Papers by Keyword: Surface Energy

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Authors: Sergey N. Filimonov
Abstract: The absolute surface energies of three major low index surfaces of cubic silicon carbide (3C-SiC) are determined by first-principles density functional theory calculations. Calculations show that among clean 3C-SiC surfaces the Si-terminated 3C-SiC(001)-(3x2) surface has the lowest energy. The second and third lowest energy surfaces are the Si-terminated 3C-SiC(111)-(√3x√3) surface and the nonreconstructed 3C-SiC(110) surface. Hydrogen passivation greatly reduces both the absolute surface energies of the low index 3C-SiC surfaces and the surface energy anisotropy. In particular, the surface energies of fully passivated 3C-SiC(110) and (111) surfaces become indistinguishable at hydrogen-rich deposition conditions.
Authors: Hisashi Serizawa, Hidekazu Murakawa
Abstract: As examples of the most typical methods to determine the shear strength of SiC/SiC composite joints, the asymmetrical four point bending test of a butt-joined composite, the tensile test of a lap-joined composite, and the compression test of a double-notched composite joint were analyzed by using a finite element method with the interface element. From the results, it was found that the shear strength in the asymmetrical bending test was controlled by both the surface energy and the shear strength at the interface regardless of their combination while the strength in the tensile test or the compression test was governed by the surface energy when both the surface energy and the shear strength were large. In addition, the interface element was employed in order to examine the influence of the specimen geometry on the microstructural fracture morphology in nanoSiC/SiC composite during a miniaturized Double Notch Shear (DNS) test. From the serial computations, it is revealed that a relationship between the inter-laminar shear strength and the yield stress seems to be very important for selecting appropriate specimen geometry of the miniaturized DNS test.
Authors: Xiao Liang Chen, Shun Hong Lin, Zuan Tian
Abstract: Due to the relatively high surface-to-volume ratio, the surface effect can be significant for micro/nano-scale materials. This paper focuses on geometric size-dependent strength mechanisms of micro/nano-scale metal single crystals. A dimensional analysis model relating surface energy with the geometric size-dependent yield strength is presented and compared with results of microscale uniaxial compression tests on Ni and Au single crystals. The results indicate this model can predict the geometric size effects on the yield strength of micro/nano-scale metal single crystals.
Authors: Xiao Liang Chen, Shun Hong Lin, Jian Ping Ding
Abstract: Due to the relatively high surface-to-volume ratio, the surface effect can be significant for nanoscale materials. A numerical method, which combines surface energy and three-dimensional (3-D) finite element analysis, is proposed to simulate the elastic and plastic deformation of materials and structures at nanoscale. To demonstrate the method is valid and efficient, the free relaxation of single crystalline Cu nanowires is investigated and the numerical results are compared to the atomic simulation results.
Authors: Hideo Koguchi
Abstract: A new formulation for an adhesive force between a substrate and an indenter is presented. The boundary condition taking into account surface stresses is used for the present analysis. The surface stress is originated from surface energy. A paraboloidal indenter is pressed to the substrate, and then adhesion occurs between both surfaces. Surface energy and surface stress will vary at the adhesion surface, and then the surfaces deform in a concave way. An attractive force occurs to keep the contact of two adhesion surfaces. In the present paper, an effect of surface stress on the adhesive force will be clarified.
Authors: Wei Wang, Nan Chun Chen, Quan Hong Li, Xin Tang, Yue Hu
Abstract: The plane surface energy of the mullite crystals (001), (010), (100) and (-100) is comparative calculated by using first-principles plane-wave pseudopotential method and the open hydrothermal system preparing mullite phase crystal test conditions. Also the plane growth habits can be predicted according to the results. The result shows that: the descending order of the mullite crystal surface energy is: E(001) > E(010) > E(-100) > E(100). On the basis of Cune-Woolf principle, the surface energy of mullite crystals (001) surface is the maximum and growth rate is the fastest. Thus the (001) crystal face is growth surface habits of mullite phase crystal. Crystal growth morphology mostly extends in one direction.
Authors: Maude Jimenez, Hassan Hamze, Audrey Allion, Gilles Ronse, Guillaume Delaplace, Michel Traisnel
Abstract: To increase the shelf-life qualities of dairy products, a heat treatment is usually done. However, heat treatments induce physico-chemical modifications of the products. Some of them lead to the expected product but an unwanted consequence of this process is the formation of a fouling deposit on the surfaces in contact with the processed fluid. To eliminate fouling, cleaning processes have to be done once a day. It increases the processing and maintenance costs. To control and to decrease the fouling are the main problems in food industries and an active research is carried out on efficient antifouling surface treatments. In the present study, a 316L 2B stainless steel was submitted to different surface treatments (Flame and plasma pre-treatments, Plasma Enhanced Chemical Vapour Deposition, hydrophobic coatings, mechanical polishing ...) to try to establish correlations between different surface parameters (roughness, hydrophobicity, nanostructuration, surface energy, ...) onto the fouling in heat exchangers. All the treated plates were then submitted to a fouling test using an aqueous solution of β-lactoglobulin at 1% (p/p) with a final calcium concentration of 910 mg/L and compared to a bare steel plate. The results obtained imply different influences of each parameter depending on the surface roughness: the effect of a non organized micrometric roughness is preponderant compared to the surface energy: the fouling comes from a mechanical effect mainly due to rubbing. However, when the surface is nanostructured, fouling decreases. When the roughness reaches the nanometer scale (between 100 and 400 nm), it is the surface energy and the polar/apolar components which become preponderant compared to the roughness. Fouling is this time mainly due to the hydrophilicity of the surface and to the adsorption of the β-lactoglobulin on acido-basic sites. Finally, when the roughness reaches less than 50 nm, polar/apolar components show no effect anymore, the preponderant parameter is the hydrophobicity of the surface.
Authors: Y.L. Hsu, C.H. Lee, S.M. Chiu, Y.C. Sung, K.Y. Yang, C.W. Chu
Abstract: The side effect of electrosurgery includes tissue charring, smoke generation and the adhesion of tissue to electrodes. These effects prolong surgery and interfere with effective coagulation. In this paper, CrWNx, CrOx and ZrOx coating were prepared by an unbalanced magnetron sputtering. The microstructure of films was characterized using XRD, XPS, TEM and AFM. The hydrophobicity and surface energy of coatings were calculated by contact angle measurement and Wu harmonic mean approach. Anti-sticking in vitro test was performed by monopolar electrosurgery using pork liver tissue. The hardness of CrWNx , ZrOx and CrOx coatings were 44 GPa, 26.3 GPa and 20.7 GPa, respectively. The CrOx coating had the lowest surface energy 33.5 mN/m and the highest contact angle of water as high as 103°. The high surface O-H bonds density of CrOx coating and N-H bonds density of CrWNx coating could explain about their lower polar component of surface energy. All the three PVD coatings remarkably reduced the quantity of tissue adhesion on the electrode from about 2 times (ZrOx and CrWNx coatings) to 4.88 times (CrOx coating) than uncoated SUS304 electrode.
Authors: Ravi Chand Singh, Manmeet Pal Singh, Hardev Singh Virk
Abstract: Gas detection instruments are increasingly needed for industrial health and safety, environmental monitoring, and process control. To meet this demand, considerable research into new sensors is underway, including efforts to enhance the performance of traditional devices, such as resistive metal oxide sensors, through nanoengineering. The resistance of semiconductors is affected by the gaseous ambient. The semiconducting metal oxides based gas sensors exploit this phenomenon. Physical chemistry of solid metal surfaces plays a dominant role in controlling the gas sensing characteristics. Metal oxide sensors have been utilized for several decades for low-cost detection of combustible and toxic gases. Recent advances in nanomaterials provide the opportunity to dramatically increase the response of these materials, as their performance is directly related to exposed surface volume. Proper control of grain size remains a key challenge for high sensor performance. Nanoparticles of SnO2 have been synthesized through chemical route at 5, 25 and 50°C. The synthesized particles were sintered at 400, 600 and 800°C and their structural and morphological analysis was carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reaction temperature is found to be playing a critical role in controlling nanostructure sizes as well as agglomeration. It has been observed that particle synthesized at 5 and 50°C are smaller and less agglomerated as compared to the particles prepared at 25°C. The studies revealed that particle size and agglomeration increases with increase in sintering temperature. Thick films gas sensors were fabricated using synthesized tin dioxide powder and sensing response of all the sensors to ethanol vapors was investigated at different temperatures and concentrations. The investigations revealed that sensing response of SnO2 nanoparticles is size dependent and smaller particles display higher sensitivity. Table of Contents
Authors: Wei Zhu, Wu Lin Song, Jian Jun Wang
Abstract: Here, modified analytic embedded atom method (MAEAM) has been utilized to simulate size effect and surface properties of aluminum (Al) nanoparticles. According to the simulation results, we can find that lattice parameter and excess stored energy are size dependent. The simulated excess stored energy ranges from 2.12 to 57.61 kJ/mol, which is in the same order of magnitude with experiment results; surface energy of Al nanoparticles ranges from 0.78 to 1.10 J/m2, which is not invariant but size related. Furthermore, non-uniform lattice distortion has been observed in Al nanoparticles, and mainly concentrates in the first and second shell of surface layers. Theoretical research based on our simulation results provides a novel method to predict excess stored energy of metallic nanoparticles.
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