Talc Layers Research Articles

Thermal Decomposition Kinetics of Clinochlore at High Temperature and Its Implications

Abstract The dehydration kinetics of clinochlore were performed using a non-isothermal thermogravimetric analysis under a dynamic nitrogen atmosphere at ambient pressure. Clinochlore, with a grain size of 5–10 μm, was analyzed using heating rates of 2, 5, 10, 20, and 40 K/min at temperatures of up to 1260 K. Thermogravimetric data of clinochlore at different heating rates were modeled using the Kissinger method, Flynn-Wall-Ozawa method, and Coats-Redfern method. The dehydration of clinochlore is ascribed to the decomposition of brucite and talc layers. The dehydration temperature of the brucite layer is 730–920 K, which corresponds to a two-dimensional phase boundary model (R2) with an activation energy of 214.94 ± 7.79 kJ/mol and a pre-exponential factor of 12.52 ± 0.62 min−1. The dehydration temperature of the talc-like layer is 960–1140 K, which follows a two-dimensional diffusion model with an apparent activation energy of 419.49 ± 23.62 kJ/mol and a pre-exponential factor of 19.97 ± 1.76 min−1. Combined with the parameters obtained in this study, the fast dehydration of clinochlore can trigger earthquakes in the subduction zone.

Structure and Properties of Water in a New Model of the 10-Å Phase: Classical and Ab Initio Atomistic Computational Modeling

The 10-Å phase is an important member of the family of dense hydrous magnesium silicates (DHMSs) that play a major role in the water budget in the Earth’s upper mantle. Its nominal composition is usually written as Mg3Si4O10(OH)2·xH2O, and its structure is often described as layers of talc with some amount of water present in the interlayer space. However, its actual structure and composition and the detailed mechanisms of retaining H2O molecules within the mineral are not yet sufficiently known. In particular, more recent spectroscopic and diffraction data indicate the presence of Si vacancies in the tetrahedral silicate sheets of the 10-Å phase leading to the formation of Q2-type Si sites terminated by silanol groups. These silanols are, in turn, hydrogen bonded to interlayer H2O molecules. Here, we use classical and ab initio molecular dynamics (MD) simulations to compare the structures and properties of ideal and defect models of the 10-Å phase under ambient conditions. For classical MD simulations, the most recent modification of the ClayFF force field is used, which can accurately account for the bending of Mg–O–H and Si–O–H angles in the mineral layers, including the structural defects. The crystal lattice parameters, elastic constants, structure, and dynamics of the interlayer hydrogen bonding network for the model 10-Å phase are calculated and compared with available experimental data. The results demonstrate that the inclusion of Si vacancies leads to better agreement with crystallographic data, elastic constants, and bulk and shear moduli compared to a simpler model based on the idealized talc structure. The results also clearly illustrate the importance of the explicit inclusion of Mg–O–H and Si–O–H angular bending terms for accurate modeling of the 10-Å phase. In particular, the properly constrained orientation of the silanol groups promotes the formation of strong hydrogen bonds with the interlayer H2O molecules.

Studying the impact of synthetic silica and cross-linked polymethyl methacrylate as anti-blocking agents on the physical properties of electric cables

One of the major problems associated with the production process of cables is the tight adhesion between the insulation and jacket (blocking), which is resulted from electrostatic and Van der Waals interactions between the two polymer layers. It makes them difficult to separate without damaging the insulation. As a conventional approach, a talc layer is applied within the insulation and jacket interface to prevent the blocking between the jacket and insulation. However, maintaining a uniform talc layer is difficult, and the uneven distribution of talc particles produces a non-smooth surface. Therefore, the conventional talc layer method has limited efficiency in reducing the bocking. In this study, a surface modification was done for both the insulation and jacket using synthetic silica and crosslinked polymethyl methacrylate (PMMA). This study evaluated the effect of these two additives on other physical properties, including heat stability, insulation resistance, tensile strength, elongation at break, and pressure stability. This study reveals that the application of synthetic silica has successfully reduced the blocking between insulation and jacket and favorably contributed to increasing insulation resistance. The optimum levels of anti-blocking agents to be used in the insulation and jacket compound have also been estimated by this investigation.

Mechanism of olivine and glass alteration under experimental H2O-CO2 based supercritical gas: Application to modern and ancient Venus

Extreme conditions encountered in some geological contexts (deep serpentinization, interaction of Venus atmosphere with its basaltic surface, volcanic degassing) activate mechanisms and rates of silicate alteration that are poorly understood. In the present study, we investigate the mechanisms of mineral reactions in a natural geological system at high temperature, under conditions where the low solvation of cations by fluids likely promotes surface reactions such as surface diffusion and/or local recrystallization. We focus on vitreous glasses and olivine, reputed to be the most alterable phases in volcanic rocks, by reacting samples for one week in a Ni-based alloy experimental vessel. For the framework of our experimental study, we chose to apply the deep atmosphere conditions on Venus: 470 °C and 90 bar of reconstituted Venus-like gas. We also tested the effect of water (Early Venus or wet volcanic degassing) by adding water vapor at up to 320 bar total pressure. The mineral reactions affecting the samples were identified by a set of spectroscopic surface analyses of the altered samples: Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction in grazing incidence mode, X-ray Photo electron Spectroscopy and Raman spectroscopy.Samples of obsidian and tholeiitic glasses are found to be sensitive to a threshold water pressure, depending on glass composition, below which the reaction is limited to some elemental mobility in the glass (alkali enrichment, calcium loss) leading to a possibly more stable surface layer of tens to hundreds of microns. Above this threshold water pressure (ca. 50 bar H2O for the obsidian but >250 bar H2O for the tholeiitic glass), water promotes the depolymerization of the glass and the crystallization of stable minerals. This crystalline rim is less protective that the chemically modified layer.Olivine samples react differently depending on whether the olivine is isolated or included in a basaltic rock. In the latter case only, iron coatings are formed, which are identified as hematite, suggesting that this phase is not fed by olivine itself but rather by surface diffusion from neighboring Fe-rich phases. This supports the conclusions from experimental studies and orbital observations on the short-term visibility of unaltered olivine in Venus lava flows: such a coating is enhanced when Fe-bearing minerals are in the proximity of olivine. Under high water vapor pressure, Fe-bearing talc (and not serpentine) forms by a likely topotactic reaction that also incorporates silica from the gas. This talc layer may form a protective layer, implying that serpentinization of ultramafic rocks at high temperature may not be as prevalent as one might think in a gas-dominated system like the Early Venus surface.

Fluid pathway evolution and mass transfer during Mg-dominated mineral transformations

Understanding the alteration of oceanic crust is of fundamental importance to unraveling geochemical and physicochemical processes on Earth. Mineral transformation during geological processes can result in mass transfer, changes in solid mass and volume while generating pathways that enhance fluid access to more remote areas of the crust and mantle. In this study, two hydrothermal experiments were conducted at different conditions, one at 160 °C and ~ 6 bar, and the other at 500 °C and 5 kbar. The reaction products were characterized using XRD and HRTEM. Saponite and talc were identified as products by XRD patterns in low- and high-temperature systems, respectively. This is consistent with HRTEM observations, in which layers with a thickness of ~1.2 and 1.0 nm were observed in products. These results confirm the successful transformation of brucite to saponite at 160 °C, and saponite to talc at 500 °C. HRTEM images clearly show the direct connection between brucite layers and saponite layers and between saponite layers and talc layers, suggesting that solid-state transformation is the main mechanism in both reaction processes. Based on the structural differences, the transformation from brucite to saponite undergoes as much as a 1.6-fold increase in volume and created expandable interlayer spacings of ~0.55 nm, which allows for fluid transport. Further conversion of saponite to talc at 500 °C results in a volume decrease. Inter-particle porosities are created during the progressive reduction of the layer spacing commencing from the outer edges of saponite crystals, potentially enhancing fluid flow. Therefore, the observation that mineral transformations proceed from the edges to interiors of the minerals suggests that fluid pathways at the nanoscale were generated during mineral transformations. The thermostability of the structural water was enhanced through mineral transformations, although water content decreased from ~30.9 wt% to ~4.7 wt%, with implications for water transfer processes in a down-going plate from the surface into Earth's interior. Also, ~2.0 wt% exchangeable cations were sequestered and preserved in the interlayer spaces during the transformation of brucite to saponite. These exchangeable cations, however, were ultimately expelled with the reduction of interlayer spacing during the conversion of saponite to talc. Thus, mineral transformations may have significant effects on mass transfer in various geological processes.

Effective removal of 2,4,6-trichlorophenol by FeSx/talc composite under microwave

Microwave-enhanced degradation is an effective method to remove organic contaminants from aqueous solutions. In this study, we prepared a novel iron sulfide/talc composite. Under microwave irradiation, the hydroxyl and sulfate radicals are rapidly released from the as-prepared FeSx/talc composite (TF), which could remove 106.8 mg/(min·g) of 2,4,6-TCP in 4 min. The maximum chemical oxygen demand (COD) removal was more than 90.1% when the concentration of TF is 1 g/L and the irradiation time of microwave radiation was 5 min, significantly higher than that treated by FeSx particles or talc. It is attributed to the synergetic effect between talc layers and FeSx particles, which greatly enhances the catalytic degradation performance of the composite for organic pollutants. With the advantages of low cost, high physico-chemical stability, and high reusability, this novel FeSx/talc composite could be a potential treating material for rapidly remove organic pollutants from wastewater.

Serpentinization of olivine–gabbro in Central Indian ridge: Insights into H2 production during alteration in lower oceanic crust and sustenance of life at slow–spreading ridges

ABSTRACT We investigated the textural-compositional characteristics across olivine interfaces in variably serpentinized olivine-gabbro samples dredged from the “Vityaz Megamullion” in the northern Central Indian Ridge (CIR). The results are used to understand the role temperature and different chemical properties in infiltrating fluid (e.g. seawater/hydrothermal solution) on the pattern of compositional evolution during progressive alteration in olivine-gabbro. The development of two distinct types of replacement rims (i.e. type-1 and type-2) are conspicuous in our samples. Type-1 pseudomorphic mesh rim, that formed within individual olivine grains, occurs in two different textural modes: (a) as successive layers of Fe-rich (XMg = 0.89 ± 0.02) lizardite ± magnetite, clay and calcite towards the olivine interface, and (b) as homogeneous rim of comparatively Fe-poor lizardite (XMg = 0.93 ± 0.01) ± magnetite. Replacement of olivine by talc and chlorite is evident towards the clinopyroxene and plagioclase grain boundaries, respectively. Local precipitation of clay minerals is also observed at the inner interface of talc layer and within intra-olivine fractures. Type-2 rim is characterized by the development of inter-olivine Mg-rich lizardite (XMg = 0.97 ± 0.01) + magnetite layer cross-cutting type-1 veins; thus, post-dates type-1 replacement. The process of CIR olivine-gabbro alteration records at least two stages of serpentinization. Any presence of brucite has not been observed, suggesting relatively higher silica activity at reacting interfaces during olivine-gabbro alteration than that of peridotite serpentinization at temperature log a SiO 2 aq , log a H 2 O , log a Al 3 + a H + 3 and log a Ca 2 + a H + 2 ) and/or temperature during progressive alteration of olivine. Type-2 replacement attests greater extent of magnetite precipitation as compared to type-1 serpentinization, which may indicate increasing fluid-rock ratio in the system and/or decreasing magnitude of Fe intake into serpentine structure with ongoing alteration. Importantly, it implies release of H2(aq) during olivine-gabbro serpentinization, which is consistent with that observed during peridotite serpentinization. This corroborates that alteration in the deepest part of the oceanic crust may play an important role on the sustenance of biosphere in slow-spreading ridges.

Arsenic-Bearing Serpentine-Group Minerals: Mineral Synthesis with Insights for the Arsenic Cycle

AbstractWhen present at elevated levels in drinking water, arsenic is toxic, and magnesian clays are gaining recognition as a source of elevated arsenic in groundwater. In the crust and upper mantle of Earth, arsenic incorporation into clay minerals is influenced by geochemical conditions associated with hydrothermal fluids and metamorphic processes (e.g. serpentinization), meaning that As is a useful tracer of fluid-flow in the deep Earth. To improve understanding of arsenic speciation in groundwater, sediments, soils, and hydrothermal-metamorphic systems, the present study examined arsenic incorporation into magnesian clays by synthesis of serpentine minerals (200oC, 10 d) with varied concentrations of Si, Al, As5+, and As3+. The synthesis experiments produced two distinct crystal types, tubular and platy serpentines, each with 10–15% randomly interstratified talc layers. X-ray absorption spectroscopy indicated that As5+ and As3+ occurred in the tetrahedral sheet. Single-crystal analysis revealed that tubular crystals contained up to 1 wt.% arsenic [Mg2.8(Si1.8As0.2)O5(OH)4] (mean 0.2 wt.% As). The mean composition of platy, high-Al crystals is (Mg1.8Al0.7)(Si2.0)O5(OH)4, and that of platy, medium-Al crystals with As3+ is (Mg2.07Al0.52) (Si1.97As3+0.03)O5(OH)4. Charge, geometry, and radius of tetrahedral AsO43– oxyanions are similar to tetrahedral SiO44–, and this facilitates fixation of As5+ into the tetrahedral sheet of clay minerals. The geometry and size of the larger As3+ in tetrahedral sites (as a pyramidal AsO33– oxyanion) may limit incorporation relative to As5+. Arsenic-bearing Mg clays crystallize in alkaline environments where AsO43– or AsO33– are the dominant As species and where high pH accompanies crystallization of serpentine, talc, chlorite, or Mg-smectite. The presence of tetrahedral As in these clays raises the possibility of tetrahedral As in other Mg clays (e.g. sepiolite or kerolite) as well.

Photocatalytic Degradation of 2,4-Dichlorophenol by TiO2 Intercalated Talc Nanocomposite

Novel nanocomposites have been prepared by intercalating TiO2 nanoparticles into talc. The nanocomposites have been verified by X-ray diffraction (XRD) from the appearance of a characteristic diffraction peak of TiO2. Thermal behavior of the prepared samples is examined by thermogravimetric analyzer (TGA), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS), which have shown no TiO2 particles on the surface of the talc. The TiO2 particles are found in the layers of talc by transmission electron microscopy (TEM) and the Brunauer-Emmett-Teller (BET) method, which have shown the increase of specific surface areas and total pore volumes and the decline of average pore diameters. As the strong adsorption ability of talc can intensify the power of photon absorption and capture-recombination carriers, more than 99.5% of 2,4-dichlorophenol can be degraded in 1 h by the nanocomposite under an ultraviolet lamp in neutral solution and room temperature after reaching adsorption equilibrium, and the result of adsorbance is in accord with the first-order kinetic. The degradation rate was maintained at about 99% after 20 times. Therefore, the prepared talc/TiO2 nanocomposite is an efficient, stable, and recyclable material for wastewater treatment.

Ensemble Shear Strength, Stability, and Permeability of Mixed Mineralogy Fault Gouge Recovered From 3D Granular Models

AbstractWe conduct numerical shear experiments on mixtures of quartz and talc gouge using a three‐dimensional (3D) distinct element model. A modified slip‐weakening constitutive law is applied at contacts. We perform velocity‐stepping experiments on both uniform and layered mixtures of quartz and talc analogs. We separately vary the proportion of talc in the uniform mixtures and talc layer thickness in the layered mixtures. Shear displacements are cycled through velocities of 1 and 10 μm/s. We follow the resulting evolution of ensemble shear strength, slip stability, and permeability of the gouge mixture and explore the mesoscopic mechanisms. Simulation results show that talc has a strong weakening effect on shear strength—a thin shear‐parallel layer of talc (three particles wide) can induce significant weakening. However, the model offsets laboratory‐derived strong weakening effects of talc observed in uniform mixtures, implying the governing mechanisms may be the shear localization effect of talc, which is enhanced by its natural platy shape or preimposed layered structure. Ensemble stability (a − b) can be enhanced by increasing talc content in uniform talc‐quartz mixtures. Reactivation‐induced permeability increase is amplified with increased quartz content before the maturation of shear localization. Postmaturation permeability enhances on velocity upsteps and diminishes on velocity downsteps. Talc enhances compaction at velocity downsteps, potentially reducing fault permeability. Evolution trends of stability relating to the composition and structure of the fault gouge are straightforwardly obtained from the 3D simulation. Local friction evolution indicates that talc preferentially organizes and localizes in the shear zone, dominating the shear strength and frictional stability of faults.

Polysulfone mixed-matrix membrane incorporating talc clay particles for gas separation

Mixed-matrix membranes (MMMs) have showed advantages in membrane-based gas separation in recent years. However, there is still intensive demand for the development of membranes incorporated by proper fillers for further enhancement of gas separation performance. In this study, mixed-matrix membrane (MMMs) has been synthesized by incorporating of different content of talc into polysulfone (PSf) polymer specifically upon the separation of carbon dioxide from methane. The influence of filler content on the gas separation performance of the fabricated membranes was studied. The prepared MMMs were analyzed by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), derivative thermo-gravimetric (DTG), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and pure gas permeation testing. XRD analysis suggested that talc layers crystalline structure was changed slightly due to blending and just limited PSf chain intercalation occurred. The results showed that the rate of gas permeation increased with increasing talc content while the selectivity declined at 0.5 wt% due to filler agglomeration as confirmed by FESEM. The best results were obtained at 0.1 wt% talc compared to neat PSf with superior gas separation behavior.

Influence of weakening minerals on ensemble strength and slip stability of faults

AbstractWe explore the impact of phyllosilicate (weak but velocity strengthening) in a majority tectosilicate (strong but velocity weakening) matrix on bulk shear strength and slip stability of faults. Numerical simple shear experiments using a distinct element model (DEM) are conducted on both uniform mixtures of quartz and talc analogs and on textured mixtures consisting of a talc layer embedded in a quartz matrix. The mechanical response of particles is represented by a linear elastic contact model with a slip‐weakening constitutive relation representing the essence of rate‐state friction. The weight percentage of the talc in the uniform mixtures and the relative thickness of the talc layer in the textured mixtures are varied to investigate the transitional behavior of shear strength and slip stability. Specifically, for uniform mixtures, ~50% reduction on bulk shear strength is observed with 25% talc present, and a dominant influence of talc occurs at 50%; for textured mixtures, a noticeable weakening effect is shown at a relative layer thickness of 1 particle, ~50% shear strength reduction is observed with 3‐particles, and a dominant influence occurs at 5 particles. In terms of slip stability, a transition from velocity weakening to velocity strengthening is observed with 10% to 25% talc present in the uniform mixtures or with 3 particles to 5 particles in the textured mixtures. In addition, further analysis suggests that quartz has a high tendency toward dilation, potentially promoting permeability; while talc dilates with increased slip rate but compacts rapidly when slip rate is reduced, potentially destroying permeability. The simulation results match well with previous laboratory observations.

Talc as Reinforcing Filler in Polypropylene Compounds: Effect on Morphology and Mechanical Properties

Talc represents one of the most useful mineral fillers which are compatible with the polypropylene (PP). It is characterized with its lamellar structure. The introduction of 30% by weight of talc, three types differing with the particle size d50 and the composition, has not only a positive influence on stiffness and crystallinity but also it decreases the impact strength and tenacity. The abrasive wear behavior depends mainly on the particle size of talc. Microscopic observations revealed that the talc layers are aligned along the injection flow direction, and uniformly dispersed in the PP matrix.

Thermal behaviour of stevensite at temperatures up to 800°C.

Stevensite is a Mg-trioctahedral smectite with layer charge stemming from vacancies in the octahedral sheet. In the present work we studied the thermal behavior of Jbel Ghassoul stevensite from Morocco, known as Ghassoulite or Rhassoulite, free of talc layers. The clay fraction of the material was separated by sedimentation, it was subsequently heated from 250° to 800° C and the end products were examined with X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. The influence of heating on the stevensite structure begins at 400°C and is completed at 500°C. It involves irreversible collapse of the layers at ~10Å, which do not re-expand in ethylene glycol (EG) vapors. In contrast, heating at lower temperatures does not affect the stevensite layers, which expand completely in EG. The FTIR spectra indicate the formation of talc-like (kerolite) layers after heating at temperatures exceeding 400°C. Within the current experimental setup, the transition to kerolite layers takes place without the formation of an intermediate mixed-layer stevensite/talc phase. Heating at higher temperatures does not change the transformation pattern, until 800°C where complete dehydroxylation of the 2:1 layer takes place, which is associated with the formation of enstatite. The results of this study clearly demonstrate that opposite to common trioctahedral and dioctahedral smectites, stevensite converts to another layer silicate prior to dehydroxylation.

The Effect of Talc on the Mechanical, Crystallization and Foaming Properties of Poly(Lactic Acid)

ABSTRACTPoly(lactic acid) (PLA)/talc composites containing different contents of talc were prepared by melt blending. Multiple properties of the prepared composites were investigated including mechanical, rheological and crystallization as well as foaming properties. Tensile test results indicated that the mechanical properties of the composite with 3% wt. talc showed significant reinforcement and toughening effect. When the talc content reached 10%, Young's modulus of the composite was increased by 35% compared with pure PLA. The morphological results showed that the talc layers were partially delaminated and uniformly dispersed in the PLA matrix at low loading. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results indicated that 3% wt. talc significantly increased the crystallinity of the PLA matrix. The thermogravimetric analysis (TGA) results demonstrated that the thermal stability of PLA/talc composites was enhanced as well. Moreover, talc at low loading could act as a plasticizer in the polymer flow, which was investigated by rheological tests. The batch foaming experiments revealed that 3% wt. talc loading had the most notable heterogeneous nucleation effect, with the cell size decreasing from 15.4 μm for neat PLA to 8.5 μm and the cell density increasing by 298%.

Structure and properties of highly filled poly (vinyl alcohol)/talc composites prepared through thermal processing: effects of talc size

Poly (vinyl alcohol) (PVA), a multi-hydroxyl polymer with excellent comprehensive properties, is an expected candidate to prepare high-performance polymer-based composites without using any coupling agents or compatibilisers. However, the poor thermal processability of PVA is its biggest obstacle. In this paper, by adopting polyol as a plasticiser, highly filled PVA/talc composites with good mechanical properties were successfully obtained through melt extrusion and injection, and the effects of talc size on structure and properties of the composites were studied. The results showed that talc highly filled PVA composites had satisfying melt processability, and the decrease of talc particle size increased the –OH groups on the edges of the talc layers, thus improving the compatibility between talc and PVA, and making talc particles dispersed more uniformly in PVA matrix. As a result, the composites with smaller talc particles had the higher threshold filler concentration to form the filler networks and the better flow behaviour. The smaller talc flakes also exhibited higher orientation in PVA matrix and induced more PVA molecular chains to orient along the melt flow direction, leading to the enhancement of the mechanical properties of the composites.

Mechanical, morphological, and thermal properties of nanotalc reinforced PA6/SEBS‐g‐MA composites

ABSTRACTTernary butylene‐styrene‐g‐maleic anhydride (SEBS‐g‐MA) (100/20 w/w) blend with varying content of nanotalc (1, 3, and 5 wt %) were prepared by melt compounding followed by injection molding. Thermal properties were investigated by thermogravimetric analysis (TGA) and the results show that the thermal properties of nanocomposites are slightly improved by the addition of nanotalc content. The morphology of nanocomposites using wide angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM) revealed the delamination of talc layers in the ternary nanocomposites. The dynamic mechanical properties of the samples were analyzed by using dynamic mechanical thermal analyzer (DMTA). The results show that the storage modulus of the blend monotonically increased while tan δ curve show the diffuse pattern with the nanotalc content. The mechanical properties of PA6/SEBS‐g‐MA nanocomposites were studied by tensile, flexural, and impact tests. The tensile and flexural properties continuously increased while izod impact and elongation‐at‐break decreased with nanotalc content. Various theoretical predictive models were used to correlate tensile modulus with the experimental data. The experimental data shows the positive deviation with the applied models. Bela Pukanszky model has been used to calculate the value of parameter B by employing tensile strength data. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41381.

Compatibilization of polypropylene/polyamide 6 blends using new synthetic nanosized talc fillers: Morphology, thermal, and mechanical properties

ABSTRACTNew synthetic nanotalc and a commercially available natural fine talc (Luzenac© A3) were chosen in order to establish a comparative study in terms of their contributions on the improvement of the morphology as well as the final properties of PP/PA6 blends prepared by melt processing. At first, the TEM and SEM micrographs showed that both talc particles have a preferential affinity for the more hydrophilic polyamide 6 phase compared with the continuous PP matrix. Moreover, in both cases, the addition of talc fillers induces a significant decrease of the size of the PA6 domains but the better compatibilization efficiency was obtained in the presence of synthetic nanotalc particles. In this work, the positive change induced by the talc nanofillers on the crystallization kinetics and final morphology was highlighted. In addition, compared with natural talc, a highly level of dispersion of talc layers has been obtained with the synthetic nanotalc which is more hydrophilic. Thus, this better dispersion greatly improves the thermal stability of PP/PA6 blends and leads to better mechanical properties (+ 40% in Young's modulus). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40453.

Crystal-chemistry of interstratified Mg/Fe-clay minerals from seafloor hydrothermal sites

Seafloor hydrothermal sites generate abundant Mg- and Fe-rich clays. These clays are structurally and compositionally interesting because these environments are characterized by large, dynamic temperature and chemical gradients in their deposition environment, which promote the formation of chemically and structurally complex clays, including interstratified phases. The system is also interesting as a proxy for the study of the large Mg- and Fe-rich phyllosilicate deposits on Mars, which are broadly characterized as smectitic clay of hydrothermal, volcanic or sedimentary origin. Thirty submarine samples and four terrestrial ones, for comparison, were studied by means of X-ray diffraction (XRD), thermogravimetry (TG), mid-IR and Mössbauer spectroscopies and chemical analysis. The samples include nontronite and the mixed-layer phases glauconite–nontronite, talc–nontronite and talc–saponite. Some of the talc–saponite samples have Fe contents well above those typical for these Mg-rich, trioctahedral phases (up to 1.69 Fe per O10[OH]2, in the tetrahedral and octahedral sheets). Tetrahedral Fe ranges from 0 to 0.66atoms per O10[OH]2 across the samples. As found in previous studies of similar specimens, Fe promotes the retention of molecular water that is released upon heating above 200C, and is mainly emplaced in non-expandable layers (talc and glauconite layers). In talc–nontronite and talc–saponite octahedral Fe (both di- and trivalent) appears to be bound to this trapped molecular water, whereas in glauconite–nontronite the bond appears to be with tetrahedral Fe. Samples typically show more than one dehydroxylation event in the TG analysis. The weight loss at each dehydroxylation event is broadly consistent with the proportion of individual layers as determined by means of XRD, but there is no good correlation between both. By contrast, the weight loss at each dehydroxylation event correlates with the chemistry of the layers, where certain cations promote chemical domains in the octahedral sheet (e.g., trioctahedral, nontronite-like, and montmorillonite-like) that dehydroxylate at the several temperatures. The correlations found for talc–nontronite and glauconite–nontronite samples suggest that the distribution of cations in the octahedral sheets of most, but not all, samples is intermediate between total dispersion and total segregation, perhaps random. The talc–nontronite samples have talc layers with cation-deficient octahedral sheets. The above results are best explained by layers of polar character, where the octahedral sheets are composed of domains with different chemical characteristics corresponding to the two types of layers in the interstratified clay. The existence of molecular water (bands at 1635 and 3300–3500cm−1, or ~6.1 and 2.9–3.1μm, respectively) bound in non-expanding layers is relevant to the mineral characterization of Martian Fe-rich clays with spectroscopic methods, where molecular water is so far assumed to be linked to smectite. The variety of mixed-layer clays in which Fe is found in the submarine samples suggests that mixed-layering may be important in Martian clays, which are spectroscopically variable but generally Fe-rich.

Size-controlled synthesis of Fe3O4 magnetite nanoparticles on the exterior of talc layers

The purpose of this study was to investigate the effect of OH concen- tration on the size of Fe3O4 nanoparticles (Fe3O4-NPs). Fe3O4-NPs with different cubic nanocrystal structure and percentage Fe3O4 content were successfully pre- pared, by use of the chemical co-precipitation method, on the exterior surface of talc, as solid substrate, by an environmentally friendly process. Ferric chloride, ferrous chloride, and sodium hydroxide were used as iron oxide precursors and reducing agent. The results showed that the morphology of the Fe3O4-NPs can be adjusted by changing the reaction conditions, for example volume of reducing agent and concentration of iron salts. Different size, dispersal, and the magnetic properties were obtained by changing the concentration of iron salts and NaOH. The products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. The reaction was conducted in a non- oxidizing, oxygen-free environment. Because the interlamellar spacing of the talc was almost unchanged (ds = 0.94-0.87 nm), the Fe3O4-NPs were formed on the exterior surface of the talc. The average diameter of the Fe3O4-NCs could be varied from 6.62-8.13 nm in adjusting the concentration of NaOH. The size of the nanoparticles decreased as the amount of reducing agent was increased. These talc- Fe3O4 nanocomposites (talc-Fe3O4-NCs) may have potential applications in the chemical and biological industries.