Cerium Hydroxide Research Articles

Synthesis and optical properties of nanostructured Ce(OH)4

Nanocrystalline cerium hydroxide (NCs-Ce(OH)4) is a intermediate product of CeO2, synthesized successfully using a novel and simple wet chemical rout at an ambient temperature for the preparation of NCs CeO2 powder and film on mass scale for various purposes. The synthesized NCs-Ce(OH)4 was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA), Fourier transform infrared (FTIR), UV-visible and photoluminescence (PL) spectroscopy. The average crystallite size of NCs-Ce(OH)4 has been estimated by the Scherrer equation to be 3–4 nm. The SEM examinations show that the surface texture was uniformly agglomerated and homogeneous. Thermal analysis suggests that cerium (IV) ion is in the tetra hydrated form. Absorption and luminescence spectroscopic studies have been examined for future application in the development of optical devices.

Tuning hydrated nanoceria surfaces: experimental/theoretical investigations of ion exchange and implications in organic and inorganic interactions.

Long-term stability and surface properties of colloidal nanoparticles have significance in many applications. Here, surface charge modified hydrated cerium oxide nanoparticles (CNPs, also known as nanoceria) are synthesized, and their dynamic ion exchange interactions with the surrounding medium are investigated in detail. Time-dependent zeta (zeta) potential (ZP) variations of CNPs are demonstrated as a useful characteristic for optimizing their surface properties. The surface charge reversal of CNPs observed with respect to time, concentration, temperature, and doping is correlated to the surface modification of CNPs in aqueous solution and the ion exchange reaction between the surface protons (H(+)) and the neighboring hydroxyls ions (OH(-)). Using density functional theory (DFT) calculations, we have demonstrated that the adsorption of H(+) ions on the CNP surface is kinetically more favorable while the adsorption of OH(-) ions on CNPs is thermodynamically more favorable. The importance of selecting CNPs with appropriate surface charges and the implications of dynamic surface charge variations are exemplified with applications in microelectronics and biomedical.

Adsorption of Phosphate by Cerium Hydroxide

This study investigated the ability of cerium hydroxide (CE) to adsorb phosphate, and compared it to the aluminum compounds boehmite (BE) and gibbsite (GB), which possess high phosphate adsorption ability. Specific surface area, number of hydroxyl groups, and amount of phosphate adsorbed were measured. Results indicated that specific surface area increased in the order GB < CE < BE, number of hydroxyl groups increased GB < BE < CE, and amount of phosphate adsorbed increased GB < BE < CE. These results showed that the adsorption mechanism of phosphate using CE was more closely related to chemical factors involved in the exchange of phosphate with hydroxyl groups onto CE than to physical factors such as specific surface area. [DOI: 10.1380/ejssnt.2010.258]

MORPHOLOGY CONTROL OF CERIUM PHOSPHATES VIA SOLUTION PROCESSES FOR NEW SUNSCREEN APPLICATION

Plate-like hydrated cerium phosphate, Ce2(PO4)2HPO4 · H2O , ca. 3 μm in diameter, was obtained by the hydrothermal reaction of Ce(SO4)2 in H3PO4 aqueous solution at 150–200°C. Ce2(PO4)2HPO4 · H2O transformed to CeP2O7–CePO4 mixture around 700°C while maintaining the plate-like morphology. Plate-like CePO4 and CeP2 O 7 were also synthesized as single phase by heating plate-like Ce2(PO4)2HPO4 · H2O at 700°C with cerium hydroxide and NH4H2PO4 , respectively. Plate-like cerium phosphates showed excellent comfort, absorption ability of UV-ray and lower oxidation catalytic activity than undoped ceria. The UV-shielding ability was in the order Ce2(PO4)2HPO4 · H2O &gt; CeP2O7 &gt; CeP2O7–CePO4 mixture &gt; CePO4 &gt; K0.8Li0.266Ti1.734O4.

Screening study of spray solution parameters for depositing cerium-based conversion coatings on Al alloy 2024-T3

Cerium-based conversion coatings were deposited on aluminum alloy 2024-T3 by a spray process using a solution containing cerium chloride, hydrogen peroxide, and gelatin. As deposited coatings were composed of hydrated cerium oxide and were post-treated in a phosphate solution to improve corrosion performance. Coating solution parameters, including the pH (1–2.5), cerium chloride concentration (0.025–0.125 M), and hydrogen peroxide content (0–1.2 M), were varied to investigate the effect(s) of solution parameters on the corrosion performance of the post-treated coatings. Results indicated that thickness of coatings deposited from solutions with different pH values were similar, while coating thickness increased with increasing concentration of cerium chloride and hydrogen peroxide in the solutions. Electrochemical impedance spectroscopy and observations of the surface appearances of the coatings indicated that coatings deposited from solutions with a pH 2, a cerium concentration of 0.1 M, and a hydrogen peroxide concentration of 0.8 M exhibited the best corrosion resistance.

Effect of Phosphate Source on Post-Treatment of Cerium-Based Conversion Coatings on Al 2024-T3

The surface morphology, electrochemical characteristics, and salt spray corrosion performance were studied for cerium-based conversion coatings on Al 2024-T3 that were post-treated in heated aqueous solutions of orthophosphate, pyrophosphate, and polyphosphate compounds. Phosphate post-treatment reduced cracking in the coatings, which resulted in better corrosion protection compared to coatings that were highly cracked or contained other defects. In addition, post-treatment in orthophosphate solutions converted the as-deposited hydrated cerium oxide to hydrated , which further improved corrosion protection. Electrochemical analyses showed that cerium-based conversion coatings that contained hydrated cerium phosphate after post-treatment had the highest resistance , the most noble pitting potentials , and the best corrosion protection of the post-treatments that were tested. While pyrophosphate and polyphosphate post-treatments reduced cracks in the coatings, they did not promote the formation of hydrated cerium phosphate. The results suggest that the corrosion protection of cerium-based conversion coatings on Al 2024-T3 is dependent on both the surface morphology and the phase of the coating.

The effect of post-treatment time and temperature on cerium-based conversion coatings on Al 2024-T3

Corrosion performance, morphology, and electrochemical characteristics of cerium-based conversion coatings on Al 2024-T3 were examined as a function of phosphate post-treatment time and temperature. Corrosion resistance improved after post-treatment in 2.5 wt.% NH 4H 2PO 4 for times up to 10 min or temperatures up to 85 °C. Electrochemical impedance spectroscopy and polarization testing correlated to neutral salt spray corrosion performance. Hydrated cerium oxide and peroxide species present in the as-deposited coatings were transformed to CePO 4·H 2O for post-treatments at longer times and/or higher temperatures. Based on these results, processes active during post-treatment are kinetically dependent and strongly influenced by the post-treatment time and temperature.

Investigation of Ce/Al2O3 composite coating on anodised aluminium film by ac deposition method

In order to prepare Ce/Al2O3 composite coating on oxide film quickly, a new process of ac deposition method in a solution containing H2O2 and CeCl3 was introduced. Scanning electron microscopy/energy dispersive X-ray spectroscopy, electron probe microanalyser, X-ray diffractometer and X-ray photoelectron spectroscopy were adopted to analyse the coating. The results showed that the Ce/Al2O3 composite coating was easy to prepare when the Al2O3 film thickness was over 6·8 μm. The Ce sediment was amorphous of cerium (III and IV) hydroxide and located into the pores near the surface of Al2O3 films layer. The forming mechanism of the composite coating was discussed accordingly.

Improvement in corrosion resistance of magnesium coating with cerium treatment

Corrosion protection afforded by a magnesium coating treated in cerium salt solution on steel substrate was investigated using open circuit potential, polarization curves, and electrochemical impedance spectroscopy (EIS) in 0.005 M sodium chloride solution (NaCl). The morphology of the surface was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The cerium treated coating was obtained by immersion in CeCl3 solution. The results showed that the corrosion resistance of the treated magnesium coating was improved. The corrosion potential of the treated coating was found to be nobler than that of the untreated magnesium coating and the corrosion current decreased significantly. Impedance results showed that the cerium treatment increased corrosion protection. The improvement of anti-corrosion properties was attributed to the formation of cerium oxides and hydroxides that gave rise to a physical barrier effect.

The Effect of Phosphate Source on the Post-treatment of Cerium Based Conversion Coatings on Al 2024-T3 and its Correlation to Corrosion Performance

The surface morphology, electrochemical characteristics, and salt spray corrosion performance was studied for cerium-based conversion coatings (CeCCs) that were post-treated in heated aqueous solutions of orthophosphate, pyrophosphate, and polyphosphate compounds. Phosphate post-treatment reduced cracking in the coatings, which resulted in better corrosion protection compared to coatings that were highly cracked or contained other defects. In addition, post-treatment in orthophosphate solutions converted the as-deposited hydrated cerium oxide to hydrated CePO4, which further improved corrosion protection. Electrochemical analyses showed that CeCCs that contained hydrated CePO4 after post-treatment had the highest resistance (~100 kΩ-cm2), most noble pitting potentials (~ -270 mV), and best corrosion protection of the post-treatments that were tested. While pyrophosphate and polyphosphate post-treatments reduced cracks in the film, they did not promote formation of CePO4⋅H2O. The results suggest that the corrosion protection of CeCCs on Al 2024-T3 is dependent on both the surface morphology and phase of the coating.

Synthesis of Monodispersed rod-like and spherical CeO2 particles by mild solution process

Monodispersed rod-like and spherical ceria particles were successfully synthesized by a mild solution process followed by calcination treatment. The morphological control of cerium precursor was realized by using different cerium salts and precipitate reagents such as urea, hexamethylenetetramine and alkylamine. The effects of pre-aging temperature and time on the morphologies of final products were investigated in details. Monodispersed spherical precursor was obtained after pre-aging at 25°C for 3 days, while rod-like cerium carbonate precursor was produced after pre-aging at 50°C. Monodispersed rod-like cerium hydroxide precursor was formed by using triethanolamine as precipitant. Ceria particles with the same morphologies and similar particle size could be obtained after calcination in air at 400°C.

SYNTHESIS OF PLATE-LIKE CERIUM PHOSPHATES AND THEIR PHOTOCHEMICAL PROPERTIES VIA SOFT CHEMICAL REACTIONS

Plate-like cerium phosphates have attracted attention because of their unique UV-shielding ability with low photocatalytic activity and excellent comfort when applied on skin. Plate-like hydrated cerium phosphate, Ce2(PO4)2HPO4·H2O, ca 3 μm in diameter, was obtained by the hydrothermal reaction of Ce(SO4)2 in H3PO4 aqueous solution at 200 °C for 3 h. Ce2(PO4)2HPO4·H2O transformed to CeP2O7-CePO4, mixture around 700 °C with the transcription of plate-like morphology. Plate-like CePO4 and CeP2O7 were also synthesized as single phase by heating plate-like Ce2(PO4)2HPO4·H2O with cerium hydroxide and NH4H2PO4, respectively. Plate-like cerium phosphates showed excellent comfort, absorption ability of UV-light and lower oxidation catalytic activity than undoped ceria. The UV-shielding ability of them was in the order Ce2(PO4)2HPO4·H2O > CeP2O7 > CeP2O7-CePO4 mixture > CePO4 > K0.8Li0.266Ti1.734O4.

Fabrication and analysis of anti-corrosion coatings on in-situ TiB 2p reinforced aluminum matrix composite

Anodizing and rare earth sealing were combined to investigate the feasibility of in-situ TiB 2p/A356 composite for corrosion protection. Optical microscope observation found that the thickness of anodic film was non-uniform. Scanning electron microscope analysis showed that anodic film of the composite mainly presented porous structures and had many cavities, micro-pores and micro-cracks. Ce sealing treatment was proposed to remedy the surface defects in order to further enhance the corrosion resistance of the composite surface. The sealing layer was composed of spherical deposits and main compositions were cerium oxide and cerium hydroxide. These deposits completely sealed the porous structures as well as covered most defects of anodic film. The salt spray corrosion test and electrochemical corrosion test were used to evaluate the corrosion resistance of the coatings. The results indicated that the synergism effect of anodized film and Ce sealing layer resulted in a higher degree of protection in a chloride-containing environment than a single anodized coating for TiB 2p/A356 composite. The cerium sealed anodized film effectively held back corrosive intermediate and protected the composite matrix.

Adsorption of selected ions on hydrous cerium oxide

Hydrous cerium oxide was synthesized and laboratory study was conducted to address its applicability for decontamination of barium, strontium, molybdenum, europium, iodine, samarium and cesium ions from radioactive liquid wastes using radiotracer technique. The adsorption of Ba(II), Sr(II), Mo(II), Eu(II), I(I), Sm(III) and Cs(I) on hydrous cerium oxide has been investigated as a function of pH, concentration and temperature of the adsorptive solution and the result obtained show that these parameters affect the extent of adsorption. The ion-exchange capacity decreased at higher temperatures which could be due to decrease of active sites as well as hydrophilic properties of surface adsorbent. Hydrous cerium oxide shows relatively high adsorption in acidic and neutral media towards the radiotracers studied, which can be attributed to large hydrated radius and ion exclusion effect.

Effect of solvent on physical properties of samaria-doped ceria prepared by homogeneous precipitation

Samaria-doped ceria solid solutions were prepared by homogeneous precipitation with hexamethylenetetramine using water and mixtures of alcohol/water as solvent. The mixed solvent influences several physical properties of the synthesized material when compared to those of samples prepared in water. The solid solution is formed, at least partially, during precipitation as demonstrated by Raman spectroscopy data. The dried precipitate is crystalline and single phase with fluorite-type structure, and consists of a mixture of anhydrous and hydrated cerium oxide with average sizes in the 5–8 nm range. Thermal decomposition of the as-synthesized material occurs at 400 °C. High densification was obtained at low temperatures (∼1200 °C). The electrical conductivity of grains and grain boundaries is improved for synthesized samples when compared to specimens prepared by mixing of starting oxides. These improved characteristics of synthesized powders are attributed to the interaction among the solvent and hydroxyl and water species on the surface of nanoparticles. The strength of this interaction is related to the carbon content in the alcohol chain.

Synthesis and catalytic properties of microemulsion-derived cerium oxide nanoparticles

The synthesis of cerium dioxide nanoparticles using an inverse microemulsion technique and precipitation method was investigated. Cerium hydroxide nanoparticles were synthesized by adding diluted ammonia to n-heptane–surfactant–cerium nitrate system. The micelle and particle size in the range of 5–12 nm were controlled by varying the molar water to surfactant ratio and analyzed by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM). Cerium hydroxide nanoparticles were isolated and subsequently treated at 100–600 °C to obtain nanoscale ceria. Crystallite sizes of cerium dioxide in the range of 6–16 nm were estimated by Scherrer analysis by X-ray diffraction (XRD) and HRTEM. The catalytic activity of particles annealed at 400 and 600 °C in soot combustion reactions was characterized by temperature-programmed oxidation (TPO) indicating a size-dependant activity. Crystallite sizes and catalytic stability of elevated ceria systems were tested in second combustion cycles.

Encapsulated cerium nitrate inhibitors to provide high-performance anti-corrosion sol–gel coatings on mild steel

A rapid cure silane sol–gel coating containing encapsulated corrosion inhibitors that can be applied to a mild steel substrate to form a crack-free coating has been developed. The benefit of this system is that it appears to emulate the protection mechanism found with traditional chrome (VI) based systems, but without the environmental disadvantages, namely that it is non-toxic and non-carcinogenic. The high corrosion resistance performance of this coating is derived from the combination of the hydrophobic nature of the sol–gel coating and the presence of the encapsulated rare earth corrosion inhibitor which can be released at defects within the coating resulting in cerium hydroxide precipitation which hinders the reduction reaction at cathodic sites. The proposed mechanism for this protection is based upon an evaluation of the barrier properties of the coating using electrochemical impedance spectroscopy and long-term immersion/salt spray tests.

Porous CeOX/SiC Nanocomposites Prepared from Reverse Polycarbosilane-Based Microemulsions

Reverse microemulsions consisting of aqueous cerium nitrate solution as the internal phase and polycarbosilane dissolved in heptane as the continuous phase were used as a precursor for the controlled synthesis of dispersed cerium oxide particles inside a porous SiC matrix. According to dynamic light scattering experiments, the effective diameter of the cerium hydroxide particles obtained after ammonia addition is effectively controlled in a range of 2–10 nm with the molar water/surfactant ratio (Rw = 6–16). Pyrolysis at 1200 to 1500 °C produces materials with specific surface areas up to 240 m2 g−1. Whereas crystallization of the matrix is achieved only at higher temperature, cerium oxide particles form agglomerates composed of smaller nanoparticles that tend to dissolve into the ceramic matrix at 1500 °C leaving macropores behind. The high specific surface area is attributed to the presence of mesopores with a broad size distribution. Excess carbon present after pyrolysis is removed by oxidation at 900 °...

Formation of Ce 0.8Sm 0.2O 1.9 nanoparticles by urea-based low-temperature hydrothermal process

The synthesis and formation mechanism of the nano-sized Ce 0.8Sm 0.2O 1.9 particles prepared by a urea-based low-temperature hydrothermal process was investigated in this study. From ex situ X-ray diffraction and induced coupled plasma-atomic emission spectroscopy investigations, it was found that large quantities of cerium hydroxide co-precipitated with some samarium hydroxide at the initial stage of the hydrothermal process. The remaining Sm 3+ ions in the solutions were further hydrolyzed and deposited on the surface of the cerium hydroxide-rich precipitates to form a core–shell-like structure. During the hydrothermal process, the core–shell-like structure transformed to a single cubic fluorite phase which is due to the incorporation of the deposited samarium hydroxide into the cerium oxide-rich core. Further, the average grain size of the synthesized nanocrystalline Ce 0.8Sm 0.2O 1.9 was reduced with increasing the urea concentration in the solution. The density of the disk prepared with the synthesized Ce 0.8Sm 0.2O 1.9 powders was found to increase with a decrease in the grain size of Ce 0.8Sm 0.2O 1.9. The existence of SO 4 2− anions in the SDC powders prepared at low-urea concentration may result in the SDC disks with low density due to their decomposition during sintering process.

Nanocrystallized ceria-based coatings prepared by electrochemistry on TA6V titanium alloy

Nanocrystallized ceria-based coatings were prepared on TA6V titanium alloy by using a three-step procedure: substrate pre-treatment, electrochemical impregnation and final heat treatment. UV–vis and Raman in situ spectroscopies performed at the substrate interface during the electrochemical impregnation, showed experimentally for the first time that the interfacial deposit is made up of cerium hydroxide, incorporating also water molecules and nitrate ions coming from the electrolyte. Thermogravimetric analysis indicated also that the composition of the coating after the impregnation is given by the global formula CeO 2·3.4H 2O, while XRD analysis revealed that ceria with cubic fluorite crystalline structure is finally produced. Different preparation conditions were studied in view to control the nanosize of the supported ceria crystallites. It appeared that the final heat treatment is the most efficient operational parameter for the tuning of the particle size, that it can be thus well controlled from 5 to 30 nm between 300 and 700 °C.