Solid state recycling of 5083 Al alloy by hot extrusion

The machined chips of 5083 Al alloy were recycled by hot extrusion at 723 K with an extrusion ratio of 44:1 in air. Corrosion and mechanical properties of the recycled specimens have been compared with those of a virgin extrusion which was processed from the ingot block. As a result of salt immersion tests, mass loss of the recycled specimen was not less than twice of that of the virgin extrusion. The deterioration in corrosion properties for the recycled specimen was attributed to the excessive contamination of Fe which promoted galvanic corrosion. As a result of tensile tests, the recycled specimen exhibited a good combination of high strength and high elongation to failure at room temperature. The excellent mechanical properties for the recycled specimen were attributed to the refined microstructure. However, the elongation to failure of the recycled specimen at elevated temperatures more than 573 K was lower than that of the virgin extrusion. The contamination of oxide particles is likely to be responsible for the lower elongation in the solid recycled specimen. <br />

Cation dynamics in dimethyl-pyrrolidinium-based solid-state ion conductors

Dimethyl-pyrrolidinum-based salts have been investigated by means of DSC, conductivity, NMR and Raman spectroscopy. The investigation aims to study the effect of the anion on the behaviour of the salt, in terms of plastic properties as well as rotational degrees of freedom of the cation. The materials range from the non-plastic iodide salt to the highly plastic BF₄ salt, which flows under its own weight at elevated temperatures. The different rotational and translational motions of the cations, and the difference between rotator and plastic phases are discussed.<br />

High mobility I− / I3− redox couple in a molecular plastic crystal: A potential new generation of electrolyte for solid-state photoelectrochemical cells

A series of new electrolyte materials based on a molecular plastic crystal doped by different iodide salts together with iodine have been prepared and characterized by thermal analysis, ionic conductivity, electrochemical and solid-state NMR diffusion measurements. In these materials, the plastic crystal phase of succinonitrile acts as a good matrix for the quaternary ammonium based iodides and iodine and appears to act in some cases as a solid-state &ldquo;solvent&rdquo; for the binary dopants. The materials were prepared by mixing the components in the molten state with subsequent cooling into the plastic crystalline state. This resulted in waxy-solid electrolytes in the temperature range from &minus; 40 to 60 &deg;C. The combination of structural variation of the cations, and fast redox couple diffusion (comparable with liquid-based electrolytes), as well as a high ionic conductivity of up to 3 &times; 10^{&minus; 3} S cm^{&minus; 1} at ambient temperature, make these materials very attractive for potential use in solid-state photoelectrochemical cells.<br />

Rapid I−/I3− diffusion in a molecular-plastic-crystal electrolyte for potential application in solid-state photoelectrochemical cells

High current-carrying capacity and rapid, liquidlike diffusion were achieved in a dye-sensitized solar cell (DSSC) based on the plastic-crystalline electrolyte succinonitrile and the I^&minus;/I₃^&minus; redox couple (see diagram). This could lead to the development of true solid-state DSSCs without conventional organic-liquid electrolytes, which can cause problems with long-term device stability.<br />

Solid state ion transport and phase behaviour in composites of N,N-methyl propylpyrrolidinium tetrafluoroborate and amorphous polyethylene oxide

The binary and ternary addition of 2 wt.% LiBF₄ and 2 wt.% amorphous polyethylene oxide (aPEO) respectively to the plastic crystal forming salt P₁₃BF₄ (where P₁₃⁺=methylpropyl pyrrolidinium cation) was investigated with specific focus on the phase behaviour and evaluation of transport characteristics. Differential scanning calorimetry (DSC), optical thermomicroscopy, solid state nuclear magnetic resonance (NMR), and AC impedance spectroscopy were used to develop an understanding of the conduction process in the pure and mixed systems. The morphology of the ternary compound appeared as hexagonal spherulites upon solidification. Multinuclear NMR Pulsed Field Gradient measurements (¹H,¹⁹F,⁷Li) to probe both cation and anion diffusion coefficients are reported. The anion is shown to be the most diffusive (at 320 K:¹⁹F=2.5&times;10^&minus;11 m² s^&minus;1; 1H: 1.8&times;10^&minus;11 m² s^&minus;1; ⁷Li: 1.1&times;10^&minus;11 m² s^&minus;1) in the ternary compound, with enhanced conductivity (2.7&times;10^&minus;5 S cm^&minus;1 at 310 K) just below the melt.<br />

Solid state NMR characterization of polyrrole : the nature of the dopant in PF6− doped films

³¹P and ¹⁹F solid state NMR have been used to study the nature of the PF₆&minus; anion in polypyrrole films at various levels of oxidation. It appears that the symmetric PF₆&minus; unit remains undistorted and unchanged throughout, suggesting that it is predominantly acting only as a counterion and not as a true &lsquo;dopant&rsquo;, since any distortion in the phosphorous environments would result at the very least in chemical shift anisotropy of the ³¹P nucleus. A second set of phosphorous and fluorine resonances, which are consistent with a difluoride phosphorous compound, appeared in the films. Upon electrochemical reduction of the polymer, the undistorted PF₆&minus; anion leaves the film whereas the second phosphorous species remains. Re-oxidation of the polymer reverses the processes observed during reduction.<br />

Structural characterization of conducting polypyrrole using 13C cross-polarization/magic-angle spinning solid-state nuclear magnetic resonance spectroscopy

¹³C nuclear magnetic resonance (n.m.r.) has been used to study polypyrrole and <i>N</i>-substituted polypyrrole in the solid state. The extent of oxidation appears to be counterion-dependent; in particular, the quinoid structure appears favoured in the films prepared with dodecyl sulfate. Resonances associated with the quinoid unit are lost upon reduction of the polypyrrole film, which supports the idea that the quinoid structure is associated with the oxidized form of polypyrrole. <i>N</i>-substituted polypyrroles have a more distinct resonance at 110 ppm, which is linked to lower degrees of oxidation or charge delocalization in these systems. The decrease in conductivity of polypyrrole upon thermal ageing in air is associated with both the loss of counterion (&lsquo;thermal dedoping&rsquo;) and the decomposition of the quinoid structure in the polymer backbone. There is no indication of carbonyl formation in the solid-state n.m.r. spectra obtained in the present study.<br />

Solid state lithium ion conduction in pyrrolidinium imide–lithium imide salt mixtures

The properties of the binary salt system based on mixtures of methyl ethyl pyrrolidinium bis(trifluoromethane sulfonyl) imide (P₁₂) and lithium bis(trifluoromethane sulfonyl) imide (Li imide) are reported. The lithium containing mixtures were found to be more than two orders of magnitude more conductive than the parent P₁₂ phase and the 33 mol% Li imide systems showed a solid state conductivity around 1&times;10^&minus;4 S/cm at 20&deg;C. This solid state conductivity is believed to take place in plastic crystal phases of the P₁₂ compound.<br />

Composite cell components for elevated temperature all-solid-state Li-ion batteries

Application of Li-ion batteries with liquid electrolytes at elevated temperatures (above 60&deg;C) is limited due to the decomposition of the electrolyte. Stable solid state electrolytes can solve this problem, but the conductivity of these electrolytes are relatively low, the interfacial contacts with the electrodes are poor, and the charge transfer kinetics in the electrodes are limited. Solutions for these problems by using composite electrodes and electrolytes have been investigated and the results are described. A new concept for making all-solid-state Li-ion batteries that can be applied in the temperature range between room temperature and about 150&deg;C will be presented.<br />

Plastic crystal electrolyte materials : new perspectives on solid state ionics

Plastic crystal materials have long been known but have only relatively recently become of interest as solid&ndash;state ion conductors. Their properties are often associated with dynamic orientational disorder or rotator motions in the crystalline lattice. This paper describes recent work in the field including the range of organic ionic compounds that exhibit ion conduction at room temperature. Conductivity in some cases is high enough to render the compounds of interest as electrolyte materials in all solid state electrochemical devices. Doping of the plastic crystal phase with a small ion such as Li+ in some cases produces an even higher conductivity. In this case the plastic crystal acts as a solid state &ldquo;solvent&rdquo; for the doped ion and supports the conductive motion of the dopant via motions of the matrix ions. These doped materials are also described in detail.<br />

Solid state NMR characterization of lithium conducting ceramics

⁷Li solid state NMR has been used to characterize lithium aluminium titanium phosphate and lithium lanthanum titanate ceramics. Both materials have high ionic mobilities at room temperature and this is reflected in their static ⁷Li powder patterns. In the case of the phosphate based ceramic, a narrow Lorentzian peak is observed above 300 K, which narrows further with increasing temperature. The accompanying quadrupolar structure, with <i>C</i>_Q (quadrupolar coupling constant) ~ 40 kHz, suggests that the lithium ions are hopping rapidly between equivalent, high electric field gradient sites. The ²⁷Al and ³¹P magic angle spinning (MAS) spectra reveal an asymmetric phosphorus peak and two distinct aluminium resonances. The room temperature powder pattern of Li_0.33La_0.57TiO₃ shows a dipolar broadened peak which narrows quite suddenly at 310 K revealing quadrupolar satellites with C_<i>Q</i> ~ 900 Hz. A second lithium site is also observed in this material, as indicated by a further, weaker quadrupolar structure (<i>C</i>_<i>Q</i> ~ 40 kHz).<br />

Solid state NMR analysis of polypyrrole grown in a phosphonium ionic liquid

³¹P, ¹⁹F and ¹³C solid state NMR analysis has been used to investigate the intercalation/de-intercalation of both anions and cations in electrochemically synthesized polypyrrole films. Use of a phosphonium-based ionic liquid, tri(hexyl)(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)amide, allows the separate detection of the cation and anion by analysis of the phosphorous and fluorine resonances, respectively. Initial results indicate the incorporation of both cations and anions during film growth in the ionic liquid. There is a notable change in the ³¹P chemical shift of the cation on incorporation into the film, consistent with a significant change in environment compared to the pure ionic liquid. Despite its large size, the phosphonium cation can be completely expelled from the film by oxidation.<br />