Microscopy optical

Microscopy is the study of fine structure and morphology of polymers with the use of a microscope [1-4]. In polymer science the term morphology refers to form and organization on a size scale above the atomic arrangement, but smaller than the size and shape of the whole sample. 

Microscopy can be done at two levels. Optical microscopy, with a magnification range of up to about 1000, reveals coarse structures and is useful as a screening tool to separate the several types of morphology. Transmission electron microscopy, with magnifications of 100,000 times, can be used to study the several morphological details. 

Optical microscopy is most often used for the examination of particles from about 3 pm to 150 pm in size, although a lower limit of 0.8 pm is often quoted. Above 150 pm a simple magnifying glass is suitable. 

The most severe limitation of optical transmission microscopy is its small depth of focus, which is about 10 pm at a magnification of lOOx and about 5 pm at lOOOx. This means that, for a sample having a wide range of sizes, only a few particles are in focus in any field of view. Further, in optical transmission microscopy, the edges of the particles are blurred due to diffraction effects. This is not a problem with particles larger than about 5 pm since they can be studied by reflected light, but only transmission microscopy, with which silhouettes are seen, can be used for smaller particles. 

Optical microscopy goes back as far as the 16th century, when magnifiying glasses and optical lenses became available. Antoni van Leeu- 

A) Conventional microscope with finite optics B) Microscope with finite optics and telan optics for insertion of optical components 

The image generation in microscopy cannot be explained sufficiently by means of geometric optics alone wave optics must also be considered (1 ], [6]. Imaging a point source generates a diffraction pattern in the focal plane. The central parts of this Airy disk contain most of the intensity therefore, the diameter of this kernel can be defined as the smallest resolvable image element (Fig. 3 A - D). The diameter of the kernel /k is given by 

The resolution limit for two points is reached when the maximum of the first diffraction spot coincides with the first minimum of the second one. Abbe developed this theory and proved it experimentally in his historical papers [1]. The resolution is calculated from the available numerical aperture and the wavelength a by 

As an example, a lens and condenser of NA = 1.4 and 2 = 530nm give a smallest separation of c/=200nm. Resolution can be improved either by a higher NA, which is difficult to obtain in lens design, or by using shorter wavelength, as in ultraviolet microscopy [7]. 

Optical microscopy refers to direct optical methods employed to study stmetures and surfaces of particles or droplets. Microscopy utilizes the tight reflected or refracted ( bent ) or fluorescence from the object under investigation. Conventional optical microscopy can only access the upper end of the colloid size range with a resolution between 0.5 and 1 pm. A magnification of lOOOx is the usual maximum limit available on an optical microscope and the depth of field (distance in front of and beyond the subject that appears to be in focus) is about 1 mm. 

Introduction to Applied Colloid and Surface Chemistry, First Edition. Georgios M. Kontogeorgis and S0ren Kiil. 2016 John Wiley Sons, Ltd. Published 2016 by John Wiley Sons, Ltd. 

Optical/ light 2 pm Simple, cheap Not very high resolution Polymer spherulites Liquid crystals 

SEM 5 orlOnm Excellent visualization of structures Not quantitative Monolayers, structures in general 

TEM 1 or 2 nm Very high resolution Instability to e-beams, sample preparation can be tedious Heavy metals Solid crystals Block copolymers 

In optical microscopy the contrast between different components arises from differences in their refractive indices. Ice cream is too opaque for its structure to be observed. However, samples can be prepared so that the ice crystals, air bubbles and fat droplets can be visualized separately. Lactose crystals, if any are present, can be clearly observed using crossed polars. They have a characteristic arrowhead shape that makes them easily distinguishable. 

Careful temperature control is necessary so that ice crystals neither melt nor grow while they are imaged. This can be achieved by performing the sample preparation and microscopy inside temperature-controlled chambers or by carrying out the whole experiment in a cold room. The temperature of the cold chamber is set to the required imaging temperature, for example — 5 °C for ice cream that has just come out of the factory freezer, or —18 °C for ice cream that has been hardened and stored. A small sample of ice cream is smeared onto 

The ice crystals are larger in water ices, and the ice content is higher than in ice cream. This means that the crystals are harder to disperse, so the solvent dispersion/squashing step may need to be repeated. Polarized light microscopy can be used to distinguish overlapping ice crystals. 

Reflected light microscopy can be used either on thin sections or thicker polished sections. Reflected light is used primarily for identifying opaque minerals such as metals, sulfides, and some oxides. Each of these minerals has a unique appearance in reflected light. 

Polarizing light microscopy employs crossed polarizers to view the sample. With isotropic specimens, the field of view is dark, while anisotropic, birefringent samples or areas of a sample will appear bright. Polarizing microscopy is employed to view spherulitic structure [66-68] and deformation morphologies (crazes, shear banding) [69] in polymer blends. Samples for 

Confocal microscopy, popular in characterization of biological systems, offers the ability to view the three dimensional structure of materials. A pinhole is placed in the back focal plane (focal plane in front of the detector), which suppresses light from other planes from reaching 

Optical fluorescence microscopy was employed to study the phase morphology of PVOH and PVAc blends [78]. Fluorescein (green) and anthracene (blue) were added to provide the contrast as fluorescein preferred the PVOH domains and anthracene concentrated in the PVAc domains. 

Optical microscopy methods have been reviewed in [79]. 

In its simple form, an optical microscope acts as a magnifying glass because it renders structural features visible that would otherwise be invisible to the naked eye. Optical microscopes may operate in either transmission or reflection mode. 

Optical microscopy is particularly useful for investigating various anisotropic features of polymeric systems. Polymers are intrinsically anisotropic objects and, when arranged in anisotropic structures such as crystalline and liquid crystalline phases, they display macroscopic optical anisotropy. These are investigated using a polarizing microscope, i.e., under crossed polarizers. 

A polarizing microscope makes use of polarized light and requires (1) a polarizer to be placed between the light source and the sample and (2) an analyzer placed after the sample. The polarizer generates plane-polarized light when the polarizer and analyzer are at right angles to each other, i.e., when they are crossed, in absence of a sample, or when the sample is isotropic. 

Molecules in anisotropic samples will be preferentially oriented along one direction, e.g., the nematic director for crystalline polymers or the fiber axis. The refractive index in the direction parallel to the orientation will differ from that in the perpendicular direction and, therefore, the sample is said to be birefringent. When polarized light passes through an anisotropic sample oriented in different directions, it is split into two components that are not in phase these will combine to give elliptically polarized light. Thus, oriented samples such as crystalline, liquid crystalline polymers and fibers are visible under polarized light. 

One of the main disadvantages of optical microscopy is its low resolution, which is of the order of half the wavelength of light. 

Applications. Optical microscopy finds several important applications in filled systems, including observation of crystallization and formation of spherulites and phase morphology of polymer blends. In the first case, important information can be obtained on the effect of filler on matrix crystallization. In polymer blends, fillers may affect phase separation or may be preferentially located in one phase, affecting many physical properties such as conductivity (both thermal and electrical) and mechanical performance. 

Major results. Carbon black has a better affinity to polyamide than polypropylene. Even if carbon black was added to polypropylene, it was preferentially transferred to the polyamide phase during mixing. In a polymer blend of two polymers, polyamide formed the minor phase and, due to preferential location of carbon black in its phase, the carbon black concentration in the polyamide phase was much higher than expected Irom the amount of carbon black added. This high concentration of carbon black in the minor phase resulted in substantially increased conductivity of the blend.  

In the conventional light microscope or optical microscope (OM), an object is illuminated and 

The information obtained in the OM normally concerns the size, shape, and relative arrangement of visible features. Local measurement of optical constants such as the refractive index (see Section 2.2.4) and the birefringence (see Section 2.2.5) is also possible. Many techniques are used to enhance contrast and thus make more of the structure visible. Images are typically recorded with a high quality digital camera, which may be linked to a computer system for image processing and analysis. 

Binocular stereo microscopes [17] are compound microscopes that provide two different images of the specimen through the two eyepieces. These are views from slightly different directions. The observer sees this as a 

The simplest method is optical microscopy, in which visible light (photons) is used to observe a sample. It has a resolution limit around 0.25-0.5 pm, which is on the order of 2/2, where 2 is the wavelength of incident light. From a strict colloid science point of view, it lies near the upper limit of colloid particle sizes and appears to be of limited utility. However, it is of great help in the identification of minerals, because it allows observation of crystal habits (the shape and size of crystals, which are determined by their internal symmetry). With experience, many minerals can be identified in a soil sample under a microscope, even from simple inspection. A unique feature of optical microscopy is the availability of polarized light, which is handy in distinguishing minerals or even different crystal types of the same compound (Bullock et al. 1985 Cady, Wilding, and Drees 2010). 

Three main developments of optical microscopy are possible  

Phase-contrast microscopy, which utilizes the difference between the diffracted waves from the main image and the direct light from the light source. 

Differential interference contrast (DIG) microscopy, which provides a better contrast than the phase-contrast method. This utilizes a phase difference to improve contrast, but the separation and recombination of a light beam into two beams is accomphshed by prisms. 

Polarised l t microscopy, in which the sample is illuminated with Hnearly or circularly polarised light, either in a reflection or transmission mode. One polarising element, located below the stage of the microscope, converts the illumination to polarised light, while a second polariser is located between the objective and the ocular and is used to detect polarised light. Various characteristics of the specimen can be determined, including anisotropy, polarisation colours, birefringence, and polymorphism. 

The optical microscope can be used to observe dispersed particles and floes, with particle sizing carried out using manual, semiautomatic, or automatic image analysis techniques. 

Of the many techniques available for the analysis of solid materials, perhaps the simplest is optical microscopy. Two modes of optical microscopy are typically 

The ability to discern flne details within a magnifled image is referred to as the resolution of a microscope. Since light is used as the illumination source in optical microscopy, the resolution is expressed in the same units as the wavelength of 

The denominator of Eq. 1 represents the numerical aperature (NA) of the objective lens, related to its light gathering ability. Other primary factors that influence the resolution of a lens is the wavelength of light used, the index of refraction tf) of the environment surrounding the lens (e.g., 1.00 for air), and the angle of illumination 6). 

It may be seen by Eq. 1 that higher spatial resolutions i.e., smaller R values) are possible through use of shorter wavelengths. To illustrate this concept, subsequent sections of this chapter will examine the high resolutions inherent in microscopes that use an electron beam rather than visible light. However, we first must ask ourselves whether it is possible to improve the resolution limits of optical microscopy. If this is possible, the cost of such a modification would be far less than the price of electron microscopes (currently 600K- 1.5M). 

There is an aperture associated with each condenser lens, and the apertures and lenses control the area illuminated and the angular divergence of the illumination. The details of the illumination system are described later (Section 3.1.5). In both optical and electron microscopes the resolution and contrast of the image may be degraded if the illumination is not properly adjusted. 

After the radiation has passed through the specimen, the scattered radiation is collected by an objective lens. This lens is the most critical, and imperfections in it will affect the image quality directly. An aperture associated with the objective lens, the objective aperture, is often used in transmission electron microscopy. In optical microscopy the size of the objective lens usually acts as the limiting aperture. 

The eyepiece lens in an optical microscope forms a virtual image for the eye to focus on. When an optical microscope is set up for photomicroscopy a projector lens is used in place of an eyepiece. This forms a real image on the photographic film. The TEM is like this, but there are at least two lenses after the objective, the intermediate lens and the projector lens. Each produces a real and magnified image, the projector 

It is beyond the scope of this text to describe the design features and operation of specific microscopes and their attachments. Any attempt to discuss microscope operation or construction in specific detail could rapidly become outdated. Manufacturers or their representatives are the best source for operating instructions for their own microscopes. 

A variety of apertures have been used to deliver nanometer-sized spots of light. While early NSOM tips were fabricated out of etched quartz crystals and micro-pipettes, tapered optical fibers with tip diameters of ca. 100 nm are now typically used. A metallic thin film such as aluminum is usually applied around the sides of the tapered region of the NSOM tip to focus the light toward the sample. For optical fibers, the numerical aperture is related to the difference in the indices of refraction of the cladding and core (Eq. 2)  

The optical microscope is a sophisticated instrument capable of providing images with a resolution of the order of 1 p,m, molecular information via birefringence, and chemical information via colour changes or through the use of specific dyes. When these factors are combined with relative ease of sample preparation (c.f. electron microscopy) and purchase cost, optical microscopy is a powerful technique for the study of many materials, particularly those that transmit in the visible region of the spectrum. 

For more details on the above imaging modes and more specialized optical techniques the reader is referred to Applied polymer light microscopy by D. A. Heiiisley.  

Just as important as the proper use of the microscope is the specimen preparation. When using transmitted-light microscopy, it is necessary to prepare thin samples, about 5-50 pm thick. This is also true even for transparent polymers because of the small depth of field of an optical microscope. If information is required about an inner part of the material, the only course of action is to cut a thin section with a microtome. Melt-pressed films can be prepared by melting the polymer and squeezing it between two glass slides to make it thin. Many of the generally known specimen preparation methods are applicable to polymers. A recent overview of all methods as a useful tool for polymers is given in [Ij. 

Another way to characterize the electrochemical activity of miCToelectrode arrays is to map the electroactive species generated at each electrode by confocal Raman spectroscopy. Indeed, the use of confocal signal detection enables Raman spectroscopic measurements of very small sample volumes (even down to a few om ). Applied to a microelectrode array, it provides a statistical picture of the distribution of active sites on the array (60). As in the case of SECM, these two optical methods are particularly useful to verify if individual diffusion layers do not overlap and if the microelectrodes in the array are diffusely independent, particularly for random microelectrode arrays. 

Sampling and subsequent preparation techniques determine the nature and extent of useful information obtained [33]. Microtomy is probably the best technique. To preserve the microstructure, it is advisable to embed, grind and polish the sample. Unfilled plastic samples for optical microscopy are prepared by using a microtome to cut thin sUces, typically 3-20 fim thick, fi om the plastic part. These slices are then placed between two glass slides and examined using transmitted polarised Ught. Magnifications up to lOOOx are typically used. Thus, optical microscopy allows one to see the microstructure of the plastic. 

Plastic parts containing glass or mineral fibre reinforcements generally cannot be sectioned using a microtome because the fibres tend to break or fall out of the sectioned sample. Such samples must be embedded in epoxy, polyester or acrylic, and polished using silicon carbide papers and diamond impregnated cloths. If morphology is more important than 

Current conventional light microscopy allows real-time, high-resolution 3D imaging. Volume or 3D imaging can be obtained in a number of ways, such as stereo viewing, confocal microscopy (cfr. 

Images from a light microscope may be analysed (measured) and processed (by enhancement techniques) during any or all phases. Automatic analysis on the shape of features can be carried out. Mor- 

Transmitted light/bright field Macro-, microstructures, colour, homogeneity, refractive index measurement 1 mm-0.3 fxm l-lOOOx  

Wischin s study [201] ofnucleation and growth ofthe product barium during decomposition of BaN6. In other rate processes where the crystallites are small, opaque, of roughened surface, etc., reactant and product cannot be distinguished and microscopic observations yield no useful data. 

The various techniques which may be used to provide optimum conditions for the examination of specimens have been described [202—205]. If the sample is opaque, then microscopic investigation is limited to the surface. The depths of penetration for the study of transparent crystals are controlled by the limited depth of field of the optical microscope at high magnifications. This limitation can sometimes be overcome by cleavage of the crystal at an appropriate value of a and examination of the surfaces exposed [120], 

References to the profitable exploitation of microscopic techniques in kinetic studies can be found in the work of Thomas and co-workers [91, 206—210], Herley et al. [211] and of Flanagan and his collaborators [212,213]. The rates of advance of reaction interfaces have been measured from direct observations on single crystals and the kinetic parameters so obtained are compared with results for mass loss determinations. The effects of the introduction of crystal imperfections and the role of such species in mechanisms of reaction are also considered. 

Surface features can also be revealed by etching, which permits identification of points of intersection of line dislocations with the surface, and this is valuable in determining the role of these imperfections in chemical processes [45,214] and, in particular, nucleus formation. Smaller topographical details can be rendered visible by the evaporation of a thin ( 0.5 nm) film of gold onto the surface [215,216]. Heights and depths of surface features can be determined by interferometry [203—205]. Microcinematography has also been used [217] to record the progress of solid phase reactions. 

Analytical Instrumentation A Guide to Laboratory, Portable and Miniaturized Instruments G. McMahon 

The sample is placed on a microscope slide, prepared as needed and mounted on a stage. Discriminator 

The objective lens is the discriminator. It forms a real intermediate image that is then greatly magnified by the eyepiece. The objective lens and eyepiece are maintained at a fixed distance and focusing is achieved by moving the whole assembly up and down in relation to the sample. 

The detector is the eyepiece that magnifies the image, and of course the human eye. Output 

Sometimes the images can be displayed digitally on a PC and manipulated there as required. 

Assume that a crystal is placed so that an axis of the indicatrix is vertical and that incident light propagates parallel to this axis from below the crystal. Let the incident light pass through a polariser below the crystal and let there be a crossed polariser analyser) above the crystal. If the orientation of the crystal around the vertical axis is such that the incident light is polarised parallel to either of the principal axes of the 

The conclusion is that if different parts of the structure contain crystallites with their axes in different directions from each other the structure will be visible in the polarising microscope. In addition to all the usual measurements of size and shape that can be made with the optical microscope, it is possible to deduce the relative alignments of the axes of the crystallites within the structure from the relative brightness of its various parts. 

Other methods for making the various parts of transparent objects visible in the optical microscope are staining techniques and dark-ground and phase-contrast microscopies. These techniques are explained in the standard optics textbooks and similar methods for use in electron microscopy are described in the next section. 

The simplest method for measuring the birefringence for a moderately thick sample involves machining a tapered region on it, so that its thickness varies within this region. If the axes of the indicatrix are set at 45° to the directions of transmission of the crossed polariser and analyser of a 

This method is applicable only to rather special types of sample and other optical methods are more usually used. They are not discussed in this book because they are rather more complicated. 

A spherullite is usually pictured as an array of lamellae radially disposed to one another and as a result is spherically birefringent. A spherullite has two unique refractive indices the radial (Ht) and the tangential ( t)- The refractive index ellipse can represent the variation in refractive index in the plane, where the length of the major axis of the ellipse is proportional to the maximum refractive index in the plane and the length of the minor axis is proportional to the minimum refractive index. If the larger refractive index is in the tangential direction, i.e. rit, the spherulite is termed negative. Spherulites show a characteristic Maltese cross pattern with a maximum in the intensity in the direction at 45 ° to the polarizer/analyser pair. 

OM is a useful and inexpensive tool for evaluating the quality of dispersions as determine by the extent of particle agglomeration, or flocculation (loose agglomerates), in dispersions, paints, plastics, flushes, or inks. 

Other applications include analysis of large size particles in residues isolated from manufacturing processes or abrasive particles in raw materials or from contamination during manufacture. 

For aqueous dispersions water or dilute surfactant solutions are used for sample preparation. Thin plastic films may be observed directly without special preparation. For plastic dispersions or concentrates, a thin slice of the sample is cut using special knifes or preferably using microtome equipment prior to analysis. 

The optical micrographs are stored as images on a computer and image analysis software is used to measure particle size, particle area, and aspect ratio. The size distribution may be plotted as histogram or a line curve for easy evaluation of the results. 

Zeinolebadi, In-situ Small-Angle X-ray Scattering Investigation of Transient Nanostructure of Multi-phase Polymer Materials Under Mechanical Deformation, Springer Theses, 

4 Thermoplastic Polyurethane Elastomers Under Uniaxial Deformation 

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NSOM Near-Held scanning optical microscopy [103a] Light from a sharp tip scatters off sample Surface structure to 3 nm... 

Kirilyuk V, Kirilyuk A and Rasing Th 1997 A combined nonlinear and linear magneto-optical microscopy Appl. Phys. Lett. 70 2306-8... 

Herman B and Jacobsen K 1990 Optical Microscopy for Biology (Wiley)... 

Cork T and Kino G S 1996 Confocal Scanning Optical Microscopy and Related Imaging Systems (New York Academic) Gu Min 1996 Principles of Three Dimensional Imaging In Confocal Microscopes (Singapore World Scientific)... 

Sheppard C J R 1987 Scanning optical microscopy Adv. Opt. Electron Microscopy 10 1-98 Cooke P M 1996 Chemical microscopy Anal. Chem. 68 333-78... 

Ribbe A E 1997 Laser scanning confocal microscopy in polymer science Trends Polym. Sc/. 5 333-7 Oliveira M J and Hemsiey D A 1996 Optical microscopy of polymers Sonderb. Prakt. Metallogr. 27 13-22 Nie Sh and Zare R N 1997 Optical detection of single molecules Ann. Rev. Biophys. Biomol. Struct. 26 567-96 Masters B R 1994 Confocal redox imaging of cells Adv. Mol. Cell Biol. 8 1-19... 

B1.19.4 SCANNING NEAR-FIELD OPTICAL MICROSCOPY AND OTHER SPMS... 

Of the methods described in this section, scaiming near-field optical microscopy (SNOM or NSOM) is tlie closest to being able to provide useful infonuation that is unobtainable by other means. Indeed, this teclmique has already been made available as a conunercial instmment. A detailed review of SNOM has been written by Pohl 11931. 

Durig U T, Pohl D W and Rohner F 1986 Near-field optical-scanning microscopy J. Appl. Phys. 59 3318 Pohl D W 1991 Scanning near-field optical microscopy (SNOM)/Icfr/. Opt. Electron. Microsc. 12 243... 

Betzig E, Finn P L and Weiner J S 1992 Combined shear force and near-field scanning optical microscopy/4pp/. Phys. Lett. 60 2484... 

Fischer U Ch, Durig U T and Pohl D W 1988 Near-field scanning microscopy in reflection Appl. Phys. Lett. 52 249 Cline J A, Barshatzky FI and Isaacson M 1991 Scanned-tip reflection-mode near-field scanning optical microscopy Ultramicroscopy 38 299... 

Betzig E and Chichester R J 1993 Single molecules observed by near-field scanning optical microscopy Science 262 1422... 

Takahashi S, Futamata M and Ko]ima I 1999 Spectroscopy with scanning near-field optical microscopy using photon tunnelling mode J. Microscopy 194 519... 

One interesting new field in the area of optical spectroscopy is near-field scaiming optical microscopy, a teclmique that allows for the imaging of surfaces down to sub-micron resolution and for the detection and characterization of single molecules [, M]- Wlien applied to the study of surfaces, this approach is capable of identifying individual adsorbates, as in the case of oxazine molecules dispersed on a polymer film, illustrated in figure Bl.22,11 [82], Absorption and emission spectra of individual molecules can be obtamed with this teclmique as well, and time-dependent measurements can be used to follow the dynamics of surface processes. 

Figure Bl.22.11. Near-field scanning optical microscopy fluorescence image of oxazine molecules dispersed on a PMMA film surface. Each protuberance in this three-dimensional plot corresponds to the detection of a single molecule, the different intensities of those features being due to different orientations of the molecules. Sub-diffraction resolution, in this case on the order of a fraction of a micron, can be achieved by the near-field scaiming arrangement. Spectroscopic characterization of each molecule is also possible. (Reprinted with pennission from [82]. Copyright 1996 American Chemical Society.)...

Hamann H F, Gallagher A and Nesbitt D J 1999 Enhanced sensitivity near-field scanning optical microscopy at high spatial resolution Appl. Phys. Lett. 75 1469-71... 

Ambrose W P, Goodwin P M, Martin J C and Keller R A 1994 Alterations of single-molecule fluorescence lifetimes in near-field optical microscopy Science 265 364-7... 

Higgins D A and Barbara P F 1995 Excitonic transitions in J-aggregates probed by near-field scanning optical microscopy J. Chem. Phys. 99 3-7... 

Hollars C W and Dunn R C 2000 Probing single molecule orientations in model lipid membranes with near-field scanning optical microscopy J. Phys. Chem 112 7822-30... 

Detailed x-ray diffraction studies on polar liquid crystals have demonstrated tire existence of multiple smectic A and smectic C phases [M, 15 and 16]. The first evidence for a smectic A-smectic A phase transition was provided by tire optical microscopy observations of Sigaud etal [17] on binary mixtures of two smectogens. Different stmctures exist due to tire competing effects of dipolar interactions (which can lead to alternating head-tail or interdigitated stmctures) and steric effects (which lead to a layer period equal to tire molecular lengtli). These... 

Figure 4.12 Spherulites of poly( 1-propylene oxide) observed through crossed Polaroid filters by optical microscopy. See text for significance of Maltese cross and banding in these images. [From J. H. MaGill, Treatise on Materials Science and Technology, Vol. lOA, J. M. Schultz (Ed.), Academic, New York, 1977, with permission.]...

Microscopic identification models ate similar to the CMB methods except that additional information is used to distinguish the source of the aerosol. Such chemical or morphological data include particle size and individual particle composition and are often obtained by electron or optical microscopy. 

The properties and performance of cemented carbide tools depend not only on the type and amount of carbide but also on carbide grain size and the amount of biader metal. Information on porosity, grain size and distribution of WC, soHd solution cubic carbides, and the metallic biader phase is obtained from metaHographicaHy poHshed samples. Optical microscopy and scanning and transmission electron microscopy are employed for microstmctural evaluation. Typical microstmctures of cemented carbides are shown ia Figure 3. 

The analysis of siUcon carbide involves identification, chemical analysis, and physical testing. For identification, x-ray diffraction, optical microscopy, and electron microscopy are used (136). Refinement of x-ray data by Rietveld analysis allows more precise deterrnination of polytype levels (137). 

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