1,720,964 research outputs found
The study of nonequilibrium Fe-Ti alloys prepared by high-energy mechanical deformation
No full textWe have studied the nature of the solid-state amorphization induced by mechanical deformation (ball milling) in the case of the Fe2Ti phase [mechanical milling (MM)] and that of the iron and titanium phases mixed in the atomic proportion Fe67Ti33 [mechanical alloying (MA)]. Neutron and x-ray diffraction, Combined with Mossbauer spectroscopy at room temperature, of samples mechanically treated for different times indicate that the MM of the Fe2Ti compound leads to a highly fragmented and disordered (micro)crystalline phase. No changes of the Fe2Ti (MgZn2-type) structure are observed in the mechanically and thermally treated Fe2Ti alloys. Conversely, the MA of the pure elements shows a partial amorphization reaction. The chemical short-range order observed in the neutron-diffraction data indicates that a true alloying of the elements occurs. In addition, the thermograms of the MA specimens are different from those of the equivalent MM products. In fact, the phases observed after annealing at 600 degrees C of the specimens MA 2 and 4 h are a mixture of alpha-iron and of disordered Fe-Ti intermetallic. A fully amorphous structure is obtained after annealing the samples MA treated for 8 and 16 h. (C) 1996 American Institute of Physics
Structural evolution of mechanical alloyed Fe-Al powders after consolidation and thermal ageing
No full textUNKNOWN GA2O3 STRUCTURAL PHASE AND RELATED CHARACTERISTICS AS ACTIVE LAYERS FOR O2 SENSORS
No full textThe structural characterization of the Ga2O3 thin films, deposited onto Al2O3 substratum by reactive radio frequency magnetron sputtering, was performed with a theta:2theta powder diffractometer in the Bragg-Brentano geometry. With reference to the pattern of the substratum alone, spectra of the films show additional broad lines indicative of very small coherent domains of diffraction. However, it is not possible to match the observed lines with any of the Ga2O3 phases known in the literature (alpha, beta, gamma, delta and epsilon). Furthermore, there is a texture of this unindexed phase which develops as a function of the deposition temperature. The electrical characteristics, performed at ambient pressure in a flux of an 02/N2 mixture for various operating temperatures, show that film conductivity depends on the 02 partial pressure in the range 1%-21% according to an empirical power law sigma almost-equal-to kp(O2)n with n almost-equal-to 1/4
MECHANICAL ALLOYING OF IMMISCIBLE CU(70)TM(30) ALLOYS (TM=FE,CO)
No full textFour series of copper-based alloys with compositions Cu70Co30, Cu70Fe30Cu70Co15Fe15 and Cu-70(CoFe)(30) were synthesized by mechanical alloying (MA). The interest in these materials is as parents of alloys which will show the giant magnet resistance (GMR) effect. The structural evolution was studied as a function of the MA time by means of Mossbauer spectroscopy, X-ray and neutron diffraction techniques and differential scanning calorimetry (DSC). In spite of the positive heat of mixing of the alloy constituents, the complete dissolution of the minority phases (iron and/or cobalt) into the copper f.c.c. lattice was observed for each specimen after 16 h of MA. This alloying was accompanied by changes in lattice parameter \Delta a(0)/a(0)\ of up to 0.5% with respect to pure copper. Analysis of the crystallization products arising from DSC treatments up to 600 degrees C revealed a separation into copper f.c.c. and iron-based b.c.c, phases. In the case of the ternary Cu-70(FeCo)(30) alloys, the FeCo intermetallic compound was obtained by heating both alloys which originated as ternaries and also as pseudo-binaries based on copper plus the intermetallic phase. Mossbauer spectra of the annealed Cu70Fe30 specimens also revealed a non-magnetic phase of iron with a f.c.c. environment, which was probably stabilized by the presence of copper and small quantities of nitrogen
X-ray powder diffraction and Mossbauer study of nanocrystalline Fe-Al prepared by mechanical alloying
No full textIron-aluminium alloys of composition Fe50Al50 and Fe75Al25 were produced by mechanical alloying (MA) of the pure elemental powders. A structural refinement of X-ray powder data on the mechanically alloyed products according to the Rietveld method has detailed the progressive dissolution of aluminium into the lattice of alpha-iron as a function of MA time. With respect to pure iron, a volume expansion of approximate to 3% is measured in both compositions mechanically alloyed for 32 k In the iron and aluminium phases, the Debye-Waller static disorder increases as a function of MA time and the intrinsic shape of the peak profiles becomes predominantly Cauchy. These changes are accompanied by an increase in the average microstrain and by a reduction in the average crystallite size (which includes also the effect of dislocations). The Mossbauer spectra show that in the equiatomic case the initial sharp magnetic sextet of alpha-iron is progressively reduced and is replaced by a doublet, while for the Fe75Al25 composition a broad magnetic sextet is eventually obtained. Thermal scans at 600 degrees C of the specimens mechanically alloyed for 2, 4 and 8 h precipitate essentially the Al5Fe2 phase. In the case of the Fe50Al50 specimens, annealing of the powders mechanically alloyed for 16 and 32 h precipitates mainly the partially ordered FeAl intermetallic compound, whilst no ordering is obtained in the Fe75Al25 case. Copyright (C) 1996 Acta Metallurgica Inc
COPPER COBALT FCC METASTABLE PHASE PREPARED BY MECHANICAL ALLOYING
No full textThe solid state reaction of the normally immiscible copper and cobalt powders has been studied at the equiatomic composition with the mechanical alloying (MA) technique, supplemented by the milling of cobalt and copper elemental powders. The diffraction of unmilled pure cobalt powder shows the coexistence of the two face-centred-cubic (f.c.c.) and hexagonal-close-packed (h.c.p.) allotropes. After 1 h of milling the neutron diffraction pattern reveals only the highly distorted h.c.p. phase. Further, the degree of distortion in the h.c.p. phase is highly dependent on the crystallographic directions. Mechanical alloying of the Cu-Co equiatomic mixture creates an almost entirely fc.c. single phase after 2 h of treatment. The lattice parameter of the Cu(Co)extended solid solution decreases on increasing the milling time. Moreover, a thermal treatment at 700-degrees-C of the powders MA 16 h demixes the pure constituents. A comparison with previous data on the Cu-Co system prepared by rapid quenching, evaporation and magnetron sputtering methods confirms the MA method to be an efficient synthesis tool of new metastable non-equilibrium phases
A study of Cu<sub>50</sub>Fe<sub>50</sub> produced by mechanical alloying and its thermal treatment
No full textA specimen of Cu50Fe50 equiatomic composition was mechanically alloyed (MA) by ball milling starting from the pure elements, which are immiscible according to the equilibrium phase diagram. Structural analysis by x-ray and neutron diffraction has shown that the mechanical process initially reduces the crystallite size of both elements as a function of the milling time. The diffraction data show that the bcc iron phase is subsequently consumed, due to progressive incorporation of the iron atoms into the fcc copper matrix. The Mossbauer spectra of a specimen MA for 16 h has a broad magnetic profile typical of a Fe-Cu extended solid solution, with some evidence of two local environments of the iron atoms and a small admixture of the gamma-Fe. The annealing of these MA treated specimens effects a decomposition of the extended solid solution into FCC copper and both alpha- and gamma-iron allotropes. This decomposition process is discussed in relation to spinodal decomposition and to nucleation-and-growth mechanisms
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
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