Additional High-temperature Annealing Research Articles

Eutectoid decompositions in Ce-containing ABO3 perovskites: Part I, the case of cooperative growth in CeAlO3.

Oxidation of perovskite CeAlO3 results in the eutectoid transformation to CeO2 and Al2O3. This phase transformation was recorded using thermal gravimetric analysis, X-ray diffraction, and scanning transmission electron microscopy. Lamellar features in the resultant microstructure indicates cooperative growth. Processing conditions dictate the lamellae sizes, which can be as small as a few nanometers, and coarsen into large domains with additional high temperature annealing.

Effect of homogenization on the structure, hardness and corrosion resistance of 1570C alloy

Influence of homogenizing annealing on the parameters of grain structure, phase constituents involving nanoscale aluminides of transition metals, hardness and corrosion resistance of the aluminum alloy 1570C (Al-5Mg-0.18Mn-0.2Sc-0.08Zr, mass.%) ingot was studied to optimize its heat treatment regimes according to a two-stage annealing scheme. At the first step, the ingot was annealed at 360°С for 6 hours (conventional route). At the second step, the annealing was performed at various temperatures in the range of 400 – 520°C for 1 hour. It was found, that additional high-temperature annealing resulted in some reduction in the alloy strength. However, it was quite effective to eliminate the chemical heterogeneity of the cast structure and increase the corrosion resistance maintaining grain size, dispersity and coherency of Al3(Sc, Zr) precipitates.

Improved Optical and Electrochromic Properties of NiOx Films by Low-Temperature Spin-Coating Method Based on NiOx Nanoparticles.

Solution approaches to NiOx films for electrochromic applications are problematic due to the need of an additional high-temperature annealing treatment step in inert gas. In this study, nanostructured NiOx powder with grain size of about 10.1 nm was synthesized for fabrication of NiOx films for electrochromic application. Non-toxic dispersants of isopropanol and deionized water were used and the whole process was carried out in air. The effects of the number of spin-coating layers, annealing temperature, and the volume ratios of isopropanol to deionized water were systematically investigated. Large transmittance change of 62.3% at 550 nm, high coloration efficiency (42.8 cm2/C), rapid switching time (coloring time is 4 s, bleaching time is 3 s), and good stability were achieved in the optimized NiOx film. The optimized process only required a low processing temperature of 150 °C in air with spin-coating three times and 1:2 volume ratio of isopropanol to deionized water. Finally, good cycle durability of up to 2000 cycles without obvious degradation was demonstrated by cyclic voltammetry tests in a LiClO4/propylene carbonate electrolyte. This study provides a simple and effective approach for fabrication of NiOx films at low temperature in air, which is attractive for further commercialization of electrochromic devices.

Calorimetric study of Eu2O3–ZrO2 feedstock powders and sintered materials

The synthesis of ceramic materials based on europia–zirconia system and obtained by solid-state reaction in high-temperature vacuum press was investigated. Firstly, phase composition and calorimetric behavior of feedstock powders was investigated. The second part of the paper concerns the synthesis process of non-stoichiometric mixtures of feedstock powders prepared by four different methods of mixing. The influence of the homogenization method on the calorimetric behavior and phase composition of obtained sinters was studied. Finally, the influence of the additional high-temperature annealing was also investigated. From the obtained results, it can be concluded that the mixing procedure had a very strong influence on the morphology of obtained sinters. This is due to the structural inhomogeneity, as indicated by differences in phase composition. The synthesis process has a gradual character, and the obtaining of materials with different level of homogeneity allowed the determination of the order of subsequent intermediate phase formation.

Pulsed laser-induced formation of silica nanogrids

Silica grids with micron to sub-micron mesh sizes and wire diameters of 50 nm are fabricated on fused silica substrates. They are formed by single-pulse structured excimer laser irradiation of a UV-absorbing silicon suboxide (SiO x ) coating through the transparent substrate. A polydimethylsiloxane (PDMS) superstrate (cover layer) coated on top of the SiO x film prior to laser exposure serves as confinement for controlled laser-induced structure formation. At sufficiently high laser fluence, this process leads to grids consisting of a periodic loop network connected to the substrate at regular positions. By an additional high-temperature annealing, the residual SiO x is oxidized, and a pure SiO2 grid is obtained.PACS81.07.-b; 81.07.Gf; 81.65.Cf

Effect of Annealing on Nanocrystalline Structure of Nb<sub>3</sub>Sn Diffusion Layers in Composites with Internal Tin Sources

Multifilamentary Nb3Sn-based superconducting composites manufactured by an internal-tin method have been studied by transmission (TEM) and scanning (SEM) electron microscopy. The main goal of this study is to reveal the effect of diffusion annealing regimes as well as the external diameter of the wires on the structure of nanocrystalline Nb3Sn layers (average grain size, grain size distribution, layer thickness, amount of Sn, etc.). It is demonstrated that multistep diffusion annealing results in quite a complete transformation of Nb filaments into Nb3Sn though some amount of the residual Nb remains in the filaments center. With an external diameter decrease the superconducting layers structure has been found to refine and get somewhat more uniform. An additional high-temperature annealing results in marked growth of Nb3Sn grain sizes and their scattering in sizes, which may negatively affect the current-carrying capacity of a wire.

Rapid synthesis of TiC–Fe 3C composite by electric discharge assisted mechanical milling of ilmenite (FeTiO 3) with graphite

Carbo-thermic reduction of ilmenite (FeTiO 3) to TiO 2 and/or TiC is traditionally carried out by a high temperature annealing treatment at ∼1500 °C. In this work, electric discharge assisted mechanical milling (EDAMM) has been used to synthesise TiC + Fe 3C from FeTiO 3 in 5 min. In this study we report of the reduction of FeTiO 3 with C that does not require an additional high temperature annealing treatment.

Elastic modulus of multi-walled carbon nanotubes produced by catalytic chemical vapour deposition

Carbon nanotubes (CNTs) are ideal structures for use as reinforcement fibres in composite materials, due to their extraordinary mechanical properties, in particular high Young’s modulus (E∼1 TPa). Usually the high value of E is taken as granted for all types of carbon CNTs. Here we demonstrate that multi-walled carbon nanotubes (MWCNTs) produced by catalytic chemical vapour deposition (CCVD) have low moduli (E<100 GPa) independently of their growth conditions. We attribute this to the presence of structural defects. Additional high-temperature annealing failed to improve the mechanical properties. This study urges a better control of the growth process in order to obtain high strength CCVD grown MWCNTs suitable for reinforcement in large-scale industrial applications.

High-resolution x-ray diffraction and high-resolution scanning electron microscopy studies of Si-based structures with a buried amorphous layer

Structural and geometrical parameters of Si samples with buried amorphous layers, produced by oxygen implantation and high-temperature annealings, were measured by high-resolution x-ray diffraction and high-resolution scanning electron microscopy. By using a newly developed simulation procedure precise fittings of x-ray diffraction spectra were made and important parameters were derived, such as the averaged fluctuations of the thickness of the amorphous layer (“interface roughness”) and of the interplanar spacing in the Si top layer. The data obtained revealed a reduction in interface roughness, i.e., an improvement of the samples’ quality after additional high-temperature annealing. This conclusion was supported by electron microscopy images demonstrating a more complete dissolution of SiO2 precipitates as a result of additional heat treatment. The importance of more sophisticated annealing was also confirmed by the Moiré x-ray diffraction topographs taken on the topography beamline of the European Synchrotron Radiation Facility.

Grain boundary ensembles due to grain growth in copper with strong recrystallization texture

A strong cube texture was generated in copper after cold rolling and primary recrystallization. Additional successive annealing was performed to stimulate grain growth in the as-recrystallized microstructure. Microstructural changes, evolution of texture and distributions of grain boundaries and triple junctions during grain growth were investigated. A progressive strengthening of the cube texture entailed an increase in the fraction of low-angle boundaries. Slightly misoriented cube oriented grains clustered to form Σ1–Σ1–Σ1 triple junctions. Their fraction increased remarkably with the texture strengthening. The fraction of Σ3–Σ3–Σ1 junctions formed during grain growth at lower temperature remained constant upon additional high temperature annealing. The frequencies of triple junctions containing several random or special boundaries with Σ>3 tended to decrease during grain growth at higher annealing temperature.

Melt processing of high- Tc Nd [sbnd]-Ba [sbnd]-Cu [sbnd]-O superconductors in air

We have succeeded in fabricating Nd-Ba-Cu-O bulk superconductors, which exhibit high T c and a sharp superconducting transition, by the melt process in air without additional high temperature annealing in a reduced oxygen atmosphere. The key to this achievement is the use of Ba-rich Nd 4−2 z Ba 2+2 z Cu 2− z O 10− δ as a precursor. Fabricated bulk samples exhibit onset T c values of 94–95 K and the secondary peak effect in the M-H loop like the case of Nd-Ba-Cu-O superconductors produced by melt processing in a reduced oxygen atmosphere. The peak position and the irreversibility field for the best sample were about 1.2 T and 5 T at 77.3 K, respectively, and the estimated J c at the peak field was about 2.3 × 10 4 A cm −2.

CuCl quantum dots in CuCl-doped NaCl crystals

CuCl microcrystallites with mean radius of about 3nm were found in CuCl-doped NaCl crystal stored for a long time and without any additional high-temperature annealing of the sample. Three components were identified in the delay of the emission from CuCl microcrystallites at 4.2 K: i) fast component having a lifetime τ=0.4 ns, ascribed to the radiative decay of Z 3-confined exciton, already reported; ii) intermediate component ( τ=3.3 μsec) preliminarily ascribed to the triplet state of Z 3-confined exciton and iii) slow non-exponential component in ms time scale, explained by recombination of free electrons and holes via Z 3-confined exciton state.

Plasma-enhanced CVD of high quality insulating films

A modified plasma-enhanced chemical vapor deposition process (He-PECVD) is described, and used to deposit high quality silicon-based insulators at low substrate temperature (≤ 350°C). This process utilizes very high levels of helium dilution of the reactive gases to eliminate many of the problems normally associated with plasma deposition. SiO 2 films deposited by He-PECVD approach the standards of high quality thermally grown oxide and very thin films (≤ 100 Å) with excellent electrical integrity can be deposited over large areas routinely. MOSFET's incorporating deposited gate oxides highlight the fundamental difference between deposition and growth by revealing a strong correlation between the ultimate device performance and pre-deposition silicon surface treatment. By minimizing the extent of process-induced surface damage, good quality deposited oxide FET's can be fabricated without the need for additional high temperature annealing. The He-PECVD process can also be applied to the deposition of Si 3N 4 films, also with marked improvements in film quality.

Superbeta polysilicon emitter transistors

In-situ phosphorus-doped polysilicon emitters deposited on monocrystalline silicon substrates at a temperature of 627°C and subjected to no additional high-temperature annealing are shown to be capable of giving Gummel numbers G <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</inf> in excess of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> scm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> . Polysilicon emitters formed in this way have been used to produce superbeta transistors with performance comparable to the record levels recently reported for MIS emitter devices. In particular, common-emitter current gains β in excess of 30000 have been obtained at low V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CB</inf> values.