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Formation of equiaxed crystal structures in directionally solidified Al-Si alloys using Nb-based heterogeneous nuclei
The design of chemical compositions containing potent nuclei for the enhancement of heterogeneous nucleation in aluminium, especially cast alloys such as Al-Si alloys, is a matter of importance in order to achieve homogeneous properties in castings with complex geometries. We identified that Al3Nb/NbB2 compounds are effective heterogeneous nuclei and are successfully produced in the form of Al-2Nb-xB (x = 0.5, 1 and 2) master alloys. Our study shows that the inoculation of Al-10Si braze alloy with these compounds effectively promotes the heterogeneous nucleation of primary α-Al crystals and reduces the undercooling
needed for solidification to take place. Moreover, we present evidences that these Nb-based compounds prevent the growth of columnar crystals and permit to obtain, for the first time, fine and equiaxed crystals in directionally solidified Al-10Si braze alloy. As a consequence of the potent heterogeneous particles, the size of the α-Al crystals was found to be less dependent on the processing conditions, especially the thermal gradient. Finally, we also demonstrate that the enhanced nucleation leads to the refinement of secondary phases such as eutectic silicon and primary silicon particles.The authors are thankful for the financial support from the Technology Strategy Board (TSB) through the TSB/101177 Project and to the Engineering and Physical Sciences Research Council (EPSRC) through the EP/J013749/1 and EP/K031422/1 Projects
Synthesis and characterization of multiferroic BiMnO
We report on the high pressure synthesis of BiMnO, a manganite
displaying a "quadruple perovskite" structure. Structural characterization of
single crystal samples shows a distorted and asymmetrical coordination around
the Bi atom, due to presence of the lone pair, resulting in
non-centrosymmetric space group Im, leading to a permanent electrical dipole
moment and ferroelectric properties. On the other hand, magnetic
characterization reveals antiferromagnetic transitions, in agreement with the
isostructural compounds, thus evidencing two intrinsic properties that make
BiMnO a promising multiferroic material.Comment: 4 pages, 3 figure
Organic Inhibitors to Prevent Chloride-Induced Corrosion in Concrete: Atomistic Simulations of Triethylenetetramine-Based Inhibitor Film
Inhibitors are largely used to prevent chloride-induced corrosion in reinforced concrete structures thanks to both a barrier effect on chloride penetration and a competition with the adsorption of the inhibitor. The interaction mechanisms between passive film on carbon steel, the inhibitor molecule, and chlorides still require deeper understanding. Theoretical studies based on molecular mechanics (MM) and molecular dynamics (MD) methods can be useful to better understand the passive film formation and its interaction with chlorides. In this work, the interaction between a triethylenetetramine (TETA) inhibitor film on γ-FeOOH surface and chlorides is studied using MD methods. After MM optimization in the initial adsorption stage, some chlorides are close to protective TETA film. After MD run at room temperature effectively, chlorides remain close to the protective film. In order to have an effective barrier on chloride attack, the metal oxide must remain wholly covered by the protective film. The TETA film well covers the lepidocrocite surface but cannot kinetically efficiently prevent the chloride-induced corrosion compared to other organic films exposing COO− groups because it does not exert any repulsion to chlorides
Hydrogen charging of carbon and low alloy steel by electrochemical methods
Atomic hydrogen can be the result of different processes like electroplating, chemical and electrochemical pickling treatments, in welding or by cathodic processes in corrosive fluids. Moreover, adsorption of atomic hydrogen can affect materials in contact with high pressure gaseous hydrogen. Once entered the material, atomic hydrogen interacts with the metal structure and may produce a "damage" of various forms, such as Hydrogen Induced Cracking (HIC), delayed fracture, blistering and hydrogen embrittlement. In particular, when H2S is present ("sour service"), metallic materials, such as carbon and low alloy steels, may suffer hydrogen damage and hydrogen embrittlement. Sour service materials must be used in compliance with international accepted standards, used worldwide in oil and gas activities, when fluids are classified as sour. The present study has been carried out in order to set up an electrochemical method to charge with hydrogen two typical pipeline materials, carbon and low alloy steels. The reason of the use of an electrochemical method is to avoid any critical conditions from the point of view of preparation, safety and disposal. Hydrogen content in the specimens was measured by two different methods: hot glycerol bath and Inert Gas Fusion (IGF) analysis. Hydrogen content in the specimens is about 0.6-2 ppm; mechanical performances were assessed by means of J integral tests: a pronounced decrease of fracture toughness was observed for H charged specimens.{GRAPHIACAL ABSTRACT
Solitary fibrous tumour of the supraglottic larynx.
Solitary fibrous tumour (SFT) is a rare, benign, mesenchymal neoplasm that usually arises in the pleura, but rarely involves other sites outside the serosal space (mediastinum, lung, liver, thyroid gland); larynx involvement is very rare with only sporadic cases reported in the literature. We report a case of SFT in a 41-year-old woman with supraglottic laryngeal invovlement; symptoms included dysphonia and mild odynophagia lasting 2 years, and fibre-optic laryngeal evaluation showed a sub-mucosal mass involving the left supraglottis and medial wall of the pyriform sinus. MRI represents the gold standard tool for differential diagnosis (with schwannoma, paraganglioma and haemangioma) and correct staging, while immunohistochemical and cytomorphologic analysis (bcl-2 and CD34 positivity in 90% of cases) is needed for definitive diagnosis. Surgery is the main treatment (endoscopic and open conservative technique), and its goal is a balance between safe oncological resection and good preservation of laryngeal functions; in this particular case an open laryngeal approach was scheduled due to the size of the tumour. Prognosis is good and in only a few cases (especially in pleural SFT) does the biological behaviour take a malignant course
Internal-strain mediated coupling between polar Bi and magnetic Mn ions in the defect-free quadruple-perovskite BiMnMnO
By means of neutron powder diffraction, we investigated the effect of the
polar Bi ion on the magnetic ordering of the Mn ions in
BiMnMnO, the counterpart with \textit{quadruple} perovskite
structure of the \textit{simple} perovskite BiMnO. The data are consistent
with a \textit{noncentrosymmetric} spacegroup which contrasts the
\textit{centrosymmetric} one previously reported for the isovalent and
isomorphic compound LaMnMnO, which gives evidence of a
Bi-induced polarization of the lattice. At low temperature, the two
Mn sublattices of the and sites order antiferromagnetically
(AFM) in an independent manner at 25 and 55 K, similarly to the case of
LaMnMnO. However, both magnetic structures of
BiMnMnO radically differ from those of LaMnMnO.
In BiMnMnO the moments of the sites form
an anti-body AFM structure, whilst the moments \textbf{M} of the
sites result from a large and \textit{uniform} modulation along the b-axis of the moments \textbf{M} in the
-plane. The modulation is strikingly correlated with the displacements of
the Mn ions induced by the Bi ions. Our analysis unveils a strong
magnetoelastic coupling between the internal strain created by the Bi
ions and the moment of the Mn ions in the sites. This is ascribed to
the high symmetry of the oxygen sites and to the absence of oxygen defects, two
characteristics of quadruple perovskites not found in simple ones, which
prevent the release of the Bi-induced strain through distortions or
disorder. This demonstrates the possibility of a large magnetoelectric coupling
in proper ferroelectrics and suggests a novel concept of internal strain
engineering for multiferroics design.Comment: 9 pages, 7 figures, 5 table
Effetto dell’intermittenza della corrente di protezione nei sistemi di protezione catodica dell’acciaio
The paper reports the results of a preliminary research study on the effects of protection current intermittence
on the cathodic protection conditions of buried or immersed pipelines. It is well known that cathodic protection
has chemical and electrochemical beneficial effects on carbon steel, which do not disappear instantly in
correspondence to the current interruption. According to this premise, laboratory tests of intermittent cathodic
protection in which the current has been interrupted cyclically were carried out on carbon steel specimens in
soil-simulating solution. The effects of the duration of the current-off time, the number of on-off cycles, and of
the applied current density have been studied. Potential has been monitored weekly and the residual corrosion
rate was calculated by means of a simple electrochemical model
Utilizzo di nitrati come inibitori di corrosione per le armature nel calcestruzzo
Corrosion inhibitors have been long considered as an effective preventative technique to slow down the onset
and/or propagation of corrosion phenomena in reinforced concrete. Several substances have been evaluated
as possible candidates, and great interest has been dedicated to nitrite ion. When investigating how these
substances slow down corrosion related processes – chlorides diffusion, critical chloride threshold, CO2
penetration and corrosion propagation –interactions between inhibitor and concrete are also vital.
Recently, nitrate based compounds have been proposed as corrosion inhibitors, as they present lower cost
than nitrites and are already used in concrete as set accelerators. Some studies have shown that nitrates
inhibiting mechanism is similar to that of nitrites. This work proposes the evaluation of a nitrate based
substance as possible corrosion inhibitor in concrete, and compares its performance with a nitrite based
inhibitor
Commensurate structural modulation in the charge- and orbitally-ordered phase of the quadruple perovskite (NaMn)MnO
By means of synchrotron x-ray and electron diffraction, we studied the
structural changes at the charge order transition =176 K in the
mixed-valence quadruple perovskite (NaMn)MnO. Below we
find satellite peaks indicating a commensurate structural modulation with the
same propagation vector q =(1/2,0,-1/2) of the CE magnetic order that appears
at low temperature, similarly to the case of simple perovskites like
LaCaMnO. In the present case, the modulated structure
together with the observation of a large entropy change at gives
evidence of a rare case of full Mn/Mn charge and orbital order
consistent with the Goodenough-Kanamori model.Comment: Accepted for publication in Phys. Rev. B Rapid Communication
3D Printed Short Carbon Fibres Reinforced Polyamide: Tensile and Compressive Characterisation and Multiscale Failure Analysis
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