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In recent years, microwave processing of metal/alloy powders have gained considerable potential in the field of material synthesis. Microwave heating is recognized for its various advantages such as: time and energy saving, rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved mechanical...
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... Microwave Power Institute 43-1-7 of the green compacts was carried out using a multimode cavity 2.4 GHz, 6 kW commercial microwave furnace. The experimental setup is shown in Figure 1. A multi-layered insulation package was used to provide sufficient insula- tion to obtain high and uniform temperatures throughout the sample. The outer package was made of thick ceramic fiber (alumina and silicon carbide) sheets. A mullite tube was placed at the centre of the package, and samples were placed inside the mullite tube. The entire package was placed on a turntable to ensure uniform exposure of the sample to the microwave field. A reduced atmosphere was maintained during the sintering by first creating a vacuum of 8-10 torr inside the furnace followed by back filling ultra high purity (UHP) hydrogen. Throughout the sinter- ing, hydrogen gas flow was maintained at 2 lpm. This gas was diluted with nitrogen gas before venting to the atmosphere. For this experiment a thin layer of graphite coating outside the mullite tube was used as a susceptor. The susceptors usually couple very well with the microwaves and are used for initially raising the temperature of the compact. Sintering was carried out for 30 min in hydrogen atmosphere with dew point - 35°C. The power setting for the first experiment was 0. kW starting power followed by 0.2 kW increment after each min. The maximum power was 1.2 to 1.3 kW. The final temperatures achieved for the different particle sizes ranged from 927°C to 100°C, while the total time of 60 min and power setting were fixed for all experi- ments. For the second part of the experiement, a power of 1. kW was maintained from the start to the finish of the experiement. Temperature was 103°C and total time span 13 min. After sintering, the microwave power was switched off and samples were allowed to furnace cool. Unlike a conventional furnace, the temperature of the samples inside a microwave furnace can- not be monitored using a thermocouple [Pert et al., 2001]. The temperature of the sample was monitored using an infrared pyrometer (Type: RAYMA25CCF; manufacturer: Raytek Co., Santa Cruz, CA, USA). The infrared pyrometer was coupled with data acquisition and display software on a personal computer. The pyrom- eter is emissivity based and the temperature measurements for all the compacts were done by considering emissivity of copper (0.65) [Nayer, 1997]. Typically, emissivity varies with temperature. However, as very little variation in the emissivity was reported in the temperature range used in the present study, hence, the ef- fect of variation in emissivity was ignored in the present investigation. Figure 2 compares the thermal profiles of the copper powder compacts of varying particle size, sintered in multimode microwave furnace. It is interesting to note that the porous metal compact couple with microwaves heats rapidly. As par- ticle size increases the heating rate decreases and after certain time heating rate becomes constant at a particular power setting. It is well known that microwaves for electrically conducting materials such as copper do not penetrate a bulk sample beyond the skin depth. The skin depth is given by the well-known ...
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Powder metallurgy is one of the highly established methods to synthesize metals, alloys and composites. Sintering is one of the important steps in powder metallurgy methodology and is usually realized through conventional resistance furnaces. The sintering usually takes a few hours to realize density in excess of 90%. The present study highlights t...
Citations
... In 2009, Mondal et al. [15] observed that during the interaction of the microwaves with metallic powders with different dimensions, the metallic particles were heated. ...
A new method for the synthesis and deposition of tungsten oxide nanopowders directly on the surface of a carbon-fiber-reinforced polymer composite (CFRP) is presented. The CFRP was chosen because this material has very good thermal and mechanical properties and chemical resistance. Also, CFRPs have low melting points and are transparent under ionized radiation. The synthesis is based on the direct interaction between high-power-density microwaves and metallic wires to generate a high-temperature plasma in an oxygen-containing atmosphere, which afterward condenses as metallic oxide nanoparticles on the CFRP. During microwave discharge, the value of the electronic temperature of the plasma, estimated from Boltzmann plots, reached up to 4 eV, and tungsten oxide crystals with a size between 5 nm and 100 nm were obtained. Transmission electron microscopy (TEM) analysis of the tungsten oxide nanoparticles showed they were single crystals without any extended defects. Scanning electron microscopy (SEM) analysis showed that the surface of the CFRP sample does not degrade during microwave plasma deposition. The X-ray attenuation of CFRP samples covered with tungsten oxide nanopowder layers of 2 µm and 21 µm thickness was measured. The X-ray attenuation analysis indicated that the thin film with 2 µm thickness attenuated 10% of the photon flux with 20 to 29 KeV of energy, while the sample with 21 µm thickness attenuated 60% of the photon flux.
... Usually, they belong to the spectra between 300 MHz (l = 1 m) and 300 GHz (l = 1 mm), with 12 cm and 33 cm used commonly for domestic and industrial applications, respectively (Díez et al. 2011). They are generated artificially with a magnetron, and this technology was first used during the early stages of radar technology in World War II and since then, microwave applications in the ceramics (Mondal et al. 2008) and polymer industries (Ludlow-Palafox and Chase 2006), telecommunications, heating, rubber vulcanization, and radar equipment (Mishra and Sharma 2016) have grown consistently. Microwave absorption (critical for heating) is a function of the material's conductive properties where highly conductive materials absorb more radiation and heat up faster compared to low conductivity materials that become microwave transparent and cannot be heated (Goodman 2014). ...
Fast-accumulating waste plastic can be thermochemically recycled via microwave-assisted pyrolysis to recycle their embedded energy by restructuring them into useful gaseous, liquid, and solid products that can be used for power cogeneration, transportation (fuel), and construction applications, respectively. Among them, the liquid product can be used as a diesel substitute in compression ignition engines due to its higher calorific value and relatively lower exhaust emissions. The nature of microwave heating yields a better quality product that enhances process economics while reducing its environmental footprint. Some techno-economic studies show that microwave-assisted pyrolysis is a scalable waste-to-energy route with high initial capital investment, but lower operational costs compared to conventional pyrolysis. They also indicate that the fixed capital costs increase exponentially with plant size, but with correct optimization of critical parameters, the process can achieve breakeven in 2½ to 5 years at a 7% return on investment. However, more techno-economic studies, life cycle and life cycle costing studies are required to verify these numbers while also identifying the interdependence of critical parameters like residence time, reactor temperature, microwave power, and feedstock type, etc., with response surface methodology. This review consolidates the basics, important parameters, advantages, and limitations of microwave-based pyrolysis with suggestions on the synergistic integration with conventional plastic waste management methods. Overall, this technology offers significant economic opportunity and carries the potential to mitigate environmental harm when integrated with a circular economy.
... As the temperature for sintering increases, the density of metals and ceramics appears to grow, and the porosity appears to decline, as demonstrated by the data for ZIF-8. At 95°C, the apparent density of ZPI at 95°C decreases, but there is no sign of solvent leaking [64][65]. This decrease in apparent density can be the consequence of changes to ZPI's microstructure, such as localized melting at the primary particle contact, which causes previously closed pores to open, the volume appears to increase, and the density appears to decrease. ...
This study includes Metal-Organic Frameworks (MOFs) which are a type of porous materials that have advanced significantly in recent years. Due to their porous structure, they outperform traditional adsorbents in hot areas like carbon dioxide collection and dihydrogen and methane storage. Because of this, MOFs’ shape presents a unique challenge compared to other conventional porous materials. Metal-organic frameworks (MOFs) have shown potential in a wide range of applications, including molecular sieving, energy storage, ion separation, and biomedicine. The production of coherent material masses is accomplished through
sintering, which can occur both naturally in mineral deposits and artificially when processing metal, ceramic, and plastic materials. Sintering is a well-known and commercially available method that can be scaled up for industrial use. Pressure-assisted sintering was used to quickly create crystalline macro-porous monoliths from metal-organic framework (MOF) powders. They produce microcrystalline powders with sorption capabilities, which have been praised for their potential in massive industrial separation processes. Taking into existence the behavior and mechanism of coordination polymer and metal-organic frameworks, consider Zn (HPO4)(HPO4)2. 2H2 Imidazole (ZPI: a melting coordination polymer, (Im) imidazole) and ZIF-8 were studied. Simple compaction and subsequent sintering allowed for the creation of a bulk body of coordination polymers without sacrificing the macroscopic crystallinity. The temperature, heating rate, and physical characteristics of the coordination polymers were found to be determinants of their reliability. Both coordination polymers shrunk between 10 and 20%, while the ZPI shrunk by less than 1%. Through this study, we can understand the thermal, mechanical, chemical, and physical properties of the sintered metal-organic frameworks.
... During the experiment it was observed that the metallic samples were heated and in some cases arcing electric discharges occurred. The heating of metalic samples by the microwave field was attributed to the Eddy curent process [1]. ...
The aim of this research is to understand the plasma initiation process generated by metallic wires when interacting with high energy density microwaves. Lead (Pb) and molybdenum (Mo) wires of 0.5 mm diameter were investigated in this experiment. The end of the metallic wire was placed into the nodal point of a waveguide cavity attached to a microwave generator, where it was exposed to the high energy density of the microwave field. Following the interaction between microwaves and the metallic wire, a plasma was initiated having as effect the wire vaporization. The experiments were conducted in atmospheric air at ~1 bar pressure. From optical emission spectroscopy investigations it was observed that electronic excitation of the plasma has high values and it is in a local thermal equilibrium. The theoretical calculation of the voltages induced in the metallic wires when exposed to high magnitude of the microwave field are similar to those measured in air breakdown experiments. The SEM analysis of the tips of the metallic wires showed that the field effect process is responsible for the ignition of the metallic wires and plasma generation.
... Heating. The absorption of microwave energy by a powder material depends on its grain-size characteristics [13,14]. Therefore, the particle size of the starting ilmenite concentrate can influence the temperature and phase formation in microwave heating. ...
The general chemical and phase composition of the ilmenite concentrate from the Irshansk deposit was determined. The content of titanium (in terms of TiO2) in this concentrate was more than 50 wt.%. Ilmenite was the main phase component, which partially turned into pseudorutile through secondary processes. The concentrate was oxidized using microwave heating. Prior to microwave heating, particles of the starting ilmenite concentrate were ground for 3 min in a planetary-ball mill to an average size of 10 μm. A 100 g sample of the ground concentrate was heated for 30, 60, 90, and 120 min. In the heating for 30 min, pseudorutile disintegrated and pseudobrookite formed. Subsequent heating for 60 and 90 min led to the formation of rutile and increased the amount of pseudobrookite. Microwave heating for 120 min resulted in the complete decomposition of ilmenite. Pseudobrookite, rutile, and quartz were identified in an averaged sample by X-ray diffraction. Iron oxides were not found in the averaged sample. Interaction of the ilmenite concentrate sample with air during heating led to intensive surface oxidation of the material to form a larger amount of rutile and to release of iron oxide from the pseudobrookite as hematite. Electron microscopy of the oxidized particles revealed that titanium was mainly contained in fine concentrate subparticles up to 1 μm in size, and impurities (silicon and aluminum compounds) formed coarser agglomerates. The sizes of ore macroparticles hardly changed after microwave heating. Comparison of the effects from microwave and conventional heating on the ilmenite concentrate showed that heating in a resistance furnace for 120 min did not result in complete oxidation of ilmenite even at higher temperatures. Additional grinding of the starting ilmenite concentrate increased the heating and oxidation temperatures of the material subjected to microwave processing.
... In the microwave, first, within the material heat is generated and then the entire volume is heated. This is advantageous because of increased diffusion, rapid heating rates, decreased sintering temperatures, reduced energy consumption and considerably reduced processing times, improved physical and mechanical properties [8]. Microwave sintering of materials was mostly limited until the end of the last century to ceramics, polymeric materials, inorganic, and semiconductors. ...
Copper is a widely used material in various industries due to its properties like good corrosion resistance, thermal and electrical conductivity, stability at high temperatures, etc. To increase the mechanical and tribological properties, additional reinforcement should be added to the copper matrix. Adding tin into copper will result in the formation of bronze which is stronger and harder than either of the pure metals. This study deals with the comparative study of mechanical and tribological properties of microwave sintered and conventionally sintered Cu-6Sn. The mechanical properties of Cu-6Sn processed through powder metallurgy are compared with that of Cu-6Sn processed through casting. Hardness and wear resistance was observed to be higher for conventionally sintered specimens. Microwave sintered Cu-6Sn exhibit enhanced mechanical properties compared to Cu-6Sn processed through casting.
... The wall thickness measured from the X ray-CT is compared with the numerical thickness calculated from the 2D temperature contours. Temperatures above 1025°K [20] are assumed to cause powder sintering to the sidewalls after a single laser track is scanned on the powder bed. The numerical thickness is measured after each layer deposition and therefore ten wall thicknesses are measured and the measured location after each layer deposition is shown in Fig. 6. ...
Laser Powder Bed Fusion (L-PBF) is a Metal Additive Manufacturing (MAM) technology which offers several advantages to industries such as part design freedom, consolidation of assemblies, part customization and low tooling cost over conventional manufacturing processes. Electric coils and thermal management devices are generally manufactured from pure copper due to its high electrical and thermal conductivity properties. Therefore, if L-PBF of pure copper is feasible, geometrically optimized heat sinks and free-form electromagnetic coils can be manufactured. However, producing dense pure copper parts by L-PBF is difficult due to low optical absorptivity to infrared radiation and high thermal conductivity. To produce dense copper parts in a conventional L-PBF system either the power of the infrared laser must be increased above 500W, or a green laser should be used for which copper has a high optical absorptivity. Increasing the infrared laser power can damage the optical components of the laser systems due to back reflections and create instabilities in the process due to thermal-optical phenomenon of the lenses. In this work, a multi-physics meso-scale numerical model based on Finite Volume Method (FVM) is developed in Flow-3D to investigate the physical phenomena interaction which governs the melt pool dynamics and ultimately the part quality. A green laser heat source and an infrared laser heat source are used individually to create single track deposition on pure copper powder bed above a substrate. The effect of the dissimilar optical absorptivity property of laser heat sources on the melt pool dynamics is explored. To validate the numerical model, experiments were conducted wherein single tracks are deposited on a copper powder bed and the simulated melt pool shape and size are compared. As the green laser has a high optical absorptivity, a conduction and keyhole mode melting is possible while for the infrared laser only keyhole mode melting is possible due to low absorptivity. The variation in melting modes with respect to the laser wavelength has an outcome on thermal gradient and cooling rates which ultimately affect the mechanical, electrical, and thermal properties.
... Electromagnetic radiation propagation in different media has been a topic of great scientific and technological interest for many important applications in the fields of telecommunication, energy transportation and photon processing [1,2]. Usually, bulk metals reflect the microwave field [3]. However, under certain conditions it has been shown that metallic powders and thin wires can absorb microwaves [4,5]. ...
Single crystal In2O3 nanoparticles were synthesized using microwaves vaporization of a thin metallic In wire in air. The output of an 800 W microwave generator was coupled through an antenna to a cylindrical wave guide cavity in with a metallic In wire was placed in the electromagnetic node, where a high power density was achieved. The wire strongly absorbed the microwaves, resulting in its heating, vaporization and finally a plasma plume formation. Optical emission spectroscopy investigations indicated that a high electronic temperature was reached in the plasma plume. The vaporized material was collected on a Si wafer placed near the cavity wall. Scanning electron microscopy investigations showed that the deposited material consisted of an agglomeration of In2O3 nanoparticles. X-ray diffraction and transmission electron microscopy (TEM) investigations indicated that the nanoparticles were very crystalline, with random orientation. X-ray photoelectron spectroscopy analysis confirmed the formation of stoichiometric In2O3. High resolution TEM investigations found that the deposited nanostructures were single crystals, with faceted surfaces. This simple method could have many applications for metal nanocrystal oxides synthesis.
... It is known that the absorption and reflection processes of the microwaves strongly depend on the material properties. Gases and liquids can absorb the microwaves [1][2][3], while bulk metals reflect them [4]. ...
... To evaluate microwave absorption efficiency of the metallic powders, Mondal et al. [4] exposed copper powders with different particles size to a microwave field. In their experiment, the powders reached a temperature of 1200 °C for 6 μm particles size, while metal powders with 383 μm particles size reached only 800 °C. ...
The effects induced by microwave field upon tungsten wires of different diameters were investigated. Tungsten wires with 0.5 and 1.0 mm diameters were placed in the focal point of a single-mode cylindrical cavity linked to a microwave generator and exposed to microwave field in ambient air. The experimental results showed that the 0.5 mm diameter wire was completely vaporized due to microwaves strong absorption, while the wire with 1 mm diameter was not ignited. During the interaction between microwaves and tungsten wire with 0.5 mm diameter, a plasma with a high electronic excitation temperature was obtained. The theoretical analysis of the experiment showed that the voltage generated by metallic wires in interaction with microwaves depended on their electric resistance in AC and the power of the microwave field. The physical parameters and dimension of the metallic wire play a crucial role in the ignition process of the plasma by the microwave field. This new and simple method to generate a high-temperature plasma from a metallic wire could have many applications, especially in metal oxides synthesis, metal coatings, or thin film deposition.
... Similar findings are available in other relevant reports [64,65] that increase in roughness or porosity of surface leads to a decrease in contact angle. The reason for higher porosity on the surface of the sample sintered by R3 may be attributed to a lack of significant diffusion in the compacted metallic sample, which remained as pores in the final sintered product [66]. ...
... The optimum set of process parameters for the microwave sintering route, i.e., R3, were yielded in lower mechanical as well as corrosion properties as compared to R1. The reason may be credited to the absence of substantial diffusion of the metallic compact as the metallic components tend to reflect the microwave radiations and permits only limited surface penetration of 36.8% of surface value [66]. However, a little bit of diffusion was occurred due to the presence of refractory susceptors, as they completely absorbed the microwave radiation and started heating the surface of the sample. ...
In the present work, an optimum set of microwave sintering parameters was used to fabricate a newly developed biomaterial, namely Mg3Zn1Ca15Nb, with improved mechanical and bio-corrosion properties. In the recent work by authors, sintering parameters were optimized using the conventional sintering route (R1) to sinter Mg3Zn1Ca15Nb, which resulted in improved mechanical and degradation properties. Subsequently, to achieve better properties of Mg3Zn1Ca15Nb over R1, a microwave sintering route (R2) was used to sinter the same material at similar parameters, which were used in R1. However, the obtained properties of magnesium alloy matrix composite (MgMCs) sintered using R2 were found to be lower than the R1. This article was aimed to optimize the sintering parameters by microwave sintering route (R3) to get significant results over R1. Sintering parameters such as heating rate, sintering temperature, and holding time were taken for optimization. Also, the influence of sintering parameters on the mechanical and bio-corrosion properties of MgMCs was studied. Experimentations were proceeded according to central composite design (CCD). The mechanical and bio-corrosion properties of Mg3Zn1Ca15Nb, sintered using R3 was better than the R2. However, these properties were still behind the properties of the sample sintered using R1. Scanning electron microscopy (SEM) images of the sample showed clustering of powders and micro-cracks on the surface of the sample sintered using R2. However, by increasing the heating rate, a reduction in powder clustering and micro-cracks were observed. Additionally, the microscopic image showed a reduction in the size of porosity with an increase in heating rate. No phase formation was observed in the microwave sintered samples as per X-ray diffraction (XRD) analysis. In addition to this, the hydrophilic nature of Mg3Zn1Ca15Nb showed a good agreement for cell adhesion. Subsequently, the bio-corrosion behavior of fabricated samples was tested in simulated body fluid (SBF) containing pH 7.4 at 37±0.5 C. The obtained corrosion rate of the sample sintered using R3 was less than R2, whereas it was still higher than R1.
