High-Temperature Sulphidation of Fe-Cr Alloys

Scales resulted from a sulphidation of Fe _100?x Cr _x alloys (x ≤ 26) at 1073K in the atmosphere of H ₂/H ₂ S with the partial pressure of sulphur of 10^?8 atm were investigated by means of transmission and conversion electron Mössbauer spectroscopies, X-ray diffraction, electron microscopy and microprobe analysis. Although crystallographically single-phase, the scales were revealed to be composed of FeS (x ≤ 10) and Fe _1?x Cr _x S (x > 10).     

Dynamics of a quantum phase transition in a ferromagnetic Bose-Einstein condensate

We discuss dynamics of a slow quantum phase transition in a spin-1 Bose-Einstein condensate. We analytically determine the scaling properties of the system magnetization and verify them with numerical simulations in a one dimensional model.     

Hysteresis loss component under non-sinusoidal flux waveforms

Separation of total energy dissipation per magnetisation cycle into a frequency-dependent dynamic component and a frequency-independent hysteresis component is a common practise in evaluating electromagnetic losses in Si–Fe electrical steel sheet. The assumed frequency-independent hysteresis component is defined by a coefficient C₀ (J/kg). In this work, the value of C₀ was determined using a linear extrapolation method and quasi-static hysteresis energy loss per cycle. The extrapolation method gave a considerable error when applied to non-sinusoidal excitation voltages (pulse width modulation and square) in a frequency range from 25 to 100 Hz. For this reason the coefficient values obtained from the quasi-static measurements at 0.01 Hz were assumed.     

Potential benefits of adaptive frequency-gain characteristics for speech reception in noise.

Some current single-microphone hearing aids employ techniques for adaptively varying the frequency-gain characteristics in an attempt to improve speech reception in noise. The potential benefit of this strategy depends on the spectral spread of masking and the degree to which it can be reduced by changing the frequency-gain characteristic. In this study these benefits were examined for subjects with normal hearing under static listening conditions. In the unprocessed condition, subjects were presented with nonsense syllables in an octave-band noise centered on 0.5, 1, or 2 kHz. The frequency-gain characteristic was then modified with the goal of reducing the intensity of the frequency region containing the octave-band noise. This processing resulted in increases as large as 60 percentage points in consonant-correct scores with the low- and mid-frequency octave noise bands, and a small increase with the high-frequency noise. Masking patterns produced by the octave noises were also measured and were related to the intelligibility results via an analysis based on Articulation Theory. The Articulation Index was also used to compare the effectiveness of three adaptive rules. A simple multiband volume control is expected to provide much of the benefit of more sophisticated systems without the need for separate estimation of input speech and noise spectra.     

A new thermobalance for studies of the high-temperature sulphidation of metals and alloys

A new thermogravimetric apparatus for studying the kinetics of metal sulphidation in a H₂/H₂S gas mixture is described. The main difference between this device and other equipment is the application of hydrogen to obtain a H₂/H₂S mixture at suitable sulphur partial pressures at a total mixture pressure of 1 atm.The use of the carrier gas allows the measurement of sulphidation kinetics under dynamic conditions and consequently over a much wider pressure range of sulphur vapour, down to 10^–12 atm.The author would like to thank Dr Marek Jodko for his help in devising the chemical analysis of H₂S in a H₂/H₂S gas mixture and for stimulating discussions relating to the design of the above apparatus.     

(Barely) solid Li(NH3)4: the electronics of an expanded metal

The highly expanded metal, lithium(0)tetraamine, and its electronic structure is as full of complexity and surprises as the lithium solutions in anhydrous ammonia from which it crystallizes at 90 K. Our theoretical studies of the Phase II, Z = 8, I43d structure of this material reveal that the molecular building block is an almost ideal tetrahedron, in agreement with recent experiments. Close in enthalpy at P = 1 atm, and consistent with the low melting point, are bcc and Cs-IV configurations. Under pressure, the I43d structure emerges as more stable than its alternatives. In this phase six relatively narrow bands, four of them occupied, separate from the conduction and valence bands. We trace these bands to pockets of electron density arising between sterically encumbered ammonias, six such pockets in the Z = 8 unit cell. The observed band structure can be explained by considering a Jortner-type model, where pseudoatoms are placed in these holes. The electride Li(NH(3))(4), while not a very good metal, is a unique material, by virtue of its low melting point.     

Rubidium Polyhydrides Under Pressure: Emergence of the Linear H3− Species

The structures of compressed rubidium polyhydrides, RbH_n with n>1, and their evolution under pressure are studied using density functional theory calculations. These phases, which start to stabilize at only P=2 GPa, consist of Rb⁺ cations and one or more of the following species: H^? anions, H₂ molecules, and ${{\rm H}{{- \hfill \atop 3\hfill}}}$ molecules. The latter motif, the simplest example of a three‐center four‐electron bond, is found in the most stable structures, RbH₅ and RbH₃, which metallize above 200 GPa. At the highest pressures studied, our evolutionary searches find an RbH₆ phase which contains polymeric (${{\rm H}{{- \hfill \atop 3\hfill}}}$ )_∞ chains that show signs of one‐dimensional liquid‐like behavior.     

ChemInform Abstract: Compressed Cesium Polyhydrides: Cs+ Sublattices and H3‐ Three‐Connected Nets.

Evolutionary algorithms coupled with first‐principles DFT calculations are employed to predict the structure of cesium polyhydrides under pressure.