Iron compounds Aluminium hydroxide

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. 

It was shown in [18] that practically monophase fine barium hexaaluminate can be obtained by mechanical activation of a mixture of barium oxide with Y-AI2O3, which exhibits acid properties to a larger extent than a-Al203, and by consequent thermal treatments at increased temperature. The product then is grinded in the presence of water. The synthesis was shown to proceed almost completely after activation for 5 min in the AGO-2 planetary mill and thermal treatment at 1300°C for 1 h. Mechanical activation of the mixture of aluminium hydroxide with barium oxide, followed by thermal treatment at 900°C, results in the formation of the final product and a-Al203 as an admixture which remains even at 1300°C. Mechanochemical synthesis helped also to synthesize barinm hexaaluminate in which a part of aluminium cations is replaced with manganese, iron, cobalt cations. Such compounds are nsed as active ceramics in catalysis [17]. 

It is believed that eertain of the quinolone functional groups (3-carboxyl and 4-oxo) form insoluble chelates with aluminium and magnesium ions within the gut, which reduces their absorption. " The stability of the chelate formed seems to be an important factor in determining the degree of interaction. It has been suggested from animal studies that adsorption of quinolones by aluminium hydroxide re-precipitated in the small intestine may be a factor in the reduced bioavailability of quinolones. See also Quinolones + Iron or Zinc compounds , p.336. 

Ferruginous and aiuminous clay soils are frequent products of weathering in tropical latitudes. They are characterized by the presence of iron and aluminium oxides and hydroxides. These compounds, especially those of iron, are responsible for the red, brown and yellow colours of the soils. The soils may be fine grained, or they may contain nodules or concretions. Concretions occur in the matrix where there are higher concentrations of oxides in the soil. More extensive accumulations of oxides give rise to laterite. 

It is otherwise with cotton, which is almost chemically pure cellulose, and hence is chemically indifferent in a tinctorial sense. Here combination with the dye results from the use of mordants which are adsorbed colloidally on the fibre before dyeing. The mordant can then enter into chemical union with the dye as a complex compound. For an important group of acid dyes (p. 335) the mordants are chiefly metallic hydroxides, namely, those of chromium, aluminium, iron, antimony, tin, etc., whilst for basic dyes tannin is the usual mordant. 

Renz 4 describes an additive compound of indium trichloride and pyridine, tripyridino-indium trichloride, [In(C5H5N)3]Cl3, which is prepared by adding pyridine to a solution of indium trichloride in alcohol. After standing for a short time, small needle-shaped crystals separate of melting-point 253° C. The compound is not hygroscopic like indium chloride, is somewhat sparingly soluble in alcohol, and is insoluble in ether. It decomposes on warming with water with formation of indium hydroxide, In(OH)3. Aluminium trichloride and iron trichloride form similar addition products. 

The chromous salts, derived from the oxide CrO, arc analogous to the salts of divalent vanadium, manganese, and iron. This is seen in the isomorphism of the sulphates of the type R" SOj-THgO. The stability of such salts increases in the order of the atomic number of the metal. The chief basic oxide of chromium is the sesquioxidc CraO, which is closely allied to ferric oxide, and, like the latter, resembles aluminium oxide. The hydroxide, Cr(OH)3, with bases yields chromites analogous to, but less stable than, the aluminates. Chromic sulphate enters into the formation of alums. The chromic salts are very stable, but in the trivaJent condition the metal shows a marked tendency to form complex ions, both anions and cations thus it resembles iron in producing complex cyanides, whilst it also yields compounds similar to the cobaltamines. 

In basic inorganic chemical analysis, the cations that students may be required to identify are aluminium, ammonium, calcium, copper(II), iron(II), iron(III), lead(II) and zinc. The reagents used are usually sodium hydroxide and ammonia solutions. Whether a precipitate (an insoluble hydroxide) is formed, the colour of the precipitate and further reaction, if any, of the precipitate with excess sodium hydroxide and/or ammonia solution, aU give clues to the identity of the cations present. The liberation of ammonia when sodium hydroxide solution is added to an unknown compound and gendy heated indicates the presence of the ammonium ion. Flame tests are also used to identify certain cations, for example, sodium, potassium and copper(II), as they give distinctive coloured flames when heated in a non-luminous flame. 

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