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461.
The thermal decomposition of FeSO4·6H2O
was studied by mass spectroscopy coupled with DTA/TG thermal analysis under
inert atmosphere. On the ground of TG measurements, the mechanism of decomposition
of FeSO4·6H2O is:
i) three dehydration steps
FeSO4·6H2O FeSO4·4H2O+2H2O
FeSO4·4H2O FeSO4·H2O+3H2O
FeSO4·H2O FeSO4+H2O
ii) two decomposition
steps
6FeSO4 Fe2(SO4)3+2Fe2O3+2SO2
Fe2(SO4)3 Fe2O3+3SO2+3/2O2
The intermediate compound was identified as Fe2(SO4)3 and the final product as the hematite Fe2O3. 相似文献
462.
TG-DTG technique and Harcourt-Esson integrated equation were used to study the dehydration process of zinc phosphate tetrahydrate α-Zn3(PO4)2·4H2O nanoparticle and its thermal decomposition kinetics. The results show that there are three stages of dehydration between 300 and 800 K during the thermal decomposition of α-Zn3(PO4)2·4H2O nanoparticle. The first stage is controlled by chemical reaction with an activation energy of 69.48 kJ·mol^-1 and a pre-exponential factor of 1.77×10^6 s^-1. The second is controlled by nucleation and growth with an activation energy of 78.74 kJ·mol^-1 and a pre-exponential factor of 5.86×10^9 s^-1. The third is controlled by nucleation and growth with an activation energy of 141.5 kJ·mol^-1 and a pre-exponential factor of 1.01×10^12 s^-1. The kinetic compensative effects not only exist in Arrhenius equation but also in Harcourt-Esson equation. Activation energy E is dependent on both the decomposition fraction α and temperature T. 相似文献
463.
A platinum-lined, flowing autoclave facility was used to investigate the solubility/phase behavior of nickel oxide (NiO) in aqueous sodium phosphate solutions between 290 and 560 K. A layer of hydrous nickel oxide was concluded to exist on the nickel oxide surface below 468 K; only at higher temperatures did the anhydrous nickel oxide phase control the nickel ion solubility behavior. The measured solubility behavior was examined via a nickel(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria were obtained from a least-squares analysis of the data. The existence of two new nickel ion complexes are reported for the first time: Ni(OH)2(HPO4)= and Ni(OH)3(H2PO4)=. The positive entropy change associated with the formation of Ni(OH)3(H2PO4)= leads to its dominance in alkaline phosphate solutions at elevated temperatures. 相似文献
464.
B. V. L’vov 《Journal of Thermal Analysis and Calorimetry》2006,84(3):581-587
The main purpose of this
paper is to prove the applicability of the mechanism of congruent dissociative
vaporization (CDV) to the solid-state decomposition kinetics through the comparison
of the fundamental theoretical relationship Ei/Ee=(a+b)/a resulted
from this mechanism with experiment. It has been shown that the ratios of Ei and Ee
parameters of the Arrhenius equation measured in the isobaric and equimolar
modes (in the presence and absence of H2O vapour) for
22 reactants with the general formula aSalt⋅bH2O or aOxide⋅bH2O are in agreement with
the values of (a+b)/a. The relative standard deviation is only 17% and
the correlation coefficient is close to 0.99. A probability of accidental
correlation for all set of the E parameters
taken from the literature is lower than 4⋅10–16
. This strongly supports the validity of the CDV mechanism. The problem of
stability of polyatomic molecules of inorganic salts in the gaseous state,
which are the primary decomposition products of crystalline hydrates, was
also discussed on the basis of recent mass spectroscopy studies. It was concluded
that any doubts in the applicability of the CDV mechanism as a general mechanism
of solid-state decomposition reactions are unsound. 相似文献
465.
AbstractThe phase transitions and dehydration of chalcanthite were investigated by electrical conductivity and Raman spectroscopy at 1.0–24.0?GPa and 293–673?K in a diamond anvil cell. At ambient temperature, two secondary phase transitions were observed according to discontinuous changes in the slope of Raman shifts, full width at half maximum and electrical conductivities at ~7.3 and ~10.3?GPa. The dehydration temperatures were determined by the splitting of Raman peaks and changes in electrical conductivity as ~350 and ~500?K at respective ~3.0 and ~6.0?GPa. A positive relationship for chalcanthite between dehydration temperature and pressure is established. 相似文献
466.
R. L. Frost J. M. Bouzaid A. W. Musumeci J. T. Kloprogge W. N. Martens 《Journal of Thermal Analysis and Calorimetry》2006,86(2):437-441
The thermal
stability and thermal decomposition pathways for synthetic iowaite have been
determined using thermogravimetry in conjunction with evolved gas mass spectrometry.
Chemical analysis showed the formula of the synthesised iowaite to be Mg6.27Fe1.73(Cl)1.07(OH)16(CO3)0.336.1H2O
and X-ray diffraction confirms the layered structure. Dehydration of the iowaite
occurred at 35 and 79°C. Dehydroxylation occurred at 254 and 291°C.
Both steps were associated with the loss of CO2. Hydrogen
chloride gas was evolved in two steps at 368 and 434°C. The products of
the thermal decomposition were MgO and a spinel MgFe2O4.
Experimentally it was found to be difficult to eliminate CO2
from inclusion in the interlayer during the synthesis of the iowaite compound
and in this way the synthesised iowaite resembled the natural mineral. 相似文献
467.
Thermoanalytical Study of the Dehydration of Cyclodextrin Inclusion Complexes of Clofibric Acid 总被引:1,自引:0,他引:1
Hydrated inclusion complexes of the hosts β-CD (CD=cyclodextrin), γ-CD and permethylated β-CD with the guest clofibric acid
were analysed by TG and DSC methods to characterise their dehydration behaviours. Activation energies for dehydration of the
β- and γ-CD clofibric acid complexes, determined by isothermal thermogravimetry, are significantly lower (∼20-25%) than those
for the corresponding uncomplexed hydrated CDs. These data can be reconciled with X-ray structural data which show that H2O molecules in the complexes occupy different crystal sites from those occupied in the parent CDs.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
468.
L. BENEŠ E. ČERNOŠKOVÁ J. MÁLEK K. MELÁNOVÁ P. Patrono V. Zima 《Journal of inclusion phenomena and macrocyclic chemistry》2000,36(2):163-178
The dehydration of VOPO4.2H2O hasbeen studied by thermogravimetric analysis (TGA),differential thermal analysis (DTA) and differentialscanning calorimetry (DSC). From the shift of the DTA,DTG, and DSC peaks, activation energies of thedehydration processes have been calculated based onKissinger's method. The most suitable kinetic modelsfor two-step dehydration have been found. 相似文献
469.
470.
A. Kochanowski R. Dziembaj M. Molenda A. Izak E. Bortel 《Journal of Thermal Analysis and Calorimetry》2007,88(2):499-502
Key issue in the gelcasting method is the way water is released from
the ceramic–hydrogel system. It is the first step to the formation of
ceramic materials called green body.
The purpose of the presented
investigations is to establish the range of temperatures in which dehydration
of the various hydrogels takes place, and at what temperatures the eight prepared
hydrogels are disintegrated.
The set of hydrogels polymers was
obtained by radical polymerization from ionic and non-ionic monomers. The
polymers were solved in water causing formation of clear gels. The dehydration
and thermal decomposition of the obtained hydrogel samples was studied using
thermal analysis techniques. The amount of water contained in hydrogels was
determined as well as the temperature and products of polymer disintegration.
Enthalpies of dewatering were also determined. 相似文献