Carbon bonding environments (measured by nuclear magnetic resonance spectroscopy) and compressive stress in plasma-deposited hydrogenated diamond-like carbon (DLC) films have been examined systematically as a function of substrate bias voltage. These results are related in terms of random network theory to show that hard DLC formed in an intermediate voltage range (100–400 V) consists of small graphitic clusters linked in a random network which is stiffened by a high density of quaternary carbon.
absolute number densities of neutral atom and ion a t the ground states by using the absorption or fluorescence technique (1 0, 51, 52). Registry No. Ar, 7440-37-1; Mg, 7439-95-4. LITERATURE CITED (1) Demers, D. R.; Allemand, C. 0. Anal. Chem. 1981, 53, 1915. (2) Fassel. V. A.; Knlseley, R. N. Anal. Chem. 1974, 46, 1llOA. (3) Houk, R. S.; Fassel, V. A.; Flesch, G. D.; Svec, H. J.; Gray, A. L.; Taylor, C. E. (IO) Nojlri, Y.; Tanabe, K.; Uchida, H.; Haraguchl, H.; Fuwa, K.; Wlnefordner, J, D.The use o f aolkhtate %I NMR spectroscopy to analyze q N 4 powders b demonstrated for a series of commercial and research samples. I n particular, two dlfferent commercial powders contaln 20% and 30% amorphous Si3N4 content, as identtfied by the applicatlon of methods described herein.These same materlals had been analyzed by X-ray dmtaction as only crystalline SiaNp NYR spectroscopy is capable of dlstlngulohlng among dlfferent amorphous silicon specks normally found In preparatlons of S13N4 powders. These Include amorphous S13N4, sHlcon oxynltrldes, sllicates, and elemental slllcon. The measurement of concentration of these species Is made for correlatlon wHh properties of powder sinterability.Sinterable silicon nitride (Si3N4) has been intensely investigated since 1974 because of potential applications as a tough, refractory ceramic material (1). The production of reliable and cost-effective structural Si3N, ceramic by sintering of powders must begin with powders that have, among other qualities, an a-phase content in excess of 85% (2). Excessive @-Si3N4 in the powder interfers with microstructure changes that accompany sintering. On the other hand, some a-Si3N4 (amorphous) can aid densification of the final material (3).Oxygen and elemental silicon can also aid sintering, although concentrations in excess of 2% can deteriorate mechanical properties at elevated temperatures. Oxygen normally appears as amorphous silicon oxynitrides and silicates.In view of what is known about the effects of the powder's phase and purity on sinterability and fiial ceramic mechanical properties, it is necessary to have rapid, reliable methods for the determination of the crystallinity and purity of batches of Si3N4 powder before carrying out final product formation and sintering. Traditionally, X-ray powder diffraction has been used to determine the presence of @-Si3N4, silicon oxynitrides, silicates, and silicon in the a-Si,N4 powders. The powder diffraction technique fails, however, in the identification of amorphous species. All amorphous species contribute to the background diffraction signal whose intensity is difficult
Increased interest in ceramic materials, particularly for high-temperature, high-stress applications, has created the need for rapid and reliable analytical techniques to monitor microcrystalline structure of commercial ceramic powders. A comparative evaluation of commercially available PSiC powders is undertaken to analyze the potential of nuclear magnetic resonance (NMR) in the characterization of PSiC powder. NMR provides an acceptable, rapid method for characterization of powders both during powder manufacturing as well as for powder analyses prior to sintering studies. The results of transmission electron microscopy and X-ray diffraction are correlated with the NMR spectra to explain some newly observed features in the NMR spectra of PSiC powders and to illustrate the sensitivity of NMR to microcrystalline disorder. [Key words: microscopy, nuclear magnetic resonance, transmission electron microscopy, X-ray diffraction, silicon carbide.]
Polyester blends may undergo transesterification during processing, resulting in molecular rearrangements, transient properties, and eventually, degradation. To suppress transesterifcation, the use of organophosphites has been suggested in the patent and technical literature. The effectiveness of organophosphites, however, is variable and sometimes inconsistent. Our recent studies suggest a clue to the inconsistent behavior and provide a simple way to enhance the effectiveness of these stabilizers. Using solid state 31P NMR it was shown that for bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite a conversion of the phosphite group to a phosphonate, via hydrolysis, is a prerequisite for a n effective inhibition of transesterification. This conversion occurs readily during melt compounding if the polymers are not completely dry. However, if rigorous drying is employed and phosphite conversion does not occur, then transesterification is not arrested. It was also found that over a period of time the conversion of the phosphite to a phosphonate may take place at room temperature as well. After aging for about a year in the laboratory, the originally ineffective compound, has become a very effective inhibitor of transesterification in blends containing poly(ethy1ene terephthalate), poly(buty1ene terephthalate), polycarbonate, and polyarylate. Thus, a simple way to enhance the phosphite effectiveness is to expose it to a humid environment prior to blending.
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