Conversion of wooden structures into porous SiC with shape memory synthesis

Synthesis of structured silicon carbide materials can be accomplished using wooden materials as the carbon source, with various silicon impregnation techniques. We have explored the low cost synthesis of SiC by impregnation of carbon from wood with SiO gas at high temperatures, which largely retains the structure of the starting wood (shape memory synthesis). Suitably structured, porous SiC could prove to be an important type of catalyst support material. Shape memory synthesis (SMS) has earlier been tried on high surface area carbon materials. Here we have made an extensive study of SMS on carbon structures obtained from different types of wood.     

From oxygen adsorption to the growth of thin oxides on silicon surfaces

Oxidation of silicon surfaces at relatively low temperatures is shown to go through several activated steps, in the form of configurations inert to further uptake of oxygen. Starting from room temperature adsorption, different configurations of oxygen atoms adsorbed on and in the Si(1 1 1) and Si(0 0 1) surfaces are found, with history and/or coverage dependent energy barriers connecting them. From well below to slightly above an effective oxide coverage of a monolayer, clustering of up to three oxygen atoms around one single silicon atom has been predicted for the Si(0 0 1) surface to represent one such energy minimum; this model is confirmed here experimentally. These and other clusters are shown to agglomerate into silicon dioxide islands before coalescing into a contiguous, inert layer upon higher oxygen supplies. Another problem addressed here is the presence of molecular adsorbates in the oxidation reaction path, an issue which is still debated in the literature. For the Si(1 1 1) surface a molecular, charged oxygen species has earlier been found at temperatures up to room temperature, but not for the Si(0 0 1) surface. This is confirmed in the present experiments, and new data for this state shows that it is highly mobile until quenched at a critical oxygen coverage. It is not the initial state of oxygen on silicon, and therefore not the precursor for atomic insertion of oxygen; rather, it is found to co-exists with atomic oxygen inserted in back-bonds, at a certain, low coverage regime in which parts of the Si(1 1 1) surface are still ordered.     

Low dielectric constant materials for advanced interconnects

Materials with low dielectric constants are being developed to replace silicon dioxide as interlevel dielectrics. This paper discusses material issues and the characterization of low-k materials for integration into advanced interconnects. Measurement techniques for the characterization of low-k films are discussed, and the results for several classes of low-k materials are presented. The properties of these materials are discussed in relation to structure-property relationships. For more information, contact P. Ho, University of Texas, Institute for Materials Science, Austin, Texas 78712; (512) 471-8961; fax (512) 471-8969; e-mail paulho@mail.utexas.edu.     

Automobile exhaust as a means of suicide: an experimental study with a proposed model

Experiments were conducted to investigate the concentration of carbon monoxide (CO) in a car cabin under suicide attempts with different vehicles and different start situations, and a mathematical model describing the concentration of CO in the cabin was constructed. Three cars were set up to donate the exhaust. The first vehicle didn't have any catalyst, the second one was equipped with a malfunctioning three-way catalyst, and the third car was equipped with a well-functioning three-way catalyst. The three different starting situations were cold, tepid and warm engine start, respectively. Measurements of the CO concentrations were made in both the cabin and in the exhaust pipe. Lethal concentrations were measured in the cabin using all three vehicles as the donor car, including the vehicle with the well-functioning catalyst. The model results in most cases gave a good prediction of the CO concentration in the cabin. Four case studies of cars used for suicides were described. In each case measurements of CO were made in both the cabin and the exhaust under different starting conditions, and the mathematical model was tested on these cases. In most cases the model predictions were good.     

Kleine Ursache – großer Schaden – Fortsetzung einer komplexen Baumaßnahme im Anschluss an eine Havarie

Simple cause – extensive damage. Continuation of a complex project in connection with an accident. In September 2008 at the Müritz‐Elde‐channel the new weir Lewitz could be started‐up. The originally planned construction period amounted to 15 months; however, about three years were actually needed. During the production of a temporary bypass in March 2006 an accident occurred. The consequences of the damage had to be eliminated first, before the planned project could be continued. Subsequently, the construction sequences and procedures had to be adapted to the changed boundary conditions. The accident, the removal of the damages and the effects to the building contract are represented in the following.