Nanosize silicon nitride: characteristic of doped powders and of the related sintered materials

The paper reports on both the characteristics of ultrafine silicon nitride powder produced by plasma synthesis and the microstructure and properties of the relative sintered material. The powder, already containing yttria and alumina as sintering aids, has a bimodal particle size distribution and it is partly amorphous. The chemical composition and morphology of the particles are shown. Yttria and alumina were not found in separate particles but the elements constituting them (i.e., Y, Al, O) are either in solid solutions in the crystalline particles or dispersed within the amorphous portion of the powder. Dense materials were obtained by pressureless sintering at 1750 °C. Microstructure and composition of silicon nitride grains and of grain boundary phases are analyzed and discussed. When compared to a micro-sized Si₃N₄, nanoindentation tests clearly revealed the inverse Hall Petch relation. The nanosize Si₃N₄ shows a Young’s modulus which is almost independent on the peak load. PACS 81.05.J,M; 81.40; 81.05.Y; 81.05.J; 46.30.P     

Machines in art and chemistry

The present paper is intended to expose an example of similarity between chemistry and art not based on shape or appearance, but rather on the common origins of the concepts involved. Specifically, the subject of this text is about machines and machinery and makes a parallel between the construction of multi-machines in art and chemistry.     

Aesthetics in chemistry

This highlight article invites supramolecular chemists to read the recent paper of Joachim Schummer on the origin of molecular nanotechnology.     

New synthetic routes to β-hydroxyselenides and β-azidoselenides.

β-hydroxy and yet unknown β-azidoselenides are prepared from β-bromophenyl and yet unknown β-bromomethylselenides. First evidence of selective reaction of selenenylbromides with the less substituted double bonds of polyolefins, is disclosed.