Phase Formation Rate Research Articles

Immobilization of heavy metals with chlorine and liquid phase formation during thermal treatment of MSWI fly ash

Due to effective detoxification, thermal treatment is a preferred treatment technology of municipal solid waste incineration (MSWI) fly ash. However, immobilization behavior of heavy metals during thermal treatment is unclear. In this work, a circulated fluidized bed fly ash with SiO2 addition and a grate furnace fly ash with high silica-aluminum coal ash addition were used to investigate combined effect of active chlorine content, liquid polymerization degree, temperature of initial liquid phase formation and liquid phase formation rate on the immobilization ratios of Zn, Pb and Cd by principle component analysis (PCA). The results show that the decrease in active chlorine content favors the immobilization of Zn, Pb and Cd because chlorination volatilization is reduced. Both the increase in liquid polymerization degree and the formation of initial liquid phase at low temperature promote the immobilization of Zn, Pb and Cd for physical encapsulation. However, a rapid formation of liquid phase is not favorable for the immobilization of Zn, Pb and Cd, because transfer of heavy metals between crystals and liquid phase is impeded by high viscosity of liquid phase during fusion. The results can provide a reference for how to achieve the immobilization of heavy metals by adjusting the chemical composition of MSWI fly ash during thermal treatment.

Investigation of the properties of alumophosphate solutions and products crystallized from them

The physicochemical properties of freshly prepared alumophosphate solutions obtained in the Al(OH)3 – H3PO4 – H2O system with the molar ratio n(Al2O3) : n(P2O5) = 1.0 : 2.75 have been investigated. The density and temperature dependence of the dynamic viscosity of the studied solutions with a concentration of P2O5 300–485 g/l were studied. The values of the apparent activation energy of the viscous flow (Eη) of alumophosphate solutions are calculated and the concentration range (390–420 g/l P2O5) is established, in which Eη is practically constant and is 15.0 kJ/mol. It is suggested that the change in the activation energy of the viscous flow of alumophosphate solutions is due to their structure determined by the composition of aluminum phosphate complexes. The influence of the viscosity properties of alumophosphate solutions and their concentration on the crystallization process of hydrated alumophosphate, in particular, the duration of the induction period and the rate of phase formation, is shown.

Microstructure and magnetization study of Li and Li–Zn ferrites synthesized by an electron beam

Lithium ferrites are widely used in high frequency electronic devices. The present work reports structural and magnetization analysis of lithium (Li0.5Fe2.5O4) and lithium-zinc (Li0.4Fe2.4Zn0.2O4) ferrites synthesized by electron beam heating (RT) of powdered and compacted samples. The synthesis was carried out at 600 and 750 °C for up to 120 min using 2.4 MeV electron beam generated by an ILU-6 pulsed electron accelerator. The characteristics of the samples synthesized by RT were compared with the ones of samples obtained by traditional thermal heating under the same temperature and time conditions. From XRD and thermomagnetometric analyses, α-Li0.5Fe2.5O4 ordered spinel phase and Li0.5(1−x)Fe2.5−0.5xZnxO4 ferrite phase with different zinc substitution were formed from Fe2O3/Li2CO3 and Fe2O3/Li2CO3/ZnO reagents, respectively. RT synthesis significantly increases the rate of interaction between the initial powders and, as a consequence, the rate of ferrite phase formation. In this case, lithium-containing ferrites can be successfully achieved from compacted powders at 750 °C, which is lower than the temperature of synthesis in conventional thermal heating. The average crystallite sizes calculated from the XRD and BET analyses were 114 nm for Li, 120 nm for Li–Zn ferrites and 142 for Li, 150 nm for Li–Zn, respectively. The specific saturation magnetization and Curie temperature were estimated and are 60 emu/g for Li, 70 emu/g for Li–Zn ferrites and 632 °C for Li, 492 °C for Li–Zn ferrites, respectively. The data obtained in this work are of considerable interest for the creation of a technology for producing ferrites at low synthesis temperatures.

Synthesis of beta alumina films using the process of chemical vapor deposition under lithium-rich atmosphere

This study demonstrates the growth of Li-β-alumina films by laser chemical vapor deposition and investigates the effects of deposition temperature (T_dep), molar ratio of Li/Al (R_Li/Al) and total pressure (P_tot) on the phase formation, microstructure, orientations and deposition rate (R_dep) of the film. Single-phase Li-β-alumina films were deposited at T_dep = 1100 K–1300 K, R_Li/Al = 20–50 and P_tot = 600–1000 Pa. Li-β-alumina films with the hexagonally faceted platelet morphology (flake-like) were deposited at P_tot = 1000 Pa, whereas bulky grains were formed at P_tot=600 Pa. The maximum R_dep of Li-β-alumina films was 30 μm h⁻¹ at Tdep=1225 K, R_Li/Al=30 and P_tot=600 Pa. At room temperature the ionic conductivity of Li-β-alumina film prepared by laser CVD reached 2×10^-4 S/cm, demonstrating superior performance and significant potential in lithium battery.

On the rate of microstructural degradation of Al-Ta-Ti-Zr refractory metal high entropy superalloys

Refractory metal high entropy superalloys (RSA) are being developed for high temperature structural applications. However, recently the microstructures of several RSA have been shown to be unstable, precipitating potentially deleterious intermetallic phases during prolonged exposure at elevated temperatures. For such instability to be acceptable it is necessary for the intermetallic phase formation to be sufficiently sluggish so as to not compromise alloy performance over the time scales likely to be experienced in service. However, the rate of intermetallic phase formation in RSA are not yet known. To address this issue, here, two quaternary Al-Ta-Ti-Zr refractory superalloys that contain all of the key microstructural features of more compositionally complex RSA have been studied following exposures of 1, 10 and 100 h at temperatures between 700 and 900 °C and compared to those previously obtained following 1000 h exposures. Critically, needles of an Al-Zr-rich intermetallic phase were observed following only 1 h exposure at 900 °C, demonstrating rapid formation kinetics. Furthermore, the microstructures continued to coarsen from 100 to 1000 h, indicating low morphological stability. Higher Al content increased both the prevalence of the Al-Zr-rich intermetallic phase and raised the solvus of the desirable B2 phase. Consequently, this work highlights additional challenges in RSA development for elevated temperature applications.

Sequential Formation of CO2 Hydrates in a Confined Environment: Description of Phase Equilibrium Boundary, Gas Consumption, Formation Rate and Memory Effect

Since 1980, one of the most promising solutions for the exploitation of natural gas hydrate reservoirs was found to be the replacement of methane with carbon dioxide in order to improve the efficiency of methane recovery and, at the same time, permanently store carbon dioxide. However, the process efficiency is still too low and far from reaching technical maturity and becoming economically competitive. In this sense, studying the intrinsic properties of CO2 hydrates formation and dissociation processes may help in better defining the reasons for this low efficiency and finding feasible solutions. This work deals with carbon dioxide hydrates formation in a natural silica-based porous medium and in fresh water. A lab-scale apparatus was used for experiments, which were carried out consecutively and with the same gas–water mixture in order to detect the possible occurrence of the “memory effect”. Six tests were carried out: the quantity of gas available for the formation of hydrates led to an initial pressure equal to 39.4 bar within the reactor (the initial pressure was 46 bar; however, the dissolution of CO2 in water during the first test caused a reduction in the quantity of gas available for the process). Each experiment started and ended at temperatures equal or higher than 20 °C. Considering the local pressures, these temperatures ensured the complete dissociation of hydrates. Besides thermodynamic parameters, the gas consumption and the rate constant were evaluated throughout the whole of the experiments. Conversely to what is asserted in the literature, the results demonstrated the weak persistence of the memory effect at a temperature slightly above 25 °C. As expected, ice formation competed with hydrates; however, during tests, it caused the partial release of carbon dioxide previously trapped into hydrates or dissolved in water. Finally, the rate constant completely agreed with the labile Cluster Theory and proved that primordial clusters and hydrate crystals formed and dissociated during the whole test. The first phenomenon was predominant during the formation phase, while the opposite occurred during the following step. The rate constant was found to be an effective parameter to quantify differences between measured and real equilibrium conditions for the system.

Special regularities for lowering temperature during growth of high-quality CdTe semiconductor layers

To obtain epitaxial layers of A2B6 semiconductors with increased structural perfection from their own liquid phase, it has been proposed to use a technological process in which the synthesis temperature varies in such a manner that ensures a constant growth rate of layers during the whole process. The regularities of temperature variation with time for this process have been found on the basis of diffusion crystallization model. The developed model is realized by numerical methods and applied to description of the growth of cadmium telluride layers. Quantitative data on variations of synthesis temperature have been obtained, which can serve as a basis for choosing the temperature-time regimes of growth of cadmium telluride layers with a constant and required rate of solid phase formation.

Effect of annealing on microstructure and magnetocaloric properties of plastically deformed La0.7Ce0.3Fe13.68Mn0.2Si1.4 alloys

In this study, we have employed a near-net-shape hot forging deformation with ∼67% reduction ratio, and an annealing process at 1223–1423 K to prepare bulk La0.7Ce0.3Fe13.68Mn0.2Si1.4 alloys. The deformed samples are featured by a unique microstructure consisting of layered α-Fe and La-rich phases. These layered phases gradually degrade during the subsequent annealing, and eventually appear as the magnetocaloric phase (the 1:13 phase) matrix embedded mainly with the α-Fe particles. Upon annealing at 1323 K, the deformed sample has the largest 1:13 phase formation rate. Significant magnetic entropy change of 15.6 J/kg K and a relatively small magnetic hysteresis of 30.9 J/kg at 5 T are achieved in the current forged La-Ce-Fe-Mn-Si alloy on an optimal annealing condition, i.e., 1323 K for 24 h. The large magnetic entropy, rapid 1:13 phase formation rate and near-net shape make the hot-forged La-Ce-Fe-Mn-Si alloys promising magnetic refrigerants.

Single-burn clinkering of endodontic calcium silicate-based cements: Effects of ZnO in the C3S phase formation and hydration rate

Calcium silicate-based cements were synthesized with 1–4 wt% ZnO at 1300 and 1500 °C. Powder and in-situ XRD tests were conducted in anhydrous and hydrating samples. Results showed that ZnO addition significantly increased the alite (C3S) content into cements, thus allowing the single-burn clinkering of cement with over 80 wt% C3S. ZnO incorporation progressively reduced the relative content of triclinic C3S while increasing the monoclinic C3S content. No significant hydration delays were observed when ZnO was added up to 1 and 3 wt% for the cement synthesized at 1300 and 1500 °C, respectively. ZnO proved to be an efficient mineralizer even in a single-burn step and does not seem to retard the C3S hydration when incorporated into its structure.

Formation of the Phase Composition of Crystalline Silica in the Processing of Amorphous Precursors in Super- and Subcritical Water Media

The regularities of the formation of the phase composition of crystalline silica during the processing of amorphous precursors in the aqueous fluid media below and above the critical point of water aimed at the formation of optimal support for the methane oxidative coupling (OCM) catalyst were studied. It was shown that the phase composition of SiO2 and the rate of phase formation strongly depend on the processing conditions (temperature, time, phase state of the water fluid) and the presence of trace amounts of impurities in the initial amorphous material. Nevertheless, for different precursors, the phase formation occurs, apparently, via the formation of the same bulk-hydrated structures. Optimization of the processing in the water fluid and subsequent heat treatment made it possible to obtain an OCM catalyst that is significantly more efficient than the one obtained by the conventional procedure using an amorphous support. It was concluded that the catalytic properties are entirely determined by chemical and phase transformations occurring in the active component (Na2WO4–Mn2O3) on the support surface and do not depend on the doping of the support with the ions composing the active phase.

Investigation of the Effects of Al2O3 Content and Cooling Rate on Crystallization in Fe2O3–CaO–Al2O3 System Using In Situ Confocal Laser Scanning Microscopy

Sinter is a major Fe source, that is, used extensively in blast furnace processes worldwide. The chemical and physical properties of sinter are crucial factors that affect the operating stability of blast furnaces. The quality of sinter is largely determined by the phase fraction of the silico‐ferrite of calcium and aluminum (SFCA), which is a low‐melting‐point bonding phase formed during sintering. Calcium ferrite (CF)‐containing alumina is known to be the structural basis for SFCA and SFCA‐1, and provides basic information regarding the influence of Al2O3 on the formation of CF solid solutions. In this work, experiments are conducted to investigate the crystallization behaviors of an Fe2O3–CaO–Al2O3 system based on its Al2O3 content and cooling rate. The effects of Al2O3 additions are used to analyze changes in the phase formation temperature, phase ratio, and rate of decrease by using an in situ confocal laser‐scanning microscope, optical microscope, electron probe micro analyzer, and horizontal tube furnace. The temperatures at which the primary phase forms for various Al2O3 contents and cooling rates differ from the equilibrium temperatures, and the phase‐formation temperature ranges vary with the cooling rate.

Influence of Packing Atmosphere on the Microstructures and Transport Properties of Bi-2223/AgAu Tapes

Oxygen partial pressure was the key factor to tune the phase evolution mechanism of Bi-2223 system. In order to investigate the influence of packing atmosphere on the phase formation rate of Bi-2223, microstructures‚ and the current capacity of final tapes‚ 37-filamentary Bi-2223/AgAu tapes were fabricated by powder-in-tube (PIT) process, and the powder packing process operated in the glove box under different atmosphere of pure O2‚ air, and N2–7.5%O2, with the oxygen partial pressure of 100%‚ 25%, and 7.5%, respectively. With different packing atmosphere, the phase formation rate of Bi-2223 increased obviously during the first heat treatment process (HT1). While, based on the same HT1 process, the maximum Bi-2223 phase content was obtained in the tapes with packing atmosphere of N2–7.5%O2‚ which should be attributed to the suitable Bi-2223 content and distribution. Due to the improvement of superconducting phase content and better texture structure, the critical current density increased with decreasing oxygen partial pressure of packing atmosphere and the maximum value of 19.9 kA/cm2 was reached. Moreover‚ the in-field current capacities of these Bi-2223/AgAu tapes have also been enhanced with low oxygen partial pressure in packing atmosphere, attributed to the improvements of intergrain connectivity.

PROSPECTS FOR THE DEVELOPMENT OF METHODS FOR SYNTHESIZING PEROVSKITE STRUCTURE TITANATES AND DOPING THEM WITH RARE-EARTH ELEMENTS

The paper presents an overview of methods for obtaining perovskite structure titanates and doping them with rare-earth elements. The results of scientific research conducted by authors from different countries related to the study of the effect of doping perovskite structure titanates with rare-earth elements on their electromagnetic properties are discussed. The paper also comprises information on the use of perovskite structure titanates in various industries. As exemplified by barium titanate (BaTiO3), a comparative analysis of some morphological properties (particle size, structure) and electromagnetic characteristics (dielectric constant, Curie temperature, modulus of longitudinal oscillations (d33)) of powders obtained (and doped) by different methods is carried out. Techniques for various BaTiO3 preparation methods such as solvothermic, hydrothermal, sol-gel, chemical deposition, and solid-phase sintering are described. The paper provides the results of studies on the effect of changes in process parameters (temperature, pH, composition of the initial mixture of materials and concentration of reagents) on the phase, morphology and BaTiO3particle formation rate in hydrothermal synthesis (using BaCl2, TiCl4and NaOH as initial materials). In addition, experiments were conducted to study the effect of microwave radiation power in ВаСОз and ТЮ2 solid-phase sintering on the dielectric and ferroelectric properties of ВаТЮз ceramics. The analysis of methods for obtaining BaTiO3 and doping it with rare-earth elements found that at present the hydrothermal method and the method of solid-phase sintering (including with microwave radiation) can be regarded as advanced technologies for obtaining perovskite structure materials with predetermined properties.

Effect of CaO/Fe2O3 on fusion behaviors of coal ash at high temperatures

The ash fusibility, usually investigated and evaluated by the ash chemical composition, is widely used for guiding the coal utilization in boiler and gasifier. The ratio of basic and acidic oxides (B/A) in coal ash is the most important parameter for ash fusibility evaluation. While the coal ash has the identical B/A ratio, SiO2/Al2O3 and CaO/Fe2O3 ratio also show significant influence on the ash fusibility. However, the researches on CaO/Fe2O3 on ash fusibility are rare. In order to quantify the influence of CaO/Fe2O3 on the ash fusibility, thermal mechanical analyzer (TMA) is applied to investigate the ash fusion behavior of coal ash with various CaO/Fe2O3 ratios. XRD, FactSage and DSC are combined to explore the ash fusion characteristics and mechanisms. The results showed that AFTs increased with the increasing of CaO/Fe2O3 ratio, which was attributed to variation of Fe2O3 content and iron valence. However, the ash with low CaO/Fe2O3 ratio trended to form mullite, increasing AFTs. Hence, the optimal CaO/Fe2O3 ratio for fluxing effect existed to balance the mineral component and iron valence. The different shrinkage curves were attributed to the different fusion events and different mechanism. The fusion process of ash (CaO/Fe2O3 = 0.25) exhibited as the behavior of a pure substance, which has the narrow fusion range. And the fusion range was dominated by the low temperature eutectics including spinel, quartz, corundum, and anorthite, which were beneficial for preventing ash sintering. Meanwhile, the fusion process of ash sample (CaO/Fe2O3 = 4) occurred step by step, and it had a wide fusion range. The low-melting point minerals such as wollastonite, clinopyroxene, calcium silicate induced and manipulated the fusion process. These ash samples with the wide fusion range were favored for slagging process. Besides, the shrinkage rate of ash was mainly determined by the slag formation rate when viscosity was low, but it was dependent on slag formation rate as well as viscosity for the high viscosity slag. Two correlated relations between shrinkage rate and ratio of liquid phase formation rate and viscosity for ash with CaO/Fe2O3 < 1 and CaO/Fe2O3 ≥ 1 were established to prevent ash sintering at high temperatures.

The Effect of Surface Preparation on the Precipitation of Sigma During High Temperature Exposure of S32205 Duplex Stainless Steel

Although the formation of sigma phase in duplex stainless steels is reasonably well documented, the effect of surface finish on its formation rate in surface regions has not been previously noted. The growth of the sigma phase precipitated in the subsurface region (to a maximum depth of 120 μm) has been quantified after heat treatment of S32205 duplex stainless steel at 1073 K (800 °C) and 1173 K (900 °C) after preparation to two surface finishes. Here, results are presented that show that there is a change in the rate of sigma phase formation in the surface region of the material, with a coarser surface finish leading to a greater depth of precipitation at a given time and temperature of heat treatment. The growth rate and morphology of the precipitated sigma has been examined and explored in conjunction with thermodynamic equilibrium phase calculations.

Enhancement of the Phase Formation Rate during In-Field Solid-Phase Reactive Sintering of Mn-Bi

Enhancement of the Phase Formation Rate during In-Field Solid-Phase Reactive Sintering of Mn-Bi

Synthesis of Al-doped Nano Ti-O scaffolds using a hydrothermal route on Titanium foil for biomedical applications

Al-doped and undoped Ti-O nanowire scaffolds were fabricated on the surface of titanium foil via a one-step hydrothermal reaction in the presence of an alkali solution at 120±1°C temperature and at 15psi pressure. Grazing Incidence X-Ray and electron microscopy analyses confirmed that the phase composition, length and diameter of the nanowires depend on alkali concentration and reaction time, and the Al doping. Whereas, Al doping retarded the oxide phase formation and transformation rate and changed the morphology of the nanowires. Preliminary hemolysis test showed better biocompatibility of the Al-doped scaffolds compared to the undoped ones.

Kinetics and thermodynamics of Si(111) surface nitridation in ammonia

Kinetics and thermodynamics of Si(111) surface nitridation under an ammonia flux at different substrate temperatures are investigated by reflection high-energy electron diffraction. Two different stages of the nitridation process were revealed. The initial stage is the fast (within few seconds) formation of ordered two-dimensional SiN phase, occuring due to the topmost active surface Si atom (Sisurf) interaction with ammonia molecules. It is followed by the late stage consisting in the slow (within few minutes) amorphous Si3N4 phase formation as a result of the interaction of Si atoms in the lattice site (Siinc) with chemisorbed ammonia molecules. It was found that the ordered SiN phase formation rate decreases, as the temperature increases. The kinetic model of the initial stage was developed, in which the ordered SiN phase formation is the two-dimensional phase transition in the lattice gas with SiN cells. The enthalpy of the active surface Si atom generation on the clean Si(111) surface was estimated to be about 1.5eV. In contrast, the amorphous Si3N4 phase formation is the normal (thermally activated) chemical process with the first-order kinetics, whose activation energy and pre-exponential factor are 2.4eV and 1081/s, respectively.

Preparation of Na-β-alumina films by laser chemical vapor deposition

This study demonstrates the growth of Na-β-alumina films by laser chemical vapor deposition and investigates the effects of deposition temperature (Tdep), molar ratio of Na/Al (RNa/Al) and total pressure (Ptot) on the phase formation, microstructure, orientations and deposition rate (Rdep) of the film. Single-phase Na-β-alumina films were deposited at (Tdep)=1310K–1360K, RNa/Al>20 and Ptot>600Pa. Na-β-alumina films with the hexagonally faceted platelet morphology were deposited at Ptot=1000Pa, whereas flake-like grains were formed at Ptot=600Pa. Na-β-alumina was co-deposited with α-Al2O3 at Ptot<600Pa and Tdep>1350K, in which the film morphology showed flake-like grains with smaller granules. The maximum Rdep of Na-β-alumina films was 44μmh−1.

Rate of Lyotropic Nematic Phase Formation: Derivation and Application of Time–Concentration–Temperature–Transformation Diagrams

The effect of both temperature and composition on the rate of transformation of a nematic phase from an isotropic solution is examined from a theoretical standpoint. The kinetics of the transformation are presented as a time–concentration–temperature–transformation (TCTT) diagram, analogous to the time–temperature–transformation (TTT) diagrams commonly used in metallurgical process design. The transformation is regarded as a nucleated process in which the transformation rate is proportional to the number of stable nuclei, and this in turn depends on a balance between the energy gained by nematic ordering and the energy expended in forming the nematic–isotropic interface. The nematic ordering term is estimated as a function of both concentration and temperature via two different approaches: (i) the lattice theory as described by Flory and Warner and (ii) the Maier–Saupe theory of nematic ordering. Although there are differences in detail, both approaches yield the same qualitative result. The present work provides the details necessary for developing a specific example application of our recently reported generalized system-independent model of nucleation and growth. The TCTT diagram is in essence a phase diagram augmented by kinetic information for nematic ordering, and thus is expected to be a powerful graphical tool in liquid crystal process engineering and other applications.