Alum dehydrations

The chemistry of this reaction differs from that discussed for alum dehydration above for two main reasons. At the temperature of this reaction, water is more volatile and is not adsorbed within the interface in sufficient quantities to promote the difficult recrystallization step. Secondly, the present reactant releases water close to its melting point and dynamic reorganization of the siuface layer may reduce local strains compared with those that may be developed at lower temperatures within alum dehydration interfaces of residual sulfates. 

These examples demonstrate conclusively that the availability of volatile product in the immediate vicinity of the site of a reversible dissociation can markedly influence the apparent kinetic characteristics of crystolysis reactions. Some systems are highly sensitive to such effects but others, such as chrome alum dehydration, are markedly less affected. The kinetics of CaC03 dissociation vary considerably with reaction conditions (83), and here the pattern of reaction rates is also influenced by heat flow during the endothermic, reversible reaction. It follows that it cannot be assumed, without examination of the influence of the procedural variables, that measured kinetic parameters are determined by a slow rate-limiting step. 

Crushed limestone Fine alum Dehydrated milk Cinders coal... 

Potassium Aluminum Sulfate. Potassium aluminum sulfate [7784-24-9]. KAl(SO 12H20, is a white, astringent crystal known as potassium alum, ordinary alum, or potash alum. Its formula weight is 474.39 mp 92.5 °C sp gr 1.75 and solubiUty 11.4 g per 100 mL H2O at 20°C (8). It is soluble in dilute acid and insoluble in alcohol. It dehydrates at about 200 °C to porous desiccated potassium alum [10043-67-1], KAl(SO dried or burnt alum, which has a formula weight of 258.20. 

The reaction is cataly2ed by all but the weakest acids. In the dehydration of ethanol over heterogeneous catalysts, such as alumina (342—346), ether is the main product below 260°C at higher temperatures both ether and ethylene are produced. Other catalysts used include siUca—alumina (347,348), copper sulfate, tin chloride, manganous chloride, aluminum chloride, chrome alum, and chromium sulfate (349,350). 

Since data obtained for dehydration reactions of alums give Q /Q ratios of around unity and also of the order 103, it seems probable that both models may be applicable in specific systems. 

Gamer and Jennings [431] studied nucleation during the dehydration of potassium and ammonium chromium alums. Detailed kinetic measurements were made for the relatively enhanced rate of nucleation which followed admission of water vapour to the solid after a period of vacuum nucleation. This catalytic effect of water vapour is ascribed to its participation in the reorganization of the lattice which had collapsed during previous treatment in vacuum. 

Measurements of the kinetics of the individual nucleation and growth steps in the reactions of several hydrated sulphates have been referred to in Sect. 1.2 though, perhaps surprisingly, these data were not combined in a kinetic analysis for the overall reaction in studies of the alums [51,431, 586] or NiS04 7 H20 [50]. Indeed, Lyakhov and Boldyrev [81], in one of the few reviews of the field, maintain that the satisfactory topochemi-cal description of dehydrations is a problem which at present remains... 

Reference has already been made to the dehydration of alums (Sect. 1.2 and Table 10), decomposition of ammonium metal phosphates (Sect. 4.1.5) and the use of KMn04—KCIO4 solid solutions in mechanistic studies of the decomposition of potassium permanganate (Sect. 3.6). 

Figure 1 Anti-HA IgG titres ( SD) ( Y-axis) in mice immunized with a single subcutaneous injection of (Alum-adsorbed) DRV liposomes composed of PC, DOPE, and DOTAP (molar ratios 4 2 1) and containing pl.l7/SichHA DNA and killed influenza virus ( ), killed influenza virus only (A), or DNA only ( ). For other details see the text. Abbreviations HA, hemagglutinin DRV, dehydration-rehydration vesicles PC, phosphatidylcholine DOPE, dioleoyl phosphatidylcholine DOTAP, 1,2-dioleyloxy-3-(trimethylamonium propane).

Hexaethylenediamino-hexol-tetrachromic Sulphate, [Cr4(OH)6en6](SO4)3.10H2O, is prepared from partially dehydrated chromic alum. The bluish-grey powder obtained is heated with ethylene-diamine monohydrate on a water-bath till a red-coloured mass is produced, which consists of a mixture of potassium sulphate, luteo-chromic sulphate, and the sulphate of the hexol compound, and from the mixture the latter compound is obtained by dissolving out the more soluble salts with water. The crude, difficultly soluble sulphate is purified by dissolving in dilute sulphuric acid and reprecipitating with excess of ammonia. It crystallises in small needles which are almost insoluble in water and soluble in dilute acids. 

Early History.—Although the destructive distillation of partially dehydrated sulphate such as alum was undoubtedly practised very early, even perhaps in the tenth century, the first definite details of the process emanated from Basil Valentine towards the end of the fifteenth century, who described the distillation of green vitriol with silica the name oil of vitriol is derived from this process. Basil Valentine also obtained an acid product by the combustion of a mixture of sulphur and saltpetre, the identity of this sulphuric add with oil of vitriol being first proved by A. Libavius in 1595. 

KA13(S04)2(0H)6. Based on an invention made by G.S. Tilley in 1924. The ore is first dehydrated at up to 600°C. It is then leached with a solution of sulfuric acid and potassium sulfate. After clarification of the leachate, potassium alum is crystallized out. Hydrothermal treatment of potassium alum precipitates a basic potassium alum, K2S04-3A1203 4S03-9H20, simultaneously regenerating potassium sulfate and sulfuric acid. Calcination of this potassium alum yields a mixture of alumina and potassium sulfate, which is leached out. Piloted by Kalunite in Salt Lake City, UT, in 1943 but later abandoned. See also Alumet. 

Figure 1.8. Micrographs of product nuclei formed on dehydration of alums. For more detailed explanations see reference [30]. (Reproduced with permission of the Royal Society, London.)...

Coalesence of neighbouring nuclei decreases the acceleratory contribution, leading to the deceleratory behaviour characteristic of the later stages of reaction. Hemispherical nuclei, indicative of equal rates of growth in all directions, are found, for example, in the decomposition of barium azide [17] and in the dehydration of chrome alum [10,19,20]. Other reactions develop nuclei of different shapes characteristic of preferred advance in certain ciysteillographic directions. 

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