Powder Based Methods

Moreira, M.L., Andres, J., Varela, J.A. and Longo, E. (2009) Synthesis of fine microsized BaZr03 powders based on a decaoctahedron shape by the microwave-assisted hydrothermal method. Crystal Growth and Design, 9, 833-839. 

The Microtrac-XlOO (a laser particle size analyzer) was used to determine the size distribution of the powder. The method is based on a liquid mode of operation, that is before laser scanning, the powder is added to a solution of deionized water, containing a surfactant. 

Spray pyrolysis routes have been extensively investigated to prepare Pt-based catalysts. Typically, a liquid feed of metal precursor and carbon is atomized into an aerosol and fed into a continuous furnace to evaporate and heat-treat to form a collectable powder. The method has good control over final aggregate particle size and metal particle size distributions, as well as producing powder without further isolation or separation. Hampton-Smith et al. have reviewed efforts of Superior MicroPowder (now Cabot Fuel Cells) in this area. ... 

At the end of the 1960 s, the Kurtz and Perry powder SHG method was introduced.(8) For the first time, rapid, qualitative screening for second order NLO effects was possible. The stage was set for a rapid introduction of new materials, both inorganic and organic. The early history summarized here is based on a more extensive report presented by Zyss and Chemla (8) in their series "Nonlinear Optical Properties of Organic Molecules and Crystals."... 

Coatings can be prepared by hot flocking, in which the heated part is dipped into a fluidized bed of ETFE powder and then is removed to cool. ETFE coatings can also be applied by other powder coating methods (e.g., electrostatically) or by spraying of water- or solvent-based suspensions followed by drying and baking [27],... 

The x-ray powder diffraction method dates back to Debye and Scherrer who were the first to observe diffraction from LiF powder and succeeded in solving its crystal structure. Later, HulF suggested and Hanawalt, Rinn and FreveP formalized the approach enabling one to identify crystalline substances based on their powder diffraction patterns. Since that time the powder diffraction method has enjoyed enormous respect in both academia and industry as a technique that allows one to readily identify the substance both in a pure form and in a mixture in addition to its ability to provide information about the crystal structure (or the absence of crystallinity) of an unknown powder. 

Lasocha W, Schenk H (1997) A simplified, textirre-based method for intensity determination of overlapping reflectiorts in powder diffraction. J Appl Crystallogr 30 561-564 Lee Y, Cahill C, Hanson J, Parise JB, Carr S, Myrick ML, Preckwinkel UV, Phillips JC (1999) Characterization of K -ion exchange into Na-MAX using time resolved synchrotron X-ray powder diffraction and rietveld refinement. In 12th Int l Zeolite Assoc Meeting, Baltimore, Maryland, IV 2401-2408... 

This chapter focuses on the application of quantitative phase analysis (QPA) techniques for the extraction of phase abundance from diffraction data. Rather than repeat the extensive coverage of the QPA methodology covered in other texts, the focus will be on the basis and application of the most commonly used techniques. These were identified from participant responses to the recent round robin on QPA sponsored by the International Union of Crystallography (lUCr) Commission on Powder Diffraction (CPD). By far the greatest number of participants in that study used whole pattern (Rietveld based) methods but there are still several users of traditional single peak based methods and there are still many applications for which these methods suffice. Issues in the measurement of precision and accuracy will also be discussed. 

Fig. 3 Classification of powder-based forming methods used to make ceramic shapes.

The terms batch equilibration [653], pH drift method [654], addition method [552], solid addition method [655], powder addition method (cited in [656] after [654]), potentiometric titration [234] ( sic —in the present book, the term potentiometric titration is reserved for a different method, described in Section 2.5), and salt addition [573] ( sic —in the present book, the term salt addition is reserved for a different method, described later in this section) refer to the same method, which is now described. A series of solutions of different pHs is prepared and their pHs are recorded. Then, the powder is added and the final pH is recorded. The addition of a solid induces a shift in the pH in the direction of the PZC. The pH at which the addition of powder does not induce a pH shift is taken to be the PZC. Alternatively, the PZC is determined as the plateau in the pHfln, (pH ,.,., .j) curve. The method assumes that the powder is absolutely pure (free of acid, base, or any other surface-active substance), which is seldom the case. Even with very pure powders, the above method is not recommended for materials that have a PZC at a nearly neutral pH. Namely, the method requires accurate values of the initial pH, which is the pH of an unbuffered solution. The display of a pH meter in unbuffered solutions in the nearly neutral pH range is very unstable, and the readings are not particularly reliable. The problem with pH measurements of solutions is less significant at strongly acidic or strongly basic pHs (see Section 1.10.3). The above method (under different names) became quite popular, and the results are referred to as pH in the Method columns in the tables in Chapter 3. The experimental conditions in the above method (solid-to-liquid ratio, time of equilibration, and nature and concentration of electrolyte) can vary, but little attention has been paid to the possible effects of the experimental conditions on the apparent PZC. The plateau in the pH, , (pH, ,, ) curve for apatite shifted by 2 pH units as the solid-to-liquid ratio increased from 1 500 to 1 100 [653]. Thus, the apparent PZC is a function of the solid-to-liquid ratio. 

Extraction of Active Compounds from Food. Vitamins are the group of compounds more usually extracted from foods using SFE (83). A method for the analysis of the natural contents of vitamins A and E in milk powder based on SFE, a miniaturized alkaline saponification procedure, and HPLC was proposed by Turner and Mathiasson (84). Modifications of the sample matrix, the combination of static and dynamic extraction modes, and the effect of changes in extraction parameters such as temperature, flow rate, time, collection solvent, and collection temperature were optimized, obtaining recoveries of 99% and 96% for vitamins A and E, respectively. Another method for the determination of vitamins A and E based on the coupling of SFE-enzymic hydrolysis-HPLC has also been proposed providing recoveries between 79% and 152% (85). 

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