Temperature-time study of the magnetoelectric multiferroic (1-x)BiFeO 3 -(x)PbTiO 3 by x-ray and electron diffraction on the reported morphotropic phase boundary (MPB) compositions revealed that this MPB does not correspond to the equilibrium state. The MPB like state is rather of metastable nature and arise due to kinetic arrest of metastable rhombohedral (R3c) phase, along with the equilibrium tetragonal (P4mm) phase. The life time of the metastable R3c nuclei is very sensitive to composition and temperature, and nearly diverges at x ! 0.27. The MPB like state appears only if the system is cooled before the metastable R3c nuclei could vanish. These findings resolve the long standing controversy with regard to seemingly erratic phase formation behaviour reported by different groups and provides a rational basis for developing genuine equilibrium MPB compositions in this system for better piezoelectric properties. V C 2013 AIP Publishing LLC. [http://dx.
The mechanisms of
bacterial contact killing induced by Cu surfaces
were explored through high-resolution studies based on combinations
of the focused ion beam (FIB), scanning transmission electron microscopy
(STEM), high-resolution TEM, and nanoscale Fourier transform infrared
spectroscopy (nano-FTIR) microscopy of individual bacterial cells
of Gram-positive Bacillus subtilis in
direct contact with Cu metal and Cu5Zn5Al1Sn surfaces after high-touch
corrosion conditions. This approach permitted subcellular information
to be extracted from the bioinorganic interface between a single bacterium
and Cu/Cu5Zn5Al1Sn surfaces after complete contact killing. Early
stages of interaction between individual bacteria and the metal/alloy
surfaces include cell leakage of extracellular polymeric substances
(EPSs) from the bacterium and changes in the metal/alloy surface composition
upon adherence of bacteria. Three key observations responsible for
Cu-induced contact killing include cell membrane damage, formation
of nanosized copper-containing particles within the bacteria cell,
and intracellular copper redox reactions. Direct evidence of cell
membrane damage was observed upon contact with both Cu metal and Cu5Zn5Al1Sn
surfaces. Cell membrane damage permits copper to enter into the cell
interior through two possible routes, as small fragmentized Cu2O particles from the corrosion product layer and/or as released
copper ions. This results in the presence of intracellular copper
oxide nanoparticles inside the cell. The nanosized particles consist
primarily of CuO with smaller amounts of Cu2O. The existence
of two oxidation states of copper suggests that intracellular redox
reactions play an important role. The nanoparticle formation can be
regarded as a detoxification process of copper, which immobilizes
copper ions via transformation processes within the bacteria into
poorly soluble or even insoluble nanosized Cu structures. Similarly,
the formation of primarily Cu(II) oxide nanoparticles could be a possible
way for the bacteria to deactivate the toxic effects induced by copper
ions via conversion of Cu(I) to Cu(II).
The precipitation of cementite (M 3 C) from as-quenched martensite during tempering at 500 and 700°C was investigated in a Fe-1C-1Cr (wt%) alloy. Tempering for a short duration at 700°C results in a Cr/Fe ratio in the core region of M 3 C precipitates which is equal to the bulk alloy composition, while a shell on the surface of the precipitates exhibits a higher Cr concentration. With a prolonged tempering up to 5 h, the shell concentration gradually increases toward the equilibrium value, but the core region has not yet reached the equilibrium value. After tempering for 5 s at 500°C, there is no Cr enrichment found at the M 3 C-matrix interface, while a transition to partitioning of Cr is found during the first 5 min of tempering at 500°C. These experimental results indicate that M 3 C grows without significant partitioning of substitutional elements at both temperatures initially, i.e., growth is carbon diffusion controlled. This stage is, however, very short, and soon after 5 s at 700°C and 5 min at 500°C, Cr diffusion becomes important. Calculations using the diffusion simulation software DICTRA and precipitation simulation software TC-PRISMA were performed. The diffusion simulations using the local equilibrium interface condition show excellent agreement with experiments concerning Cr enrichment of the particles, but the size evolution is overestimated. On the other hand, the precipitation simulations underestimate the size evolution. It is suggested that a major improvement in the precipitation model could be achieved by implementing a modified nucleation model that considers nucleation far from the equilibrium composition.
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