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Surface area and morphology of materials play an important role on their gas sensing performance because of the varying number and nature of adsorption sites. Current work reports a comparative study of LaFeO3 synthesized by the facile hydrothermal method using two precursors; citric acid and KOH. The microstructure observed through FESEM and TEM showed different morphologies for the two precursors and calcination time (2?h & 6?h). Prior to calcination, higher surface area (50.54?m2/g) was obtained for LaFeO3 prepared using KOH as compared to that for LaFeO3 using citric acid (3.21?m2/g). Surface area increased from 3.21 to 7.06?m2/g for citric acid and decreased from 50.54 to 11.42?m2/g for KOH as calcination takes place for 6?h. Needle-shaped morphology of p-type LaFeO3 with high surface area (50.54?m2/g) for KOH would provide large active sites which would enhance sensitivity towards gases. Hence, LaFeO3 samples prepared using KOH with and without calcination are expected to give better performance for gas sensing than LaFeO3 samples synthesized using citric acid. 相似文献
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This paper introduces a simplified method for low-temperature pressureless sintering of Al2O3-Ni-SiC nanocermets in air environment. In this method, a thin and continuous Ni shell was coated on the surface of Al2O3 particles using electroless deposition method. The composite powders were subsequently compressed to prepare bulk specimens. By preventing the ceramic particles from direct contact during the densification of green specimens, sintering temperature of cermet materials was reduced from that of Al2O3 (>?1400?°C) to the range of Ni solid-phase sintering temperature. Furthermore, dissolution of a low amount of phosphorus in the composition of Ni coatings caused the further decrease of the sintering temperature to 800?°C. At such low temperatures, pressureless sintering of the cermets in the air environment was successfully performed instead of the common hot pressing process in a reducing atmosphere. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD) characterizations indicated that the microstructure of such sintered samples consists of a continuous Ni network surrounding Al2O3 grains, without any structural defects or Ni oxidation. Furthermore, mechanical properties of the cermet materials were improved through reinforcement of the continuous Ni network by different amounts of SiC nanoparticles. The results showed that Al2O3-Ni-5?wt% SiC nanocermets sintered at 800?°C obtain the highest compressive strength of 242.5?MPa, hardness of 56.8 RA, and the lowest wear weight loss of 0.04?mg/m. 相似文献
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I. Morjan I. Voicu F. Dumitrache I. Sandu I. Soare R. Alexandrescu E. Vasile I. Pasuk R. M. D. Brydson H. Daniels B. Rand 《Carbon》2003,41(15):2913-2921
Carbon nanopowders were obtained by the laser pyrolysis of ethylene. The high-temperature gradients and very rapid reaction times characteristic of the process lead to the formation of very fine powders. Carbon powders obtained in runs with different laser power values (400–900 W), pressures (250–950 mbar), and gas flows (100–300 sccm) were characterised by transmission electron microscopy (TEM), including high-resolution mode (HREM), electron energy loss spectroscopy (EELS), X-ray diffraction (XRD) and Raman spectroscopy. The carbon particles were found to be approximately spherical in shape, with diameters around 45 nm, which may coalesce into larger agglomerates. The particles were found to be made up of layers forming a turbostratic structure. The experimental parameters influence the soot morphology and particle microstructure. Increasing the laser power and gas pressure leads to less coalescence and increased order. Structural parameters are presented for particles produced under different conditions. 相似文献
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《Ceramics International》2017,43(6):5145-5149
Large quantities of hexagonal boron nitride (h-BN) nanotubes (BNNTs) with high purity have been successfully synthesized under ammonia gas flow at 1200 °C via catalytic pyrolysis of organic-inorganic hybrid precursor which was pre-prepared through a wet chemistry method at 95 °C. Several characterizations, such as SEM, TEM, XRD, FTIR, EDS, XPS and SAED measurements, were used to confirm the morphology, composition and crystalline structure of the as-synthesized powders. It was observed that the obtained product was a kind of nanotubes (NTs) in hexagonal BN phase with a curved shape and smooth surface. The diameter of BNNTs was distributed in a range of 60–200 nm while its length was about tens of microns. The possible growth mechanism of BNNTs was also proposed in this paper. 相似文献
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The suitability of MgO as a densification aid for α-SiC has been investigated. Samples of SiC containing additions of MgO, both alone and in combination with A12O3 and Y2O3, have been hot pressed at temperatures between 1500 and 1900°C and pressureless sintered at temperatures up to 2000°C. The MgO reacts with surface SiO2 from the SiC grains to form a liquid phase which promotes densification by particle rearrangement and solution-reprecipitation processes. With combined additions of MgO, Al2O3 and Y2O3, a eutectic in the system MgO –Al2O3 –Y2O3 allows extensive liquid formation at 1700°C independent of the SiO2 content of the SiC powder, enabling efficient densification by hot-pressing. Volatilisation due to reactions between the MgO and the SiC or with the furnace environment, however, oppose densification by pressureless sintering, and must be compensated for by the use of Mg-containing powder beds. 相似文献
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β-SiC surface layers were synthesized by implantation of C+ into Si substrates at a comparatively low temperature of 400°C with a metal vapour vacuum arc ion source. X-ray diffraction patterns showed that these layers had a strong (111) preferred orientation. The amount of β-SiC formed increased significantly with the rise of the implantation dose, but the crystallinity of the layers formed relied little on the implantation dose. Both the broad X-ray diffraction peaks and the scanning electron microscopy photograph showed that the grain size of the sample with a dose of 7×1017 cm−2 is relatively small. 相似文献
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The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi2(Zn1/3Nb2/3)2O7 (BZN) and Bi2(Zn1/3Nb2/3−xVx)2O7 (BZNV, x = 0.001) sintered under air and N2 atmosphere were investigated. The pure phase were obtained between 810 and 990 °C both for BZN and BZNV ceramics. The substitution of V2O5 and N2 atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 °C under N2 atmosphere with r = 76.1, Q = 850 and Qf = 3260 GHz while the best properties of BZNV ceramics were got at 930 °C under air atmosphere with r = 76.7, Q = 890 and Qf = 3580 GHz. The temperature coefficient of resonant frequency τf was not obviously influenced by the different atmospheres. For BZN ceramics the τf was −79.8 ppm/°C while τf is −87.5 ppm/°C for BZNV ceramics. 相似文献
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Ceramic matrix composites (CMCs) were prepared from a polysiloxane network filled with rice husk ash (RHA), a reactive filler. CMCs were obtained by pyrolysis at 1000 and 1600 °C of green bodies prepared from a mixture of polysiloxane network and RHA at a weight ratio of 4:1, respectively. The RHA and the CMCs were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), in addition to density and mechanical measurements. The CMCs were obtained without macroscopic defects, and their initial observed porosity was reduced by polymeric infiltrations cycles of the polymeric precursor, which improved their flexural strength and modulus up to 100%. 相似文献
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The sol–gel synthesis and characterization of mullite precursor derived from rice husk silica and aluminum nitrate hydrate [(Al(NO3)3·9H2O] has been investigated. The samples were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) coupled with Rietveld analysis, and scanning electron microscopy (SEM). FTIR results showed the presence of Si–O–Si, Al–O–Al, and Si–O–Al functional groups, which were associated with mullite, corundum, quartz, and cristobalite, as verified by XRD analysis. It is concluded that mullite formation started at 1150 °C, and its abundance increased rapidly with an increase in temperature from 1150 to 1350 °C, resulting in increased phase content from 30.9 to 67.7 wt%. Although mullite was formed at a low temperature, the complete reaction between corundum and silica to form mullite was not achieved. This finding demonstrated that rice husk silica is a potential alternative raw material for the production of mullite ceramic. 相似文献
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《Ceramics International》2022,48(4):4456-4463
Direct reaction of precursors with the products of detonation remains an underexplored area in the ever-growing body of detonation synthesis literature. This study demonstrated the synthesis of silicon carbide during detonation by reaction of elemental silicon with carbon products formed from detonation of RDX/TNT mixtures. Continuum scale simulation of the detonation showed that energy transfer by the detonation wave was completed within 2–9 μs depending on location of measurement within the detonating explosive charge. The simulated environment in the detonation product flow beyond the Chapman-Jouguet condition where pressure approaches 27 GPa and temperatures reach 3300 K was thermodynamically suitable for cubic silicon carbide formation. Carbon and added elemental silicon in the detonation products remained chemically reactive up to 500 ns after the detonation wave passage, which indicated that the carbon-containing products of detonation could participate in silicon carbide synthesis provided sufficient carbon-silicon interaction. Controlled detonation of an RDX/TNT charge loaded with 3.2 wt% elemental silicon conducted in argon environment lead to formation of ~3.1 wt% β-SiC in the condensed detonation products. Other condensed detonation products included primarily amorphous silica and carbon in addition to residual silicon. These results show that the energized detonation products of conventional high explosives can be used as precursors in detonation synthesis of ceramic nanomaterials. 相似文献
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《Ceramics International》2016,42(3):3762-3768
Indium oxide (In2O3) is a n-type semiconductor with various applications in thin film coatings, on the basis of its optical properties, and in gas sensing equipment, due to its high sensitivity to various oxides such as COx and NOx. In this study, a synthesis process for obtaining In2O3 nanoparticles is examined. The precursor used is indium nitrate hydrate (InN3O9·H2O) because of its high solubility in water. By dissolving the nitrate salt in a PVA (polyvinyl alcohol) solution, the precursor is dispersed homogeneously, which reduces the agglomeration of the resulting powder. Calcination at a low temperature of 200–250 °C burns out the organic materials of the PVA with NOx gas emission and allows the oxidation of the indium, resulting in indium oxide nanoparticles. The influence of the PVA solution characteristics and the heat treatment temperature on the powder morphology and size was analyzed by using SEM, TEM, XRD, TGA/DSC, and four point BET for a specific surface area analysis. The measured specific surface area varies from 3 m2/g to 76 m2/g depending on the calcination temperature, and the particle size of the synthesized powders is under 10 nm for the samples heat treated at 300 °C. 相似文献
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Alumina (Al2O3)-carbon nanotube composite materials were synthesized by spraying a slurry of ferrocene (Fe(C5H5)2) and alumina in xylene, at 1000±50 °C, using argon (≤1.5 bar) as carrier gas. The as-prepared materials were formed in large flakes (ca. 2 cm) and consist of nanotubes intricately matted in a glassy alumina matrix. Based on the structural and microstructural investigations done by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), a possible growth mechanism has been suggested. 相似文献
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Stanis?aw Porada 《Fuel》2004,83(9):1191-1196
Pyrolysis examinations conducted under non-isothermal conditions as well at low heating rate can show that the processes of hydrogen and methane formation are the result of several constituent reactions. In the presented paper a number of these reactions has been determined separately for each of the above mentioned gaseous products. The kinetic parameters of the reactions as well as the yields of products have also been calculated. It has been found that, during coal pyrolysis, methane is formed as a result of six constituent reactions and hydrogen is produced as a result of five constituent reactions. The values of activation energy and frequency factor for the reactions in question were determined. These values fall within the range, which is typical of chemical reactions. 相似文献
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Yiwei Ao Yunxia Yang Shuanglong Yuan Hengyao Hu Hongchen Gu Guorong Chen 《Ceramics International》2007,33(8):1547-1550
Nanosized γ-Al2O3 particles were prepared by the sol–gel method with aluminum ion hydrolysis control performed by nitric acid. The as-prepared particles were mixed with deionized-water and stabilizer, and cycled in a high speed sand mill to form a stable γ-Al2O3 suspended slurry, which was then coated on the surface of the glass substrate to form a γ-Al2O3 protective film. Observations of SEM and visible transmission spectra show that a well-dispersed γ-Al2O3 slurry could be obtained after three-cycle grinding suitable to coat fluorescent lamp glass with a dense and uniform film of visible light transmission up to 95%. 相似文献
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ZnO nanostructures were grown by microwave assisted wet-chemical growth, at different microwave powers and for different growth durations. The grown nanostructures were analysed for their morphological, structural, compositional and optical characteristics. The total microwave power per growth run (product of microwave power and growth duration, with units in watt-min), has a linear relationship with most of the characteristics of the grown ZnO nanostructures. It is shown that by altering the microwave power per growth run, the morphology of the individual ZnO nanostructure can be changed from cones with hexagonal cross section, to faceted hexagonal nanorods, to hollow hexagonal nanorods. It is observed that, while the fast growth rate along the high energy polar faces (0001) and (000ī) of ZnO is the reason behind the formation of one dimensional ZnO structures (cones and rods), the process of formation of hallow ZnO rods is due to further etching/material-removal from the tip of the rods, at high microwave power conditions at long growth durations. 相似文献
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Changhyun Jin Hyunsu Kim Sunghoon Park Hyoun Woo Kim Sangmin Lee Chongmu Lee 《Ceramics International》2012
SnO2 nanobelts functionalized with Au were prepared using a three-step process consisting of the thermal evaporation of Sn powders, sputter deposition of Au, and annealing. Multiple-networked sensors were fabricated using Au-functionalized SnO2 nanobelts. Scanning electron microscopy revealed nanobelts with widths ranging from a few hundred nanometers to a few micrometers, thicknesses of a few hundred nanometers, and lengths ranging from a few to a few tens of micrometers coated with the Au nanoparticles with a mean diameter of ∼200 nm. The bare SnO2 nanobelts showed responses of 2.80 and 2.20% to C2H5OH concentrations of 50 and 100 ppm, respectively. In contrast, the Au-functionalized SnO2 nanobelts showed responses of 313.25 and 194.77%, respectively, to the same C2H5OH concentrations. Furthermore, SnO2 nanobelts functionalized with Au showed a higher response than those functionalized with other metal catalysts, such as Pd, Pt and Ag. Both the response and recovery times of the SnO2 nanobelts were decreased slightly by Au-functionalization regardless of the C2H5OH concentration. In addition, this paper discusses the enhanced sensing properties of SnO2 nanobelts functionalized with Au. 相似文献
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Evolution of chemistry and morphology during the carbonization and combustion of rice husk 总被引:3,自引:0,他引:3
Tzong-Horng Liou 《Carbon》2004,42(4):785-794
Both fine carbon/silica and pure silica powders can be obtained by carbonization and combustion of rice husk under non-isothermal conditions, and the products can be used for preparation of high-quality ceramic materials. Studies on the morphology, chemical and physical characteristics of products were carried out by N2-adsorptionmeter, SEM, XRD, FTIR, ICP-MS and EA. Results indicate that decreasing the heating rate increased the specific surface area, pore volume and pore diameter. At a heating rate of 5 °C/min, the specific surface areas of both the carbon/silica and pure silica powders were 261 and 235 m2/g, and the average pore diameters were 2.2 and 5.4 nm, respectively. The products obtained from various heating rates were all amorphous. Thermogravimetric analysis was employed to study the reaction characteristics during carbonization or combustion, indicating that decomposition process of rice husk could be divided into three temperature zones. This results of the study can also provide the important information on the recovery of biomass material from rice husk. 相似文献