New aspects of ta application for studies of Ca-Mg carbonate minerals exemplified by upper permian rocks

The paper discusses the influence of variable experimental conditions on the thermal decomposition of carbonate minerals. This study was based on Ca-Mg carbonate minerals from Upper Permian dolomite and zuber rocks as well as on calcite and magnesite samples from geological formations of various ages. X-ray diffraction was applied for comparative purposes. Experimental conditions were chosen based on the authors' experience related to studies of both fossil and contemporary organic matters as well as various materials of geological provenience. Since the main factor in thermal analysis of carbonates is the appropriate choice of experimental conditions for outflow of gaseous reaction products, the thermal analyses were carried out with various sample holders, various sample masses and varied thickness of sample layers in holders, using also a dynamic atmosphere. The results obtained indicated that different experimental conditions produced extremely different TA data, e.g. the traditional analysis in crucible sample holders with a thick sample layer (great sample mass) showed well expressed double thermal effects of dolomite. For thin sample layer both peaks of thermal decomposition of carbonate components occurred in very close or almost identical temperatures. The presented results enabled to devise a detailed procedure referring to the choice of experimental conditions and interpretation possibilities as well as to recommend specific TA instruments design and sample holders types. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of the pyrites content of bauxites by thermal methods

A derivatographic method has been developed for the identification and determination of the pyrites content of bauxites and clay minerals. If the sample contains at least 0.2% of pyrite, then at 400–450° a weight increase is indicated on the DTG curve, while a heat liberation is shown on the DTA curve. The amplitude of or the area under, these maxima is proportional to the pyrites content of the sample, although the correlation is not linear. In addition, the effect of experimental conditions on the thermal decomposition of pyrites has been studied.     

Aqueous suspensions of natural swelling clay minerals. 1. Structure and electrostatic interactions

In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only. The validity of this approach was further extended to other clay data from the literature, in particular, synthetic Laponite. For all of the investigated samples, experimental osmotic pressures can be properly described by a Poisson-Boltzmann approach for ionic strength up to 10(-3) M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson-Boltzmann treatment shows differences in the repulsive potential strength that are not directly linked to the structural charge of the minerals but rather to the charge location in the structure for tetrahedrally charged clays (beidellite and nontronites) undergoing stronger electrostatic repulsions than octahedrally charged samples (montmorillonites, laponite). Only minerals subjected to the strongest electrostatic repulsions present a true isotropic to nematic phase transition in their phase diagrams. The influence of ionic repulsions on the local order of clay platelets was then analyzed through a detailed investigation of the structure factors of the various clay samples. It appears that stronger electrostatic repulsions improve the liquidlike positional local order.     

Sorption study of 25 volatile organic compounds in several Mediterranean soils using headspace-gas chromatography-mass spectrometry

A sorption study of 25 volatile organic compounds (VOCs) in different agricultural soils was carried out by using headspace-gas chromatography-mass spectrometry. The extraction of the VOCs from soil samples was carried out following the EPA method with some differences such as addition of potassium chloride and different instrumental conditions which provide higher sample throughput. In addition, a complementary study on several procedures for soil fortification with VOCs was also assayed, fortification with minimal sample handling was selected in order to minimise evaporation losses of the VOCs. The effect of clay minerals (7.0-69.7%) and organic carbon (0.2-3.5%) contents on acid and alkaline (pH 5.3-8.8) soils were evaluated. Based on the results, all compounds assayed were more sorbed in alkaline soils than acid ones; chlorobenzenes interact more strongly with agricultural soils than do alkylbenzenes. The organic carbon content affects the sorption of 25 VOCs in alkaline soils (the highest sorption was found for the most organic soil), while in acid soils VOC sorption increases as the organic carbon content decreases. The clay mineral fraction plays an important role in the sorption of VOCs in acid soil owing to pi-/n-electron interactions, this effect being more marked for chlorobenzenes.     

Effects of solid acidity of clay minerals on the thermal decomposition of 12-aminolauric acid

In this study, the effects of four types of clay minerals on the thermal decomposition of 12-aminolauric acid (ALA) were investigated. The decomposition temperature of ALA in ALA–clay complexes was in the range of 200–500 °C. The derivative thermogravimetry results indicated that all clay minerals exhibited catalytic activity on the decomposition of ALA. Pure ALA decomposed at approximately 464 °C, a temperature higher than the decomposition temperature of ALA in the presence of clay minerals. The decomposition temperature of ALA in different ALA–clay complexes follows the order illite (452 °C) > kaolinite (419 °C) > rectorite (417 °C) > montmorillonite (400 °C). This order is negatively correlated with the amounts of solid acid sites in the clay minerals, indicating that ALA is catalyzed by the solid acid sites in these minerals.     

Distribution and Composition of Organic Matter in Oil- and Bitumen-cotaining Rocks in Deposits of Different Ages

The core samples of oil- and bitumen-containing rocks from Tatarstan's deposits of different ages were studied by thermal analysis methods (DTA, TG, DTG). Based on the obtained data, a procedure was elaborated for determining the enclosed organic matter content and the index of its fraction composition. A significant increase of the organic matter content in the core and its enrichment in high-molecular aromatic structures were shown to occur for the oil-containing rock samples when passing from the Devonian to Carboniferous and Permian deposits. The core samples of the Devonian oil-containing rocks may be divided into three groups: the samples taken from the zones where waste water flooding has been started relatively recently (1), or fresh water flooding has been carried on for a long time (2) and the samples of rock containing clay minerals as impurities. Thus, thermal analysis can be used in geochemical studies to identify the organic matter enclosed by oil- and bitumen-containing rocks. This revised version was published online in August 2006 with corrections to the Cover Date.     

Adsorption of dicarboxylic acids by clay minerals as examined by in situ ATR-FTIR and ex situ DRIFT

The adsorption of dicarboxylic acids by kaolinite and montmorillonite at different pH conditions was investigated using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) and ex situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The sorption capacity of montmorillonite was greater than that of kaolinite. Adsorption of dicarboxylic acids (succinic acid, glutaric acid, adipic acid, and azelaic acid) was the highest at pH 4 as compared with those at pH 7 and 9. These results indicate that sorption is highly pH-dependent and related to the surface characteristics of minerals. The aliphatic chain length of the dicarboxylic acids highly influenced the sorption amount at acidic pH, regardless of the clay mineral species: succinic acid [HOOC(CH2)2COOH] < glutaric acid [HOOC(CH2)3COOH] < adipic acid [HOOC(CH2)4COOH] < azelaic acid [HOOC(CH2)7COOH]. With in situ ATR-FTIR analysis, most samples tend to have outer-sphere adsorption with the mineral surfaces at all tested pHs. However, inner-sphere coordination between the carboxyl groups and mineral surfaces at pH 4 was dominant from DRIFT analysis with freeze-dried complex samples. The complexation types, inner- or outer-sphere, depended on dicarboxylic acid species, pH, mineral surfaces, and solvent conditions. From the experimental data, we suggest that organic acids in an aqueous environment prefer to adsorb onto the test minerals by outer-sphere complexation, but inner-sphere complexation is favored under dry conditions. Thus, organic acid binding onto clay minerals under dry conditions is stronger than that under wet conditions, and we expect different conformations and aggregations of sorbed organic acids as influenced by complexation types. In the environment, natural organic material (NOM) may adsorb predominantly on positively charged mineral surfaces at the aqueous interface, which can convert into inner-sphere coordination during dehydration. The stable NOM/mineral complexes formed by frequent wetting-drying cycles in nature may resist chemical/microbial degradation of the NOM, which will affect carbon storage in the environment and influence the sorption of organic contaminants.     

Infrared study of influence of temperature on clay minerals

The effect of temperature on the infrared absorption bands of different clay minerals has been investigated with a view to identify the thermal transformation occurring between 30 and 1000°C.     

Effect of grinding on thermal reactivity of ceramic clay minerals

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 microscopy (SEM). 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.     

Thermal analysis as a tool in the study of GMM in Angra Dos Reis region,Rio de Janeiro,Brazil

Angra dos Reis/Itaguai region of the state of Rio de Janeiro, Brazil, is a very problematic area due to the instability of slope and landslides, due to geological and geomorphological conditions and to the significant and continuous human occupation over favorable areas is prone to the triggering of landslides. The samples were analyzed by thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA). This paper analyzes and characterizes the clay minerals and presence of water, gravitational mass movements’ sites and compares it with sites where gravitational mass movements do not occur. Indeed, this analysis also attempts to verify the presence of minerals.     

The effect of oxidation and reduction on thermal expansion of magnetite from 298 to 1173 K at different vacuum conditions

Three thermal expansion curves of natural and synthetic magnetite (Fe₃O₄) have been measured under different vacuum conditions (10⁻⁴ and 10⁻⁶ mbar). The different behavior in thermal expansion depends on vacuum level, which controls the partial oxidation of the sample. If the vacuum is poor, that is in mildly oxidizing conditions, the thermal expansion curve presents a discontinuity at 875 K and the samples oxidizes. In non-oxidizing conditions the discontinuity is not present and the thermal expansion coefficient is markedly smaller. The experimental curves indicate that virtually all thermal expansion data on magnetite in the literature were measured on oxidized or partially oxidized samples.     

The effect of mineral composition on the sorption of cesium ions on geological formations

The sorption of cesium-137 on rock samples, mainly on clay rocks, is determined as a function of the mineral composition of the rocks. A relation between the mineral groups (tectosilicates, phyllosilicates, clay minerals, carbonates) and their cesium sorption properties is shown. A linear model is constructed by which the distribution coefficients of the different minerals can be calculated from the mineral composition and the net distribution coefficient of the rock. On the basis of the distribution coefficients of the minerals the cesium sorption properties of other rocks can be predicted.     

Crystal chemistry of clay minerals in bottom sediments of the Sea of Okhotsk as a paleoclimatic indicator

X-ray diffraction and infrared spectroscopy were used to study the mineral composition of bottom sediments of the Sea of Okhotsk with ages ranging from Holocene (10 My ago) to Pleistocene (10 to ～74 My ago). The concentrations of nonlayered minerals (quartz, plagioclase, carbonates, and biogenic silica) were determined from IR spectra, which made it possible to estimate the actual abundance of the clay component in test samples. Calibration curves used in the calculation were plots of the optical density in the maximum of the analytical absorption band of the analyzed component versus its concentration in the sample. These curves were constructed for standard mixtures of known compositions. The crystal-chemical parameters and quantitative ratios of clay minerals were elucidated by the computer simulation of X-ray diffraction profiles; clear correlations were found between these parameters and paleoclimatic changes. Our results show that the clay minerals from the bottom sediments of the Sea of Okhotsk can serve to search for paleoclimatic events in the North-Eastern Asia.     

Molecular dynamics simulations of sorption of organic compounds at the clay mineral/aqueous solution interface

The adsorption of trichloroethene, C₂HCl₃, on clay mineral surfaces in the presence of water has been modeled as an example describing a general program that uses molecular dynamics simulations to study the sorption of organic materials at the clay mineral/aqueous solution interface. Surfaces of the clay minerals kaolinite and pyrophyllite were hydrated at different water levels corresponding to partial and complete monolayers of water. In agreement with experimental trends, water was found to outcompete C₂HCl₃ for clay surface sites. The simulations suggest that at least three distinct mechanisms coexist for C₂HCl₃ on clay minerals in the environment. The most stable interaction of C₂HCl₃ with clay surfaces is by full molecular contact, coplanar with the basal surface. This kind of interaction is suppressed by increasing water loads. A second less stable and more reversible interaction involves adsorption through single-atom contact between one Cl atom and the surface. In a third mechanism, adsorbed C₂HCl₃ never contacts the clay directly but sorbs onto the first water layer. To test the efficacy of existing force field parameters of organic compounds in solid state simulations, molecular dynamics simulations of several representative organic crystals were also performed and compared with the experimental crystal structures. These investigations show that, in general, in condensed-phase studies, parameter evaluations are realistic only when thermal motion effects are included in the simulations. For chlorohydrocarbons in particular, further explorations are needed of atomic point charge assignments. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 144–153, 1998     

Al-pillared montmorillonite clay minerals: low-pressure CO adsorption at room temperature

Three kinds of Al-pillared montmorillonite clay minerals (AlPMON) ion-exchanged with cobalt(II), nickel(II), or copper(II) ions were prepared (abbreviated as CoAlPMON, NiAlPMON, or CuAlPMON, respectively). For the 673-K- and 873-K-treated samples, carbon monoxide (CO) adsorption measurement was performed at room temperature under an atmosphere of low CO pressure. The 873-K-treated CuAlPMON sample exhibited more efficient adsorption properties for CO molecules, in comparison with both-temperatures-treated CoAlPMON and NiAlPMON samples and the 673-K-treated CuAlPMON sample. In addition, irreversibly adsorbed CO was present only on the CuAlPMON sample that had been treated at 873 K; the sites responsible for strong CO adsorption were formed in the sample after the pretreatment at the higher temperature.     

Synthesis and properties of polyimide-clay hybrid films

Polyimide-clay hybrid films with four different sizes of clay minerals have been synthesized to investigate the effect of the size of clay minerals to the properties of the hybrids. Hectrite, saponite, montmorillonite, and synthetic mica were used as clay minerals. Those clays consist of stacked silicate sheets about 460 Å (hectrite), 1650 Å (saponite), 2180 Å (montmorillonite), and 12300 Å (synthetic mica) in length, 10 Å in thickness. The longer the length of clay mineral was, the more effectively properties of polyimide were improved. In the case of polyimide-mica hybrid, only 2 wt % addition of synthetic mica brought permeability coefficients of water vapor to value less than one-tenth of that of ordinary unfilled polyimide, and thermal expansion coefficient was lowered at the level of 60% of the original one. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2289–2294, 1997     

Effect of dendrimer modified montmorillonite on structure and properties of EPDM nanocomposites

The purpose of this work was to study the effect of dendrimer modified clay minerals on the structure and properties of ethylene-propylene-diene monomer (EPDM) nanocomposites.Flame-retardant and dendrimer modified organic montmorillonite (FR-DOMt) was successfully prepared by Na⁺-montmorillonite, tetrahydroxymethyl phosphonium chloride (THPC), N, N-dihydroxyl-3-aminomethyl propionate, and boric acid. This dendritic type of organoclay (OC) was used in preparation of EPDM/FR-DOMt nanocomposites. The properties of these nanocomposites were studied. The dispersion status of the layered silicates in EPDM was revealed by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD and TEM results showed that FR-DOMt was exfoliated in the EPDM matrix when 10 phr of FR-DOMt was incorporated. The mechanical behavior, thermal stability, and flame retardance of the samples were examined. The experimental data demonstrated that the EPDM hybrids owned an improved tensile strength and elongation at break. In addition, the nanocomposites exhibited higher thermal stability and flame retardance than that of unfilled EPDM matrix.     

Thermal transport and chemical effects of fillers on free-radical frontal polymerization

Frontal polymerization (FP) is a process in which a front propagates in a localized reaction zone, converting monomer into polymer through the coupling of thermal diffusion with the Arrhenius kinetics of an exothermic reaction. Fillers are added to control the rheological properties of the formulation and to enhance the mechanical properties of the product. However, the thermal and chemical effects of these fillers on the front propagation have not been thoroughly explored. Herein we report the thermal and chemical effects of fillers on free-radical frontal polymerization. It was found that fillers with high thermal diffusivities, such as milled carbon fiber and boron nitride increased the front velocity. Despite their high thermal diffusivities, fillers such as aluminum and alumina decreased the front velocity. This is likely due to the radical-scavenging ability of aluminum oxide, which was explored with clay minerals. It was found that the presence of water within clay fillers can also decrease the front velocity. To probe the chemical effects, acid-activated clay minerals were utilized. The results demonstrate that some fillers can increase front velocity through their high thermal diffusivities while others decrease it by acting as radical scavengers.     

Effect of extrusion and photo-oxidation on polyethylene/clay nanocomposites

Polyethylene (a 1:1 blend of m-LLDPE and z-LLDPE) double layer silicate clay nanocomposites were prepared by melt extrusion using a twin screw extruder. Maleic anhydride grafted polyethylene (PEgMA) was used as a compatibiliser to enhance the dispersion of two organically modified monmorilonite clays (OMMT): Closite 15A (CL15) and nanofill SE 3000 (NF), and natural montmorillonite (NaMMT). The clay dispersion and morphology obtained in the extruded nanocomposite samples were fully characterised both after processing and during photo-oxidation by a number of complementary analytical techniques. The effects of the compatibiliser, the organoclay modifier (quartenary alkyl ammonium surfactant) and the clays on the behaviour of the nanocomposites during processing and under accelerated weathering conditions were investigated. X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), rheometry and attenuated reflectance spectroscopy (ATR-FTIR) showed that the nanocomposite structure obtained is dependent on the type of clay used, the presence or absence of a compatibiliser and the environment the samples are exposed to. The results revealed that during processing PE/clay nanocomposites are formed in the presence of the compatibiliser PEgMA giving a hybrid exfoliated and intercalated structures, while microcomposites were obtained in the absence of PEgMA; the unmodified NaMMT-containing samples showed encapsulated clay structures with limited extent of dispersion in the polymer matrix. The effect of processing on the thermal stability of the OMMT-containing polymer samples was determined by measuring the additional amount of vinyl-type unsaturation formed due to a Hoffman elimination reaction that takes place in the alkyl ammonium surfactant of the modified clay at elevated temperatures. The results indicate that OMMT is responsible for the higher levels of unsaturation found in OMMT-PE samples when compared to both the polymer control and the NaMMT-PE samples and confirms the instability of the alkyl ammonium surfactant during melt processing and its deleterious effects on the durability aspects of nanocomposite products. The photostability of the PE/clay nanocomposites under accelerated weathering conditions was monitored by following changes in their infrared signatures and mechanical properties. The rate of photo-oxidation of the compatibilised PE/PEgMA/OMMT nanocomposites was much higher than that of the PE/OMMT (in absence of PEgMA) counterparts, the polymer controls and the PE–NaMMT sample. Several factors have been observed that can explain the difference in the photo-oxidative stability of the PE/clay nanocomposites including the adverse role played by the thermal decomposition products of the alkyl ammonium surfactant, the photo-instability of PEgMA, unfavourable interactions between PEgMA and products formed in the polymer as a consequence of the degradation of the surfactant on the clay, as well as a contribution from a much higher extent of exfoliated structures, determined by TEM, formed with increasing UV-exposure times.     

新疆高碱煤分选组分中碱性矿物赋存及差异演化研究

以新疆五彩湾高碱煤为原料,通过有机重液浮选和理化分析及热力学模拟解析活性矿物质热演化特性。结果表明,五彩湾煤以密度在1.40-1.50 g/cm~3的组分为主(质量分数超过70%)。可溶性Na和K等主要存在于较低密度组分(-1.40 g/cm~3)中;在高密度(+1.50 g/cm~3)组分中发现了以硅铝酸盐形式存在的碱及碱土金属(AAEMs)。Ca主要以方解石形式存在,伴随高岭土和石英富集在高密度组分中。在低温(500℃)灰化时少量Na释放,大量可溶钠盐的残留导致各分选组分中Na的扩散量相差不大。在815℃热处理温度下,低密度组分中大部分Na挥发到气相中;高密度组分中的部分碱金属可被黏土(高岭土)和石英等矿物质捕获,抑制其释放。Fact Sage热力学模拟发现,温度低于550℃时Na盐仍稳定存在于灰中;温度高于550℃时Na盐开始挥发,同时部分Na向NaAlSiO_4转化;在约620℃时,Na盐消失,同时NaAlSiO_4的含量逐渐趋于稳定。SiO_2含量的差异显著影响含Na等矿物质的演变行为。在500-815℃,Ca以CaSO_4和硅铝酸钙的形式稳定存在,而M g则在不同形式的硅酸盐之间发生转变。