Synthesis and characterization of proton conducting oxyanion doped Ba2Sc2O5

In this paper we report the successful synthesis of the cubic oxyanion containing perovskites, Ba2Sc2-xPxO5+x (x=0.4, 0.5), with the samples analysed through a combination of X-ray diffraction, NMR, TGA, Raman spectroscopy and conductivity measurements. Conductivity measurements indicate a p-type contribution to the conductivity in oxidizing conditions at elevated temperatures, with evidence for proton conduction in wet atmospheres. For the latter bulk conductivities of 5.9 x 10-3 and 1.3 x 10-3 Scm-1 at 500○C were obtained for x=0.4 and 0.5 respectively, comparable to other perovskite proton conductors, while the stability towards CO2 containing atmospheres was improved compared to BaCeO3 based systems.\ud Related Si doped systems have also been prepared, although in this case small Ba2SiO4 impurities are observed. We also provide evidence to suggest that “undoped” Ba2Sc2O5 contains carbonate groups, which accounts for its thermal instability

Oxyanion doping strategies to enhance the ionic conductivity in Ba2In2O5

In this paper we report the successful incorporation of phosphate and sulphate groups into the ionic conductor, Ba2In2O5, with the samples analysed through a combination of X-ray diffraction, NMR, TGA, Raman spectroscopy and conductivity measurements. The results show that such oxyanion incorporation leads to a conversion from an ordered brownmillerite-type structure to a disordered perovskite-type, and hence increases the conductivity at temperatures < 800○C. In wet atmospheres, there is evidence for a significant enhancement of the conductivity through a protonic contribution.\u

Structure of cellulose microfibrils in primary cell-walls from collenchyma

In the primary walls of growing plant cells, the glucose polymer cellulose is assembled into long microfibrils a few nanometers in diameter. The rigidity and orientation of these microfibrils control cell expansion; therefore, cellulose synthesis is a key factor in the growth and morphogenesis of plants. Celery (Apium graveolens) collenchyma is a useful model system for the study of primary wall microfibril structure because its microfibrils are oriented with unusual uniformity, facilitating spectroscopic and diffraction experiments. Using a combination of x-ray and neutron scattering methods with vibrational and nuclear magnetic resonance spectroscopy, we show that celery collenchyma microfibrils were 2.9 to 3.0 nm in mean diameter, with a most probable structure containing 24 chains in cross section, arranged in eight hydrogen-bonded sheets of three chains, with extensive disorder in lateral packing, conformation, and hydrogen bonding. A similar 18-chain structure, and 24-chain structures of different shape, fitted the data less well. Conformational disorder was largely restricted to the surface chains, but disorder in chain packing was not. That is, in position and orientation, the surface chains conformed to the disordered lattice constituting the core of each microfibril. There was evidence that adjacent microfibrils were noncovalently aggregated together over part of their length, suggesting that the need to disrupt these aggregates might be a constraining factor in growth and in the hydrolysis of cellulose for biofuel production

Hydropyrolysis: implications for radiocarbon pre-treatment and characterization of Black Carbon

Charcoal is the result of natural and anthropogenic burning events, when biomass is exposed to elevated temperatures under conditions of restricted oxygen. This process produces a range of materials, collectively known as pyrogenic carbon, the most inert fraction of which is known as Black Carbon (BC). BC degrades extremely slowly, and is resistant to diagenetic alteration involving the addition of exogenous carbon making it a useful target substance for radiocarbon dating particularly of more ancient samples, where contamination issues are critical. We present results of tests using a new method for the quantification and isolation of BC, known as hydropyrolysis (hypy). Results show controlled reductive removal of non-BC organic components in charcoal samples, including lignocellulosic and humic material. The process is reproducible and rapid, making hypy a promising new approach not only for isolation of purified BC for 14C measurement but also in quantification of different labile and resistant sample C fractions

Characterisation of Ba(OH)(2)-Na2SO4-blast furnace slag cement-like composites for the immobilisation of sulfate bearing nuclear wastes

Soluble sulfate ions in nuclear waste can have detrimental effects on cementitious wasteforms and disposal facilities based on Portland cement. As an alternative, Ba(OH)2–Na2SO4–blast furnace slag composites are studied for immobilisation of sulfate-bearing nuclear wastes. Calcium aluminosilicate hydrate (C–A–S–H) with some barium substitution is the main binder phase, with barium also present in the low solubility salts BaSO4 and BaCO3, along with Ba-substituted calcium sulfoaluminate hydrates, and a hydrotalcite-type layered double hydroxide. This reaction product assemblage indicates that Ba(OH)2 and Na2SO4 act as alkaline activators and control the reaction of the slag in addition to forming insoluble BaSO4, and this restricts sulfate availability for further reaction as long as sufficient Ba(OH)2 is added. An increased content of Ba(OH)2 promotes a higher degree of reaction, and the formation of a highly cross-linked C–A–S–H gel. These Ba(OH)2–Na2SO4–blast furnace slag composite binders could be effective in the immobilisation of sulfate-bearing nuclear wastes

Characterization of and structural insight into struvite-K, MgKPO4·6H2O, an analogue of struvite

Struvite-K (MgKPO4·6H2O) is a magnesium potassium phosphate mineral with naturally cementitious properties, which is finding increasing usage as an inorganic cement for niche applications including nuclear waste management and rapid road repair. Struvite-K is also of interest in sustainable phosphate recovery from wastewater and, as such, a detailed knowledge of the crystal chemistry and high-temperature behavior is required to support further laboratory investigations and industrial applications. In this study, the local chemical environments of synthetic struvite-K were investigated using high-field solid-state 25Mg and 39K MAS NMR techniques, alongside 31P MAS NMR and thermal analysis. A single resonance was present in each of the 25Mg and 39K MAS NMR spectra, reported here for the first time alongside the experimental and calculated isotropic chemical shifts, which were comparable to the available data for isostructural struvite (MgNH4PO4·6H2O). An in situ high-temperature XRD analysis of struvite-K revealed the presence of a crystalline–amorphous–crystalline transition that occurred between 30 and 350 °C, following the single dehydration step of struvite-K. Between 50 and 300 °C, struvite-K dehydration yielded a transient disordered (amorphous) phase identified here for the first time, denoted δ-MgKPO4. At 350 °C, recrystallization was observed, yielding β-MgKPO4, commensurate with an endothermic DTA event. A subsequent phase transition to γ-MgKPO4 was observed on further heating, which reversed on cooling, resulting in the α-MgKPO4 structure stabilized at room temperature. This behavior was dissimilar from that of struvite exposed to high temperature, where NH4 liberation occurs at temperatures >50 °C, indicating that struvite-K could potentially withstand high temperatures via a transition to MgKPO4

A comparison of the molecular weights of polyaniline samples obtained from gel permeation chromatography and solid state 15N n.m.r. spectroscopy.

Polyaniline samples of different molecular weights were prepared using aniline enriched with 15N. Molecular weights were determined by gel permeation chromatography (g.p.c.). 15N n.m.r. spectroscopy confirmed that both samples were in the emeraldine oxidation state, and end group analysis techniques were used to compare molecular weights derived from g.p.c. with those from the n.m.r. data. In addition, the 15N solid state n.m.r. spectra of emeraldine hydrochloride and a solvent-cast, oriented film of emeraldine base are presented

A comparison of the molecular weights of polyaniline samples obtained from gel permeation chromatography and solid-state nitrogen - 15 nuclear magnetic resonance spectroscopy.

Polyaniline samples of different molecular weights were prepared using aniline enriched with 15N. Molecular weights were determined by gel permeation chromatography. 15N NMR spectroscopy confirmed that both samples were in the emeraldine oxidation state, and end group analysis techniques were used to compare molecular weights derived from G.P.C. with those from the NMR data

A solid-state NMR study of molecular mobility and phase separation in co-spray-dried protein-sugar particles

NoMolecular mobility and physical form of co-spray-dried sugar¿lysozyme formulations were evaluated. Co-spray-dried trehalose:lysozyme and sucrose:lysozyme formulations in 1:9, 1:1 and 9:1 ratios (w:w) were stored at 0% RH and 75% RH for 5¿6 days. Molecular mobility and physical form of the co-spray-dried formulations after storage were determined by using 13C and 1H solid-state NMR as well as X-ray powder diffractometry. The results showed that increasing sugar content in co-spray-dried formulations stored at 0% RH decreased molecular mobility of the amorphous formulations indicating a close association of the protein and sugar. Exposure of sugar¿lysozyme 1:1 and 9:1 formulations to 75% RH led to separation of sugar and protein phases, where the sugar phase was crystalline. The intimate sugar¿lysozyme interaction of the formulations stored at 0% RH and the phase separation of the sugar-rich formulations stored at 75% RH were also confirmed by using 13C solid-state NMR spin-lattice relaxation time-filter (T1-filter) measurements. The propensity of sucrose and trehalose to crystallise was similar; however, the results suggest that part of the sugar in the phase-separated formulations remained amorphous and in close association with lysozyme

The Role of Catalyst Support, Diluent and Co-Catalyst in Chromium-Mediated Heterogeneous Ethylene Trimerisation

Sequential treatment of a previously-calcined solid oxide support (i.e. SiO2, γ-Al2O3, or mixed SiO2–Al2O3) with solutions of Cr{N(SiMe3)2}3 (0.71 wt% Cr) and a Lewis acidic alkyl aluminium-based co-catalyst (15 molar equivalents) affords initiator systems active for the oligomerisation and/or polymerisation of ethylene. The influence of the oxide support, calcination temperature, co-catalyst, and reaction diluent on both the productivity and selectivity of the immobilised chromium initiator systems have been investigated, with the best performing combination (SiO2−600, modified methyl aluminoxane-12 {MMAO-12}, heptane) producing a mixture of hexenes (61 wt%; 79% 1-hexene), and polyethylene (16 wt%) with an activity of 2403 g gCr−1 h−1. The observed product distribution is rationalised by two competing processes: trimerisation via a supported metallacycle-based mechanism and polymerisation through a classical Cossee-Arlman chain-growth pathway. This is supported by the indirect observation of two distinct chromium environments at the surface of the oxide support by a solid-state 29Si NMR spectroscopic study of the Cr{N(SiMe3)2}x/SiO2−600 pro-initiator