Fabrication of Si3N4/SiC nanocomposites toughened by in-situ formed low-dimensional nanostructures

We report the fabrication of Si₃N₄/SiC nano/nano-composite reinforced by single-crystal low-dimensional nanostructures via spark plasma sintering of nanocomposite powders containing in-situ formed Si₃N₄ nanowires/nanobelts. The fabricated nanocomposite is analyzed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and selective area electron diffraction. The results show that the in-situ formed Si₃N₄ nanowires/nanobelts are uniformly distributed within the matrix. Such a nanocomposite could exhibit improved mechanical properties, due to the superior mechanical properties and uniform distribution of the nano-reinforcements.     

A simple approach to controllably grow network-like branched single-crystalline Si3N4 nanostructures

We reported a simple, large-scale, and controllable growth method for network-like branched single-crystalline Si₃N₄ nanostructures by catalyst-assisted pyrolysis of a polysilazane. The templates were a silicon wafer deposited with a 5 nm Fe film. The processes simply involved in thermal cross-linking of the polymer precursor, crushing of the solidified preceramic polymer chunks into fine powder, and thermal pyrolysis of the powder under the protection of ultra-high purity nitrogen. The collected white network-like branched nanostructures were formed through “metal-absorption on the surface of nanostructures” model by vapor-liquid-solid mechanism. Microstructure characterizations indicate that the nanostructures are single-crystalline hexagonal α-Si₃N₄. The reaction mechanism of Si₃N₄ nanonetworks was also proposed.     

Controlled synthesis of CuO nanostructures by a simple solution route

A simple solution route has been developed to prepare nanostructured CuO with Cu(NO₃)₂·3H₂O and NaOH as starting materials. CuO nanoribbons or nanorods and their assemblies into hierarchical structures have been synthesized, respectively, by controlling the molar ratio of NaOH to Cu(NO₃)₂, reaction temperature and the concentration of the starting NaOH solution. Experiments demonstrate that the molar ratio of NaOH to Cu(NO₃)₂ is an important parameter which may decide whether CuO exists in nanoribbons (nanorods) or assemblies into hierarchical structures. Whether Cu(NO₃)₂ is dissolved in ethanol or water also influences the formation of monodispersed CuO nanoribbons (nanorods). The growth mechanism of these nanostructures is discussed. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy (HRTEM) and their optical absorption spectra were also studied.     

Sliding friction and wear behaviors of plasma sprayed aluminum–bronze coating in artificial seawater

The friction and wear behaviors of plasma sprayed aluminum–bronze (CuAl) coating sliding against silicon nitride (Si₃N₄) in artificial seawater were investigated and compared with those in pure water and dry sliding. The morphologies of the worn surfaces were analyzed by three‐dimensional non‐contact surface mapping and scanning electron microscopy. Moreover, chemical states of the tribochemical products of CuAl/Si₃N₄ in seawater were characterized by X‐ray photoelectron spectroscopy. Results show that the plasma sprayed CuAl coating possessed a specific wear rate (in order of 10^?7 mm³/Nm) in seawater more than 600 times smaller than that in dry sliding due to the great alleviation in abrasion wear and splats delamination. Besides, the CuAl/Si₃N₄ had a friction coefficient of 0.06 in seawater, significantly lower and more stable than those in pure water and dry sliding. The tribochemical products of CuAl/Si₃N₄ in seawater, which were proved to be silica, alumina, and their hydrates, transformed into a loosened wear‐debris layer under the coagulation effect of the seawater and dominated the excellent lubrication state in artificial seawater. Copyright © 2014 John Wiley & Sons, Ltd.     

Growth,characterization and interfacial reaction of magnetron sputtered Pt/CeO2 thin films on Si and Si3N4 substrates

Growth of magnetron sputtered Pt/CeO₂ thin films on Si and Si₃N₄ were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS). Interaction of Pt/CeO₂ films with Si on Si and Si₃N₄ substrates was extensively investigated by XPS. XRD studies show that films are oriented preferentially to (200) direction of CeO₂. XPS results show that Pt is mainly present in +2 oxidation state in Pt/CeO₂/Si film, whereas Pt⁴⁺ predominates in Pt/CeO₂/Si₃N₄ film. Concentration of Pt⁴⁺ species is more than four times on Si₃N₄ substrate as compared with that on Si. Ce is present as both +4 and +3 oxidation states in Pt/CeO₂ films deposited on Si and Si₃N₄ substrates, but concentration of Ce³⁺ species is more in Pt/CeO₂/Si film. Interfacial reaction between CeO₂ and Si substrate is controlled in the presence of Pt. Pt/Ce concentration ratio decreases in Pt/CeO₂/Si₃N₄ film upon successive sputtering, whereas this ratio decreases initially and then increases in Pt/CeO₂/Si film. Copyright © 2015 John Wiley & Sons, Ltd.     

The Role of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgO Additives on the Photoluminescence Properties of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Nanoparticles

The current research addressed synthesizing and studying photoluminescence studies of β-Si₃N₄ nanoparticles. The effect of MgO and Y₂O₃ as the typical additives on photoluminescence behaviour was evaluated. The β-Si₃N₄ with MgO and Y₂O₃ additive specimens were fabricated by a solid state technique (ball-milled method). The as-prepared products were characterized by X-ray diffraction technique, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman analysis. The results showed that after ball-milled process, hexagonal β-Si₃N₄ with MgO or Y₂O₃ as the additives with the size distribution of 45–50 nm was obtained. The optical properties of the as-synthesized product were also investigated by photoluminescence and diffuse reflection spectroscopy. The obtained results confirmed that employing MgO as an additive, in comparison to the Y₂O₃, could enhance emission properties in the synthesized silicon nitride nanoparticles. The obtained results also showed that MgO–Si₃N₄ pair acted as FRET system to enhance the emission intensity of β-Si₃N₄ nanoparticles.     

Silicon nitride nanofibers produced by the pyrolysis of SiCl<Subscript>4</Subscript> in H<Subscript>2</Subscript> and N<Subscript>2</Subscript> media

The synthesis of fibrous Si₃N₄ nanostructures by gas-phase chemical deposition during the pyrolysis of silicon tetrachloride in a hydrogen and nitrogen atmosphere was investigated. It was shown that the products contained both amorphous Si₃N₄ nanofibers and their α and β phases both with and without a silicon coating. In addition to the Si₃N₄ nanofibers the products also contained nanoribbons. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 81–84, March–April, 2007.     

Synthesis of stoichiometric Y2Si2O7 powders by sonohydrolysis-assisted sol–gel route

Stoichiometric compounds Y₂Si₂O₇ were synthesised by an intensified sonohydrolysis–condensation reaction using hydrate yttrium nitrate and tetraethyl orthosilicate as starting materials. The resulting powders were characterized by means of thermo gravimetric–differential thermal analysis, high temperature X-ray diffraction, electron probe microanalysis, scanning electron microscopy, laser scattering particle size analyzer, N₂ adsorption–desorption isotherms measurements and specific surface area analysis. We found that the phase formation and texture were very dependent on the sol–gel process parameters such as starting compounds, catalyst, water content, molar ratios of Y³⁺/Si⁴⁺ and other experiment conditions. The combined effects of polyethylene glycol and acetic acid on the prepared powders have been discussed. The investigation on thermal stability of the obtained disilicate is also presented for potential high temperature membrane or thermal barrier/environmental barrier coating application.     

Facile hydrothermal synthesis of 3D hierarchical Bi2SiO5 nanoflowers and their luminescent properties

Facile hydrothermal synthesis of novel hierarchical flowerlike Bi₂SiO₅ nanostructures consisting of single-crystal nanosheets is reported using polyvinylpyrrolidone (PVP, K30) as capping reagent in the presence of NaOH. The obtained products are systematically characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. Control experiments are carried out to investigate various factors that affect the morphology and size of the products. The results indicate that the nucleation and growth of the flowerlike nanostructures are dominated by a nucleation–dissolution–recrystallization growth mechanism. It is demonstrated that the concentrations of PVP and NaOH play important roles in the formation of the hierarchical nanoflowers. Moreover, the room-temperature photoluminescence properties of the Bi₂SiO₅ nanoflowers are also investigated.     

Preparation and properties of Ni–Co–P/nano‐sized Si3N4 electroless composite coatings

Ni–Co–P/nano‐sized Si₃N₄ composite coating was successfully fabricated on aluminum alloys by electroless plating in this work. The surface and cross‐sectional morphologies, composition, microstructure, microhardness, friction and wear behavior of deposits were investigated with SEM, EDS, XRD, Vickers hardness and high‐speed reciprocating friction, respectively. It was found that a Ni–Co–P/nano‐sized Si₃N₄ composite coating on aluminum alloy substrate is uniform and compact. The existence of nano‐sized Si₃N₄ particles in the Ni–Co–P alloy matrix causes a rougher surface with a granular appearance, and increases the microhardness but decreases the friction coefficients and wear rate of electroless coatings. Meanwhile, the effects of heat treatment at 200, 300, 400 and 500 °C for 1 h on the hardness and tribological properties were researched. It is revealed that both of the microhardness and tribological properties of Ni–Co–P coatings and Ni–Co–P/Si₃N₄ composite coatings increase with the increase of heating temperature in the range of 200–400 °C, but show different behavior for the two coatings after annealing at 500 °C. Copyright © 2011 John Wiley & Sons, Ltd.     

On nanocomposite fabrication: using rheology to characterize filler/polymer interactions in epoxy-based nanocomposites

The interactions that occur between an amorphous silicon nitride (Si₃N₄) nanofiller and an epoxy matrix are examined, as revealed by rheological changes in a diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin prior to curing and thermal analysis, scanning electron microscopy, and dielectric spectroscopy of the resulting amine-cured systems. The results show that isothermally heating the as-received Si₃N₄ in DGEBA at 100 °C leads to increases in the viscosity of the mixture. Analysis of rheological data obtained from unfilled, as-received Si₃N₄-filled, and calcined Si₃N₄-filled epoxy systems leads us to interpret this increase in viscosity as arising from reactions between epoxide groups of the DGEBA and nanoparticle surface groups, notably involving surface amines, which are stimulated by the elevated temperature. The extent of this filler/resin reaction depends on the material processing protocol used, particularly prior calcination of the Si₃N₄ and the temperature and duration of nanoparticle/DGEBA mixing. Glass transition temperature data show that cured samples prepared using different methods have significantly different glass transition temperatures, which is a consequence of the epoxide/amine stoichiometric imbalances that result from prior reactions between the Si₃N₄ and the DGEBA. Consistent behavior was observed in the dielectric response. These results demonstrate that ultimate macroscopic properties of Si₃N₄/epoxy nanocomposites are critically affected by details of the processing protocol. Furthermore, we infer that, by using controlled prior calcination of the Si₃N₄, it is may be possible to vary the initial surface chemistry of the nanoparticles so as to adjust their reactivity with epoxy-containing moieties. Here, this is exemplified using only two somewhat extreme thermal treatments and a bifunctional DGEBA-type compound but, we suggest, that the concept may be extended to many other mono- and polyfunctional epoxy-containing compounds in order to generate a wide range of different grafted nanoparticle systems. This strategy may provide a versatile means of adjusting the surface chemistry of inorganic nitride nanoparticles, in order to tailor their surface chemistry and thereby modify resulting nanocomposite properties.     

Deep Oxidation of Methane on a Pt/Si3N4 Catalyst

We have studied platinum catalysts supported on silicon nitride Si₃N₄ in the process of deep oxidation of methane. We have used transmission electron microscopy and X-ray photoelectron spectroscopy to study the surface properties of the Pt/Si₃N₄ samples before and after the catalytic reaction. We have established that the metallic platinum particles in freshly prepared systems are characterized by average sizes of 1.7-5.3 nm, while after the catalytic reaction we observe formation of Pt crystallites up to 30-70 nm in size. We hypothesize that the observed deactivation of platinum catalysts in deep oxidation of methane is connected with crystallization of the metallic particles and their entrainment with the reaction products during catalysis.     

Controllable growth of silver nanostructures by a simple replacement reaction and their SERS studies

Hierarchical silver nanostructures, consisting of dendritic (symmetric branched) and fractal patterns (randomly ramified), were synthesized very easily by dropping a droplet of AgNO₃-HF solution on silicon wafers. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and open circuit potential-time (Ocp-t) measurement demonstrated that the two nanostructures converted with the reaction composition. The structural evolution was tentatively explained with the theory that oriented growth was determined by the anisotropy of the solid–liquid interfacial energy and the oriented attachment-based aggregation mechanism. Results on surface-enhanced Raman scattering (SERS) signals of the silver films with hierarchical nanostructures demonstrate that SERS is sensitive to silver nanostructures.     

Upgraded charge transport in g-C3N4 nanosheets by boron doping and their heterojunction with 3D CdIn2S4 for efficient photodegradation of azo dye

The facilitation of charge transport toward the targeted chemical reaction is a challenging task for two-dimensional (2D) nanomaterials. We demonstrate the effectiveness of two different strategies, non-metal doping and heterojunction formation, to adjust the electronic and molecular structures of g-C₃N₄ nanosheets (CN), which could widen the visible-light response and improve the photo-induced electron–hole separation. The g-C₃N₄ nanosheets containing impurity levels (boron doping (BCN)) were prepared by a high-temperature solid-state reaction. Additionally, by anchoring the 3D dichalcogenide structures (CdIn₂S₄) elicited by a wet chemical route, hybrid BCN/CdIn₂S₄ nanostructures were obtained. The resulting BCN/CdIn₂S₄ (BCN–CIS3) nanostructures exhibited an excellent degradation efficiency (95%) for methyl orange (MO) compared to pristine g-C₃N₄ nanosheets (CN) (28%) and boron-doped g-C₃N₄ (BCN) (35%). All the optimized photocatalysts were thoroughly characterized using various techniques and investigated for comparative structural, optical, morphological, and catalytic properties. Our results reveal that introducing boron atoms into the lattice of g-C₃N₄ nanosheets leads to reduction in the band-gap energy and rapid electron transfer. The formation of heterojunctions with the 3D CdIn₂S₄ further assists in improving the degradation efficiency by minimizing the undesired electron–hole recombination, as confirmed by time-resolved photoluminescence (TRPL) analysis. This work proposes feasible strategies and their synergy to develop innovative materials for sustainable energy conversion and environmental remediation applications.     

A Hierarchical Nanostructured Carbon Nanofiber–In2S3 Photocatalyst with High Photodegradation and Disinfection Abilities Under Visible Light

Photocatalytic degradation of pollutants under visible light provides a new door to solve the water contamination problem by utilizing free and renewable sunlight. The search for highly efficient photocatalysts with hierarchical nanostructures remains crucial for accessing this new door. In this work, a new hierarchical nanostructured photocatalyst is designed and synthesized, for the first time, by anchoring In₂S₃ flower‐like nanostructures on non‐woven carbon nanofiber (CNF). The nanostructures of these CNF–In₂S₃ composites were fine‐tuned, with the aim of achieving the highest photocatalytic activity under visible light. The formation mechanism of the hierarchical nanostructure is also investigated. The results indicate that the optimized hierarchical CNF–In₂S₃ photocatalyst is superior in photodegradation and disinfection efficiency to that of pure In₂S₃ under visible‐light irradiation. The prominent photocatalytic activities of these hierarchical CNF–In₂S₃ photocatalysts can be attributed to the excellent properties of enhanced light absorption, large surface area, and efficient charge separation, which are all derived from the special three‐dimensional hierarchical nanostructures. Therefore, this work presents the great potential of this hierarchical nanostructured CNF–In₂S₃ photocatalyst in practical environmental remediation fields.     

Copper Oxide Nanoparticles with Graphitic Carbon Nitride for Ultrasensitive Photoelectrochemical Aptasensor of Bisphenol A

In this work, g‐C₃N₄, CuO and g‐C₃N₄/CuO?X (where × can be 3, 6, or 9) were synthesized through hydrothermal and calcination methods and used to fabricate photoelectrochemical (PEC) aptasensor for detection of bisphenol A (BPA). CuO nanoparticles covered with g‐C₃N₄ were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The aptasensor based on g‐C₃N₄/CuO‐6 possessed high PEC activity due to its good conductivity and low electron recombination rate. PEC experiments demonstrate that the aptasensor based on g‐C₃N₄/CuO‐6 exhibits a broad linear range towards BPA from 0.02–10 ng L^?1 and 50–1200 ng L^?1 and reveals superior stability, selectivity and repeatability. Thus, g‐C₃N₄/CuO‐6 composite is a promising material for the determination of BPA in PEC field and has commercially viable.     

Neue Vertreter des Er6[Si11N20]O‐Strukturtyps Hochtemperatur‐Synthesen und Kristallstrukturen von Ln(6+x/3)[Si(11–y)AlyN(20+x–y)]O(1–x+y) mit Ln = Nd,Er, Yb,Dy und 0 ≤ x ≤ 3, 0 ≤ y ≤ 3

New Representatives of the Er₆[Si₁₁N₂₀]O Structure Type. High‐Temperature Synthesis and Single‐Crystal Structure Refinement of Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) with Ln = Nd, Er, Yb, Dy and 0 ≤ x ≤ 3, 0 ≤ y ≤ 3 According to the general formula Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) (0 ≤ x ≤ 3, 0 ≤ y ≤ 3) four nitridosilicates, namely Er₆[Si₁₁N₂₀]O, Yb_6.081[Si₁₁N_20.234]O_0.757, Dy_0.33Sm₆[Si₁₁N₂₀]N, and Nd₇[Si₈Al₃N₂₀]O were synthesized in a radiofrequency furnace at temperatures between 1300 and 1650 °C. The homeotypic crystal structures of all four compounds were determined by single‐crystal X‐ray diffraction. The nitridosilicates are trigonal with the following lattice constants: Er₆[Si₁₁N₂₀]O: a = 978.8(4) pm, c = 1058.8(3) pm; Yb_6.081[Si₁₁N_20.243]O_0.757: a = 974.9(1) pm, c = 1055.7(2) pm; Dy_0.33Sm₆[Si₁₁N₂₀]N: a = 989.8(1) pm, c = 1078.7(1) pm; Nd₇[Si₈Al₃N₂₀]O: a = 1004.25(9) pm, c = 1095.03(12) pm. The crystal structures were solved and refined in the space group P31c with Z = 2. The compounds contain three‐dimensional networks built up by corner sharing SiN₄ and AlN₄ tetrahedra, respectively. The Ln³⁺ and the “isolated” O^2– ions are situated in the voids of the structures. According to Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) an extension of the Er₆[Si₁₁N₂₀]O structure type has been found.     

Phase equilibria in the Sm–Al–Si system at 500 °C

The isothermal section at 500 °C of the Sm–Al–Si system has been experimentally investigated by using scanning electron microscopy, electron microprobe analysis and X-ray powder diffraction. Four intermetallic compounds have been confirmed: τ₁-SmAl₂Si₂ (hP5-CaAl₂Si₂ type), τ₂-SmAl_xSi_1?x (tI12-Th₂Si type), τ₄-SmAl_0.5Si_0.5 (oS8-CrB type) and τ₅-Sm₆Al₃Si (tI80-Tb₆Al₃Si type). A new ternary intermediate has been found: τ₃-Sm₄Al₃Si₃ that crystallizes orthorhombic isostructural with Pr₄Al₃Ge₃.     

Radiation‐Induced Synthesis of Nanostructured Conjugated Polymers in Aqueous Solution: Fundamental Effect of Oxidizing Species

Synthesis of conjugated poly(3,4‐ethylenedioxythiophene) (PEDOT) polymers is achieved through the radiolysis of N₂O‐saturated aqueous solutions of 3,4‐ethylenedioxythiophene by using two different oxidizing species: HO^. (hydroxyl) and N₃^. (azide) radicals. Both oxidative species lead to self‐assembled polymers that are evidenced in solution by cryotransmission electron microscopy and UV/Vis absorption spectroscopy and, after centrifugation and deposition, by scanning electron microscopy and attenuated total reflectance FTIR techniques. Whereas HO^. radicals lead to PEDOT‐OH globular nanostructures with hydrophilic properties, N₃^. radicals enable the formation of amphiphilic PEDOT‐N₃ fibrillar nanostructures. These results, which highlight the differences in the intermolecular interaction behaviors of the two kinds of PEDOT polymers, are discussed in terms of polymerization mechanisms.     

Neue anorganische Ringsysteme. XIX. Weitere Neue Cyclosilazane und Cyclosiloxazane mit N-N-Bindungen im Ring

Novel Inorganic Ring Systems. XIX. Additional Novel Cyclosilazanes and Cyclosiloxazanes Containing N? N Bonds in the Ring Structure According to the reaction paths of Schema 1 the compounds I–XIII have been prepared, confirmed in their constitution (Tab. 1–4) and described in their properties (Tab. 1). The seven membered ringsystem Si₃N₂O₂ of compound X and the eight membered ring system Si₄N₄ (?SiNSi₂NSiN₂ of compound XIII have been unknown so far. The properties of the 3 isomeric Si₄N₄-ringsystems (Schema 2) are compared.