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1.
《Advanced Powder Technology》2021,32(8):3101-3106
Carbothermal reduction-nitridation method is an effective means for synthesizing Si3N4 powder. Herein, spherical monodisperse silica was used as silicon source. The effects of reaction temperature, nitrogen flow rate and Si3N4 seeds content on the products were studied. It was found that high-purity α-Si3N4 (>99.0 wt%) was synthesized from C/SiO2 = 3:1 at 1400 °C, reaction time of 6 h and nitrogen flow rate of 800 ml/min. The powder, with an average size of 0.5 μm, showed good dispersity and regular morphology because spherical monodisperse silica could be completely coated with carbon. The more contact sites between SiO2 and C, the higher concentration of SiO(g) would be produced in the initial stage. It also indicated that the nucleation rate of α-Si3N4 increased, thereby inhibiting the formation of an agglomerate phase and suppressing the grain growth of α-Si3N4. Furthermore, higher nitriding temperature and Si3N4 seeds content both decreased the grain size and increased β-Si3N4 content. The forming mechanism of non-agglomerated and submicron-sized α-Si3N4 was clarified. 相似文献
2.
A composite joining technique, using a Ni–56Si filler alloy and Mo as interlayers, was used to join SiC to SiC and to Kovar.
The wetting of the Ni–Si alloy on SiC ceramic was studied in a vacuum at 1,350 °C by the sessile drop technique as a function
of time; the non-reactive wetting characteristics in the Ni–Si/SiC system were confirmed, with an equilibrium contact angle
of about 23°. SiC/SiC joints were fabricated by two processes using a Ni–Si/Mo/Ni–Si structure as the interlayer. SiC/Kovar
joints were produced by means of a multilayer structure: molybdenum, which is used as the interlayer, was joined to Kovar
on one side by means of transient liquid phase bonding and to SiC on the other side, using a Ni–Si coating as a filler alloy.
The resulting joints were analyzed and discussed in terms of joint morphology and microstructure, joint strength, and fracture
behavior. Two interfacial layers form at the Kovar/Mo and the Mo/Ni–Si interfaces due to dissolution and interdiffusion phenomena
between the metallic elements, without there being any observable reactions with the SiC component. The type of joining process
and the experimental conditions used play a key role in determining the joint microstructure and composition, the joint strength
and its fracture behavior. 相似文献
3.
《Nanostructured Materials》1994,4(4):365-369
Elemental Cu and NbC powders were mechanically alloyed with either graphite or hexane to form nanocomposite CuNbC powders. These powders were consolidated by hotisostatic-pressing at one-third of the melting temperature of NbC to form a 100% dense compact, while maintaining a crystallite size well within the nano-regime. 相似文献
4.
Waheed S. Khan Chuanbao Cao Zhou Chen Ghulam Nabi 《Materials Chemistry and Physics》2010,124(1):493-498
Metal–semiconductor Zn–ZnO core–shell microcactuses have been synthesized on Si substrate by simple thermal evaporation and condensation route using NH3 as carrier gas at 600 °C under ambient pressure. Microcactuses with average size of 65–75 μm are composed of hollow microspheres with high density single crystalline ZnO rods. The structure, composition and morphology of the product were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). A vapor–liquid–solid (VLS) based growth mechanism was proposed for the formation of Zn–ZnO core–shell microcactuses. Room temperature photoluminescence (PL) investigations revealed a strong and broad blue emission band at 441 nm associated with a weak ultraviolet (UV) peak at 374 nm. This blue emission (BE) is different from usually reported green/yellow-green emission from Zn–ZnO or ZnO structures. The field emission (FE) measurements exhibited moderate values of turn-on and threshold fields compared with reported large field emissions for other materials. These studies indicate the promise of Zn–ZnO core–shell microcactuses for the applications in UV-blue light display and field emission microelectronic devices. 相似文献
5.
6.
Highly microporous metal-MCM-41 ordered mesoporous structure catalysts having different metal/Si (V, Mo, Nb) atomic ratios and combinations of metal sources were hydrothermally synthesized. The structural properties estimated using different techniques were found to be in agreement with each other. Metals were successfully incorporated into MCM-41 without deteriorating the ordered hexagonal structure. The metal ions in the synthesis solutions probably settled on the hydrophilic end of the template hence the metal incorporation resulted improvements in the micropore structure. Low loading of metals caused an increase in the surface area and pore volume values of the catalysts. The highest total (1310 m2 g?1) and micropore surface area values (1083 m2 g?1) were obtained by Nb incorporation. The micro- and mesopore dimensions of MCM-41 increased from 0.5 to 1.1 nm and from 2.5 to 2.8 nm, respectively, with metal incorporation. Low V/Si ratios and presence of Nb in the starting solution enhanced narrow mesopore size distribution. The pore dimension and wall thickness values estimated from nitrogen adsorption and X-ray diffraction methods were consistent with the corresponding values obtained using transmission electron microscopy. 相似文献
7.
V. Ibarra-Galván C. I. Villavelázquez-Mendoza E. Elorza Rodriguez A. López-Valdivieso S. Song Hu R. Muñiz-Valencia 《Particulate Science and Technology》2017,35(2):173-176
A direct method to synthesize porous hausmannite (Mn3O4) microparticles by the KMnO4–AC reaction and combustion system is reported in this paper. In order to synthesize the manganese oxide, four experimental factors were considered: pH (3.0, 4.5 and 6.0), AC content (2.08 × 10?2 and 8.33 × 10?2 M), initial Mn(VII) content (4.55 × 10?4 and 9.1 × 10?4 M) and stirring velocity (300 and 500 rpm). The AC was added to the Mn(VII) aqueous solution and stirred for 2 h. For different pH levels, the Mn(VII) content in the solution was measured by UV/Vis spectrometry at 540 nm in order to evaluate the Mn reduction. Later, the manganese-loaded AC was calcined at 700°C in dry air at 1900 sccm during 60 min, indicating that the Mn3O4 content is directly proportional to the acidity of the solution. Spongy and porous Mn3O4 microparticles were synthesized considering the following levels: pH (3.0), an AC content (8.33 × 10?2 M) and an initial Mn(VII) content (9.1 × 10?4 M) with 500 rpm. 相似文献
8.
《Materials Letters》2004,58(1-2):150-153
In the present study, the composites of SiC–TiC are prepared by spark plasma sintering (SPS) in vacuum without additive. The relationship of density and temperature of SiC–TiC composites with different content of TiC is studied. The maximum relative density reached was 98%. The mechanical properties of SiC–TiC composites with different content of TiC, which were sintered at 1800 °C, have been evaluated. From the fracture surface observation, two models of fracture mechanisms of the composites existed: transgranular and intergranular. 相似文献
9.
M. Alagiri S. Ponnusamy C. Muthamizhchelvan 《Journal of Materials Science: Materials in Electronics》2012,23(3):728-732
Nickel oxide nanoparticles have been synthesized in the presence of agarose polysaccharide by sol–gel method. The structure,
morphology, optical and magnetic properties of the product was examined by X-ray diffraction, transmission electron microscopy,
UV–visible spectrophotometer and superconducting quantum interference device magnetometer. The result of thermogravimetric
analysis of the precursor product showed that the proper calcination temperature was 400 °C. X-ray diffraction result revealed
that the obtained product was nickel oxide with face-centered cubic structure. TEM image demonstrated that the nickel oxide
nanoparticles have spherical shape with size around 3 nm. Analysis of FTIR spectra confirmed the composition of product. The
optical absorption band gap of the NiO nanoparticles was estimated to be 3.51 eV. Magnetic measurement showed that the nickel
oxide nanoparticles exhibit superparamagnetic behavior at 300 K. Moreover, the nanoparticles show ferromagnetic interactions
at 4.2 K owing to the existence of uncompensated moments on the surface of the nanoparticles. 相似文献
10.
Titanium nitride powders were synthesized from titanium dioxide at 1173–1373 K in ammonia atmosphere. The reduction–nitridation products with various fractions obtained at various temperatures were analyzed by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The reaction sequence from TiO2 to TiN in ammonia atmosphere was changed by increasing the reaction temperature. The reaction sequence at 1173 K was found as TiO2 → TiN1?xOx → TiN. When the reaction temperature was above 1273 K, the reaction sequence changed to as follows: TiO2 → Ti9O17 → TiN1?xOx → TiN. Ti3O5 was not found as an intermediate phase on account of its instability in NH3 atmosphere. The morphology of the synthesized TiN is closely related to that of the raw materials. 相似文献
11.
Carbon nanotubes (CNTs) were introduced into the precursor infiltration and pyrolysis (PIP) carbon fiber reinforced silicon carbide matrix (Cf/SiC) composite via the infiltration slurry. The weight fraction of CNTs in the composite was 0.765‰. The fiber–matrix interface coating was prepared through chemical vapor deposition (CVD) process using methyltrichlorosilane (MTS). Effects of the CNTs on mechanical and thermal properties of the composite were evaluated by three-point bending test, single-edge notched beam (SENB) test, and laser flash method. Attributed to the introduction of the small quantity of CNTs, flexural strength and fracture toughness of the Cf/SiC composite both increased by 25%, and thermal conductivity at room temperature increased by 30%. 相似文献
12.
T. S. Argunova M. Yu. Gutkin K. D. Shcherbachev J. H. Je J. -H. Lim O. P. Kazarova E. N. Mokhov 《Journal of Materials Science》2017,52(8):4244-4252
Bulk AlN crystals grown by sublimation on SiC substrates exhibit relatively high dislocation densities. The kind of defect formation at early growth stages influences the structural quality of the grown crystals. In this work, the dislocation distribution near to the interface is understood through investigation of thin (≤1.5 mm) continuous (non-cracked) freestanding crystals obtained in one process with the evaporation of the substrates. The AlN specimens were characterized using synchrotron radiation imaging techniques. We revealed by triple-axis X-ray diffraction study that, near to the former interface, randomly distributed dislocations configured to form boundaries between \(\sim \)0.02\(^{\circ }\) misoriented sub-grains (from [0001] direction). Threading dislocation structure similar to that in epitaxial GaN films was not detected. To explain these observations, a theoretical model of misfit stress relaxation near the interface is suggested. 相似文献
13.
Karen J. Buechler David R. Chacon David R. Scott Alan W. Weimer 《Journal of Materials Science》2001,36(14):3395-3402
The effect of additives is investigated for the carbothermal reduction synthesis of nanophase silicon carbide/silicon nitride composite powders. Mixtures of silica, carbon, seed silicon nitride, and additive are reacted in a thermogravimetric analyzer. The mass loss information combined with compositional and spectroscopic analysis allows product quality (morphology, surface area, -Si3N4 and -SiC contents, oxygen content, etc.) information to be obtained. It was observed that all of the additives used in this study increased the reaction rate. Lithium carbonate produced a silicon nitride/silicon carbide composite that was not significantly different from experiments without promoter. However, the product quality was severely affected in other instances. 相似文献
14.
Antonio E. Martinelli Domingos S. A. Paulo Rubens M. Nascimento Michele P. Távora Uílame U. Gomes Clodomiro Alves Jr 《Journal of Materials Science》2007,42(1):314-319
Fe-reinforced composites were manufactured by the addition of 10–20 wt.% NbC or TaC particles aiming at improved mechanical
and wear behavior. Two varieties of Fe powders from Hoeganaes Corp. were used, Ancorsteel 1000B and 45P. Composites produced
using the former variety included a small amount of Fe3P to induce liquid-phase sintering whereas 45P powder was pre-alloyed with P by the manufacturer. The hardness of the matrix
was adjusted adding carbon to the composite mixture. The powders were milled for different times and annealed prior to pressing.
A dilatometric study was carried out under hydrogen to establish optimum sintering profiles. Relative densities up to 97%
TD were achieved. Both microstructure and density of the sintered pellets were evaluated in order to establish correlations
involving composition, processing parameters and microstructure of the composite. 相似文献
15.
《Nanostructured Materials》1998,10(8):1393-1400
Chemical reduction was used to produce nanocrystalline Ag-Pd alloy particles for applications in electronic component fabrication. The alloy particles were prepared at room temperature from formaldehyde-sodium hydroxide solutions and silver and palladium nitrates. Characterization of these particles by X-ray powder diffraction (XRD) reveals bi-metal and nanocrystalline silver-palladium alloys. Energy dispersive and XRD analysis of these products shows a complete range of solid solution. Characterization of the morphology, and the oxidation behavior of the Ag-Pd alloy powders are reported. 相似文献
16.
Siavash Imanian Ghazanlou Amir Hassan Shafie Farhood Sahand Hosouli Somayeh Ahmadiyeh Ali Rasooli 《Materials and Manufacturing Processes》2018,33(10):1067-1079
Ni–Co/SiO2 composite coating was electrodeposited on the steel substrate. The coatings were characterized by X-ray diffraction and scanning electron microscopy. The microhardness of the composite coatings was studied by variation of the electroplating parameters, such as the pulse current (PC) and direct current (DC) electrodeposition methods, deposition temperature, electrolyte pH, concentration of surfactants, sodium dodecyl sulfate (SDS), and cetyltrimethylammonium bromide (CTAB). Zeta potential of SiO2 particles measurements was performed with various pH, SDS, and CTAB concentrations. The data depict that the hardness of Ni–Co/SiO2 nanocomposite coatings manufactured by PC electrodeposition increases with the increase of bath temperature, pH, SDS, and CTAB concentration up to 50°C, 4.6, 0.3, and 0.2?g/L, respectively. Beyond mentioned optimum values, the microhardness of nanocomposite coating decreases. Using DC method led to reduce the microhardness. Utilizing SiO2 microparticles instead of SiO2 nanoparticles for reinforcing resulted in declining the microhardness. The friction coefficient and wear results demonstrated that using PC method and nanosized particles led to reduce the friction coefficient and increase the resistance to wear. Anodic polarization results illustrated that using SiO2 nanoparticles and PC method to prepare coating caused corrosion resistance of coating in a 3.5?wt% NaCl solution to enhance. 相似文献
17.
《Materials Letters》2004,58(17-18):2326-2330
HAuCl4 was reduced by ethylene glycol, in the presence of polyvinylpyrrolidone (PVP) under microwave (MW) heating in a continuous wave (CW) mode for 2 min. Dominant products were polygonal nanoplates and close-to-spherical nanoparticles of gold. In addition, small amounts of single crystalline gold nanorods and nanowires (0.5–3% of total number of products) with diameters of 20–100 nm and lengths of 0.6–5 μm were produced. The diameter and length of gold nanorods and nanowires could be controlled by changing the HAuCl4·4H2O/PVP ratio. The formation mechanism of anisotropic gold nanostructures was discussed. 相似文献
18.
19.
《Composites Part A》1999,30(4):399-403
Molten aluminum reduces and penetrates silicate ceramics to produce a metal–ceramic composite which yields an Al2O3 skeleton infiltrated with a solidified Al–Si alloy. Penetration experiments have been used to study the influence of p(O2), temperature and substrate composition on penetration kinetics and composite microstructure. The limiting kinetic step for Al penetration is the chemical reaction between Al and the ceramic. For dense substrates the maximum reaction rates are observed between 1000–1200°C and are independent of p(O2). For porous substrates it is necessary to reach a critical temperature or p(O2), before infiltration starts. Increasing the Si concentration in the molten Al results in the reduction of the reaction rates. 相似文献
20.
Rajeev Kumar Anil Kumar Mandeep Kaur Sandeep Kumar P. R. Sengupta V. Raman Gopal Bhatia 《Journal of Materials Science》2009,44(17):4633-4638
Carbon-micro or nano silicon carbide–boron carbide (C-micro or nanoSiC–B4C) composites were prepared by heating the mixtures of green coke and carbon black as carbon source, boron carbide and silicon
at temperature of 1,400 °C. Green coke reacts with silicon to give micron sized silicon carbide while the reaction between
silicon and carbon black gives nano silicon carbide in the resulting carbon–ceramic composites. The green coke was coated
with a suitable coal tar pitch material and used to develop carbon-(micro or nano) silicon carbide–boron carbide composites
in a separate lot. The composites were characterized for various properties including oxidation resistance. It was observed
that both types of composites made from uncoated as well as pitch-coated green coke exhibited good oxidation resistance at
800–1,200 °C. The density and bending strength of composites developed with pitch-coated green coke improved significantly
due to the enhanced binding of the constituents by the pitch. 相似文献