Ceramic casting method and formula

Abstract

The invention discloses a casting method of an aluminum nitride ceramic component. The method comprises the following steps: providing aluminum nitride ceramic slurry, wherein the slurry comprises aluminum nitride powder; a solvent; and a polymeric binder, where the slurry comprises no more than 5 wt% of the polymeric binder; carrying out slip casting on the slurry to form a green body product; and sintering and drying the green body product to manufacture the aluminum nitride ceramic part.

Description

Technical Field

[0001] The present invention relates to a method of casting an aluminum nitride ceramic component, such as a heater component. Background Art

[0002] Aluminum nitride ceramic components, such as those used in ceramic heaters, are typically manufactured by casting the components from a ceramic precursor, such as an aluminum nitride ceramic slurry. The aluminum nitride ceramic slurry comprises aluminum nitride ceramic particles suspended in a liquid. The slurry also typically includes a binder. Such a slurry is described, for example, in US 9340462, which comprises aluminum nitride with an yttrium oxide additive and a binder. A tape casting slurry based on yttrium aluminum garnet (YAG) is also described in US7799267.

[0003] This slurry is used to cast a "green" part, which is then sintered to form the final product. The sintering process typically burns off any liquid and binder and fuses and densifies the ceramic particles together, leaving only the densified ceramic that forms the final product.

[0004] To manufacture the aluminum nitride ceramic components of ceramic heaters, a tape-casting method is typically used. The ceramic slurry is applied to a tape or strip in a continuous process to produce a green product. The tape with the ceramic slurry is sintered to provide the final product. To integrate the ceramic components into the heater, the tape is laid down in layers and the electronic hardware is laminated to the sintered ceramic between the layers.

[0005] This tape casting process is efficient and can produce high-quality ceramic products. However, the shapes that can be manufactured are limited. Integrating electronic hardware is also challenging, and the multi-layer structure provides locations for defects between layers.

[0006] The present invention was born in such background. Summary of the invention

[0007] According to a first aspect of the present invention, a method for casting an aluminum nitride ceramic component is provided. The method comprises: providing an aluminum nitride ceramic slurry, the slurry comprising: aluminum nitride powder; a solvent; and a polymer binder, wherein the slurry comprises no more than 5wt% of the polymer binder; using the slurry to slip cast a green product; and sintering and drying the green product to manufacture the aluminum nitride ceramic component.

[0008] The slurry may include no more than 2.5 wt % polymer binder, and optionally includes between 0.1 wt % and 1.5 wt % polymer binder.

[0009] The polymer binder may include polypropylene carbonate.

[0010] The solvent may include DMP, DMC, MEK or NUP. The slurry may include between 30 wt% and 40 wt% solvent.

[0011] The aluminum nitride powder may include aluminum nitride particles having a median diameter between 1 micrometer and 10 micrometers.

[0012] The slurry may further include a dispersant. The dispersant may include an isobutyl methacrylate polymer and / or a phosphate ester. The slurry may include about 0.5 wt % to about 1.5 wt % of the dispersant.

[0013] The slurry may include one or more additional ceramic additives. The slurry may include up to about 10 wt % of the additional ceramic additives, and preferably includes up to about 5 wt % of the additional ceramic additives. The additional ceramic additives include ceramic materials other than aluminum nitride, and may include, for example, aluminum oxide and / or yttrium oxide.

[0014] The method may further include providing a slip casting mold having a mold surface, slip casting the slurry on the mold surface, and drying the slurry to produce a green product.

[0015] The method may include applying a lubricant to the mold surface prior to slip casting the slurry onto the mold surface.

[0016] The method may include arranging the electronic component on the mold surface, and slip casting the slurry onto the electronic component on the mold surface such that the electronic component is embedded in the green product.

[0017] The mold surface may be substantially free of macropores.

[0018] The method may include using the green product as another slip casting mold to slip cast another layer of ceramic slurry on the green product to produce a laminated green product.

[0019] In this case, the first ceramic slurry can be used to form a green product and the second ceramic slurry can be used to form another layer of ceramic slurry. The first ceramic slurry can be different from the second ceramic slurry. The first and second ceramic slurries can, for example, include different ceramic additives.

[0020] The method may include sintering the green product to produce an aluminum nitride ceramic component.

[0021] The aluminum nitride ceramic component may be a heater component.

[0022] The present invention also extends to an aluminum nitride ceramic slurry for slip casting aluminum nitride ceramic parts, the slurry comprising aluminum nitride powder; a solvent; and a polymer binder; wherein the slurry comprises no more than 5 wt % of the polymer binder. The slurry may have the above-mentioned preferred and / or optional features.

[0023] Within the scope of the present application, it is expressly intended that the various aspects, embodiments, examples and alternatives listed in the preceding paragraphs, the claims and / or the following description and drawings, in particular their individual features, may be used independently or in any combination. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination, unless these features are incompatible. The applicant reserves the right to change any initially filed claim or to file any new claim accordingly, including the right to amend any initially filed claim to rely on any other claim and / or to incorporate any features of any other claim, even if the claim was not originally filed in this way. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] One or more embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0025] Figure 1 and Figure 2 is a scanning electron microscope (SEM) micrograph of a sample of a ceramic component made according to the present invention.

[0026] General and specific embodiments of the present invention will be described below with reference to the accompanying drawings. DETAILED DESCRIPTION

[0027] Aluminum nitride ceramic components (such as ceramic heater components) can be manufactured using a slip casting process. Such components are made using a specially formulated aluminum nitride ceramic slurry. The aluminum nitride ceramic slurry includes aluminum nitride powder, a polymer binder, and a liquid component including a solvent. The proportion of the polymer binder in the slurry is no more than 5wt%, preferably no more than 2.5wt%, and optionally between about 0.1wt% and 1.5wt%.

[0028] The slurry may also include another ceramic additive (ie, a ceramic component other than aluminum nitride). The liquid component may include a solvent mixture (ie, a mixture of more than one solvent) and may include a dispersant and / or a plasticizer in addition to the solvent.

[0029] The slurry components, the method of making the slurry, and the method of slip casting will now be described in more detail.

[0030] Slurry components

[0031] Aluminum nitride powder: The aluminum nitride powder includes aluminum nitride particles that can have any suitable size distribution and shape distribution. Suitable powders can, for example, include substantially spherical particles having a median size of 1 to 10 microns. However, other shapes and sizes can also be used and can be selected, for example, depending on the application. The slurry preferably includes about 50 wt% to about 65 wt% aluminum nitride powder.

[0032] Solvent: The solvent preferably comprises a solvent mixture and may include, for example, one or more of DMC, DMP, MEK and NMP. The slurry preferably comprises about 30 wt% to about 40 wt% of the solvent.

[0033] Polymer binder: The polymer binder can be any suitable polymer material capable of binding the ceramic slurry. An example of a suitable polymer binder is polypropylene carbonate, such as 40 in the form of commercial products. The proportion of polymer binder in the slurry is not more than 5wt%, preferably not more than 2.5wt%, and optionally between about 0.1wt% and 1.5wt%. A particularly preferred proportion is about 0.3 to 0.5wt%.

[0034] Dispersant: The slurry may optionally include a dispersant. Examples of suitable dispersants are isobutyl methacrylate polymers (e.g., Acryloid B67) and phosphate esters (e.g., Rhodafac RE610). When a dispersant is included, the slurry may include about 0.5 wt % to about 1.5 wt % of the dispersant. The slurry may contain a mixture of dispersants: for example, a mixture of Acryloid B67 and Rhodafac RE610.

[0035] Ceramic Additives: Optionally the slurry may include a ceramic additive. Examples of suitable additives are yttrium oxide (Y2O3) and aluminum oxide (AI2O3). When a ceramic additive is included, the slurry may include up to about 10 wt% of the additional ceramic additive. The ceramic additive powder may include particles having any suitable size distribution and shape distribution.

[0036] Plasticizer: Optionally the slurry may include a plasticizer. Optionally the plasticizer may also act as a solvent. The plasticizer may be in the form of a monomer of the polymer binder. An example of a suitable plasticizer is propylene carbonate, which may be particularly useful as a plasticizer when the polymer binder is polypropylene carbonate. When a plasticizer is included, the slurry may include up to about 2 wt% of the plasticizer.

[0037] Method for preparing slurry

[0038] The slurry is made using a multi-stage grinding process, such as that described in US7799267.

[0039] In the first grinding stage, any ceramic additives are mixed with any dispersants and with the first solvent or first solvent mixture. The mixture is then ground on a drum with grinding media (e.g., zirconium oxide grinding media). The grinding period can be any suitable period of time, but is preferably at least 4 hours.

[0040] In the second grinding stage, the mixture produced in the first grinding stage is mixed with a second solvent or solvent mixture, an aluminum nitride ceramic, and a plasticizer. The mixture is then ground on a drum with grinding media (e.g., zirconium oxide grinding media). The grinding time can be any suitable time, but is preferably at least 4 hours.

[0041] In the final grinding stage, the mixture produced in the second grinding stage is mixed with a binder and a third solvent or solvent mixture. The mixture is then ground on a drum with grinding media (e.g., zirconium oxide grinding media). The grinding time can be any suitable time, but is preferably at least 4 hours. After the final grinding stage, the slurry can be used for slip casting.

[0042] Grouting molding method

[0043] The slip casting process is carried out using a suitable slip casting mould. The mould may be made of any suitable material, such as gypsum (plaster of Paris). The mould comprises a mould surface against which the slurry rests. The moulding surface is smooth, in particular free of macroscopic pores, i.e. free of pores with a diameter greater than 50 microns, preferably free of pores with a diameter greater than 10 microns.

[0044] Preferably, a lubricant is applied to the mold surface. A particularly suitable lubricant is WD40, but other lubricants such as PTFE and petroleum jelly may also be used.

[0045] The part is then made by slip casting the slurry onto a slip casting mold. To do this, a certain amount of slurry is poured into the mold cavity and contacted with the mold surface. The slurry is then poured from the cavity, and a layer of slurry material remains on the mold surface due to the presence of a binder in the slurry. The slurry is left for a short period of time, during which time the solvent is absorbed into the pores of the mold. When the solvent is removed in this way, the slurry dries into a green body that shrinks slightly away from the mold surface. The shrinkage allows the green body to be demolded. Lubricants can further facilitate demolding, especially relatively small amounts of binder in the slurry. A low proportion of binder results in a relatively low strength of the green body, but surprisingly, it has been found that a lower amount of binder can give the green body sufficient strength to be demolded.

[0046] After demoulding, the green body is sintered according to known sintering methods to form the final product.

[0047] The slip casting method produces ceramic parts with good structural integrity, which preserves the shape of the green product. Compared with traditional strip casting techniques, the slip casting process allows the manufacture of more complex parts such as tubes, cones or other shapes with bends, edges and curved surfaces.

[0048] In some embodiments, different ceramic slurries with different ceramic components can be used. For example, a first ceramic slurry can be used with a first ceramic additive, and a second ceramic slurry can be used with a second ceramic additive that is different from the first ceramic additive.

[0049] Different ceramic slurries can be used to coat different areas of the same component, thereby providing different properties to different areas. Alternatively, different ceramic slurries can be layered. For example, a first ceramic slurry can be used to make a green product, which can then be used as a mold that defines a mold surface to slip cast a second ceramic slurry, thereby providing a layered structure in which each layer has different properties.

[0050] The described method can also be used to form ceramic components with integrated electronic components (such as wires, circuit components, thermocouples and other electronic functional components). In this case, the electronic components can be first arranged so that they are supported on or above the mold surface of the mold, and then the slurry can be poured onto the mold surface around the electronic components. To this end, the electronic components can be arranged directly on the mold surface, or the electronic components can be fixed or otherwise suspended above the mold surface. The slurry is then poured out of the mold, leaving a layer of slurry on the mold surface and the electronic components. When the slurry is dried and the green product is formed, the electronic components are embedded in the green product.

[0051] Example

[0052] Samples 1 and 2

[0053] Two ceramic parts were made using two slurry mixtures according to Sample 1 and Sample 2 listed in the table below.

[0054]

[0055] To make the samples, the first-stage grinding components were mixed and the mixture was milled on a roller using zirconium oxide grinding media for four hours. The second-stage grinding components were added and the mixture was milled on a roller again using zirconium oxide grinding media for four hours. The final-stage components were added and the mixture was rolled so that all parts were thoroughly mixed.

[0056] The slip casting mold is made by molding plaster around a silicon RTV mold of the desired shape (including a cuboid, hemisphere, cone, and plate). The mold surface is coated with WD40 and electronic components are arranged on the mold surface.

[0057] The slurry mixtures of the two samples were slip cast into respective molds, the slurry was poured off to leave a coating on the mold surface and the electronic components, and then the slurry was dried to produce a green product.

[0058] After drying, the green product with embedded electronic components can be removed from the mold.

[0059] The green product is then sintered at an appropriate temperature between 1700 and 1850° C. The sintered component retains the shape of the green product and maintains its structural integrity with the electronic components embedded in the product.

[0060] Samples 3 and 4

[0061] Two samples were made using a slurry having the composition of Sample 2 described above, wherein the aluminum nitride powder included particles of different size distributions.

[0062] Sample 3

[0063] Median particle size: 1.2 microns

[0064] D10 particle size: 0.7 micron

[0065] D90 particle size: 3.2 microns

[0066] Sample 4

[0067] Median particle size: 9.4 microns

[0068] D10 particle size 1.9 microns

[0069] D90 particle size: 34 microns

[0070] Figure 1 and 2 are SEM micrographs of samples 3 and 4, showing the solid ceramics with low porosity and good integrity.

Claims

1. A method for casting an aluminum nitride ceramic component, the method comprising: An aluminum nitride ceramic slurry is provided, the slurry comprising: Aluminum nitride powder; Solvents; and polymer binders; wherein the slurry comprises no more than 5 wt % of a polymer binder; Slip casting a green product using the slurry; and The green product is sintered to dryness to produce an aluminum nitride ceramic component.

2. The method according to claim 1, wherein the slurry comprises no more than 2.5 wt% polymer binder, and preferably comprises between 0.1 wt% and 1.5 wt% polymer binder.

3. The method of claim 1 or 2, wherein the polymer binder comprises polypropylene carbonate.

4. The method according to any one of the preceding claims, wherein the solvent comprises DMP, DMC, MEK or NUP.

5. A method according to any one of the preceding claims, wherein the slurry comprises between 30 wt% and 40 wt% solvent.

6. A method according to any one of the preceding claims, wherein the slurry further comprises a dispersant.

7. The method of claim 4, wherein the dispersant comprises an isobutyl methacrylate polymer and / or a phosphate ester.

8. The method of claim 4 or claim 5, wherein the slurry comprises from about 0.5 wt% to about 1.5 wt% dispersant.

9. A method according to any one of the preceding claims, wherein the slurry comprises one or more additional ceramic additives.

10. The method of claim 7, wherein the slurry includes up to about 10 wt% of an additional ceramic additive.

11. The method according to any one of the preceding claims, further comprising: providing a slip casting mold having a mold surface; The slurry is slip cast onto the mold surface, and the slurry is dried to produce the green product.

12. The method according to claim 9, comprising: A lubricant is applied to the mold surface prior to slip casting the slurry onto the mold surface.

13. The method according to claim 9 or claim 10, comprising: placing electronic components on the mold surface; as well as The slurry is slip cast onto the electronic component over the mold surface such that the electronic component is embedded in the green product.

14. A method according to any one of the preceding claims, comprising: The green product is used as another slip casting mold to slip cast another layer of ceramic slurry on the green product, thereby manufacturing a laminated green product.

15. The method of claim 12, wherein a first ceramic slurry is used to form the green product and a second ceramic slurry is used to form the further layer of ceramic slurry, the first ceramic slurry being different from the second ceramic slurry.

16. A method according to any one of the preceding claims, comprising: The green product is sintered to produce an aluminum nitride ceramic component.

17. A method according to any one of the preceding claims, wherein the aluminium nitride ceramic component is a heater component.

18. An aluminum nitride ceramic slurry for slip casting aluminum nitride ceramic parts, the slurry comprising: Aluminum nitride powder; Solvents; as well as Polymer binders, The slurry comprises no more than 5 wt % of a polymer binder.

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