Thermal decomposition of pyrite

Thermal decomposition of natural pyrite (cubic, FeS₂) has been investigated using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. X-ray diffraction analysis of pyrite ore from different sources showed the presence of associated minerals, such as quartz, szomolnokite, stilbite or stellerite, micas and hematite. Hematite, maghemite and pyrrhotite were detected as thermal decomposition products of natural pyrite. The phase composition of the thermal decomposition products depends on the temperature, time of heating and starting size of pyrite crystals. Hematite is the end product of the thermal decomposition of natural pyrite.     

Synthetic high-charge organomica: effect of the layer charge and alkyl chain length on the structure of the adsorbed surfactants

A family of organomicas was synthesized using synthetic swelling micas with high layer charge (Na(n)Si(8-n)Al(n)Mg(6)F(4)O(20)·XH(2)O, where n = 2, 3, and 4) exchanged with dodecylammonium and octadecylammonium cations. The molecular arrangement of the surfactant was elucidated on the basis on XRD patterns and DTA. The ordering conformation of the surfactant molecules into the interlayer space of micas was investigated by (13)C, (27)Al, and (29)Si MAS NMR. The arrangement of alkylammonium ions in these high-charge synthetic micas depends on the combined effects of the layer charge of the mica and the chain length of the cation. In the organomicas with dodecylammonium, a transition from a parallel layer to a bilayer-paraffin arrangement is observed when the layer charge of the mica increases. However, when octadecylammonium is the interlayer cation, the molecular arrangement of the surfactant was found to follow the bilayer-paraffin model for all values of layer charge. The amount of ordered conformation all-trans is directly proportional of layer charge.     

Thermal and mineralogical contribution to the ancient ceramics and natural clays characterization

In the present work 39 ancient ceramic sherds from the archaeological excavation of Abdera, North-Eastern Greece, dating to 7^th century B.C., and 11 local raw clay bricks, fired at temperatures ranging from 500 to 1000°C, were characterized by ICP-AES, powder X-ray diffraction (PXRD) and thermal analysis (TG-DTA) techniques. It has been found that the mineralogical composition of the most studied sherds is quartz, feldspars and micas, which is in agreement with the composition of the local bricks. Chlorite is also present in a few samples, while there is one completely different sherd, which belongs to the Ca-rich clays. From the simultaneous TG/DTG and DTA data, under nitrogen atmosphere in the temperature ranges ambient to 1000°C, we comment on the possible firing temperature and distinguish between samples of different origin. The existence of muscovite or illite in most of the samples denotes that the firing temperature was lower than 950°C, while the existence of chlorite means that the firing process in these samples stopped before 700°C. A very different thermogram gave the Ca-rich ceramic sherd, due to the existence of calcite, denoting that the firing temperature was about 700°C.     

Thermal differential diagnosis of mica mineral group

The following criteria can be used for differential diagnosis of mica mineral group: weight loss < 350°C; weight loss during dehydroxylation (500–1000°C); peak temperature of structural decomposition and formation of high temperature phases; course of dilatometric curves during dehydroxylation and structural decomposition interval (Fig. 1).Using the single criteria by stepwise comparing a complete thermal differentiation is possible between the members of mica mineral group.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday     

Particle-induced-gamma-ray-emission spectrometry applied to the determination of light elements in individual grains of granite minerals

The quantitative determination of Li, Be, B, F is feasible using a sensitive and non-destructive method by the analysis of the prompt -rays induced with charged particles (PIGE). The irradiation source is a Van de Graaff accelerator, and -analysis has to be performed during the irradiation. Measurements were made at the CERI laboratory in Orléans with the PIGE method using a 100×300 m² focused beam of 3MeV particles. Among the applications, micas along a drill core from the Beauvoir granite were analyzed. Bulk analyses of light elements in the drill core have previously been made. Coarse-grained micas were selected, individually irradiated and directly analyzed in polished thin sections from different elevations in the drill core. The sensitivity depends on the cross-sections of the nuclear reactions, on the particle current and on the duration of the irradiation. With a particle current irradiation of 25 nA during 1000 seconds, a 20 ppm limit of detection is reached for Be, 25 ppm for Li, 900 ppm for B and 450 ppm for F. A large variation of Be contents in the micas was found at equal drill hole elevations, and there was no strong correlation between whole-rock compositions and the mineral chemistry. The latter have been determined both by PIGE and by mineral separation and ICP analyses. On the other hand, a strong Li–F correlation was observed between the fluor-polylithionite and muscovite end-members, supporting previous analyses from equal elevation wells on sorted micas. Be–Li correlation is poorly defined, but the contents of the micas analyzed remained between the contents of bityite (Be–Li bearing mica) and lepidolites (Li-bearing micas) end-members. This suggests a solid-solution between the end-members, the extent of which is very narrow because the Be contents were not higher than 500 ppm. The detection limit is a function of the spatial resolution, because the current of the incident (or p) particles decreases with the impact size. The results show that the analysis of small individual grains of minerals with PIGE can thus be complementary to other analytical methods such as the electronic microprobe.     

Thermal stability and flammability of silicone polymer composites

Silicone polymer composites filled with mica, glass frit, ferric oxide and/or a combination of these were developed as part of a ceramifiable polymer range for electrical power cables and other high temperature applications. This paper reports on the thermal stability of polymer composites as determined by thermogravimetric techniques, thermal conductivity and heat release rate as measured by cone calorimetry. The effects of fillers on thermal stability and flammability of silicone polymer are investigated. Of the fillers studied, mica and ferric oxide were found to have a stabilising effect on the thermal stability of silicone polymer. Additionally, mica and ferric oxide were found to lower heat release rates during combustion, but only mica was found to increase time to ignition.     

Some novel layered-silicate nanocomposites based on a biodegradable hydroxybutyrate copolymer

This paper describes the preparation, characterization, mechanical properties and thermal stability of layered silicate nanocomposites based on poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-co-PHH, known as Nodax^TM). The dispersed phases were organically modified montmorillonites (clay 20A and clay 25A), mica, and talc, and they were introduced by solution mixing. Wide-angle X-ray scattering results and transmission electron microscopy (TEM) images confirmed that these two clays were intercalated and finely distributed in the Nodax^TM matrix. This type of layered filler led to remarkable improvements in mechanical properties even at very low loadings. Minimizing aggregation was more of a problem in the case of the mica and the talc, at least in this particular matrix. In some cases, these layered fillers slightly decreased the thermal stability of the Nodax^TM.     

Tailoring and investigation of surface chemical nature of virgin and ion beam modified muscovite mica

We report that the surface chemical properties of muscovite mica [KAl₂(Si₃Al)O₁₀(OH)₂] like important multi-elemental layered substrate can be precisely tailored by ion bombardment. The detailed X-ray photoelectron spectroscopic studies of a freshly cleaved as well as 12-keV Ar⁺ and N⁺ ion bombarded muscovite mica surfaces show immense changes of the surface composition due to preferential sputtering of different elements and the chemical reaction of implanted ions with the surface. We observe that the K atoms on the upper layer of mica surface are sputtered most during the N⁺ or Ar⁺ ions sputtering, and the negative aluminosilicate layer is exposed. Inactive Ar atoms are trapped, whereas chemically reactive N atoms form silicon nitride (Si₃N₄) and aluminum nitride (AlN) during implantation. On exposure to air after ion bombardment, the mica surface becomes more active to adsorb C than the virgin surface. The adsorbed C reacts with Si in the aluminosilicate layer and forms silicon carbide (SiC) for both Ar and N bombarded mica surfaces. Besides the surface chemical change, prolonged ion bombardment develops a periodic ripple like regular pattern on the surface.     

Thermal,chemical, and mineralogical characterization of ceramic tobacco pipes from Cyprus

This study is focused on simultaneous thermoanalytical investigations by TG/DTG-DTA technique applied for characterization of samples collected from archaeological site of Nicosia, Cyprus, dating to seventeenth century and gave new information on the firing technology. The ceramic samples derived from Ottomanic tobacco pipes were characterized by the related techniques such as X-ray powder diffraction for the mineralogical composition, and inductively coupled plasma-atomic emission spectrometry and micro-X-ray fluorescence spectroscopic analysis for the chemical content. It was found that they consisted mainly of quartz, calcite, feldspars, and micas. For the majority of the investigated ceramic samples, the thermal behavior investigation collaborates with their mineralogical findings, and resulted to the firing temperature at ~700 °C, due to the existence of calcite. Only in two samples with very high content in quartz, absence of calcite, low amounts of adsorbed water and of total mass loss, and absence of micas, the firing process resulted up to 1000 °C.     

IR-spectral study of the effect of WO3 on the structure of tellurite glasses

The comparison of IR-spectra of tellurite glasses and their crystal products containing from 5 up to 45 mol% WO₃ indicates that the modifier does not change the coordination of tellurium. The IR-spectra of glasses containing small WO₃ amounts show a band at 925 cm^?1, which shifts up to 950 cm^?1 with the increase in the tungsten concentration. The effect is specific of the vitreous state and may be explained by the change in the coordination of tungsten.     

Novel mixed ligand coordination compounds of some rare earth metal cations containing acesulfamato/N,N-diethylnicotinamide

The mixed ligand coordination compounds containing acesulfamato and N,N -diethylnicotinamide biomolecules of some rare earth metal cations (Eu³⁺, Tb³⁺, Ho³⁺, Er³⁺ and Yb³⁺) were synthesized, and their structural properties were investigated. Possible structural formulas have been proposed by determining the chemical composition of molecules (elemental analysis), binding properties (infrared spectroscopy, mass analysis, solid-state UV-vis spectroscopy), thermal degradation properties (TGA / DTA curves). Based on the data collected, it is suggested that rare earth metal cations with a 3+ oxidation state have sextet coordination. The geometries of the structures were thought to be distorted octahedral. The charge balance of the coordination sphere is balanced by a monoanionic acesulfamato located outside the coordination sphere. When the thermal behaviours of the complexes were examined, it was determined that the compounds with Eu³⁺, Tb³⁺, and Yb³⁺ metal cations contained one hydrate water outside the coordination sphere. Hydrate waters do not exist in the Ho³⁺ and Er³⁺ metal cation-centred complexes. At the end of the thermal decomposition analysis of all complex structures, it was determined that they leave the relevant metal oxides in the reaction vessels as final decomposition products.     

Thermal stability of ionene polymers

Two different cationic polymers of the same chemical type and with very similar chemical structures were reacted with a natural bentonite over a wide range of polymer/clay ratios. This study involved the synthesis of cationic aliphatic ammonium polyionenes, specifically 3,6-ionene and 3,6-dodecylionene. Ionenes are ion-containing polymers that contain quaternary nitrogen atoms in the main macromolecular chain as opposed to a pendant chain. The CHN content, basal spacing, and elemental composition of each of the polymer–clay complexes were analyzed by X-ray diffraction, X-ray fluorescence, and thermogravimetry. All the polycations reacted to form interlayer complexes with clay, which displaced more Na⁺ and little Ca²⁺. Sodium and calcium were both present as interlayer cations in the clay and its complexes. The TG/DTG curves show that both polymers underwent thermal degradation in more than one stage. Specifically, 3,6-ionene was found to undergo two stages of decomposition and 3,6-dodecylionene undergo three stages. The behavior of the TG/DTG curves and the activation energy values suggest that 3,6-dodecylionene (E = 174,85 kJ mol^?1) complexes have greater thermal stability than 3,6-ionene (E = 115,52 kJ mol^?1) complexes. The mechanism of degradation suggests a direct interaction with the dodecyl chain containing 12 carbons, which are present in 3,6-dodecylionene but not in 3,6-ionene.     

CO在Ag掺杂的氧化锰八面体分子筛上吸附的TAP研究

利用产物瞬时分析反应器中进行的单脉冲实验, 考察了393～493 K温度范围内CO在Ag掺杂的氧化锰八面体分子筛上的吸附行为. 实验表明: CO在催化剂表面发生化学吸附, 并与晶格氧反应生成CO₂. 通过对该过程反应物及产物脉冲响应曲线的模拟, 得到了各基元反应的动力学参数. CO和CO₂在该催化剂表面的脱附活化能分别为83和31 kJ/mol, CO与晶格氧的反应活化能为116 kJ/mol.     

Evaluation of organic molecules originated during composting process

The composting process using sugarcane bagasse, animal manure, and urea as source of organic matter, microorganism, and nitrogen, respectively, were evaluated regarding the thermal behavior considering the maturation period: 0 (raw), 15, 22, 30, and 60 days. Thermogravimetric and differential thermal analysis curves were obtained in a synthetic air atmosphere and heating rate of 10 °C min⁻¹ in the range of 30–600 °C. The raw compost showed 80% organic matter, which was reduced up to 58% to 60 days compost. Two main mass losses were verified, corresponding to characteristics exothermic peak in differential thermal analysis curves depending on the maturation period. The variation in organic composition was evaluated by Fourier transform infrared spectroscopy verifying the structures (lignin, cellulose, and hemicelluloses) changes with composting process, and the gas chromatography–mass spectrometry was used to identify substance soluble in hexane.     

Application of thermogravimetry in the quality control of mebendazole

A study was made of the thermal behavior of the starting materials, their mixtures and the resulting mebendazole tablets. The thermal curves were obtained with a Shimadzu thermobalance, model TGA-50, using an air flow of 50 mL min^–1 and a heating rate of 10°C min^–1 in the temperature interval 30–900°C. The reaction constant velocities for the mebendazole salt and tablets were determined isothermally, using the Arrhenius expression. The thermal stability of mebendazole tablets is lower than that of the mebendazole salt, due to the presence of starch and lactose in the composition. Analysis of the data reveals that thermogravimetry is a powerful tool in pharmaceutical technology and quality control.The authors thank CNPq/PADCT for financial support.     

Evaluation of kinetic parameters from a single TG curve based on the similarity theory and process symmetry

The equation for calculation of the activation energy of the diffusion of the evolved products through the matrix (E) from a single TG curve were proposed by solving Fick's laws. The solution is based on the similarly theory by utilizing a Fourier number.The proposed method was examined by using mass loss data for the dehydroxylation of some micas with and without FeO (muscovite and its varieties and lepidolite) as determined from their TG curves. TheE values for the first stage of the dehydroxylation of these micas areE ₁,=85±10 kJ mol^–1; for the final stageE ₂=380±40 kJ mol^–1 and for the mass loss connected with fluorineE _F=85±10 kJ mol^–1.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayPart of this work was carried out in the Institute of Geochemistry of the USSR Academy Science (Irkutsk). I wish to thank Dr. S. B. Brandt for helpful discussions.I am pleased to express my gratitude to Prof. S. Yariv for his important comments.I am grateful to the Ministry of Absorption of the Government of Israel for financial support of this work.     

Structure and phase transitions of alkyl chains on mica

We use molecular dynamics as a tool to understand the structure and phase transitions [Osman, M. A.; et al. J. Phys. Chem. B 2000, 104, 4433-4439. Osman, M. A.; et al. J. Phys. Chem. B 2002, 106, 653-662] in alkylammonium micas. The consistent force field 91 is extended for accurate simulation of mica and related minerals. We investigate mica sheets with 12 octadecyltrimethylammonium (C(18)) ions or 12 dioctadecyldimethylammonium (2C(18)) ions, respectively, as single and layered structures at different temperatures with periodicity in the xy plane by NVT dynamics. The alkylammonium ions reside preferably above the cavities in the mica surface with an aluminum-rich boundary. The nitrogen atoms are 380-390 pm away from the superficial silicon-aluminum plane. With increasing temperature, rearrangements of C(18) ions on the mica surface are found, while 2C(18) ions remain tethered due to geometric restraints. We present basal-plane spacings in the duplicate structures, tilt angles of the alkyl chains, and gauche-trans ratios to analyze the chain conformation. Agreement with experimental data, where available, is quantitative. In C(18)-mica with less than 100% alkali-ion exchange, the disordered C(18) rods in the island structures [Hayes, W. A.; Schwartz, D. K. Langmuir 1998, 14, 5913-5917] break at 40 degrees C. At 60 degrees C, the headgroups of the C(18) alkyl chains rearrange on the mica surface, and the broken chain backbones assume a coillike structure. The C(18)-mica obtained on fast cooling of this phase is metastable due to slow reverse rearrangements of the headgroups. In 2C(18)-mica with 70-80% ion exchange, the alkali ions are interspersed between the alkyl chains, corresponding to a single phase on the surface. The observed phase transition at approximately 53 degrees C involves an increase of chain disorder (partial melting) of the 2C(18) ions without significant rearrangements on the mica surface. We propose a geometric parameter lambda for the saturation of the surface with alkyl chains, which determines the preferred self-assembly pattern, that is, islands, intermediate, or continuous. lambda allows the calculation of tilt angles in continuous layers on mica or other surfaces. The thermal decomposition seems to be a Hofmann elimination with mica as a base-template.     

Auto-orientation of G-wire DNA on mica

Scanning probe microscopy was used to examine the orientation of Tet1.5 quadruplex DNA polymers, a.k.a. “G-wires”, after adsorption onto freshly cleaved Phyllosilicate micas. The G-wires appear to have a preferential orientation at 60° intervals after thorough rinsing and slow drying. The angles the G-wires made with the fast scan direction of the SPM probe were measured and the frequency-angle information was quantitatively characterized by an empirical correlation coefficient. Careful measurements indicate the Tet1.5 G-wires orient along the b lattice vector of mica, the next nearest neighbor potassium vacancy. A model is proposed to explain this auto-orientation affect due to alignment of the G-wires’ phosphate backbone through magnesium tether cations. Pairs of adjacent, parallel phosphate groups of the G-wires (0.95 nm apart) appear to align with the next nearest neighbor potassium vacancy sites of mica (0.90 nm apart). This behavior is not observed in solution. The potential for using the auto-orientation phenomena in the development of high-density biomolecular nano-electronic devices is explored.     

Kinetic parameters for thermal decomposition of supramolecular polymers derived from flunixin-meglumine adducts

Meglumine, (2R,3R,4R,5S)-6-methylaminohexane-1,2,3,4,5-pentol, is a carbohydrate derived from sorbitol in which the hydroxyl group in position one is replaced by a methylamine group. It forms binary adducts with substances having carboxyl groups, which have in common the presence of hydrogen bonding as the main force in the stabilization of these species. During melting, adducts of meglumine with flunixin (2-[[2-methyl-3-(trifluoromethyl)phenyl]amino]pyridine-3-carboxylic acid) polymerize or self-assemble in amorphous supramolecular structures with molecular weights around 2.0 × 10⁵ kDa. DSC curves, in a first heating, show isomorphic transitions where the last one at 137 °C for the flunixin-meglumine adduct originated the supramolecular amorphous polymers with glass transition around 49.5 °C. The kinetic parameters for the thermal decomposition step of the polymers were determined by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and heating rates of 5, 10, 15, and 20 °C min⁻¹, the E _α and B _α terms could be determined and, consequently, the pre-exponential factor, A_α, as well as the kinetic model, g(α).     

Cellulose Iβ investigated by IR-spectroscopy at low temperatures

Highly crystalline oriented Halocynthia roretzi cellulose Iβ films were investigated by IR-spectroscopy between ?180 and +10 °C. Changes in the IR-spectra induced by temperature were compared to published changes induced by mechanical stretching. This made it possible to conclude that frequency shifts in the O–H stretching region of the IR-spectra due to temperature were not predominantly an indirect effect of thermal expansion leading to greater O–O distances, but were due directly to the effect of temperature on the O–H···O hydrogen bonds. Temperature induced frequency shifts of C–H stretching bands were consistent with the presence of weak inter-sheet C–H···O bonds. Furthermore, no phase transition in cellulose Iβ was found between ?180 and +10 °C.