Fundamentals of Pulsed and Direct Current Electrophoretic Infiltration Kinetics

2012 ◽  
Vol 507 ◽  
pp. 53-57
Author(s):  
Timothy R. Palmer ◽  
Cullen R. Buie
Keyword(s):  
Process Design ◽  
Low Voltage ◽  
Maximum Yield ◽  
Constant Voltage ◽  
Dimensional Parameter ◽  
Advanced Composites ◽  
Pulsed Dc ◽  
Deposition Yield ◽  
20 Nm ◽  
And Diffusion

The present research endeavors to demonstrate the applicability of electrophoretic deposition (EPD) for the infiltration and coating of porous materials to create advanced composites. Motivated by improved materials requirements of tokamak fusion reactors, the composites are created by depositing ceramic nanoparticles in porous metallic matrices using both constant voltage and pulsed DC EPD. Silicon dioxide particles with a nominal diameter of 20 nm are used as inexpensive surrogates for more application-appropriate boron carbide due to their similar surface chemistry. Fabricated materials are characterized using scanning electron microscopy (SEM) and energetic dispersive x-ray spectrometry (EDX) to visualize coating quality and penetration of the material into the substrate. At low voltage, the deposited mass in constant voltage EPD increases linearly with time while at high voltage it asymptotically approaches a maximum yield of 1.988 grams. Pulsed EPD experiments demonstrate a reduction in deposition yield but also elimination of macro-pore generation in the low voltage case. A non-dimensional parameter, ξ*, relating electrokinetics and diffusion is derived which improves process design for pulsed EPD systems.

The Optimization of Thermocouple Galvanometer System Dynamics When Measuring Temperature Transients

1973 ◽  
Vol 6 (9) ◽  
pp. 384-388
Author(s):  
W. H. McKenzie ◽  
A. H. Richards
Keyword(s):  
System Dynamics ◽  
Natural Frequency ◽  
Time Constant ◽  
Exponential Type ◽  
Natural Frequencies ◽  
Low Voltage ◽  
Damping Ratio ◽  
Dynamic Performance ◽  
Ultra Violet ◽  
Dimensional Parameter

When using thermocouples directly connected to ultra-violet galvanometers for recording temperature transients, the low-voltage outputs necessitate the use of galvanometers with low natural frequencies. This puts a limitation on the overall dynamic performance. In a particular application, the user has to select the damping resistor for the galvanometer and the work describes how this is done so that the system is optimised for minimum integrated errors during a transient. The transient considered was of an exponential type which occurs frequently in practice and it is shown that the correct damping ratio and hence damping resistor for the galvanometer depends upon the non-dimensional parameter defined by the product of the natural frequency of the galvanometer and the time constant of the exponential. The results show that the usual value of damping ratio of 0·64 based on minimum sinusoidal distortion has to be modified for best dynamic performance. However, if the non-dimensional parameter is sufficiently large, higher values of damping can be used, which produce a large trace with acceptably small errors.

Effect of separated layer thickness on magnetoresistance and magnetic properties of Co/Dy/Co and Ni/Dy/Ni film systems

2018 ◽  
Vol 32 (01) ◽  
pp. 1750275 ◽  
Author(s):  
T. M. Shabelnyk ◽  
O. V. Shutylieva ◽  
S. I. Vorobiov ◽  
I. M. Pazukha ◽  
A. M. Chornous
Keyword(s):  
Magnetic Properties ◽  
Layer Thickness ◽  
Phase State ◽  
Diffusion Processes ◽  
Hysteresis Loops ◽  
Before And After ◽  
Beam Sputtering ◽  
Diffraction Patterns ◽  
20 Nm ◽  
And Diffusion

Co(5 nm)/Dy(t[Formula: see text])/Co(20 nm)/S and Ni(5 nm)/Dy(t[Formula: see text])/Ni(20 nm)/S trilayer films are prepared by electron-beam sputtering to investigate the influence of dysprosium layer thickness (t[Formula: see text]) and thermal annealing on the crystal structure, magnetoresistance (MR) and magnetic properties of thin films. The thickness of Dy layer changed in the range from 1 nm to 20 nm. The samples annealed for 20 min at 700 K. Electron diffraction patterns reveal that the as-deposited and annealed systems Co/Dy/Co and Ni/Dy/Ni had fcc-Co + hcp-Dy and fcc-Ni + hcp-Dy phase state, respectively. It is also shown that at the t[Formula: see text] = 15 nm the transition from amorphous to crystalline structures of Dy layer is observed. An increase in the Dy layer thickness results in changes in the MR and magnetic properties of the trilayer systems. It is shown that MR is most thermally stable against annealing to 700 K at t[Formula: see text] = 15 nm for Co/Dy/Co as well as for Ni/Dy/Ni. For t[Formula: see text] = 15 nm the, value of MR for both system increases by two times compared to those of pure ferromagnetic (FM) samples. The coercivity (B[Formula: see text]), remanent (M[Formula: see text]) and saturation (M[Formula: see text]) magnetization of the in-plain magnetization hysteresis loops are related to the Dy layer thickness too. The coercivity depends on the FM materials type and diffusion processes at the layer boundary. Accordingly, M[Formula: see text] and M[Formula: see text] are reduced with t[Formula: see text] increasing before and after annealing for both trilayer systems.

Thermodynamics and Diffusion of Free Trions in Mixed Type GaAs/AlAs Quantum Wells

1995 ◽  
Vol 417 ◽  
Author(s):  
H. W. Yoon ◽  
Arza Ron ◽  
M. D. Sturge ◽  
L. N. Pfeiffer
Keyword(s):  
Quantum Wells ◽  
Mixed Type ◽  
Radiative Decay ◽  
Bath Temperature ◽  
Simultaneous Presence ◽  
Spatially Resolved ◽  
Decay Times ◽  
Free Particles ◽  
20 Nm ◽  
And Diffusion

AbstractAn emission line which depends on the simultaneous presence of excitons and < 2×1010 cm−2 free photoexcited electrons in a 20 nm quantum well is shown to be due to the recombination of free negatively charged excitons ( “trions”). The binding energy is 1.3 meV and the lifetime is 1/4 that of the exciton. The increase in the radiative decay times of excitons and trions with increasing bath temperature is consistent with that of free particles. More directly, from time- and spatially-resolved measurements, we find that trions are localized at 5 K, and with increasing bath temperature both excitons and trions become mobile. The diffusivity of trions and excitons increases linearly with bath temperature, and at 10 K, the trion diffusivity is found to be factor of two lower than the exciton diffusivity. Our results are the first direct experimental evidence for free trions in GaAs quantum wells.

Change in Tunneling Spectrum of a Co/AlOx/Co Junction under Constant Voltage Stress

2008 ◽  
Vol 1108 ◽  
Author(s):  
Kouhei Horikiri ◽  
Kazuo Shiiki
Keyword(s):  
Barrier Layer ◽  
Photoelectron Spectroscopy ◽  
Bottom Electrode ◽  
Low Voltage ◽  
Inelastic Electron ◽  
Constant Voltage ◽  
Tunneling Spectrum ◽  
Voltage Stress ◽  
Electrode Interface ◽  
Tunneling Resistance

AbstractTo investigate the aging effect of a tunneling junction under constant voltage stress, the tunneling resistance and inelastic electron tunneling (IET) spectra were measured. At a low voltage, up to about 0.5 V, the tunneling resistance of junctions increased gradually over time, while above about 0.6V, it decreased gradually. This change was observed independent of voltage polarity. When the applied voltage was positive, the IET spectrum did not change, whereas when it was negative, the IET spectrum changed—the asymmetric peak became symmetric. X-ray photoelectron spectroscopy (XPS) analysis showed that the junction exhibiting an asymmetric peak contained metallic Al at the AlOx/bottom electrode interface, and the junction exhibiting a symmetric peak contained a homogeneous barrier layer. An increase in the tunneling resistance indicates that the amount of metallic Al decreased in the AlO x barrier layer. Transformation from an asymmetric to a symmetric peak indicates that the metallic Al in the AlOx/bottom electrode interface was oxidized, which led to the AlOx layer becoming homogeneous.

Interfacial morphology of low-voltage anodic aluminium oxide

2013 ◽  
Vol 46 (5) ◽  
pp. 1386-1396 ◽  
Author(s):  
Naiping Hu ◽  
Xuecheng Dong ◽  
Xueying He ◽  
Sandip Argekar ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Low Voltage ◽  
Scattering Length ◽  
Aluminium Oxide ◽  
Current Control ◽  
Native Oxide ◽  
Pure Aluminium ◽  
Constant Voltage ◽  
X Ray ◽  
Film Density ◽  
Anodic Aluminium Oxide

X-ray reflectivity (XRR) and neutron reflectivity (NR), as well as ultra-small-angle X-ray scattering (USAXS), are used to examine the in-plane and surface-normal structure of anodic films formed on aluminium alloy AA2024 and pure aluminium. Aluminium and alloy films up to 3500 Å thick were deposited on Si wafers by electron beam evaporation of ingots. Porous anodic aluminium oxide (AAO) films are formed by polarizing at constant voltage up to 20 V noble to the open circuit potential. The voltage sweet spot (5 V) appropriate for constant-voltage anodization of such thin films was determined for both alloy and pure Al. In addition, a new concurrent voltage- and current-control protocol was developed to prepare films with larger pores (voltages higher than 5 V), but formed at a controlled current so that pore growth is slow enough to avoid stripping the aluminium substrate layer. USAXS shows that the pore size and interpore spacing are fixed in the first 10 s after initiation of anodization. Pores then grow linearly in time, at constant radius and interpore spacing. Using a combination of XRR and NR, the film density and degree of hydration of the films were determined from the ratio of scattering length densities. Assuming a chemical formula Al2O3·xH2O, it was found thatxvaries from 0.29 for the native oxide to 1.29 for AAO grown at 20 V under concurrent voltage and current control. The average AAO film density of the porous film at the air surface is 2.45 (20) g cm−3. The density of the `barrier' layer at the metal interface is 2.9 (4) g cm−3, which indicates that this layer is also quite porous.

Nano-Columnar Pore Formation in the Photo-Electrochemical Etching of n-Type 6H SiC

2007 ◽  
Vol 556-557 ◽  
pp. 741-744 ◽  
Author(s):  
Yue Ke ◽  
Robert P. Devaty ◽  
Wolfgang J. Choyke
Keyword(s):  
Growth Mechanism ◽  
Pore Formation ◽  
Electrochemical Etching ◽  
Constant Voltage ◽  
Sem Images ◽  
Etching Condition ◽  
20 Nm ◽  
Porous Sic

We have fabricated columnar nano-porous SiC by photo-electrochemical etching on the C-face of n-type 6H SiC at constant voltage. SEM images reveal that the pores are long, straight and parallel with diameters of about 20 nm. We have produced such layers up to 250 μm thick. The pore morphologies for both Si and C-face SiC samples are compared and discussed as a part of the effort to understand the growth mechanism. It is found that the constant voltage etching condition on C-face SiC is crucial for this nano-columnar pore formation.

Structural, Mechanical and Corrosion Properties of Mg/SiO2 and MgO/SiO2 Multilayer Coatings for Magnesium Implant Devices

2015 ◽  
Author(s):  
R. Kotoka ◽  
S. Fialkova ◽  
S. Neralla ◽  
S. Yarmolenko ◽  
D. Pai ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Single Layer ◽  
Multilayer Coatings ◽  
Sem Images ◽  
Corrosion Properties ◽  
Glass Substrates ◽  
Pulsed Dc ◽  
Mechanical And Corrosion Properties ◽  
Pulsed Dc Magnetron Sputtering ◽  
20 Nm

In this study, Mg/SiO2 and MgO/SiO2 multilayer coatings with bilayer thicknesses (Λ) 10, 20, 40, 100, 200 and 1000 nm were deposited on glass substrates using DC and reactive pulsed DC magnetron sputtering processes. The aim of these coatings is to control the initial degradation and provide mechanical strength to magnesium implant during handling and installation. The initial thickness calibrations and deposition rates optimization were conducted using stylus profilometer. After deposition of the multilayer coatings, the values of their bilayer thicknesses (Λ) were obtained from X-ray reflectometery. The mechanical properties, surface morphology and roughness of multilayer coatings were studied using nanoindentation, SEM and AFM respectively. The nanoindentation results showed higher hardness of MgO/SiO2 multilayer coatings compared to single layer Mg. The roughness analyses showed improved roughness for bilayer thicknesses (Λ) less than 20 nm. It was observed from the SEM images that SiO2 coatings has pores. By adding Mg and/or MgO in the form of multilayers improves the pores significantly. The Mg/SiO2 multilayer coatings showed controlled degradation rate when immersed in saline solution compared to the monolithic SiO2 coating. In conclusion, conditions for depositing Mg/SiO2 and MgO/SiO2 multilayer coatings has been optimized. Alternating brittle SiO2 ceramic layers with soft and ductile Mg layers significantly improved the hardness of the Mg coating. Hardness of multilayer coatings can be fine-tuned by modifying bilayer thicknesses. Significant improvement in the corrosion and mechanical properties of the multilayer coatings can be used to protect surface of magnesium implant material during handling, storage and installation.

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