Glass Analysis Using X-Ray Fluorescence

The simplest form of glass is single component fused silica (SiO2). This material is, however, very difficult to process, and highly expensive. To minimize these difficulties, some other oxides are added offering specific properties to the resultant glass. Most glasses comprise about 70% silica, which is a glass former, soda as a flux in the form of carbonate and sulfate (about 14%), and lime as a stabilizer in the form of limestone (about 10%). Other types of oxides, like alumina or magnesia, enhance the physical characteristics of glass, especially the resistance to atmospheric conditions. In-depth coloring is obtained by incorporation of different metallic oxides, such a chromium, iron, manganese or copper oxides.

Instrumentation

In this article, an ARL OPTIM’X XRF spectrometer from Thermo Electron (Fig. 1) has been used to derive limits of detection and precision for glasses analysis. The ARL OPTIM’X is a wavelength dispersive system which offers superior resolution and light elements capability. It is fitted with an air-cooled Rh End-Window Tube with thin Be window (0.075 mm), and has a maximum power of 50 W. Due to close coupling between the X-ray tube anode and the sample, the performance of the ARL OPTIM’X is similar to a 200 W conventional WD-XRF instrument. The instrument can be incorporated with the unique SmartGonio, a series of Multichromators, or both.

Figure 1. ARL OPTIM’X XRF Spectrometer.

Calibration and Limits of Detection

A series of pressed glass samples have been measured on an ARL OPTIM’X. Calibration curves have been derived by relating intensities for each oxide (or element) to concentrations in standard samples. X-ray fluorescence measures pure elements, but the results can be related directly to the oxide forms of these elements when only one single form is present in the sample. Using the calibration curves, limits of detection have been derived using the SmartGonio for most common oxides/elements found in soda-lime glasses (Fig. 2). Table 1 shows limits of detection for various elements in soda-lime glasses prepared as pressed powders.

Figure 2. Soda-lime glasses.

Table 1. Analytical parameters and limits of detection for various oxides/element in soda-lime glass (100 sec. counting time).

OXIDE/ELEMENT LINE CRYSTAL DETECTOR LOD[PPM]
Na2O Kα1,2 AX-06 FPC 100
MgO Kα1,2 AX-06 FPC 60
Al2O3 Kα1,2 PET FPC 47
SiO2 Kα1,2 PET FPC N.R.
P2O5 Kα1,2 PET FPC 48
SO3 Kα1,2 PET FPC 23
Cl Kα1,2 PET FPC 24
K2O Kα1,2 LiF 200 FPC 14
CaO Kα1,2 LiF 200 FPC 12
TiO2 Kα1,2 LiF 200 FPC 12
Cr2O3 Kα1,2 LiF 200 FPC 9
MnO Kα1,2 LiF 200 FPC 9
Fe2O3 Kα1,2 LiF 200 FPC 9
ZnO Kα1,2 LiF 200 SC 3.6
SrO Kα1,2 LiF 200 SC 2.4
ZrO2 Kα1,2 LiF 200 SC 1.8
BaO Lβ1 LiF 200 FPC 51
PbO Lβ1 LiF 200 SC 9

N.R. = LoD is not relevant for major elements.
FPC = flow proportional counter.
SC = scintillation counter.
Excitation conditions: 40 kV/1.25 mA.
Collimator: 0.29°.

Precision Tests

Precision tests have been done by repeatedly analyzing the same pressed pellet sample for eleven consecutive analyses. Eighteen elements/oxides are determined using a counting time of 36 seconds per analytical line. The results are summarized below for two different glass samples shown in Tables 2 and 3. For higher precision this counting time can be increased. Doubling the counting time will improve the precision by a factor of about 1.4 (square root of 2)

Table 2. Repeatability for the analysis of the major and minor oxides in sample A.

RUN Na2O % MgO % Al2O3 % SiO2 % K2O % CaO % Fe2O3 % SO3 PPM TiO2 PPM P2O5 PPM Cl PPM Cr2O3 PPM MnO PPM As2O3 PPM SrO PPM ZrO2 PPM BaO PPM PbO PPM
Time (s) 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36
Run 1 13.98 0.185 1.79 72.59 0.588 10.85 0.330 582 579 166.9 113.4 93.6 48.4 101.6 127.4 209.1 454.3 228.2
Run 2 13.93 0.193 1.81 72.60 0.582 10.82 0.333 640 563 146.3 129.5 91.4 44.7 101.5 124.8 204.6 392.6 218.9
Run 3 13.97 0.177 1.80 72.64 0.588 10.82 0.330 608 563 193.3 111.2 91.1 43.8 95.9 127.1 207.0 361.8 197.8
Run 4 14.01 0.178 1.80 72.64 0.582 10.87 0.330 645 581 199.2 104.6 96.2 29.9 103.8 127.0 205.4 375.7 234.6
Run 5 13.95 0.182 1.80 72.60 0.588 10.83 0.329 576 564 158.1 111.8 94.6 41.8 103.7 122.7 204.7 385.2 228.5
Run 6 13.94 0.177 1.81 72.61 0.589 10.82 0.329 573 569 171.3 107.9 85.2 49.5 95.0 126.3 203.8 355.4 194.8
Run 7 13.86 0.185 1.80 72.64 0.588 10.83 0.330 658 569 203.6 113.4 88.9 40.3 96.0 125.0 205.4 434.1 234.4
Run 8 13.92 0.186 1.81 72.59 0.585 10.84 0.331 652 566 190.4 135.6 94.5 44.7 96.8 125.9 203.4 315.1 207.3
Run 9 13.94 0.184 1.81 72.63 0.591 10.82 0.334 651 579 150.7 110.1 88.6 43.1 114.9 127.1 206.6 401.2 220.8
Run 10 13.98 0.183 1.80 72.63 0.586 10.87 0.332 617 526 255.0 104.0 83.6 41.9 99.2 125.8 206.2 402.2 214.6
Run 11 13.95 0.188 1.78 72.62 0.588 10.83 0.330 619 561 218.3 97.9 80.6 38.9 97.7 126.8 203.1 429.8 197.8
Avg. 13.95 0.183 1.80 72.62 0.587 10.84 0.331 620 565 186.6 112.7 89.9 42.4 100.5 126.0 205.4 391.6 216.1
Std.Dev. 0.04 0.005 0.01 0.02 0.003 0.02 0.0015 32 15 32.5 11 5 5.2 5.7 1.4 1.8 39.7 15

Table 3. Table 3: Repeatability for the analysis of the major and minor oxides in sample B.

RUN Na2O % MgO % Al2O3 % SiO2 % K2O % CaO % Fe2O3 % SO3 PPM TiO2 PPM P2O5 PPM Cl PPM Cr2O3 PPM MnO PPM As2O3 PPM SrO PPM ZrO2 PPM BaO PPM PbO PPM
Time (s) 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36 36
Run 1 13.35 0.180 1.67 73.07 0.556 10.77 773.3 0.177 556.0 200.6 100.7 63.4 9.3 118.2 122.4 227.2 883.9 895.6
Run 2 13.33 0.180 1.68 73.08 0.564 10.76 757.9 0.181 568.0 159.5 111.2 65.9 3.9 112.0 122.2 226.1 960.6 914.5
Run 3 13.28 0.186 1.67 73.08 0.554 10.81 789.6 0.180 555.1 193.3 115.7 64.7 18.2 115.6 119.3 225.3 925.4 911.5
Run 4 13.28 0.185 1.66 73.11 0.559 10.83 768.2 0.186 587.2 156.6 103.5 74.7 8.7 105.6 126.5 225.1 891.3 900.0
Run 5 13.35 0.181 1.67 73.05 0.554 10.79 763.9 0.181 594.7 187.4 97.9 63.6 12.3 106.8 126.3 226.2 948.8 904.8
Run 6 13.32 0.172 1.67 73.11 0.566 10.80 767.3 0.186 541.4 183.0 114.6 59.5 14.7 115.2 125.5 226.3 960.5 904.6
Run 7 13.33 0.185 1.67 73.06 0.554 10.79 758.9 0.180 570.3 193.3 101.8 67.9 6.1 113.5 124.9 226.9 960.6 910.1
Run 8 13.26 0.185 1.69 73.04 0.555 10.78 771.7 0.185 565.2 191.8 95.2 66.9 9.3 101.6 124.7 227.4 918.0 919.7
Run 9 13.33 0.180 1.64 73.11 0.561 10.82 775.7 0.183 553.7 219.7 113.4 61.5 9.3 109.6 124.6 222.9 916.9 913.4
Run 10 13.30 0.193 1.68 73.08 0.556 10.80 764.1 0.188 572.6 243.2 101.3 64.4 1.0 103.4 123.0 226.0 980.8 912.7
Run 11 13.31 0.184 1.66 73.06 0.561 10.78 785.3 0.186 566.0 191.8 109.0 70.8 13.8 106.9 122.1 227.7 950.9 875.6
Avg. 13.31 0.183 1.67 73.08 0.558 10.80 770.5 0.183 566.4 192.8 105.8 65.8 9.7 109.9 123.8 226.1 936.2 905.7
Std.Dev. 0.03 0.01 0.01 0.03 0.004 0.02 10 0.003 15 24.2 7.2 4.3 4.9 5.4 2.2 1.4 31.2 12

Conclusion

All limits of detection obtained show that the ARL OPTIM’X can offer adequate analysis results, notably for bottle glass application. The repeatability of the analysis is high for major and minor elements, even for Na2O and MgO. Longer counting time may be utilized in case elements present below 100 ppm need to be controlled precisely. These results show that the ARL OPTIM’X spectrometer is well suited to produce precision results for the determination of the main oxides and the coloring agents in glasses.

About Thermo Fisher Scientific-Elemental Analysis

For over 75 years, Thermo Fisher Scientific has been a worldwide supplier of spectrochemical instrumentation to major industries such as steel, transportation, cement, construction, food, pharmaceuticals, chemicals, academic research, petroleum and electronics. They offer unsurpassed capabilities in the areas of optical emission (OE), X-ray fluorescence (XRF), X-ray diffraction (XRD) and automation of spectrometers.

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

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

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