Henry White

Structural development during deformation of polyurethane containing polyhedral oligomeric silsesquioxanes (POSS) molecules

A unique polyurethane (PU) elastomer containing inorganic polyhedral oligomeric silsesquioxane (POSS) molecules as molecular reinforcements in the hard segment was investigated by means of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) techniques. The mechanical properties of POSS modified polyurethane (POSS-PU) were also compared to those of polyurethane without POSS. The crystal structures of two different POSS molecules were first determined by X-ray powder diffraction analysis, yielding a rhombohedral cell with aa 11.57 A ˚, aa 95.58 for octacyclohexyl-POSS (1,3,5,7,9,11,13,15octacyclohexylpentacyclo[9.5.1.13,9.15,15.17,13] octasiloxane) and aa 11.53 A ˚, aa 95.38 for hydrido-POSS (1-[hydridodimethylsiloxy]3,5,7,9,11,13,15-heptacyclohexylpentacyclo [9.5.1.13,9.15,15.17,13] octasiloxane). WAXD results showed that reflection peaks distinct to POSS crystal diffraction were seen in POSS-modified polyurethane, which suggests that POSS molecules formed nanoscale crystals in the hard domain. During deformation, the average size of POSS crystals in POSS-PU was found to decrease while elongation-induced crystallization of the soft segments was observed at strains greater than 100%. The SAXS results showed microphase structure typical of segmented

Nanoscale reinforcement of polyhedral oligomeric silsesquioxane (POSS) in polyurethane elastomer

A unique class of polyurethane (PU) elastomer containing inorganic molecules (polyhedral oligomeric silsesquioxane, POSS) as molecular reinforcement in the hard segment was investigated by means of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. WAXD results indicate that POSS molecules form nanoscale crystals showing distinct reflection peaks. The formation of POSS crystals is probably prompted by the microphase separation between solid-like hard segments and rubbery soft segments in PU. The microphase separation of hard and soft segments was observed by SAXS, which shows a long period of 111 A for 34 wt% POSS-PU and 162 A for 21 wt% POSS-PU, and hard segment domains with sizes of about 34 A for both of them. WAXD results from a series of POSS compounds with a corner substituted by a functional group of varying length were compared with POSS-PU, which also confirms the presence of nanoscale POSS crystals in the polymer matrix. © 2000 Society of Chemical Industry

Focused ion beam/lift-out transmission electron microscopy cross sections of block copolymer films ordered on silicon substrates

Thin poly(styrene210-b-2-vinylpyridine 200) and poly(2-vinylpyridine94-b-styrene760-b-2-vinylpyridine94) films spun cast on silicon and annealed at 1808C for 3 days were directly cross sectioned in less than 1 h using the focused ion beam (FIB) lift-out technique. We show that with the FIB procedure, it is possible to produce cross sections that reveal structure near the silicon interface and hence the surface induced phase transitions could be examined and compared quantitatively with theoretical models. Atomic force microscopy, dynamic secondary ion mass spectrometry, and transmission electron microscopy were used to characterize the films.q 2000 Elsevier Science Ltd. All rights reserved.

Internal carburization and carbide precipitation in Fe-Ni-Cr alloy tubing retired from ethylene pyrolysis service

The events leading to the failure of an alloy grade HP Nb ethylene pyrolysis heater tubing were examined. X-ray maps indicated that a complex oxide coating, which inhibits carbon (C) diffusion, forms on the process side of the tubing during service. Phase equilibria studies predict that even without process C diffusion, metal carbides will precipitate out of the face centered cubic (FCC_Al) matrix. It was estimated that a 6 mm thick tube operating at 1100 °C would completely carburize in two years if the protective coating is damaged.

Scaled Up Pulsed Deposition Technology: Carburization Resistant Ablation Coatings for Ethylene Pyrolysis Coils

Products derived from ethylene have and will continue to replace metallic materials traditionally used for transportation, building materials, and products we use in our everyday lives. As the demand continues to increase, a more suitable material for the outlet coils of ethylene pyrolysis heaters will have to be identified. In this study, we discuss utilization of scaled up pulsed deposition technology to deposit adherent carburization resistant coatings on the inner diameter of ethylene pyrolysis tubing with the intent of extending tube life. Ablation target material selection was based primarily on elevated temperature properties and the ability of the coating to prevent transformation of the inherent protective chromium oxide surface film to metal carbides while in service. The near optimal settings of the processing parameters for pulsed laser deposition of ceramic SiC on heat resistant tubing traditionally used for ethylene service were investigated using a semi quantitative controlled random search methodology. Minimization of the objective function which was based on width, thickness and coverage of the thin film resulted in an optimal deposition time of 4.3 minutes and surface finish of 272 nm.

Limiting Catalytic Coke Formation by the Application of Adherent SiC Coatings via Pulsed Laser Deposition to the Inner Diameter of Tube Material Traditionally Used for Ethylene Pyrolysis Service

Pulsed laser deposited coatings can be used to enhance the corrosion resistant of materials traditionally used for industrial applications. In this paper, we describe our initial results on coating HK40 (a material used for ethylene heater tubing) with silicon carbide (a carburization resistant coating) to increase tube life. A 1 um thick film of silicon carbide was successfully deposited onto a heated HK40 substrate. An array of characterization techniques (scanning electron microscopy, atomic force microscopy, and scratch tests) demonstrated that the processing conditions were suitable for good coverage and promising adhesion behavior.