Thermal decomposition mechanism and non-isothermal kinetics of the polyoxometalate of ciprofloxacin with 12-tungstoboric acid

The polyoxometalate complex (CPFX-HCl)(4)H5BW12O40-12H(2)O was prepared in aqueous solution for the first time, and characterized by elemental analysis, IR spectrum, and TG-DTG. The TG-DTG curves showed that its thermal decomposition was a four-step process consisting of the simultaneous collapse of Keggin anion. The intermediate and residue of the decomposition were identified by mean of TG-DTG, IR, and XRD technique. The non-isothermal kinetic data were analyzed by the Achar method and Coats-Redfern method. The apparent activation energy (E) and the pre-exponential factor (In A) of each decomposition were obtained. The most probable thermal decomposition reaction mechanisms were proposed by comparison of the kinetic parameters. The kinetic equation for both the second stage and the third stage can be expressed as d alpha/dt = Ae(-E/RT) -(1 - alpha)(2), and the fourth stage d alpha/dt = Ae(-E/RT) -(1 - alpha). And their mathematic expressions of the kinetic compensation effects of thermal decomposition reaction were also determined.

Theoretical Studies on the Thermal Decomposition Mechanism of Potassium Nitroformate

The microcosmic reaction mechanism of the thermal decomposition of potassium nitroformate（KNF） has been investigated by density functional theory within the generalized gradient approximation. The geometric structures of reactants, intermediates, transition states, and products are fully optimized. The frequency analysis approves the authenticity of intermediates and transition states. Our results show that there are four feasible reaction pathways. The main pathway of the reaction is KNF → B1 → TSB1 → B2 → TSB2 → B3 → TSB3 → B4 → KNO2 ＋ NO2 ＋ NO ＋ CO, and the energy barrier of the rate-limiting step is 216.30 k J·mol^-1. The dominant products predicted theoretically are KNO2, NO2, NO, and CO, which is in agreement with the experiment.

Thermal decomposition mechanism and kinetics of bastnaesite in suspension roasting process:A comparative study in N_(2) and air atmospheres

To investigate the thermal decomposition behavior and reaction kinetics of bastnaesite in suspension roasting,the gas and solid products of bastnaesite roasted in N2 and air atmospheres were examined using a gas analyzer,X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectrometry(EDS).Subsequently,the kinetic parameters of bastnaesite in the suspension roasting process were derived and calculated using the isothermal method.The results show that the decomposition product of bastnaesite in N_(2) is CeOF.However,once the roasting temperature exceeds 600℃,CO is generated in addition to CO_(2),and all the XRD diffraction peaks of CeOF are shifted to the right,indicating that CO_(2) can oxidize CeOF and lead to the transformation of Ce(Ⅲ) into Ce(Ⅳ).When roasted in air,the decomposition product CeOF can be completely converted to CeF3 and Ce_(7)O_(12) as it easily oxidizes.Additionally,the reaction rate of bastnaesite in air is higher than that of N_(2),and the starting reaction temperature is lower than that of N_(2).A large number of irregular cracks and holes appear on the surface of solid-phase products following suspension roasting,which are due to the thermal decomposition of bastnaesite that produces CO_(2) as well as the reconstruction of the lattice of the solid-phase products.The reaction kinetic model of bastnaesite roasted in N_(2)(temperature range 600-750℃) and air(temperatu re range 500-575℃) confo rms to the A_(3/2) model with the mechanism function G(α)=-ln(1-α)^(2/3),and the reaction activation energy is 59.78 kj/mol and lnA is 1.65 s^(-1) in N_(2) atmosphere.In air,the reaction activation energy is 100.30 kj/mol and lnA is 9.63 s^(-1).

Thermal decomposition mechanism of low-content-fluorite Bayan Obo rare earth concentrate roasted with sodium carbonate and its consequent separation study

Thermal decomposition and phase transformation for the mixture of Bayan Obo rare earth concentrate(BORC)and sodium carbonate(Na2CO3)roasted at different temperatures with weight ratio of 100:20 were studied in detail in our study.The aim of our study is to reveal the nature of roasting reaction between BORC and Na2CO3 and thus providing a new method for processing BORC.The results indicate that BORC can be decomposed completely with Na2CO3 at around 600℃after 3 h.During the calcination process,Ce0.5Nd0.5O1.75,NaF,Na3PO4,and a rare earth double phosphate phase Na3RE(PO4)2 are formed after the decomposition of BORC with Na2CO3.In addition,the thermal decomposition mechanism is determined in the paper.Based on these facts,a clean technique processing BORC was developed.And a CeF3 powder,whose composition was measured and stability was also evaluated,was obtained for some potential application from the new technique.This research is of significance in terms of the Na2CO3-roasting BORC solid reaction study and sheds a light on a potential clean technique for BORC.

Crystal structures and thermal decomposition mechanism of four lanthanide complexes with halogen-benzoic acid and 1,10-phenanthroline

This paper describes syntheses and structure determination of four lanthanide complexes [Nd(2-Cl-4-FBA) 3 phen] 2 (1, 2-Cl-4-FBA = 2-chloro-4-fluorobenzoate, phen = 1,10-phenanthroline), [Ln(2,5-DClBA) 3 phen] 2 (Ln = Sm(2) and Tb(3), 2,5-DClBA = 2,5-dichlorobenzoate) and [Sm(2-Cl-4,5-DFBA) 3 (phen)(H 2 O)] 2 (4, (2-Cl-4,5-DFBA = 2-chloro-4,5-difluorobenzo- ate). The complexes were characterized by elemental analysis, infrared and ultraviolet spectra, and X-ray single-crystal diffraction. In the molecular structures of 1 4, two Ln 3+ ions are linked by four carboxyl groups, with two of them in a bridging bidentate mode and the other two in a bridging-chelating tridentate mode, forming four binuclear molecules. In addition, each Ln 3+ ion is also chelated to one phen molecule and one carboxyl group in the complexes, except each Sm 3+ ion in 4 which is bonded to one carboxyl group by unidentate mode and one H 2 O molecule. There are two different coordination polyhedrons for each Nd 3+ ion in the two similar molecular structures of 1 and they are a distorted monocapped square antiprismatic and a distorted tricapped triangular prism conformation, respectively. The coordination polyhedron for each Ln 3+ ion in 2 4 is a nine-coordinated distorted mono-capped square antiprismatic conformation. The complex 3 exhibits green luminescence under the radiation of UV light. The thermal decomposition behaviors of the complexes have been discussed by simultaneous TG/DSC-FTIR technique. The 3D surface graphs for the FTIR spectra of the evolved gases were recorded and the gaseous products were identified by the typical IR spectra obtained at different temperatures from the 3D surface graphs. Meanwhile, we discussed the nonisothermal kinetics of 1 4 by the integral isoconversional non-linear (NL-INT) method.

Effect of inorganic salt on the thermal degradation of nitrocellulose and reaction mechanism of its mixture

In this study,to better understand the reaction mechanism between inorganic salts and nitrocellulose,CaCO_(3) and Li_(2)CO_(3) were evaluated with respect to their effects on the thermal degradation of NC in nitrogen atmosphere using TG/DSC at three different heating rates(2,5,10 K/min).The numerical relationship between activation energy(E)and conversion rate was obtained by FWO and KAS method,and it was discovered that CaCO_(3) could improve the thermal stability of NC.Activation energy values were calculated by Kissinger method,and it was found that NC that contain Li2CO3had the highest activation energy while NC containing CaCO3had the lowest E value.By combining the thermal analysis data with Malek method,the most probable mechanism model of thermal degradation is obtained as Sesták-Berggren model,which expression is f(α)=α^(m)(1-α)^(n).As a result of this study,there are certain guiding principles that can be applied to the pyrolysis reaction model and to the actual production process of nitrocellulose.

Preparation，Structural Characterization and Thermal Decomposition Mechanism of Rare Earth Salts of 3－Nitro－1，2，4－Triazol－5－One

Eleven rare earth salts of 3-nitro-1, 2 , 4-triazol-5-one (NTO) was prepared by using aqueous solutions of lithium salt of NTO and corresponding rare earth nitrates. The formulae of these salts are determined as RE(NTO)3. nH2O, where RE is Y, La, Ce, Pr, Nd, Sm, Eu, Gd,Tb, Dy or Yb, and n is 6, 7, 7, 7, 8, 7, 7, 7, 5, 5 and 6 correspondingly. Their thermal decomposition mechanism was studied by using DSC, TG-DTG and FT-IR techniques under linearly increasing temperature.

Preparation, Structural Characterization and Thermal Decomposition Mechanism of [Cu（TO）2（H2O）4]（PA）2

[Cu（TO）2（H2O）4]（PA）2 was prepared by the reaction of aqueous 1,2,4-triazol-5-one （TO） solution with the solution of copper picrate Cu（PA）2 and characterized by elemental analysis, FT IR and X-ray powder diffraction analysis. The title complex has been studied by means of TG-DTG and DSC under conditions of linear temperature increase. The thermal decomposition residues were examined by FT IR analysis. Thermal decomposition mechanism of the title complex was proposed. In the temperature range of 30-680 ℃, the thermal decomposition process was composed of four major stages. The first stage was an endothermic process with the loss of four coordination water molecules. Since the dehydration product was unstable, when it was heated, it would be decomposed much more easily. The second stage was composed of an acute endothermic process and a continued strong exothermic process and the main decomposed residues were CuCO3, Cu（NCO）2 and polymers during this stage. The third stage was a sharp exothermic process, which resulted from the decomposition of the polymer. After the forth stage, the final decomposed residues were certainly copper oxide. The Arrhenius parameters have been also studied on the dehydration process and the first-step exothermic decomposition of [Cu（TO）2（H2O）4]（PA）2 using Kissinger＇s method and Ozawa-Doyle＇s method. The results using both methods were consistent with each other. The Arrhenius equation can be expressed as in k=24.0-179.8 × 10^3/RT for the dehydration process and in k= 16.7-206.0 × 10^3/RT for the first-step exothermic decomposition, on the basis of the average of Ea and In A through the two methods.

Syntheses,Crystal Structures and Kinetic Mechanisms of Thermal Decomposition of Rare Earth Complexes with Schiff Base Derived from o-Vanillin and p-Toluidine

Three complexes, [Pr（NO3）3（HL）2] （1）, [Nd（NO3）3（HL）2] （2） and [Er（NO3）3（HL）2] ·0.5H2O （3）, were synthesized from the reaction of a Schiff base ligand 2-[ （4-methylphenylimino）methyl ]-6-methoxyphenol （C15 H15 NO2, HL） with Ln（NO3）3·6H2O （Ln = Pr, Nd, Er）. Characterization by single-crystal X-ray diffraction technique, elemental analysis, molar conductance, FT-IR, UV-Vis, ^1H NMR and thermal analysis shows the title complexes are neutral molecules where the central Ln（ Ⅲ） ion is ten-coordinated in biapical anti-hexahedron prism geometry, with four oxygen atoms of the phenolic hydroxy and methoxy groups in the two bidentate Schiff base ligands and six oxygen atoms provided by the three bidentate NO3 - anions. Additionally, the kinetic mechanism of thermal decomposition of complex 3 was determined with a TG-DTG curves by both integral and differential methods. The functions of thermal decomposition reaction mechanism and the equation of kinetic compensation effect were obtained.

Infl uencing Mechanism and Interaction of Muscovite on Thermal Decomposition of Ammonium Polyphosphate

The interaction mechanism and phase evolution of ammonium polyphosphate（APP）mixed with muscovite（APP/muscovite）were studied by TG,XRD and SEM,respectively,during heating.When the temperature is not higher than 300 ℃,muscovite has no effect on the thermaldecomposition of APP,and the initialdecomposition temperature of APP/muscovite at 283 ℃ is basically the same as the APP at 295 ℃,and the main thermaldecomposition products are polyphosphoric acid and NH_4H_2PO_4 at 300 ℃.The polyphosphoric acid,the decomposition products of APP,can enable K and Siout of muscovite and interact with muscovite chemically to generate Al_2O_3·2SiO_2,α-SiO_2 and phosphates（AlPO_4 and K_5P_3O_（10））compounds during 400 ℃-800 ℃,which own obvious adhesive phenomenon and porous structure with the apparent porosity of 58.4%.Further reactions between phosphates other than reactions among Al_2O_3·2SiO_2 and α-SiO_2 can generate KAlP_2O_7 at 1 000 ℃ and the density of residualproduct is improved by low melting point phosphate filling pore to form relatively dense structure and decrease the apparent porosity to 44.4%.The flame resistant and self-supported ceramic materials are expected to enhance the fire-retarding synergistic effect between APP and muscovite.

Synthesis, Crystal Structure and Kinetic Mechanism of Thermal Decomposition of a Zinc(II) Complex with N-Salicylidene-p-toluidine

The title complex, Zn（C24H13NO）2Cl21, has been synthesized by the reaction of zinc chloride with Schiff base ligand N-salicylidene-p-toluidine and its structure was determined by single-crystal X-ray diffraction. The crystal is of monoclinic, space group Cc with a = 14.896（3）, b = 12.506（2）, c = 15.352（3） A,β = 114.711 （4）°, V = 2598.0（8） A^3, C28H26ZnCl2N2O2, Mr = 558.80, Z = 4, Dc = 1 .429 g/cm^3,μ = 1.179 mm^-1, Flack parameter = 0.027（19）, F（000） = 1152, R = 0.0709 and wR = 0.1041 for 3117 observed reflections （Ⅰ 〉 2σ（Ⅰ））. In complex 1, the center Zn ion is four-coordinated by two O atoms from two Schiff base ligands and two Cl atoms in a distorted tetrahedral geometry. Additionally, the thermal decomposition of complex 1 as well as its kinetic mechanisms and equations is studied under the non-isothermal integral and differential methods in air by TG-DTG curves.

Kinetics of the Thermal Decomposition of Wangjiatan Siderite

The thermal decomposition processes of Wangjiatan siderite samples were studied in nitrogen by thermogravimetric（TG）analysis.The mechanism of thermal decomposition of the siderite obeyed an F n kinetic law and the n-order was between 1.16 and 1.29.The results from non-isothermal experiments show that the size of particles has an obvious effect on the logarithm of pre-exponential factor in kinetics parameter of the thermal decomposition of Wangjiatan siderite.A linear relationship is shown between the size of particles and the logarithm of pre-exponential factor.An F 1 kinetic model containing size factor describes the thermal decomposition of Wangjiatan siderite well.

Non-isothermal Kinetics of the Thermal Decomposition of 3-Nitro-1,2,4-triazol-5-one Magnesium Complex

The thermal decomposition of 3-nitro-1,2,4-triazol-5-one magnesium complex and its kinetics were studied under the non-isothermal condition by DSC and TG/DTG methods. The kinetic parameters were obtained from analysis of the DSC and TG/DTG curves by the Kissinger method,the Ozawa method,the differential method and the integral method. The most probable mechanism functions for the thermal decomposition of the first stage,the second stage and the third stage were suggested by comparing the kinetic parameters. The entropy of activation (ΔS ≠),enthalpy of activation (ΔH ≠) and free energy of activation (ΔG ≠) at Tpdo are -66.74 J·mol -1 ·K -1 ,119.2 kJ·mol -1 and 152.44 kJ·mol -1 ,respectively.

Influences of Heat Treatments on Crystallization in SiO_2-Al_2O_3-MgO-K_2O-F Glass-ceramics

Five kinds of heating treatment processing were chosen according to the experiment result of differential scanning calorimeter to prepare SiO2-Al2O3-MgO-K2O-F glass ceramics samples.The effects of heat treatment processing on the crystallization of these samples were explored by X-ray diffraction and scanning electron microscopy techniques.The results indicate that phase separations can occur in the bulk regions of the glass sample when holding at 670 ℃ for 3 h.The phase separation can accelerate the precipitation of the crystallization phase： when the temperature directly rises to 950 ℃ after the phase separation,there are mainly interlocked plate-shapes mica phases;If holding at 860 ℃ for 3 h first after the phase separation,the star-shape cordierite phases form;Thereby,elevating temperature to 950 ℃ and holding for 1 h will bring plate-shapes mica phases growing at inter-phases of the star-shape cordierite and finally the homogeneously distributed mica- cordierite composites form.However,if heating at 950 ℃ directly without holding at 670 ℃,there is a small quantity of phase separation appearing at 670 ℃ and a little crystallization phases precipitating at last.

Effect of reclaimed sand additions on mechanical properties and fracture behavior of furan no-bake resin sand

In this work, the effects of reclaimed sand additions on the microstructure characteristics, mechanical properties and fracture behavior of furan no-bake resin sand have been investigated systematically within the temperature range from 25 to 600 oC. The addition of 20%-100% reclaimed sand showed dramatic strength deterioration effect at the same temperature, which is associated with the formation of bonding bridges. Both the ultimate tensile strength(UTS) and compressive strength(CS) of the moulding sand initially increase with the increase of temperature, and then sharply decrease with the further increase of temperature, which is attributed to the thermal decomposition of furan resin. The addition amount of reclaimed sand has a remarkable effect on the room temperature fracture mode, i.e., with the addition of 0-20% reclaimed sand, the fracture mode was mainly cohesive fracture; the fracture mode converts to be mixture fracture mode as the addition of reclaimed sand increases to 35%-70%; further increasing the addition to 100% results in the fracture mode of typical adhesive fracture. The fracture surface of the bonding bridge changes from a semblance of cotton or holes to smooth with the increase of test temperature.

Direct Synthesis, Crystal Structure and Thermal Kinetics of Supramolecular Complex [Co（H2O）6]·（Hnip）2·（H2nip）2·（DMA）2·（H2O）8 （nip=5-nitroisophthalate, DMA=CH3NHCH3）

The crystal of [Co（H2O）6]·（Hnip）2·（H2nip）2·（OMA）2·（H2O）8 has been cultured using direct method and characterized by X-ray single crystal diffractometry, elemental analysis and FTIR spectroscopy. It crystallizes in triclinic system, P-1 space group with the cell parameters of a=0.7012（1） nm, b=1.1378（2） nm, c=1.6612（3） nm, α= 84.92（3）°, β=85.19（3）°, γ=85.91（3）°, V= 1.3128（5） nm^3, Z=1, Dc= 1.573 g·cm^-3. Final R indices [1〉2σ（I）] are： R1 =0.0279, wR2=0.0765 while R indices for all data are： R1 =0.0327, wR2=0.0806. The Co coordination octahadra are each surrounded by two Hnip, two H2nip, two DMA and eight water molecules that are linked by hydrogen bonds and π-π stacking interactions. Thermal analyses of DSC and TG-DTG have been performed on the complex to predict its thermal decomposition mechanism and determine the most probable kinetic model function using Kissinger, Ozawa, integral and differential methods.