Effect of deuteration on the thermal dehydration of lithium sulfate monohydrate

Effects of deuteration on the thermal stability, enthalpy change and kinetic parameters for the thermal dehydration of Li₂SO₄·H₂O were examined by means of TG and DSC. The enthalpy change for the monohydrate was smaller by 1.63±0.75 kJ/mol than that for the monodeuterate. The rate constant for the monohydrate was a little larger than that for the monodeuterate. However, the thermal stability, activation energy and frequency factor were practically unaffected by deuteration of the hydrate. It is suggested that the activation entropy as well as the activation energy should be considered in explaining the kinetic deuterium isotope effect in the thermal dehydration of Li₂SO₄·H₂O.

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Zusammenfassung Die Wirkung der Deuterisierung auf die Thermostabilität, die Enthalpie-Änderungen und kinetischen Parameter der thermischen Dehydratisierung von Li₂SO₄·H₂O wurden durch TG und DSC untersucht. Die Enthalpie-Änderung für das Monohydrat wurde um 1.63±0.75 kJ/mol niedriger gefunden als für das Monodeuterat. Die Geschwindigkeitskonstante für das Monohydrat war etwas größer als für das Monodeuterat. Die Thermostabilität, die Aktivierungsenergie und der Frequenzfaktor wurden jedoch von der Deuterisierung des Hydrats praktisch nicht beeinflußt. Es wird vorgeschlagen, daß bei der Erklärung des kinetischen Deuterium-Isotop-Effekts bei der thermischen Dehydratisierung von Li₂SO₄·H₂O sowohl die Aktivierungsentropie als auch die Aktivierungsenergie berücksichtigt werden müssen.

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, Li₂SO₄·H₂O. 1.63+0.75 /. , . , , . , Li₂SO₄·H₂O.

     

Dependence of kinetics of copper sulfate pentahydrate dehydration on water vapor pressure

The dependence of the growth rate v_g of nuclei during CuSO₄·5H₂O dehydration upon water vapor pressure P_H2O has been investigated. At small P_H2O (less than 1 Torr at 50°C), v_g falls rapidly with decreasing P_H2O, and simultaneously v_g anisotropy disappears. At P_H2O = 1–9 Torr, v_g for elliptic and round nuclei is constant and independent of P_H2O. The influence of initially keeping the samples in water vapor upon the kinetics of the following dehydration has been studied. Treatment by water vapor leads to slowing of dehydration and increasing its degree of transformation. On the basis of data obtained a kinetic interpretation of the Topley-Smith effect has been proposed.     

Thermal analysis and decomposition kinetics of the dehydration of copper sulfate pentahydrate

Journal of Thermal Analysis and Calorimetry - The thermal decomposition kinetics of individual stages of copper sulfate pentahydrate (CuSO4·5H2O) was investigated by TG–DSC, and the...     

Calculation of the kinetic parameters of dehydration of lithium peroxide monohydrate in nonisothermic regime by derivatographic method

The dehydration of lithium peroxide monohydrate was studied by derivatography under nonisothermic conditions for the calculation of main kinetic parameters in the temperature range 90–146°C. Experimental conditions (sample size and the linear heating rate) caused by thermoconductivity of the object under investigation were determined. It is shown that the process under study proceeds according to the kinetic law close to the first order one (n = 0.85±0.03). Values of the activation energy and the pre-exponential factor [E _a = 86.0±0.8 kJ mol^?1, k ₀ = (2.19±0.16)×10¹¹ min^?1] were obtained. A suggestion was formulated that the dehydration mechanism of lithium peroxide monohydrate was analogous to that of the hydrates of the alkaline earth metal (calcium, barium, and strontium) peroxides.     

Some mathematical aspects of nonisothermal kinetics

The results of an attempt to derive correct nonisothermal kinetic equations from isothermal ones through the classical nonisothermal change (CNC) of the postulated primary kinetic equations are presented. An alternative possibility through use of the model of infinitesimal isothermal portions (MIIP) is discussed.

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Zusammenfassung Die Autoren stellen die Ergebnisse eines Versuchs vor, korrekte Gleichungen für die nicht-isotherme Kinetik durch den klassischen nichtisothermen Übergang aus den als primär postulierten isothermen kinetischen Gleichungen abzuleiten. Als alternative Möglichkeit wird das Modell der infinitesimalen isothermen Abschnitte diskutiert.

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The dehydration of nickel sulfate

Nickel sulfate was recrystallized to obtain the 7 H₂O, β6 H₂O and various habits of α6 H₂O. Dehydration and phase transitions were studied using X-ray analysis and DSC with effluent gas analysis. NiSO₄ · 7 H₂O dehydrates spontaneously via 7 → 6β → 6α at room temperature, while the dehydration pathway of NiSO₄ α6 H₂O is 6α → 6γ → 4 → 1. The effect of time and storage on the 6α—6β phase transition was investigated.     

The dehydration of copper(II) acetate monohydrate

The thermal dehydration of copper(II) acetate hydrate has been studied between 353 and 406 K, over a range of humidities. The dehydration is controlled by nucleation-and-growth kinetics at low temperatures, with an activation energy of 154 kJ·mol⁻¹, which changes to contracting-disc kinetics at higher temperatures with a lower activation energy of 76 kJ·mol⁻¹. Frequency factors have also been derived; the value for the high temperature process is low (10⁷s⁻¹) and that for the low temperature step is high (10¹⁷s⁻¹). Optical microscopy has been used to clarify the bulk kinetics; there is evidence for a reactive layer at the surface of the decomposing solid. In celebration of the 60^th birthday of Dr Andrew K. Galwey     

New approximations of the temperature integral for nonisothermal kinetics

The accuracy and scope of application of previously reported approximations of the temperature integral were evaluated. The exact solution was obtained independently by solving the temperature integral numerically be Simpson's rule, the trapezoidal rule and the Gaussian rule. Two new approximations have been proposed: $$\begin{gathered} P(X) = e^{ - x} (1/X^2 )(1 - 2/X)/(1 - 5.2/X^2 ) \hfill \\ P(X) = e^{ - x} (1/X^2 )(1 - 2/X)/(1 - 4.6/X^2 ) \hfill \\ \end{gathered} $$ whereX=E/RT. The first equation gives higher accuracy, with a deviation of less than 1% and 0.1% from the exact solution forX≥7 andX≥10, respectively. The second equation has a wider scope of application, with a deviation of less than 1% forX≥4 and of less than 0.1% forX≥35.     

Vibrational spectra of 6Li/7Li and H/D substituted single crystal lithium sulfate monohydrate

Infrared and Raman spectra of several isotopic species of Li₂SO₄·H₂O were investigated. Bands with a lithium-isotopic shift of 3–8% were observed in the spectral region from 300–580 cm⁻¹. The spectra of the deuterated single crystals indicate a coupling between the lithium vibrations and the librational modes of the water molecules. The assignment of the bands with appreciable ⁶Li/⁷Li isotope effect to translational modes of the lithium atoms is confirmed by a rough normal coordinate calculation.     

Thermal dehydration kinetics of disaccharides

The vacuum decomposition of sucrose and cellobiose has been observed in the 150–250°C temperature range. The predominant decomposition product of both sugars is H₂O with less than 5% CO, CO₂, CH₂O, CH₃CHO, CH₃OH, and C₂H₅OH formed. The detailed rates and temperature dependences suggest that with the possible exception of C₂H₅OH, the minor products are formed in secondary reactions of the dehydration products. Further it is shown that the so-called “melting with decomposition” of a sugar is in reality a high-temperature dissolution of the disaccharide in the eliminated water.     

Characterization of dehydration behavior of untreated and pulverized creatine monohydrate powders

Creatine, which is well known as an important substance for muscular activity, is synthesized from amino acids such as glycine, arginine and ornithine in liver and kidney. It then accumulates in skeletal muscle as creatine phosphoric acid. The aim of this study was to understand the dehydration behavior of untreated and pulverized creatine monohydrate at various temperatures. The removal of crystal water was investigated by using differential scanning calorimetry (DSC), X-ray powder diffraction and scanning electron microscopy (SEM). The X-ray diffraction pattern of untreated and pulverized creatine monohydrate agreed with reported data for creatine monohydrate. However, the diffraction peaks of the (1 0 0), (2 0 0) and (3 0 0) planes of pulverized creatine monohydrate were much stronger than those of untreated creatine monohydrate. On the other hand, the diffraction peaks of the (0 1 2) and (0 1 3) planes of untreated creatine monohydrate were much stronger than those of pulverized creatine monohydrate. The dehydration of untreated and pulverized creatine monohydrate was investigated at various storage temperatures, and the results indicated that untreated and pulverized creatine monohydrate were transformed into the anhydrate at more than 30 °C. After dehydration, the particles of untreated and pulverized creatine anhydrate had many cracks. The dehydration kinetics of untreated and pulverized creatine monohydrate were analyzed by the Hancock–Sharp equation on the basis of the isothermal DSC data. The dehydrations of untreated and pulverized creatine monohydrate both followed a zero-order mechanism (Polany–Winger equation). However, the transition rate constant, calculated from the slope of the straight line, was about 2.2–7.7 times higher for pulverized creatine monohydrate than for untreated creatine monohydrate. The Arrhenius plots (natural logarithm of the dehydration rate constant versus the reciprocal of absolute temperature) of the isothermal DSC data for untreated and pulverized creatine monohydrate were linear. The activation energies of dehydration in the 40–60 °C range for untreated and pulverized creatine monohydrate were 15.02 and 10.1 kJ/mol, respectively. Dehydration of untreated creatine monohydrate had a pronounced effect on the particle size of the powder. Compared with pulverized creatine monohydrate, the particle size of untreated creatine monohydrate was significantly decreased by dehydration.     

Isothermal and nonisothermal crystallization kinetics of irradiated nylon 1212

The crystallization behavior of nylon 1212, irradiated at ⁶⁰Co γ‐rays (50 kGy), was studied by a rheometer, polarized optical microscopy (POM), and differential scanning calorimeter (DSC). The results showed that irradiated nylon 1212 samples exhibited abnormal crystallization behavior during the crystallization process: The Avrami exponent n was calculated and was found to be in the range from 2.06–2.41 for isothermal crystallization, and from 2.67–4.91 for nonisothermal crystallization; the spherulite morphology also changed largely by polarized optical microscopy (POM); the crystallization activation energy ΔE for isothermal and nonisothermal crystallization process of irradiated nylon 1212 are determined to be 57.4 kJ/mol and 78.65 kJ/mol, respectively, which are lower than that of nonirradiated nylon 1212. At the same time, a new method by a combination of the Avrami and Ozawa equations was successfully applied to analyze the noncrystallization process of irradiated nylon 1212. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2326–2333, 2005     

Dehydration kinetics of theophylline-7-acetic acid monohydrate

A hydrated form of theophylline-7-acetic acid obtained by recrystallization from water is described and characterized in terms of thermal properties, physical stability with respect to relative humidity and dehydration kinetics. The hydrate resulted to be stable at ambient conditions. Fitting of experimental dehydration data to solid state reaction equations suggests a three dimensional phase boundary reaction proceeding from the surface of the crystal inward along three dimensions. The relevant activation energy calculated from the Arrhenius plot is 173 kJ/mol.     

New crystals in the lithium sulfate family

The preparation and structures of caesium lithium sulfate, Cs_1.15Li_2.85(SO₄)₂, and caesium lithium rubidium sulfate, Cs_0.90Li_2.88Rb_0.22(SO₄)₂, are described and discussed in the context of simple and double sulfate polymorphism. The latter structure is related to the former through the substitution of Rb for Cs. In both crystals, the sulfate ions occupy two non‐equivalent sites, but the ions are disordered in Cs_1.15Li_2.85(SO₄)₂.     

Isothermal dehydration of copper sulfate pentahydrate and trihydrate

Isothermal dehydrations of the pentahydrate and trihydrate of copper sulfate are studied in the temperature ranges of 47–63°C and of 70.5–86°C respectively. Both dehydration processes involve the loss of two molecules of water in the temperature ranges studied. The topochemical kinetics of the reactions is well described by Avrami-Erofeev equation with x = 2 over the α-range of 0.1–0.9. Activation energies of 104 ± 10 kJ mol⁻¹ and 134 ± 3 kJ mol⁻¹ are evaluated and are approximately equal to the respective values of the heat of reaction. The methods of Jacobs and Kureishy and of Ng in obtaining activation energy from the decomposition curves are also discussed.