Heating Tests Research Articles

A simulation of Al-Si coating growth under various hot stamping austenitization parameters: An artificial neural network model

22MnB5 hot stamping steels are pre-coated with an Al-Si layer to prevent oxidation and decarburization during the austenitization process, which includes heating and soaking within a furnace. Above ∼577 °C, the Al-Si coating transforms into Fe-Al and Fe-Al-Si intermetallic phases because of diffusion and solidification. In the present work, a deep neural network (DNN) model was developed to predict coating intermetallic growth under various heating rates and soaking conditions. The DNN model was trained using experimental data (energy dispersive x-ray spectroscopy chemical scans) collected from our coating growth characterization work. The heating rate (r), heating time (th), soaking time (ts), and the distance of each measured point away from the coating surface (d) are defined as input parameters, and the outputs are the weight percentage of Al, Fe, and Si. The model successfully predicted the chemical composition of the training dataset, which consisted of a single-stage heating process, followed by a soaking stage at a constant temperature. To validate the model, complex two-stage heating tests were conducted, and the intermetallic coating growth was quantified. The DNN model successfully predicted the two-stage heating test coating profiles, despite a minimal error that was due to the variation in as-received coating thickness. The DNN model predicts the overall experimental trends that show the heating rate has little effect on the transformed intermetallic species, but it affects the transformation rate of the intermetallic phases. Moreover, the higher heating rate test (after 750℃) resulted in the formation of the island shaped τ1 and/or τ2 phase, while the heating rate before 750℃ does not affect the morphology of the τ1 and/or τ2 phase.

Comparative Evaluation of the Anesthetic Efficacy of Needle-Free Anesthesia and Conventional Anesthesia in Patients With Symptomatic Irreversible Pulpitis: A Randomized Clinical Trial.

Introduction Pain is the primary reason for which most of the patients seek endodontic treatment. Local anesthesia is considered to be the most important step in the procedure to reduce the pain. However, the majority of the patients do not cooperate due to the fear of syringe anesthesia. The aim of this clinical trial was to compare the anesthetic efficacy of needle-free anesthesia and conventional anesthesia in patients with symptomatic irreversible pulpitis undergoing root canal therapy. Materials and methods A total of 54 patients were enrolled in the study, and the treatment was administered by a single operator. The initial assessment of vitality included cold testing, heat testing, and electric pulp testing. Preoperative pain was assessed using the Visual Analog Scale (VAS) before the administration of anesthesia. Local anesthesia was administered according to the group assigned: Group 1 (conventional anesthesia) and Group 2 (needle-free anesthesia). The pain was assessed during the administration of anesthesia. Following the administration of anesthesia, the vitality of the tooth was evaluated using cold testing, heat testing, and electric pulp testing. Subsequently, the tooth was isolated with a rubber dam, and the access cavity was prepared. The pain was assessed during access cavity preparation and during the first file insertion. Working length was determined using an apex locator (Root ZX Mini, J Morita, Saitama, Japan) and was confirmed using intraoral periapical radiographs. Later on, further treatment was carried out. Results A total of 54 participants were included in this clinical trial. There was no significant difference in mean age distribution between the two groups (p=0.852). Considering the frequency distribution of gender, there was no significant difference; however, Group 1 had more female participants (59.3%) compared to Group 2 (33.3%). There was a significant reduction in the mean pain score in Group 2 compared to Group 1 during the delivery of anesthetic agents (p=0.000). Conclusion Needle-free anesthesia proves to be equally effective as the conventional syringe system in patients experiencing symptomatic irreversible pulpitis undergoing root canal treatment. However, it is noteworthy that patients exhibited greater comfort levels with needle-free anesthesia systems specifically during the administration of the anesthetic solution.

Synthesis of (TiTaNb)<sub><i>x</i></sub>Hf<sub><i>y</i></sub>Zr<sub><i>z</i></sub>C high-entropy carbides resistant to high thermal oxidation by mechanical alloying and spark plasma sintering

This study presents the synthesis of (TiZrHfTaNb)C, (TiTaNb)0.45Hf0.275Zr0.275С and (TiTaNb)0.3Hf0.35Zr0.35С single-phase, high-entropy carbides through mechanical alloying and plasma sintering. High-entropy carbides hold promise for applications in jet engine components. We identified optimal mechanical alloying conditions to achieve powder homogeneity and minimize iron fouling. The microstructure, phase, and chemical compositions of the samples were investigated. At 1600 °C, a sample with a face-centered cubic (FCC) lattice and low content of zirconium and hafnium oxides was formed. Elevating the sintering temperature to 2000 °C facilitated oxide dissolution and the formation of single-phase, high-entropy carbides. The microhardness of the samples ranged from 1600 to 2000 HV, while the compressive strength varied between 600 and 800 MPa. Plasma heating tests demonstrated excellent resistance to thermal oxidation for (TiTaNb)0.3Hf0.35Zr0.35С, withstanding temperatures up to 2250 °C.

Wear performance of short fiber added polyamide composites produced by additive manufacturing: Combined impacts of secondary heat treatment, reinforcement type, and test force

AbstractIn recent years, the number of studies focusing on the additive manufacturing has increased seriously to elucidate the critical points such as physical, chemical, and mechanical properties. Contrary to common trends and for the first time in the literature, this experimental endeavor aims to comprehend the combined impact of reinforcement type and heat treatment on the wear features of additively manufactured polyamide 6 (PA6) composites. As reinforcement materials, glass, and carbon fibers were utilized and all samples were created through the fused filament fabrication. Half of the samples were subjected to annealing treatment after the main production, and characterization works were performed using a fused emission scanning electron microscope, differential scanning calorimetry, and dynamic mechanic analysis. From the outcomes, it is seen that heat treatment has a positive effect on the hardness, and wear resistance of the composites. Besides, glass fiber‐reinforced samples display lower friction coefficient and lower volume loss results than other samples. For all samples, secondary annealing causes a positive impact on wear endurance in most cases. On the other side, the wear mechanism of the tested samples changes with the test force level and reinforcement type. At lower test forces, abrasive wear‐induced debris parts are detected on the deformed surfaces of PA6 and carbon‐added samples, but this case is opposite for the highest force of 40 N.Highlights Additive manufacturing was underlined as a promising way to create polymer composites with high dimensional accuracy. The combined effect of secondary annealing and reinforcement type on the wear resistance of 3D‐printed PA6 composites was examined for the first time in the literature. Carbon and glass fibers were compared to explore their effect on friction coefficient and wear behavior of polymer composite samples produced via FFF technology. Hardness and surface roughness measurements were used to comprehend the dry sliding wear results. Depending on the increasing test force levels and reinforcement type, deformation, and abrasion mechanisms were analyzed.

Endodontic Retreatment of Maxillary First Molar with Three Roots and Seven Canals: A Case Report

A 25-year-old female existing with mild pain and discomfort during mastication in her right posterior maxillary tooth. On clinical examination, the maxillary first molar tooth was restored with a composite filling. The tooth did not respond to heat or cold test, and it was tender to percussion. Radiograph examination revealed poor obturation of the canals and the periodontal ligament space was broad but there was no definitive periapical radiolucency. Conservative non-surgical root canal treatment was performed; a total of seven root canals were detected and they were obturated by using the calcium-based sealer. Radiograph with RVG and CBCT also confirmed that all seven canals were properly obturated. Twelve months later, there were no clinical or radiographic changes of the treated tooth. These findings suggested that careful examination of the floor of the pulp chamber with RVG and CBCT help to find extra root canals.

Simultaneous secondary electron microscopy in the scanning transmission electron microscope with applications for in situ studies.

Scanning/transmission electron microscopy (STEM) is a powerful characterization tool for a wide range of materials. Over the years, STEMs have been extensively used for in situ studies of structural evolution and dynamic processes. A limited number of STEM instruments are equipped with a secondary electron (SE) detector in addition to the conventional transmitted electron detectors, i.e. the bright-field (BF) and annular dark-field (ADF) detectors. Such instruments are capable of simultaneous BF-STEM, ADF-STEM and SE-STEM imaging. These methods can reveal the 'bulk' information from BF and ADF signals and the surface information from SE signals for materials <200 nm thick. This review first summarizes the field of in situ STEM research, followed by the generation of SE signals, SE-STEM instrumentation and applications of SE-STEM analysis. Combining with various in situ heating, gas reaction and mechanical testing stages based on microelectromechanical systems (MEMS), we show that simultaneous SE-STEM imaging has found applications in studying the dynamics and transient phenomena of surface reconstructions, exsolution of catalysts, lunar and planetary materials and mechanical properties of 2D thin films. Finally, we provide an outlook on the potential advancements in SE-STEM from the perspective of sample-related factors, instrument-related factors and data acquisition and processing.

Strengthened Buried Interface via Metal Sulfide Passivation Toward High‐Performance CsPbBr3 Perovskite Solar Cells

Although SnO2 has been widely used as the electron transport material (ETM) of the perovskite solar cells (PSCs), the energy level mismatch at the SnO2/CsPbBr3 buried interface is as high as 1 eV, which is disastrous for the CsPbBr3‐based PSCs. Herein, a buffer layer of metal sulfide (CdS, ZnS) is introduced to solve this problem. The power conversion efficiency (PCE) of CsPbBr3 PSCs has been increased from 8.16% to 9.48% for ZnS‐treated SnO2 (ZnS‐SnO2), and a champion efficiency of 10.61% has been achieved in CdS‐treated SnO2 (CdS‐SnO2) devices. Aside from the reduced energy loss, the mobility of the SnO2 ETM has been greatly enhanced after the metal sulfide treatment. The CdS‐SnO2 devices also enjoy the benefits of reduced defect density and speeded carrier extraction, contributing to an almost 30% performance enhancement. This 10.61% PCE is among the highly efficient CsPbBr3‐based PSCs reported to date. Finally, CdS‐SnO2 devices survive a harsh damp heat test (120 °C with a relative humidity of 50%) for a month with less than 15% efficiency loss, demonstrating the superior stability of our CsPbBr3 PSCs.

1D simulation analysis and optimization design of engine cooling system

The engine cooling system takes away the heat absorbed by high-temperature parts during the operation of the car engine in a timely manner, keeping it working within the normal temperature range. This article applies Flowmaster software to establish a one-dimensional cooling system model for a certain model of National Five diesel engine. Relevant boundary conditions are inputted to complete steady-state simulation calculations of the system under different operating conditions, obtaining the flow rate, pressure distribution, and temperature rise of each component. At the same time, three optimization schemes are designed based on the original cooling system to predict and evaluate the working capacity of the cooling system, Based on the calculation and analysis results, improvement suggestions are proposed to guide the structural design and testing of the cooling system, greatly reducing research and development time and reducing research and development costs. The calculation results show that the flow rate of each component in the rated point, heating test condition, and idle condition of the original plan has decreased compared to the flow rate of a certain four machine on the same platform under the same working condition (the air compressor flow rate is higher than the limit value), and the temperature difference of the radiator and heating flow rate do not meet the specification requirements. Suggest using Plan 3 to increase the water pump speed ratio to 1.25, with a warm air flow rate of 5.33L/min under idle conditions, which is 72% higher than the original plan and meets the vehicle limit requirements. In addition, to ensure the accuracy and reliability of the model and calculations, this project conducted cooling system tests on an engine bench. The comparison between the simulation calculation data and the experimental data showed that the simulation calculation results were consistent with the experimental results.

Combined effect of Cerium oxide nanoparticles loaded scaffold and photobiomodulation therapy on pain and neuronal regeneration following spinal cord injury: an experimental study.

Spinal cord injury (SCI) remained one of the challenges to treat due to its complicated mechanisms. Photobiomodulation therapy (PBMT) accelerates neuronal regeneration. Cerium oxide nanoparticles (CeONPs) also eliminate free radicals in the environment. The present study aims to introduce a combined treatment method of making PCL scaffolds as microenvironments, seeded with CeONPs and the PBMT technique for SCI treatment. The surgical hemi-section was used to induce SCI. Immediately after the SCI induction, the scaffold (Sc) was loaded with CeONPs implanted. PBMT began 30min after SCI induction and lasted for up to 4weeks. Fifty-six male rats were randomly divided into seven groups. Glial fibrillary acidic protein (GFAP) (an astrocyte marker), Connexin 43 (Con43) (a member of the gap junction), and gap junctions (GJ) (a marker for the transfer of ions and small molecules) expressions were evaluated. The behavioral evaluation was performed by BBB, Acetone, Von Frey, and radiant heat tests. The SC + Nano + PBMT group exhibited the most remarkable recovery outcomes. Thermal hyperalgesia responses were mitigated, with the combined approach displaying the most effective relief. Mechanical allodynia and cold allodynia responses were also attenuated by treatments, demonstrating potential pain management benefits. These findings highlight the potential of PBMT, combined with CeONPs-loaded scaffolds, in promoting functional motor recovery and alleviating pain-related responses following SCI. The study underscores the intricate interplay between various interventions and their cumulative effects, informing future research directions for enhancing neural repair and pain management strategies in SCI contexts.

Influence of liquid-to-solid ratios on properties and microstructure of coal gasification slag-based one-part geopolymer

Limited studies have been conducted on the synthesis of one-part geopolymer involving coal gasification slag by alkali fusion and component additive method (AFCAM). The ratio of liquid-to-solid (L/S) is the key aspect that has a major impact on the one-part geopolymer's compressive strength (UCS). Our research aims to determine how different L/S ratios affect the microstructure and characteristics of one-part geopolymers. MIP analysis and hydration heat test were conducted to analyze the influence caused by different L/S ratios. The results showed that as the L/S ratio increased, the UCS of geopolymers decreased, and the setting time of fresh slurry increased steadily. Additionally, geopolymer with 0.25 as an L/S ratio (G-L/S-0.25) achieved a higher UCS at 48.31 MPa, whereas the total setting time was more than 23 h. The low L/S ratio produced more gel pores and less total porosity in the geopolymer matrix, which improved the UCS. Moreover, lower porosity suggested that the geopolymer sample had higher compactness and a better internal structure. It is found that the dissolution of the fusion product released heat in the first hour, and no coal gasification slag dissolution heat was detected after one hour. This suggested coal gasification slag showed low reactivity as the additive and was embedded in the geopolymer matrix after 28-day curing. The tested results showed that G-L/S-0.25 had a greater reaction degree. This study illustrated the effects of the L/S ratio on one-part geopolymer and provided a new thought to enhance the UCS of coal gasification slag-based geopolymer.

Study on the correlation between indoor accelerated corrosion testing of concrete epoxy polysiloxane coating and real-sea environmental testing in the East China Sea

In order to reveal the correlation between the accelerated corrosion test of epoxy polysiloxane coating and the real sea environmental test, the real sea environmental test was carried out in the atmosphere and tidal range area of Zhairuoshan Island in the East China Sea, and the multi-factor coupling test I (Cycle of 7-day xenon lamp aging test + 7-day Wetting-drying test) and test II (Cycle of 7-day xenon lamp aging test + 3-day damp heat test + 4-day salt spray test) were designed with reference to the environment of the East China Sea. The correlation between indoor accelerated corrosion test and real sea environmental test was analyzed by using Grey Relation Analysis, Spearman's rank correlation coefficient and Acceleration factor conversion method. The results show that both the indoor accelerated corrosion test and the real sea environmental test have corrosive effects on the epoxy polysiloxane coating of concrete. In the indoor accelerated corrosion test, it was found that the Wetting-drying test caused the highest loss of light rate. In the real sea environmental test, the loss of light rate of the coating in the atmosphere is higher than that in the tidal area, and the color difference is slightly lower. When the loss of light rate is used as the criterion, the grey correlation coefficient between the multi-factor coupling test I and the tidal range test is 0.63, and the maximum acceleration factor during the test is 5.3, indicating a good correlation between the two tests. Through this study, an effective indoor accelerated corrosion test method with good correlation and acceleration characteristics to the loss of light rate of concrete epoxy polysiloxane coating in a real sea environment was obtained.

Preparation of stable colloidal dispersion of surface modified Fe3O4 nanoparticles for magnetic heating applications

The effect of surface modification on enhancing the magnetic heating behavior of magnetic nano fluids were investigated, for this purpose Fe3O4 nanoparticles were synthesized using co-precipitation method and surface modification was done using citric acid, ascorbic acid, tetraethyl orthosilicate (TEOS), polyvinyl alcohol (PVA) and polyethylene glycol (PEG). Experimental heating tests using AC magnetic field were done in the frequency of 100 kHz and different magnetic field (H) intensities. Theoretically the specific absorption rate (SAR) in magnetic nano fluids is independent of nanoparticles concentration but the experimental results showed different behavior. The theoretical SAR value @ H = 12kA.m–1 for Nano fluids containing bare Fe3O4 nanoparticles was 11.5 W/g but in experimental tests the obtained value was 9.72 W/g for nano fluid containing 20,000 ppm of dispersed nanoparticles. The experimental SAR calculation was repeated for sample containing 10,000 ppm of nanoparticles and the results showed increase in experimental SAR that is an evidence of nanoparticles agglomeration in higher concentrations. The surface modification has improved the dispersion ability of the nanoparticles. The Ratio of SAR, experimental, 20000ppm to SAR, experimental, 10000ppm was 0.85 for bare Fe3O4 nanoparticles dispersion but in case of surface modified nanoparticles this ratio has increased up to 0.98 that shows lower agglomeration of nanoparticles as a result of surface modification, although on the other hand the surface modification agents were magnetically passive and so it is expected that in constant concentration the SAR for bare Fe3O4 nanoparticles to be higher than this variable for surface modified nanoparticles. At lower concentrations the dispersions containing bare Fe3O4 nanoparticles showed higher SAR values but at higher concentrations the surface modified Fe3O4 nanoparticles showed better results although the active agent amount was lower at them. Finally, it should be noted that the nanoparticles that were surface modified using polymeric agents showed the highest decrease in experimental SAR amounts comparing theoretical results that was because of the large molecules of polymers comparing other implemented surface modification agents.

Effects of the thermal treatments on the optical properties of SiO2 anti-reflective coatings on sapphire windows

The SiO2 films were deposited on sapphire substrates using radio frequency (RF) magnetron sputtering to enhance the mid-wave infrared (IR) transmittance. The effects of thermal treatments by annealing and in-situ heating on the SiO2 films were investigated. After annealing at 600 °C, the surface morphology, microstructure, chemical states, and optical constants were investigated. No obvious microcracks or delamination were observed on the film surfaces, indicating excellent adhesion to the sapphire substrates. With an increase in the annealing time, gradual oxidation of Si atoms within the SiO2 thin films occurred, resulting in the release of OH groups and evaporation of moisture. The refractive index exhibited slight changes, while the extinction coefficient showed a significant reduction, thus the transmittance was improved. According to the in-situ heating tests from the annealed samples, it revealed a slight increase in average transmittance with prolonged annealing time. Finally, we assessed the performance of the annealed samples by rapid heat shock to 600 °C at a very short time, which demonstrated outstanding optical performance and heat-resistant properties. The present work supports the feasibility of applying the SiO2 films under harsh high-temperature environments.

High‐temperature phase transformation and thermodynamic properties of Ca3(VO4)2

AbstractCa3(VO4)2 is a promising candidate for applications in ferroelectric, laser host, and optical materials owing to its unique whitlockite structure and excellent physicochemical properties. In this study, the Ca3(VO4)2 powder was fabricated via a conventional solid‐phase route in air, using V2O5 and CaO as precursors. The trigonal Ca3(VO4)2 belongs to the space group R3c, having unit cell parameters of a = 10.8074 Å, b = 10.8074 Å, and c = 37.98871 Å, respectively. Ca3(VO4)2 melts congruently at 1680 K, as determined from differential scanning calorimetry measurements of the thermal profile of the second heating test. Enthalpy changes in Ca3(VO4)2 were experimentally determined for the first time across temperatures between 573 and 1623 K by drop calorimetry. The temperature‐dependent molar heat capacity of Ca3(VO4)2 was calculated from the enthalpy changes at elevated temperatures. Thermodynamic properties (entropy, enthalpy, and Gibbs free energy changes) were also calculated. The thermodynamic properties measured in this study were further applied to evaluate the appropriate precursors for fabricating Ca3(VO4)2 via solid‐state calcination. The results strongly recommend the use of V2O5 and Ca(OH)2 precursors for preparing the Ca3(VO4)2 samples because of their thermodynamic advantages.

Mechanical properties and microstructure of waterborne polyurethane-modified cement composites as concrete repair mortar

With the increase in service life, the durability of a large number of concrete structures deteriorates year by year under the influence of the external environment, requiring urgent repair and reinforcement. Ordinary cement concrete materials have disadvantages such as high brittleness, low tensile strength, poor bonding ability, and insufficient durability, making it difficult to meet the repair needs of high-quality building structures. Therefore, self-synthesized anion WPU was used to study its effect on the mechanical properties of cement-based repair mortar. The research found that waterborne polyurethane (WPU)-modified cementitious composite repair materials exhibit better bonding strength with old concrete substrates compared to traditional cement-based materials. Additionally, the incorporation of WPU significantly reduces the brittleness of the repair material, ensuring enhanced efficiency in the repair process. However, according to the hydration heat test results, the addition of WPU delays the hydration process of the composite repair materials. In addition, the addition of WPU enhances the flexibility and bonding ability of the materials, with flexural strength and tensile strength at the age of 28 days reaching 13 MPa and 6 MPa, respectively. Through stress‒strain curve analysis, it was found that the maximum strain amplification of WPU cement mortar can reach 134 %. Combined with SEM testing, it was observed that cured WPU films were present in specimens aged 28 days with P/C ratios of 10 % and 15 %. WPU and cement hydration products permeate each other, forming a three-dimensional polymer network structure, improving the pore structure, and fully exerting the flexibility of WPU. This also validates the experimental results of increased ultimate tensile strain. WPU cement-based composite repair materials have higher bonding strength at a high P/C ratio (15 %), and WPU alone, used as an interface agent for pretreating the interface of old concrete, can improve the interface bonding strength, up to twice that of the group without the surface agent.

Seasonal performance of an energy pile heat pump system and prediction of building thermal load

Ground source heat pumps (GSHPs) are widely used for cooling and heating buildings, which can reduce the burning of fossil fuels and contribute to the reduction of carbon emissions. Energy piles, as underground heat exchangers, have advantages over conventional buried borehole pipes, saving drilling costs and accelerating the construction period. However, few studies have focused on the actual operation of an energy pile heat pump system, and the prediction of the building thermal load can reduce the instrument arrangement and test recording time. Hence, a heat pump system was built in this study to serve a single lab using energy piles with a cap structure as the energy supply, and summer cooling and winter heating tests were conducted. Under the test conditions in this study, the GSHP had a faster start-up speed and less power consumption than the air source heat pump (ASHP), and the average coefficient of performance (COP) of the energy pile heat pump system was 3.78, which is 40.0 ∼ 51.2% higher than that of the corresponding ASHP (the normative reference COP is 2.50 ∼ 2.70). The methods of higher-order surface fitting and an artificial neural network model were both suitable for predicting building thermal load.

Experimental comparison of a DC PV cooker and a parabolic dish solar cooker under variable solar radiation conditions

Solar cookersare not all-weather cooking devices and operate poorly during cloudy and low sunshine conditions. Their performance is evaluated usually during high solar radiation conditions. The objective of this study is to compare two solar cookers under variable non-ideal weather conditions. The comparison is carried out under variable solar radiation conditions to compare the all-weather performance of these two cookers. This is a major novelty compared to previous work reported where solar cookers are tested under high and ideal solar radiation conditions. Experiments to compare a PV DC battery-powered solar cooker and a parabolic dish solar cooker are presented in this paper. A total of six water heating tests are carried out to comprehensively compare these two types of solar cookers under different solar radiation conditions. Also, four food cooking tests are carried out with different types of food. The PV solar cooker shows almost constant input electrical power in the range of 160–180 W during the experimental tests whereas the input thermal power for the parabolic dish is highly variable depending on the solar radiation conditions (200–1200 W). The output water heating powers obtained using the PV cooker (66–100 W) are comparable to those obtained with parabolic dish solar cookers (78–142 W), regardless of the significantly lower input heating power. Water is boiled in all the heating tests with the PV cooker, whereas water is boiled for tests with low solar radiation variability for the parabolic dish solar cooker. Higher water heating efficiencies within a small range (0.38–0.57) are obtained for the PV cooker compared to the parabolic dish solar cooker (0.11–0.42). The water heating efficiency of the parabolic dish solar cooker is highly affected by ambient solar radiation and windspeed conditions. Food was well cooked with the PV cooker in all four food cooking tests, whereas food in only two tests with low solar radiation variability was well cooked for the parabolic dish solar cooker. The PV cooker proves to be an all-weather cooker from the experimental results obtained. Future work will extend the use of the PV system for other domestic applications such as lighting and refrigeration together with solar cooking for a multipurpose DC decentralized system for communities without grid connectivity.

Influence of microwave irradiation and water-based cooling on the fracturing behavior and failure mode transition of CSTBD granite

Utilizing microwave heating in conjunction with water-based cooling technology can effectively reduce the fracture toughness of hard rocks. However, the fracturing characteristics and failure modes of hard rocks following microwave heating and water-based cooling remain undisclosed. Granite, being one of the most common types of hard rocks, was selected for this study, employing Cracked Straight Through Brazilian Disc (CSTBD) specimens for laboratory testing. CSTBD specimens with various crack angles (0, 30, 60, and 90°) underwent treatment with varying microwave durations (30, 60, 180, 300, and 420 s). Subsequently, Brazilian splitting tests were conducted on the damaged specimens. To simulate the entire process of microwave heating and mechanical testing of CSTBD specimens, we developed a coupled Finite Element Method – Distinct Lattice Spring Model (FEM-DLSM) approach. The results indicate that microwave heating with water-based cooling significantly influences the fracture toughness of CSTBD granite. Mode-I fracture toughness decreases with microwave heating temperature at a low crack angle (pure tensile failure and tensile–shear mixed failure) and increases at a high crack angle (compressive–shear failure and compressive failure). Mode II fracture toughness decreases with microwave heating temperature at any crack angle. Microwave heating with water-based cooling causes a decrease in the transition angles from tensile–shear failure to compressive–shear failure and from compressive–shear failure to compressive failure. Thermally induced microcracks in the rock specimen are responsible for changes in fracture toughness and failure mode transitions. After microwave heating and water-based cooling, numerous microcracks are induced in the rock interior. While macroscopic cracks predominantly control failure, growing microcracks, by weakening the rock matrix, shift the initiation position of the failure crack from the tip of the macroscopic crack to other positions, following the principle of the weakest failure path.

Multifunctional sulfonium-based treatment for perovskite solar cells with less than 1% efficiency loss over 4,500-h operational stability tests

The stabilization of grain boundaries and surfaces of the perovskite layer is critical to extend the durability of perovskite solar cells. Here we introduced a sulfonium-based molecule, dimethylphenethylsulfonium iodide (DMPESI), for the post-deposition treatment of formamidinium lead iodide perovskite films. The treated films show improved stability upon light soaking and remains in the black α phase after two years ageing under ambient condition without encapsulation. The DMPESI-treated perovskite solar cells show less than 1% performance loss after more than 4,500 h at maximum power point tracking, yielding a theoretical T80 of over nine years under continuous 1-sun illumination. The solar cells also display less than 5% power conversion efficiency drops under various ageing conditions, including 100 thermal cycles between 25 °C and 85 °C and an 1,050-h damp heat test.

Research on fire early warning index system of coal mine goaf based on multi-parameter fusion

In order to improve the precision of goaf fire early warning outcomes, this paper obtains the temperature characteristic index of goaf fire early warning by using a coal spontaneous combustion thermogravimetric test and a coal spontaneous combustion programmed heating test. The major gas index and auxiliary gas index for early warning are derived using the integration of the Graham coefficient and grey correlation approach. The D-S evidence theory, which involves optimizing weight allocation, is utilized to integrate the early warning temperature index and various gas indexes. Based on the fusion results, a coal mine goaf fire early warning index system is developed through multi-parameter fusion. The early warning index system is then validated through a programmed heating experiment. The results show that the process of coal spontaneous combustion can be categorized into six distinct stages: latent stage, oxidation stage, critical stage, pyrolysis stage, fission stage, and combustion stage. These stages are determined by the characteristic temperatures of coal spontaneous combustion, which are 31.7 °C, 54.8 °C, 153.7 °C, 204.5 °C, and 241.6 °C. The major gas index for early warning of goaf fires can be determined by 100∆(CO)/∆O2(%). Additionally, auxiliary gas indexes such as C3H8/CH4, C3H8/C2H6, C2H4/C2H6, and C2H2 can be used for goaf fire early warning. The programmed heating experiment shows that the early warning system software is designed by the multi-parameter fusion goaf fire early warning index system is accurate and effective. The selection of the goaf fire early warning index is more rational and precise when using the multi-parameter fusion goaf fire early warning index system based on the D-S evidence theory of weight allocation. It offers robust support for enhancing the goaf fire early warning index system and predicting coal mine goaf fires.