JPH06134719A - Method of manufacturing workpiece - Google Patents

Abstract

PURPOSE: To provide a method for manufacturing an artifact from a particulate material, especially to manufacture e.g. the artifact of a holder embodiment consisting of a ceramic material suitable for holding an electrode material of a high temp. recharging type electrochemical battery. CONSTITUTION: The method consists of a stage wherein at least one core 20 wherein at least a part is formed of ice is located in a mass of the particulate material 18, a stage wherein the particulate material 18 around each core 20 is compressed and consolidated and a green artifact in which at least a part of each core 20 is embedded is formed, a stage wherein each core 20 is removed from the green artifact to leave a cavity therein and a stage wherein the green artifact is then sintered to produce a sintered unitary artifact having at least one cavity left therein by removing the core 20.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of manufacturing a processed product from a granular material. The invention particularly relates to a method of manufacturing a workpiece in the form of a holder made of a ceramic material, which is suitable, for example, for holding the electrode material of high temperature rechargeable electrochemical cells.

[0002]

SUMMARY OF THE INVENTION In the present invention, placing at least one core, at least a portion of which is formed from ice, in a mass of granular material, and compressing and strengthening the granular material around each core, Forming an unprocessed workpiece with each core at least partially embedded, removing each core from the untreated workpiece to leave a cavity inside, and sintering the untreated workpiece. To produce a single sintered work piece, the removal of the core leaving at least one cavity therein, to produce a sintered work piece from a sinterable granular material.

The particulate material may be a metal, but ceramic materials or precursors thereof are preferred. The sinter product thus produced consists of a ceramic material having a grain size of 10 to 200 μm.

By "precursor" of a particulate ceramic material is meant a particulate material or mixture which, when heated during the sintering stage, transforms into a sintered ceramic material of a sintered work piece. The granular ceramic material or its precursor has an average particle size of 20 to 50 μm when using isostatic pressing, and 50 to 10 when using uniaxial pressing or die pressing.
It is preferred to have an average particle size of 0 μm.

The particulate material may be a solid electrolyte ceramic material or a precursor thereof, especially when the workpiece is in the form of a holder which holds the active electrode material of a high temperature electrochemical power storage battery.

Since each core contains ice, the step of removing the core may include sublimating at least a portion of the ice in each core at a temperature and pressure at which the ice evaporates without melting. In other words, the core removal step may thus at least partially comprise removing at least a portion of each core by freeze-drying without the generation of liquid moisture.

Each core is typically manufactured by freezing in a suitable mold or slab shape and molding at atmospheric pressure into a suitable shape. The water used for such molding is gas-free and does not contain dissolved gases, particularly preferably carbon dioxide. Therefore, carbon dioxide gas is not generated during sublimation. Carbon dioxide can adversely affect the solid electrolyte material or its precursor. The water can be easily boiled before freezing to remove gas from the water. Deionized water is preferred. Therefore, each core may be formed by molding by freezing under atmospheric pressure. The water used for that purpose contains no gas.

Although each core may, of course, be formed entirely of ice, according to a particular embodiment of the invention, each core may be formed by molding a mixture of ice and sinterable particulate material. Thus, each cavity of the sintered product contains therein a filler in the form of a porous liquid permeation formed of a granular material. The filler acts to increase the strength of the sintered product. Alternatively, each core may be formed from a composite material that includes an inner portion in the form of a mandrel, such as reusable steel. This inner part has on its top a surface layer containing frozen ice.

The placement of each core and mass of particulate material, and subsequent compression strengthening of the particulate material, can be carried out at temperatures and pressures such that each core remains solid during these stages.
Thus, the placement of each core within the particulate material can be performed at temperatures below 0 ° C. under atmospheric pressure. The compression strengthening is performed at a temperature below -4 ° C and the core is removed after the compression strengthening has been performed by reducing the ambient pressure on the untreated work piece to a value at which the ice on the core sublimes. Especially for the removal of the core, the unprocessed processed product is heated to a temperature of -30 ° C to 0 ° C and a pressure of 10 to 500P.
a, preferably under ambient pressure of 50-500 Pa. In a specific example, the untreated processed product is -15 ° C ~
Place at a temperature of 10 ° C. and an ambient pressure of 100 Pa.

The method may include forming one or more closed cavities in the green work piece. in this case,
The removal of the core can be done entirely by sublimation / lyophilization. Water vapor diffuses and passes through the reinforced particulate material until the core is gone and only water vapor remains in each cavity.
Alternatively, depending on the shape of each core, if one or more openings that connect one or more cavities in the work piece to the outside of the work piece are formed in the untreated work piece, then only the surface layer on the core ,
For example, it is preferable to sublimate the ice layer on the mandrel as described above. The core can then be physically removed from the work piece by rotating the mandrel from the work piece when the mandrel is thread shaped.

When one or more cores are in the form of mandrels, each mandrel is described in British Patent Publication No. 2 250 46.
It may be in the shape of a screw as described in No. 7A. Alternatively, each mandrel may be of conventional shape with a smooth cylindrical outer surface and domed ends. In either case, the pressing may be in the form of hydrostatic pressing, for which seeds such as latex seeds are used on ice coated mandrels. A layer of granular material is provided around the ends of the mandrel and adjacent the longitudinal section, with a sheath surrounding the granular layer. If the mandrel is thread-shaped, it can be axially removed from the untreated workpiece as described above after sublimation of the surface layer. With a smooth cylindrical shape, you only have to pull it out in the axial direction.

Alternatively, the method may be used to manufacture a holder in the form of a laterally compressed and flattened casing. In this case, the casing may be press molded as described in British Patent Publication No. 2255 309A. In this case, uniaxial press molding or die press molding is usually used. Each core is shaped and the granular material is arranged such that at least a portion of each core is in the form of a thin slab or layer sandwiched between a pair of layers of granular material.
As a result, after sintering, at least a portion of each cavity is in the form of a narrow gap between opposing plates of sintered ceramic material. Each slab or layer has at least one opening therethrough and filled with particulate material. The granular material within each opening forms a sintered bridge across the interstices between the plates concerned after being reinforced and sintered within the interstices by compression. This bridge may act as a strut or tether between the plates involved to strengthen the holder. This approach is suitable when the holder is for holding the solid electrolyte material of a high temperature electrochemical cell. Thus, as mentioned above, the holder is press-molded to have a compressed or flattened shape, and the holder is, for example, a laterally flattened casing having a pair of opposite outer facing major surfaces. Is. At least one of the cavities is near at least one of the major surfaces of the holder.

In this case, when one or more cavities are closed as described above, each core is completely surrounded by the granular material, so that after compression the cores are completely embedded in the reinforced granular material, Sintering yields a work piece with closed cavities. The method includes forming a filling opening that leads into the cavity from outside the holder after sintering.

In this case, the work piece cavity can be kept closed until filled with the active electrode material. Thus, a suitable filling opening for the active electrode material can be machined into the cavity, if necessary, just prior to filling with the active electrode material. This keeps the surface of the work piece exposed to the cavities clean and pure and prolongs the shelf life of the work piece. This can be important when the active electrode material is a molten alkali metal (eg sodium). Of course, alternatively, the core may have a protruding portion that projects through the particulate material and leaves a feed or fill opening when the core is removed. In this case, during the removal of the core by heating, the material of the sublimed core can be discharged from this opening rather than having to permeate through the particulate material. The core material permeates through the particulate material when the cavity is closed.

In general, compression strengthening of granular material is carried out by hydrostatic pressing or uniaxial (die) pressing after placing a core in the mass of granular material inside a mold, or uniaxial pressing followed by hydrostatic pressing. It can be performed by performing molding.
The strengthening produces a green workpiece surrounding the core. The core should be strong enough so that it does not change during subsequent core removal and sintering. Press molding is 30-150 MPa, preferably 30-100
It can be carried out at a pressure of MPa. In order to obtain good green density and green strength in the green article, the method may include mixing a suitable binder into the particulate material before the core is placed. This binder can act as a lubricant for the lubrication of the press molding. Suitable binders include, for example, polymers or waxes that are soluble in aqueous or organic solvents. Such polymers or waxes include polyvinyl butyrate, polyvinyl acetate, polyvinyl alcohol, polyethylene glycol, polyethylene oxide as well as other polymers known in the art.
Includes waxes and binders. These binders may make up 0.5 to 30% by weight of the binder / electrolyte / precursor mixture, conveniently 0.5 to 15% by weight.

When the ceramic workpiece has a flattened shape and each core is a slab, the compression strengthening of the granular material can be done by uniaxial press molding or die press molding with a metal die. However, if more complex ceramic workpieces are needed, it is preferable to use hydrostatic pressing with soft bags or sheaths for compression strengthening.

In general, the binder remains in place after the ice portion of the core has sublimed. This can be desirable. This is because it allows the binder to remain in place after the initial removal of the core material, strengthening the green workpiece before sintering. The binder typically evaporates during the initial stages of heating performed to sinter the workpiece.

When the holder is used for connection to a bath of active electrode material, for example a molten sodium bath, it is thin and of low volume, ie a narrow gap as described above close to at least one surface of the holder. Two cavities can be formed in the holder. However, when the holder is not used for the connection of anode material to the bath, the holder may further have a bath formed by other cavities and which may have a substantially higher volume.

Thus, the method may use, for example, two or usually three cores embedded in the granular material to provide the sintered workpiece with two or three cavities. One of the cores is a thicker core than the other to provide a bath and the other core is thin and used to provide electrode space near the surface of the workpiece for enhanced ionic conduction. Two cores are used when the work piece comprises a bath of active electrode material and the work piece is used in an electrochemical cell in which the work piece is located on one side of the other active electrode material of the cell. Three cores are used when the workpiece includes a bath of active electrode material and is used in an electrochemical cell sandwiched between two electrode portions of the other active electrode material of the active cell. When three cores are used, the thick core is the central core and the two smaller thin cores are located on opposite sides.

As mentioned above, an important application of the sintered ceramic workpiece produced by this method is expected as an electrode holder for high temperature rechargeable electrochemical cells, usually an anode holder of molten alkali metal. In this case, the solid electrolyte material or its precursor used is selected to provide a ceramic workpiece which is the ionic conductor of the alkali metal in question. Sodium / Sulfur Batteries or Porous, Permeable and Transition Metal Halide Active Cathode Materials Dispersed in a Matrix of Electronically Conductive Material Impregnated with Alkali Metal Haloaluminate Molten Salt Electrolyte For batteries containing molten sodium anodes and cathodes containing, the workpiece electrolyte material can be Nasicon, β-alumina or preferably β ″ -alumina.

Suitable ceramic solid electrolytes further include β-
Β- in which the sodium ion of alumina or β ''-alumina is at least partially replaced by another metal ion
Alumina or an analog of β ″ -alumina may be included. Therefore (in batteries where the anode is such other metal), such a ceramic is a conductor of such other metal ions.

The holder, when made of a solid electrolyte ceramic material, is commonly used in high temperature rechargeable electrochemical power storage batteries that include a pair of electrodes, an anode and a cathode, and the holder. One electrode is held in the holder, the wall of the holder acting as a solid electrolyte separator between the anode and the cathode. The solid electrolyte separator is the ionic conductor of the active anode material of the battery.

Furthermore, such a solid electrolyte holder can provide an electrode structure of the battery, for example, an anode structure, when holding the electrode material of the battery.

Conveniently, the electrode held by the holder is the anode, and (when the ceramic solid electrolyte material is Nasicon, β-alumina or β ″ -alumina) the active anode material is usually an alkali metal (eg sodium). Is a metal like.

The present invention relates to a sintered ceramic workpiece manufactured by the method as described above.

[0026]

The invention will now be described by the following exemplary embodiments with reference to the accompanying drawings.

Reference numeral 10 in FIG. 1 generally designates a mold / die mechanism during uniaxial pressing of the holder in the form of a compressed, laterally flattened casing in accordance with the method of the present invention. The mechanism 10 includes a die or die body 12, a movable die plunger 14, and a movable die plunger 16.
Includes and.

An agglomerate of granular β ″ -alumina particles 18 having a particle size of 50 to 100 μm mixed with 15% by weight of water-soluble wax, that is, polyethylene glycol, is shown inside the body of the mold. A core 2 made of ice produced by press-molding finely crushed ice in a suitable mold at −2 ° C. and a pressure of 20 MPa.
0 (see also FIG. 2; core is shown at 20) embedded within the mass of particles 18. Therefore, crush the finely crushed ice under the appropriate pressure of a uniaxial die / plunger set of appropriate shape
It can be press molded at 2 ° C. to form a core with through openings 22 (described below). The core may then be stored at, for example, -15 ° C until use.

Still referring to FIG. 2, a flat rectangular slab or plate shaped core 20 extends through the core and is evenly distributed over the entire region at regular intervals and interconnects a plurality of major surfaces 24. It has a section 22.

In accordance with the method of the present invention, the mechanism 10 is shown in FIG.
Plunger 14 is retracted as shown in Fig.
6 is set in a predetermined position. A particulate mixture of premixed β-alumina particles 18 and wax is filled into the mold as described below and a preformed ice core 20 is embedded in the mixture 18 as shown. This operation fills the mold interior with a rather flat layer containing about half of the mixture 18, placing the core 20 on top of this layer and the remaining mixture 18 over the core 20 inside the mold in a second. It is carried out by filling as a flat layer. The second flat layer is the opening 22 and the core 20 and the body 1 of the mold or die.
The surrounding space between the two walls is also blocked. Next, the plunger 14 acts as an anvil to compress the mixture 18 around the core 20 and in the openings 22.
6 is moved in the uniaxial direction indicated by arrow 26. The plunger 14 is then retracted in the opposite direction and the unprocessed work piece, including the core 20, is removed from the mold 12.

In this press molding, the core 20 has a temperature of -15 ° C.
Mixture 18, mold 12, and plungers 14, 16 are -10
Temperature of ℃, around -10 ℃, for example 45-50MP
It is carried out under the pressure of a. Alternatively, the mixture may be compressed under a room temperature environment if the operation can be performed sufficiently quickly so that the ice does not melt. However, the core, the powder, and the mechanism 10 may each have a temperature of −15 ° C. or − depending on the case.
Precool to 10 ° C.

As will be explained later, the untreated workpiece is first lightly heated under vacuum to sublimate the ice core. The untreated work piece is then further heated in air to 400 ° C. (in some cases up to 500 ° C.) to remove free water and polyethylene glycol associated with the particulate mixture. The untreated work piece is then further heated in air to 1600 ° C. to sinter the β ″ -alumina particles to form a continuous single sintered polycrystalline β ″ -alumina work piece. To do.

This work piece is a flat-shaped hollow casing and has a flattened continuous internal cavity in the form of a gap formed by a core 20 formed from a sintered material 18 formed by the main surfaces of the casing. Between the sintering plates. Β ″ -alumina material 18 in opening 22
Is sintered and integral with the major surface 24 of the casing,
The main surface is reinforced and strengthened and a pillar (connecting member or support) is formed at a distance from the main surface. The major surface 24 of the casing is provided by a plate formed from a layer of mixture particles 18 on opposite sides of the core 20 in the mold 12. These major surfaces 24 are joined at the periphery of the casing by the mixture 18 filled in the peripheral space between the edges of the core 20 and the mold 12.

In this regard, the core 20 (FIG. 2) may have an outer protrusion in the form of a tab or ear 28 intermediate along one lateral edge. The core is inserted into the mold 12 so that the ears 28 contact the mold wall at 30 (FIG. 1). After removing the core and sintering, the ear 28 leaves a space. This space forms an opening for feeding or filling from the outside of the casing through the lateral edges into the internal cavity of the casing made by the core 20.

In contrast, in FIG. 3 the ears 28 have been eliminated and instead a pair of truncated cylindrical bosses 32 have been used. Each of these bosses is located in a central location on the opposite, outwardly facing major surface of the core. One boss is shown in FIG. The core of FIG. 3 is placed in the mold such that there is no mixed material 18 between the boss 32 and the plunger 14 and between the boss 32 and the anvil 16, respectively. After removing the core and sintering, the spaces created by these bosses provide the casing with a pair of opposing central openings through the major surface of the casing wall.

As a variant of the method described above, it is necessary to provide a special part (for example the ear 28 in FIGS. 1 and 2 or the boss 32 in FIG. 3) for the opening leading into the casing before sintering. There is no. In general, water vapor from the ice core 20 can diffuse through the walls of the casing before the walls become dense due to sintering, so evaporation or sublimation can occur without openings to the interior of the casing. If desired, openings can be provided after sintering, for example by machining, which lead into the interior of the casing.

Another variation of the method involves the use of molding surfaces on at least one of the plungers 14, 16 as shown at 34 on the upper plunger 14 in FIG. The surface in question taps in from the peripheral strip 36 by 38 shallow steps. This feature enhances the compactness along the perimeter of the untreated casing and the final casing after sintering. The degree to which the dense state increases depends on the compressibility of the core 20 and the mixture 18.

Another variant of the method involves the use of a plunger whose pressing surface is coated with a layer of soft material, for example polyurethane. This applies a uniform pressure over the entire surface of the casing.

In this regard, the casing, in use, holds the molten sodium anode material of a high temperature electrochemical power storage battery having the molten sodium anode material, and the opening provided by the ear 28 or boss 32 is: The inner cavity of the casing with a bath of molten sodium and / or
Or used as an inlet / outlet to communicate with other similar casings containing molten sodium.

Similar to the cores of FIGS. 2 and 3, the core 20 of FIG. 4 is in the form of a rectangular flat slab or plate, which extends through a plurality of evenly spaced and evenly spaced from each other. It has an opening 22. As in FIGS. 2 and 3, each opening 22 in the core 20 interconnects the plates that provide the major surface 24 of the core 20 and is generally hourglass-shaped when viewed in the side cross-sectional view shown in FIG. It is in the form of a passage. The opening has walls that are convexly curved inward so as to have a narrow waist portion that communicates with the inlets at opposite side ends of the passage. The inlet is conically flared, tapered inward, and convexly curved in a lateral cross section. The peripheral edge 39 of the core 20 is rounded, convexly curved and has a lateral cross section similar to the walls of the passage 22.

The hourglass ties or struts resulting from the shape of the passages 22 where the passages have rounded edges, where they meet the major surfaces, and the casing (caused by the rounded edges 39 of the core 20). The rounded peripheral edges help prevent cracking of the sintered work piece. Such cracks can be caused by thermal stress and stress resulting from pressure changes through the casing wall. In fact, as mentioned above, no opening to the unprocessed workpiece is necessary to allow the release of subliming or evaporating ice. Therefore (as opposed to the ear 28 of FIG. 2 and the boss 32 of FIG. 3)
The core of FIG. 1 has nothing to provide such an opening. Water vapor may in fact diffuse through the walls of the unprocessed workpiece. The walls are sufficiently porous to allow this diffusion, but are substantially gas tight after sintering. The absence of such openings can be an advantage, as the interior of the holder is protected and kept pure for long shelf life. If desired, the opening leading into the internal cavity of the workpiece can be machined just prior to use, for example by drilling.

In FIG. 4, the core is designated generally by 20, and the same reference numerals are used for the same parts as in FIG. Figure 4
2 is different from the core 20 of FIG. 2 and FIG. 3 in that the core 20 of FIG. 4 has particles of the wicking material, for example, the β ″ -alumina particles 18 used in the processed product as described above. A surface layer 40 containing a mixture of polyethylene glycol and an appropriate amount of carbon spheres of similar dimensions. During sintering, the carbon burns out, leaving a porous sintered β ″ -alumina layer that covers the cavities or interstices of the sintered casing. This porous lining is suitable for wicking molten sodium from the inside of the cavity into the molten sodium layer coating the inside surface of the cavity by capillary action during use, as will be explained later.

As mentioned above, in use, the holder produced by the mechanism shown in FIG. 1 is typically an anode holder containing molten sodium in a high temperature electrochemical power storage cell (although, of course, a cathode holder). May be). In such a cell, the holder is arranged sandwiched between two cathode parts in the cell housing. In this case, the holder produced by the mechanism of Figure 1 may have a machined opening for connection to an external molten sodium bath, as described above.

The reference numeral 42 in FIG. 5 generally indicates the apparatus used in the method of the present invention. The device 42 is in the form of a press jig that includes a hollow cylindrical soft iron outer housing 44 having a portion that is longitudinally split and held by an outer steel ring clamp 46. The jig 42 has a cylindrical latex plug 4 whose upper end is elastically soft.
It is shown in the upright operating state, closed at 8. Flexible polyurethane may be used in the plug 48 instead of latex.

A vertically split mold 50 having a portion retained by the housing 44 is coaxially disposed within the housing 44 below the plug 48. The top of the mold 50 has a central opening 52 that is closed by a plug 54 of a material similar to the plug 48. As will be described in more detail below, the mold 50 has a threaded hollow interior with an opening 52 communicating therewith. The mold 50 further has a mouth 56 at its lower end which leads to the interior.

A threaded mandrel 58 is coaxially disposed within the hollow interior of the mold 50, radially spaced inward from the mold, and loosely engaged with the mold. The mandrel 58 has a central stem or stem portion 62 with a root portion 60 received at the mouth 56 and a screw 64 extending helically and extending from the root portion 60 to the opposite end of the stem portion 62.
Have.

As can be seen in FIG. 5 and as previously described, the internal cavity of mold 50 has a threaded shape and is provided with helically extending female threads 68.

The pitch of the screws 64 is the same as the pitch of the screws 68. Mandrel 58 may be spaced radially inward from the walls of the cavity of mold 50 within the mold,
It is also dimensioned to be axially spaced from the threads of the screw 68 so that the threads of the screw 64 complementarily engage the threads of the screw 68. Therefore,
The mold 50 and the mandrel 58 form a male and female thread shaped annular space 70 therebetween. In this space 70,
Latex seeds 7 that are elastically soft and continuous in an airtight state
2 is equipped. Sheath 72 abuts the threaded inner surface of mold 50 and forms an inner surface lining.
The sheath is open at its upper end and projects outwardly through an opening 52 having a perimeter of the open upper end clamped between the plug 48 and the top of the mold 50. The plug 54 closes this upper end. Therefore, a spiral-shaped space 70 exists between the sheath 72 and the outer surface of the mandrel 58.

In use, the jig 10 is installed as shown in FIG. The clamp 46 connects the housing 44 to the cylindrical outer surface of the mold 50, the plug 48 and the root portion 60 of the mandrel 58.
Abut. Accordingly, the plug 48 seals one end of the housing 44, and the root portion 60 of the mandrel 58 with the open end 74 of the sheath 72 sandwiched between the root portion and the housing 44 causes the lower end of the housing to reach the lower end. Seal it.

To manufacture the electrode holder according to the method of the present invention, the jig 42 is installed as shown in FIG. However, the plugs 48 and 54 are removed, and the mandrel 58 is
The lowermost clamp 46 around the root portion 60 of the is sufficiently clamped to simply prevent the powder from leaking out of the space 70.

Then a suitable powder, for example a particle size of 20-5
The β-alumina or β ″ -alumina having a size of 0 μm and mixed with 15% by mass of polyethylene glycol provided the seeds 72 and the mandrel 58 through the opening 52 while applying appropriate vibration for compressing and solidifying the powder. Space between 7
Filled within 0. When the space 70 is filled with powder 76, the plug 54 is inserted into place and then the plug 48.
Is then inserted and then the clamp 46 is finally tightened to completely seal the housing 44 against the plug 48 and the root portion 60 of the mandrel 58. A small open space 78 is left above the powder 76 and below the plug 54.

The mold 50 includes one or more suitable passageways and, for example, one or more suitable passageways in the plug 48 (not shown).
Pinholes (not shown) that communicate with the outside via
Is equipped with.

Next, to hydrostatically press the untreated thread-shaped hollow electrode holder from the layer of powder 76 filled in the space 70, under appropriate pressure, the passages in the mold 50 and various pins. Water is introduced to the outside of the seeds 72 through the hole. This pressure can be, for example, 35 to 50 MPa.

After press molding, the pressure is reduced, and the sheath 72, which is elastically soft and is formed so as to automatically fit with the inner surface of the mold 50, bounces back and comes into contact with the mold 50. Away from the holder. After the clamp 46 is loosened, the raw holder and mandrel 58 is removed from the mold 50.
Can be axially removed downward from the inside of the.

Pinholes are distributed between the mold 50 and the sheath 72 on the threaded inner surface of the mold 50 to provide a layer of water under said pressure. This water presses the sheaths inwardly, compressing the powder 76 against the threaded outer surface of the mandrel 58.

As described with reference to FIGS. 1-3, press molding may be carried out in an environment containing powder 76 and jig 42 set at, for example, -10.degree. The water used in isostatic pressing is also at -10 ° C and contains a suitable antifreeze that dissolves in water.

The mandrel 58, its root 60, stem 62 and screw 64 are shown in FIG. A feature of mandrel 58 is that the mandrel is made of stainless steel and has an ice surface layer 80 of about 0.5 mm thickness.

This surface layer is generally similar to the mold 50 shown in FIG. 5, but with a split mold (not shown) having an inner surface that is threaded and sized and shaped to provide the surface layer 80 on the steel portion of the mandrel. ) Is formed by placing the steel part of the mandrel inside. The layer is typically formed by freezing deionized water on the steel portion of the mandrel and then removing the mold. In this regard, the surface of the steel portion of the mandrel may be treated, for example by roughing. The inner surface of the mold can be treated, for example by providing a plastic lining. As a result, ice layer 80 adheres more strongly to the steel portion of the mandrel than the mold, making mold removal easier. The mandrel 58 with an ice layer can be stored at -15 ° C.

A test apparatus demonstrating the feasibility of the core removal step of the present invention is shown in FIG. However, of course, a commercially available freeze-drying device may be used instead of this device. Device 82
Includes a vacuum dryer 84 having a large inner diameter tube 86 leading to a vacuum pump (not shown) connected to the end of the tube 86 remote from the dryer 84. The tube 86 has a U-shaped portion 88 immersed in a container-shaped cold trap 90.

In use, -60 such as liquid nitrogen 94
The container 90 is filled with a refrigerant having a temperature lower than ℃,
The dryer 84 was set at -15 ° C and press-molded-
Untreated workpiece at 15 ° C. (untreated spiral hollow holder around flattened untreated casing or mandrel around core 20 as shown at 92 in FIG. 7, 28 and layer 76 in FIG. 5). Is placed in the dryer 84, and a vacuum state of about 100 Pa is generated in the tube 86 via a vacuum pump.

On untreated workpieces with openings leading to cavities (see FIGS. 2, 3 and 5) or on completely closed untreated workpieces without openings leading to internal cavities. (See FIG. 4) In the tests performed by the applicant, the ice core 2
It has been found that a zero or ice layer 80 can easily sublime in some cases without producing liquid water. In these tests,
The vacuum core mass loss resulting from ice sublimation was used to monitor the removal of the ice core. Ice cores with a mass up to 30 g can be removed in about 12 hours, and the dryer can slowly heat to room temperature during this time, while the sublimed vapors in the U-tube section 88. Turned out to freeze. Similar results were obtained with a commercial freeze dryer.

In the casing manufactured as described with reference to FIGS. 1-4, there was a polyethylene glycol binder that provided sufficient green strength to handle during sintering after sublimation / freeze drying. . According to the method described with reference to FIGS. 5 and 6, the steel portion of the mandrel 50 had to be removed after sublimation / freeze drying, but the layer 80
Sublimation allowed the steel portion of the mandrel 50 to be easily rotated and removed from the untreated workpiece which also retained the appropriate untreated strength for removal and subsequent sintering.

In the embodiment of the present invention, the core 20 (see FIGS.
The mandrel 50 (see FIG. 4) or layer 80 (see FIGS. 5 and 6) is molded from deionized water as described above. Individually, the mixture may have an average particle size of between 50 and 1
It is composed of β ″ -alumina powder of 00 μm or 20 to 50 μm and polyethylene glycol. Polyethylene glycol was mixed with β ″ -alumina as a 30 mass% aqueous solution, and the ratio was polyethylene glycol and β ″ −.
It reaches 15% by weight, based on the dry basis of the mixture with alumina.
After mixing in this manner, spray drying is performed at a dryer outlet temperature of 130 ° C. to reduce the water content to 10% by mass or less.

Β ″ -alumina precooled to −10 ° C.
Similarly, mechanism 10 (FIG. 1) or jig 4 precooled to -10 ° C.
2 (FIG. 5) and then press molded at a pressure of 48-50 MPa (FIGS. 1 and 5) or 230-240 MPa (FIG. 5) to reduce the wall thickness of the casing or layer 76 (FIG. 5). Decrease about 40% of the original value, for example 5 mm to 2 mm.

After sublimation and freeze-drying as described with reference to FIG. 7 to remove the steel portion of the mandrel 50 (FIGS. 5 and 6), the unprocessed workpiece was subjected to the following heating conditions in the atmosphere. Heat to remove polyethylene glycol and residual water by evaporation and dissociation from β ″ -alumina, then sinter the work piece.

Room temperature to 400 ° C. at 25 ° C./hour (in air) 400 to 1600 ° C. at 100 ° C./hour (in air) 1600 to 1617 ° C. at 60 ° C./hour (under air) 1617 to 1000 at 240 ° C./hour ° C (under air) 1000 ° C at 360 ° C / hour-room temperature (under air) Temperature set for press molding, ie, -10 to -15
FIG. 8 shows that at 0.degree. C., a pressing pressure of 35-100 MPa can easily be used without melting the core 20 (FIG. 1) or the surface layer 80 (FIG. 6). FIG. 9 shows a water phase diagram using a plot of pressure against temperature. It can be seen from FIG. 9 that the freeze / sublimation cycle (shown by the arrow line in FIG. 9) used in the method of the present invention is possible. Liquid atmospheric pressure is 1 atm (about 100 kPa)
Frozen at −15 ° C., then pressure is 10 ⁻³
It is reduced to atmospheric pressure (about 100 Pa). At this pressure, it sublimes when the temperature rises.

[Brief description of drawings]

FIG. 1 is a schematic side cross-sectional view of an untreated holder manufactured according to the method of the present invention, showing the state of a blank placed in a mold during uniaxial press molding of an untreated workpiece by a die. It is a figure.

2 is a three-dimensional schematic view of a core used in the mold of FIG.

FIG. 3 is a three-dimensional schematic view of another core used in the mold of FIG.

FIG. 4 is a schematic side cross-sectional view of another core used in the mold shown in FIG.

FIG. 5 is a schematic side cross-sectional view of another untreated holder manufactured according to the method of the present invention, showing a state during hydrostatic pressing around a mandrel placed in a mold. Is.

6 is a side sectional view of the mandrel shown in FIG.

FIG. 7 is a schematic diagram of an apparatus used for sublimation according to the present invention.

FIG. 8 is a graph showing a plot of melting point of ice against pressure.

FIG. 9 is a phase diagram of water showing phase in a plot of pressure against temperature.

[Explanation of symbols]

 14, 16 Plunger 20 Core 22 Opening 24 Main surface 32 Boss 44 Housing 58 Mandrel

Claims (11)

[Claims] 1. Placing at least one core, at least a portion of which is formed from ice, in a mass of particulate material;
Compressing and strengthening the granular material around each core to form an unprocessed workpiece in which each core is at least partially embedded, and removing each core from the unprocessed workpiece to create a cavity inside. A sinterable granular material comprising the steps of leaving and sintering an unprocessed work piece to produce a single sintered work piece with at least one cavity left inside by removal of the core. A method of manufacturing a sintered product from a product. 2. The granular material is a ceramic material or a precursor thereof, and thus the sintered products produced are 10 to 200.
Method according to claim 1, characterized in that it consists of a sintered ceramic material having a grain size of μm. 3. The ceramic material is a solid electrolyte ceramic material or a precursor thereof when the workpiece is in the form of a holder for holding the active electrode material of a high temperature electrochemical power storage battery. The method described in. 4. The core removing step comprises subliming at least a portion of the ice in each core at a temperature and pressure at which the ice evaporates without melting.
4. The method according to any one of 3 to 3. 5. The method according to claim 1, wherein each core is formed by molding by freezing under atmospheric pressure and the water used for that is gas-free. Method. 6. Each core is formed by molding a mixture of ice and sinterable particulate material, and thus each cavity of the sintered work piece comprises:
A method according to claim 5, characterized in that it contains a filler in the form of a porous liquid permeable form formed from a granular material, which filler acts to increase the strength of the sintered workpiece. 7. The core is formed of a composite material having on its top an inner portion having a surface layer that is reusable and contains frozen ice. 7. The method according to any one of items 6 to 6. 8. Placing each core within the mass of particulate material and subsequent compression strengthening of the particulate material is carried out at a temperature and pressure such that each core remains solid during these steps. Method according to any one of claims 1 to 7, characterized. 9. The placement of each core in the granular material is carried out at a temperature below 0 ° C. under atmospheric pressure, the compression strengthening being −4 ° C.
Lower temperature and the removal of the core is carried out after the compression strengthening has been carried out by lowering the ambient pressure on the untreated work piece to a value at which the ice in the core sublimes. The method according to 8. 10. The core is removed by -3
The method according to claim 9, which is carried out at a temperature of 0 ° C to 0 ° C and an ambient pressure of 10 to 500 Pa. 11. A sintered ceramic material produced by the method according to claim 1.