Prolonged Heating Time Research Articles

Time-Dependent Resistance of Sol–Gel HfO2 Films to In Situ High-Temperature Laser Damage

Laser damage in films under long-term high-temperature conditions is a significant concern for advancing laser applications. This study focused on HfO2 films prepared using the sol–gel method with HfCl4 as a precursor. It examined the effects of temperature on various properties of the films, including their optical properties, microstructure, surface morphology, absorption, and laser-induced damage threshold (LIDT). The prepared film demonstrated desirable characteristics at the high temperature of 423 K, such as high transmittance, low absorption, and high LIDT. As the duration of its high-temperature exposure increased, the LIDT of the films gradually decreased. An intriguing finding was that the film’s LIDT exhibited an exponential decay pattern with prolonged heating time. This observation could be attributed to the power-law increase in defects on both the internal and surface areas of the film as the duration of high-temperature exposure lengthened. Moreover, even after a 15-day heating period at 423 K, the film maintained an LIDT of 12.9 J/cm2, indicating its potential applicability in practical high-temperature environments. This study provided a general pattern and a universal formula for understanding the laser damage of sol–gel films at high temperatures over time. Furthermore, it opened possibilities for future developments of laser films suitable for extreme environments.

Evaluation of mechanical properties, heating rate and radio frequency explosive puffing (RFEP) quality of purple sweet potato under different moisture contents and moisture equilibrium process

The effects of different initial moisture contents (15–55%) and moisture equilibrium process (MEP) on the mechanical properties of the gas-blocking surface layer of purple sweet potato chips and the radio frequency (RF) heating rate, uniformity, and radio frequency explosion puffing (RFEP) quality were discussed in this article. Low-field nuclear magnetic resonance indicated that hot-air pre-drying reduced the amount of free water and caused the transfer of immovable water to bound water. This process was accompanied by an increase in the thickness and elastic modulus of the gas-blocking surface layer, resulting in a significant increase in the RF heating rate and uniformity. Prolonged RF heating time led to a decrease in anthocyanin content. The results demonstrated that the puffing rate initially increased and then decreased with increasing initial moisture content. The puffed sample with an initial moisture content of 45% exhibited the highest puffing rate, crispiness, and porosity. X-ray micro-tomography results reveal that MEP improved the morphology of puffed products, ensuring even distribution of small pores and reducing the presence of hard edges. In conclusion, considering the heating time and anthocyanin retention rate, the initial moisture content ranges from 35% to 45% after MEP was the best pre-treatment.

Microwave‐Assisted Rapid Synthesis of MOF‐Based Single‐Atom Ni Catalyst for CO2 Electroreduction at Ampere‐Level Current

AbstractCarbon‐based single‐atom catalysts (SACs) have attracted tremendous interest in heterogeneous catalysis. However, the common electric heating techniques to produce carbon‐based SACs usually suffer from prolonged heating time and tedious operations. Herein, a general and facile microwave‐assisted rapid pyrolysis method is developed to afford carbon‐based SACs within 3 min without inert gas protection. The obtained carbon‐based SACs present high porosity and comparable carbonization degree to those obtained by electric heating techniques. Specifically, the single‐atom Ni implanted N‐doped carbon (Ni1−N−C) derived from a Ni‐doped metal–organic framework (Ni‐ZIF‐8) exhibits remarkable CO Faradaic efficiency (96 %) with a substantial CO partial current density (jCO) up to 1.06 A/cm2 in CO2 electroreduction, far superior to the counterpart obtained by traditional pyrolysis with electric heating. Mechanism investigations reveal that the resulting Ni1−N−C presents abundant defective sites and mesoporous structure, greatly facilitating CO2 adsorption and mass transfer. This work establishes a versatile approach to rapid and large‐scale synthesis of SACs as well as other carbon‐based materials for efficient catalysis.

Microwave-Assisted Rapid Synthesis of MOF-Based Single-Atom Ni Catalyst for CO2 Electroreduction at Ampere-Level Current.

Carbon-based single-atom catalysts (SACs) have attracted tremendous interest in heterogeneous catalysis. However, the common electric heating techniques to produce carbon-based SACs usually suffer from prolonged heating time and tedious operations. Herein, a general and facile microwave-assisted rapid pyrolysis method is developed to afford carbon-based SACs within 3 min without inert gas protection. The obtained carbon-based SACs present high porosity and comparable carbonization degree to those obtained by electric heating techniques. Specifically, the single-atom Ni implanted N-doped carbon (Ni1 -N-C) derived from a Ni-doped metal-organic framework (Ni-ZIF-8) exhibits remarkable CO Faradaic efficiency (96 %) with a substantial CO partial current density (jCO ) up to 1.06 A/cm2 in CO2 electroreduction, far superior to the counterpart obtained by traditional pyrolysis with electric heating. Mechanism investigations reveal that the resulting Ni1 -N-C presents abundant defective sites and mesoporous structure, greatly facilitating CO2 adsorption and mass transfer. This work establishes a versatile approach to rapid and large-scale synthesis of SACs as well as other carbon-based materials for efficient catalysis.

An Improved Model for Biogenic Ammonium Urate.

The pathological crystallization of ammonium urate inside the urinary tract is a well-documented medical condition; however, structural studies of the biogenic material have proven challenging owing to its propensity to precipitate as a powder and to exhibit diffraction patterns with widely varying intensities. Using block Rietveld refinement methods of powder diffraction data, here we identify ammonium urate hydrate (AUH) as a likely component in natural uroliths. AUH has a planar 2-D hydrogen-bonded organic framework of urate ions separated by ammonium ions with water molecules residing in bisecting channels. AUH is stable up to 150 °C for short time periods but begins to decompose with prolonged heating times and/or at higher temperatures. Changes in the solid-state structure and composition of synthetic material over a temperature range from 25 to 300 °C are elucidated through thermogravimetric and spectroscopic data, combustion analysis, and time-resolved synchrotron powder X-ray diffraction studies. We contend that biogenic ammonium urate is more accurately modeled as a mixture of AUH and anhydrous ammonium urate, in ratios that can vary depending on the growth environment. The similar but not identical diffraction patterns of these two forms likely account for much of the variability seen in natural ammonium urate samples.

Effects of Stigmasterol on 3-Chloropropane-1,2-diol Fatty Acid Esters and Aldehydes Formation in Heated Soybean Oil.

In this study, we investigated the inhibitory effects of three soybean isoflavones and two soybean phytosterols on the formation of 3-chloropropane-1,2-diol fatty acid esters (3-MCPDE) and aldehydes in heated soybean oil model. 0.4 mM of genistin, genistein, daidzein, stigmasterol, and β-sitosterol significantly reduced 3-MCPDE formation by 25.7, 51.4, 21.4, 61.6, and 55.7%, and total aldehydes formation by 42.03, 43.94, 28.36, 54.74, and 39.23%, respectively. Further study showed that stigmasterol reduced the content of glycidyl esters (GEs) and glycidol, two key intermediates of 3-MCPDE, and prevented fatty acids degradation in the oils. Moreover, the effects of continuous frying time on the content of stigmasterol and the migration of stigmasterol were evaluated in the fried dough sticks model system. The content of stigmasterol in soybean oil was found to be significantly decreased with prolonged heating time. The concentrations of stigmasterol in fried dough sticks and the migration rates of stigmasterol from soybean oil to fried dough sticks decreased with repeated frying sessions. In addition, stigmasterol undergoes oxidative changes during heat treatment, and the oxidation products including 5,6α-epoxystigmasterol, 5,6β-epoxystigmasterol, 7α-hydroxystigmasterol, 7β-hydroxystigmasterol, stigmasterlol-3β,5α,6β-triol, and 7-ketostigmasterol were identified in the frying oils but not in the fried dough sticks. Overall, stigmasterol could be added to soybean oil to reduce 3-MCPDE and aldehydes formation, and reacting with GEs/glycidol and protection of lipid acids from oxidation may be the mechanism of action of stigmasterol.

Improved water solubility, antioxidant, and sustained-release properties of curcumin through the complexation with soy protein fibrils

Food protein fibrils are progressively recognized as promising matrixes for the preservation and delivery of bioactive compounds. In this study, soy protein fibrils (SPF) formed at 4, 8, and 12 h (80 °C, pH 2.0) were utilized as carriers to complex with curcumin at pH 3.2. SPF with extreme aspect ratios exhibited a higher surface hydrophobicity compared to soy protein isolate (SPI), which improved its ability to form soluble complexes with curcumin. However, a prolonged heating time of 12 h decreased the surface hydrophobicity of SPF since the formation of compact fibrillar aggregates. Further experiments revealed SPF8 (heated for 8 h) had a higher affinity for curcumin, and its predominant interactions were hydrophobic interaction and hydrogen bonding. The curcumin solubility of SPF8-Cur (405.7 μg/mL) significantly enhanced compared to that of SPI-Cur (95.6 μg/mL) at the ratio (protein/fibril to curcumin) of 12.5. The DPPH• and ABTS•+ scavenging capacities of the SPF8-Cur complex were each roughly 1.7 and 2.7 times greater than those of free curcumin. Moreover, SPF8-Cur complex presented excellent antioxidant and outstanding sustained-release properties, further offering opportunities for the release of curcumin in the intestine and improving the bioaccessibility and bioavailability of curcumin.

The Optimization of Spheroidizing Heat Treatment Parameters on SCM440 Alloy Steel Wires Using Taguchi Robust Design

In the fastener industry, SCM440 alloy steel wire is widely used in the production of cold forging parts, such as high-strength steel fasteners, auto parts, hardware supplies, etc. The wire manufacturers use an intercritical process for spheroidized annealing the alloy steel wires. The quality of a spheroidized annealed wire affects the cold forging quality of fasteners. A series of experimental tests on SCM440 alloy steel wires is carried out in a commercial hydrogen furnace. Various parameters such as spheroidized annealing temperature (A), prolonged heating time (E), holding temperature and time (B, C), cooling rate and temperature (D, F) affect the quality characteristics of wires, such as tensile strength, hardness and ductility. The effects of intercritical spheroidized annealing treatment on mechanical properties are investigated using Taguchi robust design to obtain optimal spheroidized annealing conditions to improve the mechanical properties of alloy steel wires for cold forming. It is experimentally revealed that the spheroidized annealing temperature (A), cooling rate and temperature (D, F) significantly affect the quality of spheroidizing annealed SCM440 alloy steel wires. The optimal spheroidized annealing conditions for SCM440 alloy steel wire are spheroidized annealing temperature of 771°C and prolonged heating for 5.0 h, then holding the temperature of 725°C for 1.0 h, and slowly cooling to the temperature of 713°C at the rate of -9°C /h. Therefore, the optimal mean tensile strength of 520.0 MPa, optimal mean hardness of 80.8 HRB, and optimal mean ductility of 0.488 are obtained. The variations of the properties are significantly reduced to achieve a much even quality for annealed wires. The optimal spheroidizing heat treatment parameter settings evidently improve the performance measures and the cold formability of SCM440 alloy steel wires is effectively improved.

Total oxidizable precursors assay for PFAS in human serum

Per- and polyfluoroalkyl substances (PFAS) are a class of chemicals including over 4700 substances. As a limited number of PFAS is routinely analyzed in human serum, complementary analytical methods are required to characterize the overlooked fraction. A promising tool is the total oxidizable precursors (TOP) assay to look for precursors by oxidation to perfluoroalkyl acids (PFAA). The TOP assay was originally developed for large volumes of water and had to be adapted for 250 μL of human serum. Optimization of the method was performed on serum samples spiked with model precursors. Oxidative conditions similar to previous TOP assay methods were not sufficient for complete oxidation of model precursors. Prolonged heating time (24 h) and higher oxidant amount (95 mg of Na2S2O8 per 225 μL of serum) were needed for complete conversion of the model precursors and accomplishing PFAA yields of 35–100 %. As some precursors are not fully converted to PFAA, the TOP assay can only provide semi-quantitative estimates of oxidizable precursors in human serum. However, the TOP assay can be used to give indications about the identity of unknown precursors by evaluating the oxidation products, including perfluoroalkyl sulfonic acids (PFSA) and perfluoroalkyl ether carboxylic acids (PFECA). The optimized TOP assay for human serum opens the possibility for high-throughput screening of human serum for undetected PFAA precursors.

Formation of AGEs in fish cakes during air frying and other traditional heating methods

This study investigated the formation of advanced glycation end products (AGEs) in fish cakes under air frying, deep frying, pan frying and baking. The results showed that the AGEs contents on the surface of fish cakes significantly increased with prolonging heating time. The AGEs contents under different methods were following: deep frying > air frying ≈ pan frying > baking. However, the AGEs contents in the interior of fish cakes were hardly influenced by the methods and time. The correlation analysis showed that the AGEs contents were negatively correlated with the moisture content, positively correlated with the yellowness (b*) value, oil content and oxidation products. Additionally, the air-fried fish cake exhibited a denser texture compared to the others, and its colour was similar to the deep-fried ones. Conclusively, the air-fried fish cake showed low oil and AGEs contents, and similar colour to the deep-fried fish cake.

High conductive Cu3SnSXSe4-X counter electrodes for dye-sensitized solar cells

Orthogonal Cu3SnS4 (CTS) nano-crystalline were synthesized. It is clarified that Cu7S4 seeds first nucleated in the solvothermal process at 130 °C. When the temperature elevated to 180 °C, Sn4+ began to enter the Cu7S4 lattice to form orthorhombic CTS nano-crystals. Secondary phase of SnS occurred at 200 °C and could not be eliminated by prolonging heating time. The as-prepared CTS@SnS nano-crystals were selenized at 500 °C for 20 min to form CTSXSe4-X. The SnS were completely eliminated and main S sites in CTS were substituted by Se anions during the selenization. The CTSXSe4-X films with different thickness were used as counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). CTSXSe4-X CEs have good conductivity and effective electrocalalytic activity for I3- reduction. In the optimal case of 1.7 μm thick CTSXSe4-X CE, power conversion efficiency of 7.57% was achieved which is 88.6% of that of the same structural device with commercial Pt CE.

Performance enhancement of a baffle-type solar heat collector through CFD simulation study

The application of solar energy conversion has been extensively utilized as an alternative energy source to generate heat. This approach would be a step towards sustainable energy development particularly in the manufacturing industry with energy-intensive process. In this paper, thermal enhancement on the key component of a solar energy device – solar heat collector (SHC), has been evaluated by proposing a baffle-type SHC with various geometric configuration in the air passage namely longitudinal baffle and transversal baffle. The performance of SHC is evaluated in term of efficiency, temperature distribution, airflow pattern and pressure drop across the collector outlet through Computational Fluid Dynamic (CFD) investigation. It was observed that maximum collector efficiency was achieved in the Longitudinal-SHC (L-SHC), with a value of 46.2 % followed by Transversal-SHC (T-SHC) and without baffles. Maximum drying temperature at the collector outlet was 332.43 K for L-SHC, showing temperature rise of 0.35 % and 4.21 % from T-SHC and without baffles, respectively. The velocity vector indicated that turbulence flow was created in the T-SHC which consequently improved the heat transfer. Whereas in L-SHC, enhancement was achieved through the prolonged heating time in the passage. Considering the thermo-hydraulic performance factor evaluated, these enhancement features had diminished the effect of pressure drop.

Colloidal Physicochemical Properties and Variation Mechanisms of Lithium Complex Grease under Limited Operating Temperature

Abstract This study aims to investigate the colloidal physicochemical properties and variation mechanisms of lithium complex grease after heating at a limited operating temperature (180°C). Experimental lubricating grease samples were prepared by static heating in the laboratory for different times to simulate the limited operating temperature. The variations in grease mass loss and consistence were studied. Rheological behavior tests were carried out to explore the structural strength and structural recovery properties of all grease samples by using a continuous shear and oscillatory shear rheometry model of rotational rheometer. The fibrous microstructure was investigated by field emission scanning electron microscope, and infrared spectra were recorded using a Fourier transform infrared spectrometer. A structural evolution model of grease colloidal dispersion system was established and used to elucidate the variation mechanism of grease colloidal physicochemical properties under limited operating temperature conditions. The colloidal property of lithium complex grease gradually changed with prolonged heating time. The consistence of grease increased with increasing heating time. The typical shear yield phenomenon became less obvious, and the structural recovery property evidently weakened obviously with prolonged heating time. The variation mechanism of grease colloidal physicochemical properties could be mainly attributed to the thickener oxidation of grease. Results provide experimental support for grease application and failure analysis under harsh conditions.

Antioxidative Properties and Chemical Changes of Quercetin in Fish Oil: Quercetin Reacts with Free Fatty Acids to Form Its Ester Derivatives.

In this research, we studied the antioxidative properties and chemical changes of quercetin in fish oil during accelerated storage at 60 °C for 5 days. Gas chromatography (GC) analysis showed that quercetin inhibited aldehyde formation and unsaturated fatty acid oxidation in fish oil significantly; however, the inhibitory effects decreased gradually with prolonged heating time. Moreover, quercetin was consumed with increasing heating time. Some new phenolic derivatives were discovered in the fish oil with quercetin, with their structures fully elucidated by LC-MS/MS and comparison with newly synthesized ones (characterized by MS and NMR spectroscopy). Based on their chemical structures, we proposed that quercetin reacted with EPA and DHA to form the corresponding quercetin fatty acid esters in fish oil. In addition, the newly formed quercetin-3-O-eicosapentaenoate and quercetin-3-O-docosahexaenoate showed weaker DPPH and ABTS radical cation scavenging activity but much improved lipophilicity, higher cell membrane affinity, and hence enhanced cellular antioxidant activity compared with the parent quercetin. Overall, quercetin could be used as a safe dietary polyphenol to inhibit lipid oxidation. The newly formed quercetin-polyunsaturated fatty acid esters may render improved bioactivity to humans, which needs further investigation.

Assembly behavior, structural characterization and rheological properties of legume proteins based amyloid fibrils

The assembly behavior of three selected legume proteins was monitored using thioflavin T (ThT) fluorescence intensity, atomic force microscopy (AFM) and dynamic light scattering (DLS) in this test. It was found that the cowpea protein (CoP) had the highest ability to form amyloid fibrils due to the higher ThT fluorescence intensity of CoP fibrils than chickpea protein (ChP) fibrils and lentil protein (LP) fibrils. These legume proteins were partially denatured during initial heating period, and then the elongation of fibrils was occurred with prolonged heating time. Correspondingly, the particle size of legume proteins decreased firstly, probably resulting from the degraded polypeptides and disrupted structure under the heat treatment and acid hydrolysis. Then the particle size of proteins increased with increasing heating time due to the reorganization of ordered structure. From the results of SDS-PAGE and AFM, vicilin fractions were more beneficial to the formation of fibrils, and the longer and flexible fibrils were observed in the vicilin enriched CoP fibrils, whereas the semiflexible fibrils and rigid fibrils were occurred in LP and ChP fibrils, respectively. In addition, the rheological properties of CoP fibrils were superior to ChP and LP fibrils, owing to the tight entanglement of the longer and flexible CoP fibrils. This work will strengthen the understanding of the formation mechanism of different legume proteins based fibrils and explore their potential application.

Microstructure and Properties of Fe-Based Alloy Coating on Gray Cast Iron Fabricated Using Induction Cladding

Gray cast iron is widely used for the cylinder bore of marine diesel engine. With the aim to improve the properties of the cylinder liner and maintain the matching ability with piston ring under the harsh working condition, the Fe-based alloy coating is fabricated on the gray cast iron using induction cladding. Owing to the high carbon content in both coating and substrate materials, it is extremely difficult to control the coating process and the coating quality. The additive of welding flux and prolonged heating time is proposed to prepare good quality coating. The coating forming mechanism is investigated, and the electrochemical corrosion and tribological properties of the coating are examined. The results show that the Fe-based coating possess better corrosive and tribological performance than gray cast iron, and it is seemed to be a potential candidate for improving the performance of the cylinder liner.

High bond strength Cu joints fabricated by rapid and pressureless in situ reduction-sintering of Cu nanoparticles

By using a novel in situ reduction-sintering process, the native oxide on Cu nanoparticle surface was removed and obvious oxide was not found even after sintering in air. Pressureless sintering at 220 °C for 5 min resulted in a high joint shear strength of over 30 MPa. The growth of oxide on Cu nanoparticle surfaces during storage was studied and the level of oxide film that hinders sintering was also determined. The consolidation behavior of Cu nanoparticles during sintering was observed. The results show that the sintering density of Cu nanoparticles peaked after only 5 min and the formation of dislocations were observed in the sintered structure after prolonged heating times.

Thermal Boundary Evolution of Molten Pool During Wire and Arc Additive Manufacturing of Single Walls of 5A06 Aluminum Alloy

Molten pool uniformity is a prerequisite for wire and arc additive manufacture to achieve a uniform surface appearance. The thermal boundary is a key indicator to evaluate the thermodynamic state of the molten pool. This paper focuses on thermal analysis through finite element simulation and characterizes the thermal evolution of a molten pool during bottom-up deposition. The peak temperature of the substrate plate increases from 375.7 °C to 623.1 °C when peak current increases from 120 A to 180 A. The temperature gradient decreases from 40 °C/mm to 30 °C/mm. Weld speed increases from 0.15 m/min to 0.25 m/min; the temperature gradient is kept at about 30 °C/mm. Dimensionless thermal conductivity, Ge number, is proposed and defined as the criteria to estimate layer size variation. For Ip = 140 A, the average value of the Ge number is 87.7, and it shows the best numerical stability. Dimensionless thermal conductivity, Ge, is proposed and defined as the criteria to estimate the occurrence of layer size variation. Prolonging heating time and increasing cycle frequency, Ge number shows favorable stability during bottom-up deposition. The experimental results are consistent with analytical conclusions, which proves the validity of the Ge number as an indicator of deposition stability.

Hydrolysis of Fe(III) in the presence of mixed anions and promoters

Forced hydrolyses in the precipitation systems (a) Fe(NO3)3/Fe2(SO4)3 and FeCl3/Fe2(SO4)3 and (b) FeCl3/N-guanylurea sulphate were investigated using 57Fe Mossbauer and FT-IR spectroscopies and scanning electron microscopy (FE SEM). Forced hydrolyses of Fe(NO3)3/Fe2(SO4)3 solutions at 90 °C yielded superparamagnetic goethite nanorods, whereas in the case of FeCl3/Fe2(SO4)3 solutions the clusters of akaganeite nanoneedles were formed. With a prolonged heating time at 90 °C the conversion of these akaganeite nanoneedles into goethite nanorods was observed. Forced hydrolysis in the system FeCl3/N-guanylurea sulphate at 160 °C generated only hematite and goethite phases and their fractions depended on the concentration of FeCl3 and the amount of N-guanylurea sulphate in the solution. Different shapes of iron(III) oxyhydroxides and hematite in dependence on the experimental conditions were monitored with FE SEM. Specifically adsorbed sulphates on these particles, as shown by FT-IR spectroscopy, served as directing agents in the particle/crystal growth.

Thermal-induced luminescence enhancement of BAC-P in bismuth-doped phosphogermanosilicate fibers.

The thermal quenching effect has been systematically investigated in bismuth (Bi)-doped phosphogermanosilicate fiber with varying thermal conditions. For the first time, to the best of our knowledge, the activation of phosphor-related Bi active center (BAC-P) is achieved by thermal quenching at 400°C with a heating time of 10 min, evidenced by the enhanced luminescence of BAC-P (${\sim}{1.3}$∼1.3 times) at 1300 nm. The experimental results reveal that a relatively low heating temperature with prolonged heating time stimulates the growth of BAC-P, whereas higher operating temperatures ($ {\ge} 500^\circ $≥500∘C) result in the irreversible destruction of BAC-P. The underlying mechanism for the thermally stimulated BAC-P process is also analyzed and discussed.