Nitride Nanofibers Research Articles

The ethanol-sensing properties of porous GaN nanofibers synthesized by electrospinning

Through precursor, subsequent calcination and ammoniation, gallium nitride nanofibers (GaN-NFs) and gallium nitride nanoparticles (GaN-NPs) were synthesized by electrospinning and sol–gel method, respectively. The structure and morphology characteristics of the products were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) nitrogen adsorption–desorption measurements. Gas sensors were fabricated as side-heated structure. The ethanol sensing properties of the GaN-NFs and GaN-NPs were compared at operating temperatures from 280 to 360°C and ethanol concentrations ranging from 50 to 1000ppm. The results indicate that the porous GaN-NFs show improved response to ethanol with good selectivity, which is attributed to the 1D porous nanostructure. The ethanol sensing mechanism of the porous GaN-NFs was also discussed.

Novel thermal interface materials: boron nitride nanofiber and indium composites for electronics heat dissipation applications

With increased power density and continued miniaturization, effective thermal dissipation is of significant importance for operational lifetime and reliability of electronic system. Advanced thermal interface materials (TIMs) with excellent thermal performance need to be designed and developed. Here we report novel TIMs consisted of boron nitride (BN) nanofibers and pure indium (In) solder for heat dissipation applications. The BN nanofibers are fabricated by electrospinning process and nitridation treatment. After surface metallization by sputtering, the porous BN film is infiltrated with liquid indium by squeeze casting to form the final solid composites. The new composites show the in-plane and through-plane thermal conductivity respectively of 60 and 20 W/m K. The direction dependence thermal properties of the TIM are due to the anisotropic thermal performance of BN nanofibers in the composite. A low thermal contact resistance of 0.2 K mm2/W is also achieved at the interface between this new composite and copper substrate. These competent thermal properties demonstrate the great potential of the BN–In TIMs in thermal management for electronic system.

Self-propagating high-temperature synthesis of nanostructured aluminum nitride powder with the use of aluminum fluoride and sodium azide

Aluminum nitride nanofibers are synthesized by the direct reaction of aluminum fluoride with sodium azide. The reaction product (grayish white powder) is investigated using a scanning electron micro-scope. The results testify that the product has fibrous morphology with a fiber diameter reaching 100 nm. The effect of the pressure of external nitrogen in a reactor, the relative density of the starting charge, and the sample diameter on the temperature and rate of combustion of the AlF3-3NaN3 system is shown. Optimum production conditions of the synthesis of aluminum nitride nanofibers are determined.

Processing and Characterization of Silicon Nitride Nanofiber Paper

Papers of silicon nitride nanofibers were synthesized by a carbothermal reduction process. These nanofiber papers were synthesized in situ and did not require a secondary processing step. The process utilized silica nanopowders and silica gel as the precursor material. Processing geometry played a crucial role in regulating the growth of the nanofiber papers. Characterization of the nanofiber papers indicated that the nanofibers were of the alpha silicon nitride phase. Both mechanical stiffness and strength of the nanofiber papers were measured. Thermal conductivity and specific heat of the papers were also measured and were found to be lower than many common thermal insulation materials at much smaller thicknesses and were comparable to those values that are typically reported for carbon‐nanotube‐based buckypaper. Results of the mechanical and thermal characterization indicate that these silicon nitride nanofiber papers can be utilized for specialized thermal insulation applications.

Heteroepitaxial Growth of Single-Walled Carbon Nanotubes from Boron Nitride

The growth of single-walled carbon nanotubes (SWCNTs) with predefined structure is of great importance for both fundamental research and their practical applications. Traditionally, SWCNTs are grown from a metal catalyst with a vapor-liquid-solid mechanism, where the catalyst is in liquid state with fluctuating structures, and it is intrinsically unfavorable for the structure control of SWCNTs. Here we report the heteroepitaxial growth of SWCNTs from a platelet boron nitride nanofiber (BNNF), which is composed of stacked (002) planes and is stable at high temperatures. SWCNTs are found to grow epitaxially from the open (002) edges of the BNNFs, and the diameters of the SWCNTs are multiples of the BN (002) interplanar distance. In situ transmission electron microscopy observations coupled with first principles calculations reveal that the growth of SWCNTs from the BNNFs follows a vapor-solid-solid mechanism. Our work opens opportunities for the control over the structure of SWCNTs by hetero-crystallographic epitaxy.

Effects and Control of Polymer‐Converted Carbon Impurity in Synthesizing Continuous Boron Nitride Nanofibers by Electrospinning

Application of polymer as thickener of precursor solution for preparing boron nitride (BN) nanofibers by electrospinning brings carbon impurity in the nitride products. The control and removal of the carbon impurity are a key step in the synthesis of the BN nanofibers. In this article, the control and removal of the carbon impurity are well realized by introducing O2 and NH3 simultaneously. The carbon content in the BN nanofibers can be well controlled by changing O2/NH3 ratio, temperature, time, and gas flow rate. The effects of the carbon impurity on the structure of the BN products are investigated systematically.

Characterization and the hydrogen storage capacity of titania-coated electrospun boron nitride nanofibers

In the present work, titania-coated (TiO2) boron nitride nanofibers were produced by the electrospinning method, and the effect of heat treatment on the nanofibers was studied. Electrospinning method is often adopted for the synthesis of one-dimensional nanofibers due to high productivity, simplicity, and cost-effectiveness. In this study, boric oxide was deposited on co-electrospun polyacrylonitrile and TiO2. TiO2-coated boron nitride nanofibers, with a diameter of 100 nm, were obtained after heat treatment and nitridation. The effects of heat treatment on the morphology, surface area and hydrogen storage capacity were studied extensively. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) showed long, bead-free nanofibers and the presence of TiO2 nanoparticles on the nanofibers. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy depicted hexagonal structures of boron nitride. The hydrogen uptake capacities of the nanofibers were investigated by pressure composition isotherm (PCI) in the pressure range of 1–70 bar at room temperature.

Synthesis of Continuous Boron Nitride Nanofibers by Electrospinning

Abstract Continuous boron nitride nanofibers (BNNFs) have been gotten by electrospinning. The appropriate precursor of BNNFs was electrospinned to green born nitride nanofibers (GBNNFs) with temperatures from 80°C to 100°C in the protection of N2. By successive heat treatments in N2, the organics in GBNNFs disappeared and BN ceramics nanofibers came into being. The average diameters of BNNFs by electrospinning are less than 10 μm

Comparison of Silicon Nitride Nanofibers Synthesized Using Silica Nanopowders and Silica Gel

Nanofibers of alpha silicon nitride were grown by a vapor-solid mechanism at 1450?C, through the carbothermal reduction process. Two different precursor silica sources were used: silica nanopowders and silica gel. The effect of processing geometry, particularly the stacking orientations of the graphite substrates, silica pellets, and crucibles, on the density of nanofiber growth was also explored. The silicon nitride nanofibers appear with a predominantly rectangular cross section from silica nanopowder precursors and with a circular cross section for silica gel precursors. Silica gel precursors produce nanofiber products that are smaller in cross section but greater in length than the products from silica nanopowder precursors. The processing geometry must be suitably designed such that the vapor-solid mechanism that is responsible for the formation of the nanofibers is not disrupted.

Effects and Control of Polymer-Converted Carbon Impurity in Synthesizing Continuous Boron Nitride Nanofibers by Electrospinning

Effects and Control of Polymer-Converted Carbon Impurity in Synthesizing Continuous Boron Nitride Nanofibers by Electrospinning

Formation of Refractory Carbide and Nitride Nanofibers by Thermal Decomposition of Poly(vinyl alcohol)-Titanium Lactate Hybrid Nanofibers

Poly(vinyl alcohol)-titanium lactate hybrid nanofibers (precursors) were formed by electrospinning employing water as a solvent for the spinning solution. The precursors were converted into titanium carbide (TiC) or nitride (TiN) nanofibers by heating them in Ar or N2 atmospheres. TiC nanofibers could be obtained below theoretical temperature calculated from thermodynamics data, indicating that metal and carbon sources were intimately mixed together. TiN nanofibers also could be obtained near theoretical temperature under N2 gas flow.

Chromium nitride and carbide nanofibers: from composites to mesostructures

This work describes an easy two-step approach for metal nitride/carbide nanocomposite ceramic nanofibers via heat treatment of electrospun precursor fibers. Possibilities to tune their composition, carbon scaffold organization and texture depend on the calcination temperature, and yield two different types of fiber structures. Fiber mats with various morphologies were obtained from polyacrylonitrile–chromium chloride precursor electrospun fibers, while well defined rod-like fiber non-woven mats were obtained when a methylated polyurea was used as an additive to the previous system. It was observed that the use of a two component organic system, involving a fiber stabilizing polymeric template (PAN) and a specific nitrogen/carbon donor (PUF), enables to maintain the morphology of the initial fibers during heat treatment and prevents the system from forming sintered membranes at high humidity conditions. The chromium content found for PAN-free and PAN-containing was 9 and 12 wt%, respectively. Moreover, thermal treatment at temperatures higher than 1000 °C led to graphitization of the carbon subphase of both series. Nitrogen sorption studies revealed that the graphitization process increases the specific surface area of the fibers, which possess a pore system with a wide diameter distribution and inkbottle-shaped pores. Conductivity studies revealed that the fiber systems are suitable for electrochemical applications.

Fabrication of nanostructured metal nitrides with tailored composition and morphology

Unprecedented multi-channel TiN micro/nanotubes as well as various metal nitride nanofibers, including TiN, VN, NbN and ternary metal nitride nanofibers, were fabricated by a template free electrospinning method combined with post-nitridation.

Boron nitride nanofibers by the electrospinning technique

An interesting boron nitride ceramic was introduced in nanofibrous form. Boron nitride nanofibers were prepared using a simple and cheap strategy. Calcination of poly(vinyl alcohol) electrospun nanofibers embedded with boron nitride nanoparticles resulted in a nanofibrous form. The electrospun nanofiber mats were prepared by electrospinning of a colloidal solution composed of an aqueous poly(vinyl alcohol) solution and boron nitride nanoparticles. Calcination of the obtained BN/PVA nanofiber mats in an argon atmosphere at 1,000 °C for 5 h resulted in boron nitride nanofibers. The boron nitride nanofibers showed a higher band gap than the nanoparticles; the latter showing a band gap of 2.75 eV. however, the nanofibrous shape enhanced the band gap to 4.52 eV.

Surface modification of silicon nitride nanofibers with titanium nitride particles

Silicon nitride nanofibers coated with titanium nitride particles are formed by deposition of TiO(OH) 2 and Ti(O) 2 (OH) 2 using controlled hydrolysis of TiCl 4 followed by nitriding in an NH 3 flow. The nitriding at 700-900°C permits the formation of 5 to 15 nm titanium nitride particles. The amorphous layer on Si 3 N 4 fibers limits the nucleation of titanium nitride and thus the formation of continuous coatings. Titanium peroxyhydroxide Ti(O) 2 (OH) 2 as a precursor is preferable for depositing titanium nitride coatings on silicon nitride fibers.

Synthesis of continuous boron nitride nanofibers by solution coating electrospun templatefibers

Continuous boron nitride nanofibers (BNNFs) have been synthesized from boric oxide (B2O3) coatings deposited on stabilized electrospun polyacrylonitrile fibers (S-PANFs). TheB2O3 overcoatings were prepared by impregnating the S-PANFs withB2O3 ethanol solutions. By successive heat treatments at800 °C inNH3/O2 mixture,1100 °C inpure NH3,and 1500 °C inN2, the S-PANFs werefully removed and the B2O3 coatings deflate to form solid fibers and transform into theBNNFs. The S-PANF template was fully removed by introducingO2 during nitridation, and thus resulted in the formation of the BNNFs. The diameter of theBNNFs can be effectively controlled by changing the mass concentration of theB2O3 solution, and diameters from 43 to 230 nm were obtained by changing theB2O3 mass concentration from 0.25% to 4.8%. The obtained BNNFs are crystallized with the(002) planes oriented in parallel to the fiber axis. This method provides a powerfultool for obtaining BNNFs with controllable diameters, especially extremely thinBNNFs.

Large-Scale Production of Aligned Long Boron Nitride Nanofibers by Multijet/Multicollector Electrospinning

Boron nitride nanofibers (BNNFs) with alignment and large length have been prepared on a large scale by electrospinning the precursor fibers and subsequent nitridation. A multijet/multicollector electrospinning system is constructed by simply arranging three jets and three tip collectors abreast. By this system the aligned precursor fibers with lengths over 13 cm are collected throughout a very large length of 68 cm. The alignment of the electrospun precursor fibers is mainly induced by the converging electric field generated by the applied tip collectors. Composite B2O3/polyvinylbutyral (PVB) fibers (BOFs) were used as the precursor fibers, where PVB was added for increasing the spinnability of the electrospinning solutions. However, the presence of PVB in the BOFs results in the formation of carbon residue in the nitrided products, which is a stubborn problem for preparing the BNNFs. We successfully solved this problem by introducing a small amount of O2 at appropriate temperature during nitridation with NH3. The morphology of the nitrided products is strongly dependent on the diameter and B2O3/PVB ratio of the BOFs and the BNNFs with diameters as small as below 100 nm were obtained by controlling them. The obtained BNNFs were crystallized with (002) base planes preferentially oriented in parallel to the fiber axis. A high onset oxidation temperature of 890 °C was demonstrated for the BNNFs.

GaN Nanofibers based on Electrospinning: Facile Synthesis, Controlled Assembly, Precise Doping, and Application as High Performance UV Photodetector

Nitride nanofibers have been synthesized based on a simple electrospinning technique for the first time. No catalysts or templates are needed in this new synthetic method. Highly oriented GaN nanofiber arrays, as well as a high-performance UV photodetector based on single GaN nanofiber assembled FET devices, can be facilely fabricated using this technique. Precise doping of other elements into the GaN nanofibers is easy by this solution-based synthetic method.

CNx nanofibers converted from polypyrrole nanowires as platinum support for methanol oxidation

A new kind of carbon nitride (CNx) nanofiber has been prepared by the calcination of polypyrrole nanowires at 800 °C. The product maintained a wire-like morphology during calcination, and the pyrrolic nitrogen in the polypyrrole nanowires gradually changed to pyridinic and graphitic nitrogen as annealing temperature increased. These CNx nanofibers, prepared at 800 °C, have a nitrogen concentration of about 10%. Pt nanoparticles with average size of ∼3 nm could therefore be easily immobilized onto the CNx nanofibers because of the inherent chemical activity arising from the nitrogen incorporation. The Pt/CNx composite catalyst thus obtained has a large electrochemically active area and gives good electrocatalytic performance for methanol oxidation, both in activity and stability, suggesting it has potential application in fuel cells.

ChemInform Abstract: A Simple Method to Synthesize Polyhedral Hexagonal Boron Nitride Nanofibers.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.