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.     

Extractability and phytotoxicity of heavy metals present in petrochemical industry sludge

Bioavailability of heavy metals present in industrial sludges and their subsequent phytotoxicity are crucial parameters to assess the associated health hazards and suitability for land application. The present study is an effort to determine the extractability of heavy metals present in different phases of the sludges, coming out of two different operations involved in petrochemical industry viz. spent caustic treatment (SCT) and waste water treatment (WWT) following the BCR sequential extraction procedure. The maximum amount of Cd and Cu was found associated with oxidizable phase, whereas Cr and Ni were best recovered in residual fractions of both the sludges. Maximum Pb was recovered in oxidizable and residual phase in the WWT and SCT sludges, respectively. The stabilization treatment undergone by sludges strongly influenced the heavy metal distribution and the phases to which they were associated. The total metal concentration in both the sludges did not exceed the limit set out by the European Legislation and was found as Cd = 0.449, Pb = 3.340, Ni = 6.530, Cr = 21.087, & Cu = 27.129 μg g^?1 and Cd = 0.549, Pb = 5.664, Ni = 7.161, Cr = 27.096, & Cu = 35.479 μg g^?1 in the SCT and WWT sludges, respectively. Phytotoxicity of the sludges was assessed against the germination index and the relative root and shoot growth. Sludge leachates did not adversely affect the seed germination and the early seedling growth of Mung (Phaseolus mungo) and Gram (Cicer arietinum), indicating that these metals were concentrated in the non-bioavailable fractions of sludges.     

Conducting polymer embedded with nanoferrite and titanium dioxide nanoparticles for microwave absorption

The present paper deals with the synthesis of conducting ferrimagnetic polyaniline nanocomposite embedded with γ-Fe₂O₃ (9–12 nm) and titanium dioxide (70–90 nm) nanoparticles via a micro-emulsion polymerization. The microwave absorption properties of nanocomposite in 12.4–18 GHz (Ku-band) frequency range shows shielding effectiveness due to absorption (SE_A) value of ?45 dB, which is much higher than polyaniline composite with iron oxide and polyaniline–TiO₂ composites. The higher EMI shielding is mainly arising due to combined effect of γ-Fe₂O₃ and TiO₂ that leads to more dielectric and magnetic losses which consequently contributed to higher values of shielding effectiveness. XRD analysis of the nanocomposite reveals the incorporation of nanoparticles in the conducting polymer matrix while the thermal gravimetric analysis (TGA) demonstrates that the nanocomposite is stable up to 250 °C.     

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.     

An Experimental Determination of a Real Fire Performance of a Non-Load Bearing Glass Wall Assembly

A glass wall assembly was exposed to an intense real-scale compartment fire. The wall assembly consisted of four glass sections, two of which were fitted with tempered double-pane glass and the other two sections were fitted with tempered single-pane glass. At each glass section, temperatures were measured at the exposed face and the unexposed face. Total heat flux gauges were used to measure both the temporal variation of the energy incident on the glass wall and the transmitted energy rate detected through two of the glass sections. Visual and infrared cameras were used to image the unexposed face of each wall assembly during the fire exposure. Results of glass breakage and subsequent glass fall out were compared to studies in the literature for glass sections exposed to compartment fires. The behavior of the glass wall assembly under a fire load is presented.

Effect of wind and buoyancy on hydrogen release and dispersion in a compartment with vents at multiple levels

The natural and forced mixing and dispersion of hydrogen released in an accidental manner in a partially enclosed compartment with vents at multiple heights is investigated using theoretical tools. The key to the analysis is determination of the position of the neutral buoyancy plane, where the pressure in the compartment is equal to that of the exterior. Air flows in through vents below the position of neutral buoyancy and exits from vents above it. CFD simulations are conducted to confirm the physical phenomena and to compare with the analytical results. The analytical model is useful in understanding the important physical processes involved during hydrogen release and dispersion in a compartment with vents at multiple levels, with and without a steady wind. Parametric studies are conducted to identify the relative importance of various parameters. Model results indicate that the steady-state hydrogen volume fraction in the compartment is lower when the hydrogen release rate is smaller and the vent cross-sectional area is larger. Results also indicate that the fastest way to reduce flammable levels of hydrogen concentration in a compartment can be accomplished by blowing through the vents.     

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.