阅读说明：本技术 一种晶体纳米二氧化硅及其制备方法 (Crystalline nano silicon dioxide and preparation method thereof ) 是由 张治军 李小红 刘培松 高春浩 于 2020-06-12 设计创作，主要内容包括：本发明属于纳米材料技术领域,具体涉及一种晶体纳米二氧化硅及其制备方法。所述晶体纳米二氧化硅的制备方法,包括以下步骤：将硅源、碱和有机修饰剂按摩尔比为1:(0.05～0.2):(0.1～1)加入到反应介质中,在温度为260～380℃、压力为30～40 MPa下条件反应30～500 h,经后处理即得晶体纳米二氧化硅。本发明制备的纳米二氧化硅具有完整晶型结构且修饰有有机官能团,提高了其在有机介质中的分散性,可应用于电子封装材料、机械润滑、陶瓷等行业。(The invention belongs to the technical field of nano materials, and particularly relates to crystalline nano silicon dioxide and a preparation method thereof. The preparation method of the crystalline nano silicon dioxide comprises the following steps: adding a silicon source, an alkali and an organic modifier into a reaction medium according to a molar ratio of 1 (0.05-0.2) to (0.1-1), reacting for 30-500 hours at the temperature of 260-380 ℃ and the pressure of 30-40 MPa, and performing post-treatment to obtain the crystalline nano silicon dioxide. The nano silicon dioxide prepared by the invention has a complete crystal structure and is modified with organic functional groups, so that the dispersibility of the nano silicon dioxide in an organic medium is improved, and the nano silicon dioxide can be applied to industries such as electronic packaging materials, mechanical lubrication, ceramics and the like.)

1. A preparation method of crystalline nano-silica is characterized by adding a silicon source, alkali and an organic modifier into a reaction medium according to a molar ratio of 1 (0.05-0.2) to (0.1-1), reacting at 260-380 ℃ and 30-40 MPa for 30-500 h, and carrying out post-treatment to obtain the crystalline nano-silica.

2. The method of claim 1, wherein the silicon source is at least one of sodium silicate, sodium metasilicate, and silica sand.

3. The method of claim 1, wherein the base is at least one of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

4. The method of claim 1, wherein the organic modifier is an organosilicon compound.

5. The method for preparing crystalline nano-silica according to claim 4, wherein the organosilicon compound is an alkoxysilane, a chlorosilane, a nitrogen silane or a fluorosilane having a carbon chain length of 1 to 20.

6. The method of claim 1, wherein the reaction medium is water and/or an organic solvent, and the organic solvent is C₁-C₁₂At least one of alcohol, acetone and xylene.

7. The method for preparing crystalline nanosilica as claimed in claim 1, wherein the temperature is raised to 260-380 ℃ at a temperature raising rate of 5-30 ℃/h, and the post-treatment is washing and drying.

8. Crystalline nanosilica prepared by the process of any of claims 1 to 7.

Technical Field

The invention belongs to the technical field of nano materials, and particularly relates to crystalline nano silicon dioxide and a preparation method thereof.

Background

The crystalline silica has the advantages of hard texture, good wear resistance, stable chemical performance, high dielectric, low thermal expansion coefficient, good electrical insulation and ultraviolet resistance, and is widely applied to novel functional materials such as superplastic materials, insulating materials, electrode materials, superconducting materials and the like. The crystal silicon dioxide used in China at present is mainly imported, the particle size distribution of the product is wide, and the impurity content is high. At present, the crystalline silica is mainly prepared by a physical method, quartz is crushed into superfine quartz powder with a certain size by a mechanical method, and the crystalline silica with different size distributions is obtained by screening, but the crystalline silica prepared by the physical method has high cost, the size and the shape are difficult to control, and the purity is greatly influenced by raw materials.

The chemical method for preparing the crystalline silicon dioxide is reported only rarely, and mainly because the chemical method requires high temperature and high pressure in the growth process, the size of crystal particles is difficult to control in the preparation process, and the prepared product has poor dispersibility, serious agglomeration and large particle size, and is difficult to realize the efficient preparation of the crystal particles with the size below 500 nm. Chinese patent application No. CN201110360535.6 discloses a method for preparing monodisperse crystalline silica spherical particles through carbon coating, which comprises the steps of coating a layer of uniform carbon layer of 50-200 nm on monodisperse spherical nano-silica with the particle size of 5-20 mu m, then treating for 2-20 h at high temperature (800-1200 ℃) in nitrogen or argon atmosphere (tubular furnace), converting amorphous silica into crystalline silica, and then removing a surface coating layer. Although the method can obtain crystalline silica with different sizes, the product has the problems of incomplete crystal structure conversion, complex treatment process, large particle size and the like.

The invention utilizes a chemical surface modification method as an important means for controlling the size and the dispersibility of nano particles, can consume partial active silicon hydroxyl on the surface of nano silicon dioxide, reduce the surface activity and generate steric hindrance to prevent the agglomeration of particles, and can change the compatibility of the nano silicon dioxide and an organic medium. Therefore, it is of great importance to prepare crystalline silica by developing a method combining crystalline silica growth with in situ surface modification.

Disclosure of Invention

In order to overcome the problems in the prior art, the invention provides a preparation method of crystalline nano silicon dioxide. The silicon dioxide directionally grows into the nano silicon dioxide with a complete lattice structure through high-temperature high-pressure hydrothermal reaction, and the prepared crystal nano silicon dioxide has good dispersibility.

The invention also provides the crystalline nano-silica prepared by the method, and the crystalline nano-silica has good dispersibility and uniform and controllable size.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a preparation method of crystalline nano-silica comprises the steps of adding a silicon source, alkali and an organic modifier into a reaction medium according to a molar ratio of 1 (0.05-0.2) to (0.1-1), reacting for 30-500 hours at the temperature of 260-380 ℃ and the pressure of 30-40 MPa, and carrying out post-treatment to obtain the crystalline nano-silica.

Preferably, the silicon source is at least one of sodium silicate, sodium metasilicate and quartz sand.

Preferably, the alkali is at least one of sodium hydroxide, sodium carbonate and sodium bicarbonate.

Preferably, the organic modifier is an organosilicon compound.

Further preferably, the organosilicon compound is alkoxysilane, chlorosilane, azasilane or fluorosilane with a carbon chain length of 1-20, such as hexamethyldisilazane, diethoxydimethylsilane, aminopropyltriethoxysilane, hexadecyltrimethoxysilane, dimethyldiethoxysilane or tetrafluorosilane.

Preferably, the reaction medium is water and/or an organic solvent, and the organic solvent is C₁-C₁₂At least one of alcohol, acetone, xylene; c₁-C₁₂Alcohols such as methanol, ethanol, etc.

Preferably, the temperature is raised to 260-380 ℃ at the temperature raising rate of 5-30 ℃/h, and the post-treatment is washing and drying.

The crystal nano silicon dioxide is prepared by the method.

Compared with the prior art, the invention has the beneficial effects that:

1. the method takes sodium silicate, sodium metasilicate or quartz sand as a silicon source, adopts a one-step method to prepare surface-modified crystal nano silicon dioxide, takes the nano silicon dioxide with a complete crystal structure as a core, and modifies the surface with an organic modifier;

2. the method completes the growth and modification of the crystal nano-silicon dioxide in one step, thereby not only avoiding the problems of large particle size, poor dispersibility and the like of the crystal silicon dioxide prepared by a physical method, but also avoiding the problems of excessive temperature and the sintering of inert gas for converting to form crystals, greatly saving the production cost, being suitable for batch preparation, and avoiding the problems of incomplete crystal structure conversion and the like caused by insufficient sintering;

3. because the hydrolysate of the organic modifier contains active groups which can react with silicon hydroxyl groups of the silicon dioxide, the hydrolysate can be bonded on the surface of the silicon dioxide to prevent further growth of particles, thereby effectively controlling the size (less than 100 nm) of the crystal nano silicon dioxide and preventing agglomeration among the particles; meanwhile, the surface modifier can change the original polarity of the nano particles and improve the dispersion stability of the nano particles in an organic solvent.

Drawings

FIG. 1 is a graph of temperature and pressure during the preparation of crystalline nanosilica in example 1;

FIG. 2 is an XRD pattern of the crystalline nanosilica prepared in example 2;

FIG. 3 is a TEM photograph of the crystalline nano-silica prepared in example 3;

FIG. 4 is a photograph of the water contact angle of the crystalline nano-silica prepared in example 4;

fig. 5 is an XRD pattern of amorphous nano-silica prepared in comparative example 1.

Detailed Description

The invention is further illustrated, but not limited, by the following examples and the accompanying drawings.