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Journal of Thermal Analysis and Calorimetry
Authors:
Sara Palmer
,
J. Kristóf
,
Veronika Vágvölgyi
,
Erzsébet Horváth
, and
R. Frost

Abstract  

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.

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Abstract  

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.

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Journal of Thermal Analysis and Calorimetry
Authors:
Y. Zhao
,
R. Frost
,
Veronika Vágvölgyi
,
E. Waclawik
,
J. Kristóf
, and
Erzsébet Horváth

Abstract  

Yttrium doped boehmite nanofibres with varying yttrium content have been prepared at low temperatures using a hydrothermal treatment in the presence of poly(ethylene oxide) surfactant (PEO). The resultant nanofibres were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM images showed the resulting nanostructures are predominantly nanofibres when Y-doping is less than 5%; in contrast Y-rich phases were formed when doping was around 10%. The doped boehmite and the subsequent nanofibres/nanotubes were analyzed by thermogravimetric and controlled rate thermal analysis methods. The boehmite nanofibres produced in this research thermally transform at higher temperatures than boehmite crystals and boehmite platelets. Boehmite nanofibres decompose at higher temperatures than non-hydrothermally treated boehmite.

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Journal of Thermal Analysis and Calorimetry
Authors:
Veronika Vágvölgyi
,
R. Frost
,
M. Hales
,
A. Locke
,
J. Kristóf
, and
Erzsébet Horváth

Abstract  

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.

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Journal of Thermal Analysis and Calorimetry
Authors:
Veronika Vágvölgyi
,
M. Hales
,
W. Martens
,
J. Kristóf
,
Erzsébet Horváth
, and
R. Frost

Abstract  

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.

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Journal of Thermal Analysis and Calorimetry
Authors:
Veronika Vágvölgyi
,
Lisa Daniel
,
Caroline Pinto
,
J. Kristóf
,
R. Frost
, and
Erzsébet Horváth

Abstract  

The thermal decomposition of the clay mineral attapulgite has been studied using a combination of dynamic and controlled rate thermal analysis. In the dynamic experiment two dehydration steps are observed over the 20–114 and 114–201°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. Calculations show the amount of water in the attapulgite mineral is variable. Dehydration in the CRTA experiment occurs as quasi-isothermal equilibria. Dehydroxylation occurs as a series of non-isothermal decomposition steps. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of a clay mineral such as attapulgite 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 layers of attapulgite as the attapulgite is converted to an anhydride.

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