氧化铈复合热稳定剂

采用煅烧碳酸铈的方法制备氧化铈,将其单独用作热稳定剂,并与三碱式硫酸铅、硬脂酸钙二元或三元复配,应用刚果红法考察其对PVC热稳定性的影响.研究结果表明:单一氧化铈具有一定的热稳定作用,这主要是由于稀土可与多个氯原子配住,使PVC中的C-Cl稳定,从而提高了PVC的热稳定性;氧化铈(0.67%)+硬脂酸钙(1%)+三碱式硫酸铅(0.33%)三元复配效果最好,PVC热降解温度为206℃,热稳定时间为1 450 s.     

Preparation and Spherical Agglomeration of Crystalline Cerium(IV) Oxide Nanoparticles by Thermal Hydrolysis

Crystalline cerium(IV) oxide nanoparticles with a cubic fluorite structure could be synthesized from cerium(IV) ammonium nitrate solutions with a relatively high concentration of cerium(IV) (such as 0.5 mol/dm³) via thermal hydrolysis at 150°–240°C. The effects of the treatment temperature, the salt concentration, and the addition of sulfate ions on the crystallite size and morphology of the synthesized particles were investigated. The crystalline nanoparticles had a tendency to agglomerate and form spherical secondary particles with the addition of either ammonium sulfate or sulfuric acid. The existence of sulfate ions in the acidified solution was confirmed to be a factor of consequence for spherical agglomeration of the nanoparticles.     

Characterization and Sintering of Reactive Cerium(IV) Oxide Powders Prepared by the Hydrazine Method

Nanocrystalline cerium(IV) oxide (CeO₂) powders have been prepared by adding hydrazine monohydrate to an aqueous solution of hydrous cerium nitrate (Ce(NO₃)₃·6H₂O), followed by washing and drying. The lattice parameter of the as-prepared powder is a = 0.5415 nm. The powder characteristics and sinterability of reactive CeO₂ have been studied. The surface areas of powders that have been heated at low temperatures are high, and these surface areas do not decrease to 10 m²/g until the temperature is >1200°C. Crystallite size and particle size are strongly dependent on the heating temperature. Optimum sintered densities are obtained by calcining in the temperature range of 700°–800°C. Ceramics with almost-full density can be fabricated at a temperature as low as 1150°C.     

Selective sorption of a Ge(IV) oxoanion by composite sorbent with hydrous oxide of cerium

In this work, composite sorbent based on hydrous cerium oxide was used for selective removal of a Ge (IV) oxoanion. Experiments were carried out by batch equilibrium tests and dynamic column sorption. The best sorption capacity of the Ge(IV) anion was reached at a pH of 9, where the sorption capacity was about 1.1 g/L. The negative effect of chlorides and sulfates was not observed in the concentration range of 100–1000 mg/L. The optimal flow rate for Ge(VI) sorption by sorbent CeO₂/XAD-7 was determined to be 6–12 BV/h. For regeneration, 10 BV of 1 mol/L HCl solution was used.     

Oxidation of Silicon Nitride Hot-Pressed with Ceria

Short-term (<30 h) oxidation of CeO₂-doped hot-pressed Si₃N₄, studied at 773 to 1623 K in flowing dry air, resulted in parabolic-weight gain curves and in oxidation-rate constants nearly independent of the amount of grain-boundary second phase. Exolution of CeO₂ crystals occurs from the oxide layer; their morphology depends on oxidation temperature. Either a direct redox reaction between CeO₂ and Si₃N₄ or solution of Si₃N₄ in the glassy silica-rich oxide layer, followed by its oxidation by dissolved oxygen, have been proposed as possible oxidation mechanisms, both appearing strongly dependent on the low solubility of cerium oxides hi silicate melts. The value of the activation energy for oxidation of 385 kj·mol⁻¹ suggests additive and impurity migration from the bulk to the Si₃N₄/oxide reaction interface as the most probable rate-limiting step.     

Catalytic Properties of Ceria and CeO2-Containing Materials

Over the past several years, cerium oxide and CeO₂-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO₂-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO_x reduction catalysts is described. A survey of the use of CeO₂-containing materials as oxidation and reduction catalysts is also presented.     

Synthetic Inorganic Ion-Exchangers. Part XII. Hydrous Cerium(IV) Oxide: Anion-Exchange Properties and Some Ion-Exchange Separations

Abstract

The anion-exchange behavior of hydrated cerium(IV) oxide has been studied. The distribution coefficients of several anions on cerium dioxide were determined. On the basis of the distribution coefficients some selective ion-exchange separations of anions are reported.     

Catalytic Properties of Ceria and CeO2-Containing Materials

Over the past several years, cerium oxide and CeO₂-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO₂-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO _x reduction catalysts is described. A survey of the use of CeO₂-containing materials as oxidation and reduction catalysts is also presented.     

偶联剂改性氧化铈提高硅凝胶的耐热氧性能

针对硅凝胶在使用过程中发生的变硬变脆等老化问题,本文以乙烯基硅油为基胶,含氢硅油为交联剂,氧化铝为填料制备了相应的硅凝胶弹性体。通过热重分析和马弗炉等温失重确定了硅凝胶基胶的热氧老化方式和氧化铈的抗热氧老化性能,并用三种不同类型的偶联剂对氧化铈进行了表面改性,探究了偶联剂改性氧化铈对硅凝胶耐热氧老化性能的影响。结果表明,添加偶联剂改性氧化铈可以明显提高硅凝胶的耐热性能,250℃老化8天,添加1%（质量分数）纳米氧化铈硅凝胶的拉伸强度与老化前相比增加了7.8倍,与此同时,添加1%（质量分数）KH560、6121和7707型偶联剂改性氧化铈的硅凝胶拉伸强度分别增加了2.5倍、4倍和4.7倍。综上,在老化前期,添加KH560偶联剂改性氧化铈的硅凝胶力学性能变化最小,抗热氧老化性能最佳。     

Oxo-acidity and its influence on the electrochemical properties in molten mixtures of CeCl3 and equimolar NaCl---KCl, at 1000 K

Mixtures of cerium trichloride (5−30 mol. %) in equimolar NaCl---KCl were studied from the viewpoint of oxo-acidity. The solubility of cerium (III) oxide and the equilibrium constant of the reaction H₂O (g) + 2Cl^- 2HCl (g) + O₂₋ were determined at every composition.

The influence of oxo-acidity on the elctrochemistry of the melts is discussed, particularly in relation to the low efficiency of cerium electrometallurgy.     

Hydrothermal Synthesis of Cerium(IV) Oxide

CeO₂ powders have been prepared from cerium(III) nitrate, cerium(IV) sulfate, and cerium(IV) ammonium sulfate under hydrothermal conditions at 120° to 200°C for 5 to 40 h. The effects of the starting cerium compounds, hydrothermal treatment temperature, and the concentration of the solutions on the crystal growth of CeO₂ were investigated. CeO₂ powders hydrothermally synthesized at 180°C for 5 h from cerium(IV) salts had very fine particle sizes (30 Å); on the other hand, the powder from the cerium(III) salt had a relatively coarse particle size (160 Å). Although the crystallite size of the powder synthesized from the cerium(IV) compounds depended on the treatment temperature, that from the cerium(III) compound was insensitive to the treatment temperature. The mechanisms for the growth of CeO₂ particles under hydrothermal conditions are discussed.     

Meso/Macroporous Ceria with Enhanced Surface Oxygen Activity via Plant-Leaf Mineralization

Biomorphic cerias were produced through mineralizing plant-leaf templates (camphor and common oleander) with a cerium nitrate precursor. They were mesoporous while inheriting the species-dependent macrofeatures of plant-leaf templates, like macropores, channels, and microfibrous clusters, to have a meso/macroporous hierarchy. Surface oxygen activity was enhanced for the biomorphic cerias, as was revealed by temperature-programmed reduction measurements, suggesting their potentials in mid-temperature (300°–600°C) applications of oxygen storage, catalysis, gas sensing, etc.     

Polymerization of acrylamide initiated with electrogenerated cerium (IV) in the presence of EDTA

Polymerization of acrylamide was carried out with cerium (IV)-EDTA redox initiator system with and without electrolysis. The effect of temperature, time, cerium (IV), and EDTA concentrations on the polymerization yield and molecular weight were studied and compared with electrolytic conditions. At low concentrations of cerium (IV) the electrolytic method continuously supplying Ce (IV) from Ce (III) has an advantage over the nonelectrolytic method for which polymerization did not occur under these conditions. A possible polymerization mechanism is suggested.     

Nano-crystalline Ceria Catalysts for the Abatement of Polycyclic Aromatic Hydrocarbons

Nano-crystalline cerium oxide catalysts have been prepared by precipitation and evaluated for the total catalytic oxidation of naphthalene, which is a polycyclic aromatic hydrocarbon (PAH). Ceria synthesised by precipitation with urea was the most active catalyst for oxidation of naphthalene to carbon dioxide. The urea precipitated CeO₂ demonstrated over 90% naphthalene conversion to carbon dioxide at 175°C (100 ppm naphthalene, GHSV=25,000 h⁻¹), whilst ceria precipitated via a carbonate only gave 90% conversion at 275°C. Comparison with known high activity total oxidation catalysts, Mn₂O₃ and 0.5% Pt/γ-Al₂O₃, showed that the urea precipitated CeO₂ was a more effective catalyst for naphthalene total oxidation. At temperatures below those required to achieve catalytic activity the adsorption capacity of urea precipitated ceria for naphthalene was considerably greater than any of the other catalysts examined. The high adsorption capacity of the material provides the advantage that it can be used as a combined catalyst and adsorbent to remove PAHs from waste streams.     

Preparation and Properties of Tricyclopentadienyl Cerium (IV) Chloride and Bisindenyl Cerium (IV) Dichloride

The reactions of dipyridinium cerium (IV) hexachloride with tetracyclopentadienyl cerium or sodium cyclopentadienide and tetraindenyl cerium or sodium indenide in tetrahydrofuran yield tricyclopentadienyl cerium (IV) chloride and bisindenyl cerium (IV) dichloride. Infrared spectra, thermal stabilities and other characteristics of the compounds have been studied.     

Optimisation of CGO suspensions for inkjet-printed SOFC electrolytes

A detailed procedure for the preparation of gadolinium doped (10 mol%) cerium (IV) oxide (CGO) suspension for inkjet printing is described in this paper. The optimisation of inkjet printing parameters for the deposition of solid oxide fuel cell electrolytes was also performed using a custom-built drop visualisation system. Additionally, the uniformity of the deposited drop relics on porous substrates was evaluated. The ink used in this study was an evaporative type comprising a solvent mixture of terpineol and methanol, ethyl cellulose and CGO powder. Successful printing of regular drops was achieved after printing optimisation. It has been demonstrated that inkjet printing is a promising technique for high quality membrane fabrication for applications including solid oxide fuel cells. The ink formulation and optimisation procedure would also be applicable for other ceramic ink development.     

Reactive Ceria Nanopowders via Carbonate Precipitation

Nanocrystalline CeO₂ powders have been successfully synthesized via a carbonate precipitation method, using ammonium carbonate (AC) as the precipitant and cerium nitrate hexahydrate as the cerium source. The AC/Ce³⁺ molar ratio ( R ) affects significantly precursor properties, and spherical nanoparticles can be produced only in a narrow range of 2 < R ≤ 3. The precursor, having an approximate composition of Ce(OH)CO₃·2.5H₂O, decomposes to CeO₂ at temperatures ≥300°C. The CeO₂ powder calcined at 700°C exhibits high reactivity and can be densified to >99% of theoretical at 1000°C.     

Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide Powders

Nanocrystalline cerium(IV) oxide (CeO₂) powders were prepared by heating solutions of cerium(IV) salts in the presence of urea under hydrothermal conditions at 120° to 180°C. The effects of the concentration of urea and hydrothermal treatment temperature on the morphology and crystallite size of the synthesized particles were investigated. The synthesized particles were angular, ultrafine CeO₂, with a cubic fluorite structure. Their crystallite size decreased from 20 to 10 nm with increasing urea concentration from 2 times to 8 times that of the Ce⁴⁺ ion. The size only slightly changed by calcining at temperatures below 600°C.     

Thermal decomposition of cerium(III) acetate studied with sample-controlled thermogravimetric–mass spectrometry (SCTG—MS)

Thermal decomposition of cerium(III) acetate hydrate, Ce(CH₃CO₂)₃·1.5H₂O, to cerium(IV) oxide, CeO₂, in helium has been successfully investigated by sample-controlled thermogravimetry combined with evolved gas analysis by mass-spectrometry (SCTG–MS). Cerium(III) anhydrous acetate decomposed to cerium (IV) oxide through four decomposition steps in the temperature range of 250–800 °C. SCTG–MS was very useful to distinguish the successive decomposition accompanying the formation of the intermediate products to identify simultaneous gas evolution during the mass losses. The decomposition intermediates quenched from SCTG were characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES). The XANES revealed clearly the coexistence of Ce(III) and Ce(IV) and the valence change from cerium(III) to cerium(IV). The three decomposition intermediate products were presumed to be Ce₂O(CH₃CO₂)₄, Ce₂O₂(CH₃CO₂)₂ and Ce₂O₂CO₃. A detailed thermal decomposition mechanism of Ce(CH₃CO₂)₃·1.5H₂O is discussed.     

Recrystallization of Cerium Oxide in Porcelain Enamels

The effect of cerium oxide incorporated as the principal opacifying agent in the frit batch on the properties of white cover-coat porcelain enamels was studied. The effect of several variables on the opacity of the enamel was investigated as a function of firing temperature. Variables studied included (a) the amount of cerium oxide added, (b) the manner in which cerium oxide was incorporated into the enamel, i.e., mill addition, frit addition, or combination of both, (c) composition of the base glass, (d) weight of application, and (e) type of mill addition. Porcelain enamels were produced which had good acid resistance, high gloss, and a reflectance of 80% or more. Mill-added cerium oxide seemed to be less effective than that which was incorporated in the porcelain enamel as a component of the frit. The spectrophotometric analysis indicated good color stability of cerium oxide enamels.