Microwave Thermal Treatment Research Articles

Microwave-Assisted Pyrolysis of Carbon Fiber-Reinforced Polymers and Optimization Using the Box-Behnken Response Surface Methodology Tool.

This article introduces an eco-friendly method for the reclamation of carbon fiber-reinforced polymers (CFRP). The research project involved numerous experiments using microwave-assisted pyrolysis (MAP) to explore a range of factors, such as the inert gas flow, the power level, the On/Off frequency of rotation, and the reaction duration. To design the experiments, the three-level Box-Behnken optimization tool was employed. To determine the individual and combined effects of the input parameters on the thermal decomposition of the resin, the data were analyzed using least-squares variance adjustment. The results demonstrate that the models developed in this study were successful in predicting the direct parameters of influence in the microwave-assisted decomposition of CFRPs. An optimal set of operating conditions was found to be the maximum nitrogen flow (2.9 L/min) and the maximum operating experimental power (914 W). In addition, it was observed that the reactor vessel's On/Off rotation frequency and that increasing the reaction time beyond 6 min had no significant influence on the resin elimination percentage when compared to the two other parameters, i.e., power and carrier gas flow rate. Consequently, the above-mentioned conditions resulted in a maximum resin elimination percentage of 79.6%. Following successful MAP, various post-pyrolysis treatments were employed. These included mechanical abrasion using quartz sand, chemical dissolution, thermal oxidative treatment using a microwave (MW) applicator and thermal oxidative treatment in a conventional furnace. Among these post-treatment techniques, thermal oxidation and chemical dissolution were found to be the most efficient methods, eliminating 100% of the carbon black content on the surface of the recovered carbon fibers. Finally, SEM evaluations and XPS analysis were conducted to compare the surface morphology and elementary constitution of the recovered carbon fibers with virgin carbon fibers.

Microwave Thermal Treatment for the Recovery of Re in Copper and Molybdenum Concentrates

Background: Rhenium [Re] is obtained as a by-product during the extraction of copper and molybdenum ores. In current extractive metallurgy, Re extraction involves a heat treatment that causes Re losses by volatilization and release of toxic gases into the environment. Objective: This research proposes a novel microwave heat treatment [MWHT] to enhance Re ex-traction avoiding Re losses and toxic gas release into the environment. Method: A novel MWHT and traditional thermal processes used in mining were applied to Cu-Mo concentrates. The elemental composition analysis of the concentrate was performed by atomic spec-trometry. The crystalline phase was identified by X-ray diffraction. Particle structure observations were performed with an optical microscopy [OM] and scanning electron microscopy [SEM] with a Field Emission, including semiquantitative analysis [EDS]. Thermal behavior and non-isothermal reduction processes were studied using Thermogravimetry Differential Thermal Analysis [TG-DTA]. Result: Re, S and As release decreased 5% during MWHT, compared to 34% of traditional meth-ods. Molybdenite [MoS2] and Chalcopyrite [CuFeS2] were the crystalline phases in the ore after MWHT. Rhenium was found as an oxide [ReO3] and metallic Re. Samples under MWHT showed structural transformations in the mineral particles, with minimal mass losses and high Re and Mo concentrations. The structural transformation of the ore involved microcracks formation. Conclusion: The MWHT induces a combination of particle degradation mechanisms and lower temperature requirements that prevent Re losses. Lower gas emissions turn this technology into an environmentally friendly one. Crystalline transformation of the Re-chalcopyrite phase enhances Re release during leaching, the next step after MWHT in the hydrometallurgical extraction.

Production of Biohydrogen from Microalgae Biomass after Wastewater Treatment and Air Purification from CO2

This article explores the feasibility of producing biohydrogen from microalgae following their use in wastewater purification from food industry facilities and the removal of high levels of carbon dioxide (CO2) from the air. The authors investigated various methods for disrupting the cell membranes of microalgae and their impact on biohydrogen yield. The microalgae biomass obtained after wastewater and air purification underwent pre-treatment using physicochemical and chemical methods, including microwave radiation, acid treatment, and thermal treatment. The highest hydrogen production occurred during thermal and acid treatments of biomass with the addition of starch (44.24 mL/L of suspension). The use of microwave radiation for processing did not yield significant results. A comparison of the biohydrogen values obtained from untreated and treated biomass revealed that treatment enhances biohydrogen yield.

Dielectric Properties of Healthy Ex Vivo Ovine Lung Tissue at Microwave Frequencies

Knowledge of dielectric properties of lung tissue is fundamental for the improvement of lung disease diagnostics and therapeutic solutions (e.g. microwave imaging and microwave thermal ablation treatment). Although lung disease rates are increasing, lung tissue remains one of the least characterized tissues due to its heterogeneity, variability in air content, and handling difficulties. In this work, dielectric properties of ex-vivo ovine lung tissue samples were measured in the frequency range 500 MHz – 8 GHz, together with measurements of sample density (air content). Different Cole-Cole models were applied to the measured dielectric properties values. The best fitting model was chosen, and results were compared with available literature. Furthermore, the dielectric property measurements were correlated with the air content of the samples. Updated Cole-Cole models for lung tissue of different density is provided in the 500 MHz – 8 GHz range. The existence of air content threshold in lung is shown. Below this limit, the properties begin to change drastically with the change in density.

NEUTRALISATION OF ASBESTOS-CONTAINING WASTE

Abstract. The paper presents the characteristics of asbestos as a mineral. Asbestos is a trade name for six serpentine fibrous minerals and amphiboles. The processes of removing asbestos-containing products, which poses a high risk of emission of asbestos fibers harmful to human health, is described. First, make an inventory of asbestos-containing waste to determine the sequence of actions. Products can be qualified for immediate disposal or for temporary preservation, as required by law. When removing asbestos-containing products, the contractor should set up warning boards, fence the area, and take technical measures to eliminate the emission of asbestos fibers. Asbestos-containing products must be moistened with water before being removed. Trained employees should be equipped with personal protective equipment as well as working clothes and footwear. Asbestos-containing waste should be taken to a hazardous waste landfill or an inert or other than inert waste landfill, and placed in areas specially adapted for this purpose. Precautions during inventory and liquidation of asbestos-containing waste are specified. An innovative technology for asbestos neutralization MTT (Microwave Thermal Treatment) is characterized. The impact of asbestos products on health is discussed. The most dangerous cases of diseases are asbestosis, pleural and pericardial diseases, as well as lung cancer and mesothelioma. The need for research on the concentration of respirable asbestos fibers in the atmospheric air is emphasized.

Preparation and Optimization Green Gel Casting Technique for Manufacturing Near-Net-Shape Ceramics Using Genetic Algorithm

Gel casting technique is a promising technology that has ability to produce near-net shape ceramics via using toxic and non-ecofriendly agents. The current work aim to develop green gel casting technique using water as a solvent, agar as a gelling agent, and the microwave thermal treatment instead of cross linker. 8mo l% Yttria stabilized zirconia was selected as a case study to produce near-net shape ceramics. The experimental work involved the preparation of Yttria stabilized zirconia nanoparticles via chemical precipitation method. The effect study of agar ratio, Yttria stabilized zirconia solid loading percent on the physical, mechanical, surface properties of the prepared ceramics and selecting of suitable casting conditions. The study has been found that the microwave thermal treatment develops thermally activated cross linking in the agar aqueous solution leading to higher glass transition temperature for agar. The green combination (agar aqueous solution and microwave treatment) can be used as alternative to (monomer, solvent, cross linker) Companion. Also, using the ultrasonic treatment can effectively eliminate needs for dispersants, also the vacuum de-airing treatment. Yttria stabilized zirconia ceramic with high dimensional accuracy, low surface roughness (Ra=2. 81 nm) can be obtained using an agar ratio of (0.4%) and solid loading of (65%). The sample can be moulded with complex shape and the green gel, also the pre-sintered body is machineable. The sintered samples have a porosity of (31%) and compressive strength of (234MPa). Regression analysis and genetic algorithm are showed that the obtained microhardness, compressive strength, and surface roughness are predictable.

Asbestos waste recycling using the microwave technique – Benefits and risks

Hazardous waste containing asbestos can be neutralised by temperature destruction using the Microwave Thermal Treatment (MTT). With this method, the temperature and time required for asbestos destruction can be significantly reduced. The literature indicates that a temperature of 1000 °C is adequate for this purpose and can be lowered using fluxes.The article presents a method for identifying trace asbestos contamination in testing a thermal recycling product of asbestos-cement waste using MTT.A low asbestos-fibre content, e.g. at a concentration of less than 0.1%, in any medium, requires the separation and concentration of these fibres before qualitative analysis.The tests used electrostatic separation and instrumental methods to identify asbestos in a sample (OM, SEM–EDS). The presence of chrysotile traces (or poorly processed asbestos fibres) in neutralised asbestos waste was established. The efficiency of asbestos destruction was proved to be insufficient. As such, the MTT technique should be used as a process of inerting or reducing the harmfulness of asbestos waste, rather than recycling it. Lowering the temperature in this process is economically desirable but may run the risk of incompletely destroying the asbestos and leaving behind hard-to-detect traces.

Photoluminescent Properties of Hydroxyapatite and Hydroxyapatite/Multi-Walled Carbon Nanotube Composites

Hydroxyapatite (HAp) and hydroxyapatite/multi-walled carbon nanotube (MWCNT) composites were obtained by the co-precipitation method, followed by ultrasound-assisted and microwave radiation and thermal treatment at 250 °C. X-ray diffraction (XRD) confirmed the presence of a hexagonal phase in all the samples, while Fourier-transform infrared (FTIR) spectroscopy elucidated the interaction between HAp and MWCNTs. The photoluminescent technique revealed that HAp and the composite with non-functionalized MWCNTs present a blue luminescence, while the composite with functionalized MWCNTs, under UV-vis radiation shows an intense white emission. These findings allowed presentation of a proposal for the use of HAp and HAp with functionalized MWCNTs as potential materials for optoelectronic and medical applications.

Investigation of Microwave and Thermal Processing of Electrode Material of End-of-Life Ni-MH Battery

Ni-metal hydride (NiMH) batteries should be recycled, as they contain base metals (Ni, Co) and rare earth elements (La, Ce). In this study, thermal and microwave treatments are investigated as a pre-treatment method for decomposing electrode material (Ni(OH)2 and LaNi5). The kinetic analysis of thermal decomposition electrode material yields the activation energy of 41.3 kJ/mol. The maximum percentage of lanthanum nickel oxide phase and cerium oxide phase is obtained at 1000°C of thermal treatment and 15 min of microwave exposure. The formation of melted balls of Ni and its oxide (Ni ~ 72.8%) was observed in microwave exposure, and the tendency of ball formation decreased with increasing exposure time. The effect of microwave exposure and thermal treatment on the acid leaching (1 M HCl, at S/L-1:20, at 70°C for 2 h) was studied. The leaching results showed NiO and CeO2 phases in the leach residue of thermal and microwave treated products.

Comparative Study of Luminophores in the System ZrO2–Y2O3–Eu2O3 Obtained by Wet Mixing and Coprecipitation Followed by Microwave Treatment

It is shown that the high-temperature (1100°C) microwave treatment of the ZrO2–Y2O3–Eu2O3 luminophores obtained by wet mixing using zirconium oxochloride and yttrium acetate leads to a significant growth in the luminescence brightness that exceeds that of an industrial luminophore based on Y2O3 : Eu3+ by a factor of 1.75. For a luminophore with the identical composition obtained by the coprecipitation of hydroxides from a solution of the corresponding nitrates, a similar microwave thermal treatment leads to a sharp decrease in the brightness. The observed differences in the characteristics of the synthesized luminophores are compared to the changes in the functional composition of their surface and dispersity as a result of the microwave treatment.

Microstructural Analysis of Zinc Niobate Ceramics Processed by Microwave Thermal Treatment

In this work are presented analyzes from calcination and sintering of zinc niobate ceramics by microwave processing. In order to obtain minimum processing parameters, the behavior of the material was first studied for the calcination at different temperatures in the range of 450 to 1150°C, with duration time of 10 minutes. The sintering was carried out between 950 and 1050°C. The results showed that the crystalline structure of the calcined and sintered samples was influenced by the temperature, because, according to the increase in temperature, the evolution of the formed crystalline phases was observed and only the Zn3Nb2O8 and ZnNb2O6 phases prevailed in the final microstructure. The densification of the sintered ceramics was influenced by the time and temperature of the heat treatment, with lower residual porosity and grain growth with the increase of the sintering temperature in the microwave oven.

Biomimetic Composite Scaffold Based on Naturally Derived Biomaterials.

This paper proposes the development of a biomimetic composite based on naturally derived biomaterials. This freeze-dried scaffold contains a microwave-synthesized form of biomimetic hydroxyapatite (HAp), using the interwoven hierarchical structure of eggshell membrane (ESM) as bio-template. The bone regeneration capacity of the scaffold is enhanced with the help of added tricalcium phosphate from bovine Bone ash (BA). With the addition of Gelatin (Gel) and Chitosan (CS) as organic matrix, the obtained composite is characterized by the ability to stimulate the cellular response and might accelerate the bone healing process. Structural characterization of the synthesized HAp (ESM) confirms the presence of both hydroxyapatite and monetite phases, in accordance with the spectroscopy results on the ESM before and after the microwave thermal treatment (the presence of phosphate group). Morphology studies on all individual components and final scaffold, highlight their morphology and porous structure, characteristics that influence the biocompatibility of the scaffold. Porosity, swelling rate and the in vitro cytotoxicity assays performed on amniotic fluid stem cells (AFSC), demonstrate the effective biocompatibility of the obtained materials. The experimental results presented in this paper highlight an original biocomposite scaffold obtained from naturally derived materials, in a nontoxic manner.

Facile synthesis of few-layer and ordered K-promoted MoS2 nanosheets supported on SBA-15 and their potential application for heterogeneous catalysis

Supported MoS2 based materials are widely used as heterogeneous catalysts. In this work, we propose a rapid and facile method (ultrasound-induced impregnation assisted by microwave thermal treatment) to synthesize mesoporous silica (SBA-15)-supported, few-layer, ordered and K-promoted MoS2 nanosheets with different K/Mo ratios. The prepared catalysts are characterized by various physical and chemical techniques. Their catalytic performance is evaluated by methyl mercaptan (CH3SH) synthesis from CO/H2/H2S. The results show that our catalysts exhibit a much higher CO conversion and selectivity to CH3SH than the catalysts prepared using the conventional impregnation and reported in the literature. The good performance arises because of two main factors: MoS2 nanosheets of only 2–4 layers and K promotion. Experimental characterizations and (density functional theory) calculations show that the former is the typical nano-size effect, and the latter stabilizes CS bonds when activating COS molecules.

Development of an intensive microwave-thermal treatment technology for heterogenic environments

The study suggests a technology of intensive, energy-efficient microwave-thermal mass transfer during washing and drying of agricultural and industrial products in a non-resonant microwave chamber with a uniform heating field. The chamber is equipped with a vacuum pump and an ultrasonic generator and is functionally connected to the evaporator and condenser of the heat pump. The traveling wave mode in the microwave chamber and intense evaporation are facilitated by the microwave field energy concentrator in the volume of the environment and the absorbing ferrite coating, which converts the ballast energy of the field into thermal energy on a perforated partition for products. This helps to reduce the significant cost of time and energy in the case of washing and drying heterogenic environments.The article substantiates the direction of developing the physicotechnical foundations of microwave-thermal treatment of environments with the aim of washing products using ultrasonic and microwave generators in a vacuum chamber to intensify the process. The authors show the necessity of developing the theory and practice of manufacturing and using radio-absorbing materials converting field energy to thermal energy. A coordinated integration of the upgraded microwave and additional convection drying technologies is proposed for the purpose to harmonize economical, intensive and environmentally friendly mass transfer of moisture during drying of the processed environment. It was found that the achievement and use of a synergistic effect, namely the energy efficiency of the process of complete drying in the middle of the chamber, contributes to the intensive evaporation of moisture from products in a uniform electromagnetic field in the chamber and the current dehumidification of moist air by the heat pump evaporator. Dry air is supplied into the microwave chamber after it is heated by the heat pump condenser. This contributes to a significantly more effective washing and drying of products. The application of this circuit solution and the optimal parameters of the regime in practice make it possible to solve the contradictory problem of increasing the efficiency and environmental friendliness of the processes in everyday life as well as in agricultural and industrial production.

Experimental, heat transfer and microbial inactivation modeling of microwave pasteurization of carrot slices as an efficient and clean process

The coupled 3D and transient form of heat and Maxwell’s equations were solved to determine the temperature distribution within a carrot slice in the microwave cavity during pasteurization as a clean and energy saving process. To precisely simulate the turning of the sample, the dissipated thermal energy was applied to the carrot as a rotating heat source field. The temperature evolution pattern through time was determined for various power levels and compared to measured experimental data to validate the simulation. Additionally, an inactivation modeling for Enterococcus faecalis, Bacillus cereus, Staphylococcus aureus and Shigella flexneri based on the cumulative exposure time to the elevated temperatures was proposed. According to the results, it was shown that due to the temperature variation profiles, three inactivation phases (heating process; holding temperature; microwave turn off phase) can be introduced. The most inactivation was occurred through the first and second phases for 600 W and also the temperature level was not sufficiently high to produce a major inactivation for 200 W during the last phase. Additionally, the 400 W microwave power created the highest inactivation of bacteria through the last phase. Based on the obtained results the energy demand of the microwave thermal treatment was 52.3% lower than conventional steam surface pasteurization and also it can be used as a clean process in pasteurization of carrots instead of chemical pasteurization.

Effect of conventional and microwave thermal treatments on floatability of low- and high-rank lignites

ABSTRACT Thermal treatment is one of the well-known methods used before froth flotation to remove the polar groups from coal surfaces to make them more hydrophobic. In this study, the effect of conventional and microwave thermal treatments on the wettability of low and high-rank lignite was investigated using flotation experiments, zeta potential, and bubble-particle attachment time measurements, as well as hydrophilicity index analyses. The results showed that both of the thermal treatments increased hydrophobicity, and therefore floatability of the coal samples. The optimum results were achieved with conventional and microwave thermal treatment for the low and high-rank coals, respectively.

Insights over Titanium Modified FeMgOx Catalysts for Selective Catalytic Reduction of NOx with NH3: Influence of Precursors and Crystalline Structures

Titanium modified FeMgOx catalysts with different precursors were prepared by coprecipitation method with microwave thermal treatment. The iron precursor is a key factor affecting the surface active component. The catalyst using FeSO4 and Mg(NO3)2 as precursors exhibited enhanced catalytic activity from 225 to 400 °C, with a maximum NOx conversion of 100%. Iron oxides existed as γ-Fe2O3 in this catalyst. They exhibited highly enriched surface active oxygen and surface acidity, which were favorable for low-temperature selective catalytic reduction (SCR) reaction. Besides, it showed advantage in surface area, spherical particle distribution and pores connectivity. Amorphous iron-magnesium-titanium mixed oxides were the main phase of the catalysts using Fe(NO3)3 as a precursor. This catalyst exhibited a narrow T90 of 200/250–350 °C. Side reactions occurred after 300 °C producing NOx, which reduced the NOx conversion. The strong acid sites inhibited the side reactions, and thus improved the catalytic performance above 300 °C. The weak acid sites appeared below 200 °C, and had a great impact on the low-temperature catalytic performance. Nevertheless, amorphous iron-magnesium-titanium mixed oxides blocked the absorption and activation between NH3 and the surface strong acid sites, which was strengthened on the γ-Fe2O3 surface.

Evolving Therapy for Celiac Disease.

Gluten is known to be the main triggering factor for celiac disease (CeD), an immune-mediated disorder. CeD is therefore managed using a strict and lifelong gluten-free diet (GFD), the only effective treatment available currently. However, the GFD is restrictive. Hence, efforts are being made to explore alternative therapies. Based on their mechanisms of action on various molecular targets involved in the pathogenesis of CeD, these therapies may be classified into one of the following five broad approaches. The first approach focuses on decreasing the immunogenic content of gluten, using strategies like genetically modified wheat, intra-intestinal gluten digestion using glutenases, microwave thermal treatment of hydrated wheat kernels, and gluten pretreatment with either bacterial/ fungal derived endopeptidases or microbial transglutaminase. The second approach involves sequestering gluten in the gut lumen before it is digested into immunogenic peptides and absorbed, using binder drugs like polymer p(HEMA-co-SS), single chain fragment variable (scFv), and anti- gluten antibody AGY. The third approach aims to prevent uptake of digested gluten through intestinal epithelial tight junctions, using a zonulin antagonist. The fourth approach involves tissue transglutaminase (tTG) inhibitors to prevent the enhancement of immunogenicity of digested gluten by the intestinal tTG enzyme. The fifth approach seeks to prevent downstream immune activation after uptake of gluten immunogenic peptides through the intestinal mucosal epithelial layer. Examples include HLA-DQ2 blockers that prevent presentation of gluten derived- antigens by dendritic cells to T cells, immune- tolerizing therapies like the vaccine Nexvax2 and TIMP-Glia, cathepsin inhibitors, immunosuppressants like corticosteroids, azathioprine etc., and anti-cytokine agents targeting TNF-α and interleukin-15. Apart from these approaches, research is being done to evaluate the effectiveness of probiotics/prebiotics, helminth therapy using Necator americanus, low FODMAP diet, and pancreatic enzyme supplementation in CeD symptom control; however, the mechanisms by which they play a beneficial role in CeD are yet to be clearly established. Overall, although many therapies being explored are still in the pre-clinical phase, some like the zonulin antagonist, immune tolerizing therapies and glutenases have reached phase II/III clinical trials. While these potential options appear exciting, currently they may at best be used to supplement rather than supplant the GFD.

Comparison of solid state synthesis of zinc calcium phosphorous oxide (ZCAP) ceramics under conventional and microwave heating methods

In this study, a weight ratio of 50:30:20 of ZnO:CaO:P2O5 was calcined using microwave and conventional thermal treatment at 800 °C to synthesize zinc oxide calcium phosphorous oxide (ZCAP) ceramics. X-ray diffraction data indicated that microwave synthesized ZCAP ceramics was less crystalline than conventionally synthesized ZCAP. Micro-Raman spectroscopy and FTIR confirmed the presence of ZnO, phosphate and carbonate groups in both heat treatment methods. The reported TGA-DSC results demonstrated that carbonate amount was very less (approx. 0.1%) in microwave synthesized ZCAP while in comparison to carbonate amount was high (approx. 0.69%) in conventionally prepared ZCAP. FESEM image analysis showed that particle sizes were comparatively smaller for microwave synthesized ZCAP than conventionally synthesized ZCAP. Hence, microwave calcinations of ZnO, CaO and P2O5 is a promising method to synthesize ZCAP ceramics compared to conventional thermal calcination treatment.

Micro-Nanomaterials for Tumor Microwave Hyperthermia: Design, Preparation, and Application.

Cancer hyperthermia is attracting much attention in basic science and clinics. Among the hyperthermia techniques, microwave (MW) heating is most commonly used for cancer treatment. It offers highly competitive advantages: faster heat generation from microwave radiation, less susceptibility to heat up local tissues, maneuverability, and depth of penetration in tissues and capability of killing tumor cells. Although the encouraging clinical results are being collected, MW hyperthermia has its own challenges, such as inaccurate targeting and low selectivity, which lead to damage to the surrounding vital organs and tissues. To address these issues, this review aims to introduce micronanomaterials as promising agents for receiving the electromagnetic wave, which should be beneficial for improving the efficacy of MW hyperthermia. We have searched many peer-reviewed papers in medical and chemical material databases about micro-nanomaterials for tumor microwave hyperthermia. Distinguishing features and important progresses are introduced in this review. One hundred and forty papers were chosen and included in this review. Four parts were described, including hyperthermia techniques and the application of micro-nanomaterials, microwave thermal therapy and treatment principle, microwave absorbing micro-nanomaterials, the preparation and application of micro-nanomaterials in microwave thermal therapy. We review the most recent literatures on micro-nanomaterials-based MW heating strategies for cancer treatment, with the aim to give the reader an overview of the state-of-the-art of MW hyperthermia therapy. The future of MW responsive materials will also be discussed, including combination of imaging probes and targeting moieties.