Aluminum monovalent

A third technique employs monovalent aluminum. By bringing vapors of aluminum fluoride or aluminum chloride into contact with carbothermicahy reduced aluminum ahoy at 1000—1400°C, the fohowing reaction occurs... 

The ground state distribution of electrons in the aluminum atom is lT2T2 3T3/). The oxidation state of aluminum is +3, except at high temperatures where monovalent species such as AIQ, AIF, and AI2 have been spectrally identified At lower temperatures, these compounds disproportionate... 

Commercial grades of socbum aluminate contain both waters of hycbation and excess socbum hycboxide. In solution, a high pH retards the reversion of socbum aluminate to insoluble aluminum hycboxide. The chemical identity of the soluble species in socbum aluminate solutions has been the focus of much work (1). Solutions of sodium aluminate appear to be totaby ionic. The aluminate ion is monovalent and the predominant species present is deterrnined by the Na20 concentration. The tetrahydroxyaluminate ion [14485-39-3], Al(OH) 4, exists in lower concentrations of caustic dehydration of Al(OH) 4, to the aluminate ion [20653-98-9], A10 2) is postulated at concentrations of Na20 above 25%. The formation of polymeric aluminate ions similar to the positively charged polymeric ions formed by hydrolysis of aluminum at low pH does not seem to occur. Al(OH) 4 has been identified as the predominant ion in dilute aluminate solutions (2). 

The two-step charge transfer [cf. Eqs. (7) and (8)] with formation of a significant amount of monovalent aluminum ion is indicated by experimental evidence. As early as 1857, Wholer and Buff discovered that aluminum dissolves with a current efficiency larger than 100% if calculated on the basis of three electrons per atom.22 The anomalous overall valency (between 1 and 3) is likely to result from some monovalent ions going away from the M/O interface, before they are further oxidized electrochemically, and reacting chemically with water further away in the oxide or at the O/S interface.23,24 If such a mechanism was operative with activation-controlled kinetics,25 the current-potential relationship should be given by the Butler-Volmer equation... 

Soil-pH may influence both the concentrations of ions in the soil solution and the charge characteristics of the clay. Dispersion of clays is thus, to some extent, a pH-dependent process. At soil-pH(H2o,i i) values below 5, the aluminum concentration of the soil solution is normally sufficiently high to keep clay flocculated (Al3+ is preferentially adsorbed over divalent and monovalent ions in the soil solution). Between pH 5.5 and 7.0, the content of exchangeable aluminum is low . If concentrations of divalent ions are low, clay can disperse. At still higher pH values, divalent bases will normally keep the clay flocculated unless there is a strong dominance ofNa+-ions in the soil solution. 

Another well-studied electron transfer reaction is the oxidation of aqueous benzidine in the presence of various clays (2, 40, 43, 50, 51). An electron from the colorless benzidine molecule is abstracted by the clay with formation of a blue monovalent radical cation. Upon drying of the blue clay-benzidine system, a yellow color is produced. There is disagreement in the literature with respect to the chemical identity of the yellow product (2, 40, 52) however, in the case of hectorite, the yellow product has been suggested to be the protonated form of the radical cation (divalent radical cation) (2, 52). There is also disagreement about whether the electron-accepting sites of the clay are ferric iron at the planar surfaces, aluminum ions at the edges, or exchangeable cations <2, I). 

Unsubstituted benzidine may be oxidized at clay surfaces when mixed with some types of elay minerals (Tennakoon et al. 1974 Theng 1971). Benzidine is oxidized to a monovalent radical cation by iron (III) in the silicate lattice and by aluminum at crystal edges. However, there is no experimental evidence that... 

When the metal is heated with AICI3 at 1000°C it forms monovalent aluminum chloride, AlCl. 

It is also of interest to use MAS NMR for the study of the thermal treatment of zeolites which are not in the ammonium-exchanged form. In an X-ray study, Pluth and Smith (179) found electron density at the center of the sodalite cages in dehydrated zeolites Ca-A and Sr-A and attributed this to a partial occupancy of these sites by a four-coordinated aluminous species. No such effect was found in zeolite A exchanged with monovalent cations. Corbin et al. (180) used 27A1 MAS NMR to examine commercial samples of K-A, Na-A and (Ca,Na)-A, as received (see Fig. 41). For K-A and Na-A, only framework tetrahedral Al species were observed, with chemical shifts of 57 and 52 ppm respectively. However, in (Ca,Na)-A an additional intense resonance at 78 ppm, typical of AlfOH) but definitely not due to framework aluminum, was also found (see Fig. 41). A much weaker signal, also at 78 ppm, was detected in zeolite Sr-A its intensity increased greatly on heating the sample to 550°C. Freude et al. (183) came to very similar conclusions in their NMR study of heat-treated zeolite Ca-A. They found that maximum framework dealumination occurs at 500°C and corresponds to ac. 17% of total Al. 

Al(01I)4(Il20)2] - The high viscosity of sodium aluminate solutions is explained by hydrogen bonding between these hydrated ions, and between them and water molecules. By reaction of aluminum and its chloride or bromide at high temperature, there is evidence of the existence of monovalent aluminum, Here the aluminum atom is apparently in the sp state, with an electron pair on the side away from the chlorine atom, whereby the single pairs on the two chlorine atoms are shared to form two weak it bonds. 

The oxyacid salts of iron(III) are more numerous than those of iron(II). Among the former, the sulfates arc of interest because of the readiness with which iron(III) sulfate replaces aluminum sulfate in the alums, which are hydrated double sulfates formed by certain trivalent and alkali metal (and other monovalent) sulfates. Iron(lII) sulfate, Fe2(SOa)s, is isomorphous with aluminum sulfate, AbfSOa).), because the radius of the Fe3+ ion is so dose to that of the Al3+ ion (0.57 A). For that reason, the isomorphous relationship extends to other salts, i.e the fluorides and some of the nitrates. 

The process sequence currently used for waste salts (except those containing aluminum for which no process currently exists) is shown in Figure 1. The process includes (1) dilute hydrochloric acid dissolution of residues (2) cation exchange to convert from the chloride to the nitrate system and to remove gross amounts of monovalent impurities (3) anion exchange separation of plutonium (4) oxalate precipitation of americium and (5) calcination of the oxalate at 600°C to yield americium oxide. 

Monovalent compounds of the higher members of group 13 tend not to be stable. However, such species have been proposed as reaction intermediates see Aluminum Inorganic Chemistry and Boron Hydrides). Thus, the reaction, discovered by Alfred Stock, in which B2CI4 may be produced by the zinc discharge reduction of BCI3, is believed to proceed via the intermediacy of BCl, which inserts into a B-Cl bond of a second BCI3 molecule ... 

Thallium has two important oxidation states, Tl (-El) and Tl (+3). The trivalent form more closely resembles aluminum and the monovalent form more resembles alkali metals such as potassium. The toxic nature of the monovalent Tl is due to its similarity to potassium in ionic radius and electrical charge. Thallium sulfate use as a pesticide was restricted in 1965 in the USA and the World Health Organization (WHO) recommended in 1973 against its use as a rodenticide due to its toxicity (WHO, 1973). From 1912 to 1930, thallium compounds were used extensively for medicinal purposes for example in the treatment of ringworm (because of the depilatory effects), dysentery, and... 

It is generally accepted that aluminum is tetrahedrally coordinated in aluminosilicate glasses and melts, provided that cations such as alkali metals or alkaline earth metals are present in sufficient amounts to charge compensate the replacement of Si by AF+ [i.e., Si + —> AP" -t- (1/ )M" +, where monovalent or divalent M ions occur in nonframework sites associated with the tetrahedral aluminosilicate framework]. Experimental data for aluminosilicate glasses derived from both low-angle x-ray-scattering experiments and EXAFS studies show that as aluminum is substituted for silicon, the average T (tetrahedrally coordinated ion) -O bond... 

In the /i"-alumina structure, the phase is stabilized at high temperatures by small amounts of monovalent (e.g., Li20) or divalent (e.g., MgO, ZnO, NiO) oxidesIn these stabilized structures, the cation dopant substitutes directly for trivalent aluminum ions in the spinel block (i.e., LiXi, MgAi) and is electrically compensated by additional sodium ions (Nai) in the conduction plane. 

The current efficiency in modern cells of aluminum electrolysis may exceed 95%. It is generally accepted that the major part of loss in current efficiency is due to the reaction between dissolved metal and electrolyte. Model studies by 0degard et al. (1988) indicates that sodium dissolves in the electrolyte in the form of free Na, while dissolved Al is predominantly present as the monovalent species ALF. Any electronic conductivity is most likely associated with the Na species, which may form trapped electrons and electrons in the conduction band. Morris (1975) ascribed the loss in current efficiency during Al production to electronic conduction. In a theoretical and experimental study. Dewing and Yoshida (1976) subsequently maintained that the electronic conductivity was too low to account for the loss in current efficiency in industrial aluminum cells. However, the existence of electronic conduction in NaF-AlF3 melts was demonstrated later by Borisoglebskii et al. (1978) also. 

The presence of monovalent aluminum in the form of AIF rather than A1+ or AIF has also been suggested by Saget et al. (1975) and Yoshida et al. (1986) to explain the concentration dependence on the solubility. 

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