Section preparation technique materials

Several review articles have been published about SILAR-grown films.4-7 The SILAR technique, including its advantages and disanvantages and the equipment employed, is presented in Section 8.2. Materials that have been prepared by SILAR are reviewed in Section 8.3. Short descriptions of the related ILGAR, ECALE, and other sequential solution-phase techniques follow in Sections 8.4- 8.6. 

Many of the methods of ring synthesis which have been discussed in the preceding sections are appropriate for preparation of substituted compounds and an effort was made in those sections to point out the scope of the methods. The second broad approach to the preparation of substituted pyrrole derivatives is the introduction of substituents on existing rings. The ability to do this, of course, depends upon the inherent reactivity of the heterocycle. The material of Chapter 3.05 is therefore fundamental to the preparative techniques to be discussed in this section and that material serves as essential background. The consideration here will emphasize the practical utilization of that reactivity for preparative purposes. 

Ultramicrotomy was one of the oldest sample preparation techniques used for soft biological specimens. With the improvement in instrumentation capabilities, this approach is making a comeback into the mainstream engineering materials, especially polymers. It involves directly sectioning an extremely thin sample using an ultramicrotome and dropping it in a liquid, where it will float and can latter be retrieved. A schematic of the ultra-... 

Oxide materials which are attractive because of their catalytic activity are often employed in the form of finely divided powders of considerable surface area. The history of the material and the preparation technique employed are important aspects to be considered when electrokinetic data are compared. Oxide powders can be hot pressed into sintered pellets, supported, or impregnated, on to carbons of high specific area, and bonded with Teflon or other inert material into composite electrodes. Microporosity of the system may produce an ill-defined surface zone flooded by electrolyte with imprecise ratio of real surface area to geometric cross-section. Sput-... 

The following sections discuss Pb(Zr, TijOa ferroelectric ceramics. However, the preparation techniques are applicable to other materials. Ferroelectric single crystals are not included. 

Microtomy refers to sectioning materials with a knife. It is a common technique in biological specimen preparation. It is also used to prepare soft materials such as polymers and soft metals. Tool steel, tungsten carbide, glass and diamond are used as knife materials. A similar technique, ultramicrotomy, is widely used for the preparation of biological and polymer specimens in transmission electron microscopy. This topic is discussed in Chapter 3. 

In this section preparation and characterization of catalytic materials are briefly reviewed with respect to their applications in environmental catalysis. A number of techniques for the preparation of the supports and catalysts are emphasized. Techniques such as impregnation, homogeneous deposition precipitation, grafting, hydrolysis, sol-gel, and laser-activated pyrolysis are used for the preparation of catalysts for fundamental studies. 

Figure 3. Electron microscopic techniques used to study micromechanical processes in polymers (a) investigation of fracture surfaces by SEM (b) investigation by TEM of ultrathin sections prepared from deformed and selectively stained bulk material and (c) deformation of samples of different thicknesses (bulk, semithin, and ultrathin)9 using special tensile stages with SEM, HVEM, and TEM. The technique in (c) shows the possibility of conducting in situ deformation tests in the electron microscope.

For the observation of biological material in the electron microscope it is best to have a thin specimen with enough contrast. It was therefore of primary importance to make ultrathin sections (< 0.1 jam) of the material, which can only be done after a whole series of preparation techniques have been applied. Some specimens, however, are so thin that they need not be sectioned, but can be investigated by means of negative staining [1]. 

The particular preparation techniques and procedures relating to these five criteria are summarized below and further details, and their importance with respect to different materials and scientific and technological disciplines, are set out in the subsequent sections. 

Specimen preparation may be broadly classified into two main areas specimen preparation techniques for transmitted-light microscopy (thin sections, smears, fibers, particulate strews) and specimen preparation techniques for reflected-light microscopy (surface preparation of opaque and nearly opaque materials). However, they are by no means exclusive and, although metals, ores, and opaque minerals may be studied by reflected light only, thin sections, smears, etc., may be studied both by transmitted and by reflected light, e.g., transmitted-light and epifluorescence microscopy. The advantages of such dual observational techniques relate in particular to contrast enhancement (criterion (3)). 

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