阅读说明：本技术 一种氧化铝包覆立方氮化硼的复合粉体及其制备方法 (Alumina-coated cubic boron nitride composite powder and preparation method thereof ) 是由 方斌 李德芃 袁中行 于 2020-06-23 设计创作，主要内容包括：本发明涉及一种氧化铝包覆立方氮化硼的复合粉体及其制备方法,包括如下步骤：1)将立方氮化硼与乙醇按一定比例混合,并在一定温度和搅拌条件下加入十二烷基硫酸钠和聚乙二醇,混合均匀后得到溶液,经冷却、离心分离、洗涤得到改性纳米c-BN；2)将改性纳米c-BN搅拌条件下与无水乙醇按一定的比例混合,分散均匀,得到A溶液；并将硝酸铝加入到所述A溶液中,混合均匀,得到B溶液；3)将氨水与乙醇的混合液向步骤2)所述B溶液中缓慢加入,至溶液的pH值为7~12,持续搅拌至反应结束,将所得产物静置陈化,将固体产物离心分离后,加热脱水,制得氧化铝包覆立方氮化硼的复合粉体。本发明的制备方法具有工艺简单,成本低廉的特点,所制备的复合粉体不仅分散性好,而且包覆效果好、包覆率高,粒径尺度均匀,改善了立方氮化硼颗粒的表面特性。(The invention relates to an alumina coated cubic boron nitride composite powder and a preparation method thereof, comprising the following steps: 1) mixing cubic boron nitride and ethanol according to a certain proportion, adding sodium dodecyl sulfate and polyethylene glycol under a certain temperature and stirring condition, uniformly mixing to obtain a solution, and cooling, centrifugally separating and washing to obtain modified nano c-BN; 2) mixing the modified nano c-BN with absolute ethyl alcohol according to a certain proportion under the stirring condition, and uniformly dispersing to obtain a solution A; adding aluminum nitrate into the solution A, and uniformly mixing to obtain a solution B; 3) and (3) slowly adding a mixed solution of ammonia water and ethanol into the solution B in the step 2) until the pH value of the solution is 7-12, continuously stirring until the reaction is finished, standing and aging the obtained product, centrifugally separating the solid product, and heating and dehydrating to obtain the alumina-coated cubic boron nitride composite powder. The preparation method has the characteristics of simple process and low cost, and the prepared composite powder has the advantages of good dispersibility, good coating effect, high coating rate and uniform particle size, and improves the surface characteristics of the cubic boron nitride particles.)

1. The composite powder of alumina coated cubic boron nitride and the preparation method thereof are characterized by comprising the following steps:

1) mixing cubic boron nitride and ethanol according to a certain proportion, adding sodium dodecyl sulfate and polyethylene glycol under the conditions of a certain temperature and stirring, uniformly mixing to obtain a solution, and cooling, centrifugally separating and washing with a certain proportion of water-alcohol solution to obtain modified nano c-BN;

2) mixing the modified nano c-BN with a certain proportion of absolute ethyl alcohol under the stirring condition, and uniformly dispersing to obtain a solution A; adding aluminum nitrate into the solution A, and uniformly mixing to obtain a solution B;

3) Slowly adding a mixed solution of ammonia water and ethanol into the solution B obtained in the step 2) until the pH value of the solution is 7-12, continuously stirring until the reaction is finished, standing and aging the obtained product, centrifugally separating the solid product, and heating and dehydrating to obtain the alumina-coated cubic boron nitride composite powder.

2. The method of claim 1, wherein: in the step 1), the purity of the sodium dodecyl sulfate is 99 percent;

preferably, in the step 1), the average molecular weight of the polyethylene glycol is 2000-10000; preferably, the polyethylene glycol has an average molecular weight of 4000;

preferably, in the step 1), the particle size of the nano c-BN powder is 100-200 nm, the mass concentration of the nano c-BN is 0.001-0.009 g/ml, and the mass concentration of the polyethylene glycol is 0.001-0.004 g/ml; the mass ratio of the nano cubic boron nitride to the sodium dodecyl sulfate to the polyethylene glycol is 2-4: 1-2: 1;

preferably, in the step 1), the speed of centrifugal separation is 5000-8000 r/min, and the time of centrifugal separation is 10-20 min;

preferably, in the step 1), the washing is performed 3 to 5 times, wherein the hydroalcoholic solution is a mixed solution of distilled water and absolute ethyl alcohol in a volume ratio of 1 to 1.5:3 to 5.

3. The method of claim 2, wherein: in the step 2), 0.2g of nano c-BN powder is dispersed in 100ml of ethanol solution, and ultrasonic stirring is continuously carried out for 20-50 min, preferably for 25-35 min, and most preferably for 30 min;

Preferably, in the step 2), 6g of aluminum nitrate is dissolved in 100ml of the solution, and the ultrasonic stirring is continued for 5-10 min.

4. The method of claim 1, wherein: in the step 3), the volume ratio of ethanol to ammonia water is 4:1, the ethanol is absolute ethanol, and the ammonia water is analytically pure;

preferably, in the step 3), the solution B is continuously ultrasonically stirred for 10-30 min;

preferably, in the step 3), the speed of centrifugal separation is 5000-8000 r/min, and the time of centrifugal separation is 10-20 min;

preferably, in the step 3), the adding speed of the mixed solution of the ammonia water and the ethanol is 1-10 ml/min, and preferably 1-3 ml/min.

5. The method of claim 1, wherein: in the step 3), the reaction temperature is 25-45 ℃, ultrasonic stirring is carried out in the reaction process, and the reaction time is 30-50 min;

preferably, the reaction temperature is 30-40 ℃, the reaction time is 35-45 min, and more preferably, the reaction temperature is 40 ℃.

6. The method of claim 1, wherein: in the step 3), the standing and aging time is 48-72 hours, preferably 55-65 hours.

7. The method of claim 1, wherein: in the step 3), before heating and dehydrating, alternately cleaning the separated material by absolute ethyl alcohol and water for 3-6 times, and drying in vacuum at 30-80 ℃ for 24-48 h to prepare the cubic boron nitride composite powder coated by the aluminum hydroxide;

The number of times of alternate cleaning of absolute ethyl alcohol and water is 3-5;

preferably, the vacuum drying temperature is 50 ℃, and the drying time is 24 h;

preferably, in the step 3), the temperature for heating and dehydrating is 600-1000 ℃, and the time is 2-6 h; preferably, the temperature for heating dehydration is 800 ℃ and the time is 2 h.

8. The alumina-coated cubic boron nitride composite powder prepared by the preparation method according to any one of claims 1 to 7 has a particle size of 200 to 500 nm.

9. An alumina-coated cubic boron nitride composite powder prepared by the preparation method according to any one of claims 1 to 8; the alumina-coated cubic boron nitride composite powder is mainly used for preparing metal ceramic cutter materials.

Technical Field

The invention relates to a surface coating modification of a nano material and a preparation method thereof, in particular to an alumina coated cubic boron nitride composite powder and a preparation method thereof.

Background

Cubic boron nitride is a superhard material developed after artificial diamond. Because the hardness of the diamond is second to that of diamond, the thermal stability and the chemical inertness of the diamond are far better than those of the diamond, the diamond is not easy to generate chemical reaction with iron-based metal at high temperature, and the diamond is not only suitable for processing most of difficult-to-process materials, but also high in processing efficiency and good in quality.

In atmospheric environment, diamond is easy to react with iron element to graphitize, so that the diamond cutter has serious chemical wear and mechanical wear in the process of cutting iron-based metal, and the precise and ultra-precise cutting processing of corresponding materials is difficult to realize. With the continuous breakthrough of the synthesis technology of superhard cutter materials, the c-BN novel superhard material with excellent performance is undoubtedly becoming an ideal cutter material for precise and ultra-precise cutting processing of iron-based metals.

Cubic boron nitride, on the other hand, is also a good reinforcing phase for ceramic materials. For example, Chinese patent document CN106316398A discloses a tungsten carbide titanium-based ceramic cutting tool material added with cubic boron nitride and a preparation method thereof, in the invention, the cubic boron nitride is used as a reinforcing phase, and the effect of particle dispersion reinforcement is achieved; however, at high temperature, cubic boron nitride is easy to change phase to hexagonal boron nitride, so that the problem of reduced mechanical property is caused; and the compactness is not high. The phase transition temperature of cubic boron nitride is 1500-1550 deg.c, while the sintering temperature of alumina-based ceramic and silicon nitride-based ceramic is over 1700 deg.c, thus limiting the application of cubic boron nitride. Meanwhile, because the surface energy of the nano particles is high and the nano particles are easy to agglomerate, a good dispersion effect in a material matrix is difficult to achieve, the performance of the prepared cutter material is unstable, and the application of cubic boron nitride as a reinforcing phase in ceramics is limited.

In the field of particle modification, there have been numerous studies by related researchers. The Chinese invention patent CN104045351B researches that the surface of micron calcium fluoride is coated with aluminum oxide, the process is suitable for calcium fluoride micron particles with the particle size of 4-8 μm, the thickness of the coating layer of the calcium fluoride realized by the patent is also in the micron scale, and the reaction liquid phase system and the like of the coating layer can not be applied to the dispersion and surface coating modification of nano particles. Chinese patent document CN104962110A proposes a preparation process for coating a metal on the surface of a micron calcium fluoride particle, which adopts the principle of electroless plating, but is limited to the combination of metal and inorganic substance. Chinese patent document CN107827468A proposes a composite nanoparticle material in which the surface of nano calcium fluoride is coated with alumina and a preparation method thereof. However, in the prior art, surface modification of the nano cubic boron nitride is not attempted to solve the problem that the application of the nano cubic boron nitride in the ceramic cutter is limited.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides an alumina coated cubic boron nitride composite powder and a preparation method thereof.

The technical scheme of the invention is as follows:

a preparation method of alumina coated cubic boron nitride composite powder comprises the following steps:

1) Mixing cubic boron nitride and ethanol according to a certain proportion, adding sodium dodecyl sulfate and polyethylene glycol under the conditions of a certain temperature and stirring, uniformly mixing to obtain a solution, and cooling, centrifugally separating and washing with a certain proportion of water-alcohol solution to obtain modified nano c-BN;

2) mixing the modified nano c-BN with absolute ethyl alcohol according to a certain proportion under the condition of stirring, and uniformly dispersing to obtain a solution A; adding aluminum nitrate into the solution A, and uniformly mixing to obtain a solution B;

3) slowly adding a mixed solution of ammonia water and ethanol into the solution B prepared in the step 2) until the pH value of the solution is 7-12, continuously stirring until the reaction is finished, standing and aging the obtained product, centrifugally separating the solid product, and heating and dehydrating to obtain the alumina-coated cubic boron nitride composite powder.

Sodium dodecyl sulfate is used as modifier, polyethylene glycol is used as dispersant, and ethanol is used as solvent. In the step 3), the ammonia water and the ethanol are mixed, so that the ammonia water is diluted to a certain degree, severe and rapid local reaction caused by directly adding the ammonia water is avoided, and the generation of the aluminum hydroxide is more uniform.

Preferably, in step 1), the purity of the sodium lauryl sulfate is 99%.

Preferably, in the step 1), the mass concentration of the nano c-BN is 0.001-0.009 g/ml, and the mass concentration of the polyethylene glycol is 0.001-0.004 g/ml; the mass ratio of the nano cubic boron nitride to the sodium dodecyl sulfate to the polyethylene glycol is 2-4: 1-2: 1.

Preferably, in the step 1), the grain size of the cubic boron nitride is 100-200 nm.

Preferably, in the step 2), the concentration of the nano cubic boron nitride powder dispersed in the solution is 0.001-0.009 g/ml, most preferably 0.002 g/ml, and the ultrasonic stirring is continued for 20-50 min, preferably 25-35 min, most preferably 30 min.

Preferably, in the step 2), the concentration of the aluminum nitrate dissolved in the solution is 0.01-0.09 g/ml, most preferably 0.06g/ml, and the ultrasonic stirring is continued for 5-10 min.

Preferably, in the step 3), the volume ratio of ethanol to ammonia water is 4:1, the ethanol is absolute ethanol, and the ammonia water is analytically pure.

Preferably, in the step 3), the solution B after the mixed solution of ammonia water and ethanol is added is continuously ultrasonically stirred for 10-30 min.

Preferably, in the step 3), the adding speed of the mixed solution of the ammonia water and the ethanol is 1-10 ml/min, and preferably 1-3 ml/min.

Preferably, in the step 3), the reaction temperature is 25-45 ℃, ultrasonic stirring is performed in the reaction process, and the reaction time is 30-50 min. Preferably, the reaction temperature is 30-40 ℃, the reaction time is 35-45 min, and more preferably, the reaction temperature is 40 ℃.

Preferably, in the step 3), the standing and aging time is 48-72 hours, and preferably 55-65 hours.

Preferably, in the step 3), the speed of centrifugal separation is 5000-8000 r/min, and the time of centrifugal separation is 10-20 min.

Preferably, in the step 3), before heating and dehydrating, the separated material is alternately cleaned by absolute ethyl alcohol and water for 3-6 times, and is dried in vacuum at 30-80 ℃ for 24-48 h to prepare the cubic boron nitride composite powder coated by the aluminum hydroxide;

the number of times of alternate cleaning of absolute ethyl alcohol and water is 3-5;

preferably, the vacuum drying temperature is 50 ℃ and the drying time is 24 h.

Preferably, in the step 3), the temperature for heating and dehydrating is 600-1000 ℃, and the time is 2-6 h; preferably, the temperature for heating dehydration is 800 ℃ and the time is 2 h.

The composite nano-particles of the alumina-coated cubic boron nitride prepared by the preparation method have the particle size of 200-500 nm.

The invention has the beneficial effects that:

the preparation method has the characteristics of simple process and low cost, and the prepared nano composite powder has good dispersibility, good coating effect, high coating rate and uniform particle size, and improves the surface characteristics of the cubic boron nitride particles.

The particle size of the nano composite powder prepared by the preparation method is 200-500 nm, the reaction system and the reaction process are controlled, the chemical bonding of aluminum ions and cubic boron nitride is realized in the preparation process of the composite powder, the heterogeneous nucleation growth of aluminum hydroxide is realized, and then the nano powder material with a core-shell structure and good dispersion is prepared by dehydration.

The finally prepared coating powder can be used for preparing a ceramic cutter, changes the adding state of cubic boron nitride in the cutter, and can avoid the reduction of the performance of the ceramic cutter material caused by the phase change of the directly added cubic boron nitride particles after the cutter is sintered. The coated nano composite powder has better dispersion effect and better compatibility with a matrix, and the prepared ceramic cutting tool material has more excellent performance, thereby further expanding the application of the nano material.

Drawings

Fig. 1 shows cubic boron nitride without coating treatment.

Fig. 2 is a projection electron microscope of cubic boron nitride after coating treatment but not after calcination.

FIG. 3 is a scanning electron microscope of cubic boron nitride which is not calcined after coating.

Fig. 4 is the energy spectrum analysis of fig. 3.

Detailed Description

The present invention will be further described with reference to specific examples, but the present invention is not limited to the following examples. The method is a conventional method unless otherwise specified.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the present application. As used herein, the singular is intended to include the plural unless the context clearly dictates otherwise. Furthermore, it will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.