63Cu NMR investigation of effect of small additions of Sn to Al-1.7 at.%Cu in promoting accelerated phase transformations on aging

Very recently 63Cu NMR has been shown to be extremely sensitive in detecting and differentiating between the precipitate phases that form in Al-Cu alloys during heat treatment. This technique is now used to quantify the effectiveness of small additions of Sn to the alloy Al-1.7 at.% Cu in promoting the rapid nucleation and growth of the &theta;\u27-phase precipitate. Two parallel series of 63Cu NMR spectra were recorded for Al-1.7 at.% Cu and Al-1.7 at.% Cu-0.01 at.% Sn: (i) aged at 130&deg; C to observe the comparative rate of phase evolution and (ii) aged at 200&deg; C to observe the rate of growth of &theta;\u27-phase and to compare with the Vickers hardness of the alloys aged at 200&deg; C for similar periods. Evidence is presented that a metastable precursor phase to &theta;\u27 (labelled TPHM2757math001) is formed in Al-Cu-Sn which transforms to &theta;\u27 on further aging. <br /

Solid-state NMR characterisation of the thermal transformation of a Hungarian white illite

1H, 27Al, 29Si and 39K solid-state NMR are reported from a Hungarian illite 2:1 clay for samples heated up 1600 °C. This single-phase sample has a small amount of aluminium substitution in the silica layer and very low iron-content (0.4 wt%). Thermal analysis shows several events that can be related to features in the NMR spectra, and hence changes in the atomic scale structure. As dehydroxylation occurs there is increasing AlO4 and AlO5-contents. The silica and gibbsite layers become increasingly separated as the dehydroxylation progresses. Between 900 and 1000 °C the silica layer forms a potassium aluminosilicate glass. The gibbsite-layer forms spinel/γ-Al2O3 and some aluminium-rich mullite. Then on heating to 1600 °C changes in the 29Si and 27Al MAS NMR spectra are consistent with the aluminosilicate glass increasing its aluminium-content, the amount of mullite increasing probably with its silicon-content also increasing, and some α-Al2O3 forming

On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

Quantifying rubber degradation using NMR

Ageing can lead to the degradation of the tensile properties of natural rubber. The ageing process causes changes in the polymer segmental motion as well as the chemical structure, both of which can be monitored using nuclear magnetic resonance (NMR) spectroscopy. This work demonstrates that NMR can quantify rubber degradation due to ageing, and also that relatively simple NMR equipment can be used. This simpler equipment can be made portable and so could give a simple and fast indication of the condition of rubber in service. The 1H NMR transverse relaxation time, T2, and the 13C NMR spectrum using cross polarization and magic angle spinning (CP MAS) for samples taken at various levels of a degraded natural rubber liner were compared. These experiments showed that, as the level of degradation increased, the 1H NMR transverse relaxation time decreased. The 13C spectra showed considerable peak broadening, indicative of decreased mobility with increased level of degradation as well as the presence of degradation products. Further investigations using lower powered NMR equipment to measure the 1H NMR transverse relaxation times of two different series of natural rubbers were also performed. This work has shown that this simpler method is also sensitive to structural and mechanical property changes in the rubber. This method of monitoring rubber degradation could lead to the non-destructive use of NMR to determine the condition of a part in service.<br /

The coexistence of two S (Al2CuMg) phases in Al-Cu-Mg alloys.

International audienceThe decomposition sequence of the supersaturated solid solution leading to the formation of the equilibrium S (Al2CuMg) phase in Al-Cu-Mg alloys has long been the subject of ambiguity and debate. This paper describes the identification of two distinct S phases with different lattice parameters, in a series of Al-2.5Cu-1.5Mg alloy samples, isothermally aged at temperatures between 200 and 400 degrees C for various times, using high-resolution synchrotron X-ray powder diffraction. The two S phases, denoted SI and S2, form in competition with one another, with SI being metastable with respect to S2. The lattice parameters of S2 are found to be in good agreement with those refined by Heying et al. (Z Naturforsch 2005;60B:491) for the equilibrium S phase. Despite the differences in their lattice parameters, both SI and S2 appear to have the crystal structure proposed by Perlitz and Westgren (Ark Kemi Min Geol 1943;16B:1). The lattice parameters of both SI and S2 are well defined, with little scatter between different samples treated for different times and temperatures, and there are no signs of the large range of lattice parameters reported by recent electron microscopy observations

Revisiting the microstructure changes during rapid hardening of an Al-Cu-Mg alloy using in situ synchrotron Small angle X-ray Scattering and Nuclear Magnetic Resonance

International audienc

Revisiting the microstructure changes during rapid hardening of an Al-Cu-Mg alloy using in situ synchrotron Small angle X-ray Scattering and Nuclear Magnetic Resonance

International audienc