Powder addition method

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. 

Due to the important relationship between particle size of starting powders and resulting electrode microstructure and corresponding performance, much work has been performed to modify the particle size and morphology of the starting powders used in SOFC processing. Additional methods have been investigated to better control the microstructure and properties of fuel cell components, which are discussed in more detail in Section 6.2. 

Powder metallurgical methods These include reaction of the elements and car-bothermal reduction methods. Fine powders of the metal (Hf, V, Nb, Mo, W, etc.) and carbon (graphite, lampblack) may be mixed, possibly in wet conditions with an organic solvent to be removed later, then pressed and compacted into pellets or bricks to be heated at high temperature (1800-2000°C). To perform the carbother-mal reduction, mixtures of carbon with an oxide (of Ti, V, Cr, etc.) are compacted and heated. An additional heat treatment in a high vacuum may be useful to remove O, N, etc. below a low level. 

The crystal chemistry of BajRC C has been systematically studied by single-crystal and powder diffraction methods with R = La, Pr,... Yb, in addition to the conventional yttrium compound [(52)(53) (54) and references therein]. With the exception of La, Pr, and Tb, the substitution of Y with rare-earth metals has little or no effect on the superconductivity, with the values of Tc ranging from 87 to 95K. Also, a relatively small change is observed in the cell constants of these compounds. The La, Pr, and Tb-substituted materials are not superconductors. A detailed structural analysis of the Pr case (52) did not show any evidence of a superstructure or the presence of other differences with the atomic configuration of the yttrium prototype. 

In the context of the voltammetry of microparticles methodology, the H-point standard addition method has been adapted for determining organic dyes [241] as well as lead and tin in ceramics [242]. Let us consider a mixture of material containing unknown amounts of two electroactive compounds, A and B, and a reference compound, R. It is assumed that weighted amounts of both materials are accurately powdered and thoroughly mixed so that the mass ratio between the A,B-containing material and the reference compound, m/mR, is known. 

Laffon, C., Flank, A.M. and Lagarde, P., et al., Study of Nicalon-based ceramic fibres and powders by EXAFS spectrometry, X-ray diffractometry and some additional methods , J. Mat. Sci, 24, 1503 (1989). 

An innovative method of producing macaroni is outlined, which involves the addition of an enriching additive mixture that includes Jerusalem artichoke powder. The method allows inulin-, vitamin-, and iodine-enriched macaroni products with increased biological value to be produced. 

The direct determination of trace elements (Al, Ba, Cu, I, Mn, Mo, Pb, Rb, Se, Sr, and Zn) by ICP-MS in powdered milk was reported [14]. Samples were diluted with a 5 or 10 percent (v/v) water-soluble, mixed tertiary amine reagent at pH 8. This reagent mixture dissociated casein micelles and stabilized liquid phase cations. Mass intensity losses were not observed. The quantitative ICP-MS procedure was applied the standard additions method with a Y internal reference. This direct technique is as fast as the slurry approach without particle size effects or sensitivity losses. 

In addition to identifying and characterizing known crystalline phases, single crystal, and more recently, powder diffraction methods can be used to determine the atomic positions within the crystal structures of new and uncharacterized materials. An excellent demonstration of how XRD structure determination methods can be applied in concert with other characterization techniques for... 

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. 

Figure 4.1. The flowchart illustrating common steps employed in a structural characterization of materials by using the powder diffraction method. It always begins with the sample preparation as a starting point, followed by a properly executed experiment both are considered in Chapter 3. Preliminary data processing and profile fitting are discussed in this chapter in addition to common issues related to phase identification and analysis. Unit cell determination, crystal structure solution and refinement are the subjects of Chapters 5,6, and 7, respectively. The flowchart shows the most typical applications for the three types of experiments, although any or all of the data processing steps may be applied to fast, overnight and weekend experiments when justified by their quality and characterization goals.

In addition to reciprocal and direct space techniques considered in the previous sections, a large variety of approaches may be employed to create a model of the crystal structure in direct space. One of these, i.e. the geometrical method, has been implicitly employed in section 6.9, where the location of a single La atom in the unit cell was established from a simple analysis of the unit cell dimensions and from the availability of low multiplicity sites in the space group symmetry P6/mmm. Here we consider a more complex example, i.e. the solution of several crystal structures occurring in the series of Gd5(SixGei x)4 alloys. These examples illustrate the power of the powder diffraction method in detecting subtle details of the... 

Tablets have been the most common matrix for the SFE of active components. Pure supercritical CO2 has been used in the extraction of megestrol acetate (145), caffeine and vanillin (146), and ibuprofen (147). In the first case, a comparison between two SFE systems was done and various support materials were assessed for their suitability as adsorbents. Methanol was used as the modifier for the extraction of benzodiazepines from tablets or capsules (148) in a static and dynamic mode for 5 and 10 min, respectively, at 65°C and 101 bar. The eluate was analyzed using GC-MS. Psoralen and isopsoralen have been extracted from Baishi pills and Baidianfeng capsules-belonging, to traditional Chinese medicines—using supercritical CO2 modified with tricloromethane (149). The determination of the analytes was performed by GC. By the standard additions method, recoveries were 97.8 101.2% with RSDs (three replicates) less than 2.01%. In the same way, SFE has been applied to the isolation of pentosalen (also known as imperatorin) from Cnidium monnieri cusson powder (a traditional Chinese medicine) (150). This experiment was carried out with a homemade SFE system with the use of replicates) were 3.9% and 1.7%. The SFE method was more efficient than the...

Sodium Azide Pathway The free carboxyl group-containing compound was dissolved in thionyl-chloride and refluxed for 10 hours, followed by vacuum evaporation. To a solution of acyl chloride in 1,2-dimethoxyethane was added, under stirring, an excess of freshly activated sodium azide in solid form ("dry method"), or in aqueous solution ("wet method"). In the dry method, the mixture was refluxed overnight, filtered, and evaporated to dryness. In the wet method, the mixture was stirred for 20 minutes and precipitated by the addition of water (10 times its original volume). The precipitate was filtered, washed, and freeze-dried. The organic azide was either heated for 1 hour to 100-120°C (oil bath) as a dry powder ("dry method"), or refluxed for 1 hour in dioxane- or DMF-solution ("solution method"), which was followed by vacuum evaporation. 

Nazeri-Eshghi et al. [32] were the first to report sol-gel processing of KNbOa ceramic powders. Their method was later adopted for the deposition of epitaxial thin films by Cheng et al. [38] The precursors used were KOC2H5 and Nb(OC2H5)5. The preparation procedure is fairly simple. Potassium metal is allowed to react with anhydrous ethanol, and the solution is then mixed with Nb(OC2H5)5. The solutions are usually stable for a few weeks. It was found that the addition of small amount of 2-ethylhexanoic acid helps to modify the... 

You have to determine (a) formaldehyde and acetaldehyde in 50 samples of white wine per day (b) 2,4,6-trinitrotoluene in white powder samples which might be potential material in making bombs—3 to 5 samples per month (c) copper content in a rare Etruscan vase (d) a toxic keto compound in an antibiotic, the analysis being done in a production-line quality-control laboratory in a pharmaceutical company. In which cases and why would you use a standard-addition method and when would you use a calibration curve for evaluating current-versus-voltage curves ... 

The quadratic NLO active molecules are mostly based on donor-acceptor substituted aromatics benzene, stil-benes, diaryl acetylenes, diacetylenes, and biaryls are commonly used frameworks. In addition to the above materials, many more organic and organometallic compounds were examined by the powder SHG method, or their molecular hyperpolarizabilities were measured using EFISHG/HRS techniques, or both.t >... 

PZT ceramics can be made by normal powder processing methods. The main difficulty is the high volatility of PbO. To retain as much PbO as possible sintering may be performed with the component surrounded by a lead-rich powder such as PZ and enclosed in a lidded crucible. Even with these precautions there is usually some (typically 2-3%) loss of PbO, which is compensated for by adding additional PbO to the starting batch. A note about safety lead is toxic and exposure to lead compounds has a cumulative effect. It is therefore necessary that evaporation is controlled. 

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