Microtomy

Generally, microtomy refers to the preparation of thin slices of material by sectioning for observation in an optical microscope by transmitted light. Microtomed sections are cut with steel or glass knives to about 1 to 40/tm thickness. Ultramicrotomy methods involve the preparation of ultrathin sections of material for observation in an electron microscope. Ultramicrotome sections are cut with glass or diamond knives to a thickness ca. 30-100 nm. If imaging is to be done via many techniques, the TEM preparation method can be utilized to prepare thin sections for OM, TEM, and AFM, and the flat block face is used for SEM and/or SPM. 

Ultramicrotomy is very commonly used in the preparation of biological and polymer spec- 

The simplest and most useful of these devices for fibers, films, yams and fabrics is a modified metal plate, as shown in Fig. 4.6. Sections cut using such a plate tend to be ragged around the edges, nonuniform in thickness and often damaged and distorted. On the other hand, the method is simple, and it can provide rapid specimen observation. The plate is 3 x 1 inch in size, with slots from the edge to the center, ending in small holes, about 1 mm across. The specimen is combined with a colored filler yam and forced into the slot. A razor blade is used to cut both top and bottom surfaces, the plate is 

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The goal of our investigations was to characterise the morphology of the sample, and to determine the size and location of the PTFE and silicone oil phases by different methods [46,47], For phase characterization using Raman microscopy, no special sample preparation was necessary. For FTIR imaging, microtomed sections (5 pm in thickness) had to be prepared by cutting the sample with a diamond knife at — 80°C ("cryo-microtomy") to prevent smearing and to obtain flat surfaces. 

Despite the relatively poor spatial resolution and quite prolonged measuring times, the method has several advantages. The method is able to "look" into the sample without destroying it, and no microtomy is necessary. Then, it is possible to collect three-dimensional images (tomographs), thus making this method very attractive if three-dimensional information about certain distributions is of interest. 

Careful attention should be paid to sample preparation, however. The materials investigated may be changed by the preparation procedure (e.g., smearing during microtomy of soft materials at room temperature is avoided when using cryo-microtomy) or during the measurement (radiation damage, contact with ATR crystal, etc.). 

Specimens for AEM should be on the order of 20-100nm thick and should accurately represent the features which are to be analyzed. In general, these requirements are often difficult to achieve simultaneously, and various specimen preparation methods must be used to approach the ideal specimen. For catalyst specimens, three main specimen preparation methods can be used depending on the catalyst material, the form of the catalyst, and the information desired. These are grinding and dispersing, microtomy, and ion-beam thinning. 

Difficulties in microtomy include the presence of Si, Cl, and sometimes S in the embedding resin which may interfere with the elements under analysis failure to retain the particle within the epoxy and drift of the section with respect to the support grid. Even when these problems are minimized, it requires patience to survey many grids to find an area to analyze that relates to the catalyst surface, pore structure, defect structure, etc. 

The first step in microtomy is to embed the powder in one of a variety of media, which can be either an epoxy [21] or pure sulfur [52]. There is a range of epoxies suitable for microtomy of zeolites, but generally the requirements are that it be hard and that it infiltrate or adequately wet the zeolite powder before curing. Both LR white and Epon-type epoxies (if mixed properly) meet the hardness requirement The use of Epon enhances the wetting of siHcious or carbon-containing zeolites, but it contains low levels of chlorine which may cause overlaps in EDS and will make it impossible to analyze for Cl. Typically a small pinch of powder is blended with two drops of epoxy in the tip of an embedding capsule. Mixing can be done with a clean toothpick, combined if needed with a cycle or two of... 

The majority of synthetic polymers can be thin sectioned by microtomy for transmitted light purposes [2]. For optimum results, sectioning should be carried out at a temperature just below the glass/rubber transition temperature, Tg. 

Ultra-high molecular weight polyethylene (UHMWPE) has been used in orthopaedic prosthetic surgery for many years due to its excellent mechanical properties and frictional resistance. A large number of studies on both retrieved prostheses and raw material have, however, been necessary in order to understand and prevent degradation of the prostheses. The shape of the prostheses and the compression moulded blocks from which they are cut is usually not suitable for examination. In a number of studies microtomy has therefore been used in order to produce pieces suitable for further studies [112, 113, 114, 115, 116, 117, 118, 119, 120]. However, very often when microtomy is used, it is without any consideration of the fact that the process... 

The microtomy-based preparation can be used to show the heterogeneities in composition and texture in zeolites and co-precipitates, such as mixed oxides. Figure 9.18 shows the image of a crystal (BF), and maps of the distribution of Si, Ga and the Si/Ga ratio in a gallosilicate crystal. The excess concentration level of Ga in the heart of the crystal is clear. 

The preparation, which is rapid if it concerns dispersing the crushed catalyst on an amorphous carbon film, may take several hours for microtomy. The analysis of a sample in transmission electron microscopy requires several hours of observation if the aim is to ensure that the results are representative. This is particularly important when subsequently seeking to determine particle size distribution histograms. Reliable values of the average size and of the width of the distribution can only be obtained taking into account a number of particles greater than 100. 

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. 

The aforementioned methods of specimen preparation, except microtomy, are regarded as an important part of metallography. These methods are also used for non-metallic materials... 

Ultramicrotomy is basically the same type of method as microtomy for preparing soft specimens for light microscopy. However, ultramicrotomy can be used to section a specimen to the 100 nm scale. It is commonly used to prepare polymeric or biological TEM specimens. 

The wood of Finus pinea was reported (8) as being almost intact . Microtomy for the SEM studies showed that the cell walls often bent over, making it diflScult to obtain a smooth surface. Weakening of the middle lamella was evident by the separation of individual tracheids or rows of tracheids from each other. TEM studies revealed delamination in the middle lamella-Si region, where the fibrils in Si were loosened. 

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