Cerium Content Research Articles

A facile synthesis of 3D pyramidal hierarchical CeO2–Al2O3 nanocomposites supported nickel catalyst for cyclohexane dehydrogenation

In this study, hierarchical 10 and 20%CeO2–Al2O3 nanocomposites with 10 and 20% ceria content as well as pure γ-Al2O3 were synthesized via template-free modified co-precipitation method. The as-synthesized nanocomposites were characterized using several techniques such as BET, XRD, TEM, TGA-DTA, XPS, FE-SEM and AFM. The synthesized nanocomposites were loaded by 5% NiO via ultrasonic assisted route and successfully investigated for cyclohexane dehydrogenation in a catalytic flow system. The XRD results ensured the formation of crystalline cubic γ-alumina and cubic CeO2 with fluorite structure. Additionally, a solid-solution has been formed in all CeO2–Al2O3 nanocomposites with retaining the ceria fluorite structure. Moreover, a large fraction of dispersed CeO2 phase over the nanocomposites surface accompanied by CeAlO3 cubic phase was observed. TEM, AFM and FE-SEM technique emphasized the development of totally novel 3-dimensional hierarchical pyramidal structure nanocomposites which newly synthesized with a facile preparation procedure. Finally, the synthesized nano-composites achieved high benzene yield of 98.9 and 99%, at LHSV of 1 h−1 whereas, 100% selectivity was achieved at LHSV of 3 h−1 towards benzene production up to 350 °C of reaction temperature. At higher reaction temperature, a considerable amount of methane is clearly detected in the product gas suggesting the occurrence of cyclohexane hydrogenolysis. The obtained catalytic performance was attributed to the proposed experimental conditions, the high surface area of the synthesized hierarchical structure and the optimized ceria loading to the alumina ratios.

Study on the Potential Rare Earth Elements in Coal Combustion Product from Banjarsari Power Plant, South Sumatera

Coal combustion produt (CCP) from Banjarsari power plant, both fly ash and bottom ash are numerous and have not been utilized optimally. CCP contains rare earth elements so that the potential needs to be assessed as a resource and reserve of rare earth elements (REE) in the future. The stages of this research were sample preparation and testing of grain size distribution using the wet and dry sieving method. Grain morphology was observed under a microscope and the determination of mineralogical content with XRD, oxide content with XRF and elemental content with ICP-MS. Fly ash grain size distribution of 76.15% passed 200 mesh sieve (0.074 mm) while the bottom ash was only 0.2%. Grain morphology is sub-rounded and there are still coal that has not been completely burned. The dominant mineral content is quartz, mica mineral (muscovite), clay mineral (kaolinite), lime, siderite, magnetite and hematite. The dominant oxides are SiO2, Al2O3, Fe2O3 and CaO. Based on ICP-MS test results, 16 elements of REE were detected. The total REE contents for each sample, FA and BA were 264.97 ppm and 49.22 ppm, respectively. REE of CCP from Banjarsari power plant which has the potential to be extracted is the content of cerium 80.5 ppm, neodymium 42.9 ppm, yttrium 41.8 ppm and lanthanum 31.4 ppm from fly ash while at the bottom ash there is no potential to be extracted.

Development of Combined Rolling-Extruding Modes for Producing Longish Deformed Semi-Finished Products from Aluminum Alloy with Low Cerium Content

The paper presents the data obtained in the course of experimental studies on the production of rods from the Al-0.5% REM alloy using combined processing methods, such as combined rolling-extruding (CRE) and combined casting and rolling-extruding (CCRE). The variable parameters were the temperature of the ingot or melt, the degree of deformation and the strain rate. With the help of strain gauge equipment, experimental data were obtained on the forces acting on the rolls and the die of the CCRE-200 combined processing unit in the process of obtaining rods with a diameter of 5 and 9 mm. The estimation of the dependence of the mechanical properties of the rods on the variable factors has been carried out. The highest strength properties are possessed by a bar obtained by the CRE mode at a temperature T = 550 oC and a strain rate ξ = 0.74 s-1. When comparing the temperature of pouring the metal, the highest strength properties are possessed by a rod with a diameter of 9 mm and 5 mm and a strain rate ξ = 0.74 s-1. If compare in terms of the deformation rate, then the highest strength properties are possessed by a rod with a diameter of 5 mm and a deformation rate ξ = 1.49 s-1. The plasticity of deformed semi-finished products in all modes is at a high level, which allows further processing.

Insight into the Contributions of Surface Oxygen Vacancies on the Promoted Photocatalytic Property of Nanoceria.

Oxygen vacancies (OVs) have critical effects on the photoelectric characterizations and photocatalytic activity of nanoceria, but the contributions of surface OVs on the promoted photocatalytic properties are not clear yet. In this work, we synthesized ceria nanopolyhedron (P-CeO2), ceria nanocube (C-CeO2) and ceria nanorod (R-CeO2), respectively, and annealed them at 600 °C in air, 30%, 60% or pure H2. After annealing, the surface OVs concentration of ceria elevates with the rising of H2 concentration. Photocatalytic activity of annealed ceria is promoted with the increasing of surface OVs, the methylene blue photodegradation ratio with pure hydrogen annealed of P-CeO2, C-CeO2 or R-CeO2 is 93.82%, 85.15% and 90.09%, respectively. Band gap of annealed ceria expands first and then tends to narrow slightly with the rising of surface OVs, while the valence band (VB) and conductive band (CB) of annealed ceria changed slightly. Both of photoluminescence spectra and photocurrent results indicate that the separation efficiency of photoinduced electron-hole pairs is significantly enhanced with the increasing of the surface OVs concentration. The notable weakened recombination of photogenerated carrier is suggested to attribute a momentous contribution on the enhanced photocatalytic activity of ceria which contains surface OVs.

Zn-Co-CeO2 vs. Zn-Co Coatings: Effect of CeO2 Sol in the Enhancement of the Corrosion Performance of Electrodeposited Composite Coatings

Electrodeposition and characterization of novel ceria-doped Zn-Co composite coatings was the main goal of this research. Electrodeposited composite coatings were compared to pure Zn-Co coatings obtained under the same conditions. The effect of two ceria sources, powder and home-made sol, on the morphology and corrosion resistance of the composite coatings was determined. During the electrodeposition process the plating solution was successfully agitated in an ultrasound bath. The source of the particles was found to influence the stability and dispersity of plating solutions. The application of ceria sol resulted in an increase of the ceria content in the resulting coating and favored the refinement from cauliflower-like morphology (Zn-Co) to uniform and compact coral-like structure (Zn-Co-CeO2 sol). The corrosion resistance of the composite coatings was enhanced compared to bare Zn-Co as evidenced by electrochemical impedance spectroscopy and scanning Kelvin probe results. Zn-Co doped with ceria particles originating from ceria sol exhibited superior corrosion resistance compared to Zn-Co-CeO2 (powder) coatings. The self-healing rate of artificial defect was calculated based on measured Volta potential difference for which Zn-Co-CeO2 (sol) coatings exhibited a self-healing rate of 73.28% in a chloride-rich environment.

Investigation on structure and stability of cerium doped (Ba0.5Sr0.5)(Fe1-xCex)O3-δ (x = 0–1.0) oxides by Rietveld refinement

Perovskite-type materials have been attracted due to their relevant applications in memory devices, tunable microwave displays, oxygen-permeable membranes, sensors, and capacitors. An attempt has been made here to analyze the structure of (Ba0.5Sr0.5)(Fe1-xCex)O3-ẟ (x = 0–1.0) oxides by Rietveld refinement under different space groups. It possesses cubic (space group Pm3m, Z = 1), cubic with orthorhombic, and orthorhombic (space group Pnma, Z = 4) structures for the composition x = 0, 0.10–0.60, and 0.80–1.0, respectively. The amount of cubic phase decreases from 100% to 24% with cerium content (x) = 0–0.60 and complete transformation to the orthorhombic phase occurred at x = 0.80. Moreover, single – dual - single structural phase transitions have been observed. The average bond length decreases with cerium content. The bond angles along O–B–O and B–O–B are deviated significantly due to the tilting and rotation of (Ce,Fe)O6 octahedra. The presence of distortion/oxygen vacancies makes the compound useful in industrial applications.

The impact of cerium content on oxygen stoichiometry, defect equilibrium, and thermodynamic quantities of Sr1−xCexFeO3−δ

The structure, oxygen non-stoichiometry, and defect equilibrium in perovskite-type Sr1−xCexFeO3−δ (x = 0.05, 0.10, 0.15, 0.20) were studied. X-ray diffraction showed the formation of a cubic structure for all compositions. The electron diffraction detected an incommensurate structure with a modulation wave vector 0.41 a* in compositions with x ≥ 0.10. The phenomenon is assumed to originate from a strong steric disturbance attributed to a large difference in ionic radii of cerium and strontium. The data on the oxygen content acquired in wide ranges of oxygen partial pressure and temperature were used for the modeling of defect equilibrium in oxides. A part of anion vacancies in Sr1−xCexFeO3−δ was found to be inaccessible for oxygen ions. The main factors of cerium substitution impact on the thermodynamic parameters of defect formation reactions in Sr1−xCexFeO3−δ were revealed to be lattice contraction, steric disturbance, and cerium reduction to Ce3+. The concentration of Ce3+ ions in Sr1−xCexFeO3−δ under reducing conditions was found to be substantially greater than that of Fe2+. Interrelations between thermodynamic quantities of oxygen in Sr1−xCexFeO3−δ and thermodynamic parameters of defect formation reactions were considered.

Combined Antioxidant-Antibiotic Treatment for Effectively Healing Infected Diabetic Wounds Based on Polymer Vesicles.

Infected diabetic wounds are difficult to heal due to high reactive oxygen species (ROS) concentrations and recurrent infections. Such wounds can easily deteriorate into a diabetic ulcer, a chronic diabetic complication with a very high mortality rate. Herein, we propose a combined antioxidant-antibiotic therapy based on poly(ε-caprolactone)-block-poly(glutamic acid) polymer vesicle to treat infected diabetic wounds. This was realized by in situ decoration of stable, well-dispersed ceria nanoparticles onto ciprofloxacin (CIP)-loaded polymer vesicles. These resulting CIP-loaded and ceria-decorated polymer vesicles (CIP-Ceria-PVs) exhibited high superoxide dismutase mimetic activity to inhibit superoxide free radicals (the inhibition rate reached ∼50% at an extremely low cerium concentration of 1.25 μg/mL). When the cerium content is in the range of 5-20 μg/mL, the CIP-Ceria-PVs showed the highest protective capability to normal L02 cells from damage of superoxide free radicals. In addition, the CIP-Ceria-PVs exhibited enhanced antibacterial activity (the dosage of CIP in CIP-Ceria-PVs was reduced by 25-50% compared to free CIP). In vivo treatment of infected diabetic wounds was performed on a diabetic mice model. The CIP-Ceria-PVs could effectively cure infected diabetic wounds within 14 days. Overall, a combined antioxidant-antibiotic therapy was proposed by introducing ceria nanoparticles and CIP into polymer vesicles for the treatment of infected diabetic wounds.

One-Pot Synthesis of CeO2 Modified SBA-15 With No Pore Clogging for NO Reduction by CO

CeO2 modified SBA-15 composites have been prepared by adding cerium precursor (Ce(NO3)3·6H2O) directly into the mixture of soft template (P123), silica precursor (TEOS) and urea aqueous solution but without mineral acid. The products were characterized by X-ray fluorescence (XRF), powder X-ray diffraction (XRD), N2 physisorption and transmission electron microscopy (TEM). Results indicated that ceria were successfully grafted onto mesoporous silica matrix and no pore clogging was observed. Both ceria content and mesoporous ordering of the final products were found to depend on urea amount. Compared to CeO2/SBA-15 from conventional impregnation method, the one-pot synthesis not only showed simple and green operation, but also superior catalytic performance in NO+CO reaction after loaded with CuO. It was revealed that both the presence and location of ceria had great influence on the reducibility of CuO, and the catalytic performances were intimately related to the redox properties of crystalline CuO. That is, higher NO conversion and N2 selectivity were achieved over catalyst with easier reduction of crystalline CuO.

Investigation of the solubility of dust particles in soil solution at different temperatures (on the example of the tailings of the loparite ores' concentration)

A number of large mining enterprises are located on the territory of the Murmansk region. Dusting overburden dumps and tailings storage sites leads to a complex of long-term consequences for the environment. The output of the silty fraction (-0.071 mm) of "stale" tailings of loparite ore dressing (the first field of the tailing dump) is about 22 %. The investigated material is represented by nepheline, microcline, aegirine; loparite, analcime are diagnosed in impurity quantities; the average content of cerium, lanthanum, neodymium - rare earth elements of the light group - 0.18, 0.03 and 0.015 %, respectively. In laboratory conditions, a simulation of the ingress of a fine fraction of loparite ore dressing tailings into the soil has been carried out; the interaction of tailings material with distilled water and water extract from conditionally background soil at different temperatures has been studied. In the course of the study, it has been found that the introduction of dissolved organic matter intensifies the processes of destruction and partial dissolution of the aluminosilicate matrix of rock-forming minerals; an intensive transition of rare earth elements and heavy metals into soluble forms has been recorded. The research results indicate the ecological danger of the finely dispersed material of "stale" tailings of loparite ore dressing due to the ingress of dust particles into the soil and their interaction with soil waters.

Cerium and gallium containing mesoporous bioactive glass nanoparticles for bone regeneration: Bioactivity, biocompatibility and antibacterial activity

In recent years, mesoporous bioactive glass nanoparticles (MBGNPs) have generated great attention in biomedical applications. In this study, cerium and gallium doped MBGNPs were prepared by microemulsion assisted sol-gel method in the binary SiO2-CaO system. MBGNPs with spheroidal and pineal shaped morphology were obtained. Nitrogen sorption analysis elucidated the mesoporous structure of synthesized nanoparticles with high specific surface area. X-ray diffraction analysis confirmed the amorphous nature of the nanoparticles. The chemical compositions of all samples were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES), which revealed that the contents of cerium and gallium could be tailored by adjusting the concentrations of the precursors used for the synthesis. All MBGNPs exhibited in vitro bioactivity when immersed in simulated body fluid, except the particles doped with higher amounts than 1 mol% of cerium. MBGNPs showed antibacterial activity against S. aureus and E. coli without exhibiting cytotoxicity towards MG-63 osteoblast-like cells. Mentioned features of the obtained Ce and Ga-doped MBGNPs make them useful for multifunctional applications such as drug delivery carriers or bioactive fillers for bone tissue engineering applications.

Nanostructured quaternary Ni1-xCuxFe2-yCeyO4 complex system: Cerium content and copper substitution dependence of cation distribution and magnetic-electric properties in spinel ferrites

Quaternary Ni1-xCuxFe2-yCeyO4 complex nano-ferrites system with different cerium content ratio and copper substitution degree were synthesized via co-precipitation wet chemical technique. The newly obtained nanoparticles, with general formula Ni1-xCuxFe2-yCeyO4 (where x = 0.0, 0.3, 0.6 and y = 0.00, 0.03, 0.05, 0.08 and 0.10) were heated up to 600 °C to stabilize the specific crystalline spinel structure. The limit of cerium content was quantitively determined to be around 0.08 and up to 0.10. Furthermore, the powders were pelletized in a 13 mm wide pellets and thermally treated at 950 °C. The thermal treatment affected even more the phases segregation process, as CeO2 was identified in the sample with lowest degree of cerium insertion – 0.03. Also, a difference in color and size of pelletized samples was noticed after the 950 °C thermal treatment. The Rietveld refinement, crystal structure confirmation, morphology magnetic and electrical properties of samples have been deeply studied. The cation distribution carried out from Rietveld refinement confirms the occupancy of (Fe3+) on tetrahedral sites and [Ni2+], [Cu2+], [Fe3+] and [Ce2+] on octahedral sites in the crystal lattice. Preliminary information regarding the cation distribution in spinel structures were suggested by FTIR spectral results, precisely in the 650-520 cm−1 region, as a consequence of peak shape and lack of shiftiness of MTd – O bond. Spherical-shaped quaternary nano-ferrites of 17–28 nm were determined from FE-SEM analysis and the samples composition was confirmed by EDX analysis. Hysteresis loops shows modifications in coercivity, magnetization and magnetic remanence with Ni2+ and Cu2+ ions doping in Ni1-xCuxFe2-yCeyO4 complex systems with typical ferrimagnetic behavior. Dielectric measurements were employed in order to determine the electrical permittivity, dielectric losses and conductivity values in a 10 Hz – 1 MHz frequency range.

Thermodynamic Modeling of Reduction of Cerium from Slags of CaO–SiO2–Ce2O3–15Al2O3–8MgO by Calcium Carbide Additives

Thermodynamic modeling of the reduction of cerium from slags of the CaO–SiO2–Ce2O3 system containing 15% Al2O4 and 8% MgO, with aluminum dissolved in the metal together with calcium carbide additives at temperatures of 1550 and 1650°C was performed using the HSC 8.03 Chemistry software package (Outokumpu) based on the simplex lattice planning method used to minimize Gibbs energy. The results of thermodynamic modeling are presented in the form of composition-property diagrams (equilibrium content of cerium in the metal) for temperatures of 1550 and 1650°C. It is shown that the formation of slags within a basicity range of 2–3 containing 1–7% Ce2O3 provides an equilibrium concentration of cerium in the metal varying from 1 to 7 ppm at a temperature of 1550°C. The displacement of slags in the area of increased basicity (up to 3–5) is accompanied by an increase in the equilibrium concentration of cerium in the metal up to 7–23 ppm with a content of 3–7% Ce2O3 and as a consequence an increase in the efficiency of the process of cerium reduction. At a temperature of 1650°C, the equilibrium concentration of cerium in the metal within the basicity range of 2–3 and having a Ce2O3 content of 1–7% varies from 2 to 12 ppm. The displacement of slags in the area of increased basicity (up to 3–5) is accompanied by an increase in the equilibrium concentration of cerium in the metal to 7–33 ppm with a Ce2O3 content of 3–7%. The positive influence of the temperature factor basicity of slags and the content of cerium oxide on the process of its reduction is qualitatively explained from the standpoint of the formation of the phase composition of the slags of the studied oxide system and the thermodynamics of chemical reactions of reduction of cerium with aluminum dissolved in the metal, as well as with aluminum dissolved in the metal together with calcium carbide additives.

Crystallization behavior, quantitation of Ce3+/Ce4+ and chemical stability analysis of multiple alkaline earths borosilicate glasses for immobilizing simulated tetravalent actinides

A series borosilicate glasses containing three alkaline earth metals (Ca, Mg, Ba) and immobilized with ceria from low content (3 wt%) to exceed the solubility limit (20 wt%) were prepared by the solid-state melt method. The results of phase separation revealed by SEM, XRD and EDX show that simulated waste CeO2 loading was below 13 wt%, and the excess part was tightly connected with glass. The controlled heat treatment of the quenched blocks and the green pellets was conducted to explore the effect of ceria content of the system on the crystalline state. The solidified waste forms with a ratio of Ce3+/Ce4+ close to 1 have the lower leaching rate after 28 d (LRSi=9.84 × 10−4 g m−2 d−1, LRCa=6.68 × 10−4 g m−2 d−1) and LRCe of all samples is always maintained in the order of magnitude of 10−5 g m−2 d−1, suggesting that cerium doped multiple alkaline earths borosilicate glasses have higher chemical stability.

Effect of Cerium on the Behavior of Primary Carbides in Cast H13 Steels

Different amounts of elemental cerium were added into H13 ingots to investigate the effect of cerium content on primary carbides’ behavior. The enrichment of the elemental Cr, Mo, V, and C in the last-to-solidify region was identified by EPMA. The enrichment of alloy elements is the main reason for the precipitation of primary carbides during solidification. As the increase of cerium content, the size of the last-to-solidify region decreases first and then increases. We found a huge difference between the 2D and the 3D observations of primary carbides. The number density of the primary carbides appeared higher, while their size was smaller in the 2D observation. In the 3D observation, as the cerium content increases, the primary carbides’ size also decreases first and then increases, while the morphology of the primary carbides changes from dendritic structure to sheet structure and then to dendritic structure again. The cerium content has little influence on the thermodynamic precipitation process of primary carbides. The enrichment of the elemental cerium in the last-to-solidify region observed by TOF-SIMS accelerates the nucleation of the austenite, further leading to smaller last-to-solidify region size. The smaller last-to-solidify region size provides less space for the further growth of the primary carbide, resulting in the smaller primary carbide size.

Layered Distribution of Platinum Group Elements in Ferromanganese Nodules from the Cape Basin, Atlantic Ocean

The paper presents data on contents of the platinum group elements (Pt, Ir, Pd, and Ru) and Au in Fe–Mn nodules of different morphology and in their separate layers from the Cape Basin, Atlantic Ocean. The Layer-by-layer analysis of the Fe–Mn nodules and crusts shows that the platinum group elements (PGE) are accumulated in the ferromanganese oxyhydroxide layers relative to the clayey nuclei and the substrate of the crust. Among oxyhydroxide layers, PGE are more significantly concentrated in the hydrogenetic (sedimentation) layers of the nodules than in layers with predominant oxic and suboxic diagenetic material. Gold is demonstrated not to be accumulated in the Fe–Mn nodules. The reason for the predominant accumulation of platinum relative to palladium in nodules is the oxidative sorption on manganese oxyhydroxides suspended in seawater. An increase in the growth rate of the nodules due to the input of diagenetic material from sediments is accompanied by an increase in the Mn/Fe value in the nodules. The increase of Mn/Fe value in nodules is shown to be associated with a decrease in the Pt/Pd ratio, which indicates a dominant role of the hydrogenetic input of PGE to the nodule. The contents of iridium and ruthenium correlate with the contents of platinum and cerium.

AMPEROMETRIC DETERMINATION OF CERIUM (III) USING 2,7-DINITROZO-1,8- DIHYDROXYNAPHTHALENE-3,6-DISULFONIC ACID SOLUTION

Cerium and its compounds are widely used in the production of electronic devices and semiconductors, which is why these substances will enter the environment more often in the future. There is a need for effective express methods that can determine the trace amounts of cerium and other rare earth elements with high accuracy to control and study the possible negative impact of cerium compounds on the ecosystems. The objective of this research paper was to elaborate on an express method capable of producing accurate and reliable results on the content of cerium in wastewaters in the presence of other rare earth elements. The elaboration of the express method was carried out based on the amperometric titration method studying the effect of various buffer solutions on cerium determination. Moreover, the effect of strontium, lutetium, iron, yttrium, samarium, niobium, holmium, praseodymium, gadolinium, and erbium ions on acquisition accuracy of the cerium (III) ions in samples of process water was studied. The research results presented a method for the amperometric determination of cerium (III) applying 2,7-dinitroso-1,8-dihydroxynaphthalene-3,6-disulfonic acid on a rotating platinum disk microelectrode. The extraction-amperometric method of analysis was proposed for the analysis of process water. The optimal concentrations of background electrolytes and buffer mixtures and the voltage values, were determined; the stability constant of the complex was calculated; the lower limit of the determined cerium content was defined. No interfering influence of foreign ions on the determination of cerium (III) ions was observed. The developed method for determining cerium (III) has a simpler hardware design than the previously described method of pulsed direct current glow discharge mass spectrometry but has a higher detection limit.

Microplotter printing of planar solid electrolytes in the CeO2–Y2O3 system

The formation process for planar solid electrolytes in the CeO2-Y2O3 system has been studied using efficient, high-performance, high-resolution microplotter printing technology, using functional ink based on nanopowders (the average size of crystallites was 12–15 nm) of a similar composition obtained by programmed coprecipitation of metal hydroxides. The dependence of the microstructure of the oxide nanoparticles obtained and their crystal structure on yttrium concentration has been studied using a wide range of methods. According to X-ray diffraction (XRD), the nanopowders and coatings produced are single-phase, with a cubic crystal structure of the fluorite type, and the electronic state and content of cerium and yttrium in the printed coatings have been determined using X-ray photoelectron spectroscopy (XPS). The results of scanning electron (SEM) and atomic force microscopy (AFM) have shown that the coatings produced are homogeneous, they do not contain defects in the form of fractures and the height difference over an area of 1 µm2 is 30–45 nm. The local electrophysical characteristics of the oxide coatings produced (the work function of the coating surface, capacitance values, maps of the surface potential and capacitive contrast distribution over the surface) have been studied using Kelvin-probe force microscopy (KPFM) and scanning capacitive microscopy (SCM). Using impedance spectroscopy, the dependence of the electrophysical characteristics of printed planar solid electrolytes in the CeO2-Y2O3 system on yttrium content has been determined and the prospects of the technology developed for the manufacture of modern, intermediate-temperature, solid oxide fuel cells have been demonstrated.

Study on Ceria–Silica Interaction in Various Ce3+ Concentration for Effective Post Chemical Mechanical Planarization (CMP) Cleaning

Shallow trench isolation (STI) is a technology that isolates transistors by constructing trenches and filling them with silicon dioxide. The excess silica should be removed by a subsequent step, chemical mechanical planarization (CMP) process, without any damage to active area. To prevent the damage during polishing, the silicon nitride is used for a stopping layer.1 Therefore, in the CMP process in STI, oxide-to-nitride polishing selectivity is needed. Since ceria nanoparticles (NPs) has high removal rate on silicon oxide but low removal rate on silicon nitride, they are generally utilized for CMP in STI.2 Additionally, Ce3+ concentration on the ceria NPs is considerably related to the oxide-to-nitride selectivity. It was reported that as the Ce3+ concentration on ceria NPs increased, its oxide-to-nitride selectivity was improved.3 However, after CMP process, there exists large amount of contaminants on the substrates which is mainly originated from the abrasives and organic additives in CMP slurry. Especially, on the surface of silicon oxide, the residual ceria NPs caused problems in post-CMP cleaning. Since they have chemical interaction with silicon oxide as reported, they are not easily removed from the surface. As the demands for high-end semiconductor devices with enhanced performance soar, the contaminants should be successfully removed.4-6 Therefore, in-depth research on ceria-silica interaction for effective post-CMP cleaning receives large attention.We directly investigated the ceria-silica interaction using atomic force microscope (AFM) and quartz crystal microbalance (QCM). Using AFM, the adhesion energy between silicon oxide and ceria NPs was quantitatively measured with respect to Ce3+ concentration on the ceria NPs as shown in Figure 1. We changed the surface Ce3+ concentration on the ceria NPs using hydrogen peroxide and ultrasonication, which was classified as Ceria1 to Ceria4.7 Moreover, the adsorption behavior of ceria NPs on the surface of silicon oxide was observed by QCM depending on the surface Ce3+ concentration. From the results of adsorption rate, the activation energy for the ceria-silica adsorption was studied depending on the Ce3+ concentration on the ceria NPs, which is exhibited in Figure 2.Figure CaptionsFigure 1. Adhesion energy between ceria and silica depending on surface Ce3+ concentration.Figure 2. Plot of the natural logarithm of adsorption rate versus the reciprocal of temperature at different surface Ce3+ concentrations of ceria NPs.References M. C. Kang, J. J. Kim and D.-K. Moon, Jpn. J. Appl. Phys., 44, 5949 (2005).R. Srinivasan, P. V. R. Dandu and S. V. Babu, ECS J. Solid State Sci. Technol., 4, P5029 (2015).K. Kim, D. K. Yi and U. Paik, ECS J. Solid State Sci. Technol., 6, P681 (2017).H. S. Philip Wong, Solid-State Electron., 49, 755 (2005).M. Tsujimura, ECS J. Solid State Sci. Technol., 8, P3098 (2019).C. K. Ranaweera, N. K. Baradanahalli, R. Popuri, J. Seo and S. V. Babu, ECS J. Solid State Sci. Technol., 8, P3001 (2018).J. F. Changjian Ma, Jiaxiang Chen, Yaoyao Wen, Paul O Fasan, Hua Zhang, Nuowei Zhang,* Jinbao Zheng, and Bing-Hui Chen, Ind. Eng. Chem. Res., 56, 9090 (2017). Figure 1

Effect of CeO2 concentration on the microstructure and wear behavior of Co–WC composites

A novel tungsten carbide (WC)- and ceria (CeO2)-reinforced cobalt (Co) matrix composite coating was synthesized through a one-step co-electrodeposition method. The growth mechanism of the coating and the formation mechanism of the protrusion and gully structure on the coating surface were explored. Furthermore, the mechanism of the influence of ceria concentration on the deposition rate and content of tungsten carbide is discussed. The results revealed that the coating fabricated at 6 g/l ceria achieved a dense structure, a fine grain size, a high content of tungsten carbide (19.9 wt.%) and a high deposition rate (78.2 μm/h). The average thickness of the coating was 118.48 μm, and the composite coating had a preferred orientation of cobalt (101) texture. In addition, the maximum microindentation hardness of the coating deposited at 6 g/l ceria was obtained as 627 HV. The electrodeposits possessed a superior anti-wear behavior, which was mainly ascribed to the synergistic effect of tungsten carbide and ceria in improving the mechanical properties of the cobalt matrix composite coating.