Mechanochemical route to the synthesis of nanostructured Aluminium nitride.

Hexagonal Aluminium nitride (h-AlN) is an important wide-bandgap semiconductor material which is conventionally fabricated by high temperature carbothermal reduction of alumina under toxic ammonia atmosphere. Here we report a simple, low cost and potentially scalable mechanochemical procedure for the green synthesis of nanostructured h-AlN from a powder mixture of Aluminium and melamine precursors. A combination of experimental and theoretical techniques has been employed to provide comprehensive mechanistic insights on the reactivity of melamine, solid state metal-organic interactions and the structural transformation of Al to h-AlN under non-equilibrium ball milling conditions. The results reveal that melamine is adsorbed through the amine groups on the Aluminium surface due to the long-range van der Waals forces. The high energy provided by milling leads to the deammoniation of melamine at the initial stages followed by the polymerization and formation of a carbon nitride network, by the decomposition of the amine groups and, finally, by the subsequent diffusion of nitrogen into the Aluminium structure to form h-AlN.

MRI and dental implantology: two which do not exclude each other.

Currently, histological techniques are used to analyse implant-tissue-interactions. However, these methods are destructive and time-consuming. Furthermore, they require a large number of animals as longitudinal observations in one individual are not possible. The evaluation by non-destructive imaging techniques provides the opportunity to study the osseous integration with a reduced number of animals and a decreased biological variability. The present study examined the suitability of magnetic resonance imaging (MRI) to assess peri-implant bone formation exemplarily for a dental implant in a minipig model. Due to its compatibility to MR imaging polyetheretherketone (PEEK) coated with a thin layer of titanium was applied as implant material. Osseointegration was analysed within different peri-implant regions quantifying bone volume density and soft tissue content, which were assessed by MRI and histology, likewise. It could be proven that the examined regions showed differences in bone formation; the region adjacent to the implant apex turned out to be the most dynamic. Both methods led to comparable results with no significant differences regarding to the assessed parameters. Moreover, it was demonstrated that titanium coated PEEK showed a sufficient osseointegration and MRI provides a promising application in monitoring bone formation.

Determination of charge and molecular weight of rigid-rod polyelectrolytes.

Rod-like polyelectrolytes are an interesting model system because their persistence length is independent of the ionic strength and pH of the surrounding medium and they permit the investigation of polyelectrolytes in the absence of conformational degrees of freedom. In this work, rigid-rod poly(aramide) polyelectrolytes were synthesized by the Higashi method. Electrophoresis NMR spectroscopy in conjunction with diffusion NMR spectroscopy has been applied to determine the effective charge of the polymer. The charge was determined from the balance between the force in the electric field and the hydrodynamic friction in the steady-state electrophoretic motion. Because only organic counterions were present, and were identified in the proton NMR spectra, the counterions were investigated as well, and the fraction of condensed counterions was determined directly. From the effective charge per molecule and the knowledge of the fraction of condensed counterions, the total charge per molecule was determined. Finally, from the total charge, the number of repeat units and thus the molecular weight were inferred.

Separation of velocity distribution and diffusion using PFG NMR.

Pulsed field gradient (PFG) NMR is applied to investigate flow processes. In this case the NMR signal experiences phase modulation due to flow and signal attenuation due to the distribution of velocities. The velocity distribution consists of one part originating from diffusion and of a second part, the distribution of the directed motion. The usual PFG-experiment in which the gradient strength is incremented cannot distinguish between both. Incrementing velocity at constant gradient strength keeps the contribution from diffusion constant but changes the absolute width of the velocity distribution. So the signal is attenuated again, but only due to the distribution of the directed motion. The phase modulation as a signature of flow is not affected by this strategy, because velocity and gradient strength are Fourier conjugated. The key advantage of this approach is the possibility of measuring very low velocities, which only cause a very slight phase modulation that is easily covered by diffusion. The method is discussed here for very slow flow in a rheometer cell.

High-speed MAS-NMR investigations on radiation-modified fluoropolymers.

Fluoropolymers possess an interesting combination of physical and chemical properties. In order to utilize these properties in combination with other materials, the compatibility of the fluoropolymers with those materials has to be improved by a suitable modification process. As one modification process the irradiation with high-energy electrons has been applied. High-speed MAS solid-state NMR has been used to characterize the structural changes in fluoropolymers resulting from the irradiation. The high MAS rotation frequencies, applied here, average the anisotropy of the chemical shift and the homonuclear dipolar coupling. Despite the fact that the electron irradiation results in a low concentration of modifications, the dynamic range of the solid-state NMR experiment is sufficient to detect and characterize the modifications.

Proton fluorine wideline separation experiments on poly (vinylidene difluoride).

Two-dimensional heteronuclear proton-fluorine correlation solid-state spectroscopy is demonstrated on a sample of poly (vinylidene difluoride) (PVDF). This allows the correlation of structural information contained in the fluorine chemical shift in one dimension with information on mobility from proton wideline spectra in the second dimension. The effect of the heteronuclear fluorine-proton dipolar coupling on the proton linewidth is investigated separately. The incorporation of magnetization filters into the preparation period enables one to measure the wideline separation (WISE) spectra for the amorphous or the crystalline parts of the sample separately.

Spatially resolved solid-state MAS-NMR-spectroscopy.

A comprehensive account of spatially resolved solid-state MAS NMR of 13C is given. A device generating field gradients rotating synchronously with the magic angle spinner is described. Spatial resolution and sensitivity are compared for phase and frequency encoding of spatial information. The suppression of spinning sidebands is demonstrated for both cases. Prior knowledge about the involved materials can be used for the reduction of data from spatially resolved spectra to map chemical structure. Indirect detection via 13C NMR gives access to the information about mobility from proton-wideline spectra. Two-dimensional solid-state spectroscopy with spatial resolution is demonstrated for a rotor synchronized MAS experiment which resolves molecular order as a function of space. By comparison of different experiments the factors affecting the spatial resolution are investigated.

Spinning sidebands from chemical shift anisotropy in 13C MAS imaging.

Solid state imaging by 13C MAS imaging is described. The spinning sidebands occurring at moderate spinning speeds, which disturb the images, can be suppressed by TOSS. For rigid solids the spatial resolution that can be achieved in this way is better than that of 1H images at the same spinning speed. Spatially resolved spectra with or without spinning sidebands can likewise be recorded providing information about the isotropic and the anisotropic chemical shifts which can be exploited for the study of structure, order and dynamics. The techniques are demonstrated on a phantom made with 13C-labelled glycine.

[Subtotal parathyroidectomy in the advanced stages of renal osteodystrophy]. / Zur Problematik der subtotalen Parathyreoidektomie bei fortgeschrittenen Graden der renalen Osteopathie.

In 7 haemodialysis patients with progressing renal osteopathy a partly subtotal, partly total parathyroidectomy was carried out. Postoperatively in all cases a clinical improvement developed, which, however, in part was only transient. The laboratory parameters showed a rapid tendency to normalisation, the X-ray diagnostic finding and the bone mineral content remained essentially unchanged, also the histological skeletal findings. The results are compiled in form of tables. The value of the diagnostic measures which should precede a subtotal parathyroidectomy is discussed. At present the different postoperative courses apparently cannot be prospectively estimated with the help of the hitherto usual diagnostic measures. On the basis of the partly good results and of the operation risk which is to be thoroughly demanded of a haemodialysis patient it seems that after having used all conservative possibilities the surgical interventions nevertheless indicated in progressing renal osteopathy.