CN111474084B - Characterization method for density of silicon dioxide particles in silica sol - Google Patents
Characterization method for density of silicon dioxide particles in silica sol Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
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- G01N15/088—Investigating volume, surface area, size or distribution of pores; Porosimetry
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- G01N2015/0866—Sorption
Abstract
The invention relates to the technical field of silica sol preparationThe patent refers to the field of 'investigating or analysing materials by determining their chemical or physical properties'. The characterization method comprises the following steps: a. the specific surface area S of the obtained silica particles was measured by a solution adsorption method using a methyl red solution as an adsorbent 1 (ii) a b. By using N 2 As the adsorbed gas, the specific surface area S of the silica particles was measured by the BET method 2 (ii) a c. By (S) 2 ‑S 1 )/S 2 The relative density d of the silica particles in the silica sol is obtained. The relative density d value obtained by the density characterization method can directly and visually reflect the characteristic information of colloidal silicon dioxide, such as the density of particle frameworks, the integrity of particles, the alkali resistance of particles and the like, and the method is simple to operate and low in cost, and provides an important basis for the performance characteristic evaluation of the colloidal silicon dioxide.
Description
Technical Field
The invention relates to the technical field of silica sol preparation, in particular to a method for characterizing the density of silicon dioxide particles in silica sol.
Background
The primary particle size of the silica particles in the silica sol is a very important parameter, and is usually calculated by the formula d =2727/S, which is a specific surface area of silica, and in contrast, the evaluation of the density of the silica particles in the silica sol is much less.
When the silica sol is applied to the polishing field, the density of the silica particles affects the polishing efficiency and the surface roughness, and also affects the stability under alkaline conditions. When silica sol is applied to an abrasive for precision polishing, higher particle density results in higher polishing rate while having good stability under alkaline conditions, but at the same time, there is a risk of scratching. The lower particle density will reduce the risk of scratching but will cause a reduction in the polishing rate and at the same time will also have a poor alkali resistance. The evaluation of the density is particularly important for polishing applications.
Although the density of the silica particles can be reflected by a true density test method, the true density index cannot completely reflect the characteristic information of the skeleton density, the particle integrity, the alkali resistance and the like of the silica in the silica sol. In the prior art, polydimethylsiloxane serving as an internal standard is added into a silica sol dry solid to obtain a sample, a solid 29Si-CP/MAS-NMR spectrum is determined on the sample, and the density of the particles is evaluated according to the peak area of colloidal silica/the peak area of polydimethylsiloxane, namely the density of the particles is evaluated by testing the relative amount of residual silanol groups. However, the method needs a solid nuclear magnetic resonance technology for measurement, so that the cost is high, the equipment retention amount is very small, and the method cannot be popularized and used.
Disclosure of Invention
The invention provides a method for characterizing the density of silica particles in silica sol, aiming at the problems that the existing method for characterizing the density of silica particles in silica sol can not completely reflect the characteristic information of the silica particles in silica sol, such as the density of particle frameworks, the integrity of particles, the alkali resistance of particles and the like, and the existing method for evaluating the density of silica particles in silica sol can not be popularized and used due to high equipment requirements and high measurement cost.
In order to achieve the purpose of the invention, the embodiment of the invention adopts the following technical scheme:
a characterization method of the density of silicon dioxide particles in silica sol is characterized in that: the method comprises the following steps:
a. taking silica particles obtained after drying silica sol, using methyl red solution as adsorbent, and measuring the specific surface area S of the silica particles by a solution adsorption method 1 ；
b. Taking another silicon dioxide particle obtained after drying the silica sol, and adopting N 2 The specific surface area S of the silica particles as an adsorbed gas was measured by the BET method 2 ；
c. By (S) 2 -S 1 )/S 2 The relative density d of the silicon dioxide particles is obtained, namely d = (S) 2 -S 1 )/S 2 。
The silica particles obtained after drying of the silica sol are different from ordinary silica. The main reasons for influencing the density of the silica particles in the silica sol are: the silica particles in the silica sol have not completely bonded silanol groups in addition to the surface silanol groups during particle growth, i.e., the silanol groups in the silica sol are not completely bonded to form a siloxane skeleton Si (OSi) 4 The smaller the number of silanol groups in the interior, the larger the silica particle skeletonThe higher the integrity, the higher the density of the silica particles. However, at present, no standard density characterization and measurement method capable of directly reflecting the integrity of the framework and the density degree of the framework of the silicon dioxide particles in the silica sol exists.
Compared with the prior art, the method for characterizing the compactness of the silica particles in the silica sol provided by the invention takes the methyl red solution as the adsorbent, the methyl red can be combined with the unbound silanol groups in the silica particles and can not be combined with other sites in the silica particles, the amount of methyl red molecules combined on the surfaces of the unbound silanol groups in the silica particles can be measured by the solution adsorption method, the surface area of the unbound silanol groups in the silica particles is obtained by the sectional area of the methyl red molecules, and the specific surface area S of the silica particles is calculated by the solution adsorption method 1 . By N 2 Adsorption method, measuring the specific surface area S of the obtained silica particles by the gas adsorption BET method 2 . With (S) 2 -S 1 )/S 2 The relative density d is less than 1, and the closer the relative density d is to 1, the higher the density of the silica particles in the silica sol is, the more complete the framework is and the better the alkali resistance is.
The obtained relative density value can directly and visually reflect the characteristic information of the silica in the silica sol, such as the density of particle skeletons, the integrity of particles, the alkali resistance of the particles and the like, and the method has the advantages of simple operation, high repeatability and accuracy, low requirement on equipment and low measurement cost, and provides an important basis for evaluating the performance characteristics of the silica sol.
Preferably, the drying method of the silica sol comprises the following steps: adding H-type cation exchange resin into silica sol, vacuum drying at 50-80 deg.C to obtain gel, grinding the gel until the particle fineness is less than or equal to 75 μm, and drying at 150-200 deg.C for 2-3H.
The addition of the H-type cation exchange resin can remove the surface adsorption and free alkali of the silica particles, further reduce the interference generated by the free alkali in the specific surface area measurement process, improve the accuracy of the detection result, and meanwhile, the addition of the H-type cation exchange resin does not influence the measured specific surface area value of the silica particles.
Preferably, the silica sol is a dispersion of nano-sized silica particles in water, or is obtained by hydrolytic condensation of an alkoxysilane.
Preferably, the amount of the H-type cation exchange resin added is such that the pH of the silica sol reaches 4 to 7.
Preferably, in step a, the ratio of the mass of methyl red in the methyl red solution to the mass of the silica particles is 0.025 to 0.075.
Preferably, in step a, the methyl red solution is a benzene solution of methyl red, and the concentration of the methyl red in the methyl red solution is 0.4-0.8g/L.
The silica particles are placed in the benzene solution of methyl red, so that the adsorption efficiency of the methyl red can be further improved, and the S content can be further improved 1 The accuracy of the value.
Preferably, in step a, the solution adsorption method comprises the following steps: placing the silicon dioxide particles in methyl red solution, carrying out methyl red adsorption under the condition of oscillation or ultrasound, separating the silicon dioxide particles from the solution after the adsorption is finished, and measuring the mass m of the methyl red in the residual methyl red solution 3 (ii) a The specific surface area S of the silica particles 1 ＝(m 1 -m 3 )×R 1 ×NA/(m 2 ×C 1 ) Wherein m is 1 Is the mass of methyl Red in the methyl Red solution, m 2 For the mass of the silica particles, R 1 Represents the cross-sectional area m of methyl red molecule 2 NA denotes the Avogastron constant, C 1 Represents methyl red molecular weight g/mol.
Preferably, the methyl red adsorption is carried out under the vibration or ultrasonic condition for 2-3h.
Preferably, the method for separating the silica particles from the solution is centrifugal separation, the centrifugal rotation speed is 2000-5000rpm, and the centrifugal time is 2-10min.
Preferably, in step b, the gas adsorption BET method comprises the following steps: subjecting the silica to a reactionDegassing the granules at 150-200 deg.C for 2-3 hr, and placing in liquid nitrogen for N 2 Adsorption at a relative pressure p/p 0 Measuring the particle size in the range of 0.05-0.2 to obtain a BET curve, and determining the intercept a and the slope b of the BET curve, wherein each gram of the monomolecular layer N of the silicon dioxide particles 2 Mass of adsorption W m = 1/(a + b); the specific surface area S of the silica particles 2 ＝R 2 ×NA×W m /C 2 Wherein R is 2 Representing N in liquid nitrogen 2 Cross sectional area m of molecule 2 NA denotes the Avgalois constant, C 2 Represents N 2 Molecular weight g/mol of (1).
Drawings
FIG. 1 is a graph of methyl red concentration versus absorbance value as a standard curve in example 1 of the present invention;
FIG. 2 shows the result of the experiment 1 of the present invention passing through N 2 BET profile of the silica particles obtained by adsorption;
FIG. 3 shows a graph of the present invention by N in example 2 2 BET profile of the silica particles obtained by adsorption.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
Example 1
A method for characterizing the density of silica particles in a silica sol, comprising the steps of:
taking 100g of silica sol prepared by an alkoxy silane method, wherein the mass content of silica particles is 20%, adding H-type cation exchange resin to remove alkali adsorbed and dissociated on the surfaces of the silica particles to enable the pH value of the silica sol to reach 4, then placing the silica sol in a vacuum drying oven at 50-80 ℃ to dry to obtain gel, crushing the obtained gel by using a mortar, drying at 150 ℃ for 3H, cooling to obtain a dried silica particle sample, and placing the dried silica particle sample in a dryer to be stored for later use.
0.15g of dried methyl red reference reagent was accurately weighed using a precision balance and dissolved in an analytically pure benzene solvent to prepare 250ml of a 0.6g/L methyl red benzene solution. Taking out a part of the methyl red benzene solution to dilute by 60 times, 100 times and 150 times respectively to obtain the methyl red benzene standard solutions with the concentrations of 0.0100g/L,0.0060g/L and 0.0040 g/L. Adjusting the wavelength of an ultraviolet-visible spectrophotometer of Shanghaineae model number 752G to 430nm, respectively obtaining absorbance values of three methyl red concentrations under the condition of using a benzene solvent as a blank control solution, and drawing a standard curve according to the methyl red concentration-absorbance values, as shown in FIG. 1.
Accurately weighing 0.2106g of silicon dioxide particle sample dried in a dryer, placing the silicon dioxide particle sample into a 100ml triangular flask with a plug, adding 50ml of methyl red benzene solution with the concentration of 0.6g/L, carrying out ultrasonic treatment in a Kunshan adhesive KH-100B ultrasonic cleaner for 2h, taking 10ml of methyl red benzene solution out of the triangular flask into a centrifuge tube, centrifuging the methyl red benzene solution in a large high-speed centrifuge TGL-16 in Jiangsu at the speed of 2000rpm for 10min, separating the silicon dioxide particle sample in the solution, taking 5ml of the rest solution out of the centrifuge tube by using a pipette, and diluting by 10 times to obtain the methyl red benzene solution to be measured. And (3) respectively taking three samples of the methyl red benzene solution to be detected to test the absorbance A of the methyl red benzene solution to be detected, obtaining the concentration of the methyl red benzene solution to be detected through a methyl red concentration-absorbance value standard curve, taking the average value of the three concentrations, and multiplying the average value by 10 times to obtain the methyl red concentration of 0.5355g/L in the methyl red benzene solution after adsorption. According to S 1 ＝(m 1 -m 3 )×R 1 ×NA/(m 2 ×C 1 ) Wherein m is 1 Represents the mass g, m of the original methyl red in the methyl red benzene solution to be measured 2 Represents the mass g, m of the silica particle sample 3 Represents the mass g, R of methyl red in the methyl red benzene solution after adsorption 1 Represents the cross-sectional area m of methyl red molecule 2 NA denotes the Avogastron constant, C 1 Denotes methyl Red molecular weight g/mol, S 1 ＝(0.6-0.5355)×0.05×(116×10 -20 )×(6.022×10 23 ) /(0.2106X 269.30), specific surface area S of the silica particle sample 1 ＝39.697m 2 /g。
Loading clean empty sample tube in Kangta NOVAtouch, degassing in a degassing station in vacuum for 5min, backfilling helium after degassing is finished, unloading the sample tube, immediately covering a rubber plug, and weighing the total mass of the empty sample tube and the rubber plug by using a precision balance. Taking 0.5g of a dried silica particle sample from the dryer, putting the dried silica particle sample into a weighed sample tube, putting the sample tube back to a degassing station, degassing at 150 ℃ for 3h, cooling the sample tube to room temperature, backfilling helium, quickly covering a rubber stopper, weighing, and subtracting the gross weight of the sample tube to obtain the silica particles with the mass of 0.512g. Placing the sample tube at the temperature of 77.35K and introducing N 2 At a relative pressure p/p 0 Selecting the corresponding measured values of 4 points in the range of 0.05-0.2 to obtain a BET curve as shown in FIG. 2, and obtaining the intercept a =0.498343, the slope b =47.5767, the correlation coefficient r =0.999981 of the curve, N 2 Mass of adsorption W m = 1/(a + b), and the specific surface area S of the silica particle sample 2 ＝R 2 ×NA×W m /C 2 Wherein R is 2 Representing N in liquid nitrogen 2 Cross sectional area m of molecule 2 NA denotes the Avgalois constant, C 2 Represents N 2 Molecular weight g/mol, W of m Represents N 2 Adsorption mass g. Namely S 2 ＝(0.162×10 -18 )×(6.022×10 23 )/(28.013×(47.5767+0.498343))＝59.966m 2 /g。
The relative density d = (S) of the silica particles in the silica sol is obtained 2 -S 1 )/S 2 ＝0.338。
Example 2
A method for characterising the density of silica particles in a silica sol comprising the steps of:
taking 100g of silica sol prepared by an alkoxy silane method, wherein the mass content of silica is 30%, adding H-type cation exchange resin to remove alkali adsorbed and dissociated on the surfaces of silica particles to enable the pH value of the silica sol to reach 5, then placing the silica sol in a vacuum drying oven at 60 ℃ for drying for 2 hours to obtain gel, crushing the obtained gel by using a mortar, drying for 2 hours at 180 ℃, cooling to obtain a dried silica particle sample, and placing the dried silica particle sample in a dryer for storage and standby.
Accurately weighing the dioxygen dried in the dryerPutting 0.2172g of silicon particle sample into a 100ml triangular flask with a plug, adding 50ml of methyl red benzene solution with the concentration of 0.6g/L, carrying out ultrasonic treatment in an ultrasonic cleaner of Kunshan adhesive KH-100B for 3h, taking 10ml of methyl red benzene solution out of the triangular flask into a centrifugal tube, centrifuging for 5min at 4000rpm in a large and high speed centrifuge TGL-16 in Jiangsu, separating out a silicon dioxide particle sample in the solution, taking 5ml of the rest solution out of the centrifugal tube by a pipette, and diluting by 10 times to obtain the methyl red benzene solution to be measured. And (2) respectively taking three samples of the methyl red benzene solution to be detected to test the absorbance A of the methyl red benzene solution to be detected, obtaining the concentration of the methyl red benzene solution to be detected through the methyl red concentration-absorbance value standard curve obtained in the embodiment 1, taking the average value of the three concentrations, and multiplying the average value by 10 times to obtain the methyl red concentration of 0.5822g/L in the adsorbed methyl red benzene solution. According to S 1 ＝(m 1 -m 3 )×R 1 ×NA/(m 2 ×C 1 ) Wherein m is 1 Represents the mass g, m of the original methyl red in the methyl red benzene solution to be measured 2 Represents the mass g, m of the silica particle sample 3 Represents the mass g, R of methyl red in the methyl red benzene solution after adsorption 1 Represents the cross-sectional area m of methyl red molecule 2 NA denotes the Avogastron constant, C 1 Denotes methyl Red molecular weight g/mol, S 1 ＝(0.6-0.5522)×0.05×(116×10 -20 )×(6.022×10 23 ) /(0.2106X 269.30), specific surface area S of silica particle sample 1 ＝28.543m 2 /g。
Loading the clean empty sample tube in degassing station of Kangta NOVAtouch, vacuum degassing for 5min, backfilling helium after degassing, unloading the sample tube and immediately covering a rubber stopper, and weighing the total mass of the empty sample tube and the rubber stopper by using a precision balance. Taking 0.5g of a dried silicon dioxide particle sample from the dryer, putting the dried silicon dioxide particle sample into a weighed sample tube, putting the sample tube back to a degassing station, degassing for 2 hours at 180 ℃, cooling the sample tube to room temperature, backfilling helium, quickly covering a rubber stopper, weighing, and subtracting the gross weight of the sample tube to obtain 0.5022g of silicon dioxide particles. Placing the sample tube at the temperature of 77.35K and introducing N 2 From at a relative pressure p/p 0 Selecting 4 in the range of 0.05-0.2The corresponding measurements give the BET curve, as shown in fig. 3, with an intercept of a =0.364171, a slope of b =45.1433, a curve correlation coefficient of r =0.999987, n 2 Mass of adsorption W m = 1/(a + b), and the specific surface area S of the silica particle sample 2 ＝R 2 ×NA×W m /C 2 Wherein R is 2 Representing N in liquid nitrogen 2 Cross sectional area m of molecule 2 NA denotes the Avgalois constant, C 2 Represents N 2 Molecular weight g/mol, W of m Represents N 2 Adsorption mass g. Namely S 2 ＝(0.162×10 -18 )×(6.022×10 23 )/(28.013×(45.1433+0.364171))＝76.526m 2 /g。
The relative density d = (S) of the silicon dioxide particles in the silica sol is obtained 2 -S 1 )/S 2 ＝0.627。
Example 3
A method for characterizing the density of silica particles in a silica sol, comprising the steps of:
taking 100g of silica sol prepared by an alkoxy silane method, wherein the mass content of silica is 20%, adding H-type cation exchange resin to remove alkali adsorbed and free on the surfaces of silica particles to enable the pH value of the silica sol to reach 6, placing the silica sol in a vacuum drying oven at 80 ℃ for drying to obtain gel, crushing the obtained gel by using a mortar, drying for 2H at 200 ℃, cooling to obtain a dried silica particle sample, and placing the dried silica particle sample in a dryer for storage for later use.
Accurately weighing 0.2135g of a silica particle sample dried in a dryer, placing the silica particle sample in a 100ml triangular flask with a plug, adding 50ml of methyl red benzene solution with the concentration of 0.6g/L, carrying out ultrasonic treatment in a Kunshan adhesive KH-100B ultrasonic cleaner for 2-3h, taking 10ml of the methyl red benzene solution out of the triangular flask, placing the methyl red benzene solution in a centrifuge tube, centrifuging the methyl red benzene solution in a large high-speed centrifuge TGL-16 in Jiangsu at the speed of 5000rpm for 2min, separating the silica particle sample in the solution, taking 5ml of the rest solution out of the centrifuge tube by a pipette, and diluting by 10 times to obtain the methyl red benzene solution to be measured. Respectively taking three samples of the methyl erythrobenzene solution to be tested to test the absorbance A, and calibrating by methyl red concentration-absorbance valueAnd obtaining the concentration of the methyl red benzene solution to be detected by a quasi-curve, taking the average value of the three concentrations, and multiplying the average value by 10 times to obtain the methyl red concentration of 0.5342g/L in the adsorbed methyl red benzene solution. According to S 1 ＝(m 1 -m 3 )×R 1 ×NA/(m 2 ×C 1 ) Wherein m is 1 Represents the mass g, m of the original methyl red in the methyl red benzene solution to be measured 2 Represents the mass g, m of the silica particle sample 3 Represents the mass g, R of methyl red in the methyl red benzene solution after adsorption 1 Represents the cross-sectional area m of methyl red molecule 2 NA denotes the Avgalois constant, C 1 Denotes methyl Red molecular weight g/mol, S 1 ＝(0.6-0.5342)×0.05×(116×10 -20 )×(6.022×10 23 ) /(0.2106X 269.30), specific surface area S of silica particle sample 1 ＝40.497m 2 /g。
Loading the clean empty sample tube in degassing station of Kangta NOVAtouch, vacuum degassing for 5min, backfilling helium after degassing, unloading the sample tube and immediately covering a rubber stopper, and weighing the total mass of the empty sample tube and the rubber stopper by using a precision balance. Taking 0.5g of a dried silicon dioxide particle sample from the dryer, putting the dried silicon dioxide particle sample into a weighed sample tube, putting the sample tube back to a degassing station, degassing for 2 hours at 200 ℃, cooling the sample tube to room temperature, backfilling helium, quickly covering a rubber stopper, weighing, and subtracting the gross weight of the sample tube to obtain 0.507g of silicon dioxide particles. The sample tube was placed at 77.35K and N was passed through 2 From at a relative pressure p/p 0 Selecting the corresponding measured values of 4 points in the range of 0.05-0.2 to obtain a BET curve, and obtaining the intercept a =0.504187, the slope b =46.9182, the correlation coefficient r =0.999984 of the curve, N 2 Mass of adsorption W m = 1/(a + b), and the specific surface area S of the silica particle sample 2 ＝R 2 ×NA×W m /C 2 Wherein R is 2 Representing N in liquid nitrogen 2 Cross sectional area m of molecule 2 NA denotes the Avgalois constant, C 2 Represents N 2 Molecular weight g/mol, W of m Represents N 2 Adsorption mass g. Namely S 2 ＝(0.162×10 -18 )×(6.022×10 23 )/(28.013×(46.9182+0.504187))＝60.791m 2 /g。
The relative density d = (S) of the silica particles in the silica sol is obtained 2 -S 1 )/S 2 ＝0.334。
Example 4
Measurement of true Density of samples of the silica particles dried in examples 1-3
Accurately weighing the cleaned and dried 25ml pycnometer 4 30.203g, a 9g sample of the dried silica particles in the dryer of example 2 was charged therein, and a pycnometer and a sample weight m were precisely weighed 5 39.2223g. Injecting distilled water into the pycnometer to 2/3 of the volume, boiling to remove bubbles, standing, cooling, filling with distilled water, and measuring the weight m of pycnometer, sample and distilled water 6 It was 59.9155g. Pouring out water and sample from the bottle, washing the bottle, filling with distilled water, and measuring the weight m of the bottle and the distilled water 7 It was 55.1281g.
By the true density formula ρ = (m) 5 -m 4 )×ρ 0 /(m 7 -m 4 )-(m 6 -m 5 ) The true density of the powder particles is determined, where p 0 Is distilled water with density of 0.9975g/cm 3 The temperature at the time of the test was 23 ℃, and the true density ρ =2.1259g/cm of the silica particle sample was calculated 3 。
The true density ρ =1.8282g/cm of the silica particle sample in example 1 was calculated by the same method as described above 3 True density ρ =1.8241g/cm for the silica particle sample of example 3 3 。
The results of the density and true density tests for the silica particle samples of examples 1-3 are shown in table 1.
TABLE 1 compactness and true density of silica particle samples
The value trends of the density and the true density in table 1 correspond to each other, so that the accuracy of the method for representing the density of the invention is further proved, and meanwhile, the performance characteristics of silica particles in silica sol can be directly judged according to the value of the d value of the density, so that an important reference basis is provided for the practical application field and the application range of the silica sol.
For example, when the density d value ranges from 0.5 to 0.7, the silica in the silica sol has higher particle skeleton integrity and excellent particle alkali resistance, and is suitable for being used as an abrasive of an alkaline polishing solution in precision polishing.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A characterization method of the density of silicon dioxide particles in silica sol is characterized by comprising the following steps: the method comprises the following steps:
a. taking silica particles obtained after drying silica sol, using methyl red solution as adsorbent, and measuring the specific surface area S of the silica particles by a solution adsorption method 1 ；
b. Taking another silicon dioxide particle obtained after drying the silica sol, and adopting N 2 The specific surface area S of the silica particles is measured by the BET method as an adsorbed gas 2 ；
c. By (S) 2 -S 1 ）/ S 2 And obtaining the relative density d of the silicon dioxide particles, wherein the value of the relative density is less than 1, and the closer the value of the relative density d is to 1, the higher the density of the silicon dioxide particles in the silica sol is, the more complete the framework is and the better the alkali resistance is.
2. A method for the characterization of the density of silica particles in a silica sol according to claim 1, characterized in that: the drying method of the silica sol comprises the following steps: adding H-type cation exchange resin into silica sol, vacuum drying at 50-80 deg.C to obtain gel, grinding the gel until the particle fineness is less than or equal to 75 μm, and drying at 150-200 deg.C for 2-3H.
3. A method for the characterization of the density of silica particles in a silica sol according to claim 2, characterized in that: the silica sol is a dispersion liquid of nano-scale silica particles in water, or is obtained by hydrolytic condensation of alkoxy silane.
4. A method for the characterization of the density of silica particles in a silica sol according to claim 2, characterized in that: the addition amount of the H-type cation exchange resin is such that the pH of the silica sol reaches 4 to 7.
5. A method for the characterization of the density of silica particles in a silica sol according to claim 1, characterized in that: in step a, the ratio of the mass of the methyl red in the methyl red solution to the mass of the silicon dioxide particles is 0.025-0.075.
6. A method for the characterization of the density of silica particles in a silica sol according to claim 1, characterized in that: in the step a, the methyl red solution is a benzene solution of methyl red, and the concentration of the methyl red in the methyl red solution is 0.4-0.8g/L.
7. A method for the characterization of the density of silica particles in a silica sol according to claim 1, characterized in that: in the step a, the solution adsorption method comprises the following steps: placing the silicon dioxide particles in a methyl red solution, carrying out methyl red adsorption under the condition of oscillation or ultrasound, separating the silicon dioxide particles from the solution after the adsorption is finished, and measuring the mass m of the methyl red in the residual methyl red solution 3 (ii) a The specific surface area S of the silica particles 1 =（m 1 -m 3 ）
R 1 
NA/（m 2 
C 1 ) Wherein m is 1 Is the mass of methyl Red in the methyl Red solution, m 2 R is the mass of the silica particles 1 Represents the cross-sectional area m of methyl red molecule 2 NA denotes the Avgalois constant, C 1 Represents methyl red molecular weight g/mol.
8. A method for the characterization of the density of silica particles in a silica sol according to claim 7, characterized in that: the methyl red adsorption time is 2-3h under the oscillation or ultrasonic condition.
9. A method of characterising the compactness of silica particles in a silica sol as claimed in claim 7, characterized in that: the method for separating the silicon dioxide particles from the solution is a centrifugal separation method, the centrifugal rotating speed is 2000-5000rpm, and the centrifugal time is 2-10min.
10. A method for the characterization of the density of silica particles in a silica sol according to claim 1, characterized in that: in the step b, the determination process of the gas adsorption BET method comprises the following steps: degassing the silicon dioxide particles at 150-200 ℃ for 2-3h, and then placing the silicon dioxide particles in liquid nitrogen for N 2 Adsorption at a relative pressure p/p 0 Measuring the particle size in the range of 0.05-0.2 to obtain a BET curve, and determining the intercept a and the slope b of the BET curve, wherein each gram of the monomolecular layer N of the silicon dioxide particles 2 Mass of adsorption W m = 1/(a + b); the specific surface area S of the silica particles 2 =R 2 
NA
W m / C 2 Wherein R is 2 Representing N in liquid nitrogen 2 Cross sectional area m of molecule 2 NA denotes the Avgalois constant, C 2 Represents N 2 Molecular weight g/mol of (1).
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