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What factors influence the analysis result of carbon and sulfur analyzer?

Release time: 2019-05-05 09:38:20 Click: 3060


At present, carbon and sulfur analyzers are generally used for the analysis of carbon and sulfur elements in metals. In the use of analytical instruments by various manufacturers, there are often cases where the repeatability or reproducibility is not satisfactory. In this regard, the first doubt is the failure of the instrument, but often after checking the instrument hardware, the conclusion is that the instrument is working properly. In the following, based on the analysis of the principle, operation and analysis process of the carbon and sulfur analyzer, several factors that affect the accuracy and reliability of the analysis results of the carbon and sulfur analyzer are summarized.

1, Sample weighing

C S 量就存在差别,导致分析结果落在仪器校正曲线上的区域不同。 If the sample weighs differently, the amount of C and S contained in it will be different, resulting in different areas where the analysis result falls on the calibration curve of the instrument. Due to the limitation of the linear range of the instrument, this difference in the calibration area will cause fluctuations in the analysis results, especially when the upper and lower limits of the analytical instrument are near.

For low content samples, when the sample weighs more, the results obtained will be higher. For high content samples, the situation is reversed, and the results obtained will be lower.

In addition, the different sample sizes of the samples directly affect the high-frequency induction combustion. The combustion temperature and state of the carbon-sulfur meter are not only related to the power designed by the high-frequency furnace itself, but also related to the amount of magnetic material induced by induction. The combustion temperature is not constant, and as the material melts and burns, the amount of induction gradually decreases. For example, for some substances that are difficult to release carbon and sulfur (such as silicon, iron, etc.), because the weight of the added co-solvent is relatively constant, the heat generated is constant. At this time, too much sample will cause the sample to burn incompletely. The release of carbon and sulfur is not complete.

For instruments of different manufacturers, the linear range and the characteristics of the calibration curve are different, and the implementation method of the high-frequency control part is different. Therefore, the weighing of the sample has different effects on the accuracy and reliability of the analysis result. For specific instruments. It is necessary to familiarize with its characteristics through a large number of experiments and choose the appropriate sample size, so as to avoid the influence as much as possible.

2, Amount of co-solvent added

Another factor that affects the stability of the analysis results is the amount of co-solvent added, which is very prominent when analyzing low-level samples. 15 μ g/g 的样品时,分别加入 1.5g 2g 助溶剂(助溶剂中碳硫质量分数分别为≤ 8 μ g/g ,≤ 5 μ g/g ),因为助溶剂的加入量通常不参与分析结果计算,因此两次分析之间就引入了 0.5g 助溶剂所含碳硫量的波动。 For example, when analyzing samples with a carbon and sulfur mass fraction of less than 15 μ g / g , add 1.5 g and 2 g of co-solvent (the carbon and sulfur mass fraction in the co-solvent are ≤ 8 μ g / g and ≤ 5 μ g / g, respectively ), because The amount of co-solvent usually does not participate in the calculation of the analysis results, so the fluctuation of the amount of carbon and sulfur contained in 0.5 g of co-solvent is introduced between the two analyses . 3 μ g/g ,样品称样量为 0.5g ,由于助溶剂的加入量不同就引入了 3 μ g/g 的偏差。 It is assumed that the carbon and sulfur contents in the co-solvent are all 3 μg / g , and the sample weighs 0.5g . Due to the different amount of co-solvent added , a deviation of 3 μg / g is introduced .

Therefore, when analyzing low-level samples, try to ensure the same amount of co-solvent added, so as to reduce the uncertainties introduced by the co-solvent.

3. Stacking order of samples and cosolvent

The co-solvent not only has the effect of increasing the magnetic permeability of the sample and increasing the combustion temperature, but also has the effect of increasing the sample fluidity and diluting the sample. During the analysis, the stacking order of the sample and flux directly affects the combustion result and the stability of the analysis. For example, the iron-based sample is directly burned by high-frequency induction under oxygen, and the reaction is violent, and the splash is serious after melting, which is easy to cause damage to the quartz tube of the combustion chamber and pollution of the ceramic protective sleeve. It was replaced with tungsten particles, and the sample was placed in the upper layer. It was found that the quartz tube industry in the combustion chamber was quickly contaminated. A thick layer of iron melt was stuck on the ceramic protective sleeve, which was difficult to clean, which not only affected the combustion tube. The service life also hinders the supply of oxygen, which directly affects the stability of the analysis results. The sample is placed on the bottom layer, and the tungsten particles are placed on the upper layer. After the analysis, the quartz tube in the combustion chamber is very clean. There is no metal melt spatter on the ceramic thermal protection sleeve, and the analysis result is stable.

It can be seen that the influence of the stacking order of the sample and flux on the stability of the sample analysis results cannot be ignored.

4. crucible

Crucible blanks have always been a hot spot for carbon and sulfur analysts. 10-100 μ g/g 不等。 For untreated crucibles, the blank ranges from 10-100 μg / g . 1 μ g/g 以下。 The pretreatment process conditions are set properly, and the crucible blank can be reduced to below 1 μg / g . The test proves that the length of pretreatment time and the temperature are very important for obtaining a stable crumb blank. 800 ℃烘烧 4h 后的坩埚,用于分析钢样,得到的结果波动很大。 For example, the crucible baked at 800 ℃ for 4h is used to analyze steel samples, and the results obtained fluctuate greatly. 1100 ℃烘烧 4h 后的坩埚,坩埚空白可降至 1 μ g/g 以下。 However , the crucible blank after firing at 1100 ℃ for 4h can be reduced to below 1 μg / g .

1100 ℃下烘烧 4h ,从而最大程度降低坩埚空白对分析结果稳定性的影响。 Therefore, the crucible must be pretreated before use, and the appropriate baking temperature and time should be controlled. It is generally recommended to bake in a muffle furnace at 1100 ℃ for 4h , so as to minimize the influence of the crucible blank on the stability of the analysis results.

5. Reagent

The reagents used directly affect the stability and even accuracy of the analysis results. In the use of high-frequency infrared carbon and sulfur analyzers, the dryness and purity of the analysis gas and carrier gas are the guarantee for reducing the system blank and obtaining accurate and stable analysis results. The purification process of the carrier gas first passes through alkali asbestos and then through magnesium perchlorate. In the experiment, if the installation order of the reagents in the purifier's reagent tube is reversed, let the gas pass through magnesium perchlorate first, and then through alkali asbestos The relative standard deviation increases. This is because the alkali asbestos has a water-absorbing effect, but its water-absorbing efficiency is not as strong as magnesium perchlorate. Therefore, while the alkali asbestos absorbs the carbon dioxide contained in the gas, it will leak a small amount of water vapor and be carried into the analysis system by the carrier gas.

After the combustion of the reagent (magnesium perchlorate) used to dry the analysis gas fails, a small peak will appear on the sulfur baseline immediately after the high-frequency furnace is turned off. This is because the water vapor brought into the furnace by the outside air is not completely absorbed by the dry reagent, and the infrared absorption characteristic peak of the water vapor has a wavelength position close to the infrared absorption characteristic peak position of sulfur dioxide, which directly affects the analysis result of sulfur and causes sulfur analysis. The curve is trailing and the result is higher.

6. dust

The adsorption caused by the accumulation of the return to the city during the analysis is also an important factor that affects the stability of the analysis results. This effect is especially obvious when analyzing low-level samples. Experimental results show that as the number of analyses increases, the deviation caused by dust becomes larger and larger. After thoroughly removing the dust from the dust filter, the results of multiple analyses are consistent with the results of the first analysis. Therefore, during the analysis, the accumulation of dust in the dust filter should be cleaned up in time.

7. temperature

3 个方面。 The influence of temperature on the stability of the analysis results is mainly reflected in three aspects. First, the temperature effect of the dust filter. In the case of the same amount of dust, the higher the temperature, the worse the adsorption effect; second, the foundation of gas analysis is inseparable from the gas state equation. The temperature of the infrared analysis system constant temperature control will be different. It causes the change of the analysis gas volume, thus causing the time difference of a certain amount of analysis gas passing through the fixed-length flooding pond at different temperatures; in addition, the difference in the constant temperature control of the infrared analysis system will cause the fluctuation of the emitted light intensity of the infrared light source and the thermal The difference in the output of the electrical detector, which affects the stability of the analysis results. Generally, the instrument will be equipped with constant temperature control of these parts. During the analysis, the effect of constant temperature control should be monitored at any time to avoid the influence of temperature.

In summary, there are many factors that affect the stability of the analysis results of the carbon and sulfur analyzer. In the analysis process, especially when analyzing low-content samples, the influence of these factors can be considered comprehensively, so that the analysis results can be accurately evaluated. Avoid affecting the analysis results and schedule due to wrong estimation of the problem, and increase the maintenance cost of the instrument.

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