High pressure mass-spectrometric investigations of ion–molecule reactions in propane and argon mixtures

Ion–molecule reactions initiated by electron impact in the propane–argon mixtures have been studied by a quadrupole mass spectrometer with a high pressure ion source. The total gas pressure of investigated mixtures was 1.33 Pa. The influence of repeller potential on the ion–molecule reactions has been studied. The repeller potential was changed in the range 2–12 V. Measurements were performed for different concentrations of propane in the mixture with argon (from 10% C₃H₈ + 90% Ar to 90% C₃H₈ + 10% Ar with 10% propane increments). The major ion–molecule reactions have been identified. The primary ions produced in the gas by the electrons with the energy of 300 eV and the secondary ones from the ion–molecule reactions were observed. Relative intensities for primary and secondary ions are presented as a function of potential of the repeller electrode and concentration of propane in the mixtures with argon.     

Theoretical and experimental investigations on elastic interactions between γ′-precipitates in a Ni-Al alloy

Elastic interaction energies between two identical inhomogeneous plates in an anisotropic matrix were calculated with respect to particle separation distance and alignment orientation on the basis of the microscopic theory of elasticity developed by Yamauchi and de Fontaine. Four types of plate-arrangement along the cube directions; two plates whose faces were mutually parallel, two plates which were arranged on a cube plane as a raft, two plates which were perpendicularly arranged with face—edge configuration and two plates which were perpendicularly aligned with edge—edge configuration were energetically stable, while other arrangements were not stable. Compared with experimental observations on the local arrangement of plates in a Ni-Al single crystal, the calculated results were confirmed to be qualitatively correct.     

Spectroscopic investigations on Eu3+ ions in Li–K–Zn fluorotellurite glasses

Eu³⁺ ions incorporated Li–K–Zn fluorotellurite glasses, (70 − x)TeO₂ + 10Li₂O + 10K₂O + 10ZnF₂ + xEu₂O₃, (0 ⩽ x ⩽ 2 mol%) were prepared via melt quenching technique. Optical absorption from ⁷F₀ and ⁷F₁ levels of the Eu³⁺-doped glass has been studied to examine the covalent bonding characteristics, energy band gap and Judd–Ofelt intensity parameters. The emission spectra (⁵D₀ → ⁷F_0,1,2,3,4) of the glasses were used to estimate the luminescence enhancement, asymmetric environment in the vicinity of Eu³⁺ ions, stimulated emission cross section and branching ratios. The phonon side band mechanism of ⁵D₂ level of the Eu³⁺ ions in the prepared glass was examined by considering the excitation and Raman spectra. The radiative lifetime calculated using Judd–Ofelt parameters was compared with the experimental lifetime to estimate the quantum efficiency of ⁵D₀ level of Eu³⁺ ions in Li–K–Zn fluorotellurite glass.     

Exciton-erbium coupling in SiOx suboxide films prepared by combining sol–gel chemistry and ion implantation

The efficiencies of three methods based on a combination of sol–gel chemistry and ion implantation for obtaining an optical activation of Er atoms via the transfer of excitons energy are compared. A better coupling is observed in silica-gel containing Er prepared by addition of Er nitrate to the tetraethoxysilane sol and embedding Si nanocrystals formed by ion implantation or in a silicon suboxide derived from triethoxysilane and implanted with Er ions than in silica-gel implanted sequentially with Si then Er. The infrared emission of Er ions is reduced by the segregation of erbium oxide or the precipitation of Er₅Si₃, depending on the matrix, in films containing more than 1 at.% Er annealed at temperatures over 1000 °C.     

Ion–surface interactions: from sputtering to reactive ion etching

Abstract

An overview of ion–surface interactions is presented, pertaining to their importance in modern thin film processing. The fundamentals of the physics of energetic ion–surface collisions are reviewed briefly, with particular emphasis on low energy ions (i.e. ion energies below 1 keV). Recent examples of ion assisted processes are discussed from the areas of sputtering, ion beam etching, and reactive ion etching. These examples demonstrate that by using low energy ions, advantage can often be taken of the beneficial effects of ion–surface bombardment in controlling film removal while minimising the adverse effects of ion induced damage to the film.

MST/1690     

Phase and microstructural development in alumina sol–gel coatings on CoCr alloy

Phase transformation of -Al₂O₃ to -Al₂O₃ in alumina sol gel coatings on biomedical CoCr alloy was studied as function of heat treatment temperature and time. Transformation in unseeded coatings was significant only above 1200 °C. Addition of -Al₂O₃ seed particles having an average size of approximately 40 nm lowered the phase transformation temperature to around 800 °C. These particles were considered to act as heterogeneous nucleation sites for epitaxial growth of the -Al₂O₃ phase. The kinetics and activation energy (420 kJ/mol) for the phase transformation in the seeded coatings were similar to those reported for seeded monolithic alumina gels indicating that the transformation mechanism is the same in the two material configurations. Avrami growth parameters indicated that the mechanism was diffusion controlled and invariant over the temperature range studied but that growth was possibly constrained by the finite size of the seed particles and/or coating thickness. The phase transformation occurred by the growth of -Al₂O₃ grains at the expense of the precursor fine-grained -Al₂O₃ matrix and near-complete transformation coincided with physical impingement of the growing grains. The grain size at impingement was 100 nm which agreed well with that predicted from the theoretical linear spacing of seed particles in the initial sol.     

High pressure investigations of ion – Molecule reactions in a mixture of C3H8 and Ne

The gas phase reactions of positive Ne⁺ ions produced from neon with neutral propane have been studied with the use of a quadrupole mass spectrometer with a high pressure ion source. The measurements were performed in a mixture of 1% C₃H₈ and 99% Ne in the pressure range 1.33–40.00 Pa. The fractional abundances I_i/ΣI_i (relative intensity of the ion currents) of dominant C₂H₂⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, C₃H₅⁺, C₃H₇⁺ ions and neon ions have been determined as a function of the gas mixture pressure and of the repeller electrode potential ranged from 3 V to 10 V.     

Combined buoyancy and viscous effects in liquid–liquid flows in a vertical pipe

This paper presents experimental and numerical results of interfacial dynamics of liquid–liquid flows when an immiscible core liquid is introduced into a continuous liquid flow. The fully developed flow model predicts multiple solutions of the jet diameter over a range of dimensionless numbers: flow rate ratio, viscosity ratio, Bond and Capillary numbers. Experiments have been carried out using Polyethylene Glycol (PEG) and Canola oil to investigate the realizability of the three possible solutions predicted by the fully developed flow model. The measured values of inner fluid radii agree very well with the lower branch of the three branched solution while deviating from the top branch beyond a critical flow ratio value. This deviation is attributed to the fact that the flow develops a non-axisymmetric solution at this critical point. Computational fluid dynamics simulations have also been performed to examine the developing core annular flow and to compare the analytical solution results of liquid jet radius. The results predicted by numerical simulations agree very well with both the lower and upper branches of solution predicted by the analytical theory.     

Preparation and characterization of PAN–KI complexed gel polymer electrolytes for solid-state battery applications

The free standing and dimensionally stable gel polymer electrolyte films of polyacrylonitrile (PAN): potassium iodide (KI) of different compositions, using ethylene carbonate as a plasticizer and dimethyl formamide as solvent, are prepared by adopting ‘solution casting technique’ and these films are examined for their conductivities. The structural, miscibility and the chemical rapport between PAN and KI are investigated using X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry methods. The conductivity is enhanced with the increase in KI concentration and temperature. The maximum conductivity at 30°C is found to be 2.089 × 10^?5 S cm^?1 for PAN:KI (70:30) wt%, which is nine orders greater than that of pure PAN (< 10^?14 S cm^?1). The conductivity-temperature dependence of these polymer electrolyte films obeys Arrhenius behaviour with activation energy ranging from 0.358 to 0.478 eV. The conducting carriers of charge transport in these polymer electrolyte films are identified by Wagner’s polarization technique and it is found that the charge transport is predominantly due to ions. The better conducting sample is used to fabricate the battery with configuration K/PAN + KI/I₂+ C + electrolyte and good discharge characteristics of battery are observed.     

Eu3+ probe ion for rare-earth dopant site structure in sol–gel derived LiYF4 oxyfluoride glass–ceramic

Sol–gel route using metal alkoxides and trifluoroacetic acid as precursors has been used to prepare oxyfluoride glass–ceramic containing Eu³⁺-doped LiYF₄ nanocrystals of about tens of nm size embedded in a silica matrix through controlled crystallization at higher temperatures of the xerogel. Photoluminescence spectra and decay curves recorded in the Eu³⁺-doped LiYF₄ polycrystalline pellet and glass ceramic have been discussed using group-theoretical arguments. In the glass–ceramic Eu³⁺ ions are embedded dominantly inside the LiYF₄ nanocrystals most probably as Eu–O center and/or dimer centers in low symmetry (C_2v) sites; oxygen ions were incorporated in their neighborhood during the glass ceramization.     

Kinetic and electrical phenomena in gas–liquid systems

Disperse systems consisting of a liquid and gas bubbles located in it are considered. Two possible versions of evolution of bubbles under the conditions studied are assessed. In simple liquids, contact between two bubbles causes them to merge, as the separating film breaks. In the case of complex organic liquids, amphiphilic film is formed on the surface of bubbles, and the lifetime of bubbles in contact increases with their size. Under an external electric field, chains of bubbles are formed, lined up along the electric field potential lines. The presence of bubbles in liquid greatly lowers the breakdown threshold, as the critical parameters of the breakdown field in liquids are two to three orders of magnitude higher than those in gases at atmospheric pressure. Various breakdown mechanisms in liquids are discussed from the viewpoint of formation of the gas phase during the passage of an electric current through a liquid medium. The character of propagating a streamer in separate bubbles is studied with their random distribution in liquid and in the case of formation of some structures of bubbles; the critical parameters of disperse systems, that can lead to their electrical breakdown, are presented. Along with the general concepts of electrical breakdown in dispersed systems, experimental studies of these processes are considered, and the nature of electrical breakdown in liquid dielectrics, including transformer oil, is discussed.     

Experimental investigations on welding behaviour of sintered and forged Fe–0.3%C–3%Mo low alloy steel

Tungsten Inert Gas (TIG) welding is considered as one of the cleanest welding methods. It is generally adopted for thinner materials with moderate weld joint strengths. Welding of sintered porous materials continues to be a challenge due to the inherent porosity of the parent metals. The present research work attempts to address some of the issues relating to the welding behaviour of sintered and forged Fe–0.3%C–3%Mo low alloy steels under TIG welding. Rectangular strips of size 70 mm × 15 mm × 5 mm, obtained by blending, compacting and sintering of elemental powders of iron, graphite and molybdenum, were upset forged – both hot and cold in order to obtain alloy steel strips of various porosities. Two identical alloy steel strips of equal density were then welded both along longitudinal and transverse directions, by TIG welding, employing filler metal of suitable composition. The welded strips were then subjected to tensile test, hardness test, microstructural and Scanning Electron Microscope (SEM) fractography studies. Cold/hot upsetting of the sintered alloy preforms has led to enhanced density. As a result of improved density, their tensile strength and hardness values were also found to be enhanced. The welded alloy exhibited higher tensile strength compared to the un-welded base metal, due to strengthening by residual stress. Similarly, the strength and hardness of the welded alloy strips were found to be enhanced with increase in density. The tensile strength of welded joint is found to be higher compared to that of the base metal due to alloy metals segregation, rapid cooling and formation of acicular ferrite at the weldment of welded joint. No porosity was observed in the weld metal or Heat Affected Zone (HAZ) of the weld joint. However, the base metal had numerous micro pores, though pore migration towards weldment has not been observed.     

Fabrication,characterization and sensing properties of Cu(II) ion imprinted sol–gel thin film on QCM

Cu(II)-molecularly imprinted sol–gel films (Cu(II)-MISGF), coated on a quartz crystal microbalance (QCM) chip, were fabricated using a sol–gel procedure. Co-hydrolysis and co-condensation of Cu(II) (templates), 3-aminopropyltrimethoxysilane (APTS, functional monomer) and tetraethoxysilane (TEOS, cross-linking agent) were performed with acid and base catalysis. The properties of the Cu(II)-MISGF were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and the electrochemical methods of cyclic voltammetry (CV). Microstructural observations revealed that the acid-catalyzed system yielded more mechanically stable thin films. A combined Cu(II)-MISGF-QCM with flow injection analysis (FIA) method was utilized to investigate the sensing performance of the Cu(II)-MISGF, with special emphasis on the most important properties of sensitivity, selectivity and response time. The Cu(II)-MISGF-QCM sensor, at a TEOS/APTS molar ratio of 10, exhibited excellent selectivity and rapidly responded to Cu(II) ions.     

Solute–solute and solute–solvent interactions in transition metal alloys: Pt–Ti system

Abstract

The activity of Ti in solid Pt has been measured as a function of composition at 1573 K using a metal oxide–gas equilibration technique under controlled oxygen partial pressures. Thin foils of Pt were equilibrated with TiO_x at constant oxygen chemical potentials. Oxygen partial pressures were established using Ar–H₂–H₂O gas mixtures of controlled composition. A solid state cell, based on yttria doped thoria as the solid electrolyte, independently determined the chemical potential of oxygen in the gas phase. The concentration of Ti in solid Pt was determined using spectrophotometric methods. The activities of Ti were computed from the oxygen potentials established by the gas phase coupled with independent data on the thermodynamic properties of titanium oxides. The excess chemical potential of titanium in solid Pt at 1573 K in J mol^-1 can be represented as Δμ^E_Ti = —83 940 — 214 140 (1 — X _Ti )² with an error of ±2800 J mol^-1. The activity coefficient of Ti at infinite dilution determined from this study and that of other elements of the first transition series in solid Pt obtained from previous work confirm the trend predicted by both Miedema’s model and Engel–Brewer theory. The attractive interaction between the solute and the solvent (Pt) increases with decreasing atomic number of the solute. The self-interaction parameters of the first transition series elements in solid Pt indicate an increase in solute–solute repulsion with decrease in 3d electron concentration of the solute. The standard Gibbs energy of formation of TiPt₃ is —282·57 ± 4 kJ mol^-1 at 1573 K. The large negative values of the Gibbs energy of formation of phases in the system Pt–Ti indicate that Pt is not phase compatible with nitrides and carbides of Ti at high temperatures.     

Nanocomposites based on MWCNT and styrene–butadiene–styrene block copolymers: Effect of the preparation method on dispersion and polymer–filler interactions

Composites of Kraton-D® 1102 BT (a styrene–butadiene–styrene block copolymer) and multi-walled carbon nanotubes (MWCNTs) were prepared by melt mixing. The composites were characterized by electrical conductivity measurements (Coleman’s method), mechanical properties (DMA and stress–strain tests), thermal stability (thermogravimetry) and morphology of dispersion (SEM). Finally, the resulting composites were compared with those made by the solution casting method. The results showed a strong influence of the preparation methodology on the final properties of the composites due to changes in morphology. Composites prepared by casting showed a higher electrical conductivity than extruded ones; the composites with 6 wt.% of MWCNT prepared by extrusion presented conductivity of the same order of magnitude as the composite with 1 wt.% of MWCNT prepared by casting – 10⁻³ to 10⁻⁴ S cm⁻¹. However, the extruded samples presented better mechanical properties than the casting ones.     

Electrical and FTIR studies on Al substituted Mn–Zn mixed ferrites

Mixed ferrites of manganese and zinc with the substitution of aluminum are prepared by the ceramic double-sintering method. Confirmation of single-phase and polycrystalline ferrites is made from X-ray diffraction patterns and experimental and theoretical values of lattice constant are compared. Distribution of cations on A and B sites is concluded. A.c. conductivity and FTIR characterizations are done and the logarithm of conductivity (log ) dielectric constant () and tan at various frequencies () and temperatures (T) are reported. Hopping of electrons between localized d bands of ions is the interesting feature of these ferrites and the mechanism of hopping is discussed. Activation energy and vibration frequencies are discussed as a function of aluminum concentration.     

Effect of temperature on C–S–H gel nanostructure in white cement

Different ages of white cement pastes hydrated at 100 % RH and 25 or 65 °C were characterised with ²⁹Si MAS NMR spectroscopy. The findings showed that raising the curing temperature from 25 to 65 °C accelerated hydration of the belite phase considerably, inducing a sixfold rise in its one day degree of hydration, while alite phase hydration grew by a factor of only 1.5 in the first day. Moreover, the C–S–H gel formed at the higher temperature had a longer mean chain length and a higher initial uptake of Al³⁺. Lastly, curing at a higher temperature stabilised only one crystalline aluminate phases, calcium hemicarboaluminate.     

Microstructural and morphological characterizations of nanocrystalline Ni–Cu–Fe thin films electrodeposited from electrolytes with different Fe ion concentrations

In the current study, ternary Ni–Cu–Fe thin films have been grown from the electrolytes with different Fe ion concentrations onto indium tin oxide coated glass substrates by galvanostatic electrodeposition at ambient temperature. The microstructural, compositional, and morphological properties have been characterized with respect to Fe ion concentration using X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). EDX results indicated that the Fe content within the films increased and Ni and Cu contents decreased as the Fe ion concentration in the electrolyte was increased. From the XRD analysis, it was observed that the films have two separate, Cu-rich and Ni-rich phases. It was also observed that the phase separation becomes weaker with increasing Fe ion concentration. All of the films have face-centered cubic structure and [111] preferred crystallographic orientation. The texture degree of the Ni-rich (111) phase increased with the Fe ion concentration. SEM and AFM measurements revealed that the surface morphology is considerably affected by the Fe ion concentration. The size of the grains formed on the film surface and the surface roughness decreased as the Fe ion concentration within the electrolyte increased.