Microwave Heating Time Research Articles

Microwave-assisted synthesis of cellulose/zinc-sulfate‑calcium-phosphate (ZSCAP) nanocomposites for biomedical applications

In this study, zinc-sulfate-calcium-phosphate (ZSCAP) ceramics was prepared by calcination in the presence of microwave irradiation using precursors ZnSO4:ZnO:CaO:P2O5 in a ratio of 15:30:30:25 (by weight). The calcined ZSCAP ceramics was mixed with microcrystalline cellulose and it was further heated by microwave radiation for the preparation of cellulose/ZSCAP nanocomposites. It was found that microwave heating time played an important role in the crystalline phase of synthesized nanocomposites of cellulose/ZSCAP. Well-crystalline phases of calcium phosphate, zinc oxide and zinc sulfate were observed in the nanocomposites at 20 min of microwave heating time. Fourier transformed infrared spectroscopy (FTIR) and Raman spectroscopy confirmed that the obtained products were of cellulose/ZSCAP nanocomposites. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images indicated that reinforced ZSCAP nanostructures were embedded into cellulose matrix. Energy dispersive X-ray spectroscopy (EDS) further supported the presence of Zn, S, Ca and P in cellulose/ZSCAP nanocomposites. The thermal behavior of the products was studied using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The prepared nanocomposites showed antibacterial activity against Staphylococcus aureus and Escherichia coli. In vitro cytotoxicity assay revealed that the prepared nanocomposites had no influence on proliferation of MG-63 cells. This rapid microwave-assisted method is simple, fast and suitable for the production of cellulose/ZSCAP nanocomposites, which finds its biomedical applications in tissue engineering and bone repair.

Experimental Study of Microwave Ablation in Ex Vivo Tissues

Cancer is one of the leading causes of morbidity and mortality worldwide. Microwave ablation is a minimally invasive treatment procedure that uses heat from microwave energy to destroy cancer cells. The effectiveness of this technique is associated to the microwave power input and heating time of treatment during the process, as well as the type of cancer tissue. The microwave power absorbed of each cancer tissue type is different and effect on the choice of treatment conditions. This research aims to investigate the effects of tissue type and microwave power input on the temperature profile and the efficiency of cancer treatment during microwave ablation. An experiment in ex vivo different tissues of porcine during microwave ablation via microwave antenna is studied. The types of tissue studied include skin tissue, liver tissue and lung tissue. The microwave power input of 60 W, 80 W and 100 W are investigated. The heating time of 360 s is selected for the study. An infrared thermometer camera is used to measure the temperature profile of tissues. The results reveal that the temperature profile and the ablation size in the case of skin tissue are higher than the liver tissue and lung tissue, respectively. In addition, the temperature profile of all tissues increases with greater microwave power. This research provides the essential aspects for a fundamental understanding of heat transfer within porcine tissues in microwave ablation process and can be used as a guideline to improve the efficiency of cancer treatment.

Influence of food composition type on the microwave heating time in relation to the inactivation of Salmonella enterica serovar Enteritidis and Shiga-toxigenic Escherichia coli (STEC) O157

Influence of food composition type on the microwave heating time in relation to the inactivation of Salmonella enterica serovar Enteritidis and Shiga-toxigenic Escherichia coli (STEC) O157

Influence of microwave treatment on grinding and dissociation characteristics of vanadium titano-magnetite

The effect of microwave treatment on the grinding and dissociation characteristics of vanadium titano-magnetite (VTM) ore were investigated using scanning electron microscopy (SEM), nitrogen absorption measurements, particle size distribution measurements, X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopic analysis, and magnetic separation. SEM analysis showed that microfractures appeared in the microwave-treated VTM, which is attributed to the microwaves’ selective heating characteristic and the differential expansion between minerals and gangues. Nitrogen absorption showed that the microfractures were more pronounced when the microwave heating time was increased. Particle size distribution analysis showed that microwave treatment could improve the grindability of the VTM, thus increasing the weight percent of the fine-ground product. The increase in grindability was more significant with prolonged heating time. Moreover, the particle size distribution of the fine-ground product changed only slightly after the microwave treatment. XRD analysis showed that the crystallinity of the microwave-treated VTM increased with increasing microwave heating time. The magnetic separation tests revealed that the separation efficiency increased as a result of the intergranular fractures generated by microwave treatment. The Fe grade of the magnetic fraction of microwave-treated VTM was 1.72% higher than that of the raw ore. We concluded that the microwave treatment was beneficial, especially for the mineral processing characteristics.

Effect of short microwave heating time on physicochemical and functional properties of Bambara groundnut starch

Bambara groundnuts (Vigna subterranea) are a good source of starch that may be potentially used for various industrial applications. The effect of microwave heating time (0, 10, 30 and 60 s) on the physicochemical and functional properties of Bambara groundnut starch was investigated. Native and microwaved Bambara groundnut showed the A-type crystallinity pattern. However, there was a decrease in the relative crystallinity of the starch after microwaving. Microscopically, the native starch granules were smooth but had pinholes after microwaving. Microwaving resulted in significant (p ≤ 0.05) reduction in peak viscosity, hot paste viscosity, cold paste viscosity, pasting temperature and set back ratio. The swelling power of Bambara groundnut starch similarly decreased with increasing microwaving time. Microwave heating led to a shift in the gelatinization range to higher temperatures. However, the enthalpy of gelatinization decreased after microwaving. Short microwaving times (≤60 s) were sufficient to cause significant improvement in the pasting and thermal properties of Bambara groundnut starch. Microwaved Bambara groundnut starch with reduced swelling can be potentially used in food products that do not require high swelling such as noodles.

The Effect of Microwave Heating of Pandanus Leaves with Vacuum Dried Non-Aromatic Milled Rice on Consumer Acceptability of Cooked Rice

The aroma of cooked rice is contributed mainly by the compound 2-acetyl-1-pyrroline (2-AP) and it is also found in aromatic Pandanus leaves (Pandanus amaryllifolius). Therefore, this experiment was conducted to investigate a physical mechanism of transferring 2-AP from Pandanus leaves to non-aromatic polished rice. Milled Samba rice (medium/ bold) grains were vacuum dried for 24 hours to remove moisture and develop a porous structure on the grain. Then the rice samples were mixed with Pandanus leaves and microwaved for predetermined times in sealed bags to 65°C to explode oil glands and release 2-AP. After three weeks of chemical exchange time in bags, the consumer acceptability was tested based on preference. The results revealed that the consumer acceptability of rice could be significantly increased with appropriate microwave heating time. Data has shown that the mean acceptability rank value of 3.47 with 45 minutes microwaving (about 65°C) against the rank mean of 1.4 for the control in a five-point hedonic test. However, the increase of microwaving time above the optimum level produced an unpleasant aroma in rice and decreased the acceptability. Therefore, this physical treatment could be used to increase the palatability and acceptability of non-aromatic rice.

Effect of microwave heating damage on the electrical, thermal and mechanical properties of fibre-reinforced cement mortars

Nowadays, refurbishing of existing structures has gained interest in order to reduce both the construction materials used and the construction and demolition waste production. For that purpose, there are several methods for demolishing the damaged parts, but most of the alternatives involve high noise and dust production, which are in contraposition when structures are in urban areas. Among all the existing methods, this paper studies the possibility of using microwave heating as a demolition method, either by damaging the bulk material or the mortar to concrete interface. With that in mind, the effect of microwave heating time (range 120–600 s) on the physical, thermal, electrical, mechanical and bonding properties of steel fibre-reinforced and non-reinforced cement mortars was analysed. The aim of the paper is to establish possible correlations between the mentioned properties and the damage level caused by microwave heating. Although the results prove that pore pressure increment due to microwave heating can cause the reduction of flexural strength up to the rupture of the specimens, this fact cannot be extended to all the properties or mortar types. The fibre reinforcement plays a key role to restrain the damage. Thermal conductivity and electrical resistivity are obviously different in reinforced and non-reinforced mortars due to the inclusions of the metallic fibres. However, after undergoing microwave heating those properties were not noticeably altered nor follow a trend linked to the heating time. It is assumed that the water migration and evaporation processes are the main cause. Although the flexural strength reduction was gradual for non-reinforced mortars until total failure, the reinforced specimens only showed a 13% of reduction for the first 120 s, remaining almost constant afterwards. Although it was proved that the fibres increase the temperature on the specimen surface and its adhesion to the matrix is altered, their crack bridging effect overcomes further damage.

Synthesis and characterization of dialdehyde cellulose/ silver composites by microwave-assisted hydrothermal method

An easy and environmentally friendly strategy is shown for the synthesis of dialdehyde cellulose/silver nanoparticle composites using dialdehyde cellulose as reducing agent through the microwave-assisted hydrothermal method. The effects of the microwave heating time and temperature on the products were investigated by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TGA). The dialdehyde cellulose was found to be an efficient reducing agent for silver ions, and the microwave heating time and temperature played a vital role in the morphologies of the silver nanostructures. The influences of different additional reductants such as ascorbic acid and glucose on the shapes, size-distribution, phase, and crystallinity of the samples were comparatively investigated in detail. This strategy is environmentally friendly, surfactant-free, without any other reducing or stabilizing agent chemicals, and the as-prepared dialdehyde cellulose/silver nanoparticles were more convenient to use in biomedical fields.

Synthesis, Characterization and Optical Properties of BaMoO4 Synthesized by Microwave Induced Plasma Method

BaMoO4 crystals were synthesized by a 900 W microwave induced plasma process (MIP) for 40, 60, 120 and 140 min. Phase, morphology, vibrational mode and energy gap were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. In this research, the phase and morphology of product were influenced by microwave heating time. The sample processed for 140 min shows spherical particles tetragonal BaMoO4 phase with size of 200–700 nm in diameter. BaMoO4 with band gap of 3.35 eV shows a blue emission wavelength at 440 nm.

Hyperspectral Imaging Sensing of Changes in Moisture Content and Color of Beef During Microwave Heating Process

Moisture content (MC) and color are two important quality parameters of beef during microwave heating process. This study examined the effects of microwave heating time (0–75 s) on MC, color, and myoglobins of beef samples. The results showed that heating time significantly influenced the MC, color (L*, a*), and percentage of related myoglobins. The suitability of hyperspectral imaging (HSI) (400–1000 nm) was investigated to correlate the mean spectra of beef samples and the color and MC values during microwave treatment. After the use of pre-processing methods and optimum wavelengths selection, the SG-SPA-LS-SVM prediction model for MC (R2P = 0.869, RMSEP = 1.304, and RPD = 2.724) and the SG-RC-MLR model for a* (R2P = 0.890, RMSEP = 0.735, and RPD = 2.733) were established. The models were then used to develop the distribution maps of MC and a* values, respectively, showing that both MC and a* at the center of the meat slices were higher than those at the edge, corresponding to the temperature distribution during microwave heating. The results demonstrated the ability of HSI system for monitoring the changes of some quality parameters during microwave heating.

A solid-state microwave method to disrupt biomass microstructure for natural product extraction

This paper introduces an innovative solid-state microwave disruption (SSMD) method for the extraction of bioactive materials from plants. It is an alternative method that avoids the use of solvents for plant biomass sample pretreatment unlike those in the conventional microwave methods. SSMD method is preferred since the heating and the vaporization of the intracellular moisture within the plant biomass is able to create sufficient pressure to disrupt the biomass microstructure. In this work, the superiority of the SSMD method was validated using the bioactive extraction from Orthosiphon stamineus (Java tea) leaves. First, the degree of disruption of SSMD method under the effects of microwave power and heating time were investigated at various up-scaled conditions based on the structural analysis of the treated sample, and the extraction yields of the bioactive compounds after soaking and elution with a suitable solvent at room conditions. The results show that the SSMD-elution method gave a better extraction yield (4.65±0.08mg/g), which is comparable to that of microwave-assisted extraction (4.45±0.03mg/g) and ultrasonic-assisted extraction (4.18±0.02mg/g). In addition, this method has great operational simplicity and flexibility in terms of operating parameters, types of solvent and solvent consumption.

Carbothermic Reduction Kinetics of Phosphorous Vaporization from Tri-calcium Phosphate (TCP) Under Microwave Rapid Heating With/Without the Presence of Fe3O4

The kinetics of vapor phase dephosphorization from tri-calcium phosphate (TCP) by carbothermic reduction was studied with and without the presence of Fe3O4. Microwave heating was utilized to obtain large variations in the heating rate (HR). In the reduction of TCP alone, the phosphorous removal fraction (RF; equal to ∆P2O5/P2O 5 0 , where ∆P2O5 is the weight change and P2O 5 0 is the P2O5 weight before heating) decreased as the HR increased. In other words, a shorter residence time at a high temperature resulted in a smaller reduction fraction of TCP. An apparently third-order reaction was postulated to account for the kinetics using a fitting simulation based on the additive law of the reaction progress. On the other hand, the phosphorous removal (dephosphorization) rate (RR; equal to ∆P2O3/tMW, where tMW is the microwave heating time period) increased as the HR increased above 1200 °C. The reduction ratio of Fe3O4 above 1100 °C is higher than 97 pct regardless of the heating rate. The reduction of TCP in the presence of Fe3O4 showed that RF increased slightly with increasing HR despite a shorter residence time at a high temperature. The RR also increased with the HR even though RF decreased to half of the values observed in the cases without Fe3O4 for temperatures above 1200 °C. The practicality and optimal operation conditions of phosphorus vapor removal were discussed.

Biopolyols obtained via microwave-assisted liquefaction of lignin: structure, rheological, physical and thermal properties

The present study examined the application of polyols obtained via microwave-assisted liquefaction of lignin in the production of rigid polyurethane foam. Lignin was liquefied in crude glycerol and 1,4-butanediol at different temperatures (130–170 °C), without a catalyst and using various biomass concentrations (15 and 30 wt%). The physicochemical properties, process yield, and FTIR-based identification of the obtained polyols were investigated. Under optimal conditions, i.e., a 5-min microwave heating time and a reaction temperature of 150 °C, a polyol characterized by a suitable hydroxyl number of 670 mg KOH/g was obtained with a 93% process yield. Liquefied biopolyol was directly used for the production of rigid polyurethane foams with the addition of polymeric diphenylmethane diisocyanate at the [NCO/OH] ratio of 2:1. Mechanical properties of the obtained foams gradually improved with increasing content of biopolyol. The 5% weight loss temperature (T5) for bio-based foams was higher, respectively 6 and 13 °C compared to the petrochemical foam. Replacement of petrochemical polyether with biopolyols showed the ability to obtain rigid polyurethane foams from lignin and crude glycerol.Graphical

Microwave functionalization of titanium oxide nanoparticles with chitosan nanolayer for instantaneous microwave sorption of Cu(II) and Cd(II) from water

The present study is aimed to evaluate the microwave–enforced sorption approach (MES) for instantaneous extraction and removal of trace concentration of metal ions using microwave-synthesized titanium oxide nanoparticles-bonded-chitosan nanolayer (NTiO2-NCh). The proposed and designed nanocomposite was characterized by different techniques. The coveted ions were allowed to heat in presence of NTiO2-NCh nanocomposite inside a microwave apparatus for 5–20s to execute the sorption process. The contribution of microwave warming time, nanocomposite dose, concentration of Cd(II) and Cu(II) ions, pH and interfering ions were explored and optimized. Sorption of Cd(II) was characterized as 1050 and 1150μmolg−1 and those of Cu(II) were identified as 450 and 800μmolg−1 using 5 and 20s of microwave heating time, respectively. Optimization of the nanocomposite dose factor was found to enhance the metal uptake values of Cd(II) to 1800μmolg−1 using 5.0mg. The potential utilization of MES technique for removal and extraction of Cd(II) and Cu(II) at low concentration levels (mgL−1) from water samples was also explored. The percentage extraction values of Cu(II) and Cd(II) from water and wastewater samples were ranged as 86.80–88.01% and 72.56–70.67%, respectively using 60–70s heating via MES technique.

Microwave-assisted synthesis method for rapid synthesis of tin selenide electrode material for supercapacitors

As an important binary IV-VI semiconductor compound, tin selenide (SnSe) has been investigated intensively for a wide range of applications in energy storage and photovoltaic devices, due to its unique electronic and optoelectronic properties. In this work, we successfully synthesized SnSe powders by a simple, rapid and high-yield method called microwave-assisted synthesis for the first time and also measured their electrochemical performances. By rationally controlling the microwave heating time, we found that the 15-min reacted sample exhibited the most outstanding specific capacitance and rate capability (214.3 F/g at 1 A/g and 182.8 F/g at 20 A/g), and excellent cycling stability. The microwave-assisted synthesis method is efficient and rapid for preparing SnSe electrode materials.

Denaturation Kinetics and Aggregation Mechanism of the Sarcoplasmic and Myofibril Proteins from Grass Carp During Microwave Processing

Optimizing the physicochemical properties of microwave-cooked meat needs a better understanding of the mechanisms responsible for protein changes. This paper explored the causes of aggregation of the denatured fish protein in ready-to-eat food by determining the changes in sarcoplasmic and myofibril proteins, which includes the effects of different microwave power levels (300, 600, and 900 W) and heating times (0–60 s) on the aggregation kinetics and physiochemical properties. The determination of aggregation kinetics that accurately describes microwave cooking characteristics is crucial for the optimization of operating parameters, performance improvement of the cooked food system, and product quality. The aggregation rate and turbidity of proteins increased with increasing microwave power and time. A negative correlation was observed between the protein solubility and microwave power and time. Protein aggregation induced by microwave showed a reliable and reproducible characterization of particle size distributions. At longer microwave heating time or higher microwave power, these protein particles formed larger aggregates.

The experimental study of effect of microwave heating time on the heavy oil properties: Prospects for heavy oil upgrading

A heavy crude oil sample from an oil field in southwest Iran was placed in a Fischer assay and heated by microwave for two-minute time steps until 14min total heating time had elapsed. Unlike conventional heating technique (CHT), which caused light carbonic components to escape and raised C20+ components in oil samples, the value of light carbonic components increased under microwave heating technique (MHT) up to 6min. These materials cannot escape the oil sample in MHT because the cracked components approach a superheated state, and in this study a large portion of them remained at 6min. Moreover, in contrast to the CHT results, the C1–C20 components increased to 13.5wt% in the analysis of cracked gases during MHT. In MHT, light components increased with heating time, and C7+ components fell. This is indicative of light components escaping after 6min. Some components escaped as condensate. In CHT, the escape of only small amounts of condensates was observed at 12 and 14min, while under MHT, this phenomenon started at 8min and contained larger amounts. This phenomenon is due to secondary cracking in oil, which is created by an abrupt increase in the temperature of some components that have more capacity to absorb microwaves. The sulfur content of heavy oil in MHT tended to decrease over time, approaching 34wt% at 14min; in contrast, in CHT it remained constant. Sulfur was removed from the oil sample as H2S and SO2, predominantly in a gas state, but also as condensate, in increasing amounts over time. Sulfur removal from the heavy crude oil sample is highly important in the upgrading process because of its high coefficient of microwave absorption. H2S is produced from the start of MHT, but SO2 is observed only after 6min, and then only in the produced gas. Saturation, Aromatic, Resin and Asphaltene (SARA) components analysis showed changes in the resin and asphaltene components. The amount of asphaltene components began to decline starting early in the heating process, and approached its lowest amount at 4min (3.21wt%). Reduction of resin components in MHT began at 8min and reached 55% at 14min. Asphaltenes have a high capability to absorb microwaves due to having SNO (Sulfur, Nitrogen and Oxygen) components that create hot zones in heavy oil; these hot zones enhance cracking and upgrading. Scanning electron microscopy images of asphaltene particles showed that microwaves caused some changes in the structure of these particles. Energy-dispersive spectroscopy analysis of these particles showed that SNO components under MHT declined over heating time. The results also suggest that after sulfur, nitrogen and oxygen have the highest potential to absorb microwaves.

Influence of the Microwave Heating Time on the Self-Healing Properties of Asphalt Mixtures

This paper aims to evaluate the influence of the microwave heating time on the self-healing properties of fibre-reinforced asphalt mixtures. To this purpose, self-healing properties of dense asphalt mixtures with four different percentages of steel wool fibres were evaluated as the three-point bending strength before and after healing via microwave heating at four different heating times. Furthermore, the thermal behaviour of asphalt mixtures during microwave heating was also evaluated. With the aim of quantifying the efficiency of the repair process, ten damage-healing cycles were done in the test samples. In addition, self-healing results were compared with the fibre spatial distribution inside asphalt samples evaluated by CT-scans. Crack-size change on asphalt samples during healing cycles was also evaluated through optical microscopy. It was found that the heating time is the most influential variable on the healing level reached by the asphalt mixtures tested by microwave radiation. CT-Scans results proved that fibre spatial distribution into the asphalt mixtures play an important role in the asphalt healing level. Finally, it was concluded that 40 s was the optimum heating time to reach the highest healing levels with the lowest damage on the asphalt samples, and that heating times over 30 s can seal the cracks, thus achieving the self-healing of asphalt mixtures via microwave heating.

Thermal Decomposition of Arsenopyrite by Microwave Heating and the Effect of Removal Arsenic with Wet-magnetic separation

In order to transform arsenopyrite into pyrrhotite and to decrease As content by less than 2,000 mg/kg, pulp sample and non-magnetic pulp sample were heated in a microwave oven at different heating times and were separated through wet-magnetic separation. As the microwave heating time increased, the phase of pyrrhotite was extended to become arsenopyrite entirely. The melting pores and micro-cracks occurred on the pyrrhotite due to hot spot phenomenon with microwave heating. The heated raw pulp sample (As content : 19,970.13 mg/kg) and non-magnetic pulp sample (As content : 19,970.13 mg/kg) which were heated in a microwave oven for 10 minutes were separated through wet-magnetic separation and magnetic fraction containing less than 2,000 mg/kg of As content was recovered only from the heated sample of magnetic separation. It was discovered that for the sulfide complex ore with As penalty imposed on, if microwave heating and wet-magnetic separation are effectively utilized, magnetic fraction. We expect to be able to obtain ore minerals with an arsenic content below the penalty charge.

Microwave Heating of Crystals with Gold Nanoparticles and Synovial Fluid under Synthetic Skin Patches.

Gout is a disease with elusive treatment options. Reduction of the size of l-alanine crystals as a model crystal for gouty tophi with the use of a monomode solid-state microwave was examined as a possible therapeutic aid. The effect of microwave heating on l-alanine crystals in the presence of gold nanoparticles (Au NPs) in solution and synovial fluid (SF) in a plastic pouch through a synthetic skin patch was investigated. In this regard, three experimental paradigms were employed: Paradigm 1 includes the effect of variable microwave power (5–10 W) and variable heating time (5–60 s) and Au NPs in water (20 nm size, volume of 10 μL) in a plastic pouch (1 × 2 cm2 in size). Paradigm 2 includes the effect of a variable volume of 20 nm Au NPs in a variable volume of SF up to 100 μL in a plastic pouch at a constant microwave power (10 W) for 30 s. Paradigm 3 includes the effect of constant microwave power (10 W) and microwave heating time (30 s), constant volume of Au NPs (100 μL), and variable size of Au NPs (20–200 nm) placed in a plastic pouch through a synthetic skin patch. In these experiments, an average of 60–100% reduction in the size of an l-alanine crystal (initial size = 450 μm) without damage to the synthetic skin or increasing the temperature of the samples beyond the physiological range was reported.