Mobility of hydroxyl

The first investigations of the mobility of hydroxyl protons in H-zeolites were carried out in the mid-1970s by static NMR spectroscopy [268]. In recent papers it is shown that MAS NMR spectroscopy at elevated temperatures also allows the investigation of the proton mobility [6,269,270]. 

Relaxation phenomena (TSDC), molecular mobility (NMR, TPDMS), and chemical reactions (TPDMS of associative desorption of water) are observed for adsorbed water/LiChrolut EN adsorbent over a wide temperature range. These phenomena are characterized by very different activation energies from 10 kJ/mol (rotational mobility of hydroxyls in WAW molecules), 20-40 kJ/mol (rotational mobility of the molecules in SAW), 40-80 kJ/mol (rotational and translational mobility of the water molecules in pores of different sizes), and 60-200 kJ/mol (molecular and associative desorption of water) (Figure 5.34). As a whole, all the distribution functions of activation energy fiJS) obtained using different methods are well concordant. This is caused by the nature of activated processes whereas all the processes are caused by the molecular mobility of water dependent on the topological and chemical characteristics of confined space in nano- and mesopores in LiChrolut EN adsorbent. 

When choosing (54) a filling solution for an RE, several factors must be considered. The filling solution should not react with any species in the electrochemical cell, or interfere with the measurement in any way. While difficult to do in highly acidic or basic solution due to the high mobilities of hydroxyl and hydronium ions, it is best to match the... 

Further, the mobility of hydroxyl ions reduces significantly with the increase in KOH electrolyte. The cyclic voltammogram results pointed out the formation of PtO layer at high KOH concentration. The formation of PtO layer deactivates the catalyst. The maximum power densities of 15, 10.5 and 22.5 mW cm" were obtained for methanol, ethanol and sodium borohydride, respectively, with 3 M KOH concentration at 25°C. The catalyst loadings used at anode and cathode were 1 mg cm (Pt-black) and 3 mg cm" (Mn02), respectively. 

Electrical Conduction by Proton Jumps. As mentioned in Sec. 24, a hydroxyl ion may be regarded as a doubly charged oxygen ion 0 , containing a proton inside the electronic cloud of the ion, which has the same number of electrons as a fluoride ion. The radius of the hydroxyl ion cannot be very different from that of the fluoride ion. But it will be seen from Table 2 that the mobility of the hydroxyl ion is about four times as great. This arises from the fact that a large part of the mobility is undoubtedly due to proton transfers.1 Consider a water molecule in contact with a hydroxyl ion. If a proton jumps from the molecule to the ion,... 

The rotational mobility of adsorbed molecules is caused by its rotational degree of freedom (resulting from the fact that the molecule is tightly bound to the substrate through the only atom) and by the coupling of molecular vibrations with surface atomic vibrations. The rotational motion intensity is strongly temperature-dependent and affects spectroscopic characteristics. As a result, the rotational mobility of surface hydroxyl groups was reliably detected.200 203... 

Endrin ketone may react with photochemically generated hydroxyl radicals in the atmosphere, with an estimated half-life of 1.5 days (SRC 1995a). Available estimated physical/chemical properties of endrin ketone indicate that this compound will not volatilize from water however, significant bioconcentration in aquatic organisms may occur. In soils and sediments, endrin ketone is predicted to be virtually immobile however, detection of endrin ketone in groundwater and leachate samples at some hazardous waste sites suggests limited mobility of endrin ketone in certain soils (HazDat 1996). No other information could be found in the available literature on the environmental fate of endrin ketone in water, sediment, or soil. 

Hydroxylic solvents are capable of solvating anions through hydrogen bonding, and so halide mobilities are relatively low in alcohols, with chloride the least mobile. The mobility decreases observed for all the halides upon going up the homologous series of aliphatic alcohols may be the result of the increased size and mass of the alkyl group. A similar mass effect may be seen in the lowered mobility of the halides in dimethylacetamide compared to dimethylformamide. Here, as in the alcohol series, dipole moments and viscosities of the two solvents do not appear to be sufficiently different to explain the mobility differences. 

The epoxy matrix, containing multiple hydroxyl and amino groups, has a high tendency to adsorb water, a major cause of material failure in many applications. Finally, when one uses the epoxy as a fiber matrix, there is a distinct probability that voids will appear due to reaction by-products which do not escape during cure. Once the material vitrifies, the mobility of the molecules is reduced, making it difficult for the small molecular weight products to be eliminated. 

The principal abiotic processes that may transform thorium compounds in water are complexation by anions/organic ligands and hydroxylation. The increase in the mobility of thorium through the formation of soluble complexes with CQs, humic materials, and other anions or ligands and the decrease in the mobility due to formation of Th(OH)4 or anionic thorium-hydroxide complexes were discussed in Section 5.3.1.2. In a model experiment with seawater at pH 8.2 and freshwater at pH 6 and pH 9, it was estimated that almost 100% of the thorium resides as hydroxo complexes (Boniforti 1987). 

For large values of the difference between the mobility of the cation and that of the anion, the diffusion potential Fg will by no means be negligible. Both hydrogen and hydroxyl ions possess exceptionally large mobilities in aqueous solution and thus diffusion potentials between solutions of different concentrations of both acids and alkalis may assume large values as indicated by the following data for the values of Fg between solutions of electrolytes of concentration ratios 10 1. 

Little is known concerning the chemistry of nickel in the atmosphere. The probable species present in the atmosphere include soil minerals, nickel oxide, and nickel sulfate (Schmidt and Andren 1980). In aerobic waters at environmental pHs, the predominant form of nickel is the hexahydrate Ni(H20)g ion (Richter and Theis 1980). Complexes with naturally occurring anions, such as OH, SO/, and Cf, are formed to a small degree. Complexes with hydroxyl radicals are more stable than those with sulfate, which in turn are more stable than those with chloride. Ni(OH)2° becomes the dominant species above pH 9.5. In anaerobic systems, nickel sulfide forms if sulfur is present, and this limits the solubility of nickel. In soil, the most important sinks for nickel, other than soil minerals, are amorphous oxides of iron and manganese. The mobility of nickel in soil is site specific pH is the primary factor affecting leachability. Mobility increases at low pH. At one well-studied site, the sulfate concentration and the... 

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