X-ray diffraction hot-stage

The solid phase in equilibrium with the saturated solution must be analyzed by techniques such as hot stage microscopy, differential scanning calorimetry, or powder x-ray diffraction, to verify if the starting material has undergone a phase transformation. 

The nature of the phase formed in the slow coagulation experiment can be deduced on the basis of its thermal transitions, and from its X-ray diffraction pattern. In the DSC trace of the slowly coagulated PBT-MSA-water system shown in Figure 6, three endothermic transitions are observed between 90 °C and 240 °C. Corresponding transitions were observed by optical microscopy using a hot stage. Solid PBT fibers or films do not exhibit thermal transitions below about 650°C (1). 

Because of this diffusion mechanism, we observe the above sequence of diffusion reactions which occur with time, as given above. It is actually possible to observe these reactions by the use of a polarizing microscope hot stage wherein the reactions are caused to occur by heating while observing the final structures formed via the x-ray diffraction patterns. 

Polymorphs and solvates can be identified and characterized by several analytical techniques including powder X-ray diffraction, IR and NMR spectroscopy. Differential scanning calorimetry (DSC) is useful for monitoring phase transformations and the hot-stage microscope is best for the identification of concomitant polymorphs. 

Six polymorphic forms of aspirin have been detected using differential scanning calorimetry. A Kofler hot stage was used to confirm the melting points of the polymorphs and to observe solution phase transformations of pairs of polymorphs. Density differences are reported for four of the polymorphs which could be isolated, but only minor variations in X-ray diffraction patterns could be observed. 

Other useful microscopic analytical techniques include hot stage, fluorescence, and cathodolumines-cence microscopies micro-infrared spectroscopy micro-Raman spectroscopy ultraviolet-visible microspectrophotometry and X-ray diffraction however, the discussion of these techniques is beyond the scope of this article. Briefly stated, each of these techniques can be used to ascertain additional information about characteristic properties of a material. The microscopist must be aware of all of these techniques, and others, so as to be able to extract the necessary information from a sample when the need arises. 

Tri] Magnetron sputtering, hot stage TEM, DTA, X-ray diffraction < 950°C, amorphous W46Fei3C4i and W36FC3iC33 films... 

In many cases unique optical textures are observed for the various orientations and structures of the three classes of liquid crystals. Thin films of nematic crystals, for example, can be identified by the pattern of dark tlueads (isogyres) which can appear in the optical microscope in transmission with crossed polarizers. Hot stage polarizing optical nucroscopy is often used to identify the phases and the transition temperatures. In some cases, the optical texture is not uniquely identifiable and x-ray diffraction and thermal analysis by DSC are used to complement the microscopy. 

Single crystal neutron diffraction single crystal X-ray diffraction solid-state NMR analysis vibrational spectroscopy X-ray photoelectron spectroscopy Environmental (VT, VRH) XRPD VT SSNMR spectroscopy Raman/IR spectroscopy thermal analysis hot stage microscopy moisture sorption analysis slurry equilibration Moisture sorption analysis... 

Thermal analysis, DSC/DTA, TMA and TO A and hot-stage microscopy are, together with X-ray diffraction, the popular methods for structural assessment at different temperatures. A combination of these methods is commonly used. X-ray diffraction of aligned samples is the most reliable method for structural assessment (Chapter 6). 

At lower temperatures, a number of liquid-crystalline transitions may occur which again can be recorded by DSC/DTA as exothermic first-order transitions (Fig. 10.22). Hot-stage microscopy and X-ray diffraction are used to determine the nature of these transitions. At lower temperatures, solid crystals may be formed. The latter are revealed by DSC/DTA as an exothermic first-order transition, by TMA as an increase in sample stiffness and by X-ray diffraction as sharp Bragg reflections. Some liquid-crystalline polymers, e.g. copolyesters, are supercooled to a glassy state without crystallizing (Fig. 10.22). 

Special instrumentation allows study of gases for environmental investigations and it should be noted that hot-stage microscopy (or thermomicroscopy) and X-ray diffraction can be used to observe changes in the solid residues. 

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