Victor A. Greenhut

Geochemical factors complicating the use of aufwuchs to monitor bioaccumulation of arsenic, cadmium, chromium, copper and zinc

Abstract Material accumulating on submerged glass slides was sampled from five sites associated with coal ash settling basins and a control site. Correlation analyses demonstrated a strong, positive correlation between the five elements, arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu) and zinc (Zn) and concentrations of associated iron or manganese. Negative, weak or nonsignificant correlations were noted between the concentrations of these five elements and microfloral cell densities or per cent ash free weight of the material. Scanning electron microscopy and X-ray analyses indicated that the majority of the material was abiotic and the elemental levels associated with the abiotic components were generally higher than those of the biotic components. Hydrous iron and manganese oxides likely play dominant roles in determining the trace element concentrations in these procedurally-defined aufwuchs. These findings indicate the potential for misinterpretation of biomonitoring data employing procedurally-defined aufwuchs.

The effect of abrasive hardness on the chemical-assisted polishing of (0001) plane sapphire

A series of abrasives with various hardness values including monocrystalline and polycrystalline diamond, α- and γ-alumina, zirconia, ceria, and silica were used to examine the concept of chemical-assisted polishing for finishing the (0001), c-plane (basal plane), of sapphire. Diaspore, a monohydrate of alumina, was also evaluated. Atomic force microscopy suggested that the hydrated layer of the c-plane surface was about 1 nm thick. Polishing experiments were designed to determine whether the chemically modified surface hydration layer forms on the basal plane in water. The results indicate that harder abrasives do not necessarily cause faster material removal and better surface finish for similar abrasive particle size. Abrasives with hardness equal to or less than sapphire such as α-Al2O3 and γ-Al2O3 achieved the best surface finish and greatest efficiency of material removal. It is proposed that the (0001) c-plane sapphire surface was modified by water to form a thin hydration layer with structure and hardness close to diaspore. This reaction layer can be removed by an abrasive that is softer than sapphire but harder than the reaction layer. α-Al2O3 was particularly effective. This result is attributed to adhesion between identical reaction layers on the basal planes of the alumina abrasive and the sapphire. This demonstrates that high removal rates and good surface finish can be achieved without costly diamond polishing.

Geochemical factors complicating the use of aufwuchs as a biomonitor for lead levels in two New Jersey reservoirs

Abstract Material accumulating on glass slides was sampled monthly from two reservoirs for 1 year. Monthly changes in lead concentration in these samples were correlated with fluctuations in associated iron plus manganese concentration. Correlation with changes in algal cell density was also significant ( α = 0.05), yet not as important in the statistical model as iron plus manganese concentration. Upon microscopic examination, it was evident that the majority of the material removed from the slides was a rust-colored matrix. X-ray analysis revealed that the majority of the lead in the material scraped from the slides was associated with this iron and manganese-rich matrix surrounding the microflora, not with the microflora itself. As a result the material scraped from the slides (often defined as aufwuchs in biomonitoring efforts) could not be considered a valid biomonitor of lead levels in these reservoirs. The local geochemistry, not the biota, was the dominant factor affecting the lead concentrations in the material accumulating on the glass slides. The findings of this study indicate a potential for misinterpretation of biomonitoring efforts employing procedurally defined aufwuchs .

Formation of fault structures during coalescence and growth of gold particles in a fused silica matrix—I

Abstract The fault structures formed during annealing of gold particles in a fused silica matrix were examined employing transmission electron microscopy. For higher volume fractions of gold and short annealing times at 900°C particle-particle coalescence by bridge formation was observed. After longer annealing times, particles assumed a nearly spherical shape approximately 500 A in diameter. A limited number of planar boundaries were found to have formed as the result of particle-particle coalescences and grain growth. The predominant structural configuration was a series of parallel or nonparallel planar twin boundaries within the gold particles. In the case of intersecting twins a specific planar coincidence lattice boundary was also observed. No evidence of high angle grain boundaries and dislocation structure was observed. It is believed that the various twin structures observed are metastable, with little mobility and may be used to examine mechanisms of grain boundary migration and annealing twin formation.

A mechanism for fault formation in fine particles and implications for theories of annealing twins in f.c.c. metals—II

Abstract A mechanism is proposed for fault structure formation in annealed f.c.c. metals on the basis of experimental observations during annealing of gold particles in a fused silica matrix. The proposed model is an extension of the ‘growth accident’ model of Gleiter and accounts for particle-particle impingement and coalescence. The model explains how the high angle boundaries formed upon impingement and coalescence of two or more particles migrate to form metastable twin boundary structures. All structures observed are explained successfully by the modified growth accident model. Other theories were critically examined, but fail to explain the observed morphologies. The gold particle-fused silica matrix system may be viewed as a model system for understanding the nature of particle impingement, grain boundary migration, and annealing twin formation. The observations made and mechanism developed may be extended to recrystallization, grain growth, and annealing twin formation in bulk, polycrystalline materials.

Advanced performance structural ceramics and ceramic composites: A technological and applications progress report

ConclusionAdvanced performance ceramics have shown dramatic accomplishments during the past ten to fifteen years. Many new exciting properties and applications have developed. Fundamentally new material properties and behaviors have resulted with a number of exciting new applications. Expectations exceeded realistic evaluations of progress during the past decade although many of the target properties of elevated temperature performance, strength, toughness and non-catastrophic failure have been realized. The commercialization of advanced structural ceramics leads the general rate of economic growth, and appears to have a bright future as current stress on commercialization drives not just further materials development, but also standards of design and material selection.

Substrate Pretreatments and Strength Limiting Factors in Cu-AlN Direct Bonds

Cu-AlN direct bonds were made by the gas-metal eutectic method. Two kinds of AlN substrates from different suppliers were used for the research. The AlN surfaces were preoxidized in O 2 at three different temperatures. An optional “anneal” in Ar was applied following the oxidation procedure. Two processes were used for the bonding. The bond strengths and the failure modes were found to depend on the substrate used, the pretreatment of the AlN and bonding conditions. There was an optimum thickness for the Al 2 O 3 layer on the AlN surface. High temperature annealing in Ar was demonstrated to effectively promote bond strength. The highest peel strength measured was 50 N/cm. A thermal expansion mismatch between Al 2 O 3 and AlN was considered to be the main factor which dominated the ultimate bond strength. This mismatch resulted in a residual stress in the Al 2 O 3 layer. A measurement by XRD indicated a 300 MPa tensile stress existed in the surface Al 2 O 3 after AlN oxidation. This made Al 2 O 3 /AlN the weakest interface and limited the bond strength rather than the eutectic bond.

Characterization of chemically modified carbonaceous electrode materials by x-ray fluorescence and scanning electron microscopy

Abstract An attachment scheme which utilizes cyanuric chloride as a linking agent in the preparation of chemically modified electrodes was investigated by using simultaneous scanning electron microscopy and x-ray fluorescence. Certain contaminants were discovered on the surface of the material following various steps in the reaction scheme used for attachment. The iron storage protein, ferritin, was attached to the surface of spectroscopic-grade graphite rod. Attempts were made to establish the surface distribution of the ferritin and to correlate distribution with surface morphology.