The aim of this work was to demonstrate, by means of thermoanalytical methods (DTA, TG and DTG), that sepiolite from Vallecas
(Spain) is mixed with another mineral which is difficult to determine by X-ray diffraction and chemical analysis in routine
The low temperature endothermic effect and weight loss shown by this material can be separated into two effects: one from
sepiolite and the other from an accompanying mineral-identified as a magnesium smectile. The concentration of this latter
mineral in the mixture attained up to 15%.
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:F. Franco, L. Pérez-Maqueda, and J. Pérez-Rodríguez
Kaolinites from well-known sources (KGa-1 and KGa-2) were used to study the influence of the particle-size reduction on the
dehydroxylation process. Size reduction of particles was obtained by ultrasound treatment to avoid the effect of the progressive
amorphization of the structure, which takes place with the traditional grinding treatment. The particle-size reduction causes
an increase of the mass loss between 140 and 390°C attributed to the loss of the hydroxyl groups exposed on the external surface
of kaolinite; a shift to lower temperatures of the endothermic effect related with the mass loss between 390 and 600°C; and
a shift of the end of dehydroxylation to lower temperatures. The first modification can be explained by an increase of the
number of hydroxyls exposed on the external surface of kaolinite which is proportional to the new surface generated in the
particle reduction process, whereas the shift of the dehydroxylation to lower temperatures is related to the reduction of
the dimensions of the particles which favour the diffusion controlled mechanisms. Comparing between the DTA curves to the
TG curves of the studied samples shows that the observed modifications in the thermal properties induced by the particle-size
reduction are greater for the low-defect kaolinite. The intensity of these modifications depends on the effectiveness of the
Authors:J. L. Perez-Rodriguez, A. Duran, and L. A. Perez-Maqueda
In this study, the decomposition behaviour of unaltered and altered dolomitic rock samples used in Cultural Heritage buildings was studied by simultaneous TG–DTA experiments at different atmospheres, X-ray diffraction in a high-temperature chamber, and evolved gas analysis. The components of dolomite rock samples and hydrated calcium oxalate formed during the alteration processes of the rocks were characterized, and the decomposition mechanisms of these components were determined. The TG–DTA experiments carried out at CO2 atmosphere were used to determine the carbonate compounds in the rock samples. The TG–DTA study characterized the presence of organic compounds formed during the biological degradation of the rock samples, possibly responsible of the hydrated calcium oxalate formation.
Authors:J. Galán, A. Gonzáles-Pérez, J. Del Cactillo, and J. Rodríguez
Electrical conductivity of aqueous solutions of dodecylpyridinium chloride and bromide have been determined. From these data
the critical micelle concentration (cmc) was determined. The thermal properties as standard Gibbs free energy, enthalpy and entropy of micellization was estimated
from a uncharged-phase separation model and enables to obtain another properties like heat capacity of micellization and the
relevant parameters in the minimum of temperature dependence of cmc. The enthalpy-entropy compensation was shown for the studied compounds.
Authors:J. Pérez, F. Rodríguez, M. Alonso, M. Oliet, and J. Domínguez
The curing kinetics of lignin-novolac and methylolated lignin-novolac resins were studied using non-isothermal methods employing
differential scanning calorimetry (DSC) at different heating rates. The Belichmeier, Ozawa and Kissinger methods were applied,
which give the kinetic parameters of the curing process studied. In addition, the model-fitting Coats-Redfern method was used
to analyze the experimental data. The kinetic study evaluated the effect of the lignin (softwood ammonium lignosulfonate),
methylolated or not, on the resin curing process. Results for lignin-novolac and modified lignin-novolac resins were compared
with a commercial novolac resin as a reference. When lignosulfonate is modified by methylolation and is incorporated in the
novolac resin, there is an important reduction in activation energy. The lignin-novolac showed slightly higher values of activation
energy than methylolated-lignin resins, but lower values than commercial resins. This behavior has been attributed to the
extra methyol groups introduced by lignosulfonate.
Authors:Ewa Stepkowska, M. Aviles, J. Blanes, and J. Perez-Rodriguez
The low temperature
of decomposition of some calcium carbonates and the bending of the TG curves
of hydrated cement between 500 and 800°C suggested the presence of some
complex compound(s), which needed complementary investigation (XRD, TG). Stepwise
transformation of portlandite (and/or lime) into calcium carbonate, with intermediate
steps of calcium carbonate hydroxide hydrates (CCH-1 to CCH-5), was indicated
by the previous study of two OPC.
This was checked here on four
cements ground for tg=15,
20, 25 and 30 min and hydrated either in water vapour, successively at RH=1.0,
0.95 and 0.5 for 2 weeks each (WR1, WR2 and WR3, respectively) or as mortars
in liquid water (1m), followed by WR as above. The d spacing of portlandite
was confirmed to vary: here between the lowest and the highest standard values.
The diffractograms of n=32 different samples
were analyzed for presence of standard CCH peaks, generally slightly displaced.
These were: CCH-1 [Ca3(CO3)2(OH)2]: N=11 peaks, of three different d[hkl] spacings, CCH-2 [Ca6(CO2.65)2(OH657)7(H2O)2]: N=10 for two d[hkl], CCH-3 [Ca3(CO3)2(OH)2·1.5H2O]: N=14 for five d[hkl], CCH-4,
ikaite [CaCO3(H2O)6]: N=13 for six d[hkl], CCH-5[CaCO3(H2O)]: N=15 for five d[hkl]. Thus the most probable is the presence of the
last three. The stepwise transformation of Ca(OH)2
into CaCO3 was confirmed:
portlandite (varying d)→CCH-1→CCH-2→CCH-3→CCH-4→CCH-5→CaCO3
The content of CCH was the highest at tgr=15
min, decreasing down to tgr=25
min and increasing slightly at 30 min, as inferred from the number of the
peaks observed. After cement powder hydration at RH=1.0 (WR1) peak number
increased gradually from CCH-1 to CCH-5, whereas in the hydrated mortar (1m)
the peak number decreased from CCH-1 to CCH-5, indicating the respective progress
of the carbonation reaction.