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Preparation of monodisperse ZrO2 by the Microwave Heating of Zirconyl Chloride Solutious
No full textBased on the principle that the solubility of a salt decreases as the dielectric constant of the solvent decreases, zirconia powders were prepared by heating a zirconyl chloride solution with a 2-PrOH-water mixture as the solvent, The morphology, size, and size distribution of the resulting particles were highly sensitive to the heating method used on the starting solution. Particles formed under conventional heating methods were polydisperse, agglomerated spherical, or irregularly shaped because of inhomogeneous precipitation through the temperature gradient, the shear force induced by stirring, compositional nonuniformity, and the low heating rate, The present study demonstrated that microwaves provide an excellent means of heating uniformly and rapidly without stirring, The particles resulting from microwave treatment were monodisperse and spherical, with a mean diameter of 0.28 mu m.
Formation of monodisperse spherical TiO2 powders by thermal hydrolysis of Ti(SO4)(2)
No full textTitania powders have been prepared by the thermal hydrolysis of titanium sulfate at 80 degrees C in a mixed solvent of n-propyl alcohol (n-PrOH) and water The morphology of the powders was greatly influenced by the volume ratio in n-PrOH to water (RH ratio) of the solvent, An RH ratio of 1.0 was essential for the formation of spherical TiO2 powders, When hydroxypropyl cellulose (HPC) was used as a steric dispersant, monodisperse spherical powders 0.7 mu m in diameter mere produced. As the RH ratio was increased, the zeta potential of the powders was negatively increased and the dielectric constant of the solvent was decreased, However, powders obtained at an RH ratio of 1.0 were observed to have the highest energy barrier, The colloidal stability of the powders in a mixed solvent of n-PrOH and water is discussed, As-precipitated powders were amorphous hydrates of titania and were crystallized by calcination into anatase (>600 degrees C) and rutile (>800 degrees C)
Pyrolytic conversion of spherical organo-silica powder to silicon nitride under nitrogen
No full textMonodisperse, spherical Si3N4 powder composed of fine particulates was synthesized by pyrolyzing spherical organo-silica powder under nitrogen. The organo-silica powder was prepared by hydrolyzing a mixture of phenyltrimethoxysilane (PTMS) and tetraethoxysilane (TEOS) in a methanol solution of mater and ammonia, The organo-silica powder consisted of 81.3 at.% silicon units derived from PTMS and 18.7 at.% silicon units derived from TEOS, During the pyrolysis under nitrogen, the organo-silica powder decomposed to a mixture of free carbon and silica, with an increase of the surface area, at 500 degrees-600 degrees C, followed by the formation of alpha-Si3N4, with beta-Si3N4 as a minor phase, ai: 1450 degrees and 1500 degrees C and beta-SiC at 1550 degrees C. The pyrolyzed powders, which retained the spherical shape and monodispersity of the organo-silica powders, with a reduction in mean particle diameter, were composed of fine particulates that were similar to 40 mm in size
Preparaton of Monodisperse and Spherical Zirconia Powders by Heating of Alcohol-Aqueous Salt Solution
No full textA novel method is demonstrated which yields a spherical ZrO2 powder of narrow size distribution through heating of a zirconyl chloride solution with an alcohol-mater mixture as the solvent. The kind and composition of the solvent mixture greatly influenced the behavior of the precipitation and the morphology of the resulting particles, When l-propanol or 2-propanol was employed as the alcohol of the solvent mixture, the resulting particles had a spherical shape and a narrow size distribution. The particle size and the particle agglomeration level could be controlled by the amount of hgdroxypropyl cellulose (HPC) in the solution, As-prepared amorphous powder was crystallized to a mixture of metastable tetragonal phase and monoclinic phase at about 460 degrees C. The metastable tetragonal phase was converted to the monoclinic phase as the calcination temperature was increased. After calcination, the spherical shape of the zirconia powder was retained, while its particle size was decreased slightly
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
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