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Abstract  

On dehydration of La[Co(CN)6]5H2O, the color of the complex, changes from white to pale blue at around 230C. Heating the pale blue specimen, the color changes to deep blue at around 290C. This deep blue specimen is easily rehydrated to a pink one. As reported previously, in the pale blue specimen, Co3+ ions are situated in the center of the D4h crystal field formed by six CN- ions. The deep blue specimen is due to the presence of [Co(CN)4]2- ions in which Co2+ was situated in a Td coordination field formed by four CN- ions and the Co-C bond length is 1.67 Ĺ. The pink species corresponded to trans-[Co(CN)4(H2O)2]2- and the bond lengths of Co-C and Co-O are 1.89 and 1.85 Ĺ, respectively. The Raman spectra of the complex observed at 25C displays two bands at 2157 and 2176 cm-1 associated with the vibration of C-N bond, and the band of 2157 cm-1 was split into two bands, 2150 and 2156 cm-1, at around 100C. When the complex was heated to around 230C, three new bands were observed at 2103, 2116 and 2141 cm-1. The bands of 2103 and 2116 cm-1 were assigned to the stretching vibration of C=N bonding to Co2+. The band of 2141 cm-1 was assigned to the stretching vibration of the inverted CN- as follows: Co-C=N-La→Co-N=C-La. The activation energy for the inversion of CN- was estimated as 67 kJ mol-1.

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Apple cubes were osmotically dehydrated with 40 °Bx sucrose and sorbitol solutions. Light microscopy was used to observe the microstructure of fresh and osmotically dehydrated samples. Peleg’s model could fit the experimental data and describe the mass transfer kinetics of water loss (WL) and solid gain (SG). The use the sorbitol as osmotic agent, the increase of temperature and concentration of the solution increased the WL during the osmotic dehydration. The average cellular parameters, area and perimeter (size), and circularity, elongation, roundness, and compactness (shape) of fresh samples were 14.28±6.65×103 μm2 and 0.486 mm, and 0.73, 1.56, 0.70, 0.83, respectively. The osmotically dehydrated samples presented a decrease in area, circularity, roundness and compactness and an increase in the elongation of the cells, and these changes were higher in samples treated with sorbitol.

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Apples (Idared) were subjected to osmotic dehydration in: a) 50% solutions of fructooligosaccharides (FOS) at 40–70 °C (apple/solution 1/2), b) 50% solution of FOS at 40 °C using different amount of solution (apple-solution ratio from 1/2 to 1/5), c) 50–65% solution of FOS at 40 °C (apple/solution 1/4). The content of fructooligosaccharides in dried material was determined. An increase in temperature and amount of the hypertonic solution intensified the migration of fructooligosaccharides to the fruit tissue. There was no direct relationship between the concentration of the hypertonic solution and the FOS content of dehydrated apples. the contents of fructooligosaccharides and dry substance in fruits dehydrated under different conditions were interlinked. Dehydrated apples of a content of fructooligosaccharides of 7–9% w/w were obtained when the content of dry substance was approximately 30%.

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The kinetics of the thermal dehydration of yttrium formate dihydrate was studied by means of isothermal gravimetry under various water vapour pressures from 5×10−4 to 8 torr. On the whole, the dehydration was described as the three dimensional phase boundary reaction, R3. An unusual dependence of the rate of dehydration on the atmospheric water vapour pressure was observed: with increasing water vapour pressure, the rate increased at first, passed through a maximum, and then decreased gradually to a constant value. These phenomena were similar to the Smith-Topley effect. The mechanism of the phenomena can be described on the basis of the crystallinity of the dehydrated product phase.

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Abstract  

The thermal decomposition reactions of manganese(II) complexes with L-proline and 4-hydroxy- L-proline were studied. The Mn(II) proline complex loses the water molecule at 40–95C and then, heated above 250C it decomposes in several steps to manganese oxide. The most appropriate kinetic equations for dehydration process are the geometrical R2 or R3 ones. They give a value of activation energy, E of about 95 kJmol–1. The Mn(II) hydroxyproline complex loses the water molecules in two stages (70–110 and 110–230C) and next it decomposes to manganese oxide in several steps. The R3 or D3 (three-dimensional diffusion) models are the most appropriate for the first stage of dehydration (E is about 155 kJ mol–1). The second step of dehydration is limited by D3 mechanism (E=52 kJ mol–1).

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Abstract  

Thermoanalytical (TA) and hot-stage microscopic techniques were employed to investigate the complicated behaviour of the non-isothermal dehydration of single crystals of α-NiSO4·6H2O. Non-isothermal dehydration to the tetrahydrate proceeds in two stages: (1) surface nucleation and growth of nuclei, followed by advancement of reaction fronts inward; (2) random nucleation and growth near the reaction front as well as in the bulk. Corresponding TA curves were interpreted to represent diffusional removal of evolved water vapour through the surface layer created in stage (1). The dehydration process of the tetrahydrate to the monohydrate is explained on the basis of textural structures produced in the previous step. Crack formation in the surface layer and rapid escape of the water vapour were observed in this step.

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Abstract  

Rare earth complexes ofm-nitrobenzoic acid (LnL3·2H2O,Ln=La-Lu and Y, except Pm, HL=m-nitrobenzoic acid) were synthesized and characterized by elemental analysis, chemical analysis, IR spectroscopy and X-ray diffraction analysis. The dehydration behaviour of these complexes was studied in detail by means of TG-DTA and DSC. Dehydration occurs over the temperature range 76–215°C, and the temperature of formation of the anhydrous complexes decreases with increasing atomic number of the rare earth. The activation energies and enthalpy changes for te dehydration were obtained.

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Abstract  

The reaction process of the thermal dehydration of dilithium tetraborate trihydrate, Li2B4O7 3H2O, was reinvestigated from a viewpoint of reaction kinetics. On the basis of the results of thermogravimetry, constant rate thermal analysis, powder X-ray diffractometry, infrared spectroscopy and scanning electron microscopy, it was confirmed that the reaction proceeds via three consecutive kinetic steps characterized by different activation energies. The first and second kinetic steps, accompanied by the destruction of the original crystal structure of the reactant, seem to be assigned to the surface and internal reactions, respectively. During the third kinetic step, the thermal dehydration of hydrated amorphous intermediate, produced at the second kinetic step, and crystallization of the final dehydration product, Li2B4O7, are likely to take place concurrently.

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Abstract  

Classical thermogravimetry and its modification with Knudsen cells were employed to quantitatively investigate the osmo-dehydration of apple pulp samples. The data allowed realization of the complex mechanism of the process, which is not a mere solvent depletion, since it also implies sugar exchanges between the apple tissue and the hypertonic syrup used to dehydrate the fruit. The comparison between different hypertonic syrups, all at the same water activity, showed that maltose is more effective than either sucrose or a mixture of sugars that mimics the saccharide content of the apple. The conclusions are supported by a thermodynamic analysis of the aqueous solutions of these sugars at a concentration level as large as that of the hypertonic syrups used for the osmo-dehydration process.

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Abstract  

The differential scanning calorimetry (DSC) technique was used to analyse the thermal effects and the irreversible processes associated with the dehydration of manganese ferrite powders coprecipitated from aqueous solution of salts obtained by simultaneous dissolution of MnO2 and FeSO4x7H2O.

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