JP2017146123A - Silicon quantitative analysis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantitative method of silicon in a sample.SOLUTION: A quantitative analysis method of silicon contained in a sample includes: a step (1) of adding a fuming nitric acid to a silicon-containing solution, so as to obtain a nitric acid solution; a step (2) of adding a hydrofluoric acid to the nitric acid solution, so as to generate a silicon tetrafluoride gas; a step (3) of introducing the silicon tetrafluoride gas together with a nitric acid gas into a boric acid solution, so as to collect the silicon; and a step (4) of analyzing the boric acid solution which has collected the silicon, so as to obtain the content of the silicon in the sample.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a silicon quantitative analysis method.

  In addition to the main component elements, various industrial materials typified by iron contain elements according to the purpose in order to impart necessary properties to the material. Depending on the combination of the element to be added and the amount added, the physical properties of the material are variously affected. Silicon is one of them, and for example, it is added for the purpose of imparting heat resistance, electrical conductivity and the like. By measuring the amount of silicon in the material, a new material can be designed, and an index for producing a material having the desired physical properties can be obtained. On the other hand, when producing a high purity metal etc., it is necessary to evaluate the amount of silicon as an impurity.

  Against this background, the silicon content in various materials is quantified using a method according to each purpose in a wide range from single ppm to% order. In general, as a technique for quantifying silicon, silicon dioxide gravimetric method (Non-patent document 1), molybdosilicate blue absorptiometric method (Non-patent document 1), inductively coupled plasma (ICP) emission spectroscopy (Non-patent document 2), Further, a silicon tetrafluoride vapor separation method (Non-patent Documents 3 and 4) is known. Moreover, there exists a method shown by patent document 1, 2 as a silicon | silicone determination method which is not JIS-ized.

Japanese Patent Laying-Open No. 2005-069746 JP 2008-128992 A

JIS G1212: 1997 "Iron and steel-silicon determination method" JIS H1061: 2006 "Silicon determination method in copper and copper alloys" JIS H1403: 2001 "Analytical method of tungsten material" JIS H1404: 2001 “Analytical method of molybdenum material”

  In Patent Document 1, ammonium molybdate is added to a solution acidified with hydrochloric acid, extracted into MIBK as molybdosilicate, and the absorbance of molybdosilicate blue obtained by back-extraction into an aqueous phase with a reducing agent such as ascorbic acid is absorbed. A small amount of silicon is quantified by measuring with a photometer. However, since this method depends on the efficiency of solvent extraction and is acidic with hydrochloric acid, it is very difficult to use it for a sample that precipitates in hydrochloric acid.

  In Patent Document 2, a metal component is acid-dissolved with a first acid (specifically, 3 parts of 37% hydrochloric acid, 2 parts of 69.3% nitric acid and 5 parts of deionized water), and then a base (specifically, In particular, an aqueous solution of sodium hydroxide) is added to form a silicate, and then a second acid mixture (30 parts hydrochloric acid diluted solution and 5 parts nitric acid) is added to form silicate ions. Is analyzed by ICP emission spectroscopy. However, since this method uses ICP emission spectroscopy without separation from the matrix components, it is very difficult to quantify silicon in a low concentration range.

  On the other hand, the silicon tetrafluoride vapor separation method disclosed in Non-Patent Documents 3 and 4 is known as a highly sensitive silicon quantification method for separating silicon from matrix components. By separating the silicon from the matrix component, the silicon concentration due to the reduction of the constant volume, the effect of reducing the spectral interference, etc. are obtained, and the sensitivity is improved.

  In the conventional silicon tetrafluoride vapor separation method, hydrofluoric acid is added to a high-concentration sulfuric acid acidic solution to vaporize and separate silicon as silicon tetrafluoride and absorb it in the boric acid solution. A blue absorptiometry or boric acid absorption solution is applied to ICP emission spectroscopy. As long as silicon can be separated from the matrix component, either the molybdosilicate blue absorptiometry or the ICP method may be used as the final analysis method. However, the conventional vapor separation method of silicon tetrafluoride is applied to many samples that are insoluble in sulfuric acid or cause sulfate precipitation because vaporization separation is performed in a high-concentration sulfuric acid solution. Can not. Since there are few samples which are soluble in sulfuric acid acid solution or do not cause precipitation, the application range is very limited.

  An object of the present invention is to provide a method for quantifying silicon in a sample that cannot be applied by a conventional silicon tetrafluoride vapor separation method using sulfuric acid.

  The gist of the present invention is the following quantitative analysis method for silicon.

(A) A method for quantitatively analyzing silicon contained in a sample,
(1) adding fuming nitric acid to a silicon-containing solution to obtain a nitric acid acidic solution;
(2) adding hydrofluoric acid to the nitric acid acidic solution to generate silicon tetrafluoride gas;
(3) introducing the silicon tetrafluoride gas into a boric acid solution together with nitric acid gas and collecting silicon; and
(4) analyzing the boric acid solution that has collected silicon, and determining the silicon content in the sample;
Silicon quantitative analysis method.

(B) In the step (1), nitric acid having a concentration of 70 w / w% or more is used.
The silicon quantitative analysis method of (A) above.

(C) In the step (4), analysis of the boric acid solution in which the silicon is collected is performed by inductively coupled plasma emission spectroscopy, inductively coupled plasma mass spectrometry, or atomic absorption spectrophotometry.
The silicon quantitative analysis method of (A) or (B) above.

(D) In the step (4), when the boric acid solution in which the silicon was collected was analyzed by the molybdosilicate blue absorptiometry, the pH value of the boric acid solution in which the silicon was collected was stabilized. After adjusting to a value outside the range where the absorbance is obtained, adjust to a range where stable absorbance is obtained,
The silicon quantitative analysis method according to any one of (A) to (C) above.

(E) When adjusting the pH value of the boric acid solution in which silicon is collected to a value other than the range in which stable absorbance is obtained, an indicator that changes color in a range other than the pH range in which stable absorbance is obtained is used. ,
The silicon quantitative analysis method of (D) above.

(F) The step (1) uses a silicon-containing solution obtained by dissolving a solid with an acid.
The silicon quantitative analysis method according to any one of (A) to (E) above.

  According to the present invention, silicon in a solid or liquid that could not be quantified by the conventional silicon tetrafluoride vapor separation method using sulfuric acid can be quantified with sub-ppm accuracy. The present invention is particularly effective for quantitative analysis of silicon contained in metals, alloys, compounds and the like that are soluble in a solution containing 70 w / w% or more of nitric acid.

Apparatus example for carrying out the silicon quantitative analysis method according to the present embodiment A plot of the relationship between the concentration of fuming nitric acid that dissolves the sample and the silicon recovery rate

The present invention is a method for quantitatively analyzing silicon contained in a sample, comprising the following steps (1) to (4). At this time, for example, the apparatus shown in FIG. 1 is used to implement the present invention.
(1) adding fuming nitric acid to a silicon-containing solution to obtain a nitric acid acidic solution;
(2) adding hydrofluoric acid to the nitric acid acidic solution to generate silicon tetrafluoride gas;
(3) introducing the silicon tetrafluoride gas into a boric acid solution together with nitric acid gas and collecting silicon; and
(4) A step of analyzing a boric acid solution in which silicon is collected and obtaining a silicon content in the sample.

Hereinafter, each step will be described.
Step (1) First, it is necessary to prepare a silicon-containing solution. In the case of a liquid sample, the sample solution is a mixture of the sample and nitric acid, or a solution as it is. When the sample is solid, the sample is dissolved using an acid such as nitric acid, hydrochloric acid, or hydrogen peroxide solution to obtain a silicon-containing solution. At this time, the container used for dissolution is required to have little silicon contamination. For example, a fluororesin container such as PFA (perfluoroalkoxy) may be used.
Subsequently, fuming nitric acid is added to the silicon-containing solution thus obtained to obtain a nitric acid acidic solution. The concentration of fuming nitric acid is preferably 70% w / w or more. This is because if the amount is less than 70 w / w%, the amount of silicon collected in the step (3) decreases. In order to achieve a silicon recovery rate of 90% or higher, the concentration of fuming nitric acid is preferably 73 w / w% or higher (see FIG. 2).

About Step (2) (Vaporization Separation Step) This step is a step in which hydrofluoric acid is added to the nitric acid acidic solution to generate silicon tetrafluoride gas. In this step, for example, as shown in FIG. 1, hydrofluoric acid is introduced into a sample solution (nitric acid acidic solution) placed in a sealed container (PFA container), and silicon contained in the nitric acid acidic solution is introduced. Vaporizes as silicon tetrafluoride gas and separates from the nitric acid solution. At this time, the sealed container and the absorption tube are connected by a PTFE (polytetrafluoroethylene) tube, hydrofluoric acid is added from a syringe using a pipette, etc., and a rubber stopper is immediately put on, and N ₂ , O ₂ , Ar, etc. Purge the gas. The concentration of hydrofluoric acid is preferably 1.0 to 10.0 w / v%. The nitrogen gas flow rate is preferably 0.1 to 1.0 L / min, and the purge time is preferably 10 to 60 min.

Step (3) This step is a step of collecting silicon by introducing the silicon tetrafluoride gas together with nitric acid gas into a boric acid solution. That is, boric acid is used as the silicon absorbing solution. Boric acid is used to mask fluorine that interferes with the coloration of molybdosilicate blue. Since the background of silicon increases as the amount of boric acid increases, the boric acid concentration is preferably as low as possible. Typically, 10 mL is recommended at 0.1 w / v%. An absorption tube made of PFA is used.

About the process of (4) This process is a process of analyzing the boric acid solution which collected silicon, and calculating | requiring the silicon content in the said sample. When analyzing the boric acid solution containing silicon by inductively coupled plasma emission spectroscopy, inductively coupled plasma mass spectrometry or atomic absorption spectrophotometry, use the boric acid solution containing silicon as it is. Can do. Here, since the sensitivity is insufficient in the ICP method, it is preferable to use the molybdosilicate blue absorptiometry for the analysis of the boric acid solution in which silicon is collected. The acid solution cannot be used as it is.

  In other words, the conventional separation method for vaporizing silicon tetrafluoride is a method in which hydrofluoric acid is added in sulfuric acid to generate silicon tetrafluoride gas. Since sulfuric acid is not volatile, the pH of the absorbing solution Will not fluctuate. Therefore, in the conventional method, by adding a certain amount of acid, the pH value can be adjusted to a range in which stable absorbance can be obtained in the molybdosilicate blue absorptiometry. However, according to the present embodiment, the vaporization separation of silicon tetrafluoride is performed in fuming nitric acid having volatility. Therefore, the vaporized gas of nitric acid is transported to the absorption liquid by the nitrogen gas, absorbed into the absorption liquid, and absorbed. The pH of the liquid becomes strongly acidic. Moreover, since the flow rate of nitrogen gas is not necessarily the same in each apparatus, the pH of the absorbing solution varies on the strongly acidic side.

  Here, in the molybdosilicate blue absorptiometry, the pH value at which stable absorbance is obtained is only a limited range of 0.6 to 0.9. In order to adjust the pH of the absorbing solution in a state of dispersion on the strongly acidic side to this range, there are a method using a pH meter, a method using an indicator, etc., but the method using a pH meter is a complicated operation. There is a possibility of causing problems such as silicon contamination and silicon loss due to the solution adhering to the electrode surface. For this reason, this adjustment is preferably performed using an indicator.

  However, when the discoloration range of the indicator is in the pH range (0.6 to 0.9) at which stable absorbance is obtained in the molybdosilicate blue absorptiometry, the color development of molybdosilicate blue is disturbed. The photometric method makes accurate measurements impossible. For this reason, it is important to use an indicator that changes color in a range other than the pH range where stable absorbance can be obtained. Using such an indicator, once the pH is adjusted to a specific pH value outside the range where stable absorbance is obtained, a certain amount of acid or alkali is added, and the pH value is determined by the molybdosilicate blue absorptiometry. This is because it can be adjusted within a range where stable absorbance can be obtained.

  In particular, using an indicator that changes color at a pH value higher than the range where stable absorbance can be obtained in the molybdosilicate blue absorptiometry, alkali is added to the absorbing solution that is in a state of variation on the strongly acidic side, It is preferable to adjust to a pH value higher than the range where stable absorbance can be obtained, and then adjust the pH value to a range where stable absorbance can be obtained by adding a certain amount of acid.

  As the indicator, 4-nitrophenol is preferably used. 4-Nitrophenol has a color change point of pH 5.4, and exhibits yellow at pH 5.4 or higher and colorless at pH 5.4 or lower. Further, it is preferable to use high-purity ammonia water as the alkali and hydrochloric acid (1 + 1) as the acid. Hereinafter, a more specific pH adjustment method will be described.

  The absorption liquid after silicon tetrafluoride vaporization separation is transferred to a PTFE beaker. And 2-3 drops of 4-nitrophenol for pH adjustment are dripped. Add 5 mL of high-purity ammonia water to develop the fluorescent yellow color of 4-nitrophenol. Thereafter, hydrochloric acid (1 + 1) is added until the bright fluorescent yellow color of 4-nitrophenol disappears. At the point of disappearance, the pH of each absorbing solution is in a uniform state. 1 mL of hydrochloric acid (1 + 1) is added to adjust the pH range from 0.6 to 0.9 (particularly around 0.7), which is a pH range suitable for color development.

  A color of molybdosilicate yellow is obtained by adding 1.5 mL of 10 w / v% ammonium molybdate to the absorbent. Leave for 5 minutes or more to stabilize the molybdosilicate yellow complex. Add 2 mL of 10 w / v% oxalic acid, immediately add a reducing agent of 1-amino-2-naphthol-4-sulfonic acid, and color. The method for preparing the reducing agent conforms to Non-Patent Document 2. The solution is made up to volume in a 25 mL volumetric flask.

  The absorbance of the obtained solution is measured. In order to stabilize the molybdosilicate blue complex, measurement is performed after 30 minutes or more have passed since coloring. The cell uses a quartz cell. The measurement wavelength is a fixed wavelength of 815 nm. Pure water is used as a control solution. The amount of silicon is quantitatively analyzed by comparing the absorbance with a calibration curve sample obtained by processing in the same manner as the sample.

  The lower limit of quantification by the method according to the present embodiment was calculated by defining as 10 times the standard deviation of 10 measurements of the blank test. That is, since the standard deviation σ of the blank test is 0.0086 μg, the lower limit of quantification (10σ of the blank test) is 0.086 μg.

  Examples will be described below, but the present invention is not limited to the following examples.

[sample]
As the standard sample, copper and zinc containing copper and zinc, which cause precipitation in sulfuric acid, and pure iron insoluble in sulfuric acid were selected. The compositions of these standard samples are shown in Table 1 and Table 2, respectively. About the brass sample, in order to evaluate the silicon quantitative property of a single and a sub ppm level, it evaluated by using as a sample what diluted solid using the pure copper "CUM-26015A Cu 4N" by Furuuchi Chemical Co., Ltd. For pure iron samples, the balance is iron.

[Sample dissolution]
0.0114 g of brass standard sample and 0.9732 g of pure copper were weighed in a PFA container and dissolved in 5 mL of nitric acid. Moreover, about 0.2 g of a standard sample of pure iron was weighed in a PFA container and dissolved in 5 mL of nitric acid.

[Vaporization separation]
To the solution was added 25 mL of fuming nitric acid. The vaporization separation was performed under the following conditions.
Absorbent: 0.1 w / v% boric acid, 10 mL,
Hydrofluoric acid: 6 w / v%, 0.5 mL,
Nitrogen gas flow rate: 0.5 L / min, nitrogen gas purge time: 30 min

[PH adjustment]
The absorbent after vaporization and separation was transferred to a PTFE beaker, and 2-3 drops of 4-nitrophenol for pH adjustment were dropped. After adding 5 mL of high-purity ammonia water to develop a bright fluorescent yellow color of 4-nitrophenol, hydrochloric acid (1 + 1) was added until the color of the solution became colorless.

[Coloration]
1.0 mL of hydrochloric acid (1 + 1) was added, followed by 1.5 mL of 10 w / v% ammonium molybdate. After the addition, the mixture was allowed to stand for 5 minutes. 2 mL of 10 w / v% oxalic acid was added, and 0.5 mL of reducing agent was immediately added. The solution was made up to volume in a 25 mL volumetric flask.

[analysis]
The resulting solution was allowed to stand for 30 minutes or more, and then the absorbance was measured. A quartz cell with a width of 2 cm was used as the cell, and a wavelength of 815 nm was measured. Pure water was used as a control solution. For the calibration curve, a commercially available silicon standard solution is added in an arbitrary amount so that the concentration of silicon becomes stepwise in a solution in which 5 mL of nitric acid and 25 mL of fuming nitric acid are mixed. -What was obtained by performing coloration operation was used. The silicon content was quantitatively analyzed by comparing the absorbance with the calibration curve sample.

  Tables 3 and 4 show comparisons between the certified silicon values and the actual measured values for brass and pure iron, respectively.

  As shown in Tables 3 and 4, the quantitative values obtained by quantitative analysis by the method of the present invention were the same as the certified values. That is, it is effective for quantitative analysis of silicon with high sensitivity on the order of single and sub ppm.

  The boric acid absorption liquid containing silicon tetrafluoride after vaporization and separation was measured using ICP emission spectroscopy and ICP mass spectrometry, whereby silicon was quantified.

[sample]
The same standard sample used in Example 1 was used. Brass samples were used for ICP emission spectroscopy, and pure iron samples were used for ICP mass spectrometry.

[Sample dissolution]
Each standard sample of brass and pure iron (0.1 g) was weighed into a PFA container and dissolved in 5 mL of nitric acid.

[Vaporization separation]
The same operation as in Example 1 was performed.

[Constant volume]
In ICP emission analysis, the volume was adjusted to 20 mL.
In ICP mass spectrometry, the volume was adjusted to 100 mL.

[analysis]
A commercially available silicon standard solution was added in an arbitrary amount in a 10 mL boric acid aqueous solution so that the concentration of silicon was stepwise, and a volume adjusted to 20 mL or 100 mL was used as a calibration curve solution. The silicon content was quantitatively analyzed by comparing the counts obtained with the calibration curve sample and the standard sample.
Table 5 shows a comparison between the certified silicon value and the actual measurement value.

  As shown in Table 5, the quantitative value of silicon obtained by treating the absorption liquid after vaporization separation by ICP emission spectrometry and ICP mass spectrometry was the same as the certified value. In the present invention, ICP emission spectroscopy and ICP mass spectrometry can be used in addition to absorptiometry as a method for quantitative determination of silicon.

[sample]
As a standard sample, one containing zinc as a main component which causes precipitation of zinc sulfate in sulfuric acid was selected. The composition of this standard sample is shown in Table 6. The balance of the sample is zinc.

[Sample dissolution]
About 0.1 g of the sample was weighed in a PFA container and dissolved with 5 mL of nitric acid.

[Vaporization separation], [pH adjustment], [Coloration], [Analysis]
The same operation as in Example 1 was performed. The results are shown in Table 7.

  As shown in Table 7, the quantitative value obtained by the quantitative analysis by the method of the present invention was the same as the certified value. That is, the present invention relates to determination of silicon contained in a sample containing zinc as a main component, a hot dip galvanized steel sheet, a hot dip zinc-5 wt% aluminum alloy plated steel sheet, a hot dip zinc-55 wt% aluminum alloy plated steel sheet, a hot dip aluminum plated steel sheet, and the like. Analysis is also applicable.

According to the present invention, silicon in a solid or liquid that could not be quantified by the conventional silicon tetrafluoride vapor separation method using sulfuric acid can be quantified with sub-ppm accuracy. The present invention is particularly effective for quantitative analysis of silicon contained in metals, alloys, compounds and the like that are soluble in a solution containing 70 w / w% or more of nitric acid.

Claims (6)

A method for quantitatively analyzing silicon contained in a sample,
(1) adding fuming nitric acid to a silicon-containing solution to obtain a nitric acid acidic solution;
(2) adding hydrofluoric acid to the nitric acid acidic solution to generate silicon tetrafluoride gas;
(3) introducing the silicon tetrafluoride gas into a boric acid solution together with nitric acid gas and collecting silicon; and
(4) A method for quantitatively analyzing silicon, comprising a step of analyzing a boric acid solution in which silicon is collected to determine a silicon content in the sample. In the step (1), nitric acid having a concentration of 70 w / w% or more is used.
The silicon quantitative analysis method according to claim 1. In the step (4), analysis of the boric acid solution in which the silicon is collected is performed by inductively coupled plasma emission spectroscopy, inductively coupled plasma mass spectrometry, or atomic absorption spectrophotometry.
The method for quantitative analysis of silicon according to claim 1 or 2. In the step (4), when analyzing the boric acid solution collecting the silicon by the molybdosilicate blue absorptiometry, the pH value of the boric acid solution collecting the silicon is obtained as a stable absorbance. After adjusting to a value outside the range that can be obtained, adjust to a range where stable absorbance is obtained,
The silicon quantitative analysis method according to any one of claims 1 to 3. When adjusting the pH value of the boric acid solution that has collected silicon to a value other than the range in which stable absorbance is obtained, an indicator that changes color in a range other than the pH range in which stable absorbance is obtained is used.
The silicon quantitative analysis method according to claim 4. The step (1) uses a silicon-containing solution obtained by dissolving a solid with an acid.
The silicon quantitative analysis method according to any one of claims 1 to 5.