Methods were developed with a view to evaluating various sample preparation systems for use with X-ray fluorescence techniques in order to determine the major and minor components of ferroalloys, which are used as alloy-forming elements in steel making. The methods were compared in terms of simplicity and rapidity and these parameters were assessed in relation to the accuracy and precision of the results. The samples were prepared in three formats: metal samples, by dilution with iron and remelting in an induction furnace; pellets, by direct compaction of the ground material, and beads, by alkaline melting of the pre-oxidized sample. The tests used to optimize these methods were conducted with commercial ferroalloys, previously characterized by employing wet chemical and spectroscopic methods. Reproducibility and precision studies were conducted on samples obtained using each of the three sample preparation systems. The precisions (relative standard deviations) of major element determinations were <0.8, <1.0 and < O S % and those for minor elements were <5, <5 and <3% for metal samples, pellets and beads, respectively. The accuracy of the methods was checked by analysing reference materials of each type of ferroalloy.
An experimental study for the determination of boron in steels by inductively coupled plasma atomic emission spectrometry is presented. A comparison is made of spark ablation and pneumatic nebulization (after microwave digestion) sampling systems. A one-step microwave digestion procedure for total boron content using diluted aqua regia (HCI+HNO,, 3+1) and high pressure vessels was developed. The influence of microwave power and time on the dissolution of boron compounds is discussed. The strongest available conditions (0 Q, 600 V, 600 Hz) were required for spark ablation sampling. The stability of spark sampling during the spark ablation-ICP process was tested by plotting iron and boron emission versus sparking time. The iron content of collected and dissolved spark-produced particles was analysed and showed that the amounts of aerosol from different boron steels samples during 90 s sparking processes were fairly similar. The analytical performance of both systems was evaluated. Using pneumatic nebulization, after microwave digestion of the sample, a detection limit for boron of 2.6 ,ug g-1 and overall relative standard deviation (RSD) values of 1-3.5% were found. For spark ablation the detection limit for boron was 0.65pg g-l, the overall RSD ranging from 0.5 to 1.5%. A comparison of the data for British Chemical Standards (BCS) Certified Reference Materials (CRMs) Carbon Steel Residual Series (Group B) and Spectroscopic Standard (SS) 456/1 to 460/1, indicated that the accuracy of both methods was satisfactory.
Spark ablation coupled with excitation in an argon inductively coupled plasma is applied to the analysis of remelted ferrovanadium. A medium-voltage spark at a high-repetition rate was used as the sampling technique for samples prepared using a high-frequency remelting system. Problems of sample fracturing were avoided by dilution of the ferroalloy with pure iron. Calibration graphs were obtained with samples prepared from a commercial ferrovanadium alloy, previously analysed using standard wet chemical methods and diluted with pure iron at two different dilution ratios. The two FeV to Fe dilution ratios were selected in order to cover the desired range of concentrations. When using an Fe line as the internal standard, the relative standard deviations for the major element (V) are below 0.3% (V content, 35-80°/0). The limits of determination for the minor elements (Mn, Cu, Al and Si) are below the required IS0 specifications. The accuracy of the developed method was tested by the analysis of three reference materials.
A medium-voltage spark was used for the direct nebulization of electric arc furnace (EAF) flue dust. In order to attain the necessary sample conductivity, powder pellets are briquetted after mixing the sample 1 +1 with graphite. The elutriated material was excited in an argon inductively coupled plasma (ICP). The use of cellulose as binder provides better results in terms of reproducibility. After optimization of the spark parameters (voltage, 500 V; repetition rate, 400 s-'; and resistance, 2.2 Q), the carrier gas flow rate (2.1 I min-' of argon) and the operating power of the ICP (1.2 kW), precisions (relative standard deviation) for zinc, lead, cadmium and iron range from 0.8 to 2.0%. The stability of the spark sampling, during a complete spark ablation (SA) ICP process (~9 0 s) was tested by plotting emission intensity versus time profiles. The similarity between the amounts of analyte obtained from different pellets was proven by collecting the spark-eroded particles and analysing their carbon contents. Five steelmaking EAF flue dusts were selected for this study, using the two samples with extreme contents of the elements considered, for calibration. The results obtained by SA-ICP matched the results obtained by ICP from nebulized solutions.
A study of chromium determination in ferrochromium by X-ray fluorescence and spark ablation inductively coupled plasma atomic emission spectrometry was made. Bulk test samples were prepared by re-melting the ferroalloy diluted with iron in an induction furnace. Calibration samples were obtained from an industrial ferroalloy, using different FeCr + Fe dilution ratios, in order to cover the chromium concentration range that is probably present in these materials. A study is presented of the influence of the carbon contents on Cr Kcu line intensities and on the amount of spark aerosol produced, as well methods of compensating for the effect. The total variance and the average instrumental variation were calculated from the values obtained for samples with the same chromium concentration and variable carbon contents. The criterion applied to test the agreement of the two methods showed that the difference between the results provided by both techniques can be explained by random errors. Accuracies were tested by analysing a series of ferrochromium reference materials.
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