Dependence Of Current Density Research Articles

Electrodissolution Processes and Their Application in Manufacturing for Shaping and Finishing of Advanced Materials

Controlled material removal by anodic dissolution at high rates forms the basis of non-conventional metal shaping and finishing processes such as Electrochemical Machining (ECM), Electrochemical Micromachining (EMM), and Electropolishing (EP). These processes are employed in the manufacturing and processing industries for a variety of applications ranging from the machining of complex shaped components for heavy industries to the fabrication of microstructures in thin films and foils and microfinishing of superconducting radiofrequency cavities (1-3). Application of these processes for the production of reliable, reproducible, and high-yielding components require an understanding of the parameters that influence the anodic dissolution processes.ECM, EMM, and EP can be understood and theoretically modeled based on the same principles provided the scaling effects related to each process are considered (2). In the first part of this presentation, the high rate anodic dissolution behavior of different materials including refractory materials are described which helps in establishing the basic concepts that govern ECM/EMM/EP processes. Electrochemical reactions taking place at high anodic potentials depend on the metal-electrolyte combination and the operating conditions. These reactions include active metal dissolution, passivity, oxygen evolution, and the phenomena of passive film breakdown leading to the transpassive metal dissolution. In passivating electrolytes (containing oxidizing anions), oxygen evolution and metal dissolution take place simultaneously. The current density dependence of meat dissolution efficiency in such electrolytes provides minimized stray cutting in ECM. Mass-transport, current distribution, and surface film properties play a significant role in the metal removal rate and surface finish. Whereas the formation of a salt film on the dissolving anode in ECM electrolytes is well established, the identification of the rate-controlling species during electropolishing of metals in concentrated acid solutions remains a controversial issue.The second part of the presentation deals with the applications of these processes in the manufacturing of advanced products for the aerospace, biomedical, electronics, and photovoltaics industries. Different ECM techniques such as die-sinking, combined tool machining, EC drilling, and EC deburring are described that are used in the manufacturing of complicated shaped parts such as turbine blades. Maskless EMM methods such as Jet EMM, micro-drilling, and wire EMM are applied to fabricate precision microstructures. For process enhancement, assisted techniques such as laser, abrasive, vibration, and ultrasonic are incorporated with maskless EMM. For through mask electrochemical micromachining (TMEMM), an understanding of mass transport in a cavity and shape evolution modeling is critical. The use of laser patterned oxide film mask for Ti patterning is presented as an interesting application of TMEMM (4). A few case-studies on electropolishing are described which include the fabrication of STM probes and Nitinol stents, and microfinishing of print bands. In the microprocessor industry, a significant effort was invested in the development of EP and electrochemical mechanical planarization (ECMP) approaches as a no-contact or low-contact planarization processes for the integration of ULK/copper interconnects. The development work, including processing details and planarization efficiency of EP and ECMP, are reviewed. A critical evaluation of the current status of EP/ECMP vis a vis the chemical mechanical planarization (CMP) process is presented.References J. McGeough, Principles of Electrochemical Machining, Chapman and Hall, Wiley, London, 1974.M. Datta, Electrodissolution Processes: Fundamentals and Applications, CRC Press/Taylor and Francis, Boca Raton, 2020.E. J. Taylor and M. Inman, Electrochemical Surface Finishing, The Electrochemical Society Interface, Fall 2014, p47.P.-F. Chauvy, P. Hoffmann, D. Landolt, Electrochemical Micromachining of Titanium Through a Laser Patterned Oxide Film, Electrochem. Solid-State Lett., 4(5), C31 (2001).

Superconducting Order Parameter Nucleation and Critical Currents in the Presence of Weak Stray Fields in Superconductor/Insulator/Ferromagnet Hybrids

The stray fields produced by ferromagnetic layers in Superconductor/Insulator/Ferromagnet (S/I/F) heterostructures may strongly influence their superconducting properties. Suitable magnetic configurations can be exploited to manipulate the main parameters of the hybrids. Here, the nucleation of the superconducting phase in an external magnetic field that periodically oscillates along the film width is studied on the base of the numerical solution of the linearized system of Usadel equations. In addition, the effect of the magnetic configuration of the F-layer on the temperature dependence of the critical current density, Jc(T), is investigated in the framework of the Ginzburg–Landau phenomenological theory on the base of the oscillating model of a stray field. By following this approach, the Jc(T) dependence of a Nb/SiO2/PdNi trilayer is reproduced for different magnetic configurations of the PdNi layer.

Influence of heavy-metal capping layers on perpendicular magnetic anisotropy and spin-orbit torques of Pt/Co/HM stacks structures

The influence of perpendicular magnetic anisotropy (PMA) and current-induced magnetization switching on different capping materials, especially heavy metal (HM) materials has been rarely studied. In this work, the dependence of HM capping layer on interfacial PMA and current-induced magnetization switching in Pt/Co/HM tri-layered structures were investigated, where HM is Ta, Pt and W. We found that the Co/HM interface play a significant role on the PMA. Especially, the structure with a Ta capping layer features the largest anisotropy energy density KU of 3.15 Merg/cm3 and the largest spin-orbit torques (SOT) switching efficiency ηSOT of 0.19, which can be attributed to the different spin-orbit coupling and interfacial hybridization between Co and HM layers. Furthermore, the Pt/Co/Ta structure has dissimilar metals (Pt and Ta) with opposite spin Hall angles on the opposite sides of the ferromagnetic Co. We also investigated the Co layer thickness tCo dependence of PMA and switching current density, indicating the lower switching field can reduce the switching current density in the PMA region.

Outstanding performance of direct urea/hydrogen peroxide fuel cell based on precious metal-free catalyst electrodes

Direct urea/hydrogen peroxide fuel cells (DUHP-FCs) can produce electrical energy by recycling urea-rich wastewater. This study expands the commerciality of DUHP-FC by removing precious metals from their design. Nickel nanorod/nickel foam (NNR/NF) was fabricated using hydrothermal treatment to be used as the anode, and Prussian blue coating was deposited by potentiostatic electrodeposition onto hydrophilic carbon felt at the cathode (PB/CF). The anode exhibited a 7-folds higher current density than bare NF at 0–2 M urea, and lower charge transfer resistance. The cathode reported a high H2O2 reduction current. In addition, fuel cell tests indicated current density dependency on H2O2 concentration and cell voltage dependency on KCl concentration. A competitive maximum power density of 10.6 mW cm−2 was achieved at 0.98 open circuit voltage and 45 mA cm−2 maximum current density, in 0.33 M urea vs 2 M KCl and 2 M H2O2, exclusively via diffusive mass transfer. These findings indicate the practical application of DUHP-FC on a large scale.

Morphology, Conductivity, and Mechanical Properties of Electropolymerized Polypyrrole/Silver-Coated Granular Microsphere Composite Films

We report a facile synthesis of polypyrrole/silver-coated granular microsphere composite films through electropolymerization process in the presence of low- and high-density conductive granular microspheres. The resulting morphologies of composite films were implicitly influenced by the density of microspheres as revealed by scanning electron microscopy (SEM). Energy-dispersive X-ray (EDX) analysis confirmed the existence of elemental composition of the polypyrrole and conductive microspheres, while Fourier transform infrared (FTIR) spectroscopy verified the presence of molecular bonding associated with the dopant anion in all the synthesized films. Resistivity measurements demonstrated enhanced nonlinear conductivity and a strong dependence of current density in composite films with increasing application of electric field. Improvement in nonlinear conductivities is linked to the formation of more effective conductive pathways that boosted intermolecular and inter-particle charge carrier migration. Tensile tests reveal that the conductive granular microspheres have the general tendency to decrease internal forces in composite films.

Estimation of the Electricity Storage Volume Density of Compact SMESs of a New Concept Based on Si Microfabrication Technologies

A compact superconducting magnetic energy storage system (SMES) produced by Si micro fabrication technologies has been proposed to improve electricity storage volume density, w, in the sub-Wh/L range of conventional SMESs and to produce them at a low cost by mass production. In parallel with the experimental development reported previously, a series of trials was performed to estimate a feasible value of w based on the calculation of the magnetic field generated by the compact SMES by improving the calculation models step by step. In this work, the experimentally obtained magnetic flux density dependence of superconductive critical current density was taken into consideration for the first time in this series of trials, together with the additional improvement of the calculation models. The results of the estimation indicated that a compact SMES produced by the proposed concept can attain a w in the Wh/L range or more, ranking with or surpassing that of presently used capacitors.

Novel sample-thickness-dependent flux pinning behaviors of KFe2As2 intercalations in CaKFe4As4 single crystals

We report the strong dependence of critical current density (J c) on the sample thickness (d) along the crystalline c-axis in CaKFe4As4 single crystals. The J c can be respectively enlarged more than 3 and 50 times in H parallel to c-axis () and ab-plane () at temperature of 5 K and high magnetic fields of 8 T when the d is reduced from 88 to 2.0 . It is surprising to find that, accompanied by the enhanced J c, the fishtail effect fades away with the decreasing d. We believe that both the origins of enhanced J c and the fishtail effect in CaKFe4As4 may have close relationship with the interlayer coupling between CaKFe4As4 and the intercalations of KFe2As2. Our results not only demonstrate an encouraging prospect for application of CaKFe4As4, but also illuminate new light on the origin of fishtail effect in iron-based superconductors.

The Magnetization of HTSC Tapes Stack in the Flux Pump Regime

In the present paper, the possibility of magnetization of HTSC tape by means of pumping by a local magnetic field is considered. Within the framework of the critical state model, the calculation of the density of the induced currents and the magnetization of a square (12 × 12 mm) fragment of a second-generation HTS tape (YBCO) was made. The model considers real dependence of the critical current density on the magnetic field and has been successfully tested previously. In the sample, the currents were induced by the impact of a local magnetic field. The size of the localized area of the external magnetic field to be considered was much smaller than the size of the HTS sample. It is showed that the repeated cyclical impact of the local outer field leads to the accumulation of the total magnetic moment in the sample up to a magnitude of 94% of the theoretical magnetization limit for this sample. The results obtained make it possible to optimize the mode of magnetization of a square fragment of a tape (or a stack of tapes) when implementing a magnetic flux pump. The experimental studies showed results comprisable well with theoretical ones.

Successful DC current limitation above 100 Vm−1 for 50 ms using HTS tapes with critical currents exceeding 750 A/cm-width

High-voltage direct current transmission systems are expected to allow the transmission of huge volumes of electricity over long distances. The use of superconducting fault current limiters (SFCLs) based on second-generation (2G) high-temperature superconductor (HTS) coated conductors (CCs) is a promising solution to mitigate fault currents in DC transmission systems. To fabricate a SFCL whose size remains acceptable, which means minimizing the length of the HTS tape used, the tape must sustain a high electric field during the whole fault duration. In this paper, high performance commercial 2G HTS CCs from THEVA (more than 750 A/cm-width at 77 K in self-field), on which a 500 µm thick Hastelloy shunt was soldered, were tested by submitting them to faults of different amplitudes and durations. Measurements revealed that these HTS tapes could sustain any type of fault up to 100 V m−1, lasting up to 50 ms. Three-dimensions finite element simulations were able to reproduce accurately the experiments by using the appropriate temperature dependence of the critical current density and power law index, and by accounting for the variations in the local critical current along the length of the HTS tapes.

Performance optimization of graphene thermionicdevices based on charge and heat transport

In recent years, researchers have proposed a model of graphene thermionic energy converter (GTEC) for the utilization of high-grade thermal energy, which is used to extensively study the physical mechanism and parametric optimization. However, the influences of space charge accumulation and near-field radiative effects on the GTEC’s energy conversion performance are rarely reported. In the present work, the theories of thermionic emission, Langmuir space charge, non-equilibrium thermodynamics, and fluctuating electrodynamics are used to construct an improved model, in which the coupling effects of thermionic transport, near-field radiative heat transfer, and Newton heat transfer are considered. Firstly, the dependence of additional potential barrier, current density, power density, efficiency, and heat flows on the voltage and the vacuum gap are analyzed by neglecting the Newton heat transfer. The results show that the vacuum gap has a significant influence on the power density, while it has a negligible effect on the efficiency, the optimal power density and efficiency can be obtained at two different voltages. Secondly, the variations of power density and efficiency with voltage are analyzed on condition that the electrodes’ temperatures are restricted by the energy balance equation. It is found that Newton heat transfer has a significant influence on the power density, while it has a negligible effect on the conversion efficiency; the anode’s temperature at the optimal power density is higher than the ambient temperature, and the temperature at the optimal efficiency is close to the ambient temperature; the optimal regions of voltage, vacuum gap, and anode’s temperature are determined by considering the trade-off between power density and efficiency. The results obtained in this work can provide a theoretical basis for the development of practical devices.

Insight on the Electrochemical Degradation of Cartap in Padan 95SP: Kinetic and Mechanism

This study investigated the electrochemical degradation of Cartap (in Padan 95 SP) at BDD electrode. BDD shows high electrochemical activity, high stability as indicated in their CVs and LSV although not really high oxygen evolution potential, which depends under experimental conditions. This study confirms that the degradation of Cartap was undergone via both direct and indirect oxidations. The influence of current density on Cartap degradation was investigated in detail, indicating the dependence of Cartap removal versus current density as represented in a quadratic function. Other important parameters were figured out: half-life t 1/2 = (315 min – 108 min) depending on the applied current density ( j from 5 mA·cm -2 to 20 mA·cm -2 ). Besides, we explored a calculation method for assessing the contribution of radical species as well as their production mechanism.

Mathematical modeling of the magnetic properties of axisymmetric hard superconductors of the second kind in the Kim model

Authors perform mathematical modeling of magnetic properties, such as current distribution, intrinsic magnetic field and magnetization of a number of axisymmetric superconductors of the second kind, for example, of a sphere with the dependence of the critical current density on the local magnetic field in the Kim model. The simulation is based on equation that is integral with respect to coordinate and differential with respect to time. The equation describes time evolution of the critical current density and is solved numerically for a uniformly varying external magnetic field. The shape of the sample is set using a distorted rectangular irregular mesh with compaction to the edges of the sample. While solving the equation of current motion, the total magnetic field iscalculated at the points of the superconductor to calculate the value of the critical current density. In the article, the obtained solutions are used to visualize the current distribution in the volume of a superconductor and to construct magnetization hysteresis loops. Also, thanks to the calculations of the magnetic field in the center of the sample, the dependencies of the total penetration field for samples with different aspect ratios are obtained.

A 3D simulation comparison of carrier transport in green and blue c-plane multi-quantum well nitride light emitting diodes

Until recently, the electrical efficiency of green nitride light-emitting diodes (LEDs) was considerably lower than that of blue LEDs. This is particularly surprising as one would expect a reduced forward voltage with increasing emission wavelength. In this paper, we theoretically investigated the impact of the number of quantum wells on the forward voltage of III-nitride LEDs with x = 0.15 (blue) and x = 0.24 (green) InxGa1–xN QWs. The simulated dependence of current density (J) on applied diode bias (V) shows a significant increase of 1.9 V in the forward voltage between one and five quantum well (QW) c-plane green LED structures. Artificially turning off the polarization fields in the simulation does not entirely suppress this effect. Due to the large band offsets in the green LED multiple QW stack, simulations indicate a sequential band filling of the QW sequence. This mechanism should not be limited to c-plane LEDs and could also be present in nonpolar or semipolar devices.

Influence of field-dependent critical current on harmonic AC loss analysis in HTS coils for superconducting transformers supplying non-linear loads

There are two main obstacles in front of the development of high temperature superconducting (HTS) technology for electric power network applications; tape price and cooling cost. In order to reduce cooling cost, it is vital to evaluate AC transport current loss of the tapes precisely and then reduce it by some design innovative approaches. In addition, AC transport current loss in HTS material is a critical design variable for large-scale power network applications such as HTS transformers, superconducting fault current limiters, and power cables, since they are continuously carrying the network/load current during their operating life. In existing power networks, harmonic production sources are commonly used and thus, currents are distorted. Therefore, the effect of nonsinusoidal current on the critical apparatus in the network such as transformer must be studied. In this paper, AC transport current loss of a single-turn 2G YBCO HTS coil was modeled and numerically calculated under nonsinusoidal transport current using finite element method. Furthermore, influence of dependency of critical current density to magnetic field on the AC transport current loss of HTS coil when carries distorted currents was considered. It was observed that nonsinusoidal current causes excessive losses in HTS coil. On the other hand, a case study on an HTS transformer supplying non-linear load was considered to study the loss increment as well as heat load change. It was observed that current harmonics increases the AC loss, and heat load of transformer and decreases the efficiency, consequently.

Cross-Sectional Area Dependence of Tunnel Magnetoresistance, Thermal Stability, and Critical Current Density in MTJ

Tunnel magnetoresistance (TMR), thermal stability, and critical switching current are important metrics of a magnetic tunnel junction (MTJ). In this work, a detailed study of these metrics is conducted for the down-scaling of the transverse dimensions of the MTJ. The quantum transport and the magnetization dynamics simulations are performed using non-equilibrium Green's function in the mode-space approach and object-oriented micromagnetic framework (OOMMF), respectively. The study of areal size quantization effects on the TMR shows that most of the contribution to the TMR comes from lower energy sub-bands and that the TMR saturates for dimensions above 50 nm. An anomalous behavior is observed in the bias dependence of TMR for the lower energy sub-bands and is explained in terms of the modified Slonczewski's analytical model for conductance around zero bias. The study of TMR scaling is extended to consider non-idealities by introducing elastic dephasing into our simulations. It is shown that with down-scaling of diameters, dephasing affects the zero bias TMR predominantly below 20 nm. Furthermore, TMR is also studied in terms of sensitivity to the variations in the interface layer and the asymmetric reduction of TMR with bias and its reversal at higher bias is observed. OOMMF simulations of the larger stack, including the free layer, are carried out to understand the qualitative link between magnet switching behavior, thermal stability, and critical current density with area scaling. It is shown that the area dependence of thermal stability and critical current follows each other qualitatively and the scaling of both these metrics is correlated with different regimes of magnetization switching, such as macrospin behavior or formation of metastable complex textures. The implications of scaling, on the various MTJ metrics, are discussed in terms of the application domain.

Measurements of Temperature and Relative Humidity Dependencies of Oxygen Reduction Reaction Rate in PEFC

IntroductionFor widespread use of polymer electrolyte fuel cell (PEFC), it is necessary to reduce the amount of platinum by optimizing the cathode catalyst layer (CCL) structure. To establish the model of the CCL,[1] the intrinsic oxygen reduction reaction (ORR) rate which does not include mass transfer resistance in the through-plane direction of the CCL should be formulated. Neglecting the backward reaction, the ORR rate per unit mass of Pt, r mc, is proportional to oxygen partial pressure, p O [Pa], as follows: r mc = k mc p O [mol/(kg·s)][1] (1) k mc = k mc0 + exp(–E/RT – E c/b c) (2)where k mc is the reaction rate constant per unit mass of Pt [mol/(Pa·kg·s)], E c is the cathode electromotive force (emf) [V], E is the activation energy [J/mol], T is temperature [K] and b c is the Tafel slope [V].The objective of this study is to develop a measurement method of temperature and relative humidity dependencies of the intrinsic ORR rate constant using platinum-sputtered catalyst.ExperimentalA Japan Automobile Research Institute (JARI) standard cell whose active area was 50 mm × 50 mm was used in experiments. The membrane-anode assembly (MAA, Eiwa Corp.) was composed of a proton exchange membrane (PEM, DuPont Nafion® NR-212), an 8.3‒9.8 μm thick anode which was made of Pt/Vulcan® XC-72 catalyst (Pt/C weight ratio: 1) with a Nafion® ionomer (ionomer/carbon weight ratio: 0.74). Pt thin-layer cathode (ρs = 0.054 mg/cm2) was prepared by sputtering (AOV, SPAD-4240UM, Ar atmosphere, 5 Pa, 100 ℃, for 50 minutes) on the microporous layer (MPL) on a carbon paper (SIGRACET-GDL 29 BC, 235‒238 μm thick) to eliminate mass transfer resistance in the through-plane direction.[2] The MAA and Pt thin-layer cathode were stacked as shown in Fig. 1. A carbon current collector had a single serpentine flow channel, the width and depth of which were 1.0 mm and the width of the ribs between the channels was 1.0 mm. H2 and O2 were humidified at 75 oC. H2 and O2 flow rates were 600 and 300 cm3/min, respectively. The cell was operated at 80 oC. The pressure at the cell outlet was 1 atm.Results and DiscussionFig. 2 shows the polarization curves at different temperatures. The ORR rate constant per geometric area k gc (= ρs k mc) on the sputtered catalyst calculated from Fig. 2 is plotted with the ORR rate constant on the supported catalyst in Fig. 3. As shown in Fig. 2, current density at a fixed E cm , cathode emf vs. RHE at PEM–catalyst boundary, increased with raising temperature. The observed activation energy was 45 kJ/mol in case of the sputtered catalyst while the observed activation energy was 9–26 kJ/mol in case of the supported catalyst. This is because temperature dependency of mass transfer resistance is weaker than that of ORR, so temperature dependency of current density is not remarkable in case of supported catalyst, which has mass transfer resistance in the through-plane direction in CCL. In fact, the apparent activation energy on Pt-supported catalyst of 20–29 kJ/mol was reported.[3][4] Fig. 3 also shows that the observed activation energy on Pt-sputtered catalyst is almost independent of E cm . That indicates the effects of temperature and E cm on ORR rate constant was appropriately separated by using Pt-sputtered catalyst.Fig. 4 shows the experimental results at different RH. The current density at a fixed E cm increased by raising RH although the ORR rate constant should not depend on relative humidity. Since Pt-sputtered catalyst whose CCL thickness can be regarded as 0 does not have proton transfer resistance, this result means there are other factors affected by relative humidity. For example, as shown in Fig. 5, ECSA in working cells depends on relative humidity. It was also reported in literature.[5] In addition, RH dependency of current per ECSA in Fig. 6 was not remarkable. In fact, the current density at E cm = 0.5 V is 1.66 times higher at RH = 0.81 than 0.53 while the ratio is 1.22 in case of the current per ECSA.ConclusionsTemperature and relative humidity dependencies of ORR rate constant, k gc, were measured using platinum-sputtered catalyst. Experimental results at different temperatures showed k gc on the sputtered catalyst did not include through-plane mass transfer resistance and the effects of temperature and cathode emf on k gc was appropriately separated. Also, experimental results at different RH showed current density at a fixed E cm increased by raising RH. RH dependency of ORR rate was about 70 % reduced by eliminating the effect of ECSA. The RH dependency of ORR rate is mostly attributed to ECSA. Figure 1

Effect of Bath Temperature and Current Density on Higher Deposition Rate for Copper-Molybdenum Alloy Plated Film with High Molybdenum Content

Recently, miniaturizing electronic devices, such as handy phone, have been strongly requested. Number of mounted electronic components has been abruptly increased. Therefore, the high density of the component is mounted, the need for heat dissipation is increased. A heat radiation substrate is one of the most promising candidates to suppress increasing temperature of electronic devices. The heat radiation substrates need both high thermal conductivity and low coefficient of thermal expansion. A semiconductor has low coefficient of thermal expansion. A copper-molybdenum alloy has both high thermal conductivity and low coefficient of thermal expansion. An electroplated Cu-Mo alloy film has been investigated. However, deposition rate was decreased with high molybdenum content in the alloy. High molybdenum content is necessary to obtain low coefficient of thermal expansion. The low deposition rate is serious issue to put into industrial usage. The purpose of this study is to produce a film with high molybdenum content by high deposition rate. The chemicals used in bath preparation were CuSO4・5H2O 0.13 mol/L, Na2MoO4・2H2O 0.53 mol/L, C6H5Na3O7・2H2O 0.91 mol/L. The bath was adjusted to pH 9.0 and then electroplated. Nickel plate is used as the substrate and platinum plate is used as the anode. In this study, both bath temperature and current density have been investigated. Higher bath temperature makes deposition rate lower as shown in Fig.1. Higher current density makes deposition rate higher, but the current density dependence of the deposition rate is different on the bath temperature as shown in Fig.2. Lower dependence is observed in the case of higher bath temperature and effect of bath temperature on molybdenum content is different in the case of each current density. In the case of high current density, the molybdenum content increased with increasing bath temperature as shown in Fig.3. Therefore, when both bath temperature and current density are high, the films with high molybdenum content are plated by relatively high deposition rate as shown in Fig.4. The three micrometers thick copper-molybdenum alloy film with 23.9 at% molybdenum content film are plated for 1 hour under the condition of 50℃ bath temperature and 10 mA/cm2 current density. This deposition time to obtain 3 micrometers is one twentieth to obtain previously studied film with 17.9 at% molybdenum content. Figure 1

Temperature-dependent electrorheology of a suspension based on copolymeric P(NIPAM-co-[AMIm]Cl) colloidal particles

A imidazolium-based poly (ionic liquid), poly(1-allyl-3-methyl imidazolium chloride) (P[AMIm]Cl) was combined with the temperature-sensitive polymer poly(N-isopropylacrylamide) (PNIPAM) via random copolymerisation of the monomers [AMIm]Cl and NIPAM. The synthesised copolymer was characterised by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscope (SEM). Then its stimuli-responsive properties were studied at different electric field strengths and temperatures when it was dispersed in silicone oil. It was found that the colloidal copolymer particles were electro-responsive, showing excellent electrorheological (ER) effect. It was interesting that the ER effect of the copolymer was temperature-dependent. As the temperature increased from 5 °C to 50 °C, the dynamic yield stress of the suspension was found to increase with temperature. The temperature dependence of both yield stress and current density became stronger as the temperature was higher than 30 °C. The significant temperature-dependence of the suspension was attributed to the PNIPAM segment in the copolymer which could be swelled by silicone oil at higher temperature.

Weak emergence in the angular dependence of the critical current density of the high temperature superconductor coated conductor REBCO

Extensive critical current density measurements are reported as a function of magnetic field , temperature , angle between the applied field and the surface of the tape, and strain , on a REBCO coated conductor. The strain, , at which is maximised, is a function of , , and , which is consistent with weakly emergent behaviour. It is described by the chain model that considers competition between twinned domains with different crystallographic orientations and opposing responses under an applied uniaxial strain.Detailed effective upper critical field data are presented that show universal temperature and strain scaling. They lead to an accurate flux pinning relation for the volume pinning force, , where and and are constants, and are used to help parameterise the scaling behaviour of the angular data more accurately in those cases where cannot be measured directly. We derive approximate analytic in-field expressions that explain how the fraction, , of a-domains amongst the a- and b-domains affects the strain dependence of the critical parameters and conclude that in our tape, = 0.4, and the strain at which is the same in both domains is . We report a sharp peak in as the applied field approaches alignment with the ab-plane and the unusual result that with it, a suppression of the index of transition N also occurs. We find that the effective upper critical field increases as the field angle approaches the ab-plane significantly faster than any available theoretical model for the upper critical field .In addition, we conclude that a weak-emergence description is not limited to high temperature superconductors, but also describes some low-temperature superconductors.

Manipulation of G1Ba2Cu3O7-x Film Properties by Simply Changing Growth Temperature with RF Sputtering Method

We have investigated the relationship between Jc ( the critical current density) and H (applied magnetic field magnitude) for Gd1Ba2Cu3O7-x((Gd)BCO) films grown from 750 °C to 850 °C by RF sputtering. Measurements of JC(H, θ) (the magnetic-field angular dependence of the critical current density) reveal that film B (800 °C) shows enhanced pinning compared with C (850 °C), A (750 °C) (Gd)BCO films. The film C (850 °C) is the most anisotropic. We speculate that a lot of stacking faults exist in film C (850 °C), based on a board peak along ab-plane and no peak along c axis from the Jc angular measurements together with the small anisotropy parameter γ = 3. The speculation is proved by angular dependence measurement of film C (850 °C) after high temperature process in oxygen.