Determination of concrete water content by coupling electromagnetic methods: Coaxial/cylindrical transition line with capacitive probes

This paper deals with the development and the validation of an innovative, easy-to-use and on site technique for determination of concrete water content. The on-site technique is the capacitive probe, able to characterize in situ dielectric media in the 30–35 MHz frequency band (around 33 MHz). For the evaluation of water content in various civil engineering structures, a calibration methodology has to be developed and is presented herein. It is based on the complex permittivity estimation of various dispersive concretes, which is carried out by a cylindrical coaxial electromagnetic (EM) transition line allowing the characterization in laboratory of material samples in a large GPR frequency bandwidth [50–600 MHz]. This methodology consists then on a coupling between the results of both the capacitive probes and the coaxial EM cell extrapolated at low frequency (33 MHz). The extrapolation procedure used to link physically the results of the two techniques is provided by the 4parameter-variant of Jonscher's model which is parameterized to obtain dispersion curves of the complex permittivity for very wide frequency bands. The methodology is checked by a parametric study that associates the 4p-variant of Jonscher's model with the physical and hydric characteristics of the six concrete mix designs representing high performance and ordinary concretes at various hydric states. The surface testing results measured by capacitive probes on slabs are successfully compared to the extrapolated results obtained on cores.     

Analysis of the inducing frequency of a U-shaped ACFM system

According to the principle of the alternating current field measurement (ACFM), the inducing frequency has a significant influence on the signal acquisition and the measurement accuracy of an ACFM system. To design an ACFM prototype system with a U-shaped probe, the inducing frequency of the ACFM system is determined through simulation analysis and an experimental study in this paper. A large number of simulations are designed and run to analyze the influences of the inducing frequency on characteristic vectors of the induction electromagnetic field. By analyzing the simulation results, 6 kHz is selected to be the optimal inducing frequency for the U-shaped probe of an ACFM prototype. This frequency is tested by real crack inspection experiments using the U-shaped probe of the ACFM prototype in laboratory. The results show that 6 kHz is appropriate to realize the crack inspection and sizing with reasonable accuracy. The result in this paper will benefit the design and manufacturing of the prototype for the U-shaped probe ACFM system.     

Evaluation of chloride contamination in concrete using electromagnetic non-destructive testing methods

We present the results of the sensitivity of some electromagnetic non-destructive testing (NDT) methods to chloride contamination. The NDT methods are resistivity, using a quadripole probe, capacitive technique, with few sets of electrodes, and radar technique, using different bistatic configurations. A laboratory study was carried out involving three different concretes with different water to cement ratios. The concretes were conditioned with different degrees of NaCl saturation by means of three solutions containing 0 g/L, 30 g/l or 120 g/l. The solution was homogenized in the concrete by using a specific procedure. Results show that the EM techniques are very sensitive to the chloride content and saturation rate and, on a second level, to the porosity. Multi-linear regression processing was performed to estimate the level of sensitivity of the NDT measurements to the three indicators. Values of ten ND observables are presented and discussed. At last, the uncertainties of the regression models are studied on a real structure in a tidal zone.     

Measurement of permeability and ferrite/austenite phase fraction using a multi-frequency electromagnetic sensor

This paper presents the measurement of ferrite/austenite phase fraction using a multi-frequency electromagnetic sensor. A simple analytical model was established that can describe the response of the sensor for samples containing varying fractions of ferromagnetic phase over a wide range of frequencies (100 Hz–1 MHz). In particular, a new feature, the peak frequency of the imaginary part of the inductance, is found to be able to distinguish between samples across the whole range of the ferrite percentages. FEM models were used to simulate representative real microstructures from the samples and to relate the relative permeability to the ferrite fraction. Experimental results suggest that the accuracy of ferrite/austenite percentage measurement is within 8%.     

Atmospheric pressure pulsed-periodic source of high energy plasma flows and its applications

A new electromagnetic plasmadynamic system, pulsed-periodic plasmatron, operating at standard atmospheric pressure with high frequency has been developed. In this system plasma flow velocity reaches 3–5 ? 10³ m/s with temperature up to 15·10³ K. The results are presented on the use of the pulsed-periodic plasmatron for carbon steel (0, 45% C) surface layer hardening and boronized layer modification.     

Rheological characterisation of solder pastes and isotropic conductive adhesives used for flip-chip assembly

Solder pastes and isotropic conductive adhesives (ICAs) are widely used as a principal bonding medium in the electronic industry. This study investigates the rheological behaviour of the pastes (solder paste and isotropic conductive adhesives) used for flip-chip assembly. Oscillatory stress sweep test are performed to evaluate solid characteristic and cohesiveness of the lead-free solder pastes and isotropic conductive adhesive paste materials. The results show that the G′ (storage modulus) is higher than G″ (loss modulus) for the pastes material indicating a solid like behaviour. It result shows that the linear visco-elastic region for the pastes lies in a very small stress range, below 10 Pa. In addition, the stress at which the value of storage modulus is equal to that of loss modulus can be used as an indicator of the paste cohesiveness. The measured cross-over stress at G′ = G″ shows that the solder paste has higher stress at G′ = G″ compared to conductive adhesives. Creep-recovery test method is used to study the slump behaviour in the paste materials. The conductive adhesive paste shows a good recovery when compared to the solder pastes.     

Electro/magnetic shielding effectiveness of soft magnetic Fe80Nb6B14 amorphous alloy

Application of the Fe₈₀Nb₆B₁₄ amorphous alloy to electromagnetic shielding was examined in detail using different experimental techniques. For shields made of the optimized (annealing at 700 K/1 h) amorphous ribbons the shielding effectiveness b was measured versus frequency f and shield thickness h. It was shown that for h = 200 μm in the frequency range 2 MHz < f < 15 MHz (the near-zone, electric field) b decreases from 55 dB to 20 dB. In the frequency range 0.2 kHz < f < 10 kHz (the near-zone, magnetic field) b > 20 dB. The best shielding effectiveness, i.e. b > 100 dB was obtained for electromagnetic field in the frequency range 200 MHz < f < 1000 MHz (the far-zone).     

Mechanism of (Mg, Al, Ca)-oxide inclusion-induced pitting corrosion in 316L stainless steel exposed to sulphur environments containing chloride ion

The mechanism of oxide inclusion-induced pitting corrosion in 316L stainless steel exposed to sulphur environments containing chloride ions was investigated by scanning electron microscope analysis, electrochemical measurements and scanning Kelvin probe force microscopy (SKPFM). Two inclusion types were observed. The (Mg, Al, Ca)-oxide inclusions play an important role in pitting formation. SKPFM measurement results show that the inclusion sites exhibited a lower surface potential than the matrix. Finally, the schematic representation of the initiation and propagation process of the (Mg, Al, Ca)-oxide inclusion-induced pitting corrosion in 316L stainless steel exposed to sulphur environments containing chloride ions was established.     

Viscoelastic and conductivity properties of thermoreversible polyaniline–DNNSA gel in m-cresol

The rheological behavior of polyaniline (PANI)–dinonylnaphthalene sulfonic acid (DNNSA) in m-cresol is studied for different weight percent (w/v) of PANI–DNNSA_0.5. From rheological viewpoint the sample behaves like viscous fluid at low concentration (2 wt%) and gel at the concentration ≥8 wt%. The 4 wt% PANI–DNNSA_0.5 in m-cresol is at typical viscoelastic percolation region which is sol in the absence of shear but show invariant storage modulus with frequency at 30 °C. SEM picture indicates fibrillar network structure in the gel and the doped polyaniline remain as nanofiber at ≤2 wt% concentrations. The complete doping of PANI in all the systems is confirmed from UV–vis spectra. The dc conductivity of the gel increases with increasing the concentration of PANI–DNNSA_0.5 in m-cresol showing a jump at ～4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI–DNNSA_0.5 concentration studied here for each frequency. At lower frequency (<10⁵ Hz) ac-conductivity increase slowly with frequency but at higher frequency (>10⁵ Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by ～5 orders and also an increase of ～3 orders in ac-conductivity at the same frequency. The impedance spectroscopy results suggest the formation of combined resistance and capacitance (R–C) circuits in the gel and the increase of PANI–DNNSA_0.5 in the gel increases the capacitive feature more dominantly though the path becomes less resistive. The process also signifies the preparation of DNNSA doped PANI nanofiber in the gel medium.     

Polypyrrole nanowire modified graphite (PPy/G) electrode used in capacitive deionization

With high specific capacitance and good conductivity, polypyrrole nanowire modified graphite (PPy/G) electrode has great promising applications in capacitive deionization (CDI). Preparation parameters of modified electrode such as concentration of supporting electrolyte solution (LiClO₄), concentration of monomer (pyrrole, Py), pH of polymerization medium, polymerization potential and time have significant effects on the electrode adsorption capacity of NaCl. The experimental results indicate that the optimal preparation condition of the PPy/G electrode used for CDI is 0.10 M LiClO₄, 0.19 M Py and pH 5.91 which was controlled by phosphates buffer solution (PBS, 0.10 M), polymerized at 0.85 V vs saturated calomel electrode (SCE) with polymerization time of 150 s. The obtained electrode has an area specific capacitance of 0.188 F/cm² determined by cyclic voltammetry (CV) method in 1.0 M HClO₄ at a scanning rate of 0.05 V/s. In addition, the desalination experiments of the electrode were carried out in 500 ppm NaCl solution at a working voltage of 1.4 V. The experimental results indicate that the NaCl can be removed from the feed solution by electroadsorbing of the electrode with good desalination stability and the electrode can be regenerated efficiently by its electrodesorbing.     

Zn0.6Cu0.4Cr0.5Fe1.46Sm0.04O4 ferrite and its nanocomposites with polyaniline and polypyrrole: Preparation and electromagnetic properties

The nanosized Zn_0.6Cu_0.4Cr_0.5Fe_1.46Sm_0.04O₄ (ZCCFS_0.04O) ferrite doped with Sm was prepared by a rheological phase reaction method. These nanoparticles were further used as templates for the fabrication of polyaniline-linked ZCCFS_0.04O and polypyrrole-linked ZCCFS_0.04O nanocomposites via in situ polymerization method. The structures, morphology and electromagnetic property of ferrite powders and nanocomposites were characterized by X-ray powder diffractometer (XRD), transmission electron microscope (TEM), four-point probe resistivity instrument (SDY-4) and vibrating sample magnetometer (VSM). The electronic and magnetic properties of the nanocomposites are tailored by controlling the ferrite content. The pure polyaniline (PANI) and polypyrrole (PPy) films with thickness of 2 mm show a maximum reflection loss of ?20.93 dB and ?19.68 dB at 16 GHz and an available bandwidth (frequency difference between points where the absorption is less than ?8 dB) of 5.9 GHz and 6.2 GHz, respectively. When relative content of the ZCCFS_0.04O in PANI/ZCCFS_0.04O and PPy/ZCCFS_0.04O composites with respect to aniline (pyrrole) monomer is approximately 20 wt%, the maximum reflection loss of ?22.46 and ?20.90 dB appear at approximately 14.07 and 14.05 GHz, and available bandwidth is broadened to 11.15 and 11.30 GHz, respectively. The results show that both of PANI/ZCCFS_0.04O and PPy/ZCCFS_0.04O composites can be used as advancing microwave absorption and shielding materials due to their favorable microwave absorption properties.     

Development of high DC-bias Mn–Zn ferrite working at frequency higher than 3 MHz

Modern high-frequency electronic technology demands Mn–Zn soft ferrite for high DC-bias and low power loss applications. In this study, DMR50B ferrite material with a very attractive DC-bias property and with a lower power loss at high frequency up to 3 MHz was developed employing a conventional ceramic powder processing technique based on our previous study of DMR50 material, indicating its magnetic properties can be further improved by microstructure homogeneity. The core loss is around 200 kW/m³ at 3 MHz, 10 mT and 100 °C, and only around 20 kW/m³ at 700 kHz, 30 mT and 100 °C; its cutoff frequency f_r is ～4 MHz and its incremental permeability μ_Δ remains constant until H_DC = 100 A/m. Furthermore, the electromagnetic characteristics and the microstructure of this new DMR50B material are also discussed.     

Characterization of the plasma plume of a PIAD plasma source by means of optical emission spectroscopy

The understanding of the generation of fast ions in the advanced plasma source (APS) is important for the improvement of optical coatings. This requires a detailed characterization of the radial and axial distributions of plasma parameters in the expanding plasma downstream of the APS — the plasma plume. In an industrial vacuum chamber (1.1 m³ volume) diagnostics for optical emission spectroscopy (OES) have been installed. Radial profiles of line emission on an absolute scale are obtained by data deconvolution. First results based on a simple Corona model applied on a Helium–Argon mixture confirm the values obtained by Langmuir probe measurements. In the downstream region of the APS (10 cm–30 cm from its outlet), electron temperatures in the order of 5 to 10 eV and densities of about 10¹⁰ cm^? 3 are obtained.     

Synthesis and electromagnetic characterization of polyaniline nanorods using Schiff base through ‘seeding’ polymerization

Two kinds of Schiff base, m-phenylenediamine-glyoxal (Schiff base A) and p-phenylenediamine-glyoxal (Schiff base B), were used as ‘seed’ to induce the polymerization of aniline and hence prepare polyaniline (PANI) nanorods. The different preparation conditions including the Schiff base structure, dosage and acidity of the reaction medium, were investigated to discuss the influence of these conditions on the conductivity of the resulting samples through two-probe method at room temperature. The products were also characterized by Fourier transform infrared (FTIR), ultraviolet–visible (UV–vis), scanning electro microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) techniques. The results implied that these conditions play an important role in the formation of PANI nanorods. Moreover, the resulting PANI nanorods exhibited an unusual electromagnetic loss at the microwave frequency (f = 8.2–12.4 GHz) arose from order arrangement of polaron as charge carrier caused by a nanorods morphology and can be used for the potential application as microwave absorbing materials.     

Time-resolved plasma characterisation of modulated pulsed power magnetron sputtering of chromium

Time-resolved Langmuir probe measurements have been employed to investigate the temporal development of the plasma properties, such as electron and ion density, electron temperature as well as the floating and plasma potential, during Modulated Pulsed Power Magnetron Sputtering (MPPMS). A chromium target was sputtered with an average power of 650 W in an argon atmosphere (0.53 Pa) employing two steps of excitation of the discharge which was realised by altering the modulation frequency of the voltage supplied to the target. The overall pulse duration was kept at 750 μs and a repetition frequency of 100 Hz was used. Three distinct stages of the discharge, namely the initial and the second step of excitation as well as the transition region which connects both stable states, were found. Maximum electron densities up to 7 × 10¹¹ cm^? 3 were obtained during the transient phase.     

Reduction of a pre-formed radius in aluminium sheet using electromagnetic and conventional forming

Electromagnetic (EM) forming is a high-speed forming process that uses the forces induced on a conductive workpiece by a transient high frequency magnetic field to form the workpiece into a desired shape. This paper describes the results of a work undertaken to study the reduction of a 20 mm radius to 5 mm in 1 mm AA 5754 sheet by conventional metal forming process and by electromagnetic forming. The combination of conventional and EM forming will be referred to as “hybrid forming”. The 20 mm radius was pre-formed from flat sheet using a conventional die, punch and binder that allowed the material to draw in. The radius was then reduced to 5 mm, with no draw-in allowed for either process. Sheets were studied in the as-received condition and were also pre-strained to 5%, 10% and 15% to simulate strain path effects in a multiple stage forming operation. The process was modelled numerically to gain insight into the stress, strain and strain rate histories. The research indicates that features that are not achievable using traditional stamping techniques can be obtained with the aid of EM forming.     

Short time Fourier transform analysis for understanding frequency dependent attenuation in austenitic stainless steel

Short time Fourier transform (STFT) has been used to study the distribution of ultrasonic energy as a function of the frequency of the wave in the backscatter and the back-wall echoes obtained from austenitic stainless steel specimens with different grain sizes in a range of 30–210 μm. A 25 MHz nominal frequency immersion transducer was used in pulse-echo mode for data acquisition. In specimens with larger grain sizes (>100 μm), the frequency content of the first back-wall echo was 4.5–7.0 MHz only whereas the predominant frequency of the backscatter was in a range of 15–25 MHz up to the third/fourth back-wall echo. The amplitude and the frequency content of the back-wall echoes decreased rapidly with the propagation distance, however those of the backscatter decreased very slowly indicating high scattering and low absorption rates in the austenitic stainless steel specimens. The decrease in the center frequency of the first, second and third back-wall echoes has been correlated with the average grain size. The study demonstrates the usefulness of STFT in analyzing the frequency content of the backscatter and back-wall echoes simultaneously and thus understanding the frequency dependent attenuation in high scattering materials for microstructural characterization applications.     

Structural and magnetic properties of iron,cobalt and nickel nanoparticles

This study focuses on the synthesis and characterization of iron, cobalt and nickel nanoparticles through sol–gel method and heat-treating technique in argon atmosphere. The structure, morphology and magnetic properties of the as-synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID) magnetometer. XRD studies indicated that the as-prepared products were iron, cobalt and nickel with well crystallized bcc, fcc and fcc structure, respectively. TEM observations showed that the as-synthesized products composed of spherical shape with size around 2, 2 and 2 nm for iron, cobalt and nickel, respectively. Magnetization results revealed that the as-obtained products showed superparamagnetic character at 300 K. The magnetic anisotropy of the products is much higher than that of bulk owing to the nanostructure.     

Phase equilibria in the system Al–Co–Si

The Al–Co–Si system was studied for three isothermal sections at 600 °C (equilibria with Si), 800 °C (alloys up to 50 at.% Co) and 900 °C (alloys with more than 50 at.% Co). A total number of seven ternary compounds were characterized in the ternary system and the homogeneity ranges of the various ternary solid solutions of binary Co–Al and Co–Si compounds were studied. X-ray powder diffraction and optical microscopy was used for initial sample characterization and electron probe microanalysis of the annealed samples was used to determine the phase compositions within the ternary system. Lattice parameters have been determined for all ternary compounds and the change of lattice parameters with the composition is given for the solid solution phases.     

Effect of boronizing on the oxidation of niobium

Niobium (Nb) and its alloys are used in various industrial applications including metal processing, nuclear power generation and manufacturing of metallic superconductors and rocket nozzles. Although it is resistant to corrosion in several liquid media, Nb has a high oxidation rate in environments such as air at temperatures above 400 °C. In this study, the effect of the boronizing surface treatment on the morphology and structure of the oxide scales developed over Nb at 800–1000 °C, in air, was investigated. As-received Nb samples were observed to lose weight at and above 800 °C by the cracking, spallation and decohesion of thick Nb₂O₅ scales. However, oxide scales developed over the boronized samples at the same temperatures were comparatively protective for the metal. Based on the oxidation test results and characterization of the products, it is concluded that the positive effect of the boronizing surface treatment is due to the development of oxidation products including a liquid phase containing boron compounds.