Real-Time Sensing of Output Polymer Flow Temperature and Volumetric Flowrate in Fused Filament Fabrication Process

In this paper we addressed key challenges in engineering an instrumentation system for sensing and signal processing for real-time estimation of two main process variables in the Fused-Filament-Fabrication process: (i) temperature of the polymer melt exiting the nozzle using a thermocouple; and (ii) polymer flowrate using extrusion width measurements in real-time, in-situ, using a microscope camera. We used a design of experiments approach to develop response surface models for two materials that enable accurate estimation of the polymer exit temperature as a function of polymer flowrate and liquefier temperature with a fit of 𝑅2=99.96% and 99.39%. The live video stream of the deposition process was used to compute the flowrate based on a road geometry model. Specifically, a robust extrusion width recognizer algorithm was developed to identify edges of the deposited road and for real-time computation of extrusion width, which was found to be robust to filament colors and materials. The extrusion width measurement was found to be within 0.08 mm of caliper measurements with an 𝑅2 value of 99.91% and was found to closely track the requested flowrate from the slicer. This opens new avenues for advancing the engineering science for process monitoring and control of FFF.

Graphene Oxide Interlayered in binder-free Sulfur Vapor Deposited Cathode for Lithium-Sulfur Battery

The main drawback of Lithium-Sulfur (Li-S) batteries which leads to a short lifetime, is the shuttle effect during the battery operation. One of the solutions to mitigate the shuttle effect is the utilization of interlayers. Herein, graphene oxide (GO) paper as an interlayer has been implemented between the sulfur cathode fabricated by the vapor deposition process as a binder-free electrode and a separator in a Li-S battery in order to gain a sufficient capacity. The morphological characteristics and electrochemical performance of the fabricated electrode have been investigated. The fabricated battery demonstrates an initial discharge capacity of 1265.46 mAh g-1 at the current density of 100 mA g-1. The coulombic efficiency is obtained to be 88.49% after 40 cycles. The remained capacity for the battery is 44.70% after several cycles at different current densities. The existence of the GO interlayer improves the electrochemical properties of the battery compared to the one with a pure sulfur cathode. The obtained results indicate that after 40 cycles, the capacity retention is 2.1 times more than that of the battery without the GO implementation.

Designing multifunctional CoOx layers for efficient and stable electrochemical energy conversion

Disordered and porous metal oxides are promising as earth-abundant and cost-effective alternatives to noble-metal electrocatalysts. Herein, we leverage non-saturated oxidation in plasma-enhanced atomic layer deposition to tune structural, mechanical, and optical properties of biphasic CoOx thin films, thereby tailoring their catalytic activities and chemical stabilities. To optimize the resulting film properties, we systematically vary the oxygen plasma power and exposure time in the deposition process. We find that short exposure times and low plasma powers incompletely oxidize the cobaltocene precursor to Co(OH)2 and result in the incorporation of carbon impurities. These Co(OH)2 films are highly porous and catalytically active, but their electrochemical stability is impacted by poor adhesion to the substrate. In contrast, long exposure times and high plasma powers completely oxidize the precursor to form Co3O4, reduce the carbon impurity incorporation, and improve the film crystallinity. While the resulting Co3O4 films are highly stable under electrochemical conditions, they are characterized by low oxygen evolution reaction activities. To overcome these competing properties, we applied the established relation between deposition parameters and functional film properties to design bilayer films exhibiting simultaneously improved electrochemical performance and chemical stability. The resulting biphasic films combine a highly active Co(OH)2 surface with a stable Co3O4 interface layer. In addition, these coatings exhibit minimal light absorption, thus rendering them well suited as protective catalytic layers on semiconductor light absorbers for application in photoelectrochemical devices.

Functional Role of Aramid Coated Separator for Dendrite Suppression in Lithium-Ion Batteries

The separator is an essential important key material in lithium-ion batteries (LIBs) because it is in contact with the positive and negative electrodes and the electrolyte. Aramid coated separators (ACS) are widely used in automotive and consumer batteries as high-performance separators for LIBs with high safety and excellent lifetime characteristics. Although much effort has been made to improve the electrolyte composition, the lithium deposition on the surface of the graphite electrode at low temperature and the high charge rate is still an unsolved problem in LIBs. In this work, lithium metal is used as a counter electrode, and a separator was placed between lithium metal and graphite composite electrode. The lithium was deposited on the surface of the graphite composite electrode through the separator. Then, the functional role of ACS in the initial deposition process was investigated. The dendrite blocking effect of ACS was studied by the observation of dendrite growth and pulse cycle performance.

Preparation of Very Thin Zinc Oxide Films by Liquid Deposition Process: Review of Key Processing Parameters

We used sol-gel and spin-coating in the original configuration of a liquid deposition process to synthesize particularly thin ZnO films (<100 nm) with nano-granular morphology, high grain orientation and variable optical properties. The concentration of the zinc salt, the concentration of the chelating agent, the nature of the solvent and the substrate material have been identified as key parameters that determine the microstructure of the deposited layer and thus its final properties. The thorough and practical examination of the effects of the synthesis parameters evidenced a three-step growth mechanism for these ZnO thin films: (i) a reaction of precursors, (ii) a formation of nuclei, and (iii) a coalescence of nanoparticles under thermal annealing. The growth of these very thin films is thus conditioned by the interaction between the liquid phase and the substrate especially during the initial steps of the spin coating process. Such thin ZnO films with such nano-granular morphology may be of great interest in various applications, especially those requiring a large active surface area.

Evaluation of Additive Friction Stir Deposition of AISI 316L For Repairing Surface Material Loss in AISI 4340

Additive technologies provide a means for repair of various failure modes associated with material degradation occurring during use in aggressive environments. Possible repair strategies for AISI 4340 steel using AISI 316L deposited by additive friction stir deposition (AFSD) were evaluated under this research by metallography, microhardness, and wear and mechanical testing. Two repair geometries were investigated: groove-filling and surface cladding. The former represents repair of localized grinding to eliminate cracks, while the latter represents material replacement over a larger area, for example to repair general corrosion or wear. The 316L deposited by AFSD exhibited a refined microstructure with decreased grain size and plastic strain, lower strength, and lower hardness than the as-received feedstock. Wear testing by both two-body abrasion and erosion by particle impingement indicated that the wear resistance of the 316L cladding was as good as, or better than, the substrate 4340 material; however, there was some evidence that the resistance to intergranular corrosion was compromised due to the formation of carbides or sigma phase. In both repair geometries, the microstructure of the substrate beneath the deposited material exhibited heat affected zones that appeared to have austenized during the deposition process, and transformed to martensite or bainite during cooling. This report constitutes an initial evaluation of a novel approach to the repair of structural steel components damaged by microcracking, wear or corrosion.

Investigation on Transparent, Conductive ZnO:Al Films Deposited by Atomic Layer Deposition Process

Transparent electrodes are a core component for transparent electron devices, photoelectric devices, and advanced displays. In this work, we fabricate fully-transparent, highly-conductive Al-doped ZnO (AZO) films using an atomic layer deposition (ALD) system method of repeatedly stacking ZnO and Al2O3 layers. The influences of Al cycle ratio (0, 2, 3, and 4%) on optical property, conductivity, crystallinity, surface morphology, and material components of the AZO films are examined, and current conduction mechanisms of the AZO films are analyzed. We found that Al doping increases electron concentration and optical bandgap width, allowing the AZO films to excellently combine low resistivity with high transmittance. Besides, Al doping induces preferred-growth-orientation transition from (002) to (100), which improves surface property and enhances current conduction across the AZO films. Interestingly, the AZO films with an Al cycle ratio of 3% show preferable film properties. Transparent ZnO thin film transistors (TFTs) with AZO electrodes are fabricated, and the ZnO TFTs exhibit superior transparency and high performance. This work accelerates the practical application of the ALD process in fabricating transparent electrodes.

New insights in polydopamine formation via surface adsorption

Polydopamine is a biomimetic self-adherent polymer, which can be easily deposited on a wide variety of materials. Despite the rapidly increasing interest in polydopamine-based coatings, the polymerization mechanism and the key intermediate species formed during the deposition process are still controversial. Herein, we report a systematic investigation of polydopamine formation on halloysite nanotubes; the negative charge and high surface area of halloysite nanotubes favour the capture of intermediates that are involved in polydopamine formation and decelerate the kinetics of the process, to unravel the various polymerization steps. Data from X-ray photoelectron and solid-state nuclear magnetic resonance spectroscopies demonstrate that in the initial stage of polydopamine deposition, oxidative coupling reaction of the dopaminechrome molecules is the main reaction pathway that leads to formation of polycatecholamine oligomers as an intermediate and the post cyclization of the linear oligomers occurs subsequently. Furthermore, Tris molecules are incorporated into the initially formed oligomers.