Template-assisted electrohydrodynamic atomization of polycaprolactone for orthopedic patterning applications

This paper presents the development of the novel deposition of biodegradable polycaprolactone (PCL) polymer patterns on a metallic substrate using a jet spraying technique, template-assisted electrohydrodynamic atomization (TAEA), at ambient temperature. The structure of patterns was controlled by systematically varying the polymer concentration (2–15 wt.%) and the flow rate (1–25 μl min^? 1). Polymer deposition was carried out in the stable cone-jet mode to precisely control the surface structure and morphology. The patterns were studied by optical microscopy, scanning electron microscopy and profilometry, and a high degree of control over the pattern geometry and thickness was achieved by varying the spraying time. The hardness and the effective elastic modulus of the polymer patterns were estimated using nanoindentation. The effect of load, loading rate and the holding time on the hardness and effective elastic modulus was derived. Optimal results were obtained with 5 wt.% PCL in DMAC solution sprayed within the stable cone-jet mode operating window at a flow rate of 15 μl min^? 1 for 300 s at 11.1 kV with a working distance of 60 mm. Hexagonal patterns were well-defined and repeatable with thickness of ~ 34 μm. The hardness is 1.6 MPa at a loading rate of 0.1 μN/s and nearly halved when the load rate was increased to 1 μN/s. The effective elastic modulus of ~ 12 MPa is obtained for a load rate of 0.1 μN/s.     

Influence of electric field on the quenched-in vacancy and solute clustering during early stage ageing of Al-Cu alloy

The effects of electric field on the evolution of excess quenched-in vacancy as well as solute clustering in Al-4wt%Cu alloy, and on the vacancy migration and formation enthalpy of pure aluminum were investigated, using positron annihilation lifetime spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, transmission electron microscopy, hardness measurement and four-probe electrical resistivity measurement. The results showed that the electric field improved age hardening response obviously and postponed the decay of excess vacancies for 30 min during the early stage ageing of Al-4wt%Cu alloy. A large number of 2–4 nm GP zones with dense distribution were observed after 1 min ageing with an electric field applied. The electric field-assisted-aged sample owned a lower coarsening rate of GP zone, which was about three fifths of that in the aged sample without an electric field, from 1 min to 120 min ageing. The electric field contributed 8% increase of the vacancy migration enthalpy(0.663 ± 0.021 e V) of pure Al, comparing with that(0.611 ± 0.023 e V) of pure Al without an electric field. The increase of vacancy migration enthalpy, induced by the electric field, was responsible for the difference on evolution of quenched-in vacancy, rapid solute clustering and age hardening improvement during the early stage ageing of Al-4wt%Cu alloy.     

Electrical thermal heating and piezoresistive characteristics of hybrid CuO–woven carbon fiber/vinyl ester composite laminates

The electric heating and piezoresistive characteristics of CuO–woven carbon fiber (CuO–WCF) composite laminates were experimentally evaluated. Hybrid CuO–WCF composites were fabricated via a two-step seed-mediated hydrothermal method. The interlaminar interface between two plies of hybrid CuO–WCF/vinyl ester composite laminae was influenced by interlocked fiber–fiber cross-linking structures with CuO NRs and acted as electric heating and resistance elements. The contribution of CuO NRs (10–110 mM) to the interlaminar interface was determined by measuring the temperature profile, in order to investigate the electrical resistive heating behavior. At higher concentration of CuO NRs growth in the interlaminar region applied by 3 A, the average temperature reached to 83.55 °C at the interface area 50 × 50 mm² and the heating efficiency was 0.133 W/°C owing to radiation and convection given by 10.5 W (3 A, 3.5 V). To investigate the piezoresistive response, the through-thickness gauge factor was observed at 0.312 during Joule heating applied by 2 A, compared with 0.639 at an ambient air temperature for CuO 110 mM concentration. The morphology and crystallinity of CuO NRs were investigated using scanning electron microscopy and X-ray diffraction analyses, respectively. The temperature dependence of hybrid CuO–WCF composite laminates’ storage moduli were analyzed using a dynamic mechanical analyzer. These characterizations showed that the interlaminar interface, combined with the high specific surface area of CuO NRs, provided the electron traps for electrical conduction around multiple WCF junctions and adjacent cross-linked laminae.     

Effects of d.c. current on the phase transformation in 7050 alloy during homogenization

Evolutions of properties and morphologies of secondary phases in 7050 alloy homogenized with direct electric current were studied in detail by conductivity measurement, tensile test and energy dispersive X-ray microanalysis. With increasing temperature, the conductivity decreases, and while the ultimate tensile strength, yield strength and elongation of 7050 alloy increase in alloy homogenized with direct electric current, and reaches the saturation values at 440 °C/2 h. During homogenization, the brighter white AlZnMgCu phase having (weight ratio %) 12.1–15.2Mg, 27.2–32.1Al, 20.9–26.2Cu and 31.4–34.4Zn gradually transforms to the gray phase having (weight ratio %) 10.3–15.1Mg, 41.4–53.7Al, 22.9–35.2Cu and 5.8–13.1Zn and then to the dark gray phase having (weight ratio %) 10.6–14.2 Mg, 38.2–54.9Al, 23.3–44Cu, and 3.6–9.2Zn. With the application of direct electric current, the elemental diffusion network becomes profuse, the amount of gray phase increases, the diffusion of Zn accelerates, the apparent activation of the transformation from AlZnMgCu to Al₂MgCu decreases from 125.52 kJ/mol for the alloy homogenized without direct electric current to 118.82 kJ/mol, and the area fraction of secondary phase decreases by 38% at 450 °C.     

High piezoelectric response in the new coexistent phase boundary of 0.87BaTiO3–(0.13-x)BaZrO3–xCaTiO3

An investigation of the coexistent ferroelectric phase was carried out on the ternary system of 0.87BaTiO₃–(0.13-x)BaZrO₃–xCaTiO₃ [abbreviated as BT–BZ–xCT (where 0.00 ≤ x ≤ 0.13)]. Temperature-, frequency-dependent dielectric data, electric field-dependent strain and polarization as a function of composition are presented in order to understand the relationships of structure-properties and find the high piezoelectric response in this system. Results showed that ceramics in the composition range of 0.00 ≤ x < 0.04 were of a rhombohedral structure and transformed into a tetragonal structure at x > 0.06. The multiphase coexistence of the rhombohedral and tetragonal phase in this system was identified at x = 0.06. A large, virtually hysteresis-free electric field induced strain of 0.23% was achieved with the composition, x = 0.06, at 40 kV/cm on the boundary between rhombohedral and tetragonal phase. This relates to an extraordinarily high and normalized piezoelectric coefficient (S_max/E_max) of 1280 pm/V, which was reached at a low electric field applied at 10 kV/mm. These results indicated that a high piezoelectric response may stem primarily from the rhombohedral-tetragonal phase boundary, due to greater lattice softening and reduced energy barriers for polarized rotation.     

Effect of magnetic fields on the abnormal electroresistance behavior in epitaxial thin films of La0.8Ca0.2MnO3

We report an unusual electroresistance (ER) behavior induced by a current and its response to magnetic fields in La_0.8Ca_0.2MnO₃ epitaxial thin films. These thin films were fabricated on SrTiO₃ (1 0 0) substrate using pulsed laser deposition (PLD) technique. It is found that the electric resistivity in these films is significantly enhanced by applying a dc current over a threshold value. Simultaneously, an abnormal electroresistance behavior appears in the temperature range from 10 to 300 K. The enhanced resistance turns out to be very sensitive to a weak current. Even a very small dc current can remarkably depress the high resistance, showing an unusual colossal ER effect. The ER reaches ∼1175% at temperatures lower than ∼50 K, and ∼705% at 300 K for a current changing from 0.72 to 10.5 μA. The influence of magnetic fields on the transport was also studied. The I–V curves can be strongly influenced by a low magnetic field even at room temperature. The deduced magnetoresistance (MR) reaches 120% at 300 K upon applying a magnetic field of 0.25 T. An interesting phenomenon is that the observed MR is current dependent.     

Cryogenic design and test results of 30-m flexible hybrid energy transfer line with liquid hydrogen and superconducting MgB2 cable

In this paper we present the development of a new hybrid energy transfer line with 30 m length. The line is essentially a flexible 30 m hydrogen cryostat that has three sections with different types of thermal insulation in each section: simple vacuum superinsulation, vacuum superinsulation with liquid nitrogen precooling and active evaporating cryostatting (AEC) system. We performed thermo-hydraulic tests of the cryostat to compare three thermo-insulating methods. The tests were made at temperatures from 20 to 26 K, hydrogen flow from 70 to 450 g/s and pressure from 0.25 to 0.5 MPa. It was found that AEC thermal insulation was the most effective in reducing heat transfer from room temperature to liquid hydrogen in ∼10 m section of the cryostat, indicating that it can be used for long superconducting power cables. High voltage current leads were developed as well. The current leads and superconducting MgB₂ cable passed high voltage DC test up to 50 kV DC. Critical current of the cable at ∼21 K was 3500 A. It means that the 30 m hybrid energy system developed is able to deliver ∼50–60 MW of chemical power and ∼50–75 MW of electrical power, i.e. up to ∼135 MW in total.     

Corrosion resistance of directionally solidified Al–6Cu–1Si and Al–8Cu–3Si alloys castings

The aim of this article is to compare the electrochemical corrosion resistance of two as-cast Al–6 wt.% Cu–1 wt.% Si and Al–8 wt.% Cu–3 wt.% Si alloys considering both the solutes macrosegregation profiles and the scale of the microstructure dendritic arrays. A water-cooled unidirectional solidification system was used to obtain the as-cast samples. Electrochemical impedance spectroscopy (EIS) and potentiodynamic anodic polarization techniques were used to analyze the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that the Al–8Cu–3Si alloy has better electrochemical corrosion resistance than the Al–6Cu–1Si alloy for any position along the casting length. At the castings regions where the Cu inverse profile prevailed (up to about 10 mm from the castings surface) the corrosion current density decreased up to 2.5 times with the decrease in the secondary dendrite arm spacing.     

Microstructural and mechanical characteristics of Cu–Cu2O composites compacted with pulsed electric current sintering and hot isostatic pressing

This paper reports the influence of applied sintering process – pulsed electric current sintering (PECS) and hot isostatic pressing (HIP) – on the microstructure and mechanical properties of Cu–Cu₂O composites. In PECS fine-grained structure was obtained while in HIPing the grain growth was more noticeable, mostly due to the longer process time. The studies also showed that Cu₂O-phase distributed in Cu-matrix increased microhardness; at a fixed grains size Cu–Cu₂O structure had higher hardness than Cu so that 20% higher microhardness was obtained when Cu₂O was doubled from 19.1 to 37.2 vol%. At best, 99.1% density with 690 nm grain size and 1.35 GPa hardness were achieved by PECS whereas by HIP the same density with 1860 nm grain size gave 1.02 GPa hardness. The grain growth and the effect of second phase clustering on the grain growth were evaluated experimentally.     

Observation of self-magnetic field relaxations in Bi2223 and Y123 HTS tapes after over-current pulse and DC current operation

The development of power transmission lines based on long-length HTS tapes requires the production of high quality tapes. Due to fault conditions, technical mistakes and human errors during the operation of a DC power transmission line, an over-current pulse, several times larger than the rated current, could occur. To study the effect of such over-current pulses on the transport current density distribution in the HTS tapes, we simulated two start-up scenarios for one BSCCO and two YBCO tapes. The first start-up scenario is an initial over-current pulse during which the transport current was turned on rapidly, rising to 900 A during the first milliseconds, then reduced to a 100 A DC current. The second start-up scenario is normal operation, and involved increasing the transport current slowly from 0 A to 100 A at a rate of 1 A/s. For both scenarios, we then measured the vertical component of the self-magnetic field by means of a Hall probe above the tape, and afterward, by solving a linear equation of the inverse problem we obtain the current density profiles. We observe a change of the self-magnetic field above the edge of the BSCCO and YBCO tapes during 30 min after the 5 ms of over-current pulse and during the normal operation. The current density profiles are peaked in the centre for over-current pulse, and more peaked around the edge of the HTS tape for normal operation, which means that the limited time over-current pulse changes the current density profiles of the HTS tapes. We observe also a loop of current for YBCO tapes and we show the role of the HTS tape stabilizer.     

Surfactant-free synthesis and electromagnetic properties of Co–Ni–B composite particles

The Co–Ni–B composite particles with different mol ratio of Co to Ni were composited of spheres, spheres in-pair, hierarchical assemblies of dentrites, which were surfactant-free synthesized by chemical reduction method in aqueous solution. The complex permeability of the Co–Ni–B composite particles indicated reverse resonant peak at the frequency range of 8–16 GHz, where the complex permittivity showed the positive resonant peak and the μ_r″ of particles showed negative values, caused by the transformation between electric and magnetic energy. The imaginary parts of relative permeability (μ_r″) of Co–Ni–B composite particles indicated one broad resonant peak over the 2–8 GHz range for the high effective anisotropy. A slight decrease in complex permittivity resulted in an excellent impedance matching property. The Co–Ni–B composite alloy particles with mol ratio of 7:3 exhibited reflection loss less than ?20 dB in frequency range of 4.0–14.5 GHz for the absorber thickness of 1.1–3.2 mm, and an optimal RL of ?32.4 dB was obtained at 12.8 GHz with thickness of 1.2 mm. The broadest bandwidth of reflection loss less than ?10 dB from 13.0 to 17.0 GHz, covering almost the whole Ku-band, was obtained for a thickness of 1.1 mm layer.     

Investigation of in vitro bone cell adhesion and proliferation on Ti using direct current stimulation

Our objective was to establish an in vitro cell culture protocol to improve bone cell attachment and proliferation on Ti substrate using direct current stimulation. For this purpose, a custom made electrical stimulator was developed and a varying range of direct currents, from 5 to 25 μA, was used to study the current stimulation effect on bone cells cultured on conducting Ti samples in vitro. Cell–material interaction was studied for a maximum of 5 days by culturing with human fetal osteoblast cells (hFOB). The direct current was applied in every 8 h time interval and the duration of electrical stimulation was kept constant at 15 min for all cases. In vitro results showed that direct current stimulation significantly favored bone cell attachment and proliferation in comparison to nonstimulated Ti surface. Immunochemistry and confocal microscopy results confirmed that the cell adhesion was most pronounced on 25 μA direct current stimulated Ti surfaces as hFOB cells expressed higher vinculin protein with increasing amount of direct current. Furthermore, MTT assay results established that cells grew 30% higher in number under 25 μA electrical stimulation as compared to nonstimulated Ti surface after 5 days of culture period. In this work we have successfully established a simple and cost effective in vitro protocol offering easy and rapid analysis of bone cell–material interaction which can be used in promotion of bone cell attachment and growth on Ti substrate using direct current electrical stimulation in an in vitro model.     

A 20 keV electron gun system for the electron irradiation experiments

An electron gun consisting of cathode, focusing electrode, control electrode and anode has been designed and fabricated for the electron irradiation experiments. This electron gun can provide electrons of any energy over the range 1–20 keV, with current upto 50 μA. This electron gun and a Faraday cup are mounted in the cylindrical chamber. The samples are fixed on the Faraday cup and irradiated with electrons at a pressure ∼10⁻⁷ mbar. The special features of this electron gun system are that, at any electron energy above 1 keV, the electron beam diameter can be varied from 5 to 120 mm on the Faraday cup mounted at a distance of 200 mm from the anode in the chamber. The variation in the electron current over the beam spot of 120 mm diameter is less than 15% and the beam current stability is better than 5%. This system is being used for studying the irradiation effects of 1–20 keV energy electrons on the space quality materials in which the irradiation time may vary from a few tens of seconds to hours.     

Measurement of particle size distribution of silica nanoparticles by interactive force apparatus under an electric field

This paper describes the measurement of particle size distribution of silica nanoparticles by interactive force apparatus (IFA) under an electric field in order to suggest the application of the apparatus to the measurement of particle size distribution. The results were compared with results obtained from size measurement by dynamic light scattering. D₅₀ measured by IFA was closer to the average particle size determined by TEM (5 nm). Also, when compared the results under three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur due to electric breakdown. The distribution measured by IFA (D₅₀ = 5–7 nm) was larger than the one measured by DLS (D₅₀ = 1 nm). The electric breakdown was explained by curve fitting of three different particle size distribution functions with particle size distribution obtained from IFA measurement.     

Synthesis of porous titanium implants by environmental-electro-discharge-sintering process

Porous Ti implants with various porosities were first fabricated by environmental-electro-discharging-sintering (EEDS) of atomized spherical Ti powders. Powders in two size range (50–100 and 200–250 μm) were settled by vibration into a quarts tube and subjected to a high voltage and high density current pulse. A single pulse of 0.75–2.0 kJ/0.7 g-powder, using 150, 300 and 450 μF capacitors, was applied to produce fully porous and porous-surfaced Ti implant compacts. The solid core was automatically formed in the center of the compact after discharge and porous layer consisted of particles connected in three dimensions by necks. The solid core and neck sizes increased with an increase in input energy and capacitance. On the other hand, pore volume decreased with increased capacitance and input energy due to the formation of a solid core. Capacitance and input energy are the only controllable discharge parameters even though the heat generated during a discharge is the unique parameter that determines the porosity of compact. It was shown that EEDS of spherical Ti powders can efficiently produce fully porous and porous-surfaced Ti implants with various porosities in short times (<400 μs) by manipulating the discharging conditions such as input energy and capacitance including powder size.     

High-temperature phase transition behavior and magnetocaloric effect in a sub-rapidly solidified La–Fe–Si plate produced by centrifugal casting

A sub-rapidly solidified La Fe_(11.6)Si_(1.4)plate was fabricated directly from liquid by centrifugal casting method.The phase constitution,microstructure and magnetocaloric effect were investigated using backscatter scanning electron microscopy,X-ray diffraction,differential scanning calorimetry and physical property measurement system.When the plate was annealed at 1373 K,1 phase was formed by a solid-state peritectoid reaction.A first-order magnetic phase transition occurred in the vicinity of188 K,and the effective refrigeration capacities reached 203.5 J/kg and 209.7 J/kg in plates annealed for1 h and 3 h,respectively,under a magnetic field change of 3 T.It is suggested that centrifugal casting may become a new approach to prepare high-performance La–Fe–Si magnetocaloric plates for practical applications,which could largely accelerate the formation of 1 phase during high-temperature heat-treatment process due to refined and homogeneous honeycombed microstructure.     

Experimental investigations on the single point incremental forming of a titanium alloy component combining static heating with high tool rotation speed

The present work focuses the attention on the Single Point Incremental Forming (SPIF) process of a scaled car door shell made by Titanium alloy (Ti6Al4V). The effect of a temperature increase contemporary due to electric static heating and tool rotation speed was investigated.Preliminary tensile tests allowed to define the temperature level to be assured on the sheet in order to determine a consistent flow stress reduction. SPIF tests were carried out adopting rotation speed in the range 800–1600 RPM, while simultaneously changing the pitch value in the range 0.5–1.0 mm. Temperature during the forming process was continuously measured in the central area of the blank using a pyrometer. In addition a digital image correlation system was used for measuring the strain distribution over the formed part.The combination of the two approaches (heating by both electric bands and high tool rotation speed) revealed to be a feasible solution for manufacturing hard to work materials like Ti alloys, since the investigated case study was successfully formed by SPIF. In addition, a positive effect of the tool rotation speed in stabilizing the necking (thus allowing to reach higher level of stretching) was recognised.     

Electroresistance and magnetoresistance in La0.9Ba0.1MnO3 thin films

The electroresistance and magnetoresistance effects have been investigated in La_0.9Ba_0.1MnO₃ epitaxial thin films. Tensile strain caused by substrate mismatch makes the Curie temperature T_C of the film at ∼300 K. The influence of an applied dc-current on the resistance in the absence of a magnetic field was studied. Significant change of the peak resistance at different currents was found. The reduction of the peak resistance reaches ∼27% with an electric current density up to 1.3 × 10⁵ A cm⁻². We also studied colossal magnetoresistance (CMR) effect in the films. Applying a magnetic field of 2 T could lead to a magnetoresistance as large as 42%. The reduction of resistance caused by a current density ∼1.3 × 10⁵ A cm⁻² was found to be equivalent to the CMR effect caused by 1.5 T near T_C. The phenomenon that the resistance in CMR manganites could be easily controlled by the electric current should be of high interest for both fundamental research and practical applications.     

Design and fabrication of functionally graded PZT/Pt piezoelectric bimorph actuator

A laminated piezoelectric bimorph actuator with a graded compositional distribution of PZT and Pt was fabricated, and its deflection characteristics were evaluated. Using experimentally determined compositional dependency of elastic and piezoelectric properties in the PZT/Pt composites, the modified classical lamination theory and the finite element method were applied to find the optimum compositional profile that will give a larger deflection and smaller stress, simultaneously. The miniature bimorph-type graded actuator that consists of a composite internal-electrode (PZT/30 vol% Pt) and three piezoelectric layers of different compositions (PZT/0–20 vol% Pt) were fabricated by powder stacking and sintering. The deflection of the actuator was measured using electric strain gages mounted on the top and bottom surfaces of the actuator. The deflection was found to strongly depend on the composition distribution profile. Under an applied electric field of 100 V m⁻¹, the actuator with an optimum composition profile exhibited a curvature of up to 0.03 m⁻¹, which is a satisfactory performance for this kind of actuators. The stress generated on actuation was estimated to be as low as 0.4 MPa, which is much smaller than those of conventional directly bonded actuators and will assure a long actuation life.     

In-situ observations of solutal melting using laser scanning confocal microscopy: The Cu/Ni model system

Solutal melting was investigated in-situ by means of high temperature laser scanning confocal microscopy. This technique enabled us to track the motion of the solid–liquid interface in order to determine the evolution of the interfacial velocity. The Cu–Ni binary system was chosen as a model case and concentric samples were fabricated from both pure metals. Two holding temperatures above the melting point of Cu were investigated, i.e., 1115 and 1145 °C. As the average composition of the mounted samples was chosen to lie within the solid solution region, the reaction occurred via the following steps: i) thermal melting of Cu, ii) solutal melting of Ni, and iii) resolidification. A smooth and regular s–l interface was observed during solutal melting, except during a short period at 1145 °C where an irregularity briefly appeared. At 1115 °C, the dissolution of Ni was completed in less than 3 min and the total thickness dissolved was in the range 40–50 μm. At 1145 °C, the dissolution did not last much longer but the total thickness dissolved was significantly larger: approximately 180 μm. At both temperatures, the velocity first increased, then reached a maximum value after 20–30 s (0.6–0.8 μm/s at 1115 °C and 4.8 μm/s at 1145 °C), and finally tends progressively to zero. Post-mortem observations showed that the Ni was homogeneously dissolved over the entire sample height at 1115 °C, which excludes any effects of convection on the velocities that we measured. On the contrary, at 1145 °C, the dissolution was more important in the upper part of the sample and the interface appeared curved. The total thickness dissolved was in both cases larger than the predicted theoretical values and the melting velocities were also larger than the values obtained from finite difference calculations. The discrepancies are more pronounced at higher temperature.