ChemInform Abstract: Computer Simulation of the Structure,Thermodynamic Properties,and Transport Mechanism of CaF2-Al2O3 Melts.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: Structure and Bonding in Magnesium Difluoride Clusters: The (MgF2)n (n = 2—3) Clusters

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Electrochemical behaviour of the LiF-(CaF2)-La2O3 system

The electrochemical behaviour of the LiF-La₂O₃ and LiF-CaF₂-La₂O₃ systems was investigated by means of cyclic voltammetry. Several types of working electrodes (spectrographic pure graphite, W, Mo, Ni, Cu) were used. It was found that chemical reactions take place in the system during the dissolution of lanthanum oxide. The reduction of lithium cations occurred at the most positive potential from the species formed in the melt on ‘inert’ cathodes (W, Mo). The reactive cathodes (Cu, Ni) allowed the lanthanum deposition with depolarisation.     

Phase diagrams of MgF2-(Y,Ln)F3 systems

By means of thermal and X-ray analyses with oxygen control, 14 phase diagrams of the systems MgF₂-(Y, Ln)F₃ have been obtained, where Ln are all lanthanides except Pm and Eu. All the systems are eutectic. Solid solutions up to 12 mole% MgF₂, which decompose by the eutectoid scheme, were detected based on high-temperature modifications of trifluorides of Y, Er, Tm, Yb and Lu, with a structure of the-YF₃ type.

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Zusammenfassung Durch Einsatz der Thermo- und Röntgenanalyse mit Sauerstoffkontrolle wurden 14 Phasendiagramme der Systeme MgF₂-(Y, Ln)F₃ erhalten, wobei Ln sämtliche Lanthanoide mit Ausnahme von Pm und Eu sind. Alle Systeme zeigten sich eutektisch. Feste, sich nach dem eutektoiden Schema zersetzende Lösungen bis zu 12 Mol% MgF₂ wurden an Hand der Hochtemperatur-Änderungen der Trifluoride von Y, Er, Tm, Yb, Lu mit-YF₃-Struktur nachgewiesen.

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Résumé 14 diagrammes de phases des systèmes MgF₂ — (Y, Ln) F₃, où Ln représente tous les lanthanoïdes à l'exception de Pm et Eu ont été établis par études aux rayons X et analyse thermique, avec contrôle de l'oxygène. Tous ces systèmes présentent un eutectique. Des solutions solides jusqu'à 12 moles % de MgF₂ à décomposition eutectoïde ont été décelées à l'aide des transitions à haute température des trifluorures d'Y, Er, Tm, Yb et Lu du type-YF₃.

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- , 14 MgF₂ — (Y, Ln)F₃, Ln- , u. -. 12 .% MgF₂, , Y, r, Tm, Yb, Lu, -YF₃.

     

Zeeman effect in CaF(2Pi(3/2))

The Zeeman effect in the excited A 2Pi(3/2) state of CaF is measured and analyzed over a wide range of magnetic fields. It is found that the splitting of the Zeeman levels is largely determined by the coupling between different rotational states and there are no low-field seeking states in the J=3/2 manifold of Zeeman levels at high magnetic fields. A model of the Zeeman spectrum based on the ligand-field theory of CaF is shown to be accurate in the interval of magnetic fields 0-5 Tesla. This demonstrates that the magnetic moment of the CaF(A 2Pi(3/2)) molecule is effectively determined by the spin angular momentum of a single electron and the orbital motion of the valence electron around the Ca2+ core. An analysis of the Zeeman spectrum as a function of the molecular rotational constant indicates that 2Pi(3/2) molecules should have significant rotational constants (at least as large as twice the rotational constant of CaF) to be amenable to magnetic trapping in high fields.     

Ab initio and empirical energy landscapes of (MgF2)n clusters (n = 3, 4)

We explore the energy landscape of (MgF(2))(3) on both the empirical and ab initio level using the threshold algorithm. In order to determine the energy landscape and the dynamics of the trimer we investigate not only the stable isomers but also the barriers separating these isomers. Furthermore, we study the probability flows in order to estimate the stability of all the isomers found. We find that there is reasonable qualitative agreement between the ab initio and empirical potential, and important features such as sub-basins and energetic barriers follow similar trends. However, we observe that the energies are systematically different for the less compact clusters, when comparing empirical and ab initio energies. Since the underlying motivation of this work is to identify the possible clusters present in the gas phase during a low-temperature atom beam deposition synthesis of MgF(2), we employ the same procedure to additionally investigate the energy landscape of the tetramer. For this case, however, we use only the empirical potential.     

New phases with fluorite-derived structure in CaF2(Y,Ln)F3 systems

Crystallographic characteristics of six new phases of idealized composition Ca₈R₅F₃₁ which are formed in the CaF₂RF₃ (R = Y, HoLu) systems are reported. All the phases have a similar structure derived from CaF₂ with slight distortion and pseudocubic unit cell parameters a_ord = 13a_dis (where a_dis is the parameter of the fluorite subcell). The degree of ordering increases in the lanthanide series with decrease of ionic radius and, in every system given, with an increase in the RF₃ content of the solid solution. Significant influence of temperature and time of annealing on the degree of ordering was not detected.     

CaF2纳米粉体的制备与CaF2/Er3+纳粉体的荧光性能

分别采用四组分[m(CTAB):m(正丁醇):m(正庚烷):m(水)=11:11:19:10]反相微乳液体系和直接沉淀法制备了CaF2纳米粉体(简称nano-caFa2,nano-caFb2),其形貌和荧光性能经UV,IR,SEM及激发光谱表征.结果表明,nano-CaFa2形貌规则、单分散性良好,且粒径大小分布均匀....     

Structure of MgO-based catalysts modified with Mg(NO3)2 and LiNO3

The structure of magnesium oxide prepared by hydration in lithium nitrate and magnesium nitrate solutions and further thermal treatment is examined by X-ray analysis on a precision diffractometer using synchrotron irradiation. Magnesium oxide with a distorted lattice is formed when this preparation procedure is used, and the symmetry is reduced from cubic to rhombohedral. Distortions were more pronounced in the case of a sample treated with magnesium nitrate. The distortions are due to NO₃ groups incorporated into the oxygen framework of the oxide. Such a structure is stable up to 1000°C. The defects formed lead to the structure and charge inhomogeneity of the crystalline lattice. It is likely that these defects are responsible for the high catalytic activity of the samples.     

Thermodynamics of the System HNO3-UO2(NO3)2-H2O at 298.15 K

The sorption of ⁶⁰Co, ⁶⁵Zn, ⁷⁵Se, ¹⁰³Pd, ¹¹⁰Ag and ²⁰³Hg radionuclides by polyurethane foam (PUF) was investigated and optimized with respect to the selection of appropriate sorptive medium, metal, thiocyanate ions (except for ¹¹⁰Ag) and PUF concentration and equilibration time. The influence of common anions and cations on the sorption of each metal was examined. The sorption data subjected to different sorption isotherms have shown that the sorption of all the radionuclides followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The sorption capacity intensity and energy were evaluated for each element studied. The variation of sorption with temperature was monitored for all radionuclides except zinc and selenium. The values of H, S and G were estimated and found to be negative indicating exothermic and spontaneous nature of sorption. It was found that PUF is an effective and economical sorbent for traces of metal ions which can be used for the separation/preconcentration of these ions from their very dilute solutions and has useful applications in radioanalytical and environmental chemistry and in radioactive and industrial liquid waste management.     

Crystal Structure of Ni(NH3)Cl2 and Ni(NH3)Br2

Ni(NH₃)Cl₂ and Ni(NH₃)Br₂ were prepared by the reaction of Ni(NH₃)₂X₂ with NiX₂ at 350 °C in a steel autoclave. The crystal structures were determined by X‐ray powder diffraction using synchrotron radiation and refined by Rietveld methods. Ni(NH₃)Cl₂ and Ni(NH₃)Br₂ are isotypic and crystallize in the space group I2/m with Z = 8 and for Ni(NH₃)Cl₂: a = 14.8976(3) Å, b = 3.56251(6) Å, c = 13.9229(3) Å, β = 106.301(1)°; Ni(NH₃)Br₂: a = 15.5764(1) Å, b = 3.74346(3) Å, c = 14.4224(1) Å, β = 105.894(1)°. The crystal structures are built up by two crystallographically distinct but chemically mostly equivalent polymeric octahedra double chains [NiX_3/3X_2/2(NH₃)] (X = Cl, Br) running along the short b‐axis. The octahedra NiX₅NH₃ share common edges therein. The crystal structures of the ammines Ni(NH₃)_mX₂ with m = 1, 2, 6 can be derived from that of the halides NiX₂ (X = Cl, Br) by successive fragmentation of its CdCl₂ like layers by NH₃.     

Phase transitions of CaTiO3 ceramics sintered with the aid of NaF and MgF2

New phases with initial composition (1 ? x)CaTiO₃ ? xNaF ? xMgF₂ (0 ≤ x ≤ 0.20) have been prepared at low temperature (950 °C) from mixtures of CaTiO₃ and fluorides NaF and MgF₂. The oxyfluorides obtained have been characterized by X-ray diffraction at room temperature and indexed by isotypy with orthorhombic CaTiO₃. The microstructures of these phases are observed by scanning electron microscopy. Dielectric measurements have been carried out during cooling cycle from 500 °C to room temperature at two frequencies (100 Hz, 1 kHz). Differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermogravimetry (DTG) analyses have been performed, respectively, from room temperature up to 550 °C (DSC) and 920 °C (TG–DTG). The dielectric measurements revealed two anomalies which have been confirmed by DSC analyses. These phenomena are ascribed to second order phase transitions. The variation of the real permittivity with temperature is in agreement with the class I capacitor specifications. However, the dielectric losses have to be improved.     

Crystal Structure and Thermal Stability of Ag3(CHF2COO)3(H2O)2

X-ray diffraction analysis of [Ag₃(CHF₂COO)₃(H₂O)₂] revealed that its crystals are orthorhombic: space group Cmca, a = 13.809(4) Å, b = 15.975(2) Å, c = 12.244(2) Å, Z = 8. The thermogravimetric analysis showed that under the atmosphere of N₂ and at 101.3 kPa, silver difluoroacetate melts at 488 K; the thermal decomposition reaction occurs in the interval 493–548 K with the formation of Ag. Under the mass-spectral experiment conditions at 521 K, two processes occur simultaneously, namely, evaporation and decomposition. The following ions were detected in the mass-spectrum of silver difluoroacetate: Ag₂L⁺, Ag₂R⁺, Ag₂F⁺, Ag₂O⁺, Ag₂ ⁺, Ag⁺, LH⁺, RCO⁺, R⁺ (L = CHF₂COO, R = CHF₂).     

Preparation and Structure of [Me3N(CF3)2BCCB(CF3)2NMe3]

Bis‐trimethylamine‐ethynyl‐di‐bis(trifluoromethyl)borane [Me₃N(CF₃)₂BCCB(CF₃)₂NMe₃] ( 1 ) has been prepared from trimethylamine‐ethynyl‐bis(trifluoromethyl)borane, [HCCB(CF₃)₂NMe₃], and dimethylamino‐bis(trifluoromethyl)borane, (CF₃)₂BNMe₂. The structure of 1 has been determined by x‐ray crystallography. In the solid state the molecule possesses crystallographic C_i symmetry. The acetylenic attachment to the boron atom is characterized by a short B–C bond length of 1.565(4) Å and an essentially linear B–C–C′ bond angle of 178.1(4)°.     

Structure of chain-ends in polybutadiene produced with the CoBr2(PPh3)2/MgCl2/SiPh2(OCH3)2-Al(CH3)3 catalyst system

Polymerization of 1,3-butadiene with the CoBr₂(PPh₃)₂/MgCl₂/SiPh₂(OCH₃)₂-Al(CH₃)₃ catalyst system was conducted in the presence of ethylene. It was found that addition of ethylene causes a marked decrease in the molecular weight of polybutadiene although ethylene is not incorporated at the chain-end. The structure of chain-ends was analyzed using very low molecular-weight polybutadiene produced in the presence of ethylene, which led to the conclusion that 1,2 and 2,1 insertion reactions predominate at the initiation and propagation steps, respectively.