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Alkali sulphates

Superheater/reheater corrosion in fossil-fuel-fired boilers is caused by the deposition of alkali sulphates on to the tube surfaceThe corrosion rates increase rapidly at temperatures above 600°C as the sulphates become molten. These molten sulphates contain free SO3 which dissolves the protective oxide to form Fe-based sulphates. The corrosivity of the molten sulphates depends strongly upon their melting points, which are themselves strongly dependent upon the ratio of Na and K in the deposits. [Pg.990]

Reactions of contaminants in the fuel or air in the combustion zone can result in the formation of compounds which can condense as molten salts onto cooler components in the system. This type of process can occur when fuels containing sulphur or vanadium are burnt. In the case of sulphur contaminants, alkali sulphates form by reactions with sodium which may also be present in the fuel or in the combustion air, and for vanadium-containing fuels low-melting-point sodium vanadates or vanadium pentoxide are produced, particularly when burning residual oils high in vanadium. Attack by molten salts has many features in common which will be illustrated for the alkali-sulphate-induced attack, but which will be subsequently shown to be relevant to the case of vanadate attack. [Pg.1064]

Medium acid baths, pH 4-5 At this acidity a dichromate solution plus sulphate ion as activator is sufficient to deposit chromate films in 30 min or so at room temperature or in a few minutes at boiling point. Unfortunately, a solution of alkali dichromate and alkali sulphate is quite unbuffered, and other substances must be added to give the bath a useful life over the working pH range. Acetates have been used successfully, but salts of aluminium, chromium, manganese and zinc have been more commonly employed. The pH of the solution rises slowly during use until basic chromates or sulphates begin to precipitate. The solution can then be rejuvenated by the addition of chromic or sulphuric acid or acid salts. [Pg.728]

Procedure. The sample solution should preferably contain titanium as sulphate in sulphuric acid solution, and be free from the interfering constituents mentioned above. The final acidity may vary from 0.75 to 1.75M. If iron is present in appreciable amounts, add dilute phosphoric(V) acid from a burette until the yellow colour of the iron(III) is eliminated the same amount of phosphoric(V) acid must be added to the standards. If alkali sulphates are present in the test solution in appreciable quantity, add a like amount to the standards. Add 10 mL of 3 per cent hydrogen peroxide solution and dilute the solution to 100 mL in a graduated flask the final concentration of Ti may conveniently be 2-25 parts per million. Compare the colour produced by the unknown solution with that of standards of similar composition by any of the usual methods. [Pg.697]

Exhaustive oxidation of sulphones to sulphate using a mixture of potassium chlorate, sodium peroxide and sugar in a bomb has also been recommended220. This procedure is known as the Parr method and produces a mixture of soluble alkali sulphates. [Pg.995]

The production of sulphuric acid by the contact process, introduced in about 1875, was the first process of industrial significance to utilize heterogeneous catalysts. In this process, SO2 was oxidized on a platinum catalyst to S03, which was subsequently absorbed in aqueous sulphuric acid. Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning. Further development of the vanadium catalysts over the last decades has led to highly optimized modem sulphuric acid catalysts, which are all based on the vanadium-alkali sulphate system. [Pg.312]

In general, lack of equilibrium during the pyro-processing stage and heterogeneity of composition make it impractical to calculate the phase content of fly ash from its chemical analysis. Two other factors, common to all types of fly ash, further complicate evaluation of the potential to use fly ash. One is the presence of unburnt carbon, which should preferably not exceed a few wt% the other is the presence of alkali-sulphates (see Groppo et al., 2004). When used in cementitious formulations, free... [Pg.216]

Thompson Argent 2002) predicts the formation of an alkali sulphate-based melt, with the majority of the other elements also forming sulphates, implying a complex melt and solid solution(s) based on sulphates. At the present, information on the activity of cations in mixed sulphate melts is lacking and identification of actual phases is difficult because of the problem of concentrating the sulphate fraction. It is therefore difficult to predict with certainty exactly how a fly ash sample will behave in water and hence the need for standardized leaching tests. [Pg.624]

Rare earth doped alkali sulphates are of interest because of their optical properties. EPR spectra of y-irradiated Ce and Ce-U doped KjNa(S04)2 exhibited signals characteristic of a S04T SOjT radical pair.34 The dipolar splitting (32 G) corresponds to r = 9.8 A. The radical pairs create deep traps, apparently assisted by dopants. [Pg.322]

The alkali sulphates can also be made by neutralizing, say, a soln. of 5 grms. of sulphuric acid in 30 c.c. of water with the alkali hydroxide or carbonate, and evaporating the soln. until crystals begin to form. The process is not economical except on a small scale. It is used mainly for lithium, rubidium, and caesium sulphates. H. Erdmann 20 treated a hot soln. of crude rubidium iron alum with milk of lime made from purified lime, and filtered the liquid from the excess of lime, calcium sulphate, and ferric hydroxide, by suction. The small amount of lime in soln. is precipitated by adding rubidium carbonate. The filtrate is neutralized with sulphuric acid, and evaporated to the point of crystallization. [Pg.660]

The properties of the alkali sulphates.—Lithium sulphate can be prepared as the anhydrous and hydrated as monohydrated lithium sulphate, Li2S04.H20 and sodium sulphate as the anhydrous salt, as heptahydrated sodium sulphate, NaS04-7H20 and decahydrated sodium sulphate, Na2S04-10H20. Mono- and trihydrated sodium salts have been reported—the former by J. Thomsen,22 the latter by H. Rose—but L. G. de Goppet has questioned the two last-named hydrates. [Pg.660]

Table XXXVI.—Some Crystallographic Constants op the Alkali Sulphates. Table XXXVI.—Some Crystallographic Constants op the Alkali Sulphates.
The capillary constants 31 of molten sodium and potassium sulphate are respectively a2=17 64 and 17 25 sq. mm. while the surface tensions are respectively 182 and 177 7 dynes per cm. F. M. Jager s values for the surface tension (dynes per cm.), sp. gr., and mol. surface energy (ergs per sq. cm.) of molten alkali sulphates are indicated in Table XXXVIII. [Pg.663]

The best representative values for the melting points of the anhydrous alkali sulphates 33 are... [Pg.663]

The heats of formation 36 of anhydrous alkali sulphates from their elements is... [Pg.664]

The water solubilities of the alkali sulphates, expressed in grams of anhydrous salt per 100 grins, of soln., are... [Pg.664]

The alkali sulphites and bisulphites are produced on the large scale by treating lime and magnesia or dolomitic limestone with sulphur dioxide in the presence of water, then adding the requisite amount of alkali sulphate to the filtrate and filtering off any insoluble sulphate 3 or, alkali carbonate or bicarbonate may be treated directly with sulphur dioxide.4... [Pg.131]

Sulphuric acid is oxidised to permonosulphuric, perdisulphuric and fluorosulphonic acids when an ice-cold aqueous solution is treated with fluorine. In addition to the foregoing products, ozone and a very unstable compound believed to be a tetroxide (S04 or S2Os) are also produced.5 A similar oxidation occurs when fluorine is passed into cold solutions of alkali sulphates or hydrogen sulphates. [Pg.171]

Berthelot s experiments and conclusions have not been fully confirmed, however. According to Meyer and his co-workers,5 the crystalline product described is only formed when sulphur trioxide is present in excess, and may be regarded as an equimoleculax mixture of sulphur trioxide and sulphur 1etroxi.de, S04. There is evidence that the latter compound is produced during the oxidation of cold solutions of sulphuric acid (2-35 molar) or of alkali sulphates.8... [Pg.180]

The decomposition of the alkali perdisulphates in aqueous solution is retarded by the presence of added alkali sulphates. The influence... [Pg.183]


See other pages where Alkali sulphates is mentioned: [Pg.961]    [Pg.1064]    [Pg.175]    [Pg.216]    [Pg.219]    [Pg.214]    [Pg.249]    [Pg.492]    [Pg.497]    [Pg.499]    [Pg.528]    [Pg.656]    [Pg.662]    [Pg.662]    [Pg.662]    [Pg.663]    [Pg.671]    [Pg.672]    [Pg.677]    [Pg.685]    [Pg.696]    [Pg.705]    [Pg.705]    [Pg.712]    [Pg.718]    [Pg.722]    [Pg.830]    [Pg.880]    [Pg.899]    [Pg.877]   
See also in sourсe #XX -- [ Pg.218 , Pg.506 ]




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