The lower Permo-Triassic sediments of the Maláguide Complex contain abundant dickite. Whole rocks were studied by optical microscopy, scanning electron microscopy, and X-ray powder diffraction. The 2–20 µm and < 2 µm size fractions were extracted and analyzed by scanning and transmission electron microscopy, X-ray powder diffraction, infrared spectroscopy, differential thermal analysis, and thermogravimetry.

In the coarse-grained samples, the 2–20 µm size fraction consisted of well-crystallized dickite associated with minor quantities of kaolinite, illite, quartz, and hematite. XRD patterns of the fine-grained samples and the <2 µm fractions showed the existence of well-crystallized minerals in which several reflections of dickite (11l, 02l) were absent and the 132/13$\bar 2$ reflections were shifted. These patterns suggest the presence of an intermediate member between well-crystallized dickite and well-crystallized kaolinite. Only locally high-order reflections are present at 10.5 Å and 18–22 Å. DTA and IR data agree with those from XRD.

The observed compositional and structural variations are a function of the lithology and the particle size of the sample. The sequence kaolinite → kaolinite/dickite → dickite is proposed for the development of these materials during Alpine metamorphism.

A series of reduced-charge (RC) hectorites were prepared by multiple heat (250°C) treatments of Mg-saturated hectorites (SHCa-1 ). Cation exchange capacity (CEC) measurements and alkylammonium exchange indicated that a decrease in layer charge occurred with each Mg-250 treatment. Chemical analyses showed that decreases in structural Li and increases in structural Mg contents coincided with charge reduction. Fluorescence measurements of adsorbed quinoline indicated that the hectorite surface was acidified during charge reduction; hydroxyl group deprotonation is a possible source for the acidity. Fourier transform infrared spectra (FTIR) indicated that the Mg-250 treatment induced the loss of structural Li and shifted the SiO stretch band to a position similar to that in talc. The relative intensities of the OH and SiO stretch bands in FTIR spectra suggest that some of the hydroxyl groups in hectorite were lost, possibly by deprotonation. However, thermogravimetric data (TG) reveal no significant difference in the hydroxyl contents of the hectorites.

The FTIR spectra, CEC, layer charge, chemical, and TG data all supported the view that Mg substitution for octahedral Li occurred which resulted in a more “talc-like” structure. Charge reduction in smectites is evidently a general phenomenon and can be induced by heat treatment with the proper exchangeable cation. The ability to reduce the charge of hectorites makes it possible to prepare a series of clays which vary in charge but lack structural Fe. Such RC smectites should be suitable for expandable clay mineral studies which utilize spectroscopic techniques that are sensitive to Fe content.

Synthetic goethites studied by high-resolution thermogravimetry (HRTGA) show variability in surface characteristics and structural stability as a function of aging conditions. Goethites were synthesized at either pH 6 or 11, at temperatures of 40 or 70°C, and in the presence or absence of sorbed Mn or Pb. Data from HRTGA analysis revealed at least four distinct weight-loss events near goethite dehydroxylation that relate to 1) three events involving the evolution of water associated with surface Fe-O functional groups and 2) bulk dehydroxylation of goethite during transformation to hematite. The relative mass of evolved surface and bulk structural water was related to the predominant particle morphology as determined by transmission electron microscopy (TEM). Differentiation of surface and bulk decomposition reactions allowed the identification of bulk structural dehydroxylation. Goethite crystallin-ity, estimated by the bulk dehydroxylation temperature, appeared to depend on the kinetics of crystallization. This trend was most evident for systems aged at pH 11 and 40°C. Greater concentrations of coprecipitated Mn or Pb dramatically improved goethite crystallinity as indicated by higher dehydroxylation temperatures and smaller widths of the (110) Bragg reflection. Comparison of bulk dehydroxylation temperatures for these samples to other preparations suggests that structural defects predominated over the effects of particle size and Mn/Pb substitution in determining goethite thermal stability. A conceptual model is proposed to account for the disparate dehydroxylation profiles displayed by goethites of varying crystallinity.

Li+, Na+, Ca2+, Sr2+, Cu2+, or Zn2+-saturated samples of a cis-vacant montmorillonite from Linden, Bavaria, were heated to temperatures between 200–700°C. Half of each heated sample was subsequently autoelaved under steam at 200°C (∼1.5 MPa) to promote rehydroxylation. The smectites were characterized by cation-exchange capacity (CEC), determination of exchangeable cations, infrared (IR) spectroscopy, and thermoanalytical investigations of evolved water in a thermobalance linked with a mass spectrometer.

Changes in the montmorillonite structure and dehydroxylation behavior are related to three respective mechanisms: type of the interlayer cation, interlayer cation radius, and the movement of the interlayer cation. The migration of the smaller Li+, Cu2+, and Zn2+ ions after heating produces a strong reduction of CEC due to the Hofmann-Klemen effect before the initiation of dehydroxylation. Thereafter, the CEC of these smectites remains constant over a large temperature interval during dehydroxylation. After rehydroxylation, Cu2+ and Zn2+-rich samples release 16–23 meq/100 g of Mg2+ from the structure. No Mg2+ release is observed for the Li+-rich montmorillonite. Also the dehydroxylation behavior after rehydroxylation differs between the Cu2+, Zn2+, and Li+-rich samples. The mass curves of the evolved water during thermoanalysis of the rehydroxylated Cu2+ and Zn2+-rich smectites show a peak doublet between 480–700°C. For the Li+, Na+, Ca2+, and Sr2+-rich montmorillonites, the second peak disappeared and a third peak at ∼760°C developed after rehydroxylation. The resulting structure after rehydroxylation of all samples is celadonite-like.

Emanation thermal analysis (ETA), based on radon release measurements from previously labeled samples, was used for the first time in the characterization of the thermal behavior of natural Mg2+-vermiculite (Santa Olalla, Huelva, Spain) and of Na+- and ${\text{NH}}_4^{+}$-exchanged vermiculite samples. In addition, vermiculite samples subjected to a chemical treatment with an aqueous solution of (NH4)2SiF6 and partially or totally re-saturated with Na+ ions were also investigated by ETA. The ETA results of natural Mg2+-vermiculite, Na+-vermiculite and ${\text{NH}}_4^{+}$-vermiculite gave supplementary information about microstructure changes of the samples observed under dynamic heating conditions. The method has proved to be very useful for characterization of microstructure changes due to modification in the interlayer space of samples during the heat treatment. The crystallization of vermiculite into new phases, such as enstatite (for ${\text{NH}}_4^{+}$-vermiculite and Mg2+-vermiculite) and forsterite (for Na+-vermiculite) was also observed by ETA.

The search for signs of life is a major objective in the exploration of Mars. Of particular interest are chemical biosignatures such as biomolecules. However, molecular biosignatures are susceptible to extreme environmental conditions such as heat, ionising radiation and strong oxidants. Therefore, a knowledge of the stability of possible biosignature molecules under present and past conditions on Mars is important, as well as the nature of possible alteration products. In the light of the long volcanically active history of Mars, we have studied the thermal behaviour of selected biological compounds, namely, haemin (an iron porphyrin closely related to the haem prosthetic group), cytochrome c (a small protein) and lecithin (a mixture of phospholipids). Samples were exposed to temperatures up to 900°C under an inert atmosphere of nitrogen, either in neat form or in mineral matrices. The matrix materials used were sodium chloride, gypsum (CaSO4 ⋅ 2H2O), Ca-montmorillonite (STx-1b), the Martian regolith simulant JSC Mars-1A and some mixtures thereof. Key results are: (1) The onset of significant decomposition for haemin, cytochrome c and lecithin occurs around 240°C. At slightly higher temperatures the disappearance of all characteristic infrared spectral bands indicates complete decomposition and loss of the primary biosignatures. (2) Haemin stoichiometrically releases CO2 and HCl during the initial thermal decomposition phase, at the end of which the iron porphyrin core is still intact. High-temperature products of haemin include graphite, α-iron and cementite (Fe3C). (3) Neat lecithin forms long-chain polyphosphates at 500°C, whereas lecithin‒NaCl mixtures form diphosphate (pyrophosphate). As these anions are absent and rare, respectively, in minerals, they may potentially serve as secondary biosignatures. (4) Heating a mixture of NaCl and JSC Mars-1A at 800°C in the presence of lecithin produces the aluminosilicate mineral sodalite (Na8[AlSiO4]6Cl2), which however appears to be of limited use as a secondary biosignature.

An unusual occurrence of palygorskite was found near Montestrutto, lower Val d'Aosta (Italy), within an eclogite-facies leucogneiss of the Sesia-Lanzo zone. Under the optical microscope the mineral appears as a felt of fibres hundreds of μm long and a few μm thick. SEM observation proved each filament to be a bundle of smaller but remarkably long fibres (length mostly 15–20 μm and thickness <1 μm). EDS and TGA showed a water content [zeolitic H2O ( ≅ 6%) + structural OH2 (≅8%) + framework OH (≅2%) ≅l6 wt.%] lower than average (≅20 wt.%). Structure refinement by the Rietveld method confirmed the clay dioctahedral character and coexistence of two polymorphs, monoclinic [77.4(4)%] and orthorhombic [22.6(6)%], the latter showing anomalous variations of some cell parameters [c shortens to 5.138(3) and a lengthens to 12.903(7) Å]. The high crystallinity of this palygorskite suggests that it formed under low-T hydrothermal conditions due to interaction between Mg-rich hydrous fluids, derived from mantle ultramafics, and Al-rich continental rocks. Predominance of unusually long fibres (>5 μm) causes the Montestrutto palygorskite to be potentially carcinogenic.

The thermal decomposition of caledonite has been examined by simultaneous differential thermal analysis, thermogravimetry and mass spectrometry. Structural H2O and CO2 are liberated endothermically between 300 and 400°C leaving a residue of lead sulphate, oxysulphate, and Cu(I) and Cu(II) oxides. A series of sharp endothermic peaks between 850 and 950°C correspond to phase transition and melting reactions of the PbO-PbSO4 mixture. The sulphate anion breaks down above 880 °C. Mass spectra of the gaseous decomposition products show SO2, SO, and O2, although SO is an artefact arising from ion fragmentation of the SO2 within the mass spectrometer. The residue at 1060 °C is composed predominantly of 2PbO · PbSO4 and Cu(I) and Cu(II) oxides.

The dehydration of gypsum CaSO4.2H2O has been studied, at negligible water vapour pressure, by in situ infrared (IR) spectroscopy and by thermogravimetry to determine whether intermediate phases (CaSO4.nH2O) exist, other than the hemihydrate with n=0.5, and also to compare the mechanism of the dehydration process when measured by two techniques with very different correlation lengths. Thermogravimetry shows an apparently continuous water loss with an activation energy of 90.3 kJ.mol−1, with no changes in the activation energy as a function of the degree of dehydration. IR spectroscopy on the other hand, clearly shows the existence of three discrete phases, gypsum CaSO4.2H2O, hemihydrate CaSO4.0.5H2O and γ-CaSO4, with nucleation of each successive phase as dehydration proceeds. There is no evidence to suggest the presence of phases with any intermediate water content.

Hybrid material based on halloysite nanotubes (HNTs) and sodium perfluorooctanoate (NaPF8) was used as a consolidant for paper treatment. The consolidation efficiency was determined by thermogravimetry as well as by paper grammage determination. Morphological analysis of the treated paper was performed by means of scanning electron microscopy while the effect of modified HNTs on the thermal behaviour of the cellulose fibres was investigated by differential scanning calorimetry which determined the combustion enthalpy of the paper.Water contact angle measurements were performed to study the paper wettability. The physico-chemical properties investigated (mesoscopic structure, thermal stability and wettability) of the treated paper were correlated successfully with the consolidation loading and, consequently, to the affinity between the fluorinated modified HNTs and the fibrous cellulose structure. This study proposes a new green protocol for paper consolidation based on natural tubular nanoparticles with a flame retardant effect.

The thermal and mechanical behavior, the water uptake (WU), and water diffusion coefficient of sulfonated poly(ether ether ketone) (SPEEK) membranes annealed at 180 °C for different times were explored by high-resolution thermogravimetric analysis, mechanical tensile tests, dynamic mechanical analysis, and WU measurements. The mechanical and thermal stability increased with the thermal treatment time, i.e., with the degree of crosslinking. The effect of residual casting solvent, dimethyl sulfoxide (DMSO), on the WU within SPEEK was probed. In presence of residual DMSO, crosslinked SPEEK exhibited higher water sorption at low and medium relative humidity (RH), and lower water sorption at high RH. These membranes have properties well adapted to fuel cell applications.

To date, there are limited studies on loggerhead turtle (Caretta caretta) eggshell ultrastructure and its elemental composition. Eggs were collected from turtle nests immediately after oviposition and post hatching. Three eggshell layers were recognized. The outer calcareous layer consists of loose nodular units of different shapes and sizes with loose attachment between the units, resulting in numerous spaces and openings. Each unit consists of CaCO3 crystals in aragonite (99%) and calcite (1%). The middle layer has several strata with numerous openings connecting the calcareous and the inner shell membrane. Crystallites of the middle layer are a mix of amorphous material with aragonite (62%) and calcite (38%). The inner shell membrane has numerous reticular fibers mixed predominantly with halite (NaCl) and small amounts of sylvite. Thermogravimetry analysis of the calcareous showed a low exothermic peak at 425°C, which corresponds to a transitional phase from aragonite to calcite. A high endothermic peak at 814°C corresponds to decomposition of calcite CaCO3 to CaO and CO2. Electron diffraction confirmed the presence of NaCl halite crystal. A significant difference was found in the percentage of elements and crystal configurations in the three layers. This study has value in assessing the emergence success in this endangered species.

L'objectif de l'étude est de caractériser thermiquement des nouveaux matériaux, utilisés dans les protections thermiques : les matériaux thermo-dégradables. À cet effet, des moyens de mesure répondant aux spécificités, intrinsèques et d'utilisations, des matériaux thermo-dégradables ont été développés par l'onera.