TWI895776B - A sintering device having low surface roughness, process and use of a die for preparation of a ceramic body - Google Patents

Abstract

A device having a sintering chamber, the sintering chamber being bordered by the following device parts: i. a first punch surface of a first punch; ii. a second punch surface of a second punch; and iii. an interior surface of a die; wherein: the punches are adapted and arranged to apply a pressure of at least 1 MPa along a compression axis to a target in the sintering chamber; the first punch and the second punch are connected to an electrical power source adapted and arranged to provide a current of at least 10 kA; the first and second punches comprise at least 50 wt. % carbon, based on the total weight of the punch; the sintering chamber has a cross-sectional width W perpendicular to the compression axis of at least 300 mm; wherein the die has a surface portion χ at least 5 cm ²in area, wherein the surface portion χ is located on the interior surface of the die and wherein the surface portion χ has a mean surface roughness (Sa) in the range from 1 µm to 8 µm

Description

Sintering device with low surface roughness, process for preparing ceramic body, and use of mold for preparing ceramic body

The present invention generally relates to sintering under pressure and using an electric current, commonly referred to as spark plasma sintering (SPS). Specifically, the present invention relates to a sintering apparatus, a sintering process, a ceramic body product, an assembly including a ceramic body, and the use of a mold for the apparatus to achieve low surface roughness during the sintering process.

Sintering methods offer a way to form solid bodies from particles by applying heat and pressure. In one method, often referred to as spark plasma sintering (SPS), heating is achieved using an electric current. State-of-the-art SPS methods have been applied to a variety of materials. Existing literature focuses on small-scale systems, providing access to components with a solid extension of up to approximately 150 mm. The problems of using SPS to prepare larger parts were assessed from a theoretical perspective by Eugene A. Olevsky et al. in the following papers: "Fundamental Aspects of Spark Plasma Sintering: I. Experimental Analysis of Scalability" (J.Am.Ceram.Soc., 95[8], 2406 to 2413 (2012)) and "Fundamental Aspects of Spark Plasma Sintering: II. Experimental Analysis of Scalability" (J.Am.Ceram.Soc., 95[8], 2414 to 2422 (2012)). Several potential challenges and complexities associated with large-scale systems were identified.

An object of the present invention is to provide an improved process for preparing a ceramic body. A specific object of the present invention is to provide an improved process for preparing ceramic bodies of increased size.

An object of the present invention is to provide an improved process for preparing a ceramic body with reduced energy requirements.

An object of the present invention is to provide an improved process for preparing a ceramic body with a reduced scrap rate.

An object of the present invention is to provide an improved process for preparing a ceramic body having reduced susceptibility to cracking.

An object of the present invention is to provide an improved process for preparing a ceramic body having reduced internal stress.

An object of the present invention is to provide an improved process for preparing a ceramic body having increased mechanical strength.

An object of the present invention is to provide an improved process for preparing a ceramic body having increased density.

An object of the present invention is to provide an improved process for preparing a ceramic body having increased density homogeneity.

An object of the present invention is to provide an improved process for preparing a ceramic body having increased etch resistance.

An object of the present invention is to provide an improved process for preparing a ceramic body having reduced surface roughness.

One object of the present invention is to provide a device for executing the aforementioned improvement process.

Any of the embodiments of the present invention contributes to at least partially achieving at least one of the objectives mentioned above.

A first embodiment of the present invention is an apparatus having a sintering chamber, the sintering chamber being partially defined by: i. a first punch surface of a first punch; ii. a second punch surface of a second punch; and iii. an inner surface of a mold; wherein: the punches are adapted and configured to apply a pressure of at least 1 MPa, preferably at least 5 MPa, more preferably at least 10 MPa, and most preferably at least 15 MPa along a compression axis to a target in the sintering chamber. The punches can be adapted and configured to apply up to 50 MPa or even more; the first and second punches are connected to a power supply adapted and configured to provide a current of at least 10 kA, more preferably at least 50 kA, and most preferably at least 60 kA. The power supply can be adapted and configured to provide a current of up to 100 kA or even more. The first and second punches contain at least 50 wt.%, preferably at least 90 wt.%, more preferably at least 95 wt.%, and most preferably at least 99 wt.% carbon, based on the total weight of the punches. The sintering chamber has a cross-sectional width W perpendicular to the compression axis of at least 300 mm, preferably at least 500 mm, and more preferably at least 700 mm. W can be as high as 2000 mm or higher. Preferably, it is no greater than 1500 mm, more preferably no greater than 900 mm; wherein the mold has a surface portion x having an area of at least 5 cm², wherein the surface portion x is located on the inner surface of the mold, and wherein an average surface roughness (Sa) of the surface portion x is in the range of 1 μm to 8 μm, preferably in the range of 2 μm to 7 μm, more preferably in the range of 3 μm to 6 μm, and even more preferably in the range of 3 μm to 5 μm.

In one aspect of the first embodiment, the area of the surface portion x is preferably at least 10 cm ² , more preferably at least 50 cm ² , and even more preferably at least 100 cm ² .

In a preferred embodiment of the device, the first head has a surface portion α having an area of at least 5 cm ² , and an average surface roughness (Sa) of the surface portion α is in the range of 1 μm to 8 μm, preferably in the range of 2 μm to 7 μm, more preferably in the range of 3 μm to 6 μm, and further preferably in the range of 3 μm to 5 μm. This preferred embodiment is the second embodiment of the present invention and is preferably dependent on the first embodiment of the present invention.

In an aspect of the second embodiment, the area of the surface portion α is preferably at least 10 cm ² , more preferably at least 50 cm ² , and even more preferably at least 100 cm ² . In an aspect of the second embodiment, the surface portion α preferably at least partially overlaps with a mold-contacting surface of the first punch.

In a preferred embodiment of the device, the surface portion α at least partially overlaps with the first head surface. This preferred embodiment is the third embodiment of the present invention, which is preferably dependent on the second embodiment of the present invention.

In a preferred embodiment of the device, the surface portion α is at least partially in contact with the surface portion χ. This preferred embodiment is the fourth embodiment of the present invention and is preferably dependent on the third embodiment of the present invention.

In a preferred embodiment of the device, the second punch head has a surface portion β having an area of at least 5 ^cm² , and an average surface roughness (Sa) of the surface portion β is in the range of 1 μm to 8 μm, preferably in the range of 2 μm to 7 μm, more preferably in the range of 3 μm to 6 μm, and even more preferably in the range of 3 μm to 5 μm. This preferred embodiment is the fifth embodiment of the present invention and is preferably dependent on any of the first to fourth embodiments of the present invention. In one aspect of the fifth embodiment, the area of the surface portion β is preferably at least 10 ^cm² , more preferably at least 50 ^cm² , and even more preferably at least 100 ^cm² . In one aspect of the fifth embodiment, it is preferred that the surface portion β at least partially overlaps with a mold contact surface of the second punch. In one aspect of the fifth embodiment, it is preferred that the surface portion β at least partially contacts the surface portion x.

In a preferred embodiment of the device, the surface portion β at least partially overlaps with the second head surface. This preferred embodiment is the sixth embodiment of the present invention, which is preferably dependent on the fifth embodiment of the present invention.

In a preferred embodiment of the device, the surface portion χ has at least one or all of the following characteristics: a. a maximum height (Sz) in the range of 20 μm to 100 μm, preferably in the range of 35 μm to 87 μm, and more preferably in the range of 44 μm to 62 μm; b. a surface texture aspect ratio (Str) in the range of 0.01 to 0.75, preferably in the range of 0.1 to 0.65, and more preferably in the range of 0.41 to 0.5; c. an arithmetic mean peak curvature (Spc) of at least 4000 mm ^-1 , preferably at least 7000 mm ^-1 , and more preferably at least 8000 mm ^-1 ; d. an interface area ratio (developed interfacial area ratio) of at least 100 μm to 100 μm; ratio) (Sdr) is at least 4, more preferably at least 12, and even more preferably at least 14.

This preferred embodiment is the seventh embodiment of the present invention and is preferably dependent on any of the first to sixth embodiments of the present invention. In one aspect of the seventh embodiment, all possible combinations of features a. through d. are preferred aspects of the embodiment. These combinations include, for example, a; b; c; d; a+b; a+c; a+d; b+c; b+d; c+d; a+b+c; a+b+d; a+c+d; b+c+d; a+b+c+d.

In a preferred embodiment of the device, the surface portion α and/or the surface portion β have at least one or all of the following characteristics: a. a maximum height (Sz) in the range of 20 μm to 100 μm, preferably in the range of 35 μm to 87 μm, and more preferably in the range of 44 μm to 62 μm; b. a surface texture aspect ratio (Str) in the range of 0.01 to 0.75, preferably in the range of 0.1 to 0.65, and more preferably in the range of 0.41 to 0.5; c. an arithmetic mean peak curvature (Spc) of at least 4000 mm ^-1 , preferably at least 7000 mm ^-1 , and more preferably at least 8000 mm ^-1 ; d. an interface area ratio (developed interfacial area ratio) of at least 100 μm to 100 μm; ratio) (Sdr) is at least 4, more preferably at least 12, and even more preferably at least 14.

This preferred embodiment is the eighth embodiment of the present invention and is preferably dependent on any of the second to seventh embodiments of the present invention. In one aspect of the eighth embodiment, all possible combinations of features a. through d. are preferred aspects of the embodiment. These combinations include, for example, a; b; c; d; a+b; a+c; a+d; b+c; b+d; c+d; a+b+c; a+b+d; a+c+d; b+c+d; a+b+c+d.

In a preferred embodiment of the apparatus, the punch and the mold are at least partially contained in a vacuum chamber, a non-oxidizing atmosphere, or both. This preferred embodiment is the ninth embodiment of the present invention and is preferably dependent on any one of the first to eighth embodiments of the present invention.

In a preferred embodiment of the device, the power supply is adapted and configured to supply a DC voltage. This preferred embodiment is the tenth embodiment of the present invention, and is preferably dependent on any one of the first to ninth embodiments of the present invention.

In a preferred embodiment of the device, one or more of the following conditions are met: a. the first punch is at least 99% wt.% carbon, based on the total weight of carbon atoms in any chemical form and the total weight of the first punch; b. the second punch is at least 99% wt.% carbon, based on the total weight of carbon atoms in any chemical form and the total weight of the second punch; c. the mold comprises at least 50% wt.%, more preferably at least 90% wt.%, and even more preferably at least 99% wt.% carbon, based on the total weight of carbon atoms in any chemical form and the total weight of the mold.

This preferred embodiment is the eleventh embodiment of the present invention and is preferably dependent on any of the first to tenth embodiments of the present invention. In one aspect of the eleventh embodiment, all possible combinations of features a. through c. are preferred aspects of the embodiment. These combinations include, for example, a; b; c; a+b; a+c; b+c; and a+b+c.

In a preferred embodiment of the device, the device comprises one or more further device parts selected from the following list: a. a housing; b. a vacuum device; c. a hydraulic piston.

This preferred embodiment is the twelfth embodiment of the present invention, and is preferably dependent on any of the first to eleventh embodiments of the present invention. In one aspect of the twelfth embodiment, all possible combinations of features a. through c. are preferred aspects of the embodiment. These combinations include, for example, a; b; c; a+b; a+c; b+c; and a+b+c.

The thirteenth embodiment of the present invention is a process for preparing a ceramic body, comprising the following steps: a. providing a plurality of particles; b. providing an apparatus according to the present invention, preferably an apparatus according to any one of the first to twelfth embodiments of the present invention; c. introducing the particles into a sintering chamber; d. applying a pressure P in the range of 1 MPa to 50 MPa and a current I in the range of 10 kA to 100 kA, more preferably in the range of 25 kA to 100 kA, and even more preferably in the range of 50 kA to 100 kA to the plurality of particles in the sintering chamber, to obtain the ceramic body.

In a preferred embodiment of the process, the particles contain at least 30 wt.%, preferably at least 40 wt.%, and more preferably at least 45 wt.% yttrium in any chemical form, based on the total mass of yttrium atoms and the total mass of the particles. This preferred embodiment is the fourteenth embodiment of the present invention, which is preferably dependent on the thirteenth embodiment of the present invention.

The fifteenth embodiment of the present invention is a ceramic body obtainable by the process of the present invention, preferably the process of the thirteenth or fourteenth embodiment of the present invention.

In a preferred embodiment of the ceramic body, at least one or all of the following conditions are met: a. the value of density divided by theoretical density is less than 1.0; b. an average grain size is less than 5 μm, preferably less than 4.5 μm, more preferably less than 4 μm, and further preferably from 1 μm to 3 μm; c. the standard deviation of the average grain size distribution is within the range of 1.2±2 mm to 2.8±2 mm, preferably within the range of 1.6±2 mm to 2.4±2 mm, and more preferably within the range of 1.8±2 mm to 2.2±2 mm.

This preferred embodiment is the sixteenth embodiment of the present invention, which is preferably dependent on the fifteenth embodiment of the present invention. In one aspect of the sixteenth embodiment, all possible combinations of features a. through c. are preferred embodiments. These combinations include, for example, a; b; c; a+b; a+c; b+c; and a+b+c. In one aspect of the sixteenth embodiment, in feature a., the value of density divided by theoretical density is preferably at least 0.9, more preferably at least 0.95, and even more preferably at least 0.99.

The seventeenth embodiment of the present invention is an assembly comprising a ceramic body according to the present invention, preferably a ceramic body according to any one of the fifteenth to sixteenth embodiments of the present invention.

In a preferred embodiment of the assembly, the assembly is selected from the group consisting of: a. a plasma etcher, b. a plasma processing chamber (etching or deposition process), c. a wear plate for a bearing, and d. a mill liner for a grinder.

This preferred embodiment is the eighteenth embodiment of the present invention, which is preferably dependent on the seventeenth embodiment of the present invention. In one aspect of the eighteenth embodiment, all possible combinations of features a. through d. are preferred aspects of the embodiment. These combinations include, for example, a; b; c; d; a+b; a+c; a+d; b+c; b+d; c+d; a+b+c; a+b+d; a+c+d; b+c+d; a+b+c+d.

A nineteenth embodiment of the present invention is a mold for preparing a ceramic body by spark plasma sintering, the ceramic body having an extension of at least 300 mm. The mold has a surface portion with an area of at least 5 ^cm² , and the surface portion has an average surface roughness (Sa) within a range of 1 μm to 8 μm, preferably 2 μm to 7 μm, more preferably 3 μm to 6 μm, and even more preferably 3 μm to 5 μm. In one aspect of the nineteenth embodiment, the surface area is preferably at least 10 ^cm² , more preferably at least 50 ^cm² , and even more preferably at least 100 ^cm² .

001: First propulsion component

002: First Piston

003: First Charge

004: First punch surface

005: Inner surface of the mold

006:Mold

007: Second punch surface

008: Second Attack

009: Second Piston

010: Second propulsion component

011: Compression shaft

012: Power supply

013: Sintering Chamber

014: First punch contact surface with mold

015: Second punch contact surface with mold

016: Distance

017: Distance

100: Device

200: Preparation process for ceramic bodies

201: Step a.

202: Step b.

203: Step c.

204: Step d.

300: Cross-section of the sintering chamber

301: Mold wall thickness

302: Sintering chamber diameter

400: Core test settings

401: Retrieving core tools

402: First flat surface

403: Drilling depth

404: Sample thickness

405: Geometric Center

406: Flat ceramic sample

407: Take the core area

408: Perpendicular to the direction of motion of the flat ceramic sample

409: Take the tip of the core tool

410: Cylindrical section removed from a flat ceramic sample

The present invention is further illustrated with the aid of the following drawings. The drawings are not drawn to scale.

[Figure 1A] is a cross-sectional side view of the device according to the present invention.

Figure 1B is an enlarged view of the mold and punch.

Figure 2A is a cross-sectional side view of the apparatus of Figure 1, with the chamber loaded and ready for sintering.

Figure 2B is an enlarged view of the mold and punch in Figure 2A.

Figure 3 shows the steps in the preparation process for a ceramic body.

Figure 4 shows a cross-sectional view of the sintering chamber.

Figure 5A and Figure 5B show the core tests used in this article.

Figures 6A and 6B show possible orientations of the die and punch before and during sintering.

The following abbreviations are used in this description: AC (alternating current), DC (direct current).

sintering

The present invention relates to a sintering process. A preferred sintering process is to form a body from particles by applying pressure and heat. The heating is preferably by applying an electric current.

Preferably, sintering increases the density of the plurality of particles to form a body. Preferably, the body has a density greater than that of the plurality of particles. Preferably, sintering produces a product body having a density of at least 95%, preferably at least 99%, and more preferably at least 99.9% of its theoretical density.

device

The apparatus of the present invention is adapted and configured for sintering particles to form a body. The apparatus includes at least a first punch, a second punch, and a mold. The apparatus has a sintering chamber.

sintering chamber

The apparatus of the present invention includes a sintering chamber. The sintering chamber is preferably adapted and configured to accommodate a plurality of particles. The sintering chamber is preferably bounded by a first punch surface of a first punch, a second punch surface of a second punch, and an inner surface of a mold. The sintering chamber may be bounded solely by the first punch surface, the second punch surface, and the inner surface, or may be additionally bounded by one or more additional surfaces. The sintering chamber is preferably bounded solely by the first punch surface, the second punch surface, and the inner surface.

The sintering chamber may have one or more planes of symmetry, one or more axes of symmetry, or both. The sintering chamber may be in the form of a volume of revolution. The sintering chamber may be cylindrical.

Head

The apparatus of the present invention has a first punch and a second punch. The first punch has a first punch surface that delimits a sintering chamber. The second punch has a second punch surface that delimits the sintering chamber. One or both of the punch surfaces are preferably substantially flat.

The punch is preferably adapted and configured to apply a force to the target within the sintering chamber, preferably to generate an elevated pressure within the sintering chamber. The punch is preferably adapted and configured to generate a pressure within the sintering chamber of at least 1 MPa, preferably at least 5 MPa, more preferably at least 10 MPa, and most preferably at least 15 MPa. The punch may be adapted and configured to apply up to 50 MPa or even more.

The first and second punches are preferably positioned vertically above and below the sintering chamber, respectively. The first and second punches are preferably adapted and configured to move along the compression axis.

The punch is preferably conductive. The punch is preferably adapted and configured to provide a current of at least 10 kA, more preferably at least 50 kA, and most preferably at least 60 kA. The power supply may be adapted and configured to provide a current of up to 100 kA or even more.

The punch is preferably a carbon material, most preferably graphite. The punch preferably comprises at least 95 wt.%, more preferably at least 99 wt.%, and still more preferably at least 99.5 wt.% carbon. The punch may comprise one or more layers and regions selected from the group consisting of a material other than carbon.

mold

The apparatus of the present invention comprises a mold. The mold has an inner surface that defines a sintering chamber.

In one embodiment, the mold is electrically conductive. Preferably, the mold has anisotropic conductivity, preferably with a material orientation axis substantially aligned with the compression axis.

In one embodiment, the mold comprises one or more elements selected from Group 14 of the Periodic Table. Group 14 elements are sometimes also referred to as Group IVA elements or Group 4A elements. The mold preferably comprises one or more elements selected from the group consisting of C, Si, Ge, Sn, and Pb, preferably selected from C, Si, Ge, and Sn, and most preferably selected from C and Si. C is the most preferred Group 14 element. In one aspect of this embodiment, the mold contains 50 wt% or more, more preferably 90 wt% or more, and most preferably 95 wt% or more of the Group 14 element, based on the total weight of the mold.

In one embodiment, the mold contains at least 50 wt.% C, based on the total weight of the mold, preferably 90 wt.% or more, more preferably 95 wt.% or more, and most preferably 99 wt.% or more. In one aspect of this embodiment, the mold additionally contains one or more additional Group 14 elements, preferably selected from Si, Ge, Sn, and Pb, more preferably selected from Si, Ge, and Sn, still more preferably selected from Si and Ge, and most preferably Si. The additional Group 14 elements are preferably present in a total content of at least 0.1 wt.%, more preferably at least 1 wt.%, and most preferably at least 2 wt.%. In this embodiment, elements other than C, Si, Ge, Sn, and Pb are preferably present in a total content of no more than 1 wt.%, more preferably no more than 0.5 wt.%, and most preferably no more than 0.1 wt.%.

The mold is preferably made of carbon material, with graphite being the best.

The mold may be a single piece or multiple pieces, preferably a single piece. Preferably, the mold is a single connected body, more preferably a single cylindrical body. The mold preferably exists in 2 to 10 pieces, more preferably 2 to 5 pieces, still more preferably 2 to 3 pieces, and most preferably 2 pieces.

The mold may have one or more planes of symmetry, one or more axes of symmetry, or both. The sintering chamber may be in the form of a volume of revolution. The sintering chamber may be hollow cylindrical.

Directional

The apparatus of the present invention has a compression shaft. The apparatus is preferably adapted and configured to apply a force to the sintering chamber in the direction of the compression shaft.

The first punch is preferably movable along the compression axis. The second punch is preferably movable along the compression axis. Both punches are preferably movable along the compression axis.

In one embodiment, the compression axis is substantially vertical, preferably wherein the first punch is positioned above the second punch. In one aspect of this embodiment, the first punch surface is preferably a lower surface of the first punch. In another aspect of this embodiment, the first punch surface is substantially horizontal. In another aspect of this embodiment, the second punch surface is preferably an upper surface of the second punch. In another aspect of this embodiment, the second punch surface is substantially horizontal.

Mold contact surface

A die contact surface of a punch is defined as a surface of a punch that is adapted and configured to physically contact the inner surface of the die during the sintering process. Preferably, the die contact surface is parallel to the compression axis.

Products

The product of the present invention is a ceramic body. The ceramic body preferably has a density greater than that of the plurality of particles. Preferably, the body is a connected body. Preferably, the body has a density divided by the theoretical density of at least 0.9, preferably at least 0.95, and more preferably at least 0.99.

Preferred ceramics are inorganic materials. Preferred ceramics are non-metallic. Some preferred ceramics are oxides, nitrides, carbides, or combinations thereof. Preferred ceramics are refractory materials.

Preferred oxide ceramics can be single-element oxides or mixed oxides of more than one element. Oxide ceramics can contain some nitride or carbide content, or both. Oxide ceramics can be nitride-free, carbide-free, or neither. Preferred ceramic oxides can be stoichiometric or non-stoichiometric. Stoichiometric oxides preferably have integer ratios between the atomic numbers of their component elements. Oxide ceramics can contain two or more element groups, each element being in stoichiometric ratios with each other element of its own group, but in non-stoichiometric ratios with members of other groups.

Preferred nitride ceramics can be single-element nitrides or mixed nitrides of more than one element. Nitride ceramics can contain some oxide or carbide content, or both. Nitride ceramics can be oxide-free, carbide-free, or both. Preferred ceramic nitrides can be stoichiometric or non-stoichiometric. Stoichiometric nitrides preferably have integer ratios between the atomic numbers of their component elements. Nitride ceramics can contain two or more element groups, each element being in stoichiometric ratios with each other element of its own group, but in non-stoichiometric ratios with each member of the other group.

Preferred carbide ceramics can be single-element carbides or mixed carbides of more than one element. Carbide ceramics can contain some oxide or nitride content, or both. Carbide ceramics can be oxide-free, nitride-free, or neither. Preferred ceramic carbides can be stoichiometric or non-stoichiometric. Stoichiometric carbides preferably have integer ratios between the atomic numbers of their component elements. Carbide ceramics can contain two or more element groups, each element being in stoichiometric ratios with each other element of its own group, but in non-stoichiometric ratios with members of other groups.

A preferred component element of the ceramic is yttrium. Based on the total weight of the ceramic, the ceramic may contain at least 20 wt.%, preferably at least 30 wt.%, more preferably at least 40 wt.%, and most preferably at least 45 wt.% yttrium atoms. The yttrium content may be as high as 50 wt.% or even higher. Preferred yttrium-containing ceramics comprise oxides. Preferred yttrium-containing ceramics are oxide ceramics, preferably mixed oxide ceramics containing atoms of one or more elements other than yttrium and oxygen. Mixed oxide ceramics are often quantified based on the content of the simple oxides required to prepare them. Preferred yttrium-containing mixed oxide ceramics contain at least 20 wt.%, preferably at least 30 wt.%, more preferably at least 40 wt.%, and most preferably at least 45 wt.% yttrium oxide, based on the total weight of the ceramic. The Yttrium oxide content can be as high as 50 wt.% or even higher.

In addition to oxygen, nitrogen, and carbon, some preferred elements present in the ceramic are one or more selected from the list consisting of yttrium, zirconium, aluminum, titanium, silicon, boron, phosphorus, and curium. These elements may be components of oxides, nitrides, carbides, or combinations thereof.

Oxygen-containing ceramics are often quantified by the content of the simple oxides required to prepare them. Some preferred oxide components are silicon dioxide, boron oxide, curium oxide, yttrium oxide, aluminum oxide, zirconium oxide, titanium oxide, silicon dioxide, quartz, calcium oxide, barium oxide, nickel oxide, copper oxide, strontium oxide, arsenic oxide, sulphur oxide, euclidean oxide, vanadium oxide, niobium oxide, tungsten oxide, manganese oxide, tantalum oxide, zirconium oxide, cerium oxide, neodymium oxide, yttrium aluminate, zirconium aluminate, leucide, tungsten oxide, manganese oxide, tantalum oxide, zirconium oxide, cerium oxide, neodymium oxide, yttrium aluminate, zirconium aluminate, leucide, tungsten oxide, and gerah.

Some preferred mixed oxides are one or more selected from the group consisting of: zirconium silicate oxide, barium aluminum oxide, barium silicate oxide, titanium silicate oxide, lumber silicate oxide, lumber aluminum oxide (LAO), yttrium silicate oxide, titanium silicate oxide, tantalum silicate oxide, oxynitride, barium titanate, lead titanate, and lead zirconium titanate.

Nitrogen-containing ceramics are often quantified by the amount of simple nitride required to prepare them. Some preferred nitride components are selected from one or more of the group consisting of silicon nitride, titanium nitride, yttrium nitride, aluminum nitride, boron nitride, curium nitride, and tungsten nitride.

Carbonaceous ceramics are often quantified by the amount of simple carbides needed to make them. Some preferred carbide components are silicon carbide, tungsten carbide, chromium carbide, vanadium carbide, niobium carbide, molybdenum carbide, tantalum carbide, titanium carbide, zirconium carbide, einsteinium carbide, and boron carbide.

The ceramic may include one or more borides. Some preferred boride components of the ceramic are selected from one or more of the group consisting of molybdenum boride, chromium boride, einsteinium boride, zirconium boride, tantalum boride, titanium boride, and titanium diboride.

Some preferred ceramic species are one or more selected from the group consisting of sapphire, aluminum oxide, yttrium aluminum monoclinic (YAM) (preferably Y ₄ Al ₂ O ₉ ), yttrium aluminum garnet (YAG) (preferably Y ₃ Al ₅ O ₁₂ ), yttrium aluminum perovskite (YAP) (preferably YAlO ₃ ), chalcedony, andalusite, magnesium aluminate spinel, zirconium oxide, erbium aluminum garnet (EAG), yttrium oxynitride, silicon oxynitride, and magnesium silicate.

Starting materials

According to the present invention, a plurality of particles in a sintering chamber can be converted into a solid body by applying pressure and electric current. The particles can have the same chemical composition as the product. The preferred chemical composition for the product also applies to the preferred chemical composition for the particles.

The preferred particle size is in the range of 0.1 μm to 20 μm. The preferred average particle size is in the range of 0.3 μm to 7 μm, more preferably in the range of 0.5 μm to 5 μm.

Program conditions

Sintering of the particles is performed under pressure. A pressure of at least 1 MPa, preferably at least 5 MPa, and more preferably at least 10 MPa is applied to the particles in the sintering chamber. The applied pressure may range from 15 MPa to 30 MPa. Pressures of up to about 80 MPa or even higher may be applied.

Sintering of the particles proceeds with the application of an electric current. Preferably, a current of at least 5 kA, more preferably at least 10 kA, and even more preferably at least 50 kA is applied across the sintering chamber. Currents of up to 100 kA or even higher may be applied.

The process is preferably performed in a non-oxidizing atmosphere. The process may be performed in a vacuum, with the gas pressure surrounding the apparatus being less than 10 mPa, preferably less than 5 mPa, and more preferably less than 1 mPa. The process may be performed in an inert atmosphere, preferably argon.

In one aspect of the present invention, preferably, during the process for preparing a ceramic body according to the present invention, a potential difference is applied between a first punch surface and a second punch surface of a device according to the present invention, wherein the potential difference is in the range of 5V to 10V, more preferably in the range of 5V to 7V, and even more preferably in the range of 6V to 6.5V.

Technology Application

Ceramic bodies are used in a variety of technical applications. Specific applications include one or more of the following: plasma etchers, plasma processing chambers (etching or deposition processes), wear plates for bearings, or mill pads for grinding machines.

power supply

The power source is preferably adapted and configured to produce Joule heating in the plurality of particles. The power source may be alternating current, pulsed direct current, or continuous direct current. Continuous direct current is preferred.

In one aspect of the present invention, the power supply is preferably a rectified DC power supply. A rectified DC power supply is preferably understood to mean a power source adapted and configured to convert alternating current to direct current. Examples of rectified DC power supplies include power supplies adapted and configured to perform partial-wave rectification, full-wave rectification (e.g., a bridge rectifier), or both. Preferred rectified DC power supplies include a gate diode, a silicon-controlled rectifier, or both.

The power supply is preferably adapted and configured to provide a current of at least 5 kA, more preferably at least 10 kA, even more preferably at least 50 kA, further preferably at least 60 kA, and even further preferably at least 100 kA.

Schematic Description

FIG1A is a cross-sectional side view of a device 100 according to the present invention. The device comprises a first punch 003 having a first punch surface 004 and a second punch 008 having a second punch surface 007. Punches 003 and 008 are made of solid graphite. Punch surfaces 004 and 007 are also graphite. The first punch 003 is positioned above the second punch 008. The first punch 003 is oriented horizontally with respect to the first punch surface 004 and facing downward. The first punch 003 can be moved in a vertical direction by a first thrust member 001 connected via a first piston 002. The second punch 008 is oriented horizontally with respect to the second punch surface 007 and facing upward. The second punch 008 can be moved vertically by a second thrust member 010 connected via a second piston 009. This allows the first punch surface 004 and the second punch surface 007 to move toward each other along the compression axis 011.

The apparatus has a mold 006 shaped into a hollow graphite cylinder with an inner surface 005. The apparatus has a power supply 012 adapted and configured to supply DC current and connected to a first punch 003 and a second punch 008. The sintering chamber of the present invention is formed as a cavity bounded from above by the first punch surface 004, from below by the second punch surface 007, and from the sides by the inner surface 005. In this case, the two punch surfaces 004 and 007 are circular, and the inner surface 005 is cylindrical, so the sintering chamber is cylindrical.

Figure 1B is an enlarged view of the first and second punches (003, 008) and mold 006 in Figure 1A. Figure 1B shows that the first punch 003 has a mold-contacting surface 014 (the first punch 003 is circular). Similarly, the second punch 008 has a mold-contacting surface 015 (the first punch 008 is also circular).

FIG2A is a cross-sectional side view of the apparatus 100 of FIG1A , with the sintering chamber 013 loaded and ready for sintering. The sintering chamber 013 is bounded from above by the first punch surface 004, from below by the second punch surface 007, and from the side by the inner surface 005 of the mold 006. The sintering chamber 013 thus has a cylindrical shape. The sintering chamber 013 is filled with a plurality of particles for sintering. After being introduced into the sintering chamber, the plurality of particles can be rammed to compact them. The punch surfaces ( 004 , 007 ) then move inward to abut against the compacted particle disk. For sintering, the punch surfaces (004, 007) move inward along the compression axis 011 as indicated by the arrows. The punch surfaces (004, 007) apply force to the particles, thereby generating pressure in the chamber. Current is applied from a power source 012 across the sintering chamber 013 (between the first punch surface 004 and the second punch surface 007).

Figure 2B is an enlarged view of the first and second punches (003, 008) and mold 006 in Figure 2A. As can be seen, the inner surface 005 of mold 006 contacts the mold contact surfaces (014, 015) of the first and second punches 003, 008 before and during the sintering process.

Figure 3 shows the steps of a preparation process 200 for a ceramic body. In a first step a.201, a plurality of particles are provided. The particle size _d50 can be, for example, 3 μm. An example material for the particles is yttrium aluminum garnet (YAG). In a second step b.202, an apparatus as described in the present disclosure is provided. The sintering chamber of the apparatus can, for example, have a diameter of 500 mm. In a third step c.203, the plurality of particles are introduced into the sintering chamber of the apparatus. The plurality of particles can be rammed to compact the particles into a cylinder. In a fourth step d.204, a pressure of, for example, 50 MPa is applied to the sintering chamber, and an electric current of, for example, 80 kA is passed through the chamber to convert the particles into a product ceramic body.

Figure 4 shows a cross-sectional view 300 of the sintering chamber 013. The section line is vertical, along the diameter of the sintering chamber 013, and through the compression axis 011, showing the sintering chamber 013 from the side. The mold 006 is a hollow cylinder with a wall thickness 301. The mold thickness 301 and diameter 302 of the sintering chamber 013 are each measured in a radial direction perpendicular to the compression axis 011.

Figures 5A and 5B show the core test 400 used herein. Figure 5A shows a perspective view before the test begins. A core removal tool 401 is positioned above a first flat surface 402 of a flat-form ceramic sample 406. In this case, the flat-form ceramic sample 406 is in the form of a cylindrical disk. The tool 401 is oriented along an axis that is perpendicular to the first flat surface 402. Arrow 408 shows the direction of travel of the tool 401 along the axis toward the flat-form ceramic sample 406. Once in contact with the flat-form ceramic sample 406, the core removal tool 401 moves in a circular motion within a core removal area 407, which has a diameter that is greater than the diameter of the tip 409 of the core removal tool 401. The circular motion is parallel to the first flat surface 402 and results in the removal of a cylindrical area from the flat-form ceramic sample 406. Furthermore, the geometric center 405 of the first flat surface 402 is also the geometric center 405 of the coring region 407. Figure 5B shows a cross-sectional view from the side during a coring test. Tool 401 has been advanced a distance 403 into a flat ceramic sample 406 having a sample thickness 404. Figure 5B shows that coring tool 401 has removed a cylindrical section 410 from flat ceramic sample 406. Distance 403 is determined between first flat surface 402 and the end of tool 401. The test is completed when a crack is first observed in flat ceramic sample 406. The success level is determined as the ratio of coring distance 403 at the end of the test to the total thickness 404 of the flat ceramic sample, expressed as a percentage.

Figures 6A and 6B show possible orientations of the die and punch before and during sintering. Figures 6A and 6B are enlarged views of the die and punch in Figure 2A. Figure 6A shows a preferred orientation, in which the first and second punches (003, 008) are positioned relative to die 006 so that the difference between distances 016 and 017 (indicated by arrows) is less than 3%. This orientation can be achieved by selecting a die 006 with an inner surface 005 having a sufficiently high average surface roughness (Sa). In addition to selecting a sufficiently large average surface roughness for the inner surface 005, additional orientation improvement can be achieved by also selecting a sufficiently large average surface roughness (Sa) for the mold contact surface 014 of the first punch 003 and/or the mold contact surface 015 of the second punch 008.

FIG6B shows the orientation when the inner surface 005 of the mold 006 is too smooth, that is, the average surface roughness (Sa) value is too small. As can be seen in FIG6B , the distance 016 is significantly greater than the distance 017.

Test method

Core Test

The flat form sample ceramic obtained in the example having a first flat surface and a thickness perpendicular to the first flat surface is cored to determine whether excessive internal stress is present. The core removal tool 401 is, for example, a 10 mm diamond core removal tool commercially available from Schott Diamantwerkzeuge GmbH of Stadtoldendorf, Germany. The tool is used in a commercially available CNC machine to cut the core in the tested part. The hole formed in the part by cutting the core is from 56 mm to 60 mm, which has a nominal diameter of 58 mm. The core is cut by passing the tool 401 over the surface of the part in a spiral pattern to drill a hole in the part. Suitable CNC machines that can be used for this test are, for example, commercially available from DMG Mori Company Limited of Los Angeles, California, USA (such as its Ultrasonic 60 eVo linear model). Another supplier of suitable CNC machines is Fair Friend Ent. Co. Ltd. of Taiwan (e.g., Feeler HV-1650 model). Testing ends when the core extends all the way through the sample ceramic or when a crack is observed in the sample ceramic, whichever occurs first. The success score is given as a percentage of the core thickness cut into the test sample. A 100% success rating indicates low internal stress (if any); a success rating greater than 75% but less than 100% indicates low internal stress; a success rating between 25% and 75% corresponds to moderate stress; and a success rating less than 25% indicates high internal stress.

surface roughness

The average surface roughness Sa (also known as the arithmetic mean height) was measured using ISO 25178:2019. The maximum height (Sz), surface feature aspect ratio (Str), arithmetic mean peak curvature (Spc), and surface spread area ratio (Sdr) were also measured using ISO 25178:2019. To measure surface roughness, a VK-X200 3D laser scanning microscope, commercially available from Keyence Corporation (Japan), was used.

Particle size and average particle size

The particle size and average particle size of the ceramic particles were determined using a Laser Scattering Particle Size Distribution Analyzer (LA-960) from Horiba Scientific of Piscataway, New Jersey, United States.

Current intensity, potential difference, and resistance

The current intensity was measured using a MicroFUSION 400A silicon-controlled rectifier (SCR), commercially available from Control Concepts Inc. (USA). The potential difference was measured using a DSCA31 analog voltage input signal conditioner, commercially available from Dataforth Corporation (USA). The resistance was obtained by dividing the potential difference by the current intensity.

Density and theoretical density

The density of ceramic bodies is measured according to ASTM B962-17. The theoretical density is calculated from X-ray diffraction (XRD) data. Unit cell parameters a, b, and c are obtained from the XRD data. Unit cell volume is calculated using these unit cell parameters. The number of molecular units per unit cell is determined based on the material's crystal structure. Since the chemical structure is known, the molecular weight of the ceramic body is also known. Using this data, the theoretical density is calculated as follows: Theoretical density = (molecular weight × number of molecules per unit cell) / (unit cell volume × Avogardo's number).

Average grain size

The average grain size of the ceramic body is measured according to the standard ASTM E112-13(2021).

Example

The working method of the present invention is now further explained with the aid of specific examples. The present invention is not limited to the features of the examples, which are intended to provide specific concrete implementations of the present invention.

Example A

The apparatus is provided according to the schematic diagram shown in FIG1 . The mold has a height of 1 m, and the punches each have a circular punch surface with a diameter of 650 mm. The sintering chamber correspondingly has a cylindrical shape with a cross-sectional diameter of 650 mm.

Commercially available yttrium oxide and aluminum oxide powders with a particle size _d50 of 3 μm were mixed together, and 5 kg of the mixture was introduced into the sintering chamber, spread to an approximately horizontal height, and compacted with a force of approximately 40 tons to a compaction height of 20 mm. After sintering, this powder mixture formed yttrium aluminum garnet (YAG). Next, a mixture of commercially available powders for forming zirconia toughened alumina (ZTA) during sintering was introduced into the sintering chamber in an amount of 27 kg and spread to an approximately uniform height of approximately 100 mm. Finally, a powder mixture for forming YAG and ZTA was introduced into the sintering chamber in an amount of 7 kg and spread to an approximately uniform height of approximately 30 mm.

The punches are moved inward to reach the position shown in Figure 2. In the sintering chamber, the first and second punches apply force to the powder, achieving a sintering chamber pressure of approximately 15 MPa. The 40 to 70 kA supplied by the punches is continuously applied throughout the sintering chamber for a total of 9 to 10 hours. The product is a flat cylindrical ceramic disc with a diameter of approximately 650 mm and a thickness of approximately 26 mm.

As shown in Table 1, the example was repeated using different values for the average surface roughness (Sa) of the mold's inner surface and the mold-contacting surfaces of the first and second punches. The density ratio in Table 1 is the value obtained by dividing the bulk density of the ceramic body by the theoretical density of the ceramic body. Grain size refers to the size of the crystallites or crystals in the ceramic body.

Although the above examples are of three-layer cylindrical ceramic disks, the method disclosed herein is also applicable to single-layer and double-layer cylindrical ceramic disks.

Example B

Example B was performed in the same manner as Example A, except that the punch surface had a circular diameter of 100 mm. The results are also shown in Table 1 below. The resistance in Table 1 is the resistance measured on the mold.

When the surface roughness value is too small, the friction between the mold and the punch is very limited. As a result, the mold and the punch become misaligned with each other, causing serious problems in the production of ceramic bodies. If the surface roughness value is too large, this leads to increased electrical contact between the mold and the punch, which in turn causes additional heat to be generated in the sintering chamber during ceramic body production. The resulting ceramic body is of very poor quality.

When considering the results in Table 1 for a punch surface having a circular diameter of 100 mm, there is no indication that the surface roughness should be limited to a specific range in order to produce a sufficiently high-quality ceramic body having a diameter of 650 mm.

Further Examples

We repeated Examples A and B above, but using 300mm and 500mm circular diameter punch surfaces, respectively. We found that the results for the 300mm diameter were very similar to those for the 100mm diameter (Example B). The results for the 500mm diameter were very similar to those for Example A.

001: First driving member 002: First piston 003: First punch 004: First punch surface 005: Inner surface of mold 006: Mold 007: Second punch surface 008: Second punch 009: Second piston 010: Second driving member 011: Compression shaft 012: Power supply 100: Device

Claims (10)

A device having a sintering chamber (013), the sintering chamber (013) being partially delimited by: i. a first punch surface (004) of a first punch (003); ii. a second punch surface (007) of a second punch (008); and iii. an inner surface (005) of a mold (006); wherein: the punches (003, 008) are adapted and configured to apply a pressure of at least 1 MPa along a compression axis (011) to a target in the sintering chamber (013); the first punch (003) and the second punch (008) are connected to a power supply (012), which is adapted and configured to provide a current of at least 10 kA; The first punch (003) and the second punch (008) comprise at least 50 wt. % carbon, based on the total weight of the punches (003, 008); the sintering chamber (013) has a cross-sectional width W of at least 300 mm perpendicular to the compression axis (011); wherein the mold has a surface portion χ having an area of at least ⁵ cm2, wherein the surface portion χ is located on the inner surface of the mold, and wherein an average surface roughness (Sa) of the surface portion χ is in the range of 1 μm to 8 μm. The device of claim 1, wherein the first head has a surface portion α having an area of at least 5 cm ² , and an average surface roughness (Sa) of the surface portion α is in the range of 1 μm to 8 μm. A device as claimed in claim 2, wherein the surface portion α at least partially overlaps with the first head surface. A device as claimed in claim 3, wherein the surface portion α is at least partially in contact with the surface portion χ. The device of any one of claims 1-4, wherein the second head has a surface portion β having an area of at least 5 ^cm2 , and an average surface roughness (Sa) of the surface portion β is in the range of 1 μm to 8 μm. A device as claimed in claim 5, wherein the surface portion β at least partially overlaps with the second head surface. The device of any of claims 1-4, wherein the device comprises one or more device parts selected from the group consisting of: a.     A housing; b.     A vacuum device; c.     A hydraulic piston. A process for preparing a ceramic body, comprising the following steps: a. Providing a plurality of particles; b. Providing the apparatus of any one of claims 1 to 7; c. Introducing the particles into the sintering chamber (013); d. Applying a pressure P in the range of 1 MPa to 50 MPa and a current I in the range of 10 kA to 100 kA to the particles in the sintering chamber to obtain the ceramic body. The process of claim 8, wherein the particles contain at least 30 wt. % yttrium in any chemical form, based on the total mass of yttrium atoms and the total mass of the particles. A mold for producing a ceramic body having an extension of at least 300 mm by spark plasma sintering, wherein the mold has a surface portion with an area of at least 5 ^cm2 , the surface portion having an average surface roughness (Sa) in the range of 1 μm to 8 μm.