A review of shape memory alloy research, applications and opportunities

Formation of polycyclic aromatic hydrocarbons and their growth to soot—a review of chemical reaction pathways

Chemical vapour deposition of coatings

Chemical reactions and physical processes responsible for the formation of polycyclic aromatic hydrocarbons and soot in hydrocarbon flames are reviewed. The discussion is focused on major elements in the present understanding of the phenomena, clarification of concepts central to the present state of the art, and a summary of new results.

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Reaction mechanism of soot formation in flames

Self-healing polymeric materials: A review of recent developments

The surface growth rate of soot increases steeply with increasing equivalence ratio. We have found that the increased growth rate is accounted for primarily by the increased surface area available for growth rather than by increased concentrations of surface growth species. We have shown that the surface growth species are not depleted by the process of surface growth. Our data suggest that the surface growth seen in our flames can be accounted for primarily by reaction of acetylene with the soot particles.

Surface Growth of Soot Particles in Premixed Ethylene/Air Flames

We have measured mole fractions of two of the major stable species at the surface of a silicon substrate during filament‐assisted diamond growth as a function of the filament‐to‐substrate distance. Input gases were methane and hydrogen. A quartz probe withdrew gases at the growing surface, and the gases were sampled with an on‐line mass spectrometer. Close to the filament the methane is largely consumed, with most of the remaining gas phase carbon in the form of acetylene. Mass spectral results are compared to compositions calculated with a detailed chemical kinetics model. Our initial analysis suggests that diamond growth comes mainly from reaction of acetylene, ethylene, methane, or methyl radical.

Measurement of stable species present during filament‐assisted diamond growth

Filament‐assisted chemical vapor deposition (CVD) diamond film growth on Si(100) was studied using x‐ray photoelectron spectroscopy (XPS) to examine the sample at selected intervals during the nucleation and growth processes. The sample was transferred under vacuum from the growth chamber to the attached XPS analysis chamber without exposure to air. Before growth XPS showed that the Si sample is covered by a layer of SiO2 and carbonaceous residue; however, after 15 min of growth both of these substances are removed and replaced by a distinct SiC layer [Si(2p)=100.3 eV and C(1s)=282.7 eV].

In situ characterization of diamond nucleation and growth

The gas‐phase composition at the surface of a growing diamond film was measured as a function of the initial methane (CH4) fraction and, for a 2% methane fraction, as a function of added oxygen (O2). The results were modeled with a one‐dimensional reactor flow code that includes diffusion and detailed chemical kinetics. We found that most of the ethylene (C2H4) and ethane (C2H6) that was detected was actually not present in the growth chamber but was instead formed in the probe by recombination of methyl radicals (CH3) that were present in the gas phase. Thus, C2H4 and C2H6 acted as surrogates for CH3 in our system, and measurement of those two stable species allowed us to estimate the mole fraction of the CH3 radical. We then took advantage of the fact that CH3, CH4, H2, and H were in partial equilibrium in the diamond growth chamber in order to estimate the concentration of H. A comparison between the mole fractions of CH3 and H, as determined from our experiments, and the mole fractions calculated from...

Methyl radical and H-atom concentrations during diamond growth

We present a study of the effects of the ratio of hardness to Young’s modulus on the friction and wear behavior of layered composite coatings. Layered coating structures with the same surface coating but different interlayers were prepared by physical vapor deposition. We found that the ratio of hardness to Young’s modulus plays an important role in determining the friction coefficient and wear resistance of layered composite coatings. A low friction coefficient and high wear resistance can be achieved in structures with high ratio of hardness to Young’s modulus and moderately high hardness.

Anita M. Weiner

Papers

Surface Growth of Soot Particles in Premixed Ethylene/Air Flames

Measurement of stable species present during filament‐assisted diamond growth

In situ characterization of diamond nucleation and growth

Methyl radical and H-atom concentrations during diamond growth

Effects of the ratio of hardness to Young’s modulus on the friction and wear behavior of bilayer coatings