A new method for transforming wood structures into ceramic by carbothermal reduction of silica and carbonized wood has been developed. Application of this technique allows the preservation of wood microstructures in the ceramic state and the conversion of wood components without constraints in component size. The chosen infiltration technique of silica sol incorporation into carbonized wood structures is examined in terms of sol and wood type, carbonization conditions of the wood, and thickness of the infiltrated carbon body. Ceramization conditions were optimized, and the reaction mechanism is discussed.

The use of wood as a structure-giving material may be the key to producing temperature-resistant ceramics featuring high and directed porosity combined with necessary strength. The objective of this study was to develop a simple process to convert the evolutionarily optimized material wood into highly porous ceramics. Beech and pine, known to be relatively permeable, were pyrolyzed in a nitrogen atmosphere. The carbon-templates formed were infiltrated with various kinds of silica sol (SiO 2 ). The resulting SiO 2 /C composite was transformed into a SiC-ceramic (silicon carbide) via carbothermal reduction. Through the described process the macroscopic pore-structure of wood was transformed exactly into SiC. The SiC-ceramic produced proved to be thermo-resistant. It remained stable in oxygen atmosphere at 1200°C, after a SiO 2 coating around the SiC had been formed. This study focused on the alteration of the cell wall microstructure during the conversion of wood into SiC. Furthermore, the optimization of the individual process steps, pyrolysis, infiltration and ceramization along the most efficient route was pursued.

-European beech (Fagus sylvatica L.) is a popular and major tree species in Europe. The economic value of its timber is greatly decreased by the red heart phenomenon. The cause of red heart formation is well understood. However, scientific investigations about the technological and mechanical behaviour of red heartwood are scarce. Our study aims to provide a sound scientific basis for the characterization of technological properties, adhesion-as well as colour-behaviour of red-hearted beech. The mechanical and technological properties of redhearted beech give no evidence of different behaviour in comparison with the normal beech wood. The adhesion behaviour shows equal results. In terms of colour stability, the difference between freshly processed normal and red beech wood diminishes after certain time of exposure. red heart / adhesion behaviour / colour stability / mechanical technological property / Fagus sylvatica Résumé -Le bois de hêtre (Fagus sylvatica L.) -Propriétés technologiques, comportement au collage et stabilité de la teinte du bois de coeur rouge. Le hêtre (Fagus sylvatica L.) est une espèce d'arbre populaire important en Europe. La présence du coeur rouge provoque une réduction notable de la valeur économique des grumes qui en sont atteintes. Les causes de l'apparition du coeur rouge sont bien connues mais les études scientifiques sur le comportement technologique et mécanique du hêtre à coeur rouge sont cependant rares. La présente étude a pour but d'établir des bases solides pour la caractérisation des propriétés technologiques du hêtre à coeur rouge que sont le comportement au collage et la stabilité de teinte. Il n'existe aucun indice selon lequel les propriétés technologiques et mécaniques du hêtre à coeur rouge diffèrent de celle du hêtre normal. Pour ce qui est du comportement au collage, les résultats sont identiques alors que pour la stabilité de la teinte la différence à l'état frais de sciage entre le hêtre normal et le hêtre à coeur rouge diminue après un certain temps d'exposition. coeur rouge / comportement au collage / stabilité de teinte / propriété technologique et mécanique / Fagus sylvatica

Paper nests of social wasps are intriguing constructions for both, biologists and engineers. We demonstrate that moisture and latent heat significantly influence the thermal performance of the nest construction. Two colonies of the hornet Vespa crabro were investigated in order to clarify the relation of the temperature and the moisture regime inside the nest. Next to fairly stable nest temperatures the hornets maintain a high relative humidity inside the nest. We found that in consequence a partial vapor-pressure gradient between nest and ambient drives a constant vapor flux through the envelope. The vapor flux is limited by the diffusion resistance of the envelope. The driving force of vapor flux is heat, which is consumed through evaporation inside the nest. The colony has to compensate this loss with metabolic heat production in order to maintain a stable nest temperature. However, humidity fluctuations inside the nest induce circadian adsorption and desorption cycles, which stabilize the nest temperature and thus contribute significantly to temperature homeostasis. Our study demonstrates that both mechanisms influence nest thermoregulation and need to be considered to understand the thermodynamic behavior of nests of wasps and social insects in general.

Specific modification of properties such as porosity and pore size of engineered wood‐based source material enables the custom design of porous wood‐derived SiC that is produced by carbothermal reduction between the carbonized wood‐based material and an infiltrated silica sol. In contrast to bulk wood, the anisotropic shrinkage of the source material is less distinctive and can be controlled. Furthermore, the obtained structural properties of the material are isotropic. Material processing and properties of the wood‐derived ceramic material are described in this paper.