Conventional Microwave Oven Research Articles

Identification of turntable function in a solid-state microwave heating process with diverse frequency-shifting strategies applied

The turntable has been used in conventional magnetron-based microwave ovens to improve the heating uniformity. Meanwhile, with the emerging solid-state technique, well-designed frequency-shifting strategies also show promise in achieving improved microwave outcomes without a rotating turntable. This study used modeling tools to comprehensively assess the turntable function under various conditions, where the affecting factors included vertical and horizontal positions of food, rotation status of the turntable, frequency-shifting strategy, and food configurations. Results illustrated that the elevation of food by the turntable is more critical to power efficiency and heating uniformity, while rotation mainly works to narrow the temperature difference between hot and cold spots. Moreover, the complementary-shifting strategy lessened the rotation function of the turntable. Hence, in a solid-state microwave system embedded with a proper frequency-shifting strategy, a simpler supporting component shall replace the current rotating turntable, streamlining the oven design without compromising the microwave performance. Industrial relevanceThis study comprehensively evaluated functions of the turntable, a conventional component, inside a novel microwave system design utilizing solid-state instead of the magnetron as its power source. Based on the evaluation, the well-implemented frequency strategies hold promise to achieve improved microwave performance with a simpler supporting component to elevate the food, rather than relying on a rotating turntable. These findings provide novel insights for designing the next-generation microwave ovens.

Microwave joining of copper pipes using selective microwave hybrid heating process: Simulation and experimental study

High thermal conductivity of copper poses serious challenges in its joining in conventional welding techniques leading to development of alternate welding techniques. Microwave welding is one such newly developed joining technique that use selective microwave hybrid heating (SMHH). The joining of the copper pipes using SMHH has not been explored in existing literature. The present paper attempts the microwave joining of copper pipes using SMHH. The exposure time required for joining copper pipes using SMHH was predicted by COMSOL Multiphysics software. The joining was attempted at the predicted exposure time using a novel cavity design inside a conventional microwave oven. The copper pipes have been successfully joined at temperature and exposure period of 1080ºC and 720 s respectively and was in good agreement with the predicted values i.e., 708 s. Scanning electron microscopy (SEM) revealed good metallurgical bonding between the base metal and joint interface. The presence of columnar grains has been observed at heat affected zone (HAZ) using electron back scattered diffraction (EBSD). EBSD analysis revealed randomly arranged grains with mixed modes of planes inside the base metal. The occurrence of high angle grains (HAGs) along with high dislocation density in base metal resulted in the improvement in the mechanical properties as revealed in grain average misorientation (GAM) maps. The maximum value of microhardness has been observed at the joint region (105 ± 7 Hv) followed by base metal and HAZ i.e. (97 ± 5 Hv) and (89 ± 8 Hv) respectively owing to the existence of fine grain of copper (µm) and carbide formation.

Real-time monitoring of ground-tire rubber microwave devulcanization with thermal and electrochemical sensors

Devulcanizing ground-tire rubber (GTR) properly requires the removal of the sulphur linkages that crosslink the polymer. The volatile sulphur compounds (VSCs) released during the process must be extracted from the reactor to avoid any chemical recombination, and the sulphur gas concentrations conveniently sensed during the extraction, along with a thermal sensoring of the payload, can be used to monitor the whole devulcanization process. In this contribution, a modified conventional microwave oven was used to devulcanize the GTR. The microwave-processed GTR was evaluated by determining the values of its mass loss (ML), soluble fraction (sol fraction), and the variation of its electric permittivity. Results show a direct relationship between the energy delivered, sol fraction, the VSCs concentrations, the ML, and the permittivity values. Thus, this paper demonstrates that monitoring the VSCs can provide a reliable indication of ML and, consequently, devulcanization evolution even at non-uniform temperature conditions.

Efeito do tratamento térmico nas características do concentrado proteico proveniente da carne mecanicamente separada de salmão do atlântico

The objective of the study was to develop protein concentrates from mechanically separated meat of Atlantic salmon, as well as to evaluate the influence of different heat treatments, namely: electric oven, conventional gas oven and microwave oven, on the chemical characteristics of the final product. The oven and microwave generated potentially more stable products, with lower water and moisture activity and higher protein contents. In general, all treatments originated salmon protein concentrates with expressive attributes for the development of new fortified products, being an attractive ingredient for the reuse of waste from the fish industry.

Evaluation of soy stroganoff formulations in the IF Goiano Campus Ceres

Textured soy protein is a food alternative that can partially replace animal derivatives, and meet some dietary restrictions, and its use in ready-to-eat dishes will make food practical in its preparation. The objective was to carry out the evaluation of soy stroganoff formulations at the IF Goiano Campus Ceres. Three formulations of soy stroganoff (traditional, light and lactose-free) were prepared, stored in two types of packaging (for conventional oven and microwave oven). Microbiological tests were performed for molds and yeasts (CFU/g), coliforms at 35°C and 45°C (NMP/g); physical-chemical analyzes of pH, titratable acidity, moisture, total solids; acceptance sensory tests (blind and with information) by attribute (global impression, texture, flavor, appearance, color and aroma), acceptability index (IA), purchase intention and consumer profile through a structured questionnaire with questions closed. Regarding physical-chemical determinations and sensory tests of acceptance and purchase intention, they were submitted to analysis of variance and differences in means compared by Tukey's test at a 5% significance level. The results of the microbiological analyzes were descriptively evaluated. The results of the acceptability index and consumer profile were evaluated in percentage. A completely randomized experimental design was used, in three lots, three replications and in triplicate. Except for batch 2 of treatments A, C and D (16, 30 and 16 CFU/g), in all other batches of treatments, mold and yeast values were negative, with the samples ready for consumption. It was observed for coliforms at 35 °C and 45 °C that all treatments showed negative results (>3 MPN/g), demonstrating good microbiological quality. For the physical-chemical parameters, all treatments were significantly different from each other. Treatment E (traditional, conventional oven), regardless of the evaluated attribute, had an AI above 70%, and obtained a higher purchase intention value compared to treatment C (lactose-free, microwave) with a lower value, a result that has already been expected. Treatments B, C and E, regardless of the evaluated attribute, obtained AI above 70%, with the products ready to be commercialized. It was observed that 78% of participants consume stroganoff and the majority (98%) are unaware of other types of stroganoff on the market other than the traditional one. They also reported being the flavor of chicken stroganoff that they most know (90%) and consume (90%). Most prefer to use a microwave oven to defrost ready meals. All formulations showed good microbiological parameters. Regardless of the physical-chemical parameter evaluated, all treatments were significantly different from each other. Comparing the results, it was observed that the use of information in relation to the blind test during the sensory acceptance tests interfered with the tasters' response to the different evaluated formulations. The traditional formulation for conventional oven E stood out in the acceptability index and blind purchase intention tests, this being the formulation most conducive to commercialization.

Microstructural and mechanical properties of mild steel pipes joined using selective microwave hybrid heating

Microwave joining is an eco-friendly non-conventional technique resulting in fine grain structure, overall improvement in quality, and performance of the processed materials with up to 90 % less energy consumption than conventional processes. Due to problems including difficulty in positioning the susceptor material in the joint region and reduced solid cross-section area of hollow pipes, an efficient and precise process for microwave joining metallic pipes is yet to be developed. The present work is an attempt to join mild steel (MS) pipes placed horizontally in a conventional microwave oven. COMSOL Multiphysics software has been used to simulate the microwave joined MS pipes, wherein the temperature distribution in the specimen inside the microwave cavity was analyzed. The MS pipe was successfully joined at an exposure time of 900 s with nickel powder as an interfacial material. Characterization of the welded joint has been carried out using microstructural and mechanical properties. A fully dense and homogeneous microstructure with good metallurgical bonding was revealed through scanning electron microscopy (SEM). The Vicker's microhardness of joined specimen was 262 ± 10 HV at the joint zone, while the heat affected zone (HAZ) was 240 ± 10 HV. The joined specimen exhibited an ultimate tensile strength of 217 ± 8 MPa with an elongation of 4.4 ± 0.7 %.

Particle-in-Cell Simulations of Ten-Vane Microwave-Oven Free-Running 2.45-GHz “Cooker” Magnetron: Microwave Power Increase up to 6 kW in a Pulsed Mode (3 kW With 50% Duty Cycle)

Standard operation of a conventional microwave oven 2.45-GHz “cooker” magnetron with 4.0–4.3 kV of pulsed applied voltages at 0.17–0.19-T magnetic fields results in generation of pulsed microwave power 1.8–2.8 kW, which is recalculated to an average microwave power 0.9–1.9 kW when the “cooker” magnetron operates with 50% duty cycle while driven by a “rectified” ac voltage from the wall-plug. It has been shown in many experimental studies of “cold-start” operation of a standard ten-vane 2.45-GHz “cooker” magnetron that it readily sustains, when properly conditioned, up to ~10-kV dc and up to ~14 kV of peak-to-peak ac applied voltage with just a few microamphere cold (field emission) leakage (anode) current. The latter suggests that a standard 2.45-GHz “cooker” magnetron may successfully operate in the desired, lowest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode with much more output microwave power at even higher magnetic fields when driven by up to ~10 kV of dc or quasi-dc appropriate, synchronous applied voltage. Results of improved concurrent electromagnetic particle-in-cell (ICEPIC) simulations of magnetron operation at different magnetic fields with synchronous applied voltages show that, for example, with 8.0-kV applied voltage at 0.35-T magnetic field, the 2.45-GHz “cooker” magnetron is able to generate up to 6.0 kW of pulsed microwave power with an anode current of ~0.9 A.

Synthesis of Gold Nanoparticles and Their Reduced Graphene Oxide Nanocomposites Through a Simplified Approach and Assessment of Their Bactericidal Potential

The development of metallic nanoparticles has attracted tremendous interest and has potential applications in multiple healthcare regimes. This study used irradiation from a conventional microwave oven, a straightforward, simple approach to fabricate gold nanoparticles (AuNPs) and AuNPs reduced graphene oxide nanocomposites (AuNPs-rGO). UV-visible (UV-Vis) and Fourier Transform Infrared (FTIR) spectra were recorded to reveal the composition of the nanocomposites. X-ray Diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) investigations were used to analyze the shape, size, and crystal structure of the produced AuNPs-rGO nanocomposites. The antibacterial activity of these nanocomposites was evaluated by disc diffusion assay and colony inhibition againstS. aureusGram-positive andE. coliGram-negative bacteria. Our data revealed a face-centered cubic shape attached to the AuNPs to the rGO sheets. Furthermore, these methods demonstrated that bonding AuNPs with reduced graphene oxide (rGO) layers resulted in bacterial suppression comparable to bare AuNPs. In addition, we investigated the antibacterial potential of AuNPs and nanocomposites against multidrug-resistantStaphylococcus aureusandPseudomonas aeruginousand found them very effective. The approach described here for concocting the AuNPs, and AuNPs/rGO nanocomposites effectively produce very stable, well-dispersed, spherical particles anchored to the surface of rGO sheets have the potential to be used as antibacterial formulations against multiple drug-resistant strains.

Hybrid composite materials generated via growth of carbon nanotubes in expanded graphite pores using a microwave technique

Herein we demonstrate a facile in-situ synthesis method by selection of expanded graphite as a matrix growth microreactor, nickel nitrate (Ni(NO3)2) as a growth catalyst and naphthalene as a carbon source, assisted by a conventional household microwave oven. Affection parameters related to control of the growth process, such as the microwave heating time, catalyst concentration and carbon source concentration. The optimized experimental conditions that exhibit excellent microstructure were: a carbon source concentration of 20.0 mg/ml, a catalyst concentration of 10.0 mg/ml and a microwave reaction time of 30 s. The microstructure of the synthesized composites was investigated and a solid-gas growth mechanism with this carbon source precursor is proposed. The micro morphology, formed CNT structure and resistivity of the composites are fully characterized and analyzed by thermal field emission high-resolution scanning electron microscopy (FESEM), confocal laser Raman spectrometer (Raman) and a four-point probe resistivity meter. All characterization data show a uniform CNT diameter distribution of approximately 30.0 nm with a low resistivity of the composites (1.12 × 10−5 Ω·m), indicating uniform hybrid composite material formation with novel physical properties.

Dimensional Stability of Elastomeric Impression Material After Disinfection Via Immersion and Microwave Irradiation

Aims: This study aimed to evaluate and compare the dimensional stability of two elastomeric impression materials, namely polyvinyl siloxane (PVS) and vinyl siloxanether (VSE), subjected to chemical immersion and microwave irradiation for disinfection. Materials and Methods: Sixty discs of PVS and VSE impression materials each were prepared using a stainless-steel test die and ring in accordance with ANSI/ADA Specification No. 19. Twenty discs of each impression material were disinfected by chemical immersion for 10 min; another 20 discs were subjected to dry microwave irradiation for 3 min. The other 20 discs served as a control group. Dimensional stability measurements were then performed using an image analyzer at 20× magnification. The data were analyzed by one-way analysis of variance (α=0.05) and Bonferroni (post hoc) test for multiple comparisons to detect significant differences between the groups. Results: When subjected to microwave irradiation, both PVS and VSE showed dimensional changes, but the changes were within the limit of 1.5% set by ANSI/ADA (P&lt;0.00). VSE showed markedly better results than PVS for both disinfection methods. The immersion disinfection method resulted in a higher average percentage of linear dimensional changes than both the microwave irradiation and the control for VSE and PVS impression materials. Conclusion: VSE exhibited excellent dimensional stability than PVS under both chemical immersion and microwave irradiation. Microwave irradiation using conventional microwave ovens can be used in clinical settings as an alternative to other disinfection techniques because the dimensional changes of the elastomeric impression materials subjected to microwave irradiation have been observed to be within the clinically acceptable limit set by the ANSI/ADA standard.

Incorporation of SCBA in Red Ceramics and Sintering in Microwave Oven

The present study investigated the incorporation of sugarcane bagasse ash (SCBA) in red ceramics, sintered in conventional oven and microwave oven, aiming to provide an alternative product, and a sintering process with higher energy efficiency in the production of red ceramics. The raw materials were characterized by XRF, XRD, thermogravimetry, particle size distribution and specific mass analyses. The specimens were shaped by extrusion in two different compositions, red clay and red clay with addition of 20 % SCBA and sintered at temperatures from 700 to 1100 ºC. The conventional sintering occurred for 60 min with heating rate of 10 ºC/min. In the microwave oven the sintering occurred in a hybrid way, with heating rate of 50 ºC/min for 5, 10 and 15 mins. After sintering the tests of linear shrinkage, compressive strength, water absorption, apparent porosity and apparent specific mass were performed. The addition of SCBA causes an increase in the values of water absorption and decreases the compressive strength and specific mass of the red ceramic. This occurs due to the creation of pores inside the material from the volatilization of organic matter present in the ashes. The sintering in microwave oven, when compared to conventional sintering, promotes an increase in the values of compressive strength and specific mass and reduction of water absorption values of ceramics, probably due to the refinement of the microstructure and the higher densification. Thus the incorporation of ashes can be partially compensated by a more efficient sintering. The use of SCBA and the sintering in microwave oven, showed to be viable alternatives in the development of a more sustainable and light material, promoting the management of waste, reduction in the consumption of raw materials and energy saving.

A Selective Ratiometric Fluorescent Probe for No-Wash Detection of PVC Microplastic.

Microplastics (MP) are micrometric plastic particles present in drinking water, food and the environment that constitute an emerging pollutant and pose a menace to human health. Novel methods for the fast detection of these new contaminants are needed. Fluorescence-based detection exploits the use of specific probes to label the MP particles. This method can be environmentally friendly, low-cost, easily scalable but also very sensitive and specific. Here, we present the synthesis and application of a new probe based on perylene-diimide (PDI), which can be prepared in a few minutes by a one-pot reaction using a conventional microwave oven and can be used for the direct detection of MP in water without any further treatment of the sample. The green fluorescence is strongly quenched in water at neutral pH because of the formation dimers. The ability of the probe to label MP was tested for polyvinyl chloride (PVC), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), poly methyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE). The probe showed considerable selectivity to PVC MP, which presented an intense red emission after staining. Interestingly, the fluorescence of the MP after labeling could be detected, under excitation with a blue diode, with a conventional CMOS color camera. Good selectivity was achieved analyzing the red to green fluorescence intensity ratio. UV–Vis absorption, steady-state and time-resolved fluorescence spectroscopy, fluorescence anisotropy, fluorescence wide-field and confocal laser scanning microscopy allowed elucidating the mechanism of the staining in detail.

Development of the manufacturing technique of crucibles to melt aluminum and improve its physical and mechanical properties by microwave oven

There are several techniques that are used to melt metal materials, among which we have conventional casting, by agitation, by compression and by molding. It is currently being studied in a technique based on electromagnetic radiation with the implementation of conventional microwave oven, thus improving the results in terms of time in the casting process; to carry out this electromagnetic casting process, a high-frequency wave-receiving medium is required to reach the melting temperature of the material on which it is being worked. In the case of aluminum, a working temperature of approximately 700 °C is required to achieve phase change of the material. This project produces a fine-grained silicon carbide-based crucible, taking into account that it is a semiconductor and refractory material capable of capturing electromagnetic waves, for the purpose of allowing the use of a microwave oven in the aluminum smelting process; presenting in this way a new casting technique that promises a significant saving in the execution time and saving the implementation process in recycling and reuse of aluminum and improving its physical and mechanical properties by means of irradiation casting electromagnetic.

COXSIYTEZ NANOCOMPOSITE MANUFACTURE BY SOLUTION COMBUSTION PROCESS ASSISTED BY MICRO-WAVE

A possible formation of the nanocomposite based on silicon, cobalt and tellurium was produced by the combustion synthesis process in solution (SCS) assisted by microwave in two stages, combustion using a conventional microwave oven and purification by means of calcination at 650 ºC in a muffle furnace. The new material was developed in different oxidant-fuel relationships where it observed the effects on the evolution of the phase and morphology of the powders, the structural, morphological and thermal properties were investigated by the X-ray diffraction technique (XRD), energy dispersive X-ray spectroscopy (EDX) coupled to the scanning electron microscope (SEM) and TGA and DTG curves. Through the analysis it is possible to suggest the development of a new stable material in single phase, being isostructural to the Co8Te12O32 (ICDD-50702) of nanometric dimensions with interesting potentials due to the properties of the constituent elements.

Effect of the Ni(NO3)2 additive on the electrophoretic deposition of NiO nanoparticles

In this work, we report the electrophoretic deposition of NiO nanoparticles on aluminum plates, as well as the effect of the nickel nitrate salt used as additive for coating deposition. First, the Ni(OH)2 nanoparticles were synthesized by a precipitation route with NaOH in a conventional microwave oven. This precursor was submitted to a heat treatment at 300 °C for 3 h in order to obtain the nickel oxide without any secondary phase. The NiO nanoparticles with mean crystallite size of 2.79 nm were dispersed in isopropanol and deposited by an electrophoretic procedure on aluminum substrates with 1 cm of distance and under 10 V of DC voltage for 30 min. XPS analysis of the as-prepared coatings reveals that metallic Ni is produced during the EPD process. Moreover, the presence of Ni(NO3)2 as additive on the electrophoretic procedure leads to changes in the morphological features of the coatings. In this sense, a compact and homogenous coating was formed without the presence of nickel salt, whereas a coating with porous and cavities was obtained with a 0.5 mM concentration of Ni(NO3)2. Moreover, a 1.0 mM concentration of the additive results in a poor coverage of the electrode surface. The porous structure of the coatings in combination with the formation of metallic Ni could be useful for electrochemical applications such as capacitors or electrochromic devices.

Adsorption of amoxicillin onto high surface area-activated carbons based on olive biomass: kinetic and equilibrium studies.

This study presents the extraction of antibiotic amoxicillin (AMX) from aqueous solution employing activated carbons (AC) from olive biomass (OB). Two AC were prepared using ZnCl2 (activator agent), and a conventional muffle furnace (ACF) or microwave oven (ACMW). The structure, morphology, and textural properties from both AC were analyzed by scanning electron microscope (SEM), pH of point-zero-charge (pHPZC), infrared spectroscopy (FTIR), and N2 adsorption/desorption isotherms. AC with mesoporous structures rich in oxygenated groups and high specific area (as high as 1742 m2 g-1) were helpful for the efficient and fast adsorption of AMX. The Avrami kinetic nonlinear equation showed the best fitting for the empirical data when related to the pseudo-1st and pseudo-2nd order. The isothermal experimental data followed the Liu nonlinear model, displaying at 25 °C the maximum sorption capacity of 237.02 and 166.96 mg g-1 for the ACF and ACMW, respectively. An adsorption test with synthetic hospital effluent was carried out to evaluate the possibility of applying both adsorbents in wastewater purification. The purification efficiency was up to 94.4% and 91.96% for ACF and ACMW, respectively. Therefore, the AC obtained from OB (containing a mixture of seed, pulp, and olive peel) has a high potential for application in removing emerging contaminants from the wastewater.

A Fuzzy Logic-based Control System for Microwave Ovens

Conventional microwave ovens rely on users for their cooking time. In other words, the user must set the oven’s cooking time manually. This paper aims to design a fuzzy logic-based controller to resolve the above-mentioned issue by determining the cooking time of the microwave oven automatically. The time determined depends on the quantity and type of food. During the fuzzy logic process, we used the Mamdani fuzzy model. This model involves determining the crisp input, fuzzification, rule evaluation, and defuzzification, to obtain the crisp output result. Input real variables used were the type of food and quantity of food, whereas the output variable used was cooking time. A fuzzy logic toolbox on MATLAB software was used to design and simulate the whole system. Considering the IF-THEN rules and functions, we used the value of food as 50, and the type of food as 50 and we obtained the cooking time as 25 minutes. The result showed that Fuzzy models are good at determining cooking time in Microwave ovens and that their cooking time depends on the inputs. Using fuzzy logic in microwave ovens helps to maintain food quality, saves users’ time, and controls the energy used by the oven.

Curie-temperature dependence of microwave heating behavior of NixZn(1−x)Fe2O4 powders

Recently, the microwave well absorber goes noticed as a heating aid to establish a microwave chemical plant. We determine the mechanism of the rapid and selective heating of magnetic conductive particles by electric and magnetic microwave fields. Furthermore, we investigate the dependencies of the Curie temperature of NixZn(1−x)Fe2O4 powders on their heating behaviors by employing a conventional microwave oven. In these experiments, the maximum microwave heating temperature increases with the Curie temperature of ferrites. To investigate the dependence of the microwave magnetic field strength on the heating behavior, we focus a pure magnetic field separated from 2.45 GHz microwaves onto these ferrites, and the magnetic field enhanced by a single-mode cavity is used to heat the ferrites at higher Curie temperatures. Our results indicate that there are two types of energy interactions between the ferrites and the microwave magnetic field with two different mechanisms: magnetic loss and eddy current heating. Furthermore, the heating performance of the ferrites as microwave absorbers is evaluated in comparison with SiC, which is a typical microwave absorber used in microwave processing. We believe that our findings can contribute to further advancements in microwave chemistry and related fields.

Accordion microwave oven for uniformity and efficiency heating

Conventional microwave oven heating has the problem of poor heating uniformity and low heating efficiency. A novel microwave oven heating model has been proposed for improving heating uniformity by making the electric field in the microwave oven drastically change by changing the geometry of the microwave oven during the heating process. The transformation optics method is used to solve the computational difficulties caused by the continuous change of the mesh during the motion. Finally, the experiment verified the correctness of the simulation. In addition, important factors affecting heating efficiency were discussed.

Effect of ball milling and metal filler alloy on microstructural bonding of Al2O3-SiC nano ceramic composite

The ceramic composite (Al2O3 + 5 vol% nano SiC + 5 vol% Ni) was prepared with powder processing followed by microwave hybrid sintering in a conventional microwave oven (2.45 GHz, 900 W) at 1600 °C. Post sintering the relative densification, hardness and microstructure of the ball milled and the unmilled sample were examined and compared. Also the effect of ball milling and metal filler (Nickel) on microstructural bonding of alumina/SiC nano ceramic composite has been studied. Ball milled sintered composite achieved 93% relative densification and has higher indentation resistance as compared to unmilled sintered composite.