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What factors influence the carbon and sulfur analyzer?
Release time: 2019-05-05 09:38:20 Click: 2752
At present, carbon and sulfur analyzers are generally used for the analysis of carbon and sulfur in metals. In the process of using the analytical instruments of various manufacturers, there are often repetitive or unsatisfactory situations. In this regard, the first thing to suspect is the failure of the instrument, but often after inspection of the instrument hardware, it is concluded that the instrument is working properly. In the following, according to the analysis of the principle, operation and analysis process of the carbon and sulfur analyzer, several factors affecting the accuracy and reliability of the analysis result of the carbon and sulfur analyzer are summarized.
1, Weighing of the sample
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。 Different samples weigh different amounts of C and S contained in the sample , resulting in different areas where the analysis results fall on the instrument calibration curve. 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, the results are higher when the sample is weighed larger. For high-content samples, the situation is reversed and results are lower.
In addition, the difference in sample weighing directly affects the high-frequency induction combustion. The combustion temperature and state of the carbon-sulfur meter are not only related to the power of the high-frequency furnace itself, but also to the amount of magnetically-removed material that is induced internally. The combustion temperature is not continuously constant. As the material melts and burns, the amount of induction gradually decreases. For example, for some carbon and sulfur substances that are difficult to release (such as silicon, iron, etc.), because the weight of the co-solvent added is constant, the heat generated is constant. At this time, too many samples will cause the sample to burn incompletely. Carbon and sulfur release is incomplete.
For instruments from different manufacturers, the linear range and calibration curve characteristics are different, and the high-frequency control part is implemented differently. Therefore, the weighing of the sample affects the accuracy and reliability of the analysis results. For specific instruments. You need to be familiar with its characteristics through a large number of experiments, and choose an appropriate weighing sample to avoid the impact as much as possible.
2, Adding amount of cosolvent
Another factor that affects the stability of the analysis results is the amount of co-solvent added, which is very prominent when analyzing low-content samples. 15 μ g/g 的样品时，分别加入 1.5g 与 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 μg / g , add 1.5g and 2g co-solvents (the carbon and sulfur mass fractions in the co-solvent are ≤ 8 μ g / g and ≤ 5 μ g / g, respectively ) because The amount of co-solvent added is usually not involved in the calculation of the analysis results, so a fluctuation in the amount of carbon and sulfur contained in 0.5 g of co-solvent was 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 content of carbon and sulfur in the co-solvent is 3 μg / g , and the sample weighs 0.5 g . Due to the different amounts of co-solvent added , a deviation of 3 μg / g is introduced .
Therefore, when analyzing low-content samples, try to ensure the same amount of co-solvent is added, so as to reduce the uncertainty introduced by co-solvent.
3. Sequence of sample and cosolvent
The co-solvent not only has the effect of increasing the magnetically conductive substance in the sample and the combustion temperature, but also has the effect of increasing the fluidity of the sample and diluting the sample. During the analysis, the stacking order of samples and fluxes directly affects the combustion results and analysis stability. For example, iron-based samples are directly combusted under high-frequency induction under oxygen, which is reflected violently and splashes severely after melting, easily causing damage to the quartz tube of the combustion chamber and pollution of the ceramic protective sleeve. Replaced with tungsten particles as the base, and the sample was placed on 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 was placed on the bottom layer, and the tungsten particles were placed on the upper layer. After the analysis, the quartz tube in the combustion chamber was very clean, and there was no metal melt splash on the ceramic thermal protective sleeve, and the analysis result was stable.
It can be seen that the influence of the stacking order of samples and fluxes on the stability of sample analysis results cannot be ignored.
Crucible blanks have always been a hot spot for carbon and sulfur analysts. 10-100 μ g/g 不等。 For untreated crucibles, blanks range from 10-100 μg / g . 1 μ g/g 以下。 The conditions of the pretreatment process are properly set, and the crucible blank can be reduced to less than 1 μg / g . The test proves that the length of pretreatment time and the temperature are very important to obtain a stable ground blank of the crucible. 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 after baking at 800 ℃ for 4 hours is used to analyze steel samples, and the obtained results fluctuate greatly. 1100 ℃烘烧 4h 后的坩埚，坩埚空白可降至 1 μ g/g 以下。 The crucible after baking at 1100 ℃ for 4h , the crucible blank can be reduced to less than 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 pre-treated 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 4 hours , so as to minimize the effect of the crucible blank on the stability of the analysis results.
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 is a guarantee to reduce the system blank and obtain accurate and stable analysis results. The purification process of the carrier gas first passes alkali asbestos and then passes through magnesium perchlorate. In the experiment, if the reagent installation order in the purifier reagent tube is reversed, and the gas passes through magnesium perchlorate and then passes through alkaline asbestos, the measurement results will be affected. Relative standard deviation increased. This is because although alkaline asbestos has a water absorption effect, its water absorption efficiency is not as strong as that of magnesium perchlorate. Therefore, while the asbestos absorbs the carbon dioxide contained in the gas, it will leak a small amount of water vapor and carry it into the analysis system by the carrier gas.
After the combustion of the reagent (magnesium perchlorate) used to dry the analysis gas, a small peak appears on the baseline of sulfur 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 drying reagent, and the wavelength position of the infrared absorption characteristic peak of water vapor is close to the position of the infrared absorption characteristic peak of sulfur dioxide, which directly affects the sulfur analysis result and causes sulfur analysis. The tail of the curve is high.
The adsorption caused by the accumulation of back to the city during the analysis is also an important factor affecting the stability of the analysis results, and this effect is particularly obvious when analyzing low-content samples. The 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 were consistent with the results of the first analysis. Therefore, during analysis, the dust accumulation in the dust filter should be cleaned in time.
3 个方面。 The influence of temperature on the stability of analysis results is mainly reflected in three aspects. First of all, the temperature of the dust filter is affected. At the same amount of dust, the higher the temperature, the worse the adsorption effect. Secondly, the basis of gas analysis is inseparable from the gas state equation. The temperature of the infrared analysis system is controlled by different temperatures. Changes in the volume of the analysis gas, resulting in a certain amount of time difference between the amount of analysis gas passing through the fixed length flooding pond at different temperatures; In addition, the difference in the constant temperature control temperature of the infrared analysis system will cause fluctuations in the emission intensity of the infrared light source and thermal release. The difference in the output of the electrical detector affects the stability of the analysis results. Generally, the instrument will be equipped with the constant temperature control of these parts, and the effect of constant temperature control should be monitored at any time during the analysis process to avoid the influence caused by temperature.
In summary, there are many factors affecting the stability of the analysis results of carbon and sulfur analyzers. During the analysis process, especially when analyzing low-content samples, the influence of these factors can be comprehensively considered to make an accurate evaluation of the analysis results. Avoid affecting the analysis results and progress due to incorrect estimation of the problem, and increase the maintenance cost of the instrument.