Search

Abstract: The formation of Al6Ru intermetallic compounds using high-energy ball milling was investigated. High-purity Al and Ru crystalline powders, in the relative (molar) ratio of 6:1, were milled for periods up to 30h. Samples of the milled materials were annealed at different times and temperatures. The microstructures of the annealed samples were compared to those of the as-milled samples. It was found that the obtained alloys have compositions that are in accord with the Al–Ru phase diagram. However, the X-ray analysis of a 10h milled sample, annealed at 873K for 30min, showed evidence of the formation of a quasicrystalline icosahedral alloy mixed with the crystalline Al6Ru. Scanning electron microscopy showed that the microstructures are similar to those obtained by other sample preparation techniques. [Copyright &y& Elsevier]

Abstract: The system CeCoGe3− x Si x is of special interest since there is evidence that a quantum critical point of the antiferromagnetic phase can be approached by alloying as well as by application of high pressure. With new results of AC-susceptibility and specific heat measurements on CeCoGe2.1Si0.9 under high pressure presented here, we show by comparison with former data that the tuning parameters composition and pressure, respectively, are equivalent. Alloy and pressure data fit in a common phase diagram. The quantitative behavior of c/T under pressure, too, corresponds to that under changes of composition. [Copyright &y& Elsevier]

Abstract: In this paper, synthesis, structural, microstructural and magnetic properties of high-energy ball milled BiFeO3 and Bi0.95Eu0.05FeO3 powders were thoroughly investigated through X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy and magnetization measurements. Single-phased compounds were processed by using both mechanosynthesis and post-milling annealing. The set of results did not indicate considerable alterations in the magnetic ordering of the powders, even though their ordering temperature, magnetization and coercivity were highly sensitive to the narrow grain sizes distribution of nanograins and substituting Eu ion. In addition, we have shown that enhanced magnetic properties of BiFeO3 could be achieved by a low degree of Eu substitution, yet preserving the structural and microstructural characteristics of the processed powders. [Copyright &y& Elsevier]

The system (α-Fe2O3)x(α-Al2O3)1-x was subjected to 24 h of high-energy ball-milling in different milling media and velocities, with x varying in the 0.10–0.50 range. Stainless-steel vial with stainless-steel balls and alumina vial with zirconia rods were alternately used in a planetary mill apparatus, at velocities ranging from 100 to 600 rpm. The phases present in the milled samples were characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). For the stainless-steel milling medium, the results revealed that the final products are extremely dependent on the starting concentration of hematite and on the milling velocity. Iron contamination, originated from abrasion in the metallic medium (MM), was detected for low x and, also, for intermediate x at higher milling velocities. Solid solutions of the (Fe,Al)2O3 type, with different iron concentration ranges, were identified in both milling media. In the ceramic vial, a medium in which milling velocity is also found to be a decisive factor, the FeAlO3 phase, non-isostructural to the precursors, was also recognized in addition to solid solutions. Low-temperature Mössbauer measurements verified the occurrence of four magnetic iron sites in this compound. [Copyright &y& Elsevier]

Abstract: Samples of UO2 and up to 10wt% of Gd2O3 were prepared by solid-state reaction under a reducing atmosphere, in a thermal path comprising ramps and dwell times in the temperature range of 900–1750°C. The sintered material was analyzed by X-ray diffraction and 155Gd Mössbauer spectroscopy. The results showed that for samples annealed up to 900°C, the gadolinium sesquioxide remained unreacted. However, when the temperature was increased to 1300°C, a solid-state reaction took place forming mixed oxides. For the more severe sintering condition, at 1750°C, gadolinia left urania partially unreacted producing a material consisting of two compositions, UO2 (with no dissolved gadolinium) and (U,Gd)O2. The proposed heating cycle provided pellets free from Gd2O3 phase and may be used by the nuclear fuel industry as a suitable sintering process. [Copyright &y& Elsevier]

Abstract: Multiferroic BiFe1−x Mn x O3 ceramic powders were submitted to high-energy ball-milling. The structural, microstructural and Mössbauer spectral properties of the obtained samples were carefully investigated in this paper. Nanostructuration and amorphization were achieved with the employed milling settings. The addition of Mn in BiFeO3 did not induce significant microstructural or structural changes even though it induced significant modifications in the Mössbauer hyperfine parameters. [Copyright &y& Elsevier]

Abstract: The system (α-Fe2O3) x (α-Al2O3)1− x was subjected to high-energy ball-milling, with the milling time varying between 3 and 72h. The precursor powders, alumina and hematite, were pre-mixed in nominal concentrations x =0.10, 0.25 and milled in a planetary ball-mill, under specific milling conditions. The milled samples were characterized through scanning electron microscopy, X-ray diffraction and Mössbauer spectroscopy. As a result of the above analyses, the formation of two isostructural solid solutions, α-(FeΔy Al1−Δy )2O3 and α-(Fe1−Δw AlΔw )2O3, which evolve peculiarly with the milling time, was observed. For samples with x =0.10, α-Fe and the FeAl2O4 compound were identified, in addition to the solid solutions. The presence of the spinel and metallic iron phases is attributed to the abrasion of the vial and balls. For x =0.25 samples, the iron content tends, for increasing milling times, to be equally shared between both solid solutions, verifying the driving force of the process to homogenize the system under milling. [Copyright &y& Elsevier]

Recent collections of Ipomoea from North East Brazil have revealed a number of unexpected disjunct distributions. The most remarkable is that of I. eremnobrocha D. F. Austin, previously thought to be endemic to Panama but now known from three states in NE Brazil. Revision of Panamanian material named I. eremnobrocha unexpectedly showed that two distinct species had been treated under this one name. Specimens from the Chagres National Park area in Panama are described as a new species under the name I. isthmica J. R. I. Wood & Buril while I. eremnobrocha is retained as the correct name for the plant from the Altos de Campana in Panama and NE Brazil. An amended description of this species is given and a table of differences between the related species is provided. Two recently described species from Bolivia, I. graniticola J. R. I. Wood & Scotland and I. chiquitensis J. R. I. Wood & Scotland are recorded from NE Brazil several thousand km from their type localities. Attention is drawn to the role of granite inselbergs as sites of species with a disjunct distribution. A possible relative of I. chiquitensis is described as a new species from NE Brazil under the name I. melancholica J. R. I. Wood & Buril. The new species are illustrated with line drawings and maps of the unusual distribution patterns are provided., (© The Author(s) 2017.)

From the perception of human populations, we can assess the changes occurring in certain landscapes and the factors that cause those changes. Such studies have proven helpful in increasing the knowledge of the history of a landscape, recognizing past formations and projecting its future. Our research objective was to determine how a landscape dominated by the palm tree Attalea speciosa, a species of ecological, economic, and cultural importance, has been changing over time by synthesizing and comparing historical documents and local perceptions. This study was conducted in Araripe Environmental Protection Area, Northeast Region, Brazil. To understand local landscape change, we interviewed active harvesters in four communities in which A. speciosa use has been documented. Historical documents were evaluated as a complement to the interview data. According to local informants, areas previously used for cultivation and animal husbandry that were abandoned or decimated by droughts in the region may have fostered the expansion of a monodominant A. speciosa forest. Furthermore, other forms of landscape management resulting from human population growth may also have affected the current and past distribution of this forest.