Study of Flexoelectricity in Graphene Composite Structures

MRS Advances ◽  
2016 ◽  
Vol 1 (39) ◽  
pp. 2723-2729 ◽  
Author(s):  
Mohamed Serry ◽  
Mahmoud A. Sakr
Keyword(s):  
Potential Energy ◽  
Residual Stresses ◽  
Composite Structure ◽  
Platinum Catalyst ◽  
Catalyst Layer ◽  
Energy Difference ◽  
Radius Of Curvature ◽  
Thermally Induced ◽  
Graphene Layers ◽  
Graphene Composite

ABSTRACTThis paper introduces the theoretical and experimental investigation of flexoelectric behavior in a graphene composite structure consisting of multilayer CVD-graphene deposited on an ALD-platinum catalyst layer deposited on top of n-silicon substrate. The polarization induced by varying the radius of curvature from 200–1500 mm by applying bending stresses was investigated experimentally. Meanwhile, due to the cluster-growth nature of the ALD-platinum catalyst layer, a strong correlation was observed between the resulting number of graphene layers and the Pt catalyst layer thickness, which subsequently had a strong impact on the induced polarization. A polarization current of up to 7.4 mA was detected when the composite structure was bent through a 600-mm radius of curvature. Residual stresses at the interface of the different layers were estimated experimentally in the order of 85–217 MPa. The effect of thermally-induced stresses, residual stresses at the interface layers, thickness of graphene layers, and radius of curvature were investigated theoretically using the finite element method (FEM) and first-principle analyses. Theoretically, it was confirmed that non-uniform strain results in an appreciable non-uniform graphene band gap opening, in addition to non-uniform change of the band structure across the surface and thickness which results in increasing the potential energy difference between the graphene layers. FEM confirmed that thermally induced strains could further enhance the power output of the device by inducing a flexoelectric current combined with the thermionic response. This is verified by estimating a lattice displacement up to 0.31 Å in response to 2-mW heat flux, which corresponds to an appreciable graphene band opening and a potential energy difference across the graphene layers in the order of 1.23 eV, as estimated by the tight binding model.

Residual Stress in Bone: A Parametric Study

2008 ◽  
Author(s):  
A. Hizal ◽  
B. Sadasivam ◽  
D. Arola
Keyword(s):  
Residual Stress ◽  
Particle Size ◽  
Residual Stresses ◽  
Material Removal ◽  
Surface Deformation ◽  
Radius Of Curvature ◽  
Near Surface ◽  
Size And Shape ◽  
Air Jet ◽  
Particle Size And Shape

A preliminary study was conducted to evaluate the parametric dependence of the residual stress distributions in bone that result from an abrasive air-jet surface treatment. Specifically, the influence of particle size and shape used in the treatment on the residual stress, propensity of embedding particles and material removal were studied. Rectangular beams of cortical bone were prepared from bovine femurs and treated with aluminum oxide and glass particles with different treatment angles. Residual stresses within the bone were quantified in terms of the radius of curvature of the bone specimens measured before and after the treatments, as well as a function of time to quantify decay in the stress. The sub-surface distribution was also examined using the layer removal technique. Results showed that the particle size and shape could be used to control the amount of material removal and the magnitude of residual stress within the treated surfaces. An increase in size of the glass particles resulted in an increase in the residual stress and a decrease in material removed during the treatment. The magnitude of residual stress ranged from 22 MPa to nearly 44 MPa through modulation of the particle qualities (size and shape). A microscopic examination of the treated surfaces suggests that the residual stresses resulted primarily from near-surface deformation.

scholarly journals Optimization and Tunability of 2D Graphene and 1D Carbon Nanotube Electrocatalysts Structure for PEM Fuel Cells

Catalysts ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 377 ◽  
Author(s):  
Emeline Remy ◽  
Yohann. Thomas ◽  
Laure Guetaz ◽  
Frédéric Fouda-Onana ◽  
Pierre-André Jacques ◽  
...  
Keyword(s):  
Catalyst Layer ◽  
Rotating Disk ◽  
Pem Fuel Cells ◽  
Reduction Reaction ◽  
Hydrogen Atmosphere ◽  
Rotating Disk Electrode ◽  
Carbon Supports ◽  
Graphene Layers ◽  
Scanning Transmission ◽  
Multi Walled Carbon Nanotubes

In this work, N-doped Multi-Walled Carbon Nanotubes (MWCNTs) and Few Graphene Layers (FGLs) have been functionalized with platinum nanoparticles using two methods starting with hexachloroplatinic acid as precursor: (i) ethylene glycol (EG) reduction and (ii) impregnation followed by reduction in hydrogen atmosphere. Morphological scanning transmission electron microscopy (STEM) analyses showed a homogenous dispersion of metal particles with narrow-size distribution onto both carbon supports (Pt/C loadings between 30 wt % and 40 wt %). Electrocatalytic properties of the as-synthetized catalysts toward the Oxygen Reduction Reaction (ORR) was evaluated in aqueous electrolyte using a three electrodes electrochemical cell by cyclic voltammetry (CV) in rotating disk electrode (RDE). It is shown that a mixture of Pt supported on MWCNT and FGLs allows to enhance both the electrochemical surface area and the activity of the catalyst layer. Ageing tests performed on that optimized active layer showed higher stability than conventional Pt/C.

scholarly journals The electronic thickness of graphene

2020 ◽  
Vol 6 (11) ◽  
pp. eaay8409 ◽  
Author(s):  
Peter Rickhaus ◽  
Ming-Hao Liu ◽  
Marcin Kurpas ◽  
Annika Kurzmann ◽  
Yongjin Lee ◽  
...  
Keyword(s):  
Graphene Layer ◽  
Finite Thickness ◽  
Tight Binding ◽  
Single Layer ◽  
Energy Difference ◽  
Quantum Capacitance ◽  
Density Range ◽  
Dielectric Thickness ◽  
Graphene Layers ◽  
Fabry Perot

When two dimensional crystals are atomically close, their finite thickness becomes relevant. Using transport measurements, we investigate the electrostatics of two graphene layers, twisted by θ = 22° such that the layers are decoupled by the huge momentum mismatch between the K and K′ points of the two layers. We observe a splitting of the zero-density lines of the two layers with increasing interlayer energy difference. This splitting is given by the ratio of single-layer quantum capacitance over interlayer capacitance Cm and is therefore suited to extract Cm. We explain the large observed value of Cm by considering the finite dielectric thickness dg of each graphene layer and determine dg ≈ 2.6 Å. In a second experiment, we map out the entire density range with a Fabry-Pérot resonator. We can precisely measure the Fermi wavelength λ in each layer, showing that the layers are decoupled. Our findings are reproduced using tight-binding calculations.

Analytical evaluation of thermally induced residual stresses in ground components

2003 ◽  
Vol 217 (5) ◽  
pp. 471-482 ◽  
Author(s):  
D G Walsh ◽  
A A Torrance ◽  
J Tiberg
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Critical Temperature ◽  
Yield Strength ◽  
Residual Stresses ◽  
Material Properties ◽  
Analytical Evaluation ◽  
Simple Method ◽  
Thermally Induced

Although thermally induced tensile residual stresses have been known to occur in ground components, it has not been possible to predict the critical temperature at which these stresses begin to manifest themselves in the workpiece. In this paper, a model of the formation of thermally induced tensile residual stresses is proposed and a simple method of calculating the critical temperature above which tensile residual stresses occur is developed. The analysis makes use of dimensional methods to characterize the critical temperature. In addition, a formula characterizing the yield strength as a function of temperature was developed. The model was then validated using finite element techniques and some experimental data. The analysis reveals that it is possible to determine the critical temperature above which tensile residual stresses will be manifested based on readily available material properties. A case study illustrates the application of the technique.

Composition and Performance Optimization of Catalyst Layer in a Proton Exchange Membrane Fuel Cell

1997 ◽  
Author(s):  
Curtis Marr ◽  
Xianguo Li
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Performance Optimization ◽  
Proton Exchange Membrane ◽  
Platinum Catalyst ◽  
Catalyst Layer ◽  
Proton Exchange ◽  
Mass Transport Process ◽  
And Performance ◽  
Exchange Membrane

The composition and performance optimisation of cathode catalyst platinum and catalyst layer structure in a proton exchange membrane fuel cell has been investigated by including both electrochemical reaction and mass transport process. It is found that electrochemical reactions occur in a thin layer within a few micrometers thick, indicating ineffective catalyst utilization for the present catalyst layer design. The effective use of platinum catalyst decreases with increasing current density, hence lower loadings of platinum are feasible for higher current densities of practical interest without adverse effect on cell performance. The optimal void fraction for the catalyst layer is about 60% and fairly independent of current density, and a 40% supported platinum catalyst yields the best performance amongst various supported catalysts investigated. An optimal amount of membrane content in the void region of the catalyst layer exists for minimum cathode voltage losses due to competition between proton migration through the membrane and oxygen transfer in the void region. The present results will be useful for practical fuel cell designs.

Inducing Residual Stress in Bone Using Abrasive Air-Jet Surface Treatment

2007 ◽  
Author(s):  
Alpay Hizal ◽  
Balaji Sadasivam ◽  
Dwayne Arola
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Surface Treatment ◽  
Structural Changes ◽  
Surface Deformation ◽  
Radius Of Curvature ◽  
Surface Residual Stress ◽  
Near Surface ◽  
Bone Chemistry ◽  
Air Jet

Based on past research, the growth and repair of bone is a function of physical activity (i.e. stresses) and bone chemistry. As such, the rate of recovery of an individual that has undergone total joint arthroplasty could be influenced by the introduction of changes in bone chemistry and “apparent” stress state in the bone that results from the surgical procedures and/or treatments. This preliminary study explored the opportunity for introducing residual stresses in hard tissues using an air-jet surface treatment. Cortical bone was obtained from bovine femurs and treated with an abrasive jet process. The radius of curvature of the bone specimens was estimated before and after treatment and used in estimating the magnitude of surface residual stress. An SEM analysis was also performed to examine structural changes in the bone caused by the surface treatment. Results showed that it is possible to impart residual stress within bone using an air-jet surface treatment. The magnitude of surface residual stress was 16 ± 0.8 MPa. Residual stresses appeared to result from a combination of near-surface deformation and embedded particles.

scholarly journals High-temperature Mechanical Properties and Their Influence Mechanisms of ZrC-Modified C-SiC Ceramic Matrix Composites up to 1600 °C

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1581 ◽  
Author(s):  
Jianjun Sha ◽  
Shouhao Wang ◽  
Jixiang Dai ◽  
Yufei Zu ◽  
Wenqiang Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Flexural Strength ◽  
Residual Stresses ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Thermally Induced ◽  
High Temperature Mechanical Properties ◽  
Sic Ceramic

In order to understand the influence of the mechanisms of ZrC nanoparticles on the high-temperature mechanical properties of C-SiC ceramic matrix composites, the mechanical properties were measured from room temperature (RT) to 1600 °C under vacuum. The microstructures features were characterized by scanning electron microscopy. In comparison with the composites without ZrC nanoparticles, the ZrC-modified composite presented better mechanical properties at all temperatures, indicating that the mechanical properties could be improved by the ZrC nanoparticles. The ZrC nanoparticles could reduce the residual silicon and improve the microstructure integrity of composite. Furthermore, the variation of flexural strength and the flexural modulus showed an asynchronous trend with the increase of temperature. The flexural strength reached the maximum value at 1200 °C, but the highest elastic modulus was obtained at 800 °C. The strength increase was ascribed to the decrease of the thermally-induced residual stresses. The degradation of mechanical properties was observed at 1600 °C because of the microstructure deterioration and the formation of strongly bonded fiber–matrix interface. Therefore, it is concluded that the high temperature mechanical properties under vacuum were related to the consisting phase, the matrix microstructure, and the thermally-induced residual stresses.

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