BITS Faculty Publications

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Author: search.filters.author.Mishra, Radha RamanSubject: search.filters.subject.Microwave heating

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    Exploring microwave heating characteristics of polycrystalline 3c-sic using molecular dynamics study
    (MDPI, 2024-09) Mishra, Radha Raman
    Polycrystalline silicon carbide (SiC) has been significantly used as a susceptor material during microwave-based material processing owing to its excellent microwave absorption properties. However, the interaction of microwaves with polycrystalline SiC at an atomic level has not been explored experimentally or theoretically. This work investigates the microwave heating characteristics of polycrystalline cubic 3C-SiC through molecular dynamics (MD) simulation using the Vashishta interatomic potential. The effect of change in electric field strength and frequency on the structural evolution and thermo-physical properties of polycrystalline 3C-SiC has been studied. The study revealed that the presence of grain boundaries in polycrystalline 3C-SiC structures plays a critical role in enhancing microwave absorption efficiency. Microwave exposure to polycrystalline 3C-SiC beyond 2830 K significantly increases total energy; consequently, a solid-to-liquid transition occurs in the 3C-SiC structure, initiated from the grain boundaries. Further, an increase in microwave exposure time results in a reduction in grain size due to rapid microwave absorption at grain boundaries. The phase transition temperature of polycrystalline 3C-SiC was observed to be 14% lower than that of the single-crystal 3C-SiC.
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    Microwave post-processed silicon carbide samples 3D printed using direct ink writing technique
    (Elsevier, 2025-05) Mishra, Radha Raman
    Direct ink writing (DIW) 3D-printed ceramic parts post-processing requires binder debinding and part densification during sintering. The use of conventional heating sources during the sintering of DIW 3D printed ceramics consumes significant time due to the slow conduction of heat inside the ceramic parts. Microwave energy-based post-processing can be a suitable alternative for rapid and more uniform heating of ceramic materials such as SiC, which couples microwave energy. In the present work, SiC-based ink (flow behaviour index 0.6) was prepared to build 3D-printed SiC parts using the DIW process; subsequently, parts were post-processed using microwave energy. The effects of different debinding temperatures (900 °C, 950 °C, and 1000 °C) and heating rates (15 °C/min, 20 °C/min, and 25 °C/min) were analysed on the properties of SiC samples. The microstructural characterization revealed the formation of an oxide layer on the edges of SiC particles, which results in the formation of necking between SiC particles. In contrast, an increase in the heating rate impedes the growth of the oxide layer. The phase analysis confirms the presence of SiO2 and the transformation of β-SiC to α-SiC. Higher debinding temperature and lower heating rate favour an increase in oxide layer formation; consequently, the flexural strength of SiC samples increases. The SiC samples fabricated at 1000 °C debinding temperature and a heating rate of 15 °C/min exhibit the highest flexural strength compared to SiC samples developed at higher heating rates due to poor bonding among the SiC particles.
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    Thermo-physical characteristics of 3C‐SiC structure subjected to microwave exposure: A molecular dynamics study
    (Elsevier, 2023-06) Mishra, Radha Raman; Belgamwar, Sachin U.; Roy, Tribeni
    Silicon carbide (SiC) is widely used as a susceptor for microwave hybrid heating applications owing to its exceptional microwave absorbing characteristics. In practice, it is challenging to characterize the thermo-physical behaviour of the microwave irradiated SiC-based targets experimentally due to interference of integrated measurement devices with microwaves. In this article, molecular dynamics simulations were performed to understand the atomistic response of a bulk 3C‐SiC model during microwave heating. Atomistic simulations were performed at different electric field strengths (ranging from 0.1 to 0.5 V/Å) and frequencies (ranging from 100 to 500 GHz) to develop a numerical relationship between temperature and time in order to predict the thermal response of bulk 3C‐SiC. On the other hand, the physical characteristics of the bulk 3C‐SiC were determined by the plots between mean square displacement (MSD), time and diffusion coefficients. The results showed that at 0.5 V/Å electric field strength and 500 GHz frequency, the diffusion coefficient increased up to 88% as compared to the electric field strength of 0.1 V/Å at 500 GHz. A change of 75% in the physical phase of 3C‐SiC structure with respect to the initial structure was confirmed by the distorted density distribution profile.
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    Effect of Solidification Environment on Microstructure and Indentation Hardness of Al–Zn–Mg Alloy Casts Developed Using Microwave Heating
    (Springer, 2017-09) Mishra, Radha Raman
    In the present work, microwave casting of Al 7039 was carried out using microwave energy at 2.45 GHz and 1400 W. A set of casts were developed through the in situ microwave casting process inside the applicator cavity applying three different solidification conditions, i.e., closed cavity cooling (cast C1), open cavity cooling (cast C2) and water-cooled cavity cooling (cast C3), whereas another cast was developed through conventional microwave casting (cast C4). Microstructure and microindentation hardness studies of the developed casts revealed that dense cast with smaller equiaxed grains could be obtained in the cast C3. Presence of the intermetallic phases, MgZn2, Mg2Si, Al3Fe and Al8Fe2Si, was observed in the in situ casts, whereas the cast C4 contains intermetallic phases: MgZn2, Mg2Si, Al2Cu, Al2CuMg and Al7Cu2Fe. It was found that the grain structure and major attributes of the intermetallic precipitates (size, shape and distribution) in the casts significantly depend on the solidification conditions. Average microindentation hardness of the cast C4 was found to be 191 ± 32 HV which is higher than other casts. The study showed that microindentation characteristics of the casts depend more on attributes of the precipitated intermetallic phases during solidification than the grain size
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    A Review of Research Trends in Microwave Processing of Metal-Based Materials and Opportunities in Microwave Metal Casting
    (Taylor & Francis, 2016-04) Mishra, Radha Raman
    Microwave processing of materials has emerged as a new method for processing of a variety of materials in the recent years. Microwaves have been used effectively with significant advantages, particularly in food processing and chemical synthesis. They are also found to be efficient for processing polymers, ceramics, polymeric composites, and ceramic composites. The physics of interaction of microwaves with characteristically different materials is not yet explored well; consequently, there are challenges in microwave processing of metal-based materials. Industrial processing of bulk metal is yet to be popular in spite of the fact that the feasibility of metal powder sintering was demonstrated a few decades ago. This article provides a summary of fundamental aspects of microwave processing of metal-based materials and their interaction with metallic materials. The processing challenges have been surveyed; developments in terms of techniques and tooling have been analyzed. Possible effects of microwave processing on metallic materials, in particular metal powders, bulk metals, bulk metal-metal powder systems, and sheet metals have been presented. Future research aspects of microwave processing of metallic materials with reference to metal casting have been identified.