GHz Microwave Irradiation Research Articles

Morphology of CuO through precipitation process under 2.45 GHz microwave irradiation

The morphology of CuO powders formed by a homogeneous precipitation process from aqueous copper precursor complex was investigated. The effect of 2.45 GHz microwave irradiation appeared in the characteristic morphology of the CuO microcrystal with comparison of an ordinal synthesis process. The crystallographic orientation of CuO microcrystals in the particle was examined by HRTEM. Using microwave irradiation, it was demonstrated that the morphology of the particles was kept through the decomposition of the precursor. Also the rapid transformation of a precursor to CuO in aqueous solution under microwave irradiation condition was discussed.

Crystallization of Ferroelectric Lead Zirconate Titanate Thin Films by Microwave Annealing at Low Temperatures

Lead zirconate titanate (PZT) thin films were coated on Pt/Ti/SiO2/Si substrates by the sol–gel method and then crystallized by microwave annealing using a single‐mode 2.45 GHz microwave irradiation system in the magnetic field. The crystalline phases and microstructures as well as the ferroelectric properties of the PZT films were investigated as a function of the elevated temperature generated by microwave irradiation, and the phase transition in the crystallization of the PZT thin films was discussed. X‐ray diffraction analysis and transmission electron microscopic study indicated that the crystallization to the perovskite phase in the PZT films by microwave annealing started at 430°C, and mostly finished at 450°C for 30 min. The remanent polarization of the PZT films increased with the increasing annealing temperature, and the lowest temperature required to obtain perovskite PZT films with good ferroelectric properties in the microwave irradiation processing was 450°C, which is much lower than that in conventional thermal processing.

Ferromagnetic resonance heating of Fe and Fe3O4 by 5.8 GHz microwave irradiation

Compressed Fe3O4 powder and Fe sheet were pre-heated to various temperatures higher than 300 °C in a microwave magnetic field (hrf). Then an external static magnetic field (Hext) was imposed perpendicularly to hrf and the temperature increased (ΔT: temperature difference from the pre-heated temperature, ΔTmax: ∼200 °C (Fe), ∼50 °C(Fe3O4)). It had a peak at almost the same Hext during ascent and descent of Hext because of ferromagnetic resonance (FMR). In fact, ΔT became smaller as the preheating temperature was raised to approach the Curie temperature, and Hext corresponding to the temperature peak shifted higher. This report provides FMR heating data under various conditions with quantitative discussion and proposes application of a new heat treatment to materials.

Solid-state Synthesis of Sn2TiO4: A New Synthetic Strategy for Direct Synthesis of Sn2+ Compounds Using Microwave Irradiation

Abstract Divalent tin compound, Sn2TiO4, was synthesized by a simple solid-state reaction of component oxides under 2.45 GHz microwave irradiation. The reaction rapidly proceeds with the diffusion of hot Sn2+ species toward TiO2 to form Sn2TiO4 within 1 min. A drastic enhancement of reaction kinetics could be achieved under thermally nonequilibrium conditions induced by strong coupling of SnO with microwave energy. This makes it possible to avoid the disproportionation reaction of SnO to Sn and SnO2, giving us a new synthetic strategy for direct synthesis of Sn2+ compounds.

Synthesis of natural superlattice structure in the binary ZnO–Fe<sub>2</sub>O<sub>3</sub> system by microwave irradiation

Homologous compounds, Fe2O3(ZnO)m, with the modulated natural superlattice structure were obtained within a short period by solid state reaction of component oxides under 2.45 GHz microwave irradiation. TEM observation revealed that two types of superlattice structures were observed in different Fe concentration; one is longitudinal superlattice structure in a rod shaped precipitation at high Fe concentration, and the other is modulated structure showing zigzag shape at low Fe concentration. It is conclude that the non-equilibrium nature of microwave selective heating, as well as rapid heating and quenching effects, plays a key role to form the superstructure. The obtained products exhibit ferromagnetic behavior with the Curie temperature above 300 K.

Synthesis of CuO Powder by Homogeneous Precipitation Process under Microwave Irradiation

We investigated the morphology of CuO powders synthesized by three processes: homogeneous precipitation, homogeneous precipitation under microwave irradiation, and heat treatment of precursor at 600°C. Homogeneous precipitation process was applied to a mixed aqueous solution of copper precursor complex, which was obtained from cupper nitrate and hexamethylenetetramine. The 2.45 GHz microwave irradiation to a precursor solution induced the formation of CuO powders with special morphology at 95°C in aqueous solution. Also the rapid formation of CuO from precursor by microwave was revealed in comparison with the processes without microwave irradiation.

La3+ and Zr4+ co-doped anatase nano TiO2 by sol-microwave method

Anatase nano TiO2 powders were prepared by two different methods. One is the sol-microwave method and the other is oil-bath condition synthesis. A microwave oven (800 W) was used as the microwave source. Under 2.45 GHz microwave irradiation, titanium tetra-isopropoxide (TIP) was quickly hydrolyzed and anatase TiO2 was formed in a short time (<4 min). In addition, a simple sol to gel conversion route has been followed for the preparation of anatase phase at 100 °C under oil-bath condition. The materials characterized by XRD, Raman, SEM-EDX, TEM, FT-IR and UV–vis techniques. XRD and Raman spectroscopy confirmed both pure and co-doped nano TiO2 have a high degree of crystallinity and existence of fully anatase phase at 500 °C. In the microwave method, XRD and TEM results revealed that the particle size of co-doped nano TiO2 is smaller than pure nano TiO2. The photocatalytic activity was tested on the degradation of 4-nitrophenol (4-NP). The nano TiO2 samples prepared by microwave method were more effective than oil- bath samples.

Microwave-Assisted Cross-Coupling and Hydrogenation Chemistry by Using Heterogeneous Transition-Metal Catalysts: An Evaluation of the Role of Selective Catalyst Heating

The concept of specific microwave effects in solid/liquid catalytic processes resulting from the selective heating of a microwave-absorbing heterogeneous transition-metal catalyst by using 2.45 GHz microwave irradiation was evaluated. As model transformations Ni/C-, Cu/C-, Pd/C-, and Pd/Al2O3-catalyzed carbon-carbon/carbon-heteroatom cross-couplings and hydrogenation reactions were investigated. To probe the existence of specific microwave effects by means of selective catalyst heating in these transformations, control experiments comparing microwave dielectric heating and conventional thermal heating at the same reaction temperature were performed. Although the supported metal catalysts were experimentally found to be strongly microwave absorbing, for all chemistry examples investigated herein no differences in reaction rate or selectivity between microwave and conventional heating experiments under carefully controlled conditions were observed. This was true also for reactions that use low-absorbing or microwave transparent solvents, and was independent of the microwave absorbtivity of the catalyst support material. In the case of hydrogenation reactions, the stirring speed was found to be a critical factor on the mass transfer between gas and liquid phase, influencing the rate of the hydrogenation in both microwave and conventionally heated experiments.

Electrical Properties and Microstructure of Low-Temperature-Crystallized Lead Zirconate Titanate Thin Films Prepared by 2.45 GHz Microwave Irradiation

Lead zirconate titanate (PZT) thin films were coated on Pt/Ti/SiO2/Si substrates by a sol–gel method and then crystallized at 490 °C using the magnetic field of 2.45 GHz microwave irradiation. The crystalline phases and microstructures as well as the electrical properties of the PZT thin films were investigated. X-ray diffraction analysis indicated that the films were crystallized well into the perovskite phase. Scanning electron microscopy showed that the PZT films had a typical rosette structure, which consisted of large round grains on a matrix of fine grains. A transmission electron microscopy (TEM) study revealed that the fine grains were also mainly crystallized into the perovskite phase. The average remanent polarization and coercive field of the PZT films were approximately 21 µC/cm2 and 92 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 510 and 0.07, respectively.

Parallel microwave chemistry in silicon carbide reactor platforms: an in-depth investigation into heating characteristics

The heating behavior of silicon carbide reaction platforms under 2.45 GHz microwave irradiation was investigated with the aid of online thermoimaging cameras and multiple-channel fiber-optic probe temperature sensors placed inside the wells/vials of the silicon carbide microtiter plates. Microwave irradiation leads to a rapid and homogeneous heating of the entire plate, with minimal deviations in the temperature recorded at different positions of the plate or inside the wells. In temperature-controlled experiments using dedicated multimode reactors, solvents with different microwave absorption characteristics can be heated in parallel in individual wells/vials of the silicon carbide plate reaching the same set temperature. Due to the large heat capacity and high thermal conductivity of silicon carbide, the plates are able to moderate any field inhomogeneities inside a microwave cavity. Although the heating of the plates can be performed extremely efficiently inside a microwave reactor, heating and synthetic applications can alternatively be carried out by applying conventional conductive heating of the silicon carbide plates on a standard hotplate. Due to the slower heating of the silicon carbide material under these conditions, somewhat longer reaction times will be required.

Efficient and Eco-Friendly Anionic Polymerization of Acrylamide under Microwave Irradiation and Hydrolysis of the Obtained Polymers by Microwave Irradiation

The polymerization of acrylamide was carried out using t-BuOK as an initiator in DMF under microwave irradiation. As a result, poly(β-alanine) was obtained in a good yield. With 100 W, 2.45 GHz microwave irradiation, the formation of polymer was accelerated. Furthermore, the hydrolysis of poly(β-alanine) was carried out using acids or bases under microwave irradiation. When poly(β-alanine) was hydrolyzed at 100 °C for 3 h with NaOH or KOH, the degree of hydrolysis reached 68−71%. When poly(β-alanine) was hydrolyzed at 100 °C for 3 h with HCl or H2SO4, the degree of hydrolysis reached 64−76%.

Influence of microwave irradiation on enzyme kinetics

The in vitro effect of 2.45 GHz microwave irradiation on porcine pepsin activity under controlled temperature and absorbed microwave power via kinetic parameters was evaluated. Kinetic study with respect of time of irradiation demonstrated the existence of an inactivation effect of microwaves at pH 2 on pepsin molecule. Bovine serum albumin (BSA)-bromphenol blue (BPB) complex was used as substrate for the assay of pepsin by kinetic method. Depending on absorbed microwave dose, the degree of caused inactivation varies from 39.11 to 45.91% for 5 and 20 min of pepsin MW irradiation, respectively. The Vmaxapp and Kmapp were calculated for low (5 min of MW irradiation) and higher specific absorbed dose (20 min of MW irradiation), as well as for untreated enzyme, from double reciprocal Lineweaver-Burk plot. The effect of microwaves on substrate (BSA-BPB complex) was also investigated. For reaction performed with MW irradiated substrate for 5 min the reaction rate was decreased for 15.15%, while for 20 min of substrate irradiation reaction rate was decreased for 25.52% compared to the control reaction.

Effect of Microwave Irradiation on Hydrothermal Treatment of Blast Furnace Slag

The effect of microwave irradiation on the hydrothermal treatment of blast furnace (BF) slag was investigated using a 2.45 GHz microwave irradiation system. The comparison of the features of a microwave-hydrothermal (M-H) reaction with those of a conventional hydrothermal (C-H) reaction showed that in both these reactions, tobermorite (Ca5Si6O16(OH)2·4H2O) was formed as the major phase in the treated samples. When the BF slag was hydrothermally treated by the C-H reaction, tobermorite was formed in the vapor state as the major phase at 200°C after a holding time of 48 h; in the M-H reaction, tobermorite was rapidly formed within 3 h at the same temperature. It was elucidated that microwave irradiation promoted the hydrothermal reaction to a significant extent.Furthermore, effects of microwave irradiation on BF slag subjected to hydrothermal hot-pressing were investigated. After microwave irradiation, the compressive strength of the slag compact and rate of porosity in the compact after treatment increased and decreased, respectively, in comparison with those before treatment. Moreover, microwave irradiation was advantageous over conventional heating at the same temperature in that it enhanced the compressive strength of the BF slag.

2.45 GHzマイクロ波照射による金属窒化物の合成

2.45 GHzマイクロ波照射による金属窒化物の合成

Rapid Crystallization of Sol–Gel-Deposited Lead Zirconate Titanate Thin Films by 2.45 GHz Microwave Irradiation

Pb(Zr0.52Ti0.48)O3 (PZT) thin films were coated onto Pt/Ti/SiO2/Si substrates by a sol–gel method and then crystallized by 2.45 GHz microwave irradiation in a magnetic field. The crystalline phases and microstructures as well as the electrical properties of the microwave-irradiated PZT films were investigated as a function of the elevated temperature generated by microwave irradiation. The perovskite PZT thin films with good electrical properties could be obtained by microwave irradiation at 650 °C for 60 s. The average values of the remanent polarization and the coercive field of the PZT films were approximately 27 µC/cm2 and 95 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and 0.18, respectively. It is clear that microwave irradiation is effective for obtaining well-crystallized PZT films with good properties in a short process time.

Low-temperature growth of ferroelectric lead zirconate titanate thin films using the magnetic field of low power 2.45GHz microwave irradiation

Pb(ZrxTi1−x)O3 (PZT) thin films were coated on Pt∕Ti∕SiO2∕Si substrates by the sol-gel method and then crystallized by using the magnetic field of 2.45GHz microwave irradiation. The elevated temperature generated by microwave irradiation used to obtain the perovskite phase was only 450°C, which is significantly lower than that of conventional thermal processing. The PZT films crystallized by microwave irradiation showed similar ferroelectric properties to those of the films crystallized by conventional thermal processing at 600°C. It is clear that single-mode 2.45GHz microwave irradiation in the microwave magnetic field is effective for obtaining perovskite PZT thin films at low temperatures.

Preparation of Mesoscopic TiO2–SnO2 Composite Grains by Spinodal Decomposition under 28 GHz Microwave Irradiation

Abstract TiO2–SnO2 composite with the modulated lamellar structure was obtained within a short period by microwave irradiation using 28-GHz frequency. Single-phase solid solution with the rutile-type structure was formed at the early stage of irradiation, and the prolonged irradiation caused the formation of mesoscopic lamellar structure induced by spinodal decomposition. Such a nonequilibrium nature is believed to be due to selective heating behavior under microwave irradiation.

Improved 10 V SINIS Series Arrays for Applications in AC Voltage Metrology

Recent metrological activities with programmable Josephson voltage standards (PJVS) are focused on extending the quantum accuracy to AC voltages, e.g. for the step-wise approximation of sine waves. Stimulated by the progress in this field, new requirements for the quality and availability of 1 V and 10 V circuits have been established. Based on the experience with programmable 1 V SINIS circuits fabricated at PTB and used at present by 13 National Metrological Institutes worldwide, the fabrication process and the microwave design were improved. The experience gained hereby enabled us to improve the properties of programmable 10 V SINIS arrays which were realized by us for the first time in 2000. The new 10 V circuits have 17 bit resolution and develop under 70 GHz microwave irradiation flat Shapiro steps at the 10 V level which are more than 600 muA wide. A direct comparison of the output voltage with a conventional 10 V SIS Josephson voltage standard confirmed the suitability for metrological applications. Incorporating 10 V-PJVS into existing AC metrology setups is expected to reduce their uncertainty budgets by about one order of magnitude.

Effects of 28 GHz/2.45 GHz Microwave Irradiation on the Crystallization of Blast Furnace Slag

The effects of microwave irradiation on the crystallization of 40%CaO–40%SiO2–20%Al2O3 synthesized slag and actual blast furnace slag were investigated using a 28 GHz multimode microwave irradiation system, a commercial microwave oven (2.45 GHz), and an electric resistance furnace. While it was observed that the 2.45 GHz centimeter-wave had little effect on the samples, the 28 GHz millimeter-wave was found to accelerate crystallization significantly, especially at lower temperatures at which the crystalline phases are never generated by external heating.Further, the effects of the precipitated phases and impurities on the crystallization with the 28 GHz microwave irradiation were investigated. The temperature of the glassy slag increased more rapidly when compared with the crystalline phases that exist in the actual blast furnace slag. In addition, a small amount of impurity was found to improve the heating property of the slags.

Application of 28 GHz Microwave Irradiation to Oxidation of Ilmenite Ore for New Rutile Extraction Process

Microwave heating has been applied to the oxidation in the new rutile extraction process developed by the authors in which rutile is extracted from a natural ilmenite ore by oxidation and magnetic separation followed by leaching with diluted acid. Since ilmenite FeTiO3 and pseudobrookite Fe2TiO5 strongly absorb 28 GHz microwave, Australian ilmenite ore mainly composed of FeTiO3 was rapidly heated up to about 1 273 K and oxidized in air with keeping almost constant temperature. As a result, two equilibrium phases of rutile TiO2 and pseudobrookite were quickly formed at microwave power of 1.5 kW. The growth rate of the pseudobrookite phase in the microwave irradiation was found to be much faster than that of the rutile phase in the conventional resistance furnace, indicating a drastic enhancement of the growth rate by the microwave irradiation.