Heterogeneous Equilibria in the Yb–Mn–O System

The heterogeneous equilibria attained during thermal dissociation and hydrogen reduction of YbMnO₃ and YbMn₂O₅ are investigated using the static method (vacuum circulation setup) and X-ray powder diffraction analysis of quenched solid phases. It is found that, at the boundary of the low-oxygen homogeneity region of YbMn₂O₅, this compound dissociates into YbMnO₃ and Mn₃O₄ with the liberation of oxygen. Upon the reduction, YbMnO₃ dissociates with the formation of Yb₂O₃ and MnO and the liberation of oxygen. Equations for the dissociation and reduction reactions of YbMn₂O₅ and YbMnO₃ are derived, and mass balance equations for these processes are written. A fragment of the isothermal section of the phase diagram of the Yb–Mn–O system at 900°C is constructed in the composition–oxygen pressure coordinates.     

Morphotropic phase boundary in the BNT–BT–BKT system

Lead-free x Bi_0.5Na_0.5TiO₃–y BaTiO₃–z Bi_0.5K_0.5TiO₃ piezoelectric ceramics were synthesized by a conventional solid state reaction method. The microstructure, ferroelectric and piezoelectric properties of the ceramics were investigated. Structure measurements by X-ray diffraction with Rietveld refinement have allowed us to specify more precisely the morphotropic phase boundary (MPB) in this system. For (1 ? x) BNT–x BT solid solution ceramics, the 0.94 BNT–0.06 BT morphotropic composition shows the higher values with d₃₃ = 170 pC/N, k_p = 0.35 and k_t = 0.53. In the case of (1 ? x) BNT–x BKT compositions, the d₃₃, k_p and k_t are, respectively, 137 pC/N, 0.39 and 0.54 for the 0.80 BNT–0.20 BKT ceramic. On the other hand, the ternary 0.865 BNT–0.035 BT–0.100 BKT morphotropic composition shows high piezoelectric constant and electromechanical coupling factors (d₃₃ = 133 pC/N, k_p = 0.26 and k_t = 0.57).     

Gas-solid displacement reactions in the Ti–W–C system

Displacement reactions between binary and ternary ceramics in the Ti–W–C system and reactive gaseous atmospheres are investigated in this work. Specifically, WC and 50:50 wt% TiC:WC solid solution powders were exposed to flowing hydrogen gas, or equilibrated against an excess of titanium in the presence of iodine, to form metallic tungsten and TiC solid products. In the case of pure WC reacting with hydrogen, transformation to metallic tungsten occurred as a result of removal of chemically bound carbon as gaseous hydrocarbons. In the case of pure WC reacting with titanium iodide vapors, transformation was accompanied by the appearance of TiC as a solid product formed at the gas-solid interface. In the case of 50:50 wt% TiC:WC solid solution powders, hydrogen was generally found to be an ineffective displacing reagent, whereas reaction with titanium iodide vapors was observed to proceed virtually to completion, resulting in a two phase product mixture comprising metallic tungsten and TiC. For the latter case, a variety of microstructures could be observed within a given batch, including tungsten platelets and/or lamellae in a TiC matrix, or coarse tungsten grains interspersed with TiC grains. These morphological variations are speculated to arise from compositional variation in the starting material and the occurrence of local rapid coarsening along fast diffusion pathways within reacting agglomerates and polycrystalline primary particles. The observed reaction products and relative efficacy of gaseous reagents to promote displacement reactions in the Ti–W–C system are rationalized on the basis of thermodynamic predictions. The reaction between 50:50 wt% TiC:WC solid solution powders and titanium iodide vapors constitutes the first known report of an internal displacement reaction proceeding via gaseous intermediates in a nonoxide ceramic system.     

Bubble lengths in the gas–liquid Taylor flow in microchannels

Experimental results of measurements of the bubble and slug lengths in Taylor (slug) flow are presented. The experiments were carried out using 3 different straight microchannels (microreactor with square cross-section made of polydimethyloxosilane (PDMS); microreactor with circular cross-section made of glass; microreactor with rectangular cross-section made of polyethylene terephthalate modified by glycol (PETg)) and 4 different liquids (water, ethanol propanol and heptane). The results have been compared with the available literature correlations. It is concluded, that the values obtained from the correlation proposed by Laborie et al. [Laborie, S., Cabassud, C., Durant-Bourlier, L., Laine, J.M., 1999. Characterization of gas–liquid two-phase flow inside capillaries. Chem Eng Sci 54, 5723–5735] do not agree with the results of measurements, while the agreement of these results with the predictions obtained using the correlation proposed by Qian and Lawal [Qian, D., Lawal, A., 2006. Numerical study on gas and liquid slugs for Taylor flow in a T-junction microchannel. Chem Eng Sci 61, 7609–7625] is good. New, corrected values of the pre-exponential constant and the exponents in the Qian and Lawal [Qian, D., Lawal, A., 2006. Numerical study on gas and liquid slugs for Taylor flow in a T-junction microchannel. Chem Eng Sci 61, 7609–7625] correlation are proposed.     

Phase equilibria in the calcium nitrate–water–isopropyl alcohol system

Results of an investigation of the solubility of the components of the water–isopropyl alcohol system in the temperature range of 253–268 K are given. Using fractional fusion, the concentrations of twocomponent water–isopropyl alcohol system have been determined, where fusion occurs more homogeneously. Phase diagrams of the calcium nitrate–water–isopropyl alcohol systems have been plotted at temperatures of 253, 263, and 268 K. The working area where compositions can be chosen for preparing the process liquid with a low freezing point has been determined.     

Vapor–liquid equilibrium in the sodium carbonate–sodium bicarbonate–water–CO2-system

Vapor–liquid equilibria of the carbon dioxide loaded sodium carbonate–water system were measured in the temperature range 40–80 °C and for sodium carbonate concentrations 8–12 wt%. In addition the vapor pressure of water over 10–30 wt% sodium carbonate solutions for the temperature range 27–100 °C was measured in an ebulliometer. The system was modeled using the electrolyte-NRTL model. Experimental vapor–liquid data from this study as well as data available in the literature from 25 to 195 °C and for sodium carbonate concentrations from 0.5 to 12 wt% were used for parameter fitting. The average deviation of the model predictions compared to all experimental data found is 9.8% for the partial pressure of CO₂. For vapor pressure of water the standard deviation is 0.6% up to 100 °C and 30 wt% sodium carbonate solutions.     

Effect of chromium on the kinetics of the contact melting and the graphite-to-diamond transformation in the Co–Fe–C system

We have studied the effect of chromium concentration in alloys of the Co–Fe system on their interaction with graphite at p, T parameters of thermodynamic stability of diamond. It has been found that addition of chromium to the alloys stabilizes the Me₃C-type carbide, as a result, the structure of a layer of a contact melting at the alloy–graphite interface is identical to a horizontal section of the metastable phase diagram of the Fe–C system. It is shown that addition of chromium to the Co–Fe–C system lowers the eutectic melting temperature by 80–100 K. In this case, the coefficient of carbon diffusion in the melt increases by ∼20–30%. An increased surface activity of a Cr-containing melt with respect to graphite is noted, which is the reason of intensive intrusion of the melt deep into a graphite layer along the grain boundaries. As a result, the number of nucleating diamond crystals and the degree of the graphite→diamond transformation increases.     

Effect of the graphite perfection on the HP–HT diamond synthesis in a Ni–Mn–C system

Changes in the graphite structure used as precursor for diamond synthesis is a phenomenon observed during high pressure and high temperature processes in the presence of a solvent–catalyst metals. In this work, experimental results have shown that the initial structure of the graphite material has a significant influence on the yield and the possibility of formation of diamond. An association between the degree of structural perfection of the graphite and the success in producing diamond crystals was found to exist even for conditions outside the field of diamond stability in the carbon P–T equilibrium diagram.     

Thermodynamic prediction of the nonstoichiometric phase Zr1–zCezO2–x in the ZrO2–CeO1.5–CeO2 system

A thermodynamic estimation of the ZrO₂–CeO₂ and ZrO₂–CeO_1.5 systems, as well as the cubic phase in the CeO_1.5–CeO₂ system has been developed and the complex relation between the nonstoichiometry, y, in Ce_zO_2–y and the oxygen partial pressure at different temperatures is evaluated. The behavior of the nonstoichiometry phase Zr_1–zCe_zO_2–x is described based on the thermodynamic estimation in the ZrO₂–CeO₂, CeO_1.5–CeO₂ and ZrO₂–CeO_1.5 systems. Additionally, the interdependence among miscellaneous factors, which can be used to describe the change in oxidation states of cerium such as the oxygen partial pressure, the CeO_1.5 fraction in CeO_1.5–CeO₂ in the quasi-ternary system, the nonstoichiometry y and the difference between the activity of CeO₂ and CeO_1.5 are predicted. The calculated results are found to be very useful to explain the influence of pressureless sintering at different O₂ partial pressures on the mechanical properties of CeO₂-stabilised ZrO₂ ceramics     

Decomposition reactions in the SiC–Al–Y–O system during gas pressure sintering

The substantial densification, that occurred in the SiC–Al–Y–O system was explained in the present work by analysing possible chemical reactions and their dependence on initial particle associations, i.e. homogeneity of mixing, the physical and chemical state of additives, pressurised sintering environment over the reactants and temperature of sintering. Hydroxyhydrogel powder precursors were found to be better than mechanically mixed SiC–YAG powder and pre-forming of YAG by holding the specimens at the temperature of 1400°C for 2 h were found to be the best. Decomposition reactions within the system could be controlled by using finer SiC and applying gas pressure over the reactants.     

Gas–particle partitioning of organic compounds in the atmosphere

Gas–particle partitioning of condensable organic compounds in the atmosphere is described using two methods. The first method is based on the use of a comprehensive mechanistic model of adsorption/absorption processes. The second method is based on aerosol yields estimates. The model parameters in the adsorption/absorption model are evaluated from experimental data. The concepts of concentration of adsorbed molecules on the surface of aerosol particles and diffusion of adsorbed molecules in the liquid phase are used for determining the importance of the adsorption/absorption mechanisms. The model calculations showed a qualitative agreement with available experimental data for alkanes. Furthermore, a modified version of the Carbon Bond IV chemical mechanism including an aerosol yields method to model the formation of organic aerosols in reactive plumes is used in combination with a plume dispersion model. The formation of secondary organic matter in plumes contributes significantly to the total secondary aerosol mass produced.     

Glass Formation in the MgO–B2O3–SiO2 System

Silicon - The glass formation region in the MgO–B2O3–SiO2 system was determined by the conventional melt-quenching technique at 1450 °C. The homogeneous transparent...     

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.     

Emission control in the combustion of coal–water and organic coal–water fuels

Promising methods for decreasing anthropogenic emissions due to the combustion of coals of different ranks and coal–water fuel (CWF) and organic coal–water fuel (OCWF) slurries on their basis are considered. The maximum concentrations of the main anthropogenic emissions of sulfur, nitrogen, and carbon oxides (SO _x , NO _x , and CO _x ) formed upon the combustion of solid fuels in a powdered state and as the components of CWF and OCWF slurries were determined. The concentrations of the most hazardous oxides formed upon the combustion of coals of different ranks (brown and black coals) and CWF and OCWF slurries were compared. The experimental results substantiated the use of CWF and OCWF slurries for emission control in coal-burning power engineering. The addition of a combustible liquid component to a CWF slurry (the production of an OCWF slurry) makes it possible to ensure acceptable environmental and energy characteristics.     

Vesicles from the self-assembly of coil–rod–coil triblock copolymers in selective solvents

Self-assembled vesicles formed by symmetrical coil–rod–coil triblock copolymer in selective solvents are investigated by dissipative particle dynamics method. With varying the coil length L_c and the rod length L_r, five kinds of typically ordered micelles are observed, including the special vesicles formed in the range of the rod block ratio f_r ≈ 30% ∼ 50% and the rod length L_r ≤ 9. The kinetic process of vesicle formation is also observed. The aggregates firstly experience the fusion, elongation, and deformation, and then encompass the solvents, and finally close up to a vesicle membrane, where the bilayer disc is observed as an intermediate phase transited from solid micelles to hollow vesicles. A scaling behavior of the average aggregate size with time is also obtained during the process of the self-assembly. Furthermore, the effects of polymer concentration f_p and solvent property are discussed. Vesicle structure only appears in the range of f_p = 6% ∼ 25%, where vesicle size exhibits a well linear increase with polymer concentration. Meanwhile, vesicle size decreases with an increase in the interactions a_CS between coil blocks and solvents. Due to the interfacial energy increased with a_CS, the system minimizes interfacial energy by compressing the vesicle size.