Thermochemical Mechanism Research Articles

A novel molecular structure parameter determination method for biomass thermochemical conversion mechanism investigation

The low-grade energy properties and high O content of biomass limit its efficient energy utilization. Torrefaction is known to be one of the most promising thermochemical conversion methods for upgrading biomass. 250 °C Gas-pressurized (GP) torrefaction realizes deep decomposition of hemicellulose in biomass to as high as 99.7% by deoxygenation and aromatization. However, the above thermochemical conversion mechanism at molecular-level is currently scant. Here, a novel molecular structural parameter method and pure hemicellulose torrefaction were employed to investigate the thermochemical conversion mechanism. Results demonstrate that O content of 250 °C GP torrefied hemicellulose was as low as 28.8 wt%, which was considerably lower than 44.6 wt% of traditional torrefied hemicellulose. There are five deoxygenation mechanisms of hemicellulose during the GP torrefaction: deacetylation, decarbonylation, dehydroxylation, ring opening and cyclization reactions to produce CO2/CH3COOH, CO, H2O, ketones/aldehydes and furans. The deoxygenation and aromatization reactions cause the chemical structure of hemicellulose evolution significantly, these mechanisms are: active hemicellulose undergo aromatization reaction through cyclization and deoxidation to generate preliminary 2-ring furans polymer, followed by stepwise polymerization reactions to form 4-ring and 6-ring furans polymers. These polymerization reactions further greatly enhance deoxygenation reaction. A thermochemical conversion mechanism model is developed based on the above investigation. This work provides a novel method for determining the molecular structure and reaction mechanism of thermochemical converted biomass.

Understanding the Reversible Transition of Unipolar and Bipolar Resistive Switching Characteristics in Solution-Derived Nanocrystalline Au-Co3O4 Thin-Film Memristors.

Nanocrystalline Au-Co3O4 thin films were fabricated through a facile solution-processing method, and voltage-polarity-dependent resistive switching (RS) characteristics including variability of Set/Reset voltages, stability of cycling endurance, and carriers transport mechanism were studied in the Pt/Au-Co3O4/Pt memory devices. The switching voltages of the Set and Reset processes in the bipolar RS memristors exhibited lower variability as compared to the unipolar resistance switching devices. Moreover, the switching performance of cycle-to-cycle endurance in bipolar mode had a smaller fluctuation than those of unipolar switching behavior. Based on the current-voltage curve fitting analysis, it was found that Ohmic-conduction behaviors dominated the carriers transport of low-resistance state regardless of unipolar or bipolar switching behaviors. The carrier transport of high resistance state was governed following Poole-Frenkel emission and Schottky emission mechanisms in the unipolar and bipolar switching modes, respectively. The physical switching mechanism of Pt/Au-Co3O4/Pt memory devices was proposed using the model by means of growth and disruption of conducting filaments, involved in memory effects of thermochemical mechanism and valence change mechanism in the unipolar and bipolar RS, respectively. The proposed model following the finite element method revealed the roles of electrical field distribution and temperature gradient to further clarify the RS mechanism. Our results open a door for understanding and optimizing oxide-based thin-film resistance switching memory devices.

Experimental study on thermochemical composite flooding mechanism of extra heavy oil reservoirs with erosion channels

Experimental study on thermochemical composite flooding mechanism of extra heavy oil reservoirs with erosion channels

Experimental and numerical investigation on thermochemical erosion and mechanical erosion of carbon-based nozzles in hybrid rocket motors

In order to enhance energy characteristics of propellants in hybrid rocket motors, aluminum particles are added into the solid fuel. However, these particles may lead to nozzle mechanical erosion, which significantly affects the motor performance. This paper intends to study thermochemical and mechanical erosion mechanism of carbon-based nozzles in hybrid rocket motors with aluminum metallized fuel. A firing test is performed, and 95 % hydrogen peroxide and hydroxyl‑terminated polybutadiene based fuel with aluminum particles are utilized. Experimental results show that many metal particles are ejected from the nozzle, and aluminum oxide deposits heavily on the nozzle inner surface. A method of numerical calculation coupled with two-phase flow, combustion of aluminum metallized fuel, thermochemical ablation reactions, and mechanical erosion is established. The errors of combustion chamber pressure and throat erosion rate between numerical calculation and test results are 0.53 % and 7.76 %, respectively. Simulation results indicate that with the increase of aluminum content, nozzle wall pressure gradually increases, while the mass fraction of H2O, CO2, OH, and O declines. The nozzle wall temperature and thermochemical erosion rate raise first and then reduce as aluminum content increases. The mechanical erosion is mainly distributed in the convergent section, and it raises with the increase of aluminum content. When aluminum content is up to 38 %, the maximum mechanical and thermochemical erosion rates are 0.09185 mm/s and 0.0976 mm/s, respectively. This reveals that effects of mechanical erosion on hybrid rocket nozzles should be carefully considered and evaluated under conditions of high aluminum content.

Young KREEP-like mare volcanism from Oceanus Procellarum

The Moon’s mare volcanism predominantly occurs within the Procellarum KREEP Terrane (PKT), which is widely thought to be associated with KREEP components within the lunar interior. The Chang’e-5 (CE-5) mission sampled a young (2 Ga) mare basalt Em4/P58 unit of northern Oceanus Procellarum. The geochemistry of the CE-5 mare basalt enables assessment of mantle source compositions which are essential to understand the thermo-chemical mechanism for prolonged volcanism during secular cooling of the Moon. Geochemical compositions of the CE-5 bulk soil, breccias, and basalt clasts from various depths within the drill core consistently display high concentrations of incompatible trace elements (ITE: ∼ 0.3 × high-K KREEP; ∼ 5 μg/g Th) with KREEP-like inter-element ratios, for example for La/Sm, Nb/Ta, and Zr/Y. Exotic impact ejecta, extensive magma differentiation (<70 % fractional crystallization) and significant assimilation of KREEP materials during magma transit and eruption cannot account for the ITE contents and ratios or radiogenic isotope compositions (e.g., εNdinitial of + 8 to + 9 and εHfinitial of + 40 to + 46) of the CE-5 basalts; instead, partial melting of their mantle source played a dominant role. The Chang’e-5 basalt is a chemically evolved low-Ti mare basalt (Mg# of ∼ 34) with enriched KREEP-like ITE compositions but high long-term time-integrated Sm/Nd and Lu/Hf ratios, which represent a hitherto unsampled type of mare basalt. It formed by melting of an augite-rich mantle source (late-stage magma ocean cumulates containing > 30–60 % augite, and little or no ilmenite), with a small amount of late-stage interstitial melt that resembles KREEP (∼1–1.5 modal %, equivalent to 0.2–0.3 μg/g Th in the mantle source). The voluminous mare basalts making up the Em4/P58 unit (>1500 km3) provide compelling evidence for large-scale, ITE enriched young mare magmatism within Oceanus Procellarum. In combination with remote sensing data and with the unique Th-rich Apollo 12 basalt fragment 12032,366–18 (impact ejecta likely from Oceanus Procellarum), this implies that significant portions of the FeO- and Th-rich mare regions of the western PKT may also have formed in a similar way.

Thermal chemistry and decomposition behaviors of energetic materials with trimerizing furoxan skeleton

AbstractTrimerizing furoxans are ideal molecular skeletons for the construction of high energetic substances due to their compact structures and high enthalpy of formations. To explore and compare the thermal behaviors of energetic materials with tandem trimerizing furoxan molecular skeleton, we reported the first systematic research on the thermochemical behaviors and decomposition mechanism of 3,4‐bis(3‐fluorodinitromethylfuroxan‐4‐yl)furoxan (BFTF), 3,4‐bis(3‐cyanofurazan)furazan oxide (BCTFO) and benzotrifuroxan (BTF). According to the research results of the DSC‐TG experiments, both the substituted furoxan based energetic compounds (BCTFO and BFTF) exhibited low melting points and complicated thermal decomposition behaviors around 240 °C, while the melting point of unsubstituted furoxan (BTF) was much higher. Their detailed decomposition mechanisms were proposed based on the experimental results through tandem techniques including in‐situ FTIR spectroscopy method and DSC‐TG‐FTIR‐MS quadruple technology, which indicated that the cleavage of substituent would trigger the decompositions of BFTF and the decomposition of trimerizing furoxan skeletons almost synchronous occurrence with substituents in BCTFO. The self‐oxidation‐reduction of the linear and annular trimerizing furoxans lead to similar decomposition fragmented small molecule products.

Resource utilization of semi-dry flue gas desulfurization ash by thermal treatment on sintering machine

Semi-dry flue gas desulfurization ash (SFGDA) is an abandoned Ca and S resource that is currently stacked without appropriate disposal methods. A technology with industrialization potential, SFGDA, and iron ore thermal processing is an effective approach to obtaining calcium ferrite and industrial sulfuric acid. This study investigated the thermochemical reaction mechanism of SFGDA during high-efficiency pyrolysis employing Fe2O3 and coke powder for self-heating. The results showed that the addition of coke powder enhanced the thermal efficiency and reduced the decomposition temperature, while the reaction is accelerated by the lightning-fast combination of Fe2O3 with the CaO produced during pyrolysis to generate calcium ferrite products. The optimal conditions were determined to be a coke powder dosage of 10% and Fe2O3 dosage of 50%. In semi-industrial experiments, the SFGDA achieved a desulfurization rate of 99% and a calcium ferrite content of 85%. The calcined product CaO from CaSO4 and CaSO3 in the form of calcium ferrite products, with a minimal amount of CaSO4. In addition, during the high-temperature calcination process performed by the sintering machine, the majority of the sulfur within the raw materials migrates as SO2 and is subsequently emitted into the flue gas. Following, this SO2 is captured and utilized for the production of commercially valuable sulfuric acid. When the yield of enabled to calcined product corresponds to 1 ton, it could potentially dispose of 882 kg of SFGDA, culminating in a high-value, harmless, and large-scale SFGDA treatment in steel industry.

An environment-friendly strategy for recovery of α-PbO from spent lead paste: Based on the thermochemical reduction of PbO2 with ammonium sulfate

During the process of recycling lead from waste lead-acid batteries, how to minimize the wastage of chemical reagents and prevent secondary pollution is a significant research subject. In this study, a method for preparing α-PbO based on low-temperature thermochemical reduction of PbO2 was proposed. Using (NH4)2SO4 as the roasting agent, the purity of PbSO4 in spent lead paste was improved by reducing PbO2 at low temperatures. The thermochemical mechanism revealed that the thermochemical process consists of three different stages of (NH4)2SO4 decomposition and PbO2 reduction. The purity of PbSO4 in spent lead paste could be increased to 98.43 % by controlling the thermal reaction conditions (M (SO42−: TPb) molar ratio of 1:1, roasting temperature, and time of 340 °C and 1.5 h, respectively). Then, the desulfurization of PbSO4 with (NH4)2CO3 obtained PbCO3, and α-PbO with a purity of 96.87 %-98.57 % could be obtained by pyrolysis of PbCO3. Finally, 95.63 % of NH4+, 97.34 % of SO42−, and 77.71 % of CO32− could also be recovered for the regeneration of (NH4)2SO4 and (NH4)2CO3. This study provides a feasible technology for green recycling of spent lead paste.

Investigations on substituted Si-doped Mn2O3/Mn3O4 redox pair for thermochemical energy storage

Next-generation concentrated solar power plants with thermochemical energy storage can meet the demand for peak regulation and power supply, which stimulates the development and application of low-priced metal oxide thermochemical thermal storage materials. Mn-based composite metal oxide is a competitive candidate for large-scale applications given its character of being non-toxic, cheap, and highly efficient. However, the utilization of pure Mn2O3 suffers from sintering, which limits its re-oxidation and hence affects the applicability. In this study, Si is introduced to solve the above problems and improve the reaction characteristics of pure Mn2O3. (Mn1−xSix)2O3 is synthesized by substituent doping, with the best performance at x = 3 % and 5 %, reaching 96.18 % and 94.71 % of reduction conversion rate, respectively. The performance decay of the (Mn0.95Si0.05)2O3 sample was tested and evaluated, with reduction conversions of 90.92 % and 63.64 % after 50 and 300 cycles, respectively. A series of characterization results confirm that Si4+ is successfully doped into the Mn2O3 lattice, introducing defects into the crystal structure, which is favorable for the oxidation reaction. Density functional theory calculations of oxygen adsorption/dissociation and oxygen diffusion indicate that the doped Mn-Si oxides have lower reaction potentials and energies, which explains the promotion of the re-oxidation reaction by Si. By investigating the thermochemical energy storage properties and mechanism of Mn-Si composite metal oxides, we provide guidance for large-scale, cheap, and eco-friendly energy storage applications.

Material composition and microstructure of ceramic glass й hearth of blast furnace No. 6 of JSC EVRAZ NTMK after service. Refractory microstructure after service

The results of a comprehensive study of the material microstructure of refractory samples after service in the furnace of a blast furnace with a useful volume of 2200 m3 for 14 years are presented. Structural and genetic analysis established a characteristic sequence of processes of degeneration and wear of the ceramic furnace stack, including 6 stages: the formation of micro-and macro-cracks; condensation of vaporous zinc; zinc oxidation with the formation of fire-resistant ZnO zincite and the deposition of carbon black by the; chemical interaction of zinkite with mullite and corundum to form ZnAl2O4 ganite and 2ZnO·SiO2 willemite; partial oxidation of silicon carbide with the release of silica glass SiO2, eutectic melt of complex composition, and wellimite. Due to intensive accumulation of capillary pores, infiltration of the slag melt in the volume of refractories does not occur. Wear of refractories in the furnace has a complex, mainly thermochemical mechanism and a low speed due to the formation of a garnish containing refractory compounds. Ill. 5. Ref. 14.

Insight into the kinetics and thermodynamic analyses of co-pyrolysis using advanced isoconversional method and thermogravimetric analysis: A multi-model study of optimization for enhanced fuel properties

Waste management is quite challenging and it has become a major concern across the globe. The most common wastes are in the form of polymers or plastics that are composed of a mixture of various commodity plastics like PE, PP, PVC, HDPE, LDPE, etc. Pyrolysis is found to be a promising technology for managing wastes as well as converting them into valuable hydrocarbons. The present study investigated to discern the synergism in thermal degradation behavior and to identify the interaction between polymer molecules in co-pyrolysis. The advanced isoconversional model was employed for trustworthy estimation of activation energy as the thermal effects on a reaction deviate the temperature of a sample from the set heating value. The results were also compared with the model-free methods to understand the synergism, reactivity, and thermodynamic system with the progress of the conversion. The activation energy was found to be lowest when the polymers were used in a certain proportion and the synergy effect was more significant when PP content was > 40 % in the mixture. The positive synergetic effect could be attributed to the intermolecular hydrogen transfer from a less stable polymer to a free radical de-propagating chain of the other polymer during thermal degradation. The complex governing thermochemical reaction mechanism was determined using the Criado master plot and the analysis revealed that with increasing PP content in a binary mixture the reaction mechanism shifted from R2 to R3. The high regression coefficient value (R2 > 0.99) in the regenerated TGA profiles signified a good agreement between the theoretical and experimental results. While thermodynamic analysis showed that the process was endothermic and non-spontaneous in nature. Moreover, the radical reaction during co-pyrolysis of polymers enhances intermolecular hydrogen transfer resulting in the formation of iso-alkane and iso-alkene along with secondary radicals, which undergo β-scission to form alkenes/dienes and short primary radicals. As a result, the enhanced intermolecular hydrogen transfer phenomenon initiates the co-pyrolysis reaction at a relatively lower activation energy compared to individual polymer molecules.

Oriented conversion of spent LiCoO2-lithium battery cathode materials to high-value products via thermochemical reduction with common ammonium oxalate

Recycling critical metals from spent Li-ion batteries (LIBs) is essential for the overall sustainability of future batteries. This study presents a refined thermochemical reduction-assisted water leaching approach to efficiently recover lithium and cobalt from spent LiCoO2 LIBs using ammonium oxalate as the only reducing agent. Through thermochemical reduction, LiCoO2 was converted to Li2CO3 (water-soluble) and metallic Co (water-insoluble). After leaching with water, 99.63% lithium and 99.82% cobalt were obtained as Li2CO3 and metallic Co, with 99.74% and 98.95% purity, respectively. The thermochemical mechanism revealed that the thermochemical process consists of two different stages of ammonium oxalate decomposition and controlled reduction. High purity of metallic Co products can be acquired by regulating the amount of ammonium oxalate. These findings can inspire environmentally friendly and value-added recycling of metals from spent LIBs.

Benefits of Range-Separated Hybrid and Double-Hybrid Functionals for a Large and Diverse Data Set of Reaction Energies and Barrier Heights.

To better understand the thermochemical kinetics and mechanism of a specific chemical reaction, an accurate estimation of barrier heights (forward and reverse) and reaction energies is vital. Because of the large size of reactants and transition state structures involved in real-life mechanistic studies (e.g., enzymatically catalyzed reactions), density functional theory remains the workhorse for such calculations. In this paper, we have assessed the performance of 91 density functionals for modeling the reaction energies and barrier heights on a large and chemically diverse data set (BH9) composed of 449 organic chemistry reactions. We have shown that range-separated hybrid functionals perform better than the global hybrids for BH9 barrier heights and reaction energies. Except for the PBE-based range-separated nonempirical double hybrids, range separation of the exchange term helps improve the performance for barrier heights and reaction energies. The 16-parameter Berkeley double hybrid, ωB97M(2), performs remarkably well for both properties. However, our minimally empirical range-separated double hybrid functionals offer marginally better accuracy than ωB97M(2) for BH9 barrier heights and reaction energies.

Thermochemical Mechanism of Optimized Lanthanum Chromite Heaters for High-Pressure and High-Temperature Experiments

High-pressure heaters in large volume presses must reconcile potentially contradictory properties, and the whole high-pressure and high-temperature (HPHT) community has been engaged for years to seek a better heater. LaCrO3 (LCO)-based ceramic heaters have been widely applied in multianvil apparatus; however, their performance is far from satisfactory, motivating further research on the chemical optimization strategy and corresponding thermochemical mechanism. Here, we adopted a chemical-screening strategy and manufactured tubular heaters using the electrically, chemically, and mechanically optimized Sr-Cu codoped La0.9Sr0.1Cr0.8Cu0.2O3-δ (LSCCuO-9182). HPHT examinations of cylindrical LSCCuO-9182 heaters on Walker-type multianvil apparatuses demonstrated a small temperature gradient, robust thermochemical stability, and excellent compatibility with high-pressure assemblies below 2273 K and 10 GPa. Thermochemical mechanism analysis revealed that the temperature limitation of the LSCCuO-9182 heater was related to the autoredox process of the Cu dopant and Cr and the exchanging ionic migration of Cu and Mg between the LSCCuO-9182 heater and the MgO sleeve. Our combinatorial strategy coupled with thermochemical mechanism analysis makes the prioritization of contradictory objectives more rational, yields reliable LCO heaters, and sheds light on further improvement of the temperature limitation and thermochemical stability.

Deciphering high-efficiency solar-thermochemical energy conversion process of heat pipe reactor for steam methane reforming

The high temperature heat pipe reactor (HTPR) driven by solar energy via steam methane reforming opens up a new avenue to produce hydrogen as aviation fuel with low carbon emission. Herein, the energy conversion and transfer process of steam methane reforming in the HTPR was disclosed by experiments and simulations. Firstly, the solar to thermal conversion and the heat transfer process in the start-up stage of the HTPR were investigated. The solar thermal response was immediate, and the reactor temperature difference was merely about 30 °C from top to bottom, providing a uniform thermal boundary for the steam methane reforming reaction. Then, the thermochemical conversion performance of the HTPR was unveiled. Despite the uneven energy flux on the HTPR outwall, it still provided a uniform thermal boundary with a temperature of up to 750 °C because of its high thermal conductivity. Furthermore, the solar-thermochemical efficiency of the HTPR was about 41.0% after optimizing the operating parameters, surpassing that of the state-of-the-art solar thermochemical reactor. Finally, the heat loss of the HTPR and the heat transfer mode in the reactor cavity were analyzed. The radiation of the reactor outwall accounted for 44.5% of the total heat loss, and the thermal conduction was the major heat transfer mode in the cavity. This work deepens our understanding of the thermochemical conversion mechanism of the HTPR, paving the way for improving hydrogen yields.

Selective recycling of valuable metals from waste LiCoO2 cathode material of spent lithium-ion batteries through low-temperature thermochemistry

Efficient recycling of valuable metals from spent lithium-ion batteries (LIBs) with the minimized environmental footprint is prevailing among different recycling processes. However, the extensive energy consumption, associated with secondary contaminations, is one of the leading bottlenecks during thermochemical processing. Herein, low-temperature thermochemistry route was explored by thermal reduction using biomass wastes as reductants for selective recycling of valuable metals from spent LIBs based on their inherent conversion characteristics. It can be concluded from the experimental results that corn stalk exhibits better reducing capacity than saw dust and rice straw, and different metals in cathode materials (LiCoO2) of spent LIBs demonstrate different conversion pathways with the variation of reaction temperatures. Specifically, Li in waste LiCoO2 tends to be converted into Li2CO3 under reaction temperature range of 250–500 °C, while Co will mainly exist as CoO (400–600 °C) or Co (600–800 °C). Then, the converted product of Li2CO3 can be selectively extracted by water leaching, and CoO or Co will be subjected for mild acidic leaching or magnetic separation, respectively. Detailed characterizations and thermochemical mechanism suggest that the reduction reactions are mainly controlled by one-dimensional model and different products can be obtained through regulation of reaction temperature. This win–win tactics using biomass wastes with significantly reduced roasting temperature is expected to be high-efficiency, high-selectivity and pollutant-free process for spent LIBs recycling.

Thermomechanical activation achieving orthogonal working/healing conditions of nanostructured tri-block copolymer thermosets

Conventional thermosets, despite their technological significance in today’s materials economy, present a modern sustainability challenge because of their lack of end-of-life options for recyclability or reprocessability. Emerging covalent adaptable networks (CANs) offer sustainable alternatives to permanently crosslinked materials, but ideal orthogonal working/reprocessing conditions are hardly achievable by the current thermochemical activation mechanism. Here we report a CAN system of additive/catalyst-free, fully reprocessable, crosslinked, tri-block copolymer (tri-BCP) thermoplastic elastomer networks based on acid-anhydride bond exchange operated on a thermomechanical activation mechanism. The unique functionality of the tri-BCP architecture enables self-assembly into inter-linked, hexagonally packed cylinder nanostructures that preclude any productive inter-cylinder bond exchange (and, thus, creep) without cooperative thermal and mechanical (heating and compression) processing conditions. Tri-BCP assembly into additive-free, inter-linked hexagonally packed cylinder networks Healable crosslinked networks via thermomechanical-induced inter-domain bond exchange Working conditions restrict creep, establishing orthogonal working/healing behavior Clarke et al. show crosslinked tri-block copolymers with nanostructured networks, constructed by a catalyst/additive-free self-crosslinking and self-assembly process. Compared with analogous random and di-block copolymers, these crosslinked tri-block copolymers show not only superior mechanical performance but also much greater creep resistance when operated on a morphology-regulated and thermomechanical activation mechanism.

Thermochemical Mechanism of the Epoxy-Glutamic Acid Reaction with Sn-3.0 Ag-0.5 Cu Solder Powder for Electrical Joining.

An epoxy-based solder paste (ESP) is a promising alternative to conventional solder pastes to improve the reliability of fine-pitch electrical joining because the epoxy encapsulates the solder joint. However, development of an appropriate epoxy formulation and investigation of its reaction mechanism with solder powder is challenging. In this study, we demonstrate a newly designed ESP consisting of diglycidyl ether of bisphenol F (DGEBF) resin, Sn-3.0 Ag-0.5 Cu (SAC305) solder powder, and L-glutamic acid (Glu), which is a proteinogenic amino acid for biosynthesis of proteins in living systems. The mechanism of the thermochemical reaction was explored and tentatively proposed, which reveals that the products of the reaction between SAC305 and Glu function as catalysts for the etherification of epoxides and alcohols produced by chemical bonding between DGEBF and Glu, consequently leading to highly crosslinked polymeric networks and an enhancement of impact resistance. Our findings provide further insight into the mechanism of the reaction between various formulations comprising an epoxy, amino acid, and solder powder, and their potential use as ESPs for electrical joining.

Forced turbulence affected auto-ignition and combustion modes under engine-relevant conditions

Auto-ignition phenomena are paid more attention due to their close relation with abnormal combustions in advanced internal combustion engines. Previous investigations on intensive auto-ignition and knocking phenomena have been mainly conducted under standard flow conditions, whereas the role of turbulence is not fully clarified under engine-relevant conditions. In this study, forced turbulence affected auto-ignition and combustion modes were investigated in a novel rapid compression facility fueled with isooctane/air mixtures. In combination with instantaneous pressure acquisition, high-speed photography and infrared imaging were employed for auto-ignition initiation and reaction wave propagation. The combustion modes were comparatively investigated under standard flow and forced turbulence conditions. Experimental results show that standard flow scenarios are dominated by a thermo-chemical mechanism. With the elevation of intake pressure and thereby energy density, sequential auto-ignition induced normal combustion, end-gas auto-ignition induced mild knocking, and super-knock are observed in sequence, with obvious cool flame temperature rise and two-stage auto-ignition. Under forced turbulence conditions, the adiabatic core starts to be destroyed by the colder fluid from wall boundary layers, leading to lower temperatures and larger thermal stratifications. Such that prolonged auto-ignition timing, reduced burning rate, and attenuated cool flame are observed. Energy density plays an important role in strong knocking initiation, and there are some increases in the demarcation under forced turbulence conditions. However, mixture reactivity still plays the first-order significance in intensive auto-ignition and knocking formation. The current work helps to provide useful insights into the nature of auto-ignition and knocking combustion and the gaps between fundamental platforms and practical engines.

Facilitation of the thermochemical mechanism in NiO-based resistive switching memories via tip-enhanced electric fields

Transition metal oxides have attracted considerable attention as a switching material for resistive random access memory (RRAM) based on the thermochemical mechanism (TCM). However, the heat energy required for resistance switching is applied to the entire area of the RRAM without position selectivity, causing random growth of conductive filaments (CFs) and degrading device performance. This study showed that structured electrodes can promote the TCM in nickel oxide (NiO)-based RRAM by enhancing the electric field within the switching material and controlling Joule heat generation locally. Pyramid-structured electrodes with an extremely sharp tip prepared by the template-stripping method achieve an electric field in the tip region that is ∼5 times larger than that of conventional planar electrodes. The tip-enhanced electric field can induce a local temperature rise, which facilitates the TCM for nucleation and CF growth. The resulting RRAMs exhibit low and reliable forming, SET and RESET voltages (1.96±0.14V, 1.44±0.12V, and 0.64±0.05V, respectively). Moreover, their retention time and resistance ratio (RHRS/RLRS) are greatly improved, by 10 and 102 times, respectively, compared to planar devices. This approach can achieve position selectivity in TCM-based resistance switching, and could lead to the development of high-performance RRAM.