micro-FTIR Studies Research Articles

Micro-FTIR and EPMA Characterisation of Charoite from Murun Massif (Russia)

Combined micro-Fourier transform infrared (micro-FTIR) and electron probe microanalyses (EPMA) were performed on a single crystal of charoite from Murun Massif (Russia) in order to get a deeper insight into the vibrational features of crystals with complex structure and chemistry. The micro-FTIR study of a single crystal of charoite was collected in the 6000–400 cm−1 at room temperature and after heating at 100°C. The structural complexity of this mineral is reflected by its infrared spectrum. The analysis revealed a prominent absorption in the OH stretching region as a consequence of band overlapping due to a combination of H2O and OH stretching vibrations. Several overtones of the O-H and Si-O stretching vibration bands were observed at about 4440 and 4080 cm−1 such as absorption possibly due to the organic matter at about 3000–2800 cm−1. No significant change due to the loss of adsorbed water was observed in the spectrum obtained after heating. The occurrence of well-resolved water bending vibration bands at about 1595 and 1667 cm−1 accounts for more than one structural water molecule as expected by charoite-90 polytype structure model from literature. The chemical composition of the studied crystal is close to the literature one.

The dehydroxylation of chrysotile: A combined in situ micro-Raman and micro-FTIR study

One of the most important mechanisms releasing water in subducting slabs of oceanic crust is connected to the dehydration of serpentinized oceanic rocks. This study reports on a detailed investigation of the transition from chrysotile-an important serpentine mineral-to forsterite through the release of water. The dehydroxylation of natural chrysotile and the subsequent phase change to forsterite was studied by in situ micro-Raman and micro-FTIR spectroscopy in the temperature range of 21 to 871 °C. Comparisons were made with previously published data of lizardite-1T. Micro-Raman spectra obtained in the low-frequency (100-1200 cm-1) and high-frequency ranges (3500-3800 cm-1) were complemented by micro-FTIR measurements between 2500 and 4000 cm-1 to study changes in the chrysotile structure as a function of dehydroxylation progress. In general, room-temperature chrysotile bands lie at higher wavenumbers than equivalent bands of lizardite-1T except of three bands positioned at 301.7, 317.5, and 345.2 cm-1. Different band assignments of chrysotile and lizardite-1T Raman spectra from literature are compared. The most striking assignments concern the three aforementioned Raman bands and those lying between 620 and 635 cm-1. The present data support a chrysotile- or at least curved TO layer related origin of the latter. Deconvolution of overlapping OH stretching bands at room temperature revealed the presence of five (FTIR) and four (Raman) bands, respectively. A slight change in the ditrigonal distortion angle α during heating and the effects of a radius-dependent dehydroxylation progress can be shown. Furthermore, it was possible to identify a quenchable talclike phase immediately after the onset of the dehydroxylation at 459 °C. Main bands of this phase are positioned at 184.7, 359.2, and 669.1 cm-1 and a single OH band at 3677 cm-1, and are thus quite similar to those reported for dehydroxylating lizardite-1T. Their appearance coincides with the formation of forsterite. A maximum in the integral intensity of the talc-like intermediate is reached at 716 °C. At higher temperatures, the intermediate phase breaks down and supports the accelerated growth of forsterite. The lack of OH bands with the concomitant appearance of broad chrysotile-related modes in the low-frequency range after heating the sample to 871 °C indicates the presence of a heavily disordered phase still resembling chrysotile. However, there are no spectral evidences for further Si- and/ or Mg-rich amorphous phases during the dehydroxylation and no indications for a relationship between the breakdown of the talc-like phase and the growth of enstatite as previously reported in literature.

Toughening of Nylon-6 by Semicrystalline Poly(vinylidene fluoride): Role of Phase Transformation and Fibrillation of Dispersed Particles

Superior toughness has been achieved in the nylon-6/PVDF blends with semicrystalline PVDF component as the dispersed particles. Morphological observations on the impact tested specimens unambiguously reveal the formation of voids and microfibrils across the fracture surface, suggesting that some extent of plastic deformation occurs within ductile PVDF particles. It is further confirmed by the structural evolution at crack tips through micro-FTIR studies on the quasi-static stretching of precracked films. During fracture α → β phase transformation of dispersed PVDF particles first takes place, followed by the extensive plastic deformation and fibrillation of new-formed β-crystals. It is believed that the α → β phase transformation and fibrillation of β-crystals of the dispersed PVDF particles are responsible for the toughness enhancement in the nylon-6/PVDF blends with good interfacial adhesion.

Micro-FTIR study of soot chemical composition—evidence of aliphatic hydrocarbons on nascent soot surfaces

Previous studies suggest that soot formed in premixed flat flames can contain a substantial amount of aliphatic compounds. Presence of these compounds may affect the kinetics of soot mass growth and oxidation in a way that is currently not understood. Using an infrared spectrometer coupled to a microscope (micro-FTIR), we examined the composition of soot sampled from a set of ethylene-argon-oxygen flames recently characterized (A. D. Abid, et al. Combust. Flame, 2008, 154, 775-788), all with an equivalence ratio Φ=2.07 but varying in maximum flame temperatures. Soot was sampled at three distances above the burner surface using a probe sampling technique and deposited on silicon nitride thin film substrates using a cascade impactor. Spectra were taken and analyses performed for samples collected on the lowest five impactor stages with the cut-off sizes of D(50)=10, 18, 32, 56 and 100 nm. The micro-FTIR spectra revealed the presence of aliphatic C–H, aromatic C–H and various oxygenated functional groups, including carbonyl (C=O), C–O–C and C–OH groups. Spectral analyses were made to examine variations of these functional groups with flame temperature, sampling position and particle size. Results indicate that increases in flame temperature leads to higher contents of non-aromatic functionalities. Functional group concentrations were found to be ordered as follows: [C=O]<[C–O]<[aliphatic C–H]. Aliphatic C–H was found to exist in significant quantities, with very little oxygenated groups present. The ratio of these chemical functionalities to aromatic C–H remains constant for particle sizes spanning 10-100 nm. The results confirm a previous experimental finding: a significant amount of aliphatic compounds is present in nascent soot formed in the flames studied, especially towards larger distances above the burner surface.

Molecular Origin of Enhanced Strength in the Monofilament of Syndiotactic Polypropylene Because of Annealing: A Micro-FTIR Study

The conformational and polymorphic transformations in the melt-spun monofilament of syndiotactic polypropylene upon annealing and subsequent stretching have been first explored by micro-FTIR studies. The results indicate that annealing of as-spun monofilament gives rise to an unusual increase in the molecular orientation of helical conformations in both amorphous phase and ordered crystals as a result of structural transitions of transplanar conformations to helical ones as well as mesophase to ordered crystals. The increased molecular orientation in the annealed monofilament is mainly responsible for the enhanced strength during stretching. Furthermore, high stress exerted by the molecular chains of annealed monofilament is confirmed by the significant structural transitions opposite to that induced by annealing.

Micro-FTIR Study of Molecular Orientation at Crack Tip in Nylon 6/Clay Nanocomposite: Insight into Fracture Mechanism

A study on the mechanism for the degraded toughness in nylon 6/clay nanocomposite is explored in this article. Such a nanocomposite exhibits lower specific essential work of fracture we and specific nonessential work of fracture betawp than its pure nylon 6 counterpart, as revealed by essential work of fracture (EWF) measurements. Furthermore, the molecular orientation in a small region (20x20 microm2) ahead of crack tip, obtained from micro-FTIR measurements for the first time, is found to be lower in the nanocomposite during crack initiation and propagation. The decreased molecular orientation, mostly resulted from severe microvoiding at crack tips, is responsible for the reduced specific essential work of fracture we. Meanwhile, the molecular orientation around crack tip also indicates that lower plastic deformation occurs in the plastic zone, which is well correlated with decreased specific nonessential work of fracture betawp in the nanocomposite.

In situ micro-FTIR study of the solid–solid interface between lithium electrode and polymer electrolytes

In situ micro-FTIR spectroscopy was explored to characterize the solid–solid interface between lithium electrode and polymer electrolytes. The cyclic voltammetric (CV) results indicated that the reduction reactions of oxygen and water as well as the formation of underpotential deposition (UPD) Li occur in the Li/PEO 20-LiN(CF 3SO 2) 2 electrolyte interface in the different potential region. The infrared spectral changes observed during the CV process revealed that there is a direct correlation between the CV peaks and the magnitude of the infrared peaks. It is shown that the infrared reflectivity from the solid–solid interface is very sensitive to the formation of the passive layer on the lithium electrodes. The results obtained from optical micrographs also displayed directly the formation of the passive layer along with lithium deposition and dissolution process. It is correlated well with in situ FTIR and electrochemical experiments.

Micro-FTIR study of the blend of humates with calcium hydroxide used to prepare smokeless fuel briquettes

The blend of humates with calcium hydroxide and the briquettes prepared with this blend have been used by Fourier Transform Infrared Microscopy Spectrometers. An adequate preparation of the microsamples allows to obtain good quality spectra to elucidate the coal constituents and additives of the blend. It has been followed the molecular changes produced by the effect of the temperature. It has been observed the decrease of the hydroxyl and methoxy groups and the increase of the carboxylates. Fuel briquettes have been prepared with carbonaceous materials which require the use of a binder to link particles. Moreover, a calcium additive has been sometimes added to reduce sulphur emissions during combustion. As a consequence of this addition, a chemical reaction is produced. It is observed that these prepared briquettes are waterproof.

Carbonaceous material in S-type Xihuashan granite.

In order to verify the presence of residual organic matter in some S-type granites, a method used conventionally in petroleum geochemistry for isolation of kerogen was employed to separate carbonaceous material (CM) from the Xihuashan granite, Jiangxi Prov., China. Optical, XRD and SEM/EDAX analyses identified the acid-insoluble residue as mainly composed of various mineral debris, with a minor carbonaceous fraction found in the residue. LMR and micro-FTIR studies showed that the residue contained a small amount of CM, which is heterogeneous in composition and structural state. The occurrence of CM in the granite implies that this granitic magma originated from sediments and crystallized at relatively lower temperatures and high pressures. This deduction is consistent with geological and geochemical studies of the Xihuashan granite. A tentative model was suggested which connects CM in S-type granite with organic matter in sedimentary rocks. The conditions under which CM can be preserved in S-type granite are discussed. The occurrence of some heavy hydrocarbons is expected in the Xihuashan granite.