Analyzing Glass with the ARL QUANT’X

Glass is a non-crystalline amorphous solid. A single component fused silicon dioxide or silica (SiO₂) is the purest form of glass. As pure silica is hard to process and expensive, the properties for a given application are changed by adding other oxides. Soda-lime glass contains about 70% silica with sodium oxide (Na₂O) and lime or calcium oxide (CaO), and other small additives, and is used for forming container glass and common window panes. Many metallic oxides such as iron oxide (Fe₂O₃) are used to obtain deep glass coloring.

Instrument

The ARL QUANT’X EDXRF spectrometer has the latest generation of silicon drift detector (SDD), and a 50 kV, 50 W rhodium or silver target X-ray tube. The sample is excited by primary filtered radiation used by the ARL QUANT’X spectrometer.

The ARL QUANT’X is easily adapted per application or element range using a set of nine specially designed filters to optimize the peak-to-background for elements from F to Am. A vacuum and/or helium flush optionally equipped in the instrument improve the detection sensitivity of light elements.

Sample Preparation

The instrument is calibrated using 14 flat glass reference materials. The glass standard surface is cleaned with deionized water and tissue paper, and then analyzed. The concentration ranges of the various oxides covered by the calibration are shown in Table 1.

Table 1. Concentration ranges and calibration parameter values for the analysis of glass.

N.R.: not relevant in view of the high concentration level.

Excitation Conditions

The excitation conditions used to conduct the analysis are shown in Table 2. To attain optimal sensitivities for the compounds of interest, three conditions are used and to enhance the sensitivity of light elements, measurements are done in vacuum. Light elements (Na, Si, Mg, Al and S) emit characteristic X-rays which are low in energy and are easily absorbed by air. The three conditions are measured in 240 seconds (live time) per sample.

Calibration

Calibration curves have been derived relating element characteristic X-ray intensities to oxide concentration. X-ray fluorescence measures elements, but when only a single form of oxide is in the sample, the results can be directly related to the oxide forms of these elements. Typical calibration curves acquired for Al₂O₃ and SiO₂ are shown in Figures 1 and 2, respectively. The R² and Root Mean Square Error (RMSE) values obtained for the various compounds are also shown in Table 1.

Figure 1. Calculated versus given concentrations for Al₂O₃ in glass.

Figure 2. Calculated versus given concentrations for SiO₂ in glass.

Repeatability

To assess the repeatability of the instrument, ten repeat analyzes have been carried out on two flat glass samples. The results are shown in tables 3 and 4.

Limit of Detection

The Limits of Detection (LoD) are measured using the available standard reference materials. Table 1 shows the LoD for every oxide as obtained for the measurement conditions mentioned earlier. For major compounds (Na₂O, SiO₂ and CaO) the LoD isn't relevant and isn't reported.

Table 2. Excitation condition used for the analysis of glass.

Conclusion

The suitability of the ARL QUANT’X EDXRF spectrometer for the analysis of glass samples is explained in this article. Reliable and quick analysis results with exceptional repeatability are achieved by this compact instrument. Detection limits in the lower ppm range are adequate for routine analysis of flat glass.

Table 3. Validation and repeatability results for the main oxides in a flat glass I.

Table 4. Validation and repeatability results for the main oxides in a flat glass II.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers.

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