Authors:L. Pérez-Maqueda, J. Poyato, and J. Pérez-Rodríguez
The thermal decomposition of the ammonium exchanged vermiculite takes place in three steps. A strong correlation exists between
the mass loss of ammonia and water suggesting a simultaneous release. It is proposed that proton transfer from the ammonium
ion to the hydroxyl units results in this simultaneous release. This behaviour could be explained by a mechanism where a resulting
proton, produced by the release of ammonia out of ammonium cation, combines with a structural hydroxyl to form water. Sonication
produces a substantial reduction in the particle size of the vermiculite sample. Thus, the macroscopic particle size of the
untreated material is drastically reduced to the micrometers range while the structure as assayed by XRD remains unchanged.
The particle size reduction produced by the sonication treatment modifies the thermal decomposition profile, mainly the mass
percentages of the different steps.
Authors:A. Duran, L. Perez-Maqueda, J. Poyato, and J. Perez-Rodriguez
Roman ancient mortars have been widely studied, in connection with both diagnosis and application required for restoring.
Thermoanalytical experiments performed on mortars from Pompeii and Herculaneum provided a very good understanding of the technology
employed. The mortars from Pompeii were obtained by the proper mixing of lime and marble grains while mortars of Herculaneum
by lime and silicates compounds. The position of the endothermic peak of calcite decomposition showed important variations
in the different samples studied, which was assigned to the different crystallinity and particle sizes. Experiments under
CO2 flow confirmed the presence of magnesium calcium carbonates.
Authors:J. Poyato, L. Perez-Maqueda, M. Jimenez de Haro, J. Perez-Rodriguez, J. Šubrt, and V. Balek
Emanation thermal analysis (ETA), DTA, SEM, and XRD were applied for the characterization of the effect of Na+ and NH
ions used for saturation of natural Mg-vermiculite on the microstructure during heating. The microstructure changes were characterized by ETA under in situ conditions of samples heating in air in the temperature range 20–1300°C. It was found that Na+ and NH
ions have a significant effect on the microstructure changes during heat treatment of the natural Mg-vermiculite sample saturated with these ions. For Mg-vermiculite and Na+ saturated vermiculite thet emperatures of the onset of the collapse of interlaminar space were determined by ETA. Differences in thermal stability of the microstructure of dehydrated vermiculite samples were observed by ETA: the microstructure of dehydrated Mg-vermiculite, and Na-vermiculite was found stable until 650 and 350°C, respectively. For dehydrated NH4-vermiculite the annealing of the microstructure started at 730°C. The onset temperatures of the formation of new crystalline phases were indicated by ETA as the increase of the radon release rate. The onset temperatures of the ordering of the vermiculite structure or sintering under presence of the glassy stage (for Na-vermiculite), respectively, were determined from the decrease of the radon release rate. The ETA results were confirmed by DTA, XRD and SEM.
Authors:V. Balek, J. Pérez-Rodríguez, L. Pérez-Maqueda, J. Šubrt, and J. Poyato
Thermal behaviour of natural vermiculite (Santa Olalla, Huelva, Spain) was investigated by TG, DTA, emanation thermal analysis
(ETA) and high temperature XRD on heating in the temperature range from 30 to 1100°C before and after vibratory mill grinding.
Microstructure changes of natural and ground vermiculite samples were characterized by using ETA under in situ conditions
of heating. By comparing the ETA and XRD results it was demonstrated that a decrease of radon release rate measured by ETA
characterized the decrease in the interlayer spacing of the vermiculite samples that followed the dehydration.
Authors:Veronica Ramírez-Valle, A. Lerf, F. Wagner, J. Poyato, and J. Pérez-Rodríguez
We have studied the synthesis of polypyrrole-clay nanocomposites by the in situ oxidative polymerization of pyrrole in the
interlayer space of vermiculites with different layer charges from Santa Olalla and Ojén, Spain. Moreover, the influence of
different interlayer cations (Na+, Mg2+, Fe3+) on the interaction between pyrrole and the vermiculties was studied. The resulting materials were characterized by means
of DTA-TG, XRD, FTIR and Mössbauer spectroscopy. In all samples polymerization of pyrrole was observed, presumably triggered
by the structural iron. In most cases it was found to be externally deposited. An uptake of pyrrole in the interlayer space
and PPy formation is observed in the case of the Fe3+-intercalated Ojén vermiculite, which has a lower layer charge than the Santa Olalla vermiculite.
Authors:L. Pérez-Maqueda, V. Balek, J. Poyato, J. Pérez-Rodríquez, J. Šubrt, I. Bountsewa, I. Beckman, and Z. Málek
Emanation thermal analysis (ETA), thermogravimetry, DTA and XRD were used in thermal characterization of natural vermiculite
(Santa Olalla, Huelva, Spain) and of Na+- and - exchanged vermiculite samples during heating in air in the range 25-1100C. A good agreement between the results of
these methods was found. Changes in the radon release rate measured by ETA, which reflected the decrease and collapse of the
interlayer space after the release of water as well as the formation of new crystalline phases were evaluated using a mathematical
model. The model used for the evaluation was found suitable for the quantitative characterization of microstructure changes
during in situ conditions of heating of vermiculite samples.
Authors:V. Balek, L. Pérez-Maqueda, J. Poyato, Z. Černý, V. Ramírez-Valle, I. Buntseva, and J. Pérez-Rodríguez
The effect of grinding
on thermal behavior of pyrophyllite and talc as commonly used ceramic clay
minerals was investigated by DTA, TG, emanation thermal analysis (ETA), B.E.T.
surface area (s.a.) measurements, X-ray diffraction (XRD) and scanning electron
A vibratory mill was used in this study, grinding
time was 5 min. It was found that the grinding caused an increase in surface
area and a grain size reduction of the samples. From TG and DTA results it
followed that grinding caused a decrease of the temperature at which the structure
bound OH groups released. The formation of high temperature phases was enhanced
with the ground samples. For the ground talc sample the crystallization of
non-crystalline phase into orthorhombic enstatite was observed in the range
of 800°C. For ground pyrophyllite a certain agglomeration of grains was
observed in the range above 950°C. Moreover, for both clays the ETA characterized
a closing up of subsurface irregularities caused by grinding as a decrease
of the emanation rate in the range 250–400°C. The comparison of
thermal analysis results with the results of other methods made it possible
to better understand the effect of grinding on the ceramic clays.
Authors:L. Pérez-Maqueda, V. Balek, J. Poyato, J. Šubrt, M. Beneŝ, V. Ramírez-Valle, I. Buntseva, I. Beckman, and J. Pérez-Rodríguez
Thermal behavior of talc samples (from locality Puebla de Lillo, Spain) were characterized by emanation thermal analysis (ETA),
DTA and TG. The ETA, based on the measurement of radon release rate from samples, revealed a closing up of surface micro-cracks
and annealing of microstructure irregularities of the talc samples on heating in the range 200–500°C.
For ground talc sample a crystallization of non-crystalline phase formed by grinding, into orthorhombic enstatite was characterized
as a decrease of radon mobility in the range 785–825°C and by a DTA exothermal effect with the maximum at 830°C. ETA results
characterized the microstructure development of the talc samples on heating and served to evaluate their radon mobility and
transport properties on heating and cooling. Transport properties of the talc samples were evaluated by using ETA experimental
data measured during heating to 600 and 1300°C, respectively, and subsequent cooling to room temperature.