Effects of nitrogen incorporation on N-doped DLC thin film electrodes fabricated by dielectric barrier discharge plasma: Structural evolution and electrochemical performances
JOURNAL OF ALLOYS AND COMPOUNDS
Authors: Nilkar, M.; Ghodsi, F. E.; Jafari, S.; Thiry, D.; Snyders, R.
Abstract
Hydrogenated amorphous carbon-nitride (a-C:H:N) thin films (or N-DLC) were deposited on glass and FTO substrates by a dielectric barrier discharge plasma technique using CH4/N-2 gas mixture. The XPS results reveal that as the nitrogen ratio in the CH4:N-2 gas mixture increases from 50% to 80%, the nitrogen doping level increased from 5.5 at.% to a maximum value of 11.5 at.% with especially high amounts of pyridinic (6.4 at %), and graphitic (4.7 at %) nitrogen. FEG-SEM results indicate a worm-like porous morphology for the 20%:80% CH4:N-2 sample, relying on high amounts of pyridinic and graphitic N, which is a favorable structure to boost the ions diffusion process. This optimized N-DLC electrode with high nitrogen incorporation not only exhibits a nearly electrochemical reversibility with Delta E-p (125 mV) and J(pa)/J(pc) (1.03) in K3Fe(CN)(6) electrolyte, but also a fast charge transfer constant (6.59 x 10(-4) cms(-1)). The excellent performance of this electrode is ascribed to the high nitrogen doping level, large surface area, the abundant holes, and the high nano-pore volume possessing excellent electron transfer ability for redox reaction. N-DLC thin film exhibits a promising prospect for biosensors and electrochemical electrode applications. (c) 2020 Elsevier B.V. All rights reserved.
Effects of Mixture Design Parameters on the Mechanical Behavior of High-Performance Fiber-Reinforced Concretes
JOURNAL OF MATERIALS IN CIVIL ENGINEERING
Authors: Erdem, Tahir K.; Demirhan, Serhat; Yildirim, Gurkan; Banyhussan, Qais S.; Sahin, Oguzhan; Balav, Mohammad H.; Sahmaran, Mustafa
Abstract
The main purpose of this research is to assess the influence of different design parameters on the mechanical performance of high-performance fiber-reinforced concrete (HPFRC) mixtures. Special attention is also paid to achieving deflection-hardening behavior in the presence of a large amount of coarse aggregates. Different mixture design parameters were the initial curing ages (3, 7, 28, and 90 days), ratios of Class F fly ash (FA) to portland cement (PC) (0.0, 0.2, and 0.4), addition/type of nanomaterials [nanosilica (NS), nanoalumina (NA), and nanocalcite (NC)], and combinations of fibers [polyvinyl-alcohol + steel (P, S) or brass-coated microsteel + steel (B, S)]. The experimental program included the evaluation of compressive strength, flexural strength, and midspan deflection results in addition to test parameters recorded under biaxial flexural loading via a series of square panel tests, including peak load and energy absorption capacities. Test results revealed that deflection-hardening response coupled with multiple microcracks can be obtained when large amounts of coarse aggregates are available for all HPFRC mixtures. As expected, experimental results change depending on the different curing ages and FA/PC ratios. The most distinctive parameters affecting the results are addition/type of nanomaterials and the presence of different fiber combinations. In the presence of nanomaterials, all results from the different tests improved, especially for NA and NS inclusions. With slight concessions in flexural deflection results, B fiber is shown to be a successful candidate to fully replace costly P fibers because most properties of B, S fiber-reinforced HPFRC mixtures outperformed those with P, S fibers, both under four-point bending and biaxial flexural loading.