Preparation and Characterization of the Samples

2 Preparation and Characterization of the Samples Measuring Under Vapor Pressure 

It is well known that the vapor pressure of water and ethanol increases on heating. At 100°C at 1 atm, water boils and evaporates and at 78.4°C at 1 atm, the same happens for ethanol [40]. To be able to perform measurements at temperatures much higher than the boiUng points, cells are needed withstanding vapor pressures up to 27.9 bar at 230° C for water [41], and up to 63.9 bar at 244° C for ethanol. 

The crystallinity was determined following the method described by Mathot [42], which takes into account the temperature dependence of the enthalpy of crystallization [43]  

The structure of PA6 has been investigated in detail and at least two crystal polymorphs, referred to as a and 7 have been identified [45,46]. The crystal packing of the a-polymorph consists of polymer sheets parallel to the (a,b)-plane. Within these sheets the PAG chains align anti-parallel, and are held together by hydrogen bonds. In the 7-form the polymer chains form sheets parallel to the (b,c)-plane but the individual chains align parallel. A third modification of PAG, the /3-form, has also been proposed [45,47-49]. Other authors state that the various structures found are just a or 7-structures with 

The two crystalline phases can be identified by their distinct X-ray diffraction patterns. The unit cells of the a and 7 phases are different, the unit cell for a is characterized by a = 9.56 b = 17.24 c = 8.01 a = 7 = 90° / = 67.5° [45] and the unit cell for 7 by a = 9.33 b = 16.88 c = 4.78 a = 7 = 90° (3 = 121° [46]. Therefore, the two most intense reflections of the a and 7 phases appear at slightly different angles and are at, respectively, 20° (200,ai)/24°(002 -b 202,a2), and 22°(100,7i)/23° (201 -b 200,72). 71 and 72 show up as a single peak with a small shoulder [53]. The notation of Holmes et al. [45] is used. It has to be remarked that the data in the Cambridge Structural Database in Conquest version 1.7 (software for search and information retrieval) does not correspond totally with the original article. The notation of Malta et al. [54] - who re-examined the crystal structure of the a-phase -is not used, because they switched the b and c-axis, compared to Holmes et al. who used the 2nd convention (b-unique setting) [45]. 

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The preparation and characterization of the samples are described elsewhere [43]. The results are summarized in Tables 1 and 2. The number at the end of the sample code represents the contour length derived from the molar mass of the polymers. The PVP samples were quaternized with the respective alkyl and benzyl bromides in order to yield polypyridinium cations with... 

The chemical structure of the polyimide polymers (named PI-1 and PI-2) studied by Sekkat et al. is shown in Figure 12.12. They prepared the polymer samples by spin-casting onto glass substrates. PTl was cast from a cyclohexanone solution and PI-2 from 1,1,2,2- tetrachloroethane. The Tg values of PI-1 and PI-2 were determined to be 350°C and 252 C, respectively, by scanning calorimetry method. The thicknesses of the PI-1 and PI-2 films were, respectively, approximately 0.72 im and 0.14 im, and their respective optical densities were approximately 0.79 and 0.3 at 543.5 nm. Details of the preparation and characterization of the samples can be found in References 3 and 20. In their EFISH experiment, a typical corona poling technique was used to pole the samples, with a dc electric field about 2-3 MV/cm across a 1-2 lm thick polymer film. They used the SHG output from the EFISH experiment to in situ monitor the photochemical change in the third-order susceptibility of the PI-1 and PI-2 polymers. 

V-containing silicalite (Al- and Na-free) samples were prepared hydrothermally and then treated with an ammonium acetate solution at room temperature in order to remove extralattice vanadium. Three samples with Si02A 203 ratios of 117, 237 and 545, respectively, were prepared. Hereinafter these samples will be referred to as follows V-SH117, V-SU237 and V-SH545. Details on the preparation procedure, and characterization of the samples have been reported previously (7,2). 

Characterization of the stability of chemicals during preparation and storage of the samples is indirect. 

The preparation and characterization of the VR and ESR liquid rubbers and of the two-phase epoxy thermosets were described in detail previously (3-6). DGEBA is a solid epoxy resin (Epon 825) from Shell Chemical Company. ESO and ELO are commercial products from Atochem. Samples of VO and crambe oil were obtained from the U.S. Department of Agriculture. All other reagents and solvents were purchased from Aldrich Chemical Co. and Fisher Scientific Co. and used without additional purification. 

Ni/Si02 parent catalyst is prepared by the ion exchange procedure starting with hexaammine nickel nitrate and sihca Aerosil 200 from Degussa. The preparation and characterization of this sample is hilly described in a previous woik [4]. 

TRXF was used to determine the trace elements in samples of lecithin, insulin, procaine, and tryptophan in an attempt to develop elemental fingerprints that could be used to determine the origin of the sample [80]. It was reported that through the use of matrix-independent sample preparation and an internal standard, one could use TXRF to facilitate characterization of the samples without the need for extensive pretreatment. In another work, a study was made of the capability of TXRF for the determination of trace elements in pharmaceutical substances with and without preconcentration [81]. 

Chapter B focuses attention on the preparation and characterization of samples suitable for actinide solid state research. In this context, it is perhaps worthwhile to remark how actinide solid state physics has been, in these years, a subject in which interdisciplinary cooperation has been strongly needed and achieved, perhaps more than in other fields. 

The Th4H15 samples were prepared by Cameron Satterthwaite and coworkers (1,2) and consisted of two polycrystalline samples that were determined to be within 1% of the stoichiometric composition, Tn4Hi5 o.i5 The samples differed primarily in the pressure and temperature used in their synthesis. The sample hydrided under lower pressure ana temperature conditions (1 atm of H2 and a temperature cycle initiating at 800° K and dropping to 450° K before removing the H2) is labeled the LP sample, and the one hydrided under higher pressure and temperature (1100° K ana 10,000 psi of H2) is labeled HP. The sample preparation and characterization of this stoichiometric compound is apparently critical since the results of the present study differ significantly from the previous NMR studies (12,13,14), and some difference was detected between the LP and HP samples themselves. The carbonyl hydride samples were furnished kindly by John R. Shapley (20). 

It is evident from these results that the course of the decomposition is affected by the microstructure of the sample and that reproducible preparation and characterization of nominally identical materials are important prerequisites for understanding and systematizing decomposition kinetics. 

The techniques and difficulties involved in the preparation and characterization of single crystal metal surfaces have been considered here in detail because the evaluation of chemical activity in terms of surface structure, particularly of the crystallographic surface structure, is one of the most promising applications of the vacuum microbalance. The preparation of flat, clean, undistorted single crystal samples suitable for surface studies is a difficult and tedious assignment. 

The writer is greatly indebted to C. S. Smith, C. S. Barrett, and E. A. Gulbransen for many fruitful discussions pertinent to surface studies pursued over an extended period. Much helpful assistance in the preparation and characterization of sample surfaces from the viewpoint of surface structure was provided at one time or another by Joseph Cerny, Walter Bergmann, Donald Clifton, Kaye Ikeuye, and James Hess. Without their assistance the tedious assignment involved in the meticulous preparation of sample surfaces could not have been achieved. The useful collaboration with L. P. Schulz on the characterization of metal surfaces by electron microscopy and electron diffraction techniques was an essential part of the surface studies. Assistance in the design and construction of techniques for the controlled evaporation of metals was provided by H. E. Shaw. 

Impurities. Of course, the presence of impurities in a sample will have a dramatic effect on the XRD characteristics. Zeolite preparations, as synthesized, can contain both organic and inorganic impurities. After washing and calcination, many impurities become amorphous, and the resulting XRD powder pattern will clearly show changes from the as-synthesized material. Some impurities, however, are stable to calcination and can make identification and characterization of the material (especially a new material) rather difficult. This is particularly true for cases where only a small number of samples, prepared in a narrow synthesis regime, are available for XRD examination. Common impurities found in zeolite preparations are the stable silicates, quartz and cristobalite. 

The aim of the present work is to investigate and compare the NO decomposition activities of Fe, Co, Ni " and Cu -containing ZSM-5 zeolites prepared by conventional and solid-state ion-exchange methods. Characterization of the samples by physical and chemical methods comprising acidity measurements is reported. 

The susceptibility of solid surfaces to contamination often results in a requirement for an ultrahigh vacuum (UHV) chamber for preparation and observation of particular samples. For many materials, including metals such as platinum and nickel, adsorption of hydrocarbons and chemisorption of oxygen are quite fast at atmospheric pressure, and the surface must be isolated in UHV to prevent rapid degradation. In addition, a sample in UHV may be subjected to surface analytical techniques such as X-ray photoelectron and Auger spectroscopy to verify or corroborate Raman results. As a result, much of the early and well-characterized surface Raman experiments were carried out in UHV chambers operating below 10 torr (12). 

Preparation and Characterization of Lanthanide and Actinide Solids. Standard crystalline lanthanide and actinide phosphates were prepared by literature procedures (16-18) and characterized by X-ray powder diffraction, FTIR spectroscopy, and thermogravimetric analysis (TGA). Europium was used as an analogue of the trivalent actinides. Metal-phytate solids were generated by mixing Eu(III), U(VI), or Th(IV) nitrate solutions with 0.1 M phytic acid at pH 5 and metal.phytate ratios of 1 1 2 1, and 4 1. The metal phytates precipitated immediately. The resulting slurries were stirred at 85 °C for 30 days and sampled periodically for analysis of the solids by TGA, X-ray powder diffraction, and FTIR. The rate of phosphate release to the solution was monitored colorimetrically. 

The acquisition of solid-state FTIR spectra suitable for use in the characterization of polymorphic impurities is performed using either the Nujol mull technique, diffuse reflectance (DRIFT), or attenuated total reflectance (ATR). One should avoid the use of pelleting techniques to eliminate any spurious effects associated with compaction of the KBr pellet. The simplest approach is to prepare a mull of the sample in mineral oil, sandwich this between salt plates, and measure the spectrum using ordinary transmission techniques. The main drawback of the mull technique is that regions in the IR spectrum overlapping with carbon-hydrogen vibrational modes will be obliterated because of absorbance from the oil. 

Good advice for primary actions is to collect all available data describing the nature of the sample. Information exchange is especially important if synthesis and separation of the products are done by different departments. For this purpose a rough characterization of the sample and the preparative task made by following the questionnaire of Tab. 4.2 eases the planning of experimental procedures. 

The vanadyl pyrophosphate was prepared in an organic medium according to rite modalities already described [2,3,4,8] and in-situ equilibration by running the butane oxidation reaction for about 750 h continuous on-stream rime. Data on the characterization of the sample also have already been reported [2-5,8-l 1]. 

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