Entropy stabilized oxides (ESOs) are a new class of stable hybrids and single phase metal oxides made from multiple ions with material properties somewhere between the constituent oxides, or ...occasionally entirely new properties. One of the limitations of ESOs is their energy-intensive fabrication process, which has resulted in slow development and scale-up of new ESOs. In this work, we present a novel energy-efficient ESO synthesis method that uses the ability of carbonaceous materials to heat rapidly in response to radio frequency (RF) fields in 1–200 MHz range. Using carbon fibers and graphene as RF susceptors, synthesis of (Mg0·2Co0·2Ni0·2Cu0·2Zn0.2)O is achieved through RF-initiated combustion synthesis with heating rates of 203 °C/s at 20 W of input power. This method reduces the formation time of ESOs to less than a minute, allowing for much more efficient fabrication. The corresponding morphology and composition of the as-synthesized ESO-carbon fiber and ESO-graphene were studied using extensive spectroscopy and characterization. Additionally, single carbon fibers coated with ESO were tested for tensile strength and modulus; little change in mechanical properties was observed as compared to pristine fibers. This work opens an exciting frontier for the rapid synthesis of ESO-carbon composites using RF heating as a non-contact, rapid, and efficient manufacturing process.
Polymer parts often replace traditional metallic parts in load-bearing applications due to their high strength-to-weight ratio, with thermoplastics at the forefront. Conventional manufacturing ...processes rely on using fasteners or adhesives to hold composite assemblies together, but thermoplastics can be welded together. Ultrasonic welding is widely used but becomes challenging for complex geometries, and new parameters need to be developed for different polymers and specimen geometries. In this work, we developed a closed-loop welding machine that employs the recent discovery of radio-frequency (RF) heating of carbonaceous materials. The machine is successfully able to weld polylactic acid (PLA) coupons with graphitic RF susceptors at the bondline in less than 2 min and using less than 50 W of input RF power. We found that a higher areal density of the graphitic paint lowers the mechanical properties of the weld because the carbonaceous materials hinder polymer chain diffusion. A significant change was not observed in weld properties for welding pressure ranges between 0 and 0.3 MPa. However, increasing out-of-plane welding displacement increased the modulus and strength of the weld. This work provides an interesting new automated system for welding polymer composites using RF fields, with potential applications in various manufacturing industries.
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•Comparative study of flame, chemical, plasma surface treatment of CF-PEKK composites.•Plasma treatment significantly enhances CF-PEKK paint adhesion.•Plasma treatment resulted in the ...highest increment of oxygen functionality and increased wettability.•Flame and plasma treatments reduce CF-PEKK surface crystallinity.
Polyether ketone-ketone (PEKK) is a high-performance thermoplastic, and its fiber composites have various engineering applications. Fiber reinforced composites in long-term applications require a protective layer of coatings to avoid environmental degradation. In this work, the surface energy of carbon fiber-PEKK composites was modified by flame, chemical, and plasma treatments to improve paint adhesion. A detailed study was carried out to understand the physical, morphological, and chemical surface characteristics due to different surface treatments. We found through XPS that highly active surface functionalities (− C-Ȯ/−C = Ȯ) due to oxidation at the ketone/ether groups were for surface adhesion. In support of the enhanced surface functionality, we have also evaluated the wetting behavior of paint with respect to different treated surfaces using drop shape analyzer and found that the polar component of the surface free energy increased for all treatments compared to pristine. Surface crystallinity after surface treatment was assessed using XRD; flame and plasma showed reduced surface crystallinities (25.92 % and 38.18 %, respectively), compared to pristine (46.78 %), and yielded a good adherend for coatings. Surfaces with good wettability and functionalities show good adhesion between the paint and PEKK composites as found through adhesion tests following ASTM D3359. The findings demonstrate that plasma surface treatment outperformed flame and chemical treatments in terms of adhesion of the paint to the surface.
The performance of fiber-reinforced composites significantly relies on the microstructure and properties of the fiber–matrix interface. Escalating the aspect ratio of the fiber surface by coating ...with nanoparticles is a proven technique for improving the fiber/matrix adhesion. Subsequently, improved adhesion between epoxy and fiber, which is ascribed due to improved interfacial friction, chemical bonding, and resin toughening would enhance the interfacial strength of such laminated composites. Here, graphite nanoparticles were oxidized, and these charged particles were coated onto the carbon fibers (CFs) surface using ultrasonically assisted direct current electrophoretic deposition. Functionalization of the graphite nanoparticle upon oxidation was confirmed through dispersion analysis, Fourier transformed infrared spectroscope, thermogravimetric analysis, and field emission scanning electron microscope. The CFs fabrics were grafted with different sets of samples prepared by varying voltage and deposition time. The deposition of oxidized graphite nanoparticle over the CFs was authenticated through field emission scanning electron microscope. A transverse fiber bundle test was carried out to assess interfacial strength between CF and epoxy matrix. The transverse fiber bundle test strength is found 113% higher for CF coated with oxidized graphite nanoparticles at 50 V for 5 min compared to that of as-received sized CF composites. Field emission scanning electron microscopy analysis of transverse fiber bundle test fractures samples identified multiple crack propagation zone owing to the presence of graphite nanoparticle on CF.
Electronics are integral to modern life; however, at their end-of-life these devices produce environmentally hazardous electronic waste (e-waste). Recycling the ubiquitous printed circuit boards ...(PCBs) that make up a substantial mass and volume fraction of e-waste is challenging due to their use of irreversibly cured thermoset epoxies. We present a PCB formulation using transesterification vitrimers (vPCBs), and an end-to-end fabrication process compatible with standard manufacturing ecosystems. We create functional prototypes of IoT devices transmitting 2.4 GHz radio signals on vPCBs with electrical and mechanical properties meeting industry standards. Fractures and holes in vPCBs can be repaired while retaining comparable performance over more than four repair cycles. We further demonstrate non-destructive decomposition of transesterification vitrimer composites with solid inclusions and metal attachments by polymer swelling with small molecule solvents. We hypothesize that unlike traditional solvolysis recycling, swelling does not degrade the materials. Through dynamic mechanical analysis we find negligible catalyst loss, minimal changes in storage modulus, and equivalent polymer backbone composition across multiple recycling cycles. We achieve 98% polymer recovery, 100% fiber recovery, and 91% solvent recovery which we reuse to create new vPCBs without degraded performance. Our cradle-to-cradle life-cycle assessment shows substantial environmental impact reduction over conventional PCBs in 11 categories.
This article proposes a new junction barrier Schottky diode (JBSD) design based on P-GaN/N-Ga 2 O 3 heterojunction with faster switching characteristics and higher breakdown ability than the ...traditional two-terminal power switches. Calibrated models have been used for technology computer-aided design (TCAD) simulations of the proposed JBSD after a comprehensive review of various physical models and model parameters in the present literature. Analysis in terms of static and transient behavior for a varying proportion of PN area to the Schottky contact area (PN:SBD ratio) was looked upon for the JBSD. With the increase of PN:SBD ratio, the reverse voltage handling capability increased as expected, but the reverse recovery time and maximum reverse recovery current decreased. This might be counterintuitive initially, as with an increase in PN:SBD ratio, the PN behavior would dominate over SBD, and slower transient behavior is expected. However, due to redistribution of electric field and the reduction in depletion capacitance across the JBSD with increase in PN:SBD ratio, JBSD with PN:SBD ratio of 8 gives us a breakdown at 1890 V and a switching time of 9.72 ns. Furthermore, a comparison of the transient response with state-of-the-art SiC Schottky diode reveals the efficiency of the proposed structure in terms of reverse recovery parameters to be significantly better, translating to 7.4 times lower power losses at higher frequencies. Overall, the design and analysis presented here suggest the promising potential of P-GaN/N-Ga 2 O 3 vertical devices for high-voltage and fast switching applications.
Reduction of high dark current has been a challenge for high responsivity photodetector (PD). In this context, the present article demonstrates an ultralow dark current of Ga 2 O 3 -based deep ...ultraviolet (UV)-photodetectors (UV-PDs) with enhanced photoresponses by tailoring a p/n heterojunction. An n- Ga 2 O 3 /p-CuO quasi-heterostructure-based deep UV-PDs has been fabricated on a sapphire (0001) substrate using an inexpensive electrospraying technique. After Ga 2 O 3 deposition, platinum (Pt) electrodes (<inline-formula> <tex-math notation="LaTeX">\sim 50 </tex-math></inline-formula> nm) are fabricated as a metal-semiconductor-metal (MSM) device using sputtering. The device exhibits a very low dark current in the order of few fA <inline-formula> <tex-math notation="LaTeX">(6.94\times 10^{-14} </tex-math></inline-formula> A) at 5 V because of the enhanced depletion width at p/n heterojunction and Pt/ Ga 2 O 3 metal-semiconductor contacts, which provides a narrow path for free carriers to travel from one metal contact to other under dark condition. The depletion layers get thinner due to the absorption of UV-photons in the UV-illumination condition. Hence, the photogenerated carriers get a wider channel to get collected at Pt-electrodes. Thus, in addition to ultralow dark current, the device exhibits an extraordinary photodetection characteristics, such as a high responsivity (<inline-formula> <tex-math notation="LaTeX">\sim 6.33 \times 10^{3} \mathrm{AW}^{-1} </tex-math></inline-formula>), remarkable phototo-dark current ratio (<inline-formula> <tex-math notation="LaTeX">\sim 2.99 \times 10^{6} </tex-math></inline-formula>), very high detectivity (<inline-formula> <tex-math notation="LaTeX">\sim 4.44 \times 10^{14} \mathrm{mHz}^{0.5} \mathrm{~W}^{-1} </tex-math></inline-formula>), and exceptional external quantum efficiency of <inline-formula> <tex-math notation="LaTeX">\sim 3.1 \times 10^{6} </tex-math></inline-formula> % at 5 V.
