Cations aluminium

Isse, A.A., Scialdone, O., Galia A. and Gennaro A. (2005b) The influence of aluminium cations on electrocarboxylation processes in undivided cells with A1 sacrificial anodes. J. Electroanal. Chem. 585, 220-229. 

Bayerite has a monoclinic lattice, P2,/a, its parameters being a = 0.562, b = 0.867, c = 0.471 nm, p = 90.26° [10]. It is based on AB packet composed of two tightly packed layers of hydroxyl ions with a layer of aluminium cations located between them. The arrangement of packets in bayerite can be expressed as ABAB [8]. The packets are perpendicular to the axis C and held between each other by hydrogen bonds. The average distance between two layers in a packet is equal to 0.207 nm while the distance between two neighbouring layers from different packets is 0.260 nm. 

On the other hand, the structure of Ca3Al2(OH)i2, formed via interaction of Al(OH)3 with Ca(OH)2, consists of Off ions packed with metal ions, which occupy the suitable size sites. Calcium cation is surrounded by eight Off ions, while aluminium cation is surrounded by six Off ions, corresponding distances being 0.250 and 0.192 nm, respectively. This means that the formation of stracture can proceed in a simpler manner than through the dissolution followed by crystallization. 

It was shown in [18] that practically monophase fine barium hexaaluminate can be obtained by mechanical activation of a mixture of barium oxide with Y-AI2O3, which exhibits acid properties to a larger extent than a-Al203, and by consequent thermal treatments at increased temperature. The product then is grinded in the presence of water. The synthesis was shown to proceed almost completely after activation for 5 min in the AGO-2 planetary mill and thermal treatment at 1300°C for 1 h. Mechanical activation of the mixture of aluminium hydroxide with barium oxide, followed by thermal treatment at 900°C, results in the formation of the final product and a-Al203 as an admixture which remains even at 1300°C. Mechanochemical synthesis helped also to synthesize barinm hexaaluminate in which a part of aluminium cations is replaced with manganese, iron, cobalt cations. Such compounds are nsed as active ceramics in catalysis [17]. 

The adsorption behavior of this species is relatively complex and has been discussed in detail elsewhere. Briefly, there are three different binding modes of the molecule to the surface, only one of which is ESR active, i.e. still carrying an unpaired electron. The dynamics of this species, which represents about 10% of a monolayer, has been studied with ESR. The molecule is bound to an aluminium cation site via the oxygen lone pair and resides in an environment established by a large fraction of molecules bound with both nitrogen and oxygen... 

Ringenbach et al. [81] investigated the adsorption mechanism of polycar-boxylic acid on alumina. The complex formation between polyanion and dissolved aluminium cations appears to play an important role in determining the properties of the adsorbed layer. This may explain the decrease in stability of polyelectrolyte suspensions with time. 

Traditionally papermaking is made at acid pH of about 4.5. Because of this the sizing of paper is carried out with resin acid salts in the presence of alum. Under these conditions, the resin acid anions complex with the aluminium cations and the complex formed is attracted to and deposited on the fibre surface. The purpose of sizing is to render the paper more resistant to water-based printer s ink. Today there is much interest in so-called alkaline sizing at about pH 7, which is preferred for specialist long-life papers. Here sizes such as alkyl ketene dimer replace alum. Alkaline papermaking has the further advantage that fillers such as calcium carbonate can be employed. 

The existence of coloured specimens of normally colourless minerals, such as sodium chloride and alumina, has been known for centuries. Some sodium chloride crystals appear yellow due to the selective absorption of blue light, and sapphires/rubies are coloured forms of a-alumi-na. The coloured forms of these minerals are due to defects. In sodium chloride, excess sodium can lead to additional mobile electrons which can be trapped on vacant anion sites, giving the solid a yellow hue. In the gemstones, the colour is generated by substitution of a few of the aluminium cations by other trivalent cations, such as chromium, in a solid solution. 

Other fates are possible for the enolate formed in the initial conjugate addition and an obvious possibility is an aldol reaction. With an asymmetric catalyst, the combination of three simple molecules leads to one enantiomer of one diastereoisomer of the tandem Michael-aldol product14 83. The catalyst 84 is based on a BINOL A1 complex (see chapters 25, 26). It can be drawn either as a lithium salt with an aluminium cation or, better, as a lithium aryloxide with a Lewis-acidic aluminium atom. This is better because both basic ArCT and Lewis acidity are necessary for catalysis. 

Aluminium-cation-exchanged clay montmorillonite was used as a Lewis acid. 

Aluminium cations are well known to form very strong fluoride complexes [251], and, therefore, fluoride melts interact to an appreciable degree with the Al203-containing constructional materials. This leads to dissolution of alumina in molten mixtures containing F, followed by the formation of fluoro-complexes. Addition of the Lux bases favours the interaction s running in the reverse direction, i.e. it results in precipitation of A1203 from its solutions in the fluoride melt. These ideas allow us to assume that the... 

Iodide salts of two novel four-co-ordinate aluminium cations have been prepared. They are (65 L-L = TMED or sparteine). They-are produced by nucleophilic displacement reactions on Me3N,AlH2l. The four-co-ordination was confirmed by the values of the v(AlH) wavenumbers (ca. 1890 cm ) five-coordination would have given lower values. Such a phenomenon was observed for the adduct TMED,AlHBr2 [v(AlH) at 1735 cm ], which must therefore be a molecular adduct rather than an ionic compound. 

Aluminium ion hydrolysis. The aluminium cation is present in aqueous... 

It was shown that in both structures aluminium cations having a pronounced deficit of electrons resulting from the acceptor action of SbF are active centres. The investigations with a deuterated catalyst proved that the BreSnsted sites of structure A do not... 

Figure 2.19 The structure of the aluminophosphate fluoride UT-6 is based on the CHA framework but includes coordinated fluoride ions linking octahe-drally coordinated aluminium cations (white octahedra).

Figure 1.5 A host-guest complex of EDTA binding an aluminium cation, where the ligand forms an octahedral geometry around the metal ion.

Some spectroscopic evidence for the formation of ionic bonds across adhesive interfaces is as follows. Using reflectance IR, Bistac et al. [24] showed that for an ethylene-vinyl acetate polymer grafted with 1% of maleic anhydride, and bonded to iron or zinc, new absorptions were present which were attributed to carboxylate (-COO ), and their presence coincided with strong adhesion. In an IR study of the bonding of maleic anhydride to naturally oxidised aluminium, Schneider et al [25] showed that the anhydride is hydrolysed in the early stages of adhesion, taking about 1 min on exposure to laboratory air. They suggested that the hydrolysed acid is bonded to two aluminium cations as shown in Fig. 5. 

The second model of the structure is based on the works of Allman and Tailor who identified structures of the minerals (hydrotalcite and manasseite) [28,29] and showed that magnesium and aluminium ions are located in octahedral voids of hydroxide layer. Anions X and water molecules form another layer. Using this approach, Serna assumed on the basis of electron microdiffraction data and X-ray diffraction patterns of powders that the structure of LADH-CO3 obtained by the hydrolysis of aluminium-tri-(sec-butoxide) in hthium carbonate is based on closely packing two-dimensional layer (30 ]. Two thirds of the octahedral voids in this layer are occupied by aluminium cations located in a manner similar to that of gibbsite. The remaining one third of voids is occupied by lithium cations. On... 

Table 15.4 Hydration enthalpies for the sodium, magnesium and aluminium cations... 

In order to overcome these stability problems a wide-range of alternative dopants have been studied in an effort to reproduce the transport properties of LISICON whilst eliminating the problems of aging. The introduction of trivalent cations into the basic lithium germanate structure can cause an adjustment in the lithium concentration, but in this case it is possible to introduce additional, interstitial, lithium cations or vacancies on the lithium position. Which of these types of doping occurs depends on the nature of the substitution that occurs. This can be most clearly illustrated by looking at the introduction of aluminium cations. These can enter the structure in place of and so introduce an interstitial lithium cation ... 

Table 6.8 Aluminium cation basicity (AlCB) scale (kl mol- ), from ICR ligand-exchange equilibria at 298 K (ref [137] unless noted otherwise) anchored at the ab initio value for formaldehyde.

Table 6.9 Aluminium cation affinity (AICA) scale (kj mol ) at 298 K unless noted otherwise.

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