Aluminium atoms, reaction

Obviously sufficient energy is available to break the A1—Cl covalent bonds and to remove three electrons from the aluminium atom. Most of this energy comes from the very high hydration enthalpy of the AP (g) ion (p. 78). Indeed it is the very high hydration energy of the highly charged cation which is responsible for the reaction of other essentially covalent chlorides with water (for example. SnCl ). 

The following mechanism of the reaction has been suggested it includes the coordination of the carbonyl compound with the aluminium atom in aluminium sopropoxide and the transfer of a hydride Ion ... 

The amount of aluminium introduced into the framework reached ceiling level with increase of reaction time and partial pressure of aluminium trichloride, and showed a gently-sloping peak at around 940 K reaction temperature. Moreover, they did not correspond to the amount of silicone removed from the silicalite during the reaction [8,11]. From these results, it is suggested that by the atom-planting, aluminium atoms occupy special sites in the zeolite framework, and do not substitute silicon atoms in the framework. 

We synthesized nine silicalites which had different concentrations of defect sites in the zeolite framework determined by isotope exchange method. These silicalites were treated with aluminium trichloride vapor under the same reaction conditions 923 K temperature, 1 h time, 11 kPa aluminium trichloride vapor pressure. Figure 1 shows the plots of the amount of aluminium atoms introduced into the framework against the amount of oxygen atoms on the defect sites. A... 

Sometimes, side reactions during Oppenauer oxidations can be explained by the Lewis acidity of the aluminium atom in aluminium alk-oxides.69... 

Porous oxide catalytic materials are commonly subdivided into microporous (pore diameter <2nm) and mesoporous (2-50 nm) materials. Zeolites are aluminosilicates with pore sizes in the range of 0.3-1.2 nm. Their high acidic strength, which is the consequence of the presence of aluminium atoms in the framework, combined with a high surface area and small pore-size distribution, has made them valuable in applications such as shape-selective catalysis and separation technology. The introduction of redox-active heteroatoms has broadened the applicability of crystalline microporous materials towards reactions other than acid-catalysed ones. 

Reaction (1.47) between the antimony atoms diffusing across the bulk of the AlSb layer and the surface aluminium atoms takes place at the Al-AlSb interface (interface 1), whereas reaction (1.48) between the aluminium atoms diffusing across the bulk of the AlSb layer in the opposite direction and the surface antimony atoms proceeds at the AlSb-Sb interface (interface 2). 

In the case under consideration, reaction (2.442) does not take place at all. Thus, the Fe2Al5 layer grows at the expense of diffusion of the aluminium and iron atoms across its bulk and subsequent partial chemical reactions (2.43i) and (2.432), while the FeAl3 layer grows only at the expense of diffusion of the aluminium atoms and subsequent partial chemical... 

Since k]AU k 1 e2, the value obtained is in all probability close to the reaction-diffusion coefficient of the aluminium atoms across the (Fe,Cr,Ni)2Al5 layer in the course of its formation.179... 

The melting point of titanium is 1670°C, while that of aluminium is 660°C.142 In kelvins, these are 1943 K and 933 K, respectively. Thus, the temperature 625°C (898 K) amounts to 0.46 7melting of titanium and 0.96 melting of aluminium. Hence, at this temperature the aluminium atoms may be expected to be much more mobile in the crystal lattices of the titanium aluminides than the titanium atoms. This appears to be the case even with the Ti3Al intermetallic compound. The duplex structure of the Ti3Al layer in the Ti-TiAl diffusion couple (see Fig. 5.13 in Ref. 66) provides evidence that aluminium is the main diffusant. Otherwise, its microstructure would be homogeneous. This point will be explained in more detail in the next chapter devoted to the consideration of growth kinetics of the same compound layer in various reaction couples of a multiphase binary system. 

The concept of R. Pretorius et al 261,262 can briefly be explained as follows. Consider the formation of the Ni2Al3 compound between the pure nickel and aluminium phases as an example. For the purpose of illustration, let us arbitrarily assume that at the interface between those phases the effective concentration of nickel is 70 at.% and that of aluminium 30 at.%. It is clear that in this case the limiting element is aluminium, whereas nickel is in excess. The standard enthalpy of formation of the Ni2Al3 compound is -57 kJ g-atom Hence, if the total number of the nickel and aluminium atoms is equal to the Avogadro number NA, then 57 0.30 0.60 = 28.5 kJ of heat is released in the system after consuming all the aluminium atoms in the reaction of formation of Ni2Al3. Thus, R. Pretorius et al 261,262 introduce the concept of the effective heat, AH, of formation of a compound through the equation... 

The former reaction yields one molecule of Ti3Al at the Ti3Al-TiAl interface and releases two aluminium atoms which then diffuse across the bulk of the Ti3Al layer and enter the latter reaction producing two molecules of Ti3Al at the Ti-Ti3Al interface. 

We normally think of protons as acidic rather than electrophilic but an acid is just a special kind of electrophile. In the same way, Lewis acids such as BF3 or AICI3 are electrophiles too. They have empty orbitals that are usually metallic p orbitals. We saw above how BF3 reacted with Me3N. In that reaction BF3 was the electrophile and Me3N the nucleophile. Lewis acids such as AICI3 react violently with water and the first step in this process is nucleophilic attackby water on the empty p orbital of the aluminium atom. Eventually alumina (AI2O3) is formed. 

Figure 2 Change with Nau the number of framework Aluminium atoms per unit cell in the number of potential protonic sites per unit cell nH+ (=Nai), in their acid strength, in the zeolite activity for reactions demanding strong acid sites (1) or catalyzed even by weak acid sites (2).

The Oppenauer oxidation of alcohols (by a ketone in excess, with an aluminium alkoxide as catalyst) proceeds by hydride transfer through a cyclic transition state (7) in which a molecule of the alcohol and a molecule of the reagent ketone (e.g. acetone) are simultaneously coordinated to one aluminium atom [39]. The reaction actually establishes an equilibrium... 

JV,JV-diethylamide or methanol were used as initiators. Makino et al. [51] state the steric control may be considered to take place by the steric cooperation between the ultimate unit [of the growing chain] and the approaching NCA through the coordination of an aluminium atom . Model compounds have been investigated in an effort to elucidate the stereochemical consequences of some of the proposed reactions [52]. 

One example is the displacement reaction. Aluminium is more reactive than iron to put it another way, aluminium forms positive ions more easily than iron does. Iron(IlI) oxide is an ionic compound it contains positive iron ions and negative oxygen ions. If you mix aluminium metal with iron oxide, and provide some energy by heating the mixture, the aluminium atoms will give up electrons and force them on to the iron ions, thus converting the iron oxide into metallic iron ... 

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