Raman from powdered samples

Raman spectra were recorded on a J-Y Ramanor spectrometer, using an argon ion laser (488.0 nm) excitation, for several compositions of C Fi (HF). The spectral resolution was 2 cm. Typically, 100 scans were taken and added together from powder samples that were contained in quartz X-ray capillaries the quartz line at 808 cm provided a fiducial marker in the spectra. 

As large single crystals are frequently unavailable for synthetic zeoHtes, most of the Raman spectra have been taken from powdered samples without polarization. Minimum sample sizes of about 1 mm are required for conventional Raman techniques. 

It is assumed here that the raw Raman spectra used as standards for the creation of the databases are taken from powdered samples with nonpolarized laser radiation and in the backscattering configuration, which is, by far, the most common case in pigment analysis. Polarized spectra from oriented crystals are beyond the scope of this chapter. 

Usually, particle size has relatively little effect on Raman line shapes unless the particles are extremely small, less than 100 nm. For this reason, high-quality Raman spectra can be obtained from powders and from polycrystalline bulk specimens like ceramics and rocks by simply reflecting the laser beam from the specimen surface. Solid samples can be measured in the 90° scattering geometry by mounting a slab of the solid sample, or a pressed pellet of a powder sample so that the beam reflects from the surface but not into the entrance slit (Figure 3). 

Measuring Raman spectra of polymorphs requires little or no sample preparation. Spectra can be measured from single crystals and from powders. Moreover, samples can be contained in glass capillaries or mounted on a goniometer. As mentioned earlier, fiber optics can be used to interface the instrument with the samples. Thus the measurements are straightforward and easy to perform, whereas the analyses produce information on structures and spectral fingerprints for straightforward identifications. 

Raman spectra of powdered samples in capillary tubes were obtained using a double monochromator spectrometer (Model 1401—Spex Industries, Inc.) with the blue laser line excitation (488 nm). The scattered radiation from the sample was taken at 90° to the incident beam. 

A solid compact sample or a tablet produced from powder may be placed directly in the sample holder. The spectrum is often improved by irradiating a fine hole within the sample with the laser beam and by analyzing the Raman radiation emerging from the hole. The multiple reflection of exciting and Raman radiation inside the hole enhances the efficiency of the transformation of laser radiation into Raman scattered radiation. 

In a typical in situ Raman study, CNT samples are heated in a heating stage, operated in air or controlled environment between 20°C and 600°C. Powders must be dispersed in a solvent, such as ethanol, to produce a thin film of CNTs on a glass slide. The samples are then kept in the heating stage and placed under the microscope of the Raman spectrometer. The oxidation process described in this chapter followed two different heating procedures. The first procedure (nonisothermal) includes heating from room temperature up to 600°C at a rate of... 

In brief, the investigation of ferrofluids through Raman spectroscopy permits to access the physical and chemical properties of both solid and liquid phases. Comparison between the Raman spectra obtained from liquid water and the Raman spectra obtained from the uncoated and coated nanoparticles dispersed as ferrofluid provides information about the interface nanoparticle surface-carrier liquid [63]. The onset of the hematite phase in core magnetite dispersed as magnetic fluids was followed by Raman spectroscopy, and the results showed that the laser intensity at which the phase-transition takes place was higher for nanoparticles in the colloid than that for the same core as powder samples [69]. 

Raman spectra were obtained using a Spex lAOl double monochromator and a detection system which utilized photon counting, in combination with a 6A7.1 nm laser exciting line from a krypton laser. The Spectrometer was coupled to an on-line computer which allowed the data to be collected, stored, corrected for phototube sensitivity, normalized and plotted. Powdered samples were loaded into 1 mm o.d. quartz X-ray capillaries in the Drilab, sealed temporarily with a plug of Kel-F grease, and the tube drawn down in a small flame outside the drybox. 

Raman Spectra.— MicrocrystalUne samples of the compounds were used in obtaining the Raman spectra. At the outset of the work a bulk sample (several milligrams) of each compound was used, which was enclosed in a quartz, Pyrex, or Kel-F tube of ca. 1/8 in. internal diameter. It was found in the course of the work, however, that satisfactory spectra could be obtained from samples packed in 0-6-mm. diam. quartz X-ray capillaries. This latter procedure is particularly recommended since it permits X-ray powder data and a Raman spectrum to be obtained from the same sample. 

Raman spectra were obtained from a sample packed as for the x-ray powder sample but in a 1.5 mm diameter quartz capillary. The sample was cooled by a cold nitrogen stream shrouded by a dry room temperature stream and the temperature was thereby maintained at -100 °C. The spectrum of Xe2p3AsF6 was obtained in the same way. The spectra are compared in Figure I. 

In the present work, intensity of ultramarine Raman spectra have been enhanced by the order of magnitude with solid nanosized Ag particles. Model samples have been prepared as powder mixtures of the pigment and silver particles without any compressing pretreatment. This makes the sample preparation process more easy in contrast to a more traditional way based on SERS-active film from colloidal solution of nanosized Ag particles. The technique does not require much sample material from art objects and preparation of aqueous suspension from a sample. Taking into consideration the low solubility of art pigments in water we propose the sensitive method of pigment identification in real art objeets. 

De Waal et al. [98] used Raman spectroscopy to measure the decomposition kinetics from the isothermal time-dependence of the totally symmetric Cr - 0 vibration mode in (NH4)2Cr04 between 343 and 363 K, The results were fitted to the Avrami-Erofeev equation with n = 2. for microcrystals was 97 10 kJ mol and 49 1 kJ mol for powdered samples. 

Figure 2 Partial Raman (top) and MAS NMR spectra (bottom) from hydrate samples recovered from Cascadia, taken at lOK and 173K, respectively. The spectral signatures indicate that methane is the principal guest for both large (major peak) and small cages(minor peaks). The line intensities show that the popidations are in an approximate 3-4 1 ratio (for large small cages), confirming the powder X-ray data assignment that it is a si hydrate. mbsf= meters below sea floor, cm bsf cm below sea floor. From ref. 41...

Examination of the residual solid from solubility samples is one of the most important but often overlooked steps in solubility determinations. Powder X-ray diffraction (PXRD) is the most reliable method to determine whether any solid state form change has occurred during equilibration. The sample should be studied both wet and dry to determine if any hydrate or solvate exists. Thermal analysis techniques such as differential scanning calorimetry (DSC) can also be used to identify any solid-state transformations, although they may not provide as definitive an answer as the PXRD method. Other methods useful in identifying any solid-state changes include microscopy, Raman and infrared spectroscopy, and solid-state NMR (Brittain, 1999). When changes in solid-state properties are identified in solubility studies, it is important to link the new properties to the properties of known crystal forms so the solubility result can be associated with the appropriate crystal form. 

Figure 8.5 Resonance Raman spectra excited at 632.8 nm and 488.0 nm of powdered samples of PANI-ES (A), PANI-MMT samples prepared from ex situ polymerization (B) and in situ polymerization (C). (Reprinted with permission from Macromolecules, Spectroscopic Characterization of a New Type of Conducting Polymer-Clay Nanocomposite by C. M. do Nascimento, V. R. L. Constantino and M. L. A. Temperini, 35, 20. Copyright (2002) ACS)...

Fig. 15. Resonance Raman scattering, using different laser excitation frequencies at 1.3 K [30] of (a left) a polycrystalline pressed sample of a-(BEDT-TTF)2l3 (prepared from powdered a-crystals and then tempered), (b right) of a polycrystalline pressed sample of at-(BEDT-TTF)2l3, where the surface of the pellet was polished with a razor blade (see text).

Ultrafme pure BaTi03 powders were obtained by a modified oxalate precipitation method as described previously [13], The powders had a specific surface area of 57 m g and the particle size was nearly spherical from 20 to 30 nm. The main impurities contained in the powders were at the following levels 0.04 wt% Sr, 0.02 wt% Na, and 0.006 wt% K. The Ba/Ti atomic ratio was 1 0.003 for all the powders. The X-ray diffraction (XRD) patterns of nanocrystalline powders apparently correspond to a pseudo-cubic structure without peak splitting of lines such as (002) and (200). We also used Raman spectra to detect local symmetry of the nanocrystalline powder samples. It showed that the local symmetry in the nanopowder appears to be a cubic structure even at a very low temperature of 123 K. Therefore, XRD patterns and Raman spectra revealed that the BaTiOs powder exhibited the commonly reported pseudocubic perovskite structure. 

Chemical bond information for materials can be determined with inferred and/or Raman spectroscopy, SIMS (second ion mass spectroscopy) and TOF-SIMS (time-of-flight secondary ion mass spectroscopy). Chemical bond information, especially on the materials surfaces, can be obtained with TOF-SIMS. Micro-IR and micro-Raman spectroscopes have been developed to map the chemical compositions of samples on a micrometer scale. The chemical species presented in MEAs after different lifetime tests were studied by a Raman spectrometer [36]. Cheng and co-workers observed a significant shift in the Raman bands of ruthenium oxide (RUO2) from 528, 646, and 716 cm in a single crystal to 506, 616, and 675-680 cm of amorphous ruthenium oxide at the anode side of MEAs. Although the RUO2 was initially present in the powder sample of the anode... 

Raman spectra of the hexaboride solid solution EUj Gdi ,B5 have been measured by Ishii et al. (1976). Samples were prepared by borothermal reduction of oxide mixtures. Lattice parameters obtained from powder X-ray methods confirmed the... 

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