4 research outputs found
Investigation of the Scanning Microarc Oxidation Process
Scanning microarc oxidation (SMAO) is a coating process which is based on conventional microarc oxidation (MAO). The key difference is that deposition in SMAO is achieved by using a stainless steel nozzle to spray an electrolyte stream on the substrate surface as opposed to immersing the workpiece in an electrolyzer. In the present study, SMAO discharge characteristics, coating morphology, and properties are analyzed and compared to results obtained from MAO under similar conditions. Results show that MAO and SMAO have comparable spark and microarc lifetimes and sizes, though significant differences in incubation time and discharge distribution were evident. Results also showed that the voltage and current density for MAO and SMAO demonstrate similar behavior but have markedly different transient and steady-state values. Results obtained from coating A356 aluminum sheet show that oxide thickness and growth rate in SMAO are strongly dependent on interelectrode spacing and travel speed. Analysis of the SMAO coating morphology and structure showed that a denser and slightly harder layer was deposited in comparison to MAO and is attributed to reduced porosity and increased formation of α-Al2O3. Preliminary results indicate that SMAO represents a viable process for coating of aluminum surfaces
A compact ultra‐wideband bandpass filter with ultra‐fine conductor trace based on liquid crystal polymer substrates
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Oxygen Release Induced Chemomechanical Breakdown of Layered Cathode Materials.
Chemical and mechanical properties interplay on the nanometric scale and collectively govern the functionalities of battery materials. Understanding the relationship between the two can inform the design of battery materials with optimal chemomechanical properties for long-life lithium batteries. Herein, we report a mechanism of nanoscale mechanical breakdown in layered oxide cathode materials, originating from oxygen release at high states of charge under thermal abuse conditions. We observe that the mechanical breakdown of charged Li1- xNi0.4Mn0.4Co0.2O2 materials proceeds via a two-step pathway involving intergranular and intragranular crack formation. Owing to the oxygen release, sporadic phase transformations from the layered structure to the spinel and/or rocksalt structures introduce local stress, which initiates microcracks along grain boundaries and ultimately leads to the detachment of primary particles, i.e., intergranular crack formation. Furthermore, intragranular cracks (pores and exfoliations) form, likely due to the accumulation of oxygen vacancies and continuous phase transformations at the surfaces of primary particles. Finally, finite element modeling confirms our experimental observation that the crack formation is attributable to the formation of oxygen vacancies, oxygen release, and phase transformations. This study is designed to directly observe the chemomechanical behavior of layered oxide cathode materials and provides a chemical basis for strengthening primary and secondary particles by stabilizing the oxygen anions in the lattice
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Oxygen Release Induced Chemomechanical Breakdown of Layered Cathode Materials
Chemical and mechanical
properties interplay on the nanometric
scale and collectively govern the functionalities of battery materials.
Understanding the relationship between the two can inform the design
of battery materials with optimal chemomechanical properties for long-life
lithium batteries. Herein, we report a mechanism of nanoscale mechanical
breakdown in layered oxide cathode materials, originating from oxygen
release at high states of charge under thermal abuse conditions. We
observe that the mechanical breakdown of charged Li<sub>1–<i>x</i></sub>Ni<sub>0.4</sub>Mn<sub>0.4</sub>Co<sub>0.2</sub>O<sub>2</sub> materials proceeds via a two-step pathway involving intergranular
and intragranular crack formation. Owing to the oxygen release, sporadic
phase transformations from the layered structure to the spinel and/or
rocksalt structures introduce local stress, which initiates microcracks
along grain boundaries and ultimately leads to the detachment of primary
particles, <i>i.e.</i>, intergranular crack formation. Furthermore,
intragranular cracks (pores and exfoliations) form, likely due to
the accumulation of oxygen vacancies and continuous phase transformations
at the surfaces of primary particles. Finally, finite element modeling
confirms our experimental observation that the crack formation is
attributable to the formation of oxygen vacancies, oxygen release,
and phase transformations. This study is designed to directly observe
the chemomechanical behavior of layered oxide cathode materials and
provides a chemical basis for strengthening primary and secondary
particles by stabilizing the oxygen anions in the lattice