Rod-shaped Sample Research Articles

Outstanding electromagnetic wave absorption performance of polyacrylonitrile-based ultrahigh modulus carbon fibers decorated with CoZn-bimetallic ZIFs

PAN-based carbon fibers have been widely used in aerospace materials due to high specific strength, high specific modulus and many other outstanding features. As one kind of carbon-based electromagnetic wave (EMW) absorption material, carbon fibers are expected to absorb more EMW due to multiple polarization losses and large specific surface area in which EMW can be reflected many times. However, they also have certain disadvantages when used as EMW absorption material due to their high dielectric constant, low permeability and low reflection loss strength. Herein, a facile hydrothermal synthesis method was used to construct the three-dimensional (3D) bimetal-organic framework compound onto the surfaces of polyacrylonitrile(PAN)-based ultrahigh modulus carbon fibers (UHMCFs). Through the control of key parameters in the synthesis process, 3D bimetallic ZIF particles with different morphologies were assembled on the fiber surfaces, and a further high temperature heat treatment resulted in significantly improved EMW absorption properties. The results showed that three fibrous structures including rod-shaped, threadlike and flower-like morphologies had been formed with the introduction of CoZn-ZIFs. Among them, the uniform structure of rod-shaped sample could be preserved after carbonization and it also showed optimal EMW absorption performance, e.g. its minimum reflection loss (RLmin) and effective absorption bandwidth (EAB) values were − 67.67 dB (EMW loss above 99.9 %) and 4.28 GHz, respectively, with the thickness of 2.00 mm. In the final, the EMW absorption mechanism of CoZn-bimetallic ZIF decorated UHMCFs including interfacial loss, conductive loss, polarization loss, multiple scattering and excellent impedance matching was discussed in detail.

Bimetallic Cu-Pt catalysts over nanoshaped ceria for hydrogen production via methanol decomposition

A series of Pt/CeO2 (5 wt%) and bimetallic Cu-Pt/CeO2 (4 wt% Cu and 1 wt%) catalysts supported on different CeO2 nano shapes (polyhedra, rods, and cubes) were studied as catalytic systems for hydrogen production from the methanol decomposition (MD) reaction. Supports were prepared by hydrothermal approach and the active phase was incorporated by wet impregnation. Materials were characterized by SEM, HRTEM-STEM, N2 adsorption, EDS, XRD, Raman spectroscopy, H2-TPR, and CO-DRIFTS. The catalytic properties for MD reaction were studied as a function of temperature in the 100–450 °C range and as a function of time on-stream for 24 h at 350 °C. Despite the high methanol conversion presented by the Pt/CeO2 catalysts, more important in polyhedra and rods, these catalysts exhibited a low hydrogen yield. Differences in the properties of bimetallic Cu-Pt/CeO2 samples were established to be support-morphology-dependent, and the dispersion of copper and the ceria reducibility were superior in samples supported on polyhedra and rods as in the case of platinum catalysts. An improvement of the oxygen vacancies in the bimetallic system was also observed, as a result of the close interaction between copper and ceria. TOF values indicated that catalytic performances are promoted not only by the size of the active phase nanoparticles, but also by the facet predominantly exposed by ceria. The formation of bimetallic phase and the presence of surface Cu-Pt alloy sites in the rod-shaped sample accounted for the slightly better methanol conversion in the stability tests. The H2 yield in the bimetallic samples was superior compared to platinum, which makes them suitable candidates for the hydrogen production from the methanol decomposition.

Toward In Situ Synchrotron Mapping of Crystal Selection Processes during Crystal Growth

Here, we present an automated and rapid method for nondestructive mapping of crystal grains in a rod-shaped sample. The approach was designed for application to in situ float-zone crystal growth ex...

Nanofabrication of Iron-Cobalt (FeCo) Alloy by Sol-gel Method

Background and Introduction: Metal oxides (MOs) have been extensively used in a large range of engineering and medical applications. Methods: FeCo nanoparticles (NPs) were successfully synthesized by the solgel method in the presence of a powerful reducing agent-sodium borohydride (NaBH4). The structure, morphology, and optical properties of NPs were analyzed by X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) at room temperature. Results: The XRD spectrum showed the body center cubic (BCC) structure of the samples after heat treatment at 500 °C. The SEM analysis exhibited that the particle size of as-synthesized and annealed samples was approximately 40 nm and 22 nm, respectively. Conclusion: The TEM investigations showed the rod-shaped sample of annealed NPs. The optical studies of the FTIR analysis revealed the starching bound of Fe-Co at the frequencies of 673 cm-1, 598 cm-1, and 478 cm-1.

Resonances in large ferrimagnetic YIG samples – Electrodynamic analysis

Electrodynamic (ED) analysis of the TEn0p (TEθφr) modes in a shielded single-crystal-5-mm-diameter yttrium iron garnet (YIG) sphere has been performed and compared with the results of previous experiments. Measurements and ED analysis of the HE111± mode resonances in a polycrystalline Al-doped rod-shaped YIG sample have been performed for comparison. It has been shown that electromagnetic resonances in large shielded YIG spheres behave in a similar way as typical resonances occurring in dielectric resonators under conditions when the effective permeability is positive, and as so-called magnon resonances when the effective permeability is negative. Nevertheless, both types of resonances are solutions to the same transcendental equation. Computations reported herein suggest that the physical nature of resonance systems containing dispersive gyrotropic media can be described within a common framework of electromagnetic resonance systems with unequal stored magnetic and electric energies, which offers an alternative to the more widely used quantum and harmonic oscillator models.

Nanoparticle size and 3D shape measurement by electron tomography: An Inter-Laboratory Comparison

Electron tomography (ET) has been used for quantitative measurement of shape and size of objects in three dimensions (3D) for many years. However, systematic investigation of repeatability and reproducibility of ET has not been evaluated in detail. To assess the reproducibility and repeatability of a protocol for measuring size and three-dimensional (3D) shape parameters for nanoparticles (NPs) by ET, an inter-laboratory comparison (ILC) has been performed. The ILC included six laboratories and six instruments models from three instrument manufacturers following a standard measurement protocol.A technical specification describing the normative steps of the protocol is published by the International Standards Organization (ISO). Gold NPs with 30 nm nominal diameter contained within a rod-shaped carbon support were measured. The use of a rod-shaped sample support eliminated the missing wedge effect in the experimental tilt series of projected images for improved quantification. A total of 443 NPs were initially measured by NRC-NANO and then 115 out of the 443 NPs were measured by five other labs to compare measurands such as the Volume (V), maximum Feret diameter (Fmax), minimum Feret diameter (Fmin), volume-equivalent diameter (Deq) and aspect ratio (Frat) of the NPs. The results of the five labs were compared with the results obtained at NRC-NANO. The maximum disagreement in measurements of Fmin and Fmax obtained by the participating labs did not exceed 7 %. The measured Deq was between 27.5 nm and 30.3 nm in agreement with the NP manufacturer’s specification (28 nm–32 nm). In addition to the above, the influence of the missing wedge effect and beam-induced NP movement was quantified based on the differences of the results between labs.

Electromagnetic excitation technique for nonlinear resonant ultrasound spectroscopy

Nonlinear resonant ultrasound spectroscopy (NRUS) is a method that can be used to determine the amount of microcracking in structures. The nonlinear parameter extracted in NRUS is based on the dependence of the resonance frequency on vibration amplitude in the presence of damage. NRUS measurements typically are excited with a piezoelectric transducer, but here the application of an electromagnetic transducer is explored as an alternative. The electromagnetic transducer, unlike a single piezoelectric, allows selective excitation of longitudinal, torsional, and bending vibrations in a rod-shaped sample. Measurement of the nonlinear properties of the sample for each type of vibration is therefore possible. This electromagnetic technique involves gluing a coil of wire onto the end of a rod sample and placing it in a magnetic field. By controlling which part of the coil is inside the strongest region of the magnetic field, the principal direction of the driven oscillations in the rod can be controlled. Both piezoelectric and electromagnetic excitation techniques are tested by measuring the parameter of nonlinearity for longitudinal motion, αE, in a sample of Berea sandstone. The electromagnetic technique was shown to measure a 30% higher mean value for αE than the piezoelectric technique.

Facet-Dependent Reactivity of Fe2O3/CeO2 Nanocomposites: Effect of Ceria Morphology on CO Oxidation

Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of catalytic materials, through appropriate tailoring of the particles’ shape and size, in order to acquire highly efficient nanocatalysts, is of major significance. Iron is considered to be one of the cheapest transition metals while its interaction with ceria support and their shape-dependent catalytic activity has not been fully investigated. In this work, we report on ceria nanostructures morphological effects (cubes, polyhedra, rods) on the textural, structural, surface, redox properties and, consequently, on the CO oxidation performance of the iron-ceria mixed oxides (Fe2O3/CeO2). A full characterization study involving N2 adsorption at –196 °C, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) was performed. The results clearly revealed the key role of support morphology on the physicochemical properties and the catalytic behavior of the iron-ceria binary system, with the rod-shaped sample exhibiting the highest catalytic performance, both in terms of conversion and specific activity, due to its improved reducibility and oxygen mobility, along with its abundance in Fe2+ species.

La<sub>2</sub>O<sub>3</sub>/Fe<sub>2</sub>O<sub>3</sub>-CeO<sub>2</sub> Composite Oxide Catalyst and Its Performance

The La2O3/Fe2O3-CeO2 composite oxide catalysts were prepared by coprecipitation method, sol-gel method and hydrothermal method. The effect of preparation methods on structure morphology and photocatalytic properties of La2O3/Fe2O3-CeO2 samples was investigated. The results show that the cubic CeO2 structure can be obtained at 600℃. The rod-shaped sample prepared by coprecipitation method, displays the highest crystalline and the strongest diffraction peak intensity. The spherical sample is acquired from sol-gel method, while the small granular sample prepared by hydrothermal method tends to aggregate. The maximum specific surface area of the sample prepared by coprecipitation method is 76.21 m2/g, the minimum specific area of the sample from sol-gel method is 32.66 m2/g and the maximum pore size is 13.84 nm, while the minimum pore volume and pore size of the sample by hydrothermal method are 0.038 cm3/g and 3.95 nm respectively. The band gap energy of catalyst samples is in the following order: sample-CP < sample-SG < sample-HT. The sample obtained by coprecipitation method has the best catalytic degradation performance for methylene blue. Under the excitation of visible light, the degradation rate was 99.58% at 50 minutes, which was higher than those of sol-gel method and hydrothermal method by 5.58% and 9.54% respectively. The catalytic degradation reaction is a first-order kinetic model: ln (c0/ct) = kt + qe. The maximum k-value of the sample degradation process obtained by coprecipitation method is 0.074 min-1.

Nonlinear resonant ultrasound spectroscopy using electromagnetic excitation

Nonlinear resonant ultrasound spectroscopy (NRUS) is a method that can be used for detecting microcracks in structures. NRUS detects shifts in resonance frequencies versus excitation amplitude. Excitation of the sample is typically done with a piezoelectric transducer. We have been applying an electromagnetic excitation developed for resonant ultrasound spectroscopy [S. Garrett, J. Acoust. Soc. Am. 88(1), 210–221 (1990)] as an alternative for NRUS excitation. It involves gluing a coil of wire onto the end of a rod-shaped sample and placing it in a magnetic field. By controlling which part of the coil is in the strongest part of the magnetic field, we can control the principle direction of the driven oscillations in the rod. This method allows us to selectively excite longitudinal, torsional, and bending vibrations and measure the nonlinear properties of the sample for each type of vibration. We have applied this electromagnetic method to measuring the nonlinear properties of Berea sandstone, and we plan to use it to detect stress corrosion cracking in stainless steel samples. The purpose of this presentation is to illustrate the usefulness of the electromagnetic method.

A new designed incremental high pressure torsion process for producing long nanostructured rod samples

High pressure torsion (HPT) is one of the most important and effective severe plastic deformation (SPD) processes for producing nanostructured (NS) and ultrafine grained (UFG) metals. Whereas HPT presents excellent mechanical properties, its applications are limited to small disk-shaped samples. In this study a new design of incremental HPT (IHPT) process entitled SIHPT is developed which is much convenient for the production of large NS and UFG metallic rods. In this new design, some steppers along the length of the rod-shaped sample are used while applying an axial load from two ends of it. Step twisting of stepper parts with simultaneous axial loads extend the deformed region to the whole length of the sample. The five turn IHPT process was applied to a 50 mm length and 10 mm diameter pure copper sample and microstructure, and mechanical properties were evaluated. The microstructural study of SIHPT processed samples using TEM and EBSD micrographs clearly reflected the NS sample having an average grain size of less than 100 nm. Also, microhardness measurements showed that the sample has fairly good homogeneity through both axial and radial directions. Besides, tensile test measurements indicate that there is about four times improvement in yield strength of nanostructured sample compared to unprocessed metal which is accompanied with satisfactory ductility as a result of high hydrostatic compressive stresses.

Synthesis, microstructures and properties of Al89Fe8Ti2Zr1 alloy prepared by powder metallurgy and hot extrusion

A composition of Al89Fe8Ti2Zr1 (at %) alloy was produced by using atomising powder metallurgy and subsequent hot-extrusion technique. Fine particle with a diameter smaller than 10 μm was formed by the atomised powders. The rod-shaped bulk sample with a diameter of 8 mm was obtained by hot-extrusion. The microstructural analysis of the alloy was characterised by X-ray diffraction, scanning and transmission electron microscopy. As per energy-dispersive X-ray spectroscopy analysis, the phase composition of the bulk alloy consists of α-Al and Al13Fe4 phases. The Vickers hardness of the bulk alloy was measured 160 HV, the tensile strength and elongation of the alloy after deformation treating was 600 MPa and 9% at room temperature. The bulk alloy shows excellent properties compared with conventionally produced Al alloy because of the dense structure by preparation technology.

Conversion and extracting bio-oils from rod-shaped cornstalk by sub-critical water

The rod-shaped cornstalk sample was selected to investigate the generation of bio-oils (including water-soluble oil and heavy oil) by sub-critical water under different reaction temperatures (240–350°C) and extraction times (0–120min). The gas, the water-soluble oil extracted by n-hexane and heavy oil extracted by acetone from the residue were collected and disposed, respectively. The gas chromatography-mass spectrometer (GC–MS) analysis of water-soluble oil showed that phenols were the major compounds. The pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) analysis of heavy oil showed that it was primarily consisted of phenols, carboxylic acids, aromatic ketones, and nitrogen- and sulfur-containing compounds. The results demonstrated that the optimum liquefaction condition in sub-critical water was at 260°C and 15min, and the highest bio-oil yield could be reached 33.00%. The results of experiment indicated that the structure of the lingocellulose (lignin, cellulose and hemicellulose) in the rod-shaped cornstalk was able to be broken down by sub-critical water at relatively low temperature and short extraction time without any catalyst and organic reagent.

Nano-Dot Markers for Electron Tomography Formed by Electron Beam-Induced Deposition: Nanoparticle Agglomerates Application

A method allowing fabrication of nano-dot markers for electron tomography was developed using an electron beam-induced deposition in an ordinary dual beam instrument (FIB and SEM) or an SEM. The electron beam deposited nano-dot markers are suitable for automatic alignment of tomographic series. The accuracy of the alignment was evaluated and the method was demonstrated on agglomerated nanoparticle samples using a rod-shaped sample with no missing wedge effect. Simulations were used to assess the effect of marker size on alignment accuracy.

Application of TDR Method for Moisture Profiles Measurement in Cellular Concrete

Possible applicability of TDR method for continuous monitoring of moisture content in porous building materials is studied in the paper. TDR method, originally proposed for application in soil science, represents prospective tool for long time monitoring of moisture content in laboratory as well as in-situ conditions neglecting the effect of salts presence in researched material on accuracy of measured moisture content. The basic experimental setup of the TDR method is adjusted to the measurement of water content in building materials. The practical application of the method is presented on the measurement of moisture profiles in rod-shaped sample of cellular concrete.

Nano-dot markers for electron tomography formed by electron beam-induced deposition: nanoparticle agglomerates application.

A method allowing fabrication of nano-dot markers for electron tomography was developed using an electron beam-induced deposition in an ordinary dual beam instrument (FIB and SEM) or an SEM. The electron beam deposited nano-dot markers are suitable for automatic alignment of tomographic series. The accuracy of the alignment was evaluated and the method was demonstrated on agglomerated nanoparticle samples using a rod-shaped sample with no missing wedge effect. Simulations were used to assess the effect of marker size on alignment accuracy.

A theoretically exact reconstruction algorithm for helical cone-beam differential phase-contrast computed tomography

Differential phase-contrast computed tomography (DPC-CT) reconstruction problems are usually solved by using parallel-, fan- or cone-beam algorithms. For rod-shaped objects, the x-ray beams cannot recover all the slices of the sample at the same time. Thus, if a rod-shaped sample is required to be reconstructed by the above algorithms, one should alternately perform translation and rotation on this sample, which leads to lower efficiency. The helical cone-beam CT may significantly improve scanning efficiency for rod-shaped objects over other algorithms. In this paper, we propose a theoretically exact filter-backprojection algorithm for helical cone-beam DPC-CT, which can be applied to reconstruct the refractive index decrement distribution of the samples directly from two-dimensional differential phase-contrast images. Numerical simulations are conducted to verify the proposed algorithm. Our work provides a potential solution for inspecting the rod-shaped samples using DPC-CT, which may be applicable with the evolution of DPC-CT equipments.

Detailed Mapping of Reaction Diagrams for Metastable Phases

ABSTRACTA method is presented to map reaction diagrams for metastable phases by treating a rod-shaped sample under high pressure in a known temperature gradient, such that each point on the sample is treated at a unique, known temperature. After quenching to ambient conditions the structural properties of the sample can be studied by spectroscopic or other techniques. The accuracy and resolution in temperature is mainly limited by the uncertainties in the measured temperature distribution during treatment and the uncertainty in position during analysis. The method is tested by re-mapping the polymerization reaction of C60 under high pressure in the range 0.8 – 2 GPa. Preliminary data show surprisingly sharp "reaction boundaries" at certain temperatures, signalling the onset of dimerization and polymerization of the material.

Internal friction and Young’s modulus of Si3N4/BN fibrous monoliths at various vibrational strain amplitudes

The effect of temperature and vibrational strain amplitude on Young’s modulus and an ultrasound damping (internal friction) of ceramic boron nitride samples and silicon nitride/boron nitride fibrous monoliths was studied. It was shown that the elastic moduli and the elastic vibration decrement of the low-modulus BN ceramic and of the high-modulus Si3N4/BN monoliths measured at small strain amplitudes (in the region of amplitude-independent internal friction) exhibit a noticeable temperature hysteresis. Temperature exerts the smallest effect on the amplitude-independent decrement and on the amplitude-dependent damping and Young’s modulus defect of a monolith whose filaments are arranged both along and perpendicular to the axis of a rodshaped sample. These parameters behave in the most complicated way in a sample with all its filaments aligned with the rod axis. The observed relations can be assigned to structural features of the monoliths and the considerable influence of transverse strain on the evolution of defect structure in the materials studied.

棒状磁性体試料の抵抗率と透磁率の同時測定

棒状磁性体試料の抵抗率と透磁率の同時測定