Diluted precursor solutions

Tantalum and niobium oxides dissolve very slowly in HF solutions. Thus, it is recommended to use a high concentration of HF or a mixture of HF and H2SO4 at a temperature of about 70-90°C. The best precursors for the preparation of fluoride solutions are hydroxides. Both tantalum hydroxide, Ta205 nH20, and niobium hydroxide, M Os-nHjO, dissolve well, even in diluted HF solutions. 

The electrodeposition of tellurium and silver has been investigated in dilute aqueous solutions of tellurous acid and Ag " ions (concentrations in the order of 10 to 10 " M) in 0.1 M HCIO4 [164], In particular, cyclic voltammetry experiments were conducted with rotating glassy carbon disk electrodes in baths with various concentration ratios of Ag(I) and Te(IV) precursors, and their outcome was discussed in terms of the voltammetric features. For a Ag(I)/Te(IV) ratio close to 0.8, formation of quasi pure silver telluride, Ag2Te, was reported. The authors, based on their measurements and on account of thermodynamic predictions, assumed that silver is deposited first on the electrode (Ag" + e Ag), and then Te(IV) is reduced on the previous silver deposit with formation of Ag2Te according to the reaction... 

The ACTIV-OX chlorine dioxide system evaluated in this trial overcomes many of the problems associated with chlorine dioxide for the small water user. A chlorine dioxide precursor solution and a dilute acid solution are mixed in a 1 1 ratio immediately prior to injection into the water to be treated. The dose rate of chlorine dioxide is controlled by water meter signal to two proportioning pumps. The mixing of the two chemicals immediately produces a chlorine dioxide solution which is diluted to the required strength by injection into the water to be treated (Fig 3). 

Tang et al. used columns packed with a slurry of beads suspended in supercritical C02. This packed column was filled with a dilute sol solution prepared by hydrolysis and polycondensation of tetramethoxysilane and ethyltri-methoxysilane precursors. The column was dried using supercritical C02 and heated first to 120 °C for 5 h followed by another 5 h at a temperature of 250 °C [108-110]. Column efficiencies of 127,000 and 410,000 plates/m were reported... 

In dilute aqueous solution, g(H2) = 0.45 molecule (100 eV) is well established. In more concentrated solutions of certain solutes, G(H2) decreases as the concentration of solute increases, showing that precursors of H2 are being scavenged. The question to be answered is Which are the relevant precursors According to the scheme presented in Section 2, the possibilities are H2O, H , e q, and H. Several studies have been made in attempts to answer this question the main ideas are summarized below. 

Radiolysis of aqueous nitrate solution has been investigated not only from practical viewpoints in nuclear technology, but also from scientific interests in order to understand the radiolysis of water because nitrate ion is an efficient scavenger for hydrated electron [114] and even for the precursor of the hydrated electron [115]. In practical process, the concentration range of nitrate covers from millimolars to 10 M and the radiation effect not only in diluted nitrate solutions but also in concentrated ones should be considered. 

An approach for improved processing of PMR polyimide is the addition of jV-phenylnadimide to the precursor solution of the monomeric reactants. After the in-situ condensation, a PMR-15 resin is obtained which is diluted with JV-phenylnadimide in order to improve the rheological properties of the system (118). The amount of JV-phenylnadimide (PN) added was in the range of 4 to 20 mol %. Just 4 mol % caused a significant and disproportionate reduction of the minimum viscosity with no concomitant loss of thermal stability. 

According to Eq. (8), the pATr value equals the acidity function (Hr) of that solution, in which equal concentrations of carbocation and nonionized alcohol coexist. The acidity function Hr has been derived by Deno, studying equilibria as described by Eq. (7) it approaches pH in dilute aqueous solution. For the reasons discussed above, the application of this method is limited and has been used mostly to characterize aryl-substituted carbocations (Scheme 4) which do not react with their precursor alcohols. 

Ion exchange of Na" or forms of zeolites normally starts with a dilute aqueous solution of ionic precursors. The ions are solvated or coordinated... 

Symmetrical or asymmetrical 1,3,5-triketones (31, R = Me, Et, Prn, or Pr1) can be used as precursors for the synthesis of a wide range of either compartmental acyclic or compartmental macrocyclic SBs by condensation with the appropriate a,cu-alkanediamines.147 Condensation of equimolar ratios of symmetrical 1,3,5-triketones with different diamines (en, pn, 1,4-butanedia-mine) in ethanol afforded [2 + 2] macrocyclic SBs (46). These macrocycles can be hydrolyzed by a dilute aqueous solution of acetic acid which cleaves one of the diamine bridges affording the acyclic SB (47). When excess of acetic acid was employed, cleavage of the two diamine bridges occurred.148... 

The dilution ratio, i.e. the solvenfr(resorcinol+fonnaldehyde) molar ratio, and the resorcinol/formaldehyde molar ratio were fixed at 5.7 and 0.5, respectively. The pH of the precursors solution was adjusted at the chosen value with NaOH the pH range for the gel series was fixed between 4.0 and 6.5. After gelation at 70°C, the samples were dried and pyrolyzed at 800°C imder nitrogen flow for 3 h in order to obtain carbon xerogels. 

Phenolic acids are colorless in a dilute alcohol solution, but they may become yellow due to oxidation. From an organoleptic standpoint, these compounds have no particular flavor or odor. They are, however, precursors of the volatile phenols produced by the action of certain microorganisms (yeasts in the genus Brettanomyces and bacteria) (Section 8.3). Ethyl phenols, with animal odors, and ethyl gaiacols are found in red wines (Figure 6.4). In white wines, vinyl phenols, with an odor reminiscent of gouache paint, are accompanied by vinyl gaiacols. It has been clearly established that these compounds result from the... 

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