Correlation of antioxidant depletion and mechanical performance during thermal degradation of an HTPB elastomer

Thermal degradation studies of a stabilized HTPB based elastomer were conducted at temperatures from 50 °C to 110 °C. The concentration of extractable antioxidant (AO2246) in the polymer was quantified via AO extraction and a gas chromatography-based method using internal standards. The decrease in extractable AO levels as a function of time and temperature was evaluated and correlated with mechanical property changes. Most importantly, AO depletion features were found to be temperature dependent. At elevated temperatures (>80 °C) extractable AO levels decreased rapidly and faster than the concurrent loss in mechanical properties. While extractable AO concentrations decrease quickly, the material is able to maintain some useful mechanical properties, perhaps via non-extractable or grafted AO species formed during degradation providing additional protection. At lower aging temperatures extractable or free AO levels decreased more slowly than the mechanical properties. Therefore, for condition monitoring purposes a universal correlation between AO levels and aging state or material condition could not be established. Most importantly, however, loss of mechanical properties and oxidative degradation is observed at lower temperatures despite significant levels of free antioxidant in the material. The antioxidant appears to be limited in its effectiveness to completely prevent degradation reactions, or only fractions of the total AO available are actually involved in the inhibition process.     

Microfluidic devices for energy conversion: planar integration and performance of a passive, fully immersed H2-O2 fuel cell

We describe the fabrication and performance of a passive, microfluidics-based H2-O2 microfluidic fuel cell using thin film Pt electrodes embedded in a poly(dimethylsiloxane) (PDMS) device. The electrode array is fully immersed in a liquid electrolyte confined inside the microchannel network, which serves also as a thin gas-permeable membrane through which the reactants are fed to the electrodes. The cell operates at room temperature with a maximum power density of around 700 microW/cm(2), while its performance, as recorded by monitoring the corresponding polarization curves and the power density plots, is affected by the pH of the electrolyte, its concentration, the surface area of the Pt electrodes, and the thickness of the PDMS membrane. The best results were obtained in basic solutions using electrochemically roughened Pt electrodes, the roughness factor, R(f), of which was around 90 relative to a smooth Pt film. In addition, the operating lifetime of the fuel cell was found to be longer for the one using higher surface area electrodes.     

Metal-Containing Phthalocyanines Substituted with One Branched Bulky Moiety and Six Alkylthio Groups

Summary.  Unsymmetrically substituted metal-phthalocyanines composed of three hexylthio groups and one 1-chloro-3,4-dicyano-6-[2-(2-pyridylmethylamino)phenylthio]benzene moiety was prepared by cyclization of the reactants in the presence of the anhydrous metal salts Zn(CH₃COO)₂, NiCl₂, and CoCl₂. The new unsymmetric phthalocyanines are very soluble in common organic solvents. The compounds were characterised by their elemental analyses, IR, ¹H NMR, MS and UV/Vis spectra. Corresponding author. E-mail: bayir@itu.edu.tr Received November 27, 2002; accepted (revised) December 2, 2002 Published online May 2, 2003     

Trace element determination in vitamin E using ICP-MS

Vitamin E supplements are either isolated from plants sources or prepared synthetically. Isolation from plants includes eight different tocopherol structures. Vitamin E synthesis includes seven different stereoisomers, which involves the use of several catalysts that may lead to trace element contamination in the vitamin. The use of ICP-MS is an ideal technique for detecting these trace elements. However, the oily nature of the samples requires the development of a sample preparation methodology. This study was done upon the request of synthetic vitamin E manufacturers to test the trace metal purity of their samples. In this work, the comparison of an acid microwave digestion and emulsion preparation is discussed. Cromium, nickel, tin and lead were found in the synthetic vitamin E analyzed and 200, 60, 9 and 45 ppb were the concentrations found respectively for these elements.Digesting the samples gives slightly lower detection limits compared to the emulsion preparation.     

In search of covalently bound tetra- and penta-oxygen species: a photoelectron spectroscopic and Ab initio investigation of MO4- and MO5- (M = Li,Na, K,Cs)

Although neutral and ionic O4(0/-/+) species have been observed experimentally and considered for energetic materials, O4(2-) and O5(2-) dianions have not yet been explored. O4(2-) is valent isoelectronic to the well-known ClO3- and SO3(2-) anions, and O5(2-) is valent isoelectronic to ClO4- and SO4(2-). All are stable, common anions in solutions and inorganic salts. In this article, we explore the possibility of making covalently bound O4(2-) and O5(2-) species stabilized in the forms of M+O4(2-) and M+O5(2-) (M = Li, Na, K, Cs) in the gas phase. Laser vaporization experiments using M-containing targets and an O2-seeded carrier gas yielded very intense mass peaks corresponding to MO4- and MO5-. To elucidate the structure and bonding of the newly observed MO4- and MO5- species, we measured their photoelectron spectra and then compared them with ab initio calculations and the spectra of ClO3-, Na+SO3(2-), ClO4-, and Na+SO4(2-). Careful analyses of the experimental and ab initio results showed, however, that the observed species are of the forms, O2-M+O2- and O2-M+O3-. The more interesting M+O4(2-) and M+O5(2-) species were found to be higher-energy isomers, but they are true minima on the potential energy surfaces, which suggests that it might be possible to synthesize bulk materials containing covalently bound tetra- and pentatomic oxygen building blocks.     

Evaluation of an immunobiosensor for the on-site testing of veterinary drug residues at an abattoir. Screening for sulfamethazine in pigs

A study was conducted to determine the feasibility of performing "on-site" screening for sulfamethazine (SMT), at an abattoir, using a rapid immunobiosensor method. This involved transfer of the biosensor technology and an assay developed in the laboratory, to the cold, humid conditions of a modern pig-processing factory. A pre-determined threshold limit of 0.4 microgram ml-1 SMT in bile was used to identify the likelihood that corresponding tissue samples contained SMT concentrations in excess of the European maximum permissible residue limit of 0.1 mg kg-1. Bile samples containing SMT concentrations above the threshold limit were deemed positive and the corresponding kidney and muscle samples were sent to the laboratory for HPLC analysis. The robustness of the biosensor instrumentation in the harsh operating conditions was monitored throughout the project. The performance of the assay, on-site, was assessed by the regular inclusion of QA samples and by the submission of control 'SMT-positive' pigs to the abattoir. Sampling procedures, identification and traceability were also under scrutiny. During the project, 337 (9.35%) of the total kill were tested for SMT residues, representing 75% of all producers submitting pigs for slaughter. Twelve animals, including the ten controls, gave positive bile results. HPLC analysis confirmed SMT residues in all 12 kidneys (11 in excess of the permissible level). Ten muscle samples also contained violative SMT levels. Throughout the project, the biosensor performed reliably, with no adverse reaction of any mechanical or electrical components. The SMT assay also performed reliably. This is the first report of a biosensor being used for 'on-site' drug screening.     

Automated screening of urine samples for carbohydrates, organic and amino acids after treatment with urease

Eighty-five clinical urine samples and nineteen urine samples previously found by other laboratories to suggest genetic metabolic defects were prepared for trimethylsilylation by treatment with urease, followed by azeotropic dehydration. The "Target Analyte Search" program provided with the VG Trio 2 gas chromatograph-mass spectrometer required 6 min to quantify 103 compounds relative to endogenous urinary creatinine. This technique has been used to confirm diagnoses including cystinuria, lysinuria, medium-chain acyldehydrogenase deficiency, ornithine transcarbamylase deficiency, aspartylglucosaminuria, methylmalonic, propionic and glutaric acidurias.     

Existence for the Cahn-Hilliard phase separation model with a nondifferentiable energy

Summary The Cahn-Hilliard model for phase separation in a binary alloy leads to the equations (I) u_t=w, (II) w= (u)– u with an associated energy functional F(u)=f [(u)+ +¦u¦²/2] dx. In this paper we discuss the existence theory for initial bounday value problems arising from modifications to the Cahn-Hilliard model due to the addition of the non-differentiable term ¦u¦dx to the energy F(u).