Analyzing Glass with the ARL QUANT’X

Background

ARL QUANT’X EDXRF spectrometer

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.

Element Range [%] R2 RMSE LoD [ppm]
Na2O 1.85 - 14.4 0.978 0.695 N.R.
MgO 0.01 - 3.9 0.991 0.103 130
Al2O3 0.12 - 5.7 0.999 0.044 70
SiO2 58.04 - 100 0.999 0.294 N.R.
SO3 0.05 - 0.28 0.996 0.006 20
K2O 0.04 - 13.5 0.9998 0.071 10
CaO 0.01 - 11.0 0.998 0.201 N.R.
TiO2 0.01 - 0.10 0.960 0.006 6
Fe2O3 0.02 - 0.34 0.999 0.003 3
BaO 0.003 - 5 0.9999 0.002 40

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.

Calculated versus given concentrations for Al2O3 in glass.

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

Calculated versus given concentrations for SiO2 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.

Condition Voltage (kV) Current (mA) Atmosphere Live Time (s) Analytes
Low Za 5 Auto Vacuum 120 Na, Mg, Al, Si, S
Low Zb 10 Auto Vacuum 60 K, Ca
Low Zc 12 Auto Vacuum 60 Ti, Fe, Ba

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.

Flat Glass I
Na2O MgO Al2O3 SiO2 SO3 K2O CaO TiO2 Fe2O3 BaO
% % % % % % % % % %
Rep. 1 14.27 2.216 1.113 71.118 0.1952 0.716 10.485 0.0253 0.0430 0.0108
Rep. 2 14.24 2.243 1.115 71.115 0.1956 0.717 10.533 0.0244 0.0431 0.0116
Rep. 3 14.24 2.234 1.118 71.134 0.1938 0.716 10.545 0.0245 0.0434 0.0118
Rep. 4 14.28 2.239 1.118 71.115 0.1920 0.712 10.510 0.0245 0.0438 0.0116
Rep. 5 14.28 2.231 1.114 71.075 0.1958 0.716 10.528 0.0249 0.0430 0.0133
Rep. 6 14.28 2.255 1.113 71.109 0.1935 0.713 10.539 0.0255 0.0428 0.0112
Rep. 7 14.27 2.243 1.110 71.137 0.1989 0.713 10.525 0.0255 0.0428 0.0110
Rep. 8 14.30 2.228 1.115 71.132 0.1961 0.718 10.537 0.0252 0.0435 0.0123
Rep. 9 14.28 2.232 1.124 71.131 0.1955 0.713 10.533 0.0260 0.0434 0.0105
Rep. 10 14.30 2.233 1.109 71.112 0.1966 0.716 10.528 0.0251 0.0438 0.0120
Average 14.27 2.235 1.115 71.118 0.1953 0.715 10.526 0.0251 0.0433 0.0116
StDev 0.02 0.010 0.004 0.018 0.0019 0.002 0.017 0.0005 0.0004 0.0008

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

Flat Glass II
Na2O MgO Al2O3 SiO2 SO3 K2O CaO TiO2 Fe2O3 BaO
% % % % % % % % % %
Rep. 1 12.617 < LOD 2.772 71.04 0.1348 1.981 10.939 0.0126 0.0402 0.1159
Rep. 2 12.602 < LOD 2.765 70.93 0.1357 1.989 10.975 0.0115 0.0403 0.1192
Rep. 3 12.636 < LOD 2.766 71.03 0.1335 1.994 10.979 0.0143 0.0406 0.1170
Rep. 4 12.601 < LOD 2.758 70.98 0.1336 1.993 10.990 0.0121 0.0401 0.1197
Rep. 5 12.651 < LOD 2.768 71.03 0.1349 1.985 10.981 0.0118 0.0408 0.1182
Rep. 6 12.621 < LOD 2.774 71.03 0.1335 1.991 10.947 0.0134 0.0402 0.1160
Rep. 7 12.625 < LOD 2.770 71.02 0.1336 1.990 10.982 0.0118 0.0405 0.1192
Rep. 8 12.609 < LOD 2.772 71.03 0.1343 1.990 10.975 0.0123 0.0402 0.1197
Rep. 9 12.635 < LOD 2.768 71.05 0.1329 1.993 10.983 0.0125 0.0405 0.1193
Rep. 10 12.619 < LOD 2.774 71.04 0.1347 1.991 10.965 0.0137 0.0407 0.1163
Average 12.622 - 2.769 71.02 0.1342 1.990 10.972 0.0126 0.0404 0.1180
StDev 0.016 - 0.005 0.04 0.0009 0.004 0.017 0.0009 0.0002 0.0016

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

For more information on this source, please visit Thermo Fisher Scientific - Elemental Analyzers.

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