a b s t r a c tBallistic performance, at effective strain rates of (10 4 -10 5 s À1 ), for polymeric dicyclopentadiene (pDCPD)was compared with two epoxy resin/diamine systems with comparable glass transition temperatures. The high rate response was characterized in terms of a projectile penetration kinetic energy, KE 50 , which describes the projectile kinetic energy at a velocity with a 50% probability of sample penetration. pDCPD showed superior penetration resistance, with a 300-400% improvement in ballistic energy dissipation, when compared with the structural epoxy resins. In addition, unlike typical highly crosslinked networks that become brittle at low temperatures, the improved pDCPD performance occurred over a very broad temperature range (À55 to 75°C), despite exhibiting a glass transition temperature characteristic of structural resins ($142°C). In addition to the high T g , pDCPD exhibited a room temperature glassy storage modulus of 1.7 GPa, offering the potential to circumvent the common structural versus energy dissipation trade-off encountered with conventional crosslinked polymers. Quasi-static measurements suggested that the performance of pDCPD is phenomenologically related to higher fracture toughness and lower yield stress relative to typical epoxies, while molecular dynamics simulations suggest the origin is the lack of strong non-covalent interactions and the facile formation of nanoscale voids to accommodate strain in pDCPD.Published by Elsevier Ltd.
Thin films of PbTiO, were deposited on fused silica, resistor-grade alumina, and single-crystal (100) MgO by a sol-gel processing m e t h o d . Whereas the films deposited on silica and alumina substrates were randomly oriented and polycrystalline, highly (100) oriented PbTiO, films were grown on the M g O single crystals. The perovskite-type structure was observed with films deposited on the single-crystal MgO and annealed at temperatures a s Low as 470"C, whereas a pyrochlore-type structure was observed with f i l m s on fused silica and alumina processed in a similar manner. All films heat-treated at temperatures in excess of 570°C showed significant formation of a second PbTi,O, phase. The films were characterized by electron microscopy and glancing-incidence-angle X-ray diffraction . [Key words: lead titanate, sol-gel, m a g n e s i a , microscopy, synthesis. 1 T H E sol-gel process of hydrolysis and condensation of metal alkoxides to form polymeric ceramic precursors has been the subject of considerable research interest. lntital work demonstrated the relative ease with which various silicabased, glass thin films could be fabricated; recent work has developed the potential of sol-gel processing methods for the deposition of polycrystalline electronic ceramic thin films. Processing techniques for solgel-derived thin films of BaTiO,,' PbTi03,' Pb(Zr, Ti)03,3 PLZT,4 and others have all been reported. With the exception of the work of Partlow and Greggi,' where observation of homoepitaxial growth of LiNbO, thin films was reported, there has J. E. Eulm-contributing editor Manuscript No. 198587.
Optical thin films of nitrides, oxynitrides and oxides of aluminum and silicon were deposited using ion assisted deposition. Coatings were deposited by thermal evaporation of AlN and e-beam evaporation of Si with simultaneous bombardment with 300 eV ions of nitrogen, a mixture of nitrogen and oxygen or oxygen. The chemical composition and the index of refraction of the coating was varied by varying the gas mixture in the ion beam. Optical properties of and environmental stability of coatings were examined. Results indicated that coatings are stable even under severe conditions of humidity and temperature.
Reactive ion etching of silicon oxynitride formed by plasmaenhanced chemical vapor deposition Effect of reactiveion bombardment on the properties of silicon nitride and oxynitride films deposited by ionbeam sputtering J. Appl. Phys. 75, 8145 (1994); 10.1063/1.357027 Chemical composition of soft vacuum electron beam assisted chemical vapor deposition of silicon nitride/oxynitride films versus substrate temperatureOptical thin films of nitrides, oxynitrides, and oxides of aluminum and silicon were deposited using ion assisted deposition. Coatings were deposited by evaporation of either AlN or Si with .,imultaneous bombardment with 300-eV ions of nitrogen, oxygen, or a mixture of oxygen and nitrogen. The chemical composition of the coatings was varied by varying the gas mixture in the ion beam, making it possible to vary the index ofrefraction of the coatings during deposition from 1.44 to 2.1 in the case of silicon oxynitrides, and 1.62 to 2.1 in the case of aluminum oxynitrides. Optical properties and environmental stability of the coatings were examined. Coatings are stable under severe conditions of humidity and temperature.
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