Defect Structure of Cobalt Monoxide: I, The Ideal Defect Model

The nonstoichiometry and electrical properties of Co_1-YO are considered in terms of an ideal defect model. Both intrinsic and extrinsic regions are analyzed. Interrelationships between the oxygen partial pressure and the oxide composition are derived. It has been shown that the p _O2 exponent resulting from the deviation from stoichiometry (l/ n _Y ) differs substantially from the exponent determined by measurements of electrical conductivity (1/ n _σ) The limitations of the ideal defect approximation are discussed.     

Defect Structure of Cobalt Monoxide: III, The Cluster Model

The 4:1 cluster model has been considered and its application to the available experimental data for the deviation from stoichiometry, electrical conductivity, and the Seebeck coefticient has been analyzed. It has been shown that the degree of ionization of the cluster is −5. The equilibrium constant of formation is K ₅= [( V _Co)Co _i ]⁵⁻[h^˙]⁵ p _O2^3/2= 4.6 exp[−167.5 (kJ)/ RT ]. It has been shown that the applicability of this model in describing CoO properties is limited to higher values of the deviation from the stoichiometric composition (y). At low y , defects in CoO can be considered as isolated. Then doubly ionized cobalt vacancies are assumed to be the predominant lattice defects. Their equilibrium constant of formation, determined from experimental data in the vicinity of the Co/CoO phase boundary by using an ideal approximation, is K _V = [ V ⁿ _Co][h^˙]² p _o2^−1/2= 3.2 × 10⁻⁴ exp[−121.1 (kJ)/ RT ]. Excellent agreement between the equilibrium constant K _V determined for low p _{O 2} and that resulting from the Debye Hückel model within the entire range of y has been found.     

Characterization and Catalytic Oxidation of Carbon Monoxide Over Supported Cobalt Catalysts

Three types of supported cobalt catalysts (CoO_x/SiO₂, CoO_x/TiO₂ and CoO_x/Al₂O₃) were prepared by incipient wetness impregnation with aqueous Co(NO₃)₂·6H₂O solution. The phase composition and the interactions of cobalt with supports under different calcined temperatures were investigated using thermogravimetry (TG), N₂-adsorption at −196 °C, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and diffuse reflectance spectroscopy (DRS). Their catalytic activities towards the CO oxidation were further studied in a continuous flow micro-reactor. The results showed that the interaction of cobalt oxide with supports was much stronger in the kinds of Al₂O₃ and TiO₂, while no conclusive evidence of any interaction was found for SiO₂. Besides the crystalline Co₃O₄ which was formed in three supported catalysts, both high-temperature phases CoAl₂O₄ and CoTiO₃ spinel were also detected under XRD, DRS and TPR analysis. The degree of interaction between cobalt oxide and the support not only affected the surface area and reduction behavior of the catalysts, the catalytic activity toward the CO oxidation also affected simultaneously. As the CoAl₂O₄ and CoTiO₃ spinel formed, both the surface area and catalytic activity decreased significantly.     

In situ FTIR Study of Cobalt Oxides for the Oxidation of Carbon Monoxide

A high-valance cobalt oxide, CoO _x , was prepared from cobalt nitrate aqueous solution through precipitation with sodium hydroxide and oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoO _x by temperature-programmed reduction (TPR) to 170, 230 and 300 °C. They were characterized by TPR and X-ray diffraction (XRD). Adsorption of CO and the co-adsorption of CO/O₂ over the cobalt oxides were further tested by in situ FTIR. It was shown that Co₃O₄ is quite active for the oxidation of CO at room temperature in the presence of oxygen, leading to the formation of CO₂. The variation in the oxidation of CO was interpreted with a mechanism involving two kinds of oxygen species, i.e., *-O₂ on the CoO _x surface and *-O_L on the surface of Co₃O₄ spinel structure.     

Defect Structure and Thermodynamic Properties of the Wustite Phase (Fe1-yO)

The defect structure model in the wustite phase is considered involving the 4:l cluster as a basic defect structure unit. Interactions between defects are considered in terms of the Debye-Hückel theory for strong electrolytes. It has been shown that the available data on wustite nonstoichiometry fit well the 4:l cluster model. Above 1173 K the degree of ionization of the cluster is −5. The equilibrium constant of the cluster formation determined in this work is K _c = [(( V _Fe)₄Fe _i )⁵⁻][h]⁵ [Fe_Fe]⁻⁶[V _i ]⁻¹P_O2^−3/2 f ⁶_±= 1.07 × 10⁻¹⁴ exp[396.7 (kJ)/ RT ]. The equilibrium constant is quite consistent with such thermodynamic parameters as partial molar enthalpy and entropy of oxygen in Fe_{1- y} O within the entire stability range of the wustite phase.     

Application of an Ion-Packing Model Based on Defect Clusters to Zirconia Solid Solutions: II, Applicability of Vegard's Law

Lattice parameter data of cubic phases and cube roots of unit cell volumes of tetragonal phases in homogeneous ZrO₂-containing solid solutions were compiled to examine the validity of Vegard's law. Except for ZrO₂–CeO₂ and ZrO₂–UO₂ systems, the data for cubic phases were expressed by the equation d = a _s X + b , where d , a _s, X , and b denote the lattice parameter, a constant depending on dopant species, the dopant content, and a constant independent of dopant species, respectively. For tetragonal phases, the cube roots of unit-cell volumes could be fitted by a similar equation except for the data in the ZrO₂–MO₂ systems (M = Ge and U). The constant a _s was calculated using an ion-packing model and was independent of the defect cluster models. The calculated a _s is close to the experimentally observed one, although the former is slightly smaller than the latter in the ZrO₂–MO _u systems ( u = 1 and 1.5). This difference was ascribed to the lack of consideration of the ionic distortions from the ideal sites of the fluorite-type structure.     

Defect Equilibria and Transport in YBa2Cu3O7-x at Elevated Temperatures: II, Nonstoichiometry

Aspects of nonstoichiometry for the Y-Ba-Cu (1: 2: 3) system are considered. The general formula YBa₂Cu₃O_7-x has been assumed for considerations of nonstoichiometry in 1: 2:3 oxide cuprates. Assuming that copper ions may occupy different lattice positions (independently of their valency), the equilibrium constants for oxygen intercalation were determined:     

Application of an Ion-Packing Model Based on Defect Clusters to Zirconia Solid Solutions: I, Modeling and Local Structure of Solid Solutions

Oxygen vacancies can be introduced into zirconia solid solution ZrO₂–MO _u ( u = 1 and 1.5) to maintain electroneutrality. Recently, the local structures around Zr⁴⁺ and M^{2 u +} ions in ZrO₂–MO _u solid solutions have been studied through EXAFS spectroscopy, diffuse scattering analysis, and single-crystal structure analysis. The present study constructs an ion-packing model for zirconia solid solutions based on some defect cluster models. The decrease of cell volume with the occurrence of vacancies is assumed to be expressed by decreasing the coordination number (CN) of cations around the vacancy. The distribution of CNs in a solid solution was calculated from a certain defect cluster model. The average interatomic distances, the average CN, and the short-range order parameters were calculated using this distribution of CNs. The local structures calculated from the model were compared with experimental data in the systems ZrO₂–MO_1.5 (M = Y, Gd, Yb, and Ca). In the ZrO₂–YO_1.5 system, the r (s–O) interatomic distance, where s represents Zr⁴⁺ or Y³⁺ and O represents O²⁻, decreased with Y content and therefore vacancy content. The probability of finding Y³⁺ around a vacancy increases with increasing yttria content from a comparison of the calculated results with the ones from recent EXAFS studies. The present model can qualitatively explain compositional and size dependences of the dopant on various local structures.     

In situ FT-IR Spectroscopic Studies on the Mechanism of the Catalytic Oxidation of Carbon Monoxide over Supported Cobalt Catalysts

Three types of supported cobalt catalysts (5% as metal Co loading on SiO₂, Al₂O₃ and TiO₂) were prepared by incipient wetness impregnation with aqueous Co(NO₃)₂·6H₂O solution. Then, all catalysts were calcined in air at 400 °C (assigned as 5Co/Si C400, 5Co/Al C400 and 5Co/Ti C400). Their catalytic activities towards the CO oxidation were studied in a continuous flow micro-reactor. Adsorption of carbon monoxide (CO) and the co-adsorption of CO/O₂ over cobalt oxide were further tested under in situ FT-IR. The results showed that both 5Co/Si C400 and 5Co/Al C400 had higher activity than 5Co/Ti C400. The T₅₀ (50% conversion) for both 5Co/Si C400 and 5Co/Al C400 was reached at temperatures as low as ambient temperature. According to the in situ FT-IR analysis, the variation in oxidation of CO was interpreted with different mechanisms, i.e., the reaction between adsorbed CO and lattice oxygen of cobalt oxide, and part of CO₂ formation via carbonates on 5Co/Si C400; both types of carbonates are formed on 5Co/Al C400 to promote the CO oxidation; while both strong adsorption of CO on TiO₂ and CO₂ on cobalt oxide for 5Co/Ti C400 leads to affect the activity.     

Composition-dependent intrinsic defect structures in pyroclore RE2B2O7 (RE = La,Nd, Gd; B = Sn,Hf, Zr)

Point defects are closely correlated with various properties of pyrochlore oxides and therefore play a key role on their engineering applications. Here, the native point defect complexes in RE₂B₂O₇ (RE = La, Nd, Gd; B = Sn, Hf, Zr) under stoichiometric and nonstoichiometric compositions are studied by first-principles calculations. The O Frenkel defect complex is predicted to be the predominant defect structure in stoichiometric zirconates and hafnates, whereas the cation antisite defect complex is the predominant one in stannates. In the case of BO₂ excess, the formation of the B-RE antisite defect together with the RE vacancy and the oxygen interstitial is energetically favorable, whereas the RE-B antisite defect together with the oxygen vacancy and the RE interstitial is preferable under the RE₂O₃ excess environments. Additionally, the formation energies of the native defect complexes are greatly affected by the B-site and/or RE-site cations. The strategy on tailoring the intrinsic defect structures of these pyrochlore oxides is proposed. It is expected to guide the experiments on the defect-related property optimization through stoichiometric and nonstoichiometric compositions, so as to meet the specific engineering requirements and promote their commercial applications.     

Polymorphs of Cobalt Oxide

Through controlled thermal decomposition of cobalt acetate tetrahydrate, cobalt monoxide can be synthesized with three different crystal structures: rock salt, zinc blende, and wurtzite. Using electron microscopy techniques, it is shown that the polymorphs exhibit characteristic crystallite morphologies; "tetrahedral" for the zinc blende type and "lathlike" for the wurtzite form. Atomistic simulation calculations predict the lattice energies of the three polymorphs to be relatively close, with the rock salt polymorph being most stable, followed by the wurtzite form and lastly zinc blende.     

不对称钴配合物的合成及其催化苯乙烯环氧化

将合成的N-取代的吡啶-2-醛亚胺制备成2∶1型不对称吡啶亚胺钴(Ⅱ)配合物(CoL2n,n=1,2…6),并通过红外光谱、元素分析、核磁共振氢谱、热重分析等对相关化合物进行表征。以分子氧为氧源,考察催化剂的种类、溶剂、反应温度、反应时间对苯乙烯环氧化反应性能的影响。研究表明,配合物CoL42是最有效的催化剂;配合物中亚氨氮上取代基的供电子性和空间位阻有利于提高配合物的催化活性;在优化的反应条件下,苯乙烯的转化率达99.9%,环氧苯乙烷的选择性为62.4%。     

High-Temperature Defect Structure of Lanthanum Cuprate

High-temperature (650° to 8507deg;C) electrical conductivity and Seebeck coefficient measurements as functions of oxygen partial pressure and temperature in polycrystalline lanthanum cuprate support a defect model consisting of oxygen interstitials charge compensated by electron holes. The La:Cu ratio was therefore estimated to be 2.000 ± 0.001. By comparison with existing oxygen nonstoichiometry data, the high-temperature electron hole mobility and density-of-states were estimated.     

体相掺镁球形钴酸锂前驱体的制备及表征

文章通过沉淀法合成了体相掺杂镁元素的球形钴酸锂正极材料前驱体。通过SEM形貌、密度测量、粒度表征等手段研究了共沉淀工艺对合成体相掺杂镁元素钴酸锂前驱体的影响,并通过EDS及ICP测试表征了镁元素掺杂的均匀性。研究结果表明:共结晶的反应时间对颗粒密度、颗粒形貌、粒度大小及分布有较大的影响,随着时间延长密度逐渐增加,颗粒形貌变好,粒度变大且趋于集中;共结晶体相掺杂镁的钴酸锂前驱体,镁元素能达到原子级混合均匀的要求;掺杂镁后,钴酸锂前驱体四氧化三钴物相未发生变化。掺镁钴酸锂前驱体在高压实密度钴酸锂得到了广阔的应用。     

CeO2 Nanorods and Nanocubes: Impact of Nanoparticle Shape on Dilatometry and Electrical Properties

The electrical and dilatometric properties of CeO₂ nanopowders were examined as function of particle shape and size, including nanorods and nanocubes. Nanorods show continuous irreversible shrinkage, linked to particle reordering and compaction. Thermal expansion of CeO₂ nanocubes was analyzed and was found to be consistent with literature data for microcrystalline ceria with no apparent nanosize effects. The electrical properties of the loosely compacted nanopowders were generally found to be characterized by n‐type electronic conduction, except for proton conductivity contributions associated with adsorbed moisture at temperatures below 400°C. The P_O2 and temperature dependences of the conductivity were examined in terms of defect chemical models. The lower effective enthalpy of reduction for nanorods (1.5 eV) in comparison with nanocubes (1.8 eV), both being much smaller than the value found for “bulk” ceria (4.7 eV), can be related to the larger surface to volume ratio of the nanorods, where oxide ion removal is more facile and less energy costly.     

电化学合成氧化钴/聚苯胺复合膜工艺研究

采用单因素对比试验对电化学合成氧化钴/聚苯胺复合膜工艺进行了研究,并利用电化学测试技术、扫描电子显微镜(SEM)和X射线衍射仪(XRD)对氧化钴/聚苯胺复合膜的性能进行测试。结果表明,采用恒电位法制备氧化钴/聚苯胺膜微观呈现为规则片状形貌,膜层覆盖均匀,其腐蚀电位-0.04 V,腐蚀电流47.42μA,10%HCl点滴腐蚀时间达382 s,10%NaOH点滴腐蚀时间达到364 s,中性盐雾实验48 h未见锈蚀。     

二吡啶酮配体四、六核钴簇合物的合成及结构表征

利用溶剂热反应,二吡啶酮与钴的乙酸盐反应得到两种新颖的四核和六核钴的簇合物[Co4(OH){(py)2CO(OH)}{(py)2CO}(O2CCMe3)6].3H2O1和[Co6{(py)2CO(OH)}2(O2CMe)8(DMF)(H2O)4].DMF.H2O2。晶体1的晶系数据:单斜,P2(1)/n,a=1.5784(9),b=1.7678(9),c=2.2615(13)nm,V=6.2857(6)nm3,F(000)=2672,finalR1=0.0795,wR2=0.1697[I>2σ(I)]。晶体2的晶系数据:单斜,P2(1),a=1.3721(10),b=1.4377(10),c=1.5541(10)nm,V=2.7813(3)nm3,F(000)=1436,finalR1=0.0370,wR2=0.0664[I>2σ(I)]。配合物1中有两个共边的Co3O单位组成了蝶式构型,而配合物2含有两个线形的三个Co原子组成的双锚结构。     

On the Catalytic Activity of Cobalt Oxide for the Steam Reforming of Ethanol

The paper presents an investigation on the catalytic activity for the ethanol steam reforming of Co₃O₄ oxidized, reduced and supported on MgO, and of CoO in MgO solid solution. Only samples containing metallic cobalt are found to be active for reforming reaction. H₂-TPR characterization of aged samples shows that reaction mixture oxidizes a small fraction of metallic cobalt to Co⁺². A distinct role of Co⁺² and Co⁰ in the reaction is enlightened.     

氟化工艺废铬钴催化剂回收利用技术初探

对氟化工艺废铬钴催化剂回收利用进行了研究．提出以生石灰为填料．以硫酸为浸取剂的工艺路线,同时考察了工艺条件对其溶出率的影响,并采用原子吸收光谱法对废催化剂溶出液中的钴铬2种元素进行检测。结果表明,较佳的工艺条件为：焙烧温度400℃．焙烧时间4h,废催化剂粒度筛孔0．25mm.废催化剂中钴铬的溶出率达98％以上。     

Effect of Inclusions on Densification: II, Numerical Model

Experimental studies conducted in conjunction with a numerical analysis of strain-rate gradients have established the origin of the damage process that occurs upon the densification of powders containing nonsintering inclusions and reinforcements. The underlying phenomenon is the development of localized compressive strains in the porous matrix, both around high-aspect ratio reinforcements and between closely spaced reinforcements. These regions of compression densify first and then support grain growth. This process produces nondeformable networks that constrain the shrinkage of the adjacent, porous matrix. The constraint causes desintering and cracklike void formation in the lowdensity regions. The variables shown to be of importance are the volume fraction and aspect ratio of the reinforcements. The process is shown to be sensitive to the green density, such that a high initial density reduces initial damage and lowers the differential in densification.