Filmic contamination

TEST INK

Contaminated surfaces are more difficult to wet than clean surfaces. Good wettability is the basic prerequisite for coating with paints, printing inks or adhesives. A simple method for the measurement of the surface tension on a very wide range of materials is to use test inks. For this purpose, we apply test ink to the surface. If the lines remain stable, the surface is easy to wet. The surface of the substrate then corresponds as a minimum to the surface tension of the test ink. If the ink pulls together, the wettability of the substrate is lower than that of the test ink used. The procedure is then repeated with a test ink with a lower surface tension. The higher the value is for the surface tension, the cleaner the surface. The surface tension/surface energy is stated in mN/m.

FLUORESCENCE MEASUREMENT

Organic contaminating films such as greases, oils or wax fluoresce if they are excited using UV light. Materials that do not fluoresce can also be rendered visible by including fluorescing dyes as markers. In this way we can verify, quickly and without contact, the presence of organic substances on metallic surfaces. We only need an absolutely clean surface as a reference. The higher the fluorescence value measured, the thicker the filmic contamination. The measured value is stated in RFU (Relative Fluorescence Units).

Contact angle measurement

One method for checking your component surfaces is contact angle measurement with determination of the free surface energy. It is a simple procedure that takes just seconds and can also be used on the move thanks to the handy measuring instrument.

The device dispenses drops of two liquids - one polar, e.g. water, and one disperse, e.g. diiodomethane - onto the surface to be tested. Within seconds, the device determines the contact angle, i.e. the angle that a drop of liquid on the surface of a solid forms with this surface. A contact angle < 90° indicates that the surface is well wettable, a contact angle > 90° indicates that, for example, coatings adhere poorly or not at all. The free surface energy in mN/m is also calculated from the contact angles determined for polar and disperse. The higher this is, the better the wettability by aqueous or organic liquids, the initial adhesion and also the long-term stability.

VERIFICATION AND IDENTIFICATION USING RAMAN AND FTIR SPECTROSCOPY

Chemical-filmic contamination such as oils, greases, cooling lubricants, cleaning agents, preservatives, solvents and more can be analysed directly on the surface of the component using the spectroscopic analytical methods RAMAN and FTIR. These measurement and analytical methods provide qualitative measured values. This means we can verify the presence of contamination and identify it unambiguously. Reference databases are required for these near-surface analytical methods.

VERIFICATION AND QUANTIFICATION USING GAS CHROMATOGRAPHY (GC-FID)

For this purpose, we extract the contamination from the component using a suitable solvent and analyse the organic residues released using gas chromatography coupled with a flame ionisation detector (GC-FID). As a result we obtain the sum of the soluble organic contamination in mg/component or in mg/m².

IDENTIFICATION AND QUANTIFICATION USING GAS CHROMATOGRAPHY (GC-MS)

For this purpose, we extract the contamination from the component using a suitable solvent and analyse the organic residues released using gas chromatography coupled with a mass spectrometer (GC-MS). As a result we obtain the sum of the soluble organic contamination in mg/component or in mg/m², as well as the identification of the individual components.

GRAVIMETRIC ASSESSMENT

Here we extract the contamination from the component using a suitable solvent and separate the solid residues using filtration. After the evaporation of the solvent, we determine the mass of the soluble residues gravimetrically using an analytical balance. The result is stated in mg/component or in mg/m².