首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Highly ablation resistant carbon nanotube (CNT)/phenolic composites were fabricated by the addition of low concentrations of CNTs. Tensile and compressive mechanical properties as well as ablation resistance were significantly improved by the addition of only 0.1 and 0.3 wt% of uniformly dispersed CNTs. An oxygen–kerosene-flame torch and a scanning electron microscope (SEM) were used to evaluate the ablative properties and microstructures. Thermal gravimetric analysis (TGA) revealed that the ablation rate was lower for the 0.3 wt% CNT/phenolic composites than for neat phenolic or the composite with 0.1 wt% CNTs. Ablation mechanisms for all three materials were investigated using TGA in conjunction with microstructural studies using a SEM. The microstructural studies revealed that CNTs acted as an ablation resistant phase at high temperatures, and that the uniformity of the CNT dispersion played an important role in this ablation resistance.  相似文献   

2.
Biocomposites were prepared by reinforcing polylactic acid (PLA) with randomly oriented, short Spartium junceum L. fibres. Prior to the composite production, the fibres were treated with montmorillonite nanoclay (MMT) in order to increase biocomposites resistance to the fire. Characterizations of the biocomposites in the presence and absence of MMT and Citric acid (CA) were performed by Thermogravimetric Analysis (TGA) and Microscale Combustion Calorimetry (MCC). The results indicated that biocomposites reinforced with fibres modified with MMT enhanced some of its thermal properties. Degradation level of residual fibres (char) after the TGA treatment at 800 °C was observed by Scanning Electron Microscope (SEM). The work provided us with the idea of using MMT in the presence of CA as a crosslinker in biocomposites for possible applications.  相似文献   

3.
A reduced graphene oxide (RGO)-NiFe2O4 nanocomposite was synthesized by a simple one step hydrothermal approach and its application in the electrocatalytic oxidation of hydrazine was demonstrated. The as-synthesized nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Thermogravimetric analysis, Field emission-scanning electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). The FE-SEM and TEM image analyses revealed that the NiFe2O4 nanoparticles were uniformly distributed on the RGO sheets with a diameter and length of ∼10 and ∼100 nm, respectively. The XPS analysis confirmed the ionic states of Ni and Fe to be Ni3+ and Ni2+, and Fe2+ and Fe3+, respectively. Further, the electrochemical activity of the RGO-NiFe2O4 nanocomposite was investigated by studying the oxidation of hydrazine. The RGO-NiFe2O4 modified glassy carbon electrode (GCE) showed an outstanding electrocatalytic activity towards the oxidation of hydrazine as compared to the NiFe2O4 and RGO modified electrodes. The enhanced electrocatalytic activity is due to the synergistic effect between RGO and NiFe2O4. Using amperometry, the lowest detection limit of 200 nM was achieved with the RGO-NiFe2O4 modified GCE. Therefore, the RGO-NiFe2O4 modified GCE can be used for the electrochemical oxidation of hydrazine.  相似文献   

4.
This paper focuses on the analysis of thermal and mechanical properties of novel biocomposites of Alfa fibers dispersed in a bioplastic of the Mater-Bi® type in relation with their morphology. These biocomposites obtained by twin screw extrusion were injection molded. Mater-Bi® is a commercial biodegradable thermoplastic based on poly(butylene terephthalate-co-butylene adipate) and starch. Raw and alkali treated Alfa fibers were used as reinforcement. Thermal analysis showed significant increase of the crystallization rate with the incorporation of Alfa fibers and enhancement of thermal stability by alkali treatment. Modulus and tensile strength of biocomposites also increased whereas toughness and elongation at break decreased upon increasing the fibers fraction. Scanning electron microscopy (SEM) on fractured surfaces indicated good adhesion between the matrix and the treated or untreated Alfa fibers.  相似文献   

5.
Starting from nitrate aqueous solutions with citric acid and polyethylene glycol (PEG) as additives, Y3Al5O12:Eu (YAG:Eu) phosphors were prepared by a two-step spray pyrolysis (SP) method. The obtained YAG:Eu phosphor particles have spherical shape, submicron size and smooth surface. The effects of process conditions of the spray pyrolysis on the crystallinity, morphology and luminescence properties of phosphor particles were investigated. The emission intensity of the phosphors increased with increasing of sintering temperature and solution concentration due to the increase of the crystallinity and particles size, respectively. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.10 g/ml in the precursor solution. Compared with the YAG:Eu phosphor prepared by citrate-gel (CG) method with non-spherical morphology, spherical YAG:Eu phosphor particles showed a higher emission intensity.  相似文献   

6.
Inorganic–organic nanocomposites have unlocked new opportunities in the design of innovative materials and compounds with enhanced and unique properties, based on soft chemistry. In the present study, a hybrid nanocomposite of maleimide–polystyrene (PSMA) with SiO2 and Al2O3 (PSMA-SA) was synthesized by means of the sol–gel approach in the presence of γ-aminotriethoxysilane (γ-APTES), in which tetraethoxysilane (TEOS) and aluminum isopropoxide (AIP) were used as precursors. The Michael reaction led to bonding between the PSMA and SiO2–Al2O3, giving a stable cross-linked network that prevented aggregation and mechanical mixing of the nanoparticles. XRD and FTIR analysis confirmed the effects of the coupling agent in promoting the Michael reaction. Thermal properties of the hybrid nanocomposites were tested through TGA and DSC. SEM, TEM and optical tests confirmed the controlled morphology and optical transparency of the composites. Additionally, the hybrid nanocomposites showed excellent solvent resistance and antimicrobial activity against pathogenic bacteria such as Bacillus cereus and Escherichia coli.  相似文献   

7.
The Sansevieria cylindrica (SC) fiber reinforced polyester matrix composites (SCFRPCs) were fabricated using compression molding machine. The influences of fiber length, fiber loading and chemical treatments of SCFRPCs over the mechanical and thermal stability were analyzed at different temperatures. The dynamic characteristics such as storage, loss modulus and damping were significantly influenced by the increase in fiber length and fiber loading but not in a geometric progression. Among various chemical treatments, the potassium permanganate treated SCFRPCs show the maximum increase in storage and loss modulus values. This result concluded that in addition to the reinforcing element (fiber length and wt% of fiber) the interfacial bonding between the fiber and the matrix plays a vital role in restricting the molecular mobility which was apparent from the storage modulus values. Efficient stress transfer at the interface is necessary to produce better dynamic properties rather than having more interfacial region. The change in morphology of cleaned and roughened SC fiber and the degree of interfacial adhesion between the fiber and matrix were studied using scanning electron microscope (SEM). The weight loss of SCFRPCs were also studied under varying temperatures with the help of thermo-gravimetric analysis (TGA).  相似文献   

8.
A simple chemical route for the synthesis of PbS nanoparticle coated amorphous carbon nanotubes (aCNTs) was described. The nanocomposite was prepared from an aqueous suspension of acid functionalized aCNTs, lead acetate (PbAc), and thiourea (TU) at room temperature. The phase formation and composition of the samples were characterized by X-ray diffraction and energy dispersive analysis of X-ray studies. The Fourier transformed infrared spectra analysis revealed the attachment of PbS nanoparticles on the acid functionalized aCNT surfaces. Morphology of the samples was analyzed with a field emission scanning electron microscope. UV-Vis study also confirmed the attachment of PbS nanoparticles on the walls of aCNTs. Thermal gravimetric analysis showed that the PbS coated aCNTs are more thermally stable than functionalized aCNTs. The PbS coated aCNTs showed enhanced field emission properties with a turn-on field 3.34 V μm−1 and the result is comparable to that of pure crystalline CNTs.  相似文献   

9.
Bismuth tellurium selenide (Bi2TeySe3−y) nanoparticles for thermoelectric applications are successfully prepared via a water-based chemical reaction under atmospheric conditions. The nanostructured compound is prepared using a complexing agent (ethylenediaminetetraacetic acid) and a reducing agent (ascorbic acid) to stabilize the bismuth precursor (Bi(NO3)3) in water and to favor the reaction with reduced sources of tellurium and selenium. The resulting powder is smaller than ca. 100 nm and has a crystalline structure corresponding to the rhombohedral Bi2Te2.7Se0.3. The nanocrystalline powder is sintered via a spark plasma sintering process to obtain a sintered body composed of nano-sized grains. Important transport properties of the sintered body are measured to calculate its most important characteristic, the thermoelectric performance. The results demonstrate a relationship between the nanostructure of the sintered body and its thermal conductivity.  相似文献   

10.
In the past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cell (SOFC) down to about 700 °C. In this respect, materials with a high ionic conduction at intermediate temperature have to be found and the processes to elaborate fuel cells, using these new materials, have to be developed.Apatite materials (La10−xSrx(SiO4)6Oδ) are attractive candidates for solid electrolyte working at intermediate temperature. The ceramic powder was produced by solid state reaction and was tape cast to obtain green sheets.Concerning the cathode, a perovskite oxide (La1−xSrxMn1−yCoyO3−δ) has been chosen. The perovskite powder was also shaped by tape casting with the introduction of a pore forming agent (corn-starch) to obtain the required porosity in the sintered cathode.The co-firing of the electrolyte/cathode half-cell in air at 1400 °C-2 h gives a flat sample with a dense apatite (98.2%), a 42.7% porous cathode and neither delamination nor chemical reactivity between electrolyte and cathode materials.The dimensional behaviour of the electrolyte material is stable for an oxygen partial pressure ranging from 10−10 to 0.21 atmosphere, from room temperature to 700 °C. The thermal expansion coefficients of the electrolyte and cathode materials are rather close (Δα = 2.8 × 10−6 K−1) under air.  相似文献   

11.
Chemical composition modification and surface modification of coir fibers are made in view of their use as reinforcement in coir-based green composites. Composites were prepared using coir fiber treated with varying pretreatment condition. The changes in the proportion of chemical composition and morphological properties of coir fibers with different coir pretreatment condition were discussed. It is observed that the mechanical properties of coir-based green composites; modulus of rupture and internal bond, increase as a result of chemical composition modification and surface modification. Scanning electron microscopy (SEM) investigations show that surface modifications improve the fiber/matrix adhesion.  相似文献   

12.
TiC/TiB2-based cermets were fabricated in situ by means of the thermal explosion under pressure technique starting from Ti-B4C powders with the addition of varying contents of Ni metal binder to achieve near-net-shape bulks. The combustion reaction was ignited in a graphite die heated by current. Full conversion of the reactants was obtained by thermal explosion and the process yielded TiC-TiB2-Ni materials characterised by a fine microstructure. Appreciable differences in terms of microstructure, hardness and fracture toughness by indentation were observed between core and external surface of the products due to fast cooling caused by heat transfer to the die walls. Cermets with a high content of Ni showing high hardness and fracture toughness were obtained, with values of HV5 = 2182 and KIc = 8.8 MPa m1/2 for 30 wt.% Ni and of HV5 = 1684 and KIc = 12.7 MPa m1/2 for 47 wt.% Ni.  相似文献   

13.
Zinc silicate was synthesized hydrothermally from zinc acetate and tetraethyl orthosilicate or sodium silicate. The possible lowest synthetic temperature and reaction parameters determining the morphology of the products were discussed. High base concentration favors the rod formation. XRD, TEM were used to characterized the products. Green and red photoluminescence were observed by the doping of Mn2+ or Eu3+, respectively.  相似文献   

14.
Because of major advantages (e.g. weight saving, maintenance advantages), the airframe manufacturers use more and more Polymer Matrix Composites (PMCs) in different parts of aircraft structures. But PMCs have a substantial disadvantage of low conductivity and therefore low Electromagnetic (EM) Shielding. Electromagnetic Interference (EMI) sources are all around and inside aircraft and can potentially threat the immunity of aircraft. Metallic meshes have been used to overcome this shortage. However in high frequencies most of the mentioned methods loose their performances. Regrettably on one side most of the present and upcoming systems onboard of aircraft are functional in mentioned range of frequencies. On the other side, passengers use more and more Personal Electronic Devices (PEDs) onboard of aircraft. Interferences caused by PEDs are also in the same range of frequencies. Measured susceptibility caused by PEDs is higher in composite aircrafts comparing to metallic ones. To overcome this back door lack of composite aircrafts, design of a new light weight shield particularly for aeronautic application is needed. Metallic nanoparticles have a great potential to be used as new EM shields for aerospace applications, particularly in high frequencies. Without multidisciplinary characterization of new shield, the application onboard would be suspended. Here the encouraging results of EM characterization are presented. Thermal, microscopy and mechanical tests are also performed. Based on acquired results in this work, thermal and mechanical behaviors as well as distribution of particles are all acceptable. The promising results obtained in this work can assure the designers on using metallic nanoparticles as a new shield for protection of composite aircrafts.  相似文献   

15.
The perovskite oxides are promising catalysts for VOCs combustion. The purpose of this work is to comparatively evaluate catalytic activity of some simple perovskites with various cationic compositions in combustion reactions of acetone, benzene, propane and Pb free gasoline. Nanometer particles of nominal composition: GdAlO3, SrMnO3, SrCoO3 and MnFeO3 were prepared by the sol–gel self-combustion method followed by heat treatment at 1000 °C in air. The samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and nitrogen adsorption/desorption isotherms. All samples have perovskite type structure and the crystallite size is in the range of 40–89 nm. Catalytic testing evidenced that the degree of the catalytic activity varied considerably with the perovskite composition. Among the four perovskites, SrMnO3 is generally the most active catalyst at low temperatures. MnFeO3 and SrCoO3−x catalysts proved high catalytic activity in acetone conversion only. The change in the catalytic activity as a result of the modification of the perovskite composition may be explained either by the different reactivity of the active oxygen species involved in the catalytic oxidation, or by the variation in the number of active sites on the perovskite surface determined by the specific structural properties of each perovskite.  相似文献   

16.
The influence of nature and concentration of acid species on surface morphology and physicochemical properties of titania particles synthesized by direct thermal hydrolysis of titanium tetrachloride was investigated. The acids used were hydrochloric acid, nitric acid, sulfuric acid, and perchloric acid with a concentration of 3 M. Thermal hydrolysis of titanium tetrachloride in hydrochloric acid and perchloric acid with molar ratios of [H+]/[Ti4+] = 0.5, 1.0, 1.5, and 2.0, respectively, was used to study the effect of acid concentration. The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and thermogravimetric analysis. Characterization of the samples by X-ray diffraction studies revealed the influence of acid species on the phase transformation of titania. Samples prepared by hydrochloric acid, nitric acid, and perchloric acid formed rutile phase with rhombus primary particles, while sulfuric acid resulted in anatase phase with flake-shaped primary particles. Transmission electron microscopy and dynamic light scattering results confirmed the nanosized titania particles and the agglomeration of primary particles to form secondary particles in spherical shape. The particle size of titania prepared using perchloric acid was smaller than those prepared with other acid sources. A direct correlation between [H+]/[Ti4+] ratio and particle size of titania was observed.  相似文献   

17.
Nanoboxes, nanocubes and nanospheres of cuprous oxides were readily synthesized by reducing Cu(CH3COO)2·H2O with ethylene glycol at different concentrations of poly(vinyl pyrrolidone); the formation mechanism of as-synthesized Cu2O nanostructures was investigated. Moreover, we report the highly selective adsorption characteristic of as-synthesized Cu2O nanostructures to anionic dyes and suggest the mechanism is electrostatic adsorption.  相似文献   

18.
Multi frequency measurement of dynamic mechanical properties including storage modulus, loss modulus and loss tangent of binary blends of an isotactic polypropylene (PP) and ethylene/vinyl acetate copolymer (EVA) at varying blending ratios was performed. Molecular mechanisms of various transitions were explained. The effect of blend ratio on miscibility of the blends using different approaches was studied. It was found that miscibility of blends increases at around 60 wt. % of EVA loading. Also, molecular origins of this phenomenon were proposed. The Arrhenius relationship was used in order to calculate the apparent activation energy (Ea) for the glass transitions of blend components. The Ea were compared at different compositions. The composition dependency of Ea could be explained based on miscibility of the blend components. Morphological parameters such as particle size and its distribution were obtained from SEM micrographs. The differences observed in morphological parameters and also morphological evidence of increased miscibility near 60 wt.% of EVA loading could be explained. In order to predict the dynamic mechanical properties of blends from those of their pure components, mean-field theories developed by Kerner were applied and theoretical values were calculated by solving of the appropriate equations using iteration method. Comparatively, a good agreement between theoretical and experimental data, especially in the upper and lower temperature zones was obtained. It was found that differences between experimental and theoretical values are significant in transition zone. Finally, the different causes of deviations between theoretical and experimental results were discussed.  相似文献   

19.
Polyimide/sepiolite nanocomposite films have been prepared via an in situ polymerization method. The process involves the dispersion of sepioite in N,N-dimethylacetamide, polycondensation of 2,2′-bis [4-(3,4-dicarboxyphenoxy) phenyl] propane dianhydride and 4,4′-oxydianiline in the presence of sepiolite suspension to form poly(amic acid), and the thermal imidization of poly(amic acid)/sepiolite nanocomposite. The morphology, thermal and mechanical performance, and water absorption of nanocomposite films were systematically studied with various sepiolite contents. The results indicated that sepiolite was dispersed homogeneously at a nanometer scale in polyimide matrix. Owing to such nanodispersion of sepiolite, the polyimide/sepiolite nanocomposite films exhibit dramatic improvements on the mechanical properties and the coefficient of thermal expansion while fine thermal stability and low water absorption capacity were also maintained. When the sepiolite content increased to 16% the polyimide/sepiolite nanocomposite film achieved as much as 41% and 94% increase on the tensile strength and modulus respectively, and 50% decreased in coefficient of thermal expansion.  相似文献   

20.
Bio-composites with poly(lactic) acid as matrix and various algae (red, brown and green) as filler were prepared via melt mixing. Algae initial size (below 50 μm and between 200 and 400 μm) and concentration (from 2 to 40 wt%) were varied. First, algae morphology, composition and surface properties are analysed for each algae type. Second, an example of algae particle size decrease during processing is given. Finally, tensile properties of composites are analysed. The surface of algae flakes was covered with inorganic salts affecting filler–matrix interactions. The Young’s modulus of composites increased at 40 wt% load of algae as compared with neat PLA although the strain at break and tensile strength decreased. In most cases the influence of algae type was minor. Larger flakes led to better mechanical properties compared to the smaller ones.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号