Oxidative Instability of Fuels: Nickel Catalyzed Reactions

The reactions that lead to long-term storage instability of fuels are not fully understood. Various reports in the literature link particular fuels with specific reactions, usually oxidation or free radical processes. Trace quantities of metals are present in all processed fuels. The metal source can be naturally occurring or present from fuel handling. The usual case is to look at the reaction of the metal or metal ion with molecular oxygen or other active oxygen species such as hydroperoxides. This article reports on the reaction of a nitrogen heterocycle, indole. We propose a mechanism that shows that catalytic amounts of nickel can produce compounds of higher molecular weight and increased polarity.     

Finding flaws in composites

From ultrasonics, through infrared and thermographic techniques, to more exotic, developmental methods, non-destructive testing (NDT) of composites can take many forms. George Marsh reports on some of the principles and equipment involved in this vital area.     

Permuteins of interleukin 1{beta}--a simplified approach for the construction of permutated proteins having new termini

A technique for the rapid and simple generation of permutatedversions of the interleukin-1ß (IL-1ß) geneis described. In this method, the human IL-1ß cDNAis twice amplified by the polymerase chain reaction (PCR) andthe resulting DNA fragments are ligated in tandem. Between thetwo genes, the DNA sequence encodes a short four amino acidloop to link the native N- and C-terminal ends of the IL-1ßprotein. By using PCR amplification from this starting template,a new version of the IL-1ß cDNA was obtained thatencodes a permutated form of the IL-1ß protein wherethe new N- and C-terminal amino acids correspond to residues65 and 64 of the native IL-1ß sequence, respectively.The name ‘permutein’ is proposed to describe proteinsgenerated by this technology. The molecular profile (IL-1 receptorbinding, biologic activity and solution properties) of the IL-1permutein produced by this technology, permutein 65/64, is shownto be identical to that of native IL-1ß The approachshould be useful to define further the structural features ofthis protein that are important for its function.     

Rheology of polybenzyl ether dendrimers their copolymer and blends

The dynamic rheological behavior of pure polybenzyl ether dendrimers and their copolymers have been studied in the molten state. The pure polybenzyl ether dendrimer generation 4 and generation 5 show Newtonian behavior whilst the generation 3 appears to be a very slightly shear-thinning within the deformation rates investigated, the behavior also being a function of thermal pretreatment. When the dendrimer component was included as a dendritic polystyrene copolymer (covalently attached), the viscosity was much lower compared to corresponding polystyrene of similar molecular weight. The same concentration of dendrimer could be physically blended into the polystyrene forming an immiscible mixture, which also reduced viscosity. However, if the dendritic component was covalently attached, it had a lower viscosity than if physically blended at the same concentration. Electronic Publication     

Estimation of corrosion cavity growth rate for predicting system service life

It has been shown that under real, practical conditions, values of the critical pit depth of the system, x_cr, and typical service life, t_s, impose significant restrictions on the corrosion current densities (averaged and initial) and thus on the potential and concentration drops that might be observed in the corrosion cavity. Thus, it is shown that, if x_cr does not exceed the order of 1-10 mm, and if the order of t_s is not less than 1 year, initial corrosion current densities in real, open pits cannot exceed values of 10⁻⁴-10⁻³ A/cm², with the understanding that the polarization curve (corrosion current density vs. potential and the surface concentration of species) does not change as the pit propagates. Simple analytical expressions for predicting potential and concentration drops in open corrosion cavities, and for predicting cavity propagation rate in systems containing uni- and bi-valent anions in stagnant electrolytes under well-mixed, external conditions have been obtained. These expressions can be used to extrapolate the results of short-term corrosion experiment to future times. In particular, it is shown that, if localized corrosion takes place in an electrolyte having a conductivity of the order of that of seawater, it is possible to neglect the potential drop in an open corrosion cavity and hence to consider the rate of pit propagation as being constant under constant environmental conditions. The same conclusion holds for the pitting of 316 L steel, practically for any composition of the external electrolyte.     

Polymer drying. X. A recondsideration of the kinetics of evaporation from polymer–liquid systems during the interval of transition from the rubbery to a glassy state

This kinetic restudy of the physical changes that occur during evaporation-induced transition from the rubbery to a glassy state of polystyrene–liquid systems shows that such transitions occur via two mechanistic pathways. The first is random nucleation of microdomains of self-associated polymer segments owing to a time-dependent logarithmic decrease in the number of adsorbed volatile molecules per phenyl group of residual mobile polymer segments. The second is a therodynamically driven self-association of adjacent monomer units with concomitant explusion of the adsorbed molecules, which appears to propagate via a “dominolike” chain reaction. Conceptually this is a three-dimensional “zippering-up” of suitably close polymer segments to produce the corresponding macrostructural network of self-associated polymer. The kinetics of the latter is zero-order, and this dominates the overall kinetics of evaporation during the latter portion of the transition interval, presumably owing to changes in entropy of the system as it progresses from the mobility characteristic of the rubbery state to the rigidity characteristic of a glassy state. © 1994 John Wiley & Sons, Inc.     

Bridge Deck Construction Using Type K Cement

Because drying shrinkage cracking is a major source of bridge deck cracking, and because shrinkage compensating concrete (SCC) is known to substantially reduce shrinkage cracking, the use of SCC should be closely examined in an effort to increase the durability and service life of bridge decks. One of the concerns regarding the use of SCC is its more demanding construction requirements for placement time and for curing. This paper addresses relevant material and construction issues that have resulted in the successful use of SCC for bridge decks. The Ohio Turnpike Commission (OTC) has used SCC exclusively for its new and replacement bridge decks for the past 12 years, and they have been very satisfied with its performance to date. The OTC's evaluation of SCC is that it greatly mitigates shrinkage cracking. The OTC's requirements for SCC at the concrete plant, in-transit, and at the job site are included in this paper. The OTC's construction procedures are presented in the form of a chronological sequence of photographs illustrating the construction activities on a new SCC deck placement in 1994.     

Synthesis of Solid Phosphate Compounds of Ti(III) and Ti(IV)

Several new methods for the synthesis of TiPO₄ are described. Crystalline phosphate compounds containing boron and titanium in a single III or mixed (III, IV) oxidation states have been synthesized and identified by X-ray diffraction. An additional family of phosphate compounds containing only Ti(III, IV) has also been synthesized and identified. All the compounds exhibit attractive colors, e.g., bright green, blue, purple, and black, and are stable at room temperature in air and in boiling water.     

Separation of cholesterol,and fatty acylglycerols,acids and amides by thin-layer chromatography

A rapid unidimensional thin-layer chromatographic (TLC) method for the separation of neutral lipids is described, using two sequential solvent systems of different polarity. Excellent separations of mono-, di- and triglycerides, fatty acids, fatty amides, and cholesterol are thereby achieved. Separation is accomplished at room temperature and requires 25 min. Reference to brand of firm name does not constitute endorsement by the United States Department of Agriculture over others of a similar nature not mentioned.