From surface science to catalysis: Surface “explosions” observed on Rh crystals and supported catalysts

Phenomena called surface explosions have been reported for decomposition reactions on single crystals, and have been identified by the use of desorption methods. In particular, in TPD, they are manifested by extremely narrow peaks (as little as 3 K in width) and a desorption rate which increases with time in isothermal experiments. In this paper we report such observations for acetate species on Rh single crystals, but extend this to show for the first time that such effects are not restricted to single crystal/UHV experiments, but can also be found on a Rh/Al₂O₃ catalyst under ambient pressure conditions. These reactions can be classified as second order autocatalytic surface processes, where free surface Rh sites are an essential component of the reaction. It is shown that coadsorbed adatoms are also essential for such explosions to be seen and their role is proposed to be that of a template layer acting to order the acetate in self-poisoning configurations.     

The effect of three chemical oxidants on subsequent biodegradation of 2,4‐dinitrotoluene (DNT) in batch slurry reactors

BACKGROUND: Recent studies indicate that chemical oxidation may be compatible with subsequent biodegradation in contaminated soils. To test this, soil contaminated with 2,4‐dinintrotoluene (2,4‐DNT) was treated in batch slurry reactors with (1) ozone, (2) modified Fenton chemistry (MFC), and (3) iron‐activated sodium persulfate (SPS). Chemical and subsequent biological oxidation were monitored, and compared with biodegradation alone. Release of nitrite and nitrate distinguished biological from chemical oxidation of 2,4‐DNT, respectively. DNT‐degrading microorganisms were enumerated. The disappearance of volatile fatty acids (VFAs) accumulated during chemical oxidation was also monitored. RESULTS: In the biological reactor 66% of the 2,4‐DNT was degraded, but further biodegradation was inhibited by nitrite concentrations approaching 18 mmol L^?1. At the doses tested, all oxidants achieved chemical oxidation followed by biodegradation, resulting in 98% DNT removal overall. Ozone achieved the greatest DNT removal (70%), but also caused the greatest reduction in DNT degraders and the longest rebound time (60 days) before biodegradation of the remaining DNT and VFAs. SPS resulted in the least DNT removal by chemical oxidation (37%), but showed no obvious rebound period for DNT degraders, and even signs of co‐existing chemical and biological oxidation. By releasing nitrate, which is less toxic than nitrite, the oxidants kept nitrite levels below 18 mmol L^?1, enabling the follow‐on biodegradation step to attain lower concentrations of 2,4‐DNT than biodegradation alone. CONCLUSIONS: All three chemical oxidants were compatible with biodegradation of residual 2,4‐DNT. Post‐oxidation bioremediation should be included in remedial designs. Copyright © 2009 Society of Chemical Industry     

Solution polymerizations of epoxytetrahydrophthalic anhydride and its utilization in various epoxy systems

Solution polymerization of epoxytetrahydrophthalic anhydride (ETHPA) has been thoroughly studied by using numerous solvents and catalysts. Products have been obtained in high yields, particularly when triethanolamine was the catalyst. This suggests that this catalyst should be considered for further applications utilizing ETHPA. However, the solution polymerization method cannot be used alone to define the effects of various catalysts on standard nonsolvated resin systems, because polymerization is greatly affected not only by the addition of solvent but also by the type of solvent. In addition, the action of the catalyst seems to depend greatly upon what solvent is employed. The reason for this dependence has not been established. The effects of the addition and reaction of ETHPA with commercial epoxy resin formulations have been investigated by means of heat distortion tests and differential thermal analyses. In most cases, although a moderate improvement was found in the thermal properties of the resins, occasional excellent results were obtained. A 10°C. increase in HDT is observed with a 2 wt.-% addition of ETHPA for bisphenol A epoxy resin–bicyclic anhydride mixture. The degree of elevation of T_g and HDT with the addition of ETHPA obviously depends not only on the composition of the resin system but also on its cure temperature. A good correlation occurs between heat-distortion temperatures and glass transition temperatures. Some few anomalous data, however, are found which point to the fact that further investigation is required before HDT and T_g can be interchanged without prior evidence of a definite relationship.     

Microorganism selection and biosurfactant production in a continuously and periodically operated bioslurry reactor

A continuous-flow reactor (CSTR) and a soil slurry-sequencing batch reactor (SS-SBR) were maintained in 8l vessels for 180 days to treat a soil contaminated with diesel fuel (DF). Concentrations of Candida tropicalis, Brevibacterium casei, Flavobacterium aquatile, Pseudomonas aeruginosa, and Pseudomonas fluorescens were determined using fatty acid methyl ester (FAME) analysis. DF removal (biological and volatile) and biosurfactant concentrations were measured. The SS-SBR encouraged the growth of biosurfactant-producing species relative to the CSTR. Counts of biosurfactant-producing species (C. tropicalis, P. aeruginosa, P. fluorescens) relative to total microbial counts were 88% in the SS-SBR and 23% in the CSTR. Biosurfactants were produced in the SS-SBR to levels of nearly 70 times the critical micelle concentration (CMC) early in the cycle, but were completely degraded by the end of each cycle. No biosurfactant production was observed in the CSTR. DF biodegradation rates were over 40% greater and DF stripping was over five times lower in the SS-SBR than the CSTR. However, considerable foaming occurred in the SS-SBR. Reversing the mode of operation in the reactors on day 80 caused a complete reversal in microbial consortia and reactor performance by day 120. These results show that bioslurry reactor operation can be manipulated to control overall reactor performance.     

A water transport model for the creep response of the intervertebral disc

Time-dependence in the mechanical response of the intervertebral disc has previously been shown to arise from the transport of water out of the disc. A creep model has been devised which describes the water transport in terms of the disc structure. This model assumes that the flow of water is the result of a pressure gradient across the cartilage end-plates, caused by an externally applied stress. The fluid transport properties of the cartilage determine the flow rate. Several cases are studied; those that best fit the experimental results use either a straindependent or a time- and strain-dependent pressure gradient. The permeability of the disc system is in the range (0.20 to 0.85)×10^–17 m⁴N^–1 sec^–1 and depends on the stress level. These values are lower than those reported in the literature for articular cartilage, but this can be explained in part by the differences in water content of the cartilage types. Permeability is found to decrease with applied stress, and both the strain- and time-dependence parameters increase in magnitude with stress. It can be shown that the analytical models of the creep response of the disc are analogous to three- and four-parameter viscoelastic models that employ springs and dashpots.     

Strain estimation in III-V materials by analysis of the degree of polarization of luminescence

The degree of polarization (DOP) of luminescence of III-V materials is a sensitive function of the strain in the material. The DOP can be measured with a spatial resolution of roughly 1 μm and an rms noise equivalent to a strain difference of 2 × 10⁻⁵. The DOP can be measured on cleaved facets, surfaces free of metals, or luminescent layers buried by transparent materials or thin films. Thus maps of the strain near surfaces for devices and materials can be deduced from analysis of the DOP from the facets or surfaces. Since the reliability and operation of devices depends on strain, DOP measurements have utility in studies of reliability, of enhancement of reliability, and of device operation.     

The Relationship of Glass Transition Temperature to Adhesive Strength

The effects of glass transition temperature (T_g) on mechanical properties have been further demonstrated by the observation of adirect relationship between the T_g of an epoxy adhesive and its lap shear bond strength to metal at elevated test temperatures. An additive (coupling agent) which lowers the T_g from a point near or above the test temperature to below it causes a subsequent decrease in the strength of the system and generally increased cohesive failure. Therefore effects on the T_g of the adhesive are more important than on interfacial properties. The end result is that differential thermal analysis (DTA) can be utilized as a effective screening method for adhesives and additives, and can be a good indicator of maximum use temperature. From these data T_g can also be used to estimate adhesive strength at a given use temperature.     

Synthesis and characterization of new fluorine-containing polyethers

A highly fluorinated monomer, 1,3-bis(1,1,1,3,3,3-hexafluoro-2-pentafluorophenylmethoxy-2-propyl)benzene (12F-FBE), is obtained by reaction of the sodium salt of 1,3-bis(1,1,1,3,3,3-hexafluoro-2-hydroxy-2-propyl)benzene with pentafluorobenzyl bromide. 12F-FBE reacts with diphenols to give soluble, hydrophobic, low dielectric (2.30-2.43 at 10 GHz) polyethers. Thermal stability as measured by TGA (10 wt% loss) is moderate and ranges from 445 to 464 °C in air. Glass transition temperatures are between 89 and 110 °C.