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.     

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.     

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.     

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.     

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.     

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.     

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。     

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.     

Thermal analysis and epr studies of carbon black oxidation in the presence of copper loaded Y2O3-CeO2-ZrO2 catalyst

The activity of copper-free and copper-loaded 10Y₂O₃-10CeO₂-80ZrO₂ solid solutions towards carbon black combustion was studied using simultaneous thermogravimetric analysis and differential thermal analysis techniques coupled with gas chromatography. It was demonstrated that all studied catalysts lower the temperature of carbon black combustion. The selectivity of the catalytic reaction in CO₂ formation was 100%. The comparison of electron paramagnetic resonance (EPR) spectra of pure catalysts with those of the samples (catalysts mixed with carbon black) after catalysis allowed to evidence, despite of the strong oxidizing atmosphere, a thermal reduction by carbon of Fe³⁺ (impurities), Cu²⁺ and Zr⁴⁺ during the reaction. Moreover a new EPR signal appeared after catalytic test and was attributed to the presence of paramagnetic metal-carbon or/and metal-sulphur complexes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal behaviour and vibrational characterization of MH2(IO3)3 phases (M=K,Rb and NH4)

The thermal behaviour of the MH₂(IO₃)₃ (M=K, Rb and NH₄) isomorphous compounds, as well as the IR and Raman spectra have been investigated as part of a study of the properties of solid protonic conductors. Detailed stoichiometries, sustained by TG, DTA, XRD and IR analysis, have been developed into the three phases. There were also evidences of the formation of the [I₃O₈]^– polymeric phases. Their stabilities were associated to the different polarizing power of the H, K and Rb cations.This work was supported by CONICET (Programa QUINOR) and CICPBA.     

Use of Methods of Thermal Analysis in Studying Ceramic Materials on the Basis of Al2O3, ZrO2, Si3N4, SiC and Inorganic Binder

By thermoanalytical methods TG, DTG, DTA there have been investigated the processes occurring during the formation of ceramic materials on the basis of Al₂O₃, ZrO₂, Si₃N₄, SiC,and inorganic binder. IR spectroscopy has been an additional research method. It's been determined that with the use of H₃PO₄ as the binder for ceramic materials, the mechanisms of thermal decomposition are connected with the following processes: 1. removal of weakly tied and crystallized water in the temperature range of120–230°C, the removal being characterized by the endothermic effect, 2. interaction of the initial powder components of the ceramic materials with orthophosphoric acid conditioned by a strong exothermic effect on the DTA curve in the range of 230–530°C, 3. overlapping of endo- and exo-effects, testifying to a complex mechanism of thermal transformations, 4.oxidizing of the non-reacted silicon at the temperature of 720(760)°C, an increase of mass is observed on the TG curve as a result of the formation of SiO₂ – crystoballite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ni／ZrO2-Al2O3制备表征及催化性能的研究

本文采用浸渍沉淀法制备了不同配比的ZrO2-Al2O3复合载体。并通过浸渍法制备Ni/ZrO2-Al2O3催化剂,以苯加氢制环己烷反应为探针,考察了ZrO2与Al2O3的配比对Ni催化剂催化加氢性能的影响;采用X射线衍射(XRD)、程序升温还原(TPR)、程序升温脱附(TPD)等技术考察复合载体对Ni催化剂的体相结构、还原性能以及表面吸附性能的影响。研究结果表明,ZrO2质量分数为20%的复合载体所负载的Ni催化剂有很好的加氢活性,优于单组分载体负载的Ni催化剂;采用浸渍沉淀法制备的ZrO2-Al2O3复合载体中ZrO2以非晶态形式存在,这是由于Al2O3的存在影响了ZrO2的内部结构;该载体负载的Ni催化剂较其他催化剂更容易被还原,吸附中心数量增加。     

Solvation/desolvation during the redox transformation of poly(3-methylthiophene)

Solvation/desolvation effects were studied during the redox transformation of poly(3-methylthiophene) by electrochemical quartz crystal microbalance technique. The effect was demonstrated by studying the phenomenon in different solvents, and comparing the results after a solution change. From the data obtained with the same film transferred between nitrobenzene and acetonitrile in both directions, the solvation effect was directly evidenced, and the virtual molar mass of the moving species in and from the same film was determined to illustrate semi-quantitatively the effect of the solvation.This paper is dedicated to Professor G. Horányi on the occasion of his 70th birthday and in recognition of his outstanding contribution of electrochemistryCsaba Visy, Emese Kriván are ISE members     

Investigation of the hydration process in 3CaO.Al(2)O(3)-CaSO(4) . 2H(2)O-plasticizer-H(2)O systems by X-ray diffraction

The development of the hydration process in 3CaO.Al(2)O(3)-CaSO(4) . 2H(2)O-H(2)O system is studied by X-ray diffraction in the presence of varying contents of new plasticizer admixtures belonging to the lignosulphonates class (calcium lignosuphonate-LSC) and condensates melamine formaldehyde sulfonated class-MSF (VIMC-11). The plasticizer admixtures were added in proportion of 0.1-1% solid substance. The influence of the plasticizer admixtures on the hydration process with increasing time is observed and it is shown to depend on the nature and content of the admixtures and the reaction time. The strong adsorption of admixtures on the surfaces on the anhydrous or partially hydrated particles of the system can explain the influence of the admixtures upon the kinetics of the hydration process retardation or acceleration. These plasticizer admixtures influence also the evolution of the hydrated compounds and forming of the hardening structure in the 3CaO.Al(2)O(3)-CaSO(4) . 2H(2)O-H(2)O system; their proportion in the system and the considered length of hardening are correlated. In the 3CaO.Al(2)O(3)-CaSO(4) . 2H(2)O-H(2)O system there are two different influences of the plasticizer admixtures upon the hydration process. One is a delaying action, as a result of plasticizer adsorption on the surface of the anhydrous and hydrated compound particles and another one is the intensifying action due to the stronger dispersion of the particles in aqueous medium.     

Preliminary Study on the Effect of pH on Thermal Transformation of Some Diphasic Al2O3-SiO2 Gels

Diphasic Al₂O₃-SiO₂ gels have been synthesized by hydrolyzing ethyl orthosilicate at three different pH ranges in presence of colloidal boehmite. Result shows that dominant mullitization process are sensitive to pH of the gelation process. At highly acidic pH range, solid state reaction between corundum and cristobalite occurs, and develops liquid phase for mullite nucleation. At moderately acidic pH, nucleation and crystallization are most operative for nucleation in aluminosilicate matrix. In highly basic pH region, Al-Si spinel phase develops by incorporation of Si in aluminous phase as intermediary phase. Polymorphic transformation of it may be the cause of sudden mullitization. The changes in crystallization sequence in three distinct processes may be due to variation in the nature and size of silicic acid particle formed by hydrolysis and condensation of TEOS at different pH.