CN109060976B - Method for measuring chloride ion concentration in silicon dioxide - Google Patents
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Abstract
The invention provides a method for measuring the concentration of chloride ions in silicon dioxide, which comprises the steps of dispersing the silicon dioxide in an alkaline aqueous solution to obtain a silicon dioxide dispersion liquid; heating the obtained silicon dioxide dispersion liquid at a temperature of more than 85 ℃ to dissolve silicon dioxide to obtain a silicon dioxide solution; the resulting silica solution was analyzed for chloride ions by ion chromatography. The present invention develops a method that can realize high-precision measurement at a lower detection lower limit without using a chemical or the like having a large environmental load by the above-described technical means.
Description
Technical Field
The invention relates to the technical field of ion chromatography, in particular to a method for measuring the concentration of chloride ions in silicon dioxide.
Background
Silica is an important chemical material used in various applications, such as a raw material for glass and optical fibers, a reinforcing agent for silicone resin, a filler for semiconductor sealing agents, and a flowability improver. In particular, fumed silica has a lower moisture content than precipitated silica and is an essential material for use in silicone and electronic materials.
Since the fumed silica is synthesized by burning a raw material silane in an oxyhydrogen flame, although it has a high purity as compared with the precipitated silica, it is inevitable that the raw material is silane and contains various metal impurities. Further, chlorosilane such as silicon tetrachloride is most commonly used as the raw material silane, and in this case, chlorine is also attached in a considerable amount. These impurities may cause quality defects when silica is used for the above-mentioned applications, and for example, chlorine as described above may deteriorate the performance of the above-mentioned semiconductor applications or the like as a corrosive substance.
Therefore, a technique for quantitatively analyzing a trace amount of impurities contained in fumed silica is a very important technique. The analysis of the metal impurities may be performed, for example, by Inductively Coupled Plasma (ICP) emission spectroscopy. However, in the analysis of chlorine impurities, only methods using silver nitrate and mercury thiocyanate have been known so far from the practical point of view; i.e. a method for determining the chloride ion concentration by colorimetric analysis (titration or measurement of absorbance). It is noted that the reagent mercury thiocyanate used in this method is a toxic substance, and therefore, this method has a large environmental burden and must be used with caution. (for example, non-patent document 1). In addition, the measurement accuracy of the method is low, and the lower limit value of the detection is 10-4mol/L (3.45mg/L), which cannot sufficiently satisfy the requirement of accurate measurement of the chloride ion concentration in silica, which is increasingly required to have high purity.
On the other hand, as a method for analyzing the concentration of chloride ions in an aqueous solution, a method for detecting chloride ions by ion chromatography is known (see patent documents 1 to 3 below), but the object of measurement is an aqueous solution at all, and no case is known at all for measuring the concentration of chloride ions in powdered silica.
The foregoing citations are listed below:
[ Nonpatent document 1 ] GB/T20020-2013 "fumed silica of national Standard of the people's republic of China" on pages 17 to 18 (published in 2013 in 9 and 6 months).
[ patent document 1 ] specification of chinese patent application publication No. 102507279.
[ patent document 2] specification of chinese patent application publication No. 102914600.
[ patent document 3 ] specification of chinese patent application publication No. 106226454.
Disclosure of Invention
As described above, as a method for measuring the concentration of chloride ions in silica, a method has been developed which can realize high-precision measurement at a lower detection limit without using a chemical or the like having a large environmental load; this is a significant problem for the skilled person.
In view of the above problems, the present invention has been actively studied. As a result, the present inventors have found that the above problems can be solved by dispersing silica in an alkaline aqueous solution, heating and dissolving the silica at a specific high temperature to obtain a silica solution, and analyzing the chloride ion concentration in the silica solution by ion chromatography, and have completed the present invention.
Namely, the method for measuring the concentration of chloride ions in silica according to the present invention comprises dispersing silica in an alkaline aqueous solution to obtain a silica dispersion; heating the obtained silicon dioxide dispersion liquid at a temperature of more than 85 ℃ to dissolve silicon dioxide to obtain a silicon dioxide solution; the resulting silica solution was analyzed for chloride ions by ion chromatography.
In the embodiment of the invention, the pH value of the silicon dioxide dispersion liquid is adjusted to be 10-14, so that the silicon dioxide solution with the pH value of 10-14 at 25 ℃ is obtained after the heating treatment.
In the measurement method embodiment of the present invention, the pH of the silica dispersion is adjusted to a strength of 10 to 14 so as to obtain a silica solution having a pH of 10 to 14 at 25 ℃ after the heat treatment.
In the measurement method example of the present invention, the alkaline aqueous solution is an aqueous sodium hydroxide solution.
In the measurement method examples of the present invention, the amount of the alkaline aqueous solution required for dispersing 1g of silica is not less than the minimum amount of the alkaline aqueous solution capable of dissolving all the silica dispersed in the alkaline aqueous solution during the heat treatment, and the amount of the alkaline aqueous solution is not more than 150 mL.
In the examples of the measuring method of the present invention, the analysis of chloride ions in the silica solution by ion chromatography is a measurement of chloride ion concentration based on a change in ion conductivity.
In an embodiment of the measuring method of the present invention, the heating temperature of the silica dispersion is controlled within a range of 85 to 100 ℃.
In the examples of the measuring method of the present invention, the silica is hydrophobic silica having a hydrophobic group introduced into the surface thereof, and alcohols coexist in an alkaline aqueous solution in which the silica is dispersed.
In an embodiment of the measuring method of the present invention, the alcohol added to the alkaline aqueous solution is present in an amount of 6 to 16mL per 1g of silica.
In the embodiment of the measuring method of the present invention, the alcohol is preferably methanol.
In the examples of the measuring method of the present invention, the hydrophobic silica is a product in which a dimethylsilyl group or a methyl group is introduced as a hydrophobic group on the surface of silica.
In the measurement method of the present invention, the hydrophobic silica is preferably silica having a silicone oil surface-treated with hydrophilic silica.
The present invention has an advantageous effect that the low concentration of chloride ion concentration in silica can be easily measured with high accuracy by a low detection lower limit. This method is also applicable to ion chromatography, and is easy to handle without using a reagent having a large environmental load.
Drawings
FIG. 1 is a standard graph demonstrating chloride ion in a silica solution used in an example of the present invention.
Detailed Description
Detailed embodiments of the present invention will be disclosed herein. It is to be understood, however, that the disclosed embodiments are merely exemplary of the invention and that the invention may be embodied in various and alternative forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
The silica to be measured in the present invention is not limited in kind, and may be specifically selected from precipitated silica (hydrous silicic acid), vapor phase silica (anhydrous silicic acid), and the like. Among them, fumed silica having less impurities can exert a better effect. The gas phase method silicon dioxide is formed by hydrolysis reaction of chlorosilane such as silicon tetrachloride and the like in oxyhydrogen flame. Since fumed silica is formed by hydrolyzing raw material chlorosilane, has a considerable amount of chlorine attached, and can accurately measure the content of chlorine, the fumed silica is particularly suitable for being used as a measuring object of the method for measuring the concentration of chlorine ions, and the significance of the measuring result is great. Specifically, the specific surface area is 10-400 m2The object of the present invention is fumed silica/g, wherein the specific surface area is 50 to 400m2The fumed silica is preferably used in an amount of per gram.
Although the surface of the silica product, which is generally saturated with silanol groups, exhibits hydrophilicity, the present invention is also applicable to hydrophobic silica having hydrophobic groups introduced on the surface. The hydrophobic group is introduced and treated by a silylation agent, silicone oil, siloxane, metal alkoxide, fatty acid, other heavy metal salt and other treatment agents. In particular, silica having dimethylsilyl groups or methyl groups introduced on the surface thereof by a silylating agent and silica surface-treated with silicone oil are suitable as the measurement objects of the present invention.
The carbon content of the hydrophobic silica is 0.4 mass% or more. Preferably, the carbon content is 0.4 mass% or more and 10 mass% or less; more preferably, the carbon content is 0.6 mass% or more and 8 mass% or less. The carbon content can be measured by a conventional combustion carbon content measuring apparatus (for example, "SUMIGRAPH NC-22F" manufactured by SumiGAL Co., Ltd.).
The main feature of the present invention is that the concentration of chloride ions contained in the silica is determined by ion chromatography, which is an analysis method of the concentration of chloride ions in the aqueous solution. Since powdered silica becomes a suspension after adding water, the concentration of chloride ions cannot be accurately measured even by the ion chromatography. In contrast, the present invention realizes highly accurate measurement of the chloride ion concentration by adding silica to an alkaline aqueous solution, heating and dissolving the silica to form a silica solution, and measuring the silica solution by the ion chromatography.
The step of dissolving silica in an aqueous alkaline solution to obtain a silica solution is described in detail below: first, silica to be measured is dispersed in an alkaline aqueous solution to obtain a silica dispersion. The pH value of the silicon dioxide dispersion liquid is adjusted to be 10-14, and then the silicon dioxide dispersion liquid is heated to obtain a silicon dioxide solution with the pH value (25 ℃) of 10-14. That is, in order to maintain the pH of the obtained silica solution within the above pH range even if the silica solution is neutralized with an alkali; further, since the silica is dispersed in the alkali strength, the silica can be kept highly soluble in the heat treatment, and the dissolution residual of the silica can be reduced well, the present invention mixes the silica with the highly alkaline aqueous solution to dissolve the silica well.
The base used in the aqueous alkaline solution is generally an inorganic base, and may be specifically selected from sodium hydroxide, potassium hydroxide or sodium carbonate. Among them, sodium hydroxide is preferably used from the viewpoint of solubility of silica and easy handling. The water for dissolving the alkali is preferably clean water, and specifically ultrapure water is used.
The amount of the alkaline aqueous solution required for dispersing the silica may be equal to or more than the minimum amount of the alkaline aqueous solution capable of dissolving all the silica dispersed in the alkaline aqueous solution during the heat treatment. Specifically, it is preferably dispersed in 5mL or more of an aqueous alkaline solution per 1g of silica. On the other hand, when the amount of the aqueous alkali solution is too large, the handling property is deteriorated, and therefore, the aqueous alkali solution is preferably dispersed in an amount of 100mL or less per 1g of silica, and the amount of the aqueous alkali solution to be used is more preferably controlled to 50mL or less.
More specifically, when the alkaline aqueous solution is a 5N aqueous solution of sodium hydroxide, the amount of the alkaline aqueous solution can be dispersed in an amount of 8 to 15mL per 1g of silica. Particularly, when the silica is hydrophobic silica, the hydrophobic silica is relatively difficult to be fused with an alkaline aqueous solution, and the amount of the hydrophobic silica is preferably 16 to 30mL of the alkaline aqueous solution per 1g of the silica.
The silica dispersion obtained above is subjected to heat treatment in the next step, and the obtained silica solution is dissolved. In order to measure the chloride ion concentration in the silica by ion chromatography, the silica dispersion is preferably prepared by adjusting the amount of the liquid to 35mL or more, more preferably 40 to 150mL, in the concentration state of the silica and the alkaline aqueous solution, for easy handling. However, since the amount of the liquid of the silica dispersion can be adjusted directly by adding the required amount of the alkali aqueous solution to the silica and mixing the solution, that is, by directly taking 35mL or more of the alkali aqueous solution and mixing the solution with the silica, it is preferable to obtain a thick silica dispersion first and then appropriately add an alkali, an alkali aqueous solution and/or water in accordance with the required amount of the silica dispersion to prepare the thick silica dispersion in the desired amount of the liquid. More specifically, the method of adjusting the silica dispersion is not particularly limited, and the alkali, water and alkaline aqueous solution used for adjustment respectively refer to the raw material (alkali, water) for preparing the thick silica dispersion and the aqueous solution prepared therefrom; the specific operation can be realized by adding extra water after obtaining a thick silicon dioxide dispersion liquid formed by silicon dioxide and an alkaline aqueous solution so as to adjust the liquid amount of the silicon dioxide dispersion liquid. The alkali, the alkaline aqueous solution, and water may be appropriately added to the thick silica dispersion, either individually or together, to enable dissolution of silica in a subsequent heating dissolution process.
As described above, hydrophobic silica is difficult to dissolve in an alkaline aqueous solution. Therefore, when the silica is hydrophobic silica, in order to improve the dispersibility of the hydrophobic silica in an alkaline aqueous solution, a dispersion aid, which may be an alcohol, is preferably added to the alkaline aqueous solution. The alcohol may be selected from methanol, ethanol or other low alcohol. Among them, methanol is preferable because methanol is easily dissolved in an alkaline aqueous solution.
If the alcohol content in the alkaline aqueous solution is too high, the peak separation precision is reduced when the ion chromatography is influenced, so that the chloride ion concentration measurement of the ion chromatography cannot reach sufficient precision; therefore, the content of the alcohol in the alkaline aqueous solution is preferably 15% by mass or less, more preferably 12% by mass or less. On the other hand, in order to improve the dispersibility of the hydrophobic silica, the hydrophobic silica is sufficiently dissolved in an alkaline aqueous solution in which the alcohol content is preferably 2% by mass or more, more preferably 3.5% by mass or more, during the heat treatment. In particular, it is preferable to use the alcohol in an amount of preferably 5 to 20mL, more preferably 6 to 16mL, per 1g of the silica in the alkaline aqueous solution containing the alcohol.
The silica dispersion obtained by the above-described operation is then heated at a temperature of 85 ℃ or higher. The silica is dispersed and dissolved in an alkaline aqueous solution by the heat treatment to form a silica solution. If the heating temperature in the heat treatment step is less than 85 ℃, the silica in the alkaline aqueous solution cannot be sufficiently dissolved. Therefore, in order to increase the solubility of silica, the heating temperature is preferably 88 ℃ or higher. On the other hand, when the heating temperature reaches above 100 ℃, water in the silicon dioxide dispersion liquid is boiled and largely volatilized, so the heating temperature is preferably lower than or not equal to 100 ℃; more preferably 95 ℃ or lower.
The heating time is preferably controlled to be 20 to 120 minutes because the operability is poor when the heating time is too long, and the silica is not sufficiently dissolved when the heating time is too short.
If the alkali concentration of the silica solution obtained by the above method is too high, the concentration of chloride ions measured by ion chromatography in the subsequent step may damage the separation column, the detector, and the like, and thus the pH may be adjusted to a stable range by using an acid. In particular, when a strong base having a pH value exceeding the above-mentioned suitable range of 10 to 14 is used as the alkaline aqueous solution, the pH value is preferably controlled to 14 or less. Further, if the pH of the silica solution is too low, silica may be precipitated when the chloride ion concentration is measured by ion chromatography, and therefore, the pH of the silica solution is preferably adjusted to 12.0 to 13.5.
The acid used for adjusting the pH value of the silica solution is preferably an inorganic acid, and can be specifically selected from hydrochloric acid, sulfuric acid or nitric acid; more preferably, nitric acid is selected.
The concentration of chloride ions contained in the silica solution obtained by the adjustment is measured by ion chromatography analysis to confirm the concentration of chloride ions contained in the silica. The ion chromatography is a chromatographic separation analysis method using an ion exchange resin as a stationary phase, and is a quantitative method for separating various ions by using the difference in permeation rate, diffusion rate, and the like of a plurality of ions contained in a sample, and measuring physical properties such as the conductivity of the separated ions, thereby measuring the ion content.
The separation column used for ion chromatography can be appropriately selected from anion measurement columns conventionally used in the art. The anion exchange resin of the stationary phase as the functional group comprises basic anion exchange resin of quaternary ammonium group and tertiary sulfur group, and the polymer matrix of the basic anion exchange resin comprises synthetic polymer selected from styrene, benzene acid, acrylic acid or isobutene acid. In addition, emulsion type anion exchange resins and surface coating type anion exchange resins can be used as the anion exchange resin. The mobile phase may be a solution appropriately selected from those conventionally used in ion chromatography, and specifically, a diluted aqueous solution prepared by mixing chemical agents selected from sodium hydroxide, sodium carbonate and/or sodium bicarbonate, alone or in combination, may be used as the solution. A detector for ion chromatography, which may be selected from an ion conductivity detector, a visible light detector, or an electrochemical detector; a machine for measurement by change in ion conductivity is generally used, wherein only an ionic component is detected based on the measurement mode, and an ion conductivity detector is preferably used. Further, a commercially available ion chromatography analyzer having components such as a liquid feeding pump, a sample introducing part, a concentrator, a stationary phase column, and a thermostatic chamber may be used.
The method carries out the chloride ion content of the silicon dioxide by ion chromatography, and is suitable for determining the chloride ion concentration in the silicon dioxide solution by adopting a standard curve prepared in advance. The standard curve refers to that a plurality of chlorine water solutions with known chloride ion concentrations are prepared in advance and are analyzed through ion chromatography to obtain the chloride ion concentration ppm (mg/L) and the peak areas of the chloride ions; wherein, when the ion conductivity detector is selected as the detector, a graph showing the relation of ion conductivity (μ s/cm) x detection time (min) can be obtained, and the standard curve can be obtained by making the graph into a straight line close to a least squares method. The standard solution used in the standard curve preferably comprises a solution composition of at least three different concentrations.
The concentration of chloride ions in silica of unknown concentration can be determined by using the standard curve of the concentration of chloride ions in the silica solution obtained by the ion chromatography. Specifically, it can be confirmed by the following formula (1). The chloride ion concentration of the blank solution means that silica is not dispersed in the alkaline aqueous solution, but is measured under conditions completely identical to those in the measurement of the standard solution to obtain the chloride ion concentration.
Formula (1): chloride ion concentration (ppmw) ([ chloride ion concentration (mg/L) obtained by a standard curve) -chloride ion concentration of a blank solution (mg/L) ] × silica dissolved solution capacity (L) ÷ silica amount (g) × 1000.
[ examples ] A method for producing a compound
To specifically explain the present invention, examples 1 to 4 are given below, and the analysis conditions of ion chromatography and the method for preparing a calibration curve for confirming chloride ions in a silica solution in these examples are explained. It should be understood that, the embodiments 1 to 4 are used for understanding the technical solution of the present invention, but the present invention is not limited thereto.
[ analysis conditions for ion chromatography ]
The ion chromatography apparatus used 882Compact IC Plus (manufactured by Metrohm) and the anion column used Metherosep A Supp5-250 (manufactured by Metrohm). A detector using an ionic conductivity detector.
As the eluent, a mixed solution of 3.2mmol/L aqueous sodium carbonate and 1.0mmol/L aqueous sodium bicarbonate was used. Sodium carbonate and sodium hydrogen carbonate were diluted with ultrapure water. The eluate was introduced into the apparatus at a flow rate of 0.7 mL/min.
[ method for preparing standard curve for proving chloride ion in silica solution ]
1000mg/L of a standard chlorine ion solution was diluted with ultrapure water, and chlorine aqueous solutions having various concentrations of 0.1, 0.3, 0.5, 1.0, and 1.5mg/L were adjusted. It was confirmed that these aqueous solutions had a chloride ion peak-valley detection time of 8 minutes by ion chromatography under the above conditions. In the graph obtained after the analysis of each chlorine aqueous solution by ion chromatography, the chloride ion concentration ppm (mg/L) is plotted on the horizontal axis and the peak area of chloride ions (i.e., ion conductivity (. mu.s/cm). times.detection time (min)) is plotted on the vertical axis, and a straight line is approximated by the least squares method, thereby generating a calibration curve as shown in FIG. 1.
Example 1
1.0014g of silica [ REOLOSIL QS-102] produced by Deshan chemical (Zhejiang) Co., Ltd](hydrophilic fumed silica, specific surface area 200 m)2Per g), 250mL (25 ℃ C.) of a fluororesin beaker was charged. Next, 10mL of a 5N aqueous solution of sodium hydroxide (pH 14 or higher at 25 ℃ C.) (dispersed in 10mL of an aqueous alkaline solution per 1g of silica) was added, and the mixture was gently shaken and mixed. After adding 40mL (25 ℃ C.) of ultrapure water, the beaker was covered and shaken gently in the same manner. That is, the total amount of the basic aqueous solution used for dispersing 1g of silica was 50 mL.
The obtained silica dispersion is heated for 20 minutes by using a water tank while maintaining the temperature of the water in the tank at 90 to 95 ℃. After the heating was completed, it was confirmed that the silica was dissolved. The pH of the resulting silica solution (25 ℃) was 13.8.
The fluororesin beaker was taken out from the water tank, cooled to 25 ℃, and then 3mL of a 15 mass% nitric acid aqueous solution was added thereto to lower the pH to 13.1. This solution was transferred to a 100mL measuring flask, and the fluororesin beaker was rinsed with ultrapure water to 100mL, thereby obtaining a silica solution. The pH (25 ℃) of the silica solution was 13.0.
The silica solution was analyzed by ion chromatography, and the peak area of the obtained chloride ion was 0.08705. mu.s/cm. min. From the peak areas, the concentration of chloride ions in the silica solution was determined by using the "standard curve for determining chloride ions in silica solution" prepared above, and the result was 0.551 mg/L. The chlorine ion concentration of silica not dispersed in the aqueous alkali solution was measured with respect to the blank solution obtained in the same manner as above, and it was 0.396 mg/L. The aforementioned results of obtaining the chloride ion concentration (ppmw) are expressed by the following formula (2):
formula (2): chloride ion concentration (ppmw) ([ chloride ion concentration (mg/L) determined by a standard curve) -chloride ion concentration of a blank solution (mg/L) ] × silica dissolved solution capacity (L) ÷ silica amount (g) × 1000.
The chloride ion concentration in the silica used for the determination was calculated and found to be 15.5. mu.g/g (ppmw).
Example 2
In order to confirm the accuracy of the measurement of the chloride ion concentration by ion chromatography, a 1000mg/L chloride ion standard solution was diluted with ultrapure water to prepare a 0.5mg/L chloride aqueous solution as an analysis solution. The analysis solution was analyzed by ion chromatography to determine the peak area of chloride ions. The measurement was repeated 6 times. As a result, as shown in Table 1, the relative standard deviation of the peak area of chloride ion was small and 2.34%.
Then, in example 1, the measurement of the area of the chloride ion peak by ion chromatography using the silica solution obtained in [ REOLOSIL QS-102], was repeated 6 times in the same manner. As a result, as shown in Table 1, the relative standard deviation of the peak area of chloride ion was as small as 3.24%.
As described above, in the conventional method for measuring chlorine impurities in silica described in non-patent document 1, the relative standard deviation in 2 measurements of chlorine content (mg/kg) measured by silver nitrate titration was 17.8% of the maximum value. From the comparison in table 1, it is understood that the method for measuring the chloride ion concentration in silica by ion chromatography according to the present invention has higher measurement accuracy.
TABLE 1
Example 3
The silica used in example 1 was REOLOSIL DM-10 (hydrophobic silica surface-treated with dimethyldichlorosilane, having a specific surface area of 120m, manufactured by Delaware chemical (Zhejiang) Co., Ltd.)2(g, carbon content 0.9% by mass)%) the same procedure was followed except that the amount of silica was 0.5000g, and the chloride ion in the hydrophobic silica was addedAnd (4) measuring the concentration. Since hydrophobic silica and a 5N aqueous sodium hydroxide solution were difficult to fuse, a good silica dispersion could not be obtained (the total amount of the basic aqueous solution used for dispersing 1g of silica was 100 mL). Therefore, a silica dispersion in which the hydrophobic silica was well dispersed was obtained by adding 4mL of methanol (8 mL of methanol was added per 1g of silica) before adding a 5N aqueous solution of sodium hydroxide to a fluororesin beaker, and the same measurement as in example 1 was carried out.
When the above measurement was performed, the pH of the silica solution (25 ℃ C.) obtained by heating the silica dispersion was 13.6. The pH was then lowered to 13.2 by adding aqueous nitric acid to the silica solution.
The silica solution was analyzed by ion chromatography, and the peak area of the obtained chloride ion was 0.11248. mu.s/cm. multidot.min. The concentration of chloride ions in the silica solution was determined using the above-mentioned chloride ion peak area [ standard curve for confirming chloride ions in silica solution ], and the result was 0.609 mg/L. When the chloride ion concentration of the blank solution obtained in the same manner as above was measured with respect to the hydrophobic silica which was not dispersed in the aqueous alkali solution, it was 0.539 mg/L. From these results, the chloride ion concentration in the hydrophobic silica for measurement was calculated to be 14.0. mu.g/g (ppmw) by the formula (2) described above.
Example 4
In example 3, the same operation was carried out except that REOLOSIL PM-20L (hydrophobic silica surface-treated with silicone oil, specific surface area 100m2/g, carbon content 5.5 mass%) produced by deshan chemical (zhejiang) co., ltd was used as silica, and the chloride ion concentration in the hydrophobic silica was measured.
When the above measurement was performed, the pH of the silica solution (25 ℃ C.) obtained by heating the silica dispersion was 13.6. Then, the pH was lowered to 13.1 by adding aqueous nitric acid to this solution.
When the silica solution was analyzed by ion chromatography, the peak area of chloride ion was 0.11275. mu.s/cm. multidot.min. The concentration of chloride ions in the silica solution was determined using the above-mentioned chloride ion peak area [ standard curve for confirming chloride ions in silica solution ], and the result was 0.611 mg/L. When the chloride ion concentration of the blank solution obtained in the same manner as above was measured with respect to the hydrophobic silica which was not dispersed in the aqueous alkali solution, it was 0.539 mg/L. From these results, the chloride ion concentration in the hydrophobic silica for measurement was calculated to be 14.4. mu.g/g (ppmw) by the formula (2) described above.
While the present invention has been described in detail and with reference to the accompanying drawings and examples, it will be apparent to one skilled in the art that various changes and modifications can be made therein. Therefore, certain details of the embodiments are not to be interpreted as limiting, and the scope of the invention is to be determined by the appended claims.
Claims (10)
1. A method for determining the concentration of chloride ions in silica, comprising:
dispersing silicon dioxide in an alkaline aqueous solution to obtain a silicon dioxide dispersion liquid; the surface of the silicon dioxide is introduced with hydrophobic groups, alcohols coexist in an alkaline aqueous solution of the dispersed silicon dioxide, and the coexistence amount of the alcohols is 5-20 mL of the alcohols coexisted in each 1g of the silicon dioxide;
heating the obtained silicon dioxide dispersion liquid at a temperature of more than 85 ℃ to dissolve silicon dioxide to obtain a silicon dioxide solution;
the resulting silica solution was analyzed for chloride ions by ion chromatography.
2. The method according to claim 1, wherein:
adjusting the pH value of the silicon dioxide dispersion liquid to be 10-14 strength so as to obtain a silicon dioxide solution with the pH value of 10-14 at 25 ℃ after the heating treatment.
3. The method for measuring the chloride ion concentration in silica according to claim 1 or 2, characterized in that:
the alkaline aqueous solution is sodium hydroxide aqueous solution.
4. The method according to claim 3, wherein:
the amount of the alkaline aqueous solution required for dispersing 1g of silica is not less than the minimum amount of the alkaline aqueous solution capable of dissolving all the silica dispersed in the alkaline aqueous solution during the heat treatment, and the amount of the alkaline aqueous solution is not more than 150 mL.
5. The method according to claim 4, wherein:
the analysis of chloride ions in the silica solution by ion chromatography is a measurement of chloride ion concentration based on a change in ion conductivity.
6. The method according to claim 5, wherein:
the silica dissolution temperature of the silica dispersion liquid is controlled within the range of 85-100 ℃.
7. The method according to claim 1, wherein:
the amount of the alcohol added to the alkaline aqueous solution is 6 to 16mL per 1g of silica.
8. The method for measuring a chloride ion concentration in silica according to claim 1 or 7, characterized in that:
the alcohol is methanol.
9. The method according to claim 8, wherein:
the hydrophobic silica is a product in which a dimethylsilyl group or a methyl group is introduced as a hydrophobic group on the surface of the silica.
10. The method according to claim 8, wherein:
the hydrophobic silica is silica obtained by performing surface treatment on hydrophilic silica by using silicone oil.
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