ABSTRACTWe show that bonded hydrogen in a-Si:H is readily exchanged by atomic deuterium when exposed to a deuterium plasma discharge. The effective diffusion coefficient for the D.H exchange, 10∼14 cnr/sec at 160°C, is comparable to that of interstitial hydrogen in c-Si.

Dewetting dynamics of immiscible liquid polymer bilayers were studied by atomic force microscopy. Morphological changes of the phase-separated liquids were correlated with friction and local elastic properties, and the dewetting pattern classified in terms of the relative bulk viscosities. Topographical atomic force microscopy measurements revealed that the dewetting process did not occur on the liquid–liquid interface as expected. Rather the process is three-dimensional with an apparent shear plane ‘‘deep’’ inside the low viscosity liquid film. The depth of the shear plane is immediately established in the nucleation process which was studied two and three dimensionally by friction force microscopy and compliance measurements. Since this mechanism has not been observed previously in simple liquids, the role of entanglements of these polymers is discussed together with the application of the atomic force microscopy as a three-dimensional material property specific tool capable of studying processes below the surface.

A molecular scale atomic force microscopy study of friction and elasticity is presented on a one-component lipid bilayer system - a model boundary lubricant. With a real area of contact on the order of the lattice spacings of the sample, the elastic compliances of single lipid molecules are recorded - the first report of a molecularly resolved elasticity map. The anisotropic and highly ordered structure of the lipid bilayer has been observed to cause contrast information in friction on molecularly flat areas, and to be dependent on the sliding direction. This anisotropic behavior of friction has been measured to be independent of normal elastic compliances. Only asymmetric indentation which causes in-plane compliances leads to heterogeneities in the elasticity map. In this fundamental study of friction, the effects of adhesion and elasticity are discussed.

The characterization of petroleum cracking catalysts, with which a third of the world's crude oil is processed, presents a formidable analytical challenge. The catalyst particles are in the form of microspheres of 60-70 micron average diameter which are themselves composites of up to five different micron and submicron sized phases. In refinery operation the catalysts are poisoned by trace concentrations of nickel, vanadium and other contaminant metals. Due to the replacement of a small portion of equilibrium catalyst each day (generally around 1% of the total reactor inventory) the catalyst particles in a reactor exist as a mixture of differing particle ages, poisoning levels and activities.Direct imaging SIMS has been shown to be capable of viewing both the phases and contaminants within individual catalyst particles, and differences from particle to particle. Multiple image processing techniques now allow the rapid analysis of the relative concentrations of several elements (normally 6-8) on a large number of particles (50-100) using multiple low magnification SIMS images. Using the fact that nickel concentrations increase systematically with a particle's age permits the analysis of poisoning and elemental composition as a function of a particle's "time in the reactor." Within individual particles, SIMS views coupled with elemental image ratios and overlays have also allowed the measurement of the quantity of each phase (such as zeolite and alumina) and the distribution of nickel and vanadium poisons in relationship to those phases.

A study of the clad alloy 625 deposited by HIP and weld overlay on 4130 and 21/&r-1Mo steels was conducted to evaluate the effect of cladding process on microstructure, mechanical, corrosion and stress corrosion cracking (SCC) properties relating to sour gas production service.The results showed that the microstructure of the clad and interface produced by the two cladding processes are considerably different and had a direct effect on the properties.The clad produced by HIP had a homogenous structure which showed superior resistance to pitting, hydrogen disbond and SCC.In contrast, the HIP process resulted in a high concentration of coarse carbides resulting in poor mechanical properties of the clad/steel interface properties than in the weld clad.The segregated cast structure of the weld overlay alloy 625 contributed to the reduced resistance to corrosion and SCC of the weld clad compared to HIP clad.The weld clad interface also had fewer carbides which provided good mechanical integrity.Analysis of the microstructural characteristics and properties of the two clad materials are presented.

The analytical utility of the negative molecular spectrum in secondary ion mass spectrometry (SIMS) was examined using the Fe-C system as a model system. A series of plain carbon steels ranging in carbon concentration from 0.08 to 0.8 wt pct was investigated both in the austenitized-quenched and tempered conditions to establish the mass spectral differences arising due to the difference in the state of carbon. The results showed that SIMS was sensitive to the state of carbon in the alloy and that the presence of cementite could be easily detected. The application of SIMS to characterize microstructures is demonstrated by examples.

The microstructures of 4130 and 2.25Cr-1Mo steels clad to nickel base IN625 by welding and HIPing were examined by Analytical Electron Microscopy (AEM) and Secondary Ion Mass Spectroscopy (SIMS) to determine the interfacial microstructural characteristics which could affect their mechanical properties and corrosion resistance. The interface microstructures of the clads produced by the two methods were considerably different. The clad produced by welding was characterized by a low density of carbide precipitates confined to a very narrow region (∼1 μm) at the interface of ferrite and austenite. In addition, a thin region of untempered martensite was present at the interface which could affect its resistance to hydrogen embrittlement as well as other mechanical properties. The interface of the HIP clad composite contained several regions of distinct microstructural characteristics with widely varying densities of carbide precipitates. Relative to the clad produced by welding, extensive precipitation was observed both in the steel and in the IN625 at the interface, separated by a region free from precipitation. The extent of precipitation at the interface regions appears to be controlled essentially by the extent of carbon transport across the interface. The article describes the detailed analysis of the interface characteristics, and models are proposed to explain the microstructural evolution at the interface of the HIP and weld clad composites.

The objectives of this study were to characterize the mineral phases, the diamond phase and the pore structure in the rare polycrystalline form of natural diamond, carbonado, and to determine whether the inorganic mineral content could be extracted by leaching treatments, without degrading the diamond matrix. The carbonado samples evaluated were found to contain more than two dozen impurity elements, in total concentrations varying from about 1.5 to 5 wt.%, not including oxygen. In addition to oxygen, the most abundant were sodium, potassium, calcium, strontium, barium, lead, aluminum, iron, lanthanum, cerium, yttrium, silicon, titanium, zirconium and phosphorus. Extraction of the mineral phases was accomplished by a sequential three-step leaching procedure, beginning with HClO4 to remove all elements except potassium and silicon, followed by H2O to remove potassium, and finishing with HF solution to remove silicon. The leaching rate is sample size dependent and appears to be diffusion limited. Imaging secondary ion mass spectrometry and scanning electron microscopy (SEM) characterization of fractured surfaces, comparing leached and unleached carbonado samples, showed that the minerals are contained in partially filled interconnected pores and channels and that these minerals are removed by the leaching treatment. SEM evaluation of the pure diamond phase remaining after leaching showed no evidence of foreign phases within the diamond grains or at grain boundaries. The low temperature stability of the minerals detected in the interconnecting void and channel structure suggest that these minerals were formed by a natural infiltration process after the initial formation of carbonado at elevated temperatures and pressures in the Earth.

In the field of catalysis, secondary ion mass spectrometry (SIMS) has primarily been used in the static mode to monitor the presence of surface species and contaminants. The authors have done extensive imaging SIMS of commercial catalyst systems for the purpose of trace metal characterization, particularly for fluidized catalytic cracking (FCC) catalysts. FCC catalysts are used to convert high boiling petroleum fractions into lighter fuels, especially gasoline and home heating oils. This brief report indicates the excellent match possible between the capabilities of current imaging SIMS technology and some of the characterization needs of the catalysis community. In cases where heterogeneity, poisoning, and diffusion limitations are present, imaging SIMS offers a way to gain a novel view of catalyst composition, performance and reaction pathways.

Examen de l'influence de l'yttrium sur la vitesse de croissance et l'adherence des couches de chromine et d'alumine sur les alliages. Caracterisation detaillee des couches d'oxyde. Evaluation critique des mecanismes d'action de l'yttrium sur le comportement de la couche d'oxyde et proposition de mecanismes additionnels

Alloys and coatings for high-temperature service are designed to form selectively chromia scales, alumina scales, or, to a limited extent, silica scales upon exposure to the environment. For such oxide scales to be protective, they should be both slow growing and adherent. It turns out that the addition of yttrium to such alloys can often impart both characteristics to the oxide scale. However, the actual operating mechanisms continue to be a matter of controversy among researchers in the area of oxidation. In the present study, the growth and adherence of alumina and chromia scales on alloys containing yttrium, either as an oxide dispersion or as an intermetallic phase, have been investigated in conjunction with detailed oxide scale characterization using the techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). The results of the study are used for critical assessment of the proposed mechanisms, especially the more recent ones, and to suggest some new mechanisms for adherence.

In the field of catalysis, secondary ion mass spectrometry (SIMS) has primarily been used in the static mode to monitor the presence of surface species and contaminants. The authors have done extensive imaging SIMS of commercial catalyst systems for the purpose of trace metal characterization, particularly for fluidized catalytic cracking (FCC) catalysts. FCC catalysts are used to convert high boiling petroleum fractions into lighter fuels, especially gasoline and home heating oils. This brief report indicates the excellent match possible between the capabilities of current imaging SIMS technology and some of the characterization needs of the catalysis community. In cases where heterogeneity, poisoning, and diffusion limitations are present, imaging SIMS offers a way to gain a novel view of catalyst composition, performance and reaction pathways.

AbstractSIMS data from refinery samples of several types of fluidized catalytic cracking catalysts show the metals in catalytic cracking feedstocks to initially deposit near the external surface of catalyst particles.

The distribution of nickel and vanadium has been determined on refinery samples of several types of fluidized catalytic cracking catalyst. Data from imaging secondary ion mass spectrometry show that metals in catalytic cracking feedstocks initially deposit near the external surface of catalyst particles. Nickel remains in the area where it was deposited, while vanadium shows both intraparticle and interparticle mobility. Vanadium accumulates throughout catalyst particles, but shows a preference for both rare earth exchanged Y-zeolite and alumina phases in composite catalyst. By contrast, nickel shows no preference for catalyst phases and accumulates monotonically with time. The lack of mobility in deposited nickel makes it a good measure to determine the age of individual particles.

Chemical and physical studies of molybdenum disulfide show that the extreme anisotropy which dominates the bulk properties of this layered compound is also very important in the understanding of surface properties. We observe that the basal surfaces in single crystals are chemically and optically inert. The edge surfaces are highly reactive to both oxygen and metallic impurities. Photoemission spectroscopy and optical absorption show that the edge surfaces have electronic states within the forbidden gap. The density of these surface defects is correlated with the hydrodesulfurization catalytic activity.