Aluminium oxide calcination

ALUMDJUMCOMPOUNDS - ALUMINIUM OXIDE (ALUMNA) - CALCINED, TABULAR, AND ALUMINATECETffiNTS] (Vol 2)... 

Ash.—As in tanned leather, but with a smaller quantity of substance. The result obtained does not give the true proportion of mineral matter, since the acids combined with the chromium and aluminium oxides axe eliminated during calcination. 

In nature aluminium oxide is mostly mined as the minerals bauxite and laterite, but these as extremely impure. Most bauxite is purified according to the Bayer process which removes the oxides of iron(III), silica and titanium. This takes place by autoclaving the bauxite with sodium hydroxide and sodium carbonate. The precipitated aluminium hydroxide is subsequently heated, or calcined. Calcination involves a heat treatment of a powder as a result of which the latter breaks down ... 

Aluminium oxide is the oldest ceramic material used in medicine. Bauxite and corundum are the main natural sources of aluminium oxide. Bauxite is a mixture of diaspore, gibbsite, iron hydroxides, clay minerals and quartz. It is formed by the tropical weathering of silicate rocks during which quartz and the elements sodium, calcium, magnesium and potassium are largely washed away. This is the reason why the remaining material becomes richer in the resistant elements titanium, iron and aluminium. The latter is extracted from this mixture in the form of aluminium hydroxide. In its turn this compound is converted into aluminium oxide by heating the mixture to 1200-1300 °C, this is called calcination. The hydroxide is thus made anhydrous. 

The development of stress during calcination is shown in Fig. 8.20 for boehmite membranes calcined at 600°C (thickness after calcination is 5 pm). Curve c in Fig. 8.20 represents the curve which is corrected for support effects (see the preceding section on this subject). Three heating and cooling cycles are shown. During the first heating the Al-hydroxide particles of the gel are transformed to boehmite and subsequently to (hydrated) y-aluminium oxide particles and the shape of the first peak of curve c differs from the subsequent peaks. The maximum tensile stress calculated from the deflection amounts about 30 MPa. 

Aluminium Oxide—Alumina——102—occurs in nature, nearly pure, os corundiim emery r 6y, tsapphire and fo/yoz and is fonned artificially by calcining the hydrate, or ammonia alum, at a red heat... 

CAS 1344-28-1 1333-84-2 (hydrate) EINECS/ELINCS 215-691-6 Synonyms Activated alumina Activated aluminum oxide Alumina, activated Alumina, calcined Alumina, tabular Aluminium oxide alumite Aluminium oxydes C Aluminum oxide Aluminum oxide (2 3) Alumite Alundum Calcined alumina Tabular alumina Classification Inorganic compd. 

Narita, E., Kaviratna, P., and Pinnavaia, T. J. 1991. Synthesis of Heteropolyoxometalate Pillared Layered Etouble Hydroxides via Calcined Zinc-Aluminium Oxide Precursors. Chem. Lett. S-08. 

Figure 7. Kubelka-Munk transformed diffuse reflectance spectrum of (A) untreated and (B) calcined catalyst 10-wt% Au on aluminium oxide "C" calcination conditions 400°C, air, 4 h. The change in the plasmon absorbance of the supported gold colloid due to change in particle size can be clearly seen c.f. Figure 2 curves B and C. (the Kubelka-Mumk function F(R) is not the simple absorbance spectrum but is divided by the scattering spectrum of the white alumina support, which is normally assumed to be monotonic F(R) = K/S)...

Winchell (1931) gives a preparation method for an amorphous form of altirniniim oxide, the conditions being stated as calcination of an aluminium hydroxide at 925°C for some hours . At 1000-1200 C for 1 hour this compound converts to corundum (. v.), so samples may have mixed phases. Heaton (1928) notes that synthetic aluminium oxide has been used as a substrate for lake pigments. 

This pigment is described by Riffault et al. (1874) as a combination of aluminium oxide and cobalt oxide. It is prepared by faking an alum solution and dissolving in it cobalt nitrate, sulfate or chloride. A pink-white precipitate is formed with sodium or potassium carbonate the product is then washed, dried and calcined in a crucible at high temperature. It would consequently appear to be a manufacturing variant of cobalt aluminium oxide (that is, cobalt blue ) and is also stated to be synonymous with Gahn s ultramarine qq.v.). 

The earhest modem history of cobalt aluminium oxide ( cobalt blue qq.v.) pigments commences with Leithner in Vienna, who appears to have discovered the basic process of calcining cobalt oxide and alumina (aluminium oxide) in 1775. Brachert (2001) gives Leithner s blue as a synonym for Cobalt blue. It is also sometimes given as Leidner blue this may additionally explain, by corruption, the use of Leyden blue for cobalt blue. 

Mg aluminium oxide of known composition, wrapped up in a little aluminium foil, are introduced into the copper bath and analysed. A blank value should be determined separately for the foil and allowed for in the calculation. The loss on calcination at 1100°C must be known for the aluminium oxide used if this is appreciable, allowance must be made for it. 

Gibbsite (aluminium hydroxide) is purified from bauxite (impure aluminium oxide) via the Bayer process, where the bauxite is reacted with sodium hydroxide to form the aluminium hydrolysis species, Al(OH)4, from which gibbsite can then be recovered. Corundum (aluminium oxide) can then be obtained from the gibbsite via calcination. Pyrolusite (manganese dioxide) is often utilised in the... 

Aluminium fluoride (anhydrous) [7784-18-4] M 84.0, m 250°. Technical material may contain up to 15% alumina, with minor impurities such as aluminium sulfate, cryolite, silica and iron oxide. Reagent grade AIF3 (hydrated) contains only traces of impurities but its water content is very variable (may be up to 40%). It can be dried by calcining at 600-800° in a stream of dry air (some hydrolysis occurs), followed by vacuum distn at low pressure in a graphite system, heated to approximately 925° (condenser at 900°) [Henry and Dreisbach J Am Chem Soc 81 5274 1959]. 

If treatment with ammonia gave a flocculent precipitate (ferric or aluminium hydroxide), the weighed zinc oxide is dissolved in dilute hydrochloric acid, the solution treated with ammonium chloride and excess of ammonia, and the precipitate collected, washed, again dissolved in hydrochloric acid and reprecipitated with ammonium chloride and ammonia the precipitate thus obtained is collected, washed, calcined and weighed. The weight of the ferric oxide and alumina thus obtained is deducted from that of the zinc oxide previously found. 

The NiO/NiAl30< catalyst was prepared in our laboratory by coprecipitation of nickel nitrate hexahy drate and aluminium nitrate nonahydr te following a method described elsewhere [3]. The samples were calcined in an oxidant atmosphere at 1023 K for a period of time of 3 hours. 

Cobalt Blue consists essentially of oxides of cobalt and aluminium with more or less zinc oxide. It is obtained by calcining a mixture of alum and cobalt sulphate, and is used by artists in painting porcelain. Save for this it has now no commercial value.13 Cobalt blue is also known as Cobalt Ultramarine, Thenard s Blue, and King s Blue. 

Some of the best-known examples of this type of reaction are the thermal decomposition of hydroxides to give active oxide-hydroxides and oxides (see Section 10.3.6). Another example is the calcination of a carbonate (e.g. CaC03). In fact, BET areas of up to 500 m2 g-1 can be produced by the calcination of an aluminium trihydroxide. But, unless the heat treatment is carefully regulated, as in controlled rate thermal analysis (CRTA), the pore structure of the active product tends to be highly heterogeneous (Rouquerol and Ganteaume, 1977). 

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