The oxides of aluminium

The hydroxide, M(OH)3, oxyhydroxide, MO(OH), and oxide, M2O3, of A1 (and certain other trivalent elements) exist in a and 7 forms. We give the mineral names of these A1 compounds because they are often referred to by name and also because the American nomenclature is sometimes different from that used in England. 

The 5 and 6 phases formed at intermediate temperatures are both highly crystalline phases, the former with a superstructure of the spinel type and the latter with the 3-Ga203 structure mentioned in the section on Oxides M2O3 . 

Elevation of the structure of MnsOg the Cdl2-like layers are perpendicular to the plane of the paper. 

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Aluminium and copper conductors start oxidizing at about 90°C. The oxides of aluminium (AI2O) and copper (CuO) are poor conductors of electricity. They may adversely affect bus conductors, particularly at joints, and reduce their current-carrying capacity over time, and lead to their overheating, even to an eventual failure. Universal practice therefore is to restrict the operating temperature... 

The oxidation of aluminium at room temperature is reported to conform to an inverse logarithmic equation for growth periods up to 5 years duration. At elevated temperatures, oxidation studies over shorter periods illustrate conformity to parabolic, linear and logarithmic relationships according to time and temperature. These kinetic variations are attributed to different mechanisms of film formation . ... 

In fact, most of the reactions involving the oxidation of aluminium are highly exothermic. The optimum amount of aluminium added to the composition will vary depending upon the amount of available oxygen, but the extra heat generated will more than compensate for the non-gaseous solid aluminium oxide which is formed. 

The system ammonium nitrate, aluminium, nitro compound (e.g. TNT) would be expected to undergo gradual decomposition, e.g. that in stored shells and bombs filled with such mixtures changes would occur, leading to the oxidation of the aluminium. Obviously, a mixture containing oxidized aluminium has lower explosive power than the same mixture containing metallic aluminium. It was therefore very important to determine the mechanism of the oxidation of aluminium. It became apparent that this is caused by impurities in the ammonium nitrate, not by the... 

The oxidation of aluminium is highly exothermic producing —1590 kj, as shown in Reaction 5.13. 

The volume of gas does not change in the first two reactions, i.e. 3 moles - 3 moles. Consequently, the increase in the output of heat from the oxidation of aluminium prolongs the presence of high pressures. This effect is utilized in explosive compositions for airblasts, lifting and heaving, or large underwater bubbles. However, there is a limit to the amount of aluminium that can be added to an explosive composition as shown in Table 5.18. 

The proposed block catalysts of honeycomb structure are characterized by the following component ratio, mass. % perovskite - 50-95, the oxides of aluminium or silicon, zirconium, chromium 5-50. A distinguishing feature of the catalyst is the use of perovskites CaMeOj and Ca,Lai.jMe03, where Me=Fe, Co, Ni, Mn and x=0.9-0.1, and of active components with structure-forming and thermostabilizing properties, such as aluminium, silicon, zirconium, chromium compounds. 

Silicates of chromium have not been prepared. Numerous siliceous minerals contain chromium sesquioxide, generally in combination with the oxides of aluminium and iron, e.g. chrome ochre and wolchonskoite (see p. 8). 

Apart from the reaction of the decomposition of nitrate esters some other changes can occur in mixed explosives, such as the reaction of the oxidation of aluminium, particularly marked in watcr-gel explosives. Also permitted (permissible) explosives containing ion exchange mixtures of sodium nitrate witli ammonium chloride a double exchange reaction can occur ... 

Fig. 2 is the cross-section of. Al-Cu densiw functionally graded material. It shows that there were no micro cracks, and the transition between layers was in a good state. Fig. 3 gives the result of elemental macro linear analysis. From Fig. 3, it can be seen that the Cu element content increases along FGNfs thickness, while that of, A1 decreases. The relative density of gradient layers are low but the solid aluminium layer and copper layer are high, which due to the oxidization of aluminium powder on the. surface [7]. It can reject the reaction of aluminium and copper. The detailed anah sis of oxide content in aluminium panicles will be... 

The low relative density of graded layers is due to the oxidation of aluminium powder on the surface. 

The action of nickel is so much more powerful than that of alumina that the dehydrating action of the latter is practically eliminated when catalysts containing mixtures of reduced nickel and alumina are used. In fact, the alumina apparently only acts as a support for the active metal. However, comparative measurements have shown that the oxides of aluminium, iron, magnesium, and calcium may act as strong promoters for nickel catalysts. This effect has been explained as a mechanical effect, viz., the development of a large surface by which relatively more active metal is effectively exposed.10 When only small amounts of oxide are present the effect is predominantly that of support. The increased addition of oxide may increase the catalytic activity up to a certain point beyond which it only serves to dilute the catalyst and reduce its selectivity. Other explanations of the promoter action postulate the removal of catalyst poisons by the oxide, or regeneration of the active metallic catalyst by oxidations and reductions.20... 

The particle surface of pigment Ti02 was treated with the oxides of aluminium, silicon and zirconium, and the surface of pigment Fe203 - with aluminium and silicon oxides. Pure phthalocyanine pigment - p-CuPc was used in the work. 

During the storage of PO, the formation of a high MW polypropylene oxide) with a MW of 50,000-400,000 daltons and in very small quantities, as a consequence of the contact of liquid PO with the metal walls (carbon steel) of the storage tanks, was observed. The formation of this high MW polyether is explained by the co-ordinative anionic polymerisation of PO, catalysed by the oxides of aluminium, chromium, iron and nickel existing on the metallic surfaces. 

Whereas the oxidation of aluminium metal has a standard reduction potential of-1.7 volt the oxidation of AI2O3 has only a standard reduction potential of -0.6 volt making aluminium oxide almost as corrosion resistant as the noble metal gold. 

The NiO layer is not very protective due to the restricted potential region where it is stable. It can be easily reduced cathodically, which is accompanied with detachment of the oxide layer [4], Because we already know from the quenching experiments that an oxide layer is formed on NiAl at —llOOmV, where Ni is not yet oxidised, the anodic current at this potential is ascribed to the oxidation of aluminium. For Ni the current iwnearly zero at this potential, due to near-equilibrium of the reactions 4 and 5. PossfHe reactions for the oxidation of aluminium are ... 

The oxidation of aluminium in atmospheric oxygen is extremely rapid, commencing immediately a fresh surface is formed by abrasion. Such surfaces must therefore be bonded as soon as practicably possible. 

No reactions were observed with the oxides of aluminium, titanium, chromium(III) and iron(III), but certain carbonates and sulphates were found to react ... 

The fundamental reactions of the corrosion of aluminium in aqueous medium have been the subject of many studies [7, 8]. In simplified terms, the oxidation of aluminium in water proceeds according to the equation ... 

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