ZnAc2·2H2O在空气中的热分解动力学研究

用TG/DTA,DSC和XRD技术研究了固态物质ZnAc2.2H2O在空气中的热分解过程.结果表明,ZnAc2.2H2O在空气中发生两步分解,其失重率与理论计算失重率相符.XRD结果表明,ZnAc2.2H2O分解的最终产物为ZnO.用Friedman法和Flynn-Wall-Ozawa(FWO)法求得分解过程的活化能E,并通过多元线性回归方法给出了可能的机理函数.ZnAc2.2H2O在空气中两步分解的活化能分别为119.82和66.82kJ/mol.     

Devitrification behaviour of CaO−MgO(Y2O3)−SiO2 glasses

In this paper a thermoanalytical study of the kinetic parameters and mechanism of the devitrification process of CaO·SiO₂, 1.6CaO·0.4MgO·2SiO₂ and 1.4CaO·(0.6/3)Y₂O₃·2SiO₂ is reported. The experimental results suggest that, in the studied glasses, a surface nucleation process is operative; however, in finely powdered samples, that soften and efficiently sinter before devitrifying, surface nuclei behave as bulk nuclei. In this case lamellar crystalline structures are obtained.     

Effects on the Thermal Properties and Bioactivity of Substitution of CaO by M2O3 (M=La, Y, Al) in Wollastonite Glass

The effects on the thermal properties and bioactivity of the substitution of CaO by La₂O₃, Y₂O₃ and Al₂O₃ in a glass of composition CaO·SiO₂ were studied and compared. The trivalent metal oxides were all effective in raising the glass transformation and softening temperatures when they replaced CaO in the glass of composition CaO·SiO₂. The experimental results suggest that Al₂O₃ plays the role of a glass-former, while La₂O₃ and Y₂O₃ behave as glass-modifiers. The tendency to devitrify appears to be the lower, the farther the glass composition is from those of the crystalline phases, owing to the need for diffusion over longer distances, the greater the composition difference. The substitution with the trivalent metal oxides is detrimental to the bioactivity, which is preserved only in the event of very small degrees of substitution. The most negative role appears to be played by Al₂O₃. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Role of Trivalent Element Oxides in Cao (Na2O)–M2O3–SiO2 Glasses From Tg

In this paper T _g values of calcium (sodium) silicate glasses containing added with oxides of trivalent elements are reported. The plots of T _g as a function of composition or vs. the ionic field strength prove to be useful in discussing the role of the oxides in the glass structure. It is found that, at least in the studied composition range, Sc₂O₃, Y₂O₃, La₂O₃, and In₂O₃, behave as network modifier oxides. In the compositional ranges studied, the hypothesis based on them well agree with the expectations based on the known criteria reported in literature and on FTIR spectra. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Study of A2O–(MoO3)2–P2O5 (A=Li, Na) Glasses

Alkali phosphomolybdate glasses have been prepared by quenching melted mixtures of P₂O₅, MoO₃ and A₂O(A=Li, Na). The composition dependence of the transition temperature of glasses belonging to ternary A₂O–(MoO₃)₂–P₂O₅ (A=Li, Na) systems is studied for several series of glasses corresponding to either a fixed A₂O rate or a constant Mo/P ratio. The interpretation of the results is based on the presence of different types of molybdenum and phosphorous structural groups and P–O–M (M=P, Mo) linkages in glasses. This revised version was published online in August 2006 with corrections to the Cover Date.     

Enthalpic Relaxation of 25Na2O·xTiO2·(75-x)SiO2 Glasses

The enthalpic relaxation of the title glasses, studied by differential scanning calorimetry, is well described by a mathematical model based on the stretched exponential relaxation function with the relaxation time proportional to the actual viscosity. The dependence of viscosity on temperature and the fictive temperature was expressed by Mazurin's approximation. The relaxation parameters obtained correlated significantly with the glass composition, indicating the changes in the structural of the TiO₂ role near a TiO₂ content of 3–4 mol%. This revised version was published online in August 2006 with corrections to the Cover Date.     

New elaboration of Na2O-B2O3-SiO2 glass doped with CdS nanocrystals from gel formed in aqueous solution

A new route for preparing a CdS doped sodium borosilicate glass from a gel formed in an aqueous solution is described. This elaboration process allows the preparation of a gel which starts densifying at 400°C just after the Cd sulphurizing process ensuring the protection of crystallites from oxidation. The densification of the matrix is completed at the fusion temperature (730°C), which is low enough to reduce the coalescence of the crystallites. Microstructural and optical characterization of the CdS doped glasses indicate that the crystallite size depends upon the Cd concentration. A model to calculate the crystallite size from optical absorption spectra is proposed. It indicates that the average sizes of crystallites range from 11 nm for a concentration of 0.03 mol% Cd to 3.7 nm for 0.016 mol% Cd.     

Phase Transition and Thermal Decomposition of [Cd(H2O)6](BF4)2

Phase transition and thermal decomposition of [Cd(H₂O)₆](BF₄)₂ were studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetry (TG) methods. The solid-solid phase transition at T _C1=324 K and the melting point atT _melt.=391 K were registered. The thermal dehydration process starts just above T _C1 and continues up to T _melt.,where [Cd(H₂O)₄](BF₄)₂ in the liquid phase is formed. Then, dehydration and decomposition take place simultaneously until CdF₂ is obtained. Final products of the thermal decomposition were identified using quadrupole mass spectrometry (QMS) and X-ray diffraction methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spectroscopic properties of Dy(3+) ions in NaF-B(2)O(3)-Al(2)O(3) glasses

This paper reports the optical properties of Dy(3+) in sodium fluoroborate glasses of the type XNaF.(89-X)B(2)O(3).10 Al(2)O(3).1Dy(2)O(3) (where X=8, 12, 16, 20 and 24). Judd-Ofelt intensity parameters (Omega(2), Omega(4), Omega(6)) are derived from the absorption spectra. The Judd-Ofelt theory has been applied to interpret the local environment of Dy(3+) ions and bond covalency of RE-O bond. These parameters have been used to calculate radiative transition probabilities (A(rad)), lifetimes (tau(R)) and branching ratios (beta(R)) for the excited level (4)F(9/2). The predicted values of tau(R) are compared with the measured values for (4)F(9/2) level for five glass compositions (Glass (A-E)). The stimulated emission cross-section sigma(lambda(P)) are also evaluated for the (4)F(9/2)-->(6)H(J) (J=11/2, 13/2, and 15/2) transitions.     

Effect of the ratio R = [Na2O]/[B2O3] on the structure of glass in the Na2O-B2O3-SiO2 system

Sodium borosilicate glass, with the ratio R = [Na₂O]/[B₂O₃] varied from 0.31 to 1, were studied by IR spectroscopy and Raman scattering techniques. The dependence of the structure of borosilicate glasses on their composition was studied also for the section with a constant value R = 1. The main borate and silicate groups in the system, and especially changes in the structure of glasses depending on the ratio R were identified.     

Crystallization of MgFe2O4 from a glass in the system K2O/B2O3/MgO/P2O5/Fe2O3

Spherical magnetic Mg-Fe-O nanoparticles were successfully prepared by the crystallization of glass in the system K₂O/B₂O₃/MgO/P₂O₅/Fe₂O₃. The magnetic glass ceramics were prepared by melting the raw materials using the conventional melt quenching technique followed by a thermal treatment at temperatures in the range 560–700 °C for a time ranging from 2 to 8 h. The studies of the X-ray diffraction, electron microscopy and FTIR spectra confirmed the precipitation of finely dispersed spherical (Mg, Fe) based spinel nanoparticles with a minor quantity of hematite (α-Fe₂O₃) in the glass matrix. The average size of the magnetic nano crystals increases slightly with temperature and time from 9 to 15 nm as determined by the line broadening from the XRD patterns. XRD studies show that annealing the glass samples for long periods of time at temperature ≥604 °C results in an increase of the precipitated hematite concentration, dissolution of the spinel phase and the formation of magnesium di-borate phase (Mg₂B₂O₅). For electron microscopy, the particles were extracted by two methods; (i) replica extraction technique and (ii) dissolution of the glass matrix by diluted acetic acid. An agglomeration of the nano crystals to larger particles (25–35 nm) was observed.     

具有二维纳米孔径结构Ni3(H2O)6(TMA)3-(TMA)23-·2H2O(TMA=均苯三甲酸)的合成、晶体结构和磁性研究

A novel coordination polymer nickel 1,3,5-benzenetricarboxylate (TMA) Ni₃(H₂O)₆(TMA)^3-(TMA)₂^3-·2H₂O with two-dimensional porous structure was synthesized and characterized. It crystallizes in the hexagonal system, space group P6₅22, with a=1.665 2(10) nm, c=2.045 4(11) nm, V=4.912(5) nm³, Z=6, D_c=1.916 g·cm^-3, μ(Mo Kα)=0.181 8 mm^-1, F(000)=2 892. The final R₁=0.066 4, wR₂=0.175 6 for 2 710 observed reflections [I>2σ(I)] out of 2 904 unique reflections . This coordination polymer reveals not only two-dimensional porous structure but also particular magnetic properties. CCDC: 274177.     

Phase Transitions in Crystalline [M(H2O)6](ClO4)2 (M=Mg,Mn, Fe,Co, Ni,Cu, Zn,Cd and Hg)

The results of DSC measurements in the temperature range 140–370 K on nine crystalline compounds of the type [M(H₂O)₆](ClO₄)₂, where M=Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd and Hg, are discussed. Anomalies detected in the DSC curves are related to the existence of solid-solid phase transitions and/or to the melting points of these compounds. In consequence of two different hypothetical structural modifications of [Fe(H₂O)₆](ClO₄)₂, two DSC curves are obtained. For the compounds with M=Fe, Cd and Hg, new phase transitions have been discovered. The transition temperatures of the other phase transitions are in good agreement with literature data obtained by adiabatic calorimetry. For the compounds with M=Mg, Ni and Cd, DTA measurements were also carried out and the melting points of theses compounds were established. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evidence of network demixing in GeS2-Ga2S3 chalcogenide glasses: A phase transformation study

The information of phase transformation is attained by in situ XRD experiments leading to the knowledge of topological threshold in GeS₂-Ga₂S₃ glasses. The turning point of phase transformation behavior is demonstrated to be glasses containing 14-15 mol% Ga₂S₃. To interpret it a network demixing model is further improved and proposed for the structure of these ternary or quasi-binary chalcogenide glasses. For the nearest-neighbor coordination environment of glass with a transitional composition of 85.7 mol% (6/7) GeS₂·14.3 mol% (1/7) Ga₂S₃, six-coordinated [S₃Ga-X-GaS₃] units (X=S or None) are well isolated by the [GeS₄] structures, which contributes to the decreasing of precipitation of Ga₂S₃ crystals in (100−x)GeS₂-xGa₂S₃ (x≤14.3) glasses corresponding to the experimental evidence of the phase transformation behavior. This scenario of intermediate-range structural order, firstly, includes the arrangement of structural units which is consistent with and provides an atomistic explanation of the compositional evolution of phase transformation behavior in these glasses.     

Crystallization mechanism study on ZSM-48 in the system Na2O-Al2O3-SiO2-H2N(CH2)6NH2

The crystallization mechanism of ZSM-48 in the system Na₂O-Al₂O₃-SiO₂-H₂N(CH₂)₆NH₂ was studied by using XRD, SEM, TG/DTA, FTIR, XPS and plasma spectra techniques. It is shown that the reaction mixture is crystallized through solid—solid mass transformation. It was found, by tracing the crystallization process, that a secondary gel composed of silicate and aluminosilicate, in which SiO₄ and AlO₄ tetrahedra quickly form with some Al atoms, transferred to the surface, before generating nuclei. Possibly, a C-model (can and cement model) may be used to elucidate the evolution of nucleation. SEM showed that dendritic and entangled nuclei first form in the inner portion of the solid fraction. TG/DTA showed that the organic amine content in the solid sample increases with increasing crystallinity, which gives strong evidence for the organic amine being a template. FTIR revealed that the structure consisting of six-membered rings and double five-membered rings forms after about eight days through rearrangement and coalescence.     

Über die quasi-binären Systeme NaNO2/Na2O und NaCN/Na2O. Phasendiagramme und Natrium-Ionenleitung in Na3O(NO2) und Na3O(CN)

On the Quasi-Binary Systems NaNO₂/Na₂O and NaCN/Na₂O. Phase Diagrams and Sodium Ion Conductivity of Na₃O(NO₂) and Na₃O(CN) Measurements of the electrical conductivities of Na₃O(NO₂) and Na₃O(CN) show sharp increases in conductivity at temperatures between 200° and 250°C, According to the phase diagrams of the quasi-binary systems NaNO₂/Na₂O and NaCN/Na₂O this is not an effect established by fusion. It seems to be a consequence of a “melting” of the sodium sublattice or the rotational disorder of complex anions.     

Formation of gels and gel-glasses in the VO2(V2O5)-SiO2 systems

Blue-coloured gels have been prepared in the VO₂-SiO₂ system up to 80 mol% VO₂ by sol-gel technology using TEOS and aqueous solutions of VOSO₄·5H₂O. It is established by means of VIS and ESR spectra that at low temperatures VO²⁺ complexes are formed. An oxidation of V⁴⁺ has taken place with increasing temperature, and V₂O₅ and cristobalite have been separated. Silica gel glasses stable up to 800°C have been obtained from gels containing 1–3 mol% VO₂.     

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。     

Na2O或K2O对气相合成1–苯基氮杂环庚烷的CoO/SiO2-Al2O3催化剂的作用

研究了Na2O或K2O对苯胺和1,6己二醇气相合成1-苯基氮杂环庚烷的CoO/SiO2-Al2O3催化剂的作用,并采用X射线衍射、透射电子显微镜、H2-程序升温还原、NH3-程序升温脱附等技术对催化剂进行了表征.结果表明,Na2O助剂能增加催化剂的弱酸中心数,减少中强酸中心数,使催化剂的选择性得到提高.加入K2O使催化剂的弱酸中心数显著减少,并使CoO在反应过程中易于烧结,因此不利于1–苯基氮杂环庚烷的合成.     

Carbon Dioxide Reforming of Methane over Ni Catalysts Supported on Al2O3 Modified with La2O3, MgO, and CaO

The preparation of synthesis gas from carbon dioxide reforming of methane (CDR) has attracted increasing attention. The present review mainly focuses on CDR to produce synthesis gas over Ni/MO_x/Al₂O₃ (X = La, Mg, Ca) catalysts. From the examination of various supported nickel catalysts, the promotional effects of La₂O₃, MgO, and CaO have been found. The addition of promoters to Al₂O₃-supported nickel catalysts enhances the catalytic activity as well as stability. The catalytic performance is strongly dependent on the loading amount of promoters. For example, the highest CH₄ and CO₂ conversion were obtained when the ratios of metal M to Al were in the range of 0.04–0.06. In the case of Ni/La₂O₃/Al₂O₃ catalyst, the highest CH₄ conversion (96%) and CO₂ conversion (97%) was achieved with the catalyst (La/Al = 0.05 (atom/atom)). For Ni/CaO/Al₂O₃ catalyst, the catalyst with Ca/Al = 0.04 (atom/atom) exhibited the highest CH₄ conversion (91%) and CO₂ conversion (92%) among the catalysts with various CaO content. Also, Ni/MgO/Al₂O₃ catalyst with Mg/Al = 0.06 (atom/atom) showed the highest CH₄ conversion (89%) and CO₂ conversion (90%) among the catalysts with various Mg/Al ratios. Thus it is most likely that the optimal ratios of M to Al for the highest activities of the catalysts are related to the highly dispersed metal species. In addition, the improved catalytic performance of Al₂O₃-supported nickel catalysts promoted with metal oxides is due to the strong interaction between Ni and metal oxide, the stabilization of metal oxide on Al₂O₃ and the basic property of metal oxide to prevent carbon formation.