Behavior Of Micro Research Articles

Effect of nanopowder ratio in bimodal powder mixture on powder injection molding

One of the significant advantages of nanopowder is activated sintering and better surface finish of the final components. However, because of its drawbacks like higher cost and low formability, the mixture of nano and micro powder emerged as an effective solution. In this research, effects of nanopowder in nano/micro bimodal feedstock were studied. Bimodal powder in feedstock was prepared with nano and micro sized powders. These powders were mixed with different nanopowder volume ratio from 0 to 50%. The effects of nanopowder vol.% on the critical solids loading was investigated with rheometer experiments. From debinding behavior, apparent debinding activation energy for each feedstock was determined. Sintering behavior of micro and bimodal feedstocks were analyzed by dilatometer and compared with die compacted specimen. Nanopowder effect on sintered density and hardness of the samples were verified as well.

Influence of 700 °C vacuum annealing on fracture behavior of micro/nanoscale focused ion beam fabricated silicon structures

In this paper, we describe the influence of 700 °C vacuum annealing on strength and fracture behavior of micro- and nano-scale Si structures fabricated by focused ion beam (FIB). Si nanowires (NWs) made from silicon-on-nothing (SON) membrane are fabricated using FIB. Microscale Si specimens are fabricated by conventional micromachining technologies and FIB. These specimens are tensioned to failure using specially developed microelectromechanical systems (MEMS) device and thin-film tensile tester, respectively. The mean fracture strengths of the nano- and microscale specimens are 5.6 and 1.6 GPa, respectively, which decrease to 2.9 and 0.9 GPa after vacuum annealing at 700 °C for only 10 s. These strength values do not vary with increasing annealing time. Fracture origin and its behavior are discussed in the light of fracture surface and FIB damage layer observations.

Effect of molten V2O5 salt on the corrosion behavior of micro- and nano-structured thermal sprayed SYSZ and YSZ coatings

The corrosion resistance of micro-and nano-structured scandia and yttria codoped zirconia (nano-4mol%SYSZ and micro-8.6SYSZ) and yttria doped zirconia (4YSZ) in the presence of molten vanadium oxide were investigated. To this end, duplex TBCs (thermal barrier coatings), composed of a bond coat (NiCrAlY) and a top coat (4SYSZ or 4YSZ), were deposited on the IN738LC Ni-based supper-alloy by atmospheric plasma spraying (APS). The corrosion studies of plasma sprayed TBCs were conducted in 25mgV2O5 molten salt at 910°C for different times. The nanostructured coating, as compared to its micro-structured counterpart, in spite of a further reaction with the V2O5 salt, showed a higher degradation resistance during the corrosion test due to increased compliance capabilities resulting from the presence of an extra source of porosity associated with the nano-zones. Finally, the corrosion resistance and degradation mechanism of SYSZ and YSZ coatings were compared with the presence of molten NaVO3 and V2O5 salt, respectively.

Characterization of the near-field and convectional transport behavior of micro and nanoparticles in nanoscale plasmonic optical lattices.

Here, we report the characterization of the transport of micro- and nanospheres in a simple two-dimensional square nanoscale plasmonic optical lattice. The optical potential was created by exciting plasmon resonance by way of illuminating an array of gold nanodiscs with a loosely focused Gaussian beam. This optical potential produced both in-lattice particle transport behavior, which was due to near-field optical gradient forces, and high-velocity (∼μm/s) out-of-lattice particle transport. As a comparison, the natural convection velocity field from a delocalized temperature profile produced by the photothermal heating of the nanoplasmonic array was computed in numerical simulations. This work elucidates the role of photothermal effects on micro- and nanoparticle transport in plasmonic optical lattices.

Tribological behavior in micro–sheet hydroforming

In this paper, the tribological behavior and its size effects in micro–hydromechanical deep drawing (MHDD) are theoretically and experimentally investigated. It is found that a required fluid pressure for hydrodynamic lubrication significantly increases with scaling down micro–scale due to a high sealablity at small relative punch diameter to minimum thickness. Moreover, the opposite tribological size effect from a conventional microforming appears in MHDD in which the fluid medium can be kept in open lubricant pockets (OLPs) by applying a fluid pressure and, the friction coefficient decreases as a specimen size decreases. Thus, MHDD can induce the hydrodynamic lubrication and lubrication in OLPs and improve the tribological behavior in microforming by applying the appropriate fluid pressure.

Size dependent energy release rate of notched FGM beams based on a modified couple stress theory

The experimental observations indicate that the mechanical behavior of micro and nano scale structures is size-dependent. In this study, employing the modified couple stress theory the size-dependent strain energy release rate of notched Euler-Bernoulli beams made of functionally graded material (FGM) is formulated. The normalized energy release rate for the problem of three-point bending in notched FG beams is obtained using the procedure established by Kienzler and Herrmann [Kienzler R, Herrmann G, An elementary theory of defective beams. Acta Mech 1986; 62:37–46]. It is assumed that the material properties vary continuously along the beam thickness according to a power law distribution. In order to verification, the results of the present model for a homogenous beam are compared to the results of previous works. Also, a parametric study is performed to examine the influences of the material length scale parameter, elastic properties and power law index of the micro FG beam on the normalized strain energy release rate. The obtained results show that as the ratio of the length scale parameter to the beam thickness increases, the difference between the classical and non-classical results increases too, but for the small value of the length scale parameter, the difference diminishes.Selection and Peer-review under responsibility of the Conference Committee of 6th International Conference on Advanced Nano Materials.

Long term oxidation behavior of micro- and nano-crystalline CVD diamond foils

Nano- and micro-crystalline diamond foils with a thickness of at least 30μm are manufactured by hot-filament chemical vapor deposition (HFCVD) in an industrial coating machine. Some of them are doped with trimethylborate. The diamond foils are exposed to air at 450°C and 500°C and oxidized for up to 738h. At these temperatures all investigated diamond foils exhibit a substantial weight loss, which is measured with a high precision balance. Nanocrystalline diamond foils show a high weight loss rate compared to microcrystalline diamond foils. At 500°C the weight loss rate is two to seven times higher than that at 450°C. Grain boundaries and small diamond crystals are etched much faster than larger diamond crystal. The incorporation of boron does not significantly affect the oxidation of the diamond foils.

Linear and nonlinear free vibrations of electrostatically actuated micro-/nanomechanical resonators

This paper is concerned with linear and nonlinear free vibrations of an axially stressed clamped---clamped micro-/nanobeam actuated by one-sided electrode configuration. Galerkin procedure and a proper shape function are used to establish a dynamic reduced-order model, where the integral of the electromechanical forcing term is obtained in an explicit and closed form. This model makes the analysis of dynamic behaviors convenient for the micro-/nanobeam. For linear free vibration, the fundamental natural frequency formulas of the system are validated by comparing with published experiment data while the Newton method coupled with the harmonic balance method is developed to obtain analytical approximate period and periodic solution for the nonlinear system. These approximate solutions have explicit expressions and they can readily be used to derive the effects of various physical parameters on dynamic behavior of micro-/nanobeams. Exact solution in an integral form is also presented. For small as well as large amplitudes of nonlinear vibration, the new analytical approximate solutions show excellent agreement with respect to the numerically integrated solutions obtained from the integral-form exact solutions.

Nonlinear dynamics of nano-resonators: an analytical approach

Prior to the design and fabrication of MEMS/NEMS devices, analysis of static and dynamic behaviors of these systems is necessary. In the present study, the nonlinear dynamic behavior of micro- and nano-mechanical resonators is investigated and classified based on the resonator's physical parameters for first time. The Galerkin method is used to convert the distributed-parameter model to a nonlinear ordinary differential equation where mid-plane stretching, axial stress, DC electrostatic and AC harmonic voltages are taken into account. To obtain the analytical frequency response of the micro resonator near its primary resonance, the second order multiple scales method is applied to the general equation of motion with cubic, quadratic and parametric nonlinearities. It is demonstrated that variation of the micro resonator's physical parameters strongly affects its dynamic behavior by changing equilibrium points and their stability properties and complex behaviors appear in its frequency and phase responses. The global dynamics of the resonator is classified into four different categories in terms of the system parameters in this paper. The dynamic characteristics and frequency response of each class are analyzed numerically as well as analytically. Comparison of the obtained closed-form solution with the numerical simulation results confirms its validity. A striking point of the obtained closed-form solution is that it predicts some complex nonlinear behaviors of the resonator. This paper presents a quick and efficient method for determining the global dynamics of the micro-resonators and can be useful in design and analyses of these devices.

A comparative study on dielectric, structure, and thermal behavior of micro‐ and nano‐sized CCTO in nylon 6,9 matrix

Calcium copper titanium oxalate CaCu3Ti4O12 (CCTO) particles as a filler with both micro‐ and nano‐sized into nylon 6,9 polymer have been investigated under structural, thermal, and dielectric properties to find that particle satisfy all the same. Micro‐sized CCTO particles (point out as mCCTO) was synthesized using solid‐state route using ball milling and nano‐sized CCTO particles (point out as nCCTO) was synthesized using complex oxalate precursor route. Fabrication of nylon 6,9/CCTO composite for both micro‐ and nano‐sized CCTO particles were employed separately into nylon 6,9 matrix and examined comparatively. The composite containing 20 vol% of nCCTO achieve 24.5 dielectric permittivity at 100 Hz in room temperature that was significantly higher than mCCTO which was 14 at the same condition. From the structural analysis, we obtained that the nCCTO was well dispersed in the matrix medium, whereas the mCCTO were also dispersed with some agglomeration that was the reason for the interaction failure between the particles and matrix material. The dielectric permittivity results obtained from this study specify that the composite containing nano‐sized CCTO particles may be suitable for energy storage devices and in the higher temperature sensor applications. POLYM. COMPOS., 38:927–935, 2017. © 2015 Society of Plastics Engineers

Gastrointestinal behavior of nano- and microsized fenofibrate: In vivo evaluation in man and in vitro simulation by assessment of the permeation potential

IntroductionThe purpose of this study was (i) to evaluate the gastrointestinal behavior of micro- and nanosized fenofibrate in humans and (ii) to develop a simple yet qualitatively predictive in vitro setup that simulates the observed absorption-determining factors. Materials and methodsCommercially available micro- and nanoparticles of fenofibrate (Lipanthyl® and Lipanthylnano®, respectively) were administered orally to five healthy volunteers in fasting and postprandial conditions. Intraluminal and systemic drug concentrations were determined as reference data for the development of a predictive in vitro setup. To capture the observed solubility/permeability interplay, in vitro dissolution testing was performed in the presence of a permeation bag with sink conditions. ResultsIn fasting conditions, intake of nanosized fenofibrate generated increased duodenal concentrations compared to microsized fenofibrate, which was reflected in an improved systemic exposure. In postprandial conditions, duodenal concentrations were greatly enhanced for both formulations, however without an accompanying increase in systemic exposure. It appeared that micellar encapsulation of the highly lipohilic fenofibrate limited its potential to permeate from fed state intestinal fluids. To capture these in vivo observations in an in vitro setup, classic dissolution testing was combined with permeation assessment into a permeation bag with sink conditions. In case of fasting conditions, the dissolution/permeation approach allowed for an improved discriminative power between micro- and nanosized fenofibrate by better simulating the dynamic interplay of dissolution and absorption. In case of postprandial conditions, the observed solubility–permeability interplay could be simulated using the dissolution/permeation approach in combination with biorelevant media (FeSSGFFortimel and FeSSIF-V2) to mimic micellar entrapment and reduced permeation potential of fenofibrate. ConclusionFor the first time, reduced permeation of a lipophilic drug despite increased intraluminal concentrations, was demonstrated in humans. Dissolution testing using biorelevant media in combination with permeation assessment into a sink permeation bag appeared to be a simple yet pragmatic approach to capture this solubility–permeability interplay in early formulation evaluation.

Effect of Layer and Film Thickness and Temperature on the Mechanical Property of Micro- and Nano-Layered PC/PMMA Films Subjected to Thermal Aging

Multilayered polymer films with biomimicking, layered structures have unique microstructures and many potential applications. However, a major limitation of polymer films is the deterioration of mechanical properties in working environments. To facilitate the design and development of multilayered polymer films, the impact of thermal aging on the mechanical behavior of micro- and nano-layered polymer films has been investigated experimentally. The composition of the polymer films that have been studied is 50 vol% polycarbonate (PC) and 50 vol% poly(methyl methacrylate) (PMMA). The current study focuses on the effect of film and layer thickness and temperature on the mechanical properties of the materials subjected to thermal aging. To study the effect of film and layer thickness, films with the same thickness, but various layer thicknesses, and films with the same layer thickness, but various film thicknesses, were thermally aged at 100 °C in a constant temperature oven for up to six weeks. The results show that as the layer thickness decreases to 31 nm, the film has a higher stiffness and strength, and the trend of the mechanical properties is relatively stable over aging. The ductility of all of the films decreases with aging time. To study the effect of temperature, the films with 4,096 layers (31 nm thick for each layer) were aged at 100 °C, 115 °C and 125 °C for up to four weeks. While the 100 °C aging results in a slight increase of the stiffness and strength of the films, the higher aging temperature caused a decrease of the stiffness and strength of the films. The ductility decreases with the aging time for all of the temperatures. The films become more brittle for higher aging temperatures.

Study on the mechanical properties, microstructure and corrosion behaviors of nano-WC–Co–Ni–Fe hard materials through HIP and hot-press sintering processes

Abstract This study aims to explore a series of Hot Isostatic Pressing (HIP) and hot-press sintering processes in order to examine the effects on the mechanical properties, microstructures and corrosion behaviors of micro- and nano-WC materials. The experimental results showed that the transverse rupture strength (TRS) values of micro- and nano-WC increased to 1627.3 and 1842.7 MPa after 1250 °C, 125 MPa, 100 min HIP treatments, respectively. Meanwhile, the porosity decreased slightly. The corrosion test results also showed that HIP-treated micro- and nano-WC effectively improved corrosion resistance in a 3.5 wt% NaCl solution. In addition, the lowest porosity (0.21%), highest hardness (91.7 HRA) and highest K IC (14.7 MPa√m) values appeared in nano-WC after 1250 °C, 15 MPa, 1 h hot-press sintering. Moreover, the hot-press sintering procedure significantly inhibited the grain growth of the tungsten carbide materials.

Numerical Investigation of Size Effect on Dry Friction Behavior in Micro Upsetting Process

After modifying the Wahime/Bay friction model, a new friction model suitable for micro-forming process without lubrication is established. In this model, it is shows that the friction coefficient is a function of strain hardening exponent, the normal pressure and the initial yield stress of material. Based on the experimental data, the micro-upsetting process is simulated using the proposed friction model. The simulation results are used to investigate the size effect on the dry friction behavior. It is found that the Coulomb’s friction coefficient is dropping with miniaturization of specimens when the amount of reduction is not too large.

Analytical and numerical investigation into the longitudinal vibration of uniform nanotubes

In recent years, prediction of the behaviors of micro and nanostructures is going to be a matter of increasing concern considering their developments and uses in various engineering fields. Since carbon nanotubes show the specific properties such as strength and special electrical behaviors, they have become the main subject in nanotechnology researches. On the grounds that the classical continuum theory cannot accurately predict the mechanical behavior of nanostructures, nonlocal elasticity theory is used to model the nanoscaled systems. In this paper, a nonlocal model for nanorods is developed, and it is used to model the carbon nanotubes with the aim of the investigating into their longitudinal vibration. Following the derivation of governing equation of nanorods and estimation of nondimensional frequencies, the effect of nonlocal parameter and the length of the nanotube on the obtained frequencies are studied. Furthermore, differential quadrature method, as a numerical solution technique, is used to study the effect of these parameters on estimated frequencies for both classical and nonlocal theories.

Structural analysis of hydrogenated nanocrystalline silicon thin films as a function of substrate temperature during deposition

In this contribution, the micro- and macro-structure of plasma grown hydrogenated nanocrystalline silicon (nc-Si:H) thin films were followed with respect to substrate temperature ( T s ) ranging from 80 °C to 200 °C. nc-Si:H films were deposited by plasma enhanced chemical vapor deposition technique using silane gas highly diluted by hydrogen and high RF power density. Micro-structure analysis was performed with grazing angle X-ray diffraction (GAXRD) and dispersive Raman spectroscopies. Parallelly, morphological properties of the films were investigated via field emission scanning electron microscopy (FE-SEM) by taking both surface and cross-sectional micrographs. GAXRD results suggest the presence of 4–5 nm nanocrystallites with the size almost independent of T s . The detailed analysis of the Raman spectra reveals one- and two-phonon modes due to amorphous and crystalline silicon (c-Si), where all c-Si related peaks shifted to lower frequencies. Raman nanocrystalline volume fraction is found to be greater than 50% for all T s ; it increases together with the short-range order at elevated T s . This micro-structural improvement with T s is considered to be slight when compared to the FE-SEM-observed drastic changes of morphology, particularly the size of large conglomerates (35–250 nm). The behavior of micro- and macro-structure with T s is correlated well with the previously determined bonding and lateral conductivity measurements. It seems to be the macro-structure that accounts for bonding and electrical properties of nc-Si:H thin films.

Micro- and macro-creep damage formation for P92 under multiaxial stress related to circular notched specimen

In this study, to clarify the behaviour of micro- and macro-creep damage progression for P92 under multiaxial stress field, interrupted creep tests, analysis of multiaxial stress and detailed the cross-sectional observations were conducted on a circular notched round bar specimen which produces the multiaxial stress field due to the plastic constraint. As a result, creep voids were initiated at the early stage and they were formed up to the final fracture. These phenomena were found to be detected using direct current potential drop (DCPD) method. These results concern the development of the measurement of creep crack initiation. The distribution of high void area fraction was in good agreement with that of high hydrostatic stress and high multiaxial stress. This result indicates that multiaxial stress affects the void formation. Furthermore, the micro-creep damage of each interrupted specimen was evaluated by using the electron backscatter diffraction (EBSD) method which can analyse crystallographic misorientation caused by creep strain. The results of EBSD analyses indicated that the value of grain reference orientation deviation (GROD) closely concerns the void initiation.

Distinguishing the innovation behaviour of micro, small and medium food enterprises

The European economy, and particularly the food sector, is characterised by small and medium enterprises (SMEs). Networking represents for SMEs an opportunity to meet their needs in terms of know-how, and technological and financial resources with the main purpose of fostering innovation and facing global competition. Most scientific studies investigating networking for innovation focus on SMEs as a whole without exploring possible differences between SMEs. An important question to be posed is whether the firms within groups of SMEs behave the same in terms of innovation. The purpose of this paper is to understand whether different ‘innovation profiles’ of Italian food SMEs can be distinguished and to identify the structural factors associated with different profiles, with particular attention to size and networking. The methodology consists of a cluster analysis on data obtained by standardized on-line questionnaires compiled by Italian agri-food SMEs. Moreover, besides the identification of possible heterogeneity within the SME group with regard to innovation behaviour, the paper presents further value by providing useful information on surveyed Italian food SMEs in terms of firm structure and innovation.

Rheological modeling of carbon nanotube suspensions with rod–rod interactions

To explain the shear‐thinning behavior of untreated carbon nanotube (CNT) suspensions in a Newtonian matrix, a new set of rheological equations is developed. The CNTs are modeled as rigid rods dispersed in a Newtonian matrix and the evolution of the system is controlled by hydrodynamic and rod–rod interactions. The particle–particle interactions is modeled by a nonlinear lubrication force, function of the relative velocity at the contact point, and weighted by the contact probability. The stress tensor is calculated from the known fourth‐order orientation tensor and a new fourth‐order interaction tensor. The Fokker‐Planck equation is numerically solved for steady simple shear flows using a finite volume method. The model predictions show a good agreement with the steady shear data of CNTs dispersed in a Newtonian epoxy matrix as well as for suspensions of glass fibers in polybutene,1 demonstrating its ability to describe the behavior of micro‐ and nanoscale particle suspensions. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1476–1487, 2014

Dynamics of microscopic objects in optical tweezers: experimental determination of underdamped regime and numerical simulation using multiscale analysis

This article presents new experimental observations and numerical simulations to investigate the dynamic behavior of micro–nano-sized objects under the influence of optical tweezers (OTs). OTs are scientific tools that can apply forces and moments to small particles using a focused laser beam. The motions of three polystyrene microspheres of different diameters, 1,950, 990, and 500 nm, are examined. The results show a transition from the overdamped motion of the largest bead to the underdamped motion of the smallest bead. The experiments are verified using a dynamic model of a microbead under the influence of Gaussian beam OTs that is modeled using ray-optics. The time required to numerically integrate the classic Newton–Euler model is quite long because a picosecond step size must be used. This run time can be reduced using a first-order model, and greatly reduced using a new multiscale model. The difference between these two models is the underdamped behavior predicted by the multiscale model. The experimentally observed underdamped behavior proves that the multiscale model predicts the actual physics of a nano-sized particle moving in a fluid environment characterized by a low Reynolds number.