Other Wet Methods

Various parameters can influence the quality of the films. Among them, the co-solvent, the temperature, and the precursor solution are the main parameters that can have important effects on the film characteristics. 

The resulting vapor diffuses to the substrate surface according to a CVD process. 

At the highest temperature of the process (case D), the droplet vaporizes before it can reach the surface. It is considered that solid particles are formed during a chemical reaction in this vapor phase. It is known that the films formed under the conditions of cases A and D are poorly or completely non-adherent. Adherent films are obtained when the process temperature used corresponds to case C. However, this case can rarely occur because, in general, the deposition temperature is too low to allow the vaporization of the droplet, which just decomposes without melting and vaporizing. In practice, processes corresponding to case B can allow the formation of high-quaUty films. 

The CVD method involves a chemical reaction in a vapor phase which results in deposition of a solid on a heated surface. Various PVD processes such as ion plating, sputtering, molecular beam, evaporation, and epitaxy might be also included in CVD processes [112]. The various CVD methods are powerful processes used for the fabrications of a wide variety of thin-film materials including solar cell materials and semiconductor materials for electronic applications, as well as the manufacture of coatings, powders, fibers, and monolithic components. There are two types of CVD reactors, the differential reactor and the starved reactor, according to the value of the flow rate (F,) defined as 

we have a differential reactor which is characterized by a constant composition through the reactor. This type of reactor seems to be more useful for research activities. 

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Elemental composition Pd 86.93%. O 13.07%. The oxide may be identified by x-ray diffraction. The oxide readily can be reduced with hydrogen and the water formed can be measured by gravitmetry or other wet methods. Also, palladium metal obtained from reduction of the oxide may be digested in aqua... 

In current industrial practice gas chromatographic analysis (glc) is used for quahty control. The impurities, mainly a small amount of water (by Kad-Fischer) and some organic trace constituents (by glc), are deterrnined quantitatively, and the balance to 100% is taken as the acetone content. Compliance to specified ranges of individual impurities can also be assured by this analysis. The gas chromatographic method is accurately correlated to any other tests specified for the assay of acetone in the product. Contract specification tests are performed on product to be shipped. Typical wet methods for the deterrnination of acetone are acidimetry (49), titration of the Hberated hydrochloric acid after treating the acetone with hydroxylamine hydrochloride and iodimetry (50), titrating the excess of iodine after treating the acetone with iodine and base (iodoform reaction). 

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

In the wet method, as practiced in Colombia, freshly picked ripe coffee cherries are fed into a tank for initial washing. Stones and other foreign material are removed. The cherries are then transferred to depulping machines which remove the outer skin and most of the pulp. However, some pulp mucilage clings to the parchment shells that encase the coffee beans. Fermentation tanks, usually containing water, remove the last portions of the pulp. Fermentation may last from twelve hours to several days. Because prolonged fermentation may cause development of undesirable flavors and odors in the beans, some operators use enzymes to accelerate the process. 

Figure 10-1 illustrates two statements that experience has shown to be generally valid for analytical results obtained by wet methods (1) The true value a and the mean x are different quantities, and one cannot be predicted from the other. (2) No conclusions about the frequency distribution can be drawn from a or from x. One more generalization applies to comparative x-ray methods, be they absorption (3.10) or emission (7.8) methods If the comparison is properly carried out, questions of accuracy will never arise properly includes the use of a... 

Sophisticated instrumental techniques are continually being developed and gradually replace the classical wet chemistry analytical methods. Wet chemical analysis is destructive the sample is dissolved or altered. Nowadays the analyst is highly focused on instrumental methods and chemometrics. Yet, chemical work-up methods (e.g. hydrolysis with alcoholic alkali, alkali fusion, aminolysis, and transesterification, etc.) and other wet laboratory skills should not be forgotten. 

One problem with methods that produce polycrystalline or nanocrystalline material is that it is not feasible to characterize electrically dopants in such materials by the traditional four-point-probe contacts needed for Hall measurements. Other characterization methods such as optical absorption, photoluminescence (PL), Raman, X-ray and electron diffraction, X-ray rocking-curve widths to assess crystalline quality, secondary ion mass spectrometry (SIMS), scanning or transmission electron microscopy (SEM and TEM), cathodolumi-nescence (CL), and wet-chemical etching provide valuable information, but do not directly yield carrier concentrations. 

All wet strength agents are bi- or multi-functional molecules with the capability to cross-link with each other or with cellulose. The choice of chemistry depends to a large extent on pH. In acid systems, the main wet strength agents are urea-formaldehyde (U/F) and melamine-formaldehyde (M/F) resins, whereas in neutral and alkaline systems polyamine-polyamide-epichlorohydrin resins are more effective. However, these are not the only systems in use, and a summary of these and other available methods is provided in Figure 7.22. 

Organic carbon can be determined in calcareous soils after the carbonates have been removed by treatment with sulphuric acid-iron(II) sulphate solution and the samples oven-dried at 105°C. However, as in all other wet-combustion methods, chloride ions interfere [7]. Interference from small amounts of chloride ions (up to 4mg of Ch as KC1 or NaCl) was reduced by adding 2.5% of mercury II oxide or silver I sulphate to the acid digestion mixture. 

Elemental composition Ba 46.22%, Br 53.78%. Barium maybe determined by various instrumental or wet methods (see Barium). Bromide may be analyzed by ion chromatography or titrimetry. Presence of other halide ions can interfere in titrimetry tests. 

The other prevalent method of oxidizing silicon uses wet chemical treatment, often in a sequence of steps called the RCA process [59]. In this process, silicon is both cleaned and oxidized by a process involving treatment with an alkaline mixture of ammonium hydroxide and hydrogen peroxide (called standard clean 1, or SCI), followed by treatment with an acidic HC1 and hydrogen peroxide mixture (SC2). The process leads to what is called a chemical oxide. This, like the thermal oxide, is Si02, but the wet oxidation process typically leads to a more hydroxylated Si02 surface. 

This metallurgical method, to which the name of assaying is strictly confined, when not otherwise expressed, is that uniformly practised, at the Mint, and other regular assaying establishments, being not only more expeditious than the wet method, but admitting... 

ISO 1431-3 specifies that the calibration of the ozone meter is carried out in accordance with ISO 1396443 which is the general standard for determination of ozone concentration by UV photometry. The operation of UV meters is also to be in accordance with ISO 13964. The other allowed methods are electrochemical, chemiluminescence and wet chemical. Other instrumental methods are operated in accordance with the manufacturer s instructions (having been calibrated to ISO 13964) whilst the wet chemical methods are given in detail in an appendix. Although not referenced, there is also a general method using chemiluminescence44. 

Many water soluble analytes can be sampled by bubbling the air through water in an impinger. Acid vapors, alkali vapors, or their dusts can be collected in water and their aqueous solutions analyzed by wet methods. Often, water is made basic or acidic to trap acidic or basic analytes, respectively. Other solvents can be used in the impinger, depending on the solubility of the analytes and the vapor pressure of the solvents. Certain organics in the air can also be trapped in impingers if one uses the proper solvents. 

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