Precious metal layers jewelry covered here are au

Info icon This preview shows pages 618–620. Sign up to view the full content.

Precious Metal Layers. Jewelry Covered here are Au alloy layers (mostly CuCdAu) with a high Au content ( > 12 kt). Substrate materials are brass (CuZn) but also CrNi-steel (stainless steel). For Cu alloys, a bonding agent is necessary between the Au alloy layer and the substrate material. This is generally Ni, often with a copper backing. Due to common Ni allergies in humans, for jewelry with insufficient CuCdAu- layer thicknesses, Ni is often replaced by so-called white bronze (CuZnSn). This does not make it easier to analyze the Au alloy coating, especially since to top it off a thin hard gold coating ( < 1 µ m) is often applied as scratch protection. Thus, the layer system is (from top to bottom, thickness and concentration values are approximate values) 1. Au (1 µ m, with 1% Co or Ni), 2. CuCdAu (2–5 µ m, 20% Cu, 5% Cd, rest Au), 3. Ni (2 µ m) or CuZnSn (2 µ m, 40% Cu, 20% Zn, rest Sn), 4. Cu (3 µ m), 5. Cu70Zn30 (saturation thickness).
Image of page 618

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

598 V. R¨oßiger and B. Nensel Aside from the fact that we have here a quadruple coating system, where two partial layers consist of several elements, some elements occur multiple times: Au in the 1st and 2nd layer, Zn in the 3rd layer and in the substrate material, and Cu even in the 2nd, 3rd, and 4th layer as well as in the substrate material. In view of the limited information from the XRF spectrum, it seems that simplifying assumptions are unavoidable when analyzing this system. The composition of the partial alloy layers must be entered with fixed values (cf. Sect. 7.4.4, DefMA Features 13 and 14); otherwise, the evaluation will become unstable or ambiguous. The equation system (7.26), cf. Sect. 7.4.3, will then have no explicit solution. This means that various values of the AuCdCu thick- ness with different compositions have an equally good spectra adaptation. In other words, the method fails here because the task is too complex. It is def- initely possible that measurements with different geometries and/or different excitation conditions provide additional information in order to enable an un- ambiguous solution. Now, with WinFTM-V.6 and such complex cases we can only analyze how the simplification of the DefMA influences the results. As an example, we will consider the somewhat simpler layer system AuCdCu/Ni/Cu/CuZn. The Cu-content of the substrate material shall be known. Thus, the Cu of the 3rd layer is here the problem. The interim Ni layer is not thick enough to suppress the Cu signal of the 3rd layer, which interferes with the alloy measurement. The Cu, which is rather uninteresting, provides a fluorescence signal, which the evaluation cannot differentiate from the Cu of the Au-alloy layer. Expressed more precisely: the differentiation is not sensitive enough to support a dependable measurement. What remains is an essentially realistic input of the Cu thickness fixed by WinFTM when evaluating the other measured quantities. The influence of this Cu value, on the composition and thickness of the Au alloy layer is shown in Fig. 7.113.
Image of page 619
Image of page 620
This is the end of the preview. Sign up to access the rest of the document.
  • Spring '14
  • MichaelDudley

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern