Method and system for sintering a ceramic component

Abstract

The invention relates to a method and a system for producing a sintered ceramic component, and to a computer program product. In a method (1) for producing a sintered ceramic component (20), a starting material (10) is sintered under the effect of pressure (P) to form a component (20). During sintering (15), a change in a spatial extent (∆L) of the component (20) to be produced is detected and the detected change in the spatial extent is used to determine if the target (18) of sintering (15) has been reached.

Description

[0001] Method and system for sintering a ceramic component

[0002] Description

[0003] The invention relates to a method and a system for producing a sintered ceramic component and a computer program product.

[0004] Sintering is a process for processing materials. A starting material is heated and possibly subjected to increased pressure, causing the starting material to become dense due to diffusion processes. Sintering occurs at high temperatures, but these are below the melting temperature of the main components, so that the shape of the body is at least largely retained during sintering. The body shrinks or shrinks as the starting material is densified. Sintering produces a solid component whose properties can be specifically influenced by suitable process parameters.

[0005] Sintering can be used to produce ceramic components that have a wide range of applications due to their properties, such as hardness, strength, wear resistance, temperature resistance, thermal conductivity, electrical conductivity, and ionic conductivity. Sintering can be preceded by shaping, in which a green body (preform) is produced from at least one, usually powdered, starting material. During sintering, the ceramic powder is typically exposed to temperatures above 1000°C. Due to the high temperatures involved, this process is technically complex and energy-intensive. High temperatures are required, particularly for the production of components from polycrystalline ceramic materials, in order to achieve a dense and mechanically stable structure. High densities are often desired, for example, more than 98% of the theoretically possible density, which are difficult to achieve using conventional processes.With long holding times at sintering temperature, excessive grain growth can lead to undesirable properties of the manufactured component. Elements can separate at grain boundaries, increasing the contact resistance. For components containing alkali ions whose ionic conductivity at 25°C is above 1 mS / cm, the high temperature can lead to the loss of alkali metal ions and thus a reduction in ionic conductivity. For some materials, such as LLZO, the desired crystal structure can also be damaged. Furthermore, the lengthy process is a significant disadvantage.

[0006] To shorten the duration and overcome some of the aforementioned disadvantages, field- and pressure-assisted sintering was developed. This process involves heating by means of an electric current, possibly under applied mechanical pressure. In this process, which is also known as field-activated sintering, "field-assisted sintering technology" (FAST) or "spark plasma sintering" (SPS), the tool containing the component to be sintered and / or the component to be sintered itself are heated by an electric current, which can be applied directly or, for example, by induction. In this way, significantly increased heating rates in the range of approximately 10 2 °C / min can be achieved, compared to approximately 1 to 10 K / min with "normal sintering." Furthermore, the applied pressure usually results in a reduction in the required sintering temperature, which is particularly advantageous when sintering alkaline ceramics.

[0007] The above-mentioned features can be combined as desired with the features of the invention.

[0008] For each material, each material combination, and even individual material parameters such as particle size, surface texture, etc., it is necessary to individually optimize process parameters such as temperature, pressure, (temperature and pressure) change rates, and holding times. This results in a complex and time-consuming process that must be repeated for each material change, with the parameters also exhibiting interdependencies.

[0009] The object of the invention is to provide an advanced sintering method and system, as well as a corresponding computer program product. In particular, the aforementioned disadvantages are to be at least partially remedied.

[0010] This object is achieved by the method according to claim 1 and by the system and computer program product according to the independent claims. Advantageous embodiments are specified in the subclaims.

[0011] To achieve this objective, a method for producing a sintered ceramic component is used. A starting material is sintered into a component under the influence of pressure. During sintering, a change in the spatial dimension of the component to be produced is detected. The achievement of a sintering target is determined by means of the detected change in the spatial dimension. The invention is based on the finding that the achievement of sintering targets corresponds to a characteristic change in the spatial dimension. The detection of the change in the spatial dimension therefore allows a simple and reliable statement to be made regarding the achievement of a target state of the component to be sintered. On the one hand, premature termination of sintering is prevented, thus ensuring that optimal densification of the component is achieved. On the other hand, sintering beyond an optimal point is prevented.In conventional processes, such sintering can, on the one hand, lead to deterioration of the component, e.g., through evaporation, the occurrence of undesired reactions, and / or partial or complete melting, and, on the other hand, it can take longer and require increased energy consumption. This method, on the one hand, produces a component of particularly high quality. On the other hand, it is achieved with minimal time and energy consumption. In particular, the necessary optimization steps can be shortened or eliminated.

[0012] Tests have shown that the process according to the invention can be used to produce a polycrystalline component, i.e., one composed of a large number of crystals, in which, however, almost no grain boundaries between the individual crystals are perceptible. In this way, a nearly or completely transparent, polycrystalline component can be produced. In addition, conventional components often have different properties in the region of grain boundaries than in the crystal volume; for example, ionic conductivity is typically reduced there. The invention therefore makes it possible to produce nearly or completely homogeneous components. In this way, components with particularly high ionic conductivities can be manufactured. Furthermore, very dense components, i.e., components with very low porosity, can be manufactured.

[0013] The starting material is typically in powder form. The process may include pre-pressing. For example, a preform can be produced from a powder in this way. In addition to the material from which the component is made, the preform may contain additives such as polymers. Such additives can be removed or burned out during sintering. In this way, transfer to the sintering device can be simplified. The starting material can also be only partially compacted. The starting material is in particular a ceramic material. During sintering, an elevated temperature acts on at least one area of ​​the component. In particular, the component to be sintered is heated. The heating can take place at least intermittently at a heating rate of at least 20 7min, in particular at least 30 7min, preferably at least 40 7min. The heating rate is usually not higher than 60 7min, preferably 50 7min.

[0014] Heating can be carried out in several steps. For example, heating can initially be carried out to a starting temperature of more than 300°C and / or less than 500°C, preferably approximately 400°C. This can be done within a few seconds. Heating can then continue, for example at the heating rate described above, until the sintering target is reached. For example, the component to be sintered can be heated to a temperature above 1000°C, in particular at least 1100°C, and preferably at least 1200°C.

[0015] Heating can be achieved by resistance heating of the starting material, a body adjacent to the starting material, inductive heating (e.g., a body adjacent to the starting material), and / or heating in a furnace. A body adjacent to the starting material can be a punch and / or a die and / or be made of graphite.

[0016] Sintering occurs under the influence of pressure. This means that mechanical pressure is exerted on the starting material or the component to be sintered. This can generally be achieved by pressing using one or two movable punches of any shape and / or in a die. If sintering is carried out using the FAST / SPS process, uniaxial pressure can be applied to the starting material, for example, using a hydraulically actuated punch system of the FAST / SPS system.

[0017] When the sintering objective is achieved, the sintering process is typically complete. The desired or achievable component properties are then achieved. Continued sintering beyond this point would typically lead to deterioration of the component, for example, through the onset of melting. The objective of sintering can be defined, for example, by achieving one or more desired component properties.

[0018] In one embodiment, sintering is carried out using a FAST / SPS process and / or in a FAST / SPS system. An electrical current, for example a constant direct current, a pulsed direct current, or an alternating current, can be passed through an electrically conductive tool that is adjacent to the component to be sintered. The tool can, for example, be a compression mold that can comprise an upper and a lower punch and, if necessary, a die. Each of the parts can be made of an electrically conductive material, such as graphite. The tool can be heated via the Joule effect (= resistance heating). The component to be sintered is heated by direct contact with the tool through thermal conduction. In this way, high heating rates in the range of 10 2°C / min for the starting material can be achieved. When electrically conductive starting materials are sintered, the starting material is additionally heated directly by a current flowing through it, which can further increase the heating rate and the homogeneity of the temperature distribution. These high heating rates reduce material evaporation, save energy, and enable significantly faster sintering. Current flowing through the starting material is typically implemented as a pulsed direct current.

[0019] Spatial expansion refers to the extent of the starting material or the component to be sintered or sintered, particularly along a direction such as the direction of pressure application. Typically, a change in length is detected.

[0020] In one embodiment, a temporal progression of the change in spatial expansion is detected and used to determine target achievement. The temporal progression of the spatial expansion is used to determine target achievement. It has been shown that the temporal progression provides particularly reliable information about the status of the sintering process. The temporal progression can be recorded.

[0021] In one embodiment, an inflection point is determined in the detected temporal progression. It is determined that the sintering target has been reached when the inflection point is reached. The inflection point is therefore used as an indicator for the achievement of the sintering target. In other words, it is assumed that the sintering target has been reached at the time of the inflection point. An inflection point is the point at which the temporal progression changes its curvature behavior. Here, the temporal progression changes from a left turn to a right turn or vice versa. At an inflection point, the second derivative with respect to time is zero. In one embodiment, the inflection point occurs immediately after a reduction in the gradient in the temporal progression of the change in spatial extent. The change in spatial extent therefore increases less sharply.In particular, there is a comparatively steep rise in the temporal progression of the change in spatial extent, followed by a decrease in the gradient, and then the inflection point. A turning point is used that occurs after the decrease in the gradient. In this case, the temporal progression typically changes from a right turn to a left turn. Experiments have shown that this characteristic progression is particularly suitable as an indicator of goal achievement. After the inflection point, another steep rise may occur.

[0022] In one embodiment, the turning point occurs at a temperature above 1100 °C or above 1200 °C. This ensures that a similar trend at lower temperature ranges does not erroneously lead to the target being determined as achieved too early, thus avoiding errors.

[0023] In one embodiment, sintering takes place in a vacuum. In particular, sintering takes place in an atmosphere of less than 100 Pa. The atmosphere under which sintering takes place can have a reduced pressure, independent of the mechanically applied increased pressure. Vacuum means a reduced pressure. The atmosphere can have less than 150 Pa. In particular, this means the pressure of the atmosphere after an initial evacuation of the chamber. This can also be the target pressure during sintering. Alternatively or in addition to a vacuum, sintering can take place under protective gas or—with a suitable choice of sintering device, for example, using special steel instead of graphite—under air.

[0024] In one embodiment, the pressure of an atmosphere surrounding the component to be sintered is detected during sintering and used to determine target achievement. In particular, the atmosphere exhibits a negative pressure, which is detected and used. This allows further insights into the sintering process to be obtained, thereby better preventing errors in determining target achievement.

[0025] In one embodiment, a temporal progression of atmospheric pressure is detected and used. The temporal progression of atmospheric pressure allows for further insights and thus improved error prevention. The temporal progression can be recorded. In one embodiment, it is determined that the sintering target has been achieved when the inflection point is reached, which occurs after a maximum atmospheric pressure. Tests have shown that an inflection point occurring after a maximum atmospheric pressure is particularly suitable for indicating target achievement.

[0026] In one embodiment, the maximum atmospheric pressure is caused by compression of the component. Typically, a vacuum pump is running during sintering. The vacuum pump evacuates the atmosphere surrounding the component to be sintered. If a temporary increase in pressure occurs before or during sintering, for example due to gas escaping from the starting material or due to compression of the component to be sintered, the atmospheric pressure is typically subsequently reduced again by the action of the vacuum pump. This can lead to pressure maxima, i.e. temporarily elevated pressures. The maximum is in particular a local maximum. This means that higher pressures can also occur over the entire time course.

[0027] It has been shown that a maximum caused by the compaction of the component is particularly suitable for reliably indicating the achievement of the target.

[0028] In one embodiment, at least one sintering process is terminated when the sintering goal is achieved. Sintering can comprise multiple processes, for example, exerting pressure on the component to be sintered, increasing the temperature, and / or applying a vacuum and / or a defined gas atmosphere. For example, the increase in temperature and / or the increase in pressure is terminated. Preferably, the temperature is reduced and / or the pressure is reduced, for example by at least 10%, preferably by at least 50%, and particularly preferably to approximately the level of standard conditions. In one embodiment, sintering is completely terminated when the goal is achieved.

[0029] In one embodiment, the pressure is exerted on the starting material by means of at least one movable punch. The starting material is typically located in a compression mold. The compression mold can comprise a die that delimits the starting material radially outward. Punches, e.g. in the form of rods, can contact and compress the starting material from, for example, above and below. At least one punch is typically movable in order to mechanically press the starting material. The die is in particular a body, e.g. a cylinder, with a through-hole. The outer contours of the punches are adapted to the inner contour of the hole, e.g., circular. As described, heat can be generated by current flow through the punches and / or the die.

[0030] In one embodiment, a movement of at least one movable punch is detected to detect the change in the spatial dimension. Detecting the movement of the punch during pressing makes it possible to easily detect the change in the spatial dimension of the component to be produced. In particular, a distance between the two punches is determined. Alternatively, the change in the spatial dimension can be achieved using any other means, for example, with a servo motor or with any sensor, for example based on electrical, optical, or acoustic signals.

[0031] In one embodiment, the starting material contains an alkali metal. In particular, the starting material is an inorganic material. Alternatively or in addition to the alkali metal, the starting material can contain zirconium oxide. The component to be sintered is preferably polycrystalline, i.e., it contains a large number of crystals. Preferably, the component to be sintered is not made of a glass, i.e., not of an amorphous material. The component is, in particular, an inorganic component. Several examples of the starting material are described below independently of one another; these can be combined in any desired form.

[0032] The starting material and / or the ceramic component can contain or consist of one or more inorganic materials with oxygen as the main anion in the structure. Oxygen can, for example, make up at least 95% of the total anions. In addition to oxygen, dopants such as F can be present. The starting material and / or the ceramic component can contain or consist of one or more cations that contain at least one alkali ion, such as Li, Na, and / or K. The starting material and / or the ceramic component can contain phosphorus and / or one or more silicates. The starting material and / or the ceramic component preferably contains no sulfur and / or no halides, for example with halogens such as Cl, Br, etc.

[0033] The starting material and / or the ceramic component can have a crystalline structure. For example, the ceramic component can contain or consist of garnet, NaSICON, and / or perovskite. The glass phase content of the ceramic component is in particular at most 15%, preferably at most 3%, particularly preferably at most 0.1%. The ceramic component can contain or consist of one or more materials with ionic conduction of alkali metals such as Li, Na, and / or K with a total ionic conductivity of > 0.1 mS at 25°C, in particular > 0.5 mS at 25°C, preferably > 1 mS / cm at 25°C. The ceramic component can contain Li, Na, and / or K.

[0034] In one embodiment, the manufactured component has at least one of the following properties: a relative density of at least 98%, preferably at least 99%, a total ionic conductivity of at least 1 mS / cm at 25 °C, a polycrystalline structure,

[0035] Grain boundaries with a half-width of less than 25 nm, preferably less than 10 nm, determined by TEM characterization, a deviation of the chemical composition of less than 10 atomic %, in particular less than 5 atomic %, preferably less than 1 atomic %, a grain boundary resistance of at most 1 / 1000 of the total resistance, optical transparency.

[0036] In particular, the process is carried out such that the component has one or more of the aforementioned properties. The relative density is preferably at least 99.5%, particularly preferably at least 99.8%.

[0037] The component may have grain boundaries that, when characterized by TEM (EDS mapping), have a full width at half maximum (FWHM) of less than 25 nm, in particular less than 10 nm, and preferably less than 5 nm. TEM can be tested at 200 kV using a Cs-corrected Hitachi HF5000 microscope (Hitachi High-Tech, Japan), which may be equipped with an EDS detector system (Advanced EDX System Ultrim TLE, Oxford Instruments, United Kingdom). The full width at half maximum of a function with a maximum is the difference between the two argument values ​​for which the function values ​​have decreased to half the maximum—in other words, the "width at half height."

[0038] The deviation in chemical composition can be less than 10 atom%, in particular less than 5 atom%, preferably less than 1 atom%, and most preferably less than 0.5 atom% or 0.1 atom%. This can also be determined by TEM characterization (EDS mapping) and / or HAADF (high-angle annular dark-field imaging). TEM can be tested at 200 kV using a Cs-corrected Hitachi HF5000 microscope (Hitachi High-Tech, Japan), which can be equipped with an EDS detector system (Advanced EDX System Ultra TLE, Oxford Instruments, United Kingdom).

[0039] Optical transparency can be determined with the naked eye and optical microscopy (e.g. OLYMPUS REFLECTED LIGHT PHOTO-MIC).

[0040] In one embodiment, the component contains or consists of garnet, perovskite or NaSICON.

[0041] Garnets belong to the group of island silicates with the general formula A3B2 [RÜ4]3, where A, B, and R represent crystal lattice sites with 8, 6, and 4-fold oxygen coordination, respectively. The Li-containing garnets with a cubic structure (space group Ia3d) belong to the class LisLa3M20i2 (M = Nb, Ta), and especially to the family Liy-yLasZ^. y M y Oi2 (M=Nb, Ta) exhibit particularly high ionic conductivities. Dopants that can also advantageously increase conductivity include Al and Ga, as well as Ca, W, Pr, and Fe, whereby electronic conductivity can also be achieved in some cases (mixed electronic and ionic conductivity).

[0042] Perovskites have the general structure ABO3, where the A ion is located in the center of the cubic cell and is coordinated by 12 O ions, while the B ion is located at a corner of the cubic crystal cell and is coordinated by 6 X ions.

[0043] Materials of the La2 / 3-xLi3xTiO3 (LLTO) family, where x is typically between 0.04 and 0.16, exhibit very high bulk Li conductivities, while the Li grain boundary conductivity is usually lower.

[0044] NaSICON stands for “Na Super Ionic Conductor”, for example materials of the NZSP family (Nai +x Zr2Si x P3-xOi2). These inorganic compounds can crystallize in rhombohedral or monoclinic structures and exhibit very good ionic conductivity combined with very low electrical conductivity. NaSICON are generally substances with the formula M l i + 2w+x- y +zM ll w M lll x(Zr, Hf) IV 2- w -x-yM v y (SiO4)z(PO4)3-z. Where M 1 Well, M", M 111 and M v are suitable divalent, trivalent, or pentavalent metal cations. For example, M" Mg 2+ , Ca 2+ , Sr2+ , Ba 2+ , Co 2+ and / or Ni 2+ For example, M 111 Al 3+ , Ga 3+ , Sc 3+ , La 3+ , Y 3+ , Gd 3+ , Sm 3+ , Lu 3+ , Fe 3+ and / or Cr 3 * For example, M v V 5+ , Nb 5+ and / or Ta 5+ Any combination is possible.

[0045] NaSICON can also produce substances with the formula Nai +x Zr2Si x P3-xOi2, 0 < x < 3. It can also include substances that are structurally constructed according to the formula mentioned and in which a proportion of Na, Zr, and / or Si is replaced by isovalent or equivalent elements. NaSICONs are solids. NaSICONs exhibit high conductivity for sodium ions and negligible electron conduction. Examples of NaSICONs are further Na3.4Zr2.o(SiO4)2.4(PO4)o.6 and Nai +x Zr2(SiO4) x (PO4)3-x (0 < x < 3), the latter substance also being referred to as NZSP.

[0046] In one embodiment, the manufactured component is a component for an energy application. Energy applications are applications for converting and / or storing energy, particularly in the form of electrical current, for example batteries, electrolyzers, photovoltaic systems, fuel cells, and the like. Components for an energy application are components used in such applications. Examples of components for an energy application are membranes for batteries or fuel cells. Alternatively or additionally, the component is a component for an industrial process, such as for chemical separation, detection, etc. The component can therefore be a membrane and / or a detection element or a part thereof.

[0047] A further aspect of the invention is a system for producing a sintered ceramic component. The system comprises a sintering device for producing a sintered ceramic component with means for exerting pressure on a starting material. Typically, the sintering device further comprises means for heating the starting material, in particular by resistance heating. The system further comprises a detection device for detecting a change in the spatial extent of the component to be produced, as well as means for determining whether a sintering objective has been achieved using the detected change in the spatial extent.

[0048] All features, properties, and advantages of the method described above also apply to the system. The system comprises, in particular, a data processing device with which data can be received, electronically stored, electronically processed, and / or transmitted or output. A data processing device comprises, for example, an electronic memory in which data can be stored and / or a processor in which data can be electronically processed. A data processing device can execute a computer program product.

[0049] A further aspect of the invention is a computer program product. This comprises instructions that, when executed by a system for producing a sintered ceramic component, for example a system according to the invention, cause the system to determine a sintering target based on a detected change in spatial dimension.

[0050] Below, exemplary embodiments of the invention are explained in more detail with reference to the figures. Features of the exemplary embodiments can be combined individually or in multiples with the claimed subject matter, unless otherwise stated. The claimed scope of protection is not limited to the exemplary embodiments.

[0051] They show:

[0052] Figure 1 : a schematic representation of aspects of a method,

[0053] Figure 2: a schematic representation of further aspects of a method,

[0054] Figure 3: a schematic representation of a system,

[0055] Figure 4: TEM images of a conventionally manufactured component,

[0056] Figure 5: TEM images of a component manufactured according to the invention,

[0057] Figure 6: relative densities of various components manufactured conventionally and according to the invention,

[0058] Figure 7: schematic curves of the pressure of one atmosphere and the

[0059] Change in spatial expansion during sintering,

[0060] Figure 8 Parameter curves during sintering of a first component, as well as

[0061] Figure 9 Parameter curves during sintering of a second component.

[0062] Figure 1 shows aspects of a method 1 for producing a sintered ceramic component. A starting material 10 is sintered. During sintering 15, a pressure P acts on the starting material 15. A ceramic component 20 is produced.

[0063] Figure 2 shows further aspects of a method for producing a sintered ceramic component. During sintering 15, it is determined whether a sintering goal 15 has been achieved ("Goal achieved?" 30). If yes (Y), sintering is complete (32). If no (N), the sintering process continues. Whether a sintering goal 15 has been achieved is determined by detecting a change in a spatial dimension AL of the component to be produced. The detected change is used to determine whether the goal has been achieved.

[0064] Figure 3 shows a schematic structure of a sintering device 25 for producing a sintered ceramic component as part of a system 50 for producing a sintered ceramic component. The sintering device 25 can be designed as a FAST / SPS system. The sintering device 25 comprises an evacuable chamber 40, which has a vacuum connection 41 for this purpose and is delimited by a housing. The sintering device 25 comprises a graphite matrix 42 that radially surrounds the starting material 10 to be sintered, and a means 43 for exerting a pressure P on a starting material. The means 43 is designed as a system of two punches 44, 45 that contact the starting material 10 from above and below. At least one of the punches 44, 45 is movable along its longitudinal axis in order to exert pressure P on the starting material 10 in the axial direction.A current source 47 for generating direct current pulses is electrically connected to the two punches and / or to the die.

[0065] During sintering, the spatial extent of the component changes due to material shrinkage. This can be detected, for example, by detecting the distance between the two punches 44, 45. In this way, the length of the component in the axial direction and / or the change in length can be determined. For this purpose, the system 50 comprises a detection device 48 for detecting a spatial extent of the component to be produced and means 49 for determining whether a sintering goal has been achieved using the detected change in the spatial extent. The detection device 48 can comprise a sensor and / or be connected to a drive for moving a punch. The means 49 can be embodied by a data processing device with which data can be electronically stored and / or processed.

[0066] Figure 4 shows transmission electron microscopy (TEM) images of a conventionally manufactured component 20. In addition to an all-electron image in the top left, maps for the elements Zr, Ta, La, Al, and O of the same section of component 20 are shown. The scale SC shown below corresponds to 25 nm. In all images, a vertical structure located approximately in the center can be seen, which is composed of one or more alternating light and dark lines. This area is a grain boundary 37 between two neighboring crystals 35, 36 in the polycrystalline component 20. Light areas represent increased concentrations (enrichments) of the respective element, while dark areas show reduced concentrations (depletions). This shows that Ta and Al are most strongly separated at grain boundaries 37, while Zr is absent at grain boundaries 37.Grain boundary 37 is visible in all images, and in most of them it is very clear (total electrons, Zr, Ta, La, O). The half-width is more than 25 nm.

[0067] Figure 5 shows comparable TEM images of a component 20 produced according to the invention. The scale SC shown below corresponds to 100 nm. In the overall electron image, a thin, slightly brightened vertical line is visible in the region of grain boundary 37. In all other images, grain boundary 37 is no longer visible. It can be seen that the components produced according to the invention are extremely homogeneous. The grain boundaries disappear at least almost completely. The half-width is less than 25 nm.

[0068] Figure 6 shows the lithium ion capability Li +Cond. plotted against the relative density RD of some components, based on different elements. Plotted are conventionally manufactured components, which are summarized in respective point clouds based on the furnace sintering (FS), FAST / SPS, and hot pressing (HP) processes, as well as two components (INV) manufactured according to the invention. It can be seen that the INV components manufactured according to the invention have the highest measured relative densities RD of significantly more than 99.5%. Furthermore, the lithium-ion conductivities, at more than 1 mS / cm, are among the highest measured.

[0069] Figure 7 shows schematic curves of the atmospheric pressure P Cham and the change in spatial expansion AL over time t during sintering. Sections of curves corresponding to the main sintering process are shown. A long increase in the change in spatial expansion AL is evident, reflecting the shrinkage of the component due to compaction. After almost complete compaction, the gradient decreases and an inflection point WP appears. This indicates that the sintering process is complete and can therefore be terminated. Increases in the change in spatial expansion AL beyond this value are due to undesired, partial or complete melting of the component. The inflection point WP typically occurs following a maximum P C ham, max of the pressure of the atmosphere P Cham. Figures 8 and 9 show curves of two examples, which are described in detail below. In each case, 3 to 5 g of a ceramic powder were placed into a graphite matrix with a diameter of 12 cm. Optional pre-pressing was carried out at a pressure of at least 26.5 MPa and at most 53.5 MPa. The atmosphere of the powder, i.e., the chamber of the sintering device, was maintained at a pressure P C The sintering process was continued until the atmosphere was evacuated to below 50 Pa. The vacuum pump remained switched on. A pressure P of at least 26.5 MPa and at most 53.5 MPa was applied to the starting material. To this end, the pressure P was initially increased and, once the target pressure was reached, kept constant until the end of the sintering process. The die was heated to a starting temperature of 400 °C within a few seconds. The temperature was then controlled at a heating rate of at least 40 °C / min and at most 50 °C / min until the end of the sintering process.

[0070] Materials and methods

[0071] Example 1 : Production of garnet:

[0072] 5 g of Li6.45Alo.o.5La3Zri.6Tao.40i2 powder was placed into the die, which was placed in an argon-filled glove box. The powder was pre-pressed for one minute at a pressure of 26.5 MPa before being introduced into the FAST / SPS device. The chamber was then evacuated to an atmospheric pressure of approximately 35 Pa, and the pressure on the starting material was increased to 26.5 MPa. The starting material was then heated to 400 °C and further heated at a heating rate of 40 °C / min. Al and P were continuously detected and recorded (Figure 8).

[0073] Example 2: Production of NaSICON:

[0074] 3 g of Na3.4Zr2Si2.4Po.60i2 powder were placed in the die. The powder was pre-pressed for one minute at a pressure of 53 MPa before being introduced into the FAST / SPS device. The chamber was evacuated to an atmospheric pressure of approximately 50 Pa. The pressure on the starting material was then increased to 53 MPa. The sample was then heated to 400 °C and further heated at a controlled heating rate of 50 °C / min. AL and P were detected and recorded throughout the process (Figure 9). In Figures 8 and 9, the upper diagram shows the pressure Pcham in the atmosphere with a dashed line and the change in spatial expansion AL with a solid line. The lower diagram shows the temperature T with a dashed line and the pressure P on the component to be sintered with a solid line. The time t is plotted on the x-axis.

[0075] Course of change in spatial extent AL:

[0076] Before the concrete courses of the curves are discussed using the examples, possible courses of the change in the spatial extent AL are first described using the curve shown in Figure 8 as an example:

[0077] At the beginning of the procedure, a reduction in pressure P C This can occur in the atmosphere. This can be caused by the start-up of the vacuum pump and / or by an initial compression of the still loose starting material. For example, gas contained between the particles can escape.

[0078] One or more maxima Pcham, max may occur over time in atmospheric pressure. A first maximum may occur. The first maximum may be caused by the onset of heating, the rapid initial heating, and / or the pressure acting on the component being manufactured. Gas may be released from the starting material during this process.

[0079] In some cases, a second peak may occur. This second peak may be due to decomposition of impurities, such as surface impurities of the starting material, and / or components of the starting material. This second peak may coincide with the onset of the sintering process. The second peak typically occurs at significantly higher temperatures than the first peak.

[0080] A third maximum may occur. This third maximum is primarily due to densification of the component during sintering. This marks the key densification process during sintering. At this time, a steep increase in the change in spatial expansion AL is often observed. The third maximum typically occurs at significantly higher temperatures than the second maximum.

[0081] After the third maximum in P C ham, the slope of AL typically decreases, or in other words, the first derivative of AL approaches zero. AL may now exhibit an inflection point WP. This marks the end of the sintering process. The sintering program can now be terminated.

[0082] The terms first, second, etc. maximum refer to a case in which all of the named maxima occur consecutively in the described order. However, each of these maxima is optional and may or may not occur independently of other maxima. Thus, there may be no first maximum, but a second maximum may occur. Whether a specific maximum occurs depends, among other things, on the material and the sintering parameters. Whether specific maxima occur for a specific starting material and specific conditions can be determined in advance, for example, by dynamic differential calorimetry. However, this is not necessary to carry out the method. For example, the inflection point WP can be after the first maximum P Cham, max can be used, which occurs above a temperature of 1000 °C, in particular 1100 °C or 1200 °C and / or during or after a significant increase in AL and / or below a temperature of 1300 °C, in particular 1200 °C. Alternatively or additionally, the last inflection point before the melting point can be used, which in particular leads from a right-hand bend to a left-hand bend.

[0083] Example 1 : Production of garnet

[0084] After an initial reduction in pressure, a strong first maximum in Pcham (at t = approx. 200 s) is visible. This is due to the applied pressure P, which releases gas from the starting material. When the actual sintering begins, a second maximum in Pcham appears (at t = approx. 800 s), which is due to the decomposition of lithium carbonate on the surface of the material. Carbon dioxide is released in the process. AL now rises steeply until the third maximum of Pcham occurs. After the third maximum, the slope of AL decreases and approaches zero. This indicates that the component has almost reached the theoretical density. When the inflection point (WP), here from the right-hand curve to the left-hand curve, is reached, the sintering program can be terminated.

[0085] Example 2: Production of NaSICON

[0086] The very small first maximum in P Cham after the initial reduction can be attributed to the release of gas from the sample due to rapid heating. A second peak due to decomposition of impurities or components of the starting material is not present in this example. In the actual sintering process, a third peak is visible at t = approximately 1150 s. At the same time, there is a rapid increase in AL, reflecting the densification of the component. Subsequently, the gradient of AL rapidly approaches zero, followed by the inflection point, which marks the end of the sintering process. The sintering program can now be terminated.

[0087] List of reference symbols

[0088] Source material 10

[0089] Sintering 15

[0090] Goal 18

[0091] Component 20

[0092] Sintering device 25

[0093] Goal achieved? 30

[0094] Sintering completed 32

[0095] Crystal 35

[0096] Crystal 36

[0097] Grain boundary 37

[0098] Chamber 40

[0099] Vacuum connection 41

[0100] Matrix 42

[0101] Medium 43

[0102] Stamp 44

[0103] Stamp 45

[0104] Power source 47

[0105] Yes

[0106] No

[0107] Turning point WP

[0108] Pressure P

[0109] Pressure (of the atmosphere) P cham

[0110] Maximum P cham, max

[0111] Temperature T

[0112] Change in spatial extent AL

[0113] Time t

[0114] Other various

[0115] Furnace sintering FS

[0116] Hot Pressing HP

[0117] Component manufactured according to the invention INV

[0118] Relative density RD

[0119] Lithium-ion conductivity Li + cond.

[0120] Scale SC

Claims

Claims 1. Method (1) for producing a sintered ceramic component (20), in which a starting material (10) is sintered under the action of pressure (P) to form a component (20), characterized in that during the sintering (15) a change in a spatial extent (AL) of the component (20) to be produced is detected and achievement of a target (18) of the sintering (15) is determined by means of the detected change in the spatial extent.

2. Method (1) according to the preceding claim, characterized in that a temporal course of the change in the spatial extent (AL) is detected and used to determine the target achievement.

3. Method (1) according to the preceding claim, characterized in that an inflection point (WP) is determined in the detected time course, wherein it is determined that the target (18) of the sintering (15) is reached when the inflection point (WP) is reached, in particular wherein the inflection point (WP) occurs immediately after a reduction of a gradient in the detected time course.

4. Method (1) according to one of the preceding claims, characterized in that the sintering (15) takes place in a vacuum, in particular in an atmosphere of less than 100 Pa.

5. Method (1) according to one of the preceding claims, characterized in that during the sintering (15) a pressure (P C ham) of an atmosphere surrounding the component (20) to be sintered, is detected and is used to determine the target achievement, wherein in particular a temporal progression of the pressure (P Cham) of the atmosphere is detected and used.

6. Method (1) according to the preceding claim and claim 3, characterized in that it is determined that the target (18) of the sintering (15) has been reached when the turning point (WP) is reached, which is after a maximum (P C ham, max) of the pressure (P C ham) of the atmosphere, where the maximum (Pcham.max) of the pressure (P C ham) of the atmosphere is caused in particular by a compression of the component (20).

7. Method (1) according to one of the preceding claims, characterized in that at least one sintering process (15) is terminated when the target (18) of the sintering (15) is reached.

8. Method (1) according to one of the preceding claims, wherein the pressure (P) is exerted on the starting material by means of at least one movable stamp.

9. Method (1) according to the preceding claim, wherein a movement of the at least one movable stamp is detected to detect the change in the spatial extent (AL).

10. Process (1) according to one of the preceding claims, characterized in that the starting material contains an alkali metal.

11. Method (1) according to one of the preceding claims, wherein the sintered ceramic component (20) has at least one of the following properties: a relative density of at least 98%, preferably at least 99%, a total ionic conductivity of at least 1 mS / cm at 25 °C, a polycrystalline structure, Grain boundaries with a half-width of less than 25 nm, determined by TEM characterization, a deviation of the chemical composition of less than 10 atom-%, in particular less than 5 atom-%, preferably less than 1 atom-%, a grain boundary resistance of at most 1 / 1000 of the total resistance, optical transparency.

12. Method (1) according to one of the preceding claims, characterized in that the sintered ceramic component (20) contains or consists of garnet, perovskite or NaSICON.

13. Method (1) according to the preceding claim, characterized in that the sintered ceramic component (20) is a component (20) for an energy application.

14. System (50) for producing a sintered ceramic component (20), comprising a sintering device (25) for producing a sintered ceramic component (20) with means for exerting a pressure (P) on a starting material, a detection device (48) for detecting a change in a spatial extent of the component (20) to be produced and means (49) for determining whether a target (18) of the sintering (15) has been achieved by means of the detected change in the spatial extent (AL).

15. A computer program product comprising instructions which, when the program is executed by a system (50) for producing a sintered ceramic component (20), cause the system (50) to determine whether a sintering target (18) has been reached by means of a detected change in a spatial extent.

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