The thermal analysis of euchroite shows two mass loss steps in the temperature range 100–105 °C and 185–205 °C. These mass
loss steps are attributed to dehydration and dehydroxylation of the mineral. Hot-stage Raman spectroscopy (HSRS) has been
used to study the thermal stability of the mineral euchroite, a mineral involved in a complex set of equilibria between the
copper hydroxy arsenates: euchroite Cu2(AsO4)(OH)·3H2O → olivenite Cu2(AsO4)(OH) → strashimirite Cu8(AsO4)4(OH)4·5H2O → arhbarite Cu2Mg(AsO4)(OH)3. HSRS inolves the collection of Raman spectra as a function of the temperature. HSRS shows that the mineral euchroite decomposes
between 125 and 175 °C with the loss of water. At 125 °C, Raman bands are observed at 858 cm−1 assigned to the ν1 AsO43− symmetric stretching vibration and 801, 822, and 871 cm−1 assigned to the ν3 AsO43− (A1) antisymmetric stretching vibrations. A distinct band shift is observed upon heating to 275 °C. At 275 °C, the four Raman
bands are resolved at 762, 810, 837, and 862 cm−1. Further heating results in the diminution of the intensity in the Raman spectra, and this is attributed to sublimation of
the arsenate mineral. HSRS is the most useful technique for studying the thermal stability of minerals, especially when only
very small amounts of mineral are available.
Corrosion products of mild steel exposed to four different cultures of sulfur reducing bacteria (SRB) grown in a synthetic
medium have been studied by transmission Mössbauer spectroscopy (TMS). Cultures of SRB studied are two hydrogenase positive
strains,Desulfovibrio desulfuricans (DD) andDesulfovibrio vulgaris (DV) and two hydrogenase negative strainsDesulfotomaculum orientis orientis (DO) andDesulfotomaculum nigrificans (DN). The corrosion products generated on the coupons as well as in the broth were studied. In all the cases, the corrosion
products removed from coupons showed the presence of green rust 2 (GR2), ferrous sulfides, γ-FeOOH and superparamagnetic (SPM)
α-FeOOH in different proportions. The corrosion products from the broth showed a symmetrical central doublet, which indicates
the presence of γ-FeOOH and SPM α-FeOOH along with ferrous sulfides. The corrosion products from coupons suspended in sewage
water also showed the presence of GR 2 and ferrous sulfides together with oxyhydroxides. FTIR spectrum supports the presence
of these phases in corrosion products. The formation of GR 2 on coupons seems to be the first step for the SRB induced corrosion.
The corrosion rate has been found in the order of DO>DN>DV>DD.
Authors:J. Lund, N. Hilton, J. McKisson, J. Van Scyoc, B. Brunett, H. Hermon, and R. James
We report on the design, construction, and testing of a gamma-ray imaging system with spectroscopic capabilities. The imaging
system consists of an orthogonal strip detector made from either HgI2 or CdZnTe crystals. The detectors utilize an 8×8 orthogonal strip configuration with 64 effective pixels. Both HgI2 or CdZnTe detectors are 1 cm2 devices with a strip pitch of approximately 1.2 mm (producing pixels of 1.2 mm × 1.2 mm). The readout electronics consist
of parallel channels of preamplifier, shaping amplifier, discriminators, and peak sensing ADC. The preamplifiers are configured
in hybrid technology, and the rest of the electronics are implemented in NIM and CAMAC with control via a Power Macintosh
computer. The software used to readout the instrument is capable of performing intensity measurements as well as spectroscopy
on all 64 pixels of the device. We report on the performance of the system imaging gamma-rays in the 20–500 keV energy range
and using a pin-hole collimator to form the image.
Authors:J. Terry, B. Grzenia, D. Papagiannopoulou, J. Kyger, S. Jurisson, and J. D. Robertson
99mTc compounds play a very important role in modern medicine. These compounds are among the most widely used radiopharmaceuticals. Unfortunately, due to the necessity of working with small quantities of materials, the chemistry of these materials is not completely understood. Currently, the structure of the 99mTc-DTPA (a common renal imaging agent) is unknown. In this paper, we show that X-ray absorption spectroscopy (XAS) can be used to determine the structure of Tc ycompounds b comparing XAS results to those from X-ray diffraction (XRD). Specifically, XAS data and fits for TcCl62-, TcOCl4-, and TcNCl4- were found to be in excellent agreement with the known structures from XRD. Finally, we show the XAS spectrum from a 77 ng sample of 99Tc-DTPA. To our knowledge this is the first XAS spectrum taken from this material. The near-edge region (XANES) was visible after a single scan on this material. This clearly indicates that we will be able to determine the local atomic structure of this material.
Authors:W. Meisel, CS. Vértes, and M. Lakatos-Varsányi
Integral electron Mössbauer spectroscopy (ICEMS) and additionally some electrochemical methods were used to characterize the passivation process of iron (low carbon steel) in sulfate, sulfate+sulfite (a possible model solution of acid rain) solutions and in phospate buffer. The phase compositions and thicknesses of the passive layers formed due to the electrochemical polarizations were analyzed in dependence on the duration of the anodic passivations and on the pH of the used electrolytes. The passive layer, as determined from the Mössbauer spectra, consists mainly of -FeOOH, however in sulfite containing sulfate aqueous solution at pH 3.5 Fe3C and despite ex-situ circumstances FeSO4·H2O was detected after the shortest polarization time. The film thickness, which was found to grow nearly linearly with polarization time in pure sulfate solution and in phospate buffer, reached a maximum of 60–160 nm (depending on pH) in sulfate+sulfite solution after a passivation time of about 4 hours. It has been proved, that HSO3–-ion, which is contained by acid rain, initiate pit formation under acid conditions and so enforces the corrosion of iron. The experimental results furthermore suggest, that not the whole oxidic layer is responsible for the passivity but only a very thin intermediate layer formed between an inner oxide layer of a cubic structure and the rhombic oxide (-FeOOH) cover.
Thermal decomposition of poly(lactic acid) (PLA) has been studied using thermogravimetry coupled to Fourier transform infrared
spectroscopy (TGA-FTIR). FTIR analysis of the evolved decomposition products shows the release of lactide molecule, acetaldehyde,
carbon monoxide and carbon dioxide. Acetaldehyde and carbon dioxide exist until the end of the experiments, whereas carbon
monoxide gradually decreases above the peak temperature in that the higher temperature benefits from chain homolysis and the
production of carbon dioxide. A kinetic study of thermal degradation of PLA in nitrogen has been studied by means of thermogravimetry.
It is found that the thermal degradation kinetics of PLA can be interpreted in terms of multi-step degradation mechanisms.
The activation energies obtained by Ozawa–Flynn–Wall method and Friedman’s method are in good agreement with that obtained
by Kissinger’s method. The activation energies of PLA calculated by the three methods are 177.5 kJ mol−1, 183.6 kJ mol−1 and 181.1 kJ mol−1, respectively.
Commercial light-cured dental composites were used in this study. Two laboratorial composites, Resilab (Wilcos/Brazil), Epricord
(Kuraray/Japan) were compared under cured and uncured conditions. Thermal analysis, infrared spectroscopy and scanning electron
microscopy were used to evaluate the dental composites. The mass change and heat flow signals (TG–DSC) were recorded simultaneously
by using STA 409 PC Luxx (NETZSCH), in the 25–800 °C temperature range at a heating rate of 10 °C/min under nitrogen atmosphere
(70 mL/min). Employing thermo-microbalance TG 209 C F1 Iris (NETZSCH) coupled to the BRUKER Optics FTIR TENSOR, the samples
were analyzed by combined thermogravimetric and spectroscopic methods (TG–FTIR). The initial sample mass was about ~12 mg,
the data collection have been done in the 35–800 °C temperature range at a heating rate of 20 K/min in nitrogen atmosphere
(flow rate: 40 mL/min). Finally, superficial topographic was analyzed by scanning electron microscopy (SEM). Dental composite
evaluation suggests a high thermal stability and inorganic content in RES D sample. Degrees of conversion (DC) values were
almost the same and there was no direct relationship between DC and amount of particles and size. Similar compositions were
found in all samples.
The Iron Age ceramic technology used in the manufacturing of cooking pots was studied by thermo-FTIR spectroscopy analysis.
The pottery was excavated at Tel Hadar on the eastern shore of the Sea of Galilee. The results demonstrate that the cooking
pots were manufactured using noncalcareous or slightly calcareous raw material proceeds from soil. The firing was at about
750-850C and the cementation to ceramic was obtained by low temperature sintering of the clay. The use of soil raw material
composed of smectitic (montmorillonitic) clay enabled the low temperature sintering. The clay from soil is relatively poorly
crystallized and rich in natural iron oxide, both of which induce earlier sintering. Most of the cooking pots were tempered
with broken pieces of large calcite crystals that were added to the clayey raw material from an additional source. Alternative
tempering with limestone particles composed of polycrystalline calcite is inappropriate as it brings about earlier and intense
decarbonation during the firing, which causes defects in the pots.
The thermally stimulated discharge current (TSC) and differential scanning calorimetry (DSC) spectroscopy have been recorded
in 25 μm thick samples of pristine polycarbonate (PC) and zinc oxide nano particle-filled polycarbonate. Polycarbonate (PC)/zinc
oxide (ZnO) nanocomposites of different mass ratio (e.g., 1, 3, and 5%) were prepared by sol–gel method, followed by film
casting. The glass transition temperature of nanocomposite samples increases with increase in concentration of ZnO nano fillers.
It is due to the strong interaction between inorganic and organic components. The TSC peaks of nanocomposite and pristine
PC indicate the multiple relaxation process. It has been observed that the magnitude of TSC decreases with increase in concentration
of nanofillers. The TSC characteristics of 5% filled nanocomposites shows exponential increase of current at higher temperature
region. This increase in current is caused by formation of charge-transfer complex between inorganic phase (e.g., ZnO) and
organic phase (e.g., PC). Thus, the nano material like zinc oxide transfers the charge carriers from inorganic phase to organic
phase rapidly and resultant current increases exponentially. This current is known as leakage current or breakdown current.
TSC peak height is observed as a function of the polarizing field. The height of TSC peak increases as the field increases
in pristine PC, while TSC peak height is suppressed in nanocomposite samples. This indicates the amount of space charge is
smaller in the nanocomposites with a proper addition of ZnO nano fillers than in the pristine PC.
Authors:Christine Fräulin, Günter Rinke, and Roland Dittmeyer
Cyclohexane oxidation is an economically important process. To maintain high selectivities of 70 to 90%, the reaction is performed at low conversion up to 6%. To improve this process, investigations on the reaction mechanism are of high interest, which requires measurement techniques able to detect chemical species precisely even at very low concentrations. For this purpose, an in-situ measurement technique based on laser Raman spectroscopy with superior detection sensitivity and an optically transparent microchannel to monitor the process of cyclohexane oxidation has been developed.
The challenge is now to adapt this system to required conditions. In this article, we show that the influence of pressure is negligible. However, increasing temperatures influence the intensity of the Raman spectra significantly. As the temperature influence on the intensity of the Raman light is specific for each species, a temperature dependent calibration must be done to determine the concentrations of the chemical species precisely. In order to reach low detection limits also at high temperatures, the charge-coupled device (CCD) integration time had to be increased. For temperatures below 486 K, the limits of detection are less than 0.05 m/m %.