No abstract

No abstract

A novel process using ultrasonics to enhance the exfoliation and dispersion of clay platelets in polypropylene‐based nanocomposites has been proposed and investigated. The materials studied were isotactic polypropylene of various molecular weights reinforced with organophilic montmorillonite clay (nanoclay) at 4–6 wt% loadings. X‐ray diffraction (XRD) and rheological measurements, on a model system of nanoclay in mineral oil, were first used to determine ultrasonic energy requirements. The effectiveness of the proposed ultrasonic processing technique on polypropylene nanocomposites was evaluated by XRD and transmission electron microscopy (TEM). The effects of added maleic anhydride–grafted polypropylene compatibilizer, polypropylene molecular weight, and pretreatment of the nanoclays on the nanocomposite exfoliation were also investigated. Results indicate that ultrasonic processing of polymer nanocomposites in the melt state is an effective method for improving exfoliation and dispersion of nanoclays. Issues regarding molecular weight degradation, optimization, mechanical properties, and continuous processing are beyond the scope of the present study and are currently being investigated in our laboratory. Polym. Eng. Sci. 44:1773–1782, 2004. © 2004 Society of Plastics Engineers.

Raman spectra were obtained from PdO, Rh,O, and PdRhO, thin films formed by oxidizing foil samples. Polarization measurements allow symmetry species assignments to be made for the lines from the corundum phase of Rh,O, and from PdRhO, , which has a delafossite structure.

No abstract

No abstract

Clean Si(111) surfaces were thermally nitrided at various temperatures by exposure to low pressures (1×10−6 Torr) of NO in a UHV system. The nitridation process was monitored by multiple surface analytical techniques including AES, XPS, UPS, LEED, and thermal desorption. At substrate temperatures below 800°C a silicon oxynitride was formed in which the nitrogen to oxygen ratio increased with increasing reaction temperature. These oxynitride films were converted to nitride films by loss of O and SiO when heated to temperatures greater than 850°C in vacuum. Exposure of the clean Si to NO at temperatures greater than 1000°C produced an oxygen-free nitride film. The nitride films formed by either route gave the ’’doublet’’ LEED pattern which has previously been associated with the formation of a two domain epitaxial α-Si3N4 layer. Due to the high reactivity of NO, the presence of 20%–30% C on the Si surface was not necessary for nucleation sites as had been reported for nitridation by NH3.

No abstract