Introduction |
There are not much traditional methods determining Silver in precious metal alloys, that are besides destructive and time consuming. Therefore since many years the X-ray Fluorescence Spectrometry has been introduced to solve this problem. |
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In absence of certified reference samples the no standard analysis based on fundamental parameter model is the power means for sufficiently precise determination of alloy composition and concentrations of Ag. |
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Alloy system Ag-Cu-Zn-Cd |
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The analytical instrument |
The instrument Xray ComPact 5/PIN offered by Roentgenanalytik Messtechnik GmbH has been especially developed for the analysis of jewellery alloys made of gold, silver or platinum. |
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A low power tube is used in either instrument in excitation mode. A special collimator reduces the exciting beam down to 0.6 mm in diameter. In this way a local analysis of several parts of the jewellery object and its filigree zones with irregular geometry, as usual for jewellery manufacturing, can be achieved. |
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Energy dispersive measurement is made with a PIN-diode. Thanks to the high resolution of this type of detector, the small amount of elements in complex composition can be determined. Good statistical measurement guarantees high reproducibility. |
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The following figure 1 shows a typical spectrum of AgCu alloy. |
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Figure 1: spectrum of AgCu alloy |
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Sample Preparation |
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The surface of the samples should be thoroughly cleaned free of contaminants. This will enable the irradiated area to be representative of the whole. |
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Further preparation is not necessary as the very small excited area and the use of normalized intensities reduce the geometric influence of the signal. |
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Excitation conditions |
| Tube |
W-Microfocus-glass-window |
| Voltage |
40 kV |
| Power |
approx. 30 W |
| Collimator |
0.4 mm in diameter |
| Measuring time for analysis |
60-120 s |
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Program Parameters |
| Program |
XMaster Vers. 2.0.2.3 |
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Analytical Features |
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Limits of detection |
Traces in alloys higher than 0.1% can be analysed. In most cases this sensitivity is more than sufficient for jewellery analysis. |
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Accuracy of analysis |
The accuracy of the X-ray spectrometric determination of silver shall be validated by standard samples of jewellery alloy. |
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The following table 1 enables to compare X-ray measured values with these of Silver standards. |
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Silver Alloy |
Ag |
Cu |
Zn |
Cd |
given |
is |
given |
is |
given |
is |
given |
is |
1 |
97.2 |
97.3 |
2.4 |
2.1 |
0 |
0 |
0.8 |
0.5 |
2 |
95.9 |
95.8 |
2.7 |
2.5 |
1.0 |
1.0 |
0.4 |
0.8 |
3 |
88.9 |
88.5 |
3.8 |
3.0 |
2.8 |
2.8 |
4.5 |
5.5 |
4 |
72.3 |
72.1 |
4.8 |
5.1 |
1.9 |
1.9 |
21.0 |
20.4 |
5 |
49.1 |
48.6 |
41.8 |
42.0 |
7.5 |
7.0 |
1.5 |
1.9 |
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Reproducibility |
For determination of reproducibility repeated measurements with a measuring time of 120 s have been realised within 25 min on a AgCu alloy sample with approximately 96.5% silver. |
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The following table 2 present the measurement results. |
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No of meas. |
Ag |
Cu |
1 |
96.08 |
3.91 |
2 |
96.09 |
9.31 |
3 |
96.21 |
3.80 |
4 |
96.24 |
3.76 |
5 |
96.17 |
3.83 |
6 |
96.22 |
3.78 |
7 |
96.24 |
3.76 |
8 |
96.18 |
3.78 |
9 |
96.26 |
3.73 |
10 |
96.16 |
3.81 |
Mean |
96.19 |
3.81 |
Error rel [%] |
0.06 |
1.61 |
SD [%] |
0.06 |
0.06 |
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Reproducibility of measurement Concentration in [%] |
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These results are showing the performance of the spectrometer delivering sufficiently accurate values of silver. |
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Conclusion |
The analytical results demonstrate that the standardless X-Ray fluorescence analysis is a most important alternative method for the analysis of jewellery alloys. The X-ray spectrometer Compact 5/PIN allows the determination of Silver in jewellery alloys with high accuracy and high precision. Other present precious and non-precious metals can be determined as well, such as Pd, Cd Zn, Ni. The elemental range is limited for elements with z > 22. |
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