Kinetics Of Precipitation Reactions Research Articles

Geochemical modeling to aid experimental design for multiple isotope tracer studies of coupled dissolution and precipitation reaction kinetics

Geochemical modeling to aid experimental design for multiple isotope tracer studies of coupled dissolution and precipitation reaction kinetics

Incorporation of Th4+ and Sr2+ into Rhabdophane/Monazite by Wet Chemistry: Structure and Phase Stability.

Rhabdophane is an important permeable reactive barrier to enrich radionuclides from groundwater and has been envisaged to host radionuclides in the backend of the nuclear fuel cycle. However, understanding of how An4+ and Sr2+ precipitate into rhabdophane by wet chemistry has not been resolved. In this work, Th4+ and Sr2+ incorporation in the rhabdophane/monazite structure as La1-2xSrxThxPO4·nH2O solid solutions is successfully achieved in the acid solution at 90 °C. Some specific issues such as lattice occupation of Th4+ and Sr2+, precipitation reaction kinetics, and crystal growth affected by starting stoichiometry are discussed in detail, along with investigating the chemical stability of La1-2xSrxThxPO4·nH2O precipitations and associated La1-2xSrxThxPO4 monazite. The results reveal that the excess of Sr2+ appears to be a prevailing factor with a suggested initial Sr: Th ≥ 2 to obtain the stability domain of La1-2xSrxThxPO4·nH2O (x = 0∼ 0.1). A rapid ion removal associated with a nucleation process has been observed within 8 h, and Th4+ can be removed more than 98% after 24 h in 0.01 mol/L solutions. From structural energetics based on density functional theory, the lattice occupation of Th4+ and Sr2+ is energetically favorable in nonhydrated lattice sites of [LaO8], although two-thirds of lattice sites are associated with [LaO8·H2O] hydrated sites. Intriguingly, the crystal transformation from rhabdophane to monazite associated with the transformation from [SrO8] to [SrO9] polyhedra can greatly improve the leaching stability of Sr2+.

Response of Nd3+ and Sm3+ precipitating into rhabdophane and the leaching mechanism of associated monazite ceramics

AbstractRhabdophane has been considered an important permeable reactive barrier to isolate groundwater radionuclides, and evaluating its precipitation response to different species of radionuclide in acid solutions is critical. In this work, the effects of pH values on the precipitation behavior of Nd3+ and Sm3+ into La‐rhabdophane are systematically investigated. Some specific issues such as ions removal, precipitation reaction kinetics, and crystal growth affected ions incorporation are discussed in detail, along with uncovering the veil of the Ln (La, Nd, and Sm) leaching mechanism of associated La0.666Nd0.167Sm0.167PO4 monazite ceramic based on dissolution experiments and density functional theory. The results reveal that Nd3+ and Sm3+ can be removed more than 98% in pH = 1 solution within 12 h, whereas uneven precipitation process to form unexpected stoichiometric ratio of rhabdophane has been observed in 30–50 nm short crystal. Grain growth effects based on spark plasma sintering can contribute to homogenize the materials composition with obtaining La0.666Nd0.167Sm0.167PO4 monazite ceramics. Furthermore, the binding energy of Ln–O in (1 0 0) surface of monazite plays an important role in controlling the leaching stability of Ln3+, associated with the leaching activities are energetically favorable in the order of La > Nd > Sm for La0.666Nd0.167Sm0.167PO4 monazite.

Insight into the recrystallization behavior and precipitation reaction of in-situ nano TiB2/Al Cu Mg composite during heat treatment

In this study, the quantitative results from both electron backscattered diffraction and transmission electron microscope analyses provided the fundamental insight into the recrystallized behavior and precipitation reaction of the in-situ nano TiB2/AlCuMg composite during heat treatment. The difference of coefficient thermal expansion between TiB2 particles and Al matrix enabled the formation of deformation zone around TiB2 clusters during water quenching which promoted the recrystallized behavior. Besides, the strong pinning effect induced by TiB2 distributed at recrystallized grain boundary was also observed. As a result, the fine recrystallized grains were generally distributed around particle clusters. During artificial aging process, the trace Mg remarkably enhanced the kinetics of precipitation reaction in the composite. The coexistence of θ″ and θ' precipitates confirmed the continuous transformation of θ″ into θ' via the atomic Cu rearrangement. Herein, the θ'/Al interface acted as a heterogeneous nucleation site of the Al3Zr precipitate was able to improve the nucleation and growth rate of the precipitate. Moreover, the misfit dislocations at TiB2/Al interface with larger lattice mismatch were confirmed. The synergistic effect of stress field caused by misfit dislocations and geometrically necessary dislocations facilitated the pipe diffusion was responsible for transporting solute atoms under depleted vacancy and solute atoms around the interface, benefited to the nucleation and growth of precipitates.

Mathematical Modeling of the Charging Process of Li-S Batteries By Incorporating the Size-Dependent Li2s Dissolution

Lithium-sulfur (Li-S) batteries give rise to the further development of long-driving electric vehicles [1]. During the discharge process of lithium-sulfur batteries, the nucleation and growth of Li2S precipitates result in a non-uniform Li2S particle size distribution, significantly affecting the charging process [2,3]. However, a uniform Li2S distribution at the initial state of the charging process of the batteries is assumed in the models reported in the literature, leading to an unrealistic simulation of the charging process [3,4]. To address this issue, we propose a one-dimensional transient mathematical model, which incorporates the size-dependent Li2S dissolution and redox mediation reaction between dissolved polysulfides and Li2S particles into the charging process. Simulation results show that the dissolution rate of large Li2S particles is suppressed at a lower potential due to the small specific surface area, while the smaller Li2S particles are electrochemically oxidized into dissolved polysulfides first, which further act as the redox mediators to promote the oxidation of larger Li2S particles. Capturing these effects enables an excellent agreement between the predicted and measured charging voltage profiles. Moreover, the effects of particle sizes and redox mediation reaction rates are studied. It is revealed that the optimal amount of smaller-sized Li2S particles and suitable redox mediation reaction rate allow for a lower charging over-potential. Furthermore, it is shown that the effect of redox mediation rates on the dissolution of Li2S large particles exerts a significant influence on the charging process. Key words: lithium-sulfur battery; mathematical model; dissolution kinetics; size effect; redox mediation Acknowledgment: The work described in this paper was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. T23-601/17-R) Reference [1] A. Manthiram, Y. Fu, S.-H. Chung, C. Zu, Y.-S. Su, Rechargeable Lithium–Sulfur Batteries, Chem. Rev. 114 (2014) 11751–11787. doi:10.1021/cr500062v. [2] F.Y. Fan, W.C. Carter, Y. Chiang, Mechanism and Kinetics of Li2S Precipitation in Lithium–Sulfur Batteries, Adv. Mater. 27 (2015) 5203–5209. [3] Y.X. Ren, T.S. Zhao, M. Liu, P. Tan, Y.K. Zeng, Modeling of lithium-sulfur batteries incorporating the effect of Li 2 S precipitation, J. Power Sources. 336 (2016) 115–125. [4] M. Ghaznavi, P. Chen, Sensitivity analysis of a mathematical model of lithium–sulfur cells: Part II: Precipitation reaction kinetics and sulfur content, J. Power Sources. 257 (2014) 402–411.

Ion Transport and Precipitation Kinetics as Key Aspects of Stress Generation on Pore Walls Induced by Salt Crystallization.

The stress generation on pore walls due to the growth of a sodium chloride crystal in a confined aqueous solution is studied from evaporation experiments in microfluidic channels in conjunction with numerical computations of crystal growth. The study indicates that the stress buildup on the pore walls is a highly transient process taking place over a very short period of time (in less than 1s in our experiments). The analysis makes clear that what matters for the stress generation is not the maximum supersaturation at the onset of the crystal growth but the supersaturation at the interface between the solution and the crystal when the latter is about to be confined between the pore walls. The stress generation is summarized in a simple stress diagram involving the pore aspect ratio and the Damkhöler number characterizing the competition between the precipitation reaction kinetics and the ion transport towards the growing crystal. This opens up the route for a better understanding of the damage of porous materials induced by salt crystallization, an important issue in Earth sciences, reservoir engineering, and civil engineering.

In situ high-energy synchrotron X-ray diffraction revealing precipitation reaction kinetics of silver ions with mixed halide ions

Quantitative reaction kinetics involved in the precipitation of silver ions with mixed halogen ions that are capable of forming uniform silver chlorobromide nanocubes has been studied by in situ high-energy synchrotron X-ray diffraction.

Pore-scale study of diffusion–reaction processes involving dissolution and precipitation using the lattice Boltzmann method

A pore-scale model combining the lattice Boltzmann method (LBM) and a fluid–solid interface tracking method is employed to simulate the diffusion–reaction processes involving dissolution and precipitation. Coupled sub-processes including mass transport, chemical reactions, and solid structure evolution are considered. Effects of the precipitation of the secondary solid phase on the dissolution of the primary solid phase are investigated under different dissolution–precipitation reaction kinetics, molar volumes of the primary and secondary solid phases, powder size, surface roughness, and nucleation and crystal growth mechanisms. Different morphologies of the precipitates are predicted by the pore-scale simulations. It is found that the precipitation has opposite effects on the underlying dissolution processes. The favorable effect is that the precipitation reaction consumes the product of the dissolution reaction, thus facilitating the dissolution; while the adverse effect is that the generated precipitates cover the surface of the primary solid phase, thus separating the reactive surface from the reactive components. Based on the extent to which the precipitates affect the dissolution, four types of coupled dissolution–precipitation processes are identified and discussed.

Sensitivity analysis of a mathematical model of lithium–sulfur cells: Part II: Precipitation reaction kinetics and sulfur content

A sensitivity analysis of a mathematical model of a lithium–sulfur (Li–S) battery was performed, focusing on the precipitation rate constants and sulfur content, by investigating the response of the model to the variation of these parameters over a wide mathematical range. The necessity of rapid dissolution of elemental sulfur and rapid precipitation of reduced sulfur is discussed in detail. The sensitivity analysis suggests modifying the reduction reaction steps of sulfur can improve the predictions of the model of Li–S battery. Furthermore, an upper limit on the sulfur content of the cathode exists to ensure optimal performance. Although the model provides valuable knowledge concerning Li–S batteries, a modification to the assumed five-step reduction of sulfur combined with the consideration of the insulating nature of the active material is required to improve the model.

The effect of aging on the B2-R transformation behaviors in Ti-51at%Ni alloy

Aging is an effective way to control the transformation behaviors of Ti–Ni shape memory alloys. In the present study, the transformation behaviors of Ti-51at%Ni polycrystals after aging at various temperatures (250 °C–500 °C) for different time were investigated by DSC measurement. It is found that B2-R transformation temperature (RS) of the aged samples is uniquely determined by the aging temperature for aging above 400 °C, being almost independent on aging time. Higher aging temperature causes a lowering of RS temperature. At lower aging temperatures (e.g., 250 °C, 300 °C), RS gradually increases with aging time and finally saturates. The saturated RS value is also a unique function of the aging temperature. These facts can be explained by the phase equilibrium between Ti–Ni matrix (B2) and Ti3Ni4 precipitates. The Ti3Ni4 precipitates formed at different aging temperatures alter the Ni concentration in B2 matrix and consequently cause an aging temperature dependence of the R-phase transformation of B2 matrix. By considering the kinetics of precipitation reaction, the “time-independence” of RS for high temperature aging and the “time-dependence” of RS for low temperature aging can also be reasonably understood. Besides, the R–B19′ transformation temperature (MS) gradually increases with aging time as well, which can also be understood by considering the growth of precipitates during aging.

Microstructural changes in creep exposed P91 steel weld joint

Cast plates made of 9Cr – 1MoV creep resistant steel were joined together using the GTAW and SMAW methods. Creep testing was carried out at a temperature range from 525°C to 625°C and a stress range from 50 to 240MPa. The microstructure of crept specimens was compared with weld joint at conditions after PWHT and the base material before welding. Substructures were investigated in the base material, the heat affected zones and the weld metal. Different kinetics of precipitation reactions in individual zones caused changes in creep strength and unexpected transition from Type IV cracking to Type I cracking at long creep exposure at 625°C. After creep tests at temperatures above 550°C for about 30,000 hours, coarse particles of Laves phase were observed. In addition, small plates of Z-phase were detected after creep tests at 625°C. Precipitation of Laves phase occurred in the weld metal predominately and caused depletion of solid solution about molybdenum. If the lowest stress were applied at 625°C, the growth of the Laves phase was the dominant process, which caused a significant softening and rupture in the weld metal. This effect prevailed over accumulation of cavitation failure in the heat affected zones that caused fracture of the other specimens.

Microstructural changes in creep exposed P91 steel weld joint

Cast plates made of 9Cr – 1MoV creep resistant steel were joined together using the GTAW and SMAW methods. Creep testing was carried out at a temperature range from 525°C to 625°C and a stress range from 50 to 240MPa. The microstructure of crept specimens was compared with weld joint at conditions after PWHT and the base material before welding. Substructures were investigated in the base material, the heat affected zones and the weld metal. Different kinetics of precipitation reactions in individual zones caused changes in creep strength and unexpected transition from Type IV cracking to Type I cracking at long creep exposure at 625°C. After creep tests at temperatures above 550°C for about 30,000 hours, coarse particles of Laves phase were observed. In addition, small plates of Z-phase were detected after creep tests at 625°C. Precipitation of Laves phase occurred in the weld metal predominately and caused depletion of solid solution about molybdenum. If the lowest stress were applied at 625°C, the growth of the Laves phase was the dominant process, which caused a significant softening and rupture in the weld metal. This effect prevailed over accumulation of cavitation failure in the heat affected zones that caused fracture of the other specimens.

Alkali feldspar dissolution and secondary mineral precipitation in batch systems: 3. Saturation states of product minerals and reaction paths

In order to evaluate the complex interplay between dissolution and precipitation reaction kinetics, we examined the hypothesis of partial equilibria between secondary mineral products and aqueous solutions in feldspar–water systems. Speciation and solubility geochemical modeling was used to compute the saturation indices (SI) for product minerals in batch feldspar dissolution experiments at elevated temperatures and pressures and to trace the reaction paths on activity–activity diagrams. The modeling results demonstrated: (1) the experimental aqueous solutions were supersaturated with respect to product minerals for almost the entire duration of the experiments; (2) the aqueous solution chemistry did not evolve along the phase boundaries but crossed the phase boundaries at oblique angles; and (3) the earlier precipitated product minerals did not dissolve but continued to precipitate even after the solution chemistry had evolved into the stability fields of minerals lower in the paragenesis sequence. These three lines of evidence signify that product mineral precipitation is a slow kinetic process and partial equilibria between aqueous solution and product minerals were not held. In contrast, the experimental evidences are consistent with the hypothesis of strong coupling of mineral dissolution/precipitation kinetics [e.g., Zhu C., Blum A. E. and Veblen D. R. (2004a) Feldspar dissolution rates and clay precipitation in the Navajo aquifer at Black Mesa, Arizona, USA. In Water–Rock Interaction (eds. R. B. Wanty and R. R. I. Seal). A.A. Balkema, Saratoga Springs, New York. pp. 895–899]. In all batch experiments examined, the time of congruent feldspar dissolution was short and supersaturation with respect to the product minerals was reached within a short period of time. The experimental system progressed from a dissolution driven regime to a precipitation limited regime in a short order. The results of this study suggest a complex feedback between dissolution and precipitation reaction kinetics, which needs to be considered in the interpretation of field based dissolution rates.

Reply to “Comment on upscaling geochemical reaction rates using pore-scale network modeling” by Peter C. Lichtner and Qinjun Kang

Our paper Upscaling geochemical reaction rates usingpore-scale network presents a novel application of pore-scalenetwork modeling to upscale mineral dissolution and precipitationreaction rates from the pore scale to the continuum scale, anddemonstrates the methodology by analyzing the scaling behavior ofanorthite and kaolinite reaction kinetics under conditions related to CO2sequestration. We conclude that under highly acidic conditions relevantto CO2 sequestration, the traditional continuum-based methodology may notcapture the spatial variation in concentrations from pore to pore, andscaling tools may be important in correctly modeling reactive transportprocesses in such systems. This work addresses the important butdifficult question of scaling mineral dissolution and precipitationreaction kinetics, which is often ignored in fields such as geochemistry,water resources, and contaminant hydrology. Although scaling of physicalprocesses has been studied for almost three decades, very few studieshave examined the scaling issues related to chemical processes, despitetheir importance in governing the transport and fate of contaminants insubsurface systems.

Simulation of the kinetics of precipitation reactions in ferritic steels

Computer simulations of diffusion-controlled phase transformations in model alloys of Fe–Cr–C, Fe–Cr–W–C, Fe–Cr–Si–C, and Fe–Cr–Co–V–C are presented. The compositions considered are typical for ferritic steels. The simulations are performed using the software DICTRA and the thermodynamic calculations of phase equilibria are performed using Thermo-Calc. The thermodynamic driving forces and the kinetics of diffusion-controlled precipitation reactions of M 23C 6, M 7C 3, cementite and Laves-phase (Fe, Cr) 2W are discussed. The simultaneous growth of stable and metastable phases is treated in a multi-cell approach. The results show remarkable effects on the growth kinetics due to the competition during simultaneous growth.

Dual precipitation strengthening effect of copper and niobium in high strength steel weld metal

Experimental work to produce high strength steel welds with systematic additions of copper (up to 3.5 wt.pct.) and niobium (up to 0.45 wt.pct.) at 3.6 kJ mm −1 (90 kJ in −1) heat input was carried out. Copper additions were found to precipitation strengthen the high strength steel weld metals. An estimated yield strength of 900 MPa (130 ksi) can be achieved in single-pass welds with approximately 2.8 wt.pct. of copper addition. Nevertheless, multipass welding over the copper-enhanced weld deposit resulted in monuniform and weld metal properties across the weld beads. Niobium additions did not provide as powerful a strengthening effect in the single-pass high heat input welds as the copper additions. At approximately 3.2 wt.pct. copper and 0.06 wt.pct. niobium in the weld deposits, the two elements provided the required strenghtening effect with thermally stable precipitates to produce high strength steel weld metals that exhibited acceptable properties in high heat input, single- and multi-pass conditions. The combined of copper and niobium in high strength steel weld metal derives from the combination of two kinds of precipitates with distinct precipitation reaction kinetics and thermal stability.

Experimental investigation of precipitation reactions under homogeneous mixing conditions

The theoretical description of the kinetics of precipitation reactions implicitely uses the assumption of a spatially homogeneous supersaturation in the reactor. In preliminary experiments it is shown that, since supersaturation is imposed by mixing two reactant solutions, this stands in clear contrast to reality, where a change in hydrodynamic conditions results in different spatial supersaturation patterns, which finally leads to different particle size distributions. Consequently, kinetic expressions derived herefrom will also differ when the same supersaturation, but a different mixing pattern, applies. With a newly developed experimental setup as described here it can be proven that kinetic results become independent from the mixing conditions, i.e. thermodynamically correct, when the reactants are pre-mixed at extremely high Reynolds-Numbers.

In Situ hot-stage high-resolution Transmission Electron Microscope studies of the mechanisms and kinetics of precipitation reactions

In situ hot-stage high-resolution transmission electron microscopy (HRTEM) provides unique capabilities for quantifying the mechanisms and kinetics of precipitation reactions at the atomic level. Such information is required to understand phase transformations and the behavior of material interfaces. This paper provides a brief summary of the in situ hot-stage HRTEM technique and illustrates the use of this technique to obtain information about heterogeneous nucleation processes in precipitation and crystallization reactions. Examples of other types of in situ HRTEM studies can be found in previous papers by Sinclair et al. and Howe et al.The specimen and microscope requirements for in situ hot-stage HRTEM are the same as those for static HRTEM except that one must have a hot-stage specimen holder and equipment for recording and analyzing dynamic images. A high-resolution television-rate camera connected to a standard videocassette recorder (VCR) can be used to store hours of data for low cost. The dynamic images can then be analyzed directly during playback or sent to a computer for image processing and analysis.

DSC analysis of the effect of processing technique on the dissolution/precipitation reactions in a hypereutectic Al−Si alloy

In the present study, the effect of primary processing route on the dissolution and precipitation reactions in a commercial Al−Si alloy (designated as A390) is investigated using differential scanning calorimetry (DSC). The Al−Si alloy selected for the present investigation was processed using conventional casting and spray atomization and deposition routes. The results of differential scanning calorimetry conducted on the as-processed samples indicated no significant dissolution reaction for the as-cast A390 alloy when compared to the similar results obtained for as-spray atomized and deposited samples. However, the thermal analysis conducted on the solutionized cast and spray deposited samples exhibited no significant difference in the kinetics of precipitation reactions. The results of the differential thermal analyses were finally rationalized in terms of observed microstructural features.

A Kinetic Model of Precipitate Evolution

ABSTRACTChemical reaction rate theory is used to model the kinetics of precipitation reactions in Al alloys, including the effects of continuous cooling and thermally generated point defects. The computational method models the processes of nucleation, growth, and coarsening within a single framework. Calculated time and temperature dependent precipitate number densities and sizes during the homogeneous precipitation of the A13Sc phase in an Al-.11 at% Sc alloy are shown to compare favorably with experimental observations.