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Effect of Multiwall Carbon Nanotubes on the Ablative Properties of Carbon Fiber-Reinforced Epoxy Matrix Composites
No full textThe effect of multiwall carbon nanotubes (MWCNTs) on the thermal and ablative properties of carbon fiber epoxy matrix composites was investigated. Thermochemical and oxidation reactions were found to dominate the ablation mechanism. Shear forces and high temperatures were produced using oxy-acetylene torch. Three types of composites were investigated: (a) carbon fiber epoxy matrix composites, (b) carbon fiber epoxy matrix composite containing 0.2wt% MWCNTs and (c) carbon fiber epoxy matrix composite containing 0.4wt% MWCNTs. Composites containing 0.2wt% MWCNTs showed 5.4% increase in erosion resistance, while composites containing 0.4wt% MWCNTs showed 9.6% increase in erosion resistance compared with carbon fiber epoxy matrix composites. Thermal conductivity increased with the addition of MWCNTs, i.e., 15 and 52% in composites containing 0.2 and 0.4wt% MWCNTs, respectively. Due to the addition of MWCNTs, the increased thermal conductivity of MWCNT-loaded epoxy matrix affected the ablation behavior of carbon fibers and resulted in gradual thinning of carbon fibers
Microstructural and Mechanical Profile of Carbon Fiber Epoxy Matrix Composites Containing Nanodiamonds
No full textSilica and borosilicate glass matrix composites containing carbon nanotubes
Get PDFDue to their remarkable properties and unique dimensions, carbon nanotubes (CNTs)
are considered as an exciting nano-reinforcement in a variety of inorganic matrix composites.
However, published data is unable to clearly define the role of CNTs on the properties of these
composites, in particular, the mechanical properties including hardness, stiffness, strength and
fracture toughness. This lack of knowledge is due in part to manufacturing issues, such as the
dispersion of CNTs, densification of composites and microstructural changes during sintering.
Moreover, interest in the electrical and thermal properties of inorganic matrix composites
demands a comprehensive functional property evaluation. The still unexplored technological
properties of these composites, such as thermal shock, ageing, friction and wear resistance, also
deserve particular attention, in order to identify the extent of improvement that can be achieved
due to CNTs. The microstructural characterisation including the nature of CNT distribution and
their embedded morphology in brittle and amorphous matrices is still unclear, together with the
nature of the CNT/matrix interface. Finally, the effect of different CNT aspect ratios on
properties is yet to be investigated in order to choose the most suitable CNT sizes for desired
composite performance.
The present study is, therefore, aimed at developing a model composite system of
uniformly dispersed CNTs of different sizes and loadings in a dense, brittle and amorphous
matrix, and exploring the real effect of CNTs on physical, mechanical, functional and
technological properties of these composites together with their microstructural and interfacial
characterisation.
Indigenously synthesised and functionalised multiwalled carbon nanotubes (MWCNTs)
of four different aspect ratios (~31-65) were used as reinforcement, up to 10wt% (13.2vol%)
loadings, while silica (SiO2) glass was chosen as an inorganic matrix. Heterocoagulation upon
colloidal mixing provided composite powders with homogeneously dispersed MWCNTs while
pressureless sintering produced dense (96-99%) composites. The randomly oriented MWCNTs in the glass matrix showed a mechanical MWCNT/glass interface due to the interlocking of
MWCNTs with the matrix. The indentation fracture toughness was improved, by up to ~100%,
but hardness and stiffness decreased by 21-38% and 20-37%, respectively. The electrical
conductivity increased by >11 orders of magnitude but the thermal conductivity showed limited
improvement, i.e. 41-48%.
The effect of different MWCNT sizes on the mechanical properties, such as hardness,
elastic modulus and indentation fracture toughness, could not be determined due to the
decrease in the densities of the composites containing higher aspect ratio MWCNTs; however,
the functional properties, such as electrical and thermal conductivity, increased in proportion to
the MWCNT size.
The presence of MWCNTs in the thermal shock resistant silica glass matrix did not
produce thermal cracking after a single quench to 20oC from 1200oC or multiple quenches from
1000oC; however, devitrification of the glass was observed. During the thermal ageing of
composites (up to 1000oC for up to 96h), no significant degradation was observed at lower
temperatures (500oC) except limited surface MWCNT oxidation. However, at 750oC,
considerable MWCNT oxidation was noticed, and at 1000oC, cristobalite was also formed
producing surface cracking on cooling. The decarburisation depth due to MWCNT oxidation
increased with time and temperature, and completely porous composites were obtained after
oxidation of all of the embedded MWCNTs. The friction coefficient decreased with increase in
MWCNT content, while the formation of a stable graphitic layer in composites containing 10wt%
MWCNTs reversed the otherwise increasing wear rate.
Finally, the established composite processing route was applied to a commercial
borosilicate glass system containing up to 10wt% (17vol%) MWCNTs. The microstructure along
with the resulting mechanical and functional properties ensured the applicability of the
developed model system, which is believed to serve as a guide in future for preparation of other
technically relevant inorganic matrix composites containing CNTs for improved properties
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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