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Preliminary Preparation Techniques

1 Sawing 1.1 Principle This technique is used to make slices of bulk samples in order to reduce their dimensions and then prepare them using other preparation or finishing techniques (final thinning for transmission electron microscopy). In most cases, this means obtaining a slice with parallel faces of the right thickness (a foil or disk 1- to 0.1-mm thick). The sawing technique uses the mechanical effect of abrasion. The friction of the material grains (abrasive), which are harder than the specimen to be machined, cuts precisely into materials. A fluid must be used, serving as both lubricant and coolant. This technique is used to cut practically all materials (bulk and multilayer, compact or porous) of any shape. They can be single phase or multiphase, from very hard to soft. Fine particles must be embedded so as to make them into a machinable block.

1.2 Operating Mode 1.2.1 Equipment and Supplies There are two types of wheel saw and one type of wire saw. Wheel saws are driven by an adjustable-speed electric motor turning an axle on which a cutting wheel or saw blade (toothless) containing abrasive grains is mounted. To prevent flutter during rotation, the wheel or blade is held in place by rigid, stabilization flanges (reinforcement flanges) that have a smaller diameter than the wheel or blade. The saw uses friction to cut the sample and wear it down. A lubricant is used to facilitate the cut, prevent mechanical blockage, and keep the frictional temperature from getting too high. The difficulty lies in selecting the wheel/abrasive/lubricant combination with regard to the material’s properties, and then in selecting the speed/cutting force combination. Manufacturers offer pre-made solutions, whose purchase price must J. Ayache et al., Sample Preparation Handbook for Transmission Electron Microscopy, C Springer Science+Business Media, LLC 2010 DOI 10.1007/978-1-4419-5975-1_2, 

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Preliminary Preparation Techniques

be taken into account. The blade contains the abrasive, and the binder, which may be made of metal or synthetic material, constitutes the blade’s matrix. The binder is an important factor in cutting because if the abrasive grains wear or break down during cutting, they must be replaced by the underlying grains embedded in the binder’s bulk. This cannot occur unless the binder also wears away. The binder/abrasive combination is determined by the manufacturer for a given application or material. Therefore, the manufacturer’s instructions must be followed. Wheels with a diameter ranging between 50 and 300 mm are available commercially. A small blade wheel is more stable than a large one and provides greater cutting precision. The thicker the blade, the more stable the wheel, and therefore, the better the precision. However, the rate of material removal decreases, and therefore cutting speed decreases as well. Cutting wheels are generally made with a metal binder (bronze, nickel alloy, etc.) or a so-called resinoid binder (bakelite, etc.) with the abrasive embed