Method for detecting concentration of polybasic mixed acid

Abstract

The invention discloses a polybasic mixed acid concentration detection method. The method comprises the following steps: S1) weighing a sample and diluting; the method comprises the following steps: S1) water bath digestion, S3) total H < + > determination, S4) hydrofluoric acid concentration determination, S5) sulfuric acid and phosphoric acid concentration determination, and S6) nitric acid concentration determination.According to the method, only an acid-base titration electrode and a fluorine ion meter are needed, more titration electrodes and titration reagents are not needed, the operation is simple, and the accuracy is high.

Description

Technical Field

[0001] This invention belongs to the field of chemical multi-component mixed acid component detection technology, specifically relating to a method for detecting the concentration of multi-component mixed acids. Background Technology

[0002] Etching solutions containing multiple mixed acids (such as a quaternary mixed acid system of sulfuric acid, phosphoric acid, nitric acid, and hydrofluoric acid) are widely used in wafer thinning processes for monocrystalline or polycrystalline silicon. However, high-precision and highly repeatable analytical methods for the content of each component in these mixed acids remain a challenge for the industry. CN 114264769 B mentions an acid-base titration method that utilizes the differences in the ionization degrees of different acids to separate them through potentiometric titration. However, this method is only applicable to mixed systems of strong and weak acids, and can only be analyzed when the differences in the ionization degrees of the different components in the solution are significant (e.g., a mixed solution of nitric acid and acetic acid). If the solution is a mixed system of strong acids (e.g., a mixed solution of nitric acid and sulfuric acid), this method will not be effective. This literature also mentions a method using BaCl2 precipitation titration to determine sulfate ions, but BaCl2... 2+ Fluoride ions readily precipitate from various acid radicals, which limits the application range of precipitation titration. CN 110907509 B mentions a method for detecting fluoride ion concentration, which utilizes the high selectivity of a fluoride ion electrode and has become a widely used method. However, this method can only detect fluoride ion concentration and cannot determine the concentration of other components in the solution. Summary of the Invention

[0003] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for detecting the concentration of a multi-component mixed acid includes the following steps: S1): Sample dilution: Weigh the sample and dilute it, recording the dilution factor; S2): Water bath digestion: Place the diluted solution in a water bath at 80-90℃ for 25-35 minutes, then cool to room temperature; S3): Total H + Determination: The diluted digestion solution of mixed acid in S2 was titrated with sodium hydroxide standard solution. The equivalence point and the amount of titrant consumed to reach the equivalence point were obtained by monitoring the potential change. The total hydrogen ion concentration and amount of substance neutralized by the titrant were calculated. S4): Hydrofluoric acid concentration determination: The fluoride ion concentration-potential curve is determined using sodium fluoride standard solution. Then, the diluted digestion solution in S2 is detected using a fluoride ion meter to obtain the fluoride ion concentration of the original solution and calculate the amount of fluoride ion. S5): Determination of sulfuric acid and phosphoric acid concentrations; S6): Nitric acid concentration determination: based on total H₂ + Subtracting hydrofluoric acid, sulfuric acid, and phosphoric acid yields the concentration of nitric acid.

[0004] Furthermore, step S4 specifically includes the following steps: S41): Use a pipette to add 1 mL, 5 mL and 10 mL of standard NaF solution to three 100 mL volumetric flasks, respectively; S42): Use a fluoride ion meter to test the solutions in the three volumetric flasks respectively, record the relationship between the potential value and the concentration, and obtain the concentration-potential curve; S43): Take out a portion of the mixed acid dilution solution from S2, weigh it, dilute it, and record the dilution factor; S44): The redistribution solution in S43 is tested using a fluoride ion meter, and the fluoride ion concentration in the redistribution solution is obtained based on the concentration-potential curve; S45): Calculate the total fluoride ion concentration in the diluted digestion solution of mixed acid.

[0005] Furthermore, step S5 specifically includes the following steps: S51): Weigh a portion of the sample from the solution to be tested and place it in a PTFE crucible; S52): Add 8-15g of deionized water; S53): Place the PTFE crucible on a heating platform and heat it. Record the residue after evaporation as the evaporating liquid. S54): Pour the evaporated liquid into a beaker, wash the residue in the crucible with water and pour it all into the beaker, titrate the solution in the beaker with a standard sodium hydroxide solution of known concentration, and obtain two equivalence points by monitoring the potential change; S55): Calculate the mass concentrations of phosphoric acid and sulfuric acid in the solution.

[0006] Furthermore, the concentration of the standard NaF solution is 1000 ppm.

[0007] Furthermore, the evaporation conditions for step S54 are: temperature 200℃, time 1-2h.

[0008] The beneficial effects of this invention are: The method of this invention only requires an acid-base titration electrode and a fluoride ion meter, without the need for additional titration electrodes and reagents. It is simple to operate and highly accurate. This invention removes the volatile components from polybasic mixed acids by evaporation, leaving the non-volatile components for titration. This solves the problem that nitric acid, phosphoric acid, and sulfuric acid in polybasic mixed acid solutions, especially polybasic strong acid mixed solutions, cannot be directly separated by potentiometric titration. Furthermore, it eliminates the need for multiple electrodes, avoiding the problem of insufficient accuracy caused by different electrodes.

[0009] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0010] Figure 1 The detection curve was obtained by titrating the quaternary mixed acid system in step S2 with NaOH standard solution in an aqueous solvent and passing it through a pH electrode. Figure 2 The detection curve obtained by titrating the phosphoric acid and sulfuric acid mixture in step S54 with NaOH standard solution in an aqueous solvent was obtained by using a pH electrode. Detailed Implementation

[0011] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0012] like Figures 1 to 2 The method for detecting the concentration of a polyacid mixture shown includes the following steps: S1): Sample dilution: Weigh the sample and dilute it, recording the dilution factor. Record the sample mass m1 and the diluted mass m2, and denote the dilution factor as N1 = m2 / m1; S2): Water bath digestion: Place the diluted solution in an 80-90℃ water bath for 25-35 minutes, then cool to room temperature; the purpose is to digest the bound H in the solution. + This releases the fluoride ions, preventing interference during subsequent titration and converting bound fluoride ions into a free state detectable by a fluoride ion meter.

[0013] S3): Total H + Determination: The diluted digestion solution of mixed acid in S2 was titrated with a standard sodium hydroxide solution. The equivalence point and the amount of titrant consumed to reach the equivalence point were obtained by monitoring the potential change. The total hydrogen ion concentration and amount of substance neutralized by the titrant were calculated using the following formula: w(H + )= n(H + ) / V 液 ,n(H + ) = (w(NaOH)*V1), where w(H + The total H in the sample solution is... + Concentration, w(NaOH) is the concentration of sodium hydroxide, V1 is the amount of titrant consumed to reach the equivalence point, V 液 n(H) represents the volume of the diluted digestion solution in S2. + The total H+ in the diluted digestion solution is... +The amount of substance; The concentration of each single acid during acid-base titration is detected according to the reaction formula H. + +OH - =H2O is the basic principle. In this invention, the mixed acid system is a quaternary strong and weak mixed acid system with known composition but unknown concentration, including nitric acid and hydrofluoric acid. According to the change of the ionization equilibrium constant, the ionization constant of each acid in the mixed acid is consulted to determine the proton ionization order in each acid, thereby confirming the acid corresponding to the titrant consumed in each jump. For example, if the digestion solution is a quaternary mixed acid, the volume corresponding to the second equivalence point during titration represents the total H₂. + The volume of NaOH consumed, the total H+ in the solution + The amount of substance is equal to the amount of hydrogen provided by each component. + The sum of the amounts of substance satisfies the following relationship: n(H + )= 1n(HNO3)+ 1n(HF)+ 3n(H3PO4)+ 2n(H2SO4); S4): Hydrofluoric acid concentration determination: The fluoride ion concentration-potential curve is determined using sodium fluoride standard solution. Then, the diluted digestion solution in S2 is detected using a fluoride ion meter to obtain the fluoride ion concentration c(HF) of the original solution, and the amount of fluoride ion n(HF) = w(HF)*m2*0.01 / 20.01 is calculated. Specifically, step 4 includes the following steps: S41): Using a pipette, add 1 mL, 5 mL, and 10 mL of standard NaF solution to three 100 mL volumetric flasks, respectively; the concentration of the standard NaF solution is 1000 ppm, and the final fluoride ion concentrations in the solutions are 10 ppm, 50 ppm, and 100 ppm, respectively.

[0014] S42): Use a fluoride ion meter to test the solutions in the three volumetric flasks respectively, record the relationship between the potential value and the concentration, and obtain the concentration-potential curve; S43): Take out a portion of the mixed acid dilution solution from S2, weigh it, and then dilute it until the final solution has an HF mass concentration (wt%) below 0.01%. This solution is called the re-diluted solution. The sample weight is m3 and the diluted mass is m4. The dilution factor N2 = m3 / m4. S44): The redistribution solution in S43 was tested using a fluoride ion meter, and the fluoride ion concentration w(F) in the redistribution solution was obtained from the concentration-potential curve. + ); S45): Calculate the total fluoride ion concentration w(F) in the diluted digestion solution. + ) Total = N2* w (F +)*20 / 19 / 100*100%.

[0015] S5): Determination of sulfuric acid and phosphoric acid concentrations: Record the measured sulfuric acid concentration as w(H2SO4) and phosphoric acid concentration as w(H3PO4); preferably, step 5 specifically includes the following steps: S51): Weigh a portion of the sample from the solution to be tested and place it in a PTFE crucible, recording the mass as m5; S52): Add 8-15g of deionized water; S53): The PTFE crucible is placed on a heating table for heating. The evaporation conditions are: temperature: 200℃, time: 1-2h. The residue after evaporation is called the evaporating liquid, and the residue after heating consists of phosphoric acid and sulfuric acid. S54): Pour the evaporated liquid into a beaker, rinse the crucible with water to remove any residue, and pour the rinsed liquid back into the beaker. Titrate the solution in the beaker with a standard sodium hydroxide solution of known concentration. Obtain two equivalence points by monitoring the potential change. Record the volumes of sodium hydroxide consumed at the two equivalence points as V2 and V3, respectively. The titration curves for sulfuric acid and phosphoric acid are shown below. Figure 2 As shown, the first equivalence point represents the two ionizations of sulfuric acid and the first ionization of phosphoric acid, and the second equivalence point represents the second ionization of phosphoric acid. S55): Calculate the mass concentrations of phosphoric acid and sulfuric acid in the solution. w(H3PO4)=(V3-V2)*c(NaOH)*97.994 / m5 / 1000; w(H2SO4)=c(NaOH)*(2*V2-V3) / 2*98.079 / m5 / 1000.

[0016] S6): Nitric acid concentration determination: Calculate the nitric acid concentration according to the formula: w(HNO3) = w(H + )- w(H2SO4)- w(H3PO4)- w(HF), where w(HNO3) is the concentration of nitric acid.

[0017] To further illustrate the purpose and practical effect of this method, solutions of known concentrations were used to verify its accuracy. 75.04 g of HF solution (48.968%), 253.21 g of HNO3 solution (70.76%), 103.10 g of H3PO4 solution (85.4%), 58.05 g of H2SO4 solution (96.593%), and 10.6 g of H2O were accurately weighed, totaling 500 g.

[0018] The percentage concentration of each component in the sample was calculated based on the theoretical weighing value, and the results were obtained according to the detection method proposed in this invention. The error was compared with the standard value, and the results are shown in the table below. As shown in the table, this method has high detection accuracy, and the relative error of the detection results of each component in the quaternary mixed acid is less than 1%. The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for detecting concentration of multi-element mixed acid, characterized in that: The method comprises the following steps: S1): sample weighing and dilution: weighing the sample and diluting to record the dilution multiple; S2): water bath digestion: placing the diluted solution into an 80-90 DEG C water bath for digestion for 25-35 min, and then cooling to room temperature; S3): Total H + Determination: The mixed acid dilution digestion solution in S2 is titrated with a sodium hydroxide standard solution, the equivalence point and the amount of titrant consumed to reach the equivalence point are obtained by monitoring the potential change, and the total hydrogen ion concentration and the amount of substance neutralized by the titrant are calculated; S4): hydrofluoric acid concentration determination: using a sodium fluoride standard solution to determine the concentration-potential curve of fluorine ions, and then using a fluorine ion meter to detect the diluted digestion solution in S2, so as to obtain the fluorine ion concentration of the original solution and calculate the amount of substance of fluorine ions; S5): sulfuric acid and phosphoric acid concentration determination; S6) Nitric acid concentration determination: The total H + Subtracting the hydrofluoric acid and sulfuric acid from the phosphoric acid gives the nitric acid concentration.

2. The method for detecting concentration of multi-element mixed acid according to claim 1, characterized in that: The step S4 specifically comprises the following steps: S41): using a pipette to add 1 mL, 5 mL and 10 mL of the standard NaF solution into three 100 mL volumetric flasks respectively; S42): using a fluorine ion meter to detect the solutions in the three volumetric flasks respectively, recording the potential value and the concentration value, and obtaining the concentration-potential curve; S43): taking out part of the mixed acid diluted digestion solution in S2, weighing, diluting, and recording the dilution multiple; S44): using a fluorine ion meter to detect the rediluted solution in S43, and obtaining the fluorine ion concentration in the rediluted solution according to the concentration-potential curve; S45): calculating the total fluorine ion concentration of the mixed acid diluted digestion solution.

3. The method of claim 1, wherein: The step S5 specifically comprises the following steps: S51): weighing part of the sample from the to-be-detected solution and placing it in a PTFE crucible; S52): adding 8-15 g of deionized water; S53): placing the PTFE crucible on a heating table for heating, and recording the residual part after evaporation as an evaporation solution; S54): pouring the evaporation solution into a beaker, washing the residues in the crucible with water and pouring them all into the beaker, using a standard sodium hydroxide solution with a known concentration to titrate the solution in the beaker, and obtaining two equivalent points by monitoring the potential change; S55): calculating the mass concentration of phosphoric acid and sulfuric acid in the solution.

4. The method of claim 1, wherein: The concentration of the standard NaF solution is 1000 ppm.

5. The method of claim 3, wherein: The evaporation condition of S54) is that the temperature is 200 DEG C, and the time is 1-2 h.

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