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Posts Tagged ‘CRYSTAL growth’

Formation of coni alloy thin films on silicon by electroless deposition






Abstract: Electroless deposition of CoNi alloy thin films on a Si substrate was investigated by varying different processing parameters. The quality of the film was strongly influenced by the concentration of the electrolyte and the presence of NH4F. A quality adhesive CoNi thin film was formed when the concentration of NiSO4·6H2O exceeded 0.03M, and this is attributed to self-activation at higher Ni ion concentrations. The presence of NH4F in the electrolyte influenced the crystallinity of the film and the deposition rate. The dominant growth mechanism was demonstrated by OCP (open-circuit potential). The concentration of NH4F affected the composition of CoNi thin films, exerting a complexing effect of ammonium ions in the bath containing more than 0.5M NH4F. The deposition rate of the film increased with increased NH4F concentration. Hydrazine, used as a reducing agent, did not affect the composition of the CoNi thin film, but the deposition rate increased with an increase of hydrazine. The microstructure and crystalline phase of CoNi thin films deposited by electroless deposition were characterized by a X-ray diffraction (XRD) technique and X-ray photoelectron spectroscopy (XPS). A detailed study of the effects of other processing parameters such as metal ion concentrations, the presence of NH4F, and the amount of hydrazine was also carried out. [Copyright &y& Elsevier]


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Anodic growth of titanium oxide: electrochemical behaviour and morphological evolution

Abstract: The mechanism of growth of anodic titanium oxide in sulphuric acid has been investigated by potentiostatic and potentiodynamic anodizing, electrochemical impedance spectroscopy and transmission electron microscopy. It was found that most of the charge passed during growth is consumed in oxygen evolution at the oxide–solution interface and the measured current relates to the electronic conduction properties of the oxide. Further, it was confirmed that an amorphous to crystalline transition takes place during potentiodynamic growth, and the transition triggers the additional generation of oxygen bubbles that occurs within the oxide. Depending on the growth conditions, the oxygen bubbles can rupture with local re-growth of the film then occurring. [Copyright &y& Elsevier]

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Recrystallization of the hot isostatic pressed nickel-base superalloy fgh4096. ii: characterization and application

Abstract: Recrystallization of the hot isostatic pressed nickel-base superalloy FGH4096 undergoes three characteristic periods, viz., incubation, nucleation and growth. Working temperature has a great effect on its boundary migration and nucleation. In recrystallization process, the nucleation rate is obviously accelerated with the increasing working temperature. To obtain fine grains, hot working should be carried out at the temperature of 1050–1080°C. After two passes multiple forging, the grain size is significantly refined from 30.0 to 2.2μm, and the refinement mechanism is found to be the repeated dynamic recrystallization (DRX) in the multiple forging process. Equiaxed-flatted gradient microstructure is obtained via the gradient temperature heat treatment (GTHT). [Copyright &y& Elsevier]

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Grain growth characteristics and its effect on deformation behavior in nanocrystalline ni

Abstract: The grain growth characteristics and its effect on deformation behavior of nanocrystalline(nc)-Ni having a grain size of 60nm have been studied. The kinetics of thermal grain growth was studied by DSC and resistivity experiments. Thermal instability leading to grain growth in nc-Ni was assessed by determining the activation energy required for grain growth in the temperature range of 100–400°C. The activation energy was found to be ∼100kJ/mol below Curie temperature and ∼298kJ/mol above Curie temperature. The effect of grain size on nano-hardness and loading rate was investigated using nanoindentation technique. The deformation parameters like strain rate sensitivity (m) and activation volume () for different grain sizes in nc-Ni were also evaluated. The interaction of dislocations-grain boundaries mediated mechanism was appeared to be the rate controlling plastic deformation mechanism. [Copyright &y& Elsevier]

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Growth kinetics of tial3 layer in multi-laminated ti–(tib2/al) composite sheets during annealing treatment

Abstract: The growth of TiAl3 is a critical stage during the fabrication of TiAl sheets employing Ti and Al sheets. In the present work, Al sheets were replaced by TiB2/Al composites for (i) the production of TiB2–TiAl composite sheets and (ii) a better deformation compatibility. The formation mechanism and growth kinetics of TiAl3 layer in the multi-laminated Ti–(TiB2/Al) composites were systematically investigated between 600°C and 650°C. The formation of TiAl3 was a reaction–diffusion process accompanied by its order–disorder transition, its growth towards TiB2/Al layers was found faster than that towards Ti layers. The introduction of TiB2 particles had little influence on the growth of TiAl3 layer which followed the parabolic growth law. The activation energy for growth of TiAl3 layer was estimated to be 254.9kJmol−1. [Copyright &y& Elsevier]

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Carbon nanotubes grown on electrospun polyacrylonitrile-based carbon nanofibers via chemical vapor deposition

Carbon nanotubes (CNTs) grown on electrospun polyacrylonitrile-based carbon nanofibers (CNFs) via chemical vapor deposition were studied in this paper. Analyses of Raman spectra and X-ray diffraction patterns revealed that incorporation of CNTs could improve the crystalline and structure integrity of the obtained CNFs/CNTs composite. About 7.4 wt% of CNTs were grown on the electrospun CNFs confirmed by thermal gravimetric analysis. The electrochemical results showed that the surface activity and the cycle retention of the CNFs/CNTs composite were enhanced due to its three-dimensional nanostructure, enhanced pore distribution, and good conductivity. The CNFs/CNTs composite offers a great potential for high-performance lithium-ion batteries as the electrode. [ABSTRACT FROM AUTHOR]

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On the merits of raman spectroscopy and thermogravimetric analysis to asses carbon nanotube structural modifications

Raman spectroscopy, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy, and transmission electron microscopy are used to assess structural changes generated on the surface of multi-walled (MWCNTs) and single-walled (SWCNTs) carbon nanotubes. Different levels of structural modifications are generated by the use of acidic oxidative treatments. It is found that Raman spectroscopy is a very powerful technique to assess structural modification of SWCNTs with initial low defect concentration. For MWCNTs grown by chemical vapor deposition, which already contain a high density of structural defects in their as-produced state, Raman spectroscopy is not a very sensitive tool to detect the generation of further defects or other structural modifications introduced through acidic treatments. For this later case, TGA is a sensitive technique to assess structural modifications on the nanotubes. [ABSTRACT FROM AUTHOR]

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Positive temperature coefficient of resistance effect in natio-doped 0.94batio-0.06(bina)tio ceramics

The positive temperature coefficient of resistance (PTCR) characteristics of NaTiO (NT)-doped 0.94BaTiO-0.06(BiNa)TiO (BBNT) ceramics were investigated in order to evaluate the effect of NT as a new additive for lead-free PTCR thermistor application. The BBNT ceramic sintered at 1325°C exhibited a relatively high Curie temperature ( T) of 158°C while its PTCR characteristic was not satisfactory for thermistor application. However, doping with NT significantly influenced the PTCR behavior of BBNT ceramic. It is considered that NT was responsible for grain growth of the BBNT by forming a liquid phase during sintering due to its low melting temperature of 1300°C. The grain growth resulted in the enhanced PTCR characteristics of BBNT ceramic. In particular, 0.1 mol% NT doped BBNT ceramic exhibited excellent PTCR performance of low resistivity at room temperature (1.6×10 Ω cm), resistivity increase near T (1.28×10) and high T of 158°C, suitable for lead-free PTCR thermistor application. [ABSTRACT FROM AUTHOR]

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An improved model of the seeded batch crystallization of glucose monohydrate from aqueous solutions

Abstract: The current research has produced an accurate model of the non-nucleating seeded batch crystallization of glucose monohydrate which includes complex phenomena including crystal growth rate dispersion and the effect of the mutarotation reaction. The model is able to predict the population density of crystals in the batch as a function of particle size and batch time, as well as total glucose concentration in the mother liquor and the fraction of glucose in the α-d-glucopyranose form. A previous model of similar systems was limited by considering only systems with monosize seed crystals, and where growth rate dispersion had a negligible effect on the particle size distribution. Because of the nature of the ‘common history’ crystals that are produced by the growth of glucose monohydrate, the modifications required to the model to account for these additions to the model are remarkably simple. By predicting the full population density the model produces an accurate mass balance for the crystallization process, since the second moment of the crystal size distribution (CSD) may be calculated analytically at every point in the simulation. This enables the competitive kinetics between the rate of crystal mass deposition of α-glucose and the rate of production of α-glucose via the mutarotation reaction to be more accurately accounted for, and hence the significance of the mutarotation reaction on the crystal growth to be more accurately predicted. [Copyright &y& Elsevier]

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Crystal growth of high magnetostrictive polycrystalline fe81ga19 alloys

Abstract: High magnetostrictive Fe81Ga19 alloy was prepared by induction heating zone melting method. The microstructure, solute partition behaviour, orientation evolution and magnetostriction are investigated. During the crystal growth process, the initial small grains gradually grow into large columnar crystals, and the solid–liquid interface shows slightly concave morphology. The equilibrium solute partition coefficient (k 0), effective solute partition coefficient (k e) and solution diffusion coefficient (D) are calculated to be 0.74, 0.76 and 1.04×10−9 m2/s, respectively. In the steady growth stage, the composition distribution of the FeGa rod is uniform with average level about 18.50at% Ga, which is close to the nominal composition. The deviation of the 〈001〉 orientation from the axial direction evolves from about 8° to 3° along the growth direction, and the corresponding magnetostriction increases from the initial 180ppm to the final 305ppm. [Copyright &y& Elsevier]

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