Chemische Verschiebung der Röntgen-Sauerstoff-K α-Linien in den relativ polaren Oxiden BaO,SrO, CaO und MgO

Zusammenfassung Die chemische Verschiebung der Sauerstoff-K-Linien in den Oxiden BaO, SrO, CaO und MgO wurde nach der Störungsrechnung 1. Näherung mit wasserstoffähnlichen Funktionen berechnet. Das Kristallfeld wurde durch ein einfaches elektrostatisches Potential approximiert. Die Ergebnisse zeigen gute Übereinstimmung mit dem Experiment.

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Chemical shift of the X-ray-oxygen-K -lines of the fairly ionic oxides BaO, SrO, CaO, and MgO

The chemical shift of the oxygen-K-lines for the oxides BaO, SrO, CaO and MgO have been calculated by the first order perturbation theory with the help of hydrogen like functions. The crystal field has been approximated by a simple electrostatic potential. The results are in good harmony with the experiment.

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Résumé Le déplacement chimique des raies K de l'oxygène pour les oxydes BaO, SrO, CaO et MgO a été calculé par la théorie des perturbations au premier ordre à l'aide de fonctions hydrogénoïdes. Le champ cristallin a été approché par un simple potentiel électrostatique. Les résultats sont en bon accord avec l'expérience.

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Der Deutschen Forschungsgemeinschaft dankt D. H. für die finanzielle Unterstützung, die die Durchführung dieser Arbeit wesentlich erleichterte.     

Influence of MgO (CaO) on the structure of silicate-phosphate glasses

Thermal and structural properties of model silicate-phosphate glasses containing the different amounts of the glass network modifiers, i.e. Mg²⁺ and Ca²⁺ were studied. To explain the changes of the parameters characterizing the glass transition effect (T_g, Δc_p) and the crystallization process (T_c, ΔH) depending on the cations modifiers additions, analysis of the bonds and chemical interactions of atoms in the structure of glasses was used. ³¹P MAS-NMR spectra of SiO₂–P₂O₅–MgO(CaO)–K₂O glasses show that the phosphate complexes are mono- and diphosphate. It has been found that increasing amounts of Mg²⁺ or Ca²⁺ cations in the structure of glasses causes the reduction of the degree of polymerization of the phosphate framework (Q¹→Q⁰). The influence of increasing of modifiers in the structure of silicate- phosphate glasses on the number of non-bridging oxygens per SiO₄ tetrahedron and density of glasses was presented.     

氧化锶催化性质：Ⅱ.SrO,MgO上异丙醇的分解反应

ＳｒＯ，ＭｓＯ对异丙醇的分解反应有各自的作用形式，因而产物分布也有明显差别．ＭｇＯ上异丙醇分解，在较低温度时，主要产物为丙酮和丙烯；随温度升高，生成丙烯的量增加，而丙酮的量减少，直至消失，在ＳｒＯ上，异丙醇在较高温度时反应，产物几乎为丙酮，丙烯的生成量极少。认为：产物中丙烯来源于异丙醇在催化剂表面强酸中心上的脱水；丙酮在ＭｇＯ上来源于强碱中心和酸中心协同作用异丙醇的脱氢，而在ＳｒＯ上则是ＳｒＯ表面极强的碱中心作用异丙醇而脱氢制得。     

Electronic structure of the [MgO3]+ cation

Accurate ab initio calculations are performed to investigate the stable isomers of [MgO(3)](+) and its lowest electronic states at both molecular and asymptotic regions. The calculations are done using large basis sets and configuration interaction methods including the complete active space self-consistent field, the internally contracted multi-reference configuration interaction, the standard coupled cluster (RCCSD(T)) approaches and the newly implemented explicitly correlated coupled cluster method (RCCSD(T)-F12). The presence of three stable forms is predicted: a cyclic global minimum c-MgO(3)(+), which is followed by a quasi-linear isomer, l2-MgO(3)(+). A third isomer of C(s) symmetry (l1-MgO(3)(+)) is also found. Moreover, we computed the one-dimensional cuts of the six-dimensional potential energy surfaces of the lowest doublet and quartet electronic states of [MgO(3)](+) along the R(MgO) and R(OO) stretching coordinates covering both the molecular and the asymptotic regions. These curves are used later for discussing the metastability of this cation and to propose plausible mechanisms for the Mg(+) + O(3) atmospherically important ion-molecule reaction and related reactive channels.     

Theoretical investigation of small MgO, CaO and NaCl clusters

We study the size dependence of the electronic and structural properties of small MgO, CaO and NaCl clusters (up to 12 atoms), thanks to a selfconsistent tight binding approach in which we treat electrostatic and covalent effects on the same level. We discuss the conditions under which the ionic charges get reduced and the interatomic distances are contracted or dimerized.     

Untersuchungen in den Zweistoffsystemen La2O3—(CaO,SrO, BaO)

Zusammenfassung Der Einbau von Lanthanoxid in die Erdalkalioxide CaO, SrO und BaO wurde auf röntgenographischem Wege untersucht. Bei 1000°C geglühte Proben zeigen folgende Löslichkeiten für La₂O₃: 1 Mol% in BaO, 2,4 Mol% in SrO und praktisch keine Löslichkeit in CaO.

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The incorporation of lanthanum oxide into CaO, SrO and BaO was studied by X-ray methods. The incorporated quantities of La₂O₃ in samples decarbonized at 1000°C were found to be 1 mol% for BaO, 2.4 mol% for SrO and no solubility for CaO.

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Mit 2 Abbildungen     

Tetradecanol dehydrogenation over CuO catalyst supported on BaO, CaO and MgO

Bimetallic Cu/Mg, Ca, Ba mixed oxide compounds acted as catalyst in the dehydrogenation of tetradecanol into tetradecanal, and were characterized by thermal gravimetric analysis, surface area, X-ray diffraction, temperature-programmed reduction and desorption of CO₂. Alkaline earth oxides increased the total basic site concentration in the order of Mg>Ca>Ba. A correlation was found between the total basic site concentration and initial dehydrogenation rate. This revised version was published online in June 2006 with corrections to the Cover Date.     

MgO和CaO助剂在Fe-K催化剂中的作用

制备了以MgO和CaO为助剂的乙苯脱氢制苯乙烯用Fe-K催化剂,并考察了助剂对催化剂催化性能的影响.应用SEM、XRD、TPR和Mssbauer谱等手段表征了MgO和CaO对活性前驱体K2Fe22O34晶相形成及其表观体相结构的影响.结果表明,引入MgO助剂,半径相近的Mg2 与Fe3 极易发生取代形成固溶体,使活性前驱体K2Fe22O34晶相的形成温度有所降低,同时给体相结构引入氧空位,从而有利于乙苯发生晶格氧转移机理的脱氢反应,使催化剂活性提高.引入CaO助剂,提高了K2Fe22O34晶相的结晶度和苯乙烯选择性,但催化剂活性有所下降.CaO对Fe-K催化剂的还原有一定的阻碍作用,是催化剂的稳定性助剂.     

Ab initio study of the positronation of the CaO and SrO molecules including calculation of annihilation rates

Ab initio multireference single‐ and double‐excitation configuration interaction calculations have been performed to compute potential curves for ground and excited states of the CaO and SrO molecules and their positronic complexes, e⁺CaO, and e⁺SrO. The adiabatic dissociation limit for the ²Σ⁺ lowest states of the latter systems consists of the positive metal ion ground state (M⁺) and the OPs complex (e⁺O^?), although the lowest energy limit is thought to be e⁺M + O. Good agreement is found between the calculated and experimental spectroscopic constants for the neutral diatomics wherever available. The positron affinity of the closed‐shell X ¹Σ⁺ ground states of both systems is found to lie in the 0.16–0.19 eV range, less than half the corresponding values for the lighter members of the alkaline earth monoxide series, BeO and MgO. Annihilation rates (ARs) have been calculated for all four positronated systems for the first time. The variation with bond distance is generally similar to what has been found earlier for the alkali monoxide series of positronic complexes, falling off gradually from the OPs AR value at their respective dissociation limits. The e⁺SrO system shows some exceptional behavior, however, with its AR value reaching a minimum at a relatively large bond distance and then rising to more than twice the OPs value close to its equilibrium distance. © 2012 Wiley Periodicals, Inc.     

Optical surface properties and morphology of MgO and CaO nanocrystals

Optical absorption and photoluminescence emission properties of dehydroxylated MgO and CaO nanocrystals are discussed with respect to particle morphology and size. On MgO nanocubes with pronounced corner and edge features two emission bands at 3.4 and 3.3 eV result from the excitation of 4-coordinated surface O(4C)(2-) anions in edges at 5.4 eV and of regular oxygen-terminated corners at 4.6 eV, respectively. Morphologically ill-defined CaO particles are a factor of 5 larger, do not display regular corner features, and show only one photoluminescence emission band at 3.0 eV. The associated excitation spectrum indicates electronic excitations above the energy required to excite regular oxygen-terminated CaO corners. It is concluded that in the case of morphologically well-defined MgO nanocubes variations in the next coordination of oxygen-terminated corners can effectively be probed by photoluminescence spectroscopy and thus allows for discrimination between 3-coordinated surface O(2-) in regular corner sites and kinks.     

Crystallization of spodumene-diopside in the las glass ceramics with CaO and MgO addition

Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount of CaO and MgO in Li₂O-Al₂O₃-2SiO₂ were investigated. With CaO and MgO addition, the crystallization temperature (T _p) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol⁻¹ to 537±5 kJ mol⁻¹. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated with crystallization and morphology of glass ceramics.     

ICP-AES法测定铁矿中的CaO、MgO、Al2O3和MnO

用电感耦合等离子发射光谱仪（ICP-AES）测定了铁矿中的CaO、MgO、Al2O3和MnO，用钇内标元素校正基体干扰，对分析谱线、共存元素、酸性条件等进行了讨论。     

Electronic structure of silanes in the semi-empirical equivalent orbital method

The problem of the prediction of the valence IPs for silanes is considered. It is shown that the data on the silicon band structure combined with the photoelectron spectra of SiH₄, and Si₂H₆ permit to obtain the parameter scale, which includes all the nearest neighbour, second neighbour and the main third neighbour interaction parameters. Using the derived parameter scale the vertical ionization potentials of Si₃H₈, SiH(SiH₃)₃, Si(SiH₃)₄, the infinite polysilane valence band structure and the inner a _1g level for disilane are calculated. All the calculated levels are located above ? 20 eV and are expected to be measurable by the He (I) photoelectron spectroscopy.     

Heterogeneous CaO(SrO,BaO)/MCF as highly active and recyclable catalysts for the glycolysis of poly(ethylene terephthalate)

Research on Chemical Intermediates - A new group of basic species, CaO(SrO and BaO), supported on mesocellular siliceous foam (MCF) has been prepared and used for catalyzing glycolysis of...     

钙镁负载型固体碱催化剂制备生物柴油

固体碱催化剂;酯交换反应;脂肪酸甲酯;生物柴油     

Transesterification of ethyl butyrate with methanol using MgO/CaO catalysts

A series of mixtures of MgO/CaO with different Mg/Ca molar ratios (between 3 and 15), as well as the corresponding pure oxides, was prepared by the coprecipitation method in a basic medium and subsequent calcination. Their textural and structural characterization was carried out by using XRD, FT-IR, SEM and N₂ sorption at 77 K. The alkalinity was studied by CO₂-TPD and catalytic decomposition of 2-propanol. The MgCa oxides obtained after calcination at 1073 K exhibit X-ray diffraction patterns with clearly visible signals corresponding to crystalline CaO and MgO. Textural properties are improved by the presence of Mg, with the porosity increased and the particle sizes decreased with respect to pure CaO. FT-IR spectroscopy reveals the presence of surface carbonate. These catalysts are active in the transesterification of ethyl butyrate with methanol at 333 K and atmospheric pressure, a model reaction to evaluate the potential of these basic catalysts in triglycerides transesterification for biodiesel production. The highest activity was found for a Mg:Ca molar ratio of 3, with conversion close to 60%, whereas MgO was inactive. Moreover, lixiviation of the active phase was not observed thus excluding the contribution of the homogeneous catalysis to the studied transesterification process.     

Donor characteristics of transition-metal-doped oxides: Cr-doped MgO versus Mo-doped CaO

The ability of Mo (Cr) impurities in a CaO (MgO) matrix to act as charge donors to adsorbed gold has been investigated by means of scanning tunneling microscopy and density functional theory. Whereas CaO(Mo) features a robust donor characteristic, as deduced from a charge-transfer-driven crossover in the Au particles' geometry in the presence of dopants, MgO(Cr) is electrically inactive. The superior performance of the CaO(Mo) system is explained by the ability of the Mo ions to evolve from a +2 oxidation state in ideal CaO to a +5 state by transferring up to three electrons to the Au adislands. Cr ions in MgO, on the other hand, are stable only in the +2 and +3 charge states and can provide a single electron at best. Since this electron is likely to be captured by cationic vacancies or morphological defects in the real oxide, no charge transfer to Au particles takes place in this case. On the basis of our findings, we have developed general rules on how to optimize the electron donor characteristics of doped oxide materials.     

ICP-AES法同时测定烧结矿中CaO、MgO、SiO2、Al2O3、MnO和P

目前,在不锈钢炼铁工艺中,烧结矿的生产节奏越来越快,分析质量的要求也越来越高,以往采用化学方法对烧结矿的控制分析已不能适应大生产的需要。用X荧光光谱仪对烧结矿进行工艺控制分析已成为当今冶金行业控制分析的趋势。X荧光分析需要大量的标准样品,但与被测矿成分完全一致的标样不易制备。本法采用ICP-AES技术,在待测溶液中加入钇内标,采用基体匹配消除基体铁的影响,同时测定烧结矿中CaO、MgO、SiO2、Al2O3、MnO和P六种组分。