Andreas O. Gabriel

Synthesis and thermally induced ceramization of a non-oxidic poly(methylsilsesquicarbodi-imide) gel

A novel polymeric organosilicon gel with the composition [MeSi(NCN)1.5]n synthesized by the reaction of MeSiCl3 with Me3Si–N=C=N–SiMe3 is reported. The reaction is performed without any solvent and with catalytic amounts of pyridine and provides highly cross-linked poly(methylsilsesquicarbodi-imide) in the form of a stable non-oxidic gel with unusual low open porosity (<1 m2 g−1). The Si–C–N gel transforms to an amorphous silicon carbonitride ceramic, SiC1.1N1.6, by the thermally induced ceramization at 1200 °C in inert atmosphere (argon). The gel-derived silicon carbonitride is thermally stable up to 1450 °C. The synthesis, characterization and pyrolysis behavior of the new polyorganosilicon gel is discussed.

Synthesis of Polycrystalline Silicon Carbide by a Liquid-Phase Process

Communication: Silicon carbide is an important non-oxide ceramic; however, production methods have until now remained difficult and/or expensive. In this communication is reported the production of silicon carbide via thermal decomposition from the novel Si-carbodiimide polymer poly-(methylsilasesquicarbodiimide), PSMC, which is prepared in a quantitative and economical solution reaction. A mechanism for the polymer-to-ceramic conversion is proposed. The possibility of fabricating continuous fibers of amorphous SiCN or polycrystalline SiC by gelling PSMC is suggested.

A Topography-Informed Morphology Approach for Automatic Identification of Forest Gaps Critical to the Release of Avalanches

Human assets in Alpine regions are prone to gravitational natural hazards such as rock fall, shallow landslides and avalanches. Forests make up a substantial share in that landscape and can mitigate those hazards. Management of avalanche protection forests must cope with avalanches potentially released in forest gaps, which can damage downslope forests. The Swiss guidelines “Sustainability and success monitoring in protection forests” prescribe forest-gap extents in slope-line direction critical to the release of avalanches in forested areas. This article proposes a topography-informed morphology approach (TIMA) to automate the detection of critical gaps based on a digital terrain model and a canopy height model (CHM) derived from airborne LiDAR-data. TIMA uses complementary information about topography to probe forest gaps computed from the CHM with templates meeting critical-gap extents adjusted to local topography. The method was applied to a test site in Klosters-Serneus (Switzerland). The comparison of a critical-gap map with the results of a field assessment at 19 sample locations resulted in 84% overall accuracy. Moreover, plausibility of gap detection could be improved by including linear features forest roads and torrent channels in TIMA to account for decoupled snow layer resulting from abrupt breaks on the hillslope. If the TIMA concept can be successfully applied to the case of avalanches, this would encourage its use in assessing other gravitational natural hazard processes.