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Sintering characteristics of Si3N4 with additives from Y2O3-La2O3 binary system
No full textSi3N4 was sintered with sintering aids from La2O3-Y2O3 binary system varying their compositions from 10La2O3 90Y2O3 to 90La2O310Y2O3. Three eutectic compositions were found in the said system which governs densification of Si3N4, 60La2O340Y2O3 was found to be the best sintering composition and it can yield YLaO3 phase at the grain boundaries
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Statistical analysis of mechanical properties of pressureless sintered multiwalled carbon nanotube/alumina nanocomposites
No full textMechanical properties of pressureless sintered 0.15-1.2 vol. multiwalled carbon nanotube reinforced alumina matrix nanocomposites have been analyzed using the 2-parameter Weibull statistics. Electron microscopy and phase analysis of nanocomposites sintered at 1700°C for 2 h in Argon revealed existence of interpenetrating network of nanotubes in alumina, formation of thin interface resembling stoichiometric aluminum monoxycarbide and matrix grain refinement by nanotubes. Statistical analyses indicated that with increasing Vickers hardness testing load (4.9-19.6 N) and flexural strength measurement temperature (room temperature to 1100°C), Weibull modulus of nanocomposites increased significantly suggesting improved consistency at higher load and temperature. The highest Weibull moduli were obtained for nanocomposites containing either 0.15 or 0.3 vol. nanotube which were �40 and �15 higher than single phase alumina for hardness and strength, respectively, supporting the specimen size effect on reliability of present brittle ceramic matrix nanocomposites. Superior mechanical reliability of nanocomposites over pure alumina was primarily attributed to the presence of structurally intact nanotubes forming effective interface region to ensure proper load sharing, matrix grain refinement, and especially, at higher testing load and temperature, overall averaging effect of flaws to yield higher Weibull moduli. © 2012 Elsevier B.V. All rights reserved
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Non-isothermal oxidation kinetics of single- and multi-walled carbon nanotubes up to 1273 K in ambient
No full textNon-isothermal oxidation kinetics of single- and multi-walled carbon nanotubes (CNTs) have been studied using thermogravimetry up to 1273 K in ambient using multiple heating rates. One single heating rate based model-fitting technique and four multiple heating rates based model-free isoconversional methods were used for this purpose. Depending on nanotube structure and impurity content, average activation energy (E-a), pre-exponential factor (A), reaction order (n), and degradation mechanism changed considerably. For multi-walled CNTs, E-a and A evaluated using model-fitting technique were ranged from 142.31 to 178.19 kJ mol(-1), respectively, and from 1.71 x 10(5) to 5.81 x 10(7) s(-1), respectively, whereas, E-a for single-walled CNTs ranged from 83.84 to 148.68 kJ mol(-1) and A from 2.55 x 10(2) to 1.18 x 10(7) s(-1). Although, irrespective of CNT type, the model-fitting method resulted in a single kinetic triplet i.e., E-a, A, and reaction mechanism, model-free isoconversional methods suggested that thermal oxidation of these nanotubes could be either a simple single- step mechanism with almost constant activation energy throughout the reaction span or a complex process involving multiple mechanisms that offered varying E-a with extent of conversion. Criado method was employed to predict degradation mechanism(s) of these CNTs
Temperature and load dependent mechanical properties of pressureless sintered carbon nanotube/alumina nanocomposites
No full textMultiwalled carbon nanotube (MWCNT)/alumina (Al2O3) nanocomposites having different CNT contents have been fabricated by wet-mixing and pressureless sintering in Argon at 1700 degrees C. Depending on indentation load, the highest improvement of 15-34% in hardness was achieved in 0.3 vol.% MWCNT/Al2O3 nanocomposite. Indentation size effect (Mayer's exponent = 1.753) on hardness was the most prominent in 1.2 vol.% MWCNT/Al2O3 nanocomposite due to presence of clustered CNTs, non-uniform interface and porous microstructure. similar to 34% increase in fracture toughness was achieved in 0.3 vol.% MWCNT/Al2O3 nanocomposite than pure Al2O3 (similar to 3.84 MPa m(0.5)). High MWCNT loaded nanocomposites had reduced R-curve sensitivity because of increased matrix grain refining effect and reduced matrix compressive residual stress. High temperature flexural strength results indicated that strength retention of nanocomposites up to 1100 degrees C in ambient was much better compared to pure Al2O3. To predict structure-property relationship in nanocomposites, detailed microstructural and fractographic studies were also performed. (C) 2011 Elsevier B.V. All rights reserved
Role of interface on electrical conductivity of carbon nanotube/alumina nanocomposite
No full textInterface of multiwalled carbon nanotube (MWCNT)/alumina (Al2O3) nanocomposites have been studied using TEM. At low sintering temperature (T-sin = 1500 degrees C), a 3-5 nm thick amorphous interface region was noticed. Nanocomposite sintered at 1700 degrees C possessed a well-defined graphene layer coating on matrix grains as the interface between CNT and Al2O3. A mechanism of such layered interface formation has been proposed. No traceable chemical reaction product was observed at the interface even after sintering at 1700 degrees C. It was noticed that while DC electrical conductivity (sigma(DC)) of 1500 degrees C sintered 2.4 vol% MWCNT/Al2O3 nanocomposite was only similar to 0.02 S/m, it raised to similar to 21 S/m when sintering was done at 1700 degrees C. Such 10(3) times increase in sigma(DC) of present nanocomposite at a constant CNT loading was not only resulted from the exceptionally high electron mobility of CNT but the well-crystallized graphene interface on insulating type Al2O3 grains also significantly contributed in the overall increase of electrical performance of the nanocomposite, especially, when sintering was done at 1700 degrees C. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved
Sintering and properties of silicon nitride densified with liquids in the system MgOAlNSiO2
No full textSilicon nitride was pressureless sintered at 1700–1800°C with liquids in the ternary system MgO-AlN-SiO2; liquids rich in nitrogen and high MgO content sintered readily; Si3N4 of 98% theoretical density was obtained. Heat treatments of the samples were carried out to crystallise the grain boundary phase. Hightemperature flexural strength, fracture toughness and creep of the samples were measured. Increase in nitrogen content with constant MgO:SiO2 ratio produced products with better thermomechanical properties. Superior products were obtained with high nitrogen and low MgO content in the sintering liquid due to a slower sintering rate and acicular grain growth. The best product had a flexural strength (4-point bending test, 40-20 mm) of 490 MPa and fracture toughness of View the MathML source. The creep strain rate and stress of a sample sintered with a liquid with a high MgO content were 1·0 × 10−5 h−1 (at 1200°C) and 100 MPa, respectively
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