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At least 145 records · Page 8Linked to original sources
PubMed1992

Graphite-like lubrication of mesothelium by oligolamellar pleural surfactant.

Six studies have been completed to reevaluate pleural surfactant as a possible boundary lubricant in mesothelial sliding. It is capable of remarkable antiwear action, giving a mean scar diameter on a standard "four-ball test" comparable to the best commercially available lubricants and reducing friction to values anticipated from lamellated solid lubricants such as graphite. Pleural surfaces displayed appreciable hydrophobicity, which was almost eliminated by rinsing with a lipid solvent from which phospholipid was recovered and quantified. These quantities indicated that equivalent of 7.3 adsorbed monolayers of surface-active phospholipid, which was in general agreement with the number of layers of a graphite-like surface coating visualized by electron microscopy by use of a novel fixation procedure that avoids conventional aldehydes known to destroy hydrophobic surfaces. Graphite-like (dry) lubrication by adsorbed surface-active phospholipid is discussed as an excellent lubrication system available wherever the distribution of fluid allows the pleura to make contact.

Animals↗
PubMed2004

In vitro and in vivo hemocompatibility evaluation of graphite coated polyester vascular grafts.

Attempts have been made in this study to prepare a homogeneous and stable coating of graphite on polyester vascular grafts (GPVG) using an electrophoresis method to evaluate thromboresistant and blood compatibility of GPVG in comparison to non-coated PVG and InterGard (collagen sealed PVG) as control. Lactate dehydrogenase (LDH) activity measurement was carried out on all PVG types to evaluate platelet adhesion. To examine tissue reaction GPVG and non-coated sheets of knitted polyester fabric were implanted simultaneously in the dorsal flank of rats subcutaneously. The GPVG, non-coated and control were implanted in descending aorta as end-to-end or end-to-side implantation substitution in 25 sheep for 4-60 weeks. Results showed that the graphite coating on polyester vascular grafts reduced the number of adherent platelets and prevent platelet activation and spreading on the surface in comparison with non-coated and control. Pathological investigation showed inflammatory reactions were totally resolved after 12 weeks and there was no difference in the tissue reaction between graphite coated, non-coated and control patches. All grafts remained patent and there was no significant difference in patency rate between these three types of PVG. We found that GPVG has no need for pre-clotting and it showed lower platelet aggregation, thinner capsule formation and lower calcification after 15 months. However, suturing of GPVG was more difficult in comparison with the other types.

Animals↗
PubMed1994

Determination of cadmium and lead in raw milk by graphite furnace atomic absorption spectrophotometer.

A simple, uncontaminated method was described for graphite furnace atomic absorption spectrophotometry used for determination of Cd and Pb in milk serum prepared by spontaneous souring. Samples of raw milk were collected from the bulk holding tanks of 107 dairy farms in six counties in Taiwan. Raw milk samples were placed at room temperature (28 degrees C) for 48 h, to allow the pH to decrease below 4.6 and the casein and fat to precipitate. Milk serum was filtered and then directly injected into a graphite tube. The standard addition method was employed, and .1% phosphoric acid was the matrix modifier. During ashing, a 15-s oxygen influx prevented charcoal accumulation on the graphite tube. The mean recoveries of Cd and Pb from three added concentrations were 93.7% and 94.5%, respectively. The analyzed Cd and Pb concentrations in milk powder using this method were close to the certified values. The mean Cd and Pb contents obtained from 107 samples were .044 ng/ml, ranging from .021 to .173, and 2.03 ng/ml, ranging from .98 to 4.45, respectively. There were no significant differences among the six counties.

Animals↗
PubMed1975

[A polarization effect-free graphite double extrapolation chamber for the absolute dosimtery of high energy electrons].

Theoretical principles, constructional features and operation of an improved extrapolation-chamber intended for absolute ionization dosimetry of high-energy electrons are described. The construction allows a precise variation of the cylindrical measuring volume by varying thickness and diameter (exactly from 0 to 30 or 3 to 30 mm resp.), whereat measurements can be taken either using cylindrical graphitic walls or "no walls". The improvements consist in a combination of the following characteristics: high electric and mechanical stability; avoidance of disturbances due to electrostatic charges; elimination of the polarity error; practically homogeneous graphitic construction without foreign materials; graphite as a preferential reference material; measurements by chemical dosimetry following within the same apparatus. Results of measurements are reported concerning the verification of the complete or partial equilibrium of electrons, the deviations from the ideal cavity conditions of Bragg and Gray, and the comparison with ferrous sulfate dosimetry. Absolute measurements of the ion dose being accurate to about 0.5% can be obtained with the chamber. Thus, the chamber seems qualified to be used as a primary standard.

Graphite↗
PubMed2004

[Study on the determination of trace gallium in molybdenum-coated pyrolytic graphite tube by electrothermal absorption spectrometry].

The effects on gallium atomization in the pyrolytic graphite tube imposed by different matrix modifiers and different coatings were discussed detailedly in this paper. In the presence of matrix modifier of Ni(NO3)2 the matrix interference was eliminated efficiently. The pyrolytic graphite tubes were coated differently with lanthanum, zirconium, and molybdenum to avoid producing gallium carbide. Results showed that the tube with molybdenum coating was the best. On this basis, the mechanism of gallium atomization in the molybdenum-coated pyrolytic graphite tube using Ni(NO3)2 as a matrix modifier was studied furthermore; in addition, the parameters of the operation were optimized. As a result, a new method improved in many aspects was developed to detect trace gallium in complicated sample of gangue. The outcomes of practical applications indicated that the method could satisfy the requests of analysis and that the manipulations were simple to achieve. The characteristic content, the detection limit, and the adding recoveries were 2.12 x 10(-11) g, 1.4 x 10(-10) g and 97.4%-102.7% respectively, and the relative standard deviation was less than or equal to 3.6% (n = 11).

Absorption↗
PubMed1991

[Contribution to graphite dust lungs].

This is a report on a male patient of 71 years of age who had been a graphite mill worker for about 14 years. Despite respiratory insufficiency he was rejected in 1985 as an applicant for being recognised as a victim of a professional disease, because the radiologically visible changes in the lung were only discrete. Perbronchial lung biopsy was performed in January 1990 as his dyspnoea increased. Histological examination revealed graphite dust disease of the lung. Asteroid bodies in multinucleated giant cells were an unusual finding. Energy-dispersing x-ray microanalysis proved that the so-called graphite dust disease lung was actually a type of mixed dust pneumoconiosis.

Aged↗
PubMed1989

[Evaluation of the carcinogenic hazard in the manufacture of graphite articles].

As a result of complex hygienic, clinical and cancer epidemiologic studies, dust proved to be a major occupational hazard. Coke and graphite dust absorbs polycyclic aromatic hydrocarbons, including benz(a)pyrene in concentrations exceeding maximum permitted levels. Screening of 746 graphite workers followed by clinical examination established increased incidence of diseases of the upper respiratory tract (chronic rhinitis pharyngitis, laryngitis, etc.), bronchi and lungs (chronic bronchitis or pneumonia) and skin (hyperkeratosis, naevi, etc.). Among respiratory diseases were hypertrophic laryngitis, papillomatous bronchitis and angiofibroma of the larynx which are now considered to be precancer. Cancer epidemiologic studies referred graphite workers to a group of high risk of cancer.

Adult↗
PubMedDate not supplied

[Effect of the state of graphite surfaces on the activity of immobilized glucose oxidase].

The work deals with immobilization of glucose oxidase on modified graphite. The effect of the carrier surface composition on the major properties of the immobilized enzyme was examined. The level of activity of the immobilized enzyme is shown to depend on the quantity of Ti and Zr oxides applied on the graphite surface. The high activity of the enzyme immobilized on graphite will enable it to be used for construction of enzyme electrodes.

Adsorption↗
PubMed2002

Slurry sampling for the determination of thallium in soils and sediments by graphite furnace atomic absorption spectrometry.

The analytical conditions for thallium determination in soils and sediments by slurry sampling graphite furnace atomic absorption spectrometry were studied and optimized. Elimination of a strong background for soils rich in organic materials by application of tungsten carbides coated graphite tubes/platforms was studied in detail. Tungsten carbides increased the maximum permissible pyrolysis temperature from 300 to 900 degrees C. The mechanism of tungsten carbide formation on different graphite surfaces was proposed. Application of a strong basic anion-exchange resin for interference elimination in thallium determination in marine sediments was described. Calibration was performed directly using aqueous standards both for soil and sediment analysis. Analysis of CRM confirmed the reliability of the approach. The precision and accuracy of thallium determination by the described method for soils and sediments was acceptable. A characteristic mass of 13.8 pg was obtained and the limit of detection for the proposed method was around 0.06 microg g(-1) Tl.

Journal Article↗
PubMed2004

Slurry sampling of sediments and coals for the determination of Sn by HG-GF AAS with retention in the graphite tube treated with Th or W as permanent modifiers.

A method for the determination of Sn in slurry samples of sediment and coal by hydride generation graphite furnace electrothermal atomic absorption spectrometry (HG-GF AAS) is proposed. The slurries were prepared by mixing the ground sample (particle size < or =50 microm) with 2.0 mol L(-1) HCl for the sediment samples or with 2.0 mol L(-1) HCl+1.0% v/v HF in a saturated boric acid medium for the coal samples. The slurry was placed in an ultrasonic bath for 30 min, before and after standing for 24 h, with occasional manual stirring. The graphite tube was treated with 0.5 mg of Th or W as a permanent modifier. Sn determination was carried out by electrothermal atomic absorption spectrometry at the optimized retention temperatures of 450 and 300 degrees C for Th and W treatment, respectively. With this coupling, kinetic interference in the formation of the hydrides is avoided, and excellent detection limits can be obtained by using peak height. For the chemical vapor generation device, an optimized volume of 2 mL of sample slurry and an optimized NaBH4 concentration of 5% m/v were employed. The vapor produced was transported and retained on the graphite tube surface, which was further heated for Sn atomization. The accuracy of the method was verified by analyzing five certified sediments and three coals. By using the external calibration against aqueous standard solutions, the results obtained were in agreement with the certified values only for the sediment samples. For the coal samples, an addition calibration curve, obtained for one certified coal, was necessary to achieve accurate results. The obtained limits of detection were 0.03 microg g(-1) for sediment and 0.09 microg g(-1) for coal with Th as permanent modifier. The relative standard deviations were lower than 15%, demonstrating an adequate precision for slurry analysis. Sediment and coal samples from Santa Catarina, Brazil, were also analyzed.

Journal Article↗
PubMed2006

Surface modification of amine-functionalised graphite for preparation of cobalt hexacyanoferrate (CoHCF)-modified electrode: an amperometric sensor for determination of butylated hydroxyanisole (BHA).

A cobalt hexacyanoferrate (CoHCF)-modified graphite paraffin wax composite electrode was prepared by a new approach. An amine-functionalised graphite powder was used for the fabrication of the electrode. A functionalised graphite paraffin wax composite electrode was prepared and the surface of the electrode was modified with a thin film of CoHCF. Various parameters that influence the electrochemical behaviour of the modified electrode were studied by varying the background electrolytes, scan rates and pH. The modified electrode showed good electrocatalytic activity towards the oxidation of butylated hydroxyanisole (BHA) under optimal conditions and showed a linear response over the range from 7.9 x 10(-7) to 1.9 x 10(-4) M of BHA with a correlation coefficient of 0.9988. The limit of detection was 1.9 x 10(-7) M. Electrocatalytic oxidation of BHA was effective at the modified electrode at a significantly reduced potential and at a broader pH range. The utility of the modified electrode as an amperometric sensor for the determination of BHA in flow systems was evaluated by carrying out hydrodynamic and chronoamperometric experiments. The modified electrode showed very good stability and a longer shelf life. The modified electrode was applied for the determination of BHA in spiked samples of chewing gum and edible sunflower oil. The advantage of this method is the ease of electrode fabrication, good stability, longer shelf life, low cost and its diverse application for BHA determination.

Journal Article↗
PubMed1996

The graphite furnace and its role in atomic spectroscopy.

The diversity of applications of the graphite furnace is extraordinary, encompassing the fields of physics, thermochemistry, spectroscopy and analytical chemistry. In this respect, the graphite furnace has been used on a continuous basis as a research tool for nearly a century. Following its introduction as an atomization source for atomic absorption spectrometry by L'vov in 1959, its role in atomic spectrometry expanded considerably to encompass analytical applications in emision, fluorescence, absorption and mass spectrometry. In addition to its conspicuous use as an atomization source in these areas, it is frequently employed as a vaporizer when used in the format of combined and tandem sources with other instrumentation. The unique physico-chemical micro-environment which can be attained within the graphite furnace has also been used to advantage in a number of investigations, including the determination of gas- and solid-phase diffusion coefficients of high-temperature metal vapours, the heats of sublimation of refractory metals, fundamental optical constants and the measurement of the heats of desorption of adatoms from high-temperature surfaces. The range of such applications remains to be more fully explored. The attractive features of this source, viz., the high atomization/vaporization efficiency, comparatively long atomic vapour residence times, controllable chemical and thermal environment and its ability to handle high dissolved solids content samples (</=100%) serve to ensure its place in analytical atomic spectroscopy for years to come.

Journal Article↗
PubMed2004

Variation in surface energy heterogeneity of graphite due to adsorption of polyoxyethylene sorbitan monooleate.

The heterogeneity of surface energy of graphite before and after adsorption of polyoxyethylene sorbitan monooleate (Tween80) was investigated by the nitrogen adsorption technique. The nitrogen adsorption energy distributions (AEDs) were calculated from the low-pressure isotherm data (i.e., the data of submonolayer adsorption) according to the regularization method. Based on the AED of pristine graphite, two types of dominant energetic surface are identified and assigned respectively to the basal surface and the irregular surface, including the stepped edges and defect sites. When the adsorption amount of Tween80 is raised, both the surface energy and the energy heterogeneity of graphite gradually decline. It is thus demonstrated that Tween80 prefers interacting with and screening higher energetic surfaces to lower ones.

Journal Article↗
PubMed2005

Comparison of morphology and mechanical properties of surfactant aggregates at water-silica and water-graphite interfaces from molecular dynamics simulations.

Cationic surfactants are important for a wide range of applications, including controlled drug delivery systems, emulsifiers, and chemical mechanical polishing. It is therefore important to better understand surfactant structure and properties at the solid-liquid interface. Here, classical molecular dynamics simulations with empirical potentials are used to compare the structures and mechanical properties of cationic surfactant micelles at hydrophobic (graphite) and hydrophilic (silica) surface-water interfaces. In particular, the morphology of monolayers and bilayers of C12TAB (n-dodecyltrimethylammoniumbromide) at these interfaces, and their responses to atomic force microscopy indentation, are examined. The simulations predict that surfactant monolayers and bilayers on silica evolve into a spherical micelle structure, in agreement with theoretical models of surfactant morphology. In contrast, surfactant monolayers on graphite evolve into a hemi-cylindrical structure, in agreement with experimental findings. In the simulated indentation of the micelle/silica system, the spherical micelle breaks apart and forms a surfactant monolayer. The indentation force curve has a maximum value of 2.25 nN. On the other hand, the simulated indentation of the micelle/graphite system causes the hemi-cylindrical micelle structure to break apart and the surfactant tails to wrap around the graphite indenter. The indentation force curve has a maximum value of 13 nN.

Journal Article↗
PubMed1984

Trace analysis of lead in blood, aluminium and manganese in serum and chromium in urine by graphite furnace atomic absorption spectrometry.

A graphite furnace atomizer with automatic sampler is used to measure low levels of trace metals in biological samples by atomic absorption spectrometry. With blood and serum, the sample treatment consists of diluting (1:1) with aqueous Triton X-100 solution, centrifuging in the case of blood, and dispensing the liquid directly into a pyrolytic coated graphite tube. Sample volumes for blood and serum range from 5 to 10 microL. Stabilized urine (25 microL) is analyzed directly. The possibility of contamination is minimized by this simple procedure. The methods described minimize sample handling and involve reagents which are virtually free of contamination of the analytes. Background correction is necessary except for the determination of aluminium in serum, and precisions range from 0.7% to 4.3% RSD. The standard additions technique is used to establish the calibration and the required volume of sample and aqueous addition is automatically dispensed directly into the graphite tube.

Aluminum↗
PubMed2004

High dispersion and electrocatalytic properties of platinum nanoparticles on graphitic carbon nanofibers (GCNFs).

Highly dispersed platinum nanoparticles were electrodeposited on graphitic carbon nanofibers (GCNFs) by cyclic voltammetry (CV) in 7.7 mM H2PtCl6+0.5 M HCl aqueous solutions. The graphitic carbon nanofibers (GCNFs) used in this paper were grown directly on a graphite disk by chemical vapor deposition (CVD). The micrographs and element composition of Pt/GCNFs/graphite electrode were characterized by scanning electron microscopy (SEM) and electron diffraction spectroscopy (EDS). The electrocatalytic properties of Pt/GCNFs/graphite electrode for methanol oxidation have been investigated by CV and excellent electrocatalytic activity can be observed even at very low platinum loading (md=8.79 microg cm(-2)). The highest mass activity (MA) for methanol oxidation reaches 323 Ag(-1) when Pt/GCNFs/graphite electrode was cycled at a sweep rate of 50 mVs(-1) by CV in 2 M CH3OH+1 M H2SO4 aqueous solutions. This may be attributed to the small particle size and high dispersion of platinum particles coated on GCNFs and shows good potential application in direct methanol fuel cell (DMFC). Additionally, the long-term cycling stability of platinum catalysts was also investigated.

Journal Article↗
PubMed2004

Nanospray mass spectrometry with indirect conductive graphite coating.

An easy and cost-effective method to manufacture a robust conductive graphite coating for nanospray mass spectrometry (nESI-MS) and capillary electrophoresis (CE)-nESI-MS is described. The method involves graphite coating of a tube sleeve, into which the nESI emitter is inserted and connected to a transfer capillary, instead of coating the actual emitter. The coating, made of graphite from a pencil and epoxy glue, was stable over long periods of use (>80 h) and showed excellent resistance toward various solvents. Stable electrospray was achieved in the investigated flow range (150-900 nL x min(-)(1)), and salbutamol, diphenhydramine, and nortriptyline (M(w): 239-263 g x mol(-)(1)) were detected in the nanomole per liter range during continuous pumping. CE-nESI-MS analysis gave excellent signal-to-noise ratios for 100-fmol injections. The technique allows simple exchange of the nESI emitter to suit a specific flow rate, and it minimizes risk of corona discharge.

Journal Article↗
PubMedDate not supplied

Resonance energy in graphite.

According to Zhu et al. the resonance energy/electron (REPE) in infinite graphite sheets is equal to 0.17 eV. In the present work the REPE was calculated for parallelogram-shaped graphite sheets (PSGSs). The number of Kekulé structures and contributions of benzene-like and naphthalene-like conjugated circuits were taken into account. Analogously to polyacenes, it was found that REPE = 0.00 eV in PSGSs. The convergence is slow. These results indicate that PSGS is less "aromatic" than its infinite counterpart. Therefore addition reactions are expected to be less difficult to carry out in PSGSs than in infinite or rectangular graphite sheets.

Journal Article↗