High-toughness ceramic composite material and method for producing the same

Abstract

This invention discloses a high-toughness ceramic composite material and its preparation method, belonging to the field of ceramic materials technology. The composite material is made from the following raw materials: alumina powder, nanocellulose, coal tar pitch, and sintering aids. This invention uses nanocellulose and coal tar pitch as precursors, generating graphene-like substances through in-situ pyrolysis during hot pressing sintering. The two synergistically construct a multi-dimensional carbon network and tightly coat Al2O3 grains. By controlling the specific ratio of nanocellulose to coal tar pitch and incorporating an 800℃ pre-carbonization step during sintering, the fracture toughness of the resulting composite material is significantly higher than that of a single carbon source system. This invention avoids the problems of high cost, uneven dispersion, and easy destruction of sheets associated with directly adding graphene, and has advantages such as low cost, good process compatibility, and significant toughening effect, showing broad application prospects in aerospace, electronic devices, and mechanical seals.

Description

Technical Field

[0001] This invention relates to the field of ceramic matrix composites, specifically to an alumina-based ceramic composite material and its preparation method, which uses nanocellulose and coal tar pitch as precursors and is toughened by in-situ pyrolysis to generate graphene-like substances. Background Technology

[0002] Alumina (Al2O3) ceramics have advantages such as high hardness, high temperature resistance, and corrosion resistance, but their fracture toughness is low (typically 3-5 MPa·m). 1 / 2 Alumina ceramics are prone to brittle fracture. To improve toughness, existing technologies mainly employ the addition of toughening phases such as particles, whiskers, or directly added graphene. CN120247577A discloses an alumina ceramic composite material that uses the direct addition of graphene powder (1.5-3 parts) to synergistically toughen with silicon carbide whiskers; CN113860857A also discloses an alumina ceramic composite material that uses the addition of graphene and zirconium oxide to achieve a synergistic toughening effect, thereby improving the toughness of the alumina ceramic material.

[0003] However, directly adding graphene has three inherent drawbacks: (1) graphene powder is expensive, limiting its large-scale application; (2) the two-dimensional sheet structure of graphene is easily damaged during ball milling, reducing the toughening effect; and (3) graphene is difficult to disperse uniformly in ceramic matrices, easily agglomerates, and has weak interfacial bonding with the matrix. Therefore, it is urgent to develop a new toughening technology that can replace the direct addition of graphene.

[0004] In recent years, the technical route of in-situ generation of graphene-like materials during ceramic sintering using biomass or fossil-based carbon sources as precursors has attracted attention. Nanocellulose, as a green, renewable, and high-carbon-content biomass material, has been proven to be convertible into graphitized carbon materials at high temperatures and used for carbon source introduction and in-situ toughening of alumina ceramics. Coal tar pitch, as a byproduct of coal chemical industry, can be converted into highly crystalline graphene nanosheets under aluminum catalysis, and the Al2O3 matrix itself can provide an aluminum source. However, there are currently no reports on the in-situ generation of graphene-toughened alumina ceramics by combining nanocellulose and coal tar pitch as binary carbon sources and utilizing their synergistic effect, nor are there any systematic studies on the toughening effect of comparing the dosages of the two materials. Summary of the Invention

[0005] This invention provides a high-toughness ceramic composite material and its preparation method, using nanocellulose and coal tar pitch as composite precursors, and generating graphene-based toughened alumina ceramics through in-situ pyrolysis. By controlling the specific ratio of nanocellulose to coal tar pitch, synergistic toughening is achieved, resulting in a significant improvement in fracture toughness.

[0006] A high-toughness ceramic composite material is made from the following raw materials in the following weight percentages:

[0007] Alumina (Al2O3) powder: 93-98.5 wt%

[0008] Nanocellulose: 0.3-3 wt%

[0009] Coal tar pitch: 0.1-2 wt%

[0010] Sintering aid: 0.5-2 wt%.

[0011] The mass ratio of nanocellulose to coal tar pitch is 1:0.2-0.8, more preferably 1:0.3-0.5. In particular, the synergistic toughening effect is optimal when the mass ratio of nanocellulose to coal tar pitch is 1:0.4.

[0012] The nanocellulose has a diameter of 5-50 nm, a length of 1-20 μm, a crystallinity of ≥70%, and an ash content of ≤0.5%. The coal tar pitch is refined coal tar pitch with a softening point of 80-120℃, a quinoline insoluble matter (QI) content of ≤1.0 wt%, an ash content of ≤0.2 wt%, and a sulfur content of ≤0.5 wt%. The sintering aid is at least one of MgO and Y2O3, preferably MgO or a MgO-Y2O3 composite system (MgO:Y2O3 mass ratio 1-5:1).

[0013] This invention also discloses a method for preparing the above-mentioned high-toughness ceramic composite material, comprising the following steps:

[0014] (1) Weigh alumina powder, nanocellulose, coal tar pitch and sintering aid according to the ratio, add anhydrous ethanol as grinding medium, use zirconia balls as grinding media, and perform wet ball milling in a planetary ball mill. The ball milling speed is 150-250 r / min and the ball milling time is 6-12 h. The mass ratio of zirconia balls, anhydrous ethanol and mixed powder is (8-12):(1-3):1.

[0015] (2) Drying and sieving: The ball-milled slurry is dried in a vacuum drying oven at 40-60℃ for 10-24 h, and then passed through an 80-200 mesh sieve to obtain mixed powder.

[0016] (3) Secondary mixing: The sieved powder is placed in a three-dimensional vibrating mixer and mixed at a speed of 50-80 r / min for 4-10 h to eliminate stratification caused by density differences.

[0017] (4) Hot pressing sintering: The mixed powder is loaded into a graphite mold and placed in a vacuum hot pressing sintering furnace for sintering under an inert atmosphere (nitrogen or argon).

[0018] Further, the sintering process in step (4) is as follows: the temperature is increased from room temperature to 800℃ at a rate of 5-15℃ / min, and held for 20-60 min to allow the nanocellulose and coal tar pitch to undergo preliminary pyrolysis; the temperature is then increased to 1000℃ at a rate of 5-15℃ / min, and then increased to 1450-1700℃ at a rate of 3-8℃ / min, and held for 0.5-3 h; an axial pressure of 20-40 MPa is applied throughout the sintering process, with the pressure starting at 200-300℃, and the pressure is maintained until the end of the holding period; the furnace is cooled to room temperature, the pressure is released, and the high-toughness ceramic composite material is obtained.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This invention uses nanocellulose and coal tar pitch as precursors to generate graphene-like substances in situ during hot pressing and sintering. The nanocellulose undergoes pyrolysis to form carbon nanofibers / multilayer graphene frameworks, while the coal tar pitch, catalyzed by an alumina matrix, is transformed into highly crystalline graphene nanosheets via an Al4C3 intermediate. Together, they construct a multidimensional carbon network that tightly encapsulates Al2O3 grains, achieving a uniform distribution and chemical bonding interface of graphene through "self-assembly," while also offering cost advantages.

[0021] The pyrolysis process of nanocellulose and coal tar pitch produces complementary carbonization behaviors. The free radicals generated by cellulose pyrolysis promote the orderly arrangement of the coal tar pitch mesophase, and the polycyclic aromatic hydrocarbons of coal tar pitch grow on the surface of the cellulose-derived carbon skeleton to form a more continuous and dense carbon layer, thereby reducing the graphene defect degree to below 0.55, which is superior to the single carbon source system.

[0022] By systematically controlling the mass ratio of nanocellulose to coal tar pitch, a synergistic toughening "window" was discovered for the first time: when the mass ratio is 1:0.3-0.5, the fracture toughness is much higher than that of a single carbon source system and a technology that directly adds graphene. Within this mass ratio range, one-dimensional carbon nanofibers provide pull-out and bridging toughening, while two-dimensional graphene nanosheets provide crack deflection and exfoliation toughening, with multiple mechanisms superimposed to dissipate fracture energy. Detailed Implementation

[0023] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0024] Example 1

[0025] This embodiment provides a high-toughness ceramic composite material and its preparation method. The raw materials include the following components: 96.5 wt% alumina powder (average particle size 0.5 μm, purity 99.99%), 2.0 wt% nanocellulose (average diameter 20 nm, length 5 μm, crystallinity 75%), 0.8 wt% refined coal tar pitch (softening point 95℃, QI≤0.8%, ash content≤0.2%, sulfur≤0.3%), and 0.7 wt% MgO.

[0026] Preparation method: Weigh the materials according to the ratio, add anhydrous ethanol (powder:ethanol=1:2), zirconia balls (Φ3, 5, 10 mm mixed, balls:material=10:1), ball mill at 200 r / min for 8 h; vacuum dry at 50℃ for 12 h, pass through a 100 mesh sieve; three-dimensional vibration mixing at 60 r / min for 6 h; hot pressing sintering: hold at 10℃ / min to 800℃ for 30 min, 10℃ / min to 1000℃, 5℃ / min to 1600℃ for 1.5 h, pressure 30 MPa (starting from 200℃), nitrogen protection.

[0027] Example 2

[0028] Raw materials and proportions: 96.44 wt% alumina powder, 2.2 wt% nanocellulose, 0.66 wt% refined coal tar pitch, and 0.7 wt% MgO. The mass ratio of nanocellulose to coal tar pitch is 1:0.3.

[0029] Preparation steps: basically the same as in Example 1.

[0030] Example 3

[0031] Raw materials and proportions: 96.6 wt% alumina powder, 1.8 wt% nanocellulose, 0.9 wt% refined coal tar pitch, and 0.7 wt% MgO. The mass ratio of nanocellulose to coal tar pitch is 1:0.5.

[0032] Preparation steps: basically the same as in Example 1.

[0033] Example 4

[0034] Raw materials and proportions: 96.42 wt% alumina powder, 2.4 wt% nanocellulose, 0.48 wt% refined coal tar pitch, and 0.7 wt% MgO. The mass ratio of nanocellulose to coal tar pitch is 1:0.2.

[0035] Preparation steps: basically the same as in Example 1.

[0036] Example 5

[0037] Raw materials and proportions: 96.42 wt% alumina powder, 1.6 wt% nanocellulose, 1.28 wt% refined coal tar pitch, and 0.7 wt% MgO. The mass ratio of nanocellulose to coal tar pitch is 1:0.8.

[0038] Preparation steps: basically the same as in Example 1.

[0039] Example 6

[0040] Raw materials and proportions: Same as in Example 1 (2.0 wt% nanocellulose, 0.8 wt% coal tar pitch, mass ratio 1:0.4).

[0041] Preparation steps: basically the same as in Example 1, except that the sintering temperature is set to 1550℃ (holding temperature for 1.5 h), and the other steps remain unchanged.

[0042] Example 7

[0043] Raw materials and proportions: 96.5 wt% alumina powder, 2.0 wt% nanocellulose, 0.8 wt% refined coal tar pitch, and 0.5 wt% MgO + 0.2 wt% Y2O3 as sintering aid (mass ratio approximately 2.5:1).

[0044] Preparation steps: basically the same as in Example 1.

[0045] Comparative Example 1

[0046] Raw materials and proportions: 97.3 wt% alumina powder, 2.0 wt% nanocellulose, and 0.7 wt% MgO.

[0047] Preparation steps: basically the same as in Example 1.

[0048] Comparative Example 2

[0049] Raw materials and proportions: 97.3 wt% alumina powder, 2.0 wt% refined coal tar pitch, and 0.7 wt% MgO.

[0050] Preparation steps: basically the same as in Example 1.

[0051] Comparative Example 3

[0052] Raw materials and proportions: 97.15 wt% alumina powder, 2.5 wt% nanocellulose, 0.25 wt% refined coal tar pitch, and 0.7 wt% MgO. The mass ratio of nanocellulose to coal tar pitch is 1:0.1.

[0053] Preparation steps: basically the same as in Example 1.

[0054] Comparative Example 4

[0055] Raw materials and proportions: 96.7 wt% alumina powder, 1.5 wt% nanocellulose, 1.8 wt% refined coal tar pitch, and 0.7 wt% MgO. The mass ratio of nanocellulose to coal tar pitch is 1:1.2.

[0056] Preparation steps: basically the same as in Example 1.

[0057] Comparative Example 5

[0058] Raw materials and proportions: 96.0 wt% alumina powder, 1.5 wt% graphene powder (average flake diameter 5 μm), 1.8 wt% silicon carbide whiskers, and 0.7 wt% MgO.

[0059] Preparation steps: basically the same as in Example 1.

[0060] Comparative Example 6

[0061] Raw materials and proportions: Same as in Example 1 (nanocellulose 2.0 wt%, coal tar pitch 0.8 wt%, MgO 0.7 wt%).

[0062] Preparation steps: basically the same as in Example 1, except that the 800℃ pre-carbonization step is not performed. Instead, the temperature is directly increased from room temperature to 1000℃ at 10℃ / min, and then increased to 1600℃ at 5℃ / min and held for 1.5 h.

[0063] Performance testing

[0064] Samples of the materials prepared in the examples and comparative examples were taken and their performance was tested.

[0065] (a) Bending strength test: conducted in accordance with GB / T 6569-2006 "Test method for bending strength of fine ceramics".

[0066] (b) Fracture toughness test: The test shall be conducted in accordance with GB / T 44547-2024 "Test method for fracture toughness of fine ceramics - single-sided V-beam (SEVNB) method".

[0067] (c) Density and porosity test: The density and apparent porosity of fine ceramics were determined by Archimedes' water displacement method in accordance with GB / T 25995-2010 "Test Method for Density and Apparent Porosity of Fine Ceramics".

[0068] (d) Vickers hardness test: conducted in accordance with GB / T 16534-2009 "Test method for Vickers hardness of fine ceramics".

[0069] The test results are shown in Table 1.

[0070] Table 1 Comparison of Performance Test Results

[0071]

[0072] The fracture toughness, flexural strength, and density of alumina ceramic composites prepared by different ratios of nanocellulose and coal tar pitch were tested to systematically investigate the effect of the ratio of the two materials on the toughening effect. The results showed that when the mass ratio of nanocellulose to coal tar pitch was in the range of 1:0.2-0.8, the fracture toughness of the composite material was significantly higher than that of the single carbon source system, and the flexural strength and density also reached optimal levels. The specific ratio of the two carbon sources exhibits a synergistic effect, fully leveraging their complementary advantages in carbonization behavior to form a continuous and dense graphene composite coating layer.

[0073] Comparative experiments on sintering process parameters show that sintering temperature has a significant impact on the properties of composite materials, with the optimal sintering temperature resulting in the best performance. More importantly, the 800℃ pre-carbonization step during hot pressing sintering is a crucial process for ensuring the complete pyrolysis of the carbon source precursor and the formation of high-quality graphene-like materials. Omitting this step and directly heating to the sintering temperature significantly reduces the fracture toughness and density of the resulting composite material, proving that the pre-carbonization step is indispensable.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-toughness ceramic composite material, characterized in that, It is made from the following raw materials in weight percentage: 93-98.5 wt% alumina powder, 0.3-3 wt% nanocellulose, 0.1-2 wt% coal tar pitch, and 0.5-2 wt% sintering aid.

2. The high-toughness ceramic composite material according to claim 1, characterized in that, The mass ratio of nanocellulose to coal tar pitch is 1:0.2-1:0.

8.

3. The high-toughness ceramic composite material according to claim 1, characterized in that, The nanocellulose has a diameter of 5-50 nm and a length of 1-20 μm.

4. The high-toughness ceramic composite material according to claim 1, characterized in that, The sintering aid is at least one of MgO and Y2O3.

5. A method for preparing a high-toughness ceramic composite material as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Alumina powder, nanocellulose, coal tar pitch and sintering aid are mixed in proportion, anhydrous ethanol and zirconium oxide balls are added and wet ball milling is carried out, dried, sieved and mixed twice to obtain mixed powder; (2) The mixed powder is placed in a graphite mold and hot-pressed under an inert atmosphere. The sintering temperature is 1550-1650℃, the pressure is 20-40 MPa, and the temperature is held for 1-2 h to obtain the high-toughness ceramic composite material. The heating process for hot pressing sintering is as follows: from room temperature, the temperature is increased to 800℃ at a rate of 5-15℃ / min and held for 20-60 min, then increased to 1000℃ at a rate of 5-15℃ / min, and then increased to the sintering temperature at a rate of 3-8℃ / min.

6. The method for preparing the high-toughness ceramic composite material according to claim 5, characterized in that, In step (1), the ball milling speed is 150-250 r / min and the ball milling time is 6-12 h; the drying temperature is 40-60℃ and the drying time is 10-24 h; the sieve mesh size is 80-200 mesh; the secondary mixing is three-dimensional vibration mixing, with a speed of 50-80 r / min and a time of 4-10 h.

7. The method for preparing the high-toughness ceramic composite material according to claim 5, characterized in that, The sintering pressure is 30 MPa, the sintering temperature is 1600±20℃, and the holding time is 1.5 h.

Images