The preparation of ferrosilicon alloys samples for XRF analysis

Introduction Ferroalloys are important components in metals production. Iron and steel smelters are leading users of ferroalloys. Ferrosilicon (FeSi) is one of the most widely used ferroalloys with a high rate of consumption.

Currently, “wet chemistry” is the most common technique to perform precise analysis of FeSi alloys. However it requires long sample preparation time, as well as high labor costs. X-ray fluorescence (XRF) spectrometry is an excellent alternative technique for the analysis of FeSi alloys, offering easy routine sample preparation and high throughput. Compared to “wet chemistry”, the analysis of FeSi alloys by XRF spectrometry, commonly measured as pressed pellets or loose powders, shows limitations in precision due to strong metallurgical and particle size effects in these types of samples. These problems can be overcome if samples are analyzed as glass disks, thereby enhancing the accuracy and precision of results. We have now developed an application for the analysis of ferroalloys (in particular for FeSi) glass disks by XRF.

Method Apparatus and Instrumental Conditions Glass disks were prepared using the Eagon 2® automatic fusion instrument (Figure 1). Its innovative design combines the advantages of both gas burner and muffle furnace technology with none of their associated disadvantages. The Eagon 2 instrument is designed for high performance. It optimizes the operator’s safety and it is easy to use. It has 2 fusion positions which can run independently or simultaneously, based on the user’s choice. Moreover, the Eagon 2 instrument can be integrated into a fully automated sample preparation system. For easy routine sample preparation, up to 32 fusion methods can be stored on the instrument.

Global Sample Preparation Method The glass disks were prepared by mixing 0.2 g of sample material with oxidizing agents and lithium borate flux. The mixture was then fused using the Eagon 2 automatic fusion instrument following a specially developed program which includes different oxidation steps prior to fusion. As a result, 2 glass disks (32 mm thick and weighing approximately 6.2 g each) were obtained. While the original recipe was developed for FeSi, the program has been extended to cover FeSiCr, FeSiMn, SiMn and SiCa alloys and it is now commercially available. A full cycle for the preparation of 2 glass disks takes about 40 minutes.

Results Sample preparation and measurement repeatability In order to evaluate sample preparation repeatability, 10 glass disks of the same material were prepared as described above and measured on a Zetium 1 kW system (Figure 2).

Results for the analysis of Mg, Al, Si, P, Ca, Ti, Mn and Fe are reported in Table 1. The absolute and relative RMS (used as a measure of standard deviation of results from the mean value) are also shown in Table 1.

Table 1. FeSi sample preparation repeatability test Element Mg (%) Al (%) Si (%) P (%) Ca (%) Ca (%) Mn (%) Fe (%) Glass disk 01 0.047 1.72 76.90 0.044 0.47 0.18 1.13 19.14 Glass disk 02 0.045 1.74 77.00 0.040 0.47 0.18 1.14 19.00 Glass disk 03 0.046 1.76 76.92 0.045 0.47 0.18 1.14 19.09 Glass disk 04 0.052 1.76 76.93 0.042 0.46 0.17 1.13 19.06 Glass disk 05 0.051 1.76 76.87 0.040 0.46 0.17 1.14 19.13 Glass disk 06 0.053 1.74 76.86 0.045 0.46 0.16 1.14 19.16 Glass disk 07 0.046 1.77 76.81 0.041 0.47 0.17 1.13 19.19 Glass disk 08 0.050 1.75 76.89 0.040 0.48 0.17 1.14 19.10 Glass disk 09 0.043 1.73 76.82 0.041 0.45 0.17 1.14 19.22 Glass disk 10 0.050 1.72 76.60 0.045 0.48 0.17 1.16 19.42 Mean 0.0483 1.745 76.86 0.0422 0.467 0.173 1.138 19.15 Min 0.043 1.72 76.60 0.040 0.46 0.159 1.13 19.00 Max 0.053 1.77 76.60 0.48 0.48 0.183 1.16 19.42 RMS abs 0.0034 0.0175 0.106 0.0021 0.0095 0.0067 0.0067 0.114 RMS rel. (%) 7.0 1.00 0.14 4.9 2.0 3.9 0.59 0.60 Table 2. FeSi measurements repeatability test Element Mg (%) Al (%) Si (%) P (%) Ca (%) Ca (%) Mn (%) Fe (%) Glass disk 02 0.045 1.72 76.97 0.040 0.45 0.17 1.13 19.07 Glass disk 02 0.054 1.73 77.07 0.041 0.47 0.17 1.13 18.96 Glass disk 02 0.050 1.74 76.97 0.040 0.47 0.17 1.13 18.96 Glass disk 02 0.051 1.76 76.92 0.044 0.47 0.18 1.14 19.11 Glass disk 02 0.050 1.75 76.95 0.043 0.46 0.16 1.13 19.06 Glass disk 02 0.045 1.75 76.98 0.041 0.47 0.17 1.14 19.05 Glass disk 02 0.045 1.76 76.94 0.045 0.46 0.18 1.13 19.08 Glass disk 02 0.049 1.74 76.98 0.043 0.47 0.16 1.13 19.06 Glass disk 02 0.052 1.74 76.97 0.040 0.47 0.18 1.13 19.04 Glass disk 02 0.052 1.74 76.98 0.045 0.47 0.17 1.13 19.02 Mean 0.0493 1.743 76.97 0.0422 0.466 0.170 1.133 19.05 Min 0.045 1.72 76.92 0.040 0.45 0.16 1.13 18.96 Max 0.054 1.76 77.07 0.045 0.47 0.18 1.14 19.11 RMS abs 0.0033 0.0115 0.041 0.0020 0.0070 0.0067 0.0024 0.038 RMS rel. (%) 6.6 0.66 0.05 4.8 1.50 3.9 0.21 0.20 For the evaluation of the measurement repeatability, 10 consecutive measurements were performed on the same glass disk. Results are reported in Table 2.

Results shown in this data sheet were normalized after taking into account the carbon concentration measured using a combustion gas analyzer.

Conclusion This data sheet demonstrates the high quality and reproducibility of the sample preparation method for ferroalloy samples prepared as glass disks using the Eagon 2 fusion instrument. Results obtained for the analysis of ferrosilicon alloys using Zetium 1 kW show the high accuracy of the measurements. Easy routine, acid-free sample preparation as well as reduced throughput time are important advantages that distinguish this analytical method from others.

The preparation of ferrosilicon alloys samples for XRF analysis

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