Arab Journal of Nuclear Science and Applications, 46(4), (94-99) 2013

Transcription

1 Arab Journal of Nuclear Science and Applications, 46(4), (94-99) 2013 Analysis of Some Elements in Egyptian Silver Coins by Different Techniques S. A. Abd El Aal, W. A. Ghaly, H.T.Mohsen,, A. A. El Falaky 1 and A. I. Helal NRC, Central Lab. AEA 1 Faculity of Science, Zagazig university Received: 27/4/2011 Accepted: 5/6/2011 ABSTRACT Some selected Egyptian silver coins in the Ottoman Empire Period are analyzed using energy dispersive X-ray technique(edx) attached with scanning electron microscope (SEM) unit, X-ray fluorescence (XRF) technique and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). The X-ray spectrum and LA-ICP-MS of the coins showed peaks in the surface of the 2,5 and10 Qirsh coin. INTRODUCTION Various Muslim dynasties ruled Egypt from 641AD on, including Ayyubid Sultans to 1250 AD and Mamluks to 1517 AD, when it was Conquered by the Ottoman Turks, interrupted by the occupation of Napoleon ( ). A semi- independent dynasty was founded by Muhammad Ali in 1805 which lasted until Egyptian Coins issued prior of the advent of the British protectorate series of Sultan Hussein Kamil introduction in 1916 were very similar to Turkish coins of the same period. They can be distinguished by the presence of the Arab word Misr Egypt on the reverse, which appears immediately above the Muslim accession date on the ruler, which is presented in the Arabic numerals. Each Coin is individually dated according to the requal years. The composition of ancient coins reflects political or economic trends in ancient societies. In the Ottoman era the gradual debasement of coins was associated with the decline of the empire. The social and economic consequences of debasement are clear if we consider that in the ancient world the value of a coin was equal to the value of the precious metal in the coin. Non-spatially resolved methods such as neutron activation method (NAA) and X-ray fluorescence have been used to analyze a great number of coins (1). Spatially resolved EDX, XRF and spatial resolution by the mass spectrometric technique called laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) have also played a role in minimising the impact of corrosion layers which affect the analysis for obtaining reliable results (2). EXPERIMENTAL The Energy Dispersive X-ray Fluorescence (EDXRF) spectrometer is used to analyze the coins. Figure (1) represents the schematic diagram of the EDXRF system used for the study. The system consists of a low power air-cooled X-ray tube as an excitation source. The operating voltage and the current of the X-ray tube were 30 kv and 0.6 ma, respectively. The X-rays from the tube was exposed on a molybdenum secondary exciter and the generated characteristic X-rays of molybdenum were used to excite the elements present in the studied coins samples. The measurement time for the determination of the main components was 300 seconds. The

2 characteristic X-rays emitted from the elements present in each sample were collected using a Si(Li)detector and a PC-based multi-channel analyzer. Fig. (1): Schematic diagram of the XRF system. The experimental conditions of the LA-ICP-MS Joel plasmax2, which was used for the analysis of coin samples are shown in Table (1). Table (1): Optimized Experimental Parameters for LA-ICP-MS for analyzing coin samples Rf power Coolant gas flow rate Auxiliary gas flow rate Nebulizer gas flow rate Resolution Laser power Frequency 1200 W 14 L/min 0.3 L/min 0.85 L/min mj 20 Hz RESULTS AND DISCUSSION Coin debasement has been studied by three analytical methods. Low vacuum Energy dispersive X-ray technique (EDX) attached with scanning electron microscope unit (SEM), X-ray fluoresces technique XRF, and laser ablation inductively coupled plasma mass

3 spectrometer (LA-ICPMS). They are used for the study of the elemental composition of the three selected silver coins from the Ottoman era in the period around 1372 AD. Fig. (2): 2, 5 and 10 silver Qirsh coins at 1327 AD in the Ottman Empire period For obtaining reliable results, cleaning of the corroded layers of 3 coins namely 2, 5 and 10 Qirshs by ultra sonic cleaners is essential before analysis. The results from the examination of the coins using XRF technique showed that there was mercury in the surface of the 10 Qirsh coin Table (2 ). Table (2): Elemental analysis by XRF of the selected coins. Element Concentration (%) 2 Qirsh 5 Qirsh 10 Qirsh Al ± 0.36 Si 0.42 ± ± ± 0.31 S 0.07 ± ± Fe 0.41± ± Co ± 0.06 Ni ± Cu 3.58 ± ± ± ± ± ± ± 0.11

4 Cu Counts[x1.E+3] Cl Si Al Cu Cu Co Co kev Fig.(3): XRF spectrum of 10 qirsh silver coin. The results from the examination of the coins using EDX technique showed that there was mercury in the surface of the 10 Qirsh coin while no remarkable concentrations of is observed in the other coins (table 3 ). Table (3) Qirsh coins elemental analysis by EDX at Ottoman period. Silver Qirsh coins (1327 AD) Element 10 Qirsh 14 gm 5 Qirsh 7gm 2 Qirsh 2.8 gm Mg Al Si S Ca Fe Cu Total % 100% 100% 100% Laser ablation method is also applied for the same measurements of the three coins. The size of the ablated material is in the range of (μg). The LA method is applied in two modes, the raster one

5 (Fig 4-a) to identify the surface composition and the drilling one (Fig 4-b) to know the metallographic variations with the depth ie the relationship for distance/concentration for the sample. Profile analysis can provide information for the distribution of the various elements (major and trace elements) in the metallographic structure. a b 1300 X 10 m Fig. (4): LA in the raster mode (a) and in the drilling mode (b) for 10 shots at 7 Joules Table (4) LA results of the raster mode elemental analysis of the coins (%). Element 10 Qirsh 5 Qirsh 2 Qirsh Cu Au Tl Pb The obtained results (Table 4) showed that mercury exists as a major element in the 10 Qirsh coin. In general laser ablation produced more mass from the surface for mercury than from the core which is drilled up to 50 micrometers, while the silver signal was increasing towards the core (Fig 5).

6 Intensity (%) Depth (µm) Fig. (5): Variations of silver and mercury concentrations as a function of the depth in Micrometers in 10 Qirsh coin. The results shows the much higher levels of mercury in the surface of the 10 Qirsh coins compared to the silver rich areas in the bulk of the coins. The mixing of mercury with silver to the coin surface meant that debasement which may occur in the coins could be discovered by these analytical techniques without any change to the coins outward appearance. More analytical quantitative analyses were performed on the surface of other coins. The analyzed elements were,, Cu, Au, Tl and Pb but concentration does not give the sense of contamination rather than amalgamation.drilling the coins 2 and 5 Qirshs don t show remarkable variation of certain element towards the bulk as shown in Fig.(5) which may mean that plating with mercury was not observed in their metallographic structure. REFERENCES (1) M.M.Al-Kofahi and K.F.Al-Tarawneh, X-ray Spectrometry 29, 39 (2000). (2) R. ZAGHLOUL et al., Journal of Radioanalytical and Nuclear Chemistry, Articles, VoL 109, No , (1987). (3) L.Dussubieux and L.Van Zelst, Appl.Phys.A 79,353, (2004). (4) C. V.Mogire, B. Stern, J. G. McDonnell, Nucl. Inst.and Meth. in Phys. Res. B , (2007). (5) G. Sarah, B. Gratuze and J.Barrandon, J. Anal. A. Spectrom, 22, , (2007). 44