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1.
Bayer hydrotalcites prepared using the seawater neutralisation (SWN) process of Bayer liquors are characterised using X-ray diffraction and thermal analysis techniques. The Bayer hydrotalcites are synthesised at four different temperatures (0, 25, 55, and 75 °C) to determine the effect of synthesis temperature on the thermal stability of the Bayer hydrotalcite structures and the mineralogical phases that form. The interlayer distance increased with increasing synthesis temperature, up to 55 °C, and then decreased by 0.14 Å for Bayer hydrotalcites prepared at 75 °C. The three mineralogical phases identified in this investigation are; (1) Bayer hydrotalcite, (2), calcium carbonate species, and (3) hydromagnesite. The DTG curve can be separated into four decomposition steps; (1) the removal of adsorbed water and free interlayer water in hydrotalcite (30–230 °C), (2) the dehydroxylation of hydrotalcite and the decarbonation of hydrotalcite (250–400 °C), (3) the decarbonation of hydromagnesite (400–550 °C), and (4) the decarbonation of aragonite (550–650 °C). 相似文献
2.
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
3.
Sara J. Palmer J. Kristóf Veronika Vágvölgyi Erzsébet Horváth R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,96(2):449-454
The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg6Al2(OH)16[Fe(CN)6]0.5·7H2O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg6Al2(OH)16[Fe(CN)6]0.66·9H2O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite. 相似文献
4.
Sara J. Palmer R. L. Frost T. Nguyen 《Journal of Thermal Analysis and Calorimetry》2008,92(3):879-886
Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were
characterized by XRD, and TG/DTA to determine the stability of the hydrotalcites synthesized. The thermal decomposition of
carbonate hydrotalcites consist of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation
and decarbonation of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where
the first step is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting
with the interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding
metal oxides, including MgO, Al2O3, MgAl2O4, NaMg4(VO4)3 and Na2Mg4(MoO4)5. The presence of oxy-anions proved to be beneficial in the stability of the hydrotalcite structure, shown by the delay in
dehydroxylation of oxy-anion containing hydrotalcites compared to the carbonate hydrotalcite. This is due to the substantial
amount of hydroxyl groups involved in a network of hydrogen bonds involving the intercalated anions. Therefore, the stability
of the hydrotalcite structure appears to be dependent on the type of anion present in the interlayer. The order of thermal
stability for the synthesized hydrotalcites in this study is Syn-HT-V>Syn-HT-Mo> Syn-HT-CO3-V>Syn-HT-CO3-Mo>Syn-HT-CO3. Carbonate containing hydrotalcites prove to be less stable than oxy-anion only hydrotalcites. 相似文献
5.
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
6.
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
7.
Ray L. Frost János Kristóf Erzsébet Horváth 《Journal of Thermal Analysis and Calorimetry》2009,98(2):423-428
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
8.
N. Voyer A. Soisnard Sara J. Palmer W. N. Martens R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,96(2):481-485
Zn-Al hydrotalcites and Cu-Al hydrotalcites were synthesised by coprecipitation method and analysed by X-ray diffraction (XRD)
and thermal analysis coupled with mass spectroscopy. These methods provide a measure of the thermal stability of the hydrotalcite.
The XRD patterns demonstrate similar patterns to that of the reference patterns but present impurities attributed to Zn(OH)2 and Cu(OH)2. The analysis shows that the d003 peak for the Zn-Al hydrotalcite gives a spacing in the interlayer of 7.59 ? and the estimation
of the particle size by using the Debye-Scherrer equation and the width of the d003 peak is 590 ?. In the case of the Cu-Al
hydrotalcite, the d003 spacing is 7.57 ? and the size of the diffracting particles was determined to be 225 ?.
The thermal decomposition steps can be broken down into 4 sections for both of these hydrotalcites. The first step decomposition
below 100°C is caused by the dehydration of some water absorbed. The second stage shows two major steps attributed to the
dehydroxylation of the hydrotalcite. In the next stage, the gas CO2 is liberated over a temperature range of 150°C. The last reactions occur over 400°C and involved CO2 evolution in the decomposition of the compounds produced during the dehydroxylation of the hydrotalcite. 相似文献
9.
Ray L. Frost Anthony W. Musumeci Thor Bostrom Moses O. Adebajo Matt L. Weier Wayde Martens 《Thermochimica Acta》2005,429(2):179-187
The thermal decomposition of hydrotalcites with chromate, molybdate and sulphate in the interlayer has been studied using thermogravimetric analysis coupled to a mass spectrometer measuring the gas evolution. X-ray diffraction shows the hydrotalcites have a d(0 0 3) spacing of 7.98 Å with very small differences in the d-spacing between the three hydrotalcites. XRD was also used to determine the products of the thermal decomposition. For the sulphate-hydrotalcite decomposition the products were MgO and a spinel MgAl2O4, for the chromate interlayered hydrotalcite MgO, Cr2O3 and spinel. For the molybdate interlayered hydrotalcite the products were MgO, spinel and MgMoO4. EDX analyses enabled the formula of the hydrotalcites to be determined. Two processes are observed in the thermal decomposition namely dehydration and dehydroxylation and for the case of the sulphate interlayered hydrotalcite, a third process is the loss of sulphate. Both the dehydration and dehydroxylation take place in three steps each for each of the hydrotalcites. 相似文献
10.
Veronika Vágvölgyi M. Hales W. Martens J. Kristóf Erzsébet Horváth R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2008,92(3):911-916
The understanding of the thermal stability of zinc carbonates and the relative stability of hydrous carbonates including hydrozincite
and hydromagnesite is extremely important to the sequestration process for the removal of atmospheric CO2. The hydration-carbonation or hydration-and-carbonation reaction path in the ZnO-CO2-H2O system at ambient temperature and atmospheric CO2 is of environmental significance from the standpoint of carbon balance and the removal of green house gases from the atmosphere.
The dynamic thermal analysis of hydrozincite shows a 22.1% mass loss at 247°C. The controlled rate thermal analysis (CRTA)
pattern of hydrozincite shows dehydration at 38°C, some dehydroxylation at 170°C and dehydroxylation and decarbonation in
a long isothermal step at 190°C. The CRTA pattern of smithsonite shows a long isothermal decomposition with loss of CO2 at 226°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of zinc
carbonate minerals 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. The CRTA technology offers a mechanism for
the study of the thermal decomposition and relative stability of minerals such as hydrozincite and smithsonite. 相似文献
11.
Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition
process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements.
A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation
and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous
hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition
processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were
estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic
analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate
the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for
the decarbonation process. 相似文献
12.
R. L. Frost A. W. Musumeci J. Theo Kloprogge M. L. Weier M. O. Adebajo W. Martens 《Journal of Thermal Analysis and Calorimetry》2006,86(1):205-209
The thermal decompositions of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer have been studied using thermogravimetry combined with mass spectrometry. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 11.1 and 10.9 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. XRD was also used to determine the products of the thermal decomposition. For the hydrotalcite decomposition the products were MgO, Fe2O3 and a spinel MgAl2O4. Dehydration and dehydroxylation take place in three steps each and the loss of cyanide ions in two steps. 相似文献
13.
Sara J. Palmer H. J. Spratt R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,95(1):123-129
Thermal analysis complimented with evolved gas mass spectrometry has been applied to hydrotalcites containing carbonate prepared
by coprecipitation and with varying divalent/trivalent cation ratios. The resulting materials were characterised by XRD, and
TG/DTG to determine the stability of the hydrotalcites synthesised. Hydrotalcites of formula Mg4(Fe,Al)2(OH)12(CO3)·4H2O, Mg6(Fe,Al)2(OH)16(CO3)·5H2O, and Mg8(Fe,Al)2(OH)20(CO3)·8H2O were formed by intercalation with the carbonate anion as a function of the divalent/trivalent cationic ratio.
XRD showed slight variations in the d-spacing between the hydrotalcites. The thermal decomposition of carbonate hydrotalcites
consists of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation and decarbonation
of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where the first step
is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting with the
interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding metal
oxides and spinels, including MgO, MgAl2O4, and MgFeAlO4. 相似文献
14.
Ray L. Frost Sara J. Palmer Laure-Marie Grand 《Journal of Thermal Analysis and Calorimetry》2010,101(3):859-863
Insight into the unique structure of layered double hydroxides (LDHs) has been obtained using a combination of X-ray diffraction and thermal analysis. Indium containing hydrotalcites of formula Mg4In2(CO3)(OH)12·4H2O (2:1 In-LDH) through to Mg8In2(CO3)(OH)18·4H2O (4:1 In-LDH) with variation in the Mg:In ratio have been successfully synthesised. The d(003) spacing varied from 7.83 Å for the 2:1 LDH to 8.15 Å for the 3:1 indium containing LDH. Distinct mass loss steps attributed to dehydration, dehydroxylation and decarbonation are observed for the indium containing hydrotalcite. Dehydration occurs over the temperature range ambient to 205 °C. Dehydroxylation takes place in a series of steps over the 238–277 °C temperature range. Decarbonation occurs between 763 and 795 °C. The dehydroxylation and decarbonation steps depend upon the Mg:In ratio. The formation of indium containing hydrotalcites and their thermal activation provides a method for the synthesis of indium oxide-based catalysts. 相似文献
15.
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
16.
Ray L. Frost Sara J. Palmer János Kristóf Erzsébet Horváth 《Journal of Thermal Analysis and Calorimetry》2010,101(1):73-79
Dynamic and controlled rate thermal analysis has been used to characterise synthesised jarosites of formula [M(Fe)3(SO4)2(OH)6] where M is Pb, Ag or Pb–Ag mixtures. Thermal decomposition occurs in a series of steps. (a) dehydration, (b) well defined
dehydroxylation and (c) desulphation. CRTA offers a better resolution and a more detailed interpretation of water formation
processes 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 water formation
reveal the subtle nature of dehydration and dehydroxylation. CRTA offers a better resolution and a more detailed interpretation
of the decomposition processes 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 separation of the dehydroxylation steps, since in these cases a higher energy (higher temperature)
is needed to drive out gaseous decomposition products through a decreasing space at a constant, pre-set rate. 相似文献
17.
Kathleen H. Bakon Sara J. Palmer Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2010,100(1):125-131
The mineral reevesite and the cobalt substituted reevesite have been synthesised and studied by thermal analysis and X-ray diffraction. The d(003) spacings of the minerals ranged from 7.54 to 7.95 Å. The maximum d(003) value occurred at around Ni:Co 0.4:0.6. This maximum in interlayer distance is proposed to be due to a greater number of carbonate anions and water molecules intercalated into the structure. This increase in carbonate anion content is attributed to an increase in surface charge on the brucite like layers. The maximum temperature of the reevesite decomposition occurs for the unsubstituted reevesite at around 220 °C. The effect of cobalt substitution results in a decrease in thermal stability of the reevesites. Four thermal decomposition steps are observed and are attributed to dehydration, dehydroxylation and decarbonation, decomposition of the formed carbonate and oxygen loss at ~807 °C. A mechanism for the thermal decomposition of the reevesite and the cobalt substituted reevesite is proposed. 相似文献
18.
19.
Anand Kumar Sharma Shyam Kumar Narender Kumar Kaushik 《Journal of Analytical and Applied Pyrolysis》1982,3(3):271-279
Beryllium titanyl oxalate tetrahydrate and beryllium zirconyl oxalate tetrahydrate were prepared in aqueous medium and characterized by elemental analyses, magnetic susceptibility measurements and IR spectral studies. The thermal behaviour of these compounds under non-isothermal conditions was investigated by thermogravimetric, derivative thermogravimetric and differential scanning calorimetric (DSC) techniques. The intermediates obtained at the end of the various thermal decomposition steps were identified on the basis of elemental analyses and IR spectral studies. The decomposition proceeds through three major steps, viz, dehydration of the hydrate, decomposition of the oxalate to carbonate and decomposition of the carbonate to oxide. The graphical method of Coats and Redfern was employed to calculate kinetic parameters such as apparent activation energy and order of reaction. Heats of reaction for the different decomposition steps were calculated from the DSC curves. 相似文献
20.
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