Herstellung neuer Hartmetalle mit Gradientenmikrostruktur durch Mikrowellensintern

Fabrication of New Cemented Carbides with Graded Microstructure by Microwave Sintering State of the art technologies for producing coated cermets and cemented carbides are in‐situ processes based on application of a reactive sintering atmosphere as well as ex‐situ processes, e. g., thermal CVD. Within the frame of the project summarised in the present paper, application of microwave radiation as heating source within both processing routes has been shown to be a viable and powerful new technology to accelerate processing rates as well as to integrate different processing steps into one process of sinter‐coating. Upon microwave sintering in reactive, e. g. nitrogen containing atmosphere, functionally graded materials are obtained from all Ti‐containing materials, with extended compositional gradients and dense Ti(C,N)‐coatings even in grades, which do not develop such coatings upon conventional vacuum sintering followed by reactive atmosphere heating. Microwave sintering offers therefore a much higher degree of variation in composition and gradient extension as compared to conventional processing routes. The acceleration of mass transport is impressive, yielding in some materials undesirably thick coatings at processing times of less than 1 h at temperature. Therefore further investigations are necessary in order to gain insight into the metallurgical processes occurring under the action of a microwave field. The thermal CVD‐process is not accelerated by the presence of the microwave field in such a significant way as the reactive atmosphere sintering is. However, using microwave heating a new reactor principle is developed, the so called “warm wall” reactor, in which only the samples are coated due to selective microwave heating, not the reactor. The coating process is performed at ambient pressure of an inert gas, immediatly after the sintering step, using precursors well known from conventional CVD. Due to microwave sintering no Co is enriched at the surface of the tool bits. Microwave sintering was expected to significantly increase the variability of processes which yield functionally graded cemented carbides and cermets and at the same time to improve the quality of the products or enable the synthesis of new materials. Based on preliminary results of cutting performance as well as process reproducibility and due the development of graded structures in materials which do not develop such microstructures under conventional processing conditions, these expectations were more than fulfilled.     

基于微波辐照合成类石墨烯氮化碳的研究进展

类石墨烯氮化碳具有与石墨烯非常相似的结构特征,已在光催化、润滑等领域表现出极优越的性能,成为二维纳米功能材料领域的新热点。本文重点介绍了基于微波辐照合成类石墨烯氮化碳的研究进展,并通过与氧化刻蚀、液相超声剥离、热聚合等传统合成方法的比较,分析了微波合成在制备效率、效果上的优势;并指出采用高功率微波设备和石墨粉、短切碳纤维等对微波具有强烈响应的微波吸收剂,通过增强能量传递与吸收效率,强化微波电磁场环境下合成反应的非稳态程度,有助于提高合成效率、效果,并获取得到特殊形态、结构的新产物。     

Prospects of microwave processing: An overview

Microwave processing has been emerging as an innovative sintering method for many traditional ceramics, advanced ceramics, specialty ceramics and ceramic composites as well as polymer and polymer composites. Development of functionally gradient materials: joining; melting; fibre drawing; reaction synthesis of ceramics; synthesis of ceramic powder, phosphor materials, whiskers, microtubes and nanotubes; sintering of zinc oxide varistors; glazing of coating surface and coating development have been performed using microwave heating. In addition, microwave energy is being explored for the sintering of metal powders also. Ceramic and metal nanopowders have been sintered in microwave. Furthermore, initiatives have been taken to process the amorphous materials (e.g. glass) by microwave heating. Besides this, attempt has been made to study the heating behaviour of materials in the electric and magnetic fields at microwave frequencies. The research is now focused on the use of microwave processing for industrial applications.     

Prospects of microwave processing: An overview

Microwave processing has been emerging as an innovative sintering method for many traditional ceramics, advanced ceramics, specialty ceramics and ceramic composites as well as polymer and polymer composites. Development of functionally gradient materials, joining, melting, fibre drawing, reaction synthesis of ceramics, synthesis of ceramic powder, phosphor materials, whiskers, microtubes and nanotubes, sintering of zinc oxide varistors, glazing of coating surface and coating development have been performed using microwave heating. In addition, microwave energy is being explored for the sintering of metal powders also. Ceramic and metal nanopowders have been sintered in microwave. Furthermore, initiatives have been taken to process the amorphous materials (e.g. glass) by microwave heating. Besides this, an attempt has been made to study the heating behaviour of materials in the electric and magnetic fields at microwave frequencies. The research is now focused on the use of microwave processing for industrial applications.     

Microwave–material interaction phenomena: Heating mechanisms,challenges and opportunities in material processing

Efforts to use microwaves in material processing are gradually increasing. However, the phenomena associated with the processing are less understood; popular mechanisms such as dipolar heating and conduction heating have been mostly explored. The current paper reviews most of the significant phenomena that cause heating during microwave–material interaction and heat transfer during microwave energy absorption in materials. Mechanisms involved during interaction of microwave with characteristically different materials – metals, non-metals and composites (metal matrix composites, ceramic matrix composites and polymer matrix composites) have been discussed using suitable illustrations. It was observed that while microwave heating of metal based materials is due to the magnetic field based loss effects, dipolar loss and conduction loss are the phenomena associated with the electric field effects in microwave heating of non-metals. Challenges in processing of advanced materials, particularly composites have been identified from the available literature; further research directions with possible benefits have been highlighted.     

Microwave processing: fundamentals and applications

In microwave processing, energy is supplied by an electromagnetic field directly to the material. This results in rapid heating throughout the material thickness with reduced thermal gradients. Volumetric heating can also reduce processing times and save energy. The microwave field and the dielectric response of a material govern its ability to heat with microwave energy. A knowledge of electromagnetic theory and dielectric response is essential to optimize the processing of materials through microwave heating. The fundamentals of electromagnetic theory, dielectric response, and applications of microwave heating to materials processing, especially fiber composites, are reviewed in this article.     

碳基材料吸波性能研究进展

随着雷达探测技术的迅猛发展和电磁波辐射污染的日益加剧,新型吸波材料的研究和开发成为各国研究的热点。单一吸收剂存在吸波频带窄和吸收强度低等缺点,无法满足新型吸波材料频带宽、厚度薄、质量轻、吸收强的要求。碳材料具有密度低和吸波性能好等优点,通过与其他吸收剂的双组分、多组分复合,或对复合材料的微观结构进行设计,碳系复合材料表现出优异的吸波性能。简要介绍了吸波材料的工作机理,然后分别从炭黑、碳纤维、碳纳米管、石墨烯和其他碳系材料等5个方面综述了碳系材料在电磁波吸收中的应用和发展,归纳了碳系材料吸波性能的最新研究进展,最后提出了当前研究中存在的不足并明确了研究方向。     

电磁波吸收材料用于微波融冰雪路面的研究进展

电磁波吸收材料与传统路面材料相结合,所形成的微波融冰雪路面具有高效、环保等优势。为进一步提高路面的微波融冰雪能力,介绍了微波融冰雪路面的工作原理及影响除冰效率的主要因素,阐述了电磁波吸收材料在微波照射下的发热机理。在此基础上,综述了9种电磁波吸收材料的电磁特性,并着重介绍了碳纤维、磁铁矿石与钢纤维用于路面微波除冰雪的研究进展,并从发热速率与经济性角度对比分析其应用前景。最后,指出了目前研究中存在的问题,展望了今后的研究趋势。     

An overview on microwave processing of material: A special emphasis on glass melting

Material processing adopting microwave heating has emerged as an alternative tool owing to faster processing, a cleaner environment, and several other advantages. This review provides a summary of recent reports of microwave synthesis of materials. This study reviews the use of microwave energy for application in several material processing technologies apart from food processing. A special emphasis has been made in the processing of glass adopting microwave energy. Melting of glass comprising SiO₂, P₂O₅, B₂O₃ as the main building block has been discussed. It has been revealed that silica, a microwave transparent material as reported earlier, can be heated under microwave heating directly. Microwave absorption of raw materials and different glass system has been discussed. Dielectric properties, particularly loss tangent or loss factor, are presented for some glass composition. Less evaporation of ingredient and low contamination from the crucible wall are noticed during glass melting using microwave heating. Enhanced iron redox ratio (Fe⁺²/∑Fe) in microwave processing may be considered an advantage in the preparation of heat absorbing filter glass. Small-scale glass melting using the microwave heating has a significant impact on energy and time saving. However, the challenges associated with the upscaling glass melting with microwave heating and future scope have been talked about.     

微波合成无机纳米材料的研究进展

微波加热作为一种合成纳米材料的新方法，近年来得到飞速发展。介绍了微波加热原理，阐述了微波合成无机纳米材料的一些研究进展，主要是液相微波加热在制备金属氧化物和金属硫化物纳米材料以及微波烧结在合成陶瓷材料的应用，并对该领域未来作了一些展望。     

Rapid,High‐Temperature,In Situ Microwave Synthesis of Bulk Nanocatalysts

Carbon‐black‐supported nanoparticles (CNPs) have attracted considerable attention for their intriguing catalytic properties and promising applications. The traditional liquid synthesis of CNPs commonly involves demanding operation conditions and complex pre‐ or post‐treatments, which are time consuming and energy inefficient. Herein, a rapid, scalable, and universal strategy is reported to synthesize highly dispersed metal nanoparticles embedded in a carbon matrix via microwave irradiation of carbon black with preloaded precursors. By optimizing the amount of carbon black, the microwave absorption is dramatically improved while the thermal dissipation is effectively controlled, leading to a rapid temperature increase in carbon black, ramping to 1270 K in just 6 s. The whole synthesis process requires no capping agents or surfactants, nor tedious pre‐ or post‐treatments of carbon black, showing tremendous potential for mass production. As a proof of concept, the synthesis of ultrafine Ru nanoparticles (≈2.57 nm) uniformly embedded in carbon black using this microwave heating technique is demonstrated, which displays remarkable electrocatalytic performance when used as the cathode in a Li–O₂ battery. This microwave heating method can be extended to the synthesis of other nanoparticles, thereby providing a general methodology for the mass production of carbon‐supported catalytic nanoparticles.     

Recent Advances in Atomic Metal Doping of Carbon‐based Nanomaterials for Energy Conversion

Nanostructured metal‐contained catalysts are one of the most widely used types of catalysts applied to facilitate some of sluggish electrochemical reactions. However, the high activity of these catalysts cannot be sustained over a variety of pH ranges. In an effort to develop highly active and stable metal‐contained catalysts, various approaches have been pursued with an emphasis on metal particle size reduction and doping on carbon‐based supports. These techniques enhances the metal‐support interactions, originating from the chemical bonding effect between the metal dopants and carbon support and the associated interface, as well as the charge transfer between the atomic metal species and carbon framework. This provides an opportunity to tune the well‐defined metal active centers and optimize their activity, selectivity and stability of this type of (electro)catalyst. Herein, recent advances in synthesis strategies, characterization and catalytic performance of single atom metal dopants on carbon‐based nanomaterials are highlighted with attempts to understand the electronic structure and spatial arrangement of individual atoms as well as their interaction with the supports. Applications of these new materials in a wide range of potential electrocatalytic processes in renewable energy conversion systems are also discussed with emphasis on future directions in this active field of research.     

微波加热制备特种陶瓷材料研究进展

特种陶瓷广泛应用于航天航空、电子信息、新能源、机械、化工等新兴工业领域,其高温制备过程仍以传统燃气窑炉和电加热炉为主;碳排放高、能耗大,节能减排形势严峻。当前,我国面临实现“双碳”目标的巨大压力,研究推广清洁高效的加热技术迫在眉睫。微波加热是利用材料自身对微波进行吸收,将电磁能转化为热能,能量的转移发生在分子水平上,通过这种方式,加热在整个材料内外同时产生,整个材料体系中的温度梯度非常低。除体积加热外,选择性加热、功率再分配、热剧变以及微波等离子效应等也是微波烧结的显著特征。微波加热具有节能环保、改善制品性能、减少燃烧碳排放等优点,国内外有许多关于微波合成各种氧化物、碳化物、氮化物陶瓷粉体和微波烧结陶瓷复合材料的报道。本文首先对微波和微波混合烧结的基本理论进行综述,然后介绍了微波加热制备陶瓷粉体与微波烧结制备陶瓷材料的最新研究进展,最后总结了微波加热在陶瓷工程制品烧结中的一些研究成果,体现出微波烧结的优越性,并提出了微波烧结制备特种陶瓷的关键问题和今后的发展方向。     

Rational Design of Carbon Nanomaterials for Electrochemical Sodium Storage and Capture

Electrochemical sodium storage and capture are considered an attractive technology owing to the natural abundance, low cost, safety, and cleanness of sodium, and the higher efficiency of the electrochemical system compared to fossil‐fuel‐based counterparts. Considering that the sodium‐ion chemistry often largely deviates from the lithium‐based one despite the physical and chemical similarities, the architecture and chemical structure of electrode materials should be designed for highly efficient sodium storage and capture technologies. Here, the rational design in the structure and chemistry of carbon materials for sodium‐ion batteries (SIBs), sodium‐ion capacitors (SICs), and capacitive deionization (CDI) applications is comprehensively reviewed. Types and features of carbon materials are classified into ordered and disordered carbons as well as nanodimensional and nanoporous carbons, covering the effect of synthesis parameters on the carbon structure and chemistry. The sodium storage mechanism and performance of these carbon materials are correlated with the key structural/chemical factors, including the interlayer spacing, crystallite size, porous characteristics, micro/nanostructure, morphology, surface chemistry, heteroatom incorporation, and hybridization. Finally, perspectives on current impediment and future research directions into the development of practical SIBs, SICs, and CDI are also provided.     

炭纤维预制体的微波加热性能及其加热机理探讨

通过研究微波功率、炭纤维预制体的密度和叠层层数对预制体微波加热效果的影响, 分析了微波电场在预制体中的分布特点, 提出了炭纤维预制体的微波加热模型, 并对其损耗机制进行了探讨. 结果表明: 在(2450±50)MHz的微波波段, 炭纤维预制体能吸收微波而加热, 其损耗机制主要为偶极子极化、界面极化及电导损耗.     

Recent Advances in Functionalized Carbon Dots toward the Design of Efficient Materials for Sensing and Catalysis Applications

Since the past decade, enormous research efforts have been devoted to the detection/degradation and quantification of environmental toxic pollutants and biologically important molecules due to their ubiquitous necessity in the fields of environmental protection and human health. These fields of sensor and catalysis are advanced to a new era after emerging of nanomaterials, especially, carbon nanomaterials including graphene, carbon nanotube, carbon dots (C‐dots), etc. Among them, the C‐dots in the carbon family are rapidly boosted in the aspect of synthesis and application due to their superior properties of chemical and photostability, highly fluorescent with tunable, non/low‐toxicity, and biocompatibility. The C‐dot‐based functional materials have shown great potential in sensor and catalysis fields for the detection/degradation of environmental pollutants. The major advantage of C‐dots is that they can be easily prepared from numerous biomass/waste materials which are inexpensive and environment‐friendly and are suitable for a developing trend of sustainable materials. This review is devoted to the recent development (since 2017) in the synthesis of biomass‐ and chemical‐derived C‐dots as well as diverse functionalization of C‐dots. Their capability as a sensor and catalyst and respective mechanism are summarized. The future perspectives of C‐dots are also discussed.     

微波高温加热技术进展

微波高温加热技术被认为是本世纪最有可能取代传统外部加热技术而应用于材料制备的先进技术之一.总结了近年来微波高温加热技术在理论与模拟、结构材料和功能材料方面的研究进展,并对微波高温技术在产业化方面的应用现状和发展前景进行了论述.     

碳基采暖电热材料研究进展

近几年,由于节能与环保的需求,电取暖的方式得到大力的推广,电热材料的研究与应用受到人们广泛的重视。非金属碳基电热材料是新型的节能型电热采暖材料,本文重点对影响非金属碳基电热材料中的炭黑基电热材料、碳纤维基电热材料、碳晶电热材料电热性能的因素及相关应用进行了综述。     

Carbon‐Based Metal‐Free Catalysts for Energy Storage and Environmental Remediation

Owing to their high earth‐abundance, eco‐friendliness, high electrical conductivity, large surface area, structure tunability at the atomic/morphological levels, and excellent stability in harsh conditions, carbon‐based metal‐free materials have become promising advanced electrode materials for high‐performance pseudocapacitors and metal–air batteries. Furthermore, carbon‐based nanomaterials with well‐defined structures can function as green catalysts because of their efficiency in advanced oxidation processes to remove organics in air or from water, which reduces the cost for air/water purification and avoids cross‐contamination by eliminating the release of heavy metals/metal ions. Here, the research and development of carbon‐based catalysts in supercapacitors and batteries for clean energy storage as well as in air/water treatments for environmental remediation are reviewed. The related mechanistic understanding and design principles of carbon‐based metal‐free catalysts are illustrated, along with the challenges and perspectives in this emerging field.     

含碳纳米管微波吸收材料的制备及其微波吸收性能研究

用竖式炉流动法,以二茂铁为催化剂,噻吩为助催化剂,苯为碳源通过催化裂解反应制备了碳纳米管,碳纳米管的外径为20-50nm,内径10-30nm,长度50-1000μm.分别以碳纳米管、羰基铁粉、碳纳米管与羰基铁粉的混合物为吸收剂制备了微波吸收材料,研究了上述三种微波吸收材料在2-18GHz的吸波性能,与纯碳纳米管和纯羰基铁粉微波吸收材料相比, 碳纳米管与羰基铁粉复合微波吸收材料在2-18GHz的吸收峰明显向低频移动.在含碳纳米管的微波吸收材料中,碳纳米管作为偶极子在交变电场的作用下,产生极化电流,电磁波的能量转换为其他形式的能量,瑞利散射效应和界面极化也是含碳纳米管微波吸收材料的主要吸波机理.