Microcosmic-macroscopic prestress synergistically enhanced aluminum oxide ceramic preparation method and product thereof

Abstract

The invention discloses a preparation method of microcosmic-macroscopic prestress synergistically enhanced aluminum oxide ceramic and a product of the microcosmic-macroscopic prestress synergistically enhanced aluminum oxide ceramic. Low-shrinkage mineral kyanite particles are utilized on the surface of an aluminum oxide matrix, so that the surface layer of the matrix is subjected to microcosmic compressive stress, and the matrix is strengthened for the first meanwhile, the matrix is secondarily strengthened by wrapping type compact constraint macroscopic compressive stress on the surface layer of the matrix, so that the microcosmic-macroscopic residual compressive stress is synergistically enhanced, and the composite reinforced aluminum oxide ceramic consisting of the aluminum oxide matrix as well as the ion exchange-like layer and the prestressed coating on the surface of the matrix is formed; the breaking strength of the aluminum oxide ceramic is obviously improved, and the service life is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of structural ceramic materials, and in particular to a preparation method of alumina structural ceramics and products thereof. Background Art

[0002] Alumina ceramics have become a vital material in modern national defense and industrial construction. Their excellent properties, including high strength, high temperature resistance, corrosion resistance, and wear resistance, make them play a key role in many fields such as aerospace, new energy, high-end equipment, machinery, petroleum, and electronics. However, alumina ceramics are typical brittle materials with relatively low tensile strength, which can easily cause sudden brittle fractures. This defect has limited their application in many fields such as medicine, chemical industry, machinery, and aerospace. How to effectively improve the flexural strength of alumina ceramics has become a key direction in current related research fields.

[0003] At present, various strengthening methods for alumina ceramics have been proposed in the relevant fields. At the macroscopic scale, there are layered structures and bionic designs; at the microscopic scale, there are particle dispersion reinforcement, fiber reinforcement, whisker reinforcement, phase change toughening (ZTA), microcrack toughening and nano-toughening. Although the above toughening methods have a certain strengthening effect on the toughening of alumina ceramics, they are limited by the complex manufacturing process, high production cost, limited action scale and other reasons.

[0004] Prestressed reinforcement design is to apply pre-compressive stress in materials or components to offset the tensile stress applied externally, thereby improving the crack resistance of the matrix and increasing the fracture strength, reliability and durability of the material. This design method has been widely used in the fields of concrete structures and tempered glass (i.e. prestressed glass). The two implementation methods of prestressed reinforcement are coating method and ion exchange method. Some scholars have strengthened alumina ceramics by coating method, but because alumina ceramics do not contain sodium ions, they cannot be strengthened by ion exchange method. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing micro-macro prestressed synergistically reinforced alumina ceramics, by using low-shrinkage mineral kyanite particles on the surface of the alumina matrix to subject the matrix surface to micro-compressive stress to strengthen the matrix once, and at the same time, by wrapping the compact constrained macro-compressive stress on the matrix surface to strengthen the matrix twice, thereby synergistically achieving the enhancement of micro-macro residual compressive stress, and achieving the purpose of improving the flexural strength of alumina ceramics and extending the service life. Another purpose of the present invention is to provide a product obtained by the above-mentioned method for preparing micro-macro prestressed synergistically reinforced alumina ceramics.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for preparing a micro-macro prestressed synergistically reinforced alumina ceramic, comprising the following steps:

[0008] (1) Preparation of alumina ceramic composite matrix

[0009] 93-97wt% alumina powder and 3-7wt% kyanite are used as raw materials, and the kyanite-alumina powder-kyanite are added into a mold in the order of dry pressing, pre-sintering, and natural cooling to obtain an alumina ceramic composite matrix;

[0010] (2) Preparation of prestressed coating slurry

[0011] The raw material of the prestressed coating is composed of a base material and an additive; the raw material composition of the base material is 10-45wt% of alumina powder and 55-90wt% of kyanite; the additive is a castor oil dispersant and an organosilicon defoamer, and the amount thereof is 1-3wt% of the base material respectively; after the raw material of the prestressed coating is prepared, water is used as a medium and ball milling is performed at a mass ratio of material: water = 1: 3.0-5.0, and the prestressed coating slurry is obtained after sieving;

[0012] (3) Preparation of prestressed coating

[0013] A prestressed coating slurry is applied on the upper and lower surfaces of the alumina ceramic composite substrate by a glaze spraying method, and after natural air drying, a prestressed coating is formed on the surface of the alumina ceramic composite substrate to obtain an alumina ceramic body, wherein the thickness of the prestressed coating / the thickness of the alumina ceramic composite substrate is less than 0.05;

[0014] (4) Preparation of reinforced alumina ceramics

[0015] The alumina ceramic green body is sintered by heating to 1500-1580° C. at a rate of 2-6° C. / min for 1-2 hours, and then naturally cooled to obtain a composite reinforced alumina ceramic.

[0016] Furthermore, the particle size of the alumina powder in step (1) of the present invention is D 50 =400~600nm, the particle size of kyanite is D 50 =0.9~1.7μm.

[0017] In the above scheme, the pressure of dry pressing in step (1) of the present invention is 70-150 MPa; the pre-burning temperature is 1000-1200°C, and the insulation time is 30-60 min; the ball milling speed in the ball milling treatment of step (2) is 200-400 r / min, and the ball milling time is 12-24 h.

[0018] The product is made by the preparation method of the micro-macro prestressed synergistically reinforced alumina ceramics. The composite reinforced alumina ceramics are composed of an alumina matrix, an ion exchange-like layer on the surface of the matrix and a prestressed coating, and have a flexural strength of 383 to 439 MPa.

[0019] The present invention has the following beneficial effects:

[0020] (1) The present invention artificially adds low-shrinkage mineral kyanite particles on the surface of the substrate. The kyanite particles have the property of irreversible expansion when heated. During the cooling process, the surface substrate shrinks while the kyanite does not shrink, so that the substrate is subjected to compressive stress, which is similar to the pinning effect produced by the large-radius ions replacing the small-radius ions in the ion exchange method. On the other hand, a low-expansion coefficient coating is applied to the surface of the substrate to form compressive stress on its surface. The primary reinforcement through microscopic simulation of pinning particles on the surface and the secondary reinforcement through the coating of macroscopic prestressed coatings work synergistically, significantly improving the flexural strength of alumina ceramics and extending their service life.

[0021] (2) The raw materials of the present invention are non-toxic and pollution-free, environmentally friendly, and the entire preparation process is green, clean and pollution-free. At the same time, the reinforcement process is significantly different from other reinforcement ceramic processes, using pressureless sintering, the process is simple and easy, the cost is low, and it is easy to industrialize and promote.

[0022] The present invention will be described in further detail below with reference to the embodiments. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing a micro-macro prestressed synergistically reinforced alumina ceramic, the steps of which are as follows:

[0024] (1) Preparation of alumina ceramic composite matrix

[0025] By particle size D 50 = 93-97 wt% of alumina powder with a particle size of 400-600 nm, D 50 = 3-7wt% of kyanite with a diameter of 0.9-1.7μm is used as a raw material, and kyanite-alumina powder-kyanite is added into a mold in the order of kyanite, and an alumina ceramic composite matrix is ​​obtained by dry pressing, pre-sintering, and natural cooling; wherein the molding pressure is 70-150MPa, the pre-sintering temperature is 1000°C, and the holding time is 60min; the raw material composition of the alumina ceramic composite matrix of each embodiment is shown in Table 1;

[0026] (2) Preparation of prestressed coating slurry

[0027] The raw material of the prestressed coating is composed of a base material and an additive; the raw material composition of the base material is 10-45wt% of alumina powder and 55-90wt% of kyanite; the additives are castor oil dispersant and organosilicon defoamer, and the amount thereof is 1-3wt% of the base material respectively; after the above raw materials of the prestressed coating are prepared, ultrapure water is used as a medium and ball milling is performed according to the mass ratio of material: water = 1: 3.0-5.0, material: ball = 1: 10, the ball milling speed is 200-400r / min, the ball milling time is 12-24h, and the prestressed coating slurry is obtained after sieving; the raw material composition of the prestressed coating of each embodiment is shown in Table 2;

[0028] (3) Preparation of prestressed coating

[0029] A prestressed coating slurry is applied on the upper and lower surfaces of the alumina ceramic composite substrate by a glaze spraying method, and after natural air drying, a prestressed coating is formed on the surface of the alumina ceramic composite substrate to obtain an alumina ceramic body, wherein the thickness of the prestressed coating / the thickness of the alumina ceramic composite substrate is less than 0.05;

[0030] (4) Preparation of reinforced alumina ceramics

[0031] The alumina ceramic body is sintered by heating to 1500-1580°C at a rate of 2-6°C / min for 1-2h, and then naturally cooled to obtain a composite reinforced alumina ceramic.

[0032] The process parameters of each embodiment are shown in Table 3.

[0033] Table 1 Raw material composition of alumina ceramic composite matrix in various embodiments of the present invention

[0034]

[0035] Table 2 Raw material composition of prestressed coating in various embodiments of the present invention

[0036]

[0037] *Amount relative to base material

[0038] Table 3 Process parameters of various embodiments of the present invention

[0039]

[0040] The composite reinforced alumina ceramic products prepared in the embodiments of the present invention are composed of an alumina substrate, an ion exchange layer and a prestressed coating on the surface of the substrate, and have a water absorption rate of less than 0.02%. A blank alumina substrate is used as a comparative example. The flexural strength of the composite reinforced alumina ceramics prepared in the embodiments of the present invention and the corresponding comparative examples are shown in Table 4.

[0041] Table 4 Flexural strength of alumina ceramic products of various embodiments of the present invention and comparative examples

[0042]

Claims

1. A method for preparing micro-macro prestressed synergistically reinforced alumina ceramics, characterized in that The following steps are involved: (1) Preparation of alumina ceramic composite matrix 93-97wt% alumina powder and 3-7wt% kyanite are used as raw materials, and the kyanite-alumina powder-kyanite are added into a mold in the order of dry pressing, pre-sintering, and natural cooling to obtain an alumina ceramic composite matrix; (2) Preparation of prestressed coating slurry The raw material of the prestressed coating is composed of a base material and an additive; the raw material composition of the base material is 10-45wt% of alumina powder and 55-90wt% of kyanite; the additive is a castor oil dispersant and an organosilicon defoamer, and the amount thereof is 1-3wt% of the base material respectively; after the raw material of the prestressed coating is prepared, water is used as a medium and ball milling is performed at a mass ratio of material: water = 1: 3.0-5.0, and the prestressed coating slurry is obtained after sieving; (3) Preparation of prestressed coating A prestressed coating slurry is applied on the upper and lower surfaces of the alumina ceramic composite substrate by a glaze spraying method, and after natural air drying, a prestressed coating is formed on the surface of the alumina ceramic composite substrate to obtain an alumina ceramic body, wherein the thickness of the prestressed coating / the thickness of the alumina ceramic composite substrate is less than 0.05; (4) Preparation of reinforced alumina ceramics The alumina ceramic green body is sintered by heating to 1500-1580° C. at a rate of 2-6° C. / min for 1-2 hours, and then naturally cooled to obtain a composite reinforced alumina ceramic.

2. The method for preparing micro-macro prestressed synergistically reinforced alumina ceramics according to claim 1, characterized in that: The particle size of the alumina powder in step (1) is D 50 =400~600nm, the particle size of kyanite is D 50 =0.9~1.7μm.

3. The method for preparing micro-macro prestressed synergistically reinforced alumina ceramics according to claim 1, characterized in that: The pressure of dry pressing in step (1) is 70-150 MPa; the pre-sintering temperature is 1000-1200° C., and the holding time is 30-60 min; the ball milling speed in the ball milling treatment in step (2) is 200-400 r / min, and the ball milling time is 12-24 h.

4. A product obtained by the method for preparing micro-macro prestressed synergistically reinforced alumina ceramics according to any one of claims 1 to 3, characterized in that: The composite reinforced alumina ceramics are composed of an alumina matrix, and a quasi-ion exchange layer and a prestressed coating on the surface of the matrix.

5. The product according to claim 4, characterized in that: The flexural strength of the composite reinforced alumina ceramic is 383-439 MPa.

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