阅读说明：本技术 一种高强度和高硬度的细晶α相氧化铝陶瓷的制备方法 (Preparation method of high-strength and high-hardness fine-grain alpha-phase alumina ceramic ) 是由 范宇驰 严广山 颜鹏 王连军 江莞 于 2020-12-25 设计创作，主要内容包括：本发明涉及一种高强度和高硬度的细晶α相氧化铝陶瓷的制备方法,将所述无定形氢氧化铝加热,烧结,获得。本发明所得材料具有高强度、高硬度。(The invention relates to a preparation method of high-strength and high-hardness fine-grain alpha-phase alumina ceramic, which is obtained by heating and sintering amorphous aluminum hydroxide. The material obtained by the invention has high strength and high hardness.)

1. A preparation method of ultra-fine grain alpha-phase alumina ceramics comprises the following steps:

the preparation method is characterized in that the amorphous aluminum hydroxide is heated in the air at the temperature of over 1100 ℃ to obtain flaky alpha-phase aluminum oxide, and then the flaky alpha-phase aluminum oxide is sintered to obtain alpha-phase aluminum oxide ceramic.

2. The method according to claim 1, wherein the amorphous aluminum hydroxide is prepared by the following method:

adding graphene oxide into an ammonium formate-formic acid buffer solution to obtain a dispersion liquid A; preparing a mixed solution B of an aluminum sulfate solution and an ammonium formate-formic acid buffer solution;

and heating the dispersion liquid A to 60-70 ℃, then dropwise adding the mixed liquid B into the dispersion liquid A to react for 2-3h, heating to 100 ℃, and reacting for 3h to obtain the amorphous aluminum hydroxide.

3. The preparation method according to claim 2, wherein the concentration of graphene oxide in the dispersion liquid a is 0.6-1.0 mg/mL; the concentration of aluminum sulfate in the mixed liquid B is 0.005-0.05 mol/L; the volume ratio of the dispersion liquid A to the mixed liquid B is 1: 1; the dripping time is 30-35 min.

4. The preparation method according to claim 1, wherein the amorphous aluminum hydroxide is a flake powder having a thickness of 20 to 50 nm.

5. The method as claimed in claim 1, wherein the heating temperature is 1100 ℃ and the heating time is 1300 ℃ for 1-8 h.

6. The production method according to claim 1, wherein the crystal grain size of the flaky alpha-phase alumina is 35nm or less.

7. The method of claim 1, wherein the sintering is one of liquid phase sintering, pressureless sintering, spark plasma sintering, and hot press sintering.

8. The preparation method according to claim 1, wherein the sintering process is spark plasma sintering, and the process parameters are as follows: the sintering temperature is 1200 ℃, the heating rate is 100/min, the heat preservation time is 10min, the mold is a graphite mold, and the sintering pressure is 50 Mpa.

9. An ultra-fine grained alpha phase alumina ceramic prepared by the method of claim 1.

10. Use of the ultra fine grained alpha phase alumina ceramic of claim 9.

Technical Field

The invention belongs to the field of alumina ceramic materials and preparation thereof, and particularly relates to a preparation method of a high-strength and high-hardness fine-grain alpha-phase alumina ceramic.

Background

The alpha alumina ceramic has high rigidity, excellent thermal stability and relatively low density, can be used in severe environments such as high temperature and high pressure, is a common ceramic material, can be used for preparing products such as insulating and pressure-resistant materials, refractory materials, surface coating materials, high-performance composite materials and the like, and has wide application prospect.

At present, the preparation method of the ultrafine grain alpha alumina powder mainly comprises a hydrothermal method, a ball milling method and the like. The hydrothermal method has the advantages of long preparation period of ultrafine crystal grains, difficulty in controlling the uniformity of the crystal grains, high requirement on equipment and difficulty in popularization and application, and the crystal grain size of the ultrafine crystal grain alpha alumina powder prepared by the method is smaller. The ball milling process is one of the common methods for preparing superfine alpha alumina powder. Micron-grade high-purity α Al2O3 powder was first ball-milled by a planetary ball mill using stainless steel balls. And corroding the ground powder at room temperature by using hydrochloric acid, removing impurities such as Fe and the like introduced in the ball milling process, and obtaining dispersed alpha AlO3 nano particles. And collected using hydrochloric acid as a coagulant, thereby providing high-purity dispersed ultrafine alpha alumina nanoparticles having a narrow particle size distribution. The method has the advantages of easy introduction of impurities, low yield, and reduced strength and hardness of the sintered alumina block.

Patent CN107253701 discloses a method for preparing ultra-thin two-dimensional nano material, which can not prepare amorphous aluminum hydroxide flake powder with a thickness of 20-30nm and obtain flake alpha-phase ultra-fine grain alumina, and the invention overcomes the defect that the prior art can not prepare thicker amorphous aluminum hydroxide flake powder and flake alpha-phase ultra-fine grain alumina.

Disclosure of Invention

The invention aims to solve the technical problem of providing a preparation method of high-strength and high-hardness fine-grain alpha-phase alumina ceramic, and overcoming the defects of overhigh sintering temperature, overlarge grain size and low hardness strength in the prior art.

The invention relates to a preparation method of ultra-fine grain alpha-phase alumina ceramic, which comprises the following steps:

the preparation method comprises the steps of preparing amorphous aluminum hydroxide by using graphene oxide as a template, heating the amorphous aluminum hydroxide in air at a temperature of over 1100 ℃ to obtain flaky alpha-phase aluminum oxide, and sintering to obtain alpha-phase aluminum oxide ceramic.

The preferred mode of the above preparation method is as follows:

the amorphous aluminum hydroxide has the following characteristics:

adding graphene oxide into an ammonium formate-formic acid buffer solution to obtain a dispersion liquid A; preparing a mixed solution B of an aluminum sulfate solution and an ammonium formate-formic acid buffer solution;

heating the dispersion liquid A to 60-70 ℃, then dropwise adding the mixed liquid B into the dispersion liquid A for 30-35min gradually, reacting for 2-3h, heating to 100 ℃, reacting for 3h, performing suction filtration, drying, and washing and suction filtration for many times to remove residual salt completely to obtain the amorphous aluminum hydroxide.

The graphene oxide is mainly prepared by modified Hummers, and the preparation method can be seen in Acs Nano,2010,4(8):4806-4814 y.

The concentration of the graphene oxide in the dispersion liquid A is 0.6-1.0 mg/mL; the concentration of aluminum sulfate in the mixed liquid B is 0.005-0.05 mol/L; the volume ratio of the dispersion liquid A to the mixed liquid B is 1: 1.

the ammonium formate-formic acid has a pH of between 4 and 5, preferably between 4.4 and 4.5.

The aluminum sulfate is aluminum sulfate octadecahydrate, and the purity is higher than 99.99%.

The amorphous aluminum hydroxide is flaky powder with the thickness of 20-50 nm.

The heating temperature is 1100-1300 ℃ for 1-8 h.

The crystal grain size of the flaky alpha-phase alumina is below 35 nanometers.

The sintering is one of liquid phase sintering, pressureless sintering, spark plasma sintering and hot pressing sintering.

Further, the sintering specific process is spark plasma sintering, and the process parameters are as follows: the sintering temperature is 1200 ℃, the heating rate is 100/min, the heat preservation time is 10min, the mold is a graphite mold, and the sintering pressure is 50 Mpa.

The invention relates to an ultra-fine grain alpha-phase alumina ceramic prepared by the method.

The invention also discloses application of the ultrafine grain alpha-phase alumina ceramic.

Advantageous effects

The method synthesizes the alpha alumina polycrystalline plate with ultra-fine grain size by taking the graphene oxide as a template for the first time, the flaky alpha alumina contains microcrystals below 35 nanometers, and microcrystals with smaller sizes are arranged among fine grains. The sintered alumina ceramic has finer grains, higher strength and higher hardness. The bending strength and the hardness of the alumina ceramic respectively reach 456.24MPa and 20.4 GPa.

The preparation method of the ultrafine grain flaky alpha-phase alumina ceramic with high strength and hardness is different from the preparation method of patent CN107253701, the method of the invention prepares ultrafine grain flaky alpha-alumina powder by two-step heating reaction to obtain thicker alumina powder, dropwise adds the mixed solution of aluminum sulfate solution and ammonium formate-formic acid buffer solution into the dispersion of graphene oxide in the ammonium formate-formic acid buffer solution which is heated to 60-70 ℃, and heats to 100 ℃ after reacting for a certain time to completely react. The invention can control the thickness of the ultra-fine crystal particle flaky alpha alumina powder by changing the content of the precursor and the temperature during the reaction, is thicker than the ultra-thin two-dimensional nano material in the patent CN107253701, and is beneficial to liquid phase sintering, and the amorphous phase is obtained in the patent. Compared with a hydrothermal method and a ball milling method, the grain size is finer, and impurities are not introduced. The method synthesizes the alpha alumina multi-chip powder with ultra-fine grain size by taking the graphene oxide as a template for the first time. After sintering such as spark plasma sintering and hot pressing, the sintering temperature is low, and the sintered alumina ceramic has small crystal grains (as can be seen from the comparison of the average crystal grain sizes in fig. 7 and 8), high hardness and high strength.

Drawings

FIG. 1 is a transmission electron microscope image of ultra-fine grained flaky alpha alumina prepared in example 1 of the present invention;

FIG. 2 is a transmission electron micrograph of the ultra-fine grained lamellar alpha alumina prepared in example 1 of the present invention and an electron diffraction pattern (inset) thereof;

FIG. 3 is a scanning electron microscope cross-sectional view of a commercial alumina powder sintered into an alumina ceramic in comparative example 3;

FIG. 4 is a scanning electron microscope of the cross section of the flaky alpha alumina powder alumina ceramic with ultra-fine grains prepared in example 1 of the present invention;

FIG. 5 is a scanning electron microscope image of the ultra-fine grained flaky alpha alumina powder prepared in example 1 of the present invention;

FIG. 6 is a scanning electron microscope image of the flaky alpha-alumina powder prepared in comparative example 1.

FIG. 7 is a graph showing the distribution of grains of the commercial alumina powder sintered into alumina ceramic in comparative example 3.

FIG. 8 is a distribution diagram of grains of an alumina ceramic sintered from an ultra-fine grained flaky alpha alumina powder in example 1 of the present invention.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Table 1 shows the raw material or reagent specifications and sources used in the examples of the present invention. The graphene oxide used in the examples of the present invention was prepared by a modified Hummers method laboratory.

The specific steps are that 1g of natural graphite is put into a beaker by adding 25ml of sulfuric acid at room temperature, and then 3.5g of potassium permanganate is slowly added after stirring (ice bath) at 0 ℃. The mixture was then warmed to 40 ℃ and stirred vigorously for 2 hours. After the reaction, 200ml of water were added to dilute the mixture, after which 5ml of 30 wt% hydrogen peroxide were added, which reacted with excess potassium permanganate (10 min course). The mixture precipitate was then washed by vacuum filtration using 1M hydrochloric acid solution. After adding 200ml of water, the mixture was put into a dialysis tube for one week to remove residual impurities. To the mixture was added 1L of water, and then the mixture was centrifuged at 4000rpm for 30 minutes to separate graphene oxide for subsequent experiments.

The microscopic accuracy test (Vickers Hardness tester) is a product of model FV-700 manufactured by Future-Tech company of Japan. The hardness value was calculated by making an indentation in the polished surface of the sample. In the experiment, each sample is kept under the load of 29.4N for 10s, 10 points are measured on each sample, and the calculation formula is as follows:

HV＝PF＝Pd2/2sin68°＝1.8544Pd2

in the formula:

p is a load; d is the diagonal length; f is the indentation area;

the three-point bending resistance test method adopts the national bending resistance strength standard (GB/T6569-86), and the test strip has the size of 35mm multiplied by 3mm multiplied by 4 mm. The rate of head descent was 0.5 mm/min. The bending strength R divided by three points is calculated by the following formula. R ═ (3F × L)/(2b × h)

In the formula: f is a breaking load; l is the span; b is the width; and h is the thickness.

Example 1

The preparation method of the ultra-fine grain flaky alpha alumina powder comprises the following steps:

(1) an ammonium formate-formic acid buffer solution was prepared by using 13.5g of ammonium formate and 820. mu.l of formic acid in 600ml of ultrapure water to maintain a pH of about 4.4.

(2) A dispersion liquid (a) of graphene oxide in an ammonium formate-formic acid buffer solution and a mixed liquid (B) of an aluminum sulfate solution and the ammonium formate-formic acid buffer solution were prepared, and then placed in an ultrasonic bath for 25 minutes, respectively, to perform ultrasonic dispersion.

(3) A was stirred vigorously and the temperature was raised. When the temperature reaches 60 ℃, B is gradually added to A dropwise, and after 2 hours of reaction, the temperature is increased to 100 ℃ again and is kept for 3 hours to complete the reaction.

(4) The prepared graphene oxide/alumina composite was filtered to remove residual salts by using vacuum filtration, and dried in a freeze dryer for 24 hours. The amorphous dry powder was heated in air at 1100 ℃ for 2 hours to convert from the amorphous phase to alpha alumina and remove the graphene oxide template.

(5) The prepared superfine crystal grain flaky alpha alumina powder is sintered and formed by a discharge plasma sintering furnace, and the technological parameters are as follows: the sintering temperature is 1200 ℃, the heating rate is 100/min, the heat preservation time is 10min, the mold is a graphite mold, and the sintering pressure is 50 Mpa. The bending strength is 472.24MPa by a three-point bending test method; and the hardness was measured by a Vickers hardness tester to be 19.4 GPa.

As shown in fig. 1 and fig. 2, it is shown that: in the transmission electron microscope image of the alumina polycrystalline plate prepared in the embodiment, the flaky alumina crystal grain of the ultrafine crystal grain is less than 35nm, and the crystal grain size is small.

As shown in FIG. 4, the scanning electron microscope cross-sectional images of the ultra-fine grained flaky alpha alumina powder and the alumina ceramic shown in FIG. 8 show the grain distribution of the alumina ceramic sintered from the ultra-fine grained flaky alpha alumina powder in example 1 of the present invention and the comparison between FIG. 3 and FIG. 7 in comparative example 3: in the embodiment, after the superfine crystal grain flaky alpha-alumina powder is sintered, the crystal grain size is smaller.

Example 2

Steps (1) and (2) were the same as in example 1.

(3) A was placed in a flask with vigorous stirring and the temperature was raised. When the temperature reached 70 ℃, B was gradually added dropwise for 35 minutes, and after 2 hours of reaction, the temperature was increased to 100 ℃ again and maintained for 3 hours to complete the reaction.

(4) The prepared graphene oxide/alumina composite was filtered to remove residual salts by using vacuum filtration, and dried in a freeze dryer for 24 hours. The amorphous dry powder was heated in air at 1200 ℃ for 2 hours to convert from the amorphous phase to alpha alumina and remove the graphene oxide template. (5) The prepared superfine crystal grain flaky alpha alumina powder is sintered and formed by a hot-pressing sintering furnace, and the technological parameters are as follows: the sintering temperature is 1300 ℃, the heating rate is 100/min, the heat preservation time is 10min, the mold is a graphite mold, the sintering pressure is 60MPa, and the bending strength is 456.25MPa measured by three-point bending resistance; and the hardness was measured by a Vickers hardness tester to be 19.1 GPa.

Example 3

Steps (1) and (2) were the same as in example 1.

(3) A was placed in a flask with vigorous stirring and the temperature was raised. When the temperature reached 65 ℃, B was gradually added dropwise for 40 minutes, and reacted for 2 hours. After 2 hours, the temperature was raised to 110 ℃ again and maintained for 2.5 hours to complete the reaction.

(4) The prepared graphene oxide/alumina composite was filtered to remove residual salts by using vacuum filtration, and dried in a lyophilizer for 26 hours. The amorphous dry powder was heated in air at 1150 ℃ for 1.5 hours to convert from the amorphous phase to alpha alumina and remove the graphene oxide template.

(5) The powder is dry-pressed and processed under 200Mpa isostatic pressure. And placing the pre-pressed alumina ceramic powder in a carbon tube furnace under the protection of argon gas, embedding and sintering the powder, wherein the sintering temperature is 1300 ℃, and preserving heat for 1.5 hours to prepare the alumina ceramic material block. The bending strength of this sample was about 423.75MPa by the three-point bending method using an AGS-X type universal mechanical tester from Shimadzu, Japan, and the hardness was 18.9GPa by a Vickers hardness tester.

Comparative example 1

Guolin et al, in CN107253701, a method for preparing ultrathin two-dimensional nanomaterial, prepares ultrathin two-dimensional nanomaterial alumina. Different from this patent, what this patent adopted is two-step heating method, adopts aluminium sulfate solution and ammonium formate-formic acid buffer's mixed solution dropwise add to the dispersion of oxidation graphite alkene in ammonium formate-formic acid buffer gradually, obtains the slice powder of the thicker amorphous oxyhydrogen aluminium oxide of 20nm-50nm in this patent. The method of the patent is difficult to obtain thicker amorphous aluminum hydroxide flaky powder, the patent is different from the method of calcining at 1100 ℃ to obtain flaky alpha-phase alumina, and finally vacuum sintering is carried out, while the patent adopts the method of calcining at 650 ℃ for 2h to obtain white ultrathin amorphous two-dimensional flaky alumina powder.

As fig. 6 shows: the flake aluminum oxide prepared in comparative example 1 has a thicker thickness than the flake alpha aluminum oxide powder of inventive example 1, in which ultra fine grains are formed, as compared to fig. 5.

Comparative example 2

The white amorphous two-dimensional flaky alumina powder prepared in the Guolin patent CN107253701 in the comparative example 1 and the example 1 is sintered and molded by a spark plasma sintering furnace, and the technological parameters are as follows: the sintering temperature is 1200 ℃, the heating rate is 100/min, the heat preservation time is 10min, the mold is a graphite mold, and the sintering pressure is 50 Mpa. The bending strength of the sample is tested on a universal testing machine by adopting a three-point bending method, the bending strength is measured by adopting the three-point bending test method to be 393.5Mpa, and the hardness is measured by a Vickers hardness tester to be 17.96 GPa. The alpha alumina powder body of the patent adopts the same sintering process to prepare the alumina with the bending strength of 472.24 MPa; and the hardness was measured by a Vickers hardness tester to be 19.4 GPa.

The bending strength of the flaky alpha alumina powder alumina ceramic with ultrafine grains is 20 percent higher than that of the alumina ceramic prepared in the patent, the Vickers hardness is 8 percent higher than that of the alumina ceramic, and the grain size after sintering is slightly smaller than that of the ceramic in the patent.

Comparative example 3

Alumina powder (TM-DAR) of Japan Daling industry Co., Ltd, which is purchased from the market, is sintered and formed by a hot pressing sintering furnace, and the technological parameters are as follows: the sintering temperature is 1300 ℃, the heating rate is 100/min, the heat preservation time is 10min, the mold is a graphite mold, the sintering pressure is 60MPa, and the bending strength is 366.12MPa measured by a three-point bending test method; and the hardness was measured by Vickers hardness to be 17.36 GPa. The alpha alumina powder body of the patent adopts the same sintering process to prepare the alumina with the bending strength of 456.25 MPa; and the hardness was measured by a Vickers hardness tester to be 19.1 GPa. The bending strength of the alumina ceramic is improved by 25 percent compared with the commercial alumina sintered ceramic, the hardness is improved by 10.4 percent, and the grain size after sintering is smaller than that of the commercial powder sintered ceramic.