Flat RF coils in static field gradient nuclear magnetic resonance.

The use of flat RF coils allows considerable gains in the sensitivity of static field gradient (SFG) nuclear magnetic resonance (NMR) experiments. In this article, this effect is studied theoretically as well as experimentally. Additionally, the flat coil geometry has been studied theoretically depending on magnetic field gradient, pulse sequence and amplifier power. Moreover, detecting the signal directly from the free induction decay (FID) turned out to be quite attractive for STRAFI-like microimaging experiments, especially when using flat coils. In addition to wound rectangular flat coils also spiral flat coils have been developed which can be manufactured by photolithography from printed circuit boards.

Numerical modelling of the generation and transport of heat in a bottom ash monofill.

Municipal solid waste is incinerated to reduce its volume, toxicity and reactivity. Several studies have shown that the resulting bottom ash has a high exothermic capacity. Temperature measurements in municipal solid waste incineration (MSWI) bottom ash landfills have found temperatures up to 90 degrees C. Such high temperatures may affect the stability of the landfill's flexible polymer membrane liner (FML) and may also lead to an accelerated desiccation of the clay barrier. The purpose of this study was to gain detailed knowledge of temperature development under several disposal conditions in relation to the rate of ash disposal, the variation of layer thickness, and the environmental conditions in a modern landfill. Based on this knowledge, a simulation was developed to predict temperature development. Temperature development was simulated using several storage periods prior to the deposition and several modes of emplacement. Both the storage time and the mode of emplacement have a significant influence on the temperature development at the sensitive base of the landfill. Without a preliminary storage of the fresh quenched bottom ash, high temperatures at the bottom of a landfill cannot be avoided.

NMR studies of water diffusion and relaxation in hydrating slag-based construction materials.

The NMR relaxation properties of hydrating blast-furnace slag cements have recently been shown to be dominated by the effect of water self-diffusion in internal magnetic field gradients in the pastes. While this was suggested on the basis of NMR relaxometry and magnetic susceptibility data, we report here the results from first direct studies of the water self-diffusion in the hydrating paste using a specialized PFG sequence and very intensive magnetic field gradient pulses.

Determination of genuine diffusivities in heterogeneous media using stimulated echo pulsed field gradient NMR.

Pulsed field gradient (PFG) NMR diffusion measurements in heterogeneous media may lead to erroneous results due to the disturbing influence of internal magnetic field gradients. Here, we present a simple theoretical model which allows one to interpret data obtained by stimulated spin echo PFG NMR in the presence of spatially varying internal field gradients. Using the results of this theory, the genuine self-diffusion coefficients in heterogeneous media may be extrapolated from the dependence of the apparent diffusivities on the dephasing time of the simulated echo PFG NMR sequence. Experimental evidence that such extrapolation yields satisfactory results for self-diffusion of hexadecane in natural sediments (sand) and of n-octanol in doped MgO pastes is provided.

Action and distribution of organic solvent contaminations in hydrating cement: time-resolved insights into solidification of organic waste.

Cementitious materials are widely used as binders both in construction and in environmental technology (e.g., for stabilization and solidification). When dealing with materials contaminated with organic solvents, it is important to have an idea about the interaction between the solvents and the hydrating cement. Here, we introduce nuclear magnetic resonance relaxometry experiments as a way to study both the influence of organic model contaminants on the hydration kinetics of cement and the distribution of the contaminant in the cement matrix during the first hours and days of hydration. All solvents were found to lead to some delay in the hydration kinetics. While nonpolar compounds only lead to a minor delay and qualitatively to the same hydrating kinetics as in an uncontaminated cement mixture, the polar solvents lead to much more pronounced delays in the hydration kinetics. For toluene contents in the low percent range, there was no indication for the formation of macroscopic liquid pockets in the hydrating cement paste. The findings are consistent with recent results on the distribution of toluene in fully hydrated concrete samples.

NMR imaging of heavy metal absorption in alginate, immobilized cells, and kombu algal biosorbents.

In this contribution, an NMR imaging study of heavy metal absorption in alginate, immobilized-cell biosorbents, and kombu (Laminaria japonica) algal biomass is presented. This method provides the good possibility of directly monitoring the time evolution of the spatial distribution of the ions in the materials. From these results, we demonstrate that rare earth ions are absorbed with a steep reaction front that can be described very well with a modified shrinking core model, while copper ions are absorbed with a more diffuse front.

Susceptibility NMR microimaging of heavy metal uptake in alginate biosorbents.

Susceptibility NMR microimaging is introduced as a new method for quantitative mapping of the paramagnetic-ion concentration in ion exchange materials such as alginate biosorbents. Sharp ion intrusion fronts are observed, suggesting nonFickian diffusion.