The use of the IKP method for evaluating the kinetic parameters and the conversion function of the thermal decomposition of NaHCO3 from nonisothermal thermogravimetric data

Three linear isoconversional methods (Friedman, Flynn–Wall–Ozawa, and Kissinger–Akahira–Sunose) and the invariant kinetic parameters (IKP) method were used in order to examine the kinetics of the nonisothermal decomposition of a sodium bicarbonate (NaHCO₃). The objective of the paper is to show the usefulness of the IKP method to determine both the kinetic parameters and the kinetic model of the investigated process. The activation energy (E_a) value obtained by the IKP method is in good agreement with the values obtained by isoconversional methods. The IKP method associated with the criterion of coincidence of kinetic parameters for all heating rates led us to the following kinetic triplet: E_a = 95.5 kJ mol^?1, A = 2.65 × 10¹⁰ min^?1, and conversion function f(α) = (1 ? α) (first‐order reaction model, F1). © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 462–471, 2007     

钙钛矿型复合氧化物La_(0.3)Ca_(0.7)Ni_(0.7)Co_(0.3)O_3的制备与表征

以甘氨酸和硝酸盐为原料,采用燃烧法制得陶瓷粉末,在马弗炉中焙烧2 h制备了钙钛矿型复合氧化物La0.3Ca0.7Ni0.7Co0.3O3,其结构经扫描电镜, XRD和IR表征.     

Cobalt spin state above the valence and spin-state transition in (Pr0.7Sm0.3)0.7Ca0.3CoO3

(Pr_0.7Sm_0.3)_0.7Ca_0.3CoO₃ belongs to a class of cobalt oxides undergoing a first-order transition (T* ≈90 K) associated to a coupled change in the valence and spin-state degrees of freedom. The Curie–Weiss regime present around room temperature (T >> T*) was analyzed in detail to address the controversial issue of the cobalt spin states above the transition. This magnetic investigation indicates that the Co⁴⁺ are in an intermediate spin-state, while the Co³⁺ are in a mixed state combining low-spin and high-spin states. These results are discussed with respect to the literature on related compounds and recent results of X-ray absorption spectroscopy.     

Quantitative kinetic determination of Sb(V) and Sb(III) by spectrophotometric H-point standard addition method

The H-point standard addition method (HPSAM) was applied to kinetic data for simultaneous determination of Sb(V) and Sb(III) and also selectively determines Sb(V) in the presence of Sb(III). The method is based on the differences between rate of complexation of pyrogallol red with Sb(V) and Sb(III) at pH=2. Sb(V) can be determined in the range of 0.3-2.0 μg ml⁻¹ with satisfactory accuracy and precision in the presence of excess Sb(III). Good selectivity was obtained over the variety of metal ions. The proposed method was used for determination of Sb(V) and Sb(III) in river and spring water samples.     

Analysis of crystallization kinetics of poly(ether ether ketone) by a nonisothermal method

During cooling at a rate of 10°C/min from the melt state of PEEK we have followed the growth of spherulites using an optical microscope equipped with a camera. The isothermal growth rates of crystallization in the temperature range of 266–308°C could be estimated by means of a differential equation. These continuous growth rate data were used further for kinetic analysis, which indicated that PEEK exhibited an unmistakable regime II → III transition at 296°C. The results compared favorably with those obtained by the traditional isothermal method, which is time consuming. Due to chain folding, the Thomas–Staveley constant should be closer to 0.25 instead of 0.1 or 0.3. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2393–2399, 1998     

Thermal Reduction of Mechanically Activated Cinnabar (HgS) and Stibnite (Sb2S3)

The reduction of cinnabar (HgS) and stibnite (Sb₂S₃) by hydrogen was investigated. These investigations were performed in the temperature region 636–765 K for cinnabar and in the region 825–954 K for stibnite. It has appeared that the mechanical activation positively affects the thermal reduction of the sulphides. The thermal decomposition of HgS is accompanied by a change in mechanism taking place at 744 K. As to Sb₂S₃, the change in mechanism inthe investigated temperature region was not observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Investigations of (PVA)0.7(NaBr)0.3(H2SO4)xM solid acid polymer electrolyte using positron annihilation lifetime spectroscopy

The free‐volumes of solid polymer electrolytes (SPE) were characterized using positron annihilation lifetime (PAL) spectroscopy, FTIR, and scanning electron microscope (SEM) techniques. The SPE based on poly(vinyl alcohol) (PVA) and sodium bromide (NaBr) complexed with sulfuric acid (SA) H₂SO₄ at different weight percent ratios were prepared using solution cast technique. The PAL results indicate that a higher SA content (more than 0.87 mol/L) in (PVA)_0.7(NaBr)_0.3 matrix increase the free‐volume hole size from 58 ų to 87 ų. The increase in the SPE free‐volume with higher SA content was associated with a decrease in the SPE crystallinity. It is postulated that the incorporated SA interrupt polymeric chain packing and retard crystallization during electrolyte films formation. The FTIR spectral studies indicate that the SA content higher than 0.87 mol/L induces chemical modifications within the PVA, which results in chain scission. The PAL study shows that the chain scissions within the polymer matrix affect the free volume hole density (I₃) and hence the microstructure. I₃ was found to be decreased from ?11 to ?6 %, resulting in lower fractional free‐volume holes in the SPE films. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2038–2044, 2010     

LiNi0.3Co0.7O2的结构及其锂电池行为的研究

利用XRD、XPS、CV等方法研究了LiNi_0.3Co_0.7O₂的结构及其锂电池行为。结果表明:LiNi_0.3Co_0.7O₂具有六方晶系空间群结构,其晶胞参数a=0.2826nm,c=1.4130nm;其表面存在Li₂O;Li⁺在其中的化学扩散系数为1～7×10^-8cm²·s^-1;其锂电池在4.30～3.00V间放电容量可达120～140mA·h·g^-1,放电机理为Li⁺在其中进行两步嵌入反应。     

Microwave-assisted synthesis of sulfide M2S3 (m = Bi, Sb) nanorods using an ionic liquid

Single-crystalline Bi(2)S(3) and Sb(2)S(3) nanorods have been successfully synthesized by the microwave-assisted ionic liquid method. The starting reagents were Bi(2)O(3) or Sb(2)O(3), HCl, Na(2)S(2)O(3), and ethylene glycol (EG) or ethanolamine, and the ionic liquid used was 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF(4)]). Our experiments showed that the ionic liquid played an important role in the morphology of M(2)S(3) (M = Bi, Sb). Single-crystalline Bi(2)S(3) nanorods could be prepared in the presence of [BMIM][BF(4)]. However, urchinlike Bi(2)S(3) structures consisting of nanorods were formed without using [BMIM][BF(4)]. Single-crystalline Sb(2)S(3) nanorods were obtained in the presence of [BMIM][BF(4)]. However, single-crystalline Sb(2)S(3) nanosheets could be prepared in the absence of [BMIM][BF(4)]. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction (ED).     

Laser-induced transformation of stibnite (Sb2S3) and other structurally related salts

Photoinduced transformation/degradation of stibnite (Sb₂S₃) by the use of micro-Raman spectroscopy was explained. The transformation products were compared with those obtained by the thermal degradation of stibnite carried out in independent experiments. The proposed mechanism of photodegradation of Sb₂S₃, also found to occur in other related SbS₃-pyramid-containing sulfosalts, helps to overcome the future erroneous interpretation of the bands in the Raman spectra of this important group of minerals as well to stress particular concern on the adjustment of the laser-excitation intensity when using micro-Raman and FT-Raman spectroscopy instrumentation in the study of other photosensitive and photodegradable compounds (including minerals).     

Kinetic analysis of nonisothermal solid-state reactions: determination of the kinetic parameters by means of a nonlinear regression method

A nonlinear regression method has been proposed for a simultaneous calculation of the activation energy, frequency factor, and reaction order from a single TG curve. This method was based on the new temperature integral approximation proposed in this paper and the Levenberg–Marquardt method. The newly proposed nonlinear regression method was applied for determining the kinetic parameters from two simulated TG curves. The results of the calculations were compared with values obtained by the traditional method. It can be concluded from this comparison that the new nonlinear regression method is more accurate than the traditional method for the determination of the kinetic parameters of solid-state heterogeneous reactions.     

二次Li／LiNi0.3Co0.7O2电池反应研究

利用循环伏安，库仑滴定，Ｘ射线衍射，恒电流阶跃等方法研究了Ｌｉ／ＬｉＮｉ０．２Ｃｏ０．７Ｏ２电池反应。结果表明该电池在４．３０－３．００Ｖ间放电容量可达１２０－１４０ｍＡ．ｈ．ｇ＾－１，充，放电机理为Ｌｉ＾＋在ＬｉＮｉ０．３Ｃｏ０．７Ｏ２中进行两步脱嵌与嵌入反应。     

Determination of the kinetic parameters of thermal decomposition of [Co(NH3)6]2(C2O4)3· 4H2O by Kissinger's method

The values of the kinetic parametersE andA were determined by Kissinger's method on the basis of the DTA, DTG and DSC curves of particular stages of the thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃· 4H₂O in air and argon atmospheres. It is shown that the use of Kissinger's method for different kinds of experimental curves (DTA, DSC, DTG) leads to close results.

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Zusammenfassung Für verschiedene Schritte der thermischen Zersetzung von [Co(NH₃)₆]₂(C₂O₄)₃· 4H₂O in Luft bzw. Argon wurden nach dem Kissinger-Verfahren auf der Basis von DTA-, DTG- und DSC-Kurven Werte für die kinetischen ParameterE undA ermittelt. Es wurde gezeigt, daß das Kissinger-Verfahren für die verschiedenen Arten von experimentellen Kurven (DTA, DSC, DTG) genaue Ergebnisse liefert.

     

Micro-structural study of the GeS2-In2S3-KCl glassy system by Raman scattering

Room temperature Raman spectra of samples on three serials within the GeS(2)-In(2)S(3)-KCl glassy system have been investigated systematically. According to XRD patterns and Raman spectra of several pseudo-binary systems, the Cl atoms, which was added into the GeS(2)-In(2)S(3) glasses through KCl, was considered to be leading to the breaking of In-In bonds among the S(3)In-InS(3) ethane-like units and the forming of InS(4-x)Cl(x), InS(6-x)Cl(x) mixed polyhedra. Considering the effect of K(+) ions upon mixed anion units (InS(4-x)Cl(x) and InS(6-x)Cl(x)) and the corresponding micro-structural model, the Raman spectral evolution of the GeS(2)-In(2)S(3)-KCl glasses can be elucidated successfully. The microstructure of the GeS(2)-In(2)S(3)-KCl glasses was considered to be that the potassium atoms, which exist in the form of chlorine atoms as its nearest neighbor, are homogeneously dispersed in the glassy net formed by the micro-structural units such as InS(4), InS(6), InS(4-x)Cl(x), InS(6-x)Cl(x), GeS(4) polyhedra and S(3)In(Ge)-In(Ge)S(3) ethane-like units.     

Preparation and characterization of Ti_(0.7)Sn_(0.3)O_2 as catalyst support for oxygen reduction reaction

Sn-doped TiO_2 nanoparticles with high surface area of 125.7 m~2·g~(-1) are synthesized via a simple one-step hydrothermai method and explored as the cathode catalyst support for proton exchange membrane fuel cells.The synthesized support materials are studied by X-ray diffraction analysis,energy dispersive X-ray spectroscopy and transmission electron microscopy.It is found that the conductivity has been greatly improved by the addition of 30 mol%Sn and Pt nanoparticles are well dispersed on Ti_(0.7)Sn_(0.3)O_2 support with an average size of 2.44 run.Electrochemical studies show that the Ti_(0.7)Sn_(0.3)O_2 nanoparticles have excellent electrochemical stability under a high potential compared to Vulcan XC-72.The as-synthesized Pt/Ti_(0.7)Sn_(0.3)O_2 exhibits high and stable electrocatalytic activity for the oxygen reduction reaction.The Pt/Ti_(0.7)Sn_(0.3)O_2 catalyst reserves most of its electrochemically active surface area(ECA),and its half wave potential difference is 11 mV,which is lower than that of Pt/XC-72(36 mV) under 10 h potential hold at 1.4 V vs.NHE.In addition,the ECA degradation of Pt/Ti_(0.7)Sn_(0.3)O_2is 1.9 times lower than commercial Pt/XC-72 under 500 potential cycles between 0.6 V and 1.2 V vs.NHE.Therefore,the as synthesized Pt/Ti_(0.7)Sn_(0.3)O_2 can be considered as a promising alternative cathode,catalyst for proton exchange membrane fuel cells.     

Synthesis and Reaction Chemistry of Sb(ECH2CH2NMe2)3 (E = O,S)

The antimony aminoalkoxide and aminothiolates Sb(ECH₂CH₂NMe₂)₃ [E = O ( 1 ), S ( 2 )] were synthesized and their ability to form adducts with other metal moieties investigated. Compound 1 forms 1:1 adducts with NiI₂ ( 3 ) and M(acac)₂ [M = Cd ( 4 ), Ni ( 5 )], while 2 undergoes ligand exchange with AlMe₃ to afford Me₂AlSCH₂CH₂NMe₂ ( 6 ). The structures of 2 – 4 and 6 were determined. Compound 2 incorporates three S, N‐chelating ligands though the interaction with nitrogen is weaker than in analogous alkoxide complexes. Product 3 reveals one iodine has migrated from nickel to antimony, and all three alkoxide ligands bridge the two metals through μ₂‐O atoms. In contrast, in 4 , only one alkoxide links the antimony and cadmium. Compound 6 adopts the same structure, a chelating S,N ligand generating a tetrahedral center at aluminum, as known tBu₂AlSCH₂CH₂NR₂ species (R = Me, Et).     

Efficient enantioselective synthesis of (2R,3R)- and (2S,3S)-3-hydroxyleucines and their diastereomers through dynamic kinetic resolution

(2R,3R)- and (2S,3S)-3-Hydroxyleucines, components of cyclodepsipeptides, papuamides and polyoxypeptins, were efficiently synthesized along with their diastereomers from the corresponding β-keto-α-amino acid ester through dynamic kinetic resolution using RuCl₂(binap)-catalyzed hydrogenation.     

Preparation and Magnetic Property of La_(0.7)Sr_(0.3)MnO_3 Nanorod by Combination Sol-Gel with Molten Salt

La0.7Sr0.3MnO3(LSMO) nanorods were synthesized by a method combining sol-gel with molten salts at 950 °C for 10 h, which employed KCl+NaCl(mass ratio 4:1) as eutectic molten salts. The morphologies and magnetic properties of the resulting LSMO nanorods were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), and vibrating sample magnetometer(VSM) measurements. It was found that the obtained perovskite manganite LSMO was a uniform nanorod with a d...