Wet-chemical Method

The Pechini method was originally developed for preparing lead and alkaline-earth titanates and niobates and combinations thereof by way of resin intermediates [34]. On ignition of the resin the organic portion is removed, leaving the selected composition of mixed oxides chemically combined. The oxides are then sintered into dense ceramic bodies. This method is also applicable to solid electrolytes, allowing a very intimate mixture of the starting materials. 

Generally, wet chemical methods require the availability of compounds which are soluble in water or in another solvent The dissolution in a solvent allows intimate mixture on an atomic or molecular scale. However, it has to be ensured that no compound precipitates before the others when the solvent is evaporated, or else insoluble products are formed. The importance of wet chemical methods lies in the possibility of simple upscaling to industrial needs. 

The co-precipitation technique starts with an aqueous solution of nitrates, carbonates, chlorides, oxychlorides, and so on, which is added to a pH ontrolled solution of NH4OH, allowing the hydroxides to precipitate immediately. This method requires water-soluble precursors and insoluble hydroxides as a final product. The hydroxides are filtered and rinsed with water when chlorides are employed as starting materials and chlorine is not desired in the final product. After drying the filtrate, it is calcined and sintered. This method is being applied very successfully for oxygen-ion-conducting zirconia ceramics [35]. 

The precipitation step may be replaced by spray drying of a homogeneously stirred solution of, for example, nitrates [36], or by spraying the precursors into a very hot flame at about 1500-2200 °C. This method is called flame pyrolysis. 

The sol-gel method also benefits from intimate mixture on the molecular level. This process may be divided into two categories  

The Pechini method was originally developed for preparing lead and alkaline-earth 

Method Salts Complexing agent Molecular weight (g mor ) Molecular formula 

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Throughout the history of the development of fats and oils, many wet chemical methods have been developed to assess the quaUty of the raw materials and products. As sophisticated instmmentation develops, many of the wet methods are being replaced. Particular attention is being given to methods that eliminate the use of solvents which cause an environmental disposal problem. Many in-line sensors are also being developed to allow corrections of critical parameters to be made more quickly in the process. 

Chemical products are produced from technical-grade oxide in two very different ways. Molybdenum trioxide can be purified by a sublimation process because molybdenum trioxide has an appreciable vapor pressure above 650°C, a temperature at which most impurities have very low volatiUty. The alternative process uses wet chemical methods in which the molybdenum oxide is dissolved in ammonium hydroxide, leaving the gangue impurities behind. An ammonium molybdate is crystallized from the resulting solution. The ammonium molybdate can be used either directly or thermally decomposed to produce the pure oxide, MoO. ... 

Wet chemical methods determining titratable amine ate reported for products entering urethane (amine number as meq/g) or epoxy (AHEW = amine hydrogen equivalent weight) trade appHcations. For secondary amines /V-nitrosamine contaminants are reportable down to ppb using Thermoelectron Corporation thermal energy analy2er techniques. 

Classical wet chemical methods and instmmental techniques are used for the analysis of soluble sibcates (91). Sibca is deterrnined by gravimetric techniques or by the fluorosibcate volumetric procedure. 

Since 1970, new analytical techniques, eg, ion chromatography, have been developed, and others, eg, atomic absorption and emission, have been improved (1—5). Detection limits for many chemicals have been dramatically lowered. Many wet chemical methods have been automated and are controlled by microprocessors which allow greater data output in a shorter time. Perhaps the best known continuous-flow analy2er for water analysis is the Autoanaly2er system manufactured by Technicon Instmments Corp. (Tarrytown, N.Y.) (6). Isolation of samples is maintained by pumping air bubbles into the flow line. Recently, flow-injection analysis has also become popular, and a theoretical comparison of it with the segmented flow analy2er has been made (7—9). 

Finished zinc and zinc aHoys are usuaHy analyzed for metals other than zinc by emission spectroscopy and the zinc determined by difference. ASTM method E 27 describes a technique using a dissolved sample and photographic detection. The internal standard is the zinc line at 267.0 nm. However, procedures using soHd samples are generaHy preferred and photoelectric detection often replaces optical detection. Samples are cast and machined on the surface where the arc is stmck. Up to 15 elements can be determined in a few minutes by modem automatic spectrometers. ASTM gives wet chemical methods for metals other than zinc (79). 

Analytical results of distilled spidts are expressed either by chemical class or by individual constituent. When these results are expressed by chemical class, the most prevalent constituent within that class is used as the marker, eg, acetic acid for acids, acetaldehyde for aldehydes, and ethyl acetate for esters. Wet chemical methods are employed in the deterrnination of results by chemical class, while more advanced and refined techniques are employed in the deterrnination of individual chemical constituents. 

There are other methods of preparation that iavolve estabhshing an active phase on a support phase, such as ion exchange, chemical reactions, vapor deposition, and diffusion coating (26). For example, of the two primary types of propylene polymerization catalysts containing titanium supported on a magnesium haUde, one is manufactured usiag wet-chemical methods (27) and the other is manufactured by ball milling the components (28). 

Composition. The results of elemental analyses are almost always included among the specifications for a commercial catalyst. Depending on the accuracy desired and whether or not the catalyst can be rendered soluble without great difficulty, elemental analysis may be performed by x-ray methods, by one of the procedures based on atomic absorption, or by traditional wet-chemical methods. Erequentiy it is important to determine and report trace element components that may have an effect on catalyst performance. 

Analytical methods for qualitative and quantitative determination of all kinds of surfactants have long been established. There can be found either wet chemical methods—like titration—or methods of instrumental analytics. A classical method for anionic surfactants is the so-called two-phase-titration [63]. Using this method nearly every molecule bearing an anionic group is detected. The correct determination of sulfosuccinates is limited to the interferences of the other ingredients and byproducts present. With few exceptions all sulfosuccinates react with special indicators, e.g., hyamin 1622 (Rohm and Haas), to form an anionic-cationic complex and hence are to be analyzed by active content titration. 

As a matter of fact, semiconductor/liquid junctions provide the most efficient wet chemical method presently known for converting sunlight into electrical or... 

A number of techniques have been employed that are capable of giving information about amorphous phases. These include infrared spectroscopy, especially the use of the attenuated total reflection (ATR) or Fourier transform (FT) techniques. They also include electron probe microanalysis, scanning electron microscopy, and nuclear magnetic resonance (NMR) spectroscopy. Nor are wet chemical methods to be neglected for they, too, form part of the armoury of methods that have been used to elucidate the chemistry and microstructure of these materials. 

Competitive reduction of Au(III) and Ag(I) ions occurs simultaneously in solution during exposure to neem leaf extract leads to the preparation of bimetallic Au-core/Ag-shell nanoparticles in solution. TEM revealed that the silver nanoparticles are adsorbed onto the gold nanoparticles, forming a core/sheU structure. Panigrahi et al. [121] reported that sugar-assisted stable Au-core/Ag-shell nanoparticles with particles size of ca. 10 nm were prepared by a wet chemical method. Fructose was found to be the best suited sugar for the preparation of smallest particles. 

Wet chemical method (manual calibration, data collection, calculations)... 

Electroanalysis as a representative of the wet-chemical methods has many attractive advantages, such as... 

Great progress has been demonstrated in the last 20 years in the development of wet chemical methods for the fabrication of inorganic films for electronic applications. A variety of solution chemistries and film fabrication strategies have been developed that may be used to fabricate thin films with excellent... 

The fat content of products and ingredients can be measured by either wet chemical methods or instrumental methods. The normal wet chemical method is the use of a Soxhlet extractor and petrol. 

Fig. 6.4. Effects of the pore size of filter paper used during fluid sampling on the analytical concentrations reported for aluminum and iron (Kennedy el al., 1974). Samples were acidified, stored for 19 ( ) or 94 ( ) days, and analyzed by standard wet chemical methods. Dotted lines show dissolved concentrations determined by a solvent extraction technique.

It is common to find analytical methods classified as classical or instrumental, the former comprising wet chemical methods such as gravimetry and titrimetry. Such a classification is historically derived and... 

Table 8.9 shows an analysis of a silicate rock and compares the precision of X-ray fluorescence analysis with wet chemical methods and arc/spark emission spectrometry. 

Instrumental analysis can also involve chemical reactions, but it always involves modern sophisticated electronic instrumentation. Instrumental analysis techniques are high-tech techniques, often utilizing the ultimate in complex hardware and software. While sometimes not as precise as a carefully executed wet chemical method, instrumental analysis methods are fast and can offer a much greater scope and practicality to the analysis. In addition, instrumental methods are generally used to determine the minor constituents or constituents that are present in low levels, rather than the major constituents of a sample. We discuss wet chemical methods in Chapters 3 and 5. Chapter 15 is concerned with physical properties Chapters 7 to 14 involve specific instrumental methods. 

With the wet chemical methods and methods involving physical properties now behind us, we begin a thorough discussion of the methods, data handling, and calculation and reporting of results relating to instrumental analysis. 

Distinguish between wet methods of analysis and instrumental methods of analysis. What do the analytical strategies for the wet chemical methods and instrumental methods have in common ... 

Gravimetric analysis is a wet chemical method of analysis in which the measurement of weight is the primary measurement, and most of the time the only measurement, that is made on the analyte and its matrices. 

Phosphorus is a common component of additives and appears most commonly as a zinc dialkyl dithiophosphate or triaryl phosphate ester, but other forms also occur. Two wet chemical methods are available, one of which (ASTM D1091) describes an oxidation procedure that converts phosphorus to aqueous orthophosphate anion. This is then determined by mass as magnesium pyrophosphate or photochemically as molybdivanadophosphoric acid. In an alternative test (ASTM D4047), samples are oxidized to phosphate with zinc oxide, dissolved in acid, precipitated as quinoline phosphomolybdate, treated with excess standard alkali, and back-titrated with standard acid. Both of these methods are used primarily for referee samples. Phosphorus is most commonly determined using x-ray fluorescence (ASTM D4927) or ICP (ASTM D4951). 

Control analyses rely on the use of appropriate procedures or measurements assuring the identity of the materials involved in each step of the manufacturing process from receipt of raw materials to delivery of the finished products. NIR spectroscopy is an advantageous alternative to wet chemical methods and instrumental techniques such as IR, Raman and nuclear magnetic resonance (NMR) spectroscopies for positive identification. 

For the decomposition of organic materials, wet chemical methods are most frequently used. The wide acceptance of these methods is due to the multitude of decomposition reagents available, simple handling procedures and high sample throughput. The error sources listed above can largely be eliminated if wet chemical methods are properly handled. 

During all membrane exposures, concentrations of halogens and chlorine dioxide were periodically monitored by "wet chemical methods". Halogens were determined by the DPD colorimetric method described in references [13] and [14]. Chlorine dioxide at reasonably high concentrations (>10 ppm) can be determined by direct colorimetry [] ]. The intrinsic green color appears to obey Beer s law. At lower concentration levels, this chemical is determined by the DPD method. 

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