Alkali-metal Sulphates

Early discussions, by Tammann and by Hedvall, considered the possible existence of a common characteristic (approximate) temperature for a solid at which chemical interactions with other reactants became detectable. For example [111], such a characteristic temperature for CaO, measured in various reactions with CuS04, Co3(P04)2, MgC03, and MnSi03, was found to be 788—838 K. Similarly, the onset of reaction of BaO with the sulphates of Mg, Ca, Sr, Co, Cu, and Zn occurred between 601 and 645 K. In the latter example, it has been shown that the fusion of Ba(OH)2 (an impurity not easily excluded from BaO) could contribute to the initiation of reaction. Eutectic formation during the reactions of BaCl2 with alkali metal sulphates... 

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 Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning.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. 

Krupay and Ross83 studied the influence of the addition of alkali metal sulphates to V205 on the reaction between CO and N20. Some curious discrepancies in their paper unfortunately invalidate some of their conclusions. 

Ai85,86 is discussed on p. 114. Agarwal et al.102 as well as Sharma et al.103 studied this reaction using silica-supported V2Os-alkali metal sulphate catalysts. A two-step oxidation-reduction mechanism gave the best description of the process. The activity increased with increasing atomic number of the added alkali metal for which no interpretation was offered. In an electron microscopic study of these catalysts Sharma et al.103 showed that K2 S04 and V2 05 are present as separate phases but that the sulphate causes the presence of a larger amount of V2 05 in the form of needle-like crystals which appear to be more active for the methanol oxidation. A similar result was obtained by these authors for catalytic oxidation of toluene over these catalysts.104... 

The mercurosulphate electrode is most suitable for work with the sulphate solutions. It is prepared analogously as the calomel electrode, with one exception that the paste is composed of mercurous sulphate, ground together with mercury and an alkali metal sulphate solution of a definite concentration. In the electrode the equilibrium is attained, according to the equation... 

I carbonates Co-Na, Co-K, Ni-Na, Ni-K nitrates Zn-alkali metals sulphates (schoenites) Mg-Na carbonates Al-K, Ce-Na nitrates rare earth-alkali metals sulphates (alums) Me111-alkali metals carbonates Ce-alkali metals nitrates Ce-alkali metals sulphates U-alkali metals alkali metals vanadates alkali metal chromates, Ag chromate, alkali metal molybdates and tungstates... 

Ammonium nitrate, NH4NOa.—The nitrate can be prepared by the general methods applicable to the ammonium salts. It is also produced by heating the nitrate of an alkali-metal with ammonium sulphate at 160° to 200° C., the fused ammonium nitrate being separated from the solid alkali-metal sulphate by centrifuging.11 Another method consists in cooling a concentrated solution of sodium nitrate and ammonium sulphate to —15° C., sodium sulphate being precipitated. On evaporation of the mother-liquor, most of the sodium sulphate is deposited addition of nitric acid to the clear solution causes crystallization of the ammonium nitrate.12 When sodium nitrate is... 

The rate of alkali-metal sulphate deposition will decrease when the temperature of collecting target surface exceeds 1075 K as shown in Figure 2. The decrease in the deposition of alkali-metal sulphates is related to the concentration of the volatile alkali-metals in the flue gas and the saturation vapour pressure of sodium and potassium sulphates ( ). The initial deposit on cooled surfaces contains a small amount of chloride as shown in Figure 2. 

Alkali-metal sulphates frequently constitute a liquid phase in ash deposits, and the molten sulphates readily wet and spread on the surface of boiler tubes. In a reducing atmosphere and when in contact with carbon, sulphates are reduced to sulphides which wet and spread on any surface. The coefficient of surface tension of sulphates is fairly high, 0.20 N m" for Na2SO4 and 0.14 N m" for K2SO4 near their respective melting point temperatures (25,26). ... 

Initial Deposit. The initial deposit material on cooled tubes in coal fired boilers consists largely of flame vitrified silicate ash, iron oxide, and calcium and alkali-metal sulphates. Trace amounts of chloride will also deposit and under reducing conditions some iron and calcium sulphides can be present. 

Y. Kaneko and H. Kojima, Dissociation Behaviour of Vanadium Dioxide and Basicity in Fused Alkali Metal Sulphate Mixtures, Proceedings of the First International Symposium on Molten Salts Chemical Technology, 1983) pp. 441-444. 

Method for improving the dyeing of protein fibres of either peanut or soya bean fibres with acid wool dyes using alkali metal sulphate solutions acidified with sulphuric acid as the coagulating bath... 

Catalyst and Alkali Metal Sulphate Mixture Recommended ... 

Hot corrosion is a complex phenomenon involving sulphidation, oxidation or both. Hot corrosion is a form of accelerated oxidation which affects the surfaces exposed to high-temperature gases contaminated with sulphur and alkali metal salts. These contaminants combine in the gas phase to form alkali metal sulphates. If the temperature of the alloy or coating surface is below the dew point of the alkali sulphate vapours and above the sulphate melting points, molten sulphate deposits are formed. Molten sodium sulphate is the principal agent in causing hot corrosion. 

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