CN103992114A - Preparation method of boron carbide ceramic powder dispersion - Google Patents

Abstract

The invention discloses a method for preparing a boron carbide ceramic powder dispersion, which comprises the following steps: adding 0.01-10% polyethyleneimine and 0.01-10% polyethylene glycol into water, mixing uniformly, according to mass percentage, Then add 10-50% boron carbide ceramic powder and mix evenly; then add it to a ball mill and mill it for more than 3 hours to obtain a suspension; let the suspension stand for 15-60 minutes to remove the coagulated boron carbide ceramic powder particles to obtain boron carbide ceramic powder dispersion body. Through the present invention, a simple, cheap and environmentally friendly boron carbide ceramic powder dispersion can be obtained, and slurry for preparing ceramic systems by slip casting, gel casting, injection molding and other wet forming methods can be provided.

Description

A kind of preparation method of boron carbide ceramic powder dispersion

technical field

The invention relates to the technical field of powder dispersion, in particular to a preparation method of boron carbide ceramic powder dispersion.

Background technique

Boron carbide ceramics are an important engineering material. Its hardness is second only to diamond and cubic boron nitride, and its constant high-temperature hardness (>30GPa) at high temperature is far superior to diamond and cubic boron nitride. Its theoretical density is 2.52g/cm ³ , its melting point is 2450°C, and its microhardness is 4950kgf/mm ² . Boron carbide ceramics have the characteristics of light weight, semiconductor properties, seed absorption, high grinding efficiency, and no reaction with strong acids and alkalis. Due to the above-mentioned excellent properties, boron carbide ceramics are widely used in metallurgy, chemical industry, machinery, aerospace and other fields. For example: boron carbide can be used as an abrasive to process gemstones, ceramics, bearings and knives; it can be used as a refractory material in the metallurgical field; densified boron carbide can also be made into nozzles, mechanical seals or bulletproof materials; Larger thermal neutron capture interfaces can absorb large quantities of seeds and are used for nuclear reactor shielding.

Due to the small size and high surface energy of ultrafine powder, it is easy to spontaneously agglomerate to form secondary powder particles when dispersed in liquid to reduce the total surface energy of the system. Under the condition of powder suspension impregnation, if there are agglomerates in the powder, it is easy to cause component segregation in the local area of the material, which has many adverse effects on the structure and performance of the material. Therefore, the powder agglomeration phenomenon and how to take effective methods to reduce or even eliminate the agglomeration so as to achieve the purpose of powder dispersion in the suspension should be paid attention to in the preparation and use of powder.

The dispersion state of powder in liquid medium is mainly affected by the interaction between powder particles. At present, there are usually the following three stabilization mechanisms to uniformly and stably disperse the powder particles in the liquid medium:

(1) Electrostatic stabilization mechanism (electric double layer stabilization mechanism): in the liquid medium, by adjusting the pH value or adding an appropriate electrolyte, the surface of the powder particles attracts ions with opposite electrical properties to form an electric double layer. Coulomb repulsion greatly reduces the attraction of powder particle agglomeration, thus making the powder particles dispersed. The surface potential of the powder particles and the concentration of the solution are the two most important factors for the electrostatic stability of the powder particles in the liquid medium.

(2) Stabilization mechanism of steric hindrance: adding an electrically neutral polymer to the liquid medium, the polymer is adsorbed on the surface of the powder particles, forming a coated powder particle cluster. The mutual steric hindrance between polymers produces repulsive force, which stabilizes the suspension. The dispersion of powder particles in organic solvents with low dielectric constant (that is, weak polarity or nonpolarity) is often considered to be based on the mechanism of steric hindrance. If polyethylene glycol is added in the liquid phase reaction, the polyethylene glycol molecules will produce steric hindrance, thereby hindering the further agglomeration and growth of powder particles.

(3) Electric steric hindrance mechanism: select a polymer electrolyte that not only provides steric hindrance but also has electrostatic repulsion as a dispersant, adjust the pH of the suspension, and make the polymer electrolyte adsorbed on the surface of the particles reach the saturated adsorption capacity and The maximum degree of ionization, thereby increasing the repulsion of the electric double layer, makes the powder particles uniformly and stably dispersed. Commonly used dispersants are polymer electrolytes and anionic polymer electrolytes, represented by ammonium or sodium salts of polyacrylic acid and polymethacrylic acid.

The dispersion methods of powder particles in liquid can be roughly divided into three categories:

(1) Select the appropriate medium: By selecting an appropriate dispersion medium, a well-dispersed suspension can be obtained, which is determined by the properties of the powder itself. The liquid medium used for dispersion is divided into two types: polar medium and non-polar medium. The principle of choosing the dispersion medium is: the polar powder particles are easy to disperse in the polar medium, and the non-polar powder particles are easy to disperse in the non-polar medium.

(2) Adding a dispersant: By adding a dispersant, the physical and chemical conditions required for good dispersion of polar powder particles in polar media can be provided. The addition of dispersant can increase the mutual repulsion between powder particles. There are two main types of dispersants commonly used: inorganic electrolytes, such as sodium polyphosphate, sodium silicate, sodium hydroxide, etc., organic polymers, such as polyacrylamide series, tannin and other surfactants. The dispersing effect of surfactants is mainly manifested in the adjustment of the surface wettability of the particles, and is widely used in industry because of its good dispersing effect.

(3) Mechanical force dispersion: Dispersion under the action of mechanical force is usually considered as a simple physical dispersion, which is mainly a form of fully dispersing nanoparticles in the medium by means of mechanical energy such as external shear force or impact force. By applying mechanical force to the dispersion system, the physical and chemical properties of the substances in the system will change, accompanied by a series of chemical reactions to achieve the purpose of dispersion. The destruction of powder particle agglomeration is mainly by mechanical disintegration and power ultrasonic disintegration. The mechanical disintegration of agglomerates is mainly realized by mechanical forces such as impact, shearing and stretching. It is a simple and easy method. The specific forms include: grinding dispersion, colloid mill dispersion, ball mill dispersion, sand mill dispersion, high-speed stirring, etc. Ultrasonic dispersion is to place the suspension to be treated directly in the ultrasonic field, and control the appropriate ultrasonic frequency and action time to fully disperse the particles. On the one hand, ultrasonic waves propagate in the form of standing waves in the particle system, causing the particles to be periodically stretched and compressed; on the other hand, ultrasonic waves can produce "cavitation" in the liquid to disperse the particles.

In EP1153652, it is described that a mixed powder (hard metal powder mixture) of tungsten carbide and cobalt is dispersed in a polyethylene submerged with cationic polyelectrolyte under the condition of partially adding other hard materials such as TiC, TaC and TiN. Aqueous or ethanolic media methods of amines. Here, by adding a mass fraction of 0.1 to 10%, preferably a mass fraction of 0.1-1%, polyethyleneimine (PEI) with a molar mass of 5000-50000, preferably 10000 to 30000 g/mol, the hard metal powder mixture is achieved Good dispersibility in water.

In WO93/21127, surface-modified nano-ceramic powders such as Si ₃ N ₄ , SiC, Al ₂ O _{3 ,} etc. were prepared by using low-molecular organic compounds (molar mass up to 500g.mol) The powder is dispersed in water or organic solvents such as alcohols.

DE19751355 describes a method for dispersing fine-grained inorganic powders into preferably water or an aqueous medium, wherein the substance used for dispersion is a substance of biological origin, such as a sugar derivative, a starch derivative, or a chitin derivative . Here in particular the production of stable dispersions in aqueous media over a long period of time is meant.

The disadvantage of the method realized according to the prior art is that it disperses the powder in an organic solvent medium or an organic solvent-water medium instead of pure water, which is costly and environmentally unfriendly. The dispersed powder includes cemented carbide powder, part of ceramic powder such as TiC, TaC, TiN, and part of nano powder such as nano Si ₃ N ₄ , SiC, Al ₂ O ₃ and so on. However, there is no corresponding research invention for the preparation of specific boron carbide ceramic powder dispersions.

Contents of the invention

The purpose of the present invention is to provide a method for preparing boron carbide ceramic powder dispersion, which solves the problem that there is no corresponding preparation method for boron carbide ceramic powder dispersion in the prior art.

In order to solve the above problems, the present invention adopts the following technical solutions:

A preparation method of boron carbide ceramic powder dispersion, comprising the following steps:

In terms of mass percentage, add 0.01-10% polyethyleneimine and 0.01-10% polyethylene glycol into water, mix well, then add 10-50% boron carbide ceramic powder, mix well; then add to ball mill for ball milling The suspension is obtained after more than 3 hours; the suspension is left to stand for 15-60 minutes to remove the coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The mass percentage of the boron carbide ceramic powder is 30-40%, the mass percentage of the polyethyleneimine is 1-3%, and the polyethylene glycol is 3-5%.

The mass percentage of polyethyleneimine is 2.5%.

The diameter of the boron carbide ceramic powder is 1-40um.

The molecular weight of the polyethylene glycol is 5000-20000.

The ball milling time is 3-4 hours.

Beneficial effects of the present invention: through the present invention, a simple, cheap and environmentally friendly boron carbide ceramic powder dispersion can be obtained, and it can be used to prepare ceramic systems by wet forming methods such as slip casting, gel casting, and injection molding. slurry.

Description of drawings

Fig. 1 is the SEM picture of the boron carbide ceramic powder that embodiment adopts.

Fig. 2 is the characterization of dispersion properties of the dispersions corresponding to different ball milling times in Example 1.

Fig. 3 is the dispersion performance characterization of the corresponding dispersions of different dispersion media in Example 2.

Fig. 4 is the dispersion performance characterization of the corresponding dispersions of different types of dispersants in Example 3.

Fig. 5 is a characterization of the dispersion properties of the dispersions corresponding to different mass fractions of polyethyleneimine in Example 4.

Detailed ways

Below in conjunction with embodiment the present invention is further explained. The following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention.

A preparation method of a boron carbide ceramic powder dispersion, using water as a dispersion medium, water-soluble polyethyleneimine (PEI) and polyethylene glycol (PEG) as a dispersant, comprising the following steps: by mass percentage, Add 0.01-10% polyethyleneimine and 0.01-10% polyethylene glycol into water, mix well, then add 10-50% boron carbide ceramic powder, mix well; then add to ball mill and mill for 3 hours or more, preferably 3-4 hours obtaining a suspension; standing the suspension for 15 to 60 minutes to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The density of the boron carbide ceramic powder used in the embodiment is about 2.6g/cm ³ , a small amount of boron carbide ceramic powder is taken arbitrarily, placed evenly on the scanning electron microscope test bench, and the particle distribution is observed, as shown in Figure 1, the boron carbide ceramic powder The particle size ranges from 1 to 40um. The mass percentage of the boron carbide ceramic powder in the suspension is 10-50%, preferably 30-40%.

Polyethylenimine is usually a water-soluble colorless or pale yellow viscous liquid, and commercially available products are usually 10% to 50% aqueous solution, such as the 50% aqueous solution product of Sigma-Aldrich Company No. 482595 with an average molecular weight of 1300 and The 50% aqueous solution product numbered 03880 with a molecular weight in the range of 600,000 to 1,000,000 can be used in the present invention. The mass percentage of polyethyleneimine in the suspension is 0.01%-10%, preferably 1-3%, more preferably 2.5%.

Polyethylene glycol is a white hard waxy flake solid with a molecular weight of 5,000-20,000. The mass percentage of polyethylene glycol in the suspension is 0.01-10%, preferably 3-5%.

The method used to characterize the stability and dispersibility of boron carbide ceramic powder particles in the suspension is to observe the change of the clear/suspended interface of the suspension over time. The specific characterization method is as follows: pour the suspension into a test tube and calibrate the initial height h ₀ of the liquid surface, and measure the height h _i of the clear/suspended interface of the suspension at the same interval (i=1,2,3,4...) , For example, the interface height is measured every half hour, after several hours, the stability of the suspension is judged according to the interface height and the curve of the interface height changes with time is drawn. The faster the liquid level in the clarified part of the suspension decreases, the worse the suspension stability and dispersibility of the ceramic particles.

Example 1

In this example, under the premise of keeping other preparation conditions unchanged, the ball milling time was changed, and the influence of different ball milling times on the dispersion stability was observed.

1.75g polyethyleneimine (mass percentage is 2.2%), 2.5g polyethylene glycol (mass percentage is 3.15%) are dissolved in 50ml deionized water, mix well, and then stir and add 25g boron carbide ceramic powder (mass percentage 31.5%); then ball milling in a planetary ball mill for a certain period of time (0h, 1h, 3h, 5h respectively); standing for 30min to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The dispersibility characterization results of the dispersions corresponding to different ball milling times are shown in Figure 2. The characterization results of dispersion properties show that the ball milling dispersion method can significantly improve the dispersion of the suspension. With the increase of ball milling time, the dispersibility of the suspension is gradually improved, and when the ball milling time exceeds 3 hours, a suspension with better dispersibility can be obtained. Although purely for ball milling powder mixing, the longer the ball milling time, the better the dispersion performance of the suspension obtained. However, for the entire preparation process of composite materials, due to the consideration of time cost and preparation needs, when the ball milling time is between 3 and 4 hours, a relatively stable suspension can be obtained for a period of time for the subsequent preparation process, while Although too long ball milling time is beneficial to improve the dispersibility of the suspension, it is not beneficial to the whole preparation process.

Example 2

In this example, under the premise of keeping other preparation conditions unchanged, deionized water and absolute ethanol were respectively selected as the dispersion medium, and the influence of different dispersion mediums on the dispersion stability was observed.

1.75g polyethyleneimine (mass percentage is 2.2%), 2.5g polyethylene glycol (mass percentage is 3.15%) is dissolved in 50ml dispersion medium (respectively deionized water, dehydrated alcohol), mix homogeneously, and Then add 25g of boron carbide ceramic powder (31.5% by mass) with stirring; then ball mill for 3h in a planetary ball mill; stand still for 30min to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The dispersion characterization results of the corresponding dispersions in different media are shown in Figure 3. The characterization results of dispersion properties show that deionized water and absolute ethanol are used as dispersion media to disperse boron carbide ceramic powder to a certain extent. Under certain other conditions, when absolute ethanol is used as a dispersant, the dispersibility of boron carbide ceramic powder is poor, and the precipitation is basically complete in about 2.5 hours. When deionized water is used as a dispersant, the boron carbide powder has better dispersibility, and can still maintain a certain interface height after 3 hours. Therefore, deionized water is a more suitable dispersant.

Example 3

In this example, under the premise of keeping other preparation conditions unchanged, polyethyleneimine, polyethylene glycol, polyethyleneimine+polyethylene glycol were selected as dispersants respectively, and the influence of different dispersants on the dispersion stability was observed .

Dispersant (being respectively mass percentage 3% polyethyleneimine, mass percentage 3% polyethylene glycol, mass percentage 1.2% polyethyleneimine+mass percentage 1.8% polyethylene glycol) is dissolved in 50ml deionized water, mix uniform, and then add 25g of boron carbide ceramic powder with stirring; then ball mill in a planetary ball mill for 3h; stand still for 30min to remove the coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The dispersibility characterization results of the corresponding dispersions of different types of dispersants are shown in Figure 4. The characterization results of dispersion properties show that the effect of using polyethylene glycol alone as a dispersant is not ideal, and coagulation occurs in a short period of time, which cannot meet the needs of the actual preparation process; the combination of polyethylene glycol + polyethyleneimine Composite use as a dispersant has better dispersibility, and the suspension can still maintain a certain degree of dispersibility within 3 hours of standing. Although it also tends to reduce its dispersibility after about 3.5 hours, it can meet the actual requirements. The preparation process requires the stability of the suspension; the effect of using polyethyleneimine alone is between the two. From the above results, it can be seen that polyethylene glycol + polyethyleneimine is selected as the composite dispersant.

Example 4

In this example, under the premise of keeping other preparation conditions unchanged, polyethyleneimines with different mass fractions were selected, and the influence of different mass fractions of polyethyleneimines on the dispersion stability was observed.

A certain mass percentage of polyethyleneimine (mass percentage is 1%, 2.5%, 3.5%), mass percentage is 3.1% polyethylene glycol is dissolved in 50ml deionized water, mix well, and then add 25g boron carbide with stirring Ceramic powder; then ball milling in a planetary ball mill for 3 hours; standing for 30 minutes to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion. The dispersion characterization results of the corresponding dispersions of polyethyleneimine with different mass fractions are shown in Figure 5. Numbers 1, 2, and 3 represent 1%, 2.5%, and 3.5% polyethyleneimine mass fractions, respectively. It can be seen from the results that the suspension has the best dispersion performance when the mass fraction of polyethyleneimine is 2.5%, and the dispersion performance is weakened in different degrees when the ratio is greater or less than this ratio.

Example 5

In terms of mass percentage, dissolve 0.01% polyethyleneimine and 0.01% polyethylene glycol in deionized water, mix well, and then add 10% boron carbide ceramic powder with stirring; then ball mill in a planetary ball mill for 3 hours; Stand still for 15 minutes to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The characterization results of the dispersion stability prepared in this embodiment are shown in Table 1:

Table 1

Example 6

In terms of mass percentage, 10% polyethyleneimine and 10% polyethylene glycol were dissolved in deionized water, mixed evenly, and then stirred and added with 50% boron carbide ceramic powder; then ball milled in a planetary ball mill for 4 hours; Stand still for 60 minutes to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The characterization results of the dispersion stability prepared in this embodiment are shown in Table 2:

Table 2

Example 7

In terms of mass percentage, dissolve 0.01% polyethyleneimine and 10% polyethylene glycol in deionized water, mix well, and then add 10% boron carbide ceramic powder with stirring; then ball mill in a planetary ball mill for 3 hours; Stand still for 15 minutes to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The characterization results of the dispersion stability prepared in this embodiment are shown in table 3:

table 3

Example 8

In terms of mass percentage, dissolve 10% polyethyleneimine and 0.01% polyethylene glycol in deionized water, mix well, and then add 50% boron carbide ceramic powder with stirring; then ball mill in a planetary ball mill for 4 hours; Stand still for 60 minutes to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The characterization results of the dispersion stability prepared in this embodiment are shown in Table 4:

Table 4

Example 9

In terms of mass percentage, dissolve 1% polyethyleneimine and 3% polyethylene glycol in deionized water, mix well, and then add 30% boron carbide ceramic powder with stirring; then ball mill in a planetary ball mill for 3 hours; Stand still for 30 minutes to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The characterization results of the dispersion stability prepared in this embodiment are shown in Table 5:

table 5

Example 10

In terms of mass percentage, dissolve 3% polyethyleneimine and 5% polyethylene glycol in deionized water, mix well, and then add 40% boron carbide ceramic powder with stirring; then ball mill in a planetary ball mill for 4 hours; Stand still for 30 minutes to remove coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion.

The characterization results of the dispersion stability prepared in this embodiment are shown in Table 6:

Table 6

Claims (6)

1. a preparation method of boron carbide ceramic powder dispersion, is characterized in that, comprises the following steps: In terms of mass percentage, add 0.01-10% polyethyleneimine and 0.01-10% polyethylene glycol into water, mix well, then add 10-50% boron carbide ceramic powder, mix well; then add to ball mill for ball milling The suspension is obtained after more than 3 hours; the suspension is left to stand for 15-60 minutes to remove the coagulated boron carbide ceramic powder particles to obtain a boron carbide ceramic powder dispersion. 2. the preparation method of boron carbide ceramic powder dispersion according to claim 1, is characterized in that, described boron carbide ceramic powder mass percentage is 30～40%, and described polyethyleneimine mass percentage is 1～3% , the polyethylene glycol mass percentage is 3-5%. 3. The preparation method of boron carbide ceramic powder dispersion according to claim 2, characterized in that, the polyethyleneimine mass percentage is 2.5%. 4. The method for preparing boron carbide ceramic powder dispersion according to claim 1, characterized in that the diameter of the boron carbide ceramic powder is 1-40um. 5. The method for preparing boron carbide ceramic powder dispersion according to claim 1, characterized in that the polyethylene glycol has a molecular weight of 5000-20000. 6. The method for preparing boron carbide ceramic powder dispersion according to claim 1, characterized in that, the ball milling time is 3-4 hours.