Protective coating against wear and tear consisting of sintered metal and an applied PTFE layer

Tip

In order to protect and make more visible extremely thin and sensitive, non-conductive layers, it is recommended that protective layers be applied, either by spattering or by a galvanic process. In order to give additional stability of the layers to be examined, these may be applied before the embedding process, for example glued together with an adhesive medium and hardened under light. See the REM photograph in picture 2.

	Picture 1 Angled polish at an angle of 5.5°, cauterised in 10% oxalic acid with the application of 3 volts for 10 seconds to make visible the fine fissures in the sintered metal layer.
	Picture 2 REM - reproduction of a Teflon surface spattered with gold for better visibility. The thickness of the of the irregular PTFE-layer is roughly 2 µm.

Preparation table

Cutting operation

Use the ACCUTOM 2 on a low setting with a bakelite-bonded Al₂O₃ disc

Embedding

Cold embedding medium - 1.25 inch sample DEMOTEC 10

Sanding by hand

Sanding medium	Grain-size	Speed [RPM]	Time
SiC moist sandpaper	220	200	Until Sample flat
SiC moist sandpaper	320 - 1200	200	10 seconds each time

Following the sanding operation, the extremely thin, light-hardening adhesive medium DEMOTEC 200 is infiltrated into the vacuum.

Semi-automatic polishing

Polishing medium	Grain-size	Base	Trial pressure [N]	Speed [RPM]	Time [min]
Colour-diamond suspension	6µm	Silkoflex	15	100	10
Colour-diamond suspension	3µm	Silkoflex	15	100	4
Colour-diamond suspension	1µm	Silkoflex	13	100	3
SiO2 Suspension	0,05µm	Mikromant®	13	100	3

The structure of the carrier material was made visible by means of cauterisation in 3% alkaline HNO₃. Cauterisation lasting just a few seconds in 10% oxalic acid with the application of 3 volts revealed fine hairline fractures in the sintered metal layer.