Hybrid Microwave Research Articles

A parametric study of conventional and high-speed microwave sintering of robocast porcelain

The combination of three-dimensional (3D) printing technologies and microwave (MW) sintering offers new perspectives for minimizing material, energy and time waste. This study aimed at conducting a parametric study on the sintering of robocast porcelain by conventional and MW heating in a multimode cavity (2.45 GHz, 3 kW). The effect of heating rate, dwell temperature and dwell duration on sample density, shrinkage and microstructure was investigated on small pellets. With conventional heating, a good densification was achieved with a 2 h dwell at 1250 °C, independent of heating rate (1–20 °C/min). A similar density was reached using microwave hybrid heating at a much higher heating rate (100 °C/min), shorter dwell (30 min) and slightly higher sintering temperature (1300 °C). Without susceptor, a longer pre-heating step was required to initiate the sample heating, thus extending the heat treatment duration. This study provides seeding data for the development of greener processes for aluminosilicate ceramic manufacturing.

Zinc oxide nanorods effect in micro structural and mechanical characteristics of aluminium composite material

In the present study, aluminium zinc oxide (Al-ZnO) nanorods composites with 3.5 and 5 wt% ZnO in Al were manufactured using powder metallurgy and microwave hybrid sintering. A fairly uniform reinforcement distribution and clear interface was perceived in the micro structural and energy dispersive spectroscopy analysis of composite material. It was observed from XRD analysis that no secondary (intermetallic) phase of Al and ZnO were present in the composite material. The simultaneous thermal analysis of the composites was done to understand the variation in the exothermic peak temperature and weight change percentage of composite material. The developed composite material with 5 wt% ZnO exhibited promising results in terms of micro-hardness (∼2 times), nano hardness (∼3.5 times) and elastic modulus (∼1.9 times) greater value compared to Al. The increased addition of ZnO nanorods in aluminium shows enrichment in properties rendering the material suitable for different engineering applications.

Multi-physics simulation study of microwave hybrid sintering of aluminium and mechanical characteristics

In the present study, a finite element model of microwave hybrid sintering along with experimental validation was developed. Multiphysics simulation at 2.45 GHz was carried out to understand the heat transfer behaviour and electric field distribution during the microwave hybrid sintering process. The proposed work presents an innovative and integrated approach for sintering aluminium utilizing microwave energy. Comparison with numerical simulation results and experimental data of temperature variation during microwave hybrid sintering was done. The maximum error predicted by the simulation model and experimental investigation for temperature variation in sintering was found to be within 10%. The X-ray diffraction analysis, relative density and microstructure analysis of the sintered aluminium was done to gain an insight into the material characteristics. The microhardness and nanoindentation tests were carried out to determine the hardness and elastic modulus. Good consolidation behaviour of aluminium with an achieved density of 0.9774, microhardness of 36Hv, nano-hardness as 0.5664 GPa and 57.301 GPa elastic modulus value has been observed. The study will develop a cogent link between the numerical model and experimental data for microwave hybrid sintering.

Comparison of intermetallic compound growth and tensile behavior of Sn-3.0Ag-0.5Cu/Cu solder joints by conventional and microwave hybrid heating

Microwave hybrid heating (MHH) is a possible approach for soldering; yet, the long-term reliability of solder joints is still unclear. In this work, a comparative study was carried out on the influence of isothermal aging on SAC305/Cu solder joints by conventional reflow and MHH. The conventional reflow oven was set to 260 °C at 60 s holding time, and MHH was carried out at high operating power at 40 s. The reflowed sample was isothermally aged at 150 °C for various aging times (0, 240, 480 and 960 h) in a laboratory oven. The conventional reflow and MHH transformed the IMC structure from scallop-like to a planar-like Cu6Sn5 with a linear increase in thickness and a thin layer of Cu3Sn was observed at 240 h of aging. While Ag3Sn particles grew larger at longer aging time. The MHH shows a thinner Cu6Sn5 layer, and a smaller grain size compared to conventional reflow. The ultimate tensile strength (UTS) for conventional reflow (32.7 MPa) is 26.8% lower compared to MHH (44.7 MPa). The UTS for MHH is greater than conventional reflow as the isothermal aging time increases.

Microstructure and Tribological Characterization of Composite Castings Developed through In-situ Microwave Hybrid Heating

Microstructure and Tribological Characterization of Composite Castings Developed through In-situ Microwave Hybrid Heating

Aluminum Yttrium Oxide Metal Matrix Composite Synthesized by Microwave Hybrid Sintering: Processing, Microstructure and Mechanical Response

Aluminum Yttrium Oxide Metal Matrix Composite Synthesized by Microwave Hybrid Sintering: Processing, Microstructure and Mechanical Response

Dielectric behaviour of BZT-BCT nano pseudobinary system near TCP-assisted morphotopic phase boundary

The present study investigates the comparative dielectric studies in nano pseudobinary system synthesized by conventional and hybrid microwave sintering. The material was formed near Tri Critical Point (TCP)-assisted Morphotropic Phase Boundary (MPB) region from equal weight percentage of Lead Zirconate Titanate (BZT) and Barium Calcium Titanate (BCT) employing high energy ball milling. In the temperature dependent LCR study, a diffused phase transition (DPT) behaviour was identified for both conventional and hybrid microwave sintered samples. In each case, modified Currie-Weiss relation indicates an anomaly in the paraelectric state. Further, another approach using macroscopic composition-fluctuation model also exhibits the anomalous behaviour. Universal dielectric response (UDR) demonstrates that such behaviour is created by a temperature assisted relaxation phenomena by the formation of oxygen vacancies. Beyond 260 °C, microwave sintering creates more oxygen vacancies across grain boundary region as compared to the conventional sintering and in turn plays the key role for enhanced dielectric permittivity.

Effect of Variations in Microwave Processing Temperatures on Microstructural and Mechanical Properties of AA7075/SiC/Graphite Hybrid Composite Fabricated by Powder Metallurgy Techniques

Due to the demand in present industrial, aerospace, defense sectors for lightweight high-performance aluminum (Al) particle-reinforced metal matrix composites, the advancement of techniques to fabricate these composites with superior mechanical properties have gained technological interest in the modern world. In this direction, SiC and graphite reinforced AA7075 matrix composite material has been fabricated in this study, through hybrid microwave sintering techniques. The microwave sintering temperatures for the optimized volume fraction composition of AA7075/SiC/graphite hybrid composite has been varied from 400 to 550 °C with a step value of 50 °C. The obtained results showed a superior improvement in the mechanical properties for microwave sintered composites as compared to the conventionally sintered composites. Mechanical properties are found to show increasing trend with increasing microwave sintering temperatures up to 500 °C, after that, a downfall is observed in their mechanical properties, which can be attributed to the increased average grain size of the composite at 550 °C. Selection of SiC as primary reinforcement material helped in achieving high mechanical strengths, and through microwave sintering, an increment of 37.2% in tensile, 26.6% in compression, and 16.5% in hardness is achieved. From this investigation, it is also observed that the selection of materials that shows high response to microwaves helps in achieving the enhanced mechanical properties for the hybrid composites processed by microwave sintering techniques.

Diamond NV Centers Based Quantum Sensor Using a VCO Integrated With Filtering Antenna

This paper presents a diamond nitrogen-vacancy (NV) center based magnetic field sensor using a voltage-controlled oscillator (VCO) integrated with a filtering antenna. In existing NV-based quantum sensing systems, microwave source and delivery units are implemented by a set of bulky and costly instruments. This limits its practical applications as well as portability. Here, a VCO integrated with the filtering antenna is designed, providing a more uniform, efficient, broadband and lower phase noise microwave field coupling to the NV centers. As a result, the sensitivity and the dynamic range have been improved over the conventional scheme using separate microwave components, such as antennas, transmission lines, and resonators. Moreover, in this work, the optic filter, and photodetector are also integrated using the hybrid microwave integrated circuits (HMIC) technique for the first time. This significantly increases the integration level and reduces the cost of the NV-based magnetometers. The experimental results indicate that our VCO integrated filtering antenna achieves a sensitivity of 8.52 μT/Hz^1/2 and a dynamic range up to 32.73 dB, which are both greatly improved compared to the VCO with a single resonator. This validates the effectiveness of the approach.

Hybrid Microwave Imaging of 3-D Objects Using LSM and BIM Aided by a CNN U-Net

This paper presents an efficient and accurate three-dimensional (3-D) quantitative hybrid microwave imaging method. The linear sampling method (LSM) is first carried out to quickly find the approximate shapes and locations of the unknown objects in the imaging domain based on the scattered field data recorded by receivers which are placed in the far-field zone and wrap the domain. Then the full-wave inversion (FWI) is implemented in a downsized domain which tightly encloses the unknown objects instead of in the whole domain through the Born iterative method (BIM) to quantitatively retrieve the dielectric model parameters of the objects. Because the LSM fails to obtain the sufficiently accurate shapes of the unknown objects, a trained 3-D CNN U-Net is inserted between the LSM imager and the BIM solver to further refine the obtained shapes of LSM, which is expected to aid the following FWI. The proposed hybrid method is validated via the quantitative imaging of both inhomogeneous isotropic scatterers and multiple homogeneous anisotropic scatterers. It is shown that the hybrid method can achieve both higher reconstruction accuracy and lower computational cost compared with the direct BIM inversion. Meanwhile, its antinoise ability is also tested.

Worm-like porous and defect-structured cadmium stannate photoanodes for enhanced solar water oxidation.

The work aims to elucidate the importance of hybrid microwave annealing technology (HMA) in ultrafast fabrication of deficient cadmium stannate (Cd2SnO4) photoanodes with a worm-like porous structure and significant enhancement of solar water oxidation performance and stability. Comparison of three synthetic routes and experimental characterization revealed that relative to conventional thermal annealing (CTA) or even with extra HMA for 5 min (optimal), direct HMA for only 8 min can form cubic Cd2SnO4 thin films of unique worm-like and highly porous nanostrucures with a large interfacial surface area, high degree of phase crystallinity and high-concentration defects. The obtained results from the photoluminescence spectra and the charge efficiency measurements collaboratively verified that compared to using CTA treatment solely, the HMA treatment is effective in significantly improving charge separation, recombination and transfer processes, mainly by an over 13.5-fold increase in the bulk charge separation efficiency. Benefiting from these merits, under optimized conditions the HMA treated Cd2SnO4 film exhibited a remarkable 6-fold and 2-fold solar photocurrent enhancement compared with those of the CTA treated one and the combined CTA-HMA treated one, respectively, and an IPCE of 39% at 300 nm and 18% at 350 nm at 1.7 V versus RHE. Despite a high external bias required in this case, the study provides a simple route for synthesis of ideal Cd2SnO4 photoanodes which can be further extended to doping engineering and non-noble metal cocatalyst deposition.

Effect of simultaneous use of microwave and ultrasound irradiation on the sulfuric acid hydrolysis lignin (SAHL) depolymerization

Individual and combined effects of microwave (MW) and ultrasound (US) irradiations on the depolymerization of sulfuric acid hydrolysis lignin (SAHL) were investigated in a hybrid microwave–ultrasound chemical reactor.

A hybrid microwave sintered PZT composite as a flexible piezoelectric nanogenerator.

Interest in piezoelectric nanogenerators has grown extensively due to high piezoelectric coefficients. Piezoelectric ceramic-based devices have dominated research in large-scale energy harvesting. Morphotropic phase boundary PbZr0.52Ti0.48O3 (MPB-PZT) synthesized using Hybrid Microwave Sintering (HMS) at a low temperature (940 °C) for 20 min has emerged as a dense ceramic. The Rietveld refinement studies confirm its dual phase (tetragonal (P4mm) and rhombohedral (R3m)). The PZT ceramic is exploited as a piezoelectric material, which can improve the output piezoelectric potential of a piezoelectric nanogenerator (PENG). Multi-walled carbon nanotubes (MWCNTs) are evenly distributed in the PZT composite to reduce the internal resistance of the PENG. According to the percolation theory, small amounts of MWCNTs dispersed within the composite ink can significantly improve the output voltage of the PENG by acting as conductive bridges between the polymer (polyvinylpyrrolidone (PVP)) and ceramic particles. The concentration of PZT and the amount of MWCNTs are changed to enhance the device's output voltage. As a result, an optimized PENG with a PZT (1.5 g)/MWCNT (0.06 wt%)/PVP (4 g) (PVP - polyvinylpyrrolidone) composite film is obtained. The PENGs are mechanically poled. The optimised output voltage of the PENG is 16 Vpp, which could light up a series of 20 commercial light emitting diodes (LEDs). The PENG is attached to footwear and is noticed to efficiently harvest energy from daily human activities which demonstrate its practical applications.

Corrosion Properties of Cu/Sn–3.0ag–0.5cu/Cu Solder Butt Joints Fabricated by Conventional Reflow and Microwave Hybrid Heating

Corrosion Properties of Cu/Sn–3.0ag–0.5cu/Cu Solder Butt Joints Fabricated by Conventional Reflow and Microwave Hybrid Heating

Application of graphite rods in producing Inconel 625 (UNS N06625) joints through the use of microwave radiation energy

Microwave energy is very efficiently being harnessed to join metallic materials these days. Although, use of microwaveenergy to join metallic materials is in its initial stage but, it has led to an outstanding development in the field of manufacturing. In this research work, joining of Inconel 625 (UNS N06625) without any filler material has been performed with the help of a novel process by harnessing microwave energy from a 900 W microwave applicator. Major novelty of thiswork is the application of graphite rods in accelerating the joining process based on the use of microwave radiation energydue to which it could become possible to join the Inconel specimens without using any filler powder. Selective microwave hybrid heating has been performed using six graphite rods and the process time taken for successful joining of Inconel625 specimens has been 360s. Three repetitions have been done using the mentioned process parameters. Mechanical characterization of the developed joints has been done with the help of Vickers micro-hardness tester and tensile testingmachine. The mean microhardness of the joints has been observed to be 325.1 HV at the joint region which came out to be 10.32 % more than that of the base alloy. The mean ultimate tensile strength has been observed to be 319.9 MPa with mean elongation of 5.3% which has been observed to be less than that of the base alloy.

A comparative study of interface material through selective microwave hybrid heating for joining metal plates

The development of joints using microwave hybrid heating (MHH) received extensive attention over conventional heating due to its uniform heating, environment friendly characteristics. For effective microwave joining of bulk metals, joint region was targeted selectively naming it as selective microwave hybrid heating (SMHH). Microwave joining of stainless steel using Nickel as interface material is explored extensively through MHH; however no comparative study showing better interface material for microwave joining of Stainless steel is reported. In the present study, SS304-SS304 lap joint is simulated for two different interface materials that are nickel and Inconel-718 for an exposure time of 22 min. These joints were developed using pulverized charcoal as a susceptor material and at the power output of 700 W. Microwave hybrid heating has been simulated by implementing different assumptions and boundary conditions at better mesh quality. A time-temperature curve, resistive heating, electric field distribution, and temperature profile along different directions are those parameters that have been discussed to examine better interface material. From the results, it is observed that Inconel-718 shows better resistive heating when compared to nickel interface material, however electric field distribution remains similar for both interface materials. Further, the time-temperature profile revealed that the time taken for Inconel-718 interface material to reach fusion zone is lesser than Nickel interface material.

Filler powder free joining of SAF 2507 using selective microwave hybrid heating technique

Microwave Hybrid Heating (MHH) based joining of super duplex stainless steel (SAF 2507) with cross-sectionaldimensions 3.5 mm ×3 mm has been carried out for the first time by using a microwave applicator of 900 W operated at2.45 GHz for 400 s. Graphite rods have been used instead of traditionally used charcoal powder to serve as susceptormaterial. Graphite rods are good susceptor of microwave radiations therefore the presence of these rods helps in initiatingand carrying forward the joining process. Moreover, the melting temperature can be achieved for specimens underinvestigations through this novel process thereby eliminating the need of using any filler powder. Absence of filler powderreduces the process cost significantly. The joints have been mechanically characterized by Vickers micro-hardness andphysically characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) tests. It hasbeen observed through these tests that micro-hardness of the joints was more than the base alloy due to transfer of carbonfrom graphite rods to the joint zone.

Hydroxyapatite reinforced surface modification of SS-316L by microwave processing

The current study was focused to modify the surface layer of stainless steel (SS-316L) for enhancing its bioactivity by reinforcing hydroxyapatite (HAp) powder through exploiting the principle of hybrid Microwave Heating (MH) technique. The modified substrates were subjected to post heat-treatment at 400 °C and 700 °C for 1 h. The microstructural analysis of the modified composite layer revealed the existence of HAp particles along with some reaction induced products primarily in the iron-based austenite dendritic matrix. The heat-treated substrates showed a higher microhardness value than that of as-deposited substrates due to densification of the modified layer after heat-treatment. The porosity, surface imperfections and flaws were reduced after heat treatment. The scanning electron microscopy (SEM) images taken over the modified and unmodified SS-316L after immersion test in simulated body fluid showed rapid apatite forming ability on the modified substrates. The apatite growth ability of the modified substrates was reduced after heat treatment performed at 700 °C due to a reduction in the amorphous phase and porosity contents.

Development of Magnesium Nanocomposites by Powder Metallurgy for Multifunctional Applications: Review

Magnesium is a lightweight metal that holds great potential in automotive, aerospace and biomedical applications. Magnesium when incorporated with nanoparticles, exhibits simultaneous improvements in mechanical, tribological and biological properties without altering its density. This article presents a short review and analysis of mechanical (tensile and compressive), ignition, damping, tribological and in vitro degradation (corrosion and biocompatibility) behaviour of magnesium- based nanocomposites. Owing to the flexibility in tailoring for multiple applications, powder metallurgy routes are being explored to target unique microstructures, novel compositions and high performance in magnesium-based nanocomposites. The mechanical and in vitro study of magnesium nanocomposite synthesized by powder metallurgy route demonstrates improved strength, controlled degradation and good biocompatibility. The article also proposes a powder metallurgy route incorporating hybrid microwave sintering as a promising environment-friendly technique to develop magnesium nanocomposites for biomedical applications.

Significance of fabrication parameters over the mechanical and metallurgical properties of AMMC joint formed by microwave hybrid heating

Purpose The purpose of the study is to fabricate a joint between two aluminium metal matrix composites using microwave hybrid heating (MHH). Design/methodology/approach Taguchi design of experiments was applied to conduct the experimental study. The mechanical properties such as ultimate tensile strength, micro-hardness and porosity were studied. Grey Relational Analysis was applied to understand the significance of fabrication parameters of best performing sample. The dominant factor of fabrication was analysed using ANOVA. The best performance sample was further characterised using X-ray diffraction and field emission scanning electron microscopy. Energy dispersive X-ray was used to analyse the elemental composition of the sample. Findings The Aluminium Metal Matrix Composite (AMMC) joint was successfully fabricated using MHH. The mechanical properties were mainly influenced by the fabrication factor of exposure time. Originality/value The formation of AMMC joint using MHH might explore the way for the industries in the field of joining.