In this paper, the high-frequency infrared carbon and sulfur analyzer is used to determine the sulfur content in the soil and clay, and the sulfur content in the standard sample is determined after optimizing the analysis conditions such as the choice of flux, analysis time, oxygen blowing flow and weighing sample volume. The measurement results are within the standard value range.
In industrial and agricultural production, it is often necessary to understand the sulfur content in soil and clay. Conventional sulfur determination methods include barium sulfate gravimetric method and combustion iodometric method. The barium sulfate gravimetric method is a classic method for determining sulfur content, but the analysis steps are cumbersome and the process is lengthy; the combustion iodometric method has higher technical requirements for analysts, the stability of the results is relatively poor, and the analysis time is longer. Therefore, the author uses a high-frequency infrared carbon and sulfur analyzer to determine the sulfur content in soil and clay. The method is simple and easy, and the measurement results are accurate.
1 Experimental part
1.1 Main instruments and reagents
High-frequency infrared carbon and sulfur analyzer: HCS-040G type, Shanghai Dekai Instrument Company;
Electronic balance: AB104-N type, Shanghai METTLER TOLEDO Instrument Co., Ltd .;
Flux: pure iron, metal tungsten particles;
Oxygen: purity is not less than 99.5%;
Desiccant: high-efficiency color-changing desiccant;
Stainless steel standard sample: GBW01604, sulfur content is (0.0130 ± 0.0005)%;
Low alloy steel standard sample: GSBA68073-92-2, sulfur content is 0.035%;
Clay standard sample: GBW03103, sulfur content is (0.0108 ± 0.004)%;
Soil standard sample: GBW07401, sulfur content is (0.031 ± 0.010)%;
Clay samples: W06-WW05112, W06-WW05113, W06-WW06089;
Soil samples: W06-WW05306, W06-WW05307, W06-WW06012.
1.2 Measurement conditions
Total system pressure: 0.08MPa; combustion gas flow: 2L / min; analysis gas flow: 4L / min; oxygen blowing time: 30s; minimum analysis time: 35s; cut-off level: 7mV
1.3 Experimental method
(1) Instrument preparation: Before measuring the sample, preheat the instrument for more than 30 minutes to make it in a stable state.
(2) Blank test: Weigh about 0.3g of pure iron flux and about 2g of metal tungsten particles. If the blank test is performed three times in succession, the sulfur content is less than the detection limit (0.0003%). In the blank deduction, it can be ignored, that is, the blank value is 0.
(3) Clay sample analysis: Weigh about 0.15g of standard sample in a porcelain crucible, add 0.3g of iron flux, and add about 2g of tungsten particles on the surface. Measure three times in succession, take the average value to correct the instrument, and obtain the correction coefficient. Weigh about 0.15g of clay sample in a porcelain crucible, add 0.3g of iron flux, about 2g of tungsten particles, and measure.
(4) Soil sample analysis: Weigh about 0.15g of low alloy steel standard sample in a porcelain crucible and add about 2g of tungsten particles on the surface. Measure three times in succession, take the average value to correct the instrument, and obtain the correction coefficient. Then analyze the soil sample, first add 0.2g iron flux to the bottom of the crucible, then add about 0.15g sample, 0.2g iron flux, and finally add about 2g tungsten particles for measurement.
2 Results and discussion
2.1 Flux
There are many fluxes for determining sulfur. Commonly used fluxes are tin particles, tungsten particles, pure copper or CuO, pure iron, etc. [3]. According to different samples, different fluxes are used. In this experiment, pure iron-tungsten particles are used as fluxes. Adding iron flux has two functions: (1) Because the soil and clay are low magnetic samples, the energy absorbed in the high-frequency alternating magnetic field is small, and the heating temperature is slow. The addition of pure iron can increase the magnetic permeability of the sample, greatly Increase the heating rate of the sample; (2) Reduce the sample melting temperature. In addition, iron releases a large amount of heat during the combustion and oxidation process, which can increase the furnace temperature and make the sample completely burn.
Tungsten has a high melting point but is easy to oxidize. It can release a lot of heat during the oxidation process, which can increase the heat capacity of the melt. The formation of WO3 is conducive to the release of SO2. In addition, the volatile escape of WO3 increases the diffusion rate of sulfur. It is fully oxidized, which is very conducive to the determination of sulfur.
Through repeated experiments, it is concluded that when measuring the soil, iron flux should be added to the bottom of the crucible in advance, followed by the sample, iron flux, and finally tungsten particles to determine the ideal result, otherwise the result is obviously low.
2.2 Standard samples
In this experiment, the national first-class steel standard material was selected as the standard. Normally, when analyzing a certain material, the standard material of the same material should be used as the standard to calibrate the instrument to obtain accurate results. However, due to the proper selection of analysis conditions and flux, this method can produce accurate results even when using steel standard materials as standards to calibrate the instrument. It can be seen from the sample release curve that the release of sulfur is ideal.
2.3 Sample quality
The sample weight should not be too high. Excessively high will cause splashing during the measurement and lower the measurement result. The test shows that the measurement result is the best when the sample mass is 0.15g, but the highest cannot exceed 0.25g.
2.4 Oxygen blowing flow
The amount of oxygen blowing flow has an effect on the measurement results. Excessive flow will cause the molten sample to splash. Too small flow will cause the combustion temperature to be low. Eventually, the measurement result will be low. The effect of oxygen blowing at 2L / min is better.
2.5 Precision test
Weigh about 0.15g of clay sample in a porcelain crucible, add 0.3g of iron flux and about 2g of tungsten particles, and measure. The measurement was performed 8 times in succession, and the measurement results are shown in Table 1.
Add 0.2g of iron flux to the bottom of the crucible, then add about 0.15g of soil sample, 0.2g of iron flux, and finally add about 2g of tungsten particles for measurement. 8 consecutive measurements, the results are shown in Table 1. Table 1 Results of precision test%
Sample measured value average RSD soil 0.0302 0.0313 0.0296 0.02990.0343 0.0330 0.0298 0.03080.0315.10 clay 0.00984 0.00993 0.00877 0.010100.00922 0.01050 0.01000 0.009860.009785.51
2.6 Accuracy test
According to the analysis method of clay and soil samples in 1.3, the standard samples of clay and soil were measured respectively and measured three times in succession. It can be seen from Table 2 that the measurement result of the standard substance is in good agreement with its standard value.
Table 2 Accuracy test results% Sample standard value Measured value average clay (GBW03103) 0.0108 ± 0.00400.00984 0.009220.008770.00928 soil (GBW07401) 0.031 ± 0.0100.0322 0.02970.03080.0309
2.7 Method comparison test
The clay sample and the soil sample were measured by this experimental method and the barium sulfate gravimetric method. The measurement results are listed in Table 3. The results of this method and barium sulfate gravimetry are basically the same, indicating that the results of this method are accurate and reliable.
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