Method for improving SiO2 compactness, dense SiO2 particles and application thereof

Abstract

The invention discloses a method for improving SiO2 compactness, dense SiO2 particles and application thereof, and relates to the technical field of inorganic materials, the method for improving SiO2 compactness comprises the following steps: dispersing nano SiO2 in a continuous phase, reducing the temperature to crystallize the continuous phase, and removing the crystallized continuous phase to obtain the dense SiO2 particles; according to the invention, the problems of small particle size, large specific surface area and macroscopic loose state of nano SiO2 are solved, the application field of nano SiO2 is expanded, and spherical SiO2 can be obtained or quartz products can be manufactured by further treating dense SiO2 particles.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic materials, and in particular to a method for improving the compactness of SiO2, compact SiO2 particles and applications thereof. Background Art

[0002] Nano-SiO2 is an inorganic chemical material, commonly known as white carbon black. Because it is ultra-fine nano-scale, with a size range of 1 to 100nm, it has many unique properties, such as optical properties against ultraviolet rays, and can improve the anti-aging, strength and chemical resistance of other materials, etc. It has a wide range of uses.

[0003] The preparation methods of nano-SiO2 are mainly chemical methods, including chemical vapor deposition, liquid phase method, ion exchange method, precipitation method and sol-gel method, but the main production methods are still the gas phase method with silicon tetrachloride as raw material, the precipitation method with sodium silicate and inorganic acid as raw materials, and the sol-gel method with silicic acid vinegar as raw materials. The nano-SiO2 prepared by chemical method has high purity and uniform particle size distribution. However, due to its small particle size, large specific surface area, and macroscopic loose shape (bulk density is generally about 50g / L), nano-SiO2 is currently mostly used as filler, and it is difficult to convert nano-SiO2 into high-purity and dense SiO2 products. Summary of the invention

[0004] In order to solve the problems of small particle size, large specific surface area and loose macroscopic appearance of nano-SiO2, the present invention provides a method for improving the density of SiO2. The obtained dense SiO2 particles can be further processed to obtain spherical SiO2 or manufacture quartz products.

[0005] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0006] One of the purposes of the present invention is to provide a method for improving the density of SiO2, dispersing amorphous SiO2 in a continuous phase, lowering the temperature to crystallize the continuous phase, removing the crystallized continuous phase, and obtaining dense SiO2 particles.

[0007] In the present invention, the purpose of lowering the temperature is to crystallize the continuous phase. Since the continuous phase is incompatible with SiO2, the continuous phase will repel and squeeze SiO2 during the crystallization process, causing SiO2 to softly agglomerate to form larger SiO2 particles. The SiO2 particles become dense after being squeezed by the continuous phase.

[0008] A second object of the present invention is to provide a dense SiO2 particle obtained by the aforementioned method for improving the density of SiO2.

[0009] The third object of the present invention is to provide the application of the aforementioned dense SiO2 particles in the processing of spherical SiO2 and quartz products.

[0010] The beneficial effects of the present invention are as follows: the present invention solves the problems of small particle size, large specific surface area and loose macroscopic appearance of nano-SiO2, expands the application field of nano-SiO2, and can obtain spherical SiO2 or manufacture quartz products by further processing dense SiO2 particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 XRD pattern of dense amorphous SiO2 particles prepared in Example 1;

[0012] Figure 2 This is the XRD pattern of the crystalline SiO2 particles prepared in Comparative Example 1. DETAILED DESCRIPTION

[0013] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments and diagrams.

[0014] The present invention provides a method for improving the density of SiO2, which comprises dispersing amorphous SiO2 in a continuous phase, lowering the temperature to crystallize the continuous phase, removing the crystallized continuous phase, and obtaining dense SiO2 particles.

[0015] In the present invention, in order to improve the density of SiO2 particles, the following steps are performed at least once: dispersing amorphous SiO2 in a continuous phase, lowering the temperature to crystallize the continuous phase, and removing the crystallized continuous phase.

[0016] In the present invention, the amorphous SiO2 is nanoscale or microscale amorphous SiO2.

[0017] In the present invention, the continuous phase includes but is not limited to one of crystallizable substances such as low melting point molten salt, epoxy resin, paraffin, etc.

[0018] Furthermore, the melting point of the low-melting-point molten salt is lower than 400°C.

[0019] Furthermore, the low melting point molten salt includes but is not limited to at least one of potassium nitrate, sodium nitrate, calcium nitrate, sodium nitrite, potassium chloride, sodium chloride, and zinc chloride.

[0020] Furthermore, the dosage ratio of the amorphous SiO2 to the continuous phase is 0.2kg:(2-10)L, and the dosage of the continuous phase is measured based on its flow state.

[0021] The present invention provides a dense SiO2 particle obtained by the aforementioned method for improving the density of SiO2.

[0022] Furthermore, the dense SiO2 particles are in an amorphous state.

[0023] The present invention also provides the application of the aforementioned dense SiO2 particles in the processing of spherical SiO2 and quartz products.

[0024] Example 1

[0025] Add 0.2 kg of amorphous SiO2 with an average particle size of 20 nm into 5 L of molten salt (53 wt% potassium nitrate, 40 wt% sodium nitrite, 7 wt% sodium nitrate) at 180°C and mix evenly. Allow the mixture to cool to room temperature naturally. Dissolve the obtained solid in water, filter, wash, dry and break it up to obtain dense amorphous SiO2 particles.

[0026] Example 2

[0027] Add 0.2 kg of amorphous SiO2 with an average particle size of 30 nm into 5 L of molten salt (70 wt% calcium nitrate, 30 wt% sodium nitrate) at 240°C and mix evenly. Let the temperature naturally cool to room temperature. Dissolve the obtained solid in water, filter, wash, dry and break it up to obtain dense amorphous SiO2 particles.

[0028] Example 3

[0029] Add 0.2 kg of amorphous SiO2 with an average particle size of 100 nm into 5 L of molten salt (zinc chloride) at 190°C and mix evenly. Cool the mixture to room temperature naturally. Dissolve the obtained solid in water, filter, wash, dry and break it up to obtain dense amorphous SiO2 particles.

[0030] Example 4

[0031] Add 0.2 kg of amorphous SiO2 with an average particle size of 20 nm into 5 L of molten salt (sodium nitrate) at 320°C and mix evenly. Cool the mixture to room temperature naturally. Dissolve the obtained solid in water, filter, wash, dry and break it up to obtain dense amorphous SiO2 particles.

[0032] Example 5

[0033] Add 0.2 kg of amorphous SiO2 with an average particle size of 20 nm into 5 L of epoxy resin (type E-51) and mix evenly. The resulting mixture is cooled from room temperature to 0°C to allow the epoxy resin to crystallize. The crystallized epoxy resin is heated to 60°C and filtered. The filter residue is washed, dried and broken up with acetone to obtain dense amorphous SiO2 particles.

[0034] Example 6

[0035] Add 0.2 kg of amorphous SiO2 with an average particle size of 20 nm into 5 L of epoxy resin (type E-51) and mix evenly. The resulting mixture is cooled from room temperature to 0°C to allow the epoxy resin to crystallize. Repeat the crystallization four times. The crystallized epoxy resin is heated to 60°C and filtered. The filter residue is washed with acetone, dried, and broken up to obtain dense amorphous SiO2 particles.

[0036] Example 7

[0037] Add 0.2 kg of amorphous SiO2 with an average particle size of 5 nm into 5 L of paraffin (58#) at 80°C and mix evenly. The resulting mixture is naturally cooled to room temperature to allow the paraffin to crystallize. The crystallized paraffin is dissolved in gasoline, filtered, and the residue is dried and broken up to obtain dense amorphous SiO2 particles.

[0038] Example 8

[0039] 0.2 kg of amorphous SiO2 with an average particle size of 100 nm was added to 5 L of molten salt (zinc chloride) at 190°C and mixed evenly, and then cooled to room temperature naturally. The obtained solid was dissolved in water, filtered, washed, dried, and broken up to obtain dense amorphous SiO2 particles.

[0040] Example 9

[0041] Add 0.2 kg of amorphous SiO2 with an average particle size of 20 nm into 2 L of molten salt (53 wt% potassium nitrate, 40 wt% sodium nitrite, 7 wt% sodium nitrate) at 180°C and mix evenly. Allow the mixture to cool to room temperature naturally. Dissolve the obtained solid in water, filter, wash, dry and break it up to obtain dense amorphous SiO2 particles.

[0042] Example 10

[0043] Add 0.2 kg of amorphous SiO2 with an average particle size of 20 nm into 10 L of molten salt (53 wt% potassium nitrate, 40 wt% sodium nitrite, 7 wt% sodium nitrate) at 180°C and mix evenly. Allow the temperature to cool naturally to room temperature. Dissolve the obtained solid in water, filter, wash, dry, and break it up to obtain dense amorphous SiO2 particles.

[0044] Embodiment 11

[0045] Add 0.2 kg of amorphous SiO2 with an average particle size of 1 μm into 5 L of molten salt (53 wt% potassium nitrate, 40 wt% sodium nitrite, 7 wt% sodium nitrate) at 180°C and mix evenly. Allow the mixture to cool to room temperature naturally. Dissolve the obtained solid in water, filter, wash, dry and break it up to obtain dense amorphous SiO2 particles.

[0046] Comparative Example 1

[0047] The method of Example 1 is followed, except that a high melting point molten salt is used.

[0048] Add 0.2 kg of amorphous SiO2 with an average particle size of 20 nm into 5 L of molten salt (sodium nitrate) at 550°C and mix evenly. Cool the mixture to room temperature naturally. Dissolve the obtained solid in water, filter, wash, dry and break it up to obtain loose crystalline SiO2 particles.

[0049] Comparative Example 2

[0050] The method of Example 1 is followed, except that the amount of amorphous SiO2 is adjusted.

[0051] 1 kg of amorphous SiO2 with an average particle size of 20 nm is added to 5L of molten salt (53wt% potassium nitrate, 40wt% sodium nitrite, 7wt% sodium nitrate) at a temperature of 180°C and mixed. Due to the small proportion of molten salt, it is difficult to disperse amorphous SiO2 in the molten salt.

[0052] Depend on Figure 1 and Figure 2 It can be seen that Example 1 prepares amorphous SiO2 particles, while Comparative Example 1 prepares crystalline SiO2 particles.

[0053] The particle size, bulk density, specific surface area and crystal form of the SiO2 particles prepared in the above examples and comparative examples were tested. The results are shown in Table 1.

[0054] Bulk density test is based on GB / T5162-2006;

[0055] The specific surface area test is based on GB / T19587-2017.

[0056] Table 1

[0057]

[0058]

[0059] From Table 1 we can see that:

[0060] Compared with natural quartz sand, Examples 1 to 11 obtained dense amorphous SiO2 particles with a D50 particle size of 36 to 43 μm and a bulk density of 0.46 to 0.53 g / cm 3 , with a specific surface area of ​​11.2 to 21.3 m 2 / g. In particular, Example 11 uses micron-sized amorphous SiO2 as the raw material. As the raw material particle size increases, the surface energy of the SiO2 particles decreases, and the bonding between the SiO2 particles becomes slightly difficult. Therefore, the particle size of the SiO2 particles obtained after compression is relatively smaller.

[0061] It can be seen from Examples 5 and 6 that increasing the number of crystallizations increases the packing density, improves the compactness between particles, and decreases the specific surface area.

[0062] Compared with Example 1, Comparative Example 1 uses a high-melting-point molten salt, and the obtained SiO2 particles have a very small particle size, resulting in a smaller packing density and a larger specific surface area. The possible reason is that due to the high temperature of the molten salt, the nano-SiO2 changes from an amorphous state to a crystalline state, and the surface polarity of the nano-SiO2 decreases, resulting in a decrease in binding force, making it difficult to form large, dense agglomerates.

[0063] Application Example 1

[0064] The SiO2 particles prepared in the above embodiments and comparative examples were sintered (the flame temperature of the spheroidizing furnace was 2600°C) to prepare spherical SiO2, and the particle size, specific surface area, sphericity and porosity were tested. The results are shown in Table 2.

[0065] Specific surface area test is based on GB / T19587-2017;

[0066] Sphericity test is based on GB / T 32661;

[0067] The porosity test is based on GB / T19587-2017.

[0068] Table 2

[0069]

[0070] Application Example 2

[0071] The SiO2 particles prepared in the above examples and comparative examples were calcined (calcination temperature was 1400°C, calcination time was 6 h) to prepare high-purity quartz sand, and the specific gravity of the calcined product was tested. The results are shown in Table 3.

[0072] The specific gravity was tested using the Archimedes drainage method.

[0073] Table 3

[0074] proportion Example 1 2.18 Example 2 2.13 Example 3 2.17 Example 4 2.15 Example 5 2.19 Example 6 2.21 Example 7 2.17 Example 8 2.15 Example 9 2.17 Example 10 2.19 Embodiment 11 2.18 Comparative Example 1 2.16 Natural quartz sand 2.20

[0075] It can be seen from Table 2 and Table 3 that the amorphous SiO2 particles prepared in Examples 1 to 10 can be used for processing spherical silicon oxide and quartz sand.

[0076] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for improving the compactness of SiO2, characterized in that: Amorphous SiO2 is dispersed in the continuous phase, the temperature is lowered to crystallize the continuous phase, and the crystallized continuous phase is removed to obtain dense SiO2 particles.

2. The method for improving the compactness of SiO2 according to claim 1, characterized in that: The following steps are performed at least once: dispersing amorphous SiO2 in a continuous phase, lowering the temperature to crystallize the continuous phase, and removing the crystallized continuous phase.

3. The method for improving the compactness of SiO2 according to claim 1 or 2, characterized in that: The amorphous SiO2 is nanometer-scale or micrometer-scale amorphous SiO2.

4. The method for improving the compactness of SiO2 according to claim 1 or 2, characterized in that: The continuous phase is one of low melting point molten salt, epoxy resin and paraffin.

5. The method for improving the compactness of SiO2 according to claim 4, characterized in that: The melting point of the low-melting-point molten salt is lower than 400°C.

6. The method for improving the compactness of SiO2 according to claim 5, characterized in that: The low melting point molten salt is at least one of potassium nitrate, sodium nitrate, calcium nitrate, sodium nitrite, potassium chloride, sodium chloride and zinc chloride.

7. The method for improving the compactness of SiO2 according to claim 1 or 2, characterized in that: The dosage ratio of the amorphous SiO2 to the continuous phase is 0.2kg:(2-10)L, and the dosage of the continuous phase is calculated based on its flow state.

8. Dense SiO2 particles obtained by the method for improving the density of SiO2 as described in any one of claims 1 to 7.

9. The dense SiO2 particles according to claim 8, characterized in that: The dense SiO2 particles are in an amorphous state.

10. Use of the dense SiO2 particles according to claim 8 or 9 in the processing of spherical SiO2 and quartz products.

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