Method for detecting content of sodium stearate in oxide remover for hot-rolled steel pipe

Abstract

The invention belongs to the field of metallurgical analysis, and relates to a method for detecting the content of sodium stearate in an oxide remover for a hot-rolled steel pipe, which comprises the following steps: placing the oxide remover in deionized water, uniformly mixing, then dropwise adding an acid solution, heating to boil, controlling the pH value to be 2-4, keeping stirring, and reacting to obtain a sample solution; cooling the sample solution to room temperature, adding an organic solvent, keeping stirring, and filtering insoluble substances to obtain filtrate; and pouring the filtrate into a separating funnel, vigorously oscillating, standing, transferring an organic phase into a weighed distillation flask, distilling to obtain stearic acid, and calculating to obtain the content of sodium stearate. The method for measuring the content of sodium stearate in the oxide removing agent has relatively high accuracy and precision.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical analysis and relates to a method for detecting the content of sodium stearate in an oxide remover for hot-rolled steel pipes. Background Art

[0002] During the steel pipe rolling process, it is necessary to spray an oxide remover into the pierced shell to remove the scale instantaneously generated on the inner surface of the shell. Currently, the commonly used oxide remover is composed of sodium sulfate, borax, sodium phosphate and sodium stearate. A certain amount of sodium stearate is required in the used oxide remover because sodium stearate is an organic substance and can burn rapidly at high temperatures. The combustion characteristics of sodium stearate in the oxide remover are utilized to let the violently burning flame roast large pieces of scale, causing it to burst and break away from the pipe body. The content of sodium stearate is a key factor for whether the oxide remover can completely remove the scale. When the content of sodium stearate is low, the oxide remover loses its function, and internal scratches and internal scarring defects will immediately occur. When the content of sodium stearate is high, it will cause local accumulation of the antioxidant after combustion on the inner surface of the shell.

[0003] In order to avoid the adverse effects of too high or too low content of sodium stearate on the steel pipe, it is usually necessary to detect the content of sodium stearate in the purchased oxide remover, and only after passing the detection can it be sprayed. Therefore, the accurate determination of the content of sodium stearate is very important. Currently, pure sodium stearate can be detected by gas chromatography. Since the antioxidant is a mixture containing various inorganic salts that are difficult to volatilize, using gas chromatography for detection will damage the gas chromatograph. There is no detection method for the content of sodium stearate in the antioxidant in various literatures. Therefore, it is necessary to develop a detection method for the content of sodium stearate in the oxide remover. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for detecting the content of sodium stearate in an oxide remover for hot-rolled steel pipes. Since borax, sodium sulfate, and sodium phosphate in the antioxidant components for hot-rolled steel pipes are all soluble in water, while sodium stearate is slightly soluble in cold water and soluble in hot water. Stearic acid is insoluble in water and soluble in organic solvents. First, sodium stearate is converted into stearic acid, dichloromethane is added, and stearic acid is extracted into the organic phase and separated, and the content of sodium stearate is obtained by calculation. This method for determining the content of sodium stearate in the oxide remover has high accuracy and precision.

[0005] The technical solution adopted by the present invention to solve the technical problems is:

[0006] A method for detecting the content of sodium stearate in an oxide remover for hot-rolled steel pipes, comprising:

[0007] (1) Place the deoxidizer in deionized water at 50 - 70 °C and mix evenly. Then, dropwise add a 1 - 2 mol / L sulfuric acid solution at a dropping rate of 6 - 15 drops / min, heat to boiling, and continue boiling until the pH value remains between 2 - 4 without change. Stop adding the sulfuric acid solution, keep stirring, and react for 20 - 40 min to obtain a sample solution. The mass - to - volume ratio of the deoxidizer to water is 5 - 15 g:100 mL. The deoxidizer includes sodium stearate, sodium sulfate, sodium phosphate, and borax.

[0008] (2) Cool the sample solution to room temperature, add dichloromethane, keep stirring for 20 - 40 min, filter the insoluble matter to obtain a filtrate.

[0009] (3) Pour the filtrate into a separating funnel, shake vigorously, and after standing for 20 - 40 min, transfer the organic phase to a weighed distillation flask, and distill until no dichloromethane drips from the condenser within 2 - 3 min to obtain stearic acid, and calculate the sodium stearate content.

[0010] Further, the mass - to - volume ratio of the deoxidizer to water is 10 - 15 g:100 mL.

[0011] Further, the temperature of the deionized water is 60 - 70 °C.

[0012] Further, the organic solvent is dichloromethane. Firstly, dichloromethane is immiscible with water and can be separated by liquid - liquid extraction. Secondly, dichloromethane has a high solubility for stearic acid and high extraction efficiency.

[0013] Further, the dropping rate is 8 - 10 drops / min.

[0014] Further, the pH value is 2 - 3. By controlling the pH value, it is determined whether sodium stearate is completely converted into stearic acid. If the pH value is too high, sodium stearate cannot be completely converted into stearic acid; if the pH value is too low, sulfuric acid will be wasted.

[0015] Further, the deoxidizer includes 9.9 - 15.1% sodium stearate, 14.9 - 25.1% sodium sulfate, 24.9 - 35.1% sodium phosphate, and 29.9 - 40.1% borax by mass percentage.

[0016] Further, the specific calculation method of the sodium stearate content in step (3) is as follows: Calculate according to the formula where C 硬脂酸钠 is the content of sodium stearate, m1 is the mass of the distillation flask, m2 is the sum of the mass of the distilled stearic acid and the distillation flask, M 硬脂酸 is the relative molecular mass of stearic acid, M 硬脂酸钠 is the relative molecular mass of sodium stearate, m 除氧化物剂is the mass of the deoxidizer used.

[0017] Further, the stirring speed is 400 - 700 rpm.

[0018] The advantages and positive effects of the present invention are:

[0019] The detection method for the content of sodium stearate in the antioxidant for hot-rolled steel pipes of the present invention does not rely on a chromatograph, the analysis process is rapid and simple, the results are accurate and reliable, with high accuracy and precision, and can meet the production and detection requirements of enterprises. Specific Embodiments

[0020] The present invention will be further described in detail below through specific embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0021] Embodiment

[0022] 1. Main reagents and materials

[0023] Experimental water: deionized water;

[0024] Sulfuric acid, anhydrous sodium sulfate, borax, sodium phosphate, sodium stearate and dichloromethane are all of analytical grade;

[0025] Since there is no commercially available standard substance for the deoxidizer, the standard deoxidizer is prepared by itself, and the specific composition is shown in Table 1.

[0026] Table 1 Composition of the standard deoxidizer

[0027]

[0028]

[0029] 2. Test steps:

[0030] A detection method for the content of sodium stearate in a deoxidizer for hot-rolled steel pipes includes:

[0031] (1) Weigh 20 g of the standard deoxidizer sample and put it into a beaker, add 200 mL of deionized water at 60 °C and mix evenly. Then, dropwise add 1 mol / L sulfuric acid solution at a dropping speed of 8 - 10 drops / min, heat to boiling, control the pH value to be 2 - 3, keep stirring at 500 rpm, and react for 30 minutes to obtain a sample solution;

[0032] (2) Cool the above sample solution to room temperature, add 100 mL of dichloromethane, keep stirring at 500 rpm for 30 minutes, filter the insoluble matter to obtain a filtrate;

[0033] (3) Pour the filtrate into a clean separatory funnel, shake it vigorously, and after standing for 30 minutes, transfer the organic phase to a weighed distillation flask. Distill to obtain stearic acid, weigh the mass of the distillation flask at this time, calculate the content of sodium stearate according to the formula, and the results are shown in Table 2:

[0034]

[0035] where C 硬脂酸钠 is the content of sodium stearate; m1 is the mass of the distillation flask, g; m2 is the sum of the mass of the distilled stearic acid and the distillation flask, g; M 硬脂酸 is the relative molecular mass of stearic acid; M 硬脂酸钠 is the relative molecular mass of sodium stearate; m 除氧化物剂 is the mass of the deoxidizer used, g.

[0036] 3. Accuracy and precision

[0037] Table 2 Content of sodium stearate in the deoxidizer

[0038]

[0039]

[0040] Note: The recovery rate is the ratio of the measured value of sodium stearate to the calculated value by weighing; the relative standard deviation is the ratio of the standard deviation between the measured values of samples of Standard 1, Standard 2, and Standard 3 and between the measured values of samples of Standard 4, Standard 5, and Standard 6 to the average value of the measured values.

[0041] The recovery rates of the samples from Standard 1 to Standard 6 in Table 2 are all around 90%. It can be seen that the content of sodium stearate obtained by this method is very close to the content of sodium stearate calculated by weighing. This indicates that the method for determining the content of sodium stearate in the deoxidizer has high accuracy.

[0042] The relative standard deviation in Table 2 is less than 1.79%. In the analysis method, it is usually required that the precision result is less than 3%. This indicates that the method for determining the content of sodium stearate in the deoxidizer has high precision.

[0043] 4. Spike recovery

[0044] A spike recovery test was carried out on the production sample A. The treatment of the production sample A was the same as that of Standard 2. The spiked substance was analytical pure solid sodium stearate, and the spiked amount and recovery rate results are shown in Table 3.

[0045] Table 3 Spiked amount and recovery rate results of production sample A are shown in Table 3

[0046]

[0047] As can be seen from Table 3, the spike recovery results are between 86.57 - 90.44%, indicating that the sample composition has no obvious effect on the detection of sodium stearate in this method. At the same time, it also shows that the detection of sodium stearate in the antioxidant by this method has high accuracy.

[0048] Comparative Example 1

[0049] The difference from the Example is only that in test step (1), the acid solution dropped is 1 mol / L hydrochloric acid solution.

[0050] Comparative Example 2

[0051] The difference from the Example is only that in test step (1), the acid solution dropped is 1 mol / L phosphoric acid solution.

[0052] Comparative Example 3

[0053] The difference from the Example is only that in test step (1), the acid solution dropped is 1 mol / L acetic acid solution.

[0054] Comparative Example 4

[0055] The difference from the Example is only that in test step (2), the organic solvent added is ethyl acetate. The detection results of Comparative Examples 1 - 4 are shown in Table 4.

[0056] Table 4 Detection Results of Comparative Examples 1 - 4

[0057]

[0058] Using hydrochloric acid solution in Comparative Example 1, the recovery rate decreases because hydrochloric acid is a volatile acid and easily volatilizes hydrogen chloride gas, resulting in inaccurate results and having a strong pungent smell, making the operation inconvenient.

[0059] Using phosphoric acid solution and acetic acid solution in Comparative Example 2 and Comparative Example 3, the recovery rate decreases significantly because phosphoric acid is a moderately strong acid and acetic acid is a weak acid, which can only be partially ionized in aqueous solution and the reaction is incomplete.

[0060] Using ethyl acetate in Comparative Example 4, the recovery rate is relatively low because ethyl acetate has a certain solubility in acidic aqueous solution and part of the ethyl acetate will dissolve in the aqueous phase, affecting the extraction effect.

[0061] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for detecting the content of sodium stearate in a deoxidizer for hot-rolled steel pipes, characterized in that: include: (1) placing an oxidation remover in deionized water at 50 to 70° C. and mixing the mixture uniformly, then dropping a 1 to 2 mol / L sulfuric acid solution at a dropping speed of 6 to 15 d / min, heating and boiling the mixture until the pH value remains between 2 and 4 and does not change, stopping the dropping of the sulfuric acid solution, and stirring the mixture for 20 to 40 minutes to obtain a sample solution; the mass ratio of the oxidation remover to the volume of water is 5 to 15 g:100 mL; the oxidation remover comprises sodium stearate, sodium sulfate, sodium phosphate and borax; (2) Cool the sample solution to room temperature, add dichloromethane, keep stirring for 20 to 40 minutes, filter the insoluble matter, and obtain a filtrate; (3) Pour the filtrate into a separatory funnel, shake vigorously, and let stand for 20 to 40 minutes. Then transfer the organic phase to a weighed distillation flask and distill until no dichloromethane drips out of the condenser within 2 to 3 minutes to obtain stearic acid. Calculate the sodium stearate content.

2. The detection method according to claim 1, characterized in that: The temperature of the deionized water is 60-70°C.

3. The detection method according to claim 1, characterized in that: The mass ratio of the deoxidizing agent to the volume of water is 10-15 g:100 mL.

4. The detection method according to claim 1, characterized in that: The dropping speed is 8 to 10 d / min.

5. The detection method according to claim 1, characterized in that: The pH value is 2-3.

6. The detection method according to claim 1, characterized in that: The deoxidizing agent comprises 9.9-15.1% by mass of sodium stearate, 14.9-25.1% by mass of sodium sulfate, 24.9-35.1% by mass of sodium phosphate and 29.9-40.1% by mass of borax.

7. The detection method according to claim 1, characterized in that: The stirring speed is 400-700 rpm.

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