Center for Electron Microscopy (ZELMI)

Metallographic preparation for light microscopy, scanning electron microscopy and the electron beam microprobe.

In metallographic preparation, the aim is to prepare the microstructure of a sample for qualitative and quantitative investigations. For this purpose, the material must be brought to a suitable size and the surface must be displayed without defects. This is usually done after the sample has the right size, by grinding and polishing with suitable materials.
The preparation process and the surface, which is then polished to a high gloss, is examined using a light microscope. The specimens are etched if necessary. For electron microscopic examinations, etching is generally unfavorable, since it creates a chemically based topography.
For light microscopy, etching is often helpful for visualizing the microstructure.

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Metallographic preparation is suitable for all solid materials - metals - plastics - teeth - stones and the like.
Powders and bones can also be processed after metallographic preparation.
Another preparation area is the thin section preparation of geological specimens, for which there is a special laboratory in TUB Geology.
Biological specimens also require specialized preparations, only some of which are located in ZELMI.

Office KWT 2
Room KWT-A 05

sawing

The samples need to be resized to the appropriate size.

embedding

embedding

Small specimens are cast into manageable molds with cold embedding medium. For larger samples, this step can be skipped if they continue to be prepared manually.

The advantage may be the conductivity, which is maintained without embedding.

grinding

grinding

The specimens are sanded with coarser sandpaper so that a flat surface is created. Subsequently, the grit is reduced in further sanding steps until one has a very finely sanded surface. Common sanding steps are depending on the initial condition of the sample with sanding grits of 800 - 1200. Sanding papers with grit 2400 and 4000 already belong to pre-polishing steps by the grit.

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polishing

polishing

 

The ground area is still very uneven (grinding grooves). By polishing with different grits these grooves are gradually leveled and thus eliminated.

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The polishing stages range from 9 µm diamond suspension to 0.5 µm polishing agent with different types of cloth. Between each polishing stage, the specimens must be cleaned.

The goal of obtaining a scratch-free surface can only be achieved through a stepwise clean preparation.

Vibration polishing

Vibration polishing

The Vibromet oscillates horizontally at 7200 cycles per minute. As a result, the specimens move independently in the polishing fluid and an effective polishing process takes place.

The results obtained are particularly convincing in EBSD examinations.