Alumina crucible with long service life as well as preparation method and application thereof

Abstract

The invention discloses a long-life alumina crucible as well as a preparation method and application thereof. The raw material composition of the alumina crucible comprises pretreated quartz particles; the pretreated quartz particles are obtained through a pretreatment process; according to the pretreatment process, the surfaces of fused quartz particles are coated with a modifier through a granulation process, and the pretreatment process specifically comprises the steps that the fused quartz particles, the modifier and a binding agent are mixed, granulated and dried, and pretreated quartz particles are obtained. The fused quartz particle raw material is subjected to modification pretreatment, so that the crystallization behavior of fused quartz is reduced or inhibited, the stability of the fused quartz particles in the crucible firing and high-temperature service process is improved, and the binding property of the fused quartz particles and the fine powder component is enhanced, so that the mechanical properties such as breaking strength and fracture toughness of the alumina crucible are improved; therefore, the service life and the stability of the crucible are improved, and the performance of the alumina crucible can completely meet the requirement of the service life under extreme conditions in the fields of rare noble metal smelting and the like.

Description

Technical Field

[0001] The invention relates to the technical fields of preparation and sintering of alumina crucibles and refractory materials, and in particular to a long-life alumina crucible and a preparation method thereof and application thereof in (rare) precious metal smelting. Background Art

[0002] High-temperature alloys are irreplaceable key materials for high-temperature parts in the aviation industry and gas turbines. Their comprehensive performance has a great impact on the development of aviation and gas turbines. The purity of the master alloy is one of the key factors in the performance of high-temperature alloys, and the content of harmful impurities has a huge impact on the performance of alloys and subsequent high-temperature parts. The crucible used for high-temperature alloy smelting is a container for alloy smelting and is in direct contact with high-temperature alloys. Its quality during use and service will also have a significant impact on high-temperature alloys. Therefore, in the vacuum induction melting process, the important role of the crucible is obvious. At present, crucibles for vacuum induction melting mainly rely on imports, and a large number of crucible products from a foreign company are still used on the market. The high price of the product, poor service, and slow delivery have brought great troubles to the operation of customers in the precision casting industry.

[0003] At present, due to the crystallization of the quartz particles used, alumina crucibles on the market are prone to cracking and peeling during use. In order to reduce the risk of alloy cross-contamination and ensure the quality of castings, the service life of most crucibles used in the precision casting industry is 1 to 5 times, which increases the cost of use and the waste of materials. In order to limit the crystallization performance of quartz particles and increase the service life of alumina crucibles, a large number of literatures have introduced suitable additives into the formula to improve the sintering performance and crystallization performance of quartz, but few literatures have proposed pre-treatment and modification of quartz raw materials to further improve the mixing uniformity of additives and quartz particles, further improve the use stability of quartz particles, and thus improve the service performance and number of uses of the crucible during use.

[0004] The patent specification with publication number CN114133256A discloses a ceramic crucible for medium frequency furnace and its preparation method. The main ingredients are all powder materials, without granular materials. During the preparation method, the main material mixture containing fused quartz powder, white corundum powder, α-alumina powder, γ-alumina powder and white carbon black and the auxiliary material mixture containing boric acid are directly mixed without any distinction, and the patented technical solution does not involve the problem of crystallization.

[0005] The patent specification with publication number CN108374196A discloses a fused quartz crucible for polycrystalline silicon ingot casting and a preparation method thereof. The patented technology uses fused quartz sand with a particle size of less than 500 μm as raw material, and also does not involve any granular material. Boron carbide and the like are used as crystallization inhibitors to prepare the crucible.

[0006] In fact, for alumina crucibles with fused quartz particles as one of the main raw materials, the existing technology does not provide a particularly good solution for how to make full use of the modifier so that the modifier can act on the fused quartz particles in a targeted and better manner, inhibit the crystallization of the fused quartz particles, and at the same time enhance the bonding between the fused quartz particles and the fine powder components to improve the flexural strength, fracture toughness and other mechanical properties of the alumina crucible.

[0007] The patent specification with publication number CN106336208A discloses a method for preparing a homogeneous fused quartz crucible, including steps A: preparing slurry: placing SiO2 powder, zirconium oxide grinding balls, and deionized water in a mass ratio of 1:2.6:0.4 in a ball mill for initial ball milling; after grinding, adding polyvinyl alcohol, lactic acid, tartaric acid, and sodium bicarbonate to the ball mill for further grinding, and after grinding, the filtered slurry is fixed to volume with deionized water to prepare a slurry with a solid content of 75-80 vol%, which is the required slurry; B: vibration grouting molding; C: drying: drying the green body in step B in room temperature air; and then placing the green body in a blast drying oven for drying; D: firing: firing the green body dried in step C in a high-temperature furnace at a temperature of 1200-1300°C, and keeping it warm to prepare the required fused quartz crucible. In the patented technical solution, Si3N4 powder with a particle size of 50-80μm can be added to the fused quartz powder to inhibit the precipitation of quartz crystals. Specifically, in the initial ball milling process of step A, Si3N4 powder accounting for 0.35-0.65% of its mass percentage is added to the SiO2 powder, and the hardness of the crucible obtained is finally improved. However, the SiO2 used in the patented technical solution is in the form of powder with a particle size of 180-200μm. It will not form an obvious core-shell coating structure when mixed with Si3N4 powder with a particle size of 50-80μm, and it is also inferred from the dosage ratio of the Si3N4 powder that the Si3N4 powder cannot effectively wrap a large amount of SiO2 powder. Summary of the invention

[0008] In view of the above technical problems and the deficiencies in the art, the present invention provides an alumina crucible with a long service life, a preparation method thereof and an application thereof in (rare) precious metal smelting.

[0009] The present invention reduces or inhibits the crystallization behavior of fused quartz by modifying and pretreating the fused quartz particle raw material, improves the stability of the fused quartz particles during crucible sintering and high-temperature service, enhances the bonding of the fused quartz particles with the fine powder components to improve the mechanical properties of the alumina crucible, such as the flexural strength and fracture toughness, and further improves the service life and stability of the crucible, so that the performance of the alumina crucible fully meets the service life requirements under extreme conditions in the fields of rare and precious metal smelting. At the same time, the preparation process of the present invention is simple and easy to promote and apply.

[0010] [1] A long-life alumina crucible, wherein the raw material composition comprises, by mass percentage, 55% to 80% of an alumina component and 20% to 45% of a silicon dioxide component;

[0011] The silicon dioxide component includes pre-treated quartz particles and silicon dioxide micropowder that can be added selectively (that is, can be added or not added);

[0012] Taking the total mass of the raw materials of the alumina crucible as 100%, the mass of the pretreated quartz particles accounts for 20% to 40%, for example, 30%;

[0013] The pretreated quartz particles have a core-shell coating structure with fused quartz particles as cores and modifiers as shells, and are obtained through a pretreatment process; the pretreatment process is to coat the modifier on the surface of the fused quartz particles through a granulation process, specifically comprising: mixing fused quartz particles, modifiers and binders, granulating, and drying to obtain the pretreated quartz particles; based on the total mass of the fused quartz particles and the modifier as 100%, the mass proportion of the modifier is 1% to 10% (for example, 3%); the particle size of the fused quartz particles is 0.2 to 1 mm;

[0014] The modifier includes at least one of a high melting point oxide, a low melting point oxide, a non-oxide, and a fiber material;

[0015] The high melting point oxide-containing material comprises at least one of Al2O3, La2O3, Cr2O3, CeO2, Y2O3, AlPO4, P2O5, Ga2O3, TiO2, In2O3, and V2O5, preferably at least one of Al2O3, Y2O3, and TiO2;

[0016] The low melting point oxide-containing compound includes at least one of boric acid (H3BO3), phosphoric acid, and B2O3, preferably includes at least one of boric acid and B2O3;

[0017] The non-oxide comprises at least one of BN, AlN, Si3N4, B4C, and TiB2, preferably at least one of Si3N4, B4C, and TiB2;

[0018] The fiber material includes at least one of SiO2 fiber, C fiber, and Al2O3 fiber.

[0019] The present invention uses a pretreatment process to coat the surface of the fused quartz particles with a layer of modifier. In order to ensure that the modifier layer has a certain thickness so as to enhance the bonding between the fused quartz particles and the fine powder components to improve the mechanical properties of the alumina crucible, such as the flexural strength and fracture toughness, the present invention requires that the mass of the modifier accounts for more than 1% based on the total mass of the fused quartz particles and the modifier as 100%. If the modifier is used in too little proportion, a modifier coating layer of effective thickness cannot be formed on the surface of the fused quartz particles, and naturally it cannot enhance the bonding between the fused quartz particles and the fine powder components to improve the mechanical properties of the alumina crucible, such as the flexural strength and fracture toughness.

[0020] The study found that during the operation of the pretreatment process, if there is no binder, it is impossible to form Figure 1 The core-shell coating structure shown in the figure has fused silica particles as core and modifier as shell.

[0021] In some preferred examples, the alumina crucible, based on the total mass of the fused quartz particles and the modifier as 100%, the mass proportion of the binder is 0.5% to 5%, for example, 1%. Under preferred conditions, on the one hand, the fused quartz particles and the modifier can be fully mixed and effectively coated and modified, and on the other hand, the added binder can be effectively removed during the sintering stage, without causing defects in the bonding between the modified layer and the shell.

[0022] In some preferred examples, the alumina crucible, the binder includes at least one of polyvinyl alcohol solution, acrylic resin, and polyacrylic acid, and further preferably includes polyvinyl alcohol solution. Polyvinyl alcohol is a water-soluble polymer compound, acrylic resin is a transparent material synthesized by polymerization reaction, and polyacrylic acid is a high molecular polymer, wherein polyvinyl alcohol has a large number of hydroxyl groups in its molecular structure, has better water solubility and film-forming properties, and has higher viscosity and stability.

[0023] Furthermore, the concentration of the polyvinyl alcohol solution may be 2 wt % to 10 wt %.

[0024] In some embodiments, in the alumina crucible, the alumina component may include corundum particles, corundum fine powder, and alumina fine powder.

[0025] In some embodiments, the particle size of the corundum particles may be 0.2 to 1 mm;

[0026] In some embodiments, the particle size of the corundum fine powder may be 180-800 mesh;

[0027] In some embodiments, the fine aluminum oxide powder may have a particle size of 0.3 to 10 μm.

[0028] In some embodiments, for the alumina crucible, based on the total mass of the raw materials of the alumina crucible as 100%, the mass proportion of the corundum particles may be 20% to 45%, for example, 30%, the mass proportion of the corundum fine powder may be 20% to 35%, and the mass proportion of the alumina fine powder may be 5% to 25%, for example, 15%.

[0029] In some embodiments, in the alumina crucible, the particle size of the pretreated quartz particles may be 0.2-1 mm.

[0030] In some embodiments, in the alumina crucible, the particle size of the silica powder may be 0.2-3 μm.

[0031] [2] The method for preparing an alumina crucible according to [1] comprises the steps of:

[0032] S1, ball-milling and blending an alumina component, a silica component and an organic binder to obtain a slurry;

[0033] S2, pouring the slurry into a mold, leaving the mold to stand for a period of time after the slurry fills the mold, demoulding, drying, and sintering to obtain an alumina crucible.

[0034] The method for preparing an alumina crucible is a method for preparing an alumina crucible by utilizing slip casting.

[0035] In step S1, a horizontal ball mill may be used for ball milling, and alumina grinding balls may be used as grinding media. The purity of the alumina grinding balls is preferably above 95%, and the ball milling time may be 3 to 30 hours.

[0036] In step S1, the organic binder may be a polyvinyl alcohol solution. Further, the concentration of the polyvinyl alcohol solution may be 2 wt% to 10 wt%, such as 5 wt%.

[0037] In step S1, the solid content of the slurry may be 60 wt% to 90 wt%, such as 80 wt%.

[0038] In step S2, the standing temperature may be room temperature.

[0039] In step S2, the standing time may be 1 to 10 hours, for example, 2 hours.

[0040] In step S2, the drying temperature may be 100-220°C, such as 110°C.

[0041] In step S2, the drying time may be 24 to 28 hours.

[0042] Based on the performance indicators of alumina crucible, mainly phase composition, porosity and bulk density, in step S2, the sintering temperature is preferably 1150-1500°C, such as 1300°C.

[0043] In step S2, the sintering atmosphere may be an air atmosphere.

[0044] In step S2, the sintering time may be 72 to 180 hours.

[0045] In step S2, the heating rate of the sintering process may be 1-10°C / min, for example, 5°C / min.

[0046] The alumina crucible of the present invention is preferably prepared by the above preparation method, and the alumina crucible prepared by the above preparation method has the advantages of easy sintering, high thermal shock stability, and not easy to stick to slag. Therefore, it can meet the service life requirements under extreme conditions in the fields of rare and precious metal smelting, and can be widely used in temperature sudden change environments.

[0047] [3] Application of the alumina crucible according to [1] in precious metal smelting.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. The crucible of the present invention has excellent sintering properties, thermal shock stability, and slag resistance. Its high-temperature thermal shock stability (1100°C, water cooling) can achieve more than 50 hot and cold cycle times without cracking or inner wall peeling. It can meet the needs of the precision casting industry, increase the service life of the crucible, and reduce the cost of using the crucible.

[0050] 2. The preparation process of the present invention is simple and easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic diagram of the structure before and after the pretreatment process of fused quartz particles of the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0053] The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or conditions recommended by the manufacturers.

[0054] Embodiment 1:

[0055] (1) Weigh 99 parts of fused silica particles, 1 part of H3BO3, and 1 part of a binder polyvinyl alcohol solution, the concentration of which is 10 wt %, and add them to a mixing granulator for thorough mixing, granulation, and drying to obtain pretreated quartz particles having a core-shell coating structure with fused silica particles as cores and a modifier as a shell. The particle size of the fused silica particles is 0.2 to 1 mm. The particle size of the pretreated quartz particles is 0.2 to 1 mm.

[0056] (2) Weigh by mass: 30 parts of corundum particles, 30 parts of pretreated quartz particles prepared according to (1), 20 parts of corundum fine powder, 15 parts of alumina fine powder, 5 parts of silica micropowder, and add them together with a polyvinyl alcohol solution with an organic binder concentration of 5wt% to a ball mill for blending and kneading to obtain a slurry with a solid content of 80wt%. The particle size of the corundum particles is 0.2-1mm. The particle size of the corundum fine powder is 180-800 mesh. The particle size of the alumina fine powder is 0.3-10μm. The particle size of the silica micropowder is 0.2-3μm. This step uses a horizontal ball mill for ball milling, using alumina grinding balls as the grinding medium, the purity of the alumina grinding balls is above 95%, and the ball milling time is 3h.

[0057] (3) Grouting: Pour the slurry into the plaster mold and let it sit until the mold is full of slurry.

[0058] (4) Demolding: Demolding after standing at room temperature for 2 hours.

[0059] (5) Drying: Dry at 110°C for 24 hours.

[0060] (6) Firing: sintering at 1300°C in air atmosphere for 72 h with a heating rate of 5°C / min, followed by cooling to room temperature to obtain an alumina crucible.

[0061] Embodiment 2:

[0062] The only difference from Example 1 is that the mass fractions of fused silica particles and H3BO3 are changed in (1), specifically, 97 parts of fused silica particles and 3 parts of H3BO3 are weighed, and the rest are the same to obtain an alumina crucible.

[0063] Embodiment 3:

[0064] The only difference from Example 1 is that in (1) an equal mass of TiB2 is used to replace H3BO3, and the rest is the same, to obtain an alumina crucible.

[0065] Embodiment 4:

[0066] The only difference from Example 1 is that in (1), an equal mass of B4C is used to replace H3BO3, and the rest is the same, and an alumina crucible is obtained.

[0067] Comparative Example 1:

[0068] The only difference from Example 1 is that (1) is omitted and in (2), the pretreated quartz particles are replaced by fused quartz particles of equal mass with a particle size of 0.2 to 1 mm. The rest are the same to obtain an alumina crucible.

[0069] Performance characterization:

[0070] In order to further illustrate the performance of the alumina crucible of the present invention, specific effect data are provided below. The sintering density, compressive strength, flexural strength, fracture toughness, thermal shock stability and X-ray diffraction (XRD) results of Examples 1 to 4 and Comparative Example 1 were tested respectively, as shown in Table 1 below. If the fused quartz raw material crystallizes into a cristobalite phase, the crystallization is checked by the XRD diffraction peak of the crucible sample, which is expressed by the cristobalite phase content (the total mass of all crystal phase components detected by the crucible XRD is 100%).

[0071] Table 1

[0072]

[0073] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A long-life alumina crucible, characterized in that: In terms of mass percentage, the raw material composition includes 55% to 80% of an aluminum oxide component and 20% to 45% of a silicon dioxide component; The silicon dioxide component includes pre-treated quartz particles and optionally added silicon dioxide fine powder; Taking the total mass of the raw materials of the alumina crucible as 100%, the mass of the pretreated quartz particles accounts for 20% to 40%; The pretreated quartz particles have a core-shell coating structure with fused quartz particles as core and modifier as shell, and are obtained through a pretreatment process; The pretreatment process is to coat the modifier on the surface of the fused quartz particles through a granulation process, specifically comprising: mixing the fused quartz particles, the modifier and the binder, granulating, and drying to obtain the pretreated quartz particles; Taking the total mass of the fused quartz particles and the modifier as 100%, the mass of the modifier accounts for 1% to 10%; the particle size of the fused quartz particles is 0.2 to 1 mm; The modifier includes at least one of a high melting point oxide, a low melting point oxide, a non-oxide, and a fiber material; The high melting point oxide-containing material comprises at least one of Al2O3, La2O3, Cr2O3, CeO2, Y2O3, AlPO4, P2O5, Ga2O3, TiO2, In2O3, and V2O5, preferably at least one of Al2O3, Y2O3, and TiO2; The low melting point oxide-containing compound comprises at least one of boric acid, phosphoric acid and B2O3, preferably at least one of boric acid and B2O3; The non-oxide comprises at least one of BN, AlN, Si3N4, B4C, and TiB2, preferably at least one of Si3N4, B4C, and TiB2; The fiber material includes at least one of SiO2 fiber, C fiber, and Al2O3 fiber.

2. The alumina crucible according to claim 1, characterized in that: Taking the total mass of the fused quartz particles and the modifier as 100%, the mass proportion of the binder is 0.5% to 5%.

3. The alumina crucible according to claim 1, characterized in that: The binder includes at least one of polyvinyl alcohol solution, acrylic resin, and polyacrylic acid, preferably includes polyvinyl alcohol solution; The concentration of the polyvinyl alcohol solution is 2wt% to 10wt%.

4. The alumina crucible according to claim 1, characterized in that: The aluminum oxide component includes corundum particles, corundum fine powder and aluminum oxide fine powder; The particle size of the corundum particles is 0.2 to 1 mm; The particle size of the corundum fine powder is 180-800 mesh; The particle size of the alumina fine powder is 0.3-10 μm.

5. The alumina crucible according to claim 4, characterized in that: Taking the total mass of the raw materials of the alumina crucible as 100%, the mass of the corundum particles accounts for 20% to 45%, the mass of the corundum fine powder accounts for 20% to 35%, and the mass of the alumina fine powder accounts for 5% to 25%.

6. The alumina crucible according to claim 1, characterized in that: The particle size of the pretreated quartz particles is 0.2-1 mm.

7. The alumina crucible according to claim 1, characterized in that: The particle size of the silicon dioxide powder is 0.2-3 μm.

8. The method for preparing an alumina crucible according to any one of claims 1 to 7, characterized in that: Includes steps: S1, ball-milling and blending an alumina component, a silica component and an organic binder to obtain a slurry; S2, pouring the slurry into a mold, leaving the mold to stand for a period of time after the slurry fills the mold, demoulding, drying, and sintering to obtain an alumina crucible.

9. The preparation method according to claim 8, characterized in that: In step S1: A horizontal ball mill is used for ball milling, and alumina grinding balls are used as grinding media. The purity of the alumina grinding balls is above 95%, and the ball milling time is 3 to 30 hours. The organic binder is a polyvinyl alcohol solution, and the concentration of the polyvinyl alcohol solution is 2wt% to 10wt%; The solid content of the slurry is 60wt% to 90wt%; In step S2: The static temperature is room temperature; The standing time is 1 to 10 hours; The drying temperature is 100-220°C; The drying time is 24 to 28 hours; The sintering temperature is 1150~1500℃; The sintering atmosphere is air atmosphere; The sintering time is 72 to 180 hours; The heating rate of the sintering process is 1-10°C / min.

10. Use of the alumina crucible according to any one of claims 1 to 7 in precious metal smelting.

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