Water-vapor pressure and thermodynamics of the dehydration of manganese,nickel, cadmium,and lead perchlorate hydrates

The water-vapor pressure has been measured by a static method, the temperature limits for existence have been determined, and the parameters of the equation lgp [Torr]=b —a/T have been calculated for the following crystal hydrates: Mn(ClO₄)₂ · 2H₂O (90–130°C, a=3527.0,b=8.487), Ni(ClO₄)₂ · 4H₂O (60–100°C,a=3606.7,b=9.704), Ni(C1O₄)₂ · 2H₂O (110–160°C,a = 4261.7,b = 10.103), Cd(ClO₄)₂ · 6H₂O (25–58.2°C,a = 3143.7,b = 9.356), Cd(ClO₄)₂ · 2H₂O (90–144.8°C,a=3823.3,b = 9.472), Pb(ClO₄)₂ · 3H₂O (10–47°C,a = 2932.9,b = 9.391 and 47–81.5°C,a = 2448.1,b=7.877), Pb(ClO₄)₂ · H₂O (60–102.4°C,a=3610.2,b = 9.857). A hitherto unknown metastable hydrate Cd(ClO₄)₂ · 4H₂O with a phase transition at 30.9°C (20–30.9°C,a = 3669.5,b = 11.343 and 30.9–63.7°C,a=3058.6,b = 9.339) has been detected.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 466–470, March, 1993.     

The dehydration behavior of nafagrel hydrochloride hydrates

Nafagrel hydrochloride has two kinds of stable pseudopolymorphs such as hemihydrate and monohydrate. The dehydration of crystal water of these hydrates took place in one step under nitrogen gas atmosphere, whereas the two dehydration steps could be detected for the monohydrate under self-generated atmosphere such as the quasi-sealed and/or the completely sealed systems. These observations indicated that the crystal water of the monohydrate consisted of two different crystal waters. Prediction of the stability for the hydrates using the kinetic parameters indicated that the dehydration of the monohydrate occurred faster than that of the hemihydrate.     

Investigation of dehydration processes III. Thermal dehydration of strontium iodide hydrates

The dehydration phenomena of strontium iodide with different crystal water contents, prepared at room temperature, were studied with thermogravimetry and differential scanning calorimetry. The existence of strontium iodide dihydrate was proved during the dehydration of samples containing less then six moles of crystallization water. Evidence is given for the appearance of a liquid phase in the dehydration of strontium iodide dihydrate. The pertinent enthalpy values are reported.

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Zusammenfassung Die Dehydratisierungserscheinungen von bei Zimmertemperatur hergestelltem Strontiumjodid mit verschiedenem Kristallwasser wurden durch Thermogravimetrie und Differential-Abtastkalorimetrie untersucht. Die Existenz von Strontiumjodid-Dihydrat wurde während der Dehydratisierung von weniger als 6 Mol Kristallwasser enthaltenden Proben bewiesen. Beweis für das Auftreten einer Flüssigphase während der Dehydratisierung von Strontiumjodid-Dihydrat wird erbracht. Die bezüglichen Enthalpiewerte werden angegeben.

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Résumé On a étudié, par thermogravimétrie et analyse calorimétrique différentielle, la déshydratation de l'iodure de strontium contenant diverses sortes d'eaux de cristallisation préparé à température ambiante. On montre l'existence de l'iodure de strontium bihydraté formé lors de la déshydratation d'échantillons contenant moins de six molécules d'eau de cristallisation. On met en évidence l'apparition d'une phase liquide lors de la déshydratation de l'iodure de strontium bihydraté. Les enthalpies respectives sont données.

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. , , . . .

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We express our thanks to Dr. Gy. Pokol for his assistance in the computations.     

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 dehydration and structural models of two new vanadyl sulfate hydrates

The preparation of a new modification of vanadyl sulfate trihydrate, VOSO₄ · 3H₂O, is described. In the course of its thermal dehydration, another new phase, VOSO₄ · 2H₂O, is observed as an intermediate. Crystal data for the two compounds are: VOSO₄ · 3H₂O, orthorhombic, a = 8.980 ± 0.006, b = 9.026 ± 0.009, c = 7.776 ± 0.003 Å, space group P2₁2₁2; VOSO₄ · 2H₂O, monoclinic, a = 8.913 ± 0.027, b = 8.93 ± 0.09, c = 7.80 ± 0.06 Å, β = 92.4 ± 0.6°. From the topotaxy of the dehydration reaction, structural models for the two phases are deduced. They consist essentially of VOSO₄ layers similar to those in α-VOSO₄ and interlayer water.     

Application of DTA for investigation of hydration and dehydration of crystal hydrates

The results of the investigation of the hydration processes of the dehydration products of magnesium carbonate trihydrate are shown. The DTA curve was used to calculate the functionQ(t). It was found that the results were in good agreement with the equation , whereQ is the heat evolved during the hydration timet;Q ₀,Q _f are the same for the initial and final products, respectively,k ₁ andk ₂ are the hydration constants.

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Zusammenfassung Die benutzte Methode wurde am Beispiel der Untersuchung des Hydrationsvorganges der Dehydratisierungsprodukte des Magnesiumkarbonat-Trihydrats demonstriert. Zur Errechnung der FunktionQ(t) dienten die DTA-Kurven. Die Ergebnisse folgten gut der Gleichung , woQ die freigesetzte Wärme während der Hydratationszeitt, Q ₀,Q _f dieselbe für die Anfangs- und Endprodukte,k ₁,k ₂ die Hydratationskonstanten bedeuten.

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Résumé Pour illustrer la méthode employée, on communique les résultats se rapportant à l'étude du phénomène d'hydration des produits de déshydratation du carbonate de magnésium trihydraté. On calcule la fonctionQ(t) à l'aide des courbes d'A.T.D. Les résultats obtenus sont en bon accord avec les valeurs de l'équation oùQ est la chaleur dégagée pendant le temps d'hydratationt, Q ₀ etQ _f sont les valeurs correspondantes pour les produits initiaux et finals,k ₁ etk ₂ les constantes d'hydratation.

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. Q(t) (). , , ,t,Q ₀ Q _f — , ,k ₁ k ₂ — .

     

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.     

Mechanochemical destruction of crystalline hydrates of cobalt and zinc acetylenedicarboxylates during dehydration

Upon the dehydration in vacuo, crystals of cobalt and zinc acetylenedicarboxylates (CoADC?2H₂O and ZnADC?2H₂O) remain stable only to a certain minimum content of coordination water. Once this content is reached, gaseous decomposition products are abruptly released giving rise to chemically reactive moieties that can initiate the solid-phase polymerization of metal-containing monomers. During the dehydration, stretching and bending bands of carboxyl groups become broader and are shifted, which is indicative of the appearance of a mechanical strain in the crystals. Besides, the removal of one water molecule from the coordination sphere of Zn²⁺ leads to a strong shift of the Zn—O stretching band to lower frequencies. At the moment of an extensive release of gaseous products (CO₂ and H₂O), the deformation gradients increase so that narrow reflections of the crystalline phase are absent in the X-ray powder diffraction pattern. The development of strains in the crystals is facilitated also by the accumulation of free CO₂ molecules in the solid phase, as evidenced by the appearance of the bands at 2338 and 655 cm^–1 in the IR spectra. The energy of dehydration of crystalline hydrates estimated by quantum chemical calculations (DFT) is 150—200 kJ mol^–1. This high energy can lead to mechanochemical activation of the destruction of the crystal and coordination structures of CoADC?2H₂O and ZnADC?2H₂O upon their dehydration.     

Effect of grinding on the dehydration behavior of nedocromil sodium hydrates

Nedocromil sodium has a number of known hydrate states, a monohydrate, a trihydrate and a heptahemihydrate, including an amorphous state. Effect of grinding on the hydration states of nedocromil sodium crystals was studied. After grinding the trihydrate, heptahemihydrate was observed in the ground sample, even though, the water content in the ground sample was not sufficient to cover the heptahemihydrate’s hydration level. On the other hand, in the ground heptahemihydrate, trihydrate was existed. Apparent activation energies (ΔE) for hydrates, monohydrate→anhydrate, trihydrate→monohydrate and heptahemihydrate→amorphous(anhydrate), were calculated using TG data. ΔE for the dehydration of heptahemihydrate was significantly lower than that of other hydrates. Obtained ΔE data explained the inter-conversion behavior of nedocromil sodium induced by grinding.     

Studies on the dehydration and decomposition of calcium and dicalcium magnesium aconttate hydrates

The thermal decomposition of calcium and dicalcium magnesium aconitate hydrates were studied by TG/DTG, DTA, EGA, SEM and other physico-chemical techniques. The decomposition proceeds in four stages: dehydration; oxidation of the carboxylic acid portion of the salt; complete fragmentation of the hydrocarbon portion; and finally, decarboxylation of the metal carbonate to the oxide. The crystal morphologies of the hydrate and anhydrous salts of each compound are very similar. Tricalcium aconitate consists of well-developed twinned crystals and stellate clusters intergrown with flat platy crystals. On the other hand, dicalcium magnesium aconitate crystals are monoclinic with well-developed pinacoidal faces. The activation energy,E _d (43±2 kJ mol^?1 water), calculated from Borchardt and Daniels' method, for the dehydration process of calcium aconitate trihydrate is of the same order of magnitude as some simple metal salt hydrates. The rate constant, k_d increased from 0.04/min at 238°C to greater than 0.86/min at 295°C. It is concluded that the dehydration process is due to cation bound water.     

Thermogravimetric investigation of the kinetics and thermodynamics of dehydration of amorphous silica

Several commercial and laboratory-synthesized specimens of silica gel have been studied, using thermogravimetry. Two forms of adsorbed water have been found: the first form, which evaporates in the temperature range 100–200°, is polymolecular water layer in open pores and loosely-bonded molecules on the surface and in the bulk of the globules; the second form, which evaporates in the temperature range 200–700°, comprises water molecules hydrogen-bonded to silanol groups, and evidently coordinated to silicon atoms. The dehydration heat of the first form, determined from the DTA curves, depends on the ratio of the two forms, and varies from 3.7±0.6 kcal/mole H₂O for coarse-grain silica gel produced at pH=7 to 12±1 kcal/mole H₂O for fine-grain silica gel of commercial chromatography grade.The activation energy of evaporation of water determined from the TG curves is about 10 kcal/mole in the temperature range 150–200°.

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Zusammenfassung Verschiedene handelsüblich und im Laboratorium synthetisierte Proben von Kieselgel wurden durch Thermogravimetrie untersucht. Zwei Formen von adsorbiertem Wasser wurden gefunden: die erste im Temperaturbereich von 100 bis 200° entweichende, ist eine polymolekulare Wasserschicht in offenen Poren und lose gebundenen Molekülen an der Oberfläche und in der Masse der kugelförmigen Teilchen; die andere Form, welche im Temperaturbereich von 200 bis 700° verflüchtigt wird, besteht aus Wassermolekülen, die durch Stickstoffbindungen an Silanolgruppen und offensichtlich koordinativ an Siliziumatome gebunden sind. Die aus den DTA-Kurven ermittelte Dehydratisierungswärme der ersten Gruppe hängt vom Verhältnis der beiden Formen ab und variiert von 3.7±0.6 kcal/Mol H₂O für grobkörniges Kieselgel, das bei pH=7 hergestellt wird, bis zu 12±1 kcal/Mol H₂O für feinkörniges Kieselgel der handelsüblichen »chromatographischen« Qualität.Die aus den TG-Kurven ermittelte Aktivierungsenergie der Verflüchtigung des Wassers beträgt im Temperaturbereich von 150 bis 200° etwa 10 kcal/Mol.

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Résumé Plusieurs échantillons de gels de silice commerciaux et synthétisés au laboratoire ont été étudiés par TG. Deux formes d'eau adsorbée ont été mises en évidence: la premiè re s'évapore entre 100 et 200° et consiste en une couche d'eau polymoléculaire dans les pores ouverts et à l'intérieur des globules; la seconde forme s'évapore entre 200 et 700° consiste en molécules d'eau liées par ponts d'hydrogène à des groupes silanol et, évidemment, par des liaisons de coordination aux atomes de silice. La chaleur de déshydratation de la première forme, déterminée à partir des courbes ATD, dépend de la proportion des deux formes et varie depuis 3.7±0.6 kcal/mole pour le gel de silice à gros grains produit à pH-7 jusqu'à 12±1 kcal/mole H₂O pour le gel de silice à grains fins de qualité commerciale «pour Chromatographie».L'énergie d'activation de l'évaporation de l'eau, calculée à partir des courbes TG, est d'environ 10 kcal/mole dans l'intervalle de température compris entre 150 et 200°.

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, . , 100–200° . , 200–700°, , , , - . , , 3.7 + 0.6 / H₂O , pH=7 12±1 / ₂ , . , , 10 / 150–200°.

     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. V

Non-isothermal thermal studies of the dehydration of the double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues were carried out where M(I) = TI(I) and M(II) = Mg(II), Co(II), Ni(II), Cu(II) or Zn(II). Thermal parameters like activation energy, order of reaction, enthalpy change, etc. were evaluated from the analysis of TG, DTA and DTG curves. These thermal parameters were compared with those of other series, like NH₄(I), K(I), Rb(I) and Cs(I) studied earlier. On deuteration the nature of dehydration altered in the case of Tl₂Zn(SO₄)₂·6H₂O only. The thermal stability of the salt hyd discussed in relation to the salt hydrates of other series. The role of divalent cation on the thermal properties of dehydration of salt hydrates is also discussed. The order of reaction was always found unity. The values of ΔH were within ≈12–≈16 kcal mol^?1.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. III

Dehydration of double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O where M(I)Rb(I) and M(II)Mg(II), Mn(II), Co(II), Ni(II), Zn(II) and Cu(II) has been studied by derivatograph. Thermal parameters like activation energy, order of reaction, enthalpy change etc. for each step of dehydration have been evaluated from the analyses of TG, DTA and DTG curves and these parameters are compared with corresponding salt hydrates of the NH₄ and K(I) series. These double salt hydrates are deuterated and studied similarly. Activation energies for the first step of dehydration of these salt hydrates increase with the increase of second ionisation potential of the central metal except for Mg. The nature of dehydration changes in the cases of double salt hydrates of Mg(II) and Ni(II) on deuteration. The order of reaction for each case of dehydration has been found to be unity. The enthalpy change per mole of water varies from 11.4 to 17 kcal.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. VI

Non-isothermal studies of the dehydration of double salt hydrates of the type K₂AB₄·M(II)SO₄·6H₂O where AB₄BeF^2?₄ or SeO^2?₄ and M(II)Mg(II), Co(II), Ni(II), Cu(II) or Zn(II) and their D₂O analogues were carried out. Thermal parameters like activation energy, order of reaction, enthalpy change, etc., for each step of dehydration were evaluated from the analysis of TG, DTA and DTG curves. These parameters were compared with the corresponding double sulphate, i.e., K₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues. The role of divalent cation on the thermal properties of dehydration of the salt hydrates and also the effect on the thermal properties due to deuteration were discussed. The order of reaction was always found unity. The values of ΔH were within ～11-～19 kcal mol^?1     

液体的饱和蒸气压与内压

本文用统计热力学的方法, 建立了液体饱和蒸气压, 与内压间的关系式。对C6H6、CCl4、cy-C6H12、C(CH3)4、n-C6H14和(CH3)2CO等六种液体的检验结果表明, 上述关系式能适用于广阔的温度范围。