Search Results
Abstract
DSC analysis is applied to investigate the precipitation reaction in the AA6005 extrusion alloy for different heat treatment practices often presented in commercial production. The quenching practice is shown to have a big impact on the response of the AA6005 alloy to an artificial ageing treatment. The range of β″ precipitation is displaced to lower temperatures in samples quenched in air following the solution treatment. This acceleration, however, does not produce a favorable effect on age hardening capacity since much of the solute Mg and Si is removed from the solid solution before the principal hardening phase can precipitate. The DSC results are in good agreement with the age hardening curves. Natural ageing before artificial ageing promotes clustering activities during a subsequent thermal exposure and produces a strong delay in β″ precipitation.
Abstract
A method for americium-241 and strontium-90 codeposition with precious metals on the cathodic substrate was examined. The influence of pH, current density, solid phase concentration and suspension ageing was determined. The particle size distribution in fresh and aged suspension was measured. It is suggested that the mechanism of americium codeposition is different than that of strontium.
Abstract
A rapid microwave-assisted sample digestion with a high-pressure closed-vessel system is reported for radiostrontium assay in salmon fishbone by β-counting. This allows saving more than one day of analysis time (24 h). Total dissolution of 1.5 g of dried fishbone is possible by using 8 ml of 7.8M nitric acid. The separation scheme gives a strontium chemical recovery of (73±13)% with a detection limit of 24 Bq.kg-1 .
Abstract
Results of micro-PIXE analysis of senile plaques (SP) in Alzheimer's disease (AD) brain have been utilized to independently confirm levels of iron (Fe) as measured by LMMS in adjacent brain sections. LMMS concentrations were calculated based on the preparation and analysis of an iron calibration curve prepared in our laboratory. The LMMS standards consist of ironcis-dicyclohexano-18-crown-6 ether coordination complexes dissolved in Spurr's low viscosity embedding medium. To our knowledge, this is the first report of the use of micro-PIXE, with its spatial resolution and detection limits comparable to that of LMMS, in the validation of LMMS results. The agreement observed between results obtained for Fe by micro-PIXE and LMMS indicates that the use of our LMMS standards, at least in the case of Fe, yields accurate results.
Abstract
Mössbauer spectroscopy was used in order to get information about the anomalous austenite formation1 taking place between 450–600 °C in steel containing 12%Cr and 4%Ni. Even below the equilibrium transition temperature (640 °C) of 
transformation a monotonic increase of the relative spectral area of the line belonging to austenite was observed in the Mössbauer spectra of the steel isothermally aged at 550 °C with increasing ageing time. At the same time, the Cr content of the ferrite phase decreases. Time dependence of the quantity of austenite formed during the isothermal ageing follows the Avrami-kinetics with an exponent n=0.3.
Abstract
Heat-treatable aluminium alloys are widely used for structural applications. Their strength is obtained through age hardening phenomena, that are sensitive to microalloying. In the present paper the results of thermal analyses on the ageing behaviour of an Al-Cu-Mg-Si alloy with silver and zirconium additions are presented. Specimens were water quenched after solution heat treatment, then aged at 453 K and a hardness-versus-time plot was drawn. Samples representative of different ageing conditions were subjected to DSC scans. Peaks were identified taking into account θ and Q phases precipitation sequences. Solution treated samples showed GP/θ″/θ′/Q sequence, while in peak aged condition GP and θ″ precipitation peaks disappeared and a reduction of θ′ peak area was observed, witnessing the concurrent presence of θ″ and θ′ phases at peak hardness condition. Experimental data were compared with results from analogous investigations performed on a conventional commercial Al-Cu-Mg-Si alloy.
to accelerated ageing and others to natural ageing in various art galleries and historic castles [ 14 , 15 ]. Figure 6 shows the DMA measurements: tan delta curves for lead white and azurite tempera paint samples exposed at Tate Britain (London, UK
The effect of ageing temperature (belowT g) on physical ageing of glassy PET has been investigated by differential scanning calorimetry. The position of the glass transition endotherm was found to be strongly dependent on the annealing conditions (time, annealing temperature). A single relaxation time model is proposed for the analysis of physical ageing.
Improved controlled relative humidity dynamic mechanical analysis of artists’ acrylic emulsion paints
Part II. General properties and accelerated ageing
Abstract
After improvements were made to a modified Polymer Labs MkIII DMTA instrument to facilitate repeatable controlled humidity (RH) experiments using isothermal and thermal scanning conditions, the viscoelastic properties of titanium white pigmented artists’ acrylic emulsion films were measured in tensile mode. The effects of temperature, relative humidity and accelerated ageing regimes on two brands of titanium white paints were explored. These paints are highly responsive to changes in temperature and relative humidity, formulation differences affect properties slightly, and while light ageing had a negligible effect, thermal ageing resulted in decreased storage modulus and increased film density.
A multi-analytical approach to studying binding media in oil paintings
Characterisation of differently pre-treated linseed oil by DE-MS, TG and GC/MS
. Therefore, to begin to understand the role of individual factors, such as oil pre-processing and oil/pigment interactions in the ageing and mechanical behaviour of paint requires modelling. The oil used in this study was sourced from a single seed lot
