Using nuclear magnetic resonance (NMR) and infrared (ir) absorption spectroscopy, this paper demonstrates the effects of deposition temperature, annealing temperature, and dopant-atom incorporation on the hydrogen microstructure of plasma-deposited amorphous silicon. Multiple-quantum NMR studies indicate clusters of five to seven hydrogen atoms in films prepared at temperatures ranging from 113 to 324 C. In the range from 270 to 324'C, only these small clusters exist, but lower-temperature films also contain larger clusters. A comparison of the ir and NMR results allows the assignment of the 2080-cm ' absorption to small hydrogen clusters. Annealing studies indicate hydrogen rearranges prior to evolution. Deposition temperature and annealing temperature have similar effects on hydrogen concentration, but deposition temperature was found to control the density and microstructure of the film. The addition of dopant atoms also affects the hydrogen microstructure, with phosphorous causing larger hydrogen clusters to form, and boron reducing clustering in the film. This perturbation of the film's microstructure suggests that the effects of dopant addition are much more complex in amorphous than in crystalline semiconductors.We surmise that hydrogen microstructure, rather than hydrogen content, determines amorphous-silicon properties.

The primary objective of this work was to demonstrate the conversion of scrap tires to activated carbon. We have been successful in this endeavor, producing carbons with surface areas greater than 500 m2/g and significant micropore volumes. Tire shreddings were pyrolyzed in batch reactors, and the pyrolysis chars activated by reaction with superheated steam. Solid products of pyrolysis and activation were studied with nitrogen adsorption techniques. We find that the porosity development during steam activation of tire pyrolysis char is similar to that reported for various other chars. A maximum in micropore volume is observed as a function of conversion, but the total surface area increases monotonically with conversion. We suggest that the activation process consists of micropore formation, followed by pore enlargement. The process conditions used in this study are a good starting point from which to optimize a process to convert tires to activated carbon. IntroductionScrap tires are a major environmental problem. An estimated 2.5 x lo9 kg of scrap tires are generated each year in North America (Williams et al., 1990). The conventional method of reusing waste rubber is to convert it into rubber reclaim, which is suitable for mixing with virgin rubber compounding materials. However, rubber reclaim generated from scrap tires does not have suitable properties for use in tire manufacture and must be used for low-value rubber goods (Makarov and Drozdovski, 1991). Moreover, production with rubber reclaim can be more costly than production with virgin raw materials (Crane and Kay, 1975). As a result, the majority of scrap tires accumulate in dumps, posing hazards such as disease and accidental fires.Tires contain carbon-black-reinforced rubber, and both inorganic and organic belt materials. The rubber component may be natural rubber, but styrene-butadiene (about 25% styrene) copolymer rubber (SBR) is more common. A typical tire compounding composition contains 62 wt. Vo SBR, 31 wt. % carbon black, and small amounts of other materials including extender oils, sulfur, zinc oxide, and stearic acid. Carbon black is used to reinforce the rubber. The rubber is cross-linked by vulcanization, which involves reactions with sulfur. Small amounts of zinc oxide and stearic acid are added to control Correspondence concerning this article should be addressed to M. A. Petrich. the vulcanization process and enhance the properties of the final products (Studebaker and Beatty, 1978).The potential value of reusing the polymeric base of old tires has received considerable attention. Alternatives include production of goods with reclaim, use of ground rubber as construction filler, and degradation to basic raw materials by pyrolysis (Makarov and Drozdovski, 1991). Filler and reclaim applications have relatively small economic potential. Incineration of tires may be an effective means of waste volume reduction, but incineration does not recover much of the intrinsic value of the materials in the tire (Williams et al., 1990). The hydrocarbon...

Growth and bonding structure of hard hydrogenated amorphous carbon thin films deposited from an electron cyclotron resonance plasma Hard~carbon films prepared by the rf-plasma decomposition of acetylene have been investigated by high-resolution Be nuclear magnetic resonance spectroscopy, x-ray photoelectron spectroscopy (XPS), and the H( 15Na,y)C nuclear resonant reaction. It was found that the ratio of Sp2:Sp3 bound carbon was 1.6, and that virtually all Sp3 carbon atoms are, in fact, bound to one or more hydrogen atoms. Bulk layers contain about 40% hydrogen; however, results of the measurements ofthe hydrogen concentration, as well as those ofXPS, confirm that the composition and properties of these carbon films are a strong function of their distance from the initial growth interface, and are spatially varying over the first 40 nm.

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0 Evidence is provided for the existence of a second discrete chemical form of meropenem at clinically relevant concentrations prepared from the marketed formulation of the drug. Proton and carbon-13 NMR spectra in D 2 O, coupled with tandem mass spectroscopy (MS/MS) and cross polarization/magic angle spinning (CP-MAS) NMR experiments, allow structural assignment of the compound as a covalent carbon dioxide adduct of meropenem. This carbon dioxide adduct exists in equilibrium with the free drug in solution and can be observed in the solid state following lyophilization. The equilibrium constant of formation of the adduct (K eq ) 20 ± 8 M -1 ) was estimated in D 2 O at 25°C.