Synthesis and characterization of Co2+ doped TiO2 nanoparticles

Scrolled titania nanotubes were synthesized by a hydrothermal method using commercial TiO2 powder in proton-deficient aqueous systems. In presence of CoCl2 extended hydrothermal treatment of TiO2 nanotubes lead to formation Co2+ doped TiO2 nanoparticles. TEM and HRTEM measurement were used for determining the shape, dimension and structure of doped nanoaprticles. XRD confirmed anatase crystalline structure od Co2+ doped TiO2. The presence of Co2+ ions did not induce distortions of the overall anatase crystal structure of TiO2 matrix. The concentration of Co2+ ions was 1.5% compared with the amount of Ti4+ ions.Physical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200

Prepoznavanje faza koje sadrže Fe u mikrostrukturi livene legure AA6026 i njihova evolucija tokom postupka homogenizacije

The Fe-bearing intermetallic phases present in the as-cast AA6026 alloy and their evolution during homogenization treatments at 480-550°C were investigated using optical microscopy, SEM, and TEM techniques in combination with EDS analysis. In addition to the α-Al(Fe,Mn)Si phase with dendritic morphology, two types of plate-like Fe-bearing microconstituents were revealed in the microstructure of the as-cast alloy. The EDS microanalysis and electron diffraction showed that one set of platelets represented thin sections of α-Al(Fe,Mn)Si microconstituent. The other set of plate-like microconstituents was identified as a tetragonal, silicon-rich δ-Al4(Fe,Mn)Si2 phase. The formation of the δ-Al4(Fe,Mn)Si2 phase was attributed to the chemical composition of the alloy. During homogenization, the metastable δ-Al4(Fe,Mn)Si2 transformed into the α-Al(Fe,Mn)Si phase and fragmented. The dendritic α-Al(Fe,Mn)Si microconstituents underwent fragmentation. However, while the α-Al(Fe,Mn)Si microconstituents preserved a b.c.c. crystal lattice throughout the process, the product of the transformation of the δ-Al4(Fe,Mn)Si2 phase exhibited primitive cubic lattice.Ispitivanje prisustva faza koje sadrže Fe u mikrostrukturi livene legure AA6026, kao i njihova evolucija tokom postupaka homogenizacije na temperaturama od 480-550 °C, sprovedena su korišćenjem optičke mikroskopije, skenirajuće elektronske mikroskopije (SEM) i transmisione elektronske mikroskopije (TEM) u kombinaciji sa analizom EDS-a. Osim faze α-Al(Fe,Mn)Si sa dendritskom morfologijom, identifikovane su dve vrste pločastih mikrokonstituenata koji sadrže Fe u mikrostrukturi livene legure. EDS mikroanaliza i elektronska difrakcija pokazali su da jedan skup ploča predstavlja samo tanke sekcije mikrokonstituente α-Al(Fe,Mn)Si. Drugi skup pločastih mikrokonstituenata identifikovan je kao četvrtasta, silicijumom bogata faza δ-Al4 (Fe,Mn)Si2 . Formiranje faze δ-Al4 (Fe,Mn)Si2 povezano je sa hemijskim sastavom legure. Tokom homogenizacije, metastabilna faza δ-Al4 (Fe,Mn)Si2 transformisala se u fazu α-Al(Fe,Mn)Si i fragmentirala. Dendritski mikrokonstituenti α-Al(Fe,Mn)Si takođe su fragmentirali. Međutim, dok su mikrokonstituenti α-Al(Fe,Mn)Si sačuvali kubnu kristalnu rešetku tipa b.c.c. tokom procesa, proizvod transformacije faze δ-Al4 (Fe,Mn)Si2 pokazao je prostu kubnu rešetku

Spherical assemblies of titania nanotubes generated through aerosol processing

We report on the possibility to build hierarchically organized three-dimensional (3D) titania spherical particles having high surface-to-volume-ratio, by aerosol processing of nanotubular building blocks. Morphology and crystal structure of titania based spherical assemblies, obtained in the temperature range from 150 to 650°C, were characterized by means of scanning and transmission electron microscopy, x-ray powder diffraction and Raman spectroscopy. Initial shape of 1D building units, nanotubes, was well preserved in the spherical assemblies processed at 150 and 450°C. Processing at 650°C resulted in a collapse of the nanotubular building blocks and formation of the assemblies of irregularly shaped TiO2 nanoparticles. Structural analysis revealed several phase transitions in titania spherical assemblies in course with the temperature increase indicating possibility of in-situ phase composition adjustment during aerosol processing. © 2015 Elsevier Ltd and Techna Group S.r.l

Homogenization of an al-mg alloy and alligatoring failure: alloy ductility and fracture

High-strength Al-Mg alloys have a propensity toward hot fracture and failure by alligatoring during hot rolling. In this study the effect of homogenization conditions on the susceptibility of an Al-5.1Mg-0.7Mn alloy toward alligatoring was investigated. It was found that the plates homogenized in a temperature range of 460-520 degrees C were prone toward alligatoring, but once homogenized at 550 degrees C they were not prone toward it any longer. The characterization of the fracture showed a predominance of the intergranular ductile fracture, but the type of the constitutive particles filling the voids changed with the homogenization regime. Grain decohesion and grain-boundary embrittlement show that certain thermal treatments resulted in a microstructure that promoted slip localization

Electron microscopy observations of twin-twin intersections in a particle hardened copper-titanium alloy

The twin-twin intersections in the precipitation hardened two-phase copper-titanium alloys were studied using conventional and high-resolution electron microscopy. The incident twin propagation through an obstacle twin was accommodated by both slip and twinning. The ledge associated with the twin-twin intersections was associated with complex sessile configurations. The existence of an accommodation mechanism without shear transfer on conventional {111} planes in the obstacle twin led to the formation of strong rotation fields and activation of secondary twinning in the obstacle twin

Precipitation of the beta-phase and corrosion behavior of an al-6.8 wt.% mg alloy

This study was performed on the Al-Mg alloy with the chemical composition: Al-Mg6.8-Mn0.51-Fe0.2-Si0.1. As-received cold rolled material (O-temper) was subjected to (i) cold rolling and annealing at 265 degrees C and 320 degrees C, followed by (ii) sensitization treatment at 100 degrees C. Microstructure characterization showed beta-phase precipitation were grain boundaries and preexisting Mn-rich particles. The annealing temperature had significant beta-phase morphology: microstructure of sensitized specimens annealed at 265 degrees C was characterized by formation of discontinuous particles, while annealing at 320 degrees C resulted in the formation of the thin film at grain boundaries. Presence of the thin film induced corrosion resistance degradation and also affected grain boundary morphology: initially smooth, curved grain boundaries became strongly faceted

INTERGRANULAR CORROSION SUSCEPTIBILITY OF AN AA5083 Al-Mg ALLOY PROCESSED BY ACCUMULATIVE ROLL BONDING (ARB)

Intergranular corrosion (IGC) susceptibility of an AA5083 Al-Mg alloy sheets, highly deformed by accumulative roll-bonding (ARB), was investigated. It was shown that ARB processed specimens were resistant to IGC as the mass loss was <15 mg/cm2. The degree of plastic strain during ARB processing did not affect IGC susceptibility and a value of corrosion potential. After sensitization treatment at 150°C, ARB processed specimens stayed resistant to IGC, in spite of β-phase precipitation along grain boundaries and within the structure. A high degree of deformation achieved by ARB processing, and a large amount of β-phase precipitated during the sensitization, did not cause an increase in IGC susceptibility due to favorable morphology and a distribution of β-phase in the structure

The effect of ECAP and Cu addition on the aging response and grain substructure evolution in an Al-4.4 wt.% Mg alloy

The effect of ECAP conducted at 200 degrees C on the grain substructure evolution in an AA5182 alloy and the same alloy with 1.2 wt.% Cu addition was investigated. Severe plastic deformation was found to accelerate the precipitation kinetics in the AA5182 + Cu alloy, leading to the formation of a fine dispersion of the stable S phase precipitates. These particles homogenized slip, causing a delay of the band/cell substructure formation in the AA5182 + Cu alloy compared to the AA5182 alloy processed in the same manner. Aside from the conventional particle hardening effect, the precipitates also play a role in retarding the recovery and recrystallization processes, retaining the effects of strain in the material after ECAP at elevated temperature

Influence of the Thermomechanical Treatment on the Intergranular Corrosion Susceptibility of Zn-Modified Al-5.1 Wt Pct Mg-0.7 Wt Pct Mn Alloy Sheet

In this study, the effect of thermomechanical treatment on intergranular corrosion (IGC) susceptibility of the Zn-modified Al-5.1 wt pct Mg-0.7 wt pct Mn alloy plates was investigated. The specimens underwent varied amounts of cold work, while final annealing was conducted in the 493 K to 533 K (220 A degrees C to 260 A degrees C) temperature range. It was shown that the extent of cold work, especially at lower temperatures of treatment, had a profound effect on the corrosion resistance of the alloy. Such observation was in direct correlation with the morphology of precipitated ternary grain boundary phase (Al-Mg-Zn). Microstructural characterization showed that, depending on the amount of cold work, different deformation substructures were created, which, in turn, influenced kinetics and the mechanism of precipitation. Wetting of the grain boundaries by the ternary grain boundary phase (Al-Mg-Zn) was a signature of the IGC susceptible state and occurred in the specimens that were subjected to a lower degree of cold work. The specimens that underwent a higher degree of cold work (over 30 pct) showed superior corrosion resistance as a result of ternary grain boundary phase (Al-Mg-Zn) precipitation in the form of discrete particles at the grain boundaries as well as in grain interiors