Use of inorganic adsorbers in radium analysis

Two new simple methods were studied for the analysis of radium in fresh waters by concentration and purification. Both methods are based on the use of an inorganic selective adsorber, namely basic lead rhodizonate, LERHO, and partially reduced tin dioxide (PRTD). The procedures were checked by using filtered fresh waters spiked with 0.1 Bq of²²⁶Ra, and in the presence of few μg/l of barium. In each experiment¹³³Ba radioisotope was added to water samples to measure the yield of the overall procedure by γ-counting. Barium and radium were adsorbed from basic solutions on LERHO packed chromatographic column in the first procedure, while batch experiments were preferred for the adsorption on PRTD. After separation,²²⁶Ra and barium were eluted from the exchangers and co-precipitated onto small filters as thin film, supported on an inactive barium sulphate substrate, to be submitted to alpha-and gamma-spectrometry. Both methods gave promising results.     

Gapping by squashing: metal-insulator and insulator-metal transitions in collapsed carbon nanotubes

Squashing brings circumferentially separated areas of a carbon nanotube into close proximity, drastically altering the low-energy electronic properties and (in some cases) reversing standard rules for metallic versus semiconducting behavior. Such a deformation mode, not requiring motion of tube ends, may be useful for devices. Uniaxial stress of a few kbar can reversibly collapse a small-radius tube, inducing a 0.1 eV gap with a very strong pressure dependence, while the collapsed state of a larger tube is stable. The low-energy electronic properties of chiral tubes are surprisingly insensitive to collapse.     

Abrupt topological transitions in the hysteresis curves of ferromagnetic metalattices

When a metal is confined to the interstices of an inert colloidal crystal, the intrinsic order parameter(s) of electronic and magnetic phenomena within the metal interact with the structural order parameter of the surrounding (and confining) colloidal crystal. If the magnetic stiffness length is comparable to the colloidal lattice constant, the interplay of competing interactions stabilizes multiple topologically distinct magnetic phases separated by sharp transitions in the hysteresis curves. The colloidal confinement also induces substantial coercivity in metals that are perfectly soft in the bulk.     

Helium in one-dimensional nanopores: free dispersion, localization, and commensurate/incommensurate transitions with nonrigid orbitals

The single-particle states of helium within a bundle of carbon nanotubes can range from nearly free-particle dispersion to localization, even within a single bundle. At intermediate effective masses, the corrugation in the external potential can be comparable to the intrasite He-He hard-core interaction. This results in a commensurate/incommensurate transition, where the mobility of the doubly occupied domain-wall solitons at high density greatly exceeds the corresponding hole mobility below the transition.     

Modeling electrostatically induced collapse transitions in carbon nanotubes

Molecular dynamics simulations demonstrate how a mechanically bistable single-walled carbon nanotube can act as a variable-shaped capacitor. If the voltage is tuned so that collapsed and inflated states are degenerate, the tube's susceptibility to diverse external stimuli--temperature, voltage, trapped atoms--diverges following a universal curve, yielding an exceptionally sensitive sensor or actuator. The boundary between collapsed and inflated states can shift hundreds of angstroms in response to a single gas atom inside the tube. Several potential nanoelectromechanical devices could be based on this electrically tuned crossover between near-degenerate collapsed and inflated configurations.     

Characterization of biochar of pine pellet

Journal of Thermal Analysis and Calorimetry - Recently, biochar was introduced as a bioadsorbent material to remove various contaminants in effluents, such as pigments, dyes, heavy metals,...     

Non-isothermal decomposition kinetics of the interaction of poly(ethylene terephthalate) with alkyd varnish

The recycling of soft drink bottles poly(ethylene terephthalate) (PET) has been used as an additive in varnish containing alkyd resin. The PET, called to recycled PET (PET-R), was added to the varnish in increasing amounts. Samples of varnish containing PET-R (VPET-R) were used as a film onto slides and its thermal properties were evaluated using thermogravimetry (TG). Throughout the visual analysis and thermal behavior of VPET-R it is possible to identify that the maximum amount of PET-R added to the varnish without changing in the film properties was 2%. The kinetic parameters, such as activation energy (E) and the pre-exponential factor (A) were calculated by the isoconversional Flynn-Wall-Ozawa method for the samples containing 0.5 to 2.0% PET-R. A decrease in the values of E was verified for lower amounts of PET-R for the thermal decomposition reaction. A kinetic compensation effect (KCE) represented by the lnA=−13.42+0.23E equation was observed for all samples. The most suitable kinetic model to describe this decomposition process is the autocatalytic Šesták-Berggren, being the model applied to heterogeneous systems.     

Non-isothermal kinetic for lyophilized leachate from sanitary landfill and composting usine

Leachate samples from a sanitary landfill of Araraquara city and composting usine of Vila Leopoldina, São Paulo, Brazil were lyophilized to remove the water content. TG/DTG curves at different heating rates were recorded. The second step of the thermal decomposition of leachate from the Araraquara landfill (CB₁), from the composting usine from Vila Leopoldina (CB₂) from the organic phase extracted (FO) and aqueous phase (FA) were all kinetically evaluated using the non-isothermal method.By Flynn-Wall isoconversional method the following values were obtained: E=234±3.65 kJ mol^?1 and logA=29.7±0.58 min^?1 for CB₁; E=129±1.66 kJ mol^?1 and logA=11.8±0.10 min^?1 for CB₂; E=51.6±1.35 kJ mol^?1 and logA=6.09±0.09 min^?1 for FO and E=76.91±6.33 kJ mol^?1 and logA=8.88±0.7 min^?1 for FA with 95% confidence level. Applying the procedures of Málek and Koga, SB kinetic model (?esták-Berggren) is the most appropriate to describe the decomposition of CB₁, CB₂, FO and FA.