EP0688662A1 - Process and device for manufacturing a cup-shaped body - Google Patents

Abstract

To shape a pot-shaped body (42), a matrix insert (10) is placed in a shaping holder (50). The sections (14,16) of the matrix insert are drawn radially outwards at an equal gap to the circumference of the pot-shaped body (42). Also claimed is a prodn. process where the body is removed by simultaneous removal of the parts (14, 16) of the matrix insert (10) from the body (42), over its whole peripheral surface. <IMAGE>

Description

The invention relates to a device for producing a pot-shaped body from a powder mixture made of oxide ceramic, in particular a hollow cylindrical body made of β '' aluminum oxide, closed on one side, as solid electrolytes for preferably a sodium-sulfur battery, with a space that can be filled with a powder mixture and between a die insert consisting of several parts and a core protruding into it and compressing the powder mixture from the inside to the outside is formed, the parts of the die insert being movable radially outwards for shaping the cup-shaped body.

Furthermore, the invention relates to a method for producing a pot-shaped body from a powder mixture made of oxide ceramic, in particular a hollow cylindrical body made of β ″ aluminum oxide, closed on one side, as solid electrolytes for z. B. a sodium-sulfur battery, the powder mixture in a body-defining, between a cavity of a multi-part insert and formed in this protruding core filled, compacted from the core, shaped by radially moving the parts of the die insert apart and then sintered, starting materials or homogenized powder being at least compacted and broken up when the powder mixture is obtained.

The need for high-performance electrochemical energy stores is increasing in particular in view of the fact that the use of electric road vehicles is required to cope with environmental problems. In the past, lead / acid batteries and to a small extent nickel / cadmium batteries have prevailed among the electrochemical elements. The former show a high level of development, even if use in important areas is not possible due to their high weight and the high maintenance requirements. Therefore, use in electric road vehicles can not be described as practicable.

The known disadvantages can be overcome with a sodium-sulfur battery, which differs fundamentally from the conventional accumulators. The sodium-sulfur battery (Na / S battery) has liquid reactants and a solid electrolyte.

Molten sodium as one and molten sulfur as the other reaction substance and a solid electrolyte separating the two reactants are required for the function of the cell. This solid or solid electrolyte of ceramic material has the property of conducting sodium ions, but not electrons. The electrolyte is basically in the form of a cylinder or crucible closed on one side, inside which is the sodium and outside of which is the sulfur. Since the latter is a non-conductor even in the molten state, the sulfur can be introduced into an electrically conductive carbon felt. This forms the continuation of the metal housing of the cell which serves as a positive current connection and, with its large surface area, ensures that the electrochemical processes are sufficient run fast. A metallic lid that is in contact with the sodium serves as a negative power connection. During discharge, i.e. when the power connections are connected to each other via a load, sodium ions migrate through the solid electrolyte to the sulfur. The sodium ions react with sulfur, taking up electrons to form sodium polysulfide. The electron current corresponding to the sodium ion current flows through the external load.

The heart of a single battery cell is the solid electrolyte with the chemical composition Na₂O x 11 Al₂O₃. This mixed oxide can be stabilized with Li₂O. In order to achieve good conductivity for sodium ions, the mixed oxide must be in the β '' phase.

A method and a device of the type mentioned at the outset can be found in EP 0 575 921 A1. Pot-shaped bodies, in particular bodies made of ceramic solid-state electrolytes with a wall thickness of <1.8 mm, can be reproducibly and manufactured within predetermined tolerance ranges using technically simple means.

The present invention is based on the problem of developing a device and a method of the type described above in such a way that further manufacturing simplifications result, with particular care being taken to ensure that the pot-shaped bodies to be molded are not damaged even with very thin wall thicknesses. The bodies should also be compacted in such a way that the finished body, after sintering, comes very close to the theoretical density, but without the risk of crack formation or texture formation (grain or crystal growth).

In terms of the device, the problem is solved according to the invention in that, for shaping the cup-shaped body, the die insert is arranged in a shaping receptacle in which the parts of the die insert are spaced evenly apart can be moved radially outward to the circumference of the cup-shaped body. For this purpose, magnets extending in the axial direction of the die insert are preferably arranged in the mold receptacle.

The measure according to the invention ensures that the die parts are evenly and radially removed from the molded body at the same time, so that an inadmissible loading of the outer wall is avoided, which could otherwise result in destruction; because during the shaping the body is not supported by the core, so that if there was no surface contact between the parts of the female insert and the body, there is a selective pressure load on the body which could lead to destruction.

The fact that it is ensured that an uneven load on the pot-shaped body (green body) is excluded during molding ensures that the end products are free of defects, so that only a statistical check has to be carried out.

In order to ensure this uniform removal of the die insert parts, i.e. the spontaneous movement outwards, it is proposed that the die insert received by a die has on the one hand an upper annular edge protruding from its circumferential surface and on the other hand a bevelled or chamfered circumferential bottom area so that the mold receptacle prevents this Edge adapted diameter and that both the die and the mold receptacle each have a circumferential extension at a distance from each other, which is equal to the distance between the annular upper edge and the bevelled circumferential bottom area. The dimensions should be matched to one another such that a gap is preferably formed between 10 microns and 100 microns between the inner diameter of the mold holder and the outer diameter of the circumferential annular edge.

To mold the body from the die insert, it is proposed that the die insert can be introduced into the mold receptacle via a double punch comprising an inner and an outer punch, the shaped body being supported by the inner punch after removal of the die parts.

According to an inventive proposal to be emphasized, the core delimiting the interior of the die insert consists of a metal mandrel with a membrane surrounding it, the metal mandrel having a plurality of fluid outlet openings which are connected via channels running peripherally in the metal mandrel. In particular, the metal mandrel has an axially running central bore with radial bores extending therefrom, which are connected via the annular and crossing spiral grooves forming the channels.

A method of the type mentioned is characterized in that the parts of the die insert are simultaneously removed from the body over its entire circumferential surface for molding. The parts are preferably pulled away magnetically or electromagnetically parallel to the peripheral surface.

In order to ensure the required sinterability of the shaped body (green body), starting materials or calcined powder are ground and isotropically compressed into tablets in a perforated rubber plate in order to subsequently break the tablets thus obtained. For this purpose, the starting materials or the homogenized powder are introduced into recesses in a perforated rubber plate, preferably made of silicone rubber, and is isotropically compressed therein, the recesses should have a volume corresponding to approximately 5 to 30% of the volume of the rubber plate in order to obtain optimal results.

The isotropic pressed granules obtained by breaking the tablets have a diameter of approximately 100 μm. Each granulate is made from 100,000 to 10 000,000 primary particles isotropically constructed, which has a vibratory density of preferably between 0.4 and 1 g / cm³ before compression. The pressed granulate produced has an excellent flow behavior, the bulk density preferably being 0.8 g / cm 3.

A quasi-co-precipitated powder is preferably used as the powder for producing the pot-shaped body, which is calcined, ground, then isotropically pressed into bodies such as tablets, the bodies then being broken up to obtain isotropic pressed granules. Quasi co-precipitated is understood to mean that the starting substance is a suspension and not a solution of ALO (OH).

The granulate filled in the space between the core and the die insert is compressed to the hollow cylindrical body to such an extent that it has a density which corresponds to approximately 30% to 70% of the theoretical density of the finished sintered body.

If the body consists of β ″ aluminum oxide, the density of the body after compression, that is to say the density of the green body after pressing, should be between 1.4 and 1.8 g / cm 3, preferably about 1.6 g / cm 3 be.

In order to achieve optimal manufacturing conditions and to ensure short cycle times for the production of shaped bodies, it is further provided that the pressing and shaping of the body takes place spatially separated from one another.

Further details, advantages and features of the invention result not only from the claims, the features to be extracted from them - individually and / or in combination - but also from the following description of an exemplary embodiment which can be found in the drawing.

Fig. 1

eine prinzipielle Anordnung zum Pressen eines topfförmigen Körpers und

Fig. 2

eine Prinzipdarstellung des nach Fig. 1 gepreßten und auszuformenden Körpers.

Show it:

Fig. 1

a basic arrangement for pressing a pot-shaped body and

Fig. 2

a schematic diagram of the body pressed and molded according to FIG. 1.

The teaching according to the invention is described below on the basis of a hollow cylindrical body made of β ″ aluminum oxide which is closed on one side as a solid electrolyte, in particular for a sodium-sulfur battery, without this resulting in any restriction. Rather, the invention can be used wherever cup-shaped bodies are to be produced from a powder mixture made of oxide ceramic.

In order to produce a pot-shaped solid electrolyte from β ″ aluminum oxide, a homogeneous mixture consisting of AlO (OH) and Na and Li compounds was calcined at about 1450 ° C., preferably in air, for two hours. The weight ratios of the Al-Na and Li compounds were chosen so that after the calcination to more than 98 percent by weight a β '' phase with the chemical composition Na _1.67 Al _10.67 Li _0.33 O ₁₇ formed. The rest was determined by X-ray analysis as sodium aluminate (NaAlO₂).

The calcined powder was then ground in an attritor mill for a period of preferably more than 10 hours, preferably 15 hours, in order to achieve an average grain size in the range of 1.1 μm. After the grinding balls had been separated off, the powder was dried at preferably slightly more than 100 ° C., preferably 105 ° C. The powder was then isotropically compressed in a perforated silicone rubber plate at a pressure of 300 bar into tablets with a height of 5.5 mm and a diameter of 5 mm. The filling volume of the perforated rubber plate was approximately 5 to 30% by volume of the perforated plate itself.

After the isotropic pressing, the tablets were crushed in an impact mill, whereby an isotropic granulate with an average grain size in the range of 100 μm was obtained. Each granulate is made up of an average of approximately 1,000,000 primary particles. The result was excellent flow behavior, a prerequisite for maintaining tight shape tolerances in the manufacture of the solid electrolyte or for preventing warping and cracking during sintering.

In order to press and shape the solid electrolyte, the basic structure uses a device which can be seen in FIGS. 1 and 2. Here, the pressing (FIG. 1) takes place spatially separate from one another and the molding (FIG. 2) in a second work station.

The device for pressing or compacting the granulate powder comprises a die insert (10) which is received by a die (12) in the form of a hollow cylinder. The hollow cylindrical die insert (10) itself consists of several, preferably 4 die parts (14, 16) which merge into one another on all sides. The die insert (10) delimits a cavity (18) in which a core (20) extends. The core (20) consists of a metal mandrel (22) which is surrounded by a rubber membrane and which is tightly connected to the bottom (region 24).

Granule powder (34) is now filled into the space (30) formed between the core (20), that is to say the rubber membrane (26) and the die insert (10) up to its upper surface (28), via a filling funnel (32). The device can be set in a shaking motion so that the granulate powder (34) fills the space (30) to the required extent. Unnecessary granulate powder (34) is removed by sweeping over the top (28) of the die insert (10).

The die insert (10) is then covered by a stamp (68) in order to then compact the granulate powder (34) from the inside outwards from the core (20).

For this purpose, the steel mandrel (22) has fluid outlet openings which start from a central bore (36) and radial bores (38, 40) connected to it. Furthermore, the outlet openings are connected to one another via a ring and spiral grooves, so that the fluid emerging via the central bore (36) and the radial bores (38), (40) into the space between the steel mandrel (22) and the rubber membrane (26) is uniformly distributed and thus the granulate powder (34) can be pressed into the desired cup-shaped geometry. The pressure is preferably built up with oil.

After the granulate powder (34) is compressed, the pressure is reduced. At the same time, the stamp supported on the surface (28) is raised and the core (20) is lowered.

In order to form the compact (green compact) (42) remaining in the female insert (10), the female insert (10) with the female mold (12) is displaced in a molding or ejecting position (FIG. 2), which is spatially separated from the pressed or forming station (Fig. 1) is arranged.

In order to eject the compact (42), a double punch arrangement (44) is provided, which consists of an inner punch (46) and an outer punch (48) arranged coaxially to one another.

For molding, the inner punch (46) is first moved to immediately below the compact. The inner punch (46) and the outer punch (48) are then moved synchronously upwards for jointly ejecting the preferably four-part die insert (10) with the compact (42). The die (12) with the die insert (10) is arranged coaxially to a mold holder (50) which is arranged above the die (12).

In order to ensure that the parts (14), (16) of the female insert (10) are simultaneously and radially removed from the outer surface of the compact (42) when the compact (42) is formed, the following design measures are provided.

As the drawings show, the die insert (10) has a circumferential projecting annular edge (52). The die insert (10) is chamfered on the bottom (inclined surface 54). The shaped receptacle (50) arranged above the die (12) and coaxially to its longitudinal axis (56) has an inner diameter which is equal to the outer diameter of the upper edge (52). If consequently the female insert (10) is moved over the outer die (48) of the double die arrangement (44) into the mold receptacle (50), the die insert (10) is guided circumferentially by the die (12) on the one hand and on the other hand by the mold receptacle (50) added. For this purpose, the shaping receptacle (50) has an inner diameter that is equal to the outer diameter of the annular edge (52) of the die insert, the cylindrical section (58) of which is present outside the edge (52) and the bottom region, has an outer diameter that is the same or only is slightly smaller than the inner diameter of the die (12).

Preferably, a gap is formed between the mold receptacle (50) and the edge (52) or the cylindrical section (58) of the die insert (10) and the die (12), which is in the range between 10 and 100 microns.

Furthermore, the graphic representation of FIG. 2 shows that the shape holder (50) is flared in its upper edge area (60). The conically widened region (60) runs at a distance from a section (62) of the die (12) which receives the edge (52) of the die insert (10) and forms a step and which is equal to the distance between the annular edge (52) and the tapered bottom area (54) of the die insert (10). This distance is in the drawing marked with b.

The mold holder also has magnets (64), (66) running parallel to the longitudinal axis (56), by means of which the parts (14), (16) of the die insert (10) are then spontaneously pulled radially outward from the compact (42) are when the die insert (10) with its bevelled bottom area (54) reaches the area of the step (52). Because of the coordinated dimensions, the ring-shaped edge (52) also reaches the area of the conical widening (60) of the mold receptacle (50) at this moment, so that the die insert parts (14), (16) are pulled off the compact (18) 42) takes place. This, in turn, ensures that the hollow compact (42) cannot be subjected to any forces leading to deformation, which could be noticeable through cracks or warps during the subsequent sintering.

This sudden radial pulling away of the female insert parts (14), (16) from the compact (42) due to the proposed geometrical adjustments of both the female insert (10) and the female mold (12) and the mold holder (50) can be seen as a spontaneous pulling away from the Compact (42) can be called.

This pulling away takes place continuously since the opening angle α in the area of the conical widening (60) of the mold holder (50), against which the lower edge of the annular edge (52) of the die insert (10) is supported, with the angle of inclination α in the bottom area (54 ) of the die insert (10) matches. The slanted bottom area (54) slides along the lower edge of the step-shaped receptacle (62) of the die (10).

As soon as the die insert parts (14), (16) are withdrawn at the required distance a from the compact (42), only the inner punch (46) is raised further in order to make the compact (42) accessible.

In order to ensure to a sufficient extent the uniform radial removal of the parts (14), (16) of the die insert (10) without having to pay attention to its alignment with the magnets (64, 66), there are preferably 8 in the mold holder (50) Magnets (64), (66) arranged evenly distributed.

The compact (42) is then sintered in air at a maximum temperature of 1605 ° C. An isotropic shrinkage of approx. 23% (axial and radial) takes place without warping or cracks.

In order to enable a pressure-free escape of moisture and air from the compact (42) during sintering, it is provided that the granulate powder (34) is compressed during pressing to such an extent that a density is obtained which is approximately 30 to 70%. preferably corresponds to 50% of the theoretical density.

Solid electrolytes of the composition described at the beginning showed the following properties: Density: 3.23 g / cm³ 98.2% of theoretical density Flexural strength: 347 MPa Weibull modulus: 15.3 Specific electrical resistance at 380 ° C: 4.3 Ω cm Structure or grit: <6 µm β '' phase component: 99%

Claims (13)

Device for producing a pot-shaped body (42) from a powder mixture (34) made of oxide ceramics, in particular a hollow cylindrical body made of β ″ aluminum oxide as solid electrolyte for preferably a sodium-sulfur battery, with a space (30) that can be filled with powder mixture , which is formed between a matrix insert (10) consisting of several parts (14, 16) and a core (20, 22, 26) protruding into it and compressing the powder mixture (34) from the inside to the outside, whereby for shaping the cup-shaped Body the parts of the die insert are movable radially outwards,
characterized,
that for shaping the cup-shaped body (42), the die insert (10) is arranged in a shaping receptacle (50) in which the parts (14, 16) of the die insert can be pulled radially outward with uniform objections to the circumference of the pot-shaped body (42) . Device according to claim 1,
characterized,
that in the mold receptacle (50) in the axial direction of the die insert (10) are the parts (14, 16) of the die insert which pull radially outward magnets (64, 66). Device according to claim 1 or 2,
characterized,
that the die insert (10) received by a die (12) has an upper circumferential annular rim (52) projecting from its circumferential surface and a bottom region (54) tapering in the direction of the bottom thereof, that the molding receptacle (50) adapts to the edge Has diameter and that both the die insert and the mold receptacle each have a circumferential extension (60, 62) with a distance b from each other, which is equal to the distance between the annular upper edge and the beveled bottom area. Device according to at least claim 3,
characterized,
that a gap is preferably formed between 10 microns and 100 microns between the inner wall of the mold holder (50) and the outer surface of the peripheral edge (52) of the female insert (10). Device according to at least claim 3,
characterized,
that the beveled bottom area (54) of the die insert (10) assignable extension (62) step-shaped receptacle for the peripheral edge (52) of the die insert (10) in the die (12) is arranged position. Device according to at least one of the preceding claims,
characterized,
that the mold insert (12) can be inserted into the mold receptacle (50) via a double stamp (44) comprising an internal and an external stamp (46, 48), the molded body after removal of the matrix insert parts (14 , 16) is supported by the inner stamp (46). Device according to at least one of the preceding claims,
characterized,
that the inner space (30) which can be filled with the powder mixture (34) delimits the core (20) from a metal mandrel (22) with this surrounding membrane (26), that the metal mandrel has several fluid outlet openings which are connected via channels running peripherally in your metal mandrel and that the metal mandrel preferably has a central bore (36) and radial bores (38, 40) extending therefrom, which are connected via the ring-forming and intersecting spiral grooves. Method for producing a pot-shaped body (42) from a powder mixture (34) made of oxide ceramic, in particular a hollow cylindrical body made of β ″ aluminum oxide, closed on one side, as a solid electrolyte for e.g. B. a sodium-sulfur battery, the powder mixture in a body-defining, between a cavity of a multi-part (14), (16) existing matrix insert (10) and a protruding into this core (20) formed intermediate space (30 ) filled, compacted from the core, shaped by radially moving the parts of the die insert apart and then sintered, starting materials or homogenized powder being at least compressed and broken up to obtain the powder mixture,
characterized,
that to form the body (42), the parts (14, 16) of the female insert (10) are simultaneously removed from the body (42) over its entire circumferential surface. A method according to claim 8,
characterized,
that the parts (14, 16) of the die insert (10) extending parallel to the circumferential surface of the body (42) are preferably pulled away magnetically or electromagnetically therefrom. Method according to at least one of the preceding claims,
characterized,
that the starting materials or the powder are or is compressed to tablets after their or their calcination, the powder mixture obtained by breaking the tablets in the form of pressed granules preferably being built up isotropically on average from 100,000 to 10,000,000 primary particles. Method according to at least one of the preceding claims,
characterized,
that the powder or the starting materials is introduced into recesses in a perforated rubber plate, preferably made of silicone rubber, and is or are compressed isotropically, the recesses having a volume which corresponds to approximately 5 to 30% of the volume of the rubber plate. Method according to at least one of the preceding claims,
characterized,
that the isotropic granules before the introduction and compaction in the space (30) has a vibration density between 0.4 and 1 g / cm³, in particular the vibration density of the powder mixture to be introduced into the space (30) is approximately 0.8 g / cm³. Method according to at least one of the preceding claims,
characterized,
that the body (42) after its shaping has a density which corresponds to approximately 30 to 70% of the theoretical density of the sintered body, and in particular in the case of a body consisting of β ″ aluminum oxide, its density after shaping is between 1.4 and 1 , 8 g / cm³, preferably about 1.6 g / cm³.

Images