Composition Of Solid Phase Research Articles

Phase Equilibria in Ferrous Calcium Silicate Slags: Part I. Intermediate Oxygen Partial Pressures in the Temperature Range 1200 °C to 1350 °C

Ferrous calcium silicate slags are used in primary and secondary metallurgical processes (described by the FeO-Fe2O3-CaO-SiO2 system). Despite the industrial and scientific importance of this system, the phase equilibria have not been fully investigated. Characterization of this slag system is necessary to improve the design and optimization of new and existing metallurgical processes, particularly in relation to fluxing practice and operating temperatures. Experimental methods have been developed to investigate the phase equilibria of these slags involving the equilibration of samples at fixed oxygen partial pressures, rapid quenching, and the analysis of the compositions of solid and liquid phases using electron probe X-ray microanalysis (EPMA) with wavelength dispersive detectors. Liquidus and solidus data are reported for the primary phase fields of spinel, pseudo-wollastonite, and tridymite in the temperature range of 1200 °C to 1350 °C at an oxygen partial pressure of 10−6 atm, and at 1250 °C at an oxygen partial pressure of 10−5 atm. The resulting data have been used to construct liquidus and solidus isotherms in the “FeO”-CaO-SiO2 system directly relevant to industrial processes.

Thermo-sensing silicon–germanium–boron films prepared by plasma for un-cooled micro-bolometers

In this work we report a study of silicon–germanium–boron alloys (a-SixGeyBz:H) deposited by low frequency plasma enhanced chemical vapor deposition (LF PECVD) at relatively low temperatures, which are compatible with the IC silicon technology for applications as low resistance thermo-sensing films in micro-bolometers. Three values of germanium gas content (Gey) were used during the film deposition, Gey=0.3, 0.45 and 0.55. Deposition and film properties were compared with a reference intrinsic film (a-SixGey:H) in order to study the Gey effect on the temperature dependence of conductivity (σ(T)) and specifically on the activation energy (Ea). We observed a variation on the activation energy from Ea=0.34eV to Ea=0.18eV and on the room temperature conductivity from σRT=6×10−5 (Ωcm)−1 to σRT=2.5×10−2 (Ωcm)−1, for the reference intrinsic film and for the boron alloy with Gey=0.55, respectively. The solid phase composition of the films was characterized by SIMS measurements. The effect of patterning the films (μm scale) with photolithography and the deposition on a SiNx micro-bridge on the film electrical properties was also studied.

Sorption of different cations onto clay minerals: Modelling approach with ion exchange and surface complexation

The present article investigates the sorption of heavy metals, U(VI) and Eu(III), as an analog of An(III), on montmorillonite, illite and kaolinite suspensions in aqueous Na-electrolyte solutions by applying the Gibbs energy minimization computer code. Due to the complex nature of the sorption process, several simplifying assumptions should be made to solve the problem. The cation exchange capacity of clays, the density of the aluminol (>AlOH) and silanol (>SiOH) edge-type sites, responsible for the pH-dependent surface complexation, their acidity constants were derived from the reference data and fixed as non-adjustable parameters. The site-binding constants for all selected cations were calculated according to the direct correlations with their aqueous hydrolysis constants, and an exchange parameter K ex was accepted depending on the clay type, the valence of the exchanging cations and the solid to liquid ratio. The last parameters could be adjusted for goodness of fit in some cases. Relatively good correspondence between model sorption edges, distribution coefficients and those from experimental measurements was found; moreover, these observations are also consistent with the conceptual framework of the abundant reference data. The comparative model presented here is aimed to predict sorption uptake of cations over the whole spectrum of conditions in real systems having complex solid phase composition and water chemistries.

Accurate vapor pressure equation for trimethylindium in OMVPE

From the vapor pressure equation of a metalorganic precursor, its partial pressure is calculated. The accuracy of that vapor pressure equation is therefore important when calculating the deposition efficiency of a precursor. Knowing the exact value of the vapor pressure is even more important to accurately plot the solid composition versus gas phase composition in the case of an alloy. For indium-containing Organo-Metallic Vapor Phase Epitaxy (OMVPE), trimethylindium (TMI) has been the preferred precursor. However, the four established vapor pressure equations reported in the literature for TMI have been found to differ significantly. These equations offer overestimated vapor pressure of TMI, often by as much as 20–40%. Not knowing the accurate vapor pressure has been a concern to growers. In this study, we report the comparative evaluation of these four established equations by using accurate measurements of actual consumptions of TMI from its depletion studies, coupled with gas phase concentration studies with Epison III ultrasonic monitor. Our studies conclude that the vapor pressure equation, log P (Torr)=10.98–3204/T (K), provides the most accurate vapor pressures of TMI within a wide range of growth conditions currently used in OMVPE. Also reported are the cylinder design aspects and Uni-Flo™ II cylinder design that lead to stable depletion of TMI under high throughput conditions of temperature, flow and pressure employed industrially.

Coupled thermal, hydraulic and geochemical evolution of pyritic tailings in unsaturated column experiments

The evolution of pore-water and the composition of solid phases in the vadose zone of pyritic tailings was studied by means of unsaturated column experiments. Several columns of water-saturated mine tailings were dried during 125 days under controlled laboratory conditions. The columns were dismantled at four successive drying stages and the evolution of pore-water, mineralogy, water content and temperature was characterized. Sulfide and aluminosilicate minerals present in the waste dissolved, releasing sulfate and other solutes (mainly Fe, Zn, Cu, Al, Mg and Ca) to the pore-water. Evaporation caused a crust of efflorescent, water-soluble sulfates to develop over the complete top surface of the columns and into the pores of the underlying waste material. This crust, which has also been identified in the field, changed the hydraulic properties of the tailings and produced a decrease in the evaporation rate of the columns. Moreover, these water-soluble precipitates (mainly rozenite, szomolnokite, halotrichite, hexahydrite, mirabilite and gypsum) acted as temporary sinks for Cd, Pb, Co and Ni, which could be released to the surface run-off or the groundwaters during rainfall events under field conditions. Pore-water evolution was determined not only by geochemical processes (dissolution of sulfides and aluminosilicates, precipitation of secondary phases) but also by thermal and hydraulic processes. Progressive dilution was observed in the lower part of the columns. Dilution was caused by the thermally driven vapor flux from the top of the column to its colder bottom and subsequent condensation therein. This process, which may also occur in tailings under sub-arid climate, played a key role on the evolution of pore-water with increasing drying.

A population balance model of the solution‐mediated phase transition of citric acid

AbstractThe Solvent‐Mediated Anhydrous to Monohydrate Phase Transition (SMPT) of citric acid in water was monitored using in situ Raman spectroscopy and image analysis. The solid phase composition, solute concentration, and crystal size distribution were measured during experiments designed to investigate the different steps of the SMPT process: dissolution of the metastable form, nucleation, and growth of the stable form. A Population Balance Model (PBE) was developed to depict the time evolutions of the two populations of particles involved. Nucleation and growth phenomena were analyzed and described through simplified kinetic laws. The related kinetic parameters were estimated through the nonlinear least squares minimization of model‐experiments prediction errors. The overall PBE model was finally found to satisfactorily describe the SMTP process; the time variations of the solute concentration and solid phase composition in particular. It is clearly shown that the secondary nucleation of stable monohydrate particles depends on both the supersaturation and the overall solid content. Surprisingly, as far as the nucleation of stable particles in the presence of metastable solid is concerned, the rate of particle generation was found to exhibit identical dependency on the metastable and stable content, a feature which remains to be further investigated and explained. © 2007 American Institute of Chemical Engineers AIChE J, 2007

A study of the solubility of yttrium, praseodymium, neodymium, and gadolinium sulfates in the presence of sodium and potassium in sulfuric-phosphoric acid solutions at 20°C

Solubility of yttrium, praseodymium, neodymium, and gadolinium sulfates in the presence of sodium and potassium ions and the composition of solid phases were studied at 20°C in relation to the concentration of acids in sulfuric acid, phosphoric acid, and sulfuric-phosphoric acid solutions containing up to 36 wt % H2SO4 and 33.12 g 1−1 H3PO4.

Non-isothermal autohydrolysis of barley husks: Product distribution and antioxidant activity of ethyl acetate soluble fractions

Non-isothermal treatments of barley husks in aqueous media were performed under a variety of operational conditions, to cause the hydrolytic degradation of hemicelluloses. The amount and composition of solid and liquid phases were determined. Liquors from treatments were extracted with ethyl acetate in order to remove non-saccharide components (mainly derived from the extractive acid-soluble lignin fractions), and the extracted fractions were quantified and assayed for antioxidant activity using the DPPH radical scavenging test. Posthydrolysis of autohydrolysis liquors led to xylose-containing solutions suitable as fermentation media. The dependence of the major process parameters (concentrations of monosaccharides and monosaccharide-degradation products obtained after autohydrolysis–posthydrolysis, yield of ethyl acetate soluble compounds and antioxidant activity of isolates) on the severity of treatments was assessed. The ethyl acetate soluble fraction obtained under the best processing conditions showed an antioxidant activity in the range reported for synthetic antioxidants.

Xylooligosaccharides Production from Arundo donax

Samples of Arundo donax were subjected to isothermal autohydrolysis, defined by temperature, 150-195 degrees C; time, 0-15 h; and liquor to solid ratio, 8 g/g. The effect of the operational variables on the yield and composition of both liquid and solid phases obtained after the treatments has been studied. The oligomer concentration and composition have been determined. In the conditions leading to maximum oligomers concentration (defined by dimensionlees time theta=1) it can be produced up to 17.7 g oligomers/100 g raw material and four acetyl groups/10 xylose monomers. These oligomers are the mean of 50% of nonvolatile compounds. In these conditions, cellulose is almost quantitatively retained in the solid phase, whereas lignin is solubilized at 9%.

Hydration of alkali-activated slag: thermodynamic modelling

The composition of solid and liquid phases of alkali-activated slag systems was investigated by thermodynamic modelling. The calculations predict the formation of C(–A)–S–H, stratlingite and hydrotalcite in different alkali-activated slag systems, which agrees well with experimental findings. In addition traces of FeS and ettringite are predicted to precipitate. The type of alkaline activator (Na-silicate, NaOH) has no influence on the type of hydrates formed but influences the Ca/Si ratio of the C–S–H. The addition of sodium silicate leads to the formation of C–S–H with a higher Ca/Si ratio (1.1–1.2), whereas NaOH results in a Ca/Si ratio of 0.8to1.1. In contrast, the kind and concentration of the activator has strong influence on the composition of the pore solution. Low concentrations of the alkaline activator result in lower Na, Si and Al concentrations and lower pH values. In all pore solutions a high concentration of sulphide (HS–) is expected to be present.

A Numerical Approach for Multicomponent Vapor Solid Equilibrium Calculations in Gas Hydrate Formation

A new numerical approach has been developed for vapor solid equilibrium calculations and for predicting vapor solid equilibrium constant and composition of vapor and solid phases in gas hydrate formation. Equation of state methods generally do a good job of determining vapor phase properties, but for solid phase it is much more difficult and inaccurate. This proposed new model calculates vapor solid equilibrium constant and vapor and solid phase composition as a function of temperature and partial pressure. The results of this proposed numerical approach, for vapor solid equilibrium, have a good agreement with the available reported data. This new numerical model also has an advantage to tune coefficients, to cover different sets of experimental data accurately.

Quantitative in situ monitoring of citric acid phase transition in water using Raman spectroscopy

Citric acid exhibits two solid (anhydrous/monohydrate) phases in water. Below 34 °C, the more stable form being the monohydrate. This organic compound was selected as a model product to evaluate the continuous monitoring of solvent-mediated phase transition using in situ Raman spectroscopy. Specific calibration of the spectral data was developed at 15 °C for assessing in-line both the overall solid concentration in suspension (from 5% to 25%, w/w) and the composition of the solid phase (from 0% to 100% content of anhydrous). It is shown that, in addition to such key-measurements, supersaturation can also be computed in-line from the mass balance of the solute. In order to validate the technique, seeded phase transition experiments were performed at 15 °C and the kinetic process involved during the transition of anhydrous to monohydrate was successfully monitored. Both overall solid concentration and solid phase composition measurements were validated using off-line analytical methods (titration of solute concentration and DSC, respectively). The accuracy of the Raman measurements was found to be of the order of 5%.

Initial Condition and Calculation Method for the Numerical Simulation of LPE

A diffusion-limited model has been used to describe supersaturation in liquid phase epitaxy (LPE). LPE is not often treated in chemical engineering, but the equations in a diffusion-limited model are similar to those used in thermal engineering. Therefore, we can deal with these equations analytically and solve them numerically. This paper solves the problem that the numerical solutions of the diffusion-limited model depend on the mesh sizes and comprises two parts. The first part provides an update of the traditional equation to describe the initial condition in the diffusion-limited model. The second part is a proposal of methods to calculate the compositional variation using the diffusion-limited model. The mesh sizes for the numerical simulations are determined systematically to calculate the solid phase composition within a desired tolerance limit.

Quarter-Salt Formation Defining the Anomalous Temperature Dependence of the Aqueous Solubility of Sodium Monododecyl Phosphate

The salts of monoalkyl phosphates (MAPs) have been identified as a class of inherently mild surfactants for use in household and personal products. They represent an anionic species intermediate in terms of pKa between the sulfates and the carboxylates and are analogous to the carboxylates in that they form acid-salts (which are here termed quarter-salts)-hydrogen-bonded dimers consisting of an undissociated MAP acid and an MAP monosalt. These complexes precipitate from solutions of the monosalt over a range of lower MAP concentrations giving rise to an unusual solubility/temperature relationship. The solubility of monosodium monododecyl phosphate (NaC(12)MAP) increases with temperature up to 0.01 M at approximately 60 degrees C, which corresponds to the conventional Krafft point as shown by the appearance of micelles in solution. The solubility then increases further to approximately 0.04 M as the solubility temperature declines from 60 to 38 degrees C. The transition between these two trends is characterized by a rather sharp temperature maximum in the solubility curve. In a third stage, the solubility then rises rapidly with very small change of temperature. This unusual overall behavior is shown to correspond with three distinct solid-phase compositions for the precipitates at temperatures below the solubility curve. At the lowest concentrations and up through the Krafft Point, the solid phase has been identified as the stoichiometric quarter-salt. Over the declining temperature portion of the solubility curve, the supernatant solution coexists with a macroscopic mixture of separate quarter-salt and monosalt solids. In the high-concentration third region the solid phase is exclusively the MAP monosalt. The coprecipitation of quarter-salt and monosalt from the monosalt solution occurs reversibly in the declining portion of the solubility curve and is accompanied by an increase in pH. The four phase system (solution, vapor, and two pure solid phases) retains one degree of freedom according to the phase rule since the system is in effect three component in that region.

A study of the composition of solid phases formed in the reaction of titanite with phosphoric acid

The composition and structure of titanium phosphate products formed in decomposition of titanite with phosphoric acid were studied. The sorption capacity of the products obtained for alkali and alkaline-earth elements was determined. The possibility of using phosphate products as titanium-containing pigment fillers was examined.

Thermodynamic Study of Heavy Metals Behaviour During Municipal Waste Incineration

The incineration of municipal solid waste (MSW) contributes significantly to the presence of heavy metals in urban area aerosols. It is thus important to ascertain the quantities and chemical forms of the heavy metals (HM) that are emitted from the incineration plant stacks. The behaviour of HM, which depends strongly on the thermal and chemical environments, was investigated herein with a modelling approach, consisting of several parts. First, a refuse bed combustion model was developed for simulating on-grate MSW incineration. It describes most of the physico-chemical and thermal phenomena occurring during waste combustion. Second, results from the bed model were taken as boundary conditions to perform 3D simulations of the post-combustion zone and of the boiler. The case studied was of the Strasbourg incineration plant. Finally, the local thermal conditions and the local elementary compositions of gas and solid phases obtained from these simulations were used to carry out thermodynamic calculations of the speciation of HM at each point in the incinerator. The results for four metals (Cd, Zn, Pb, Cr) are presented, discussed and compared to available data. Predicted species are in agreement with observations for volatile metals, except lead, whose volatilization seems overestimated.

A pulse plating method for the electrosynthesis of ZnSe

Polycrystalline, thin films of ZnSe semiconductor compound were formed by cathodic electrodeposition from acidic aqueous selenite solutions of zinc sulphate, by using a potentiodynamic technique involving the application of repeated double pulses of controlled potential. Conditions for obtaining coherently uniform deposits with enhanced ZnSe to Se ratios were specified, on the basis of X-ray diffraction (XRD) and scanning electron microscopy results, by investigating the combined effect of the potential and length of each pulse as determined by duty cycle and frequency. It was shown that pulse plating process is a viable alternative to potentiostatic electrodeposition allowing improved control of the solid phase composition.

Physicochemical modeling of precipitating and dissolving of gypsum in chloride solutions

Physicochemical modeling is used to study the isolation of sulfate ions as α (β)-CaSO4 · 2H2O from aqueous solutions. The equilibrium compositions of liquid, solid, and gas phases of the NA2SO4-CaCl2-CO2-H2O system are calculated at 25°C, CO2 partial pressures of 10−1.53 kPa, CaCl2/Na2SO4 molar ratios of 0.2–3.0, and CaCl2 concentrations from 0.01 to 0.15 mol/kgH2O. The Gibbs energies of formation for α(β)-gypsum were determined from experimental solubility data on the α(β)-gypsum-air-water system by solving the inverse problem of physicochemical modeling. The data obtained are ΔG° f298 (α-CaSO4 · 2H2O) = −1796.446 kJ/mol and G° f298 (β-CaSO4 · 2H2)) = −1797.317 kJ/mol.

Layer development and growth history of polycrystalline zeolite A membranes synthesised from a clear solution

A case study is presented on the specific layer growth history of an α-Al 2O 3 supported NaA zeolite membrane synthesised from a clear solution. Using a defined set of synthesis parameters, the layer development over time (1.0–4.0 h) was described in terms of morphology, growth rate and elemental composition. It was shown that membrane growth proceeds along two distinct morphological pathways over the duration of synthesis – an initial layer of semicrystalline, hemisphere-shaped grains transforming into a fully crystalline layer with cubic morphology at the end of the growth process. A two-step growth rate trend was observed and could be correlated to the respective growth phases within the two underlying morphology types. The development of the hemisphere-shaped grains was associated with a period of accelerated growth during the first 2.5 h of synthesis (3.3 × 10 −10 m s −1), followed by a period of slower growth for the formation of the cubic morphology (1.9 × 10 −10 m s −1). Localised changes in supersaturation, combined with the possible effects of grain crowding, were offered as feasible explanations for the observed morphology and growth rate tendencies. Following the elemental make-up of the developing membrane showed a gradual decrease in the Na/Si ratio with increasing crystallisation times, which was explained by the consumption of the amorphous content in the membrane as growth proceeds. The solid phase compositions (Na/Si ratio) could however not explain the observed morphology and growth rate changes.

Surface-phase equilibria in MBE of strained In1-xGaxAs heteroepitaxcial layers

A thermodynamic analysis of surface-phase equilibria in the MBE growth of In1-xGaxAs layers on lattice-mismatched GaAs and InP substrates is done. It is shown that, in In-stabilized conditions, the substrate-induced strain enhances the arsenic equilibrium pressure over In-Ga-As liquid phase in the whole range of the solid phase composition in the case of GaAs substrate, whereas in the case of the InP substrate, the pressure is enhanced by the strain at x<0.47 and lowered at x>0.47. For both substrates, locking the surface monolayer composition occurs. In the As-stabilized conditions, the strain results in the lattice-pulling effect. [DOI: 10.1380/ejssnt.2006.53]