Polycrystalline diamond (PCD) compacts, made by conventional high pressure-high temperature (HPHT) technology, contain Co catalyst in inter-granular spaces causing degradation of PCD mechanical ...strength and thermal stability during rock cutting due to thermal expansion and graphitization. To solve this problem a catalyst-free synthesis of PCD based on HPHT sintering of fluorinated nanodiamond (FND) and submicron size aluminum mixtures was explored in the present work. The feasibility of using FND has been established by evaluation of phase stability of FNDs of 5, 10, and 90 nm sizes under industrially favorable P-T conditions (7.5–8 GPa, 1500–1700 °C) for PCD synthesis. It was found that surface fluorine slows down the graphitization of nanodiamond particles. Enlargement of diamonds from 5 and 10 nm up to a 10 μm has been observed for FND/Al systems. This phenomenon can be associated with the Wurtz-type reaction under the HPHT conditions leading to formation of inter-granular carbon‑carbon bonds between the nanoparticles and formation of the fluid Al-C-F phases in the samples volume, accelerating the mass transport and re-crystallization of nanodiamond. PCD samples sintered from mixtures of fluorinated micro-diamonds, nano-diamonds FND-90 and 3 wt% aluminum exhibited enhanced up to 1200 °C thermal stability and as high wear resistance as leached commercial PCD.
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•Nanodiamonds with fluorinated surface are highly resistant to graphite phase transition under HPHT conditions.•Enlargement of fluoro nanodiamond particles up to micron size during in situ Wurtz-type reaction with aluminum is discovered.•HPHT sintering of fluoro nanodiamond with aluminum increases the interfacial bonding in the polycrystalline diamond.•Materials with high thermo-mechanical properties can be produced from mixtures of fluorinated diamonds with aluminum.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
One of the most important problems in the development of proton exchange membrane fuel cells remains the selection of an efficient electrocatalyst support capable of providing a low loading of active ...metal with minimal changes in the electrochemical surface, electronic conductivity, and activity. In this work, carbon nanotube arrays (CNTAs) grown directly on commercial gas diffusion layers (GDLs) are used to form electrodes of a new type. The CNTAs are used in the electrode as a microporous layer. The catalytic layer is formed in the microporous layer by a method that does not destroy the carbon support structure and consists of the controlled impregnation of CNTAs with the Pt-precursor with subsequent reduction in platinum particles in the surface volume of the layer. The resulting electrode was studied by scanning/transmission electron microscopy and Raman spectroscopy. This electrode provides increased electrical conductivity of the layer and can also improve stability and longer service life due to the enhanced adhesion of carbon materials to the GDL.
Using neutron diffraction, Raman spectroscopy and HRTEM, we studied the effect of low deuterium concentrations (~2 at.%) on phase transformations at high temperatures (up to 1100 °C) and high ...pressure (8 GPa) of a mixture of amorphous C60/C70 fullerenes (50/50) and on the nanostructure, anisotropy and distortions of the amorphous-like graphite that forms at 800 °C from this mixture. It was also shown that deuterium contributes to the transformation of the mixture of amorphous-like fullerenes into amorphous-like and nanocrystalline graphite. It significantly changes the structure of the formed amorphous-like graphite, preventing the formation of graphite nanoclusters in it, reducing the distortion inherited from the mixture of amorphous-like fullerenes and changing the degree of anisotropy of this amorphous-like phase.
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•Transformations of amorphous С60/С70 mixture at high temperatures and pressures.•Acceleration of transformations with the introduction of D (2 at.%).•Anisotropy of amorphous graphite formed from a mixture of fullerenes.•Two types of graphite nanoclusters released in this amorphous graphite.•Prevention of the formation of graphite nanoclusters with the introduction of D.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Pt/C and Pt/x-SnO2/C catalysts (where x is mass content of SnO2) were synthesized using a polyol method. Their kinetic properties towards oxygen reduction reaction were studied by a rotating disk ...electrode (RDE) technique in a temperature range from 1 to 50 °C. The SnO2 content of catalyst samples was 5 and 10 wt.%. A quick evaluation of the catalyst activity, electrochemical behavior and average number of transferred electrons were performed using the RDE technique. It has been shown that the use of x-SnO2 (through modification of the carbon support) in a binary system together with Pt does not reduce the catalyst activity in the temperature range of 1–30 °C. The temperature rising up to 50 °C resulted in composite catalyst activity reduction at about 30%.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A complex study of the structure, morphology, and electrochemical properties of the Pt20/SnO210/RGO electrocatalyst is presented. The advantage of the chemical synthesis of reduced graphene oxide ...(c-RGO) compared to thermal methods (t-RGO) is due to the formation of graphene plates with amorphous carbon black agglomerates and the chemical composition of the surface. The nature of the interaction between platinum and tin dioxide particles and a conclusion about the formation of heterostructures Pt-SnO2 with the surface interaction of lattices excluding the formation of hetero phases has been established. This achieves high dispersity during the formation of platinum particles without significant agglomeration and increases the electrochemical surface area (ESA) of platinum to 85 m2 g−1 vs. carbon black. In addition, the surface interaction of particles and the formation of hetero-clusters Pt-SnO2 can cause the improved activity and stability of the Pt20/SnO210/c-RGO electrocatalyst.
Convolutional neural networks (CNNs) have been widely used in image recognition and processing tasks. Memristor-based CNNs accumulate the advantages of emerging memristive devices, such as nanometer ...critical dimensions, low power consumption, and functional similarity to biological synapses. Most studies on memristor-based CNNs use either software models of memristors for simulation analysis or full hardware CNN realization. Here, we propose a hybrid CNN, consisting of a hardware fixed pre-trained and explainable feature extractor and a trainable software classifier. The hardware part was realized on passive crossbar arrays of memristors based on nanocomposite (Co-Fe-B)x(LiNbO3)100−x structures. The constructed 2-kernel CNN was able to classify the binarized Fashion-MNIST dataset with ~ 84% accuracy. The performance of the hybrid CNN is comparable to the other reported memristor-based systems, while the number of trainable parameters for the hybrid CNN is substantially lower. Moreover, the hybrid CNN is robust to the variations in the memristive characteristics: dispersion of 20% leads to only a 3% accuracy decrease. The obtained results pave the way for the efficient and reliable realization of neural networks based on partially unreliable analog elements.
Parylene is a widely used polymer possessing such advantages as low cost and safety for the human body. Recently, several studies have been conducted showing that parylene can be used as a dielectric ...layer of memristors — new circuit design elements that are promising for the implementation of hardware neural networks. However, the mechanism of resistive switching of parylene-based memristors remains unclear. In this paper, we report the result of a comprehensive study of this mechanism for Metal/Parylene/ITO sandwich memristive devices. The obtained results clearly show that the origin of resistive switching in the devices is the formation of conductive metal bridges (filaments) from the top electrode (Cu, Ag or Al) to the bottom one (ITO). And furthermore, conductance quantization effect with both integer and half-integer multiples of the quantum of conductance G0 = 2e2/h has been observed in the samples, which also confirms the chosen switching model, and can be useful in the development of multilevel data memory cells.
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•Resistive switching in Metal/Parylene/ITO memristors is driven by the ECM mechanism.•Devices exhibit quantized conductance, including half-integer multiples of G0 = 2e2/h.•Parylene-based memristors are promising building blocks of neuromorphic systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We synthesized star-shaped pentagonal microcrystals of boron carbide with an extremely low carbon content (~5%), from m-carborane under high pressure (7 GPa) and high temperature (1370–1670 K). These ...crystals have five-fold symmetry and grow in the shape of stars. A 5-fold symmetry in large micron-sized crystals is extremely rare making this a striking observation.
We report on a comparative study of the performance level of H2/O2 PEM fuel cells in which the catalytic layers containing Pt nanoparticles were deposited on the microporous layer side of gas ...diffusion electrodes, using three different deposition techniques: (i) by magnetron sputtering, (ii) by impregnation followed by chemical reduction (using either ethylene glycol or hydrogen or sodium borohydride as reducing agent), and (iii) by spraying a catalytic ink (containing either Pt/C or bulk Pt particles). The microstructure and chemical composition of the different catalytic layers has been determined by SEM, TEM, XRD and XPS analysis. Their electrochemical surface areas have been determined by cyclic voltammetry. The i-V curves have been measured and compared. A durability stress test based on cycles of potential was used to assess the degradation rate of the different catalytic layers and to rank performance.
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•Ethylene glycol is the most effective Pt reducing agent for impregnation method.•Pt particles supported on microporous layers demonstrate improved durability.•A strong interaction between Pt active sites and carbon atoms is observed.•Pt particles supported on microporous layers and on carbon have similar structure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The present research deals with the adaptation of hydrogen-air fuel cells with proton exchange membrane (PEMFC) to autonomous periodic operation at subzero ambient temperatures. The main goal of the ...research is to limit the influence of subzero temperatures on component integrity and electrochemical performance stability of PEMFC in the cause of the freeze-thaw (F/T) cycling test. The MEAs stability in cycling from subzero (−35 °C) to operating temperature (+35 °C) was ensured without any specific preparatory operations modeling the PEMFC stop and “cold start” procedure. This is provided through the use of hydrogen-methanol compositions (no more than 4 vol % of methanol vapor) as fuel and a composite anode. Advanced membrane-electrode assembly (MEA) based on the composite anode layer (Pt40/C + Pt20/10 wt%–SnO2/C) for efficient and stable subzero operation during F/T cycling. High stability of electrochemical performance of the MEA with the composite anode at subzero ambient temperatures is shown. Advantages of use a two-component fuel PEMFC for autonomous periodic operation at subzero ambient temperatures are highlighted.
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•The hydrogen-methanol composition is applied as a fuel for cold start procedure.•Efficiency of two-component anode in methanol vapor oxidation has been proven.•Stability of fuel cell electrochemical performance at subzero temperatures is ensured.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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