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Compositional Depth Profiling by GD OES

The algorithms for quantitative depth profiling (QDP) were described in Depth Profiling. The means of controlling the GD source were described in Modes of Operation. The method of calibration was described and illustrated in Calibration. So now we put it all together and present some examples of QDP using RF-GD-OES.

Metal Coatings

Two examples are: hot-dipped Galvanized steel and Zinc-Nickel coated steel. These were used to introduce Glow Discharge. A description of these and other coated products can be found in the next section .

Another important commercial product is Galvalume. The coating is 55% Al, 43.5% Zn and 1.5% Si, and typically 20 µm thick:(1)

[Galvalume]

Galvalume - Al-Zn-Si coated steel

Key: Si x5, Vdc /10, QM a.u., Dns x10

From the Al and Zn profiles we can determine that the coating is 20 mm thick. The Al and Zn profiles are not constant through the coating indicating the coating is not homogeneous with depth. Si is concentrated more towards the steel substrate. Vdc is higher in the steel than in the Al-Zn-Si coating. The sputtering rate QM varies in the coating up and down with the Zn content but overall is about the same in the coating and steel. The density is about 4 g/m2 in the coating and increases to 7.8 g/m2 in the steel.

[TiN]

Hard Coatings

Some of the most important hard coatings are based on TiN. They are used to increase wear and corrosion resistance. They are commonly produced by chemical vapour deposition (CVD) or physical vapour deposition (PVD). An example of such a CVD coating is:(1)

The analytical result displayed in the graph has been obtained with a TiN coated tool steel, showing an intermediate TiCN layer

some

Polymer Coatings

One of the important steps in producing car bodies is the cataphoresis (e-coat) coating applied before painting. It is used to improve paint adhesion and corrosion resistance. One such coating, produced in a laboratory test, is shown here, as Atom% vs Depth (mm), to emphasise the light elements, C, O, N, etc.:(2)

Cataphoresis on steel: the steel substrate is to the right, the first layer on the steel is a zinc phosphate, and then the thick outer polymer coating to the left.


References:

  1. R Payling, M Aeberhard and D Delfosse, in Proc. 12th Intl. Federation for Heat Treatment and Surf. Eng. Cong., Melbourne, Australia, 29 Oct.-2 Nov. 2000, Vol. 2, pp 97-100 (2000).
  2. R. Passetemps, R Payling and P Chapon, Pittcon99, Florida (1999).

First published on the web: 8 October 2000.

Author: Richard Payling