Search

Carbon nanothreads are one-dimensional materials obtained by controlled compression of aromatic molecules. Benzene and other six-membered ring molecules are normally used as precursors, but recent experiments have shown that carbon nanothreads can also be synthesized from five-membered ring heterocyclic compounds such as thiophene and furan, with an improved control of the structure of the final material and potentially easier scalability. In this work we use Density Functional Theory calculations to unveil the structural, electronic and mechanical properties of carbon nanothreads derived not only from thiophene and furan, but also from pyrrole, aiming to encourage experimental efforts towards the synthesis of equivalent 1D materials. Our results show that these new structures are remarkably stable when compared to similar nanothreads derived from benzene and pyridine. The presence of heteroatoms may lead to significant variations on the electronic band gap of these materials compared to conventional nanothreads, without compromising their mechanical properties. These findings suggest that nanothreads derived from five-membered rings are suitable for the same applications proposed for conventional NTs and potential candidates for new ones.

According to Zanotto and Mauro [1],“glass is a nonequilibrium, noncrystalline con-densed state of matter that exhibits a glass transition. The structure of glasses islike that of their parent supercooled liquids. Their fate, in the limit of infinite time,is to crystallize.”Glasses are usually formed by quenching of a molten mixture insuch a way that the atoms do not have time to reach the equilibrium spatial config-uration, forming an amorphous solid with short-range order. The glass transitiontemperature,Tg, consists in the temperature range between the rigid solid-statestructure and a more flexible, viscous structure. Good candidates to make glassesmust have high viscosity in the molten state, where the atomic rearrangement isconstrained. Materials that are not able to form glasses are, sometimes, used as net-work modifiers. In this case, they induce the formation of dangling bonds in theprimary three-dimensional glass network, usually decreasing density. The physicalproperties of glasses can be tuned by adjusting their chemical composition.Silica(SiO2), the major constituent of sand, has been the raw material of glassesfor thousands of years. It is formed by SiO4tetrahedra sharing four oxygen atoms(bridging oxygen atoms) in a random spatial configuration. To overcome the highmelting point of silica (1,723 °C), alkali metal oxides such as Na2O, K2O, and Li2Oare used as network modifiers. For instance, the addition of 33 mol% of Na2Ode-creases the melting temperature to 875 °C [2, 3]. The presence of alkali metal posi-tive ions as modifiers induces the formation of nonbridging oxygen (NBO) atoms,so the SiO4tetrahedra would share less than four oxygen atoms, affecting the localstructure and properties of the glass [4–8].Germania(GeO2) is also a good glass former, like SiO2,consistingofGeO4tetrahe-dra sharing four oxygen atoms in a random spatial configuration. It was first synthe-sized by Dennis and Laubengayer in 1926 [9]. The incorporation of glass modifiersinduces an atypical behavior, known asgermanate anomaly: thermophysical proper-ties present maxima or minima depending on the amount of the modifier. In theatomic level, the anomaly is related to modifications in the coordination number ofGe atoms or to the formation of small rings of GeO4[10–13].

Preparation of bulk samples with high content of carbon nanotubes and still maintaining their impressive properties is not usual because the connection between them is very difficult. Several attempts to obtain carbon nanotube bulk samples have been made; however, the samples presented insufficient mechanical properties being brittle and difficult to handle. In the present work, multiwalled carbon nanotube/zirconia (MWCNT/ZrO2) composite compacted samples, containing nearly 40% of multiwalled carbon nanotubes or functionalized carbon nanotubes (MWCNT or f-MWCNT) dispersed in a zirconia matrix (ZrO2), were prepared for the first time. The sol–gel method was applied to warrant the connection between the MWCNT, associated with the high-pressure technique to impart mechanical properties. The samples that present the best characteristics in compaction and handling were the ones made with composite powders heat-treated at 300 °C. Subsequently, these powders were processed under high pressure (4 GPa) and high pressure/temperature (4 GPa/400 °C). These samples maintain significant content of MWCNT even after heat treatments. The physical and morphological integrity of the MWCNT were retained and yielded samples with impressive properties, such as high surface area (near 150 m2 g−1), load resistance (load/mass ratio >8000) and electrical conductivity (3 × 101 S m−1).

In this paper, the combined effect of gold nanoparticles and high-pressure densification on the luminescence of Pr3+-doped heavy metal GeO2–PbO photonic glass was investigated. Localized states related to ion-trapped exciton defects, S1 and S2, were observed at 342 and 412 nm before densification. After densification under 7.7 GPa, the structure of the glass host changed irreversibly, as indicated by the infrared spectrum, refractive index, and density measurements. Transmission electron microscopy analyses indicated that the high-pressure densification induced the formation of clusters of gold nanoparticles. The modifications observed in the absorption and luminescence spectra of Pr3+ ions in the VIS–NIR range were associated to the changes in the local field surrounding the Pr3+ ions in the host glass induced by high pressure. For excitation at 445 nm (luminescence from 3P2) and 593 nm (luminescence from 1D2), the combined effect of densification and gold nanoparticles induced an increase in the emissio...

In this work, we investigate the effect of high pressures on thermal reduction of graphite oxide (GO) using a combination of different characterization techniques and atomistic computational simulations. GO samples were submitted simultaneously to different pressures (up to 7.7 GPa) and temperatures (up to 1500 °C) using a high-pressure chamber. Reactive molecular dynamics simulations were carried out to provide some insight on the observed structural transformations. The samples annealed at ambient pressure consisted of large sheets of reduced GO, containing defects. In contrast, the morphology of the samples processed at higher pressures and temperatures was similar to those of graphite nanocrystals (significantly smaller than the pristine GO sheets). The simulations results corroborated these observations, and helped to explain the reasons for the differences in the morphology of the material when submitted to different conditions. They showed that higher pressures induced a significant reduction on the interplanar volume, inhibiting the formation of gas molecules and enhancing the diffusion and redistribution of functional groups on the GO surfaces. A sequence of reaction and diffusion pathways led the functional groups to concentrate in some regions, causing the local tearing of the structure and formation of crystalline nanodomains as observed in the experiments.

A systematic study of the high-pressure effect on the pyrolysis of solid α-amino acids L-leucine (C6H13NO2), L-alanine (C3H7NO2), L-aspartic acid (C4H7NO4) and glycine (C2H5NO2) is presented. The experiments were performed at 7.7 GPa during 1 min in the temperature range from 300 to 800 °C. The effect of the pyrolysis under high pressure on the electronic structure of carbon and nitrogen was investigated by X-ray photoelectron spectroscopy (XPS). The effect on the atomic bonding configuration was studied by infrared and Raman spectroscopy. The obtained results suggested that the thermal decomposition of amino acids under pressure at 300 and 400 °C started with dehydration followed by polymerization. For temperatures above 600 °C it was observed the formation of graphite-like structures functionalized with nitrogen and oxygen atoms.

Spectroscopic and structural properties of GeO2–PbO glasses doped with Sm3+ ion were investigated before and after densification at 7.7 GPa using X-ray difraction, Raman spectroscopy, ellypsometry, Extended X-ray absorption fine structure (EXAFS) and absorption and luminescence spectroscopy. Judd–Ofelt (J–O) intensity parameters Ωλ (λ = 2, 4, and 6) were calculated and the Ω2 parameter decreased for the glass after densification at 7.7 GPa due to the structural changes of the host glass induced by pressure. Shifts in the Raman band toward lower energies and variations in the intensities of the EXAFS curves indicated that the local environment around Sm3+ became more symmetric after densification, with shorter average Sm–O distances than in the crystalline standard. The radiative properties in the vis and NIR regions were also affected by high pressure.

We report on Raman spectroscopy, temperature-dependent in-plane resistivity, and in-plane magnetoresistance experiments in highly oriented pyrolytic graphite (HOPG) implanted with As and Mn. A pristine sample was also studied for comparison. Two different fluences were applied, $$\varphi = 0.5\times 10^{16}\,\, {\hbox {ions}}/{\hbox {cm}}^{2}$$ and $$\varphi = 1.0\times 10^{16}\,\,{\hbox {ions}}/{\hbox {cm}}^{2}$$ . The implantations were carried out with 20 keV ion energy at room temperature. The Raman spectroscopy results reveal the occurrence of drastic changes of the HOPG surface as a consequence of the damage caused by ionic implantation. For the higher dose, the complete amorphization limit is attained. The resistivity and magnetoresistance results were obtained placing electrical contacts on the irradiated sample surface. Owing to the strong anisotropy of HOPG, the electrical current propagates mostly near the implanted surface. Shubnikov–de Haas (SdH) oscillations were observed in the magnetoresistance at low temperatures. These results allow the extraction of the fundamental SdH frequencies and the carriers’ effective masses. In general, the resistivity and magnetoresistance results are consistent with those obtained from Raman measurements. However, one must consider that the electrical conduction in our samples occurs as in a parallel association of a largely resistive thin sheet at the surface strongly modified by disorder with a thicker layer where damage produced by implantation is less severe. The SdH oscillations do not hint to significant changes in the carrier density of HOPG.

GeO 2 - PbO glass system doped with Sm 3+ ion was synthesized and its structural and spectroscopic properties were investigated by X-ray diffraction, Raman spectroscopy, ellipsometry, absorption and luminescence spectra. Judd–Ofelt theory was applied to evaluate the phenomenological parameters Ω λ (λ=2, 4 and 6). Transition probabilities, radiative lifetimes, branching ratio and stimulated emission cross-section were estimated for the observed VIS-NIR emission. A novel NIR band corresponding to 4 G 5/2 to 6 F 11/2 transition was observed in the range from 1250 to 1350 nm under excitation at 488 nm. The obtained results exhibit potential applications in technological compact light sources and optical devices in the VIS-NIR region.

This paper presents an experimental study about the structural modifications of aminoacids L-leucine (C 6 H 13 NO 2 ), L-alanine (C 3 H 7 NO 2 ), L-aspartic acid (C 4 H 7 NO 4 ) and glycine (C 2 H 5 NO 2 ) after processing at high pressure and high temperature. Experiments were performed at 2.5 and 7.7 GPa at 1100 °C during 1 min, leading to the formation of graphitic structures with low degree of crystallinity. Evidences from Raman and infrared spectroscopy, X-ray diffraction, elemental analysis (CHN) and scanning electron microscopy (SEM) suggested that the resulting graphitic nanostructures depended on the initial concentration of nitrogen and oxygen of the starting samples. The results were compared to the behavior of paraffin, which does not contain nitrogen and oxygen atoms, and 5-Azacytosine (C 3 H 4 N 4 O), containing nitrogen and oxygen but in a cyclic structure.

Blue photoluminescent silica monoliths were obtained by cold sintering of nanosized precursors under high pressure. The samples were prepared from hydrophobic and hydrophilic fumed silica AEROSIL® precursors which were placed inside a soft capsule of hBN and pressed at 7.7 GPa. Practically no photoluminescence (PL) emission was observed for the nanometric powdered precursors while a relatively intense emission was measured for the sintered monoliths, which was dependent on the excitation wavelength (2.47–5.63 eV). The emission was observed in the range between 2.0 and 3.5 eV for all samples with the peak at ~2.7 eV for excitation between 3.26–3.44 eV. The blue band is probably related to the defects produced during the cold sintering process related to plastic deformation and internal stress of the monolith. The intensity of PL spectra of the monoliths obtained from the hydrophilic precursor (A200) was higher than the intensity of the spectra observed for the monoliths obtained from hydrophobic precursors (R974, R816 and R812) probably due to the presence of the carbon groups at the surface of the hydrophobic precursors, hindering the cold sintering process.

Nanofillers of polyaniline nanofibers (PANI) with graphite oxide (GO) or reduced graphite oxide (rGO) were synthesized and characterized. Four samples of PANI/graphite with 10% and 30% of GO or rGO were obtained. The addition of GO or rGO in PANI nanofibers increased the conductivity and improved the thermal stability of the nanofillers. These nanofillers were used in the in situ ethylene polymerization producing PE/PANI/graphite nanocomposites characterized by SEM and TEM, revealing very particular morphologies. PANI/GO or PANI/rGO nanoparticles showed a good dispersion in polyethylene, and an increase in the thermal stability of the final material was observed. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

B2O3–PbO–Bi2O3–GeO2 glass doped with Pr3+ was synthesized and implanted with Au+ using energy of 300 keV and fluence of 1 × 1016 cm−2. Annealing at moderate temperature, below the glass transition temperature, induced nucleation and growth of gold nanoparticles confirmed by the corresponding absorption band in the visible range and by transmission electron microscopy. The average size of the gold nanoparticles was about 2.8 nm. The annealing also induced the crystallization of a nanometer thick layer at the implanted surface of the sample due to the defects created by ion implantation. Structural and optical properties of the samples were characterized by X-Ray difraction, Raman spectroscopy, thermal analysis and absorption and luminescence spectroscopy. Broadband infrared emission was observed under 488 nm excitation covering a wide region of the optical telecommunication window (1.3 μm–1.7 μm). The intensity of this band was enhanced after thermal annealing, probably due to the local field effect of gold nanoparticles. From the optical absorption measurements, Judd–Ofelt theory was applied to evaluate the phenomenological intensity parameters Ωλ (λ=2, 4 and 6) and radiative properties like transitions probabilities, radiative lifetimes, branching ratio and stimulated emission cross-section. The large stimulated emission cross section and broadband effective bandwidth indicate that Pr3+ doped B2O3–PbO–Bi2O3–GeO2 glass containing gold nanoparticles is promising for use in optical amplification.

TiO2/SiO2 nanoparticles with 3, 5, and 10 molar percent of silica, were synthesized by hydrothermal method and characterized by SEM, TEM, N2 adsorption-desorption isotherms, X-ray diffraction, and Raman and UV-Vis spectroscopy. While pristine TiO2 thermally treated at 500°C presents a surface area of 36 m2 g-1 (±10 m2 g-1), TiO2/SiO2 containing 3, 5, and 10 molar percent of silica present surface areas of 93, 124, and 150 m2 g-1 (±10 m2 g-1), respectively. SiO2 is found to form very small amorphous domains well dispersed in the TiO2 matrix. X-ray diffraction and Raman spectroscopy data show that anatase-to-rutile phase transition temperature is delayed by the presence of SiO2, enabling single-anatase phase photoanodes for DSSCs. According to the I×V measurements, photoanodes with 3% of SiO2 result in improved efficiency, which is mainly related to increased surface area and dye loading. In addition, the results suggest a gain in photocurrent related to the passivation of defects by SiO2.

Annealing of glasses at temperatures close to Tg is a usual procedure to reduce internal stresses induced by the conventional melting/quenching process. In this work, the effect of the annealing temperature and time on short-range order of lithium disilicate glass was investigated. The total structure factor and radial distribution function of annealed samples at distinct temperatures and times were derived from synchrotron XRD measurements. The results suggest that short and medium range-orders were affected by the annealing conditions, even for temperatures well below the glass transition temperature, Tg. After annealing at temperatures close to Tg, local arrangements were identified with those corresponding to crystalline phases of lithium disilicate and lithium metasilicate. For temperatures below Tg, the diffusion of lithium atoms was already taking place, while the rearrangements of the SiO4 tetrahedra from the network former started to happen for temperatures close to or higher than Tg.

Structural and optical properties of Nd3+ doped GeO2-PbO glass modified by TiO2 were investigated. The glass composition studied was (59-x)GeO2-41PbO-xTiO2, where x = 0, 1, 2 and 5 mol%. X-ray diffraction confirmed the amorphous nature of the samples. The glass transition temperature increased with the increase of the TiO2 content. The sample containing 1 mol% of TiO2 presented the largest values of density (6.5 g/cm3), refractive index (2.01 at 550 nm) and optical bandgap (3.24 eV) compared with the other TiO2 concentrations. A blue shift in the absorption edge and an enhancement of the luminescence in the NIR spectral region under UV-VIS excitation were observed for the Nd3+ doped-58GeO2-41PbO-1TiO2 glass.

Computer simulation has been increasingly present in the discovery and understanding of materials structure and properties. First-principles simulations, in particular, allow to meaningfully explore the material world without having to resource to experimental methods. Even though their extreme usefulness, first-principle methods tend to be very computer-intensive to the point of being impractical in many situations that are important for the understanding of materials’ behavior. As an alternative, computer simulations can be carried out using interatomic potentials (IPs), in which case an analytic mathematical model for the energy of the system is fitted to a set of crystal structure parameters and experimentally determined physical properties by minimizing a cost function. How close the properties calculated using an IP can get of those experimentally determined is limited both by its analytic form and the model’s parameters. For compounds with different atomic species, the multidimensional parameter space of the cost function most possibly exhibit a very complex landscape. In these cases, global minimization methods are often required. This work explores the use of a differential evolution (DE) algorithm for the parametrization of IPs for two compounds, namely berlinite (AlPO4) and zirconium tungstate ( α -ZrW2O8). Several analytic interatomic potentials (including some previously proposed in the literature) were fitted to experimental lattice parameters, atomic positions, and elastic constants. Two-dimensional mappings of the interatomic potential parameters reveal the complex landscape of the cost function for berlinite and α -ZrW8O8, which exhibits several local minima, broad plateaus, discontinuities, and, in some cases, strong correlations between fitting parameters. The differential evolution algorithm was able to navigate the cost function landscape and, giving a sufficiently large population, was capable to found good candidates for the global minimum, despite all the mentioned difficulties. In all cases here explored, the interatomic potentials re-parametrized using DE yield calculated athermal properties in better agreement with the experimental observables as compared to previous results from the literature.

Luminescent properties and energy transfer processes in GeO2-PbO glasses co-doped with Sm3+/Yb3+ were investigated. The concentration of Sm3+ was 1 mol% while the concentration of Yb3+ was 0.2 and 0.5 mol%. Judd–Ofelt intensity parameters Ω λ ( λ = 2,4,6 ) were calculated from absorption spectra of the co-doped glass samples, together with transitions probabilities A j j ′ and radiative lifetimes τ R . Visible and NIR emission spectra were obtained under excitation of wavelengths corresponding to the 6H5/2 →(6P7/2,6P3/2,4I11/2) transitions of Sm3+ resulting in different emission channels from 4G5/2 level energy to lower energy levels. The set of co-doped and undoped glasses were placed on the top of a conventional silicon solar cell and the relative efficiency was studied. Cooperative energy transfer between the Sm3+ ion and Yb3+ ion would probably be responsible for observed enhancement in the energy efficiency of about 10%.

Pr2O3 doped 26.66B2O3–52.33PbO–16GeO2–4Bi2O3–1Pr2O3 (BPGBPr) glass was synthesized by melt quenching technique. X-ray diffraction confirmed the amorphous nature of the glass and the presence of different vibrational groups was identified by Raman spectroscopy. Differential thermal analysis indicated that the glass transition and crystallization temperature were ~354 °C and ~521 °C respectively, indicating good thermal stability. Visible and near infrared absorption spectra were measured and used to evaluate the Judd-Ofelt intensity parameters to calculate the radiative properties for the emission levels of Pr3+. Photoluminescence spectra were recorded in the visible and infrared regions at temperatures between 16 and 300 K. The spectroscopic results indicated that BPGBPr can be useful as a material for broadband optical amplifier in the region of ~1450 cm−1.

A highly transparent Sm3+ glass with composition B2O3–PbO–Bi2O3–GeO2 was obtained by the traditional melt quenching technique and characterized from structural and spectroscopic points of view. Analysis by X-ray diffraction and Raman spectroscopy confirmed the amorphous nature of the sample and revealed the expected low phonon energy. Differential thermal analysis was also carried out to obtain the glass transition and the crystallization temperatures, related to the thermal stability of the sample. Judd–Ofelt theory was applied to evaluate phenomenological intensity parameters Ωλ (λ=2, 4 and 6) from the optical absorption measurements. The transition probabilities, radiative lifetimes, branching ratio and stimulated emission cross-section were also calculated. Photoluminescence spectra recorded in the visible and infrared regions revealed intense green, orange, red and near infrared emission bands providing a new trace to develop tunable laser and optoelectronics devices.

Heavy metal oxide B2O3–PbO–Bi2O3–GeO2 transparent glass doped with Sm3+ was synthesized and implanted with Au+ using energy of 300 keV and fluence of 1 × 1016 cm−2. The annealing of the implanted glass at moderate temperature below the glass transition temperature induced the nucleation of gold nanoparticles, confirmed by the characteristic absorption band in the visible range and by transmission electron microscopy. Using Mies and Doyles theories for the surface plasmon resonance, the average size of the gold nanoparticles was about 4.6 nm, similar to the values observed by transmission electron microscopy. It was also observed the crystallization of a thin layer of the glass at the implanted surface after annealing, detected by X-ray diffraction and scanning electron microscope. Visible and near-infrared emission of Sm3+ was enhanced after annealing of the glass implanted with gold. Judd–Ofelt parameters and radiative parameters were calculated for the glass doped with Sm3+ with and without gold nanoparticles.

Spectroscopy information (functional groups and semiquantitative data) by Fourier transform infrared (FTIR) spectroscopy of Spongiophyton Krausel emend. Chaloner et al. is reported for the first time, in an attempt to identify spectroscopic patterns that would differentiate species of these taxa. A total of 33 specimens identified as S. lenticularis, S. nanum and S. minutissimum and preserved as compressions were analysed. They come from the same fossiliferous horizon of one outcrop situated in the uppermost Middle Devonian Sao Domingos Formation of the Parana Basin in southern Brazil. The results reveal that functional groups in the 3000–2800 and 1800–700 cm−1 wavenumber regions are present in all specimens. Infrared-derived ratios (CH2/CH3, Al/Ox, Ox1/Ox2, C=O cont., C=C cont., Al2 and Ar/Al) and types of kerogen led to a comparison of the morphological characteristics of the studied material and indicate that compressions of S. lenticularis, S. nanum and S. minutissimum contain different organic compounds. S. nanum and S. minutissimum show higher oxidation and lower aromaticity of its organic matter than S. lenticularis. Additionally, S. lenticularis shows low A-factor values, suggesting a composition similar to type III kerogen, while S. nanum and S. minutissimum showed intermediate to high A-factor values, suggesting a composition similar to type II kerogen. In conclusion, the chemical-analytical techniques and statistical analysis (using PCA technique) reveal a closer taxonomic relationship between S. nanum and S. minutissimum than either has with S. lenticularis, supporting their taxonomic separation, previously proposed in the literature on the basis of morphological features. Lastly, the chemical signatures support the hypothesis that links these enigmatic fossils to a type of lichen or other early inland plant.

Nitro-polycyclic aromatic hydrocarbons (NPAHs) represent a group of organic compounds of significant interest due to their presence in airborne particulates of urban centers, wide distribution in the environment, and mutagenic and carcinogenic properties. These compounds, associated with atmospheric particles of size < 1 μm, have been reported as a major risk to human health. This study aims at identifying the spectral features of NPAHs (1-nitropyrene, 2-nitrofluorene, and 6-nitrochrysene) in emissivity and transmittance spectra of samples of particulate matter < 1 μm (PM1.0) using infrared spectrometry. Carcinogenic and mutagenic risks of the studied NPAHs associated with PM1.0 samples were also determined for two sampling sites: Canoas and Sapucaia do Sul. The results showed that NPAH standard spectra can effectively identify NPAHs in PM1.0 samples. The transmittance and emissivity sample spectra showed broader bands and lower relative intensity than the standard NPAH spectra. The carcinogenic risk and the total mutagenic risk were calculated using the toxic equivalent factors and mutagenic potency factors, respectively. Canoas showed the highest total carcinogenic risk, while Sapucaia do Sul had the highest mutagenic risk. The seasonal analysis suggested that in the study area the ambient air is more toxic during the cold periods. These findings might of significant importance for the decision and policy making authorities.

Nimodipine (NIM) is a calcium channel-blocking agent, which in the solid state exhibits two crystalline modifications, Mode I and Mode II. The first one is a racemic mixture, while the second is a conglomerate. Because the drug has poor aqueous solubility and Mode I is twice as soluble as Mode II, the former is widely preferred for the development of pharmaceutical forms. In order to study the effect of thermal stimuli on the behavior of NIM, an analytical method was developed coupling ATR-FTIR spectroscopy to Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS). The method allowed to monitor the transformations of each polymorph, their respective mixtures and commercial samples, during the thermal treatment. It was observed that Mode II experienced changes during the experiments and the chemometric technique provided the abundance profile and the pure spectra of the different species involved. In this way, it was established that Mode II has two transitions, at 116.8 °C and 131.9 °C, which reflect that Mode II is first transformed into Mode I, which then melts. The liquid phase solidifies to give an amorphous (AM) vitreous solid, which does not revert to the crystalline state. The analysis of a commercial sample of NIM exhibited the similar transformations than Mode II; however, a pronounced decrease was noted in the first transition temperature (95 °C), whereas the second remained essentially unchanged (131.6 °C). This could be a result of the presence of mixtures of Mode I and Mode II (0.32:0.68) in the bulk solid, as confirmed by the analysis of a physical mixture of crystals of Modes I and II. Therefore, it was concluded that the developed ATR-FTIR/MCR-ALS method is suitable for the detailed analysis of the crystalline forms of NIM in bulk drug and enables de study of their possible thermally promoted interconversions. Fil: Calvo, Natalia Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: Balzaretti, Vilma Teresa. Universidad Nacional de Rosario; Argentina Fil: Antonio, Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: Kaufman, Teodoro Saul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: Maggio, Ruben Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina

Sol–gel processing and heat-treatment were used to obtain nanopowders with tetragonal phase of undoped zirconia reinforced with well-dispersed multi-walled carbon nanotube (MWCNTs), having contents between 1 and 5 wt.%. Amorphous nanopowders treated at 500 ° C crystallized in the tetragonal phase of zirconia with an average crystallite size of 25 nm. The nanocomposites containing 3 wt.% of MWCNTs reached 98% of the theoretical density, with an increase in hardness of about 15%, and a fracture toughness about 110% higher compared to the values obtained for pure zirconia compacted at the same conditions. The novelty in our study is the production of zirconia/MWCNTs nanocomposites with enhanced mechanical properties by compaction of nanopowders under high-pressure at moderate temperature.

The effect of high pressure on the vibrational modes of 5-azacytosine (C 3 H 4 N 4 O) and propanedinitrile (CH 2 (CN) 2 ) was investigated at room temperature using a diamond anvil cell (DAC). In situ infrared and Raman spectroscopy results indicated that the ring structure of 5-azacytosine remained preserved and the band shifts induced by high pressure were fully reversible up to 13 GPa. For the open-chain structure of propanedinitrile, a polymerization reaction was observed by infrared spectroscopy almost instantly at about 15 GPa at room temperature. The same pressure-induced polymerization was observed after a week at 1 GPa, at room temperature.

Polycyclic Aromatic Hydrocarbons (PAHs) are a group of various complex organic compounds composed of carbon and hydrogen, and two or more condensed benzene rings. They are released into the atmosphere by the incomplete combustion or pyrolysis of organic matter. Some of the major sources of PAHs are burning of coal, wood, oil or gas, vehicle engines exhaust, and open burning. PAHs are of great concern to human health mainly because of their known carcinogenic and mutagenic properties. Consequently, it is very important to study atmospheric PAHs, especially those associated with ultrafine particles. This study aims to identify the spectral features of PAHs in samples of particulate matter < 1 µm (PM1) using infrared spectrometry. Emissivity and transmittance spectra of PAHs were obtained by infrared spectroscopy. PAHs standards spectra contributed to effectively identify PAHs in PM1 samples. Emissivity and transmittance spectra in the range of 680–900 cm–1 exhibited the largest number of bands due to C–C out-of-plane angular deformations and C–H out-of-plane angular deformations. Bands of medium intensity in 2900–3050 cm–1 region were also observed due to C–H stretching typical of aromatic compounds, although with lower intensity. This study compared the emissivity and transmittance spectra acquired using two different infrared spectrometers in order to identify PAHs in samples of atmospheric particulate matter and analyzed the capability and advantages of each of the infrared spectrometers. In addition, it was confirmed that the PAHs under study can be distinguished by their infrared spectral fingerprints.

Smectite has been used to capture radioactive cations through adsorption in deep radioactive waste repositories in various parts of the world. Smectite is also important in the transport of water and some trace element cations such as rare earth elements (REE), which are captured in its structure, back to the mantle in subduction environments. Such captures are based on the ionic strength of the surrounding solution and the adsorption coefficient of smectite. However, captured cations can be released from the smectite structure once the ionic strength of the solution changes. In this work, the stability of a particular smectite (montmorillonite) structure saturated with lanthanum was verified at high pressures (up to 12 GPa) and room temperature and at high pressure and high temperature (HPHT) concomitantly. La 3+ -montmorillonite remains stable up to 12 GPa at room temperature with a small variance in its vibrational mode. At HPHT, however, the structure becomes muscovite-like and rich in La 3+ . When in contact with a Ca 2+ -enriched solution, La 3+ is partially replaced by Ca 2+ in the new phase, returning to its original Ca 2+ -montmorillonite phase, whereas another part remains La-muscovite-like. These results were confirmed by X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy.

In a subduction zone, water-rich pelagic sediments overlying the subducting oceanic plate are accumulated, forming an accretionary wedge. A portion of these sediments, primarily smectites, can subduct and lose the water present in their pores, but the mechanism of the clay structural transformation and its composition are not well-defined. Smectite clay minerals can remain stable, carrying water at pressures corresponding to the upper mantle and thus contributing to the occurrence of melting and metasomatic processes in the mantle. In this work, we performed several high-pressure and high-temperature experiments to verify the structural behavior of a potassium-saturated smectite under various pressure and temperature conditions: (1) atmospheric pressure at two different temperatures (100 °C to 700 °C); (2) room temperature (25 °C) and pressure up to 11.5 GPa — diamond anvil cell (DAC) experiments; (3) under pressures of 2.5 GPa and 4.0 GPa and temperatures from 200 °C to 700 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared spectroscopy (FTIR) analysis on all samples studied suggest that, under elevated pressures (2.5 GPa, which corresponds to a depth of approximately 75 km, and 4.0 GPa, equivalent to a depth of approximately 120 km), smectite remains stable until 200 °C. With increasing temperature, the initial structure partially loses its interlayer H 2 O and transforms into a mixed layer of illite/smectite, which is maintained until 400 °C under 2.5 GPa and until 300 °C under 4.0 GPa. Beyond these conditions, with increasing temperature, the smectite loses all of its interlayer H 2 O and transforms into muscovite. Additionally, at room temperature, smectite is stable under nearly 12 GPa. These results contribute significantly to the understanding of how pelagic sediment dehydration and transformation occur in the subduction process, as well as the behavior of smectite under the influence of increasing pressure and temperature.

This paper reports an experimental study about the pressure dependence of the vibrational modes of tricosane paraffin (C 23 H 48 ) investigated by in situ Raman and infrared spectroscopy in a diamond anvil cell (DAC). The main vibrational bands were followed up to 11 GPa and the observed behavior indicated a conformational disorder induced by pressure, corresponding to a transition from ordered to disordered state of the linear chains from 2 to 5 GPa followed by a transition to an amorphous state under pressure above 5 GPa. However, this behavior was reversible after compression–decompression cycle showing that this linear compound was structurally and chemically stable up to 11 GPa at room temperature.

Diamonds from Juina area, Brazil, are known by their superdeep origin related to recycling of oceanic crust, basalts and pelagic sediments in the lower mantle. Chemical and structural data on mineral inclusions support this hypothesis. We have studied the inclusions of five diamonds from Juininha alluvial deposits, part of the Juina province, and we have found for the first time in terrestrial rocks, a paragenetic assemblage only observed in high-pressure experiments and/or extraterrestrial rocks. The results suggest the presence of a veined-type lower mantle, where an assemblage of hydrous basaltic origin (MgFeAl-perovskite) is crosscut by pockets and/or veins of intermediate to acid compositions, dominantly constituted by SiO 2 + (K,Na)-Hollandite. The silicate paragenesis (KNa-Hollandite and SiO 2 ) can be produced by melting of a pelagic metasedimentary source subducted together with the oceanic slab down to the uppermost lower mantle. Such a veined-type lower mantle puts in evidence a derived source modified by melting/dehydration of multicomponent from a subducted slab.

The main purposes of fission track thermochronology are unravelling the thermal histories of sedimentary basins, determining uplift and denudation rates, identifying the structural evolution of orogenic belts, determining sedimentary provenance, and dating volcanic rocks. The effect of temperature on fission tracks is well known and is used to determine the thermal history; however, the effect of pressure on the stability of tracks is still under debate. The present work aims to understand the role of pressure on the annealing kinetics of apatite fission tracks. The samples of Durango apatite used in our experiments were chosen for their international recognition as a calibration standard for geological dating. Neutron irradiation of the samples, after total annealing of their spontaneous tracks, produced induced tracks with homogeneous densities and lengths. The effect of pressure associated with temperature on fission track annealing was verified by experimental procedures using a hydraulic press of 1000 t with a toroidal chamber profile. The experiments consisted of a combination of applying 2 and 4 GPa with 20 , 150 , 190 , 235 , and 290 ° C for 1 and 10 h . The annealing rate was analysed by measuring the lengths of the fission tracks after each experiment using optical microscopy. The results demonstrate that the annealing of apatite fission tracks has a pressure dependence for samples subjected to 2 and 4 GPa . However, when extrapolated to pressures of ⩽ 150 MPa , compatible with the normal geological context in which apatite fission track methodology is broadly used, this dependence becomes insignificant compared to the temperature effect.

We have investigated the structural changes induced by high-pressure in lithium disilicate glass with stoichiometric composition Li2O.2SiO2 (LS2). Using toroidal type high-pressure chambers, glass samples were processed at 2.5GPa, 4GPa, 6GPa and 7.7GPa at room temperature. Synchrotron X-ray diffraction measurements were used to obtain the radial distribution functions (RDF) in order to follow the structural changes induced after processing at high pressure. Compared to a pristine sample, the main change observed for the samples processed up to 6GPa was associated to the distortion of the SiO4 tetrahedral structure. However, for the sample processed at 7.7GPa, a drastic change in the RDF indicated the formation of a distinct amorphous phase. The observed polyamorphism is important for a better understanding of the nucleation kinetics of crystalline phases under high pressure.

The aim of this work was to investigate the formation of lithium metasilicate (Li 2 SiO 3 ) under high pressure and high temperature starting from lithium disilicate glass with the stoichiometric composition Li 2 O·2SiO 2 (LS 2 ). Monolithic LS 2 glass samples were processed at 4.25 GPa, 4.5 GPa, 5 GPa, 5.5 GPa, 6 GPa and 6.5 GPa and submitted, simultaneously, to heat treatment for nucleation and growth of the crystalline phases. The crystallization of the samples was investigated by X-ray diffraction, Raman spectroscopy and optical microscopy. In the pressure and temperature range investigated, crystalline Li 2 Si 2 O 5 remained stable up to 6 GPa and the formation of the metasilicate phase Li 2 SiO 3 started at 4.25 GPa coexisting with quartz and coesite up to 6.5 GPa. The segregation of SiO 2 phases during the crystallization of Li 2 SiO 3 was a consequence of the lithium deficiency of the starting LS 2 composition.

The aim of this work was to investigate by X-ray photoelectron spectroscopy the effect of high pressure on the chemical environments of Si 2p, O 1s and Li 1s in lithium disilicate glass ceramic with stoichiometric composition Li2O·2SiO2 (LS2). A group of samples was processed at 2.5 GPa, 4 GPa and 7.7 GPa at room temperature and a second group was crystallized under high pressure and high temperature. Large shifts of the binding energy toward higher energies were observed in the X-ray photoelectron spectroscopy spectra for samples of the first group after densification at 2.5 and 4 GPa. For samples processed at 7.7 Gpa, the major component of the binding energy for the Si 2p environment remained practically unchanged compared to the pristine sample but new components, with smaller intensities, appeared in the spectra, indicating the existence of distinct Q-species induced by high pressure. This behavior may be related to changes in the number of bridged and non-bridged oxygen atoms in the glass structure. The results for the second group of samples, crystallized under high pressure, showed evidences of three binding energies for the O atoms, one of them related to non-bridged and two of them to bridged O atoms.

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere.

Zirconium oxide is a ceramic material widely studied due to its mechanical and electrical properties that can be improved with the use of carbon nanotubes (CNTs) as reinforcement. The synthesis of CNT/zirconia composites by sol–gel method is still very scarce, due to the hydrophobic nature of the CNTs, being their dispersion in aqueous medium an intrinsic difficulty to the synthesis. In this work, we present a sol–gel synthesis for MWCNTs/zirconia composites, where two kinds of surfactants, sodium and ammonium stearates dissolved in water (1 g/100 mL), were used as dispersant agents for multiwall carbon nanotubes (MWCNTs). They are cheap and easy to prepare, and were very effective in dispersing the MWCNTs. Different quantities of MWCNTs (up to 5 wt%) were added in the solution of stearate/water and this solution with the highly dispersed MWCNTs was added to the zirconia sol–gel, producing composites of MWCNTs/zirconia with different concentrations of MWCNTs. All the powders were heat treated at 300 and 500 °C and the powder characterization was performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). The composite MWCNTs/zirconia remained amorphous at 300 °C and presented a tetragonal phase at 500 °C with an average grain size of about 20 ± 3 nm, determined by the Scherrer equation from the XRD patterns. For these crystalline samples, TEM images suggest a more effective interaction between MWCNTs with ZrO2 matrix, where it can be observed that the carbon nanotubes are fully coated by the matrix.

In this work, the pyrolysis under high pressure of hydrocarbons dispersed inside a nanosized silica matrix (Aerosil) was investigated. The samples consisted of hydrophobic nanometric silica powder terminated by methyl groups with carbon contents ranging from 0.7 to 4 wt%. The pyrolysis was carried out in the temperature range from 1000 to 1600 °C under high pressure (1.25 up to 7.7 GPa) to keep the two-dimensional distribution of carbon atoms originally at the silica grain boundaries. Evidences from Raman spectroscopy and transmission electron microscopy suggested that the resulting carbon nanostructures were actually graphene-like nanoflakes. The size of the nanostructures calculated from the ID/IG ratio increased from 6 to 30 nm for processing temperatures increasing from 1000 to 1600 °C under pressure, respectively. The results revealed that the very good dispersion of the methyl groups inside the nanosize silica matrix, and the confinement under high pressure during the pyrolysis, played both a relevant role in the resulting carbon nanostructures. Copyright © 2012 John Wiley & Sons, Ltd.

The aim of this work was to investigate the effect of high pressure and high temperature on the refractive index of lithium disilicate glass ceramic with the stoichiometric composition Li 2 O·2SiO 2 (LS 2 ). A first group of monolithic LS 2 glass samples were processed at 2.5 GPa, 4 GPa and 7.7 GPa at room temperature and a second group was submitted to high pressure and, simultaneously, to heat treatments for nucleation and growth of the crystalline phases. For comparison, samples submitted to the same heat treatments at 1 atm were also investigated. The refractive index of the samples was obtained by spectral ellipsometry and the results were clearly dependent on the particular pressure and temperature conditions. The crystallization of the samples was investigated by X-ray diffraction. For the samples processed under high temperature at 1 atm and at 2.5 GPa a fraction of the originally amorphous glass was transformed to a monoclinic phase of lithium disilicate. For the samples processed under high temperature and at 4 GPa, a large fraction of the originally amorphous glass transformed to an orthorhombic phase while, at 7.7 GPa, it was observed the formation of lithium metasilicate.

A series of Ni-Al hydrotalcite-type samples modified with copper was prepared and evaluated for use in the decomposition of ethanol. The partial substitution of Ni by Cu has small influence on the specific surface area and on the structure (XRD). However, it has a strong influence on the degree of reducibility (shifts to lower temperatures) and on the selectivity of reaction. The selectivity towards H2 and CO increases for reactions conducted at a higher temperature, which is followed by a decrease in the amount of carbon formed. Catalysts with a high Cu content exhibit lower selectivity for H2 and CO. SEM images show that carbon nanotubes with greater and more variable diameters and lengths were formed by Cu-loaded catalysts, possibly due to the sintering of copper. Nevertheless, the Raman spectra suggest that the nanotubes produced by the Cu-containing samples have higher purities and fewer defects.

O aumento de produtividade da indústria moveleira exige usinagem a altas velocidades de corte e ferramentas que suportem as elevadas exigências do processo de corte. A grande maioria das ferramentasutilizadas atualmente, em geral ligas metálicas, não apresentam as características adequadas, desenvolvendo alto desgaste na cunha de corte. A heterogeneidade da estrutura e a disposição irregular das fibras associada a característica altamente abrasiva da madeira são os principais fatores para ocorrência dos elevados desgastes. Na solução destes problemas é freqüentemente empregada ferramentas de corte com revestimentos de alta resistência ao desgaste. Nesse sentido, o uso de filmes de diamante depositados por CVD (Chemical Vapor Deposition) apresentam alto potencial de sucesso, pois combina elevada dureza, baixo coeficiente de atrito, alta condutividade térmica e elevada inércia química. Porém, este tipode ferramentas ainda não é utilizado em escala industrial devido principalmente à baixa adesão entre o filme e o substrato. Este trabalho tem por objetivo avaliar ferramentas de corte produzidas por deposição de filmes de diamantes em substratos de metal duro (WC Co) com diferentes parâmetros de processo (CVD). A avaliação das ferramentas, produzidas por diferentes condições de deposição, foi realizada através de ensaios sistemáticos em operação de torneamento de corpos de prova de madeira itaúba, sendo monitorados os desgastes desenvolvidos na cunha de corte. O comportamento dos desgastes nas ferramentas diamantadas foi comparado com os desgastes desenvolvidos em uma ferramenta de metal duro, empregada como referência. Os resultados obtidos neste trabalho mostram o grande potencial do emprego das ferramentas diamantadas na indústria moveleira. The increase in productivity of the furniture industry requires high speed machining and cutting tools to support the high demands of the cutting process. Most of the cutting tools do not have appropriate characteristics and develop high wear on the wedge cut. The heterogeneous structure and irregular arrangement of fibers associated with highly abrasive characteristic of wood are the main factors for the occurrence of high wear. In solving these problems are frequently usedcutting tools with coatings of high wear resistance. In this sense, the use of diamond films deposited by CVD (Chemical Vapor Deposition) is a high potential forsuccess, as it combines high hardness, low coefficient of friction, high thermal conductivity and high chemical inertness. However, this type of tools is not yet used on an industrial scale mainly due to low adhesion between the film and the substrate. This study aims to evaluate cutting tools produced by deposition of diamond films on carbide (WC Co) substrates with different process parameters (CVD). The evaluation of the tools producedby different deposition conditions has been implemented through systematic tests in turning operation of the Wood “itaúba”. In the same time was monitored the wear (Vbmáx) developed in the wedge cut. The wear on diamond tools has been compared with the wear developed in a carbide tool, used as reference. The results of this study show the great potential of the use of diamond tools in the furniture industry.