Alkali Sulfate Research Articles

The distribution of sulfur in present-day clinkers of variable sulfur content

This study focuses on the identification of sulfur-containing phases present in Portland cement clinkers from North American cement plants. The clinkers were studied using X-ray fluorescence, X-ray diffraction, and selective dissolution extraction techniques. The samples contained sulfate levels from a few hundredths of a percent to about 2.5%. The samples were found to contain alkali sulfates, alkali/calcium sulfates, and some sulfate substituted in the silicate phases. In no case was anhydrite (β-CaSO 4) found. The study concludes that under ambient curing conditions, the sulfur-containing phases present in present-day commercial clinkers are unlikely to cause any internal sulfate attack that might lead to expansive stress and cracking.

96/05936 Ash chemistry and sintering

The thermal behavior of a fuel ash is one important factor to consider when fireside slagging and fouling problems in steam boilers are addressed. It is well known that different types of chemical reactions and melts in deposits play an important role in the build-up of problematic fireside deposits. Low viscous melts occur in steam boilers mainly when salt mixtures are present in the ash. Such are Merent mixtures of alkali and earth alkali sulfates, chlorides and carbonates. These mixtures do not melt at a certain temperature but form a melt in a temperature range which in some cases may be several hundreds of degrees. The amount of melt is crucial for the deposit build-up. For some boilers it has been found that roughly 10 - 20 weight-% melt in an ash mixture would be enough to cause extensive deposit formation, while 60 - 80 weight-% melt would already cause the ash to be so wet it would flow down a vertical tube and not cause any further deposit growth.

Hot Corrosion of Austenitic Steel in Molten Alkali Sulphate Deposits at 850°C / Hochtemperaturkorrosion von austenitischem Stahl in Alkalisulfat-Schmelzen bei 850°C

The hot corrosion of austenitic type 347 steel coated with alkali sulphates, namely Na 2 S0 4 , CaSO 4 , K 2 S0 4 and their mixtures, oxidised at 850°C in air has been investigated by measuring the oxidation kinetics. The formation of alkali iron trisulphate (Na,K) 3 Fe(S0 4 ) 3 seems to be responsible for the accelerated corrosion of the steel in a mixture of Na 2 SO 4 + K 2 S0 4 . Na 2 SO 4 + CaSO 4 or CaSO 4 + K 2 S0 4 form low melting eutectics which first attack the protective chromia scales followed by the formation of iron trisulphate as well as fluxing products. The scale morphologies as predicted from mechanistic considerations are in fairly good agreement with the observed morphologies.

Composite effect of solid electrolytes based on alkali carbonates and sulfates

To improve both the thermal stability and the electrical conductivity, alkali ion conducting carbonates and sulfates with admixtures of alkaline earth compounds as well as insulating materials such as γ-Al2O3 were prepared and characterized by conductivity measurements, X-ray studies, DSC and SEM/EDX. The addition of the divalent carbonates and sulphates causes two effects. On the one hand side, the alkali earth compounds can be dissolved depending on the ionic radius to a more or less large extent, which is accompanied by an increase in the electrical conductivity. On the other hand side, a two phase mixture consisting of an excess of dopant is formed with an enhancement in the conductivity and improvement of the mechanical stability. This phenomenon, known as composite effect, could be observed in the following systems Na2CO3-BaCO3, Na2CO3-SrCO3, Na2SO4-BaSO4, K2SO4-BaSO4, Na2SO4-γ-Al203, K2SO4-γ-Al2O3.

Luminescence of europium in alkali sulphates

Abstract Luminescence of Europium in alkali sulphates is reported. Europium is found to be in a trivalent state in Na2SO4 and Li2SO4. In K2SO4, Rb2SO4 and Cs2SO4, both Eu3+ and Eu2+ were found for low concentration of the dopant, but for high concentration, only Eu3+ was present. Further, there was Eu3+ → Eu2+ conversion found, when the samples were exposed to gamma rays. The conversion is very prominent in Rb2SO4. When the samples were annealed to 300°C, there was back conversion to Eu3+. It is suggested that these properties are useful in radiophotoluminescence (RPL) dosimetry of the ionizing radiations. It may furnish a new type of storage phosphor for X-rays.

Waters associated with an active basaltic volcano, Kilauea, Hawaii: Variation in solute sources, 1973–1991

Chemical and isotopic analyses of samples collected from a December 1962-m-deep research borehole at the summit of Kilauea Volcano provide unique time-series data for composition of waters in the uppermost part of its hydrothermal system. These waters have a distinctive geochemical signature: a very low proportion of chloride relative to other anions compared with other Hawaiian waters—thermal (•30°C) or nonthermal (<30°C)—and with most thermal waters of the world. Isotope data demonstrate that the borehole waters are of essentially meteoric origin, with minimal magmatic input. The water chemistry exhibits marked temporal variations, including pronounced short-term (days to weeks) effects of rainfall dilution and longer term (months to years) decline of total solutes. The 1973–1974 samples are Na-sulfate-dominant, but samples collected after July 1975 are (Mg + Ca)-bicarbonate-dominant. This compositional shift, probably abrupt, was associated with an increase in the partial pressure of CO2 ( P CO2) related to volcanic degassing of CO2 accompanying a large eruption (December 31, 1974) and associated intense seismicity. Following the initial sharp increase, the P CO2 then decreased, approaching pre-eruption values in April 1976. Beginning in mid-1975, solute concentrations of the borehole waters decreased substantially, from •45 meq/L to <25 meq/L in only eight months; by 1991, total solute concentrations were <17 meq/L. This decline in solutes cannot be attributed to rainfall dilution and is inferred to reflect the decreasing availability with time of the easily leachable salts of alkali metals and sulfate, which originated in sublimates and fumarolic encrustations in fractures and cavities of rocks along the hydrologic flow paths. The overall chemistry of the summit-borehole waters is largely determined by hydrolysis reactions associated with normal weathering of host tholeiitic basalts on a geologic time scale, despite short-term perturbations in composition caused by rainfall dilution or volcanic activity.

Erosion-corrosion modelling of gas turbine materials for coal-fired combined cycle power generation

The development of coal-fired combined cycle power generation systems is receiving considerable worldwide interest. The successful development and commercialisation of these new systems require that all the component parts are manufactured from appropriate materials and that these materials give predictable in-service performance. Corrosion and erosion-corrosion, resulting from coal derived particulates, deposition and gaseous species, have been identified as potential life limiting factors for these systems. Models to predict these modes of materials degradation are under active development. This paper outlines the development and testing of models suitable for use in gas turbine environments. The complexity of the corrosion processes means that an empirical approach to model development is required whereas a more mechanistic approach can be applied to erosion processes. For hot corrosion conditions, statistically based corrosion models have been produced using laboratory tests for two coatings and a base alloy at typical type I and type II hot corrosion temperatures (900 and 700°C). These models use the parameters of alkali sulphate deposition flux and SO x partial pressure (at each temperature and for set HCl partial pressures), to predict the rate of the most likely localised damage associated with hot corrosion reactions. For erosion-corrosion modelling, a series of laboratory tests have been carried out to investigate erosion behaviour in corrosive conditions appropriate to coal-fired gas turbines. Materials performance data have been obtained from samples located in the hot gas path of the Grimethorpe PFBC pilot plant, under well characterised conditions, for testing the corrosion and erosion-corrosion models. The models successfully predict the materials damage observed in the pilot plant environments.

Numerical simulation of vapour-aerosol dynamics in combustion processes

A computer model (ABC-code) has been constructed to describe the steady one-dimensional aerosol dynamics in combustion processes for gas and particle interactions at post-combustion conditions. The aerosol general dynamic equation has been solved numerically using a discrete-nodal point method for describing the particle size distribution. In the present model we consider those mechanisms that will affect the dynamics of alkali species after volatilisation, i.e. nucleation, condensation, coagulation, chemical reactions and deposition. The main features of the ABC code have been explained and an example calculation has been carried out for simulation of aerosol dynamics and alkali vapour behaviour in a real scale pulverised coal fired boiler. The results show that for predicting the gas phase concentrations of alkali species at different temperatures it is important to know the volatilisation of sodium, potassium, chlorine and sulphur and the formation rate of alkali sulphates in the gas phase. The initial ash size distribution determines the distribution of condensed alkalis between sub- and supermicron particle modes. The choice of the homogeneous nucleation model has some importance for the calculated submicron number size distribution. The effect of heterogeneous nucleation to initiate condensation on ash particles was negligible. The predictions of our simulation are in a qualitative agreement with the experimental results. The utilisation of the present code will lead to a better understanding of aerosol behaviour which will be of great importance for the control of toxic flue gas emissions, slagging and fouling in commercial boilers.

Microcalorimetric investigations of the interactions of small ions with arterial elastin.

The enthalpies of interactions of porcine arterial elastin with alkali metal and alkali earth halides and sulphates were investigated by means of flow microcalorimetry and the stoichiometry measured using radiotracer techniques. In aqueous solutions, all alkali earth halides interacted exothermically at concentrations ranging from 0.01 to 2.5M. All the alkali metal halides, particularly NaCl, exhibited complex concentration-dependent interactions, exothermic at low concentrations and endothermic at high concentrations. Both the anion and cation contributed to the response, although the anion seemed to dominate. SO4(-2) interacted most strongly of the anions tested. All interactions were reversible in the sense that repeat experiments gave identical results, but the enthalpy of "adsorption" was generally different from that of "desorption." The enthalpy of interaction depended on the conformation of the elastin in a salt-specific manner. For example, CaCl2 and MgCl2 interacted similarly in water but very differently in 1:1 water:methanol.

Effects of added alkali hydroxides in mix water on long-term SO 42− concentrations in pore solution

In ASR (alkali silica reaction) studies it has become common to pre-dissolve NaOH or KOH in the mix water to simulate the effects of high alkali content cements. It has been found that such treatment does not result in the expected augmentation of the OH − ion concentrations, and much or all of the dissolved alkali hydroxide is immediately converted to alkali sulfate by reaction with gypsum. Much of the dissolved sulfate so produced remains in the pore solution under long-term exposure at 38°C, the common temperature employed in ASR studies. The concentration of SO 4 2− ions produced at a given alkali hydroxide dosage varies with the specific hydroxide added, increasing in the order LiOH to NaOH to KOH. If ASR reaction is occuring, the SO 4 2− ion concentration diminishes progressively with time. This effect was not due to progressive incorporation of sulfate in the ASR reaction product, as had been suspected. It may be due to secondary ettringite precipitation in ASR-induced cracks.

ChemInform Abstract: Oxidative Coupling of Methane Over Alkali Sulphates in the Presence and Absence of Tetrachloromethane.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Oxidative coupling of methane over alkali sulphates in the presence and absence of tetrachloromethane

The catalytic oxidation of methane has been investigated on Li, Na, K, Rb and Cs sulphates. The addition of small quantities of tetrachloromethane (TCM) to the reactant stream significantly improves the catalytic activity of each sulfate at 835°C. The conversion of methane on each catalyst in the presence of TCM is found to be approximately correlated with the electronegativities of the cations. The X-ray diffraction pattern for K 2SO 4 after the reaction with TCM shows the presence of the chloride in the catalyst. It appears that the improvement of the catalytic activity with TCM in the feedstream is primarily due to the formation of the chloride during the reaction.

Application of integral‐equation theory to aqueous two‐phase partitioning systems

AbstractA molecular‐thermodynamic model is developed for representing thermodynamic properties of aqueous two‐phase systems containing polymers, electrolytes, and proteins. The model is based on McMillan‐Mayer solution theory and the generalized mean‐spherical approximation to account for electrostatic forces between unlike ions. The Boublik‐Mansoori equation of state for hard‐sphere mixtures is coupled with the osmotic virial expansion truncated after the second‐virial terms to account for short‐range forces between molecules.Osmotic second virial coefficients are reported from low‐angle laser‐light scattering (LALLS) data for binary and ternary aqueous solutions containing polymers and proteins. Ion‐polymer specific‐interaction coefficients are determined from osmoticpressure data for aqueous solutions containing a water‐soluble polymer and an alkali chloride, phosphate or sulfate salt.When coupled with LALLS and osmotic‐pressure data reported here, the model is used to predict liquid‐liquid equilibria, protein partition coefficients, and electrostatic potentials between phases for both polymer‐polymer and polymer‐salt aqueous two‐phase systems. For bovine serum albumin, lysozyme, and α‐chymotrypsin, predicted partition coefficients are in excellent agreement with experiment.

Chromium content in human skin after in vitro application of ordinary cement and ferrous‐sulphate‐reduced cement

The amount of chromium found in human skin after in vitro application of cement suspensions on full-thickness human skin in diffusion cells was investigated. Cement suspensions made from ordinary Portland cement or Portland cement with the chromate reduced with added ferrous sulphate were used. The cement suspensions were either applied on the skin surface under occlusion for 48 h or applied repeatedly every 24 h for 96 h. No statistically significant difference in chromium content of skin layers between skin exposed to ordinary Portland cement, skin exposed to cement with added ferrous sulphate and unexposed skin was observed, despite a more permeable skin barrier at the alkaline pH of the cement suspensions, i.e., pH 12.5. Increased chromium levels in epidermis and dermis were seen when ordinary Portland cement was applied as a suspension with added sodium sulphate (20%) on the skin surface for 96 h. The content of water-soluble chromium in ordinary Portland cement may vary due to the alkali sulphate content of the cement.

Chemistry of deposit formation in a coal gasification syngas cooler

During entrained slagging coal gasification utilizing syngas coolers (waste heat boilers), submicrometre to 10 μm spherical ash particles can be deposited as a fouling layer on the water wall tubes. Unlike conventional pulverized-coal-fired boilers, the conditions within the gasification process are reducing ( P o 2 = 10 −11; P s 2 = 10 −5 atm). Metal sulfides along with fluoride and chloride compounds have been identified on the water wall and on the outer surfaces of the fly-ash particles, whereas alkali sulfates and iron oxide compounds are commonly repeated in layers responsible for fouling in the convection and superheater sections of coal-fired boilers. Once the initial fouling layer is formed, fly ash can adhere to it if an improper soot blowing design is chosen. The hardness and size of the deposit is a function of ash chemistry and fluid dynamics.

Absorption, Emission, and Thermoluminescence of Copper Doped Alkali Sulphate Phosphors

AbstractResults of optical absorption (OA), fluorescence, and thermoluminescence (TL) studies made on copper doped sulphates of cesium, rubidium, and potassium are reported and discussed. Optical absorption spectra revealed that the impurity enters these lattices in both its mono‐ and divalent states. Fluorescent emission of Cu+ is detected in the three phosphors. Both Cu+ and Cu2+ are found to be acting as electron traps when the samples are exposed to γ‐rays. Absorption due to Cu0 thus formed is detected around 3.45 eV in the irradiated samples. TL glow curves show a three‐peak pattern and are assigned to the thermal mobilization of hole centres formed during irradiation. Unlike in alkali halides, the TL emission spectra do not always contain the characteristic Cu+ emission band.

Microstructural investigation of natural deterioration of building materials in Gothenburg, Sweden

Site investigations of several concrete and masonry structures in Gothenburg, Sweden, revealed carbonation to have affected a number of concrete structures. At times, synergistic freeze-thaw action was found to have accelerated the deterioration process. Some of the masonry structures have developed internal and external efflorescence (the latter much more severe) in the form of alkali sulphate salts. The mechanisms involved in these processes and the influence of microclimatic conditions are discussed. The products formed that were mainly investigated by microstructural techniques (SEM with energy-dispersive X-ray analysis, X-ray diffraction analysis) are also described.

The fate of organically bound inorganic elements and sodium chloride during fluidized bed combustion of high sodium, high sulphur low rank coals

A series of experiments has been conducted to study the transformations of the organically bound inorganic elements and inherent sodium chloride under conditions relevant to fluidized bed combustion of low rank coals. Large coal particles (5.5–9.0 mm) were suspended in a convective gas flow in a single particle furnace operated at 700–830 °C. The experiments were performed under pyrolysis as well as combustion conditions. The product particles withdrawn from the furnace at various residence times were analysed using chemical methods, X-ray diffraction and electron microscopy. It was found that the transformations of the inorganic matter in high sodium, high sulphur low rank coals result in the formation of a molten ash layer on the char surface, providing evidence of the formation of low melting point eutectics. The molten ash consisted of a matrix of mixed alkali sulphates. The findings are expected to assist in explaining the role of the inorganic matter in causing operational problems during the fluidized bed combustion of low quality, low rank coals.

Thermoluminescence in mixed alkali sulphate phosphors

Abstract In this paper we report for the first time thermoluminescence in mixed alkali sulphate materials. Very intense thermoluminescence was found out in most of the phosphors, emission in Eu doped NaKSO4 and LiNaSO4 being much stronger than that observed in even the applied materials like CaSO4,: Dy. The glow peaks in most of the phosphors were rather too close to room temperature to prevent the fading. It is suggested that the improved preparations might increase the glow peak temperature and then these phosphors will be better than CaSO4: Dy.

The alkali-cement system

The effect of different concentrations of alkali metal hydroxide and sulphate solutions on the setting behaviour of ordinary Portland cement (OPC) and the compressive strength of mortars aged up to three months is studied. Potassium hydroxide solution has the greatest negative effect on the properties studied; around 35% reduction in the final setting time and late strength are attained by mixing with 1 M KOH. Solutions of potassium sulphate also cause a greater strength lowering than the sodium salt. The mechanism of setting is interpreted on the basis of the results obtained from the hydration reaction of pure cement system.