Mechanical and thermal properties of a nanopowder talc compound produced by controlled ball milling

A powdered compound constituted by over the 95% of talc Mg₃Si₄O₁₀(OH)₂ with MgCO₃ and CaMg(CO₃)₂ as minor phases was mechanically deformed by compaction and shear to a nanosized particulate (crystallite size ~5 nm) in a specifically built planetary ball mill. The mechanical milling was conducted in a controlled thermodynamic environment (25 °C and 0.13 Pa) by using low mechanical load to minimise amorphisation of the material. Mechanical τ(ε) shear analysis and thermo-structural modifications of the nanostructured talc particulate were investigated after selected milling times (0, 1, 5 and 20 h). At the very early stages of milling (1 h) layer flattening, lamination and texturing of the talc particles occurred. For prolonged milling (up to 20 h), a progressive reduction of the TOT talc stacking layer coherence, from about 20–5 nm, and an increase of (001) microstrain from about 0.6–2.2 × 10⁻² nm, as a non-linear function of the treatment time, were observed. A progressive increase of the specific surface area up to 28 m²/g as a consequence of the particle size reduction took place at intermediate milling times (5 h) and reduced to about 10 m²/g at prolonged milling (20 h). Even the thermo-structural behaviour of the particulate was significantly modified. For 20-h milled talc, a severe decrease of the dehydroxylation temperature from about 900–600 °C was observed with a concomitant anticipation of the recrystallisation of talc into MgSiO₃ (enstatite). The τ(ε) behaviour of the compound was strongly affected by the milling treatment changing from a shear-softening regime (untreated and 1 h) to a shear-hardening one (20 h). The observed changes of talc are of great importance to understand the rheology and the thermal transformation kinetics of talc compounds and can be exploited in those industrial applications that required milling of talc, such as in the production of talc-polymers nanocomposites or in medium–high-temperature ceramic processes.     

Effect of Ceria Addition to Na2O-ZrO2 Catalytic Mixtures on Lignin Waste Ex-Situ Pyrolysis

Waste lignin is a potential source of renewable fuels and other chemical precursors under catalytic pyrolysis. For this purpose, four mixed metal oxide catalytic mixtures (Cat) derived from Na₂CO₃, CeO₂ and ZrO₂ were synthesised in varying compositions and utilised in a fixed bed reactor for catalytic vapour upgrading of Etek lignin pyrolysis products at 600 °C. The catalytic mixtures were analysed and characterised using XRD analysis, whilst pyrolysis products were analysed for distribution of products using FTIR, GC-MS and EA. Substantial phenolic content (20 wt%) was obtained when using equimolar catalytic mixture A (Cat_A), however the majority of these phenols were guaiacol derivatives, suggesting the catalytic mixture employed did not favour deep demethoxylation. Despite this, addition of 40–50% ceria to NaZrO₂ resulted in a remarkable reduction of coke to 4 wt%, compared to ~9 wt% of NaZrO₂. CeO₂ content higher than 50% favoured the increase in conversion of the holo-cellulose fraction, enriching the bio-oil in aldehydes, ketones and cyclopentanones. Of the catalytic mixtures studied, equimolar metal oxides content (Cat_A) appears to showcase the optimal characteristics for phenolics production and coking reduction.     

The effect of point mutations on copper(II) complexes with peptide fragments encompassing the 106–114 region of human prion protein

Abstract  

The tetrapeptides Ac-SKHM-NH₂, Ac-TKHM-NH₂, Ac-MKHS-NH₂, Ac-S(OMe)KHM-NH₂, and Ac-MKHS(OMe)-NH₂ and the nonapeptides Ac-KTNSKHMAG-NH₂ and Ac-KTNMKHSAG-NH₂ were synthesized and their copper(II) complexes were studied by potentiometric, UV–Vis, circular dichroism (CD), and electron paramagnetic resonance (EPR) spectroscopic methods. These peptides mimic the 109–112 and 106–114 residues of the sequence of human prion protein. The imidazole-N donor atoms of histidyl residues were found to be the primary metal binding sites of all peptide fragments. This binding mode provides a good possibility for the cooperative deprotonation and metal ion coordination of two amide functions preceding histidine. The (N_im,N⁻,N⁻)-bonded species predominate in the pH range 5.5–7.0 and the free coordination sites of these species make possible the metal binding of weakly coordinating side chains. The comparison of the potentiometric and spectroscopic results revealed the stabilizing role of the oxygen donors of seryl, threonyl, or methoxyseryl residues of Ac-SKHM-NH₂, Ac-TKHM-NH₂, Ac-S(OMe)KHM-NH₂, and Ac-KTNSKHMAG-NH₂ containing the mutations in position 109. These interactions were, however, not observed in the peptides containing the specific amino acids in other locations of the peptide sequence.     

Advances in the frontal ring opening metathesis polymerization of dicyclopentadiene

The frontal ring opening metathesis polymerization of dicyclopentadiene using first and second generation Grubbs' catalysts is reported. To have sufficiently long pot lives, dimethylaminopyridine is added as an inhibitor. By choosing the proper compositions, it is possible to determine the ranges in which pure frontal polymerization occurs. A thorough study on the effect of the above components on the maximum temperatures reached by the front and on its velocities is performed. Namely, temperatures range from 164 to 205 °C depending on the type of catalyst and the above component ratios. Besides, front velocities range from 1.0 to 15.0 cm/min, which are one of the lowest and one of the highest values reported so far in any frontal polymerization experiment reported in literature. This finding allows the complete control of the frontal ring opening polymerization of dicyclopentadiene also in practical applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2776–2780     

On the Proton-Bound Noble Gas Dimers (Ng-H-Ng)+ and (Ng-H-Ng’)+ (Ng,Ng’ = He-Xe): Relationships between Structure,Stability, and Bonding Character

The structure, stability, and bonding character of fifteen (Ng-H-Ng)⁺ and (Ng-H-Ng’)⁺ (Ng, Ng’ = He-Xe) compounds were explored by theoretical calculations performed at the coupled cluster level of theory. The nature of the stabilizing interactions was, in particular, assayed using a method recently proposed by the authors to classify the chemical bonds involving the noble-gas atoms. The bond distances and dissociation energies of the investigated ions fall in rather large intervals, and follow regular periodic trends, clearly referable to the difference between the proton affinity (PA) of the various Ng and Ng’. These variations are nicely correlated with the bonding situation of the (Ng-H-Ng)⁺ and (Ng-H-Ng’)⁺. The Ng-H and Ng’-H contacts range, in fact, between strong covalent bonds to weak, non-covalent interactions, and their regular variability clearly illustrates the peculiar capability of the noble gases to undergo interactions covering the entire spectrum of the chemical bond.     

Semi‐interpenetrating polymer networks of methyl cellulose and polyacrylamide prepared by frontal polymerization

In this study, the feasibility of frontal polymerization (FP) as an alternative and convenient technique for the preparation of semi‐interpenetrating polymer networks made of methyl cellulose (MC) and cross‐linked polyacrylamide (PAAm) is demonstrated. FP was performed in water and glycerol, as largely available, nontoxic solvents. Although FP occurred in both media, differences were found by comparing the samples made in the two solvents. In particular, those prepared in water are characterized by larger inhomogeneity and less reproducibility, thus accounting for the boiling effects that influence propagating polymerization fronts when water was used. The effects of the ratio among MC and PAAm, the amount of cross‐linker and solvent medium were studied in terms of influence on temperature and velocity of FP fronts, glass transition temperature (dried samples), swelling behavior, dynamic‐mechanical properties (gels swollen in both water or glycerol), and tensile behavior. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1268–1274     

Superconductivity in lithium, potassium, and aluminum under extreme pressure: a first-principles study

Extreme pressure strongly affects the superconducting properties of "simple" elemental metals, such as Li, K, and Al. Pressure induces superconductivity in Li (as high as 17 K) while suppressing it in Al. We report first-principles investigations of the superconducting properties of dense Li, K, and Al based on a recently proposed, parameter-free, method. Our results show an unprecedented agreement with experiments, assess the predictive power of the method over a wide range of densities and electron-phonon couplings, and provide predictions for K, where no experiments exist so far. More importantly, our results help uncover the physics of the different behaviors of Li and Al in terms of phonon softening and Fermi surface nesting in Li.     

Sorption of ofloxacin and chrysoidine by grape stalk. A representative case of biomass removal of emerging pollutants from wastewater

Emerging pollutants, as antibiotics or dyes, in aquatic ecosystems are a crucial concern and numerous techniques have been developed for their removal. Efficiency, cost effectiveness, and biodegradability reveal biomass sorption as one of the most appealing methods. This study aims to evaluate the effectiveness of grape stalk as a sorbent for ofloxacin (a fluoroquinolone antibiotic) and chrysoidine (an azo-dye). The kinetic and the thermodynamic aspects of the sorption were studied. A pseudo first-order kinetic behavior is shown by both substances, though the kinetic constants of ofloxacin are almost double than those of chrysoidine. The sorption isotherms, which strictly follow the Langmuir model, show remarkable differences as a function of pH and of biomass size. The trend of Langmuir parameters, Q_max and K, as a function of pH and size, is discussed, and different binding mechanisms are proposed. Kinetic and thermodynamic parameters prefigure grape stalk as a potential biomass for scavenging toxic substances from wastewater.     

Superconductivity in doped polyethylene at high pressure

In this work we study the pressure-dependent phase diagram of polyethylene (H₂C)_x from 50 to 200 GPa. Low-symmetry, organic polymeric phases, that are dynamically stable and thermodynamically competitive with elemental decomposition, are reported. Electronic structure calculations reveal that the band gap of the lowest energy polymeric phase decreases from 5.5 to 4.5 eV in the 50–200 GPa range, but metalization occurs only for pressures well above 500 GPa. The possibility of metalization via doping was also investigated, observing that it can be achieved through boron substitution at carbon sites. We report a sizable electron-phonon coupling (λ ? 0.79) in this metallic phase, with an estimated superconducting transition temperature of about 35 K. However, a rather narrow domain of stability is found; most of the dopant elements render the polymeric phases unstable and induce amorphization. This suggests that doping under pressure, though presenting an alternative route to find high temperature superconductors, would be challenging to achieve experimentally.     

Evidence of orbital reconstruction at interfaces in ultrathin La0.67Sr0.33MnO3 films

Linear dichroism (LD) in x-ray absorption, diffraction, transport, and magnetization measurements on thin La(0.7)Sr(0.3)MnO(3) films grown on different substrates, allow identification of a peculiar interface effect, related just to the presence of the interface. We report the LD signature of preferential 3d-e(g)(3z(2)-r(2)) occupation at the interface, suppressing the double exchange mechanism. This surface orbital reconstruction is opposite to that favored by residual strain and is independent of dipolar fields, the chemical nature of the substrate and the presence of capping layers.