Thermogravimetric Studies of Solid-Phase Reactions in the System MgO – Al2O3 – SiO2 and Their Analysis in Terms of Graph Theory

Changes in the phase composition of the MgO – Al₂O₃ – SiO₂ system in the subsolidus region are studied by the thermogravimetric method. Specific features of the DTA curves are correlated with periodic changes in the concentration of phases involved in chemical reversible solid-phase reactions. Critical kinetic effects associated with conjugated solid-phase reactions in the MgO – Al₂O₃ – SiO₂ system are discussed in terms of graph theory. The phase composition of materials with a dissipative structure is shown to form by a self-organization mechanism.     

Na0.5Bi0.5TiO3 phase relations: Thermodynamics and phase equilibria in the systems Bi2O3 – TiO2, Na2O – TiO2, and Na2O – Bi2O3 – TiO2

The lead-free piezoelectric material sodium bismuth titanate (NBT, Na_0.5Bi_0.5TiO₃) has attracted considerable attention owing to its promising dielectric, piezoelectric, and electrical properties. However, the literature on the binary subsystems is contradictory and there are only limited data for the ternary system. The present work surveys all of the reports of the binary subsystems Bi₂O₃ – TiO₂ and Na₂O – TiO₂ and synthesizes these data into inclusive revised versions. The compatibilities for the ternary system Na₂O – Bi₂O₃ – TiO₂ were determined experimentally, thus enabling the construction of a complete isothermal section at 800 °C. The compatibilities associated with the problematic binary subsystem Na₂O – Bi₂O₃, which experiences extreme volatilisation, were determined through the generation of the absent standard-state thermodynamic functions for the relevant binary and ternary phases, thus providing a full suite of thermodynamic data for this system. The thermodynamic stability diagrams for Na₂O, Bi₂O₃, and TiO₂ thus were calculated. The isothermal section also addresses the contradictions in the literature concerning the formation of solid solutions of Bi₁₂TiO_20-x / Bi_12-xTi_1+xO_20+0.5x, pyrochlore (Bi₂Ti₂O₇ / Na_wBi_2-xTi_2-yO_7-z), BTO (Bi₄Ti₃O₁₂ / Na_xBi₄Ti₃O_12+0.5x), and NBT (Na_0.5Bi_0.5TiO₃ / Bi_1±xNa_xTiO_3.5±x). Further, it was observed that the congruent melting point of NBT, which was determined to be 1225 °C, was preceded by the onset of gradual structural destabilization at 940 °C. Also, the NBT rhombohedral → tetragonal phase transformation was observed at an onset temperature of ∼250 °C. The present work thus provides platform data for the fabrication and reactivities of materials in the ternary system Na₂O – Bi₂O₃· TiO₂ and its binary subsystems.     

On the Subsolidus Structure in the CaAl4O7 – Ca7Al6ZrO18 – CaAl2O4 – CaZrO3 – SrZrO3 – SrAl2O4 Region of the CaO – SrO – Al2O3 – ZrO2 System

The subsolidus structure of the CA₂ – C₇A₃Z – CA – CZ – SrZ – SrA region of the CaO – SrO – Al₂O₃ – ZrO₂ system is studied. The occurrence of the solid-phase reaction between strontium aluminate and calcium zirconate is considered from the standpoint of thermodynamics. The conodes, three-component sections, and elementary tetrahedrons are studied in the given region. A promising region for the production of special cements is determined, and rapidly hardening, high-strength, and refractory binding materials are obtained in it.     

Synthesis and Properties of Fusion-Cast Refractories in the Al2O3 – B2O3 System

Synthesis and properties of fusion-cast high-alumina refractories in the Al₂O₃ – B₂O₃ system are reported. Adding B₂O₃ is shown to improve density and fabricability of the fusion-cast products. As shown by x-ray diffractometry and petrographic analysis, the phase composition of synthetic products is represented by corundum and 9Al₂O₃ 2B₂O₃ boroaluminate. Corrosion tests in molten industrial glasses have shown the potential use of these materials in the melting technology of VS-92-grade optical lead silicate glass.     

Oxidation of Herbicides in Groundwater by the Fenton Process: A Realistic Alternative for O3/H2O2 Treatment?

Oxidation with O₃/H₂O₂ and Fe²⁺/H₂O₂ are optional for the degradation of herbicides and pesticides in water. The choice of which process will be applied depends upon the degree of degradation of organic micropollutants and the process conditions related to the formation of oxidation by-products, and also on the total costs and the safety and reliability of the process. Under real conditions, atrazine and some phenylureaherbicides were oxidized with O₃/H₂O₂. Comparable experiments under conditions of different pH, iron and DOC content were performed with Fe²⁺/H₂O₂, in order to gain information on the influence of these parameters. The oxidation results of both processes as well as the formation of bromate as one of the oxidation by-products are described. It was found that 80% of atrazine and >99% of some phenylureaherbicides could be degraded with O₃/H₂O₂ at pH 7.8 (H₂O₂/O₃ ratio 3.7 g/g). Under these conditions, bromate was formed up to 5 μg/1. Comparable results were obtained with Fe²⁺/H₂O₂ at a pH value of 5.5, whereas the formation of bromate was kept below 0.2 μg/L.     

Carbon Deposition and Catalytic Deactivation during CO2 Reforming of CH4 over Co/γ-Al2O3 Catalysts

The reaction behavior and carbon deposition during the CO₂/CH₄ reforming reaction have been investigated over the γ-Al₂O₃-supported Co catalysts as a function of Co loading (between 2 and 20 wt%) and calcination temperature (T_c=500 or 1000°C). It was found that the stability of Co/γ-Al₂O₃ catalysts was strongly dependent on the Co loading and calcination temperature. For some loadings (6 wt% for T_c=500°C and 9 wt% for T_c=1000°C), stable activities have been achieved. However, over the catalysts with high Co loadings (>12 wt%), notable amounts of carbon were accumulated during reforming, and deactivation was observed. Moreover, severe deactivation was also noted over the 2 wt% catalysts, both when carbon deposition occurred (T_c=500°C) or was absent (T_c=1000°C). In the latter case, the oxidation of the metallic sites was responsible for the deactivation. Hence, there are two different deactivation mechanisms, namely, carbon deposition and oxidation of metallic sites. The activities were stable when a balance between carbon formation and its oxidation could be achieved.     

Synthesis and crystallographic characterisation of Mg(H2dhtp)(H2O)5·H2O

A mononuclear complex of composition Mg(H₂dhtp)(H₂O)₅·H₂O has been prepared and characterised crystallographically.     

Synthesis and Some Properties of a New Compound in the CaO – Al2O3 – ZrO2 System

The phenomenon of heterovalent isomorphism discovered in the CaO – Al₂O₃ – ZrO₂ system yields a compound of a 3CaO · Al₂O₃ · 2ZrO₂ composition at 1450°C in a reducing medium. The effect of various factors on the synthesis of the new compound is described. A roentgenographic characteristic of tricalcium alumodizirconate is presented.     

Modification of Activated Carbon Fiber by Loading Metals and Their Performance on SO_2 Removal

1 INTRODUCTION More efficient SOx removal from the atmosphere as well as from flue gas is still desired because the consumption of fossil resources is steadily increasing and a large amount of SO2 is emmitted worldwide[1,2]. Activated carbons have been shown to be effective adsorbent for SO2, and in the presence of oxygen and moisture they can catalyze the conversion of SO2 to H2SO4, thus increasing adsorption capacity for SO2[3]. Activated carbon fiber (ACF) are especially in- tere…     

Stability in the system CaO–Al2O3–H2O

The solubility of AH₃, CAH₁₀, C₂AH_7.5, and C₃AH₆ was determined experimentally at 7 to 40 °C and up to 570 days. During the reaction of CA, at 20 °C and above initially C₂AH_7.5 formed which was unstable in the long-term. The solubility products calculated indicate that the solubilities of CAH₁₀, C₂AH_7.5 and C₄AH₁₉ increase with temperature while the solubility of C₃AH₆ decreases. Thus at temperatures above 20 °C, C₃AH₆ is stable, while at lower temperature also CAH₁₀ and C₄AH₁₉ are stable, depending on the C/A ratio.At early hydration times, CAH₁₀ can be stable initially at 30 °C and above, as the formation of amorphous AH₃ stabilises CAH₁₀ with respect to C₃AH₆ + 2AH₃. With time, as the solubility AH₃ decreases due to the formation of microcrystalline AH₃, CAH₁₀ becomes unstable at 20 °C and above.     

Some Factors Influencing the Morphology of α-Zirconium Phosphate and its Intercalation Reactions with a Bifunctional Thioether Amine

Crystalline samples of -zirconium phosphate, (-ZrP, -Zr(HPO₄)₂·H₂O) have been prepared by decomposition of zirconium fluoride complexes in the presence of phosphoric acid under a variety of conditions. The crystallinity and morphology have been shown to depend on a number of factors including the F^–/Zr⁴⁺ ratio, the concentration of Zr⁴⁺ ions, the material of the reaction vessel and the reaction temperature. Under conditions of rapid precipitation small plate-like crystals of -ZrP are produced whereas under conditions of slow crystallisation larger crystals with a lower aspect ratio are formed. The relative intensities of the d ₀₀₂, d ₁₁₀ and d ₁₁₂ reflections observed by X-ray powder diffraction show a correlation with the crystal morphology as determined by SEM.The intercalation reaction of 4-(methylmercapto)aniline with different samples of -ZrP under a variety of conditions has been studied. Incomplete intercalation is observed in each case, with the extent of intercalation depending on both the morphology of the -ZrP and the reaction conditions. The intercalated amine has been shown to exist as a mixture of protonated cations and neutral molecules.     

Electrical Properties and the Structure of Glasses in the xNa2O–(1 – x)2PbO · B2O3 System

The temperature–concentration dependences of the electrical conductivity and the activation energy for electrical conduction of glasses in the Na₂O–B₂O₃ and Na₂O–2PbO · B₂O₃ systems are studied. The investigation into the nature of the electrical conduction in these glasses reveals that the contribution from the electronic component (10^–3%) of the conductivity is within the sensitivity of the Liang–Wagner technique. A considerable alkali conductivity is observed upon introduction of more than 12 mol % Na₂O. The true transport number of sodium _Na is as large as unity at [Na₂O] 15 mol %. It is shown that the observed temperature–concentration dependences of the electrical and transport properties are governed by the ratio between the concentrations of polar and nonpolar structural–chemical units of the Na⁺[BO_4/2]^–, Na⁺[O^–BO_2/2] Na⁺[O^–BO_2/2], Pb²⁺ _1/2[BO_4/2]^–, Pb²⁺ _1/2[O^–BO_2/2], and [BO_3/2] types.     

Thermodynamics of Phase Relations in the Subsolidus of the MgO – Al2O3 – SiO2 System

Results of a thermodynamic analysis of the relation ΔG = f(T) for solid-phase reactions between stoichiometric components of the MgO – Al₂O₃ – SiO₂ system are reported and the thermodynamic conjugation of solid-phase reactions is considered. The thermodynamic instability of stoichiometric sapphirine and cordierite is discussed. A general scheme for the interaction between nonstoichiometric compounds, with allowance for the possible formation and phase decomposition of sapphirine and cordierite solid solutions and for the disproportion of stoichiometric sapphirine and cordierite, is proposed. It is shown that the structural changes in the crystal lattice of sapphirine and cordierite should be considered as arising from compositional changes of the corresponding solid solutions rather than polymorphous transformations. A diagram for phase relations in the subsolidus of the MgO – Al₂O₃ – SiO₂ system is proposed.     

Progress in the Study on the Phase Equilibria of the CO2·H2O and CO2-HeO-NaCI Systems

To study the feasibility of CO2 geological sequestration,it is needed to understand the complicated mul- tiple-phase equilibrium and the densities of aqueous solution with CO2 and multi-ions under wide geological condi- tions（273.15—473.15K,0—60MPa）,which are also essential for designing separation equipments in chemical or oil-related industries.For this purpose,studies on the relevant phase equilibria and densities are reviewed and analyzed and the method to improve or modify the existing model is suggested in order to obtain more reliable predictions in a wide temperature and pressure range.Besides,three different models（the electrolyte non random two-liquid（ELECNRTL）,the electrolyte NRTL combining with Helgeson model（ENRTL-HG）,Pitzer activity coefficient model combining with Helgeson model（PITZ-HG））are used to calculate the vapor-liquid phase equilib- rium of CO2-H2O and CO2-H2O-NaCl systems.For CO2-H2O system,the calculation results agree with the experimental data very well at low and medium pressure（0—20MPa）,but there are great discrepancies above 20MPa.For the water content at 473.15K,the calculated results agree with the experimental data quite well.For the CO2-H2O-NaCl system,the PITZ-HG model show better results than ELECNRTL and ENRTL-HG models at the NaCl concentration of 0.52mol·L ^-1 .Bur for the NaCl concentration of 3.997mol·L ^-1 ,using the ELECNRTL and ENRTL-HG models gives better results than using the PITZ-HG model.It is shown that available experimental data and the thermodynamic calculations can satisfy the needs of the calculation of the sequestration capacity in the temperature and pressure range for disposal of CO2 in deep saline aquifers.More experimental data and more accurate thermodynamic calculations are needed in high temperature and pressure ranges（above 398.15K and 31.5MPa）.     

Advanced Effluent Treatment with Ozonation and Biofiltration at the Paper Mill SCA-Graphic Laakirchen AG – Austria: Design and Operation Experience

The paper mill “SCA GRAPHIC LAAKIRCHEN AG” is situated in Austria and produces 486,000 to of graphic paper per year. A yearly amount of 6,923,000 m³ of wastewater with a COD-load of 7,819,000 kg is treated on site (2005). The trend towards brighter paper grades requires more intense bleaching of mechanical pulp and increased usage of chelating agents and optical brighteners. These chemicals are difficult to degrade with biological waste water treatment. Higher bleaching dissolves more lignin, which is hard to degrade as well. As a result the COD removal efficiency in the biological stage of the wastewater treatment plant drops and additional measures for enhanced COD reduction have to be implemented in order to maintain given discharge limits.