Resistive Surface Layer Research Articles

Finite element modeling of resistive surface layers by micro‐contact impedance spectroscopy

AbstractMicro‐contact impedance spectroscopy (MCIS) is potentially a powerful tool for the exploration of resistive surface layers on top of a conductive bulk or substrate material. MCIS employs micro‐contacts in contrast to conventional IS where macroscopic electrodes are used. To extract the conductivity of each region accurately using MCIS requires the data to be corrected for geometry. Using finite element modeling on a system where the resistivity of the surface layer is at least a factor of ten greater than the bulk/substrate, we show how current flows through the two layers using two typical micro‐contact configurations. This allows us to establish if and what is the most accurate and reliable method for extracting conductivity values for both regions. For a top circular micro‐contact and a full bottom counter electrode, the surface layer conductivity (σs) can be accurately extracted using a spreading resistance equation if the thickness is ~10 times the micro‐contact radius; however, bulk conductivity (σb) values can not be accurately determined. If the contact radius is 10 times the thickness of the resistive surface, a geometrical factor using the micro‐contact area provides accurate σs values. In this case, a spreading resistance equation also provides a good approximation for σb. For two top circular micro‐contacts on thin resistive surface layers, the MCIS response from the surface layer is independent of the contact separation; however, the bulk response is dependent on the contact separation and at small separations contact interference occurs. As a consequence, there is not a single ideal experimental setup that works; to obtain accurate σs and σb values the micro‐contact radius, surface layer thickness and the contact separation must all be considered together. Here we provide scenarios where accurate σs and σb values can be obtained that highlight the importance of experimental design and where appropriate equations can be employed for thin and thick resistive surface layers.

Ultrasonically nanostructured electric-spark deposited Ti surface layer on Ti6Al4V alloy: enhanced hardness and corrosion resistance

A complex approach for the production of corrosion resistant nanostructured surface layer on the Ti6Al4V alloy is reported in this article. Surface modification was conducted using sequential application of electric discharge surface alloying (EDSA) with α-titanium and ultrasonic impact treatment (UIT) induced the nanostructuring of the EDSA-formed Ti-layer. X-ray diffraction and TEM analysis show that the applied modifications form the outmost surface layer of ~20 μm thick comprised the nanoscale grain structure with a grain size of 10-30 nm. Additionally, the UIT-induced mechanochemical oxidation of the modified surface was observed by SEM with energy dispersive X-ray microanalysis. The produced nanostructured α-titanium surface layer shows enhanced microhardness and better corrosion behaviour in saline solution than those of the original and UIT-processed Ti6Al4V alloys. Thus, the complex treatment applied can be recommended for the surface finishing of the products made of multi-phase titanium alloys, such as biomedical implants.

Concentrated solar energy for in-situ elaboration of wear-resistant composite layers. Part II: Tungsten carbide surface enrichment of common steels

The present work constitutes the second part of a study concerning the application of Concentrated Solar Energy (CSE) for the in-situ elaboration of carbide-reinforced surface layers onto common steels, employing WC as a model system. As in the first part that involved titanium and chromium carbides as reinforcing compounds, “solar hardfacing” experiments were carried out in the solar furnace SF40, at the installations of Plataforma Solar de Almería (Spain). Parametric studies performed were targeted to clarify the effects of solar irradiation time and inert or reactive processing atmosphere on the structural integrity, microstructure, carbide dispersion and hardness of the surface layers obtained. The results were used, on the one hand to identify conditions for the elaboration of wear resistant surface layers and on the other hand to elucidate the fundamental mechanisms governing the dispersion of WC particles in a liquid ferrous matrix that is, subsequently, re-solidified. In contrast to the TiC particles, WC ones are subjected to liquid metal attack transforming progressively to mixed FeW carbides, as determined by scanning electron microscopy and X-ray diffraction. Under inert atmosphere, solar processing beyond a threshold time period decreases the in-depth homogeneity of the carbides dispersion and increases the extent of the attack, deteriorating hence the composite character of the layer obtained. Reactive nitrogen atmosphere mitigates the negative effects of prolonged exposure, allowing the elaboration of thick hardfacing layers. Finally, dry sliding friction tests allowed defining the friction coefficient and specific wear rate, as well as the synergy of the wear micro-mechanisms involved. These results complemented with the respective ones for titanium and chromium carbide-based hardfacing layers, provide a first framework for the rational and optimized elaboration of wear resistant carbide-based surface layers using concentrated solar energy.

Investigation into Mechanical Degradation of Lithium-Ion Batteries with Nickel-Rich Cathode Materials - A Long-Term Cycling Study

Layered lithium transition-metal oxides of type LiNi x Co y Mn z O2 (NCM, with x + y + z = 1) are well established and represent the current state of the art cathode materials for different lithium-ion battery applications. The ultimate goal in the area of NCMs is to increase the nickel fraction in the material as much as possible, as this allows for higher specific capacities (for a given charge cutoff voltage). However, recent studies have demonstrated that with increasing practically used capacity the material suffers increasingly from volume changes, eventually leading to mechanical failure. Apart from volume changes, adverse side reactions like structural/morphological changes and/or phase transitions during cycling operation are also possible causes of degradation, affecting capacity retention and overall lifetime of a battery cell. In this work, we report on a long-term study on the structural, electronic and morphological changes of high-nickel NCM/graphite full-cells from operando X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy and electrochemical impedance spectroscopy. The acquired data demonstrate that the capacity loss can be attributed predominantly to the cathode side. Using XRD we observed the presence of two differently active NCM phases. However, the NCM cathode material was still found capable of virtually complete Li (de-)lithiation, but with significantly slower kinetics due to, in part, built-up of resistive surface layers with cycling. Figure 1. a) Charge/discharge profiles of LiNi0.85Co0.1Mn0.05O2/graphite full-cells for various cycles at 1C rate and in the voltage range between 2.8 and 4.2 V. b) Phase fractions of the less and more active NCM phases after charging to 4.2 V (including a 1 h CV step). Figure 1

Investigation of Structural Changes during Long-Term Cycling of NCM-811 Used As Cathode Active Material in Li-Ion Batteries

Layered lithium transition metal oxides, typically containing nickel, cobalt and manganese (NCM, Li1+δ[NixCoyMnz]1-δO2 with x+y+z=1), are the most widely used cathode active material (CAM) in Li-ion batteries for portable devices and battery electric vehicles.1 The class of NCM materials has several advantageous properties such as high energy and power densities and good cycling stability. However, depending on the Ni:Co:Mn ratio, the electrochemical performance characteristics of the materials can differ significantly. Increasing the Ni content is a current research focus, as it typically allows for a higher reversible lithium usage at a given cell potential, thereby improving the specific capacity.2 At the same time, highly Ni-rich NCM materials undergo severe structural and mechanical changes, which adversely affect their cycling stability. In this respect, NCM-811 (Li1+δ[Ni0.8Co0.1Mn0.1]1-δO2) is currently one of the most Ni-rich NCM materials with proven cycling stability.3 In this work, we study the structural processes in NCM-811 over the course of 1000 cycles, cycled at a C-rate of C/2 until 4.5 V vs. Li+/Li in a pouch-cell setup at the Diamond Light Source (see Figure 1a). By means of in-situ synchrotron X-ray powder diffraction, the structural evolution of NCM-811 was monitored in regular intervals both in the completely charged and discharged state (under open circuit voltage conditions). As the lattice parameter ratio, c/a, directly correlates with the lithium amount, xLi, in the bulk material,4,5 the application of a calibration curve, xLi = f(c/a), allows for monitoring the effective capacity window of the NCM-811 CAM during cycling, and thus for clarifying the observed electrochemical capacity loss (ΔCEC, see Figure 2b). Due to an increasing cathode overpotential, the accessible capacity determined by XRD analysis becomes smaller within the fixed potential cut-offs both in the charged (ΔCcharge) and discharged state (ΔCdischarge). As the sum of these two loss terms, ΔCXRD, does not reach the actual capacity loss, ΔCEC, some fraction of the NCM-811 material has to be entirely lost during cycling (see Figure 1c). By using additional techniques such as electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy, this material loss can be assigned to a nm-thick, resistive surface layer around the primary particles. This resistive layer is in turn responsible for the observed overpotential losses. In contrast to the surface layer, the bulk material turned out to be stable, with a constant Ni disorder of ≈3% on the Li layer over 1000 cycles. For this reason, we think that future research on Ni-rich materials has to make substantial progress in controlling and stabilizing their surface properties. Figure 1: NCM-811/pre-lithiated graphite pouch-cells cycled at the Diamond Light Source over 1000 cycles at C/2 and ≈22°C in the potential window of 3.0-4.5 V vs. Li+/Li (cathode potential controlled vs. Li reference-electrode). (a) Discharge capacity of two cells. (b) Comparison of the observed electrochemical capacity loss and the losses determined by XRD analysis relative to the 18th cycle, illustrated for cell 1. (c) Absolute material loss under these cycling conditions relative to the pristine state for both cells (accounting to ≈2 mAh/g already in the 18th cycle). Acknowledgements: We want to acknowledge BASF SE for the support within the frame of its scientific network on electrochemistry and batteries. We also thank the Diamond Light Source for access to beamline I11 (Beamtime Award EE16866).

Experimental investigations on the rut resistant surface layer with Inclusion of Marble Dust and Sisal Fibers

Abstract Fibres are broadly used to redesign the execution of the bituminous blends. Marble dust is delivered as a waste by the forming of marble blocks. Marble dust is utilised as the replacement of filler, which is used in the midpoint gradation. In this paper, an investigation has been made to analyze the utilization of sisal fibres and marble dust to enhance the performance of asphalt concrete mix. The effects of inclusion of sisal fibre at a length of (5 mm) at five different percentages (0.1%, 0.2%, 0.3%, 0.4% and 0.5% by the weight of aggregates) and addition of marble dust as a filler at respected weights at different percentages. Optimum Bitumen Content (OBC) is based on Marshall Mix design with midpoint gradation. By Marshall Stability, we have calculated VMA, VFB, flow and air voids in the bituminous blends were researched and following tests were performed; indirect tensile strength (IDT), rutting characteristics of hot mix asphalt and Modified bituminous mix are identified and examined at OBC by using immersion type of wheel tracking device. The fibre length of 5 mm at a percentage of (0.3%) by weight of aggregate with an optimum bitumen content of 5.5% by weight of blend apparently provided better execution. Based on laboratory research, it is concluded that the sisal fibre Modified bituminous blend is a superior blend then the traditional hot mix asphalt as far as Marshall Properties, Indirect tensile strength, and rutting characteristics.

Editors' Choice—Capacity Fading Mechanisms of NCM-811 Cathodes in Lithium-Ion Batteries Studied by X-ray Diffraction and Other Diagnostics

Ni-rich layered oxides, like NCM-811, are promising lithium-ion battery cathode materials for applications such as electric vehicles. However, pronounced capacity fading, especially at high voltages, still lead to a limited cycle life, whereby the underlying degradation mechanisms, e.g. whether they are detrimental reactions in the bulk or at the surface, are still controversially discussed. Here, we investigate the capacity fading of NCM-811/graphite full-cells over 1000 cycles by a combination of in situ synchrotron X-ray powder diffraction, impedance spectroscopy, and X-ray photoelectron spectroscopy. In order to focus on the NCM-811 material, we excluded Li loss at the anode by pre-lithiating the graphite. We were able to find a quantitative correlation between NCM-811 lattice parameters and capacity fading. Our results prove that there are no considerable changes in the bulk structure, which could be responsible for the observed ≈20% capacity loss over the 1000 cycles. However, we identified the formation of a resistive surface layer, which is responsible for (i) an irreversible loss of capacity due to the material lost for its formation, and (ii) for a considerable impedance growth. Further evidence is provided that the surface layer is gradually formed around the primary NCM-811 particles.

Unveiling the Intrinsic Cycle Reversibility of a LiCoO2 Electrode at 4.8-V Cutoff Voltage through Subtractive Surface Modification for Lithium-Ion Batteries.

The thermodynamic instability of the LiCoO2 layered structure at >0.5Li extraction has been considered an obstacle for the reversible utilization of its near theoretical capacity at high cutoff voltage (>4.6 V vs Li/Li+) in lithium-ion batteries. Many previous studies have focused on resolving this issue by surface modification of LiCoO2, which has proven to be effective in suppressing phase transformation. To determine the extent to which surface protection of LiCoO2 is effective despite its thermodynamic instability and presumably incomplete reversibility involving the O1 phase, here we verify the intrinsic reversibility of bulk LiCoO2 with extended lithium extraction by ruling out the effect of a surface. Specifically, first, we show that, contrary to conventional belief, electrochemical cycling of LiCoO2 at a cutoff voltage of 4.8 V (vs Li/Li+) results in better cycle stability and lower polarizations than those at 4.6 V. We demonstrate, using an exhaustive suite of characterization tools, that the rapid cycle degradation under high-voltage cycling is mostly caused by the formation of a surface resistive layer; however, these damaged surfaces are leached out faster than they are accumulated above a certain potential, which results in superior cyclability compared with that achieved for less oxidative 4.6-V cycling. This beneficial leaching out of the resistive surface layer serves as a "subtractive" surface modification and plays a role in enhancing the cycle stability and is distinguished from conventional "additive" surface modification such as coating. This approach allows us to decouple factors of the bulk and surface degradations that contribute to the capacity fade and leads to the finding that, in the absence of a resistive surface, the capacity retention of a LiCoO2 electrode with 4.8-V cutoff cycling can be intrinsically high, indicating that the instability of the crystalline Li xCoO2 ( x < 0.5) has a limited effect on the cycle stability. Our findings also explain why the strategy of coating foreign materials on the surface of LiCoO2 can improve the high-voltage cycling to some extent despite the expected thermodynamic instability of the highly charged phase.

Characterization of Fe–C–Cr Based Hardfacing Alloys

Hardfacing is one of the adaptable methods that can build up the hard and wear resistant surface layer of different materials on the surface of substrate material. It helps them withstand wear, as well as prevent corrosion and high temperature oxidation. In the present investigation three different types of Fe–C–Cr based hardfacing electrodes with varying chemical compositions were deposited on ASTM A36 steel substrate by using manual metal arc welding (MMAW) process. ASTM A36 steel was selected as a base material after consulting with Pressure and Process Boilers, Saharanpur (India), which is a leading manufacturer of boilers. ASTM A36 steel is mostly used by this company for the production of induced draft fans. MMAW process with direct current constant current type power source was used to deposit the hardfaced layers of uniform quality. Straight polarity was used for MMAW process so that more of the arc heat should be concentrated on the electrode. The hardfaced samples were characterized using various characterization techniques and the results of the same were also outlined in the present investigation.

A Broadband Compatible Multispectral Metamaterial Absorber for Visible, Near‐Infrared, and Microwave Bands

AbstractA design of a compatible multispectral metamaterial absorber with broadband and strong absorption in the microwave, visible‐light, and near‐infrared bands is presented based on conductive carbon black (CCB)‐filled polyethylene (PE) composite films. The CCB‐filled PE composite films are employed to not only attenuate the light energy for realizing visible and near‐infrared absorbers, but also provide a conductive film to construct resistive metamaterial surfaces for realizing a microwave absorber. Considering the two natural properties of the composite films, light attenuation property and electric property, a multilayered structure based on resistive metamaterial surfaces is designed to realize a broadband compatible absorber. These resistive metamaterial surface layers are realized by the prepared composite films. The effect of different resistances of resistive metamaterial surfaces, polarization, and incident angles on the microwave absorbing performance is also analyzed in detail. Finally, a compatible multispectral absorber with a total thickness of 17 mm (0.133λmax) is fabricated and measured. Simulated and measured results both show that the presented absorber can achieve an absorption of 96.8% over a frequency range from 2.35 to 18 GHz. On the other hand, a high absorption of about 95% is obtained in visible‐light and near‐infrared bands as well.

Application of the Green’s Function in Attenuation Factor to Solve the Status of Human Health on the Earth

The activity in the high-voltage environment is at risk of being injured by electric shock. The safety of personnel in and around electric power installations has been a prime concern. Specifically, this safety is generally in terms of the allowable touch and step voltages. These voltages are related to the ground resistance of human foot. In order to increase the safety of personnel, a high resistivity surface layer of gravel normally exists in the substation switchyards or other high-voltage areas. The thickness of this layer will affect the calculation of the ground resistance of human foot. Among them, the electromagnetic field and humidity factors are also considered in this paper. As a result, the surface layer of gravel can be used to reduce the earthing resistance of human foot. The equivalent model of human foot was modeled by the circular plate conductor in the past, which considered the beauty of the environment. Most of the transmission lines are in the surface, so the transmission line generated by the discrete current will affect the earthing resistance estimation. Thus, the proposed paper will consider the composition of the Green’s function which is the mathematical calculus popularized by the basic theorem of calculus. On the other hand, the damp ingredients and temperatures on the surface will also be considered in this paper. This paper researches into the proposed method for estimating the ground resistance of human foot and proposes an equivalent model for calculating the earthing resistance of human foot. A comparison of the method is also shown in this paper.

A novel functionally gradient Ti/TiB/TiC hybrid composite with wear resistant surface layer

Ti/TiB/TiC hybrid composite was processed by a novel one-step in-situ process using spark plasma sintering (SPS). KBF4, which was used as a boron precursor for the first time, reacted with Ti to form the TiB reinforcement insitu. Graphite foils were used on either side of the compact as a carbon source to produce TiC during sintering. Ti reacted with carbon and formed TiC on both the surfaces of the composite. The thickness of the TiC layer was found to be ∼50 μm. The microstructure of the composite was graded with ultrafine TiC on top, fine needles of TiB near the surface and coarser TiB whisker reinforced Ti (Ti-4Al-2Fe/TiBw) in the bulk. The grain size of Ti also varied from 1 μm near the surface to 12 μm in the bulk. The surface layer exhibited very high hardness to the tune of 20 GPa compared to 7 GPa of the bulk Ti-4Al-2Fe/TiB composite. The functionally gradient composite exhibited only mild wear with wear rate that was almost one order of magnitude lower than that of the bulk Ti-4Al-2Fe/TiBw composite. While there were abrasive grooves formed on the Ti-4Al-2Fe/TiB bulk composite, the hybrid composite showed almost nil wear damage under the same test conditions. The surface TiC layer thus acted as an effective protection against wear and tear.

An Investigation of Grounding Resistance Estimation of Human Body by Attenuation Coefficient

It is dangerous when human are working in and around the high voltage environments. The safety of personnel in and around electric power the installations has been a prime concern. Specifically, this safety is generally in terms of the allowable touch and step voltages. These voltages are related to the ground resistance of human foot. In order to increase the safety of personnel, a high resistivity surface layer of gravel is normally existed in the substation switchyards or other high voltage areas. The thickness of this layer will affect the calculation of the ground resistance of human foot. Among them, the electromagnetic field factors are also considered in this paper. As a result, the surface layer of gravel can be used to reduce the ground resistance of human foot. The equivalent model of human foot was modeled by the circular plate conductor in the past. This paper investigates the present methods for estimating the ground resistance of human foot and proposes an equivalent model for calculating the ground resistance of human foot. A comparison of the proposed model and present methods is also shown in this paper.

Mitigating oxygen loss to improve the cycling performance of high capacity cation-disordered cathode materials

Recent progress in the understanding of percolation theory points to cation-disordered lithium-excess transition metal oxides as high-capacity lithium-ion cathode materials. Nevertheless, the oxygen redox processes required for these materials to deliver high capacity can trigger oxygen loss, which leads to the formation of resistive surface layers on the cathode particles. We demonstrate here that, somewhat surprisingly, fluorine can be incorporated into the bulk of disordered lithium nickel titanium molybdenum oxides using a standard solid-state method to increase the nickel content, and that this compositional modification is very effective in reducing oxygen loss, improving energy density, average voltage, and rate performance. We argue that the valence reduction on the anion site, offered by fluorine incorporation, opens up significant opportunities for the design of high-capacity cation-disordered cathode materials.

Corrosion Behavior of Hard Boride Layer Produced on Nimonic 80A-Alloy by Gas Boriding

The gas boriding in N2–H2–BCl3 atmosphere was applied in order to produce a wear resistant surface layer on Nimonic 80A-alloy samples. The microstructure, microhardness and corrosion resistance of the boride layer were investigated. The produced layer consisted mainly of the compact boride zone (with average thickness 71 μm), including the mixture of nickel and chromium borides of high hardness (up to 1861 HV). In order to evaluate the corrosion behavior, the two methods of corrosion tests were used: potentiodynamic corrosion test in 5% NaCl solution and immersion corrosion test in a boiling solution of H2O, H2SO4 and Fe2(SO4)3. The results showed that gas boriding could provide the excellent corrosion resistance if the whole surface of a Nimonic 80A-alloy sample was covered by the continuous boride layer. Otherwise, as a consequence of selective boriding, the significant difference in electrochemical potentials caused an accelerated uniform corrosion of the base material.

Surface barrier layer effect in (In + Nb) co‐doped TiO2 ceramics: An alternative route to design low dielectric loss

AbstractGiant dielectric permittivity (ε′) with low loss tangent (tanδ) was reported in (In + Nb) co‐doped TiO2 ceramics. Either of electron‐pinned defect‐dipole or internal barrier layer capacitor model was proposed to be the origin of this high dielectric performance. Here, we proposed an effectively alternative route for designing low‐tanδ in co‐doped TiO2 ceramics by creating a resistive outer surface layer. A pure rutile‐TiO2 phase with a dense microstructure and homogeneous dispersion of dopants was achieved in (In + Nb) co‐doped TiO2 ceramics prepared by a simple sol‐gel method. Two giant dielectric responses were observed in low‐ and high‐frequency ranges, corresponding to extremely high ε′≈106‐107 and large ε′≈104‐105, respectively. After annealing in air, a low‐frequency dielectric response disappeared and could be restored by removing the outer surface of the annealed sample, indicating the dominant electrode effect in the initial sample. Annealing can cause improved dielectric properties with a temperature‐ and frequency‐independent ε′ value of ≈1.9 × 104 and cause a decrease in tanδ from 0.1 to 0.035. High dielectric performance in (In0.5Nb0.5)xTi1−xO2 ceramics can be achieved by eliminating the electrode effect and forming a resistive outer surface layer.

Magnetotelluric monitoring of hydraulic fracture stimulation at the Habanero Enhanced Geothermal System, Cooper Basin, South Australia

Magnetotelluric (MT) data were collected across the Habanero Enhanced Geothermal System project in the Cooper Basin, South Australia. A baseline regional MT survey consisting of two profiles was collected to delineate the pre-injection resistivity structure. Two dimensional inversions of the MT data reveal three main resistivity structures to a depth of 5 km. The low resistivity surface layer (about 1.5 km thick) is interpreted as poorly consolidated sediments of Lake Eyre and Eromanga Basins. Below the conductive layer, a zone with relatively high resistivity with thickness of 2 km can be correlated to consolidated Cooper Basin sediments. A high resistivity zone below depths of 3.5 km is interpreted as the hot intrusive granodiorite (granite) of the Big Lake Suite with low porosity and permeability. This deep structure is also related to the Habanero EGS reservoir. The second MT survey was conducted during stimulation of Habanero-4 well by Geodynamics Ltd, where 36.5 ML of water with a resistivity of 13 Ωm (at 25°C) was injected at a relatively continuous rate of between 27–53 L/s over 14 days at a depth of almost 4 km. Analysis of pre- and post-injection residual phase tensors for periods greater than 10 s indicate conductive fractures oriented in a N/NNE direction. Apparent resistivity maps also revealed that injected fluids possibly propagated towards N/NNE direction. This result is in agreement with the micro-seismic events with an area of 4 km2 observed during fluid injection, as well as orientation of pre-existing N-S striking sub-horizontal fractures susceptible to slip due to stimulation. The MT responses close to injection show on average 5% decrease in apparent resistivity at periods greater than 10 s. The main reasons for observing subtle changes in resistivity at Habanero EGS is the screening effect of the conductive thick sedimentary cover (about 3.6 km thick) and the presence of pre-existing saline fluids with resistivity of 0.1 Ωm (equivalent to salinity of 16.1 g/L at 240°C) in the natural fractures. Overall, the MT monitoring at Habanero EGS highlights the need for favourable geological settings to measure significant changes in resistivity in EGS reservoirs.

The erosion performance of cold spray deposited metal matrix composite coatings with subsequent friction stir processing

This study forms an initial investigation into the development of SprayStir, an innovative processing technique for generating erosion resistant surface layers on a chosen substrate material. Tungsten carbide – cobalt chromium, chromium carbide – nickel chromium and aluminium oxide coatings were successfully cold spray deposited on AA5083 grade aluminium. In order to improve the deposition efficiency of the cold spray process, coatings were co-deposited with powdered AA5083 using a twin powder feed system that resulted in thick (>300μm) composite coatings. The deposited coatings were subsequently friction stir processed to embed the particles in the substrate in order to generate a metal matrix composite (MMC) surface layer. The primary aim of this investigation was to examine the erosion performance of the SprayStirred surfaces and demonstrate the benefits of this novel process as a surface engineering technique. Volumetric analysis of the SprayStirred surfaces highlighted a drop of approx. 40% in the level of material loss when compared with the cold spray deposited coating prior to friction stir processing. Micro-hardness testing revealed that in the case of WC-CoCr reinforced coating, the hardness of the SprayStirred material exhibits an increase of approx. 540% over the unaltered substrate and 120% over the as-deposited composite coating. Microstructural examination demonstrated that the increase in the hardness of the MMC aligns with the improved dispersion of reinforcing particles throughout the aluminium matrix.

Use of High-Voltage Cyclic Voltammetry to Characterize Bulk and Interfacial Conduction Processes in Anodic Alumina Films

A high-voltage cyclic voltammetry method is introduced that enables separate determination both the bulk conduction kinetics of anodic films and kinetics associated with interface processes. The results confirm that ionic conduction in the oxide follows a high-field exponential dependence on the electric field with a field coefficient of approximately 33nm/V, consistent with reported values for barrier-type films formed in neutral solutions. The correlation of the pre-exponential current density with the incorporation level of different acid anions from the anodizing bath suggests that conduction is enhanced by anionic contaminants. Current densities associated with self-ordered pore formation in different solutions seem to be associated with a common narrow range of electric fields. The large size of the interface potential drop suggests that it derives from the elevated conduction resistance of an anion-contaminated oxide layer close to the solution interface. Such resistive surface layers are thought to be the source of compressive stress that drives oxide flow during self-organized pore formation.

Plasma and photon interactions with organosilicon polymers for directed self-assembly patterning applications

Silicon (Si)-containing block copolymers (BCPs) are promising candidates for directed self-assembly patterning applications and are able to access structures with critical dimensions less than 10 nm. Significant etch contrast between the blocks is required to integrate BCPs for patterning applications and form an initial topographical mask. For Si-containing BCPs, O2 plasma exposure can give high etch contrast between the blocks by forming a thin etch resistant silicon oxide (SiOx) surface layer from the Si-containing block. The authors have also found that H2 and N2/H2 plasmas can form etch resistant barrier layers from organosilicon polymers (OSPs). Photodegradation of the OSPs induced by H2 plasma-generated vacuum ultraviolet (VUV) photons initiates the formation of this etch barrier layer. Fourier transform infrared transmission spectroscopy measurements show enhanced VUV-induced degradation in polymers with higher Si content due to cleavage of the methylsilyl bonds (Si-CH3) and subsequent carbon depletion, leading to formation of an etch resistant Si-enriched surface layer. Furthermore, a dynamic photolysis model based on the dissociation of Si–Si and Si–CH3 bonds shows that higher Si content in the polymer implies deeper photon penetration. The authors conclude that higher VUV fluxes and higher Si content promote the formation of etch resistant surface barriers on the Si-containing block when dry developing Si-containing BCPs with H2-rich plasmas. Finally, plasma dry development of an aligned, Si-containing BCP with sub-10 nm domains is demonstrated using a N2/H2 plasma.