Aluminium stability constants

Table 8 Stability constants of aluminium-propionate and -lactate...

Stepwise formation constants and free energy, enthalpy, and entropy changes have been calculated for the 1 1, 1 2, and 1 3 complexes of AP" with malonate and succinate ions. Table 8 gives the calculated values for the stability constants of aluminium complexes with propionate and lactate ions in aqueous solutions, with I = 1. Solution calorimetry was used to determine values for the enthalpies of formation of tris(tropolonato)Al " and tris(4-methyltropolonato)Al " (Table 9) they were used to derive gas-phase enthalpies of formation, and hence the A1—O bond energies. ... 

Agarwal, R. P., and Moreno, E. C. 1971. Stability constants of aluminium fluoride complexes. Talanta 18 873-80. Pergamon Press. 

Although Baes and Mesmer (1976) selected a value for log this value is not considered reliable since it is based on the data of Nazarenko and Nevskaya (1969) which is in poor agreement with the large number of other reported stability constants for Al(OH)3(aq). The magnitude of both the stepwise stability constant (i.e. log = -5.03 compared to log K2 = -5.65) and the enthalpy of reaction suggests that aluminium may undergo a change in coordination number in the transition of Al(OH)2" to Al(OH)3(aq). 

There are substantially more data available for the stability constant of Al(OH)4 than for other monomeric aluminium(III) species (Table 13.14). This is due to the importance of this species in the production of aluminium metal from bauxite. Data are available at zero ionic strength, which are generally in good agreement, from a relatively large number of studies. However, the data at fixed ionic strength, which largely come from data determined from measurements in chloride media, predominantly come from the work of Wesolowski and Palmer (1994) and Palmer, B n zeth and Wesolowski (2001). 

Accepted stability constant data for polymeric species of aluminium(III) are listed in Table 13.15. The accepted polymeric species include Al2(OH)2, ... 

Faucherre (1954) studied the hydrolysis reactions of aluminium(III) in barium nitrate media. They proposed stability constants for both Al2(OH)2 and AlOH at 20°C at two different medium concentrations. The constants proposed in the study appear to be relatively consistent with those obtained in other media for both species. The stability constants obtained by the study are noted by the present review but are not retained. 

The emf of the lithium-aluminium system versus pure lithium in a Lil-KI-LiCl molten eutectic is shown in Fig. 8.2 as a function of temperature and composition. It can be seen that the emf remains constant (at about 300 mV more negative than pure lithium) in the range of stability of the /3-phase (-7-47 atoms per cent of lithium), thus implying a constant lithium activity in the alloy surface. At concentrations greater than 47 atoms per cent, the lithium activity becomes strongly composition-depen-dent. 

On zeolites, coke is built by a mechanism initiated on acid sites, and the extent of this deposit is often correlated with the A1 content of the solid. In odCB conversion the stability of the catalyst, expressed as the kd constant, does not appear directly correlated with the aluminium content of the solid. Actually, for that reaction, tarry materials are formed both by... 

Thermodynamic calculations [12] show that aluminium oxide/lithium aluminate is stable at much more cathodic potentials than -1100mV.Therefore it seems likely that the oxidation reactions proceed at all potentials in the carbonate stability range. Thus some oxide will probably be formed before the polarisation measurements are started when the electrode is dipped into the molten carbonate. The constant current from -1000 mV to —800 mV reflects some further but limited growth of the oxide layer, which reaches a thickness of 1 pm after 24 hours (see Fig. 2). The crystallite size of the oxide also increases with exposition time especially during the first few hours. After about 4 hours the morphology hardly changes anymore. 

La courbe de la figure 1 montre que le logarithme de St est une fonction lineairement decroissante de la teneur du gel en aluminium, tout au moins pour des teneurs en A1 comprises entre 0.09 et 0.5. En decS, et au-delil, la stability thermique semble constants. Les catalyseurs industriels sont dans un domains oil la stability thermique est maximum et sensiblement con-stante, ce qui explique la faible quantity d acide de Lewis d6cel6e sur ces masses de contact. 

The stability of natural oxide film, which governs the corrosion resistance of aluminium, depends on pH (Figure B.1.18). Most natural, untreated and unpolluted surface waters have a pH between 6.5 and 7.5. Since the solubility of alumina is minute and is practically constant in this pH range (Figure D.1.14), pH is not an important factor for the corrosivity of natural waters. 

After 5 days of aging treatment, grain boundaries appeared on SEM micrographs. Surface modifications is assumed to be due to formation of volatile aluminium hydroxides, as expected by themodynamic modelUng [9], As the corrosion phenomenon remains limited to the surface, it is not affecting the stability of the foam in the bulk. As a proof, mechanical resistance of alumina foams is kept constant before and after aging the compressive crash strength of 10 ppi alumina foams with 85% apparent porosity has been measured at 2 MPa. 

There is a paucity of available data for the solubility of indium oxide and hydroxide phases. As the first hydrolysis constant of indium has a stability that lies between those of aluminium and gallium, it is expected that the solid hydroxide phase would also exhibit this behaviour. However, a number of studies (Heyrovsky, 1925 Oka, 1938 Moeller, 1941 Lacroix, 1949) have indicated a solubility that was larger than that seen for aluminium(III). It is believed that this would be unlikely and, as such, these data are not retained. AkseTrud and Spivakovskii (1959) obtained a solubility that was nearly four orders of magnitude smaller than... 

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