CN114572991A

CN114572991A - Nano kaolin powder and preparation method thereof

Info

Publication number: CN114572991A
Application number: CN202210262853.7A
Authority: CN
Inventors: 徐创业; 邱金勇; 申明奎; 何冬婷; 冯丽; 邬玉兰; 裴国献
Original assignee: Southwest University of Science and Technology
Current assignee: Southwest University of Science and Technology
Priority date: 2022-03-17
Filing date: 2022-03-17
Publication date: 2022-06-03
Anticipated expiration: 2042-03-17
Also published as: CN114572991B

Abstract

The invention relates to a nano kaolin powder and a preparation method thereof. According to the preparation method of the nano kaolin powder, the liquid of the slurry is converted into a critical state vapor film through a fine foaming process, the generated fine bubbles space modified particles, the drying speed is greatly increased, hard agglomeration of nano particles in the drying process is effectively prevented, and the powder is easily dispersed to obtain the active nano kaolin powder. The method well solves the problem of hard agglomeration which is difficult to avoid in the drying process of the nano particles, and has the characteristics of simplicity, high efficiency and easy industrial production.

Description

Nano kaolin powder and preparation method thereof

Technical Field

The invention relates to the technical field of nano materials, in particular to nano kaolin powder and a preparation method thereof.

Background

The nano material is a material with at least one dimension in the nano level (1 nm-100 nm) in the three-dimensional space scale, and is a new generation material consisting of nano particles with the sizes between atoms, molecules and a macroscopic system. When the size of the particles is reduced to the nanometer level, new characteristics of sound, light, electricity, magnetism or thermal performance can be caused. The nano kaolin is one of the members and has wide application in the modern industrial field. However, in a natural state, kaolinite particles are mutually adsorbed and connected to form an aggregate or an aggregate, the direct application cannot generate a nano effect, and the particles are separated by adopting a proper method to form single nano particles so as to generate the nano mutation effect. Therefore, the kaolin needs to be subjected to nanocrystallization to endow the kaolin with various nanometer characteristics, so that the application value of the kaolin is greatly increased.

However, kaolin belongs to a natural mineral material, and is mainly ground and crushed to obtain nano slurry at present, but the application of kaolin is mainly in a dry powder state, so that the kaolin needs to be dried out of the slurry, and the hard agglomeration problem is difficult to overcome in the drying process, so that the kaolin is not nano particles any longer after being dried, and the application value of the kaolin is seriously influenced. At present, the problem of hard agglomeration can be well solved by azeotropic distillation and the like, but the process method is difficult to leave a laboratory and cannot expand the production; modified spray drying and the like have the characteristics of expanded production, but are not ideal for solving the problem of hard agglomeration.

Disclosure of Invention

Based on the above, there is a need to provide a method for preparing nano kaolin powder, which can solve the problem of hard agglomeration in the drying process and has the characteristics of industrial production.

In addition, a nano kaolin powder is also provided.

A preparation method of nano kaolin powder comprises the following steps:

carrying out fine foaming treatment on the nano kaolin slurry subjected to surface coating modification so as to convert a solvent in the slurry into micro-nano foam, and dispersing the nano kaolin subjected to surface coating modification into the micro-nano foam;

drying the slurry subjected to the fine foaming treatment to obtain loose kaolin blocks; and

and (4) scattering the kaolin blocks to obtain nano kaolin powder.

According to the preparation method of the nano kaolin powder, the liquid of the slurry is converted into the critical state vapor film through the fine foaming process, the generated fine bubbles space the modified particles, the drying speed is greatly increased, the hard agglomeration of nano particles in the drying process is effectively prevented, and the powder is easily dispersed to obtain the active nano kaolin powder. The method well solves the problem of hard agglomeration which is difficult to avoid in the drying process of the nano particles, and has the characteristics of simplicity, high efficiency and easy industrial production.

In one embodiment, the step of fine foaming treatment comprises adding a foaming agent into the surface-coated and modified nano kaolin slurry and then stirring.

In one embodiment, the foaming agent comprises sodium fatty alcohol-polyoxyethylene ether sulfate and gamma-aminopropyltriethoxysilane.

In one embodiment, the step of drying comprises a thermal drying process.

In one embodiment, the preparation method further comprises the following steps of preparing the surface-coating-modified nano kaolin slurry:

mixing kaolin slurry, a grinding aid and a first dispersing agent to obtain first mixed slurry;

after primary grinding is carried out on the first mixed slurry, a modifier is added for secondary grinding to obtain nano kaolin slurry; and

diluting the nano kaolin slurry by using a first process control agent, adding the modifier again, and mixing to obtain surface-coated modified nano kaolin slurry;

the grinding aid comprises stearic acid, the first dispersing agent comprises at least one of sodium polycarboxylate, sodium tripolyphosphate, sodium hexametaphosphate, sodium silicate, sodium polyacrylat and sodium acryloyl, the modifier comprises a titanate coupling agent, a silane coupling agent or an aluminate coupling agent, and the first process control agent comprises water.

In one embodiment, the grinding aid accounts for 1 wt% to 2 wt% of the kaolin powder, the first dispersing agent accounts for 0.5 wt% to 1.0 wt% of the kaolin powder, the modifier accounts for 0.3 wt% to 0.5 wt% of the kaolin powder, and the solid content of the nano kaolin slurry diluted by the first process control agent is 30 wt% to 50 wt%.

In one embodiment, the grinding is carried out in a high energy ball mill at a rotating speed of 800RPM to 1200RPM, the primary grinding time is 2h to 4h, and the secondary grinding time is 1h to 2 h.

In one embodiment, the above preparation method further comprises the following steps of preparing the kaolin slurry:

mixing a second dispersant and a second process control agent to obtain an aqueous salt solution; and

adding kaolin powder into the saline solution under stirring to obtain a second mixed slurry, and stirring to obtain kaolin slurry;

the second dispersing agent comprises at least one of sodium polycarboxylate, sodium tripolyphosphate, sodium hexametaphosphate, sodium silicate, sodium polyacrylat and sodium acryloyl, the second process control agent comprises water, and the kaolin powder has a median particle size of 5-15 μm.

In one embodiment, the second dispersant accounts for 0.5 wt% to 1.0 wt% of the mass of the kaolin powder, and the kaolin powder accounts for 50 wt% to 65 wt% of the second mixed slurry.

A nano kaolin powder prepared according to the preparation method of any one of the above embodiments.

Drawings

FIG. 1 is a graph showing particle size analysis of kaolin powder before and after high-energy ball milling in example 1;

in FIG. 2, the graphs (a) to (f) are the scanning electron microscope results of the kaolin powders prepared in comparative example 1, example 2, example 3, comparative example 2 and comparative example 3, respectively.

Detailed Description

The present invention will be described in detail with reference to the following embodiments in order to make the aforementioned objects, features and advantages of the invention more comprehensible. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms "first", "second", and the like, as used herein, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

An embodiment of the present invention provides a method for preparing a nano kaolin powder, including step S001, step S002 and step S003, specifically:

step S001: and carrying out fine foaming treatment on the nano kaolin slurry subjected to surface coating modification so as to convert a solvent in the slurry into micro-nano foam, and dispersing the nano kaolin subjected to surface coating modification into the micro-nano foam.

Specifically, the surface coating modification is to treat the particle surface by a physical or chemical method, coat the particle surface by an inorganic substance or an organic substance, and introduce a coating layer on the surface, so that the coated and modified powder can be regarded as a composite powder consisting of a core layer and a shell layer. By coating a covering layer with different components on the surface of the powder, the wetting and adhering characteristics of the powder can be changed, the dispersion behavior of the powder in a matrix can be improved, and the interface bonding energy of the powder and the matrix can be improved. As used herein, "micro-nano foam" refers to a dispersion of a large amount of a highly fluid and low-density gas separated by a liquid, wherein the gas exists as bubbles having a diameter of several hundreds of nanometers to several tens of micrometers, which are between micro-bubbles and nano-bubbles.

In one embodiment, the preparation of the surface coating modified nano kaolin slurry comprises the steps of S011, S012 and S013, specifically:

step S011: the kaolin slurry, the grinding aid and the first dispersant are mixed to obtain first mixed slurry.

The grinding aid is used for improving the grinding efficiency, is composed of one or more substances with surface activity and other chemical aids, can obviously reduce the surface energy of ground powder in the material grinding process, overcomes the attraction among the ground powder, reduces the grinding resistance, prevents ball pasting and grinding, improves the flowability of the ground powder, reduces the power consumption of a grinding machine and improves the grinding efficiency. In some embodiments, the grinding aid includes, but is not limited to, stearic acid. In an alternative embodiment, the grinding aid is stearic acid.

In some embodiments, the grinding aid comprises 1 wt% to 2 wt% of the mass of the kaolin powder in the kaolin slurry. In an alternative embodiment, the grinding aid comprises 1.2 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, or 1.8 wt% of the kaolin powder mass. Furthermore, the grinding aid accounts for 1.1-1.9 wt% of the kaolin powder. Furthermore, the grinding aid accounts for 1.3-1.7 wt% of the kaolin powder.

The first dispersant is used for stabilizing the state of the ground material and preparing dispersed uniform nano slurry. The dispersant adsorbs to the surface of the material particles and forms a considerable repulsive force between the material particles, which keeps the distance between the particles and reduces the tendency of uncontrolled flocculation. In some embodiments, the first dispersant comprises at least one of sodium polycarboxylate, sodium tripolyphosphate, sodium hexametaphosphate, sodium silicate, sodium polyacryl, and sodium acryloyl. In an alternative embodiment, the first dispersant is a sodium polycarboxylate.

In some embodiments, the first dispersant comprises 0.5 wt% to 1.0 wt% of the mass of the kaolin powder in the kaolin slurry. In an alternative embodiment, the first dispersant comprises 0.6 wt%, 0.7 wt%, 0.8 wt%, or 0.9 wt% of the kaolin powder mass. Further, the first dispersant accounts for 0.6 wt% -0.9 wt% of the kaolin powder. Furthermore, the first dispersant accounts for 0.7 to 0.8 weight percent of the kaolin powder.

In one embodiment, the step of preparing the kaolin slurry includes steps S111 and S112, specifically:

step S111: the second dispersant and the second process control agent are mixed to provide an aqueous salt solution.

In some embodiments, the second dispersant comprises at least one of sodium polycarboxylate, sodium tripolyphosphate, sodium hexametaphosphate, sodium silicate, sodium polyacryl, and sodium acryl. It is understood that the second dispersant is for dispersing purposes and that the first dispersant may be the same or different from the second dispersant in composition.

In some embodiments, the second dispersant comprises 0.5 wt% to 1.0 wt% of the mass of the kaolin powder in the kaolin slurry. In an alternative embodiment, the second dispersant comprises 0.6 wt%, 0.7 wt%, 0.8 wt%, or 0.9 wt% of the kaolin powder mass. In an alternative specific example, the second dispersant is a sodium polycarboxylate.

In some embodiments, the second process control agent includes, but is not limited to, water. In an alternative specific example, the second process control agent is water.

In some embodiments, the second dispersant and the second process control agent are mixed and agitated. Further, the second dispersant and the second process control agent are mixed and then mechanically agitated. Furthermore, the mechanical stirring time is 1-2 h. In an alternative embodiment, the mechanical stirring time is 1.2h, 1.4h, 1.5h, 1.6h or 1.8 h.

Step S112: and adding kaolin powder into the saline solution under stirring to obtain a second mixed slurry, and stirring to obtain the kaolin slurry.

In some embodiments, the kaolin powder has a median particle size of from 5 μm to 15 μm. Further, the kaolin powder has a median particle diameter of 7 to 13 μm. In an alternative embodiment, the kaolin powder has a median particle size of 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm.

In some embodiments, the kaolin powder comprises 50 wt% to 65 wt% of the second mixed slurry. Further, the kaolin powder accounts for 52-63 wt% of the second mixed slurry. In an alternative embodiment, kaolin powder comprises 54 wt%, 55 wt%, 56 wt%, 58 wt%, 60 wt%, or 62 wt% of said second mixed slurry.

In some embodiments, the kaolin slurry is stirred for a period of time ranging from 4 hours to 8 hours. Further, the stirring time is 5-7 h. In an alternative embodiment, the stirring time is 5.5h, 6h or 6.5 h.

Step S012: and (3) grinding the first mixed slurry for the first time, and then adding a modifier for secondary grinding to obtain the nano kaolin slurry.

In some embodiments, the modifier comprises a titanate coupling agent, a silane coupling agent, or an aluminate coupling agent. In an alternative embodiment, the modifier is gamma- (2, 3-epoxypropoxy) propyltrimethoxysilane.

In some embodiments, the modifier comprises 0.3 wt% to 1.0 wt% of the kaolin powder mass. Further, the modifier accounts for 0.35 wt% -0.65 wt% of the kaolin powder. In an alternative embodiment, the modifier comprises 0.36 wt%, 0.38 wt%, 0.40 wt%, 0.42 wt%, 0.44 wt%, 0.48 wt%, or 0.50 wt% of the kaolin powder mass.

In some embodiments, the grinding is performed in a high energy ball mill at a speed of 800RPM to 1200RPM for a primary grinding time of 2h to 4h and a secondary grinding time of 1h to 2 h. Further, the grinding is carried out in a high energy ball mill at a rotation speed of 900RPM to 1100RPM, the primary grinding time is 2.5h to 3.5h, and the secondary grinding time is 1h to 2 h. Further, the grinding is carried out in a high energy ball mill at a rotation speed of 950RPM to 1050RPM, the primary grinding time is 2.5h to 3.5h, and the secondary grinding time is 1h to 2 h.

The method adopts a wet stirring and grinding mode, and under the assistance of the grinding auxiliary agent and the dispersing agent, the grinding medium and kaolin powder particles are promoted to generate the actions of mutual impact, friction, collision and shearing, so that the effect of nano-sizing the material is quickly achieved, and nano-sizing of the powder material can be efficiently and quickly achieved. Meanwhile, the coating modification of powder particles is carried out simultaneously in the grinding process, high grinding energy is utilized to generate instant heat energy, a new interface is generated by grinding and crushing, and the particles which are ground and rotated at a high speed are wound by a modifier polymer chain, so that the surface coating modification with high combination is realized.

Step S013: and diluting the nano kaolin slurry by using a first process control agent, adding the modifier again, and mixing to obtain the surface-coated modified nano kaolin slurry.

In some embodiments, the first process control agent includes, but is not limited to, water. In an alternative specific example, the first process control agent is water.

In some embodiments, the nano kaolin slurry after dilution with the first process control agent has a solids content of 30 wt% to 50 wt%. Further, the solid content of the nano kaolin slurry diluted by the first process control agent is 30 wt% -45 wt%. Furthermore, the solid content of the nano kaolin slurry diluted by the first process control agent is 35 wt% -40 wt%.

In some embodiments, the modifier comprises 0.3 wt% to 0.5 wt% of the kaolin powder mass. Further, the modifier accounts for 0.35 wt% -0.45 wt% of the mass of the kaolin powder. In an alternative embodiment, the modifier comprises 0.36 wt%, 0.38 wt%, 0.40 wt%, 0.42 wt%, or 0.44 wt% of the kaolin powder mass.

In some embodiments, the nano kaolin slurry is diluted by the first process control agent, and then the modifier is added again to be mixed, and then the mixture is stirred to obtain the nano kaolin slurry with the modified surface coating. Further, a high-speed stirrer was used for stirring. Furthermore, a high-speed friction stirrer is adopted to stir at the speed of 5000RPM to 7000RPM, and the stirring time is 30min to 60 min.

The secondary modification method greatly improves the coating rate of the particles, and further improves the dispersibility of the powder particles.

According to the invention, kaolin powder particles are rapidly nanocrystallized by high-energy ball milling and adding the grinding aid and the dispersing agent, the nanocrystallization process is extremely efficient, and the coating modification is carried out to prepare the coating modified nano kaolin slurry, so that the nano kaolin powder particles have excellent dispersibility and uniformity.

In some embodiments, the step of fine foaming comprises adding a foaming agent to the surface-coated modified nano kaolin slurry and stirring. It will be appreciated that in some embodiments, other methods of fine foaming may also be used.

In some embodiments, the surface-coated and modified nano kaolin dispersed in the micro-nano foam after the fine foaming treatment means that the solvent in the nano kaolin slurry above 99% (v/v) is converted into the micro-nano foam, the nano kaolin is included between the bubbles, and the adjacent nano particles are separated by the bubbles.

Specifically, the foaming agent refers to a substance that causes pores in a target substance, and includes three major classes of chemical foaming agents and physical foaming agents and surfactants. It will be appreciated that the fine foaming process may be carried out using any suitable blowing agent. In some embodiments, the foaming agent comprises sodium fatty alcohol-polyoxyethylene ether sulfate and gamma-aminopropyltriethoxysilane.

In one embodiment, the sodium fatty alcohol polyoxyethylene ether sulfate accounts for 0.5-1.5 wt% of the kaolin powder, and the gamma-aminopropyltriethoxysilane accounts for 0.5-1.5 wt% of the kaolin powder. Furthermore, the sodium fatty alcohol polyoxyethylene ether sulfate accounts for 0.6-1.4 wt% of the kaolin powder, and the gamma-aminopropyltriethoxysilane accounts for 0.6-1.4 wt% of the kaolin. In an alternative embodiment, the sodium fatty alcohol polyoxyethylene ether sulfate comprises 0.7 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, or 1.3 wt% of the kaolin powder mass, and the gamma-aminopropyltriethoxysilane comprises 0.7 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, or 1.3 wt% of the kaolin powder mass. The purpose of fine foaming can be better realized by adopting fatty alcohol-polyoxyethylene ether sodium sulfate and gamma-aminopropyltriethoxysilane with proper concentration.

In some embodiments, the foaming agent is added to the surface-coated and modified nano kaolin slurry and then stirred by a high-speed stirrer. Further, the mixture is stirred in a high-speed stirrer at a speed of 3000 to 5000 RPM. Further, the mixture is stirred in a high-speed stirrer at a speed of 3500RPM to 4500 RPM.

In an alternative embodiment, the fatty alcohol-polyoxyethylene ether sodium sulfate and the gamma-aminopropyl triethoxysilane are added to the surface-coated and modified nano kaolin slurry and then stirred by a high-speed stirrer, or the fatty alcohol-polyoxyethylene ether sodium sulfate is added and stirred by the high-speed stirrer, and then the gamma-aminopropyl triethoxysilane is added and stirred by the high-speed stirrer. The researchers of the invention find that the fine foaming can be well realized by adopting the two modes.

Specifically, the researchers of the present invention found that the micro-nano-scale foam generated after the fine foaming treatment has a sufficiently large volume, a certain strength, stability and is not easy to collapse. The micro-nano foam isolates the nano particles, greatly increases the distance and difficulty of particle agglomeration in the drying process, simultaneously foams to change the solvent of the slurry into a critical state vapor film, and at the moment, all flowing liquid is changed into micro-fine foam, greatly increases the specific surface area of drying, and greatly improves the evaporation rate of the solvent, so that the nano particles are not as long as being agglomerated and grown up in the drying process. In addition, the foam with certain strength changes the flowing slurry into a non-flowing solid state, particles are fixed by the solid state, and migration and agglomeration cannot occur during drying, so that the aim of obtaining the nano dry powder is fulfilled. The effect is best when the sizes of the foam and the powder particles are close to each other.

Step S002: and drying the slurry subjected to the fine foaming treatment to obtain loose kaolin blocks.

In some embodiments, the step of drying comprises a thermal drying process. Further, the thermal drying treatment includes, but is not limited to, heat drying, microwave drying, infrared drying, or flash drying. Further, the step of heat drying treatment comprises placing the slurry after the fine foaming treatment at 150-180 ℃ for 5-8 h.

Specifically, the heat drying treatment can further foam the slurry subjected to the fine foaming treatment, liquid of the slurry is converted into a critical state vapor film, and the generated fine bubbles separate the modified particles, so that the drying speed is greatly increased, and the generation of hard agglomeration is prevented.

Step S003: and (4) scattering the kaolin blocks to obtain nano kaolin powder.

Specifically, the finely foamed and dried nano kaolin clay blocks are loose powder blocks, each particle in the nano kaolin clay blocks is coated by a modifier, and the particles are isolated by bubbles, are in a loose pseudo-agglomeration state and are easy to disperse, so that the nano kaolin clay powder is obtained.

In some embodiments, the loose kaolin chunks are dispersed using a high-speed crushing disperser. Further, the loose kaolin blocks are dispersed at a speed of 6000 to 8000RPM using a high-speed crushing disperser for a total dispersion time of 25 to 35 seconds. Further, the loose kaolin blocks are dispersed by a high-speed crushing disperser at 6000RPM to 8000RPM for 30s in total, 3 times for 10s each, and 1min to 2min apart.

The invention further provides the nano kaolin powder prepared by the preparation method of any one of the embodiments.

In some embodiments, the nano kaolin powder is in a flake aggregate with a diameter of 0.5 μm to 2 μm due to surface tension and electrostatic effect. Furthermore, the nano kaolin powder is a flaky aggregate with the median diameter of 0.8-1.2 mu m due to surface tension and electrostatic effect.

In some embodiments, the dispersion rate of the nano kaolin powder is 95% to 98%.

In some embodiments, the activation index of the nano kaolin powder is 99% or more.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The following detailed description is given with reference to specific examples. The following examples are not specifically described, and other components except inevitable impurities are not included. Reagents and instruments used in the examples are all conventional in the art and are not specifically described. The experimental procedures without specifying the specific conditions in the examples were carried out under the conventional conditions such as those described in the literature, in books, or as recommended by the manufacturer.

Example 1

1. Preparation of Kaolin slurry

(1) Preparation of saline solution

Mixing water and 0.8 wt% of sodium polycarboxylate based on the kaolin powder, and mechanically stirring for 1.5h to obtain the sodium polycarboxylate solution.

(2) Preparation of kaolin slurry

Gradually adding kaolin powder with the median particle size of 5-15 mu m into the prepared saline solution under mechanical stirring to obtain a mixed solution of the kaolin powder accounting for 55 wt%, and stirring for 6 hours to obtain kaolin slurry. The kaolin slurry was analyzed by particle size measurement using a laser particle sizer (Mastersizer 3000, Malvern Panalytical, uk) and the results are shown in figure 1.

2. Preparation of modified nano kaolin slurry

(1) The kaolin slurry was added to a high energy ball mill (Superflow 12, Buhler, Switzerland) in one portion, while adding 99% pure zirconia beads having a diameter of 0.5mm, stearic acid in an amount of 1.5% by weight based on the mass of the kaolin powder, and 0.8% by weight of sodium polycarboxylate to obtain a mixed slurry.

(2) Grinding the mixed slurry in a high-energy ball mill at the speed of 1000RPM for 3h, adding gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane (KH560) accounting for 0.40 wt% of the mass of the kaolin powder, and grinding for 1h to obtain modified nano kaolin slurry A. The particle size analysis of the modified nano kaolin slurry a is shown in fig. 1.

(3) Adding water to dilute the modified nano kaolin slurry A to 40% of kaolin volume based on the total mass of the slurry, adding gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane (KH560) accounting for 0.40 wt% of the mass of the kaolin powder, stirring for 40min at 5500RPM in a high-speed friction stirrer (model: SDF-400), and performing secondary coating modification to obtain modified nano kaolin slurry B.

3. Preparation of bulk kaolin blocks

(1) And adding a composite foaming agent into the modified nano kaolin slurry B, wherein the composite foaming agent is formed by mixing 1.0 wt% of fatty alcohol-polyoxyethylene ether sodium sulfate and 1.0 wt% of gamma-aminopropyltriethoxysilane (KH550) in terms of the mass of the kaolin powder, and stirring in a high-speed stirrer at the speed of 4000RPM for fine foaming treatment.

(2) And adding the slurry subjected to the fine foaming treatment into a constant-temperature air box for 6 hours, performing further thermal foaming treatment at 160 ℃, and drying to obtain loose kaolin blocks.

4. Preparation of nano kaolin powder

Dispersing loose kaolin blocks by a high-speed dispersion machine (model: RT-N04) at 7000RPM for 3 times (10 s each time with 1-2 min interval) for 30s to obtain nanometer kaolin powder. The form of the nano kaolin powder obtained by scanning electron microscopy is shown in fig. 2 (b).

5. Determination of nano kaolin powder dispersion rate and activation index

The dispersion rate of the prepared nano kaolin powder was measured by a dispersion rate characterization method, and the activation index of the prepared nano kaolin powder was measured according to the definition of the activation index, and the results are shown in table 1.

Example 2

1. Preparation of Kaolin slurry

(1) Preparation of saline solution

Mixing water and 0.5 wt% of sodium polycarboxylate based on the kaolin powder, and mechanically stirring for 1h to obtain the sodium polycarboxylate solution.

(2) Preparation of kaolin slurry

Gradually adding kaolin powder with the median particle size of 5-15 mu m into the prepared saline solution under mechanical stirring to obtain a mixed solution of 60 wt% of the kaolin powder, and stirring for 8 hours to obtain kaolin slurry.

2. Preparation of modified nano kaolin slurry

(1) The kaolin slurry was added to a high energy ball mill (Superflow 12, Buhler, Switzerland) in one portion, while adding 99% pure zirconia beads having a diameter of 0.5mm, stearic acid in an amount of 1.0 wt% based on the mass of the kaolin powder, and 0.5 wt% of sodium polycarboxylate to obtain a mixed slurry.

(2) Grinding the mixed slurry in a high-energy ball mill at the speed of 1000RPM for 2.5h, adding gamma- (2, 3-epoxy propoxy) propyl trimethoxy silane (KH560) accounting for 0.50 wt% of the mass of the kaolin powder, and grinding for 1h to obtain modified nano kaolin slurry A.

(3) Adding water to dilute the modified nano kaolin slurry A to 30% of kaolin volume based on the total mass of the slurry, adding gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane (KH560) accounting for 0.50 wt% of the mass of the kaolin powder, stirring for 30min at 5000RPM in a high-speed friction stirrer (model: SDF-400), and performing secondary coating modification to obtain modified nano kaolin slurry B.

3. Preparation of bulk kaolin blocks

(1) And adding a composite foaming agent into the modified nano kaolin slurry B, wherein the composite foaming agent is formed by mixing 0.5 wt% of fatty alcohol-polyoxyethylene ether sodium sulfate and 1.0 wt% of gamma-aminopropyltriethoxysilane (KH550) in the mass of the kaolin powder, and stirring in a high-speed stirrer at the speed of 5000RPM for fine foaming treatment.

(2) And adding the slurry subjected to the fine foaming treatment into a constant-temperature air box for 8h, performing further thermal foaming treatment at 150 ℃, and drying to obtain loose kaolin blocks.

4. Preparation of nano kaolin powder

Dispersing loose kaolin blocks by a high-speed dispersion machine (model: RT-N04) at 6000RPM for 3 times (10 s each time with 1-2 min interval) for 30s to obtain nano kaolin powder. The form of the nano kaolin powder obtained by scanning electron microscopy is shown in fig. 2 (c).

5. Determination of nano kaolin powder dispersion rate and activation index

Example 3

1. Preparation of Kaolin slurry

(1) Preparation of saline solution

Mixing water and 1.0 wt% of sodium polycarboxylate based on the weight of kaolin powder, and mechanically stirring for 2 hours to obtain a sodium polycarboxylate solution.

(2) Preparation of kaolin slurry

Gradually adding kaolin powder with the median particle size of 5-15 mu m into the prepared saline solution under mechanical stirring to obtain a mixed solution of the kaolin powder accounting for 65 wt%, and stirring for 8 hours to obtain kaolin slurry.

2. Preparation of modified nano kaolin slurry

(1) The kaolin slurry was added to a high energy ball mill (Superflow 12, Buhler, Switzerland) in one portion, while adding 99% pure zirconia beads having a diameter of 0.5mm, stearic acid in an amount of 1.5 wt% based on the mass of the kaolin powder, and 1.0 wt% of sodium polycarboxylate to obtain a mixed slurry.

(2) Grinding the mixed slurry in a high-energy ball mill at 1200RPM for 4h, adding gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane (KH560) accounting for 1.0 wt% of the mass of the kaolin powder, and grinding for 1h to obtain modified nano kaolin slurry A.

(3) Adding water to dilute the modified nano kaolin slurry A to a state that the volume of the kaolin accounts for 35% of the total mass of the slurry, then adding gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane (KH560) accounting for 0.50 wt% of the mass of the kaolin powder, stirring for 60min at the speed of 7000RPM in a high-speed friction stirrer (model: SDF-400), and carrying out secondary coating modification to obtain a modified nano kaolin slurry B.

3. Preparation of bulk kaolin blocks

(1) And adding a composite foaming agent into the modified nano kaolin slurry B, wherein the composite foaming agent is formed by mixing 0.5 wt% of fatty alcohol-polyoxyethylene ether sodium sulfate and 1.5 wt% of gamma-aminopropyltriethoxysilane (KH550) in the mass of the kaolin powder, and stirring in a high-speed stirrer at the speed of 5000RPM for fine foaming treatment.

(2) And adding the slurry subjected to the fine foaming treatment into a constant-temperature air box for 7h, performing further thermal foaming treatment at 170 ℃, and drying to obtain loose kaolin blocks.

4. Preparation of nano kaolin powder

Dispersing loose kaolin blocks by a high-speed dispersion machine (model: RT-N04) at 6000RPM for 3 times (10 s each time with 1-2 min interval) for 30s to obtain nano kaolin powder. The form of the nano kaolin powder obtained by scanning electron microscopy is shown in fig. 2 (d).

5. Determination of nano kaolin powder dispersion rate and activation index

Comparative example 1

This comparative example was substantially the same as example 1 except that the modified nano kaolin slurry B obtained in step 2 was directly subjected to drying treatment and dispersion without being subjected to fine foaming treatment. The form of the nano kaolin powder obtained by scanning electron microscopy is shown in fig. 2 (a). The dispersion ratio and activation index of the prepared kaolin powder are shown in table 1.

Comparative example 2

This comparative example was substantially the same as example 1 except that no fine foaming treatment was performed in step 3 of this comparative example, and modified nano kaolin slurry B was dried by a spray drying method. The form of the nano kaolin powder obtained by scanning electron microscopy is shown in fig. 2 (c). The dispersion ratio and activation index of the prepared kaolin powder are shown in table 1.

Comparative example 3

This comparative example was substantially the same as example 1 except that the fine foaming treatment was not performed in step 3 of this comparative example, and the modified nano kaolin slurry B was dried by azeotropic distillation. The form of the nano kaolin powder obtained by scanning electron microscopy is shown in fig. 2 (d). The dispersion ratio and activation index of the prepared kaolin powder are shown in table 1.

Analysis of results

In FIG. 1, "Kaolin raw powder" represents Kaolin particles that have not been subjected to high energy ball milling, and "Kaolin nano-powder" represents Kaolin particles that have been subjected to high energy ball milling. From the results shown in fig. 1, it is understood that the kaolin particles subjected to high energy ball milling have a substantially uniform particle size distribution of 0.2 μm or less, indicating that the high energy ball milling can effectively promote the nanocrystallization of the kaolin particles.

The scanning electron microscope results of the nano kaolin powder according to fig. 2 show that the kaolin particles of comparative example 1, which were directly dried without fine foaming treatment (fig. 2(a)), had large lumpy agglomerates, poor dispersion uniformity, and a maximum agglomerate diameter of about 7 μm. In this dry state, the agglomerates are hardly pulverized into a fine powder because hard agglomeration of the powder has occurred.

The results of the examples (fig. 2(b) to (d)) show that a large number of fine clusters of nanoparticles of uniform size are present, but no agglomerates of excessively large particles are present, and the diameter of the sheet-like agglomerates is 0.5 μm to 2 μm. The actual size of the dried kaolin nanopowder should be much smaller than would be seen from the loose appearance of each cluster. The finely foamed and dried sample was good in dispersibility and uniformity, similar to the sample obtained by the azeotropic distillation method in comparative example 3 (FIG. 2 (f)). Both of them present uniformly dispersed lamellar structure nano particle clusters, and because kaolin nano particles have strong surface tension in air and electrostatic effect, a large amount of kaolin nano particles are pseudoaggregated to form clusters. The thickness of each lamellar structure is ultra-thin on the nanometer scale. The sheet structure of the azeotropic distillation sample is thin, and the uniformity of the finely foamed sample is more excellent. The results of comparative example 2 (FIG. 2(e)) show that the spray-dried sample shows a large number of spherical hard agglomerates having a diameter of 1 μm to 6 μm and is inferior in dispersibility and uniformity.

TABLE 1

According to the results in table 1, the dispersion rate and the activation index of the nano kaolin powder prepared by the method are far higher than those of the nano kaolin powder which is not subjected to fine foaming treatment and the nano kaolin powder which is subjected to spray drying treatment, the excellent performance similar to that of the nano kaolin powder prepared by the azeotropic distillation method can be achieved, the preparation process is simpler, and the cost is lower.

The kaolin powder prepared by the invention reaches the nanometer level, has excellent performance, skillfully solves the problem of serious hard agglomeration of the nanometer powder dried from slurry, has good powder uniformity and dispersibility, high activation index and wide application, greatly improves the performance of the composite material as the nanometer reinforced filler, and has wide application prospect.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. It should be understood that the technical solutions obtained by logical analysis, reasoning or limited experiments based on the technical solutions provided by the present invention are all within the protection scope of the appended claims of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims, and the description and the drawings can be used for explaining the contents of the claims.

Claims

1. The preparation method of the nano kaolin powder is characterized by comprising the following steps:

and (3) scattering the kaolin blocks to obtain nano kaolin powder.

2. The preparation method according to claim 1, wherein the fine foaming treatment comprises adding a foaming agent into the surface-coated and modified nano kaolin slurry and stirring.

3. The method of claim 2, wherein the foaming agent comprises sodium fatty alcohol-polyoxyethylene ether sulfate and gamma-aminopropyltriethoxysilane.

4. The method for producing according to claim 1, wherein the step of drying treatment includes a thermal drying treatment.

5. The preparation method according to any one of claims 1 to 4, further comprising the following steps of preparing the surface-coating-modified nano kaolin slurry:

after the first mixed slurry is primarily ground, adding a modifier for secondary grinding to obtain nano kaolin slurry; and

diluting the nano kaolin slurry by using a first process control agent, adding the modifier again, and mixing to obtain the surface-coated modified nano kaolin slurry;

the grinding aid comprises stearic acid, the first dispersing agent comprises at least one of sodium polycarboxylate, sodium tripolyphosphate, sodium hexametaphosphate, sodium silicate, sodium polyacrylate and sodium acryloyl, the modifier comprises a titanate coupling agent, a silane coupling agent or an aluminate coupling agent, and the first process control agent comprises water.

6. The preparation method according to claim 5, wherein the grinding aid accounts for 1 wt% to 2 wt% of the kaolin powder in the kaolin slurry, the first dispersant accounts for 0.5 wt% to 1.0 wt% of the kaolin powder, the modifier accounts for 0.3 wt% to 1.0 wt% of the kaolin powder, and the nano kaolin slurry diluted by the first process control agent has a solid content of 30 wt% to 50 wt%.

7. The method according to claim 5, wherein the grinding is performed in a high energy ball mill at a rotation speed of 800RPM to 1200RPM, and the primary grinding time is 2h to 4h and the secondary grinding time is 1h to 2 h.

8. The method according to claim 6 or 7, further comprising the step of preparing the kaolin slurry by:

mixing the second dispersant and the second process control agent to obtain a brine solution; and

adding kaolin powder into the saline solution under stirring to obtain a second mixed slurry, and stirring to obtain the kaolin slurry;

the second dispersing agent comprises at least one of sodium polycarboxylate, sodium tripolyphosphate, sodium hexametaphosphate, sodium silicate, sodium polyacrylat and sodium acryloyl, the second process control agent comprises water, and the median particle size of the kaolin powder is 5-15 μm.

9. The method according to claim 8, wherein the second dispersant accounts for 0.5 wt% to 1.0 wt% of the kaolin powder, and the kaolin powder accounts for 50 wt% to 65 wt% of the second mixed slurry.

10. A nano kaolin powder, characterized by being prepared by the preparation method according to any one of claims 1 to 9.