Microwave material processing-a review

Research on the preparation and performance of Ni2P@MOF composite nanomaterials

The present study employed a solvothermal method utilizing triphenylphosphine and nickel acetylacetonate as precursors for phosphide preparation, followed by analysis and characterization. The Ni-MOF precursor was prepared using benzene diacid, triethylenediamine, and nickel sulfate as raw materials. Ni2P was introduced into the Ni-MOF precursor during its preparation while maintaining the synthesis conditions, allowing for the adsorption of Ni2P nanoparticles during Ni-MOF synthesis to produce Ni2P@MOF composite materials. The materials underwent individual testing for UV, magnetic, and microwave absorption properties. Magnetic testing results demonstrated that the incorporation of Ni2P led to an increase in the saturation magnetization (Ms) of Ni2P@MOFs compared to the Ni-MOF, thereby enhancing its electromagnetic loss capability. Microwave absorption property testing indicated that the Ni2P@MOFs exhibited enhanced dielectric and electromagnetic loss capabilities compared to the Ni-MOF, optimizing impedance matching properties and increasing effective absorption bandwidth compared to pure Ni2P materials.

Biodegradation of Polystyrene by Plastic-Eating Tenebrionidae Larvae

Polystyrene (PS) is an extremely stable polymer with a relatively high molecular weight and a strong hydrophobic character that makes it highly resistant to biodegradation. In this study, PS was subjected to biodegradation tests by Tenebrio Molitor (T. Molitor) and Zophobas Morio (Z. Morio) larvae. Specifically, six different experimental diets were compared: (i) T. Molitor fed with bran; (ii) T. Molitor fed only PS; (iii) T. Molitor fed only PS treated with H2O2; (iv) Z. Morio fed with bran; (v) Z. Morio fed only PS; and (vi) Z. Morio fed only PS treated with H2O2. Therefore, the mass change of the larvae and the survival rate were measured periodically, while the frass collected after 15 and 30 days was analyzed by different analyses, such as spectroscopy (FTIR), spectrometry (molecular weight and polydispersity), thermal analysis (TGA) and microscopy (scanning electron microscopy observations). The obtained results suggest that in the case of T. Molitor larvae, larvae feeding on bran showed the highest survival rate of ~94% at 30 days, while in the case of the Z. Morio larvae, the highest survival rate was exhibited by larvae eating PS-H2O2. Although not strongly pronounced, the Mw and Mn of PS in the frass of both T. Molitor and Z. Morio larvae decreased over 30 days, suggesting PS biodegradation. Finally, the morphological analysis shows that PS samples isolated from the frass of T. Molitor and Z. Morio larvae showed completely different, rough and irregularly carved surface structures, in comparison to PS before biodegradation.

A review on recent biodiesel intensification process through cavitation and microwave reactors: Yield, energy, and economic analysis

The use of biodiesel as a reliable and green energy source has grown over the past few years. Biodiesel is sustainable and biodegradable because it is only made from vegetable contents and waste cooking oil. Although biodiesel has many advantages over conventional fuels, there are still a lot of technological issues that need to be addressed during the production process. The yield of biodiesel produced using conventional methods is poor and the process is time-consuming. Process enhancements like cavitation and microwave have thus been developed to address this problem. Starting with a comparison to the conventional biodiesel process, this paper has reviewed the most recent developments in the increase of mixture and transfer of heat in these two reactors. This paper examined biodiesel improvement using microwave and cavitation reactors, including biodiesel yield, by meticulously reviewing and analyzing previous works. The production of biodiesel from various raw materials using a range of catalysts, energy requirements, as well as operating factors, activation energy, and constraints also have been discussed. Additionally, the economic analysis discusses the feasibility and cost-effectiveness of implementing these technologies on a commercial scale. Overall, this review provides valuable insights into the intensification of biodiesel production using cavitation and microwave reactors while considering both the technical and economic aspects.

Structural and property changes of starch derivatives under microwave field: A review

Native starches are commonly modified for desired properties because of their limited applications. Among various modifications, microwave irradiation has been gaining strong interests and becoming a focal area to transform starch during the last few years. Such interests reside in microwave irradiation's high heating rates, lesser extent of loss in nutritional qualities, and so on when compared with other approaches. This review summaries the effects of microwave field on the structural (e.g. morphology characteristic, lamellae structure, crystallinity, and molecular structure) and physicochemical properties (e.g. pasting properties and gelatinization) of naturally existing starch derivatives. Different microwave-assisted chemical derivatizations can directly or indirectly affect starch structure from the macroscopic to the microscopic level, thereby resulting in various functionalities. Moreover, conventional starch modification processes can be optimized by applying microwave irradiation to obtain modified starch with high degree of substitution and low viscosity. The future research will help to better understand the structural changes of microwave-assisted starch chemical derivatization and thereby creating a wide range of functionalities.

Inactivation of foodborne pathogens in ground pork tenderloin using 915 MHz microwave heating depending on power level

The main purpose of this research was to investigate the effect of power level of 915 MHz microwave heating on the inactivation of foodborne pathogens in ground pork and its bactericidal mechanism. It was demonstrated that the heating rate was proportional to the power level. For instance, the heating rates observed at microwave heating powers of 2, 3, 4, and 5 kW were 1.70, 2.77, 3.35, and 4.03℃/s, respectively. The bactericidal effect of microwave heating also significantly (P < 0.05) increased with increasing power level. In particular, when ground pork was subjected to microwave heating at 5 kW, the reduction level of pathogens was>2 log units higher than at 2 kW. To determine the bactericidal mechanism of microwave heating depending on power level, changes in transmembrane potential and DNA damage were determined using fluorescence. The extent of depolarization in membrane potential of pathogens significantly (P < 0.05) increased as power level increased. There was no significant difference in degree of DNA damage at different power levels. However, the percentage of DNA damage was>86% at all power levels. The transmembrane potential assay indicates that the bacteria exhibited dramatic pore formation on the membrane at 5 kW. Through transmission electron microscopy, the electroporation effect was enhanced as power level increased. Moreover, the quality of ground pork subjected to microwave heating at 2-5 kW was determined by measuring the moisture content, cooking loss, and texture profile.

A 3D-Printed Ceramics Innovative Firing Technique: A Numerical and Experimental Study

Additive manufacturing (AM), also known as three-dimensional (3D) printing, allows the fabrication of complex parts, which are impossible or very expensive to produce using traditional processes. That is the case for dinnerware and artworks (stoneware, porcelain and clay-based products). After the piece is formed, the greenware is fired at high temperatures so that these pieces gain its mechanical strength and aesthetics. The conventional (gas or resistive heating elements) firing usually requires long heating cycles, presently requiring around 10 h to reach temperatures as high as 1200 °C. Searching for faster processes, 3D-printed stoneware were fired using microwave (MW) radiation. The pieces were fired within 10% of the conventional processing time. The temperature were controlled using a pyrometer and monitored using Process Temperature Control Rings (PTCRs). An error of 1.25% was calculated between the PTCR (1207 ± 15 °C) and the pyrometer (1200 °C). Microwave-fast-fired pieces show similar mechanical strength to the references and to the electrically fast-fired pieces (41, 46 and 34 (N/mm2), respectively), presenting aesthetic features closer to the reference. Total porosities of ~4%, ~5% and ~9% were determined for microwave, electrically fast-fired and reference samples. Numerical studies have shown to be essential to better understand and improve the firing process using microwave radiation. In summary, microwave heating can be employed as an alternative to stoneware conventional firing methods, not compromising the quality and features of the processed pieces, and with gains in the heating time.

A review on the role of susceptors in the recovery of valuable renewable carbon products from microwave-assisted pyrolysis of lignocellulosic and algal biomasses: Prospects and challenges

Sustainable bio-economics can be achieved by the processing of renewable biomass resources. Hence, this review article presents a detailed analysis of the effect of susceptors on microwave-assisted pyrolysis (MAP) of biomass. Biomass is categorized as lignocellulosic and algal biomass based on available sources. Selected seminal works reporting the MAP of pure biomasses are reviewed thoroughly. Focus is given to understanding the role of the susceptor used for pyrolysis on the characteristics of products produced. The goal is to curate the literature and report variation in the product characteristics for the combinations of the biomass and susceptor. The review explores the factors such as the susceptor to feed-stock ratio and its implications on the product compositions. The process parameters including microwave power, reaction temperature, heating rate, feedstock composition, and product formation are discussed in detail. A repository of such information would enable researchers to glance through the closest possible susceptors they should use for a chosen biomass of their interest for better oil yields. Further, a list of potential applications of MAP products of biomasses, along with the susceptor used, are reported. To this end, this review presents the possible opportunities and challenges for tapping valuable carbon resources from the MAP of biomass for sustainable energy needs.

Porous carbon black-polymer composites for volatile organic compound adsorption and efficient microwave-assisted desorption

Adsorbents with high surface area, thermal stability and microwave absorption ability are highly desired for cyclic adsorption and microwave regeneration processes. However, most polymeric adsorbents are transparent to microwaves. Herein, porous hyper-crosslinked polymers (HCP) of (4,4'-bis((chloromethyl)-1,1'-biphenyl-benzyl chloride)) with different carbon black (CB) contents were synthesized via the Friedel-Crafts reaction. CB was selected as the filler due to its low cost and high dielectric loss and was embedded inside the polymer structure during polymerization. CB-containing composites showed enhanced thermal stability at elevated temperatures, and more than a 90-times increase in the dielectric loss factor, which is favorable for microwave regeneration. Nitrogen physisorption analysis by the Bruner-Emmett-Teller isotherms demonstrated that CB presence in the polymer structure nonlinearly decreases the surface area and total pore volume (by 38% and 26%, respectively at the highest CB load). Based on the characterization testing, 4 wt% of CB was found to be an optimum filler content, having the highest MW absorption and minimal effect on the adsorbent porosity. HCP with 4 wt% CB allowed a substantial increase in the desorption temperature and yielded more than a 450% enhancement in the desorption efficiency compared to HCP without CB.

Experimental research on sintering construction spoil bricks based on microwave heating technology

The accumulation of construction spoil has brought great challenges to urban construction and environmental protection. It is an effective way to solve the problem of construction spoil accumulation by using construction spoil to sinter brick. At the same time, it can also reduce the waste of clay resources and farmland destruction caused by the production of sintered brick. Microwave sintering technology can greatly improve the sintering efficiency of materials. Sintering brick by microwave sintering technology can avoid a series of environmental problems in the traditional production process of sintered brick and can lead to an eco-friendly production of bricks. In this study, construction spoil was used as the raw material, and Al₂O₃, Fe₂O₃, and TiO₂ powders were studied as MASM for improving the temperature rise rate and sintering efficiency of the brick in microwave sintering process. The characteristics of construction spoil brick sintered by microwave were studied by series experiments including unit weight, compressive strength, and meso-analysis. Results proven that microwave sintering technology is an efficient technology for brick making. The MASM can effectively increase the temperature rise rate of the sample and simultaneously improve the impermeability of the sample and sintering efficiency.

Transient analysis of power loss density with time-harmonic electromagnetic waves in Debye media

Due to the complex permittivity, it is difficult to directly clarify the transient mechanism between electromagnetic waves and Debye media. To overcome the above problem, the temporal relationship between the electromagnetic waves and permittivity is explicitly derived by applying the Fourier inversion and introducing the remnant displacement. With the help of the Poynting theorem and energy conservation equation, the transient power loss density is derived to describe the transient dissipation of electromagnetic field and the mechanism on phase displacement has been explicitly revealed. Besides, the unique solution can be obtained by applying the time-domain analysis method rather than involving the frequency-domain characteristics. The effectiveness of transient analysis is demonstrated by giving a comparison simulation on one-dimensional example.

Microwave technology: a novel approach to the transformation of natural metabolites

Microwave technology is used throughout the world to generate heat using energy from the microwave range of the electromagnetic spectrum. It is characterized by uniform energy transfer, low energy consumption, and rapid heating which preserves much of the nutritional value in food products. Microwave technology is widely used to process food such as drying, because food and medicinal plants are the same organisms. Microwave technology is also used to process and extract parts of plants for medicinal purposes; however, the special principle of microwave radiation provide energy to reaction for transforming chemical components, creating a variety of compounds through oxidation, hydrolysis, rearrangement, esterification, condensation and other reactions that transform original components into new ones. In this paper, the principles, influencing factors of microwave technology, and the transformation of natural metabolites using microwave technology are reviewed, with an aim to provide a theoretical basis for the further study of microwave technology in the processing of medicinal materials.

Study of Microstructural and Mechanical Properties of Al/SiC/TiO2 Hybrid Nanocomposites Developed by Microwave Sintering

Aluminum hybrid metal matrix nanocomposites (Al/SiC/TiO2) were synthesized through a microwave-assisted powder metallurgy process, and their evolved microstructure and mechanical properties were investigated. The Al/SiC/TiO2 hybrid nanocomposites were prepared by reinforcing aluminum (Al) matrix with a fixed amount of silicon carbide (SiC) nanoparticles (5 wt.%) and varying concentrations of titanium dioxide (TiO2) nanoparticles (3, 6, and 9 wt.%). The morphology results revealeda uniform distribution of SiC and TiO2 reinforcements in the aluminum matrix. An increase in the hardness and compressive strength of the Al/SiC/TiO2 hybrid nanocomposites was noticed with the increasein TiO2 nanoparticles. The Al/SiC/TiO2 hybrid nanocomposites that had an optimum amount of TiO2 nanoparticles (9 wt.%) showcased the best mechanical properties, with maximum increments of approximately 124%, 90%, and 23% of microhardness (83 ± 3 HV), respectively, yield strength (139 ± 8 MPa), and ultimate compression strength (375 ± 6 MPa) as compared to that of pure Al matrix. The Al/SiC/TiO2 hybrid nanocomposites exhibited the shear mode of fracture during their deformation process.

Design, synthesis and biological evaluation of 1-Aryl-5-(4-arylpiperazine-1-carbonyl)-1H-tetrazols as novel microtubule destabilizers

A series of 1-aryl-5-(4-arylpiperazine-1-carbonyl)-1H-tetrazols as microtubule destabilizers were designed, synthesised and evaluated for anticancer activity. Based on bioisosterism, we introduced the tetrazole moiety containing the hydrogen-bond acceptors as B-ring of XRP44X analogues. The key intermediates ethyl 1-aryl-1H-tetrazole-5-carboxylates 10 can be simply and efficiently prepared via a microwave-assisted continuous operation process. Among the compounds synthesised, compound 6-31 showed noteworthy potency against SGC-7901, A549 and HeLa cell lines. In mechanism studies, compound 6-31 inhibited tubulin polymerisation and disorganised microtubule in SGC-7901 cells by binding to tubulin. Moreover, compound 6-31 arrested SGC-7901cells in G2/M phase. This study provided a new perspective for development of antitumor agents that target tubulin.

Preparation of Cu cluster catalysts by simultaneous cooling-microwave heating: application in radical cascade annulation

One of the hallmarks of microwave irradiation is its selective heating mechanism. In the past 30 years, alternative designs of chemical reactors have been introduced, where the microwave (MW) absorber occupies a limited reactor volume but the surrounding environment is MW transparent. This advantage results in a different heating profile or even the possibility to quickly cool down the system. Simultaneous cooling-microwave heating has been largely adopted for organic chemical transformations. However, to the best of our knowledge there are no reports of its application in the field of nanocluster synthesis. In this work, we propose an innovative one-pot procedure for the synthesis of Cu nanoclusters. The cluster nucleation was selectively MW-activated inside the pores of a highly ordered mesoporous substrate. Once the nucleation event occurred, the crystallization reaction was instantaneously quenched, precluding the growth events and favoring the production of Cu clusters with a homogenous size distribution. Herein, we demonstrated that Cu nanoclusters could be successfully adopted for radical cascade annulations of N-alkoxybenzamides, resulting in various tricyclic and tetracyclic isoquinolones, which are widely present in lots of natural products and bioactive compounds. Compared to reported homogeneous methods, supported Cu nanoclusters provide a better platform for a green, sustainable and efficient heterogeneous approach for the synthesis of tricyclic and tetracyclic isoquinolones, avoiding a variety of toxic waste/byproducts and metal contamination in the final products.

Effect of Electric Field Distribution on the Heating Uniformity of a Model Ready-to-Eat Meal in Microwave-Assisted Thermal Sterilization Using the FDTD Method

Microwave assisted thermal sterilization (MATS) is a novel microwave technology currently used in the commercial production of ready-to-eat meals. It combines surface heating of high-temperature circulation water with internal microwave heating in cavities. The heating pattern inside the food packages in a MATS process depends heavily on the electric field distribution formed by microwaves from the top and bottom windows of the microwave heating cavities. The purpose of this research was to study the effect of the electric field on 922 MHz microwave heating of ready-to-eat meals as they moved through the microwave chamber of a pilot-scale MATS system using the finite-difference time-domain (FDTD) method. A three-dimensional numerical simulation model was developed as a digital twin of the MATS process of food moving through the microwave chamber. The simulation showed that the electric field intensity of the MATS microwave cavity was greatest on the surface and side edge of the cavity and of the food. There was a strong similarity of the experimental heating pattern with that of the electric field distribution simulated by a computer model. The digital twin modeling approach can be used to design options for improving the heating uniformity and throughput of ready-to-eat meals in MATS industrial systems.

Prospects and Challenges of Microwave-Combined Technology for Biodiesel and Biolubricant Production through a Transesterification: A Review

Biodiesels and biolubricants are synthetic esters produced mainly via a transesterification of other esters from bio-based resources, such as plant-based oils or animal fats. Microwave heating has been used to enhance transesterification reaction by converting an electrical energy into a radiation, becoming part of the internal energy acquired by reactant molecules. This method leads to major energy savings and reduces the reaction time by at least 60% compared to a conventional heating via conduction and convection. However, the application of microwave heating technology alone still suffers from non-homogeneous electromagnetic field distribution, thermally unstable rising temperatures, and insufficient depth of microwave penetration, which reduces the mass transfer efficiency. The strategy of integrating multiple technologies for biodiesel and biolubricant production has gained a great deal of interest in applied chemistry. This review presents an advanced transesterification process that combines microwave heating with other technologies, namely an acoustic cavitation, a vacuum, ionic solvent, and a supercritical/subcritical approach to solve the limitations of the stand-alone microwave-assisted transesterification. The combined technologies allow for the improvement in the overall product yield and energy efficiency. This review provides insights into the broader prospects of microwave heating in the production of bio-based products.

Energy and Resource Utilization of Refining Industry Oil Sludge by Microwave Treatment

The oily sludge from crude oil contains hazardous BTEX (benzene, toluene, ethylbenzene, xylene) found in the bottom sediment of the crude oil tank in the petroleum refining plant. This study uses microwave treatment of the oily sludge to remove BTEX by utilizing the heat energy generated by the microwave. The results show that when the oily sludge sample was treated for 60 s under microwave power from 200 to 300 W, the electric field energy absorbed by the sample increased from 0.17 to 0.31 V/m and the temperature at the center of the sludge sample increased from 66.5 °C to 96.5 °C. In addition, when the oily sludge was treated for 900 s under microwave power 300 W, the removal rates were 98.5% for benzene, 62.8% for toluene, 51.6% for ethylbenzene, and 29.9% for xylene. Meanwhile, the highest recovery rates of light volatile hydrocarbons in sludge reached 71.9% for C3, 71.3% for C4, 71.0% for C5, and 78.2% for C6.

Microwave processing of calcium phosphate and magnesium phosphate based orthopedic bioceramics: A state-of-the-art review

The main theme of this paper is to review microwave-assisted synthesis and processing of calcium and magnesium phosphate bioceramics. Microwave processing of advanced materials has been an active field of research for the last three decades and has been already reviewed in the literature. Microwave processing of bioceramics is being pursued for almost the same period of time. Unfortunately, to the best of our knowledge, we are not aware of any comprehensive review in the literature. Our group has been a significant contributor to the field, and we feel that it is an appropriate time for reviewing the state-of-the-art of the field. The paper is divided into several sections. After rationalizing the motivation behind writing this paper in the introduction, the second section builds on some fundamental aspects of microwave-matter interactions. The third section, representing the synthesis aspects, is subdivided into five sub-sections focusing on various calcium and magnesium phosphates in both crystalline and amorphous forms. The fourth section focuses on magnesium phosphate-based bioceramics. The fifth and the sixth section describe results on the utility of microwave assistance in developing multi-functional coatings on medical implants and orthopedic cements respectively. The subsequent section reviews results on microwave sintering of calcium and magnesium phosphates. The paper concludes with remarks on unresolved issues and future directions of research. It is expected that this comprehensive review on the interdisciplinary topic will further propel the exploration of other novel applications of microwave technology in processing biomaterials by a diverse group of scientists and engineers. STATEMENT OF SIGNIFICANCE: 1. This review highlights the broad-spectrum capabilities of microwave applications in processing orthopedic bioceramics. 2. The article covers "processing" in the broadest sense of the word, comprising of material synthesis, sintering, coating formation, and setting of orthopedic cements. It also expands beyond conventional calcium phosphates to include the emergent family of magnesium phosphates. 3. In vitro/in vivo responses of microwave-processed bioceramics are discussed thus providing an integral understanding of biological aspects of these materials. 4. The comprehensive review on this interdisciplinary topic will help researchers in various disciplines to appreciate the significance and usefulness of microwaves in biomaterials processing. Further, we also believe that it will propel the exploration of other novel applications of microwave technology in the biomaterials sector.

The Advances in the Special Microwave Effects of the Heterogeneous Catalytic Reactions

In the present, microwave field has been widely used in chemical processes as an important means of intensification. The heterogeneous catalysts coupling with microwave has been shown to have many advantages, such as high catalytic performance and stability. Our objective is to focus an up-to-date overview concerning the advances in the special microwave effects of the heterogeneous catalytic reactions including special thermal effect, microwave plasma, enhanced active groups, and the flexibility of structure. This review systematically states the action mechanism and some practical application of microwave-induced catalytic process. Finally, the potential research directions in the field of microwave-induced catalysis are prospected.

Field-only surface integral equations: scattering from a perfect electric conductor

A field-only boundary integral formulation of electromagnetics is derived without the use of surface currents that appear in the Stratton-Chu formulation. For scattering by a perfect electrical conductor (PEC), the components of the electric field are obtained directly from surface integral equation solutions of three scalar Helmholtz equations for the field components. The divergence-free condition is enforced via a boundary condition on the normal component of the field and its normal derivative. Field values and their normal derivatives at the surface of the PEC are obtained directly from surface integral equations that do not contain divergent kernels. Consequently, high-order elements with fewer degrees of freedom can be used to represent surface features to a higher precision than the traditional planar elements. This theoretical framework is illustrated with numerical examples that provide further physical insight into the role of the surface curvature in scattering problems.

A composite with a gradient distribution of graphene and its anisotropic electromagnetic reflection

An electrochemical method was introduced to prepare graphene/polyurethane foams with gradient graphene distribution, and this composite shows obvious anisotropic reflection of electromagnetic waves.

Investigation of a New Spectrophotometric Method for the Analysis of Ciprofloxacin Based on Microwave Assisted Diazotization

A microwave-assisted diazotization reaction of ciprofloxacin was used for the analysis of ciprofloxacin in pharmaceutical samples. The ciprofloxacin was diazotized with phenol using acidified sodium nitrite in a domestic microwave oven. Faster microwave heating and microwave effects were found to be very effective for the process of diazotization. The microwave-assisted reaction was initiated in an acidic media and the colored product was stabilized in a slightly basic medium using a NaOH solution as a neutralizer. The product was found to exhibit the maximum absorbance at 440 nm. All of the experimental conditions like the concentration of reagents, microwave power and reaction time were optimized. The optimum concentrations for phenol, sodium nitrite, HCl and NaOH were found to be 140 ppm, 300 ppm, 0.006 M and 0.006 M respectively. The optimum reaction time was found to be 2 min and a medium high power of the microwave was found to be most effective. The limit of detection (LOD) and the limit of quantification (LOQ) were found to be 1.08 and 3.61 mg L^-1 respectively. The developed method was successfully applied for the determination of ciprofloxacin in pharmaceutical samples. This new spectrophotometric method for the analysis of ciprofloxacin is fast, sensitive, easy and cost effective.

The study on pyrolysis of oil-based drilling cuttings by microwave and electric heating

In this paper, the following questions were investigated: the proportion of mass loss, the mass fraction of oil, the structure, composition and ultimate analysis of solid residues and gas products. By comparing the treatment effect of using both microwave and electric as the source of heat to dispose the oil-based drilling cuttings (OBDC), the advantages of microwave heating treatment were demonstrated. Meanwhile, the composition of liquid products by microwave pyrolysis was analyzed. The results show that the microwave heating is better than electric heating and the former can promote the pyrolysis of petroleum hydrocarbons. The results of component analysis of the liquid products from OBDC by microwave pyrolysis show that C12∼C20 components pyrolyze at 500 °C. At the same time, a mass of C21∼C24 components volatilize. At the temperature above 500 °C, the thermal cracking reactions of >C25 components occur and a maximum content of paraffin in liquid products is obtained. As the temperature increases, the components obtained by pyrolysis become more and more complex.

Experimental study of destruction of acetone in exhaust gas using microwave-induced metal discharge

Volatile organic compounds (VOCs) are air pollutants that pose a major concern, and novel treatment technologies must be continuously explored and developed. In this study, microwave-induced metal discharge was applied to investigate the destruction of acetone as a representative model VOC compound. Results revealed that metal discharge intensity largely depended on microwave output power and the number of metal strips. Microwave metal discharge exerted the distinct combined effects of intense heat, strong light, and plasma. In the case of MW without metal discharge, the decrease in acetone at 200 ppm was remarkably limited (approximately 5.5% (mol/mol)). By contrast, in the case of microwave-induced metal discharge, a considerably high destruction efficiency of up to 65% (mol/mol) was obtained at low concentrations. This finding highlights the potential of microwave-induced discharge for VOC removal. Initial assessment indicated that energy consumption can be acceptable.

Stabilization and Mineralization Mechanism of Cd with Cu-Loaded Attapulgite Stabilizer Assisted with Microwave Irradiation

Cadmium (Cd) in soil was stabilized using copper loaded attapulgite (Cu/ATP) in a microwave (MW) system. Excellent Cd stability in soil was achieved with Cu/ATP addition due to higher adsorption energy (1.38 eV) of Cu/ATP for Cd than that of ATP (∼1 eV), confirmed by density functional theory calculations. The strong hybridization of the s, p-orbitals of Cd with the s, p, d-orbitals of Cu on ATP contributed to the strong interactions between Cd and Cu/ATP. The stability performance of Cd in Cu/ATP-treated soil was further enhanced after MW irradiation through a series of phase transformation to more stable Cd-bearing crystalline minerals. The transformation was initiated by MW-induced "hot spots", which created cationic vacancy on Cu/ATP surface and enhanced the solid-state reactions between Cd and Cu/ATP framework. The total bond orders of Cd in the formed CdAl₄O₇ crystalline mineral elevated to 3.38, which was 5-fold higher than that for Cd on Cu/ATP, ensuring the long-term stability of Cd even after 360 curing days. Cd contaminated soil from a former industrial electroplating site was successfully stabilized with the proposed strategy. The research provides an effective stabilization strategy as well as a comprehensive understanding of the mechanism of long-term Cd stabilization.

Receding horizon H∞ guaranteed cost tracking control for microwave heating medium with temperature-dependent permittivity

This paper considers the temperature spectrum tracking control of microwave heating model, in the presence of asymmetrical input saturation, nonhomogeneous Neumann boundary condition and temperature-dependent permittivity. The sufficient condition for the existence of receding horizon H_∞ guaranteed cost control is proposed based on the derived finite-dimensional ordinary differential equation (ODE) error model. Furthermore, by on-line updating and solving linear matrix inequalities (LMIs) optimization problem, the constrained tracking controller can be obtained in the sense of minimizing H_∞ norm and satisfying the quadratic cost performance. The proposed control strategy is implemented on a one-dimensional cavity heating model and its performance is evaluated through the simulation.

Complexity and Challenges in Noncontact High Temperature Measurements in Microwave-Assisted Catalytic Reactors

The complexity and challenges in noncontact temperature measurements inside microwave-heated catalytic reactors are presented in this paper. A custom-designed microwave cavity has been used to focus the microwave field on the catalyst and enable monitoring of the temperature field in 2D. A methodology to study the temperature distribution in the catalytic bed by using a thermal camera in combination with a thermocouple for a heterogeneous catalytic reaction (methane dry reforming) under microwave heating has been demonstrated. The effects of various variables that affect the accuracy of temperature recordings are discussed in detail. The necessity of having at least one contact sensor, such as a thermocouple, or some other microwave transparent sensor, is recommended to keep track of the temperature changes occurring in the catalytic bed during the reaction under microwave heating.

Review on Microwave-Matter Interaction Fundamentals and Efficient Microwave-Associated Heating Strategies

Microwave heating is rapidly emerging as an effective and efficient tool in various technological and scientific fields. A comprehensive understanding of the fundamentals of microwave–matter interactions is the precondition for better utilization of microwave technology. However, microwave heating is usually only known as dielectric heating, and the contribution of the magnetic field component of microwaves is often ignored, which, in fact, contributes greatly to microwave heating of some aqueous electrolyte solutions, magnetic dielectric materials and certain conductive powder materials, etc. This paper focuses on this point and presents a careful review of microwave heating mechanisms in a comprehensive manner. Moreover, in addition to the acknowledged conventional microwave heating mechanisms, the special interaction mechanisms between microwave and metal-based materials are attracting increasing interest for a variety of metallurgical, plasma and discharge applications, and therefore are reviewed particularly regarding the aspects of the reflection, heating and discharge effects. Finally, several distinct strategies to improve microwave energy utilization efficiencies are proposed and discussed with the aim of tackling the energy-efficiency-related issues arising from the application of microwave heating. This work can present a strategic guideline for the developed understanding and utilization of the microwave heating technology.

Fabrication of hydroxyapatite on pure titanium by micro-arc oxidation coupled with microwave-hydrothermal treatment

Porous hydroxyapatite (HA)-containing composite films were prepared by a novel method consisting of micro-arc oxidation (MAO) combined with microwave-hydrothermal (M-H) treatment. The morphology, composition and phase composition of the bioactive films were investigated with scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. MTT assay was carried out to investigate the in vitro effects of the different surfaces on bone integration properties. The prepared MAO films consisted mainly of anatase, rutile and tricalcium phosphate along with amorphous calcium (Ca) and phosphorus (P) phases. The M-H-treated composite films were composed primarily of anatase, rutile and HA. As the time and temperature of the M-H treatment increased, the number of HA crystals gradually increased. Using the M-H method, HA was obtained at a lower temperature and in a shorter period of time compared to the conventional hydrothermal method. The results suggest that the M-H method significantly decreases the hydrothermal reaction temperature and also greatly shortens the reaction time. Due to the nanocrystallinity and porosity of the prepared composite films, the method presented here shows promise for the formation of bioactive materials for medical applications.

Synthesis of β-SiC Fine Fibers by the Forcespinning Method with Microwave Irradiation

A rapid method for synthesizing β-silicon carbide (β-SiC) fine fiber composite has been achieved by combining forcespinning technology with microwave energy processing. β-SiC has applications as composite reinforcements, refractory filtration systems, and other high temperature applications given their properties such as low density, oxidation resistance, thermal stability, and wear resistance. Nonwoven fine fiber mats were prepared through a solution based method using polystyrene (PS) and polycarbomethylsilane (PCmS) as the precursor materials. The fiber spinning was performed under different parameters to obtain high yield, fiber homogeneity, and small diameters. The spinning was carried out under controlled nitrogen environment to control and reduce oxygen content. Characterization was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results show high yield, long continuous bead-free nonwoven fine fibers with diameters ranging from 270 nm to 2 µm depending on the selected processing parameters. The fine fiber mats show formation of highly crystalline β-SiC fine fiber after microwave irradiation.

Facile synthesis of (Ni,Co)@(Ni,Co)xFe3−xO4 core@shell chain structures and (Ni,Co)@(Ni,Co)xFe3−xO4/graphene composites with enhanced microwave absorption

A facile strategy was developed to fabricate (Ni,Co)@(Ni,Co)_xFe_3−xO₄ chain structures and (Ni,Co)@(Ni,Co)_xFe_3−xO₄/graphene composites, which show excellent microwave absorption performances.