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Measurement of Cr/Ni/Cu coatings of a shower head

Fischer Marketing Team | 24. April 2020

A shower head generally has a glossy silver appearance, one might assume solid metal. However, the substrate is very often plastic. The typical layer composition is chrome/nickel/copper on a plastic substrate.

The decorative chrome coatings are in the region of 0.5 ฮผm or even less, the nickel coating is 5 โ€“ 10 ฮผm, the copper layer is up to 30 ฮผm or even thicker. The x-ray fluorescence (XRF) method is a non-destructive method of measurement to be used.

Figure 1 shows the measurement setup on a FISCHERSCOPEยฎ X-RAY XDLMยฎ. A measurement application determining the chrome, nickel and copper coatings on a plastic component was used to carry out the measurement.

The following points on Figure 2 must be considered in this measurement: alignment of the specimen to the detector (proportional counter tube).

The measurement should always be taken at the highest point. In addition, it is important to know how the detector is aligned in the measuring device. If the shower head is arranged longitudinally to the detector, smaller displacements of the measuring position do not have such great effects on the result.

Avoid tilting

The specimen must not be tilted, i.e. the point to be measured must be absolutely horizontal. Particular attention must be paid to this requirement as there are often no flat surfaces on the specimen.

Correct video focusing on the measuring point

If the focus is not correct at the measuring point, the analytical software will assume an incorrect measuring distance. This can lead to faulty measurements.

XRF saturation thickness

There are physical limits to XRF measurement. If the coating thickness is too great, there is a risk of saturation. This limit can be estimated on devices with WinFTMยฎ software for an existing measuring application.

In Figure 3, the measuring range limit was determined for the copper coating, on the assumption that the chrome and nickel finishing coatings are 0.2 ฮผm and 7.5 ฮผm thick respectively. The measuring range for the chrome coating beneath these is approximately 1 to 25 ฮผm.

If all points are taken into careful consideration, the shower head can be measured non-destructively by XRF.

There is also the alternative option of determining the layer thicknesses of Cr/Ni/Cu coats coulometrically. In this method, the coatings are successively removed at the measuring area and the coating thickness determined in the COULOSCOPEยฎ CMS by way of the time taken for removal.

Table 1 shows the coating thicknesses measured: in the XRF method, four locations were measured around the each of the coulometric measuring area . The coulometric results each consist of a measurement for each coating element. The values measured for the two methods are very close to one another, but a practised observer would note that the methods do not come to exactly the same results.

The reasons for the differences may be found in the positioning of the specimen in XRF measurement; inhomogeneities in the coatings may also play a role. In the case of copper, it is also true that the specimen is close to the XRF saturation thickness and that measuring inaccuracy increases strongly as a consequence.

The COULOSCOPEยฎ CMS offers the capability of measuring copper coatings up to approximately 50 ฮผm thick. The coulometric method can thus represent an important complement to the XRF method.

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