Applied Microwave Power Research Articles

Improvement of flux-less, lead-free solder wettability on CF 4-plasma-fluorinated Sn and Ag substrates using ‘atmospheric pressure non-equilibrium plasma’

Atmospheric pressure non-equilibrium plasma inducted CF 4 gas was irradiated to Sn and Ag substrates to obtain fluorinated Sn and Ag surfaces with a high affinity of a lead-free solder without fluxes. The plasma was produced by applying microwave power inducted with Ar–CF 4–O 2 mixed gases. The plasma irradiation successfully fluorinates the metal surfaces completed within 15 min. The fluorinated metal surfaces were observed using a scanning electron microscopy (SEM) and analyzed using an X-ray photoelectron spectroscopy (XPS). The Sn and Ag surfaces were covered mainly with SnF 2 and AgF 2 through the plasma irradiation respectively. The contact angle of the solder mounted on the metal substrates was measured to evaluate the wettability. The contact angle was minimized at the flow ratio of CF 4/O 2 which was 1/9. Surface fluorination by non-equilibrium plasma irradiation would be applicable to improve the wettability of flux-less solder.

Effect of Microwave Non thermal Plasma Irradiation on the Adsorptive Properties of Active Carbon Preliminarily Impregnated with Poly(vinyl alcohol)

Microwave non thermal plasma irradiation was conducted on active carbon (AC) preliminarily impregnated with poly(vinyl alcohol) (PVA) in order to modify the adsorption properties of active carbon, particularly to increase hydrophobicity. The plasma was produced by applying microwave power on the PVA-impregnated active carbon (PVA/AC) placed in a low vacuum chamber (<10 Torr). The surface of the plasma-treated PVA/AC was imaged using scanning electron microscopy and atomic force microscopy (SEM and AFM, respectively), and analyzed using X-ray photoelectron spectroscopy (XPS). Hydrophobicity of the plasma-treated PVA/AC was compared to that of untreated PVA/AC and AC by a sinking test in water/methanol mixed solutions. The hydrophobicity drastically increased for PVA/AC treatment with 1-min plasma irradiation. The AFM results indicated that the surface roughness of the PVA/AC was dependent upon the hydrophobicity, rather than reduction of free energy due to reduction of polarized functional groups. NaOH and HCl adsorption onto the plasma-treated PVA/AC was also measured. Adsorption capacity of plasma-treated PVA/AC increased for NaOH, whereas it decreased for HCl. The plasma treatment not only increased the hydrophobicity of PVA/AC, but also changed its acid-base adsorption properties. We have developed a new material based on active carbon, which is light, hydrophobic and electrically conductive by using a combination of PVA sintering and plasma irradiation.

Hydrogen-free diamond-like carbon films prepared by microwave electron cyclotron resonance plasma-enhanced direct current magnetron sputtering

Hydrogen-free diamond-like carbon (DLC) films were prepared by means of microwave electron cyclotron resonance plasma enhanced direct current magnetron sputtering. To study the influence of enhanced plasma on film fabrication and properties, the structures as well as mechanical and electrical properties of these films were studied as a function of applied microwave power. Results showed that higher microwave power could induce higher plasma density and electron temperature. The hardness increased from 3.5 GPa to 13 GPa with a variation of microwave power from 0 W to 1000 W. The resistivity showed a drastic increase from 4.5 × 10 4 Ωcm at 0 W to 1.3 × 10 10 Ωcm at 1000 W. The variation of the intensity ratio I(D)/I(G) and the position of the G-peak of the DLC films with respect to changes in microwave power were also investigated by Raman spectroscopy.

Decomposition of poly(amide–imide) film using atmospheric pressure non-equilibrium plasma generated in a stream of H 2O/Ar mixed gases

Atmospheric pressure non-equilibrium Ar–H 2O plasma was irradiated to exfoliate a thin film of a heat-resistant polymer, poly(amide–imide) coating on enamel copper wire. The plasma was produced by applying microwave power inducted with Ar–H 2, Ar–O 2, Ar–H 2O or Ar–H 2–O 2 mixed gases. The poly(amide–imide) thin film was exfoliate by those plasma irradiations. The magnitude of exfoliation depended on the distance of the copper wire from the plasma generating material and reached a maximum at a distance around 4 cm for each plasma irradiation. Surface conditions of the copper wire varied depending on the inducted gases. Ar–O 2 plasma irradiation oxidized the copper surface while other plasmas kept the copper surface unchanged. The time it took to exfoliate the poly(amide–imide) depended on the irradiation source, either Ar–O 2 (within 60 s), Ar–H 2O (within 70 s), Ar–H 2–O 2 (within 70 s) or Ar–H 2 (within 125 s). The Ar–H 2O plasma irradiation under non-equilibrium atmospheric pressure was found to be the best method for exfoliating the poly(amide–imide) thin film coating on enamel copper wires rather than the Ar–H 2–O 2 plasma because of its simplicity and safety.

Optimal power control strategies in microwave drying

A microwave drying system, which can automatically and continuously adjust microwave power, control sample temperature and measure sample mass, was developed and used in apple drying. At three drying temperatures, i.e., 75, 65, 55 °C, applied microwave power was recorded and analyzed, and a relationship of the power with respect to drying rates was built. With this relationship, apples were further dried at the same three temperatures but using variable power during drying process based on the online obtained drying rates. A better temperature control was achieved and less energy was consumed with this method. Depending on the resulted power profiles, a linear and a three-step power control methods were further developed to simplify the control system. With the developed methods, mass measurements were no longer required and power control could be easily implemented, while temperature control and energy consumption were still acceptable.

Microwave‐Assisted Functionalization of Carbon Nanostructures in Ionic Liquids

The effect of microwave (MW) irradiation and ionic liquids (IL) on the cycloaddition of azomethine ylides to [60]fullerene has been investigated by screening the reaction protocol with regard to the IL medium composition, the applied MW power, and the simultaneous cooling of the system. [60]Fullerene conversion up to 98 % is achieved in 2-10 min, by using a 1:3 mixture of the IL 1-methyl-3-n-octyl imidazolium tetrafluoroborate ([omim]BF(4)) and o-dichlorobenzene, and an applied power as low as 12 W. The mono- versus poly-addition selectivity to [60]fullerene can be tuned as a function of fullerene concentration. The reaction scope includes aliphatic, aromatic, and fluorous-tagged (FT) derivatives. MW irradiation of IL-structured bucky gels is instrumental for the functionalization of single-walled carbon nanotubes (SWNTs), yielding group coverages of up to one functional group per 60 carbon atoms of the SWNT network. An improved performance is obtained in low viscosity bucky gels, in the order [bmim]BF(4)> [omim]BF(4)> [hvim]TF(2)N (bmim=1-methyl-3-n-butyl imidazolium; hvim=1-vinyl-3-n-hexadecyl imidazolium). With this protocol, the introduction of fluorous-tagged pyrrolidine moieties onto the SWNT surface (1/108 functional coverage) yields novel FT-CNS (carbon nanostructures) with high affinity for fluorinated phases.

Nanocrystalline hydroxyapatite bioceramic using microwave radiation: Synthesis and characterization

In this work, we synthesized bioactive hydroxyapatite (Ca10(PO4)6(OH)2, HAp) ceramic powder in the lower-end of nano-regime using microwave radiation, which offers several advantages. The powder was synthesized using calcium nitrate tetrahydrate and sodium phosphate dibasic anhydrous as the starting materials. EDTA served as the complex reagent. The pH of the final suspension was adjusted to 9 by adding ammonium hydroxide. Applied microwave power of 600W, pH of the suspension, mole ratio of Ca/P in the staring chemicals, and the chelating effect of EDTA served as the factors in the synthesis of nanocrystalline HAp powder. The synthesized powder was studied using various characterizing techniques viz., XRD, SEM, HR-TEM, EDS, TG/DTA and FT-IR to determine powder morphology, particle-size, crystallinity, phases, elemental composition and thermal behavior. Results confirmed highly crystalline nano-powder (5–30nm) with elemental composition of Ca and P in HAp phase and possessed mixed (elliptical and rod-shape) morphology. Using the Scherrer formula, the average crystallite size was found to be 12nm. The FT-IR confirmed that the powder is of typical apatite structure. Thermal analysis showed a remarkably lower initial dehydroxylation temperature, compared to micron sized HAp, as reported in literature.

Low-temperature Oxidation of Semiconductor Surfaces by use of a Novel High-density Microwave Plasma Apparatus

This paper describes a new microwave plasma oxidation apparatus with unique features addressing the near room temperature low temperature process for forming high quality dielectrics with minimum dopant deactivation and redistribution. With this new technique the oxide growth rate was studied as a function of time, gaseous ambient, pressure, applied microwave power and silicon substrate parameters to determine crystallographic oxidation rate anisotropy and dopant concentration dependent oxidation at temperatures much below 400 {degree sign}C. Furthermore, the plasma oxide was also electrically evaluated (C-V- and I-V curves) after as grown, a post plasma anneal up to maximum temperature of 700 {degree sign}C and a post-metallization forming gas anneal. The breakdown strength improved considerably up to 7 MV/cm and the interface trap density decreased much below 10^11 states/eVcm2 so that the oxide quality is comparable to thermal oxides.

Microwave Synthesis of Zeolites: Effect of Power Delivery

The effect of microwave power magnitude and pulsing frequency on the synthesis enhancement of zeolites, silicoaluminophosphate SAPO-11, silicalite, and NaY, was studied. Pulsing the microwave power compared to continuous delivery at the same averaged fed microwave power showed no effect on the nucleation and crystallization rates of SAPO-11, silicalite, or NaY. However, SAPO-11 synthesized with continuous microwave power delivery produced larger particles compared to pulsed microwave power with the same reaction time (3.77 microm for continuous versus 2.49 microm for pulsed 1 s on; 3 s off). Further, pulsed microwave power delivery used lower steady state power to maintain the same reaction temperature compared to continuous power delivery (55 W compared to 65 W, respectively). The microwave power used to heat the reaction precursors of SAPO-11 and silicalite was varied by applying cooling gas at various rates while maintaining the reaction temperatures. Significant enhancement of the crystallization rate for SAPO-11 was observed with increasing the fed microwave power (0.014 min(-1) at 65 W, 0.030 min(-1) at 130 W, and 0.066 min(-1) at 210 W), with little effect on the nucleation time. The crystallization rate to microwave power relation was found to obey a power curve (y = 0.4259x(2) - 0.2776x + 0.8517). Lower microwave power produced larger crystals but required longer reaction time to complete crystallization (3.77 microm at 65 W compared to 2.04 microm at 210 W). Conversely, silicalite synthesis at 150 degrees C was found to be independent of the magnitude of the applied microwave power.

Luminescence flashes induced by microwave radiation in undoped GaAs quantum wells

Bright flashes of exciton emission are observed in photoexcited, undoped GaAs/AlGaAs quantum wells under pulsed microwave (36 GHz) irradiation. The flash intensity is in the range of 10--100 times the steady-state photoluminescence intensity with a decay time of $(1--10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }\text{s}$ (depending on the applied microwave power and photoexcitation). These observations indicate a reservoir of long-lived carriers that is formed at low temperature due to localization of photogenerated electrons and holes at spatially separated shallow traps. Microwave-heated electrons activate the localized carriers into free states by means of avalanche impact ionization. This gives rise to rapid exciton formation with subsequent luminescence flash. A detailed model based on the coupled rate equations for free electrons, excitons and localized electrons (holes) is presented.

유전가열물질을 코팅한 활성탄소섬유의 휘발성 유기화합물 흡착 및 마이크로파 인가에 의한 탈착 연구

Adsorption of toluene by activated carbon fiber (ACF) coated with dielectric heating element and desorption by applying microwave were investigated. In order to prepare adsorbent so that VOC can be desorbed by microwave heating, fine dielectric heating element with nano size was coated on the surface of the ACF using hybrid binder. Eight adsorbents (ACF-DHE, Activated Carbon Fiber coated with Dielectric Heating Element) were prepared with different amount of dielectric heating element, kinds of hybrid binder, and solvent. In order to investigate adsorption characteristics, BET surface area, pore volume, and average pore size were measured for each adsorbent including ACF. Breakthrough experiments with toluene concentration, flow rate, bed length using fixed bed reactor were performed to investigate adsorbality of adsorbent, and results were compared with that of the ACF. Desorption reactor was constructed with modified microwave oven to investigate heating effect on ACF-DHE by applying microwave power. Each adsorbent saturated with toluene were put into desorption reactor. Composition of desorbed gas generated by applying controlled microwave power to reactor was measured. Up to now, hot air desorption method has been used. Experimental results showed that desorption method with new adsorbent prepared by coating dielectric heating element on ACF can be used for industrial application.

FORNO APRIMORADO PARA ESTUDO DE PROCESSOS DE REDUÇÃO CARBOTÉRMICA DE MINÉRIOS INCENTIVADA POR MICROONDAS

A device for microwave enhanced carbothermic reductions which permits the full control of microwave power irradiated was built. This equipament allows the measurement of effectively applied microwave power to the charge in process, the simultaneous records of its temperature and mass loss, and good reproducibility of operation parameters, is introduced by this paper. This equipment was designed to simultaneously satisfy the technical requirements for the carbothermic reduction of ores and for the microwave irradiation of metallurgical materials. This prototype works with a 2.45 GHz microwave generator with variable power up to 3 kW. It also allows acquisition of temperature and mass loss for the material under carbothermic reduction. It works under argon gas atmosphere. Operational tests for iron ore reduction with charcoal were performed. Kinetic curves of iron ore reduction and effective consumption of microwave power curves were determined. These results made possible to perform an analysis of actual energy consumption for enhanced microwave iron ore carbothermic reduction.

Synthesis of Manganese Ferrite by Microwave Discharge between Carbon Felts (MD/CF) at Ambient Pressure

Manganese ferrites were quickly prepared from manganese oxide and iron oxide powders by a microwave discharge generated between two pieces of carbon felt (MD/CF) with various powers in air atmosphere, and were characterized especially by X-ray diffractometry and Mossbauer spectroscopy. MnFe2O4 was produced within at least 40 s by MD/CF with more than 200 W microwave power in air atmosphere. With the increase of the applied microwave power, FeO powders were produced in addition to distorted MnFe2O4 by using MnO and Fe2O3 powders as starting mixture. Improved yield for MnFe2O4 were obtained by post annealing for 1 hour or by using the raw mixed materials of MnO, MnO2 and Fe2O3.

Decomposition of poly(amide-imide) film enameled on solid copper wire using atmospheric pressure non-equilibrium plasma

The decomposition of a poly(amide-imide) thin film coated on a solid copper wire was attempted using atmospheric pressure non-equilibrium plasma. The plasma was produced by applying microwave power to an electrically conductive material in a gas mixture of argon, oxygen, and hydrogen. The poly(amide-imide) thin film was easily decomposed by argon-oxygen mixed gas plasma and an oxidized copper surface was obtained. The reduction of the oxidized surface with argon-hydrogen mixed gas plasma rapidly yielded a metallic copper surface. A continuous plasma heat-treatment process using a combination of both the argon-oxygen plasma and argon-hydrogen plasma was found to be suitable for the decomposition of the poly(amide-imide) thin film coated on the solid copper wire.

Analysis and control of the thermal runaway of ceramic slab under microwave heating

Thermal runaway is a special macroscopic phenomenon of the dielectrics during microwave heating, in which there is a big jump of the steady state temperature while the applied microwave power varies slightly. It hinders the applications of microwave heating technique in industry. A simulation based on the finite difference time domain (FDTD) method to solve Maxwell’s equations coupled with the finite difference (FD) method to solve a heat transfer equation (HTE) is presented, and the temperature variation in a ceramic slab during microwave heating is obtained. The temperature variation in the ceramic slab during microwave heating is simulated with various ceramic parameters and applied microwave powers so as to analyze the condition under which thermal runaway is introduced. Moreover, a microwave power control method, based on a single temperature threshold and dual applied microwave powers, is presented, which improves microwave heating efficiency and controls thermal runaway. The relation between the final applied microwave power and the monitored temperature threshold is presented as well. This method can be applied in many fields related with microwave heating techniques.

Investigating the Existence of Nonthermal/Specific Microwave Effects Using Silicon Carbide Heating Elements as Power Modulators

The use of passive heating elements made out of chemically inert sintered silicon carbide (SiC) allows microwave transparent or poorly absorbing reaction mixtures to be heated under microwave conditions. The cylindrical heating inserts efficiently absorb microwave energy and subsequently transfer the generated thermal energy via conduction phenomena to the reaction mixture. In the case of low to medium microwave absorbing reaction mixtures, the addition of SiC heating elements results in significant reductions (30-70%) in the required microwave power as compared to experiments performed without heating element at the same temperature. The method has been used to probe the influence of microwave power (electromagnetic field strength) on chemical reactions. Six diverse types of chemical transformations were performed in the presence or absence of a SiC heating element at the same reaction temperature but at different microwave power levels. In all six cases, the measured conversions/yields were similar regardless of whether a heating element was used or not. The applied microwave power had no influence on the reaction rate, and only the attained temperature governed the outcome of a specific chemical process under microwave conditions.

Moisture transport in garlic cloves undergoing microwave-convective drying

A laboratory scale microwave dryer was used to dry the garlic cloves, applying microwave power in the range of 10–40 W, air temperature in the range of 40–70 °C and air velocity in the range of 1.0–2.0 m/s. Heat and mass transfer coefficient during the drying process varied in the range of 35.23–79.54 W/m 2C and 4.26–6.34 × 10 −2 m/s. The temperature of the product rose rapidly in the early part of the drying and became almost stable thereafter. The Biot mass transfer number confirmed that moisture diffusion was the limiting factor in microwave drying of garlic. The effective moisture diffusivity, which ranged between 1.29–31.68 × 10 −10 m 2/s increased with the increase in microwave power but decreased with increase in air velocity.

Kinetics of the radiation-induced radical species in gamma irradiated solid sodium ascorbate

In the present work, radicals induced in γ-irradiated solid sodium ascorbate (SA) were studied by electron spin resonance (ESR) spectroscopy. While unirradiated samples presented no ESR signal, irradiated samples were found to present a spectrum of an unresolved doublet with a shoulder at the low-magnetic field side. Structural and kinetic features of the radical species responsible for the experimental ESR spectrum were explored through the variations of the signal intensities associated with spectrum maxima and minima with applied microwave power, sample temperature, and room temperature storage time. Activation energies of the involved species were also determined using the data derived from annealing studies performed at high temperatures. Produced radical species were observed to be relatively stable at room temperature. This gave the opportunity to distinguish irradiated SA or SA containing irradiation products from unirradiated ones even long after irradiation. SA presented also the features of a dosimetric material, which could be used in the estimation of dose range in accidental dosimetry.

Simultaneous growth of diamond thin films and carbon nanotubes at temperatures ⩽550 °C

Diamond thin films (on silicon wafers) and carbon nanotubes (CNTs) (on Inconel plates) were simultaneously synthesized at temperatures ⩽550 °C without any additional catalyst. The synthesis was achieved in a microwave plasma enhanced chemical vapor deposition (CVD) reactor with graphite etching in a gas mixture of hydrogen and methane. The substrate stage consisted of an Inconel 600 plate and a stainless steel plate separated by a 53 mm long quartz tube. Silicon wafers were placed on the stainless steel plate located at the upper part of the substrate stage, while Inconel plates were placed at the lower part of the substrate stage. During the deposition, the substrates were heated only by the plasma and the substrate temperature was controlled by the applied microwave power, which ranged from 350 W to 950 W. The backside temperatures of Si wafers ranged from 290 °C to 550 °C, higher than the corresponding temperatures of Inconel 600, which ranged from 220 °C to 350 °C. The Raman spectroscopic and electron microscopic results show that the thin films deposited on Si consist of well faceted polycrystalline diamond, and that the black soot deposited on Inconel plates is composed of multiwall carbon nanotubes as long as one millimeter.

Molecular damages produced by gamma radiation in solid piperacillin monohydrate: an ESR investigation

In the present work, the results of an electron spin resonance (ESR) study carried out on gamma irradiated solid piperacillin monohydrate (PMH) were presented. While unirradiated PMH exhibited no ESR signal, irradiated PMH was found to have an unresolved broad resonance line of singlet appearance. Results related with the variations of peak heights with applied microwave power, sample temperature, storage time at room temperature and annealing time at high temperatures were used to determine the structural and kinetic features and activation energies of the contributing radicalic species. Two tentative radicalic species were proposed and their spectroscopic parameters were determined through spectrum simulation calculations. The dosimetric potential of PMH was also investigated and it was concluded that PMH does not present the characteristics of a good dosimetric material, but that ESR spectroscopy could be used in the discrimination of irradiated PMH from unirradiated one.