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Obtaining True Cross Sections | |
Diagram 1
Diagram 2
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Over the many years that clients and I have
been investigating the cross sections of materials by for the best
method is to fracture the material. The SEM is very clever in that
it sees a cut surface and tells us "this is a cross section cut
with a sharp scalpel blade" or "this is a cross section cut
with a blunt scalpel blade" etc etc.
Preparation method A 1. As shown in diagram 1 cut down the material to 1cm by 3cms place it into liquid nitrogen until it stops bubbling. 2. Remove the material and crack it using either heavy duty tweezers or fine pliers. If you are unable to crack the material and are forced to flex it in order for it to crack this is not good enough! In the latter case reduce or neck the material as shown, even a 0.5mm long crack could provide a great deal of detail in the SEM? 3. When the pieces have dried out (condensation) they may both be observed by LM and SEM Fibres that will not fracture by the above method could be fractured by one of two other methods. Method B 1. Insert the material in a small diameter tube (thin drinking straws are ideal). Cut the straw down to about 3cms tall. Block one end with wax, modeling clay or similar material. 2. Using a syringe force water into the straw and block the end as above. 3. Drop the straw into liquid nitrogen then follow method A part 2 above. 4. When the pieces have dried out (condensation) they may be observed by both LM and SEM Method C 1. Drill 2mm to 3mm holes in a pair of stubs as shown in diagram 2. 2. Infiltrate the holes with a water soluble carbon solution and push a bundle of fibres through the carbon solution. 3. When dry follow method A part 2 except use a blade to initiate the crack 4. When the pieces have dried out (condensation) they may be observed by both LM and SEM Method C has been used with materials like freezer bags that were failing. In this case the material was spun into a small spiral and then infiltrated with the carbon solution. |
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