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Polymeric carbons are produced by the carbonization of a wide range of organic polymeric systems. We have concentrated on the fabrication of two types of polymeric carbons, glassy carbon and carbon-fiber-reinforced carbon (CFRC), both involving phenolic resin precursors. We describe herein the technology which enables us to make dental implants and heart valves out of glassy carbon. We also show how carbon-fiber-reinforced carbon can be made in the form of rods and plates for orthopedic use and molded before firing to produce complex, rigid, individually sculptured shapes suitable for maxillofacial bone replacement. The mechanical properties will be discussed in relation to the structure of these various forms of polymeric carbon. The main purpose of the work is to show that the technology of polymeric-carbon manufacture is essentially simple and the manufacturing process is readily carried out in laboratories which have already been equipped to fabricate standard dental prostheses.
OBJECTIVE: Previous studies demonstrated that a non-carbonated blackcurrant juice drink with added calcium produced little erosion of enamel in vitro and in situ by comparison with other low pH fruit drinks. The aim of this study is to evaluate the erosive effects in situ of an experimental formulation carbonated drink with added calcium, compared to a conventional carbonated drink over a 20 day period using a similar design as in previous studies. METHOD: The study was a single centre, single blind, randomised placebo controlled three cell crossover design involving 15 volunteers. The test drinks were an experimental carbonated ready-to-drink (RTD) blackcurrant drink, a conventional carbonated RTD orange drink and water. Two enamel samples were retained in situ, in the midline of the hard palate on an upper removable acrylic appliance. Drinks were 250 ml volumes consumed four times per day during 20 working days. Measurements of enamel loss were made on enamel samples after days 2, 5, 10, 15 and 20 by profilometry. RESULTS: The experimental carbonated blackcurrant drink caused significantly less enamel loss than the conventional carbonated orange drink at all time points measured, but was not significantly different from water at days 2, 5 and 20. CONCLUSIONS: This study has shown that it is possible to modify carbonated soft drinks in a manner similarly shown with non-carbonated soft drinks, to minimise dental erosion.
A new system has been developed for the determination of total organic carbon (TOC) and inorganic carbon (IC) or total inorganic carbon (TIC) in waters. Only nonvolatile organic compounds can be detected through the present method. The system presented in this work is based on the measurement of the carbon atomic emission intensity in inductively coupled plasma atomic emission spectrometry (ICP-AES). This way, the organic matter does not undergo any preoxidation step. A semiautomatic accessory connected to the spectrometer separates the different carbon fractions (i.e., organic and inorganic). Because most of the solutions used in the present work did not contain suspended solid particles, the actual parameter that was determined was the dissolved organic carbon (DOC). The present system exhibits good sensitivities compared to those provided by conventional TOC and IC determination methods. The limits of detection obtained in the present work have been 0.07 and 0.0007 mg/L C in terms of TOC and IC, respectively. Furthermore, the system is able to handle high-salt-content solutions. This fact suggests that it would be possible to analyze seawater samples, avoiding some of the problems encountered with conventional methods, such as system blocking or interferences. The TOC and IC values found for natural samples are very close to those measured using conventional methods. The ICP-AES method has been successfully used in two interesting applications: (i) monitoring the efficiency of a water treatment plant and (ii) determining the contents of dissolved carbon dioxide, on one hand, and that of carbonate and bicarbonate, on the other, in the same sample.
Carbon fiber-reinforced carbon composites (CFRC) are considered to be promising materials for orthopedic and dental surgery. Their mechanical properties can be tailored to be similar to those of bone, and their chemical composition (close to pure carbon) promises that they will be tolerated well by the surrounding tissue. In this study, CFRC composites were fabricated from phenolic resin and unidirectionally oriented Torayca carbon fibers by carbonization (1000 degrees C) and graphitization (2500 degrees C). The material then was cut with a diamond saw into sheets of 8 x 10 x 3 mm, and the upper surface was polished by colloidal SiO2 and/or covered with a carbon-titanium (C:Ti) layer (3.3 microm) using the plasma-enhanced physical vapor deposition method. Three different kinds of modified samples were prepared: polished only, covered only, and polished + covered. Untreated samples served as a control. The surface roughness of these samples, measured by a Talysurf profilometer, decreased significantly after polishing but usually did not decrease after coating with a C:Ti layer. On all three modified surfaces, human osteoblast-like cells of the MG63 line and rat vascular smooth muscle cells (both cultured in a Dulbecco's minimum essential medium with 10% fetal bovine serum) adhered at higher numbers (by 21-87% on day 1 after seeding) and exhibited a shorter population doubling time (by 13-40%). On day 4 after seeding, these cells attained higher population densities (by 61-378%), volume (by 18-37%), and protein content (by 16-120%). These results were more pronounced in VSMC than in MG63 cells and in both groups of C:Ti-covered samples than in the polished only samples. The release of carbon particles from the CFRC composites was significantly decreased--by 8 times in the polished only, 24 times in the covered only, and 42 times in the polished + covered samples. These results show that both polishing and carbon-titanium covering significantly improve the biocompatibility of CFRC composites in vitro, especially when these two modifications are combined.
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A new type of one-dimensional (1D) carbon structure, carbon nanowires (CNWs), was discovered in the cathode deposits prepared by hydrogen arc discharge evaporation of carbon rods. Observation of high-resolution transmission electron microscopy (HRTEM) indicates that a CNW consists of a multiwalled carbon nanotube (MWNT) with a long 1D linear carbon chain (C chain) inserted into its innermost tube of 0.7 nm in diameter. The characteristic Raman peaks of CNWs appeared at around 1850 cm(-1). Raman scattering and HRTEM studies show the formation of a long linear C chain involving more than 100 carbon atoms inside a MWNT. This novel 1D carbon allotrope has potential applications in nanoelectronics, nanomechanics, and nanomaterials.
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Carbonate anions resulting from reaction of primary or secondary alcohols with carbon dioxide, when added to methanesulfonic anhydride in cooled acetonitrile solution, yield methanesulfonyl carbonates, a new class of synthetic intermediate. Base-mediated reaction of the methanesulfonyl carbonates with alcohols, thiols, and amines yields carbonates, thiocarbonates, and carbamates, respectively. Overall yields for the three steps vary from 19% to 42%.
Scanning thermal microscopy (SThM) is a relatively new technique based on atomic force microscopy in which the tip is replaced by an ultra-miniature temperature probe. This paper reports on a preliminary investigation of the application of SThM in the characterization of the thermal properties of carbon fibres and carbon-carbon (CC) composites. The technique enabled a comparative study to be made of discrete fibre and matrix thermal properties in a series of model unidirectional composites. The thermal images revealed a marked increase in thermal conductivity of the matrix with increasing temperature of treatment and hence confirmed the development of a highly ordered carbon matrix. The results were in qualitative agreement with previously determined values of thermal conductivity from which the separate values of fibre and matrix thermal conductivity had been derived. The technique was also applied to the characterization of samples of unknown processing history, enabling an estimation to be made of the heat treatment and type of the fibres and matrix present in the composite. It was concluded that SThM promises to be a powerful technique for the study of the thermal properties of CC composites and carbon fibres, as it uniquely enables variations in local thermal conductivity to be detected and resolved. Absolute quantification of the technique remains the key to its future widespread acceptance in materials characterization.
The mu-eta(3)-allenyl/propargyldipalladium complexes were synthesized by the reaction of the corresponding eta(1)-allenyl- or eta(1)-propargylpalladium complexes with Pd(2)(dba)(3). The X-ray diffraction analysis indicates that the dinuclear complex has a unique structure, in which two palladium, three carbon, two phosphorus, and one halogen atoms are in the same plane. These dinuclear complexes react with electrophiles, such as HCl or AcCl, at the central carbon of the mu-eta(3)-allenyl/propargyl ligand to give the mu-eta(3)-vinylcarbenedipalladium complexes. Intramolecular reaction proceeded smoothly to give cyclization products quantitatively. Addition of a catalytic amount of a palladium(0) complex dramatically accelerated the carbon-carbon bond formation. The MO calculations on the mu-eta(3)-allenyl/propargyl complexes indicated that the reaction proceeds via orbital control.
A method for the automated (13)C analysis of dissolved inorganic and organic carbon species has been developed to operate on a continuous-flow isotope ratio mass spectrometer (CF-IRMS). For natural and anthropogenic carbon species, the (13)C stable isotope has proven to be an excellent environmental tracer. Analytical performance tests were carried out on various organic compounds from easily oxidisable (sugar) to difficult (humic acid). A set of natural samples was also analysed to confirm the flexibility of the system. Analytical precision (2sigma) is typically <0.20 per thousand with sample reproducibility from 0.10-0.35 per thousand depending on reactivity of material. We believe this to be the first successful use of a total organic carbon (TOC) analyser for both dissolved inorganic and, specifically, dissolved organic species for (13)C stable isotope analysis in an automated CF-IRMS system. Routine analysis is achieved fairly quickly, is relatively simple with little or no sample manipulation, and will allow new and exciting studies for stable isotope research in both natural abundance and organic tracer studies not easily achieved before.
Global emissions of atmospheric CO(2) and tropospheric O(3) are rising and expected to impact large areas of the Earth's forests. While CO(2) stimulates net primary production, O(3) reduces photosynthesis, altering plant C allocation and reducing ecosystem C storage. The effects of multiple air pollutants can alter belowground C allocation, leading to changes in the partial pressure of CO(2) (pCO(2)) in the soil , chemistry of dissolved inorganic carbonate (DIC) and the rate of mineral weathering. As this system represents a linkage between the long- and short-term C cycles and sequestration of atmospheric CO(2), changes in atmospheric chemistry that affect net primary production may alter the fate of C in these ecosystems. To date, little is known about the combined effects of elevated CO(2) and O(3) on the inorganic C cycle in forest systems. Free air CO(2) and O(3) enrichment (FACE) technology was used at the Aspen FACE project in Rhinelander, Wisconsin to understand how elevated atmospheric CO(2) and O(3) interact to alter pCO(2) and DIC concentrations in the soil. Ambient and elevated CO(2) levels were 360+/-16 and 542+/-81 microl l(-1), respectively; ambient and elevated O(3) levels were 33+/-14 and 49+/-24 nl l(-1), respectively. Measured concentrations of soil CO(2) and calculated concentrations of DIC increased over the growing season by 14 and 22%, respectively, under elevated atmospheric CO(2) and were unaffected by elevated tropospheric O(3). The increased concentration of DIC altered inorganic carbonate chemistry by increasing system total alkalinity by 210%, likely due to enhanced chemical weathering. The study also demonstrated the close coupling between the seasonal delta(13)C of soil pCO(2) and DIC, as a mixing model showed that new atmospheric CO(2) accounted for approximately 90% of the C leaving the system as DIC. This study illustrates the potential of using stable isotopic techniques and FACE technology to examine long- and short-term ecosystem C sequestration.
The carbon dioxide solubility coefficient, alphaCO2, and the apparent carbonic acid dissociation constants, K'1 and K'2 were estimated in the serum of the crab Carcinus maenas at various temperatures and ionic strengths. At 15 degrees C, the indirectly determined alphaCO2 value is 0-0499 m-mole l-1 torr-1 for crabs living in normal sea water (salinity ca. 35 percent). It is apparently independent of the serum protein concentration and of the stage of the moulting cycle. For crabs living in undiluted sea water, the mean pK'1 value, determined either gasometrically or titrimetrically, is 6-027 at 15 degrees C. At the same temperature, pK'2=9-29. These values approximate to those of sea water at 35 percent salinity. pK'1 drops as temperature rises; the measured deltapK'1/deltat is -0-0053 pH unit degrees C-1 between 10 and 30 degrees C. PK'1 rises as the ionic strength is lowered. Alignment nomograms have been constructed for the determination of alphaCO2, pK'1 and pK'2 values in relation to various conditions of temperature and salinity.
Electrophilic cobalt(III) mediates an unprecedented two-carbon ring expansion of coordinated five-membered rings, leading to a remarkably general new strategy for the synthesis of seven-membered carbocycles from readily available five-membered ring substrates. The reaction, a metal-mediated [5 + 2] cyclopentenyl/alkyne cycloaddition, proceeds via initial protonation of a cobalt(I) cyclopentadiene complex, followed by rearrangement to an agostic eta3-cyclopentenyl intermediate. The cyclic eta3-allyl residue then undergoes migratory coupling with alkyne followed by carbon-carbon bond activation of the unstrained five-membered ring and recyclization to the ring expanded product, although the order of events and intimate mechanism has not been conclusively established. The reaction is highly selective with respect to which five-membered ring ligand undergoes activation, presumably a consequence of rapid cobalt-mediated interannular hydride transfer and kinetic preference for alkyne insertion into the less substituted cyclopentenyl ring. The alkyne insertion is itself highly regioselective, proceeding via migration to the sterically smaller end of the alkyne. The reaction is sensitive to both the cobalt counterion and the ancillary eta5-cyclopentadienyl substituent but proceeds for a considerable range of alkyl-, aryl-, and trialkylsilyl-substituted terminal and internal alkynes.
Palladium 15-20 nm particles stabilized by a Keggin-type polyoxometalate were prepared by reduction of K(5)PPdW(11)O(39) with H(2). The nanoparticles were shown to be effective catalysts for Suzuki-, Heck-, and Stille-type carbon-carbon coupling and carbon-nitrogen coupling reactions of bromoarenes in aqueous media. Chloroarenes were also reactive in reaction media without solvent. [reaction: see text]