Influence of Pyrolysis Parameters on the Performance of CMSM

Carbon hollow fiber membranes have been prepared by pyrolysis of a P84/S-PEEK blend. Proximate analysis of the precursor was performed using thermogravimetry (TGA), and a carbon yield of approximately 40% can be obtained. This study aimed at understanding the influence of pyrolysis parameters—end temperature, quenching effect, and soaking time—on the membrane properties. Permeation experiments were performed with N2, He, and CO2. Scanning electron microscopy (SEM) has been done for all carbon hollow fibers. The highest permeances were obtained for the membrane submitted to an end temperature of 750°C and the highest ideal selectivities for an end temperature of 700°C. In both cases, the membranes were quenched to room temperatur

Effect of natural and synthetic antioxidants incorporation on the gas permeation properties of poly(lactic acid) films

Gas permeation properties (permeability, diffusivity and solubility coefficients) were determined for carbon dioxide and oxygen in poly(lactic acid) (PLA) films enriched with 0, 2, 4 and 10 wt.% of different antioxidants, at three temperatures, 284, 293 and 303 K, using a time-lag apparatus. Three antioxidants, a natural, alpha-tocopherol (AT), and two synthetic, butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ), were tested. DSC results show that the polymer glass transition temperature slightly decreases with the increase of the antioxidant content. The crystallinity degree of PLA films decreases with the addition of BHT and TBHQ whereas the incorporation of AT increases the crystallinity of PLA films. The permeability towards water vapour, at 299 K and 45% of relative humidity, and surface energy show a decreased in the wettability of the prepared materials with the increase of the antioxidants content. The incapacity to measure gas permeation in PLA films with 10 wt.% of AT and BHT incorporated was due to phase separation, proved by SEM images. The CO2 and O-2 permeation results show that PLA barrier properties can be improved by the incorporation of antioxidants but are strongly dependent on the amount and structure of the antioxidant added. (C) 2013 Elsevier Ltd. All rights reserved

The effect of Bi doping on the thermal conductivity of ZnO and ZnO:Al thin films

The dissipation of heat generation has been one of the largest obstacles in the design of semiconductor devices and reducing the thermal conductivity is vital for improving thermoelectric efficiency. This work focuses on the Bi doping effect on ZnO, and ZnO:Al thin films produced by magnetron sputtering with thickness varying between 500 and 900 nm. The approach introduces Bi ions, a higher mass element, into the ZnO metal-oxide matrix, to hinder phonon-mediated heat conduction and, consequently, reduce thermal conductivity. Atom probe tomography (APT) was employed to survey Bi doping distribution in ZnO:Al:Bi and ZnO:Bi thin films and to study the morphology of the grain boundaries. The thermal properties of the thin films were measured by frequency-domain thermoreflectance. Based on thermal conductivity results, it is concluded that the doping of ZnO films with Al has a significant effect on thermal conductivity, being reduced from 6.0 W m−1 K−1 in its undoped state to 3.3 W m−1 K−1 for ZnO with ∼3 at.% of Al, mainly due to alloy scattering of phonons in the wurtzite cell. Further doping with Bi contributes to a slight reduction in the thermal conductivity of ZnO:Al.Bi films (2.9 W m−1 K−1), due to grain boundary scattering by Bi/Bi2O3 phases. This result is understood as the confluence of two counteracting effects. On the one hand, the thermal conductivity of the film decreases because Bi, unlike Al, is segregated to grain boundaries and does not substitute Zn in the wurtzite crystal lattice, which is unequivocally demonstrated by APT results. On the other hand, the simultaneous presence of Al and Bi triggers a morphological change with the film's microstructure becoming more columnar. This change in microstructure from 3D island growth in ZnO:Al and ZnO:Bi to a more regular columnar structure in ZnO:Al,Bi limits further reduction in the thermal conductivity.Filipe Correia is grateful to the Fundação para a Ciência e Tecnologia (FCT, Portugal) for the Ph.D. grant SFRH/BD/111720/2015. Joana Ribeiro is grateful to the FCT, Portugal, for the Ph.D. grant SFRH/BD/147221/2019. Funding is also gratefully acknowledged from FCT/PIDDAC through the Strategic Funds project reference UIDB/04650/2020–2023 and from the Spanish Ministerio de Ciencia e Innovación (MICINN) through grants SEV-2015-0496 (FUNMAT) and CEX2019-000917-S (FUNFUTURE) in the framework of the Spanish Severo Ochoa Centre of Excellence program, and grant PID2020-119777 GB-I00 (THERM2MAIN). This work (proposal ID 2018-020-022469) was carried out with the support of the Karlsruhe Nano Micro Facility (KNMFi, www.knmf.kit.edu), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT, www.kit.edu).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe