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.]

The wetting of several new materials for gas turbine engines, e.g. Sic, Si,N,, and C, by liquid Si and binary Si alloys containing Cu, Fe, and B was determined by the sessile drop method.All contact angles measured were <90". Hot-pressed Sic, Si,N,, and RefelSiC areeasily wet by Si; wetting is controlled by the balance of interfacial energies. Carbon is wet well by Si, but wetting is controlled by reaction and, in some carbons, by infiltration of Si into C. Additives to Si such as B and Fe can form compounds in reaction zones during wetting at interfacial areas.

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We present an analysis of the X-ray spectrum and long-term variability of the nearby dwarf starburst galaxy Henize 2-10. Recent observations suggest that this galaxy hosts an actively accreting black hole (BH) with mass∼10 6 ☉ M . The presence of an active galactic nucleus (AGN) in a low-mass starburst galaxy marks a new environment for AGNs, with implications for the processes by which "seed" BHs may form in the early universe.In this paper, we analyze four epochs of X-ray observations of Henize 2-10, to characterize the long-term behavior of its hard nuclear emission. We analyze observations with Chandra from 2001 and XMM-Newton from 2004 and 2011, as well as an earlier, less sensitive observation with ASCA from 1997. Based on a detailed analysis of the source and background, we find that the hard (2-10 keV) flux of the putative AGN has decreased by approximately an order of magnitude between the 2001 Chandra observation and exposures with XMM-Newton in 2004 and 2011. The observed variability confirms that the emission is due to a single source. It is unlikely that the variable flux is due to a supernova or ultraluminous X-ray source, based on the observed long-term behavior of the X-ray and radio emission, while the observed X-ray variability is consistent with the behavior of well-studied AGNs.