Residual properties of an injection-molded poly(phenylene ether ketone) carbon composite during flexural fatigue

The present work investigates the effects of cyclic fatigue loading on the residual properties of an injection-molded composite, carbon-fiber-reinforced poly(phenylene ether ketone) (CF/PEK-C), and damage development in this material under fatigue lending. Test specimens, which had been conditioned to various preselected fatigue damage stages, were measured for their residual properties. The results indicated that cyclic fatigue loading alters the constitutive behavior of the injection-molded composite, especially in the non-linear portion of the stress/strain curve. The residual strength decreases with increase in the number of fatigue cycles as a consequence of the accumulation of fatigue damage, which is dominated by the growth of microcracks. While the residual modulus increases slightly with cyclic fatigue loading, this is probably due to the oriented hardening resulting from creep deformation which is induced during cyclic loading. (C) 1997 Elsevier Science Limited.

Improvements in the selectivity of electrochemical detectors for liquid chromatography and flow injection analysis using the self-assembled n-alkanethiol monolayer-modified au electrode

4-Aminophenol (4-AP), paracetamol (PRCT), norepinephrine (NE), and dopamine (DA) (all somewhat hydrophobic compounds) were HPLC electrochemically detected while the signals from uric acid (UA) and ascorbic acid (AA) (both hydrophilic compounds at the pH studied) were minimized, taking advantage of the permselectivity of the self-assembled n-alkanethiol monolayer (C-10-SAM)-modified Au electrodes based on solute polarity, The effects of various factors, such as the chain length of the n-alkanethiol modifier, modifying time, and pH value, on the permeability of C-10-SAM coatings were examined, The calibration curves, linear response ranges, detection limits, and reproducibilities of the EC detector for 4-AP, PRCT, NE, and DA were obtained, The result shows that the EC detector can be applied in the chromatographic detection of 4-AP, PRCT, NE, and DA in urine, effectively removing the influence of UA and AA in high concentrations existing in biological samples. As a result, a great improvement in the selectivity of EC detectors has been achieved by using Au electrodes coated with neutral n-alkanethiol monolayer.

Influence of intraperitoneal injection of rare earth compounds on the activities of antioxidant enzymes and the level of lipid peroxidation in mice livers

Following intraperitoneal injection of lanthanum and terbium chloride and their complexes of diethyltriaminopentagacetic acid (DTPA) to adult mice with a dose of 0.28 mmol/kg body weight/day for three days. The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and the content of lipid end product, malonaldehyde (MDA) in the mice livers have been assayed respectively. The results show that the activity of SOD was increased and the content of MDA was reduced for LaCl3 treated mice and the two targets were not changed for TbCl3, but the activity of GSH-Px was reduced markedly for both LaCl3 and TbCl3 while the above three targets were not changed for La-DTPA and Tb-DTPA complexes.

THE EFFECT OF LOADING PARAMETERS ON FATIGUE BEHAVIOR OF INJECTION-MOLDED COMPOSITE

Flexural fatigue tests were performed on an injection-moulded glass-fiber reinforced blend of polyphenylene ether ketone and polyphenylene sulfide composite using four-point bending at a series of fixed mean stress levels with varying stress amplitude. Attention was given to identifying the effects of mean stress and stress amplitude on the fatigue life and failure mechanisms. It was found that the fatigue life of the studied material decreased sharply with increasing stress amplitude at a constant mean stress level and also decreased at a fixed stress amplitude with increasing mean stress. However, analyses of the fatigue data and failure behaviour reveal that, for the studied material, fatigue failure mechanisms depend on the relative importance of mean stress and stress amplitude. At a mean stress level of 80% ultimate flexural strength, the failure results from accumulation of creep strain, while at mean stress levels of 40%, 50% and 60% ultimate flexural strength, the magnitude of stress amplitude influences the type of failure mechanism. As stress amplitude is reduced, the fatigue failure mechanism changes from matrix yielding dominated to crack growth dominated fracture.

DIRECT-INJECTION OF URINE AND DETERMINATION OF ACETAMINOPHEN BY MICELLAR LIQUID-CHROMATOGRAPHY WITH A WALL-JET CELL CARBON-FIBER MICROELECTRODE

A wall-jet cell/carbon fibre microelectrode detector was designed and used for the micellar liquid chromatographic assay of acetaminophen. The separations were carried out in an analytical column packed with C-18 stationary phase and the mobile phase was

HIGHLY SENSITIVE AND SELECTIVE DETERMINATION OF RIBOFLAVIN BY FLOW-INJECTION ANALYSIS USING PARALLEL DUAL-CYLINDER MICROELECTRODES

A novel wall-jet cell with parallel dual cylinder (PDC) microelectrodes was constructed and used for flow injection analysis (FLA). The detector takes the advantages of ''redox recycling'' between bipotentiostated microcylinder electrodes (- 0.4 V/SCE an

ELECTROCATALYTIC OXIDATION AND FLOW-INJECTION DETERMINATION OF REDUCED NICOTINAMIDE COENZYME AT A GLASSY-CARBON ELECTRODE MODIFIED BY A POLYMER THIN-FILM

G chemically modified electrode (CME) was prepared by electrochemical copolymerization of pyrrole and Methylene Blue. The resulting CME exhibits effective electrocatalytic activity towards the oxidation of reduced nicotinamide coenzymes (NADH and NADPH),

AMPEROMETRIC DETECTION OF AMINO-ACIDS IN A FLOW-INJECTION SYSTEM WITH A NICKEL(II)-MODIFIED ELECTRODE WITH AN EASTMAN-AQ POLYMER FILM

Amperometic flow measurements were made at +0.55 V (vs. Ag/AgCl) in 0.1 mol l-1 KOH electrolyte with an Ni(II) chemically modified electrode (CME) with an Eastman-AQ polymer film. The use and characteristics of a Ni(II)-containing crystalline and polymer-modified electrode obtained by a double coating step as a detector for amino acids in a flow-injection system using reversed-phase liquid chromatography are described. The detection of these analytes is based on the higher oxidation state of nickel (NiOOH) controlled by the applied potential. The electroanalytical parameters and the detection current for a series of amines and amino acids were investigated. The use of such a CME in the flow-injection technique was found to be suitable in a solution at low pH. The linear range for glycine is 5 X 10(-6)-0.1 mol 1-1 with a detection limit of 1.0 X 10(-6) mol l-1. A 1 X 10(-4) mol 1-1 mixture of serine and tyrosine was also detected after separation on an Nucleosil C18 column.

FLOW-INJECTION ANALYSIS OF GLUCOSE AT AN AMPEROMETRIC GLUCOSE SENSOR-BASED ON ELECTROCHEMICAL CODEPOSITION OF PALLADIUM AND GLUCOSE-OXIDASE ON A GLASSY-CARBON ELECTRODE

A glassy carbon electrode (GCE) modified with palladium provides excellent electrocatalytic oxidation of hydrogen peroxide. When the electrolyte contains palladium chloride and glucose oxidase, the GCE can be modified by electrochemical codeposition at a given potential. The resulting modified surface was coated with a thin film of Nation to form a glucose sensor. Such a glucose sensor was successfully used in the flow-injection analysis of glucose with high stability and anti-poisoning ability. It gave a detection limit of 1 X 10(-7) M injected glucose, with a linear concentration range of 0.001-8 mM. There is no obvious interference from substances such as ascorbate and saccharides.

FLOW-INJECTION AMPEROMETRIC DETECTION OF HYDRAZINE BY ELECTROCATALYTIC OXIDATION AT A PRUSSIAN BLUE FILM-MODIFIED ELECTRODE

A Prussian Blue-modified glassy carbon electrode prepared by simple adsorption exhibited excellent electrocatalytic activity in the oxidation of hydrazine in acidic media. A film of the perfluorosulphonic acid polymer Nafion coated on top of the Prussian Blue-modified glassy carbon electrode can improve the mechanical stability of the Prussian Blue layer in the flow stream. Hydrazine was detected by flow-injection analysis at the modified electrode with high sensitivity. The limit of detection was 0.6 ng.

AMPEROMETRIC FLOW-INJECTION ANALYSIS OF HYDRAZINE BY ELECTROCATALYTIC OXIDATION AT COBALT TETRAPHENYLPORPHYRIN MODIFIED ELECTRODE WITH HEAT-TREATMENT

Chemically modified electrodes prepared by treating the cobalt tetraphenylporphyrin modified glassy-carbon electrode at 750-degrees (HCME) are shown to catalyze the electrooxidation of hydrazine. The oxidation occurred at +0.63 V vs. Ag/AgCl (saturated potassium chloride) in pH 2.5 media. The catalytic response is evaluated with respect to solution pH, potential scan-rate, concentration dependence and flow-rate. The catalytic stability of the HCME is compared with that of the cobalt tetraphenylporphyrin adsorbed glassy-carbon electrode. The stability of the HCME was excellent in acidic solution and even in solutions containing organic solvent (50% CH3OH). When used as the sensing electrode in amperometric detection in flow-injection analysis, the HCME permitted sensitive detection of hydrazine at 0.5 V. The limit of detection was 0.1 ng. The linear range was from 50 ng to 2.4-mu-g. The method is very sensitive and selective.

EASTMAN-AQ/NIII MODIFIED ELECTRODE CHARACTERIZATION AND APPLICATION IN FLOW-INJECTION DETERMINATION OF CARBOHYDRATES AND AMINO-ACIDS

A novel Eastman-AQ/Ni(II) chemically modified electrode (CME) produced by "double coating step" deposition of a poly(ester sulphonic acid) polymer film and Ni2+-containing crystalline species onto glassy carbon instead of a metallic nickel electrode exhibited stable electrocatalytic oxidation of numerous alpha-hydrogen compounds including carbohydrates, amines and amino acids. In cyclic voltammetry, the electrocatalysis appeared with an irreversible anodic wave at +0.55 V (vs. Ag/AgCl). The CME was adapted for constant-potential amperometric detection of these compounds in flow injection analysis. Using the CME, the linear response concentration range was between 1.0 x 10(-5) and 5.0 x 10(-2) mol/l and the detection limit was 5.0 x 10(-6) mol/l for glucose. The stability of the CME was adequate for routine quantitative application.

POLYANILINE CHEMICALLY MODIFIED ELECTRODE FOR DETECTION OF ANIONS IN FLOW-INJECTION ANALYSIS AND ION CHROMATOGRAPHY

An electrochemical detector based on a polyaniline conducting polymer chemically modified electrode (PAn CME) was developed for use in flow-injection analysis and ion chromatography. Iodide, bromide, thiocyanate and thiosulphate are detected by using ion chromatography with a PAn CME electrochemical detector. The detection limits are 1, 5, 10 and 10 mgl-1, respectively. The CME response for electroinactive anions varies selectively with the mobile phase composition in flow-injection analysis. By this approach, perchlorate, sulphate, nitrate, iodide, acetate and oxalate can be detected conveniently and reproducibly over a linear concentration range of at least 3 orders of magnitude. The electrode is stable for over 2 weeks with no evidence of chemical or mechanical deterioration.