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3478 KiB

Open AccessArticle

Microwave Crystallization of Lithium Aluminum Germanium Phosphate Solid-State Electrolyte

by Morsi M. Mahmoud, Yuantao Cui, Magnus Rohde, Carlos Ziebert, Guido Link and Hans Juergen Seifert

Materials 2016, 9(7), 506; https://doi.org/10.3390/ma9070506 - 23 Jun 2016

Cited by 20 | Viewed by 7885

Abstract

Lithium aluminum germanium phosphate (LAGP) glass-ceramics are considered as promising solid-state electrolytes for Li-ion batteries. LAGP glass was prepared via the regular conventional melt-quenching method. Thermal, chemical analyses and X-ray diffraction (XRD) were performed to characterize the prepared glass. The crystallization of the [...] Read more.

Lithium aluminum germanium phosphate (LAGP) glass-ceramics are considered as promising solid-state electrolytes for Li-ion batteries. LAGP glass was prepared via the regular conventional melt-quenching method. Thermal, chemical analyses and X-ray diffraction (XRD) were performed to characterize the prepared glass. The crystallization of the prepared LAGP glass was done using conventional heating and high frequency microwave (MW) processing. Thirty GHz microwave (MW) processing setup were used to convert the prepared LAGP glass into glass-ceramics and compared with the conventionally crystallized LAGP glass-ceramics that were heat-treated in an electric conventional furnace. The ionic conductivities of the LAGP samples obtained from the two different routes were measured using impedance spectroscopy. These samples were also characterized using XRD and scanning electron microscopy (SEM). Microwave processing was successfully used to crystallize LAGP glass into glass-ceramic without the aid of susceptors. The MW treated sample showed higher total, grains and grain boundary ionic conductivities values, lower activation energy and relatively larger-grained microstructure with less porosity compared to the corresponding conventionally treated sample at the same optimized heat-treatment conditions. The enhanced total, grains and grain boundary ionic conductivities values along with the reduced activation energy that were observed in the MW treated sample was considered as an experimental evidence for the existence of the microwave effect in LAGP crystallization process. MW processing is a promising candidate technology for the production of solid-state electrolytes for Li-ion battery. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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7312 KiB

Open AccessArticle

Polystyrene-Poly(methyl methacrylate) Silver Nanocomposites: Significant Modification of the Thermal and Electrical Properties by Microwave Irradiation

by Edreese H. Alsharaeh

Materials 2016, 9(6), 458; https://doi.org/10.3390/ma9060458 - 13 Jun 2016

Cited by 40 | Viewed by 7751

Abstract

This work compares the preparation of nanocomposites of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PSMMA co-polymer containing silver nanoparticles (AgNPs) using in situ bulk polymerization with and without microwave irradiation (MWI). The AgNPs prepared were embedded within the polymer matrix. A modification in [...] Read more.

This work compares the preparation of nanocomposites of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PSMMA co-polymer containing silver nanoparticles (AgNPs) using in situ bulk polymerization with and without microwave irradiation (MWI). The AgNPs prepared were embedded within the polymer matrix. A modification in the thermal stability of the PS/Ag, PMMA/Ag, and PSMMA/Ag nanocomposites using MWI and in situ was observed compared with that of neat PSMMA, PS, and PMMA. In particular, PS/Ag, and PSMMA/Ag nanocomposites used in situ showed better thermal stability than MWI, while PMMA/Ag nanocomposites showed improved thermal stability. The electrical conductivity of the PS/Ag, PMMA/Ag, and PSMMA/Ag composites prepared by MWI revealed a percolation behavior when 20% AgNPs were used as a filler, and the conductivity of the nanocomposites increased to 103 S/cm, 33 S/cm, and 40 mS/cm, respectively. This enhancement might be due to the good dispersion of the AgNPs within the polymer matrix, which increased the interfacial interaction between the polymer and AgNPs. The polymer/Ag nanocomposites developed with tunable thermal and electrical properties could be used as conductive materials for electronic device applications. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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2095 KiB

Open AccessArticle

Microwave-Assisted Synthesis of Arene Ru(II) Complexes Induce Tumor Cell Apoptosis Through Selectively Binding and Stabilizing bcl-2 G-Quadruplex DNA

by Yanhua Chen, Qiong Wu, Xicheng Wang, Qiang Xie, Yunyun Tang, Yutao Lan, Shuangyan Zhang and Wenjie Mei

Materials 2016, 9(5), 386; https://doi.org/10.3390/ma9050386 - 17 May 2016

Cited by 13 | Viewed by 5682

Abstract

A series of arene Ru(II) complexes coordinated with phenanthroimidazole derivatives, [(η⁶-C₆H₆)Ru(l)Cl]Cl(1b L = p-ClPIP = 2-(4-Chlorophenyl)imidazole[4,5f] 1,10-phenanthroline; 2b L = m-ClPIP = 2-(3-Chlorophenyl)imidazole[4,5f] 1,10-phenanthroline; 3b L = p-NPIP = 2-(4-Nitrophenyl)imidazole[4,5f] 1,10-phenanthroline; 4b [...] Read more.

A series of arene Ru(II) complexes coordinated with phenanthroimidazole derivatives, [(η⁶-C₆H₆)Ru(l)Cl]Cl(1b L = p-ClPIP = 2-(4-Chlorophenyl)imidazole[4,5f] 1,10-phenanthroline; 2b L = m-ClPIP = 2-(3-Chlorophenyl)imidazole[4,5f] 1,10-phenanthroline; 3b L = p-NPIP = 2-(4-Nitrophenyl)imidazole[4,5f] 1,10-phenanthroline; 4b L = m-NPIP = 2-(3-Nitrophenyl) imidazole [4,5f] 1,10-phenanthroline) were synthesized in yields of 89.9%–92.7% under conditions of microwave irradiation heating for 30 min to liberate four arene Ru(II) complexes (1b, 2b, 3b, 4b). The anti-tumor activity of 1b against various tumor cells was evaluated by MTT assay. The results indicated that this complex blocked the growth of human lung adenocarcinoma A549 cells with an IC₅₀ of 16.59 μM. Flow cytometric analysis showed that apoptosis of A549 cells was observed following treatment with 1b. Furthermore, the in vitro DNA-binding behaviors that were confirmed by spectroscopy indicated that 1b could selectively bind and stabilize bcl-2 G-quadruplex DNA to induce apoptosis of A549 cells. Therefore, the synthesized 1b has impressive bcl-2 G-quadruplex DNA-binding and stabilizing activities with potential applications in cancer chemotherapy. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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1675 KiB

Open AccessArticle

Microwave-Assisted Drying for the Conservation of Honeybee Pollen

by Angelo Canale, Giovanni Benelli, Antonella Castagna, Cristina Sgherri, Piera Poli, Andrea Serra, Marcello Mele, Annamaria Ranieri, Francesca Signorini, Matteo Bientinesi and Cristiano Nicolella

Materials 2016, 9(5), 363; https://doi.org/10.3390/ma9050363 - 12 May 2016

Cited by 34 | Viewed by 7291

Abstract

Bee pollen is becoming an important product thanks to its nutritional properties, including a high content of bioactive compounds such as essential amino acids, antioxidants, and vitamins. Fresh bee pollen has a high water content (15%–30% wt %), thus it is a good [...] Read more.

Bee pollen is becoming an important product thanks to its nutritional properties, including a high content of bioactive compounds such as essential amino acids, antioxidants, and vitamins. Fresh bee pollen has a high water content (15%–30% wt %), thus it is a good substrate for microorganisms. Traditional conservation methods include drying in a hot air chamber and/or freezing. These techniques may significantly affect the pollen organoleptic properties and its content of bioactive compounds. Here, a new conservation method, microwave drying, is introduced and investigated. The method implies irradiating the fresh pollen with microwaves under vacuum, in order to reduce the water content without reaching temperatures capable of thermally deteriorating important bioactive compounds. The method was evaluated by taking into account the nutritional properties after the treatment. The analyzed parameters were phenols, flavonoids, with special reference to rutin content, and amino acids. Results showed that microwave drying offers important advantages for the conservation of bee pollen. Irrespective of microwave power and treatment time, phenol and flavonoid content did not vary over untreated fresh pollen. Similarly, rutin content was unaffected by the microwave drying, suggesting that the microwave-assisted drying could be a powerful technology to preserve bioprotective compounds in fresh pollen. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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3084 KiB

Open AccessArticle

Enhanced Photoluminescent Properties and Crystalline Morphology of LiBaPO₄:Tm³⁺ Phosphor through Microwave Sintering Method

by Hsuan-Lin Lai, Min-Hang Weng, Ru-Yuan Yang and Shoou-Jinn Chang

Materials 2016, 9(5), 356; https://doi.org/10.3390/ma9050356 - 12 May 2016

Cited by 7 | Viewed by 4225

Abstract

An investigation of the photoluminescent properties and crystalline morphology of blue emitting LiBa_1−xPO4:xTm³⁺ phosphors with various concentrations (x = 0.005–0.030) of Tm³⁺ ions were synthesized by microwave sintering. For comparison, the LiBa_1−xPO4: [...] Read more.

An investigation of the photoluminescent properties and crystalline morphology of blue emitting LiBa_1−xPO4:xTm³⁺ phosphors with various concentrations (x = 0.005–0.030) of Tm³⁺ ions were synthesized by microwave sintering. For comparison, the LiBa_1−xPO4:xTm³⁺ powders sintered at the same sintering condition but in a conventional furnace were also investigated. LiBaPO₄ without second phase was formed no matter which furnace was used. More uniform grain size distributions are obtained by microwave sintering. When the concentration of Tm³⁺ ion was x = 0.015, the luminescence intensity reached a maximum value, and then decreased with the increases of the Tm³⁺ concentration due to concentration quenching effect. The microwave sintering significantly enhanced the emission intensity of LiBa_1−xPO4:xTm³⁺ phosphors. Additionally, the d-d interaction is the key mechanism of concentration quenching for LiBaPO₄:Tm³⁺. The chromaticity (x, y) for all LiBa_1−xPO₄:xTm³⁺ phosphors are located at (0.16, 0.05), which will be classified as a blue region. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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1169 KiB

Open AccessArticle

In Situ Monitoring of Microwave Processing of Materials at High Temperatures through Dielectric Properties Measurement

by Beatriz Garcia-Baños, Jose M. Catalá-Civera, Felipe L. Peñaranda-Foix, Pedro Plaza-González and Gabriel Llorens-Vallés

Materials 2016, 9(5), 349; https://doi.org/10.3390/ma9050349 - 7 May 2016

Cited by 33 | Viewed by 6506

Abstract

Microwave-assisted processes have recognized advantages over more conventional heating techniques. However, the effects on the materials’ microstructure are still a matter of study, due to the complexity of the interaction between microwaves and matter, especially at high temperatures. Recently developed advanced microwave instrumentation [...] Read more.

Microwave-assisted processes have recognized advantages over more conventional heating techniques. However, the effects on the materials’ microstructure are still a matter of study, due to the complexity of the interaction between microwaves and matter, especially at high temperatures. Recently developed advanced microwave instrumentation allows the study of high temperature microwave heating processes in a way that was not possible before. In this paper, different materials and thermal processes induced by microwaves have been studied through the in situ characterization of their dielectric properties with temperature. This knowledge is crucial in several aspects: to analyze the effects of the microwave field on the reaction pathways; to design and optimize microwave-assisted processes, and to predict the behavior of materials leading to repeatable and reliable heating processes, etc. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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2498 KiB

Open AccessArticle

Schottky Barrier Height Tuning via the Dopant Segregation Technique through Low-Temperature Microwave Annealing

by Chaochao Fu, Xiangbiao Zhou, Yan Wang, Peng Xu, Ming Xu, Dongping Wu, Jun Luo, Chao Zhao and Shi-Li Zhang

Materials 2016, 9(5), 315; https://doi.org/10.3390/ma9050315 - 27 Apr 2016

Cited by 4 | Viewed by 6581

Abstract

The Schottky junction source/drain structure has great potential to replace the traditional p/n junction source/drain structure of the future ultra-scaled metal-oxide-semiconductor field effect transistors (MOSFETs), as it can form ultimately shallow junctions. However, the effective Schottky barrier height (SBH) of the Schottky junction [...] Read more.

The Schottky junction source/drain structure has great potential to replace the traditional p/n junction source/drain structure of the future ultra-scaled metal-oxide-semiconductor field effect transistors (MOSFETs), as it can form ultimately shallow junctions. However, the effective Schottky barrier height (SBH) of the Schottky junction needs to be tuned to be lower than 100 meV in order to obtain a high driving current. In this paper, microwave annealing is employed to modify the effective SBH of NiSi on Si via boron or arsenic dopant segregation. The barrier height decreased from 0.4–0.7 eV to 0.2–0.1 eV for both conduction polarities by annealing below 400 °C. Compared with the required temperature in traditional rapid thermal annealing, the temperature demanded in microwave annealing is ~60 °C lower, and the mechanisms of this observation are briefly discussed. Microwave annealing is hence of high interest to future semiconductor processing owing to its unique capability of forming the metal/semiconductor contact at a remarkably lower temperature. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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6973 KiB

Open AccessArticle

A Phase-Shifting Method for Improving the Heating Uniformity of Microwave Processing Materials

by Yinhong Liao, Junqing Lan, Chun Zhang, Tao Hong, Yang Yang, Kama Huang and Huacheng Zhu

Materials 2016, 9(5), 309; https://doi.org/10.3390/ma9050309 - 25 Apr 2016

Cited by 42 | Viewed by 5999

Abstract

Microwave processing of materials has been found to deliver enormous advantages over conventional processing methods in terms of mechanical and physical properties of the materials. However, the non-uniform temperature distribution is the key problem of microwave processing, which is related to the structure [...] Read more.

Microwave processing of materials has been found to deliver enormous advantages over conventional processing methods in terms of mechanical and physical properties of the materials. However, the non-uniform temperature distribution is the key problem of microwave processing, which is related to the structure of the cavity, and the placement and physical parameters of the material. In this paper, a new microwave cavity structure with a sliding short based on phase-shifting heating is creatively proposed to improve the temperature uniformity. An electronic mathematical model based on the Finite Element Method (FEM) is built to predict the temperature distribution. Meanwhile, a new computational approach based on the theory of transformation optics is first provided to solve the problem of the moving boundary in the model simulation. At first, the experiment is carried out to validate the model, and heating results from the experiment show good agreement with the model’s prediction. Based on the verified model, materials selected among a wide range of dielectric constants are treated by stationary heating and phase-shifting heating. The coefficient of variation (COV) of the temperature and temperature difference has been compared in detail between stationary heating and phase-shifting heating. A significant improvement in heating uniformity can be seen from the temperature distribution for most of the materials. Furthermore, three other materials are also treated at high temperature and the heating uniformity is also improved. Briefly, the strategy of phase-shifting heating plays a significant role in solve the problem of non-uniform heating in microwave-based material processing. A 25%–58% increase in uniformity from adapting the phase-shifting method can be observed for the microwave-processed materials. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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5158 KiB

Open AccessArticle

Microwave Synthesized ZnO Nanorod Arrays for UV Sensors: A Seed Layer Annealing Temperature Study

by Ana Pimentel, Sofia Henriques Ferreira, Daniela Nunes, Tomas Calmeiro, Rodrigo Martins and Elvira Fortunato

Materials 2016, 9(4), 299; https://doi.org/10.3390/ma9040299 - 20 Apr 2016

Cited by 82 | Viewed by 11196

Abstract

The present work reports the influence of zinc oxide (ZnO) seed layer annealing temperature on structural, optical and electrical properties of ZnO nanorod arrays, synthesized by hydrothermal method assisted by microwave radiation, to be used as UV sensors. The ZnO seed layer was [...] Read more.

The present work reports the influence of zinc oxide (ZnO) seed layer annealing temperature on structural, optical and electrical properties of ZnO nanorod arrays, synthesized by hydrothermal method assisted by microwave radiation, to be used as UV sensors. The ZnO seed layer was produced using the spin-coating method and several annealing temperatures, ranging from 100 to 500 °C, have been tested. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectrophotometry measurements have been used to investigate the structure, morphology, and optical properties variations of the produced ZnO nanorod arrays regarding the seed layer annealing temperatures employed. After the growth of ZnO nanorod arrays, the whole structure was tested as UV sensors, showing an increase in the sensitivity with the increase of seed layer annealing temperature. The UV sensor response of ZnO nanorod arrays produced with the seed layer annealed temperature of 500 °C was 50 times superior to the ones produced with a seed layer annealed at 100 °C. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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1372 KiB

Open AccessArticle

Control of Magnetic Properties of NiMn₂O₄ by a Microwave Magnetic Field under Air

by Hiroshi Goto, Jun Fukushima and Hirotsugu Takizawa

Materials 2016, 9(3), 169; https://doi.org/10.3390/ma9030169 - 4 Mar 2016

Cited by 9 | Viewed by 8083

Abstract

NiMn₂O₄ prepared by conventional heating was irradiated with a microwave H-field using a single-mode cavity under air and magnetic properties of the microwave-irradiated material were investigated. X-ray diffraction and transmission electron microscopy demonstrated that the phase and microstructure are not [...] Read more.

NiMn₂O₄ prepared by conventional heating was irradiated with a microwave H-field using a single-mode cavity under air and magnetic properties of the microwave-irradiated material were investigated. X-ray diffraction and transmission electron microscopy demonstrated that the phase and microstructure are not affected by H-field irradiation. Measurements of the magnetization as a function of temperature revealed that the antiferromagnetic sublattice disappeared and electron spin resonance showed the existence of Mn²⁺, suggesting that Mn³⁺ is partially reduced. Moreover, the magnetization of NiMn₂O₄ was controlled from 35.3 to 18.2 emu/g and the coercivity from 140 to 750 Oe by changing the sample temperature during microwave irradiation. The reduction reaction of NiMn₂O₄ is controlled by microwave H-field irradiation, resulting in control over the magnetic properties. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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2988 KiB

Open AccessArticle

Discussion on Microwave-Matter Interaction Mechanisms by In Situ Observation of “Core-Shell” Microstructure during Microwave Sintering

by Wenchao Liu, Feng Xu, Yongcun Li, Xiaofang Hu, Bo Dong and Yu Xiao

Materials 2016, 9(3), 120; https://doi.org/10.3390/ma9030120 - 23 Feb 2016

Cited by 22 | Viewed by 6583

Abstract

This research aims to deepen the understanding of the interaction mechanisms between microwave and matter in a metal-ceramic system based on in situ synchrotron radiation computed tomography. A special internal “core-shell” microstructure was discovered for the first time and used as an indicator [...] Read more.

This research aims to deepen the understanding of the interaction mechanisms between microwave and matter in a metal-ceramic system based on in situ synchrotron radiation computed tomography. A special internal “core-shell” microstructure was discovered for the first time and used as an indicator for the interaction mechanisms between microwave and matter. Firstly, it was proved that the microwave magnetic field acted on metal particles by way of inducing an eddy current in the surface of the metal particles, which led to the formation of a “core-shell” microstructure in the metal particles. On this basis, it was proposed that the ceramic particles could change the microwave field and open a way for the microwave, thereby leading to selective heating in the region around the ceramic particles, which was verified by the fact that all the “core-shell” microstructure was located around ceramic particles. Furthermore, it was indicated that the ceramic particles would gather the microwaves, and might lead to local heating in the metal-ceramic contact region. The focusing of the microwave was proved by the quantitative analysis of the evolution rate of the “core-shell” microstructure in a different region. This study will help to reveal the microwave-matter interaction mechanisms during microwave sintering. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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Review

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1873 KiB

Open AccessFeature PaperReview

Dielectric Spectroscopy in Biomaterials: Agrophysics

by Dalia El Khaled, Nuria N. Castellano, Jose A. Gázquez, Alberto-Jesus Perea-Moreno and Francisco Manzano-Agugliaro

Materials 2016, 9(5), 310; https://doi.org/10.3390/ma9050310 - 27 Apr 2016

Cited by 51 | Viewed by 13932

Abstract

Being dependent on temperature and frequency, dielectric properties are related to various types of food. Predicting multiple physical characteristics of agri-food products has been the main objective of non-destructive assessment possibilities executed in many studies on horticultural products and food materials. This review [...] Read more.

Being dependent on temperature and frequency, dielectric properties are related to various types of food. Predicting multiple physical characteristics of agri-food products has been the main objective of non-destructive assessment possibilities executed in many studies on horticultural products and food materials. This review manipulates the basic fundamentals of dielectric properties with their concepts and principles. The different factors affecting the behavior of dielectric properties have been dissected, and applications executed on different products seeking the characterization of a diversity of chemical and physical properties are all pointed out and referenced with their conclusions. Throughout the review, a detailed description of the various adopted measurement techniques and the mostly popular equipment are presented. This compiled review serves in coming out with an updated reference for the dielectric properties of spectroscopy that are applied in the agrophysics field. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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2006 KiB

Open AccessReview

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

by Jing Sun, Wenlong Wang and Qinyan Yue

Materials 2016, 9(4), 231; https://doi.org/10.3390/ma9040231 - 25 Mar 2016

Cited by 520 | Viewed by 20674

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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