Aluminium and ammonium

These results led the forensic scientists to propose that a different type of explosive had been used, which was not nitrate-based. Ammonium perchlorate (NH4CIO4) is a strong oxidant, and when mixed with aluminium powder, or other reducing agents, forms a particularly potent explosive (a mixture of aluminium and ammonium perchlorate is used as the solid fuel for the US space shuttle). The Raman spectra of KNO3 and NH4CIO4 (Figure 4.4) clearly show the differences between the two compounds. 

Molten TNT was mixed with ammonium nitrate to give amatol , or ammonium nitrate and aluminium to give minol . Today, TNT is used as an energetic binder for cast compositions. It is used to bind together RDX, HMX, aluminium and ammonium perchlorate. 

Aqueous ammonia can also behave as a weak base giving hydroxide ions in solution. However, addition of aqueous ammonia to a solution of a cation which normally forms an insoluble hydroxide may not always precipitate the latter, because (a) the ammonia may form a complex ammine with the cation and (b) because the concentration of hydroxide ions available in aqueous ammonia may be insufficient to exceed the solubility product of the cation hydroxide. Effects (a) and (b) may operate simultaneously. The hydroxyl ion concentration of aqueous ammonia can be further reduced by the addition of ammonium chloride hence this mixture can be used to precipitate the hydroxides of, for example, aluminium and chrom-ium(III) but not nickel(II) or cobalt(II). 

Beryllium is sometimes precipitated together with aluminium hydroxide, which it resembles in many respects. Separation from aluminium (and also from iron) may be effected by means of oxine. An acetic (ethanoic) acid solution containing ammonium acetate is used the aluminium and iron are precipitated as oxinates, and the beryllium in the filtrate is then precipitated with ammonia solution. Phosphate must be absent in the initial precipitation of beryllium and aluminium hydroxides. 

The precipitate is soluble in free mineral acids (even as little as is liberated by reaction in neutral solution), in solutions containing more than 50 per cent of ethanol by volume, in hot water (0.6 mg per 100 mL), and in concentrated ammoniacal solutions of cobalt salts, but is insoluble in dilute ammonia solution, in solutions of ammonium salts, and in dilute acetic (ethanoic) acid-sodium acetate solutions. Large amounts of aqueous ammonia and of cobalt, zinc, or copper retard the precipitation extra reagent must be added, for these elements consume dimethylglyoxime to form various soluble compounds. Better results are obtained in the presence of cobalt, manganese, or zinc by adding sodium or ammonium acetate to precipitate the complex iron(III), aluminium, and chromium(III) must, however, be absent. 

Detonation occurs during the reaction of molten aluminium with ammonium peroxodisulphate in the presence of water. However, since the temperature is above 75°C, the presence of water is sufficient to decompose it and the water/molten aluminium interaction has aiready been mentioned as being explosive. 

Many of the following powdered metals reacted violently or explosively with fused ammonium nitrate below 200°C aluminium, antimony, bismuth, cadmium, chromium, cobalt, copper, iron, lead, magnesium, manganese, nickel, tin, zinc also brass and stainless steel. Mixtures with aluminium powder are used as the commercial explosive Ammonal. Sodium reacts to form the yellow explosive compound sodium hyponitrite, and presence of potassium sensitises the nitrate to shock [1], Shock-sensitivity of mixtures of ammonium nitrate and powdered metals decreases in the order titanium, tin, aluminium, magnesium, zinc, lead, iron, antimony, copper [2], Contact between molten aluminium and the salt is violently explosive, apparently there is a considerable risk of this happening in scrap remelting [3],... 

If well-dried ammonia gas is passed over freshly sublimed aluminium chloride ammonia is rapidly absorbed, heat is developed, and the whole mass fuses and then gradually solidities as more ammonia is absorbed, leaving a white voluminous powder of composition A1C13.GNH3 or [A1(NH3)6]C13. Hexammino-aluminium chloride is stable at ordinary temperature and is much less hygroscopic than the chloride. It is decomposed by water with formation of aluminium hydroxide, and when heated in dry air is oxidised, yielding the oxide and ammonium chloride. If heated in an atmosphere of dry hydrogen it loses ammonia and passes into diammino-aluminium chloride, [A1(NH3)2]C13.5 Triammino-aluminium chloride obtained in this way by Persoz was not found by Stillmann and Yoder. 

Sublimation differs from ordinary distillation because the vapour condenses to a solid instead of a liquid. Usually, the pressure in the heated system is diminished by pumping, and the vapour is condensed (after travelling a relatively short distance) on to a cold finger or some other cooled surface. This technique, which is applicable to many organic solids, can also be used with inorganic solids such as aluminium chloride, ammonium chloride, arsenious oxide and iodine. In some cases, passage of a stream of inert gas over the heated substance secures adequate vaporisation. 

The temperature also affects the process of coagulation.8 With the chlorides of potassium, sodium, lithium and ammonium the velocity of flocculation varies inversely as the temperature 9 with the chlorides of barium, strontium, calcium, magnesium and cadmium the velocity varies directly as the temperature with aluminium chloride it is independent of the temperature. Heating thus stabilises the sol towards univalent cations but diminishes the stability towards bivalent ions.10 The... 

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