Structural Phase Change Research Articles

Effect of MWCNTs-OH on the mechanical properties of cement composites: From macro to micro perspective

This study is focused on elucidating the role and mechanism of hydroxyl-functionalized multi-walled carbon nanotubes (MWCNTs-OH) as a reinforcement material in cement-based composites. The dispersion of MWCNTs-OH within the cement composites was first assessed using Raman spectroscopy. Subsequently, SEM, FT-IR, TGA, XRD, and nano-indentation techniques were employed to investigate the structural transformation and phase changes occurring in the cement matrix upon incorporating MWCNTs-OH. The results reveal that MWCNTs-OH can significantly improve the macro-mechanical properties of cement composites by their capacity for pulling out, pore-filling, inducing multi-cracking, and promoting hydration. From a micro-perspective, observations of the micro-morphology demonstrate that MWCNTs-OH reinforces cement composites through crack-bridging and pull-out effects. Regarding the hydrated calcium silicate (C-S-H), the addition of MWCNTs-OH has a negligible impact on the ratio of low-density C-S-H (LD-CSH) to high-density C-S-H (HD-CSH). Moreover, the results obtained from FT-IR and XRD tests provide evidence that the bonding between MWCNTs-OH and the cement matrix is predominantly governed by physical interactions.

Improving the strength and maintaining good ductility of as-forged Ti6Al4V alloy by regulating the microstructural defects

Solution-aging treatment is a conventional method for enhancing the strength of titanium alloys contributed by the decomposition of metastable phases, like martensite. The traditional viewpoint suggests that the martensite transformation occurring after water quenching does not significantly contribute to the strengthening of titanium alloy and this perspective actually overlooks the high strength resulting from the high-density defects formed in the martensite microstructure due to rapid cooling. So, previous studies have not fully taken advantages of the excellent strengthening capability of martensite. This study adopted a technique which combined solid solution and incomplete aging treatment to control the decomposition behavior of martensite and as a result, the strength of the as-forged Ti-6Al-4V (TC4) alloy had been obviously improved and good ductility had been maintained. Furthermore, the changes of phase structure and microstructural defects in TC4 titanium alloy during solution and aging process have been detailly studied by XRD refinement, EBSD, and TEM. Specifically, the highest tensile strength increased by 28.8 % which could reach 1224 MPa, and the elongation at fracture could still remain at 13 %. The reason is as follows. The formation of martensite after water quenching led to a substantial increase in internal microstructural defects, which were partly retained during the subsequent aging process because of lower temperature and short aging time, and the remaining martensite and microstructural defects can help maintain high strength. What's more, a small part of defects disappeared during this incomplete aging process due to martensite decomposition and recovery, which was beneficial to ductility.

Enhanced the electrochemical performance of Ni-doped α-MnO2 prepared with one-pot process for supercapacitors

Poor capacitive behavior caused by low electronic conductivity and slow reaction kinetics is the main obstacle faced by the MnO2 electrode materials in current supercapacitors. Herein, the influence of Ni doping on the capacitive behavior of α-MnO2 synthesized by a low-cost and one-pot chemical coprecipitation method was investigated. During the doping process, the amount of Ni was increased from 0.05 mmol to 0.45 mmol in steps of 0.1 mmol. The structure and chemical composition of Ni-doped MnO2 (MnO2-Ni) were characterized by XRD, FTIR, SEM, EDS, and XPS. Comprehensive studies show that no change in the crystal phase structure of MnO2, while the decrease in the nanoparticle size and the increase in electronic conductivity by Ni doping, which improve the capacitive behavior of α-MnO2. With specific capacitance values increasing with increasing amounts of Ni up to a certain limit 0.25 mmol, the specific capacitance of 325.8 F/g was given by MnO2-Ni electrode at a current density of 0.5 A/g, which was nearly 1.72 times that of MnO2 electrode of 189.47 F/g. Moreover, the MnO2-Ni electrode showed excellent capacitance retention (112%) than the MnO2 electrode (109.5%) after 3000 cycles.

Polypyrrole-coated sodium manganate microspheres cathode for superior performance Sodium-ion batteries

P2-Na0.67Mn0.67Ni0.33O2 is a promising cathode material for sodium ion batteries (SIBs) due to its low cost, high theoretical capacity, and non-toxicity. However, it still suffers from unsatisfactory cycling stability mainly incurred by the Jahn-Teller effect of Mn3+ and electrolyte decomposition on the electrode/electrolyte interface. Herein, the P2-Na0.67Ni0.33Mn0.67O2@PPy (NNMO@PPy) composite applied as cathode materials for SIBs is obtained by introducing conductive polypyrrole (PPy) as coating layer on the P2-Na0.67Ni0.33Mn0.67O2 (NNMO) microspheres. Numerous physical characterization methods indicate that the PPy layer was uniformly coated on the surface of NNMO microspheres without change in phase structure and morphology. The PPy coating layer can alleviate Mn dissolution and effectively suppress the side reactions between the electrolyte and electrode during cycling. The optimal NNMO@PPy-9 with 9 wt% PPy delivers a high capacity of 127.4 mAh/g at the current density at 150 mA g−1, an excellent cyclic stability with high capacity retention of 80.5 % after 300 cycles, and enhanced rate performance (169.3 mAh/g at 15 mA g−1 while 89.8 mAh/g at 600 mA g−1). Furthermore, hard carbon (−)//NNMO@PPy-9 (+) full cell delivers a high energy density of 305.1 Wh kg−1 and superior cycling stability with 88.2 % capacity retention after 150 cycles. In-situ X-ray diffraction experiment and electrochemical characterization verify the highly reversible structure evolution and robust P2-type phase structure of NNMO@PPy-9 for fast and stable Na+ diffusion. This effective strategy of using conductive PPy as a coating layer may provide a new insight to modify NNMO surface, improving the cycling stability and rate capability.

Study of Phase Transformations and Interface Evolution in Carbon Steel under Temperatures and Loads Using Molecular Dynamics Simulation

Carbon steel materials are widely used in mechanical transmission. Under different temperature and pressure service conditions, the microscopic changes of stress and strain that are difficult to detect and analyze by experimental means will lead to failure deformation, thus affecting their operational stability and life. In this study, the molecular dynamics method is used to simulate the heating–cooling phase transition process of common carbon steel materials. Austenite transformation temperatures of 980 K (0.2 wt.%) and 1095 K (0.5 wt.%) are acquired which is determined by the volume hysteresis before and after transformation, which is consistent with the results of JMatPro phase diagram analysis. The internal stress state of the material varies between compressive stress and tensile stress due to the change of phase structure, and the dislocation characteristics during the phase transition period are observed to change significantly. Then, an α/γ two-phase interface model is constructed to study the migration of the phase interface and the change of the phase structure by applying a continuously changing external load. At the same time, the transition pressure of α→ϵ is obtained with a value of 37 GPa under three different initial loads showing the independence of the initial load and the historical path. Based on the molecular dynamics simulation and the phase diagram calculation of the carbon steel, the analysis method for the microstructure transformation and the stress–strain behavior of the phase interface under the external load can provide a reference for the design of microstructure and mechanical properties of alloy steel in the future.

Enhancing the corrosion resistance of mild steel coated zinc studies

In the presence of a newly created brightener, the zinc metal is coated on steel using the electro deposition process. Experiments using hull cells are used to optimize the settings and components of plating baths. Tafel Polarization and EIS techniques were used to conduct corrosion experiments, which made it possible to investigate the brilliant zinc coating's effective corrosion resistance. SEM and Reflectance spectroscopy both confirm that the bright zinc coating has modified surface morphology. XRD analysis is used to study and validate changes in crystallite orientation and phase structure. Electrochemical methods and theoretical molecular dynamic (MD) simulations were used to examine the interaction between Zn and the metal surface. FTIR spectroscopy has been used in blend investigations which impacts on the physical characteristics of polymer blends. The results of these research showed how novel brighteners can improve zinc deposits' brightness and corrosion resistance when applied to mild steel substrates.

Thermal steam treatment effect of metallic sodium nanoparticles for high-carbon, low permeability Domanic rocks

In a study aimed at exploring novel methods for enhancing hydrocarbon extraction from shale reservoirs, we conducted an experimental study to model the effects of thermal steam treatment on high-carbon, low-permeability Domanic shale in the presence of sodium metal nanoparticles. We characterized the mineral composition of the rock samples and evaluated the yield and quality of extracted hydrocarbons before and after treatment. Our results demonstrated an increase in extract yield with increasing treatment temperature. Notably, we observed a significantly augmented effect when we introduced sodium nanoparticles into the reaction system, enabling a 100 °C reduction in treatment temperature while maintaining comparable capabilities for extracting organic matter. It was found that the experimental products exhibited enrichment in saturated hydrocarbons, coupled with a decrease in resinous-asphaltenic substances. Within the saturated fraction, we observed a shift towards lighter alkanes and cycloalkanes (C12–C14). Moreover, it has been found that the highest yield of low molecular weight liquid hydrocarbons is acheived in the experiment involving sodium nanoparticles at 250 °C. Upon further increasing the temperature to 300 °C, we noted a decline in liquid hydrocarbon content, accompanied by an increase in gaseous hydrocarbons (C1–C4). Besides, thermal steam treatment substantially reduced the proportion of sulfur-containing aromatic compounds, such as alkylbenzothiophenes, dibenzo- and naphthothiophenes, in the aromatic fraction. The addition of sodium nanoparticles facilitated near-complete desulfurization of this fraction. Moreover, we observed a significant reduction in the total sulfur content of the extracted organic matter. Hydrothermal treatment in the presence of nanoparticles induced transformations in the kerogen structure and structural and phase changes in the mineral components of the shale.

Crystal Structure and Properties of Heusler Alloys: A Comprehensive Review

Heusler alloys, which were unintentionally discovered at the start of the 20th century, have become intriguing materials for many extraordinary functional applications in the 21st century, including smart devices, spintronics, magnetic refrigeration and the shape memory effect. With this review article, we would like to provide a comprehensive review on the recent progress in the development of Heusler alloys, especially Ni-Mn based ones, focusing on their structural crystallinity, order-disorder atoms, phase changes and magnetic ordering atoms. The characterization of the different structures of these types of materials is needed, where a detailed exploration of the crystal structure is presented, encompassing the influence of temperature and compositional variations on the exhibited phases. Hence, this class of materials, present at high temperatures, consist of an ordered austenite with a face-centered cubic (FCC) superlattice as an L21 structure, or body-centered cubic (BCC) unit cell as a B2 structure. However, a low-temperature martensite structure can be produced as an L10, 10M or 14M martensite structures. The crystal lattice structure is highly dependent on the specific elements comprising the alloy. Additionally, special emphasis is placed on phase transitions within Heusler alloys, including martensitic transformations ranging above, near or below room temperature and magnetic transitions. Therefore, divers’ crystallographic defects can be presented in such types of materials affecting their structural and magnetic properties. Moreover, an important property of Heusler compounds, which is the ability to regulate the valence electron concentration through element substitution, is discussed. The possible challenges and remaining issues are briefly discussed.

2D thermo-fluidynamic rotary model of an elastocaloric cooling device: The energy performances

Elastocaloric cooling has been considered a promising solid-state technology for cooling and heat pumping among the alternatives to vapor compression, at room temperature range. The technology is based on elastocaloric effect that is a thermophysical phenomenon occurring in materials like Shape Memory Alloys (SMA). The effect is detectable as a temperature change in the material if adiabatically subjected to a forcing field of mechanical nature. The latter provokes to the materials a stress that can derive from tension, compression, bending, torsion solicitations. As a result, the SMA experiments a structural phase change from austenite to martensite (coupled with heat addition) and temperature rise. Dually when the stress is removed, the SMA releases heat with a temperature decrease. In this paper the SUSSTAIN-EL rotary elastocaloric heat pump has been deeply investigated to test the energy performances while it works on open loop and closed loop, through a 2D numerical model based on the finite element method, for cooling and heating operation modes. The device employs a binary NiTi SMA as elastocaloric refrigerant and air as heat transfer medium. A wide set of working conditions has been considered like variable inlet mass flow rate, rotation frequency and thermal loads. The acquired results demonstrate that, both in open and closed loop, the prototype’s energy performances are promising and highly favourable for the intended macroscale collocation of the device.

Glutamic Acid Induced Proton Substitution of Sodium Vanadate Cathode Promotes High Performance in Aqueous Zinc‐Ion Batteries

AbstractLacking strategies to simultaneously address the narrow interlayer spacing, irreversible phase transitions, dissolution and electrical transport issues of vanadium oxides is restricting their application in aqueous zinc‐ion batteries. Herein, to address these challenges concurrently, an organic‐inorganic hybrid cathode is explored, HNaV6O16·4H2O‐Glu (HNVO‐Glu), through a guest material‐mediated NVO synthesis strategy utilizing glutamic acid (Glu) to induce Na substituted by proton and enable crystal transformation of Na2V6O16·3H2O (NVO). Specially, Glu insertion kills three birds with one arrow: i) induces the formation of a structurally stable monoclinic HNaV6O16·4H2O phase by introducing H into the NVO framework, preventing structural phase change and collapse of NVO material; ii) acts as a pillar to expand the interlayer spacing, which improves the Zn2+ diffusion kinetics; moreover, the polar groups on the Glu surface weaken the electrostatic interaction between Zn2+ and the host materials, further enhancing the zinc‐ionic transport rate; iii) enhances the electrical conductivity of HNVO by converting the p‐type semiconductor into the n‐type semiconductor structure. Consequently, the HNVO‐Glu exhibits a high specific capacity (354.6 mAh g−1 at 1 A g−1), excellent Zn2+ diffusion capability (10−9 to 10−7 cm2 s−1) and outstanding cycling stability with a capacity retention of 87.2% after 12 000 cycles at 10 A g−1.

Enhancing the specific capacitance of α-MnO2 through quenching-induced changes in the crystal phase structure

The development of materials with high electrochemical performance as response to the energy demand leads to the development of methods for enhancing the specific capacity of energy storage devices, such as heat treatment, which is used to modify the structure and electrochemical performance of materials. This paper reports the enhancement of specific capacitance of α-MnO2 through the high-volume cell (HVC) induced by the quenching technique. Analysis of the transformation and structure of HVC was carried out by a combination of thermal gravimetric analysis and differential scanning calorimetry (TGA–DSC) in addition to X-ray diffraction (XRD), while the characterization of morphology, crystal structure, and capacitance were performed through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and cyclic voltammetry (CV). The α-MnO2 quenched at 437 °C promotes a structural modification that enables an increase in cell volume of 10.6% and an increase in specific capacitance of 20%. The quenching technique would be an attractive methodology to improve the electrochemical performance of materials for energy storage.

Characterization of electrical conductivity and dielectric properties of electroless NiP/rGO composite coated hemp fiber with various weight% of rGO and coating duration

The present study made an attempt to develop a conductive hemp fiber (HF) through an electroless Ni-P composite coating with reduced graphene oxide (rGO) as reinforcement. Four different Ni-P/rGO coated fibers were prepared with the variations in the coating time (20/40 min) and weight percentages of rGO (5/10 %). The coated fibers were characterized using various tools like: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field-emission scanning electron microscopy (FESEM), to identify the functional groups, phase structure, and morphological changes, induced by the rGO reinforcement. The coating duration and weight percentage of rGO had influenced the dielectric properties and electrical conductivity. In comparison, the coating duration of 40 min with 10 % addition of rGO has enhanced the electrical conductivity to 13.75 % and 37.5 % respectively. Furthermore, the mechanism behind the improvement in the conductivity is detailed in this study.

Solution-processed 2D van der Waals networks: Fabrication strategies, properties, and scalable device applications

Solution-based processing of two-dimensional (2D) materials has garnered significant interest as a facile and versatile route for the large-scalable production of 2D material films. Despite the benefits in process, these films were not considered suitable for device applications during the early stages of research because their electronic properties were far from those of 2D materials obtained through micromechanical exfoliation or chemical vapor deposition. Due to the small lateral dimensions and polydisperse thickness of constituent 2D nanosheets, the resulting film tends to be porous and exhibits numerous inter-sheet junctions, primarily contacting edge-to-edge. This nanosheet morphology leads to poor electrical conductivity of the network, and also hinders the film functioning as a semiconductor or an insulator. To produce ultrathin 2D nanosheets with narrow thickness distribution and large lateral sizes, various chemical exfoliation strategies have been explored, but these are limited by long process times, involvement of harsh chemicals, and/or undesired structural damage or phase changes. Recent breakthroughs in electrochemical exfoliation using tetraalkylammonium intercalants enabled the production of high-quality 2D nanosheets with structural characteristics favorable for producing ultrathin, conformal films of 2D materials, which allow for scalable production of high-performance electronic components that can readily be assembled into functional devices via solution-processing. In this review article, we aim to offer an extensive introduction solution-based processing techniques for acquiring 2D nanosheets, their subsequent assembly into thin films, and their diverse applications, primarily focusing on electronics and optoelectronics but also extending to other fields. Remaining challenges and potential avenues for advancement will also be discussed.

EBSD characterization of graphene nano sheet reinforced Sn–Ag solder alloy composites

This research explores the effects of incorporating Graphene Nano Sheets (GNS) on the microstructural characteristics and mechanical behavior of Sn–Ag solder alloys. The research was driven by the need for environmentally friendly, lead-free solder alloys with enhanced mechanical and thermal properties. The methodology involved incorporating graphene into the Sn–Ag alloy through stir casting, followed by a series of surface preparation techniques. The composite samples were then examined using EBSD to analyze crystallographic orientations and SEM/EDS for surface morphology and elemental composition. XRD provided insights into phase transformations and structural changes. Key findings reveal that the addition of GNS significantly refines the grain structure of the Sn–Ag alloy, leading to a bimodal grain size distribution. This refinement is attributed to the role of GNS as a nucleation site during solidification. Moreover, the study demonstrates a pronounced alteration in the texture of the material, with an increase in low-angle grain boundaries post-GNS addition. This texture change is indicative of enhanced mechanical properties. The results also show a shift in the orientation distribution function (ODF), suggesting a stronger crystallographic orientation due to GNS. These findings suggest that GNS incorporation could lead to improved mechanical and thermal properties in Sn–Ag solder, making them suitable for high-performance electronic applications. The study concludes that GNS not only serves as an effective reinforcement in Sn–Ag solder alloys but also significantly alters their microstructural and textural characteristics, contributing to the alloy's potential application in environmentally conscious electronic manufacturing.

Catalytic reduction of nitrogen monoxide using iron–nickel oxygen carriers derived from electroplating sludge: Novel method for the collaborative emission decrease of polluting gases

The valorization of electroplating sludge (ES) for high added value presents greater economic and environmental benefits than conventional treatment methods such as thermal processing, solidification, and landfill. Inspired by the mechanism of chemical looping combustion (CLC), this study developed a novel cost-effective method for denitrification by preparing FeNi-OCs from ES to achieve the synergistic reduction of CO and NO emissions. The phase structure, micromorphology, and valence state changes of the FeNi-OC catalyst during the CO-catalyzed reduction of NO and the pathway for catalytic denitrification using FeNi-OCs were analyzed. Results showed that CO could reduce FeNi-OCs to FeNi, and the reduced FeNi was subsequently oxidized back to FeNi-OCs by NO, a process analogous to CLC. During experiments, the simultaneous consumption of CO and NO gases was observed at 350 °C. This phenomenon was highly pronounced at 600 °C, where the CO and NO concentrations decreased from initial values of 8550 and 470 ppm, respectively, to 6719 and 0 ppm, respectively, with conversion rates of 21.41 % and 100 %, respectively. Hence, synergistic emission reduction was achieved. Further experiments also indicated that the addition of 1.5 % ES during iron ore sintering could substantially reduce the CO and NO concentrations in the sintering flue gas from 1268.32 and 244.81 ppm, respectively, to 974.51 and 161.11 ppm, respectively.

Characterization of FeCoNiCr high-entropy alloys manufactured by powder metallurgy technique

This study explores the phase constitution, thermal behavior, magnetic characteristics, and mechanical properties of FeCoNiCrCux high-entropy alloys (HEAs) produced via powder metallurgy, focusing on varying copper ratios (0–20%). The investigation seeks to understand how the introduction of copper influences the phase composition and properties of FeCoNiCr HEAs, particularly regarding changes in phase structure and mechanical behavior. The phase constitution was analyzed using field emission scanning electron microscopy (SEM) and X-ray diffraction (XRD). Thermal expansion and differential scanning calorimetry (DSC) were employed to study thermal behavior, while vibrating sample magnetometers (VSM) were utilized to assess magnetic properties. Mechanical properties were evaluated through hardness testing. The analysis reveals a shift in phase composition from a single-phase FCC structure to a dual-phase configuration comprising FCC and copper-rich FCC phases as copper content increases. Thermal and magnetic properties were characterized, demonstrating the alloy's behavior under varying conditions. Mechanical tests showed a decrease in hardness with increasing copper content. This study contributes to the understanding of how copper addition affects the phase constitution, thermal behavior, magnetic properties, and mechanical strength of FeCoNiCr HEAs. The observed changes in phase composition and mechanical properties offer insights for tailoring the properties of HEAs for specific applications.

The growth behavior and kinetics of intermetallic compounds in Cu–Al interface at 600°C–800 °C

Due to the low production cost and light weight, copper-clad aluminum conductors show great potential value in the field of power transmission, while the phase structure and organizational changes at the Cu–Al interface in high-temperature environments have a great impact on the electrical and mechanical properties. In this paper, Cu–Al diffusion couples are prepared to study the diffusion process, microstructure, and growth kinetics of intermetallic compounds (IMCs) in Cu–Al interface during heating from 600 °C to 800 °C, and the mechanical and electrical properties of Cu–Al diffusion couples are discussed. The results show that after heat treatment, IMC layers are formed at the Cu–Al interface and the Al-side is composed of CuAl and CuAl2, in which the CuAl phase transforms from long to thick dendrites with the increase of temperature, and finally grows into a “popcorn” form. The IMCs at the Cu–Al interface from the Cu side to the Al side are in the order of Cu3Al layer, Cu9Al4 layer, Cu3Al2 layer and CuAl layer, among which the Cu3Al2 layer is the thickest (168.42 μm at 700 °C), while the Cu3Al layer is the thinnest (37.32 μm at 700 °C). The kinetic calculations show that the diffusion layer grows up rapidly, which is caused by the generation of liquid-phase during the heating process, leading to the acceleration of the diffusion of Cu and Al. The kinetic factor of the Cu3Al2 layer is the largest (n = 0.69), causing the fastest growth rate of the Cu3Al2 layer, while the Cu3Al layer shows the largest activation energy for diffusion and the smallest diffusion rate (Q = 9.48 kJ/mol, D0 = 2.06 × 10−1 m2/s), therefore its growth rate is the slowest. Based on the thermodynamic calculations and the Cu–Al phase diagram, a growth mechanism of the Cu–Al interface is proposed, the formation sequence of IMCs at the Cu–Al interface is Cu9Al4, CuAl, Cu3Al2 and Cu3Al. The formation of IMCs layer at the Cu–Al interface leads to a significant increase in the hardness of Cu–Al samples (the hardness of the Cu3Al2 is 10 times higher than that of Cu) and an obvious decrease in electrical conductivity (the electrical resistivity of Cu–Al is 5 orders of magnitude higher than that of Cu), affecting its application in the electrical industry.

Improving multifunctional performance of Dy-doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics via tailoring Dy-doping amount and ceramic processing

[(Ba0.85Ca0.15)1-xDyx](Zr0.1Ti0.9)O3 (x mol% Dy-BCZT, x = 0.05, 0.2, 0.5, 1 and 3 mol%) multifunctional lead-free ceramics were prepared by traditional solid-state reaction method, where the influence of Dy doping amount and sintering condition was investigated. All sintered x mol% Dy-BCZT ceramics exhibit pure perovskite structure, large density, and high resistivity, which are affected greatly by Dy doping amount and sintering temperature. The phase structure changes from mainly tetragonal phase to pseudo-cubic phase with the increase of Dy doping amount, and presents irregular change on sintering temperature. Most samples have excellent dielectric, ferroelectric and stain, piezoelectric and fluorescent properties, which can be improved by changing Dy doping amount and tailoring sintering condition. Maximum piezoelectric-fluorescent coupling effect is obtained by selecting composition, optimizing Dy doping amount, and tailoring sintering condition due to morphotropic phase boundary effect and concentration quenching effect, which provides broad application prospect in the field of optoelectronics.

Structural phase transition and resistive switching properties of Cu x O films during post-thermal annealing

We studied the phase change and resistive switching characteristics of copper oxide (Cu x O) films through post-thermal annealing. This investigation aimed to assess the material’s potential for a variety of electrical devices, exploring its versatility in electronic applications. The Cu x O films deposited by RF magnetron sputtering were annealed at 300, 500, and 700 °C in ambient air for 4 min by rapid thermal annealing (RTA) method, and then it was confirmed that the structural phase change from Cu2O to CuO occurred with increasing annealing temperature. Resistive random-access memory (ReRAM) devices with Au/Cu x O/p+-Si structures were fabricated, and the ReRAM properties appeared in CuO-based devices, while Cu2O ReRAM devices did not exhibit resistive switching behavior. The CuO ReRAM device annealed at 500 °C showed the best properties, with a on/off ratio of 8 × 102, good switching endurance of ∼100 cycles, data retention for 104 s, and stable uniformity in the cumulative probability distribution. This characteristic change could be explained by the difference in the grain size and density of defects between the Cu2O and CuO films. These results demonstrate that superior and stable resistive switching properties of RF-sputtered Cu x O films can be obtained by low-temperature RTA.

Thermal activation and mechanical properties of high alumina coal gangue as auxiliary cementitious admixture

In order to use high alumina coal gangue as auxiliary cementitious admixture via a simple and convenient thermal activation technique, the thermal transformation, mineral phase transformation and structure changes of coal gangue at calcining temperatures of 500–1000 °C were analyzed using x-ray diffraction (XRD), differential thermal Analysis (DTA), thermogravimetry (TG), infrared analysis (IR) and scanning electron microscope (SEM). The mechanical properties of cement mortar with 30% coal gangue auxiliary cementitious admixture were also measured to determine the optimal calcining temperature. As calcining temperature was increased, the coal gangue experienced the following transformations: carbon combustion, dehydroxylation, metakaolin transformation and mullite transformation. The cement mortar with coal gangue auxiliary cementitious admixture calcined at 700 °C presented the highest 28-d flexural and compressive strength, increasing by 8.27% and 11.85% respectively as compared with the benchmark cement mortar. The maximum dosage of coal gangue auxiliary cementitious admixture in cement mortar was further identified to be less than 30% by mechanical properties testing. The activity of high alumina coal gangues at different calcining temperatures was explained from the view points of hydration degree and products. The present investigation can provide a useful reference to utilize high alumina coal gangue as auxiliary cementitious admixture by means of a simple thermal activation at 700 °C.