ABSTRACT
This paper presents the synthesis of Fe-Co-Ni nanocomposites by chemical precipitation, followed by a reduction process. It was found that the influence of the chemical composition and reduction temperature greatly alters the phase formation, its structures, particle size distribution, and magnetic properties of Fe-Co-Ni nanocomposites. The initial hydroxides of Fe-Co-Ni combinations were prepared by the co-precipitation method from nitrate precursors and precipitated using alkali. The reduction process was carried out by hydrogen in the temperature range of 300-500 °C under isothermal conditions. The nanocomposites had metallic and intermetallic phases with different lattice parameter values due to the increase in Fe content. In this paper, we showed that the values of the magnetic parameters of nanocomposites can be controlled in the ranges of MS = 7.6-192.5 Am2/kg, Mr = 0.4-39.7 Am2/kg, Mr/Ms = 0.02-0.32, and HcM = 4.72-60.68 kA/m by regulating the composition and reduction temperature of the Fe-Co-Ni composites. Due to the reduction process, drastic variations in the magnetic features result from the intermetallic and metallic face formation. The variation in magnetic characteristics is guided by the reduction degree, particle size growth, and crystallinity enhancement. Moreover, the reduction of the surface spins fraction of the nanocomposites under their growth induced an increase in the saturation magnetization. This is the first report where the influence of Fe content on the Fe-Co-Ni ternary system phase content and magnetic properties was evaluated. The Fe-Co-Ni ternary nanocomposites obtained by co-precipitation, followed by the hydrogen reduction led to the formation of better magnetic materials for various magnetically coupled device applications.
ABSTRACT
Two new species of Oreocharis Benth. from Fan Si Pan, the highest mountain in Vietnam (Sa Pa) are described and illustrated. Oreocharis grandiflora W.H.Chen, Q.H.Nguyen & Y.M.Shui, is similar to O. flavida Merr. from Hainan province, China, but differs mainly by its larger and infundibuliform corolla, stamens adnate to the base of the corolla tube and stamens coherent in two pairs. The second, Oreocharis longituba W.H.Chen, Q.H.Nguyen & Y.M.Shui, is similar to O. hirsuta Barnett, endemic to northern Thailand, but mainly differs in its pubescence, coherent stamens and glabrous filaments.
ABSTRACT
BACKGROUND: In our recent molecular phylogenetic study of Asian Begonia, two undescribed species, B. guixiensis sp. ined. (S. Guangxi, China) and B. longa sp. ined. (Vietnam), were sampled and placed within the strongly supported clade composed of Begonia sect. Coelocentrum and other co-distributed rhizomatous species in the Sino-Vietnamese limestone karsts. While Begonia sect. Coelocentrum has been recircumscribed based on the phylogenetic relationships, B. guixiensis sp. ined. and B. longa sp. ined. remain illegitimate names. In continuation of our studies in Asian Begonia, these two new species are described and illustrated. RESULTS: Begonia guixiensis resembles B. cylindrica in the peltate, subcoriaceous leaves, differing by the shape of ovary/fruit and the type of placentation. In aspect, B. longa bears a superficial resemblance to B. brevipedunculata in leaf shape in particular, differing by many other features such as the long internodes, shorter petioles and smaller leaves, longer peduncles and 3-locular ovary. The chromosome number of both new species is determined as 2n = 30. CONCLUSION: A careful study of the literature, herbarium specimens and living plants, both in the wild and in cultivation in the experimental greenhouse, support the recognition of the two new species, which are described and illustrated herein.
