Thermal analysis of the LiF-SrFCl-SrCO3 three-component system

Thermal analysis of the LiF-SrFCl-SrCO₃ system and its subsystems was carried out for the first time. In binary subsystems, incongruently melting compounds of compositions SrFCl · SrCO₃, 4SrFCl · SrCO₃, and LiF · SrCO₃ are formed; their crystallization volumes are closed by peritectic points. The thermoanalytical data were used to design planar and spatial phase diagrams, which illustrate the phase complex of the title system. The thermal properties of a eutectic melt were studied.     

Phase transitions in the SrSnO3-SrFeO3 solid solutions: X-ray diffraction and Mössbauer studies

SrSn_1−xFe_xO_y (0?x?1) oxides were prepared by conventional solid-state reaction in air using high-purity (?99%) SrCO₃, SnO₂ and Fe(C₂O)₂·2H₂O at elevated temperatures of 1300°C for 24 h and furnace cooled. Samples obtained from 1300°C were annealed at 620°C for 2 days and quenched in liquid nitrogen (LN). Powder XRD analysis by Rietveld refinement and Fe Mössbauer spectroscopy measurements were employed to characterize synthesized perovskites. Samples obtained from furnace cooled and LN quenched undergo two compositionally driven phase transitions, which are supposed to be of second order. The x=0-0.3 members crystallize in orthorhombic parent SrSnO₃ structure (Space group Pbnm), whereas samples x=0.4-0.9 have a simple cubic perovskite cell and end-member SrFeO_2.74 composition crystallize orthorhombic structure (Space group Cmmm). The composition of the first phase transition (x≈0.3) is slightly shifted to higher x with decreasing annealing temperature. Mössbauer data show that the Fe⁴⁺/Fe^tot ratio is depending on composition under constant synthesis conditions. The phase compositions have been discussed in terms of ternary solid solution of compounds SrSnO₃-SrFeO_2.74-SrFeO_2.5 superior to a simple binary solid solution (SrSnO₃-SrFeO₃).     

Thermal activation of Al2O3 supported MoO3 and WO3 metathesis catalysts

Alumina-supported MoO₃ and WO₃ catalysts were activated for the metathesis of propene by thermal treatment in Ar. Temperatures up to 1140 K are required for catalysts with low metal contents. These exhibit the highest specific activities though they are known to be highly resistant to reduction. It is proposed that the active sites are formed from Mo(VI) and W(VI) species under the conditions employed.

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MoO₃ WO₃, Al₂O₃, . 1140 . , , . , , Mo W.

     

Thermoanalytical study of the systems PbCO3SrCO3 and PbCO3CaCO3

This study concerns the coprecipitation of the PbCO₃SrCO₃ and PbCO₃CaCO₃ systems in different molar relationships carried out under the same experimental conditions as the PbCO₃BaCO₃ system studied previously. The precipitates obtained were studied by chemical analysis, thermogravimetry, differential thermal analysis and X-ray powder diffraction. It has been established that, for the PbCO₃SrCO₃ system, solid solutions are obtained under all the different experimental conditions and for the PbCO₃CaCO₃ system the precipitates obtained are always mixtures of PbCO₃ and CaCO₃.     

Thermal decomposition study of the coordination compound [Fe(urea)6](NO3)3

The thermochemical behavior of the coordination compound [Fe(urea)₆](NO₃)₃ was studied by simultaneous CG–TG–DTG–DTA and mass spectrometry methods non-isothermal conditions. The compound decomposes at 200 °C into a mixture of spinel-type oxides and hematite. The nature and particle size of the final decomposition products are strongly associated with the conditions during the thermal treatments, in particular the heating rate and the calcination temperature. A certain fraction of the products are formed as nanometric particles; they show superparamagnetic behavior at room temperature. The comparably low temperature of the calcination treatments of this compound is a promising perspective to attain small sized magnetic powders.     

Structural, optoelectronic, infrared and Raman spectra of orthorhombic SrSnO3 from DFT calculations

Orthorhombic SrSnO₃ was investigated using density functional theory (DFT) considering both the local density and generalized gradient approximations, LDA and GGA, respectively. The electronic band structure, density of states, complex dielectric function, optical absorption, and the infrared and Raman spectra were computed. Calculated lattice parameters are close to the experimental measurements, and an indirect band gap (2.27 eV) was obtained within the GGA (LDA) level of calculation. Effective masses for holes and electrons were estimated, being very anisotropic in comparison with similar results for orthorhombic CaSnO₃. The complex dielectric function and the optical absorption of SrSnO₃ were shown to be sensitive to the plane of polarization of the incident light. The infrared spectrum between 100 and 600 cm⁻¹ was obtained, with its main peaks being assigned, and a nice agreement between experimental and theoretical peaks of the Raman spectrum of orthorhombic SrSnO₃ was achieved.     

The non-isothermal crystallization kinetics of Sb2S3 in the (GeS2)0.2(Sb2S3)0.8 glass

The crystallization of Sb₂S₃ in the (GeS₂)_0.2(Sb₂S₃)_0.8 glass was studied under non-isothermal conditions. The influence of the sample form on crystallization was studied using bulk sample and two fractions of powder sample. The crystallization process of the sample in the form of powder was described using autocatalytic model, the crystallization of the bulk sample was described using nucleation-growth model. The parameters of both the models were determined.     

Thermal decomposition of organo-bielemental vanadium compounds Cp2V(ER3) (ER3 - GeEt3, SnEt3, CH2SiMe3 SeGeEt3)

The thermal decompositon of a number of organo-bielemental vanadium compounds with the general formula Cp₂V(ER₃) (ER₃ - GeEt₃, SnEt₃, CH₂SiMe₃, SeGeEt₃) has been investigated in solids and in solution. The main decomposition products of Cp₂V(SnEt₃) are vanadocene and hexaethyldistannane. Et₃GeH, Et₃GeCp, Cp₂V and CpV(C₅H₄GeEt₃) are formed from Cp₂V (GeET₃) decomposition. Isolated CpV(C₅H₄GeEt₃) is characterized by IR and mass spectra. The decomposition of Cp₂V(CH₂SiMe₃) is accompanied by Me₄Si, Cp₂V and CpV-(C₅H₄CH₂SiMe₃) formation, the latter is identified from the mass spectrum. Triethylgermane, vanadocene, and a diselenide of vanadium are isolated on decomposition of Cp₂V(SeGeEt₃). Based upon the experimental data, mechanisms for the decompositon are proposed.     

Mg-Al-CO3与Zn-Al-CO3水滑石热稳定性差异的研究

层状双金属氢氧化物（Ｌayered double hydroxides,简称ＬＤＨs）是一种类近年来发展迅速的阴离了型粘土,又称水滑石,其组成通式为[M（II）1－xM(III)x(OH)2]x(OH)2]^x＋Ax/n^n-mH2O,其中M（II）是二介金属离子,M（III）是三价金属离子,A^n-是阴离子,这种材料是由相互平行的层板组成,层板带有永在电荷,层间具有可交换的阴离子以维持电荷平衡,通过离子交换可在层间嵌入不同的基团,制备许多功能材料,被广泛作催化剂、吸附剂及油田化学品等,已引起人们的关注^[1-4]。有关Mg-Al-CO3与Zn-Al-CO3水滑石的合成及性能研究国内外已有大量报道^[1,2],本文对两者热稳定性存在的差异进行了研究,这对深化此类材料的认识具有参考作用。     

Non-isothermal crystallization kinetics of recycled PET-Si3N4 nanocomposites

Poly(ethylene terephthalate) (PET) is an important industrial material and has been widely applied in consumer products. Due to its slow crystallization rate, nanoparticles are incorporated into PET to function as heterogeneous nucleating agents. In this study, the non-isothermal crystallization behavior of recycled PET-silicon nitride (Si₃N₄) nanocomposites was investigated by differential scanning calorimetry (DSC). In the general analysis of the non-isothermal crystallization curves, it was found that the Si₃N₄ nanoparticles could effectively accelerate the nucleation of PET, but the crystal growth rate was slowed down when the Si₃N₄ content was more than 1 wt%. This might be attributed to the interaction between the PET chains and the surface-treated Si₃N₄ nanoparticles. Results obtained from Avrami and Mo treatments agreed well with the general analysis. Application of the Kissinger method and isoconversional method of Flynn-Wall-Ozawa also showed that Si₃N₄ nanoparticles had a good nucleation effect on the crystallization of PET, and the crystal growth was hindered by Si₃N₄ when the particle loading is higher than 1 wt%.     

Nonisothermal crystallization kinetics of amorphous Te51.3As45.7Cu3

The structure and kinetics of the crystallization reaction of amorphous Te_51.3As_45.7Cu₃ were studied under nonisothermal conditions using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Two exothermic changes were reported. Five isoconversional methods, of Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Tang, Starink, and Vyazovkin, were used to determine the variation of the activation energy for crystallization with temperature, E(T). The results show that the activation energy for crystallization associated with the first peak first decreases with increasing temperature and then increases. Different behaviour was observed for the second peak, where an increase of E with temperature followed by a decrease. The effect of heating rate on the reaction model, g(), was also different for the two crystallization peaks.     

Thermal analysis of Na2CO3 · H2O crystals

Monohydrated sodium carbonate crystals have been grown by slow evaporation of its aqueous solution maintained at 40 ± 1°C. The thermal dehydration of this crystal has been studied by dynamic and isothermal TG measurements. It is observed from dynamic TG that the single molecule of water of crystallization is lost in two steps of 0.3 mole and 0.7 mole at temperatures 426 ± 5 and 454 ± 5 K, respectively. From isothermal and dynamic TG measurements, the kinetic parameters E and Z are calculated using different known forms of the function F(). It is observed that consistency of E and Z values in isothermal and dynamic TG measurements for the two dehydration steps gives the correct function F() = −[log(1-)]^0.5. The activation energies for this function for the two dehydration steps are ≈6 and ≈9 kcal mole⁻¹, respectively.     

Cr2(WO4)3和Cr2(MoO4)3的负热膨胀特性研究

用液相反应-前驱物烧结法制备了Cr₂(WO₄)₃和Cr₂(MoO₄)₃粉体。298～1 073 K的原位粉末X射线衍射数据表明Cr₂(WO₄)₃和Cr₂(MoO₄)₃的晶胞体积随温度的升高而增大, 本征线热膨胀系数分别为(1.274±0.003)×10^-6 K^-1和(1.612±0.003)×10^-6 K^-1。用热膨胀仪研究了Cr₂(WO₄)₃和Cr₂(MoO₄)₃在静态空气中298～1 073 K范围内热膨胀行为，即开始表现为正热膨胀，随后在相转变点达到最大值，最后表现为负热膨胀，其负热膨胀系数分别为(-7.033±0.014)×10^-6 K^-1和(-9.282±0.019)×10^-6 K^-1。     

A study of the formation of LiNbO3 in the system Li2CO3Nb2O5

The formation process of LiNbO₃ in the system Li₂CO₃Nb₂O₅ was discussed from the results of non-isothermal or isothermal TG experiments and X-ray analysis. The mixture Li₂CO₃ and Nb₂O₅ in mole ratios of 1:3, 1:1 or 3:1 was heated at a rate of 5°C min^?1 or at various temperatures fixed in the range 475 to 677°C. If the system has a composition of Li₂CO₃ + 3Nb₂O₅ or 3Li₂CO₃ + Nb₂O₅, the reaction between Li₂CO₃ and Nb₂O₅ proceeds with CO₂ evolution to form LiNbO₃ at ca. 300–600°C, but Nb₂O₅ or Li₂CO₃ remains unreacted. A composition of Li₂CO₃ + Nb₂O₅ gives LiNbO₃ at 300–700°C. The diffusion of Li₂O through the layer of LiNbO₃ is rate-controlling with an activation energy of 51 kcal mol^?1. The reaction between LiNbO₃ and Nb₂O₅ gives LiNb₃O₈ at 600–700°C. At 700–800°C, a slight formation of Li₃NbO₄ occurs by the reaction between LiNbO₃ and Li₂O at the outer surface of LiNbO₃ and the Li₂O component of Li₃NbO₄ diffuses toward the boundary of the LiNb₃O₈ layer through the LiNbO₃ layer. The single phase of LiNbO₃ is formed above 850°C.     

EPR study of the NO2+3 radical in irradiated K(UO2)(NO3)3 and K2(UO2)(NO3)4 single crystals

A new radical observed at low temperature in γ-irradiated K₂(UO₂)(NO₃)₄ single crystals has been tentatively assigned to a hitherto unknown oxyanion radical, NO²⁺₃. The assignment and the lack of ¹⁴N hyperfine structure, together with the g factors which are lower than the free-spin value, are discussed in terms of an orbital level scheme.     

A comparative study of species N3 and P3

Calculations on linear and bent structures of N₃ and P₃ show that these species are quite different. N₃ is linear, P₃ is bent almost to a D_3h geometry. The symmetry of P₃ in D_3h is ²E″ but the Jahn-Teller distortion is very small, ≈4°. The many-body expansion of the energy of P_n clusters appears to be only slowly convergent.     

Normal coordinate analysis of CF3CH3

Normal coordinate calculations were made for CF₃CH₃, using a twenty-two parameter modified valence force field. Thirteen force constants were constrained to the CF₃CH₂X values and nine were adjusted to fit the twelve frequencies, resulting in an average error of 2.3 cm^/t-1. The CF₃ group force constants should be useful in calculations for other compounds containing this group.     

The effect of B2O3 addition on the crystallization of amorphous TiO2-ZrO2 mixed oxide

The effect of B₂O₃ addition on the crystallization of amorphous TiO₂-ZrO₂ mixed oxide was investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA). TiO₂-ZrO₂ mixed oxide was prepared by co-precipitation method with aqueous ammonia as the precipitation reagent. Boric acid was used as a source of boria, and boria contents varied from 2 to 20 wt%. The results indicate that the addition of small amount of boria (<8 wt%) hinders the crystallization of amorphous TiO₂-ZrO₂ into a crystalline ZrTiO₄ compound, while a larger amount of boria (?8 wt%) promotes the crystallization process. FT-IR spectroscopy and ¹¹B MAS NMR results show that tetrahedral borate species predominate at low boria loading, and trigonal borate species increase with increasing boria loading. Thus it is concluded that highly dispersed tetrahedral BO₄ units delay, while a build-up of trigonal BO₃ promote, the crystallization of amorphous TiO₂-ZrO₂ to form ZrTiO₄ crystals.     

Synthesis of Fe3O4 particle-chain microwires in applied magnetic field

Fe₃O₄ particle-chain microwires are firstly synthesized under magnetic field by a simple coprecipitation method. The increase of magnetic field caused the lengthening of the wires, and doubled densities of starting solution lead to a halved diameter. It was supposed that the magnetic field gradient and the particular growing process of particles are the main factors of the formation of these microwires. Magnetic hysteresis curves of Fe₃O₄ microwires were also measured.     

Comparative high-pressure study and chemical bonding analysis of Rh3Bi14 and isostructural Rh3Bi12Br2

The binary compound Rh₃Bi₁₄ was synthesized from the elements. The compound is isostructural with Rh₃Bi₁₂Br₂, crystallizes with the orthorhombic space group Fddd (no. 70) and lattice parameters a=6.8959(15) Å, b=17.379(3) Å, c=31.758(6) Å. The crystal structure consists of a three-dimensional (3D) framework of edge-sharing cubes and square antiprisms (RhBi_8/2). It is closely related to the intermetallic compound RhBi₄, in which two Y-like frameworks of antiprisms interpenetrate. In Rh₃Bi₁₄ and Rh₃Bi₁₂Br₂, additional bismuth and bromine anions, respectively, fill the channels of the 3D polyhedral framework formed by covalently bonded rhodium and bismuth atoms. High-pressure X-ray powder diffraction data from synchrotron measurements of Rh₃Bi₁₄ and Rh₃Bi₁₂Br₂ indicate a high stability of both compounds in the investigated range from ambient pressure to ca. 30 GPa at ambient temperature.