One-step purification of direct-spun CNT fibers by post-production sonication

Publication date: 15 July 2017
Source:Materials & Design, Volume 126
Author(s): Rajyashree M. Sundaram, Alan H. Windle
Lightweight high-performance macroscopic fibers and yarns of oriented carbon nanotubes (CNTs) with high tensile strength and stiffness and electrical conductivities are in high demand for a wide range of applications. Among various production methodologies, the direct continuous spinning of CNT fibers from a chemical vapor deposition reactor has attracted interest because of its scalability potential. However, the presence of non-CNT impurities limits achieving high fiber tensile and electrical performances reproducibly. Here, we present for the first time a one-step protocol to purify direct-spun CNT fibers by mild sonication in acetone. Sonication reduced the impurity content by ~42%, which led to enhanced CNT fiber performance. In comparison to untreated fibers, the purified fibers showed a 50% and 100% increase in specific strength and stiffness, respectively. The CNT fiber electrical conductivity increased by 3-fold after purification. This improvement in fiber performance was observed despite a reduction in the nanotube bundle orientation after sonication. The better performance of the purified fibers is attributed to improved CNT bundle packing and densification. Our process is simple, quick, effective, and uses readily available acetone and hence, shows promise as a post-production purification method to direct CNT fiber spinning.

Graphical abstract

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Controlled nanoscale precipitation to enhance the mechanical and biological performances of a metastable β Ti-Nb-Sn alloy for orthopedic applications

Publication date: 15 July 2017
Source:Materials & Design, Volume 126
Author(s): Sumit Bahl, Akash S. Krishnamurthy, Satyam Suwas, Kaushik Chatterjee
Toward engineering a new generation of low modulus titanium alloys for orthopedics, we present new insight into the control of nanoscale precipitation in a metastable β Ti-32Nb-2Sn alloy. Nanoscale α precipitates from β phase were obtained by one-step heat treatment at 500°C. The nanoscale precipitates markedly improve the tensile strength (≈1070MPa) while affording lower modulus (≈82GPa) than conventional metallic biomaterials. Besides age-hardening at 500°C, an unexpected phenomenon of age-softening is observed even in the presence of nanoscale α precipitates when aged at 600°C. This effect is attributed to significant softening of the β phase due to compositional changes, as revealed by the elemental mapping in transmission electron microscopy (TEM). TEM elemental mapping reveals that Sn partitions preferentially in the β phase on aging at 500°C and does not show any preferential partition on aging at 600°C. The passive layer at the surface enriches in Sn content after aging at 500°C and consequently affects the electrochemical behavior of the alloy. The alloy supports the proliferation, and osteogenesis of human mesenchymal stem cells. This study provides new understanding for processing Ti-Nb-Sn alloys in biomedical applications.

Graphical abstract

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Multifunctional properties and applications of yttrium ferrite nanoparticles prepared by citrate precursor route

Publication date: 15 July 2017
Source:Materials & Design, Volume 126
Author(s): Tokeer Ahmad, Irfan H. Lone, S.G. Ansari, Jahangeer Ahmed, Tansir Ahamad, Saad M. Alshehri
Yttrium Ferrite nanoparticles were prepared by citrate precursor method at reasonably low temperature. Morphological and elemental studies reveal the formation of monophasic orthorhombic YFeO3 nanoparticles with fairly uniform distribution of nearly spherical particles, high specific surface area of ~338m²/g and visible band gap of 2.5eV. The electrical properties (i.e. dielectric and conductivity) were estimated from ac spectroscopic data as a function of temperature. The wasp-waisted shaped hysteresis loop displayed low Hc of 280Oe, Ms of 2.0emug⁻¹ and Mr of 0.45emug⁻¹ indicating canted antiferromagnetism with weak ferromagnetic behaviour. In addition to ferromagnetism, a room temperature ferroelectric loop confirmed the multiferroic behaviour of the materials. The humidity sensing properties were investigated from 8 to 80% of RH (Relative Humidity) that showed a linear response with a sensitivity of 16 nF/RH% at room temperature. Dye sensitized solar cell (DSSC) was constructed in combination with TiO2 powder to determine the photo-conversion efficiency, current density and open circuit voltage. Photocatalytic generation of hydrogen by using YFeO3 nanoparticles has also been studied under the visible light irradiations which showed a significant H2 evolution reaction rate up to 131.6μmolh⁻¹g⁻¹.

Graphical abstract

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Compositional design of Fe-based multi-component bulk metallic glass based on CALPHAD method

Publication date: 15 July 2017
Source:Materials & Design, Volume 126
Author(s): J.J. Han, C.P. Wang, J. Wang, X.J. Liu, Y. Wang, Z.K. Liu
A quantificational composition design protocol (CDP) of Fe-based bulk metallic glasses (BMGs) with excellent glass-forming ability (GFA) has been proposed on the basis of the thermodynamic calculations. The stability of liquid and the crystallization of solids were both evaluated from the perspective of atomic structure and local composition. The present protocol successfully associates the stability of liquid to the melting point of alloy and the difficulty of crystallization by considering the type and competition of potential equilibrated phases. Specifically, this protocol provided the selection criteria of phases and elements from the viewpoint of structure and composition fluctuations during nucleation for each phase, whose accuracy and effectiveness were experimentally verified.

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Inhibition behavior of Cu-benzoltriazole-calcium alginate gel beads by piercing and solidification

Publication date: 15 July 2017
Source:Materials & Design, Volume 126
Author(s): Xuteng Xing, Jihui Wang, Wenbin Hu
Calcium alginate gel beads loaded with benzotriazole (defined as 'benzotriazole-calcium alginate gel beads') were successfully prepared by a piercing-solidifying method. Moreover, the insoluble Cu-benzotriazole complexes were introduced on the surface of these gel beads through the interaction between benzotriazole and Cu²⁺ to obtain Cu-benzoltriazole-calcium alginate gel beads, which act as the barrier to extend benzotriazole release time. The loading amount of benzotriazole in the Cu-benzoltriazole-calcium alginate gel beads was determined by thermo-gravimetric analysis (TGA) and the releasing process of benzotriazole was traced by UV–vis spectrophotometer. The inhibition behavior of Cu-benzoltriazole-calcium alginate gel beads for Q235 steel in 3.5% NaCl solution was investigated by polarization and electrochemical impedance spectrum techniques. The results show that complete release time of benzotriazole from benzoltriazole-calcium alginate gel beads is about 400 min, and further prolonged to dozens of hours by forming a barrier of insoluble Cu-benzotriazole complexes. In addition, Q235 steel in 3.5% NaCl solution+5.0g/L Cu-benzoltriazole-calcium alginate gel beads exhibit the lower corrosion current density and higher inhibition efficiency (87.06% at 24h) than Q235 steel in 3.5% NaCl solution.

Graphical abstract

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Effect of traffic restriction on reducing ambient volatile organic compounds (VOCs): Observation-based evaluation during a traffic restriction drill in Guangzhou, China

Publication date: July 2017
Source:Atmospheric Environment, Volume 161
Author(s): Xinyu Huang, Yanli Zhang, Weiqiang Yang, Zuzhao Huang, Yujun Wang, Zhou Zhang, Quanfu He, Sujun Lü, Zhonghui Huang, Xinhui Bi, Xinming Wang
Traffic restriction (TR) is a widely adopted control measure in case of heavy air pollution particularly in urban areas, yet it is hard to evaluate the effect of TR on reducing VOC emissions based on monitoring data since ambient VOC mixing ratios are influenced not only by source emissions but also by meteorological conditions and atmospheric degradation. Here we collected air samples for analysis of VOCs before, during and after a TR drill carried out in Guangzhou in September 2010 at both a roadside and a rooftop (∼50 m above the ground) site. TR measures mainly included the "odd-even license" rule and banning high-emitting "yellow label" vehicles. The mixing ratios of non-methane hydrocarbons (NMHCs) did not show significant changes at the roadside site with total NMHCs of 39.0 ± 11.8 ppbv during non-TR period and 39.1 ± 14.8 ppbv during TR period, whereas total NMHCs decreased from 30.4 ± 14.3 ppbv during the non-TR period to 22.1 ± 10.6 ppbv during the TR period at rooftop site. However, the ratios of methyl tert-butyl ether (MTBE), benzene and toluene against carbon monoxide (MTBE/CO, T/CO and B/CO) at the both sampling sites dropped significantly. The ratios of toluene to benzene (T/B) instead increased significantly. Changes in these ratios all consistently indicated reduced input from traffic emissions particularly gasoline vehicles. Source attribution by positive matrix factorization (PMF) confirmed that during the TR period gasoline vehicles contributed less VOCs in percentages while industrial sources, biomass burning and LPG shared larger percentages. Assuming that emissions from industrial sources remained unchanged during the TR and non-TR periods, we further used the PMF-retrieved contribution percentages to deduce the reduction rate of traffic-related VOC emissions, and obtained a reduction rate of 31% based on monitoring data at the roadside site and of 34% based on the monitoring data at the rooftop site. Considering VOC emissions from all sources in Guangzhou city, the TR control measures adopted could reduce VOC up to 15%.



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Deposition pattern and throughfall fluxes in secondary cool temperate forest, South Korea

Publication date: July 2017
Source:Atmospheric Environment, Volume 161
Author(s): Mukesh Kumar Gautam, Kwang-Sik Lee, Byeong -Yeol Song
Chemistry and deposition fluxes in the rainfall and throughfall of red pine (Pinus densiflora), black locust (Robinia pseudoacacia), and chestnut (Castanea crenata) monocultures, and mixed red pine–black locust–chestnut stands were examined in a nutrient-limited cool temperate forest of central South Korea. Throughfall was enriched in both basic and acidic constituents relative to rainfall, suggesting that both dry deposition and canopy leaching are important sources of throughfall constituents. Net throughfall fluxes (NTFs) of cations and anions significantly differed among four different stands as well as seasonally. Red pine exhibited highest fluxes (TF and NTF) for Ca²⁺, black locust for K⁺, mixed stands for Mg²⁺, and chestnut for Na⁺. In contrast, NTF of SO4^2-, NO3⁻, and NH4⁺was highest in the red pine, intermediate in the chestnut and mixed stands, and lowest in the black locust. In general, canopy uptake of H⁺ and NH4⁺ for all stands was higher in summer than in winter. Dry deposition appears to play a major role in atmospheric deposition to this cool temperate forest, especially in summer. Dry deposition for both cations and anions displayed high spatial variability, even though stands were adjacent to one another and experienced identical atmospheric deposition loads. Canopy leaching of K⁺ (95–78% of NTF), Mg²⁺ (92–23% of NTF), and Ca²⁺ (91–12% of NTF) was highest for the black locust, lowest for chestnut, and intermediate for the red pine and mixed stands. The present study documented significant changes in throughfall chemistry and NTF among different forest stands, which presumably be related with the differences in the canopy characteristics and differences in their scavenging capacity for dry deposition and canopy exchange. Difference in the canopy retention of H⁺ and base cation leaching suggests that canopy exchange was mainly driven by weak acid excretion and lesser by H⁺ exchange reaction. Our results indicate that despite a high base cation deposition, a combination of higher input of acidifying constituents, low soil pH, and total acidic deposition approaching South Korean critical loads make regional forest vulnerable to acidification.

Graphical abstract

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