The relationship between the structures of Cu(II) complexes and their chemical transformations

The paper reports an attempt to correlate the structures of hydrates of copper(II) sulphate with some characteristic features of the kinetics of their thermal decompositions. Non-isothermal thermogravimetric measurements were employed to obtain values of experimental activation energy and entropy for the dehydration of CuSO₄ · 5 H₂O, CuSO₄ · 3 H₂O and CuSO₄ · H₂O. The values ofE ^* andΔS ^* for the dehydration of CuSO₄ · 3 H₂O were found to be only little affected by the mode of preparation of this compound. On the other hand, the values ofE ^* andΔS ^* for the dehydration of CuSO₄ · ·H₂O are strongly dependent on whether this compound was prepared by thermal decomposition of CuSO₄ · 5 H₂O or CuSO₄ · 3 H₂O, or by crystallization from solution. As regards the crystalline hydrates of copper(II) sulphate, the greatest energetic hindrance for dehydration was observed for CuSO₄ · 3 H₂O. The experimental results are also discussed with respect to the present opinions concerning the possibilities of using thermal analyses to obtain information on the relationship between the structures and reactivities of solids.     

Study of the products of the dehydration reaction of CuSO4 · 5H2O in X-shaped and elliptic nuclei

The products of the dehydration of CuSO₄ · 5H₂O under different conditions have been studied by the methods of local X-ray diffraction analysis and EPR. It is shown that the dehydration in vacuo when X-shaped nuclei are formed proceeds through the formation of an intermediate product having a monohydrate composition and a crystalline lattice close to the initial lattice of the pentahydrate. Then the amorphization and crystallization of CuSO₄ · H₂O follows. When dehydration occurs in water vapour through ellipsoidal nuclei the structure of the trihydrate formed is oriented relative to the initial structure of CuSO₄ · 5H₂O.     

FePO4·4H2O的脱水动力学研究

用热分析(TG-DTG-DTA)、X射线衍射(XRD)技术研究了固态物质FePO4·4H2O在空气中脱水过程.热分析结果表明,FePO4·4H2O在空气中脱水的质量变化率与理论计算相吻合.XRD结果表明,FePO4·4H2O脱水产物为FePO4.由等转换率法得到脱水过程的活化能,依此为初始值,用多元非线性回归得到了失水反应拟合的最可几模型为两步连串反应:D4→Fn,活化能分别为79.62和103.04 kJ·mol-1,IgA值分别为8.40和11.02.     

The self-cooling effect in the process of dehydration of Li2SO4·H2O,CaSO4·2H2O and CuSO4·5H2O in vacuum

The third-law method has been applied to the results of kinetic studies reported in the literature and obtained in this work to determine the E parameters of the Arrhenius equation and investigate the impact of self-cooling on the dehydration kinetics of Li₂SO₄·H₂O, CaSO₄·2H₂O and CuSO₄·5H₂O. The values obtained (104, 98 and 88 kJ mol^-1, respectively) are about 20% higher compared to the literature data calculated by the Arrhenius-plots method. This discrepancy is connected with the severe effect of self-cooling, which can reach several ten degrees at maximum temperatures of experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,thermal investigations and kinetic data of Zn(BF<Subscript>4</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O

The thermal dehydration and decomposition of Zn(BF₄)₂·6H₂O have been studied by TG, DTA and DSC analyses. It is found that the dehydration occurs in two steps. Following the experimental results a thermal decomposition scheme of the compound under investigation is proposed. The enthalpies of dehydration have been determined as well as the formal kinetic parameters are presented.     

Simultaneous TG,DTG and DTG analyses in controlled inert gas flow for the determination of deaquation steps of polyhydrated sulfates

The thermal deaquation reactions of CuSO₄·5H₂O and NiSO₄·7H₂0 were studied by simultaneous TG, DTG and DTA. In the CuSO₄·5H₂O thermogram three distinct steps corresponding to 2 moles,2moles. 1 mole of water were observed. and in the NiSO₄·7H₂O the sequence 1 mole, 3 moles, 2 moles, I mole was determined. The deaquation steps were correlated with the structure of water of crystallization. An exothermic DTA peak was observed during the evolution of the first mole of water in NiSO₄·7H₂O.     

Growth and Thermal,Electrical, Structural Characterization of Mixed Hydrated Single Crystal

Mixed single crystal was made by mixing saturated aqueous solutions of NiSO₄ · 6H₂O and CuSO₄ · 5H₂O by volume (80:20) and the mixture was kept to form the crystals at room temperature by slow evaporation process. After some days, big pieces of greenish blue, dark colored crystals were grown. To determine the weight of NiSO₄ · 6H₂O and CuSO₄ · 5H₂O in the crystal, Ni-DMG complexiometrical and EDTA gravimetrical analysis was done respectively. From this analysis it was concluded that 5.8 molecules of water of crystallization is present in the mixed single crystal. The crystals were characterized by UV-Visible, FTIR and single crystal X-ray diffraction studies. From single crystal XRD lattice parameters have been calculated. All these structural analysis confirms formation of new single crystal. Further, DTA-TGA, dc electrical conductivity and dielectric constant studies were done from the room temperature to 400 °C.From DTA studies it was observed that 5.8 molecules of water of crystallization get dehydrated in four major steps at temperature 115 °C, 150 °C, 240 °C and 325 °C respectively corresponding to the detachment of 1 mole, 3 moles, 1 mole and 0.8 mole of water of crystallization. DC electrical conductivity and dielectric constant studies also show close agreement to the dehydration steps. The observed peaks in the conductivity verses temperature graph have been explained on the basis of release of water molecules and subsequent dissociation of these released water molecules into H⁺ and OH⁻ ions.     

Dehydration process of rhodium sulfate crystalline hydrate

The dehydration of the rhodium salt [Rh(H₂O)₆]₂(SO₄)₃·5H₂O was studied by means of thermogravimetry in the temperature range 300–460 K. The kinetics of dehydration (the ligand substitution process) was studied under non-isothermal conditions. A model-free method was used to calculate the activation energy and analyze the process steps; a non-linear regression method was applied to calculate the kinetic parameters of the multistage dehydration reactions. The features of the dehydration kinetics could be explained by the condensation process.     

Eyring parameters of dehydration processes

Thermogravimetry was used in the study of the kinetics of dehydration of MnSO₄·5H₂O, CuSO₄·5H₂O and 3CdSO₄·8H₂O under static air atmosphere. The values of the kinetic and thermodynamic parameters for each stage of thermal dehydration were calculated from α(T) data by using the integral method, applying the Coats-Redfern approximation. The best model for all stages of dehydration is random nucleation model F1. The dependencies of enthalpy on entropy of activated complexes for different kinetic models were described. The linear relation was calculated between the Gibbs energy of activated complexes and the maximum dehydration rate temperature for analysed dehydration processes.     

Effects of heating rate (1–300° h−1) on the non-isothermal thermogravimetry of CuSO4 · 5 H2O

The course of the reaction CuSO₄ · 5 H₂O ? CuSO₄ · H₂O + 4 H₂O was studied by non-isothermal thermogravimetry with various heating rates ranging from 1 to 300° h^?. The measurements were made either in static air, in a dry nitrogen stream, or in water vapor at a reduced pressure (9 mm Hg). In static air, the shape of the TG curve changed drastically at a heating rate of 13 to 15° h^?, and this change was explained by considering the nature of the plateaus and inflections present. In a dry nitrogen stream, the dehydration is made much easier at slow heating rates and occurs almost in one step at 2° h^?; in water vapor at 9 mm Hg, on the other hand, a very distinct two-step curve is obtained at 1° h^?. This can reasonably be compared with the phase diagram of copper sulfate.     

水合盐的几种脱水过程探讨

通过差热/热重联机 (DTA/TGA)和差示扫描量热法 (DSC)测定几种盐(Na2SO4·10H2O、CuSO4·5H2O、Na2S2O3·5H2O)的失水过程 ,对水合盐脱水过程几种可能的类型进行探讨。研究表明低温 (100℃以下 )水合盐脱水有两种类型 ,一种直接失去气态水 ,另一类先脱去液态水再进一步变为气态水。并从热力学上理论分析两类脱水过程的原因。     

Study of kinetics and thermodynamics of the dehydration reaction of AlPO<Subscript>4</Subscript> · H<Subscript>2</Subscript>O

The kinetics and thermodynamics of the thermal dehydration of aluminum phosphate monohydrate, AlPO₄ · H₂O were studied using thermogravimetry (TG-DTG-DTA) at four heating rates in dry air atmosphere. The activation energies of the dehydration step of AlPO₄ · H₂O were calculated through the methods of Friedman (FR) and Flynn–Wall–Ozawa (FWO) and the possible conversion function has been estimated through the Achar and Li–Tang equations. The independent activation energies on extent of conversions and the better kinetic model of the dehydration reaction for AlPO₄ · H₂O indicate single kinetic mechanism and the F _2.05 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”, respectively. The positive values of ΔH^# and ΔG^# for the dehydration reaction show that it is endothermic and non-spontaneous process and it is connected with the introduction of heat. The kinetic and thermodynamic functions calculated for the dehydration reaction by different techniques and methods were found to be consistent.     

Spectrophotometric and thermal analytical studies on the dehydration of copper(II) sulfate and its double salts

Spectrophotometric (diffuse reflection) and TG-DTA data on the dehydration of CuSO₄ · 5H₂O, Na₂Cu(SO₄)₂ · 2H₂O, M₂Cu(SO₄)₂ · 6H₂O(M⁺ = K⁺, Rb⁺, Cs⁺ and NH⁺₄) and Co₂Cu(SO₄)₃ · 18H₂O are given. Although complete dehydration of CuSO₄ · 5H₂O brings about a striking color change from blue to white, it was found that there is only a slight decrease in the v?_max. of its d-d band in the course of this change, and the total light absorption in the visible-UV region increases at the same time. The dehydration of the alkali metal and ammonium double salts, most of which contain [Cu(OH₂)₆]²⁺ aquo ions (in contrast to the [Cu(OH₂)₄]²⁺ in CuSO₄ · 5H₂O), occurs generally more easily than that of CuSO₄ - 5H₂O, and their v?_max. increases slightly in the change, leading to blue or green anhydrous products, although the formation of a white modification was observed with the potassium salt. It was also found that the v?_max. of the Cu²⁺ ion in the dehydrated cobalt(II) double salt is still lower than that in anhydrous CuSO₄, i.e., the ligand field and/or tetragonality around it is decreased by the presence of Co²⁺ ions.     

Kinetics of thermal dehydration of Ce2(SO4)2, n(H,D)2O (n=5, 8, 9)

The thermal dehydration of Ce₂(SO₄)₃·5H₂O, Ce₂(SO₄)₃·8H₂O, Ce₂(SO₄)₃·9H₂O and their isomorphous deuterated compounds was studied by means of thermogravimetric measurements. A kinetic analysis of the TG curves obtained was carried out by computer. The thermal stability, Arrhenius parameters and mechanism of dehydration were investigated.     

Products and kinetics of non-isothermal decomposition of vanadium(IV) oxide compounds

The kinetics of dehydration and decomposition of VOSO₄·2H₂O, VOSO₄ and VOSeO₃·H₂O was studied under non-isothermal heating on a derivatograph. The stages and products of the thermal decomposition were determined. It was proved that VOSO₄·2H₂O decomposes to V₂O₅ while VOSeO₃·H₂O − to V₂O₄. A number of kinetic models and calculation procedures were used to determine the values of the kinetic parameters characterizing the process. The parameters calculated were compared and analyzed. IR-spectra of the initial substances and the solid residue after decomposition are presented.     

Determination of kinetic triplet of the synthesized Ni3(PO4)2·8H2O by non-isothermal and isothermal kinetic methods

The nickel phosphate octahydrate (Ni₃(PO₄)₂·8H₂O) was synthesized by a simple procedure and characterized by FTIR, TG/DTG/DTA, AAS, and XRD techniques. The morphologies of the title compound and its decomposition product were studied by the SEM method. The dehydration process of the synthesized hydrate occurred in one step over the temperature range of 120–250 °C, and the thermal decomposition product at 800 °C was found to be Ni₃(PO₄)₂. The kinetic parameters (E and A) of this step were calculated using the Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose methods. The iterative methods of both equations were carried out to determine the exact values of E, which confirm the single-step mechanism of the dehydration process. The non-isothermal kinetic method was used to determine the mechanism function of the dehydration, which indicates the contracting disk mechanism of R₁ model as the most probable mechanism function and agrees well with the isothermal data. Besides, the isokinetic temperature value (T _i) was calculated from the spectroscopic data. The thermodynamic functions of the activated complex (ΔS ^≠, ΔH ^≠, and ΔG ^≠) of the dehydration process were calculated using the activated complex theory of Eyring. The kinetic parameters and thermodynamic functions of the activated complex for the dehydration process of Ni₃(PO₄)₂·8H₂O are reported for the first time.     

Some thermodynamic functions and kinetics of thermal decomposition of NH<Subscript>4</Subscript>MnPO<Subscript>4</Subscript> · H<Subscript>2</Subscript>O in nitrogen atmosphere

The ammonium manganese phosphate monohydrate (NH₄MnPO₄ · H₂O) was found to decompose in three steps in the sequence of: deammination, dehydration and polycondensation. At the end of each step, the consecutive one started before the previous step was finished. The thermal final product was found to be Mn₂P₂O₇ according to the characterization by X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy. Vibrational frequencies of breaking bonds in three stages were estimated from the isokinetic parameters and found to agree with the observed FTIR spectra. The kinetics of thermal decomposition of this compound under non-isothermal conditions was studied by Kissinger method. The calculated activation energies E_a are 110.77, 180.77 and 201.95 kJ mol⁻¹ for the deammination, dehydration and polycondensation steps, respectively. Thermodynamic parameters for this compound were calculated through the kinetic parameters for the first time.     

DSC study of the kinetics of the thermal dehydration of BaCl2 · 2H2O and BaCl2 · H2O

The kinetics of the thermal dehydration of various kinds of BaCl₂ · 2H₂O and of BaCl₂ · H₂O are investigated using a differential scanning calorimeter. The loss of H₂O proceeds in two steps: BaCl₂ · 2H₂O→BaCl₂ · H₂O→BaCl₂ and is therefore revealed by two endothermic peaks. In the experiments at varying temperature both steps follow a contracting-circle law, after an initial acceleratory stage according to a (n=2) power law. In the experiments at constant temperature, after an initial acceleratory stage according to a (n=2) power law, both steps (except BaCl₂ · 2H₂O single-crystals which follow a contracting-circle law) follow an Avrami-Erofeev law (withn=2) in the form used by Galwey and Jacobs. The activation energies for the various steps are compared and the different kinetic behaviour is discussed.     

Kinetics and thermodynamics of thermal dehydration of magnesium oxalate dihydrate

The kinetics and thermodynamics of the thermal dehydration of crystalline powders of MgC₂O₄ · 2 H₂O were studied by means of thermal analyses both at constant temperatures and at linearly increasing temperatures. The dehydration of the dihydrate is regulated by one of the Avrami-Erofeyev laws. The kinetic parameters from TG at constant temperatures are in good agreement with those from TG at the lowest rate of rising temperatures. The dynamic dehydration kinetics was also examined, using DSC recorded simultaneously with TG at linearly increasing temperatures. The validity of the estimated mechanism and kinetic parameters is briefly discussed.