Cerium Oxalate Research Articles

Measurement of Nucleation Rates during Nonclassical Nucleation of Cerium Oxalate: Comparison of Incubation-Quenching and In Situ X-ray Scattering

Measurement of Nucleation Rates during Nonclassical Nucleation of Cerium Oxalate: Comparison of Incubation-Quenching and <i>In Situ</i> X-ray Scattering

Investigating sedimentation process in the plutonium reconversion using Eulerian Two-Fluid simulations and experimental verification

Batch settling simulations were used to investigate the sedimentation behaviour of cerium oxalate particles (surrogate to plutonium) in the nitric-oxalic acid solution which will be useful for the design of continuous process equipment used in plutonium reconversion. The effects of overall solid fractions (OSF), initial dispersion height (ht), and cylinder diameter (d) on the settling curve were investigated numerically and comparisons were made with experimentally obtained results. Further, the solid volume fraction distributions of cerium oxalate obtained by varying the dispersion height, OSF, and cylinder diameter were numerically analysed. The increase in OSF (dispersed phase concentration) led to the presence of high solid volume fraction inside the settler. Since, the dispersed phase volume fraction is more and closely packed, it experiences the delay in settling time. The analysis of pressure variation was done by varying ht, d, and OSF. The bulk settling velocity was computed for different OSF and ht values. It was observed that the settling velocity was reduced with an increase in OSF and was independent of d. The changes in bulk settling velocity with time helped to explain the separation process in detail. The vorticity and velocity fluctuations obtained along the height of the batch settler confirmed the random motion of solid phase during settling. The clear liquid separated at the top region of the batch cylinder was investigated as a function of sedimentation velocity which will be helpful for any future design optimization of a continuous separation equipment.

Coexistence of Transient Liquid Droplets and Amorphous Solid Particles in Nonclassical Crystallization of Cerium Oxalate.

Crystallization from solution often occurs via "nonclassical" routes; that is, it involves transient, non-crystalline states like reactant-rich liquid droplets and amorphous particles. However, in mineral crystals, the well-defined thermodynamic character of liquid droplets and whether they convert─or not─into amorphous phases have remained unassessed. Here, by combining cryo-transmission electron microscopy and X-ray scattering down to a 250 ms reaction time, we unveil that crystallization of cerium oxalate involves a metastable chemical equilibrium between transient liquid droplets and solid amorphous particles: contrary to the usual expectation, reactant-rich droplets do not evolve into amorphous solids. Instead, at concentrations above 2.5 to 10 mmol L-1, both amorphous and reactant-rich liquid phases coexist for several tens of seconds and their molar fractions remain constant and follow the lever rule in a multicomponent phase diagram. Such a metastable chemical equilibrium between solid and liquid precursors has been so far overlooked in multistep nucleation theories and highlights the interest of rationalizing phase transformations using multicomponent phase diagrams not only when designing and recycling rare earths materials but also more generally when describing nonclassical crystallization.

Formation and growth of cerium (III) oxalate nanocrystals by liquid-cell transmission electron microscopy

Using rare earth elements as analogs for actinide series elements enables studying the chemistry of these radioactive materials without the inherent risks. A fundamental understanding of the nucleation and growth of actinide oxalates is crucial for processing nuclear waste. Using in-situ liquid cell TEM (LC-TEM), we show particle attachment processes occurring during the nucleation and growth of cerium oxalate. The early stages of the observed non-classical growth mechanisms have important implications for particle evolution and predictions of final particle morphology. We observed particle formation via monomer-by-monomer addition or the particle aggregation pathway depending on the selected precursor concentration. At the highest precursor concentration at a high dose rate, we observed particle alignment in a branch structure is due to the interfacial instability. It was demonstrated that in-situ LC-TEM is an invaluable tool in studying the cerium oxalate formation and ultimately a path to understanding actinide chemistry.

Transition between two solid‐solutions: Effective and easy way for fine Ce1−xGdxO2−x/2 powders preparation

AbstractCeria, pure or doped, is an important electrolyte material in solid oxide fuel cells, catalysts, and plutonium surrogates. Even though ceria is a widely studied material, its coprecipitation with the most common doping element, gadolinium, remains mostly overlooked. Here, we present a comprehensive study of gadolinium–cerium oxalates prepared by coprecipitation of gadolinium (III) and cerium (III) salts by oxalic acid under different reaction conditions and element ratios. For this purpose, we assessed the effects of basic precipitation conditions on the final oxalate size, shape, and conversion into the corresponding oxides. The results showed that coprecipitation with oxalic acid yields and ideal solid solution, which translates into the oxides. This low‐cost and straightforward synthetic route provides then high‐quality solid solutions of Ge–Gd in the oxide lattice. Thus, this approach has a high industrialization potential, with significant advantages over hydrolysis or hydrothermal techniques.

Modification of optical emission in electrospun PVA nanofibers: effect of cerium oxalate crystals doped with neodymium and praseodymium

ABSTRACT Development of functional nanofibers from transparent polymer systems attracted attention of researchers recently. Doping of functional nanoparticles in a suitable polymer matrix in the nanofiber forms enables them as active materials for photonic, electronic and for energy generation applications. Cerium oxalate crystals in its pure and rare earth-doped form are found to be a potential system for such investigations. Cerium oxalate crystals and its praseodymium (Pr3+)- and neodymium (Nd3+)-doped forms were synthesized by single diffusion gel growth method. These crystals, in the powder form, were incorporated in PVA matrix to form nanofibers (NFs) by electrospinning technique. Morphological studies were done by scanning electron microscopy (SEM). From the X-ray powder diffraction analysis, monoclinic structure of Ce2(C2O4)3 was confirmed. The notable changes observed in the FTIR spectra revealed interactions between the cerium ions and polymer PVA. The optical absorption characteristics of pure and doped PVA NFs were done by UV–Visible absorption spectroscopy. The photoluminescence spectrum of the rare earth-doped cerium oxalate-PVA NFs showed that the fiber had strong emission in the blue-green region.

Experimental investigation of sedimentation behaviour using cerium oxalate particles in oxalic‐nitric acid medium

AbstractSettling behaviour of cerium oxalate particles in the solution was investigated by batch settling tests. The settling curves were experimentally generated for different overall solid fractions (OSF), initial dispersion height (ht) and batch cylinder diameter (d). Settling curves were analysed to obtain bulk settling velocity, and it was observed that bulk settling velocity decreases with increase in OSF and remains unchanged with change in cylinder diameter. Bulk settling velocity was found more or less same with increase in initial suspension height as long as the OSF was maintained constant. The particle settling time is delayed at higher OSF due to dense particle population as the movement of one particle is affected by the presence of neighbouring particle. Regression analysis of the settling curve was performed to identify suitable mathematical model. Two parameter based model was found to represent the settling curve better in comparison to three and five parameter based models. Applicability of dispersion number for characterizing the solid–liquid suspension was checked, and it was found that the dispersion number was not unique for the solid‐liquid system where it was influenced by the operating and dimensional parameters.

Morphology-Controlled Precipitation of Cerium Oxalate Crystals: The Effect of Water in Nanostructured Solvents

The ability to control the morphology of precipitated cerium oxalate material results in determinate evidence to its final properties. In this study, we demonstrate that surfactant-free nanostructu...

Исследование совместного термического разложения оксалатов марганца и церия на воздухе и в инертной среде

Контролируемое термическое разложение оксалатных солей — перспективный метод получения высокодисперсных материалов. В работе изучался процесс совместного разложения солей Mn и Ce при варьировании соотношения катионов, газовой атмосферы процесса (воздух и инертный газ). Для этого синтезирована серия оксалатов Mn и Ce методом соосаждения из водного раствора нитратов при соотношении Mn:Ce от 0:1 до 1:0. Методами рентгенофазового анализа и сканирующей электронной микроскопии показано, что происходит формирование оксалатов церия Ce(C2O4)3×10H2O и марганца MnC2O4×2H2O, увеличение содержания марганца ведет к росту количества соответствующих солей и изменению морфологии частиц. Результаты совместного использования комплекса физико-химических методов, таких как: термический анализ, in situ рентгеновская дифракция и масс-спектрометрия — показали, что разложение оксалатов осуществляется в две стадии и зависит от соотношения катионов, а также от атмосферы разложения. На первой стадии происходит потеря веса, сопровождающаяся уходом структурной воды, данный процесс ускоряется в токе инертного газа. Вторая стадия заключается в формировании оксидов из безводной соли и сопровождается выделением CO2 или CO/CO2. На воздухе за счет экзотермической реакции окисления разложение происходит при более низких температурах, чем в инертном газе. Введение марганца не сказывается значительным образом на температурных интервалах первой и второй стадии разложения соли. Однако добавление второго катиона оказывает влияние на продукт разложения: с увеличением содержания марганца происходит уменьшение размера частиц CeO2 и формирование простых оксидов марганца Mn3O4 на воздухе и MnO в инертной среде. Исследованы каталитические свойства в реакции окисления CO Mn, Ce-оксидов, полученных при разложении оксалатов в инертном газе и на воздухе. Показано, что катализаторы, сформировавшиеся в окислительной среде, более активные.

Conversion of cerium and lanthanum from rare earth polishing powder wastes to CeO2 and La0.6Ca0.4CoO3

In the present work, a feasible approach was developed for the recovery of cerium and lanthanum from rare earth polishing powder wastes to synthesize shape-controlled CeO2 and perovskite-type La0.6Ca0.4CoO3 powders. The process proposed here includes six steps: (i) Pre-roasting treatment, (ii) H2SO4 digestion and water leaching, (iii) double salt (NaRE(SO4)2·xH2O) precipitation, (iv) conversion of NaRE(SO4)2·xH2O into RE‑carbonate, (v) oxidation and separation of cerium and lanthanum, and (vi) oxalic salt precipitation conversion and calcinations to synthesize CeO2 and glycine-nitrate combustion process to get La0.6Ca0.4CoO3.The recovery yield for the total process was 91.73% for cerium and 90.45% for lanthanum. In the preparation process of CeO2 and La0.6Ca0.4CoO3, CeO2 powders with controlled shapes were obtained by modifying the final pH value in the precipitate transformation from Ce(OH)4 to cerium oxalate and subsequent calcinations. On the other hand, based on the polarization curves, the prepared La0.6Ca0.4CoO3 exhibited a good catalytic activity for oxygen reduction reaction, showing potential applications in zinc-air batteries.

Cerium Oxalate Morphotypes: Synthesis and Conversion into Nanocrystalline Oxide.

Cerium dioxide is a scientifically and technologically important material with a wide range of potential applications, particularly in solid oxide fuel cells and catalysis. Herein, we report a study focusing on the synthesis of nanocrystalline cerium dioxide via thermal decomposition of the oxalate salt. Simply by changing reaction conditions (temperature, concentration, acidity, strike) during the precipitation of the cerium solution with oxalic acid, we were able to obtain different morphologies. The main reaction parameters were mapped and linked to the morphology of the final products. Additionally, it was proved that oxalate precipitation is a robust reaction proceeding at relatively extreme contitions. Moreover, the conversion of cerium oxalate to nanocrystalline oxide was followed to monitor the progress of the reaction, the texture evolution, and the grain growth. The results showed that, for unvaried heating cycle, the grain size of converted material is linked to morphology. The thinner was the original microcrystal the smaller were the CeO2 nanocrystals after calcination. In addition, the grains were found smaller near the edges of the ex-oxalate microcrystals. In both cases, this behavior results from asymmetrical limitations of diffusion during grain growth.

Selective cerium removal by thermal treatment of mixed rare earth oxalates or carbonates obtained from non-purified rare earth sulphate liquor

One of the world́s most abundant of all the rare earth elements (REE) is cerium. It represents about 50 wt% of total REE content in the main rare earth minerals used industrially (monazite and bastnaesite). However, cerium is not a valuable product if compared with the other REE. In the most current pyro-hydrometallurgical processes routes, a high amount of cerium goes to the rare earth liquor, incurring in high operational and capital costs in the solvent extraction step used in the separation of each individual rare earth element. In this context, this study evaluates the use of thermal treatment for rare earth oxalates and carbonates and also hydrochloric acid leaching of calcination products for selective separation of cerium from other REE. This investigation also sheds light on the mechanisms involved in the processes proposed. For this purpose, mixed rare earth and cerium oxalates, also mixed rare earth and cerium carbonates were used as precursors. The mixed rare earth salts used in the experiments were generated from a non-purified rare earth sulphate liquor. The results indicated that the minimum required temperature to fully decompose the mixed rare earth oxalates, cerium oxalate, mixed rare earth carbonates and cerium carbonate to their respective rare earth oxides (REE2O3) or CeO2, was 1100 °C, with 1 h of residence time. In the experiments carried out with mixed rare earth oxalates, Ce3+ was not fully oxidized to Ce4+, it formed a mixture of Ce2O3 and CeO2 represented by Ce4O7, which was completely dissolved in the hydrochloric acid solution (37 wt%). Therefore, in such case, cerium was not selectively removed from the mixed rare earth oxalates by thermal treatment and hydrochloric acid leaching. On the other hand, the Ce3+ presented in the composition of the pure cerium oxalate or carbonate was fully oxidized to Ce4+ (CeO2) under the same condition of calcination. As expected, CeO2 was not dissolved by the hydrochloric acid solution (37 wt%). It was concluded that mixed rare earth carbonates generated Ce0.60Nd0.40O1.80 (Ce1-xNdxO2-x/2, x = 0.40) when calcined under the same condition. This crystalline structure was not also dissolved by hydrochloric acid solution (37 wt%). As a result, a process flowsheet was proposed to remove cerium selectively from a rare earth ore.

Synthesis of Cerium Phosphate White Pigments from Cerium Oxalate

Catalytically active cerium dioxide is used as light reflection materials for cosmetic applications. Therefore, cosmetics containing this pigment too much cause oxidation of the skin. Therefore, the substitute for cerium dioxide is required to prepare the cosmetics without catalytic activity. Herein, as novel white pigments for use in cosmetics, cerium phosphates were prepared from cerium oxalate under various conditions. The chemical composition, powder properties, catalytic activity, color phase, and smoothness of the cerium phosphates were evaluated. All samples had weak unknown peaks in XRD patterns. Samples prepared at high temperature and for long time indicated the peaks of phosphate in IR spectra. Samples prepared in this work had no photo and oxidation catalytic activities. Samples prepared at high temperature and for long time indicated enough high whiteness and high smoothness.

Performance of Cerium Oxides from Different Preparation Methods for Desulfurizing Hot Coal Gas.

Four CeO2 samples were prepared by pyrolysis of cerium hydroxide, cerium nitrate, cerium oxalate, and cerium perchlorate. The structures of CeO2 samples were characterized by means of X-ray diffraction and nitrogen adsorption–desorption. Temperature-programmed reduction and thermogravimetry tests were carried out to evaluate the reduction and sulfurization behaviors of the CeO2 samples. The results indicate that the samples, prepared from different precursors, have larger surface areas and pore specific volumes, smaller average crystallite sizes, and better reducibilities (except the sample from cerium perchlorate) than the CeO2 reagent. The sulfurization performances of CeO2 samples are directly correlated with the reduction degrees of CeO2 samples. Compared with fresh CeO2 samples, reduced ones have better sulfurization performances. Among the four CeO2 samples, the one prepared from cerium nitrate, with the best reducibility, exhibits the best performance in sulfurization.

Ultrasonic‐assisted Solution‐Phase Synthesis and Property Studies of Hierarchical Layer‐by‐Layer Mesoporous CeO2

Hierarchical layer‐by‐layer quadrangle CeO2 was prepared through ultrasonic‐assisted solution‐phase synthesis strategy using cerium oxalate as the precursor. The as‐prepared mesoporous CeO2 displayed a surface area of 98.7 m2 g−1 and pore diameters of 2.0–10.0 nm. The high‐resolution TEM image revealed that the layer structures of the CeO2 were made of numerous nanocrystal particles with the crystallite size of about 13–15 nm. High energy and cavitation of ultrasonic wave assists cerium oxalate precursor in building the layer‐by‐layer quadrangle staking. UV–vis absorption spectrum showed that the direct allowed transition bandgap energy for the as‐prepared CeO2 was 2.91 eV. Moreover, the CeO2 exhibited good photocatalytic property for degrading Rhodamine B solution under UV radiation.

Ultra-fast precipitation of transient amorphous cerium oxalate in concentrated nitric acid media

Amorphous cerium oxalate precipitates as a primary transient precursor for the crystalline phase by means of a binodal phase separation.

Synthesis of cerium oxalate hydrate by precipitation technique under external magnetic field

Cerium oxalate hydrate particles were synthesized by precipitation technique under external magnetic field with respective intensities of 0, 0.1, 0.3, and 0.6 T. The particle morphologies were investigated by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Results show that external magnetic field has a great influence on the growth behavior of cerium oxalate hydrate particles. Rod-like and plate-like cerium oxalate hydrate particles with smaller size are formed without the applying of external magnetic field. However, the extremely big rod-like particles with the average size of 12.47 μm were prepared under external magnetic field of 0.6 T. The increasing magnetic field intensity makes the grain grow quickly. Thermogravimetric analysis supports the presence of 8.5 H2O molecules associated with cerium oxalate. Further, the growth mechanism of cerium oxalate hydrate under external magnetic field was briefly discussed.

Unstable amorphous cerium oxalate precipitation in concentrated HNO3 media

Unstable amorphous cerium oxalate precipitation in concentrated HNO₃ media

Determination of cerium in ferrocerium lighter flint stone using Uv-Vis spectrophotometry

Determination of cerium in ferrocerium lighter flint stone by means of spectrophotometry is described. The method is based on the formation of cerium-formaldoxime complex. In order to achieve accurate results, it was necessary to separate iron which was present in the samples. It was achieved by precipitation of cerium oxalate.

Structured solvent effects on precipitation

The synthesis of cerium oxalate, a reaction intermediate in the preparation of high performance ceramics, is studied in sessile droplets. We compare here the effect of alcoholic solvents with the usage of structured solvents, namely ultra-flexible microemulsions in the water-rich and oil-rich configurations. The nucleation and the growth of cerium oxalate particles are the result of local mixing by the Marangoni flow of droplets loaded with oxalic acid and cerium nitrate. The morphology of the particles is very different depending on the composition of the solvent and on the mixing process. We show that the variation of the particle morphology results from the difference of the structured solvent microphases during the precipitation process. When the precipitation occurs in a water continuous phase, usual needle-like oxalate particles precipitate. When the precipitate is formed in the dispersed phase of the emulsion, structured aggregates, as close-packed aggregates of needles, are compacted by microcapillarity effects.