The structural-energy state of metal nanopowders and the problems of certifying them

The basic characteristics of metal nanopowders, namely, the shape, particle sizes, the metal component content, the chemical activity parameters, the electrochemical characteristics, and the thermodynamic state of the nanoparticles and nanopowders, are considered. Experimental results are presented on the use of standard methods of analysis and the features of their use when determining the above characteristics. It is shown that, for certifying nanopowders as metastable systems, a whole range of methods of analysis is required.     

Synthesis and characterization of nanolamellar tungsten and molybdenum disulfides

Tungsten and molybdenum disulfides were produced in direct self-sustained combustion in argon between elementary sulfur and metal (W, Mo) nanopowders prepared by electrical explosion of wires. The results of XRD analysis show that the main phases of the synthesized nanopowders are hexagonal WS₂ and MoS₂. According to SEM and TEM observations, they are agglomerated nanolamellar particles of thickness 40–150 nm and width 100–3000 nm.     

Electrical properties of ZnO-based varistors prepared by combustion synthesis

Ceramic varistors are generally produced by the oxide mixing method or by chemical methods, such as sol–gel, precipitation and others. Chemical methods produce powders that are highly reactive, allowing for increased microstructural homogeneity and control of grain growth during sintering, which is essential for good varistor performance. The purpose of this work was to study the electrical characteristics of ZnO varistors produced from stoichiometric mixtures of water-soluble metal nitrates, such as precursor cations and urea as a fuel. This method, called combustion synthesis, stands out for its simplicity (a single-step reaction), purity, chemical homogeneity, and the high reactivity of the precursor powder. After sintering at 1050 °C using this method, varistors with a non-linear coefficient of 40 and the lowest leakage were obtained.     

Synthesis of ZnO nanoparticles through the impregnated layer combustion synthesis process

Zinc oxide nanopowders were synthesized by a solution combustion technique named impregnated layer combustion synthesis (ILCS), involving the impregnation of an active layer with the reactant solution and subsequently the combustion of the impregnated system. In this work three different organic fuels and two different ignition modes were tested in order to optimize the final microstructure and specific surface area (SSA) of the ZnO nanopowders. In particular, the ignition mode was found to significantly affect the final products, discriminating between an explosion procedure (flame combustion) and a self-propagating mode (smoldering combustion). The nitrate–glycine mixture and the smoldering combustion way were found to be the most suitable conditions, giving rise to softly agglomerated nanopowders with an average size of 20 nm and a very high SSA, without the need of any further crystallization treatment.     

Combustion synthesis of WC powder in the presence of alkali salts

This paper deals with the formation of tungsten carbide sub-micrometer powders from WO₃ + Mg + C + sodium salts (NaCl, Na₂CO₃) system by combustion synthesis technique. The powders were characterized by XRD and FESEM. X-ray data demonstrate the superiority of the NaCl + Na₂CO₃ combined mixture in the WC formation process. Single phase, sub-micrometer WC powders were synthesized at temperatures as low as 1600 °C. The roles of sodium salts in combustion process were discussed and chemical mechanism of WC formation was proposed. WC powder produced by salt-assisted combustion synthesis technique has a size 0.2–3 μm, crystalline shape and low agglomeration degree.     

Synthesis of ultrafine β-Ga2O3 nanopowder via hydrothermal approach: A strong UV “excimer-like” emission

Interest in nano-oxides has emerged from their technological applications in fields like microelectronics, catalysis, coatings, energy storage, and environment protection and remediation. There are various available methods for preparation and production of materials, but developing new routes to nanocrystalline materials is a challenging task for materials scientists. An innovative newly developed pathway to the synthesis of gallium oxide nanopowders, so-called “high-productivity/high-yield” process is presented here. The utilized method is simple, fast and environmental friendly. Ultrafine nanopowders of gallium oxide is prepared by addition of hydrogen peroxide (H₂O₂) to metal gallium (Ga) via a hydrothermal route at a low temperature (100 °C) and without any surfactant. β-Ga₂O₃ nanopowders are achieved directly in an autoclave when the initial molar ratio of Ga to O is 1:4. Combination of X-ray diffraction (XRD) and fluorescence analysis are employed to characterize the resulting nanopowders. Detailed results are discussed.     

电解方法制备纳米金属粉末的研究进展

介绍了国内外用电解方法制备纳米金属粉末的发展历程及研究现状。比较了各种传统和新型电解方法在制备纳米金属粉末方面的优缺点,并分析和探讨了电解法制备活泼纳米金属粉末的发展动向。分析认为,电解法与超声波、有机溶剂、离子液体、隔膜等技术的结合,将会成为一种高效、低成本、适合连续工业化生产的制备纳米金属粉末的新方法。     

Low temperature synthesis of Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 nanopowders by solution based auto combustion method

Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BZT–BCT) nanopowders were synthesized by citrate–nitrate auto combustion method using TiO₂ as a source of titanium. The formation mechanism, phase evolution and particle size were investigated using thermal analysis, Fourier transform infra-red spectroscopy, X-ray diffraction, Raman spectroscopy and transmission electron microscope. The molar ratio of metal, citric acid and ethylene diamine tetraacetic acid was kept at 1:1.5:0.1 and pH ~ 9, to get a uniform and complete combustion. Perovskite BZT–BCT was formed in the as-burnt state (280 °C), though calcination at 700 °C is required to remove a small amount of impurities, which is significantly lower than the solid state reaction method. The particle size of BZT–BCT powder was in the range of 40–70 nm.     

多铁材料BiFeO3的制备与表征

以硝酸铁和硝酸铋为反应物,柠檬酸为络合剂,硝酸为催化剂,采用柠檬酸溶胶–凝胶法制备粒径分布均匀的多铁性材料BiFeO3纳米粉体,通过TG-DSC、XRD、FT-IR、SEM及AFM等手段对样品的结构、形貌及纯净度进行表征.研究结果表明,在溶胶过程中前驱液的pH值以及干凝胶的煅烧温度等合成条件对BiFeO3纳米粉体的制备和纯净程度都有一定的影响,最佳的合成条件是前驱溶液的pH=7～8,干凝胶的煅烧温度为600℃.在该条件下得到的BiFeO3纳米粉体中无杂相Bi25FeO40和Bi2Fe4O9等,纳米颗粒尺寸在100 nm左右,分散性良好,饱和磁化强度Ms=1.08 A·m2/kg,剩余磁化强度Mr=0.13 A·m2/kg,矫顽力Hc=15.76 kA/m.     

Emerging 2D Copper-Based Materials for Energy Storage and Conversion: A Review and Perspective

2D materials have shown great potential as electrode materials that determine the performance of a range of electrochemical energy technologies. Among these, 2D copper-based materials, such as Cu–O, Cu–S, Cu–Se, Cu–N, and Cu–P, have attracted tremendous research interest, because of the combination of remarkable properties, such as low cost, excellent chemical stability, facile fabrication, and significant electrochemical properties. Herein, the recent advances in the emerging 2D copper-based materials are summarized. A brief summary of the crystal structures and synthetic methods is started, and innovative strategies for improving electrochemical performances of 2D copper-based materials are described in detail through defect engineering, heterostructure construction, and surface functionalization. Furthermore, their state-of-the-art applications in electrochemical energy storage including supercapacitors (SCs), alkali (Li, Na, and K)-ion batteries, multivalent metal (Mg and Al)-ion batteries, and hybrid Mg/Li-ion batteries are described. In addition, the electrocatalysis applications of 2D copper-based materials in metal–air batteries, water-splitting, and CO₂ reduction reaction (CO₂RR) are also discussed. This review also discusses the charge storage mechanisms of 2D copper-based materials by various advanced characterization techniques. The review with a perspective of the current challenges and research outlook of such 2D copper-based materials for high-performance energy storage and conversion applications is concluded.     

Salt-assisted combustion synthesis of highly dispersed perovskite NdCoO3 nanoparticles

Highly dispersed perovskite NdCoO₃ nanoparticles with an average particle size of about 9 nm have been successfully prepared by a novel salt-assisted combustion process. The effects of NaCl content and calcination temperature on the characteristics of the products were investigated by XRD, TEM and BET nitrogen adsorption. The facile introduction of NaCl in the conventional combustion synthesis process was found to result in the formation of well-dispersed perovskite nanoparticles and increase specific surface area of the resultants from 1.70 to 43.22 m²·g^− 1. A mechanism scheme was proposed to illustrate the possible formation processes.     

Elaborately Modified BiVO4 Photoanodes for Solar Water Splitting

Photoelectrochemical (PEC) cells for solar‐energy conversion have received immense interest as a promising technology for renewable hydrogen production. Their similarity to natural photosynthesis, utilizing sunlight and water, has provoked intense research for over half a century. Among many potential photocatalysts, BiVO₄, with a bandgap of 2.4–2.5 eV, has emerged as a highly promising photoanode material with a good chemical stability, environmental inertness, and low cost. Unfortunately, its charge transport properties are modest, at most a hole diffusion length (L_p) of ≈70 nm. However, recent rapid developments in multiple modification strategies have elevated it to a position as the most promising metal oxide photoanode material. This review summarizes developments in BiVO₄ photoanodes in the past 10 years, in which time it has continuously broken its own performance records for PEC water oxidation. Effective modification techniques are discussed, including synthesis of nanostructures/nanopores, external/internal doping, heterojunction fabrication, surface passivation, and cocatalysts. Tandem systems for unassisted solar water splitting and PEC production of value‐added chemicals are also discussed.     

Solution Processed Metal Oxide High‐κ Dielectrics for Emerging Transistors and Circuits

The electronic functionalities of metal oxides comprise conductors, semiconductors, and insulators. Metal oxides have attracted great interest for construction of large‐area electronics, particularly thin‐film transistors (TFTs), for their high optical transparency, excellent chemical and thermal stability, and mechanical tolerance. High‐permittivity (κ) oxide dielectrics are a key component for achieving low‐voltage and high‐performance TFTs. With the expanding integration of complementary metal oxide semiconductor transistors, the replacement of SiO₂ with high‐κ oxide dielectrics has become urgently required, because their provided thicker layers suppress quantum mechanical tunneling. Toward low‐cost devices, tremendous efforts have been devoted to vacuum‐free, solution processable fabrication, such as spin coating, spray pyrolysis, and printing techniques. This review focuses on recent progress in solution processed high‐κ oxide dielectrics and their applications to emerging TFTs. First, the history, basics, theories, and leakage current mechanisms of high‐κ oxide dielectrics are presented, and the underlying mechanism for mobility enhancement over conventional SiO₂ is outlined. Recent achievements of solution‐processed high‐κ oxide materials and their applications in TFTs are summarized and traditional coating methods and emerging printing techniques are introduced. Finally, low temperature approaches, e.g., ecofriendly water‐induced, self‐combustion reaction, and energy‐assisted post treatments, for the realization of flexible electronics and circuits are discussed.     

Flash Solid–Solid Synthesis of Silicon Oxide Nanorods

1D silicon‐based nanomaterials, renowned for their unique chemical and physical properties, have enabled the development of numerous advanced materials and biomedical technologies. Their production often necessitates complex and expensive equipment, requires hazardous precursors and demanding experimental conditions, and involves lengthy processes. Herein, a flash solid–solid (FSS) process is presented for the synthesis of silicon oxide nanorods completed within seconds. The innovative features of this FSS process include its simplicity, speed, and exclusive use of solid precursors, comprising hydrogen‐terminated silicon nanosheets and a metal nitrate catalyst. Advanced electron microscopy and X‐ray spectroscopy analyses favor a solid–liquid–solid reaction pathway for the growth of the silicon oxide nanorods with vapor–liquid–solid characteristics.     

金属基复合材料(MMCs)的原位制备

本文概述了几种原位法制备颗粒增强金属基复合材料 (MMCs)的基本原理和过程 ,包括原位凝固自生法、VLS法、自蔓延高温合成法 (SHS)、接触反应法、固 液反应法、混合盐反应法及直接氧化法 ,简述了原位复合材料的基本性能 ,并提出了今后的发展方向     

Synthesis and consolidation of iron nanopowders

A microwave plasma processing technique was used to synthesize iron nanopowders. The average particle size of these powders was ~10 nm and the surface area was measured to be 42m²/g. Powder production rates as high as 50 gm/hour were achieved. Magnetic property measurements on iron nanopowders yielded coercivities as high as 60 kA/m at 4 K, which decreased to ~0 A/m (a superparamagnetic transition) at room temperature. In this paper, the microwave plasma processing technique has been compared with other nanopowder synthesis techniques. Since the successful application of nanomaterials depends highly on the processing technology, results from consolidation studies on iron nanopowders are also presented. Iron nanopowders were consolidated to study performance parameters such as density, grain growth and other morphological changes. The nanopowder was consolidated using Plasma Pressure Consolidation (P²C) technique to 95% density, at a temperature and pressure of 850 °C and 63 MPa respectively. Microwave plasma synthesis is capable of producing metallic and ceramic nanopowders, which will sustain interest in research areas including magnetic storage, nano-fabrication of electronic materials and nanoglass, besides the field of catalysis.     

Ox/Red-controllable combustion synthesis of foam-like PrFeO3 nanopowders for effective photo-Fenton degradation of methyl violet

Praseodymium orthoferrite nanopowders were synthesized by Red/Ox-controlled glycine-nitrate combustion followed by heat treatment. It was found that the temperature of PrFeO₃ formation from amorphous combustion products varied from 612 °C to 647 °C, depending on the initial reaction solution. The purity, crystallite size, morphology and specific surface area of ??the samples were affected by the glycine-nitrate ratio (G/N). At nonstoichiometric G/N (more or less than 0.6), amorphous or low crystalline phases were formed. Also, at these ratios, nanopowders had the smallest crystallite size before (17.4–36.2 nm) and after (45.3–49.2 nm) heat treatment. All powders were characterized by developed porous morphology with a specific surface area of ??2.9–11.9 m²/g and a band gap of 2.07–2.13 eV. The results of ⁵⁷Fe Mössbauer spectroscopy confirmed magnetically ordered state of PrFeO₃ nanocrystals with 1 mol % of amorphous component, associated with the combustion mode of a glycine-nitrate solution. The photocatalytic activity of PrFeO₃ was evaluated by the rate of decomposition of methyl violet (MV) in the presence of peroxide under the action of visible light.     

纳米石墨的制备方法(英文)

简要概述了现有的纳米石墨制备方法,这些方法从材料来源上可以分为2类,一类由鳞片石墨来制备,另一类由富碳材料合成.由鳞片石墨制备纳米石墨的方法主要有球磨法、超声波粉碎法、爆轰裂解法和电化学插层法;由富碳材料合成纳米石墨的方法主要包括爆轰合成法、化学气相沉积法、激光脉冲沉积法和化学合成法.     

A novel method for preparation of barium strontium titanate nanopowders

Ba_0.6Sr_0.4TiO₃ (BST) nanopowders have been prepared using the modified citrate method with ammonium nitrate as a combustion promoter, and the formation mechanism, phase evolution, and particle size have been investigated using TG/DTA, XRD, and SEM. It is found that the peaks of barium carbonate disappear when the precursor powders are calcined at 650 °C. The fine particles of the nanopowders calcined with the combustion promoter addition are homogeneous and well-dispersed and their narrow size distribution is about 60-90 nm. Comparatively, the particles of the powder calcined without the ammonium nitrate addition are inhomogeneous, with an evident agglomeration. The mechanism for the above results is attributed to that a reaction can generate soft and loose precursor powders by the adoption of ammonium nitrate, and hence a pure BST phase could occur at the low synthesis temperature of 650 °C.     

Nanosheets of Nonlayered Aluminum Metal–Organic Frameworks through a Surfactant‐Assisted Method

During the last decade, the synthesis and application of metal–organic framework (MOF) nanosheets has received growing interest, showing unique performances for different technological applications. Despite the potential of this type of nanolamellar materials, the synthetic routes developed so far are restricted to MOFs possessing layered structures, limiting further development in this field. Here, a bottom‐up surfactant‐assisted synthetic approach is presented for the fabrication of nanosheets of various nonlayered MOFs, broadening the scope of MOF nanosheets application. Surfactant‐assisted preorganization of the metallic precursor prior to MOF synthesis enables the manufacture of nonlayered Al‐containing MOF lamellae. These MOF nanosheets are shown to exhibit a superior performance over other crystal morphologies for both chemical sensing and gas separation. As revealed by electron microscopy and diffraction, this superior performance arises from the shorter diffusion pathway in the MOF nanosheets, whose 1D channels are oriented along the shortest particle dimension.