The Kinetics and Mechanism of Cure of an Amino-glycidyl Epoxy Resin by a Co-anhydride as Studied by FT-Raman Spectroscopy

The thermal curing behaviour of tetraglycidyl-4,4’-diaminodiphenylmethane (TGDDM) and a co-anhydride mixture consisting of maleic anhydride (MA) and hexahydrophthalic anhydride (HHPA) was studied from 55oC to 100oC by real-time FT-Raman spectroscopy. The quantitative changes in concentrations of anhydride, epoxy, and new-formed ester were measured and empirical reaction rate curves were constructed reflecting the kinetics of the curing process. After an induction period a simple kinetic scheme that is first order in both epoxy and anhydride monomer consumption described the reaction profile until the reaction was influenced by chemo-rheological changes due to vitrification transition. FT-Raman analysis revealed that curing propagation mainly occurs by polyesterification between epoxide and anhydride. Possible side reactions including the homopolymerization of MA are considered. The main side reaction is decarboxylation of MA that may produce some autocatalysis, but this is a minor contribution to the kinetics of cure. No conclusive evidence has been found for homopolymerization of MA or initiation of the curing reaction by the reaction product of TGDDM and MA, compared to the polyesterification

Infrared Microspectroscopic Study of the Thermo-Oxidative Degradation of Hydroxy-Terminated Polybutadiene/Isophorone Diisocyanate Polyurethane Rubber

Hydroxy-terminated polybutadiene/isophorone diisocyanate (HTPB-IPDI) polyurethane rubber that was aged in air at elevated temperatures has been studied by infrared microspectroscopy. Spectra were collected in transmission mode on microtomed samples. Analysis of sets of spectra taken across the sectioned material showed that most of the degradation was occurring in the polybutadiene part of the polymer and that the urethane linkage was essentially unchanged. The trans isomer of the polybutadiene appears to be preferentially degraded compared with the vinyl isomer. The IR technique does not provide significant information about the cis isomer. The IR spectra indicated that likely degradation products included acids, esters, alcohols, and small amounts of other products containing a carbonyl functional group. Band area ratios, supported by a principal components analysis, were used to derive degradation profiles for the material. These profiles were steep-sided indicating an oxygen diffusion limited process

Application of Attenuated Total Reflectance Micro-Fourier Transform Infrared (ATR-FTIR) Spectroscopy to the Study of Coal Macerals: Examples From The Bowen Basin, Australia

Attenuated total reflectance micro-Fourier transform infrared (ATR-FTIR) spectrometry has been successfully used to characterise coal macerals, in particular telocollinite, and to investigate changes in the aromatic and aliphatic functional groups in the telocollinite, over a wide rank range (Rvmax from 0.39 to 3.52%) in coals from the Bowen Basin, Queensland, Australia. The results show that ATR-FTIR is very sensitive to the increasing aromaticity (the fraction of carbon atoms involved in aromatic units) of the telocollinites, and thus is a very useful tool to study the evolution of aromatic and aliphatic functional groups with maturation of telocollinite, and also to differentiate and characterise the various macerals in coal samples. In comparison with other micro-FTIR techniques, ATR-FTIR has many advantages: (1) no difficult and time-consuming procedures are required to obtain “pure” maceral separations, or for preparation of thin coal slices; (2) the ATR-FTIR spectra have better signal-to-noise ratio and increased sensitivity; (3) the ATR-FTIR spectra are similar to absorption spectra, but without significant spectral distortion

FT-IR Spectroscopy of Fluoro-Substituted Hydroxyapatite: Strengths and Limitations

Fluoro substituted hydroxyapatite (FHAp) samples were prepared by a cyclic pH method. Both calcined and uncalcined samples were subjected to elemental analysis (F, Ca, P) and X-ray diffraction (XRD) analysis to verify composition and phase purity. Good correlation between a-axis parameters and fluoride ion content was found for calcined samples, however, for uncalcined samples the fluoride ion content was higher than estimated from the a-axis values. Fourier transform infra red (FT-IR) spectroscopy analysis of the calcined samples showed OH band shifts and splitting in accordance with F-HO interactions affecting the OH vibration. We conclude that the OH libration (620–780 cm-1 range) is more suited for estimation of fluoride ion content than the OH stretching. In contrast, uncalcined samples all displayed FT-IR spectra similar to that of hydroxyapatite (HAp) despite the presence of fluoride ions (18–73%). FT-IR emission spectroscopy was used to probe the changes occurring in the FT-IR spectra of HAp and FHAp samples upon heating. Interpretation of the spectral changes occurring during heating to 1,000 degrees Celsius and subsequent cooling is given. Room temperature spectra of samples heated to various temperatures was used to determine the temperature necessary to produce FT-IR spectra displaying the expected OH bands. A model accounting for the combined observations is proposed

Single Crystal Raman Spectroscopy of Cerussite

Raman and infrared active modes of cerussite were assigned according to their symmetry species and compared to other aragonite group minerals. Small satellite bands at 823 and 1031 cm–1 on the low-wavenumber side of the fundamental vibrations 2 and 1, respectively, have been assigned to the isotopic substitutions of 13C and 18O. The Raman active 1 and 2 carbonate modes are observed at 1051 and 835 cm–1. The absence of the B2g component of the 1 and 2 vibrations has been explained by the small coupling between the Ag and B2g modes. The Raman active 3 carbonate anti-symmetric stretching mode is observed at 1361 (Ag), 1376 (B1g), 1419 (B3g), and 1477 (B2g) cm–1, while the corresponding infrared active bands are observed at 1396, 1432, and 1456 cm–1. The Raman active 4 carbonate bending mode is observed at 673 (Ag), 668 (B2g), 681 (B1g), and 694 (B2g) cm–1. The corresponding infrared bands are observed at 670, 679, and 698 cm–1. In both 3 and 4 the factor group splitting between the B1g and B3g modes is 1 to 3 times smaller than the separation of the Ag and B2g modes. Raman active lattice vibrations are detected at 120 (B3g), 132 (Ag), 148 (B1g), 152 (B2g), 174 (B2g), 179 (B1g), 213 (Ag), 226 (B3g), and 243 cm–1 (B2g). Corresponding infrared active bands are detected at 573, 543, 573, 423, 375, 290, 205, 165, 146, and 134 cm–1. Raman bands at 949, 966, 989, 1000, and 1104 cm–1 and at 922, 946, 967, 988, 996, and 1007 cm–1 in the infrared spectra are assigned to combination and overtone bands. Raman bands at 1676 (Ag), 1689 (Ag), 1730 (B3g), and 1740 (B1g) cm–1 are ascribed to combination modes of 1 + 4 with bands at 2052 and 2092 cm–1 assigned to 2 1. Corresponding infrared bands are observed at 1729 and 1740 cm–1 (1 + 3). Bands at 2359, 2409, 2471, and 2521 cm–1 are ascribed to 1 +3, with broad bands at 1246 and 1323 cm–1 assigned to 2 4 modes

A vibrational spectroscopic study of hydrated Fe3+ hydroxyl-sulfates; polymorphic minerals butlerite and parabutlerite

Raman and infrared spectra of two polymorphous minerals with the chemical formula Fe3+(SO4)(OH)•2H2O, monoclinic butlerite and orthorhombic parabutlerite, are studied and the spectra assigned. Observed bands are attributed to the (SO4)2- stretching and bending vibrations, hydrogen bonded water molecules, stretching and bending vibrations of hydroxyl ions, water librational modes, Fe-O and Fe-OH stretching vibrations, Fe-OH bending vibrations and lattice vibrations. The O-H...O hydrogen bond lengths in the structures of both minerals are calculated from the wavenumbers of the stretching vibrations. One symmetrically distinct (SO4)2- unit in the structure of butlerite and two symmetrically distinct (SO4)2- units in the structure of parabutlerite are inferred from the Raman and infrared spectra. This conclusion agrees with the published crystal structures of both mineral phases

Vibrational Spectroscopy of Phthalocyanine And Naphthalocyanine in Sandwich-Type (na)Phthalocyaninato and Porphyrinato Rare Earth Complexes Part 13. The Raman Characteristics of Phthalocyanine in Unsubstituted And Peripherally Octa(Octyloxy)-Substi

The Raman spectroscopic data in the range of 500-1800 cm-1 for two series of thirty homoleptic bis(phthalocyaninato) rare earth complexes M(Pc)2 and M[Pc(OC8H17)8]2 [M = Y, La-Lu except Pm; H2Pc = unsubstituted phthalocyanine, H2Pc(OC8H17)8 = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyanine] have been collected and comparatively studied using laser excitation sources emitting at 633 and 785 nm. Under both laser excitations, the marker Raman band of Pc2- and [Pc(OC8H17)8]2- in the Raman spectra of Ce(Pc)2 and Ce[Pc(OC8H17)8]2 appears as a strong scattering at 1498-1501 cm-1 with contributions from both pyrrole C=C and aza C=N stretches together with isoindole stretchings. This band has been found to upshift to 1502-1528 cm-1 in the Raman spectra of MIII(Pc)2 and MIII[Pc(OC8H17)8]2 as the marker Raman band of phthalocyanine monoanion radicals, Pc•- or [Pc(OC8H17)8]•-. With laser excitation at 633 nm, Raman vibrations derived from isoindole ring and aza stretchings in the range of 1300-1600 cm-1 for both series are selectively intensified. In contrast, when excited with laser radiation of 785 nm, the ring radial vibrations of isoindole moieties and dihedral plane deformations between 500 and 1000 cm-1 for M(Pc)2 and M[Pc(OC8H17)8]2 intensify to become the strongest scatterings. The present Raman results also reveal that the frequencies of Pc breathing, pyrrole stretching, isoindole stretchings, aza stretchings and coupling of pyrrole and aza stretchings depend on the rare earth ionic size, shifting to higher wavenumbers along with the lanthanide contraction due to the increased ring-ring interaction across the series. Moreover, under these laser excitations, in particular under 785 nm laser line, the Raman spectrum appearance, i.e. the pattern of relative intensities, also changes systematically depending on the rare earth ionic size

Calcite-filled Borings in the Most Recently Deposited Skeleton in Live-collected Porites (Scleractinia): Implications for Trace Element Archives

Skeletons of the scleractinian coral Porites are widely utilized as archives of geochemical proxies for, among other things, sea surface temperature in paleoclimate studies. Here, we document live-collected Porites lobata specimens wherein as much as 60% of the most recently deposited skeletal aragonite, i.e., the part of the skeleton that projects into the layer of living polyps and thus is still in direct contact with living coral tissue, has been bored and replaced by calcite cement. Calcite and aragonite were identified in situ using Raman microspectroscopy. The boring-filling calcite cement has significantly different trace element ratios (Sr/Ca = 6.3 ± 1.4; Mg/Ca = 12.0 ± 5.1) than the host coral skeletal aragonite (Sr/Ca = 9.9 ± 1.3; Mg/Ca = 4.5 ± 2.3). The borings appear to have been excavated by a coccoid cyanobacterium that dissolved aragonite at one end and induced calcite precipitation at the other end as it migrated through the coral skeleton. Boring activity and cement precipitation occurred concomitantly with coral skeleton growth, thus replacing skeletal aragonite that was only days to weeks old in some cases. Although the cement-filled borings were observed in only ∼20% of sampled corals, their occurrence in some of the most recently produced coral skeleton suggests that any corallum could contain such cements, irrespective of the coral's subsequent diagenetic history. In other words, pristine skeletal aragonite was not preserved in parts of some corals for even a few weeks. Although not well documented in coral skeletons, microbes that concomitantly excavate carbonate while inducing cement precipitation in their borings may be common in the ubiquitous communities that carry out micritization of carbonate grains in shallow carbonate settings. Thus, such phenomena may be widespread, and failure to recognize even very small quantities of early cement-filled borings in corals used for paleoclimate studies could compromise high resolution paleotemperature reconstructions. The inability to predict the occurrence of cement-filled borings in coralla combined with the difficulty in recognizing them on polished blocks highlights the great care that must be taken in vetting samples both for bulk and microanalysis of geochemistry