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Sustainable product development and efficient use of resources is prime and major concern in the present era of modern manufacturing practice. In the current work energy efficient microwave heating techniques is employed for the four different kind (i.e. silicon carbide, graphite, A5grade alumina and pulverized charcoal) of microwave absorbing material. The finite element modeling of susceptor heating was done using COMSOL multi-physics environment. These susceptor material were tested for different microwave power input with fixed exposure time and microwave frequency of 2.45 GHz. It was observed that the A5 grade alumina and silicon carbide material giving higher amount of heating rate for a comparable operating condition of different susceptor material. The experimental validation for the three different power input (540, 720 and 900 W) were done for silicon carbide susceptor material utilizing 2.45 GHz microwave frequency. The results obtained are in close agreement with finite element modeling. The present study will develop a cogent link between the modeling and experimental study of microwave heating behavior under room temperature application for numerous material processing applications.

Purpose This paper aims to investigate the morphology and tensile properties of SAC305 solder alloy under the influence of microwave hybrid heating (MHH) for soldering at different microwave parameters. Design/methodology/approach Si wafer was used as susceptor in MHH for solder reflow. Microwave operating power for medium and high ranging from 40 to 140 s reflow time was used to investigate their effect on the microstructure and strength of SAC305/Cu solder joints. The morphology and elemental composition of the intermetallic compound (IMC) joint were evaluated on the top surface and cross-sectional view. Findings IMC formation transformed from scallop-like to elongated scallop-like structure for medium operating power and scallop-like to planar-like structure for high operating power when exposed to longer reflow time. Compositional and phase analysis confirmed that the observed IMCs consist of Cu6Sn5, Cu3Sn and Ag3Sn. A thinner IMC layer was formed at medium operating power, 80 s (2.4 µm), and high operating power, 40 s (2.5 µm). The ultimate tensile strength at high operating power, 40 s (45.5 MPa), was 44.9% greater than that at medium operating power, 80 s (31.4 MPa). Originality/value Microwave parameters with the influence of Si wafer in MHH in soldering have been developed and optimized. A microwave temperature profile was established to select the appropriate parameter for solder reflow. For this MHH soldering method, the higher operating power and shorter reflow time are preferable.

In contrast to conventional casting, casting using in situ microwave route is an advanced and promising technique of bulk metal casting wherein bulk metal is heated and melted in microwave radiations at 2.45 GHz. In this present work, AA-6063 is used as a charge material at three microwave powers of 600 W, 750 W and 900 W. The process uses three susceptor materials—stone charcoal, wood charcoal and SiC—and solidification is done at two levels as closed and open cavity. The optimization of the process parameters has been done through Taguchi technique. Microstructure and microindentation hardness studies of the developed casts divulged that smaller equiaxed grains could be obtained in densely cast samples 15 and 9. In these cast samples, the presence of intermetallic phases of Al2Mg3, MgZn2, Mg2Si, Al2Mg was observed; however, the cast sample 18 contains intermetallic phases of Al2Mg, MgZn and Al2Mg3. It was found from this work that the grain structure and intermetallic precipitates in the developed cast depend primarily on solidification environment, microwave power and susceptors. Microindentation hardness of the cast sample 18 in the present study was about 166 HV that is higher than the other developed casts. The characterization of developed casts in terms of microstructure, elemental analysis, porosity, XRD and fractography is analyzed. The results reveal that the rapid solidification and increased microwave power alter elemental composition, distribution and size of eutectic phases resulting in increase in the microindentation hardness.

In the present work, the microstructure and mechanical properties of microwave welded Al6061-6%Graphite-SiC hybrid metal matrix composites (MMC) were investigated. The microwave welding was carried out using the principle of microwave hybrid heating and Al6061 powder as an interfacial material. The domestic microwave oven having the frequency of 2.45 GHz and 900 W power was used for the experiments. The charcoal powder as a susceptor was used during the welding process. The hybrid MMCs Al6061-6%Gr-SiC were developed through stir casting process with different weight percentage of SiC keeping graphite constant. The joints were characterized using x-ray diffraction, scanning electron microscope (SEM) equipped with energy-dispersive spectrum (EDS), Rockwell hardness tester and universal testing machine. The x-ray diffraction analysis showed the presence of harder aluminum carbide and aluminum oxide phases. The microstructural study revealed the good metallurgical bonding between the interfacial composites with absence of cracks. The elemental analysis of joint revealed the presence of aluminum, carbon and oxygen with other elements. The average ultimate tensile strength of the microwave joints was recorded as 135 MPa with 4.3% elongation. The average Rockwell hardness at the weld joint observed was 61.5 ± 5 HRB. The evaluation of mechanical properties of microwave welded composites indicated the increase in the tensile strength and hardness as the content of SiC reinforcement increased. The joint strength found to be 65.15% of parent composite, which is similar to the joint strength of welded aluminum-based composites by various techniques such as friction stir welding, laser beam welding, electron beam welding, etc. The present investigation has showed that the microwave energy can be used successfully, as an alternative method to weld the composites.

Microwave power and the susceptor quantity are important operating parameters in the microwave-assisted pyrolysis. This work aims at finding the optimal power and susceptor quantity from a discrete set of microwave powers (300 W, 450 W, and 600 W) and graphite susceptor quantity (50 g, 200 g, and 350 g) to pyrolyze waste polypropylene. The effect of microwave power and the susceptor quantity on heating rate, conversion efficiency, and heat losses in pyrolysis were analyzed using a central composite design (CCD). It was observed that a higher microwave power and lower susceptor quantity yielded higher heating rates, and lower heating rates were obtained for a lower microwave power and higher susceptor quantity. For example, a very low heating rate, averaging to 8.5 °C/min was obtained for a low microwave power (300 W) and a high susceptor quantity (350 g), whereas high values of heating rate (71.7 °C/min) were obtained for a microwave power of 600 W with 50 g of susceptor quantity. For a set of microwave powers considered in this study, it was observed that the required bed temperatures were acquired faster at a low susceptor quantity compared to high susceptor quantity. The oil produced from the pyrolysis of WPP has a high heating value of 44 MJ/kg and the carbon number distribution in the range of C8 to C12. The char produced has rich carbon content (96 wt.%) and a high specific surface area (195 m2/g). Cyclo alkenes with a selectivity of 70% and monocyclic hydrocarbons with a selectivity of 49.6 % were produced at 450 W and 600 W powers respectively for a susceptor quantity of 50 g. From this study, it is found that the microwave power and susceptor quantity are the important parameters for minimizing the microwave energy requirement in the pyrolysis. The low susceptor quantity and high microwave power were found to be the best for achieving fast heating rates and low energy requirements. The microwave power significantly playing a vital role in the polypropylene pyrolysis product spectrum for value-added hydrocarbons.

We present a new approach to the study of microwave efficiency (MW) and microwave susceptors in the process of obtaining high quality nanopowders. Susceptors accelerate the processing of various po...

Petroleum refining generates hazardous sludge with polyaromatic hydrocarbons and heavy metals. The main objective of the study was to evaluate the performance of microwave pyrolysis for the recovery of oil from furnace oil sludge. The characteristics of furnace oil tank bottom sludge such as pH, moisture, viscosity, and volatile hydrocarbon content were determined. Thermal Gravimetric Analysis has been done to determine the cracking and degradation range of oily sludge. Gas Chromatography-Mass Spectrometry was used to fingerprint the hydrocarbon. Pyrolysis experiments were conducted in lab-scale pyrolysis set up with different susceptors and sludge in a specific weight ratio. The process parameters like microwave power, sludge: susceptor ratio were optimized to increase the oil yield. Graphite mixed sludge in 1:5 ratio at 450 W power shown higher oil yield. The calorific value of oil and char were determined as 44,442.9 and 16,686.58 kJ /kg. Physicochemical characteristics of oil such as flash point, density, and kinematic viscosity are 94 °C, 874.9, kg/m3, and 4.063 cSt. Cetane index and sulfur content were measured as 40.9, 6.85 g/kg respectively. The gas analysis had shown the presence of H2, CO2, CO, and CH4 compounds. Char contains a higher percentage of carbon, Fe, Al, Ni, Pb, Cd, and S compounds.

Dewaxing is an intermediate step in investment casting which can determine the properties of final metallic product and is strongly dependent on the properties of pattern wax. Processing of pattern wax composites with the conventionally available heating processes is energy intensive and requires high processing time, thus resulting in the lower processing rate at larger scale. Use of microwave technology for the dewaxing study is highly attractive alternative owing to the advantage of energy-efficient processing. The processing time of pattern wax composite of paraffin wax, bitumen, polyethylene and EVA in microwaves oven as a function of susceptor has been investigated. Carbon black was used as microwave susceptor in wax composites at several weight percentages. The efficient processing and melting behavior of pattern wax composite utilizing microwave dewaxing, thanks to the creation of heat sensitive sites within the pattern wax composite by the susceptor material, were analyzed in this study. FTIR-ATR, rheometer, TGA, DSC, UTM, SEM and OM were used to study the behavior of the wax composite. With the increase in the susceptor (CB) loading from 0.15 to 0.75%, an increase in the thermal stability of 6.86% was observed as depicted by the increase in the on-set temperature of the specimens. 71.9% decrease in the melt flow time of pattern wax composite was observed with the incorporation of 1.5% of CB as compared to reference specimen which manifested an inverse relationship between susceptor loading and processing time in the presence of microwave.

Microwave processing of a metallic material melting and casting is a newly developed method. The irradiation of metallic specimen takes place inside the cavity of microwave applicator and it’s heated and melted due to microwave hybrid heating. In the present work, melting of AA 6061 established inside a commercial grade microwave oven with 1 kW power and 2.45 GHz frequency in ambient environmental condition. In this process pouring and solidification carried outside the applicator. The casket design and susceptor material properties influence on the microwave heating of specimen and hence melting of the charge. The interaction of microwave with specimen and its effect of heating and melting was observed in the present study. The developed specimen was characterized to check the cast quality. Microstructure study shows the homogenous grain structure with average grain diameter 3.25 µm. The average micro indentation hardness of the casts was found 89 HV.

Microwaves are the electromagnetic radiation with frequency ranging between 300 MHz and 300 GHz, with the wavelengths ranging from about 1 m to 1 mm. Microwave drilling is a machining process in which electromagnetic radiation is concentrated at 2.45 GHz by using a concentrator into a small region. In this review paper, the use of microwave radiations for drilling metals and non-metals is studied in brief and parameters, such as immersion depth, concentrator material, type of dielectric material, susceptor powder and specimen. A characterization of drilling is studied namely Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Micro tensile test, impact test, 3-point bending test, Fractography and porosity.

In the present study, 17 wt % TiN reinforced α-β SiAlON composites were sintered at low temperature by susceptor-assisted microwave heating. The effect of TiN addition on dielectrical properties of starting powders, as well as the influence of sintering temperature on phase evolution, microstructure development and mechanical properties of α/β-SiAlON-TiN composites were investigated. The obtained results showed that TiN addition increased the microwave absorbing properties which is reflected in the peak sintering temperature. Thus, the α:β ratio decreased and mechanical properties were improved, especially the fracture toughness of the composites. Furthermore, an estimate of energy consumption during microwave assisted sintering at the laboratory scale is presented. As a result, the highest values for relative density (97.1%), Vickers hardness (13.35 ± 0.47 GPa), and fracture toughness (7.52 ± 0.54 MPa m1/2) were obtained by microwave sintering for 30 min at 1300 °C.

Carbon nanomaterials have been shown to rapidly evolve heat in response to electromagnetic fields. Initial studies focused on the use of microwaves, but more recently, it was discovered that carbon nanomaterial systems heat in response to electric fields in the radio frequency range (RF, 1-200 MHz). This is an exciting development because this range of radio frequencies is safe and versatile compared to microwaves. Additional RF susceptor materials include other carbonaceous materials such as carbon black, graphite, graphene oxide, laser-induced graphene, and carbon fibers. Such conductive fillers can be dispersed in matrices such as polymer or ceramics; these composites heat rapidly when stimulated by electromagnetic waves. These findings are valuable for materials processing, where volumetric and/or targeted heating are needed, such as curing composites, bonding multi-material surfaces, additive manufacturing, chemical reactions, actuation, and medical ablation. By changing the loading of these conductive RF susceptors in the embedding medium, material properties can be customized to achieve different heating rates, with possible other benefits in thermo-mechanical properties. Compared to traditional heating and processing methods, RF heating provides faster heating rates with lower infrastructure requirements and better energy efficiency; non-contact RF applicators or capacitors can be used for out-of-oven processing, allowing for distributed manufacturing.

In several automotive applications, durability of components is a major concern. This characteristic is a function of mechanical properties and electro-chemical properties. Metals provide structural support to the automotive structure due their superior mechanical properties; however, these are prone to corrosion. Over a period of time, its luster also diminishes. To overcome these issues, polymer coatings are used to modify the surfaces with the help of techniques such as electrostatic spraying followed by furnace curing. In this work, pure polyester coating is applied on to a cold rolled closed annealed steel substrate and cured using energy derived from microwaves. An attempt is made to develop an alternative industrial technique which is economical and energy efficient. Since metals are not directly exposed to microwaves, a susceptor-based heating arrangement was made to melt the powder layer on the metallic specimen. The microwave energy transfer mechanism has been discussed to explain the temperature rise. The coated specimen was verified for thickness uniformity using optical microscopy and “coat-measure” gauge. Corrosion resistance capability was investigated using a standard salt spray test. These characteristics were found to be within the requirements of customers. The study confirms the potential utility of the process for large-scale commercialization.

Open-cell ceramic foams are promising materials in the field of microwave heating. They can be manufactured from susceptor materials and can, therefore, be used as selective heating elements. In this study, the complex permittivities of ceramic foam materials, including silicon-infiltrated silicon carbide (SiSiC), pressureless sintered silicon carbide (SSiC), silicate bonded silicon carbide (SBSiC), and cordierite were determined. The dielectric properties of the foams were determined by the cavity perturbation technique using a TE104 WR340 waveguide resonator at 2.45 GHz. Samples were preheated in a tubular furnace, enabling temperature-dependent permittivity measurements up to 200 °C. The effective dielectric constant and effective loss factor were found to depend on the porosity and material composition of the foam. The SiSiC material had a higher effective dielectric constant than the SSiC and SBSiC ceramics. The effective dielectric constant of the foams showed a trend of gradual increase with increasing temperature. Some selected dielectric mixing relations were then applied to describe the effective permittivity of the foams and compare them with predictions from finite element simulations performed using the CST Studio Suite. The foam morphologies and simple block inclusions were used in the simulations.

The feasibility to control the gas concentration and temperature distributions in a semiconductor process chamber by measuring them was investigated. Gas concentration and temperature distributions for various flow rates were measured with the computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS). The infrared absorption spectra of multiple laser paths passing through the measured area were collected and the distributions of methane concentration and temperature in the chamber were reconstructed with the computed tomography (CT) calculations. The measured results indicated that the distributions can be independently controlled by measuring with the CT-TDLAS and adjusting the flow rates and the susceptor temperature.

This study provides a novel method to prepare metal–ceramic composites from magnetically selected iron ore using microwave heating. By introducing three different microwave susceptors (activated carbon, SiC, and a mixture of activated carbon and SiC) during the microwave process, effective control of the ratio of metallic and ceramic phases was achieved easily. The effects of the three susceptors on the microstructure of the metal–ceramics and the related reaction mechanisms were also investigated in detail. The results show that the metal phase (Fe) and ceramic phase (Fe2SiO4, FeAl2O4) can be maintained, but the metal phase to ceramic phase changed significantly. In particular, the microstructures appeared as well-distributed nanosheet structures with diameters of ~400 nm and thicknesses of ~20 nm when SiC was used as the microwave susceptor.

Conductive susceptors are necessary for heating non-conductive materials in induction heating systems. Susceptor materials should have sufficient electrical conductivity and thermal/chemical stability under a range of environmental conditions. However, many susceptor materials oxidize in high-temperature environments, resulting in degradation and poor durability. Here, we used intermetallic MoSi2 ceramics as a susceptor material and designed a cylindrical susceptor to apply to rapid high-temperature induction heating in an oxidizing environment. MoSi2 was prepared by self-propagating high-temperature synthesis (SHS), and then used to fabricate cylindrical susceptors by slip casting. The optimal thickness of the susceptor was controlled by modelling. A MoSi2-based cylindrical susceptor with SiO2 protective layer showed higher heating rate (4.2–26.8 °C/s at 0.5–2.5 kW) than a commercial rod-type susceptor (7.7–13.6 °C/s at 1.0–2.5 kW) of the same material. In addition, our susceptor endured high temperatures below 1700 °C and severe thermal cycle (700–1600 °C, heating for 2min and cooling for 1min) during 36 cycles. In general, these results demonstrate that the MoSi2-based susceptor can be applied to a rapid induction heating furnace that can be used in air at a high temperature of 1600 °C (equal to the available temperature of a commercial graphite susceptor in H2).

Microwave (MW) sintering offers higher heating rate, rapid processing, reduced energy consumption, and reduced sintering temperature. However, the technique is not fully understood, difficult to control, and often relies on experience and trial-and-error approach. Consequently, hot spots, uneven heating, thermal runaway, and shape distortion develop in sintered compacts. Therefore, developing a model that can simulate the sintering process, enhance predictability, and determine the critical sintering conditions is essential. Multiphysics finite element (FE) modelling of hybrid MW sintering of a magnesium alloy AZ61 compact was undertaken in this study. The FE model coupled the electromagnetic, heat conduction, and densification equations. The model utilised parameters related to the furnace, compact, and susceptor to predict the spatial distribution of electric field, thermal response, and densification in the compact. A power-based sintering criterion was developed to predict the sintering of the compact and estimate its critical sintering energy. Modelling results showed that heating time, compact size, and thickness of the susceptor are critical to the sintering process. It was also shown that the susceptor not only mediated the sintering of the compact but also homogenised its temperature and densification. Thus, MW sintering of the compact was predicted to occur at 500 °C for 8 to 10 min with a predicted relative density of about 0.98. Experimental MW sintering data showed good concurrence with the developed model. These results are useful for controlling the MW sintering process, eliminating trial-and-error, and determining the critical sintering conditions.

Microwave cladding is an emerging surface modification technique. Temperature control is the key issue in any surface modification technique. In microwave cladding, non-contact temperature measurement methods are widely used; however, these methods report only the surface temperature of the susceptor. In the present study, a modified B-type thermocouple was used to measure the real time-temperature distribution while developing Ni-based clad. Formation of clad has been discussed with respect of time-temperature distribution. Effect of microwave power on heating profile was also investigated.

Hydropower plants are experiencing huge revenue losses due to the failure of hydro turbines caused by cavitation. Surface modification could be a feasible solution to tackle this problem. Microwave processing of metallic materials to coat/clad has gained popularity in recent years. In the current study, microwave exposure time by analyzing susceptor temperature is optimized to get sound clads. Nickel-based and Cr3C2-reinforced clad on SS-316 substrate is developed for cavitation erosion resistance. The clads have been developed in a domestic microwave oven of 2.45 GHz and 900 W. The Ni + 30% Cr3C2 developed clad has been characterized through various standard mechanical and metallurgical techniques like X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, Vicker’s micro-hardness, porosity measurement, and flexural study. The presence of various carbide and intermetallic phases Cr2Ni3, Cr7C3, CrSi, SiO2, and FeNi3 is confirmed from the X-ray diffraction pattern. The distribution of hard carbide phases into soft matrix is confirmed from the microstructural investigation. Vicker’s microhardness study confirms the enhanced average microhardness of the clad region by 2.5 times of the substrate. The analysis of porosity shows significantly less (0.98%) porosity. The flexural study of developed clads by using three-point bending test is evaluated and flexural strength and deformation index values of developed clads of 814 ± 11.5 MPa and 2.29 × 10−4 mm N−1 respectively are observed.

This study is focused on valorizing low value and low quality Indian coals via microwave pyrolysis to produce good quality carbon nanostructures in the heat-treated coal char. The effects of operating conditions such as coal type, coal:susceptor (Fe) mass ratio, and microwave power on product yield and quality are evaluated. The quality of the heat-treated coal char was assessed using different characterization techniques such as electron microscopy, porosimetry, X-ray diffraction, and Raman spectroscopy. The addition of Fe enhanced the heating rates, and led to the formation of carbon nanotubes and nanoparticles. Increasing the proportion of Fe resulted in increase in size of nanotubes and nanoparticles, which is attributed to the fusion of small tubes and particles caused by enhanced localized heating. The yield of carbon nanostructures was more from medium ash (~45%) than from high ash coal (~37%) due to the high fixed carbon and low ash content in the former. In addition to char, coal tar and non-condensable gases were characterized. The major compounds in the coal tar were aromatic hydrocarbons, simple phenols and aliphatic hydrocarbons. Hydrogen and methane were the major gases from medium ash coal, while hydrogen, methane and CO were produced in significant quantities from high ash coal. Microwave-assisted pyrolysis is shown to be a promising process to produce carbon nanostructures in a short time period as compared to conventional thermal processes.

Commercial microwave oven 800 W for sintering hydroxyapatite is being developed. The required temperature for sintering hydroxyapatite is 1200°C. A temperature 1200°C can be achieved if commercial microwave combined with susceptor and insulators material. This research is aiming to study about the effect configuration of SiC and Ceramic Fiberboard thickness to temperature rise. The results show that the presence of SiC with a thickness of the thinnest affect significantly temperature rise. The presence of CFb, as a second insulator, decrease the temperature rise and more the CFb thickness increases, more the temperature decreases.

Purpose The paper introduces and illustrates the use of numerical models for the simulation of electromagnetic and thermal processes in an absorbing ceramic layer (susceptor) of a new millimeter-wave (MMW) heat exchanger. The purpose of this study is to better understand interaction between the MMW field and the susceptor, choose the composition of the ceramic material and help design the physical prototype of the device. Design/methodology/approach A simplified version of the heat exchanger comprises a rectangular block of an aluminum nitride (AlN) doped with molybdenum (Mo) that is backed by a thin metal plate and irradiated by a plane MMW. The coupled electromagnetic-thermal problem is solved by the finite-difference time-domain (FDTD) technique implemented in QuickWave. The FDTD model is verified by solving the related electromagnetic problem by the finite element simulator COMSOL Multiphysics. The computation of dissipated power and temperature is based on experimental data on temperature-dependent dielectric constant, loss factor, specific heat and thermal conductivity of the AlN:Mo composite. The non-uniformity of patterns of dissipated power and temperature is quantified via standard-deviation-based metrics. Findings It is shown that with the power density of the plane wave on the block’s front face of 1.0 W/mm2, at 95 GHz, 10 × 10 × 10-mm blocks with Mo = 0.25 – 4% can be heated up to 1,000 °C for 60-100 s depending on Mo content. The uniformity of the temperature field is exceptionally high – in the course of the heating, temperature is evenly distributed through the entire volume and, in particular, on the back surface of the block. The composite producing the highest level of total dissipated power is found to have Mo concentration of approximately 3%. Research limitations/implications In the electromagnetic model, the heating of the AlN:Mo samples is characterized by the volumetric patterns of density of dissipated power for the dielectric constant and the loss factor corresponding to different temperatures of the process. The coupled model is run as an iterative procedure in which electromagnetic and thermal material parameters are upgraded in every cell after each heating time step; the process is then represented by a series of thermal patterns showing time evolution of the temperature field. Practical implications Determination of practical dimensions of the MMW heat exchanger and identification of material composition of the susceptor that make operations of the device energy efficient in the required temperature regime require and expensive experimentation. Measurement of heat distribution on the ceramic-metal interface is a practically challenging task. The reported model is meant to be a tool assisting in development of the concept and supporting system design of the new MMW heat exchanger. Originality/value While exploitation of a finite element model (e.g. in COMSOL Multiphysics environment) of the scenario in question would require excessive computational resources, the reported FDTD model shows operational capabilities of solving the coupled problem in the temperature range from 20°C to 1,000°C within a few hours on a Windows 10 workstation. The model is open for further development to serve in the ongoing support of the system design aiming to ease the related experimental studies.

This study deals about the influence of sintering temperature and holding time on microwave sintered PM stainless steel 316L microstructure, hardness and self-limiting characteristics. The samples exhibited increasing theoretical density upon increase in sintering temperature and superior density of 89.77% theoretical achieved at 1300 °C of 60 min holding time. Grain size distribution of microwave sintered SS316L at three different sintering temperatures (1200 °C, 1250 °C and 1300 °C) was compared, almost 68% to 75% uniformity in grain size was noticed and the largest grain (115 µm) was observed at 1300 °C with 60 min holding time. Self-limiting characteristics of microwave absorption analysed by time-temperature graph at different sintering temperatures. The effect of soaking time influenced the grain size, i.e., higher the soaking time larger the grain size. After maximum microwave absorption in core region, from outer surface region SiC susceptor play a role in contributing heat (20 °C/min) at the temperature beyond 1130 °C to achieve maximum sintering temperature.

Microwaves are type of electromagnetic radiations with a wide range of wavelength varying from 1 m to 1 mm and frequency between 300 MHz and 300 GHz for different wavelengths. Rapid heat transfer takes place through microwaves and these waves can easily penetrate throughout the material leading to localized volumetric heating. Joining of materials through microwaves seen a rapid increase in current years over conventional methods because of its high diffusion rate, lower power consumption, lower defects and improved mechanical and physical properties; at the same time; this technology is non hazardous to the environment. In this work, microwave joining technique has been used to join stainless steel of different grades (SS304 and SS316). Experiments were carried out in 900 W and 2.45 GHz microwave oven. Specimens of cross-section 6 × 5 mm2 were selected for butt joining purpose, completed by each half of SS304 and SS316. No filler powder was used during this joining process. Direct joining of stainless steel specimen SS304 and SS316 was done with the help of microwave hybrid heating technique. Charcoal powder was used as susceptor to accelerate the initial heating process. Optimum process time for joining of SS304-SS316 has been found by trial method, using constant gap of 10 s between successive trials. The joints have been characterized mechanically through micro-hardness test. Physical characterization of joint was also performed through scanning electron microscopy and energy dispersive spectroscopy method. Results show that proposed method is able to develop joints with good mechanical and physical properties.

In this paper, the feasibility of joining duplex stainless steel (SS2205) through a novel microwave joining technique has been investigated. Specimens of cross-section 3.5 mm × 5 mm were selected for butt joining purpose, completed by each half of SS2205 and SS2205. Experiments were carried out in a microwave applicator at 2.45 GHz frequency and 900 W. Duplex stainless steel specimens have been successfully joined through selective microwave hybrid heating technique at 300 s of exposure time. The vertical cavity-type feeder was used to feed charcoal in order to concentrate the heating effect around the joining region. Charcoal powder was used as a susceptor to initiate as well as accelerate the heating process. Optimum process time for joining of SS2205-SS2205 has been found by the trial method, using a constant gap of 30 s between successive trials. The joints have been characterized mechanically through the micro-hardness test. Hardness tests validate a proportional increase in hardness from heat affected zone to the joining region for all manufactured joints.

The application of microwave radiation for the processing of different materials is increasing frequently. Initially, microwaves were used for communication purpose but, due to its thermal ability currently, it is used for sintering, cladding, casting, and joining processes. Microwave joining of the materials is an emerging field of research that previously shown some encouraging outcomes. Although microwave processing of metals is a challenging task, still researchers have developed the method of heating the metals using susceptor material. This process of heating the metals is termed as microwave hybrid heating (MHH). In this review paper, the use of microwave energy for the joining of similar/dissimilar metals is studied briefly. From the review, there are several critical parameters that are discussed for successful microwave joining. The parameters included in this study are a specimen, interface powder, susceptor material, separator sheet, and insulated bricks. The importance of the characterization is studied and explained using previous results. It is concluded that there are several metals that are not being processed using microwave energy and some of the mechanical characteristics which are not used until now.

A synthetic method was developed to enable the microwave-assisted solid-state preparation of double molybdate and double tungstate scheelite-type phosphors of formula NaRE(MO4)2 (RE = La, Pr, Eu, Dy; M = Mo, W). Starting from subgram-scale stoichiometric mixtures of metal carbonates and oxides and with the aid of granular activated charcoal as a microwave susceptor, ternary (NaEu(MO4)2), quaternary (NaLa0.95Eu0.05(MO4)2), and quinary phosphors (NaLa0.95Pr0.025Dy0.025(MO4)2) were obtained upon heating in a countertop microwave oven. The synthesis of crystalline and phase-pure materials required heating times ranging from 18 to 27 min, significantly shorter than those typically encountered in solid-state reactions assisted by conventional heating. Depending on chemical composition, the speed-up factor ranged from 30 to 40. More importantly, photoluminescence studies performed on the compositionally complex quinary molybdate NaLa0.95Pr0.025Dy0.025(MoO4)2 showed that phosphors synthesized using microwave and conventional heating have nearly identical luminescence responses. The synthetic method described in this contribution is robust, fast, simple, and ideally suited for exploratory synthesis and rapid screening of group VI metalate phosphors, as well as for the preparation of binary precursors to these materials (e.g., Na2MoO4 and Na2WO4).

Knowing the advantages of microwave processing on different materials, it has established a good base for the sintering process. Although it has similar advantages for other processes, still other fields are not much established for industrial use. Microwave casting is one of the emerging fields which are yet to be studied in detail. In this paper, a literature review is carried out for the microwave casting of different materials such as metals, metal matrix composites (MCC), etc. Microwave casting is processed under an apparatus that involves microwave hybrid heating (MHH) where heat is transferred to charge using susceptor material. Further depending upon the designed apparatus, microwave casting is divided as in-situ and ex-situ casting processes. If molten material is allowed to solidify inside the microwave cavity is termed as “in-situ” casting while if molten material is allowed to solidify outside the microwave cavity it is termed as “ex-situ” casting. From the review, it can be concluded that the microwave casted materials produce better properties as compared to conventional casting processes in terms of homogeneity and mechanical properties. But most of the research is reported for low melting point materials like Aluminum and their alloys. With the implementation of a new design setup, microwave casting can be used for the materials that are having a melting point above 1000 °C.

Submitted by Luis Otávio Pontes Pechoto (luis.pechoto@unesp.br) on 2022-04-07T04:25:12Z No. of bitstreams: 2 Dissertação - Luís Pechoto. - revisado.pdf: 2141858 bytes, checksum: 083e5fe829c4bb5b67d650d5c2367035 (MD5) Dissertação - Luís Pechoto. - revisado.pdf: 2141858 bytes, checksum: 083e5fe829c4bb5b67d650d5c2367035 (MD5) Approved for entry into archive by Joao Josue Barbosa (joao.barbosa@unesp.br) on 2022-04-07T09:26:11Z (GMT) No. of bitstreams: 1 pechoto_lop_me_ilha.pdf: 2141858 bytes, checksum: 083e5fe829c4bb5b67d650d5c2367035 (MD5) Made available in DSpace on 2022-04-07T09:26:11Z (GMT). No. of bitstreams: 1 pechoto_lop_me_ilha.pdf: 2141858 bytes, checksum: 083e5fe829c4bb5b67d650d5c2367035 (MD5) Previous issue date: 2022-02-21 A fundição de metais não ferrosos é uma das técnicas industriais mais utilizadas atualmente para a produção de peças e componentes mecânicos, empregando diferentes formas de aquecimento por energia elétrica ou por combustão. Todavia a fundição de metais por meio de irradiação de micro-ondas é um tema relativamente recente e que vem ganhando destaque científico e tecnológico. O propósito deste trabalho é investigar a aplicação de micro-ondas para a fusão de metais não-ferrosos como estanho, chumbo, alumínio e cobre. Como metais em volumes massivos não absorvem micro-ondas foi empregado um anel feito de carboneto de silício como susceptor e isolado termicamente com uma manta de fibra cerâmica. Este sistema simples foi capaz de gerar a energia térmica necessária para a fusão dentro de um forno de micro-ondas comum para uso doméstico. Para análise do processamento foram processadas cargas de 50 e 100 gramas dos metais inseridos em cadinho de grafite, sendo obtidas as curvas de aquecimento durante o aquecimento e fusão dos materiais. Os resultados obtidos provam ser viável a fusão de metais não-ferrosos em tempos similares a outros métodos de aquecimento, sendo, portanto, uma técnica alternativa e simples para a fundição para metais em pequena escala. The melting of non-ferrous metals is one of the most used industrial techniques today to produce mechanical parts and components, employing different forms of heating by electrical energy or by combustion. However, the melting of metals by means of microwave irradiation is a relatively recent topic that has been gaining scientific and technological prominence. The purpose of this work is to investigate the application of microwaves for melting non-ferrous metals such as tin, lead, aluminum and copper. As metals in massive volumes do not absorb microwaves, a ring made of silicon carbide was used as a susceptor and thermally insulated with a ceramic fiber blanket. This simple system was able to generate the thermal energy needed for melting inside a common microwave oven for domestic use. For analysis of the processing, loads of 50 and 100 grams of the metals inserted in a graphite crucible were processed, and the heating curves during heating and melting of the materials were obtained. The results obtained prove to be viable the melting of non-ferrous metals in times similar to other heating methods, being, therefore, an alternative and simple technique for melting metals on a small scale.

As a new non-contact heating technology, induction heating technology has very broad application prospects in the field of fluid food heating. However, its application is inevitably affected by the heat concentration caused by uneven energy distribution. The uneven temperature distribution of the heating process will lead to the decrease in the quality of heating products. Therefore, based on the previous research, in order to improve the uniformity of heat distribution in the heating process, this study selected the susceptor with the greatest potential for efficient and the most uniform heating fluid to carry out the coupling simulation of electromagnetic heat transfer. The susceptor was simulated and optimized in three aspects: different power comparisons, the influence of structural change on temperature distribution uniformity, and the influence of physical property change of metal material on temperature distribution uniformity. The results show that the simulation results are in good agreement with the experimental results, and the error between the experimental and simulation values of the outlet temperature at Kelvin temperature is less than 0.18%. The change of geometric structure had a great influence on the uniformity of temperature distribution, and the uniformity of temperature distribution was inversely proportional to the conductivity. During the simulation, the temperature of the fluid heated by the susceptor was increased from 284.75 K to about 333K. The temperature distribution of the fluid at the outlet of the susceptor was uniform, and the temperature difference was about 1 K.

The paper describes one promising method and approach for the recycling, reuse, and co-resource treatment of waste photovoltaic silicon and lithium battery anode graphite. Specifically, this work considers the preparation of nano/micron silicon carbide (SiC) from waste resources. Using activated carbon as a microwave susceptor over a very short timeframe, this research paper shows that nano/micron β-SiC can be successfully synthesized using microwave sintering technology. The used sintering temperature is significantly faster and more energy-efficient than traditional processes. The research results show that the β-SiC particle growth morphology greatly affected by the microwave sintering time. In a short microwave sintering time, the morphology of the β-SiC product is in the form of nano/micron clusters. The clusters tended to be regenerated into β-SiC nanorods after appropriately extending the microwave sintering time. In the context of heat conversion and resource saving, the comprehensive CO2 emission reduction is significantly higher than that of the traditional SiC production method.

Induction soldering is a widely used process for the interconnection of construction parts. This technology allows a local heating process without putting the whole module into the oven, which minimizes the thermal load and thus improves the reliability of the electronic module and at the same time reduces the energy consumption of the soldering process. In this study, the internal heating of solder material is realized by induction losses within a suitable susceptor material. Therefore, a variety of ferromagnetic materials was examined as susceptor materials and different geometries and application methods were investigated. The soldering process is demonstrated at a laboratory induction setup where a controlled reflow soldering profile was applied.

A study of microwave sintering of uranium dioxide pellets has been performed with the aim to densify the material. Microwave sintering heating has been carried out in a 2.45 GHz multimode cavity, designed to fit the different requirements linked to sintering of nuclear ceramics. Hybrid and direct microwave heating (i.e., with and without susceptor) conditions were carried out. In the hybrid condition, thermal cycles at temperatures up to 1700°C, with a heating rate of 20 °C/min and dwell times of 10–60 min could be applied to the samples. The sintered specimens exhibited high values of densities (92.6–94.6% of theoretical density) with a grain size range of 9.1–11.8 μm, which is close to the results obtained with conventional sintering with longer thermal cycles. The pellet tested in the direct configuration only heated until 950°C, showing the impossibility to heat UO2 in a microwave furnace without the help of a susceptor.

The coating of the beech sawdust using a catalytic amount of graphite (as low as 0.25 wt%) allowed a step improvement in the microwave-assisted thermolysis. Results demonstrated that the pyrolysis performance was linked to an electrical conductivity threshold of the coated samples rather than a gradual increase. With as low as 0.13 mS m−1 of electrical conductivity, the 0.75 wt% graphite coated sawdust (250–500 μm) was efficiently gasified with up to 43 wt% of gas (30 wt% of carbon monoxide, 25 vol% of hydrogen). Initial particle size impacted the thermolysis performance where optimal size (250–500 μm) provided high heat homogeneity due to efficient graphite coating and low temperature gradient between the outer and inner part of the sawdust. The small initial particle size (75–250 μm) was unsuitable for microwave pyrolysis, exhibiting a too large surface area for efficient coating with 0.75 wt% of graphite which was confirmed by the absence of electrical conductivity (, Graphite catalytic coating of the wood sawdust is a step-improvement toward higher efficiency of the microwave-assisted pyrolysis of lignocellulosic biomass.

The present paper focuses on the high-pressure metal-organic vapor phase epitaxy (MOVPE) upside-down vertical reactor (where the inlet of cold gases is below a hot susceptor). This study aims to investigate thermo-kinetic phenomena taking place during the GaN (gallium nitride) growth process using trimethylgallium and ammonia at a pressure of above 2 bar. High pressure accelerates the growth process, but it results in poor thickness and quality in the obtained layers, hence, understanding the factors influencing non-uniformity is crucial. The present investigations have been conducted with the aid of ANSYS Fluent finite volume method commercial software. The obtained results confirm the possibility of increasing the growth rate by more than six times through increasing the pressure from 0.5 bar to 2.5 bar. The analysis shows which zones vortexes form in. Special attention should be paid to the transitional flow within the growth zone as well as the viewport. Furthermore, the normal reactor design cannot be used under the considered conditions, even for the lower pressure value of 0.5 bar, due to high turbulences.

Microwave melting of bulk metals is an innovative technique which works on the principle of hybrid heating. The dynamics of the process and melting time of metal are considerably influenced by the materials used in microwave processing. In the present work role of susceptor and separator materials on melting time of lead is experimented. Electromagnetic physics of the process in the view of materials which are used for tooling design and time is studied and discussed. The non-ferrous bulk metallic materials such as lead in fixed quantity was used as candidate material. Power capacity of 1100 W altered light duty commercial microwave oven, operating at 2.45 GHz is used for the study. The metallic piece was melted using susceptors-Activated charcoal and silicon carbide. The bulk pieces were preplaced inside graphite and alumina crucibles which work as a separators. The whole set up is covered with casket of refractory bricks. The temperature time characteristics of different assembly materials were examined. The result shows the considerable effect on melting temperature of lead metal with different combinations. Average temperature of above 500 °C has been observed for both crucibles with charcoal powder and below 400 °C for with silicon carbide as susceptors material with 4 min cycle time and same power level.