Domestic Microwave Research Articles

Predictive model for inactivation of salmonella in infant formula during microwave heating processing

This study aimed to study the behavior of Salmonella submitted to domestic microwave through the use of predictive microbiology. The results showed reductions of 9.22, 9.59, 8.23, and 8.57 log CFU/mL in Salmonella counts after exposure to microwave heating at 20 W (750 s), 40 W (90 s), 60 W (120 s), and 80 W (120 s), respectively, with a maximum temperature rise of 110.2 °C. For the primary inactivation model, a biphasic profile was initially observed, obtaining a linear log behavior with the increase in power values. Otherwise, the square root model was used for the secondary modeling, resulting in the equation: √kmax = 0.0055 (P + 9.98). From the validation of the secondary model, the MSE and R2 presented a good fit for the model of Salmonella spp inactivation in infant formulas by microwave heating. Overall, the models demonstrated efficacy to ensure the safety of infant formulas, preventing Salmonella contamination and should be considered considering a practical point of view.

Evaluation of the physical properties of fluorescent carbon nanodots synthesized using Nerium oleander extracts by microwave-assisted synthesis methods

Rapid and one-step green synthesis of carbon nanodots (CDs) from Nerium oleander leaves was accomplished via domestic microwave oven and microwave-assisted hydrothermal synthesizer under various physical conditions. Effects of the synthesizer system, extract type depending on the solvents used in plant extraction, and synthesis conditions; such as reaction time, reaction temperature, surface passivation agent inclusion into the reaction medium, on the physicochemical properties and optical feature of CDs were investigated. The impacts of relevant conditions on CDs feature were determined clearly via UV–visible spectrophotometry, fluorescence spectrophotometry, dynamic light scattering analysis, and Fourier transform infrared spectroscopy. According to the results, while the most effective parameter on the fluorescence feature of CDs was determined as the presence of surface passivation agent (polyethylene glycol, PEG), the alteration in the fluorescence intensity depending on the reaction time and the reaction temperature was also observed. It was reported that the synthesis system and PEG existence in the reaction medium were more effective than the other inspected parameters on the hydrodynamic particle size, in general. Under optimum conditions, nanoparticles with a hydrodynamic size of less than 5nm were obtained. The surface zeta potential charges of all particles were found as negative. While the extract type was significantly effective on the surface zeta potential of CDs synthesized by domestic microwave oven, the reaction temperature was found to be significant for the ones synthesized via microwave-assisted hydrothermal synthesis.

THE EFFECT OF DIFFERENT MICROWAVE POWERS ON THE DRYING KINETICS AND POWDER PROPERTIES OF FOAM-MAT DRIED EGG WHITE POWDER

The aim of this study is to determine the effect of different microwave powers on the drying kinetics and powder properties of foam mat dried egg white powder. For this purpose, the egg white foam was obtained by using kitchen blender (1000W, 5min) and dried in a domestic microwave oven at five different microwave powers (120-720W). According to the results, the drying time decreased from 360s to 80s according to increasing microwave power (P <0.05). In order to determine the drying kinetic of egg white foam, the experimental data was fitted to various semitheoretical models and one empirical model. Page model which showed the highest R2 values (0.983-0.994) was chosen as the most suitable model for determining the drying behavior of egg white foam. In addition, the average effective moisture diffusivity and activation energy values were calculated and ranged between 3.3389E-08 to 1.4139E-07 m2/s and 28.0640 W/g, respectively

On processing and flexural behaviour of functionally graded clads developed through microwave irradiation

In the recent decade the microwave heating has made a great impact in the domain of material processing. Present research focuses on the development of Ni/SiC based functionally graded clads (FGC) with varying percentage of reinforced SiC from 0%–30% (wt%) in the Ni based powder using microwave irradiation. The FGC was processed inside a domestic microwave applicator with frequency range of 2.45 GHz and variable power level of 180–900 W. The characterizations of so processed FGCs were carried out using back scattered electron (BSE) microscopy, energy dispersive spectroscopy (EDS), x-ray diffraction (XRD) spectroscopy, and measurement of Vicker’s micro-hardness. The micro-structural results revealed the formation of varying compositions FGC layers. The formation of different phases such as Ni2Si, Ni3C, NiSi, SiC, Cr23C6 was observed during the XRD study. The FGC top layer exhibited a maximum micro-hardness value of order 1020 ± 30 HV. Further, the flexural strength of FGC was evaluated using three point bend test. The average flexural strength value of FGC was observed as 771.2 ± 5 MPa with deformation index of 2.7 × 10–4 mmN−1.

Microwave irradiation preparation of Na3V2(PO4)3@N-doping carbon cathodes and their lithium ion storage behavior

To visit the electrochemical properties of sodium-based phosphate as a cheap cathode material for lithium ion batteries, a facile domestic microwave irradiation route has been adopted to rapidly synthesize Na3V2(PO4)3 material in 15 min. Here, the nitrogen-doping carbon has been introduced into in-situ preparation of Na3V2(PO4)3/carbon composites and its influence on electrochemical properties of Na3V2(PO4)3 was systemically studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectra. Results showed that the obtained nitrogen-doping carbon coated Na3V2(PO4)3 possesses excellent C-rate capacity performances, which are 104.5, 97.7, 97.5, 96.3, 94.1, 89.5 and 83.6 mAh g−1 at 0.1, 0.2, 0.5, 1, 2, 5 and 10 C, respectively. More importantly, the composite still possesses high capacity retention of 86.6% after 500 cycles at 5C. Electrochemical impedance spectroscopy profiles reveal that nitrogen-doing carbon strategy can efficiently alleviate the charge-transfer impedance of Na3V2(PO4)3. The improved electrochemical performance can be mainly ascribed to the unique structure, rapid microwave irradiation strategy and suitable nitrogen-doping content.

Dielectric Properties of Infant Formulae, Human Milk and Whole and Low-Fat Cow Milk Relevant for Microwave Heating

Abstract The dielectric properties of three different reconstituted infant formulae, human milk, as well as, whole and low-fat pasteurized cow milk were measured at temperature interval from (5 to 70) °C and at frequency of 2450 MHz. The dependency of the dielectric properties with temperature is presented. The values of penetration depth were determined and can be used to estimate the ideal bottle-feeding or container diameter to use in a domestic microwave oven or specific microwave equipment to pasteurize human milk in Human Milk Banks (HMB).

Fabrication and Investigation of Co-based and CeO2-modified Microwave Coatings

This paper explore the viability of novel microwave hybrid heating, Co-based coatings without CeO2 (unmodified) and with CeO2 (modified) in varying wt % (1, 2 and 3 wt %) were developed. The coatings were developed using domestic microwave oven of 2.45 GHz frequency, 900 W power and an irradiation time of 15 min. The characterization of unmodified and modified clads has been done in terms of microstructure, XRD, hardness and sliding wear behavior. The influence of sliding speed (1.2 and 2.4 m/s) and distance (3000 and 6000 m) on wear behavior were investigated. It was noticed that the wear resistance of coatings containing 1wt % of CeO2 was higher than other coatings. Further, it was found that modified coating with optimum addition of cerium oxide (1wt % CeO2) refined the microstructure, promotes the formation of hard carbides CeC2, Cr23C6 and Cr7C3, enhanced microhardness to 17% as compared to unmodified.

Synthesis of highly fluorescent carbon dots from lemon and onion juices for determination of riboflavin in multivitamin/mineral supplements

In this work, lemon and onion biomasses commonly found in street markets are for the first time used to develop a facile, fast and low-cost one-step microwave-assisted carbonization method for synthesis of highly fluorescent carbon dots (CDs). The structure and optical properties of CDs were investigated by TEM, XRD, XRF, UV–Vis, FTIR, and fluorescence spectroscopy. CDs displayed satisfactory optical proprieties, a high quantum yield of 23.6%, and excellent water solubility, and the particle size was 4.23–8.22 nm with an average diameter of 6.15 nm. An efficient fluorescent resonance energy transfer (FRET) between the CDs and riboflavin was achieved with CDs acting as donor and riboflavin as acceptor. A linear relationship between FRET and the riboflavin concentration from 0.10 to 3.0 μg/mL was observed, allowing the development of an accurate and fast analytical method to determine this vitamin in multivitamin/mineral supplements. Despite the potential interferences in these supplements, CDs were selective for riboflavin under optimized conditions. A paired t-test at a 95% confidence level indicated no statistically significant difference between the proposed and the reference methods. Recovery test presented values ranged from 96.0% to 101.4%. The limit of detection and relative standard deviation were estimated at 1.0 ng/mL and <2.6% (n = 3), respectively. CDs were successfully synthesized in a domestic microwave oven (1450 W, 6 min), presenting satisfactory parameters when compared with results of other studies reported in the literature, suggesting that the proposed method is a potentially useful method for the synthesis of CDs and determination of riboflavin.

Spectroscopic measurements of the electron temperature in low pressure microwave 2.45 GHz argon plasma

The main goal of this work is to obtain the plasma electron temperature Te by optical emission spectroscopy of low pressure microwave argon plasma, as a function of working pressure and microwave power. A plasma system was designed and constructed in our laboratory using a magnetron of domestic microwave oven with power 800W without any commercial part. The applied voltage on the magnetron electrical circuit is changed for the purpose of obtaining the variable values of the microwave power. The spectral detection is performed with a spectrometer of wavelength range (200−1000nm). The working pressure and magnetron applied voltage were 0.3-3.0mbar and 180-240V, respectively. Two methods had been applied to estimate the electron temperature, the ratio of two lines’ intensity and Boltzmann plot method. It was found that, for the plasmas investigated, an increase of the electron temperature when the applied voltage has been increasing, while the electron temperature decreases when the working pressure is increasing.

Wear studies of composite microwave clad on martensitic stainless steel

In the present work, clads were developed through microwave energy which is as an emerging trend. Martensitic stainless steel (SS-420) is considered as a substrate material to improve its surface properties. In the present work, clad powder such as tungsten carbide and cobalt-based powders were used in the weight ratio of 1:0.12, respectively. The clads were developed using domestic microwave oven at 2.45 GHz frequency and 900 W power through microwave hybrid heating technique. After performing a number of trials, the clads were developed with good metallurgical bond with an exposure time of 30 min. The main objective of clad development is to obtain a good mechanical and tribological properties. Wear studies through pin-on-disc method of the developed clad was performed on the basis of Taguchi method (L9) orthogonal array. The main influencing factors considered are sliding distance, sliding speed and load. It is observed that the sliding distance is most dominating factor than load and sliding speed.

Optimization of preconditioning process of pressure parboiled brown rice (unpolished) for microwave puffing and its comparison with hot sand bed puffing

AbstractPuffing of pre‐conditioned brown rice using microwave energy replacing the traditional puffing of preconditioned polished rice on hot‐sand‐bed has higher nutritive value and produce required amount of puffed rice as per consumer's wish. Preconditioning temperatures (60, 70, 80, 90 °C) and salt contents (0, 2, 4, 6% [w/w]) have been chosen to puff brown rice using microwave energy, and quality aspects have been evaluated and compared with those obtained with hot‐sand‐bed puffing. Optimization of processing variables was carried out for maximizing puffing percentage, expansion ratio, whiteness index, overall sensory score, and minimizing the bulk density and hardness of puffed brown rice. The sensory analysis for the product was carried out using fuzzy logic technique to obtain overall sensory score. Optimum preconditioning temperature and salt content were found to be 76.74 C and 3.74% (w/w) in microwave and 76.16 C and 2.76% (w/w) in hot‐sand‐bed puffing, respectively.Practice applicationsPuffing of brown rice (unpolished rice) using microwave oven provides an option in obtaining nutritious, fresh and hygienic puffed product on instant demand. Puffing of brown rice eliminates the energy‐intensive polishing step of the rice milling process. Optimization of the process variables can be implemented for making preconditioned brown rice in obtaining desired quality of the puffed rice using microwave energy. The prepacked preconditioned rice can be directly put inside the domestic microwave oven to get required amount of puffed product.

Application of microwave‐assisted technology: A green process to produce ginger products without waste

AbstractThis work proposed a zero waste approach based on microwave (MW) extraction combining hydrodiffusion and gravity for preserving all valuable compounds in the form of dried ginger, ginger essential oil (EO), and juice. A rotatable apparatus was developed from a domestic MW oven to ensure a uniform exposure of the material, resulting in a uniform dried ginger product with EO content more than 0.33% and moisture content less than 10%. The optimum conditions of MW density and energy, which were determined using response surface methodology, are 1 W/g and 1 Wh/g, respectively. They are much lower comparing with that required for hydrodistillation (HD). Significant difference in extraction yield obtained by MW extraction (0.6384 ± 0.0195) and HD (1.1939 ± 0.0679) was observed; however, the quality of EO derived from MW extraction in terms of antibacterial activity was higher than that of the one derived from HD, whereas the physical properties of both EOs were similar.Practical applicationsIn this study, the applicability of microwave (MW) extraction combining hydrodiffusion and gravity for ginger processing to produce dried ginger, ginger essential oil (EO), and juice without generating waste was confirmed. Although the EO yield obtained by the proposed extraction method is smaller than that obtained by hydrodistillation (HD), it was proved to be greener and more efficient than HD in terms of extraction time, EO preserving capability, resources’ consumption, and waste generation. In addition, the EO derived from MW extraction was observed to be more active in antibacterial activity due to its high content of oxygenated and monoterpene compounds. Moreover, this modified rotatable apparatus, which was simply developed from a cheap domestic MW oven to ensure uniform dried product, could be considered technically and economically feasible for actual deployment at small‐scale processing unit.

Effect of Different Amount of Silicon Carbide on SAC Solder-Cu Joint Performance by Using Microwave Hybrid Heating Method

Microwave hybrid heating (MHH) has been recognized for the soldering process especially with lead-free solder alloy. This study seeks to investigate the effect of the different amount of susceptor on the Sn-3.0Ag-0.5Cu-Copper (SAC305-Cu) joint performance by using the MHH method. The susceptor material that was used to facilitate microwave heating in this study was Silicone Carbide (SiC). Different amount of SiC was used to compare its effect on the intermetallic compound (IMC) formed and shear strength at the solder joint. Domestic microwave with operating frequency 2.45GHz and 800W was used to join the solder and Cu substrate for 5, 6 and 7 minutes. Characterization of the samples was carried out using an optical microscope, image analyzer, and lap shear test. The microstructural study showed that scallop type structure of Cu6Sn5 was found at the SAC305/Cu interface after soldering with MHH technique. Thinnest Cu6Sn5 IMC (14.909 mm) were obtained by soldering with 6 g of SiC for 6 minutes while highest shear strength was observed when 4 g of SiC was used for soldering for 7 minutes (26.71 MPa).

Effect of Microwave Radiation on Internal Inoculum of Ascochyta Blight in Lentil Seeds at Different Seed Moisture Contents

Abstract. Considering the development of pest and pathogen resistance to chemical treatments and the cost of developing new chemicals, proper physical methods for integrated pest management seem to be gaining interest. Microwave treatment has been considered a potential postharvest pest and disease management strategy in legume and grain seeds. The effect of this process on pathogens related to legumes, which could be expressed as a very fast and volumetric thermal treatment, has not been fully studied. In this study, a domestic microwave oven with full output power of 1100 W (company information) or 485 W (calibrated with 150 g of water) was used to treat red lentil seeds that were naturally infected with the Ascochyta blight (AB) pathogen, a problematic seedborne fungi of lentil. Microwave radiation was applied at three moisture contents of red lentil seeds (9.1%, 16%, and 19% wet basis) and two power levels (50% and 100%). Three exposure times for each moisture content and power level were selected to achieve the same final average temperatures with low and high moisture contents (approx. 65°C to 85°C). The complementary error function was used to model and compare the pathogen and seed death rates based on the normally distributed susceptibility of the AB pathogen and seed germination to microwave heating. At 9% moisture content with water activity of 0.4, the percentage of infected seeds decreased from 17% to 9% without significant loss of seed viability when a power level of 100% (9.7 W g-1) and exposure time of 51 s were applied, and the final average surface temperature reached 84°C. However, seed vigor, measured by the electrical conductivity of the seed leachate, decreased at this power level and exposure time. Despite the feasibility of fungi elimination at higher moisture content at the same final average temperatures, eliminating fungi from the seeds without harming their viability and vigor was challenging. Keywords: Ascochyta blight, Lentils, Microwave energy, Pathology.

Facile growth of carbon nanotubes using microwave ovens: the emerging application of highly efficient domestic plasma reactors.

The facile growth of carbon nanotubes (CNTs) using microwave radiation reveals a new way for the cost-effective synthesis of CNTs for a wide range of applications. In this regard, domestic microwave ovens can be used as convenient plasma reactors to grow CNTs in a very fast, simple, energy-saving and solvent-free manner. The special heating mechanism of microwaves can not only accomplish the fast growth of high-density CNT brushes within tens of seconds, but also eliminate the need for a flammable gaseous carbon source and an expensive furnace. By carefully selecting the substrate and catalyst, low-temperature growth of CNTs can also be achieved on low-melting point organic polymers at atmospheric pressure. Highly localized heating near the catalyst nanoparticles was observed under microwave irradiation, and this phenomenon can be utilized to grow CNTs at desired locations on the substrate to fabricate CNT-based nanoelectronics in situ. Finally, the microwave growth of CNTs is highly adaptive to different carbon sources, substrates and catalysts, showing enormous potential to generate functionalized CNT-based composites for emerging advanced applications.

Microwave assisted synthesis of biomorphic hydroxyapatite

Hydroxyapatite has been synthesized using eggshell membrane as bio-template along with the assistance of microwave heating. Eggshell membrane is infiltrated with calcium and phosphorous precursors before heating it in a domestic microwave oven. Hydroxyapatite formed retained the interwoven hierarchical structure of the eggshell membrane. Structural analysis was performed using X-ray diffraction, and the microstructural features are characterized by scanning electron microscopy. Distinct morphological features were present in microwave processed hydroxyapatite when compared to the conventionally processed one. Transmission electron microscopic investigations and BET surface area analysis were also carried out.

Reusable surface-enhanced Raman substrates using microwave annealing

In this work, we report the fabrication of large-scale homogeneous surface-enhanced Raman scattering (SERS) substrates using a microwave annealing (MWA) process on Ag thin films on silicon, using a typical low-cost domestic microwave oven, avoiding the use of chemicals and stabilizing agents, or time-consuming and expensive approaches. We provide evidence that in 5–15 s, uniform and reproducible SERS substrates of several centimeter squares can be grown, providing a Raman signal enhancement of five orders of magnitude, for an incident Raman laser with an intensity as low as ~ 0.035 mW, against the characterization of Rhodamine 6G, which is a standard test molecule for SERS. Moreover, we tested the reusability of the fabricated MWA SERS substrates under conditions as tough as ultrasonic sonication in isopropyl alcohol and acetone for 15 min, respectively, and we demonstrate that our SERS substrates can be efficiently reused for more than six times after sonication, which is quite critical since it minimizes the cost of the procedure to minimum.

Effect of microwave power irradiation on TiO2 nano-structures and binder free paste screen printed dye sensitized solar cells

Titanium dioxide (TiO2) nanostructures (nanorods and nanoparticles) were prepared using a low-cost microwave irradiation method from a polyol medium of glycerol. Titanium glycerolate and TiO2 powders were obtained in the glycerol medium for the first time with four different power densities (240 W, 480 W, 720 W, 960 W) of irradiation using a domestic microwave oven of 2.45 GHz, to understand the impact of power on morphology tuning. The structural and morphological features of the titanium glycerolate and TiO2 powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Raman spectra analysis. The TiO2 was successfully used in the fabrication of photovoltaic devices and as a proof-of-concept binder free paste was prepared and successfully employed for photo-anode using screen printing on the fluorine-doped tin oxide substrate.

Development and characterization of microwave processed cast iron joint

The feasibility of joining cast iron through novel microwave heating using susceptor (i.e. microwave hybrid heating), is carried out in present work. The joints were developed in domestic microwave applicator at 2.45 GHz frequency and 900 W. Nickel based powder slurry was placed between the faying surfaces for obtaining the joint. The detailed mechanism of joining through microwaves has been explained by using suitable illustrations. The microwave processed joint was characterized by using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction for microstructure analysis and study of developed inter-metallic phases. Results revealed that uniform and dense joint of 0.5 mm thickness were obtained. Obtained joints revealed metallurgical bonding of nickel powder with faying surfaces of base metal. This metallurgical bonding resulted into wavy interface and this was due to dilution of the base metal along the joint region. The EDS analysis confirms the uniform distribution of elements in the joint region and SEM results revealed that some porosity (in the range of 1.5–1.88%) was observed in the joint region. Tensile strength of microwave joined cast iron was ∼90% of the base metal strength. This was due to the development of high strength intermetallics and presence of nickel metal in the joint region. Microhardness at joint region was 201.7 ± 18 HV and 315 ± 10 HV along HAZ, whereas microhardness of bulk cast iron was 184 ± 4 HV. Microwave processed samples fractured along the HAZ region.

X-ray scintillator Gd2O2S:Tb3+ materials obtained by a rapid and cost-effective microwave-assisted solid-state synthesis

In this work, the microwave-assisted solid-state (MASS) synthesis is reported as a rapid, cost-effective and environmental-friendly way to prepare Gd2O2S:Tb3+ X-ray scintillation standards. The preparation procedure employs active charcoal as the microwave susceptor, using a domestic microwave oven without a setup for special gases. The MASS method drastically reduced the synthesis time and energy consumption (up to 97% in nominal power) over previous reports using conventional solid-state methods. A single-step synthesis of 10 min is enough to yield highly crystalline powders starting from Gd2O3 and Tb4O7 precursors and elemental sulfur. In order to obtain 100% pure materials with superior scintillation efficiency, two microwave treatments of 25 min each are required. Due to the reducing CO atmosphere generated in situ by the active charcoal during the microwave synthesis, no Tb4+ impurity was found according to Synchrotron Radiation X-ray Absorption (SR-XAS) experiments. Spectroscopic studies were carried out using SR Vacuum-Ultraviolet (VUV) photoluminescence and SR X-ray Excited Optical Luminescence (XEOL). The material prepared by two-step synthesis exhibited a better scintillation performance owing to higher crystal purity and emission intensity, presenting versatility for technological applications such as X-ray imaging and scintillation bio-probing.