1,721,410 research outputs found
Synthesis and processing of silicon nitride and related materials using preceramic polymer and non-oxide sol-gel approaches
No full textThe use of preceramic polymer and sol-gel processing methods in the production of silicon nitride and a number of related materials is reviewed. Amorphous ceramics in this system, which may contain additional carbon, boron and other elements, have a number of promising and/or useful high temperature properties. These include good mechanical properties and oxidation resistance at temperatures that can exceed 1500?°C with some materials, but also useful charge storage capability, catalytic activity and semiconducting or optical properties after dopin
Materials synthesis using oxide free sol–gel systems
No full textThis tutorial review highlights some active areas of research into non-oxide sol–gel chemistry. These aim to capture some of the advantages of methods developed mainly with oxides for a new generation of functional materials based on main group and metal nitrides, and semiconducting chalcogenides. Sol–gel processing has a long track record in producing useful materials for optical, magnetic, electrical, catalytic and structural applications. Controlled morphologies can be produced on all lengths scales, from ordered mesoporous arrays to thin films, fibres and monoliths. Hence there is an opportunity to produce new morphologies in non-oxides and hence new applications of these material
Stabilisation of FeCoNiCuPt high-entropy alloy nanoparticles by surface capping
No full textHigh-entropy alloys (HEA) are a distinct class of materials made up of multiple principal components (≥5) in near-equimolar ratios, resulting in extraordinary properties, including high catalytic activity, corrosion and oxidation resistance, and tunable magnetic properties. In nanoparticle form, these alloys are highly promising for a variety of advanced applications such as catalysis, magnetic storage, and biomedical technology [Zoubi et al., Nano Energy, 2023, 110, 108362]. This study used isolating medium-assisted solid-state reaction to synthesise FeCoNiCuPt HEA nanoparticles with ultrafine NaCl particles as the isolating medium [Meng et al., Mater. Adv., 2024, 5, 719]. The nanoparticles were stabilised with a range of hydrophobic and hydrophilic capping agents such as polyethylinimine, Polyvinylpyrrolidone, stearic acid, octadecylamine etc, introduced before or after the removal of the isolating medium. The formation of single-phase nanoparticles & chemical composition of FeCoNiCuPt was validated by X-ray diffraction & energy-dispersive X-ray spectroscopy. Transmission electron microscopy and dynamic light scattering were used to determine particle sizes, effective capping agent thickness, and particle stability. The results highlight the successful synthesis of FeCoNiCuPt nanoparticles, effect of capping agents on the control of particle size, and the stability of capped nanoparticle suspensions in water and organic solvents. The study emphasises the importance of selecting the appropriate capping agent to maintain nanoparticle stability and prevent agglomeration
Use of low temperature solvothermal reactions in the synthesis of nanocrystalline tantalum nitrides including nanorods
No full textSolvothermal reactions of TaCl5 with LiNH2 or Mg3N2 lead to amorphous products at temperatures up to 500 °C. Post-reaction annealing under nitrogen yields crystalline products with Ta3N5 (LiNH2) and TaN (Mg3N2) structures. When these reactions are carried out with LiNH2 in refluxing mesitylene, rods of Ta3N5-structured material are obtained. Using commercial LiNH2 these have dimensions of 5 × 200 nm but are contaminated with LiTaO3. With high purity LiNH2 a black oxide-free but carbon-containing material presents as rods of 20–50 nm length. Higher temperature reactions in an autoclave lead to isotropic nanocrystals of ca. 10 nm diameter of a nitrogen-deficient or carbide-substituted Ta3N5-type material. Carbon incorporation is attributed to solvent decomposition at the temperatures required for the reactions. The TaN derived from reactions with Mg3N2 consists of nanoparticles of 6–8 nm in diameter
Synthesis and applications of nanocrystalline nitride materials
No full textMost current applications of nitride materials are based on films deposited from the vapour phase. However, a series of other potential uses of nitrides have been envisaged based on properties such as higher conductivity than oxides, hardness, inertness and catalytic or electrochemical activity. Many current applications use nanocrystalline nitrides and increasingly the size and shape dependent properties are of interest. This feature article reviews synthesis methods to make nanocrystalline and nanoparticulate nitride materials, plus it discusses the current applications and several potential ones
Solution phase preparative routes to nitride morphologies of interest in catalysis
No full textThis review assesses the track record and prospects of non-oxide sol–gel and solvothermal routes to nitride materials for use in catalysis. There is a strongly developing body of synthesis methods that yield highly porous materials, some with engineered pore structures, nanocrystalline materials with high surface areas and anisotropic nanocrystals that have their surface area tuned to a particular crystal face. Most of the existing catalytic work on such solution-derived nitrides has focussed on utilising base properties due to surface bound amide and imide groups in silicon (imido)nitride compositions, but there are opportunities to extend these methods to other interesting nitride compositions
Synthesis of nanocomposites containing tantalum or molybdenum nitride with silicon imidonitride
No full textAmmonolysis of solutions containing tetrakis(methylamido)silane and either pentakis(dimethylamido)tantalum(V) or tetrakis(dimethylamido)molybdenum(IV) results in gels that can be pyrolysed in ammonia to yield metal-containing amorphous silicon nitride compositions. The tantalum-containing samples remain amorphous to 1000 °C, though there is evidence of some metal clustering, whereas the molybdenum-containing samples crystallise molybdenum nitride nanorods at 1000 °C
Direct solvothermal synthesis of early transition metal nitrides
No full textSolvothermal reactions of TaCl5 with LiNH2 in benzene result in nanocrystalline Ta3N5 at 500 or 550 °C. The 25 nm Ta3N5 particles have a band gap of 2.08?2.10 eV. The same reactions in mesitylene resulted in a higher crystallization temperature and large amounts of carbon incorporation due to solvent decomposition. Reactions of Ta(NMe2)5 with LiNH2 under the same conditions resulted in TaN. Rocksalt-type MN phases are obtained for Zr, Hf, or Nb when their chlorides (ZrCl4, HfCl4, or NbCl5) or dialkylamides (M(NEtMe)4, M = Zr, Hf) are reacted with LiNH2 under similar conditions. With the amides, there is some evidence for nitrogen-rich compositions (HfN>1), and carbon is incorporated into the products through pyrolysis of the dialkylamide groups
Phase-transforming electrodes
No full textLithium iron phosphate (LiFePO4) is one of the cheapest and safest materials used as the positive electrode of the lithium ion battery. Since its discovery in 1996 (1), the material has been a subject of debate regarding its outstanding performance in high-rate discharge-charge cycling applications. The surprisingly high performance is attained despite the miscibility gap (the composition range at which solutions become supersaturated and tend to separate into concentrated and dilute phases—like clear honey that partially crystallizes in the refrigerator) and phase transformation that complicates lithium insertion and extraction in this material. Such properties are typically associated with slow rates of electrical charge and discharge and even structural damage during cycling. On page 1480 of this issue, Liu et al. (2) provide experimental evidence to support new theoretical models (3, 4) that bypass the miscibility gap so that the phase transformation need not happen after all. <br/
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