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1.
Sara J. Palmer Laure M. Grand Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2011,103(2):473-478
The aluminate hydrotalcites are proposed to have either of the following formulas: Mg4Al2(OH)12(CO3
2−)·xH2O or Mg4Al2(OH)12(CO3
2−, SO4
2−)·xH2O. A pure hydrotalcite phase forms when magnesium chloride and aluminate solutions are mixed at a 1:1 volumetric ratio at
pH 14. The synthesis of the aluminate hydrotalcites using seawater results in the formation of an impurity phase bayerite.
Two decomposition steps have been identified for the aluminate hydrotalcites: (1) removal of interlayer water (230 °C) and
(2) simultaneous dehydroxylation and decarbonation (330 °C). The dehydration of bayerite was observed at 250 °C. X-ray diffraction
techniques determined that the synthesis of aluminate hydrotalcite with seawater and a volumetric ratio of 4.5 results in
very disordered structures. This was shown by a reduction in the mass loss associated with the removal of interlayer water
due to the reduction of interlayer sites caused by the misalignment of the metal-hydroxyl layers. 相似文献
2.
J. Escribano R. Masegosa D. Nava M. G. Prolongo Catalina Salom 《Journal of Thermal Analysis and Calorimetry》2006,83(3):675-679
The
mineral sabugalite (HAl)0.5[(UO2)2(PO4)]2⋅8H2O, has been studied using a combination of energy
dispersive X-ray analysis, X-ray diffraction, dynamic and controlled rate
thermal analysis techniques. X-ray diffraction shows that the starting material
in the thermal decomposition is sabugalite and the product of the thermal
treatment is a mixture of aluminium and uranyl phosphates. Four mass loss
steps are observed for the dehydration of sabugalite at 48°C (temperature
range 39 to 59°C), 84°C (temperature range 59 to 109°C), 127°C
(temperature range 109 to 165°C) and around 270°C (temperature range
175 to 525°C) with mass losses of 2.8, 6.5, 2.3 and 4.4%, respectively,
making a total mass loss of water of 16.0%. In the CRTA experiment mass loss
stages were found at 60, 97, 140 and 270°C which correspond to four dehydration
steps involving the loss of 2, 6, 6 and 2 moles of water. These mass losses
result in the formation of four phases namely meta(I)sabugalite, meta(II)sabugalite,
meta(III)sabugalite and finally uranyl phosphate and alumina phosphates. The
use of a combination of dynamic and controlled rate thermal analysis techniques
enabled a definitive study of the thermal decomposition of sabugalite. While
the temperature ranges and the mass losses vary due to the different experimental
conditions, the results of the CRTA analysis should be considered as standard
data due to the quasi-equilibrium nature of the thermal decomposition process.
The online version of the original article can be found at 相似文献
3.
The dehydration behaviors of FGD gypsums from three power plants were investigated at N2 atmosphere (autogenous and negligible partial pressure of water,
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} ) in non-isothermal and isothermal condition. The dehydration of gypsum proceeded through one step, i.e., CaSO4·2H2O → γ-CaSO4 (γ-anhydrite) or two steps, i.e., CaSO4·2H2O → CaSO4·0.5H2O (hemihydrate) → γ-CaSO4 depending on temperature and
P\textH 2 \textO P_{{{\text{H}}_{ 2} {\text{O}}}} . The discrepancies of three FGD gypsums on dehydration behavior were very likely due to the different crystalline characteristics
(size and habit) and impurities, such as fly ash and limestone. Experimental data of non-isothermal analysis have been fitted
with two ‘model-free’ kinetic methods and those of isothermal analysis have been fitted with Avrami and linear equation. The
apparent empirical activation energies (E
a) suggest that the transition from gypsum to hemihydrate is mainly controlled by nucleation and growth mechanism, while the
transition from gypsum to γ-anhydrite is mostly followed by phase boundary mechanism. 相似文献
4.
Controlled rate thermal analysis of hydromagnesite 总被引:1,自引:0,他引:1
Veronika Vágvölgyi R. L. Frost M. Hales A. Locke J. Kristóf Erzsébet Horváth 《Journal of Thermal Analysis and Calorimetry》2008,92(3):893-897
The reaction of magnesium minerals such as brucite with CO2 is important in the sequestration of CO2. The study of the thermal stability of hydromagnesite and diagenetically related compounds is of fundamental importance to
this sequestration. The understanding of the thermal stability of magnesium carbonates and the relative metastability of hydrous
carbonates including hydromagnesite, artinite, nesquehonite, barringtonite and lansfordite is extremely important to the sequestration
process for the removal of atmospheric CO2. This work makes a comparison of the dynamic and controlled rate thermal analysis of hydromagnesite and nesquehonite. The
dynamic thermal analysis of synthetic hydromagnesite proves that dehydration takes place in two steps at 135 and 184°C, dehydroxylation
at 412°C and decarbonation at 474°C. Controlled rate thermal analysis shows the first dehydration step is isothermal and the
second quasi-isothermal at 108 and 145°C, respectively. In the CRTA experiment both water and carbon dioxide are evolved in
an isothermal decomposition at 376°C.
CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of magnesium carbonates
such as nesquehonite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer
of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of
non-isothermal nature reveal partial nesquehonite structure. 相似文献
5.
Raluca Dumitru Oana Carp P. Budrugeac M. Niculescu E. Segal 《Journal of Thermal Analysis and Calorimetry》2011,103(2):591-596
The authors present their results concerning the decomposition in air of the homopolynuclear coordination compound [CoC2O4·2.5H2O]
n
. In the temperature range 20–300 °C, the heating curves TG, DTG and DTA allowed to evidence three decomposition steps. The
kinetic analysis was performed on the second step which proved to be the only workable one. The application of nonlinear regression
procedure shows that this is a complex process consisting in three successive steps. The checking of the mechanism and corresponding
kinetic parameters for quasi-isothermal data (T = 150 °C) shows that the obtained results could be used for prediction of the thermal behaviour of the investigated compound
in both isothermal and non-isothermal conditions. 相似文献
6.
Veronika Vágvölgyi M. Hales R. L. Frost A. Locke J. Kristóf Erzsébet Horváth 《Journal of Thermal Analysis and Calorimetry》2008,94(2):523-528
The understanding of the thermal stability of magnesium carbonates and the relative metastability of hydrous carbonates including
hydromagnesite, artinite, nesquehonite, barringtonite and lansfordite is extremely important to the sequestration process
for the removal of atmospheric CO2.
The conventional thermal analysis of synthetic nesquehonite proves that dehydration takes place in two steps at 157, 179°C
and decarbonation at 416 and 487°C. Controlled rate thermal analysis shows the first dehydration step is isothermal and the
second quasi-isothermal at 108 and 145°C. In the CRTA experiment carbon dioxide is evolved at 376°C. CRTA technology offers
better resolution and a more detailed interpretation of the decomposition processes of magnesium carbonates such as nesquehonite
via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample
as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature
reveal partial collapse of the nesquehonite structure. 相似文献
7.
Banjong Boonchom Chanaiporn Danvirutai 《Journal of Thermal Analysis and Calorimetry》2009,98(3):717-723
The non-isothermal kinetics of dehydration of AlPO4·2H2O was studied in dynamic air atmosphere by TG–DTG–DTA at different heating rates. The result implies an important theoretical
support for preparing AlPO4. The AlPO4·2H2O decomposes in two step reactions occurring in the range of 80–150 °C. The activation energy of the second dehydration reaction
of AlPO4·2H2O as calculated by Kissinger method was found to be 69.68 kJ mol−1, while the Avrami exponent value was 1.49. The results confirmed the elimination of water of crystallization, which related
with the crystal growth mechanism. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the dehydration reaction are calculated
by the activated complex theory. These values in the dehydration step showed that it is directly related to the introduction
of heat and is non-spontaneous process. 相似文献
8.
S. El D. Hamad 《Thermochimica Acta》1976,17(1):85-96
Thermogravimetry was used to obtain data on the isothermal rate of dehydration and hydration of the reaction Na2SO4·10H2O→Na2SO4+10H2O in the temperature range 10 to 25°C. The thermodynamic functions, ΔH, ΔG and ΔS were calculated and compared with data in the literature. The dissociation pressures of Na2SO4·10H2O at temperatures in the range 0 to 25°C were measured in a volumetric dissociation apparatus. The results obtained were compared with those using thermogravimetry and the accuracy of the two techniques was assessed. 相似文献
9.
The thermal decomposition of copper(II) acetate monohydrate (CuAc2·H2O) under 500 °C in air was studied by TG/DTG, DTA, in situ FTIR and XRD experiments. The experimental results showed that
the thermal decomposition of CuAc2·H2O under 500 °C in air included three main steps. CuAc2·H2O was dehydrated under 168 °C; CuAc2 decomposed to initial solid products and volatile products at 168–302 °C; the initial solid products Cu and Cu2O were oxidized to CuO in air at 302–500 °C. The copper acetate peroxides were found to form between 100 and 150 °C, and the
dehydration of these peroxides resulted in the presence of CuAc2·H2O above 168 °C. The initial solid products were found to be the admixture of Cu, Cu2O, and CuO, not simply the single Cu2O as reported before. Detailed reactions involved in these three steps were proposed to describe the complete mechanism and
course of the thermal decomposition of CuAc2·H2O in air. 相似文献
10.
Latifa A. Al-Hajji Muhammad A. Hasan Mohamed I. Zaki 《Journal of Thermal Analysis and Calorimetry》2010,100(1):43-49
The formation of Barium monotungstate (BaWO4) particles in equimolar powder mixtures of BaCO3 and WO3 was examined under isothermal and non-isothermal conditions upon heating in air at 25–1200 °C, using thermogravimetry. Concurrence
of the observed mass loss (due to the release of CO2) to the occurrence of the formation reaction was evidenced. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The x–t and x–T data thus obtained were processed using well established mathematical apparatus and methods, in order to characterize nature
of reaction rate-determining step, and derive isothermal and non-isothermal kinetic parameters. Moreover, the reaction mixture
quenched at various temperatures (600–1,000 °C) in the reaction course was analyzed by various spectroscopic and microscopic
techniques, for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional
diffusion of WO3 species across the product layer (BaWO4), which was implied to form on the barium carbonate particles. The isothermally determined activation energy (118–125 kJ/mol)
was found to be more credible than that (245 kJ/mol) determined non-isothermally. 相似文献
11.
In situ
developments of platelike spodumene–diopside grains were obtained by
controlled devitrification of the complex system Li2O–CaO–MgO–Al2O3–SiO2 glass. The crystallization mechanisms
of spodumene–diopside glass were measured by isothermal and non-isothermal
processes using classical and differential thermal analysis techniques. The
Avrami constant n was 2.0–2.1, indicating
two-dimensional crystal growth and platelike grains. The crystalline phases
precipitated first were high-quartzs.s., then transformed
to β-spodumene and diopside. The Flexural strength, fracture toughness
and thermal shock resistance (in 20°C water) increased from 145 MPa, 1.3
MPa m1/2, 800°C (pure spodumene) to 197 MPa,
2.9 MPa m1/2 and 920°C (spodumene–diopside)
with low thermal expansion coefficient (from 3∼9·10–7
to 11.8·10–7 K–1).
This mean in situ developments of platelike spodumene–diopside grains
reinforced the low thermal expansion coefficient glass-ceramics. 相似文献
12.
János Madarász 《Journal of Thermal Analysis and Calorimetry》2009,97(1):111-116
Thermal decomposition of a mixed valence copper salt, Na4[Cu(NH3)4][Cu(S2O3)2]2·0.5NH3 (1) prepared from pentahydrates of sodium thiosulfate and copper sulphate of various molar ratios in 1:1 v/v aqueous ammonia
solution, has been studied up to 1,000 °C in flowing air by simultaneous thermogravimetric and differential thermal analysis
coupled online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR), in comparison. Compound
1 releases first but very slowly some of the included ammonia till 170 °C, then simultaneously ammonia (NH3) and sulphur dioxide (SO2) from 175 to 225 °C, whilst the evolution of SO2 from thiosulfate ligands continues in several overlapping stages until 410 °C, and is escorted by explicit exothermic heat
effects at around 237, 260, 358 and 410 °C. The former two exothermic DTA-peaks correspond to the simultaneous degradation
and air oxidation processes of excess thiosulfate anions not reacted by formation of copper sulfides (both digenite, Cu1.8S and covellite, CuS, checked by XRD) and sodium sulfate, while the last two exothermic peaks are accompanied also by considerable
mass gains, as the result of two-step oxidation of copper sulfides into various oxosulfates. The mass increase continues further
on until 580 °C, when the sample mass begins to decrease slowly, as a continuous decomposition of the intermediate copper
oxosulfates, indicated also by re-evolution of SO2. At 1,000 °C, a residual mass value of 64.3% represents a stoichiometric formation of CuIIO and anhydrous Na2SO4. 相似文献
13.
S. Attia L. Hevroni A. Danon D. Meyerstein J. E. Koresh Y. Finkelstein 《Adsorption》2013,19(2-4):821-833
The oxygen isotopic exchange during dehydration and decomposition of five sulfate salt hydrates (CoSO4·6H2O, NiSO4·7H2O, ZnSO4·7H2O, CaSO4·2H2O, Li2SO4·H2O) was studied in detail by temperature programmed desorption mass spectrometry (TPD-MS) in a supersonic molecular beam (SMB) inlet mode. Crystals of the 18O-enriched salts were grown and the detailed desorption steps of the various gaseous products released during dehydration and decomposition of these compounds were recorded. The desorption patterns confirmed the known characteristic stepwise dehydration of these salts, where regardless of the crystalline structure and composition, in all the salts (excluding the Li and Ca sulfates) a major group of n ? 1 loosely bounded water of crystallization molecules (out of total of n molecules in the fully hydrated form) are released at adjacent temperatures in a typical low temperature range (<200 °C), while the last, most strongly bounded water molecule, consistently desorbs at relatively higher temperatures (240 < T < 440 °C). Interestingly, it is established that the oxygen isotopic exchange occurs exclusively between that latter, most strongly bound water molecule, and the salt anion. Remarkably, the results point out that the exchange process is mostly of solid-solid nature. Finally, the results point out that the probability of the isotopic exchange increases with the increment in the desorption temperature of the last dehydration step, i.e. with the bond strength in the monohydrate, between the last water molecule of crystallization and the cation. 相似文献
14.
Investigation on the Thermal Degradation of Aluminium-12-Tungstosilicate The dehydration of aluminium-12-tungstosilicate AlH[SiO4W12O36] · 29 H2O gives the anhydrous salt at 440°C. By means of X-ray heating patterns, thermal analysis, and i.r. spectroscopy the formation of the new phase 1/2 Al2O3 · SiO2 · 12 WO3 (I) at 500°C is observed, stable at room temperature. Above 800°C from I tetragonal W3, Al2(WO4)3, and amorphous SiO2 are formed. Amorphous SiO2 crystallizes to high-temperature cristobalite at 1000°C. High-resolution 27Al NMR (MAS-technique) is used to determine the coordination number of aluminium in the different phases. 相似文献
15.
Preliminary tests of the chlorination of two iron oxides (wüstite and hematite) in various chlorinating gas mixtures were performed by thermogravimetric analysis (TGA) under non-isothermal conditions. Wüstite started to react with chlorine from about 200 °C generating ferric chloride and hematite as the final reaction products. The presence of a reducing and oxidizing agent in the chlorinating gas mixtures influenced the chlorination reactions of both iron oxides, during non-isothermal treatment, only at temperatures higher than 500 °C.The chlorination kinetics of hematite with Cl2 have been studied in details between 600 and 1025 °C under isothermal chlorination. The values of the apparent activation energy (Ea) were about 180 and 75 kJ/mol in the temperature ranges of 600–875 and 875–1025 °C, respectively. The apparent reaction order with respect to Cl2 was found to be 0.67 at 750 °C. Mathematical model fitting of the kinetics data was carried out to determine the most probable reaction mechanisms. 相似文献
16.
Y. Masuda Y. Seto X. Wang Y. Yukawa T. Arii 《Journal of Thermal Analysis and Calorimetry》2000,60(3):1033-1041
Thermal and structural changes of lanthanum hexacyanocobaltate(III) pentahydrate, La[Co(CN)6]⋅5H2O were investigated by means of thermal analysis, visible electronic spectra, IR, powder X-ray diffraction, EXAFS and TG-MS.
The dehydration of La[Co(CN)6]⋅5H2O proceeded reversibly through three steps and steps corresponded to the losses of H2O, 3H2O and H2O, and the enthalpy changes for these steps were 51.3, 211.0 and 38.7 kJ mol−1, respectively.
After the dehydration, the colour of the anhydride changed from white to blue around 290°C and an abrupt mass loss occurred
at 350°C. The colour change seems to be attributable to the change of coordination geometry around the Co ions from an octahedral
structure to a tetrahedral one. LnCoO3 was obtained as a final product by heating the sample to 1000°C.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
Ray L. Frost János Kristóf Erzsébet Horváth 《Journal of Thermal Analysis and Calorimetry》2009,98(3):749-755
Controlled rate thermal analysis (CRTA) technology offers better resolution and a more detailed interpretation of the decomposition
processes of a clay mineral such as sepiolite via approaching equilibrium conditions of decomposition through the elimination
of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition
processes of non-isothermal nature reveal changes in the sepiolite as the sepiolite is converted to an anhydride. In the dynamic
experiment two dehydration steps are observed over the ~20–170 and 170–350 °C temperature range. In the dynamic experiment
three dehydroxylation steps are observed over the temperature ranges 201–337, 337–638 and 638–982 °C. The CRTA technology
enables the separation of the thermal decomposition steps. 相似文献
18.
Chanaiporn Danvirutai Pittayagorn Noisong Sujittra Youngme 《Journal of Thermal Analysis and Calorimetry》2010,100(1):117-124
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 Ea 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. 相似文献
19.
The thermal decomposition of natural iowaite of formula Mg6Fe2(Cl,(CO3)0.5)(OH)16·4H2O was studied by using a combination of thermogravimetry and evolved gas mass spectrometry. Thermal decomposition occurs over
a number of mass loss steps at 60°C attributed to dehydration, 266 and 308°C assigned to dehydroxylation of ferric ions, at
551°C attributed to decarbonation and dehydroxylation, and 644, 703 and 761°C attributed to further dehydroxylation. The mass
spectrum of carbon dioxide exhibits a maximum at 523°C. The use of TG coupled to MS shows the complexity of the thermal decomposition
of iowaite.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
V. A. Logvinenko A. V. Belyaev S. N. Vorob’eva 《Journal of Thermal Analysis and Calorimetry》2013,114(3):1177-1181
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. 相似文献