Aluminum species, hydrated

Al MAS NMR has been demonstrated to be an invaluable tool for the zeoHte sdentist It provides a simple and direct way to quantify the proportions of A1 in four [Al(4)j, five [Al(5)j and six [Al(6)j coordinations. Quantitative determination of these species is an important issue in catalysis, and major effort is devoted on this topic. As mentioned already, for A1 only the central transition (-i-half to —half selective exdtation ) is detected. The central transition is unaffected by first order quadmpolar interaction, but the presence of second order effects causes broadening and complicates the quantitation of the A1 species. Usually hydrated samples and short radiofrequency pulses are employed for quantitative determination of framework and extra framework aluminum species. It is uncertain whether hydration changes the coordination of A1 species. Certain extra framework A1 can have very large quadmpolar interactions resulting in very broad lines ( NMR invisible ) [155, 202]. Unlike Si NMR, Al has a short relaxation time due to its quadmpolar nature, and the Al NMR spectrum with good signal to noise can be obtained in a relatively short time. 

Dent Glasser et al. found that metal cations can affect the polymeric state of silicate ions, the polymerization rate and form of silicon and aluminum species, and the properties of the gel.[40 41] In addition, it has been confirmed by extensive experimental data that there is a tight correlation between the metal cations and small cage-like structural units of the resultant zeolites (see Table 5.11 for details), i.e., the size of the cations or hydrated cations matches that of these small cages. One type of cation could template different structures under different conditions as well. Studies indicate that metal cations will affect the structure of zeolites via their electropositivity, size, and geometric configuration. 

FIGURE 2.80 MAS NMR spectrum of an aluminum-containing hydrated MCM-41 with signals at 53 and 0 ppm due to Aljy and Alyi species, respectively. (Taken from Micropor. Mesopor. Mater., 125, Meynen, V., Cool, P., and Vansant, E.F., Verified syntheses of mesoporons materials, 170-223, 2009, Copyright 2009, with permission from Elsevier, and decomposed here.)... 

Jiao J, Kanellopoulos J, Wang W, Ray SS, Foerster H, Freude D, et al. Characterization of framework and extra-framework aluminum species in non-hydrated zeolites Y by Al spin-echo, high-speed MAS, and MQMAS NMR spectroscopy at = 9.4 to 17.6 T. Phys Chem Chem Phys 2005 7 3221-6. 

It is evident that the aluminum released from the framework upon hydro-thermal treatment remains in the sample, either as an intracrystalHne oxidic or cationic aluminum species or as intercrystalline material, i.e., as a separate crystalline or amorphous aluminum oxide phase [77-79]. Typical signals appear in the Al MAS NMR spectra of Y zeolites upon hydrothermal dealumination (Fig. 4). A line at 0 ppm associated with octahedrally coordinated aluminum is indicative of hydrated cationic species [79-82]. Amorphous oxidic aluminum species, which are subject to large second-order quadrupolar... 

You may be surprised to learn that many metal cations act as weak acids in water solution. A 0.10 M solution of A12(S04)3 has a pH close to 3 you can change the color of hydrangeas from red to blue by adding aluminum salts to soil At first glance it is not at all obvious how a cation such as Al3+ can make a water solution addic. However, the aluminum cation in water solution is really a hydrated species, A1(H20)63+, in which six water molecules are bonded to the central Al3+ ion. This spedes can transfer a proton to a solvent water molecule to form an H30+ ion ... 

Al(III) is an example of an aquatic ion that forms a series of hydrated and protonated species. These include AlOrf Al(OH)J, Al(OH)3, and other forms in addition to AP. (For simplicity, we omit the H2O molecules that complete the structures of these complexes.) Most of these species are amphoteric (able to act as an acid or a base). Thus the speciation of Al(III) and many other aquatic ions is sensitive to pH. In this case, an aggregate variable springs from the conservation of mass condition. In the case of dissolved aluminum, the total dissolved aluminum is given by... 

Formation permeability damage caused by precipitation of dissolved minerals such as colloidal silica, aluminum hydroxide, and aluminum fluoride can reduce the benefits of acidizing (132-134). Careful treatment design, particularly in the concentration and amount of HF used is needed to minimize this problem. Hydrofluoric acid initially reacts with clays and feldspars to form silicon and aluminum fluorides. These species can react with additional clays and feldspars depositing hydrated silica in rock flow channels (106). This usually occurs before the spent acid can be recovered from the formation. However, some workers have concluded that permeability damage due to silica precipitation is much less than previously thought (135). 

According to El-Mashri et al.,190 the A106 A104 ratio determines the hydration capacity of anodic oxides. Tetrahedral sites are hydrated easily to form a boehmite-like structure, which is known to be composed of double layers of Al-centered octahedra, weakly linked by water molecules to other layers.184 As the oxide formed in H3P04 contains about 70% tetrahedral aluminum bonds, its hydration ability should be higher than that of the oxide formed in tartrate solution. However, this has not been found in practice, which is interpreted by El-Mashri et al. as being due to some reduction of A104 by incorporated phosphate species. 

Synonyms Mica is a nonfibrous silicate occurring in plate form and includes nine different species muscovite is a hydrated aluminum potassium silicate also called white mica phlo-gopite is an aluminum potassium magnesium silicate also called amber mica other forms are biotite, lepidolite, zinnwaldite, and roscoelite... 

Sensing chemical species is a much more difficult task than the measurement of mechanical variables such as pressure, temperature, and flow, because in addition to requirements of accuracy, stability, and sensitivity, there is the requirement of specificity. In the search for chemically-specific interactions that an serve as the basis for a chemical sensor, investigators should be aware of a variety of possible sensor structures and transduction principles. This paper adresses one such structure, the charge-flow transistor, and its associated transductive principle, measurement of electrical surface impedance. The basic device and measurement are explained, and are then illustrated with data from moisture sensors based on thin films of hydrated aluminum oxide. Application of the technique to other sensing problems is discussed. 

Aluminum is present in many primary minerals. The weathering of these primary minerals over time results in the deposition of sedimentary clay minerals, such as the aluminosilicates kaolinite and montmorillonite. The weathering of soil results in the more rapid release of silicon, and aluminum precipitates as hydrated aluminum oxides such as gibbsite and boehmite, which are constituents of bauxites and laterites (Bodek et al. 1988). Aluminum is found in the soil complexed with other electron rich species such as fluoride, sulfate, and phosphate. 

Aluminum is an amphoteric element that acts as a nonmetal in alkali and develops a hydrated gelatinous aluminate of a species [Al(OH)4]. As a result of this reaction, certain suspended matter including polysaccharide polyanions coprecipitates by entrainment. This element, applied in atomic or ionic form, is a common technique for commercial isolation of pectin. In acid, Al3+ supposedly neutralizes polyanions to yield the aluminum salt. After precipitation of the pectin-aluminum complex, the metal ligand is removed by acidification and washing. 

The structure of aluminate in aqueous solution is gradually decomposed and the moiety of the network structure of aluminate, aluminum tetrahydroxide, and the hydrates occur as the predominant chemical species in the aqueous solution. The structure of chemical species in aqueous solution changes from fourfold coordination structure to sixfold coordination structure with H20 molecules. At this time, polymerization begins to proceed. Hexaaquaaluminum cation serves as a core to form the network structure of Al(OH)3 by the progress of polymerization. Finally, Al(OH)3 precipitates and crystallizes. 

This term is often given the additional restriction that is represents only the species indicated. Thus, 10-5 moles of A1C13 dissolved and made to a volume of 1 L with water would be almost exactly 3 x 10"5 M in Cl because the chloride ion does not complex or ion pair significantly with aluminum ions in solution. On the other hand, Al3+ is considerably less than 10-5 M because the hydrated aluminum ion hydrolyzes significantly to form the AlOH2+ ion. The solution could properly be described as 10 5 Fin AICI3 (see definition of F)... 

Partitioning and mobility of metal ions, metal complexes, and ligands in soils or sediments are affected by their adsorption onto a variety of substrates. As mentioned earlier (see Section 6.3.1), natural oxides offer suitable adsorption sites for some of these species and may even undergo dissolution as a result. Here, an understanding of the bonding phenomena is crucial. For example, the adsorption of [Co(III)EDTA] (here written as [ML]-) on hydrated aluminum oxide surfaces (written as =A10H) can be represented as ... 

In view of the matrix-isolation infrared studies, the theoretical calculations, and those studies of aluminum beam-water reactions, it is of considerable interest to probe the electronic structure of aluminum metal atom hydration reaction intermediates and products Isolated in rare-gas matrices. Such a study will form a useful adjunct to the infrared research. A mapping of the electronic structure of these species will provide a data set to which further theoretical calculations may compare. A more focused elucidation of the nature of the gas-phase aluminum hydration reaction s chemiluminescent continuum emitter may be provided... 

Similarly, the nitride, carbide, cyanide, carboxylate, and carbonate salts of aluminum are unstable in aqueous solution. Aluminum salts of strong acids form solutions of the hydrated cation (see Hydrates). These solutions are acidic owing to the partial dissociation of one of the coordinated water molecules (equation 6), the p/fa of [A1(H20)6] + being 4.95 (see Acidity Constants). Note that this is quite similar to that of acetic acid. The second step in the hydrolysis reaction yields a dihydroxide species that undergoes condensation to form polynuclear cations (see Section 8). Antiperspirants often include an ingredient called aluminum chlorhydrate that is really a mixture of the chloride salts of the monohydroxide and dihydroxide aluminum cations. The aluminum in these compounds causes pores on the surface of the skin to contract leading to a reduction in perspiration. 

It has been reported by F.A. Mumpton (1978) that more than 1000 occurrences of zeolite minerals in over 40 countries have been discovered since 1950. In addition to the hydrated aluminosilicate species, new minerals related to zeolites have been discovered, including the porous clathrasUs such as Melonophlogite (a silica only framework). Species in which the aluminum or silicon has been replaced by other elements (such as phosphorus, iron, and berylhum) have also been discovered as exemplified by viscite, a sihcoaluminophosphate related to analcime. At the present there are 3 8 different natural framework topologies, as shown in Table 25. 

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