Alkalinity alkaline systems

Values of E° are obtained by extrapolation from measurements in weakly acid or weakly alkaline systems. 

Three types of electrochemical water-spHtting processes have been employed (/) an aqueous alkaline system (2) a soHd polymer electrolyte (SPE) and (J) high (700—1000°C) temperature steam electrolysis. The first two systems are used commercially the last is under development. 

Papermaking Use. PAG is widely used in Europe in papermaking processes. The gradual changeover from acid to alkaline systems in U.S. paper mills is expected to be accompanied by an increase in the use of PAG as an alum replacement (35). 

The aromatic nature of lignin contrasts with the aliphatic stmcture of the carbohydrates and permits the selective use of electrophilic substitution reactions, eg, chlorination, sulfonation, or nitration. A portion of the phenoUc hydroxyl units, which are estimated to comprise 30 wt % of softwood lignin, are unsubstituted. In alkaline systems the ionized hydroxyl group is highly susceptible to oxidative reactions. 

Care is required ia miming these reactions because the decomposition of the intermediate sulfoxide and of dimsyl sodium during the heating in the strongly alkaline system is exothermic and also produces a precipitate which can interfere with heat removal. Explosions have occurred (51). 

The button cells that provide the energy for watches, electronic calculators, hearing aids, and pacemakers are commonly alkaline systems of the silver oxide-zinc or mercuric oxide-zinc variety. These alkaline systems provide a vei y high energy density, approximately four times greater than that of the alkaline zinc-manganese dioxide battery. 

Chitosan has been recently found to be soluble in alkaline media, viz. NH4HCO3 solutions, where it assumes the ammonium carbamate form Chit-NHC02 NH4, i.e., a transient anionic form that keeps it soluble at pH 9.6, while reversibly masking the polycationic nature of chitosan. Because ammonium carbamates and NH4HCO3 decompose thermally and liberate CO2, NH3 and water, this alkaline system is suitable for producing chitosan microspheres by spray-drying (Table 1) [206]. 

Inorganic reactions in the soil interstitial waters also influence dissolved P concentrations. These reactions include the dissolution or precipitation of P-containing minerals or the adsorption and desorption of P onto and from mineral surfaces. As discussed above, the inorganic reactivity of phosphate is strongly dependent on pH. In alkaline systems, apatite solubility should limit groundwater phosphate whereas in acidic soils, aluminum phosphates should dominate. Adsorption of phosphate onto mineral surfaces, such as iron or aluminum oxyhydroxides and clays, is favored by low solution pH and may influence soil interstitial water concentrations. Phosphorus will be exchanged between organic materials, soil inter-... 

C. I. Chiwetelu, V. Homof, G. H. Neale, and A. E. George. Use of mixed surfactants to improve the transient interfacial tension behaviour of heavy oil/alkaline systems. Can J Chem Eng, 72(3) 534-540, June 1994. 

It is well know that the zeolite materials synthesized in alkaline systems usually have a high number of silanol groups (=SiOH) named defect groups [10] which possess a moderated Bronsted acidity [11]. Oppositely, Silicalite-1 synthesized in fluorine media are relatively defect-free [12] and the fluorine ions remain in the small cages of the MFI structure even after the calcination process [12]. The 29Si-NMR analyses carried out on samples Na-Silicalite-1 and F-Silicalite-1 confirm the presence of silanol groups only on the SI support surface (results not showed). Delaminated zeolites (ITQ-6) are obtained by exfoliation of as-synthesized lamellar precursor zeolites [13]. After this process, the final structure of the delaminated zeolite results in a completely hydroxylated and well-ordered external surface [13]. 

Retention and drainage aids are chemicals which are added to the fibre and filler suspension to assist the efficiency of the filtration process. Growth in recent years in the use of retention aids has been greater than that of almost any other paper chemical additive. It has been caused by a combination of factors increased machine speeds, the increased use of filler in alkaline systems, the increased use of recycled paper and the growing tendency to use fillers in newsprint. Retention aids are water-soluble polymers which may be cationic,... 

Internal sizing may be carried out over a wide pH range, but it is popular now to use neutral or slightly alkaline systems. When successfully performed, it retards the rate of penetration of a fluid through capillaries formed both within and between fibres. The fluid involved is, for most commercial grades of paper, water but resistance to non-aqueous fluids may also be important in some applications. This discussion will concern itself only with sizing against aqueous systems. 

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. 

Dr. William W. Jacques further explored the carbon approach in 1896. His fuel cells had a carbon rod central anode in the electrolyte of molten potassium hydroxide. He made a fuel cell system of 100 cylindrical cells, which produced as much as 1500 W. Francis T. Bacon worked on fuel cells to produce alkaline systems that did not use noble metal catalysts in the 1930s. He developed and built a 6 kW alkaline hydrogen-oxygen system in 1959. In the same year, Dr. Harry Ihrig introduced... 

Available information on DEHPA indicates an effect of salt concentration similar to that shown for the carboxylic acids [17]. Figure 7.11 indicates a significant difference between sodium and ammonium salts and solutions containing sodium and ammonium hydroxides. Moreover, below about 5 wt% salt concentration, the solubility becomes uneconomic. However, all the data given in Fig. 7.11 are for alkaline systems. For acid systems... 

Magnetite is obtained in aqueous, alkaline systems by precipitation from a mixed Fe /Fe solution, by oxidation of Fe solution via green rust or Fe(OH)2, or by interaction of Fe with ferrihydrite. Another pathway involves high temperature reduction of Fe oxides (e. g. with H2). Maghemite forms topotactically by wet or dry oxidation of magnetite or by heating lepidocrocite and by thermal decomposition of various organic Fe-salts (cf chap. 20). 

There are probably several mineral phases, particularly for the highly alkaline systems, that remain to be discovered. Mixed hydroxides may control solubility. Calcium zincate (CaZn2(OH)6), for example, is thermodynamically more stable than Zn(OH)2 above pH 11.5 and may be important in cementitious systems. Another group of minerals is that of the hydrotalcite-like minerals, the layered double hydroxides (LDH, M2+2M3+l/yXy (OH)6 where X is an anion). Cobalt, Ni and Zn can form such minerals (Johnson Glasser 2003) under neutral to alkaline conditions. For the majority of species, however, solubility-limiting phases do not appear to control dissolved concentrations. 

In cooling water applications, great importance is placed on activity against Legionella pneumophila, the causative agent of Legionnaires disease. Bromochloro dimethylhydantoin has been shown to rapidly hydrolyze in water with the formation of hypobromous acid (21). The pKa of hypobromous acid is 8.8, whereas the pK of hypochlorous acid is 7.4. Because the undissociated hypohalous acid is the active biocide, the hypobromous-generating chemical is more active in alkaline systems. 

Table VI. Effect of Chromate on the Yields in Acidic and Alkaline-Systems at 77° K.

The Electron Excess Center. In their earlier paper Schulte-Frohlinde and Eiben (57) had assigned the line A to the O ion and the other line to the stabilized electron subsequently they have reversed this assignment, and are therefore in agreement with other authors. However, the line with g = 2.0006 has been interpreted in different ways, although all interpretations relate it to the radiation-produced electron. Thus Schulte-Frohlinde and Eiben (57, 58) consider the species responsible for this line to be a stabilized free electron, while Ershov et al. (16) and Henriksen (23) identify it with a solvated electron or a po-laron in the same sense as these two terms are used in the radiation chemistry of water and aqueous solutions. According to the above authors, this species is not found in pure ice because of Reaction 30, whereas in alkaline systems such a reaction should not occur. (Henriksen does not offer any explanation about the specific role of alkali hydroxide in stabilizing the solvated electron. ) Both of these hypotheses can be shown to be incorrect. Thus, if Reaction 30 occurred to any extent in pure ice, one should be able to detect H atoms in neutral ice with a yield of at least as high as the maximum yield of the solvated electrons, viz.. 

The initial composition for a hypothetical Europan alkaline system is taken from Alkali Valley, Oregon (Marion 2001) and represents the type of... 

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