Tracing method for determining sulfur content less than 0.003% (mass fraction) by carbon and sulfur determination analyzer

Abstract

The invention relates to the technical field of determination by a carbon and sulfur determination analyzer, in particular to a traceability method for determining the sulfur content less than 0.003% (mass fraction) by the carbon and sulfur determination analyzer. In the prior art, the traceability range does not contain less than 0.003% (mass fraction) of sulfur, and a standard substance calibration detection method cannot be adopted. The method for calculating the detection limit by measuring the blank value can be used for tracing the sulfur with low content of less than 0.003% (mass fraction). An empty burning crucible is directly used for making a blank, the stability of the blank value can not be ensured even if the crucible is burnt at present, and the invention provides a method for obtaining the stable blank value to analyze the detection limit of equipment by carrying out neutralization reaction on elemental silver, the crucible and sulfur in the air (whether the crucible is burnt at present or not). The reliability of the ultra-low sulfur content analysis method less than 0.003% (mass fraction) is judged; and the measurement result of the measurement equipment in the range is traced.

Description

Technical Field

[0001] The invention relates to the technical field of determination of carbon and sulfur analyzers, in particular to a tracing method for determining the sulfur content of less than 0.003% (mass fraction) by a carbon and sulfur analyzer. Background Art

[0002] The measuring principle of the carbon and sulfur determination instrument is as follows: a certain mass of sample is added with flux and then heated and burned at high temperature in a high-frequency furnace, so that the carbon and sulfur in the sample react with oxygen to generate carbon dioxide and sulfur dioxide gas. Driven by the carrier gas, the gas passes through the gas path processing system and enters the carbon dioxide and sulfur dioxide detection pool. The carbon dioxide and sulfur dioxide have strong characteristic absorption characteristics at specific wavelengths respectively. By measuring the change in the intensity of gas absorption light, the carbon dioxide and sulfur dioxide contents are analyzed, thereby determining the carbon and sulfur contents. Usually, standard samples with known carbon and sulfur contents are required to make curves, and the measurement results of the measured substances are compared with the standard substance curves.

[0003] The metrological performance requirements in the verification procedure of JJG 395-1997 "Carbon and Sulfur Determination Analyzer" are as follows: the minimum sulfur content is 0.001% (mass fraction). In 2016, the verification procedure of JJG 395-1997 "Carbon and Sulfur Determination Analyzer" was updated to JJG 395-2016 "Carbon and Sulfur Determination Analyzer". The new verification procedure modified the traceability range of the measurement value, among which the minimum sulfur content is 0.003% (mass fraction). Sulfur is a harmful element that increases the brittleness of the material. For most industries, materials with a sulfur content of > 0.003% (mass fraction) are applicable.

[0004] The metrological performance requirement in the calibration procedure of JJG 395-2016 "Carbon and Sulfur Analyzers" is a maximum allowable error of ±0.001% (mass fraction) for sulfur content (0.003~0.010)%. 5.1.1 The calibration standard substances and supporting equipment require that the expanded uncertainty of the certified standard shall not be greater than 1 / 3 of the indication error limit. Currently, the certified standard substances in the range of < (0.003~0.010)% (mass fraction) cannot meet the requirements.

[0005] When the sulfur content to be measured is small enough, the accuracy of the zero point (minimum content) is more important than the accuracy of the standard curve.

[0006] For aircraft engines and defense production, some high-temperature materials have a sulfur content requirement of less than 0.003% (mass fraction). The current verification procedures cannot trace the reliability of the measurement results in this range.

[0007] The reliability of the measurement results of the equipment when the sulfur content is less than 0.003% (mass fraction) is related to the product quality of the related manufacturing industry; therefore, it is currently imperative to invent a traceability method for the reliability of the sulfur content measurement results when the sulfur content of the measuring equipment is less than 0.003% (mass fraction). Summary of the invention

[0008] In order to solve the above technical problems existing in the prior art, the present invention provides a traceability method for determining the sulfur content of less than 0.003% (mass fraction) by a carbon and sulfur analyzer, which is as follows:

[0009] A traceability method for sulfur content less than 0.003% (mass fraction) determined by a carbon and sulfur analyzer, comprising the following steps:

[0010] (1) Prepare a blank crucible; use either a freshly fired crucible or an unfired crucible. A freshly fired crucible has a small amount of silver added (0.2-0.5 g, generally 0.2-0.3 g), while an unfired crucible has a large amount of silver added (0.5-1.0 g);

[0011] (2) Preheat the instrument to be tested according to the instructions, add silver into the crucible, the weight of silver is 0.2-1.0g;

[0012] (3) Measure n times respectively

[0013] (4) Calculate the detection limit according to the following formula:

[0014]

[0015] In the formula: S—standard deviation, % percentage;

[0016] —The average value of 10 measurement results, % percentage;

[0017] —The i-th measurement value, % content;

[0018] n—Number of measurements.

[0019] D=3·S………………………………(2)

[0020] Where: D—detection limit, % percentage content.

[0021] (5) Detection limit refers to the reliability of the instrument in measuring the minimum content. When using a carbon and sulfur analyzer to measure sulfur content less than 0.003% (mass fraction), when the detection limit D is less than 0.003% (mass fraction), it means that the instrument measurement result is reliable. Similarly, for the measurement of sulfur content less than 0.003% (mass fraction), the detection limit is less than the measured content requirement and the test result is reliable.

[0022] Furthermore, the blank crucible is a blank crucible obtained by firing a blank crucible in a muffle furnace at 1000° C. for half an hour in advance.

[0023] Furthermore, the blank crucible is a blank crucible that has been fired in advance.

[0024] Furthermore, the silver element is silver with a purity of more than 92.5%.

[0025] Furthermore, the silver element is silver flakes.

[0026] Furthermore, the number of measurements n≥10 times.

[0027] The traceability method for determining the sulfur content less than 0.003% (mass fraction) by the carbon and sulfur analyzer described in the present application is applied to determine the reliability of the sulfur content measurement results in the interval with a detection limit less than 0.003% (mass fraction). The method described in the present application uses the detection limit to trace the sulfur content of equipment less than 0.003% (mass fraction), and can also be applied to the detection limit of other low sulfur contents.

[0028] Compared with the prior art, the technical effects created by the present invention are:

[0029] (1) In instrumental analysis, the detection limit is related to the sensitivity and accuracy of the instrument. A low detection limit means the reliability of being able to detect low levels of a substance. In the prior art, the traceability range does not include sulfur <0.003% (mass fraction), and the standard substance calibration detection method cannot be used. The method of calculating the detection limit by measuring the blank value can be used to trace the low-content sulfur <0.003% (mass fraction). Using an empty crucible as a blank directly cannot guarantee the stability of the blank value even if the crucible is used and fired immediately. The technical solution of adding silver in this application can obtain a stable sulfur blank value regardless of whether the crucible is used and fired immediately or not. This application uses the method of calculating the detection limit to trace the reliability of low-content sulfur (<0.003% (mass fraction)), which can not only meet the needs of military production within this range, but also provide a new idea for domestic instrument manufacturers, which is conducive to the advancement of domestic instruments and equipment.

[0030] (2) The present application specifically uses the detection limit to trace the equipment with a sulfur content of less than 0.003% (mass fraction). The method of using the detection limit to assess the reliability of the instrument's minimum content test is relatively common, but this technology is generally used in the measurement of liquid analytes. For solid analytes with low sulfur content, the sulfur in the air and the sulfur in the crucible will affect the measurement of low sulfur, and it is difficult to find a stable blank. The present application proposes a method of analyzing the detection limit of the equipment by using a neutralization reaction of silver element with sulfur in the crucible and the air to obtain a stable blank value, so as to determine the reliability of the analysis method for ultra-low sulfur content of less than 0.003% (mass fraction) and to trace the measurement results of the measuring equipment in this range.

[0031] (3) The principle of using the carbon and sulfur analyzer is to add a baking agent to a certain mass of sample and then heat it at high temperature in a high-frequency furnace to burn it, so that the carbon and sulfur in the sample react with oxygen to generate carbon dioxide and sulfur dioxide gas, which are driven by the carrier gas through the gas path processing system and enter the carbon dioxide and sulfur dioxide detection chamber. Carbon dioxide and sulfur dioxide have strong characteristic absorption characteristics at 4260nm and 7400nm respectively. The content of carbon dioxide and sulfur dioxide is analyzed by measuring the gas absorption light intensity, so as to obtain the percentage of carbon and sulfur components in the sample. Use of infrared carbon and sulfur analyzer. Usually, a standard substance is selected within the measurement range to calibrate the equipment, and the calibrated equipment is used to measure the sample to be measured. The characteristic spectrum is used to measure the gas absorption light intensity. The calibration method with the standard substance is usually the standard curve method. For the determination of low content, the accuracy of the standard curve has almost no effect on the low content, but the accuracy of the zero point (low content) is more important. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a figure of the experimental result of Example. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further defined below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0034] Example:

[0035] The measurement principle of adding elemental silver is that there is a certain amount of sulfur in the crucible and the air. For low sulfur content: the amount of sulfur contained in 1g sample, the instrument manufacturer sets the instrument to dry-burn a blank dry pot. The actual sample content is 0g, and the manufacturer sets the calculation to 1g. The measurement result is not a stable value, nor is it a real value, and the detection limit cannot be calculated.

[0036] Taking advantage of the fact that silver oxide has a more stable chemical bond than sulfur dioxide, a chemical reaction occurs between the elemental silver dry pot and the sulfur in the air to obtain a stable blank with an actual weighing value.

[0037] The sample mass is 1 g, and the measurement result is a dry-burned blank crucible. The sulfur content is very low but not stable.

[0038] The sample masses are 0.2 g and 0.3 g. The sample being tested is elemental silver, and the crucible is a fired crucible.

[0039] The elemental silver was sampled six times for sulfur content testing, and the measurement results obtained stable measurement results. As shown in the above measurement results, the detection limits calculated according to the formula were 0.0006% (mass percentage) and 0.00072% (mass percentage), respectively.

[0040] The used silver was re-measured and the data obtained were as follows: Figure 1 , is a set of unstable measurement results.

[0041] Based on this, the reasonable amount of elemental silver to be used for the fired crucible is 0.2g or 0.3g. Used silver cannot be reused.

[0042] like Figure 1 : The sample mass is 0.2g, 0.3g, 0.5g. The sample to be tested is elemental silver, and the crucible is an unfired crucible. The measurement results are as shown in the figure. 0.5g is a stable measurement result. The amount of elemental silver in the unfired crucible cannot be less than 0.5g

[0043] We used n=6 for calculation in the sample, but according to the requirements of the existing technology, n for accurate calculation of the detection limit of 3 should be greater than 10 times.

[0044] The detection limit was calculated according to the following formula:

[0045]

[0046] In the formula: S—standard deviation, % percentage;

[0047] —The average value of 10 measurement results, % percentage;

[0048] —The i-th measurement value, % content;

[0049] n—Number of measurements.

[0050] D=3·S………………………………(2)

[0051] Where: D—detection limit, % percentage content.

[0052] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the technical solution of the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A traceability method for sulfur content less than 0.003% (mass fraction) determined by a carbon and sulfur analyzer, characterized in that: The steps include: (1) Prepare a blank crucible; (2) Preheat the instrument to be tested according to the instructions, add silver into the crucible, the weight of silver is 0.2-1.0g; (3) Measure n times respectively (4) Calculate the detection limit according to the following formula: Where: S—standard deviation, % percentage; —The average value of 10 measurement results, % percentage; —The i-th measurement value, % content; n—Number of measurements. D=3·S………………………………(2) Where: D—detection limit, % percentage content. (5) When the detection limit D is less than the measured content (content < 0.003% (mass fraction)), the instrument measurement results are reliable.

2. The traceability method for determining sulfur content less than 0.003% (mass fraction) by using a carbon and sulfur analyzer according to claim 1, characterized in that: The blank crucible is a blank crucible obtained by firing a blank crucible in a muffle furnace at 1000° C. for half an hour in advance.

3. The traceability method for determining sulfur content less than 0.003% (mass fraction) by using a carbon and sulfur analyzer according to claim 1, characterized in that: The blank crucible is a blank crucible that has been fired in advance.

4. The traceability method for determining sulfur content less than 0.003% (mass fraction) by using a carbon and sulfur analyzer according to claim 1, characterized in that: The silver element is silver with a purity of more than 92.5%.

5. The traceability method for determining sulfur content less than 0.003% (mass fraction) by using a carbon and sulfur analyzer according to claim 1, characterized in that: The silver element is silver flakes.

6. The traceability method for determining sulfur content less than 0.003% (mass fraction) by using a carbon and sulfur analyzer according to claim 1, characterized in that: The measurement times n≥10 times.

7. Application of the traceability method for determining sulfur content less than 0.003% (mass fraction) by using the carbon and sulfur determination analyzer as claimed in claim 1 in determining the reliability of sulfur content measurement results in the interval with a detection limit of less than 0.003% (mass fraction).

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