The preparation and properties of the solid state ionic conductor,CuZr2(PO4)3

The compound CuZr₂(PO₃)₄ has been synthesised, the conductivity and lattice parameters measured. The material was used to measure the standard free energy of formation of Cu₂S.     

Polymer–Graphene Nanocomposite Materials for Electrochemical Biosensing

Biosensing is an important and rapidly developing field, with numerous potential applications in health care, food processing, and environmental control. Polymer–graphene nanocomposites aim to leverage the unique, attractive properties of graphene by combining them with those of a polymer matrix. Molecular imprinted polymers, in particular, offer the promise of artificial biorecognition elements. A variety of polymers, including intrinsically conducting polymers (polyaniline, polypyrrole), bio‐based polymers (chitosan, polycatechols), and polycationic polymers (poly(diallyldimethylammonium chloride), polyethyleneimine), have been utilized as matrices for graphene‐based nanofillers, yielding sensitive biosensors for various biomolecules, such as proteins, nucleic acids, and small molecules.

     

Hydrogen sensing in molten aluminium using a commercial electrochemical sensor

A commercial electrochemical sensor for the determination of hydrogen in molten aluminium was critically assessed under laboratory conditions. The probes make use of a proton conducting solid electrolyte and were found to measure correct emfs for several hours. The applicability of the recently developed current reversal technique on this type of sensor was demonstrated. The long-term behaviour of the device was investigated and found to be critical. Paper presented at the 6th Euroconference on Solid State Ionic, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Humidity sensing under aggressive conditions using nafion conductors

A sensor capable of detecting moisture in a chlorine-air environment has been assembled from Nafion and platinum. Nafion acts as the solid electrolyte while platinum chemically deposited on the Nafion is the electrode material. Thermogravimetric analysis suggests that Nafion is stable up to 473 K. A Frequency Response Analyser (FRA) was used to calibrate the sensor in terms of impedance as a function of relative humidity. The frequency range was 10⁻² to 10⁷ Hz and an amplitude of 100 mV was applied. Impedance measurements show that only a bulk process occurs and when relative humidity is high, diffusion of moisture into and out of the platinum/Nafion composite becomes significant. This is reflected in the form of a spike at about 45° to the real axis. The sensor detects chlorine in air without loosing its chemical and physical stability. Conductivity increases as a function of temperature and reaches its peak at 433 K. The response time of the sensor is governed by temperature, thickness of the Nafion film and the amount of platinum on the surface. In practice the sensor can be operated with a frequency controller. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Novel rearrangement and crystal structure of tetraarylated dihydrosemibullvalene derivatives

The structure of a dihydrosemibullvalene,

, previously deduced from nmr and mass spectrometry and from chemical transformation of an analogue - is confirmed by X-ray analysis. The thermal rearrangement of other analogous arylated dihydrosemibullvalenes is disclosed.     

Synthesis of 8,9-difluoro-2-methyl-6-oxo-1,2-dihydropyrrolo[3,2,1-ij]quinoline-5-carboxylic acid

A new and efficient seven-step synthesis of 8,9-difluoro-2-methyl-6-oxo-1,2-dihydropyrrolo[3,2,1-ij]-quinoline-5-carboxylic acid ( 9 ), an important intermediate used in the synthesis of quinolone antibacterials, has been developed beginning with commercially available 2,3,4-trifluoronitrobenzene. Selective displacement of the 2-fluorine of the starting material with the anion of ethyl acetoacetate and subsequent hydrolysis and decarboxylation affords the arylacetone derivative 11 . Reduction of the ketone and nitro groups of 11 followed by condensation with diethyl ethoxymethylenemalonate gives 14 , which is cyclized to the indole derivative 15 by the Mitsunobu procedure. Friedel-Crafts cyclization of 15 and acid hydrolysis gives the title compound 9 .     

Electrochemical investigation of lithium intercalation into graphite from molten lithium chloride

Lithium reduction at a graphite electrode in molten lithium chloride was studied at temperatures from 650 to 900 °C using cyclic voltammetry and chronoamperometry. It was found that, during cathodic polarization, lithium intercalation into graphite occurred before deposition of metallic lithium started. This process was confirmed to be rate-controlled by the diffusion of lithium in the graphite. When the cathodic polarization potential was more negative than that for metallic lithium deposition, exfoliation of graphite particles from the electrode surface was observed. This was caused by fast and excessive accumulation of lithium intercalated into the graphite, which produced mechanical stress too high for the graphite matrix to accommodate. The erosion process was abated once the graphite surface was covered by a continuous layer of liquid lithium. These results are of relevance to the mechanism of carbon nanotube and nanoparticle formation by electrochemical synthesis in molten lithium chloride.     

The effect of hard and soft segment composition and molecular architecture on the morphology and mechanical properties of polystyrene-polyisobutylene thermoplastic elastomeric block copolymers

This paper reports the effects of hard (polystyrene, PS) and soft (polyisobutylene, PIB) segment composition and the molecular architecture (linear versus star, PS and PIB block length) on the morphology and mechanical properties of polystyrene/polyisobutylene (SIBS) block copolymers synthesized by living carbocationic polymerization. Atomic force microscopy, dynamic mechanical thermal analysis and tensile testing verified the phase-separated nature of the block copolymers, which behaved as thermoplastic elastomers (TPEs). The morphology of these TPEs is similar to polydiene-based TPEs, and is defined by the soft/hard segment composition. Interestingly, topology (linear vs star) did not have a major influence on morphology. Tensile testing showed that for both linear and three-arm star block copolymers, the modulus and tensile strength increased while elongation at break decreased with higher PS content. However, three-arm star block copolymers showed larger moduli than their linear homologues with similar PS content and PIB arm length, indicating the influence of molecular architecture on mechanical properties. These results might serve as a foundation for macromolecular engineering design for optimizing properties.     

Silicon surface texturing by electro-deoxidation of a thin silica layer in molten salt

A new method of silicon surface texturing is reported, which is based on thin silica layer electrochemical reduction in molten salts. A thermal silica layer grown on p-type silicon was potentiostatically reduced in molten calcium chloride at 850 °C. Typical nano–micro-formations obtained at different stages of electrolysis were demonstrated by SEM. X-ray diffraction measurements confirmed conversion of the amorphous thermal silica layer into crystalline silicon. The proposed approach shows promise in photovoltaic applications, for instance, for production of antireflection coatings in silicon solar cells.