Permeability of hydrogen in amorphous Pd(1−x)Six alloys at elevated temperatures

Hydrogen permeabilities of amorphous Pd_(1−x)Si_x (x=0.15, 0.175, 0.2) alloys in the form of ribbon, which were prepared with a single roller spinning technique, were measured at elevated temperatures up to 390°C. It was found that the hydrogen permeability of the amorphous alloys, strongly depending on the Si content, decreased with an increase in the Si content. The amorphous alloys possessed 3–5 times higher hydrogen permeability than the corresponding crystallized ones. The pressure dependence of hydrogen permeability in the amorphous alloys could be described by the simple n-th power equation, which was derived in this study.     

Localization of Iα and Iβ phases in algal cellulose revealed by acid treatments

Highly crystalline I-rich type Cladophora cellulose, which had been kept in never-dried condition, was treated in 60wt% sulfuric acid at 100°C, for 1–48h. The cellulose microcrystals thus obtained were analysed by X-ray diffractometry, FT-IR, and transmission electron microscopy. The I component was found to be more degraded than the I component. The cellulose I/I ratios of the samples acid-treated for 0, 24, and 48 h were about 8:2, 6:4, and 4:6, respectively. After the acid treatment, the microcrystals became narrower in width, and very sharp at their ends. These results indicate that the I phase is mostly located at the surface of the microcrystals, which is morphologically more susceptible to the acid treatment.     

Phase transformations in Cd–Ni nanostructured system at elevated temperatures

Russian Chemical Bulletin - Using X-ray diffraction (both in vacuum and in air), derivatomass-spectrometry and thermo-programmed oxidation, phase transformations in nanostructured Cd–Ni...     

Effect of hydrogen-sulfide on the hydrogen permeance of palladium–copper alloys at elevated temperatures

The hydrogen permeance of several 0.1 mm thick Pd–Cu alloy foils (80 wt.% Pd–20 wt.% Cu, 60 wt.% Pd–40 wt.% Cu and 53 wt.% Pd–47 wt.% Cu) was evaluated using transient flux measurements at temperatures ranging from 603 to 1123 K and pressures up to 620 kPa both in the presence and absence of 1000 ppm H₂S. Sulfur resistance, as evidenced by no significant change in permeance, was correlated with the temperatures associated with the face-centered-cubic crystalline structure for the alloys in this study. The permeance of the body-centered cubic phase, however, was up to two orders of magnitude lower when exposed to H₂S. A smooth transition from sulfur poisoning to sulfur resistance with increasing temperature was correlated with the alloy transition from a body-centered-cubic structure to a face-centered-cubic structure.     

Vibrational spectrum and hydrogen bonding in solid α-naphthol

The i.r. spectrum of α-naphthol has been obtained at different temperatures and at different degrees of deuteration. A method is proposed for determining the orientation of the crystallographic axis with respect to the incident beam. The absorption bands due to hydrogen bonded groups are then analysed in terms of a simple dipole-dipole model.     

Physico-chemical studies on some saccharides in aqueous cellulose solutions at different temperatures – Acoustical and FTIR analysis

The ultrasonic velocity (u), density (ρ) and viscosity (η) of Fructose, Lactose and Sucrose in 0.4 M of Hydroxy Propyl Methyl Cellulose (HPMC) solutions have been investigated at 303, 313 and 323 K, respectively. The acoustical parameters such as adiabatic compressibility (β), intermolecular free length (L_f), internal pressure (π_i), Rao’s constant (R_a), relaxation time (τ), acoustical impedance (Z_a), absorption coefficient (α/f²), free volume (V_f), cohesive energy (CE) and solvation number (S_n) have been computed. The non linear variations of acoustical parameters with concentration and temperature indicated the existence of strong molecular interaction in the systems studied. The FTIR spectroscopic analysis revealed the possibility of intermolecular hydrogen bonding in various saccharides.     

Relative susceptibility of the Iα and Iβ phases of cellulose towards acetylation

The relative reactivity of the I and I phases of Valonia cellulose toward partial homogeneous acetylation was investigated by FT-IR and CP/MAS ¹³C-NMR spectroscopy. At the beginning of the acetylation and when only partial reaction was achieved, it was found that the reactivity of the I phase was substantially higher than that of the corresponding I component. At a later stage of acetylation, the difference in reactivity between the two phases was less pronounced. In correlation with previous ultrastructural observations (Sassi and Chanzy, 1995), it can be concluded that at equivalent accessibility, the I phase of cellulose is indeed more reactive toward acetylation than the I phase. The homogeneous acetylation of cellulose is essentially a surface reaction that affects only the accessible parts located at the surface of the microfibrils. The decrease in the rate of I phase disappearance with acetylation time confirms therefore that the microstructure of Valonia is made of domains that are distributed throughout the thickness of its microfibrils.     

The photoacoustic spectra of substituted benzenes in the near infrared region—I

The photoacoustic spectra of three benzonitriles, five acetophenones and three benylbromides were recorded using the commercial EDT OAS 400 photoacoustic spectrometer in the near i.r. region, i.e. 3850–10000 cm⁻¹ (2.6−1.0 μm). A combined study of the mid and far i.r. absorption spectra with the near i.r. PAS spectra led to a provisional assignment of the observed PAS peaks as combinations of fundamentals and overtone bands.     

Electron transport in CaMnO3 − δ at elevated temperatures: a mobility analysis

The drift mobility of electron charge carriers in oxygen non-stoichiometric manganite CaMnO_3???δ was calculated by combining the total electrical conductivity and oxygen non-stoichiometry data at 700–950 °С and oxygen partial pressure varying between 10^?6 and 1 atm. The carrier concentration changes with pressure and temperature were obtained with the help of the earlier-developed defect model involving reactions of oxygen exchange and thermal excitation of manganese sites. The activation energy for mobility is found to increase with oxygen non-stoichiometry. High-temperature electron transport properties of the manganite CaMnO_3???δ can be explained in terms of activated jumps of n-type small polarons in adiabatic regime. The relatively small mobility of charge carriers is explained by strong localization of polarons on manganese sites.     

Five- and six-membered N-H?S hydrogen bonding in aromatic amides

The capacity of sulfur to form intramolecular five- or six-membered S?H-N hydrogen bonding in aromatic amides is assessed. The five-membered S?H-N hydrogen bonding is observed in crystal structures of five compounds, whereas the six-membered S?H-N hydrogen bonding is revealed in crystal structures of three compounds. The trityl group has been used to promote formation of the weak hydrogen bonding because it efficiently inhibits the competition of the intermolecular CO?H-N hydrogen bonding. (2D) ¹H NMR experiments indicate that both patterns also exist in chloroform.     

Studies of hydrogen bonding—XXVII. NMR studies of hydrogen bonding and solvent effect

The OH proton chemical shifts are reported of dilution study of 2-methyl-6-t-butylphenol (2M6TBP) and 2,6-di-t-butylphenol (2.6DTBP), and of the 1:1 association between the phenols and hexamethylphosphoramide (HMPA) in C₆H₁₂, CCl₄, CH₃NO₂, CH₃CN and C₆H₆ at 25, 35 and 50°C. Also the association of the phenols with CH₃NO₂, CH₃CN and CCl₄ has been studied. The phenol OH chemical shift, δ_f, found by extrapolation to zero concentration, shows the highest upfield shift in benzene. Contrary, on adding HMPA, the complex OH chemical shift, δ_x, shows the lowest downfield shift in benzene.The K_ass, δ_x, ΔH and ΔS values have been evaluated by using the Hiquchi plot method. Linear relationships were obtained between Δδ_x and ΔH, and log K_ass for the system 2M6TBP/HMPA in the various solvents. Furthermore, the difference in H-bond energy of a given system in an inert solvent (C₆H₁₂) and in aprotic solvent (CH₃CN), corresponds to the enthalpy of association of the given donor with CH₃CN in C₆H₁₂.The K_ass value for the system 2M6TBP/HMPA is 10 times greater in C₆H₁₂ than in C₆H₆ and CCl₄, 100 times than in CH₃NO₂ and 300 times than in CH₃CN.     

Iα → Iβ transition of cellulose under ultrasonic radiation

Aqueous suspensions of dispersed Glaucocystis cellulose microfibrils were sonicated at 4 °C for 3 h, using 24 kHz ultrasonic waves. This treatment induced a variety of ultrastructural defects, as the microfibrils became not only shortened, but also presented substantial damage materialized by kinks and subfibrillation. Upon analysis by X-ray diffraction and ¹³C solid-state NMR spectroscopy, it was found that the initial sample that contained 90 % of cellulose I_α allomorph became, to a large extent, unexpectedly converted into the I_β phase, while the loss of crystallinity was only moderate during the sonication treatment.     

X-ray diffraction from faulted cellulose I constructed with mixed Iα–Iβ stacking

Cellulose from higher plants is usually thought to be a composite of the Iα and Iβ allomorphs, with predominance of the latter. Instead of the pure allomorphs, this article proposes that Iα and Iβ stacking patterns coexist within each crystallite, forming a type of crystallographic defect known as stacking fault. Models of faulted crystallites are constructed with mixed Iα–Iβ stacking and their X-ray diffraction intensities are calculated using the Diffracted Intensities From Faulted Xtals (DIFFaX) computer program. Simulated powder diffractograms from faulted crystallites compare favorably with experimental data, modifying diffractogram regions that have been misfit by models based on the Iβ crystal structure. Calculations also reveal that stacking faults generate a signature in the (hkl) dependence of diffraction line broadening, guiding further experimental verification and eventual quantification of stacking faults. Our findings bring an alternative view of native cellulose polymorphism and suggest that the proposed stacking faults are ubiquitous crystallographic defects in cellulose from higher plants.     

Quantum mechanical calculations on cellulose–water interactions: structures,energetics, vibrational frequencies and NMR chemical shifts for surfaces of Iα and Iβ cellulose

Periodic and molecular cluster density functional theory calculations were performed on the Iα (001), Iα (021), Iβ (100), and Iβ (110) surfaces of cellulose with and without explicit H₂O molecules of hydration. The energy-minimized H-bonding structures, water adsorption energies, vibrational spectra, and ¹³C NMR chemical shifts are discussed. The H-bonded structures and water adsorption energies (ΔE_ads) are used to distinguish hydrophobic and hydrophilic cellulose–water interactions. O–H stretching vibrational modes are assigned for hydrated and dry cellulose surfaces. Calculations of the ¹³C NMR chemical shifts for the C4 and C6 surface atoms demonstrate that these δ¹³C4 and δ¹³C6 values can be upfield shifted from the bulk values as observed without rotation of the hydroxymethyl groups from the bulk tg conformation to the gt conformation as previously assumed.