Determination of gold content using X-ray fluorescence analysis, etc.

Transcription

1 73 * ** Determination of gold content using X-ray fluorescence analysis, etc. Taro IGARASHI*, Hiromi NAGANUMA*, Takeshi AKIEDA*, *Tokyo Customs Laboratory , Aomi, Koto-ku, Tokyo Japan With the recent rise in the price of gold, many fake gold products have appeared on the market. Since the Customs laboratory is requested to conduct analyses of imported gold products, it is necessary to establish an analytical method in order to discriminate between gold and imitations. Moreover, gold products are classified differently in the Customs Tariff Schedule depending on the type of product, such as those clad with gold plate and gold-plated products. In this study on gold products, using X-ray fluorescence (XRF) analysis and other methods, we conducted measurements of gold layer thickness, discriminated between gold products and fake products (mainly made of tungsten), and studied the difference between gold products clad with gold plate and gold-plated products. As a result, it was found that the saturation thickness of gold measured by XRF was about 1 µm, and for the fake gold products using tungsten as the base metal, it was found to be impossible to discriminate whether or not the sample contained tungsten when the gold layer thickness was more than about 4 µm. In addition, it was shown that to discriminate between products clad with gold plate and gold-plated products, it is effective to compare the gold layer thickness and to confirm the existence of nickel. X X X % K 14K 58.1 % %. % /2.5 μm/8.7 μm /1.81 μm/7.9 μm *

2 74 // 1.22 μm/9.9 μm 24K 14K X X X X X SEA12VX 3,422 1,84 φ1. mm 5 KV μa 2.3.4(1) X FP JSM-651LA 15 kv 1 na 2.3 X X (1) X = g g/cm 3 FP g 2.3.5(2) FP /2.5 μm/8.7 μm/ 1.81 μm/7.9 μm 1 X X FP Table 2) g/cm 3 14K g/cm g/cm 3 n= g/cm 3 n= X 2.3.4(2) X

3 75 Table 1Density of precious metals and main base metals Gold Silver Copper Platinum Iron Tungsten Lead Nickel Zinc Densityg/cm FP X Fig.2 /2.5 μm/8.7 μm / 1.81 μm/7.9 μm KeV μm 1.11 μm X X X KeV Lβ 8.4 KeV Lα 24K 14K X Fig.1 (a) 9.7 KeV L 11.5 KeV Lβ 13.4 Au Lα KeV Lγ 22.1 KeV Kα 24.9 KeV Au Lβ Kβ 8. KeV Kα 8.9 KeV Kβ 8.6 KeV Kα 9.6 KeV Kβ 7.5 KeV Kα 8.3 KeV Kβ 5 X X Au Lγ 7 (a) Au Lα Au Lβ Au Lγ 7 (b) Ag Kα Ag Kβ (c) Cu Kα Cu Kβ (d)zn Kα Zn Kβ (e) Ni Kα Ni Kβ EnergyKeV Fig. 1X-ray fluorescence spectra of (a) gold leaf (24K), (b) gold leaf (14K), (c) copper, (d) zinc and (e) nickel X Lγ (b) 5 W Lα W Lβ W Lγ Energy(KeV) Fig. 2X-ray fluorescence spectra of (a) gold and (b) tungsten (a).1 μm(b)3.2 μm (c)1.1 μm X Fig.3 X Fig.4 X X 1 μm X

4 76 24 (a) Cu Kα Zn Kα Au Lα Au Lβ (b) 1 μm 1 μm (a). μm(b) 3. μm(c) 4.2 μm (d) 5.4 μm X Fig.5 X Fig.6 X X 4 μm Lα X 4 μm (c) (a) W Lα W Lβ W Lγ (b) Au Lβ EnergyKeV Fig. 3X-ray fluorescence spectra of brass with laminated gold leaf; (a) gold layer thickness:.1 μm, (b) gold layer thickness: 3.2 μm and (c) gold layer thickness: 1.1 μm (c) (d) EnergyKeV Fig. 5X-ray fluorescence spectra of tungsten with laminated gold leaf; (a) gold layer thickness:. μm, (b) gold layer thickness: 3. μm, (c) gold layer thickness: 4.2 μm and (d) gold layer thickness: 5.4 μm Fig. 4Relationship between X-ray intensity of gold, copper and zinc according gold layer thickness

5 77 25 (a) Cu Kα Ni Kα Zn Kα Cu Kβ Au Lα Au Lβ Fig. 6 Relationship between X-ray intensity of gold-lβ and tungsten-lα according to gold layer thickness 25 (b) 2 Cu Kα Ni Kα X Fig.7 Zn Kα Cu Kβ X X 5 X Au Lα Au Lβ X EnergyKeV Fig. 7X-ray fluorescence spectra of surface of (a) ball point pen and (b) fountain pen X Fig.8 FP.1.3 μm 2 μm X Photo.16 Fig. 8X-ray fluorescence spectrum of surface of a charm

6 78 Surface Photo 1Observation of section of ball point pen by SEM ( 37) Photo 4Observation of section of charm by SEM ( 19) Surface Photo. 2Copper contained in section of ball point pen by XMA (37) Photo 5Gold contained in section of charm by XMA ( 19) Surface Photo 3Zinc contained in section of ball point pen by XMA ( 37) Photo 6Copper contained in section of charm by XMA ( 19)

7 79 X 1 μm 4 μm X ) JIS H ) P6, P595, P596, P.1363, P.148, P.1557, P.1657, P.1677, P.1781 (1994)