferably up to 1100 ℃, but may selectively decompose under reducing heat conditions into compounds which may be specifically converted into the desired silicon carbide-containing compound during the manufacturing process, in particular by selective synthesis crystallization.
For further details of the process for preparing the composition according to the invention, reference is made to the above description relating to other aspects of the invention, which apply analogously to the process of the invention.
Finally, according to a fifth aspect of the invention, the subject of the invention is a three-dimensional object comprising silicon carbide, which can be obtained by the above-mentioned method and/or by using the above-mentioned composition.
For more details of this aspect of the invention, reference is made to the above description relating to other aspects of the invention, which apply analogously to the three-dimensional object according to the invention.
Detailed Description
In the following, the subject matter of the invention will be explained in a non-limiting manner on the basis of preferred embodiments by means of the figures.
Fig. 1 shows a cross-sectional view along the xy-plane of an apparatus for generating three-dimensional objects comprising silicon carbide according to the invention by selective laser sintering.
In the xy-plane, perpendicular to the xz-plane, the
The build-up zone shown in the figure shows a powder bed of the
After the
The
In carrying out the method for manufacturing a three-dimensional object comprising silicon carbide according to the invention, a thin layer of the
The area of the build region is then lowered at least slightly by means of the piston 6 and
This forms a new layer of
Subsequently, the laser beam 4 irradiates and heats the layer in a site-selective manner, resulting in a new layer of the three-
Fig. 2 shows an enlarged cross-section of a build site, in particular fig. 2 shows
Reference numerals:
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