Authors:J. L. Pérez-Rodríguez, F. Franco, V. Ramírez-Valle, and L. A. Pérez-Maqueda
The differences on the thermal behaviour (DTG-DTA) of antigorite sample measured before and after sonication have been studied.
Sonication treatment produces negligible changes in the structure of the material but substantial textural modifications.
These modifications produce changes in the thermal behaviour of antigorite sample. Thus, it has been observed a decrease in
the dehydroxylation temperature as measured by DTG and DTA effects. For sonication treatments longer than 20 h, two new effects
of dehydroxylation are observed, the intensity of these two new effects increases with the sonication time showing a modification
in the release of structural OH. It has been also observed that the formation of forsterite takes place simultaneously with
the dehydroxylation of the antigorite. The high temperature exothermic effect is due to the recrystallization of forsterite
and not to the formation of forsterite as traditionally assumed. Modifications in the thermal dehydroxylation of antigorite
observed in this study are related to the pronounced decrease in particle size obtained by sonication.
Authors:M. Franquelo, M. Robador, V. Ramírez-Valle, A. Durán, M. Jiménez de Haro, and J. Pérez-Rodríguez
Roman ceramics of two hydraulic mortars used to build the pond and water channel of Mithraeum house from Mérida (Spain) have
been studied. The sizes of the ceramic fragments found were different in both of the samples studied, showing different behaviour
in the reactions with the lime. The X-ray diffraction of the ceramic shows the presence of quartz, mica (biotite), anorthite
and hematite accompanied by amorphous phase, being observed scarce vitrification. The presence of mica confirms a firing temperature
for manufacturing the ceramic below 900°C. In one of the ceramics studied, X-ray diffraction did not show calcite. However,
in the FTIR appear bands that could be assigned to carbonates absorptions and likewise, carbonates were identified in the
DTA-TG curves. Ca and small quantities of Si and Al were also identified by SEM-EDX on the surface of the pores that could
be due to an amorphous phase formed in the reaction of lime with the Si and Al of the ceramic. On the other hand, in other
ceramic samples carbonates (about 10%) were detected. The carbonates have been found filling the pores, sometimes accompanied
by a new calcium-aluminium-silicate phase produced by the reaction between the lime and the amorphous phase of the ceramic.
The carbonates and the new phases formed inside the pores are responsible for the decrease of the porosity and for the formation
of new phases during the heating of the ceramics.
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:V. Ramírez-Valle, M. Jiménez de Haro, M. Avilés, L. Pérez-Maqueda, A. Durán, J. Pascual, and J. Pérez-Rodríguez
Static and dynamic heating
of vermiculite samples from Santa Olalla, Huelva, Spain, saturated with different
cations, i.e. Na+, Cs+,
Ca2+, Ba2+ and Al3+,
have been studied. The characterization of the phases formed during heating
has been carried out by X-ray diffraction. The phases formed depend on the
cation present in the interlamellar position and the heating process. The
phases identified in the vermiculite samples saturated with different cations
and heated at different temperatures are the following: enstatite, forsterite,
spinel, cordierite, anorthite, pollucite, nepheline, coesite, celsian and
others various mixed silicates; also some dehydrated and amorphous phases
have been observed. On static heating, at the maximum temperature reached
in this work, the phases formed appear mixed with a glassy phase.
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.