CN1974385B - A kind of preparation method of monodisperse silica sol - Google Patents

Abstract

The invention discloses a nano-silica sol with monodispersity, which is prepared by reacting metal silicon powder with water under the catalysis of a certain amount of alkali. The addition rate is such that the concentration of the newly formed silica sol precursor is obtained below the concentration of new nuclei formation. Compared with the existing silica sol preparation method, the nano-silica sol prepared by the present invention has a uniform particle size distribution, and the particle size can be designed according to requirements; the preparation process is simple to operate, low in cost, and easy to accurately control.

Description

A kind of preparation method of monodisperse silica sol

technical field

The invention relates to nonmetal elements and compounds thereof, in particular to a method for preparing monodisperse nanometer silicon dioxide sol.

Background technique

Nano-silica sol is a colloidal solution formed by uniformly dispersing aggregated particles of amorphous silica in a solvent. Due to its large specific surface area, high adsorption performance, chemical stability and other excellent properties, it is widely used as a widely used inorganic polymer material in chemical, material, textile/paper, electronics and other industries. In recent years, silica sol has also been used in the medical field, such as toothpaste, dental casting and drug delivery system.

At present, the preparation methods of silica sol include silica powder dissolution method, ion exchange method, electrolytic electrodialysis method, peptization method, dispersion method and silicate hydrolysis method. However, the preparation methods of silica sol used in industry are mainly ion exchange method and reaction method of silicon powder and dilute alkali (that is, one-step dissolution method of elemental silicon).

There have been many reports on the preparation methods of monodisperse silica nanoparticles. For example, US Patent 3,538,015 and US Patent 3,440,170 add an acidic silica sol to a 10-30nm alkaline silica sol at a specific high speed, while maintaining a pH value greater than 7, to obtain a weight-average particle size of 45-100nm No aggregation, uniform spherical silica sol. US Patent 3,789,009 and US Patent 4,410,405 reported the preparation of monodispersed silica sol by ion exchange method, but the two patents did not propose a particle size distribution control method. CN1594079A uses silicic acid instead of sodium silicate in the prior art as a raw material to prepare a series of silica sols with narrow particle size distribution by controlling the feeding method, reaction pH value and temperature and other conditions. The above preparation methods all need to prepare the final silica sol product through ion exchange reaction, preparation of seed crystal, particle growth reaction, concentration step, purification step and other processes. Each step has a direct impact on the product quality of the final silica sol. The physical and chemical properties of the silica sol product, such as the particle size, uniformity, impurity content and stability, are determined by the control of various conditions in the preparation process. This results in a low concentration of the silica sol solution obtained by converting the ion exchange resin, so that the amount of steam used to concentrate the solution is large, and the production capacity of the evaporation equipment is low; the ion exchange column needs to be operated intermittently, and exchange, regeneration, and washing are carried out alternately, and the operation is complicated. In addition to consuming a large amount of hydrochloric acid, the process also consumes a large amount of washing water. Therefore, this production method has complex process, large consumption, high cost and poor economic benefit.

Compared with the preparation of monodispersed silica sol by the above-mentioned ion exchange method, the one-step dissolution method of elemental silicon reacts high-purity elemental silicon powder and dilute alkali solution to obtain denser and more uniform silica sol particles with very few impurity ions. At the same time, the one-step silicon dissolution method has the characteristics of simple process and easy operation, and has become a better choice for the production of monodisperse silica sol. In CN86100503, the inventor Zhang Yangzheng proposed a non-freezing, stable silica sol manufacturing method. In this paper, 100-300 mesh silica powder is used, without oxidation and activation, to react directly with dilute alkali at a temperature of 65-100°C, preferably at 72-83°C, to obtain the finished silica sol by filtration or centrifugation. At present, most domestic enterprises that produce silica sol by the silica powder method basically adopt the process introduced by this patent. However, the particle size of the silica sol obtained by this method is 15-20 nm, and the viscosity of the sol is relatively large. Due to the lack of precise control technology for particle size, domestic manufacturers can only produce a few types of silica sols such as 8-20 and 11-15. Small silica particle size and poor uniformity have always been the main factors restricting the production of multi-functional and high-quality silica sol products by domestic enterprises. In patent CN1830778A, by controlling the amount of silicon powder added each time to not exceed 5% of the total amount of alkaline aqueous solution, and under the condition that the time interval is less than 60 minutes, a large particle size nano-scale silica colloid with a particle size of 20-160 nanometers is synthesized . Patent CN1830777A (2006) by adding alkaline catalyst and metal silicon powder to the silica water dispersion as the seed liquid, making it react under the condition of pH 7-14, the silica sol with large particle size can be directly obtained . This patent can obtain silica sol with a particle size greater than 5 nanometers, but this patent does not propose a method for controlling the particle size distribution so that the particle size distribution can be controlled. At the same time, we found in experiments that it is difficult to prepare silica sol particles with high monodispersity, especially small particle size silica sol with particle deviation less than 5%, by adding silica powder in batches. However, due to the certain viscosity between the finer silica powder particles, it is difficult to accurately control the addition speed of the silica powder by using the method of adding silica powder and lye at the same time, which will easily lead to large deviations in the final silica sol particles.

Colloidal particles are formed through two processes of nucleation and growth in a supersaturated system. In most cases, nucleation and growth occur simultaneously during particle formation, which results in a broad size distribution of the formed particles. In order to obtain monodisperse particles, the nucleation and growth phases must be clearly separated. The inventor found through a large number of experiments that in the early stage of the reaction, by strictly controlling the amount of lye added, the reaction speed of the silicon powder is precisely controlled, so as to increase the saturation of the active silicic acid in the nucleation period as much as possible, and the formed silica sol seed particles more evenly distributed. Further adding silicon powder to the seed particles and controlling the amount of alkali solution added can produce nano-silica sol with high stability, monodispersity and good sphericity.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, to provide a technology for precisely controlling the particle size distribution of silica sol, and to use this method to prepare nano-silica sol with high stability, controllable particle size and monodispersity product.

The inventor found through a large number of experiments that in the early stage of the reaction, by strictly controlling the addition of lye, the reaction speed of the silicon powder is precisely controlled, so as to improve the saturation of the active silicic acid in the nucleation period as much as possible, and the formed silica sol species Particle distribution is more uniform. Further, silicon powder is added to the seed particles, so that the silicic acid hydrolyzed by the silicon powder is attached to the silica seed particles to increase the size of the seed particles. In order to prepare silica sol with good monodispersity, the concentration of silicic acid in the solution must be controlled to be lower than the concentration of new silica sol seed particles, so the addition of alkali solution needs to be strictly controlled. In this way, no new small particles are generated during the growth process, and nano-silica sol with high stability, monodispersity and good sphericity can be prepared.

The present invention adopts following technical scheme:

A nano-silica sol with monodispersity, which is prepared by reacting metal silicon powder with water under the catalysis of a certain amount of alkali. Particles in solution are further grown. During the reaction process, the addition rate of the dilute alkali solution is adjusted according to the growth rate of the particles (or the surface area of the sol particles in the solution), so that no new nuclei are formed during the addition of the dilute alkali solution. Proceed as follows:

1) Heat a certain amount of deionized water to 50-95°C, add silicon powder and dilute alkali solution under strong stirring, and react for a certain period of time to obtain a mixed solution containing silica sol seed particles. Wherein, the silicon powder and the dilute alkali solution can be added at the same time, or can be added step by step. In order to obtain seed particles with better distribution, it is necessary to strictly control the addition of silicon powder and alkali. If the weight ratio of silicon powder to alkali is too low, especially when the pH value of the mixed solution is lower than 9, the reaction speed of silicon powder is slow, the saturation of active silicic acid in the solution is low, and the number of seed particles formed is small And the distribution is wide; if the ratio is too large, the reaction is too fast, and secondary nucleation is prone to occur, resulting in the formation of larger particles. The weight ratio of silicon powder and alkali added in the present invention is 5-50:1, wherein 10-30:1 is the optimum ratio. In order to obtain a silica sol with good monodispersity, it is usually necessary to have a particle size deviation of 15% or less of the seed particles. In order to prepare a silica sol with a polydispersity of less than 2%, it is generally required that the particle size of the seed particles be less than 25% of the particle size of the final product obtained.

2) Add a certain amount of silicon powder to the above solution containing the seed particles to obtain a mixed suspension. Then, under strong stirring, a certain amount of dilute alkali aqueous solution is added to the above suspension at a certain speed, the dilute alkali reacts with the silicon powder, and the generated hydrated silicic acid is adsorbed on the surface of the silica sol seed particles and polymerized to make the seed particles grow further. In the process of adding lye, it is necessary to control the speed of adding lye so that the concentration of monomer hydrated silicic acid in the solution is lower than the concentration of new nuclei. In order to improve the reaction speed, the addition speed of the lye can be gradually accelerated according to the growth speed of the particles (ie, the specific surface area of the silica sol particles) during the reaction process. Because as the pH value increases, the reaction speed increases, and the concentration of silicic acid monomers in the solution also increases rapidly. Therefore, it is advisable that the adding rate of the dilute aqueous alkali solution is lower than 10% of the amount of silicon powder added per hour. During the reaction process, as the particle size increases, the specific surface area of colloidal particles in the solution increases rapidly, and the amount of adsorbed active silicic acid also increases. In order to reduce the reaction time of the whole reaction, the adding speed of the dilute alkali solution can be gradually accelerated with the growth of the particle size.

3) Repeat step 2), and according to the addition of silicon powder and lye, a series of silica sol particles with narrow particle size distribution can be obtained. After the reaction is completed, filter or centrifuge to remove the unreacted silicon powder to obtain a monodisperse silica sol product.

Continuously adjust the adding speed of the dilute alkaline aqueous solution to obtain monodisperse nano-silica with uniform particle size distribution, and the obtained silica sol is separated and concentrated to obtain the finished silica sol.

The preparation method of monodisperse silica sol comprises following more specific steps:

(1) Add silicon powder and a dilute alkali solution as a catalyst to deionized water simultaneously under strong stirring, and after heating and reacting, a solution containing silica sol seed particles is obtained;

(2) In the above-mentioned silica sol seed particle solution, add silicon powder to obtain a mixed suspension; then, under strong stirring, slowly add dilute alkali solution to the suspension to make the concentration of the generated silicic acid particles Lower than the concentration at which new sol species are formed;

(3) Repeat step (2), according to the difference in the addition of silicon powder and dilute alkali solution, a series of silica sol particles with narrow particle size distribution can be obtained; after the reaction is completed, remove unreacted silicon powder through filtration or centrifugation, A monodisperse silica sol product can be obtained.

The particle size of the silicon powder is 50-600 mesh, among which 100-400 mesh is the best.

The heating temperature is 50-95°C.

In the step (1), the weight ratio of the silicon powder and the dilute alkali aqueous solution is 5 to 50: 1, wherein 20 to 40: 1 is the optimal ratio; in the described step (2), the silicon powder and the dilute aqueous alkali solution The weight ratio is 5-50:1, wherein 10-30:1 is the best ratio.

The dilute alkaline aqueous solution used as a catalyst may be one or a mixture of sodium hydroxide, water glass, lithium hydroxide, potassium hydroxide, ammonia water, and organic amines.

The particle size of the seed particles prepared in the step (1) is required to be less than 25% of the particle size of the final product, and the deviation is less than 15%.

The adding speed of the dilute alkaline aqueous solution in the step (2) is that the adding amount of the dilute alkaline aqueous solution per hour is lower than 10% of the silicon powder adding amount.

The particle diameter of the obtained monodisperse silica sol product is 5-500 nm, and the particle diameter deviation is less than 5%.

The separation techniques used in the present invention are all prior art, and centrifugal separation or vacuum filtration can be adopted. Through this method, a silica sol product with a solid content below 35% can be synthesized, and can be further concentrated to 52% by evaporation concentration or ultrafiltration membrane concentration.

Using the above method not only provides a method for preparing monodisperse silica sol by the one-step method of elemental silicon, but also can synthesize a series of silica sol products with different particle diameters greater than 5 nanometers, solving the problem of using elemental silicon The disadvantage of the silica sol particles synthesized by the dissolution method is that the particle size is small. Because very fine silicon powder has a certain viscosity, it is difficult to accurately control the constant addition rate. Therefore, the present invention first adds silicon powder to the solution containing seed particles at one time, and then slowly adds lye. By controlling the concentration of lye The amount of addition is used to control the reaction speed, and the operation is well controllable. Compared with the method for preparing monodisperse silica sol currently adopted by enterprises at home and abroad, the present invention has the advantages of simple operation process, good repeatability, low cost and better product quality.

Description of drawings

Fig. 1 is the particle size distribution figure of 18nm sample for particle diameter;

Fig. 2 is the particle size distribution figure of 80nm sample for particle diameter;

Fig. 3 is the transmission electron microscope figure of 26nm sample for particle diameter;

Fig. 4 is a statistical diagram of the particles measured by the transmission electron microscope of the 26nm sample shown in Fig. 3 .

Detailed ways

Below in conjunction with example the present invention will be described in further detail, and the example given does not limit protection scope of the present invention:

Example 1:

(1) Take 2000 grams of distilled water and add it to a reactor equipped with a reflux condenser, add 250 grams of 200-mesh commercial silicon powder and 5 grams of sodium hydroxide, start the stirrer and heat up to 75 ° C;

(2) take by weighing 10 grams of sodium hydroxide and join in 1000 grams of distilled water;

(3) Slowly add the lye obtained in the above step (2) into the mixed solution obtained in the step (1), and control the initial addition rate to be 250 grams of solution per hour. Then gradually increase the speed of adding lye, and finish adding in about 3 hours. Then continue to react for 2-3 hours. When the solution is cooled to 50°C, filter or centrifuge to obtain nano-silica sol.

The particle size measured by a dynamic light scattering laser particle size and potential analyzer is 18 nanometers, as shown in Figure 1, where the abscissa is the particle size, and the ordinate is the percentage of different particles. SiO ₂ content is 14.5% (weight percent), viscosity 4.2CPS. The polydispersity was 0.03.

Example 2:

(1) Get 300 grams of the silica sol solution gained in Example 1 and add it to 1700 grams of distilled water. Start the stirrer and heat to 80°C;

(2) Add 100 grams of commercially available 300 mesh silicon powder and stir;

(3) Take by weighing 15 grams of sodium hydroxide and join in 1000 grams of distilled water, then add 10 grams of ammonia water, mix well;

(4) Slowly add the lye obtained in step (3) into the mixed solution obtained in step (2), finish adding in about 4 hours, and continue to react for 1 hour;

(5) continue to add 225 grams of silicon powder in step (4) gained mixed solution, stir;

(6) Weigh 20 grams of NaOH, add it to 1500 grams of distilled water, and mix evenly; slowly add the lye to the mixed solution obtained in step (5), and add it in about 8 hours. Continue to react for 2 to 3 hours. When the solution is cooled to 50°C, it is filtered or centrifuged to obtain nano-silica sol.

The particle size measured by a dynamic light scattering laser particle size and potential analyzer is 80 nanometers, as shown in Figure 2, where the abscissa is the particle size, and the ordinate is the percentage of different particles. SiO ₂ content is 15% (percentage by weight), viscosity 3.8CPS. The polydispersity is 0.013.

Example 3:

(1) Take 2000 grams of distilled water and add it to a reactor equipped with a reflux condenser, add 150 grams of 200-mesh commercially available silicon powder and 5 grams of sodium hydroxide, start the stirrer and heat up to 75 ° C;

(2) Take by weighing 10 grams of sodium hydroxide and join in 1000 grams of distilled water, then add 10 grams of ammonia water, mix well;

(3) Slowly add the lye obtained in the above step (2) into the mixed solution obtained in the step (1), and control the initial addition rate to be 150 grams of solution per hour. Then gradually increase the speed of adding lye, and finish adding in about 6 hours. Then continue to react for 1 hour;

(4) Add 500 grams of silicon powder in the above solution, and continue to stir;

(5) Take by weighing 45 grams of NaOH, join in 2500 grams of water, mix well;

(6) Add lye as shown in step (3), and add it in about 8 hours. Continue to react for 2 to 3 hours. When the solution is cooled to 50°C, it is filtered or centrifuged to obtain nano-silica sol.

The particle size measured by a transmission electron microscope is 26 nanometers, as shown in Figure 3 and Figure 4. In Fig. 4, the abscissa is the particle size, and the ordinate is the percentage of particles with different particle sizes. SiO ₂ content is 27% (percentage by weight), viscosity 4.5CPS.

Claims (8)

1. a preparation method of monodisperse silica sol, is characterized in that comprising the steps: (1) Add silicon powder and dilute alkali aqueous solution as catalyst to deionized water simultaneously under strong stirring, and described dilute alkali aqueous solution as catalyst is sodium hydroxide, water glass, lithium hydroxide, potassium hydroxide, ammoniacal liquor A mixture of one or more of them; after heating and reacting, a solution containing silica sol seed particles is obtained; (2) In the above-mentioned silica sol seed particle solution, add silicon powder to obtain a mixed suspension; then, under strong stirring, slowly add a dilute alkali aqueous solution to the suspension; make the concentration of the generated silicic acid microparticles Lower than the concentration at which new sol species are formed; (3) Repeat step (2), according to the difference in the addition of silicon powder and dilute aqueous alkali solution, a series of silica sol particles with narrow particle size distribution can be obtained; after the reaction is completed, remove unreacted silicon powder through filtration or centrifugation, A monodisperse silica sol product can be obtained; In the step (1), the weight ratio of the silicon powder to the dilute aqueous alkali solution is 5-50:1; in the step (2), the weight ratio of the silicon powder to the dilute aqueous alkali solution is 5-50:1. 2. The method for preparing monodisperse silica sol according to claim 1, characterized in that: the particle size of the silicon powder is 50-600 mesh. 3. The method for preparing monodisperse silica sol according to claim 2, characterized in that: the particle size of the silicon powder is 100-400 mesh. 4. The method for preparing monodisperse silica sol according to claim 1, characterized in that: the heating temperature is 50-95°C. 5. the preparation method of monodispersity silica sol according to claim 1 is characterized in that: in described step (1), the weight ratio of silicon powder and dilute alkaline aqueous solution is 20～40: 1; In step (2), the weight ratio of silicon powder to dilute aqueous alkali solution is 10-30:1. 6. the preparation method of monodisperse silica sol according to claim 1 is characterized in that: the seed particle diameter that described step (1) makes is less than 25% of final product particle diameter, and deviation is less than 15% . 7. the preparation method of monodisperse silica sol according to claim 1 is characterized in that: the adding speed of dilute alkali aqueous solution in the described step (2) is that the add-on of dilute alkali aqueous solution per hour is lower than silicon powder 10% of the added amount. 8. The preparation method of monodisperse silica sol according to claim 1, characterized in that, the obtained monodisperse silica sol product has a particle diameter of 5-500 nm, and the particle diameter deviation is less than 5%.

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