The effect of peptone on the structure of electrodeposited Sn-Fe binary alloys

Sn-Fe thin films were electrodeposited by constant current deposition on copper substrates using an aqueous gluconate based electrolyte with varying concentrations of the organic additive peptone. Good quality metallic deposits were obtained with surface morphologies which varied with the concentration of peptone present in the electrolyte. The effect of peptone concentration on the deposition process was studied using electrochemical polarization curves and EDX analysis. The effect of peptone concentration on deposit structure and surface morphology was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ⁵⁷Fe and ¹¹⁹Sn conversion electron Mössbauer spectroscopy (CEMS). It was concluded that the addition of small amounts of peptone to the electrolyte slightly increased the bath stability and led to changes in the alloy composition of the electrodeposits. It was found that increases in the peptone content increased the amount of the crystalline structure in the deposits with corresponding reductions in the amounts of amorphous structure present in the deposits.     

Sampling aerosols for lead isotopes on a global scale

To reliably sample aerosols in a wide range of environments from the polluted to the almost pristine, ultra-clean materials, procedures and laboratory conditions are needed. Also, when multiple samples need to be taken at numerous sites the sampling procedures need to be simple and the equipment inexpensive and easy to operate. A system described here which meets these requirements uses a disposable plastic monitor fitted with an acid-cleaned PTFE 0.45 μm front and a 30–60 μm backing filter connected to a small diaphragm pump. When ion exchange chemistry is required the system gives a Pb blank of 70 pg. Without ion exchange chemistry the blank amounts to 15 pg on a complete filter sectioned into 8-π/4 sectors giving reliable isotopic data on filters containing >400 pg of Pb. The lowest blank on the complete filter, without cutting, is 11±8 pg which permits Pb isotopes from aerosols to be measured on a 120 pg sized sample with acceptable accuracy and precision (0.2% for ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios). The factor limiting the quality of measurements below this level is the uncertainty in the blank contribution and not the sensitivity of the thermal ionisation mass spectrometer used here. The analysis of selected filters from the United Kingdom and the Republic of Ireland are used to illustrate the method. Air containing 0.11 ng m⁻³ of Pb yielded isotopic ratios ²⁰⁶Pb/²⁰⁷Pb=1.083±0.003, ²⁰⁸Pb/²⁰⁷Pb=2.361±0.003 and ²⁰⁶Pb/²⁰⁴Pb=16.9±0.3.     

Frontiers of positron and positronium chemistry in condensed media

Our work proves that positron annihilation spectroscopy is an excellent tool to follow the structural changes in chemical species. We present four examples to support the above statement. The sizes of defects in electrodeposited chromium layers were studied and estimated on the basis of positron lifetime spectra decomposed into two components. Vacancies, di-vacancies and vacancy-clusters could be identified in the electrodeposites. The changes of the size distribution of the free volume units in poly(methylmetacrylate) on the dependence of molecular weight and dispersity were described by the correlation between the lifetime ofortho-Ps and the free volume units in polymers. It was found that the free volume is affected by both the molecular weight and dispersity. The effect of dispersity was explained by the sample preparation technique, namely by the application of high pressure. The ortho-para conversion ofortho-Ps was used to follow the partial spin-crossover in [Fe(1-ethyl-1H-tetrazole)₆](BF₄)₂. The spin-crossover temperature was identified to be 105 K. A conformal structural transformation was found in [Zn(1-propyl-1H-tetrazole)₆](BF₄)₂ between 170 and 90 K by positronium lifetime measurement and the role of (BF₄)²⁻ anion, in this transformation, was proved by¹⁹F NMR spectroscopy.     

Mössbauer and X-ray diffraction study of isothermal ageing effect at 500°C in electrochemically deposited Fe−Ni−Cr alloys

Mössbauer spectroscopy, X-ray diffractometry and microprobe analysis were used to study electrodeposited Fe?Ni?Cr (40–50% Fe, 40–47% Ni, 3–5% Cr) alloys isothermally aged at 500°C from 5 minutes to 100 hours in an inert argon gas atmosphere. The main phase of the as-deposited samples exhibits ferromagnetic microcrystalline behavior, whereas the thermally prepared samples of same composition are always paramagnetic. The dominant effect of ageing is an oxidation process which resulted in the formation of hematite and magnetite iron oxides in considerable amounts and which are attributable to the presence of oxygen inclusions in the as-electrodeposited samples.     

Synthesis and characterization of multi-arm star-branched polyisobutylenes

Multi-arm star-branched polyisobutylenes were synthesized by the “arm-first, core-last” method using the 2-chloro-2,4,4-trimethylpentane/pyridine/TiCl₄ initiating system and the reactive core-forming comonomers 1,3-diisopropenylbenzene (DIPB) and divinylbenzene (DVB). Star formation was confirmed by RI and UV GPC and static light-scattering analyses. It was determined that DVB was significantly superior to DIPB. Using DVB, star polymers formed more rapidly and contained a much lower amount of residual PIB arms. Increasing the concentration of the reactive comonomer from 1 to 10 times the concentration of chain ends, [CE], increased the efficiency of the star-forming reaction substantially. Modest increases in the fraction of PIB arms incorporated into the star could be obtained by increasing the duration of the star-forming reaction. The timing of addition of the reactive comonomer to the PIB arms seems to be the process parameter most critical to the star development, since early addition at excessively low IB conversion hinders star formation by causing a copolymerization between IB and the core-forming comonomer. Late addition risks loss of a significant fraction of PIB chains due to spontaneous β-proton expulsion. A fully developed multi-arm star-branched PIB was synthesized by utilizing 10:1 [DVB]:[CE], 24 h star-forming reaction time, 14,000 g/mol target arm M_n, and addition of DVB at 99% IB conversion. The resultant star polymer contained only 4% unreacted PIB arms and possessed M_w = 345,000 g/mol by light scattering. The weight-average number of arms per star polymer was calculated to be 23. © 1996 John Wiley & Sons, Inc.     

On the Molecular Structure and Bonding in a Lithium Bismuth Porphyrin Complex: LiBi(TPP)2

A new Bi? Li porphyrin sandwich compound, LiBi(TPP)₂ has been synthesized and characterized (TPP=tetraphenylporphyrin). The unique molecular structure of LiBi(TPP)₂ is such that the Bi sits between the porphyrins and is directed towards the Li. This complex was shown to remain intact in solution by temperature‐dependent 2D NMR spectroscopy. In order to investigate the potential interaction between these two metals, DFT calculations were used and showed a Bi 6s orbital polarized towards Li which could be indicative of a Bi? Li dative bond. This bond is remarkably short, 2.87 Å, and is among the shortest Bi? Li distances seen in a small molecule.     

Electrostatic and Non‐covalent Interactions in Dicationic Imidazolium–Sulfonium Salts with Mixed Anions

A series of thioether‐functionalised imidazolium salts have been prepared and characterized. Subsequent reaction of the thioether‐functionalised imidazolium salts with iodomethane affords imidazolium–sulfonium salts composed of doubly charged cations and two different anions. Imidazolium–sulfonium salts containing a single anion type are obtained either by a solvent extraction method or by anion exchange. The imidazolium–sulfonium salts undergo a methyl‐transfer reaction on exposure to water, giving rise to a new, singly charged imidazolium salt with iodide introduced at the 2‐position of the imidazolium ring. Crystal structures of some of the imidazolium–sulfonium salts were determined by X‐ray crystallography providing the topology of the interactions between the dications and the anions. Electrospray ionization mass spectrometry and quantum‐chemical calculations were used to rationalise the relative strength of these interactions.     

Spontaneous formation of PMB esters using 4-methoxybenzyl-2,2,2-trichloroacetimidate

Carboxylic acids are converted to the corresponding 4-methoxybenzyl (PMB) esters with 4-methoxybenzyl-2,2,2-trichloroacetimidate in the absence of an acid catalyst. This operationally simple procedure is a highly effective method for the formation of PMB esters. The reaction is promoted by the carboxylic acids themselves in excellent yields (72–99%). Sterically hindered carboxylic acids, which provide lower yields with other imidates, are esterified in higher yield with the more reactive PMB imidate. No racemization is observed in the case of carboxylic acids bearing an α-stereocenter, and no isomerization is observed with Z-α,β-unsaturated acids. This method may therefore find use in the esterification of complex or sensitive substrates where more common techniques lead to decomposition.     

Lateral tyre dynamic characteristics

The ability to model the ride vibration of unsuspended vehicles is at present seriously limited by lack of knowledge about the lateral and longitudinal dynamic characteristics of rolling tyres and the interaction of these characteristics with the ground surface. In this paper, models for the lateral dynamic behaviour of a rolling tyre are reviewed. The beam model, string model and spring-damper models are described and compared. A new lateral tyre model is introduced and tested against experimental results. This model comprises a parallel spring and hysteretic damping unit, representing the tyre carcass, in series with a viscous damper representing the interaction between the tyre and ground. Model justification was made against the measurements of lateral tyre response. The results showed that the proposed model provided more accurate prediction of lateral dynamic tyre response than the other spring-damper models.     

On the nature of pulsars

The paper contains a relatively non-technical summary of some recent work by the author and Jeremy Butterfield. The goal is to find a way of assigning meaningful truth values to propositions in quantum theory: something that is not possible in the normal, instrumentalist interpretation. The key mathematical tool is presheaf theory where multi-valued, contextual truth values arise naturally. We show how this can be applied to quantum theory, with the ‘contexts’ chosen to be Boolean subalgebras of the set of all projection operators.