Thermal decomposition of ammonium sulphate

The thermal decomposition and vaporisation of ammonium sulphate, (NH₄)₂SO₄, is shown to take place via two distinct sets of reactions. In the first, ammonium pyrosulphate, (NH₄)₂S₂O₇, is the primary condensed phase product: 2(NH₄)₂SO₄ ← (NH₄)₂S₂O₇+2NH₃+H₂O The second stage concerns the decomposition of the pyrosulphate. Ammonia, sulphur dioxide, nitrogen and water are the major products, the dominant reaction being 3(NH₄)₂S₂O₇ ← 2NH₃+6SO₂+2N₂+9H₂O     

Hyperfiltration of surfactants containing solutions from the plating industry

The hyperfiltration of chromic plating rinse water, which contains a special type of surfactant, was examined using different annealed CA membranes. At low concentrations the surfactant influences the volume flow more than the rejection. An effect of the electrolytes can be neglected at low concentration. Increasing surfactant concentration as well as rising electrolyte concentration cause a remarkable drop of both volume flow and electrolyte rejection. This was measured with tetraethylammonium perfluoroctanolsulfonate, a commonly used surfactant for chromic plating.     

Cyclic alkanes as geochemical markers in coal liquefaction products

Branched-chain/cyclic alkanes have been obtained, by solvent extraction and molecular-sieve adsorption, from a UK low-temperature (Rexco) coal tar, a USA fluidized-bed pyrolysis (FMC COED) coal tar, and a novel supercritical-gas-extract of a Turkish (Elbistan) lignite. Mass spectrometry (with gas chromatography and field-desorption) established the presence of mono-, di (including sesquiterpanes), tri-, tetra- (steranes only), and pentacyclic (triterpanes only) alkanes, including several steranes and triterpanes not previously reported as coal-tar constituents. The potential of cyclic alkanes as geochemical markers, even for commercial coal products subjected to appreciable heat treatment, is demonstrated by the identification of C₁₂, C₁₃, C₁₅ and C₁₆ dicyclics (including isoprenoid alkanes), C₁₇-C₂₆ tricyclics, and C₂₇ and C₂₉ hopane-type pentacyclics (triterpanes) in FMC, and of C₁₆-C₃₈ monocyclics, C₃₄-C₃₆ dicyclics, C₂₂-C₃₆ tricyclics, C₂₇-C₃₀ tetracyclics (steranes), and C₂₇, C₂₉, C₃₀, C₃₁, C₃₂, and C₃₃ hopane-type pentacyclics (triterpanes) in Rexco tar. Tetra- and pentacyclic alkanes were also preserved in the lignite extract.     

Optical properties of electrically conducting films formed by anodic oxidation of 1,2-di(2-thienyl)ethylene

Poly (2,2-bithienyl-5,5-diylvinylene) (PBTV) films formed by anodic oxidation of 2×10^–3 M solutions of trans-1,2-di(2-thienyl)-ethylene (trans-DTE) in acetonitrile were studied by voltammetry and ellipsometry. For the doped and undoped films, refraction indices and absorption coefficients in the wavelength range of 400–800 nm were determined as functions of thickness. Differences in the structure were found depending on the height of the oxidation potential. A decrease in thickness by doping was observed and is discussed in terms of a possible cis-trans isomerization. The optical spectrum of the undoped polymer showed a high degree of -electron delocalization (high degree of conjugation).This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday.     

Noise equivalent count measurements in a neuro-PET scanner with retractable septa

The noise-equivalent count-rate (NEC) performance of a neuro-positron emission tomography (PET) scanner has been determined with and without interplane septa on uniform cylindrical phantoms of differing radii and in human studies to assess the optimum count rate conditions that realize the maximum gain. In the brain, the effective gain in NEC performance for three-dimensions (3-D) ranges from >5 at low count rates to approximately 3.3 at 200 kcps (equivalent to 37 kcps in 2-D). The gains of the 3-D method assessed by this analysis are significant, and are shown to be highly dependent on count rate and object dimensions.     

The degradation in tensile strength of polymer-coated glass optical fibres under γ-irradiation

The tensile strength of glass optical fibres when coated with various polymers has been measured as a function of -ray dose. Fibres protected with acrylate, silicone + acrylate or polyimide coatings showed little degradation after receiving a total dose of 1 MGy (they retained >95% of their preirradiated strength). For a fibre with an extruded nylon overcoat the nylon became very brittle after 0.5 MGy, but as far as could be assessed, the strength of the central glass fibre was little affected. Two other types of fibre, both protected with fluorinated polymers, were severely weakened after 0.1 MGy (their tensile strength being reduced to < 40% of their pre-irradiated strength). Experimental results are given supporting the hypothesis that the degradation results from gaseous fluorine-containing species chemically attacking the surface of the glass fibre.     

The formation of β′-sialon from a montmorillonite-polyacrylonitrile composite by carbothermal reduction: an NMR,TGA, XRD and EM study

The products of carbothermal reduction in N₂ of a nanocomposite between dodecylammonium-exchanged montmorillonite and polyacrylonitrile (PAN) have been studied by solid-state ²⁷Al and ²⁹SiNMR spectroscopy, X-ray diffraction, transmission electron microscopy and thermogravimetry. Comparison with analogous reactions involving sodium-exchanged montmorillonite and dodecylammonium-exchanged montmorillonite (without PAN) shows that in the presence of PAN, the formation of silica, cordierite or mullite is almost completely suppressed. The only crystalline phase detected between 1000 and 1300 °C was a -sialon, having a much higher SiAl ratio (7.051) than that of the precursor clay (2.441). Reduction of the octahedral AlO₆ begins near 1200 °C, forming increasing amounts of Al(N,O)₄ tetrahedra with temperature, so that by 1600 °C, complete reduction to AlN₄ (i.e. bulk AlN) has occurred. In contrast, reduction of the tetrahedral SiO₄ is appreciable at 1100 °C, and is almost complete (SiN₄ tetrahedra only) by 1200 °C. No intermediate Si(N,0)₄ environments are found. By 1600 °C, only the SiC₄ environment (i.e. bulk SiC) remains. A mechanism is suggested, involving the formation of alternating slabs of an amorphous aluminosilicate and carbon at 1000 °C, followed by diffusion of silicon from the outer regions of the aluminosilicate band towards the centre, and sequential reduction of Si(OSi)₄ and Si(OSi)₃ (OAl) groups.