Kinetic Analysis of Single or Multi-Step Decomposition Processes; Limits introduced by statistical analysis

A kinetic study on decomposition processes of some penicillin and some commercial drugs was carried out. As expected by the complex structures of penicillins, several steps with different activation energies occurred in their decomposition processes. Model-fitting and model-free kinetic approach were applied to non-isothermal and isothermal data. In the model-fitting methods the kinetic triplets (f(α), A and E _a) that defines a single reaction step resulted in being at variance with the multi-step nature of penicillins decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. The complex nature of the multi-step process of the studied compounds was more easily revealed using a broader temperature range in non-isothermal isoconversional method. The failure in the model fitting method did not allow calculating storage times. Model-fitting and model-free methods, both isothermal and non-isothermal, showed that F1 mechanism is able to describe decomposition processes for drugs (having Phosphomycin salts as active component) for which a single decomposition process occurs. Statistical analysis allowed us to select reliable kinetic parameters related to the decomposition processes for these last compounds. This procedure showed that the values obtained by extrapolation, outside the temperature range where the processes occurred must be used with caution. Indeed half-life and shelf-life values, commonly extrapoled at room temperature, seemed to be unrealistic. This revised version was published online in August 2006 with corrections to the Cover Date.     

Estimation of Flame Retardancy Effect by Thermal Analysis Using Kinetic Parameters Obtained under Non-Isothermal Conditions in Air

A series of compounds obtained from urea, phosphoric acid and inorganic salts of Zn, Ni and Ca, were tested in respect of their flame‐retardancy behavior. The estimation criteria were the kinetic parameters obtained in air, under non‐isothermal conditions, on a Perkin‐Elmer Diamond device, at heating rates of 5, 10, 12 and 15 deg·min^?1. The flame‐retardancy effect was assigned to the significant endothermic decomposition at relatively low temperature (150–200°C). The quantitative estimation of the thermal behavior was performed by comparison of the kinetic data obtained by Flyn‐Wall‐Ozawa, Friedman and NPK (Sempere‐Nomen) methods. The kinetic homogeneity and a very good quality of the model are arguments in favour of the NPK method. The Ni containing material exhibited the best flame‐retardancy behavior, i.e. higher activation energy and mass loss, respectively a single decomposition step with both physical and chemical processes. The results were validated by fire resistance tests.     

Kinetic and thermodynamic study of the Na4(UO2)2(OH)4(C2O4)2 complex

The synthesis, the characterization, and the thermal decomposition of the dioxouranium(VI) ternary complex of formula Na₄(UO₂)₂(OH)₄(C₂O₄)₂, has been studied. The identification of the compound was performed by chemical analysis and by infrared spectrometry. Thermal decomposition of the compound occurs in several steps due to the decomposition of the salt to Na₂O and UO₃ oxides. The stoichiometry of the steps, hypothesized by means of the thermodynamic and kinetic parameters, is confirmed by the evolved gas analysis studied by FTIR spectrometer coupled to TG/DSC apparatus. Model‐fitting and model‐free kinetic methods have been used in kinetic analysis. The latter allows determining kinetic scheme. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 661–669, 2003     

Thermal stabilities of new synthesized <Emphasis Type="Italic">N</Emphasis>-methoxy-polynitroanilines derivatives

The thermal decomposition of new N-methoxy-polynitroanilines was studied using the differential scanning calorimetry (DSC) method. The characteristic melting parameters were measured and the activation parameters of the most probable kinetic models of thermal decomposition were determined using a multivariate non-linear regression method. All investigated compounds followed an autocatalytic decomposition mechanism. Depending on the number and position of substituents on the aromatic ring the thermal decomposition occurs in one, two or three steps.     

迪开石热分解及重结晶的非等温动力学

采用热分析(TG-DTG-DSC)和X射线衍射(XRD)技术研究了福州迪开石在动态空气气氛条件下的热分解及重结晶过程, 利用TG和DSC数据分别对迪开石的热分解和重结晶过程进行动力学分析. 由Friedman法求得热分解过程的表观活化能, 以此为初始值, 通过非线性回归法拟合得到了热分解过程最可能的反应机理和动力学参数; 将迭代的等转化率法和最小偏差法相结合计算得到了高温下迪开石重结晶过程最可能的反应机理和动力学参数. 研究结果表明, 迪开石在450~750 ℃内发生热分解, 脱去2个水分子, 生成无定形的准迪开石, 此过程为两步连串反应, 第一步为随机成核和随后生长机理An, 第二步为自催化反应机理CnC; 在975~1050 ℃内, 准迪开石重结晶转化为莫来石, 此过程对应的反应机理为An.     

丹酚酸B的热稳定性及其热分解动力学研究

用TG-DTG 方法研究了丹参的有效成分丹酚酸B 的热降解过程. 热重分析结果表明该物质的失重过程分两步进行. 笫一步为脱去吸附水, 其温度范围为305～373 K, 第二步为丹酚酸B 分子骨架大规模降解, 其温度范围在413～864 K. 用Friedman 和Ozawa-Flynn-Wall 两种方法分别计算出该药物降解过程中的三个阶段的活化能, 采用多步线性回归方法, 并参考常用的15 种热解机理函数, 确定了丹酚酸B 热降解过程最佳动力学模型为Fn-F2-F1.     

LiOH·H_2O在空气中的失水动力学研究

用热分析技术热重法、差热分析法及微分热重法(TG-DTA/DTG)研究了LiOH·H_2O(氢氧化锂)在空气中的热分解过程.热分析结果表明,LiOH·H_2O在空气中分两步分解.用Friedman法、Flynn-Wall-Ozawa(FWO)法和ASTM E698法求取了LiOH·H_2O脱水过程的活化能E为85.71 kJ/mol,指前因子以lgA表示,其值为9.81,失水过程拟合的最可几模型为Bna,即自催化的n级反应,动力学模式函数为f(α)=α~a(1-α)~n.     

Effect of mechanical grinding on the reaction pathway and kinetics of the thermal decomposition of hydromagnesite

Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements. A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for the decarbonation process.     

Kinetic triplet evaluation of a complicated dehydration of Co<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>·8H<Subscript>2</Subscript>O using the deconvolution and the simplified master plots combined with nonlinear regression

Kinetic triplet of the complex decomposition processes of Co₃Ni₃(PO₄)₂·8H₂O was evaluated for the first time by using the deconvolution method to separate the overlapping DTG curves. After the completion of the deconvolution, five steps of the decomposition were obtained. The activation energy E and the pre-exponential factor A of each step were determined by KAS method. The kinetic compensation effect (KCE) method was applied to identify the individual step of the decomposition. Each master plot was simplified by generating the general equations and combined with the nonlinear regression curve fitting. According to kinetic analysis results obtained from this modified method, it was found that the early four steps of dehydration follow the mechanisms of nucleation and subsequent growth with different n-orders, while the last step occurs in the same mechanism but accompanied by the phase transition (lattice reorientation).     

On the thermal stability and thermal decomposition kinetics of some mono- and disubstituted furan-2,3-dions

The thermal behaviour of some compounds derived from 5-phenylfuran-2,3-dione was studied. The thermoanalytical data relating to the decomposition steps and intermediates were completed with mass spectrometric analysis and infrared spectroscopy results. For some of the investigated reactions, the kinetic and structural data correlated satisfactorily.     

二水草酸亚铁热分解反应动力学

用原位XRD技术和热重法分析了二水草酸亚铁的热分解过程, 并进行了动力学研究. 通过结合主曲线法和统计方法判定了热分解过程的动力学模型函数, 并求算了动力学参数. 在静态自产气氛下, 二水草酸亚铁脱水反应遵循随机成核与核增长模型, 草酸亚铁热分解生成氧化铁遵循相界面控制动力学模型. 结果表明, 该方法可以准确、可靠地判定非等温热分解反应的动力学模型函数,并求算动力学参数.     

Nonlinear FR-ZLC method for investigation of adsorption equilibrium and kinetics

A new method for investigation of adsorption equilibrium and kinetics, named Nonlinear Frequency Response-Zero Length Column (NFR-ZLC) method, is introduced. It combines the advantages of the Nonlinear FR method (the potential to identify a model corresponding to the most probable kinetic mechanism and to estimate the equilibrium and kinetic parameters of the identified model) and of the ZLC method (the potential to derive direct information about the processes on the particle level, by eliminating the influence of the adsorber). The frequency response functions of a ZLC system, up to the third order, and for three simple kinetic mechanisms (film resistance control, micropore diffusion control and pore-surface diffusion control) are derived and simulated. The procedure for estimation of the equilibrium and kinetic parameters is defined and illustrated based on numerical simulations.     

Kinetics of the Thermal Decomposition of Magnesium Salicylate Powder in Air

IntroductionThe chelate complexes of salicylic acid with rareearth and alkali earth ions have attracted considerableattention because of their special antibacterial proper-ties[1—3].The study of the thermal degradation of metalsalicylates is of major int…     

Thermokinetic study of CODA azoic liquid crystal and thin films deposition by matrix-assisted pulsed laser evaporation

Azoic dyes are compounds of interest from the point of view of their potential applications, such as the use of liquid crystals in optoelectronic and organic electroluminescent devices, or may be employed as template matrices for producing high-aspect ratio inorganic nanomaterials. Herein, 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene azoic dye, known as CODA, is selected as a choice compound among such materials due to its liquid crystalline properties and may be further used as nanostructured material in various applications. Thermokinetic study of CODA azoic dye thermal decomposition in air flow atmosphere was performed by employing thermogravimetric data; the kinetic parameters of the two decomposition steps were obtained under non-isothermal linear regimes, by means of multi-heating rates methods. Differential and integral “model-free” kinetic methods like Friedmann, Kissinger–Akahira–Sunose and Ortega, the invariant kinetic parameters method and the Perez-Maqueda et al. criterion (by Coats–Redfern and differential equations) were used. The kinetic study reveals very different behaviour related to the two decomposition steps of CODA, with complex processes composed of more than one kinetic mechanism for each of those, as indicated also by the Gotor et al. master plot method. Modern devices incorporating such materials tend to use them as thin films due to their specific properties; the CODA thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG laser working at the wavelength of 266 nm. The preservation of the CODA compound after the transfer on the substrates was confirmed by Fourier transform infrared spectroscopy, while the morphology and topography of the deposited materials and of the thin film surfaces were investigated by atomic force microscopy and optical microscopy.     

Decomposition of 3′‐azido‐2′,3′‐dideoxythymidine 5′‐monophosphate (AZTMP) prodrugs in biological media studied by on‐line solid‐phase extraction coupled to liquid chromatography mass spectrometry

Using a column‐switching HPLC method previously described, we studied the behavior of some mononucleotide prodrugs (pronucleotides) of 3′‐azido‐2′,3′‐dideoxythymidine in various biological media. From UV data, this method allowed quantification of transient metabolites resulting from prodrug bioconversion. The kinetic data related to the successive steps were calculated according to pseudo‐first‐order kinetic models and optimized using mono‐ or poly‐exponential regressions. Various metabolites were identified by co‐injection with authentic samples and/or ESI‐MS coupling. The results led us to propose, for each considered pronucleotide, a global decomposition pathway ending in the selective delivery of the corresponding mononucleotide. Associated to the determination of other parameters (lipophilicity, aqueous solubility), the present study contributes to the search of suitable pharmacological properties for further in vivo evaluations. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal stabilities of some benzaldehyde 2,4-dinitrophenylhydrazones

The thermal stability of some benzaldehyde 2,4-dinitrophenylhydrazones has been studied using DSC technique. The crystalline solids are thermally stable and start to decompose after melting. Non-isothermal DSC curves, recorded at several heating rates, were used to evaluate the melting properties and the kinetics of thermal decomposition. Both isoconversional and model fitting methods were used for the evaluation of the kinetic parameters. Based on the results of the model free method, a kinetic model was derived and the kinetic parameters were obtained by means of a multivariate non-linear regression. A good agreement between the experimental and fitted data was found.     

Some Polynuclear Coordination Compounds Precursors of Chromites Synthesis,Physicochemical Characterization and Thermal Stability

The polynuclear coordination compounds LnCr(tartrate)₃·nH₂O where Ln(III)=La-Er, obtained through a precipitation method, were characterized on the basis of elemental analysis, their electronic and vibrational spectra and magnetic susceptibility measurements. The possibility of obtaining chromites through the transformations of the polynuclear coordination compounds in the solid state was considered. The thermal decompositions of these compounds, studied by TG and DTA methods, were found to follow an almost uniform pattern. The decompositions occurred in six-eight steps. The first two steps involved dehydration, and the third the transformation of tartrate anions to oxalate, followed by conversion to carbonate and oxocarbonate intermediates. The final product in each case was LnCrO₃. A non-isothermal kinetic analysis of the first decomposition steps was performed, the most probable decomposition mechanism being selected and the kinetic parameters evaluated. The final products of the transformations were characterized. This revised version was published online in August 2006 with corrections to the Cover Date.     

(Zn1-xMnx)C2O4·2H2O在空气中的热分解动力学研究

用热分析（TG-DTG/DTA）、X射线衍射（XRD）技术和透射电镜（TEM）研究了固态物质Zn_1-xMn_xC₂O₄•2H₂O在空气中热分解的过程。热分析结果表明，Zn_1-xMn_xC₂O₄•2H₂O在空气中分两步分解，其失重率与理论计算失重率相吻合。 XRD和TEM结果表明，Zn_1-xMn_xC₂O₄•2H₂O分解的最终产物为Zn_1-xMn_xO,其颗粒大小约为10-13 nm。在非等温条件下对Zn_1-xMn_xC₂O₄•2H₂O的热分解动力学进行了分析。用Friedman法和Flynn-Wall-Ozawa(FWO)法求取了分解过程的活化能E，并用多元线性回归给出了可能的机理函数。Zn_1-xMn_xC₂O₄•2H₂O两步热分解的活化能分别为155.7513 kJ/mol 和215.9397 kJ/mol。     

Thermal degradation behaviour of some metal chelate polymer compounds with bis(bidentate) ligand by TG/DTG/DTA

Seven novel divalent transitional metal chelate polymers compounds (commonly known as chelate compounds or metal coordination complexes or polymer complexes) have been characterized by thermogravimetry (TG), differential thermal gravimetry (DTG) and differential thermal analysis (DTA) methods. Thermal decomposition behaviour of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) polymers with terphthaoyl-bis(p-methoxyphenylcarbamide) has been investigated by thermogravimetric analysis (TGA) at heating rate 10 °C min^?1 under nitrogen atmosphere. TG/DTA of chelate compounds were shown to be a stable compound against thermal decomposition which was measured on the basis of final decomposing temperature, but it is observed in some curves that decomposition takes place at low temperature due to the lattice water, which is always placed at outer coordination sphere of the central metal ion. The presence of both lattice and coordinated water were noteworthy investigated in Co(II), Ni(II) and Cu(II) chelate polymer compounds, whereas lattice water found in Zn(II), Cd(II) and Hg(II). However, Mn(II) showed only coordinated water. Thermal stabilities for release of lattice water, coordinated water and organic moiety that occur in sequential decomposition of chelate compounds are explained on the basis of ionic size effect and electronegativity. The processes of thermal degradation taking place in seven chelate polymers were studied comparatively by TG/DTG/DTA curves which indicating the difference in the thermal decomposition. Coats–Redfern integral method is used to determine the kinetic parameters for the successive steps in the decomposition sequence of TG curves. Scanning electron microscope images of some chelate polymers were shown in previous publication revealed that particle sizes of chelate polymers were found to be of nanomaterial level therefore, resulting chelate compounds might be called as nanomaterial.     

Thermal studies on beryllium titanyl/zirconyl oxalates

Beryllium titanyl oxalate tetrahydrate and beryllium zirconyl oxalate tetrahydrate were prepared in aqueous medium and characterized by elemental analyses, magnetic susceptibility measurements and IR spectral studies. The thermal behaviour of these compounds under non-isothermal conditions was investigated by thermogravimetric, derivative thermogravimetric and differential scanning calorimetric (DSC) techniques. The intermediates obtained at the end of the various thermal decomposition steps were identified on the basis of elemental analyses and IR spectral studies. The decomposition proceeds through three major steps, viz, dehydration of the hydrate, decomposition of the oxalate to carbonate and decomposition of the carbonate to oxide. The graphical method of Coats and Redfern was employed to calculate kinetic parameters such as apparent activation energy and order of reaction. Heats of reaction for the different decomposition steps were calculated from the DSC curves.