Increasing Heating Time Research Articles

Study on the dynamic characteristics of thermal oxidation deposition of aviation kerosene under supercritical pressure

Thermal oxidation deposition of aviation kerosene has a significant impact on the long-term operation of aircraft. In this study, a two-dimensional axisymmetric numerical model incorporating a pseudo-detailed chemical kinetic model of thermal oxidation deposition was developed based on dynamic mesh technology, and a 30-hour transient simulation of the thermal oxidation deposition process of supercritical aviation kerosene was conducted. The dynamic characteristics of the thermal oxidation deposition are examined and the effect of dissolved oxygen concentration is analyzed. According to the results, the large temperature gradient at the inlet and the higher temperatures in the second half of the channel encourage the thermal oxidation and surface deposition reactions to proceed rapidly. And it is found that the surface deposition rate decreases with increasing heating time. Both temperature and concentration determine the rate of dissolved oxygen consumption. The surface deposition rate increased by 195.33 % as the dissolved oxygen concentration increased from 10 to 40 ppm. In addition, the entry of aviation kerosene into the pseudo-critical region can indirectly reduce the rate of thermal oxidation surface deposition. This study is a guide to predict and inhibit the thermal oxidation deposition of aviation kerosene, improving the structural design of the regenerative cooling channel, and ensuring aircraft safety.

Axial compression behaviour and design of square tubed steel reinforced-concrete stub columns after fire exposure

The tubed steel reinforced-concrete (TSRC) column is an innovative type of steel-concrete composite column, the steel tube of which mainly provides confinement to concrete core without sustaining axial load directly. This paper presents the axial compressive behaviour of square TSRC stub columns after ISO 834 standard fire exposure, experimentally and numerically. Eighteen square TSRC stub columns were heated and cooled and subsequently loaded to failure under axial compression. The influences of heating time, concrete compressive strength and steel tube area ratio on the load vs. displacement response, failure mode, residual capacity and stiffness of the tested columns were investigated. Finite element analysis (FEA) models were then developed and validated against test results. The working mechanism, e.g. confinement effect and axial force distribution within the composite section, was studied via parametric studies. Both the residual ultimate capacity and axial stiffness of square TSRC stub columns decrease significantly with the increase in heating time. The negative effect of fire exposure on residual stiffness is more significant than on the residual capacity. Finally, practical equations for determining the residual ultimate capacity and residual compressive stiffness of square TSRC stub column were proposed, which remain consistent with the ambient-temperature methods given in current design standard.

Multivariate modelling analysis for prediction of glycidyl esters and 3-monochloropropane-1,2-diol (3-MCPD) formation in periodically heated palm oil

Palm oil is a vegetable oil that is widely used for cooking and deep-frying because of its affordability. However, repeatedly heated palm oil is also prone to oxidation due to its significant content of unsaturated fatty acids and other chemical toxicants such as glycidyl esters and 3-monochloropropane-1,2-diol (3-MCPD). Initially, the physicochemical properties such as colour, viscosity, peroxide, p-anisidine and total oxidation (TOTOX) of periodically heated palm oil were investigated. Chemical profiling and fingerprinting of six different brands of palm cooking oil during heating cycles between 90 and 360 min were conducted using Fourier transform infrared (FTIR) and 1H Nuclear Magnetic Resonance (NMR) metabolomics. In addition, the multivariate analysis was employed to evaluate the 1H NMR spectroscopic pattern of repeatedly heated palm oil with the corresponding physicochemical properties. The FTIR metabolomics showed significant different of the chemical fingerprinting subjected to heating duration, which in agreement with the result of 1H NMR metabolomics. Partial least squares (PLS) model revealed that most of the physicochemical properties of periodically heated palm oil are positively correlated (R2 values of 0.98–0.99) to their spectroscopic pattern. Based on the findings, the color of the oils darkened with increased heating time. The peroxide value (PV), p-anisidine value (p-AnV), and total oxidation (TOTOX) values increased significantly due to degradation of unsaturated compounds and oxidation products formed. We identified targeted metabolites (probable carcinogens) such as 3-monochloropropane-1,2-diol (3-MCPD) and glycidyl ester (GE), indicating the conversion of 3-MCPD to GE in repeatedly heated oils based on PCA and OPLSDA models. Our correlation analysis of NMR and physicochemical properties has shown that the conversion of 3-MCPD to GE was significantly increased from 180 to 360 min cooking time. The combination spectroscopic techniques with physicochemical properties are a reliable and robust methods to evaluate the characteristics, stability and chemical's structure changes of periodically heated palm oil, which may contribute to probable carcinogens development. This study has proven that combination of NMR and physicochemical analysis may predict the formation of the probable carcinogens of heated cooking oil over time which emphasizing the need to avoid certain heating cycles to mitigate formation of probable carcinogens during cooking process.

Microwave Sensitivity Enhanced Asphalt Mastic with Magnetite Powder and Its Performance after Microwave Heating

Microwave heating technology is a promising method for asphalt pavement maintenance and de-icing; however, it requires the material to have a good microwave-absorbing ability and can also result in asphalt aging. It is therefore important to develop microwave-sensitive materials used for asphalt pavement maintenance and study the effects of microwave heating on asphalt aging. This study evaluates the electromagnetic characteristics of limestone powder and magnetite powder and explores the influence of microwave heating on the high-temperature rheological and fatigue properties of microwave sensitivity enhanced asphalt mastic with magnetite powder. A vector network analyzer was used to measure the electromagnetic characteristics of limestone powder and magnetite powder. The magnetite filler asphalt mastics were prepared and subjected to microwave heating for 1 h, 2 h, 3 h, and 4 h. Temperature sweep tests, frequency sweep tests, and linear amplitude sweep (LAS) tests were conducted for magnetite filler asphalt mastics before and after microwave heating. LAS experimental results were analyzed based on viscoelastic continuum damage (VECD) theory. The results show that magnetite powders have better electric field energy storage ability, higher dielectric loss and magnetic loss, and better microwave heating efficiency. The complex shear modulus (G*) and rutting factor (G* × (sin δ)−1) rapidly decrease with the increase in temperature, indicating that the mastics’ ability to resist deformation decreases sharply. The longer the microwave heating time for magnetite filler asphalt mastics, the faster the high-temperature rheological properties decreased as the temperature rose. The fatigue life of magnetite filler asphalt mastics significantly decreases with the increase in strain and microwave heating time. It is suggested to add anti-aging agents into asphalt materials to reduce the aging effect in the process of microwave heating. This study provides a reference for the application of microwave heating technology in asphalt pavement maintenance.

Axial compressive performances of thin-walled steel tube confined steel-reinforced concrete columns after fire exposure

The thin-walled steel tube confined steel-reinforced concrete (STCSRC) column can efficiently utilise the confinement effect of steel tube on concrete. The local buckling of external thin-walled steel tubes can be delayed or avoided owing to their discontinuity at beam–column joints, thus, the structural performances of thin-walled STCSRC columns are improved. To date, the behaviour of thin-walled STCSRC columns after fire exposure under axial load has not been reported. Experimental and theoretical studies of axially-loaded circular thin-walled STCSRC stub columns were conducted in this paper, exploring mechanical performance indexes and mechanisms after fire exposure. A total of eighteen thin-walled STCSRC stub columns were designed, considering the parameters of the steel tube to concrete area ratio, heating time, and strength of the concrete. To better comprehend the behaviours of thin-walled STCSRC stub columns after fire exposure, detailed discussions in terms of the temperature distribution, failure modes, load–axial strain response, stresses of steel tubes, and load proportion of each component are presented. The heating test results reveal that the maximum temperature is lower and the time to reach the peak temperature is longer when measuring points are closer to the centre of the cross-section. The thin-walled STCSRC stub column after fire exposure presents shear failure under axial compression. The longer the heating time, the earlier the shear slippage line appears. Compared with the specimen at room temperature, the residual compressive resistance and stiffness reduce with increasing heating time. The ductility of the thin-walled STCSRC stub column improves when increasing the heating time. In addition, the diameter of the cross-section, H-shaped steel to concrete area ratio, and concrete strength have beneficial effects on residual axial load capacities and stiffnesses. Moreover, simplified calculation methods were assessed to predict the residual axial load capacities and stiffnesses of thin-walled STCSRC stub columns.

3D/4d printing of β-cyclodextrin-based high internal phase emulsions

The β-cyclodextrin (β-CD) based high internal phase emulsions (HIPEs) were prepared as building blocks for engineering high-quality 3D shapes and achieving 4D color transformation. The increase of β-CD concentration, the decrease of pH value, and the addition of NaCl contributed to the adsorption of β-CD molecules at the oil-water interface and the improvement of the microstructure, rheological properties and printing quality of the Pickering HIPEs. Moreover, the 4D printing of Pickering HIPEs was achieved by introducing pH-sensitive curcumin and heat-labile NaHCO3. With the increase in heating temperature, heating time and NaHCO3 concentration, the decomposition of HCO3− to CO32− led to an elevation in pH, which induced the conformational change in curcumin, accompanied by a decrease in L* and b × values and an increase in a × value of the samples. These findings dramatically improve the pleasure of diet and take full advantage of the custom design benefits of 3D printing technology.

Experimental investigation for combustion performance of hydrogen and natural gas fuel blends

The current study aims to investigate the effect of adding hydrogen into natural gas. Some significant parameters, such as natural gas consumption, heating time and heating value, are studied experimentally to observe the effects of hydrogen addition into natural gas on these parameters. Natural gas combustion in a gas stove is compared with the burning of hydrogen and natural gas blend in three different hydrogen volumetric fractions of 10%, 20%, and 30%. In order to minimize the errors in the experiments, the heating period is prolonged by using 5 kg of tap water heated from the ambient temperature to 60 °C. Two gas stoves are used for natural gas and hydrogen-natural gas blend simultaneously and under the same operating conditions. Tests are repeated and values are checked through an error analysis process. 0.045 m3 of natural gas and 0.011 m3 of hydrogen in the blend (with a hydrogen ratio of 20%) are consumed for the same heating load requirement. The results of this study show that 8% of the natural gas can be saved once hydrogen is added to natural gas in a 20% blend. Meanwhile, there is a 15.9% increase in heating time for the 20% volumetric hydrogen in the blend.

Effect of rice bran rancidity on the structural characteristics and rheological properties of rice bran protein fibril aggregates

Rice bran protein (RBP) was isolated from rice bran (RB) with different storage time and rice bran protein fibril aggregates (RBPFAs) were prepared by heating (90 °C) under acidic condition (pH 2.0) to investigate the effects of RB rancidity on the structural characteristics and rheological properties of RBPFAs. The results showed that the optimal RBP concentration for the preparation of RBPFAs was 40 mg/mL. As the heating time increased, the thioflavin T intensity, β-sheet content, average particle size, ζ-potential, and surface hydrophobicity of RBPFAs firstly significantly increased and then decreased (P < 0.05). When the heating time remained constant, the thioflavin T intensity, β-sheet content, ζ-potential, and surface hydrophobicity of RBPFAs significantly decreased with increasing the RB storage days from 0 to 10 d, while the average particle size significantly increased (P < 0.05). When heated for 8 h, the thioflavin T intensity of RBPFAs decreased from 1027.86 to 521.06 with increasing RB storage time, while the average particle size increased from 976.55 nm to 1285.50 nm. The viscosity, storage modulus (G′) and loss modulus (G’’) of RBPFAs gradually increased with the increase of RBP oxidation degree and heating time. Furthermore, the average particle size of RBPFAs was significantly correlated with their rheological properties (P < 0.05). Overall, RBP oxidative aggregation induced by RB rancidity inhibited the formation of RBPFAs, but enhanced their rheological properties. This study was instructive for the development and application of RBPFAs.

Study on the Purification and Reusability of Burnt Cooking Oil and Assessment of Its Physicochemical and Safety Parameters

Aims: The aim of the study was to investigate the reusability of edible oils and to find which temperature the refined oils could be used for cooking purposes.&#x0D; Study Design: The study followed a completely randomized design (CRD).&#x0D; Place and Duration of Study: The study was conducted at the Department of Agro Product Processing Technology and its corresponding laboratory on Jashore University of Science and Technology, Jashore, Bangladesh. The study took three consecutive months to complete the study.&#x0D; Methodology: The study adopted several methods to refine the burnt cooking oils and analyze their physicochemical as well as cooking qualities. At first, the heat was applied to commercially purchased palm, soybean, and rice bran oil. Produced burnt oil was refined using a base and hexane mixture. After that, these refined oils were repeatedly heated for 15, 30 and 60 minutes and physicochemical quality like peroxide value (PV), saponification number (SN), acid value (AV), etc were analyzed for each oil sample at each time interval. Furthermore, cooking quality of the refined oils was determined by frying sausages using each oil and the flavor, color, texture and overall acceptability were determined using hedonic scale.&#x0D; Results: The study found that the refining rate of each oil was at the peak when the base -to-hexane ratio was 9:1. An increasing trend was observed in the case of the peroxide value of the refined oils during repeated heating. This trend was most predominant in case of palm oil. In palm oil sample, PV of palm oil increased from 4.950±0.6 to 14.432±0.86 meqo2/kg oil at the third time of heating. The other two sample oils also crossed the standard PV of the respective oil at the third time of heating. It means all the refined oil can be used for a maximum of three times. Acid value of the oils also showed the same trend of increasing with an increase in temperature. In the case of SN, palm oil showed a higher degree of saturation with increased heating time among the refined oils. The flavor, color, texture, and overall acceptability of the sausages fried in these three showed significant differences at p&lt;0.05. This is an indicator that burnt cooking oil that was refined can be reused in cooking. &#x0D; Conclusion: Due to the increasing price of edible oils and limited resources, they can be refined from their burnt stage and reused for cooking. Therefore, refining can be a good method to solving edible oil scarcity.

BiOBr Surface-Functionalized Halide Double-Perovskite Films for Slow Ion Migration and Improved Stability

Surface-tailored lead-free halide double-perovskite (Cs2AgBiX6) thin films are utilized for ion migration studies. A thin surface layer of BiOBr/Cl is grown via intentional annealing of the halide films in ambient conditions. Herein, we physically stacked the two films, viz., Cs2AgBiBr6 and Cs2AgBiCl6, to thermally activate the halide ion migration at different temperatures (room temperature (RT)-150 °C). While annealing, the films' color changes from orange to pale yellow and transparent brown to yellow as a result of the migration of Br- ions from Cs2AgBiBr6 to Cs2AgBiCl6 and Cl- ions from Cs2AgBiCl6 to Cs2AgBiBr6, respectively. Annealing helps in homogenizing the halide ions throughout the films, consequently leading to a mixed phase, i.e., Cs2AgBiClxBr6-x/Cs2AgBiBrxCl6-x (x = 0 to 6) formation. The movement of ions is understood by absorption studies performed at regular time intervals. These investigations reveal a redshift (from 366 to 386 nm) and a blueshift (from 435 to 386 nm) in absorption spectra, indicating the migration of Br- and Cl- toward Cs2AgBiCl6 and Cs2AgBiBr6, respectively. The films characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal the presence of a peak at 2θ = 10.90° and binding energy of 158.1 eV, respectively, corresponding to the formation of Bi-O bonds at the film surface. Also, XRD studies show a lower 2θ shift of the diffraction peak in the case of Cs2AgBiCl6 films and a higher 2θ shift in the case of Cs2AgBiB6 films, which further confirms the migration of Cl- and Br- from one film to the other. XPS investigations confirm the compositional change with a gradual increment in the concentration of Br-/Cl- with an increase in heating time for Cs2AgBiCl6/Cs2AgBiBr6 films. All these studies confirm thermal diffusion of halide ions in double-perovskite films. Further, from the exponential decay of the absorption spectra, the rate constant for halide (Br) ion diffusion is calculated, which shows an increment from 1.7 × 10-6 s-1 at RT to 12.1 × 10-3 s-1 at 150 °C. The temperature-dependent rate constant follows Arrhenius behavior and renders an activation energy of 0.42 eV (0.35 eV) for bromide (chloride) ion mobility. A larger estimated value as compared to the reported values for Cs2AgBiBr6 wafers (∼0.20 eV) reveals a slow mobility of halide ions in thin films of Cs2AgBiBr6/Cl6. The formation of a BiOBr passivation layer at the surface of Cs2AgBiBr6 thin film might be one of the plausible causes of the slow anion diffusion in the present work. Slow ion migration is an indication that the films are stable and of high-quality.

Effect of thermal treatment and addition of olive oil on the antioxidant properties of tamarillo puree.

The study intended to determine the effect of temperature (100-200°C), time (2-6min), and oil on the bioactive properties and colour parameters of tamarillo puree. The increase in heating temperature (up to 175°C) and time increased the phenolic content, flavonoids content and antioxidant activity. Carotenoids were found to increase from 0.65 to 1.06 (mg β carotene/ g) in puree with oil heated at 200°C for 6min. In puree with oil, the lightness (L*) and redness (a*) values of puree were found to be reduced, but yellowness (b*), hue angle and chroma improved with treatment temperature and time. Addition of oil exhibited positive influence on retaining the bioactive compounds in comparison to puree without oil, which can be attributed to their enhanced extractability. In conclusion, the desirable effect of heating temperature and time, and addition of virgin olive oil will be helpful in canning of oil enriched tamarillo puree.

Induction brazing of NdFeB magnet with PVD-deposited AgCu alloy

The NdFeB magnets service in high-power electric-mechanical conversion devices sometimes endure high stress and high-temperature impact, and adhesion of these magnets using glue cannot ensure the reliability. In this study, the NdFeB was induction brazed with physical vapor deposition (PVD)-deposited Ag72Cu28 alloy layer, then the microstructure, mechanical properties and magnetic properties of the brazed joints were characterized, and effects of the filler metal thickness and the induction heating time were analyzed. The results show that the PVD coating can effectively prevent the surface oxidation of the NdFeB. The AgCu filler metal penetrates into the NdFeB and is partly mixed with the liquefied Nd-rich intergranular phase of the NdFeB, forming a good metallurgical bonding. The thickness of the penetration layer increases obviously with increase of the heating time and filler metal thickness. The bonding strength of the NdFeB brazed joint increases firstly and then decreases with increasing heating time, and a peak bending strength of 196.94 MPa was obtained. Fracture of the brazed joint occurs inside the NdFeB substrate close to the penetration layer. After a further annealing, the coercivity of the brazed NdFeB sample is a little higher than that of the un-brazed sample, and the squareness decreases by only a little. Properties of the brazed joints might be further improved by optimizing the amount of filler metal and the induction heating parameters.

Evaluation of heating times for loss-on-drying at 105 °C for estimation of laboratory dry matter in animal feeds.

Dry matter is a routine test for all animal feeds, facilitating feed comparisons and diet formulation. It is the most frequent test, yet the most challenging with respect to precision and accuracy. Our objective was to evaluate the accuracy, repeatability, and physicochemical impacts of oven-drying times on laboratory dry matter test results in animal feeds obtained by loss on drying at 105 °C. Eighteen primary samples collected from different feed sources were grouped into high- and low-moisture content materials. The tested methods were based on loss on drying: at 105 °C and Karl Fischer titration was adopted as the reference method. Test portions were oven dried at 105 °C for 3, 6, 12, 16, and 24 h, and test results were compared to the reference method. Test portions were also subjected to a color evaluation using a colorimetric technique. The method based on 3 h of drying provided the closest estimates to those obtained by Karl Fischer titration. Extending heating time (i.e., above 3 h) increases the bias, especially for high moisture feeds, which was attributed to a higher occurrence of non-enzymatic reactions. This was corroborated by the color of the residues, which became darker with increased heating time. The repeatability of loss on drying methods was considered adequate, ranging from 0.32 to 0.73%. The loss-on-drying method based on the binomial 105 °C × 3 h minimizes the bias in the water recovery and causes less non-enzymatic browning in the test portions. The loss-on-drying method recommended for laboratory dry matter in animal feeds is drying the test portions at 105 °C for 3 h.

안토시아닌 조성이 다른 베리류 3종의 열안정성 비교

Anthocyanins are natural pigments responsible for the red, purple, and blue colors in berries. The stability of anthocyanins can be affected by various factors, such as pH, temperature, and other components. This study investigated the degradation kinetics of anthocyanins in representative berries. Among the most consumed berries in the Korean population, black chokeberry, black mulberry, and blueberry were chosen due to their high anthocyanin contents. The berries contained anthocyanins with different aglycones and sugar moieties as follows: cyanidin-3-galactoside (63%) and cyanidin-3-arabinoside (30%) in black chokeberries, cyanidin-3-glucoside (70%) and cyanidin-3-rutinoside (25%) in black mulberries, and malvidin-3-galactoside (35%), malvidin-3-arabinoside (16%), and delphinidin-3-galactoside (14%) in blueberries. After heating at 100℃ for 60 min, the degradation of anthocyanins was highest in the black chokeberries (62%), followed by blueberries (54%) and black mulberries (50%). Within the same aglycone, glycosylated anthocyanins with glucose had higher retention compared to those with galactose or arabinose. Lightness (LSUP*/SUP) showed a tendency to increase with increasing heating time. Color difference (ΔESUP*/SUP) was lowest in the black mulberries and highest in the blueberries. These results indicate that the thermal stability of anthocyanins was in the following order: black mulberry blueberry black chokeberry.

Use of Heating Methods and Xylose to Increase Rumen Undegradable Protein of Alternative Protein Sources: 1) Peanut Meal

Peanut meal has an excellent total protein content but also has low rumen undegradable protein (RUP). High-performance ruminants have high RUP requirements. We aimed to evaluate the effects of processing peanut meal with an autoclave and conventional and microwave ovens, with and without using xylose on its ruminal kinetics degradation parameters and intestinal digestibility (ID). In situ studies were conducted to determine dry matter (DM) and crude protein (CP) rumen degradation kinetics. In vitro studies were conducted to evaluate intestinal digestibility (ID). The control treatment had a greater fraction A for DM and CP than peanut meals processed with an autoclave or conventional oven. The control had greater kd for CP compared with the microwave. The addition of xylose decreased fraction A, the degradation rate of fraction B (kd) and RUP, and increased the protein B fraction of autoclaved peanut meal. We observed a decrease in effective degradability (ED) and increased RUP for processed treatments in all experiments compared with the control. Processing methods did not affect the protein ID of autoclaved peanut meal compared to the control. An interaction between xylose and heating time was observed, where increasing heating time linearly reduced the ID of xylose-untreated treatments. Overall, these results suggest that the tested methods effectively increased the RUP content of peanut meal.

Groundwater Heat Pump assessment operation in three cities of south-central Chile: An approach based on aquifer characterization and analytical calculations of Thermal Affectation Zone

The aim of this work is the Groundwater Heat Pump (GWHP) assessment in three cities in south central Chile (Talca, Temuco, and Osorno), considering the hydraulic parameters of the aquifer, its temperature, and the Thermal Affectation Zone (TAZ) generated around the reinjection well due to the reinjected water flow, and temperature difference, due to thermal recovery.According to the hydraulic characterization, the conditions are more favorable in the city of Talca, where the hydraulic conductivity is medium to high. On the other hand, in the cities of Temuco and Osorno, the hydraulic conductivity is low or very low, except in some domains of river belts, where the hydraulic conductivity is medium to high. In all cities, the temperature of the aquifer is very good for heating and cooling. In particular, in Talca downtown there is a positive thermal anomaly that improves the GWHP performance for heating purposes.In each city, the extension of the TAZ was calculated for a reinjection rate of 5 [L/s], and a thermal recovery of 3 [°C] (heating). In each city, the TAZ was calculated for the hydraulic conductivity values corresponding to the percentiles 25, 50, and 75. The hydraulic gradient is fixed for each city. The heating time increases from north to south (Talca, Temuco and Osorno) due to the climate. In all cities and in all cases, temperature dispersion due to groundwater flow is moderate to slight and concentrated around the reinjection well. The largest extension of TAZ in the direction of groundwater flow is calculated in Talca, reaching approximately 30 m. On the other hand, the greatest reach of TAZ in the opposite direction to the groundwater flow is calculated in Osorno, reaching approximately 20 m. The effect of varying injection rates (3, 5 and 10 L/s) does not significantly affect the distance range of TAZ, yet affects the concentration of TAZ around the reinjection well.

Dynamic compressive strength and failure mechanisms of microwave damaged sandstone subjected to intermediate loading rate

To investigate the influence of microwave heating on the dynamic behavior and failure mechanisms of rock, dynamic compression tests were conducted on microwave-irradiated sandstone specimens using a modified split Hopkinson pressure bar (SHPB) system. Experimental results show that microwave radiation can effectively weaken the compressive strength of sandstone. Rock specimens show three different failure modes under impact load: tensile failure, tensile—shear composite failure and compressive—shear failure. The dynamic Poisson’s ratio, calculated using the measured P- and S-wave velocities, is introduced to describe the deformation characteristics of sandstone. With the increase in microwave power and heating time, the Poisson’s ratio declines first and then increases slightly, and the turning point occurs at 244.6 °C. Moreover, the microstructural characteristics reveal that microwave radiation produces dehydration, pore expansion, and cracking of the rock. The damage mechanisms caused by microwave radiation are discussed based on thermal stress and steam pressure inside the rock, which provides a reasonable explanation for the experimental results.

GREEN SYNTHESIS OF SILVER NANOPARTICLES AND THEIR SPECTRAL PROPERTIES

Spherical silver nanoparticles were synthesized by the chemical condensation method using aloe vera or chamomile extracts as a reducing agent. Depending on the type of extracts and its concentration, the size of AgNpcs varied from 7 to 50 nm by simply adjusting the ratio of the starting reagents. These extracts show reducing properties due to the presence of carbonyl compounds in their composition, in particular organic acids. It is shown that regu­lation of concentrations and synthesis conditions allows control of particle size. A change in the synthesis conditions affects the position of the surface plasmon resonance band, and therefore the optical properties of the studied systems. It has been proven that the synthesized silver nanoparticles do not require additional stabilization. Agglomeration processes occur only with a significant increase in concentration and heating time.

On improving process efficiency and weld quality in ultrasonic welding of misaligned thermoplastic composite adherends

This paper evaluates the potential of changing the welding force and the compliance of the energy director (ED) to reduce the effects caused by misaligned adherends, which were: increased through-thickness heating, reduced size of welded area and increased heating time. In the methodology that was followed, we welded adherends misaligned by approximately 4.5° in different scenarios: with higher welding force; with increased ED compliance by the use of a thicker ED and; with increased ED compliance by the use of a discontinuous ED. The most significant reduction of the effects caused by misaligned adherends was obtained when combining the use of both increased welding force and discontinuous ED. Such improvement derives from the imposed parallelism caused by the use of a higher welding force and from a more efficient concentration of heat generation at the weld line that occurs when a discontinuous ED is used.

Influence of microwave heating on the swelling properties of expansive soil in Hefei

The swelling deformation of expansive soil after immersion often lead to engineering disasters. In this paper, the experiments on the swelling properties of expansive soil in Hefei after microwave heating have been carried out. The results show that, the soil samples change from fine particles to coarse particles after microwave heating. With the increase of microwave heating time, the specific gravity of soil samples first increases and then decreases, while the liquid and plastic limit continue to decrease. In addition, microwave heating significantly affects the swelling behaviors of soil samples. With the increase of microwave heating time, both the free swelling ratio and vertical free swelling strain decrease. In the process of microwave heating, there are a series of physical and chemical changes in expansive soil, such as the water escaping from the interlayer structure of clay minerals, the transformation and decomposition of material components, which significantly changes the physical and mechanical properties of expansive soil.