Calcium oxide crucible and method of making same

Abstract

The application discloses a calcium oxide crucible and a preparation method thereof, and belongs to the technical field of refractory materials. The method comprises the following steps: adding an organic monomer, a crosslinking agent and a dispersing agent into an organic solvent to form a premixing solution; adding a calcium oxide mixture, a sintering aid and carbon fibers into the premixing solution to mix, and adding a catalyst and an initiator under continuous stirring to form a slurry after uniform stirring, wherein the calcium oxide mixture comprises 60-80% of granular materials and 20-40% of powder materials by weight, the weight of the calcium oxide mixture accounts for 60-80% of the weight of the slurry, and the weight of the carbon fibers accounts for 0.05-0.2% of the weight of the slurry; and the slurry is injected into a crucible mold under vibration to form a wet blank after a monomer polymerization reaction. The wet blank is sequentially subjected to demolding drying, glue removal pre-sintering and high-temperature sintering treatment to obtain the calcium oxide crucible. The application achieves the technical effect of prolonging the service life of the crucible.

Description

Technical Field

[0001] This application relates to the field of refractory materials technology, and in particular to a calcium oxide crucible and its preparation method. Background Technology

[0002] Vacuum induction melting (VIM) offers numerous advantages, including uniform alloy composition, controllable melting atmosphere and melt superheat, simple process, and low cost. However, VIM typically utilizes oxide crucibles. Under high-temperature conditions, a chemical reaction occurs between the crucible and the melt. In particular, highly reactive materials such as TiAl and TiNi exhibit strong interactions with the crucible, which can contaminate the molten alloy and increase its impurity content.

[0003] To reduce the introduction of impurity oxygen into the crucible, several thermodynamically stable oxide crucibles are currently available, including yttrium oxide, calcium oxide, and zirconium oxide. Among these, calcium oxide (CaO) crucibles are the cheapest and produce the lowest amount of oxygen (O) when melting TiAl and TiNi alloys. However, besides being prone to hydrolysis, another major drawback of CaO refractory crucibles is their poor thermal shock resistance. They are extremely prone to cracking during the hot and cold cycles of melting, significantly reducing their service life. Summary of the Invention

[0004] The main objective of this application is to provide a calcium oxide crucible and its preparation method, aiming to solve the technical problem that the calcium oxide crucibles currently in use have poor thermal shock resistance and are prone to cracking during the hot and cold cycles of melting, which greatly reduces the service life of the crucible.

[0005] To achieve the above objectives, this application provides a method for preparing a calcium oxide crucible, the method comprising:

[0006] Organic monomers, crosslinking agents, and dispersants are added to an organic solvent and mixed to form a premix;

[0007] Calcium oxide mixture, sintering aid and carbon fiber are added to the premixed liquid and mixed. Catalyst and initiator are added while stirring continuously. After stirring evenly, a slurry is formed. The calcium oxide mixture includes 60-80% by weight of granules and 20-40% by weight of powder. The weight of the calcium oxide mixture accounts for 60-80% of the slurry. The weight of the carbon fiber accounts for 0.05-0.2% of the slurry.

[0008] The slurry is injected into a crucible mold under vibration conditions, and a wet preform is formed after the monomer polymerization reaction occurs.

[0009] The wet blank is subjected to demolding and drying, debinding and pre-firing, and high-temperature sintering treatment in sequence to obtain a calcium oxide crucible.

[0010] In one embodiment, the length of the carbon fiber is 5-10 mm.

[0011] In one embodiment, the particle size of the powder is below 325 mesh;

[0012] And / or, the particle size of the granules includes 0-1mm, 1-2mm and 2-3mm, and the particle size ratio of 0-1mm:1-2mm:2-3mm is (30-50):(30-50):(0-20).

[0013] In one embodiment, the sintering aid includes at least one of ZrO2, Al2O3, and TiO2, and the weight of the sintering aid is 0.5-2% of the weight of the calcium oxide mixture.

[0014] In one embodiment, the dispersant comprises polyacrylic acid and oleic acid, and the dispersant accounts for 1-2% of the total weight of the premix and the calcium oxide raw material.

[0015] In one embodiment, the organic solvent is n-butanol, the organic monomer is methacrylamide, and the crosslinking agent is N,N'-methylenebisacrylamide.

[0016] In one embodiment, the amount of the initiator added is 0.5-1% of the total weight of the premix and the calcium oxide mixture;

[0017] And / or, the amount of catalyst added is 0.3-0.6% of the total weight of the premix and the calcium oxide mixture.

[0018] In one embodiment, the demolding and drying process includes: after demolding the wet blank, vacuum drying it at a temperature of 40-80°C for 18-36 hours to obtain a raw blank.

[0019] In one embodiment, the debinding and preheating is carried out in a vacuum or inert atmosphere, wherein the green blank is slowly heated to 800-1200°C and held for 1-1.5 hours, and the heating rate is controlled below 1.5°C / min.

[0020] The high-temperature sintering is carried out in a vacuum or inert atmosphere environment. The blank after debinding is slowly heated to 1550-1700℃, held at that temperature for 1-2 hours, and then cooled in the furnace. The heating rate is controlled below 2℃ / min.

[0021] In addition, to achieve the above objectives, this application also provides a calcium oxide crucible, which is prepared using the calcium oxide crucible preparation method described above.

[0022] The method for preparing the calcium oxide crucible provided in this application embodiment adopts a gel casting molding process. First, organic monomers, crosslinking agents, and dispersants are added to an organic solvent and mixed to form a premix. Calcium oxide mixture, sintering aid, and carbon fibers are added to the premix and mixed. Catalyst and initiator are added while continuously stirring, and after thorough mixing, a slurry is formed. The calcium oxide mixture comprises 60-80% by weight of granules and 20-40% by weight of powder. The weight of the calcium oxide mixture accounts for 60-80% of the slurry, and the weight of the carbon fibers accounts for 0.05-0. 2%; The slurry is injected into the crucible mold under vibration conditions, and a wet blank is formed after the monomer polymerization reaction. The wet blank is then subjected to demolding and drying, debinding and pre-firing, and high-temperature sintering treatment to obtain a calcium oxide crucible. The multi-grade calcium oxide mixture contains calcium oxide raw materials of different particle sizes, which has a particle dispersion strengthening effect. At the same time, the large-size particles account for the main proportion, which is conducive to forming crucible products with higher strength and lower porosity. Carbon fiber is mixed in calcium oxide, which has a fiber reinforcement effect, which can further improve the strength and thermal shock resistance of the crucible, thereby extending the service life of the crucible. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1 This is a schematic flowchart of an embodiment of the method for preparing the calcium oxide crucible of this application.

[0025] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0027] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the technical solution of this application is further described below in conjunction with the accompanying drawings and embodiments. However, this application is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims made in this application.

[0028] Vacuum induction melting (VIM) offers numerous advantages, including uniform alloy composition, controllable melting atmosphere and melt superheat, simple process, and low cost. However, VIM often utilizes oxide crucibles, which undergo chemical reactions with the melt under high-temperature conditions. This is particularly true when melting highly reactive materials like TiAl and TiNi, where the crucible can contaminate the molten alloy, increasing impurity levels. To reduce oxygen introduction from the crucible, many thermodynamically stable oxide crucibles have been developed, including yttrium oxide, calcium oxide, and zirconium oxide. Among these, calcium oxide (CaO) crucibles are the cheapest and produce the lowest oxygen (O) content when melting TiAl and TiNi alloys. However, besides being prone to hydrolysis, another major drawback of CaO refractory crucibles is their poor thermal shock resistance. They are highly susceptible to cracking during hot and cold cycles during melting, significantly reducing their lifespan. Therefore, developing CaO refractory crucibles with good thermal shock resistance is essential.

[0029] Currently, the main methods for manufacturing ceramic crucibles include traditional dry material pressing (cold isostatic pressing, etc.) molding and sintering methods, slip casting methods, and the newly developed gel casting method. Related technologies primarily employ traditional methods involving adding refractory raw materials and sintering aids, molding, and high-temperature solid-state sintering.

[0030] Water-based solvents can be used for gel molding of materials, with acrylamide as the monomer and N,N'-methylenebisacrylamide as the crosslinking agent. However, calcium oxide differs from other materials in gel molding because it is prone to absorbing water and deliquescing.

[0031] This application provides a method for preparing a calcium oxide crucible, referring to... Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of a method for preparing a calcium oxide crucible according to this application.

[0032] In this embodiment, the method for preparing the calcium oxide crucible includes:

[0033] Step S10: Add the organic monomer, crosslinking agent and dispersant to the organic solvent and mix to form a premix;

[0034] This embodiment uses gel casting to prepare calcium oxide crucibles. The gel casting process mainly utilizes the in-situ solidification of organic monomers through chemical reactions to obtain a green body with good microscopic uniformity and a certain strength, which is then sintered to obtain the finished product.

[0035] Optionally, methacrylamide is used as the organic monomer. Methacrylamide has low toxicity. Optionally, in this embodiment, N,N'-methylenebisacrylamide is used as a crosslinking agent to promote crosslinking between organic monomers. Optionally, n-butanol is chosen as the organic solvent, as it has a higher boiling point and a slower evaporation rate, which helps reduce drying cracking of the green body and prevents the deliquescence of calcium oxide. Optionally, organic acids are chosen as dispersants, including polyacrylic acid and oleic acid, with a 1:1 ratio between polyacrylic acid and oleic acid in the dispersant.

[0036] Step S20: Add calcium oxide mixture, sintering aid and carbon fiber to the premixed liquid and mix. Add catalyst and initiator while stirring continuously. After stirring evenly, a slurry is formed.

[0037] Calcium oxide is used as the matrix material for the crucible product. In this embodiment, the calcium oxide raw material is a calcium oxide mixture, which includes solid calcium oxide of different particle sizes. Specifically, the calcium oxide mixture comprises 60-80% by weight granules and 20-40% by weight powder. The particle size of the granules is larger than that of the powder. Mixing and homogenizing solid calcium oxide of different particle sizes to form a crucible product can create particle dispersion reinforcement, improving the crucible's strength. The calcium oxide mixture may include 60% by weight granules and 40% by weight powder, or 70% by weight granules and 30% by weight powder, or 80% by weight granules and 20% by weight powder. This embodiment primarily uses coarse-grained raw materials, which can yield crucible products with higher strength and lower porosity. Lower porosity means a higher solid volume content. The calcium oxide mixture accounts for 60-80% of the slurry by weight, for example, 60%, 65%, 70%, 75%, and 80%.

[0038] Optionally, the particle size of the powder in the calcium oxide mixture is below 325 mesh.

[0039] Optionally, the particle size of the granules in the calcium oxide mixture includes 0-1mm, 1-2mm, and 2-3mm, with a particle size ratio of 0-1mm:1-2mm:2-3mm of (30-50):(30-50):(0-20). The granules have a larger proportion of particles smaller than 2mm.

[0040] Carbon fibers are added to the calcium oxide mixture to further enhance the crucible strength. In this embodiment, the weight of carbon fibers accounts for 0.05-0.2% of the slurry, for example, 0.05%, 0.1%, 0.15%, or 0.2%. Optionally, the length of the carbon fibers is 5-10 mm, for example, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or 10 mm.

[0041] Sintering aids are used to lower the sintering temperature and improve sintering performance. Optionally, the sintering aid includes at least one of ZrO2, Al2O3, and TiO2, and the weight of the sintering aid is 0.5-2% of the weight of the calcium oxide mixture, for example, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.7%, or 2%.

[0042] A catalyst is used to promote the cross-linking reaction of the organic monomers. In this example, the catalyst is tetramethylethylenediamine, added at 0.3-0.6% of the total weight of the premix and calcium oxide mixture, for example, 0.3%, 0.4%, 0.5%, or 0.6%. An initiator is used to initiate the cross-linking reaction of the organic monomers. In this example, the initiator is ammonium persulfate, added at 0.5-1% of the total weight of the premix and calcium oxide mixture, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0043] Step S30: The slurry is injected into a crucible mold under vibration conditions, and a wet preform is formed after the monomer polymerization reaction occurs.

[0044] The organic monomers in the slurry undergo monomer polymerization under the action of initiators and catalysts, forming a wet preform with a certain strength. The organic monomers crosslink to form organic polymers, and the crosslinked structure of the organic polymers causes the slurry to solidify and its strength to increase. The slurry has a certain viscosity, which accelerates its injection into the crucible mold under vibration. Before slurry injection, a release agent can be sprayed onto the inner surface of the crucible mold to facilitate the subsequent demolding process.

[0045] Step S40: The wet blank is sequentially subjected to demolding and drying, debinding and pre-firing, and high-temperature sintering treatment to obtain a calcium oxide crucible.

[0046] The wet blank undergoes demolding, drying, debinding, pre-firing, and high-temperature sintering to obtain the final calcium oxide crucible product. These post-treatment steps further enhance the strength of the wet blank. The demolding and drying step may include: after demolding, the wet blank is vacuum-dried at 40-80℃ for 18-36 hours to obtain a raw blank. The vacuum drying temperature can be 40℃, 45℃, 50℃, 60℃, 70℃, 75℃, or 80℃. The vacuum drying time can be 18 hours, 21 hours, 24 hours, 27 hours, 30 hours, 33 hours, or 36 hours.

[0047] The process conditions for debinding pre-firing and high-temperature sintering are selected based on the raw materials used in the preparation crucible. In this embodiment, carbon fiber is added, and high-temperature sintering is performed in a vacuum or inert atmosphere to prevent carbon fiber burn-off. Debinding pre-firing is carried out in a vacuum or inert atmosphere, with the green blank slowly heated to 800-1200℃ and held for 1-1.5 hours, with the heating rate controlled below 1.5℃ / min. During debinding pre-firing, the pre-firing temperature can be 800℃, 900℃, 1000℃, 1100℃, or 1200℃, and the holding time can be 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, or 1.5 hours, respectively.

[0048] The high-temperature sintering is carried out in a vacuum or inert atmosphere. The debinded blank is slowly heated to 1550-1700℃, held at that temperature for 1-2 hours, and then furnace cooled. The heating rate is controlled below 2℃ / min. The high-temperature sintering temperature can be 1550℃, 1600℃, 1650℃, or 1700℃. The holding time can be 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, or 2 hours.

[0049] In this embodiment, a gel casting process is used. First, organic monomers, crosslinking agents, and dispersants are added to an organic solvent and mixed to form a premix. Then, calcium oxide mixture, sintering aid, and carbon fibers are added to the premix and mixed. A catalyst and initiator are added while continuously stirring, and the mixture is thoroughly stirred to form a slurry. The calcium oxide mixture comprises 60-80% by weight of granules and 20-40% by weight of powder, with the calcium oxide mixture accounting for 60-80% of the slurry by weight, and the carbon fibers accounting for 0.05-0.2% of the slurry by weight. The mixture is then vibrated... The slurry is injected into the crucible mold, and a wet blank is formed after the monomer polymerization reaction. The wet blank is then subjected to demolding and drying, debinding and pre-firing, and high-temperature sintering treatment to obtain a calcium oxide crucible. The multi-grade calcium oxide mixture contains calcium oxide raw materials of different particle sizes, which has a particle dispersion strengthening effect. At the same time, the large-particle material accounts for the main proportion, which is conducive to forming crucible products with higher strength and lower porosity. Carbon fiber is mixed in calcium oxide, which has a fiber reinforcement effect, which can further improve the strength and thermal shock resistance of the crucible, thereby extending the service life of the crucible.

[0050] This application also provides a calcium oxide crucible, prepared using the method described above. The calcium oxide crucible of this embodiment contains a large amount of fused calcium oxide aggregate as the matrix material. The mixture of large-particle calcium oxide and powdered calcium oxide reduces porosity and increases solid content. The addition of carbon fibers further improves the crucible's strength and thermal shock resistance. Combined with gel casting molding, a reliable crucible product is obtained, meeting the requirements for smelting high-quality high-temperature alloys, titanium-aluminum alloys, titanium-nickel alloys, and other active materials using calcium oxide crucibles.

[0051] Example 1

[0052] The specific steps for preparing calcium oxide crucibles with multi-stage particle size distribution using carbon fiber reinforced gel casting are as follows:

[0053] A premixed solution weighing 351.6 g was prepared by mixing and dissolving 56 g of methacrylamide (organic monomer) and 5.6 g of N,N'-methylenebisacrylamide (crosslinking agent) in 290 g of n-butanol (dispersant).

[0054] Add 15 grams of polyacrylic acid and 15 grams of oleic acid dispersant to the premixed solution.

[0055] 600 grams of 325-mesh fused calcium oxide powder and 900 grams of fused calcium oxide granules were mixed to form 1500 grams of calcium oxide mixture. The ratio of powder to granules was 40:60. The granules contained 450 grams of 0-1 mm, 300 grams of 1-2 mm, and 150 grams of 2-3 mm particles.

[0056] 15 grams of zirconium oxide was added to the calcium oxide mixture as a sintering aid.

[0057] Add 1.5 grams of 5-10 mm long nickel-plated carbon fiber to the calcium oxide mixture.

[0058] The above premixed solution and calcium oxide mixture were thoroughly mixed and mechanically stirred for 20 minutes to obtain a slurry with good flowability.

[0059] Add 19 grams of ammonium persulfate (initiator) and 9.5 grams of tetramethylethylenediamine (catalyst) to the slurry and stir thoroughly.

[0060] The slurry was injected into the crucible mold under vibration conditions. The mold was placed in a drying oven and dried for 24 hours before demolding. After demolding, the mold was heated to 45°C in a vacuum drying oven and dried for 24 hours.

[0061] Under vacuum conditions, the crucible is heated to 650°C at a heating rate of 1°C / min and preheated for 2 hours to remove the adhesive and eliminate organic additives.

[0062] Under vacuum conditions, the crucible sample was sintered at 1650℃ for 2 hours by increasing the temperature at 2℃ / min.

[0063] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for preparing a calcium oxide crucible, characterized in that, The method includes: Organic monomers, crosslinking agents, and dispersants are added to an organic solvent and mixed to form a premix; Calcium oxide mixture, sintering aid, and carbon fiber are added to the premixed liquid and mixed. A catalyst and initiator are added while continuously stirring, and the mixture is stirred until homogeneous to form a slurry. The carbon fiber is nickel-plated carbon fiber. The calcium oxide mixture comprises 60-80% by weight of granules and 20-40% by weight of powder. The particle size of the granules includes greater than 0 and less than or equal to 1 mm, greater than 1 and less than or equal to 2 mm, and greater than 2 and less than or equal to 3 mm. The mass ratio of granules greater than 0 and less than or equal to 1 mm: granules greater than 1 and less than or equal to 2 mm: granules greater than 2 and less than or equal to 3 mm is (30-50):(30-50):(0-20). The particle size of the powder is below 325 mesh. The weight of the calcium oxide mixture accounts for 60-80% of the slurry, and the weight of the carbon fiber accounts for 0.05-0.2% of the slurry. The slurry is injected into a crucible mold under vibration conditions, and a wet preform is formed after the monomer polymerization reaction occurs. The wet blank is sequentially subjected to demolding and drying, debinding and pre-firing, and high-temperature sintering to obtain a calcium oxide crucible. The debinding and pre-firing and high-temperature sintering are carried out in a vacuum or inert atmosphere.

2. The method for preparing the calcium oxide crucible as described in claim 1, characterized in that, The length of the carbon fiber is 5-10 mm.

3. The method for preparing the calcium oxide crucible as described in claim 1, characterized in that, The sintering aid includes at least one of ZrO2, Al2O3, and TiO2, and the weight of the sintering aid is 0.5-2% of the weight of the calcium oxide mixture.

4. The method for preparing the calcium oxide crucible as described in claim 1, characterized in that, The dispersant comprises polyacrylic acid and oleic acid, and the dispersant accounts for 1-2% of the total weight of the premix and the calcium oxide mixture.

5. The method for preparing the calcium oxide crucible as described in claim 1, characterized in that, The organic solvent is n-butanol, the organic monomer is methacrylamide, and the crosslinking agent is N,N'-methylenebisacrylamide.

6. The method for preparing the calcium oxide crucible as described in claim 1, characterized in that, The amount of the initiator added is 0.5-1% of the total weight of the premix and the calcium oxide mixture; And / or, the amount of catalyst added is 0.3-0.6% of the total weight of the premix and the calcium oxide mixture.

7. The method for preparing the calcium oxide crucible as described in claim 1, characterized in that, The demolding and drying process includes: after demolding the wet blank, vacuum drying it at a temperature of 40-80°C for 18-36 hours to obtain a raw blank.

8. The method for preparing the calcium oxide crucible as described in claim 7, characterized in that, The preheating step of removing glue includes slowly heating the green blank to 800-1200℃ and holding it at that temperature for 1-1.5 hours, with the heating rate controlled below 1.5℃ / min; The high-temperature sintering step includes slowly heating the debinding blank to 1550-1700℃, holding it at that temperature for 1-2 hours, and then cooling it in the furnace, with the heating rate controlled below 2℃ / min.

9. A calcium oxide crucible, characterized in that, The calcium oxide crucible was prepared using the method described in any one of claims 1 to 8.

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