Yuming Gao

Interactions of carbon-containing fly ash with commercial air-entraining admixtures for concrete

The most important commercial outlet for coal ash is as a partial replacement for Portland cement in the concrete industry. High levels of unburnt carbon can render ash samples unsuitable for this high-value market by interfering with the action of air-entraining admixtures, which are specialty surfactants used to stabilize air bubbles in concrete mixtures. An initial laboratory investigation was carried out to identify the fundamental interaction mechanisms between fly ash and air-entraining admixtures. The results indicate that the interaction is time-dependent and occurs to a degree that correlates only crudely with the amount of carbon present. Measurements made on a variety of model additives suggest that admixtures are preferentially adsorbed from the aqueous phase on non-microporous carbonaceous surfaces.

Mechanisms of surfactant adsorption on non-polar, air-oxidized and ozone-treated carbon surfaces

Ozone treatment of fly ash carbon has recently been reported to inhibit the adsorption of commercial surfactants in concrete paste, thus mitigating the known negative effects of carbon on ash utilization. This paper examines the general mechanism of surfactant adsorption on carbon and its suppression by surface oxidation. Experimental results are presented for two carbon types (carbon black, fly ash carbon), both raw and surface oxidized (by ozone and molecular oxygen) and several commercial anionic and non-ionic surfactants (Darex II, SDS, Tergitol). The treated carbon surfaces were characterized with XPS, FT-IR, thermal desorption in N and H / He, surface acidity, hygroscopic behavior, interfacial 22 energy and its components through contact angle measurement involving standard liquid probes. Surface oxidation is found to decrease surfactant adsorption in each of the carbon / oxidant / surfactant systems examined, and its effect correlates with the amount of surface oxides by XPS. The combined results suggest that surfactant adsorption primarily occurs on non-polar carbon surface patches where it is driven by hydrophobic interactions. The main mechanism of oxidative suppression is the destruction of this non-polar surface, though micropore blockage and increased negative surface charge may also contribute for some systems.  2003 Elsevier Science Ltd. All rights reserved.

Mercury Vapor Release from Broken Compact Fluorescent Lamps and In Situ Capture by New Nanomaterial Sorbents

The projected increase in the use of compact fluorescent lamps (CFLs) motivates the development of methods to manage consumer exposure to mercury and its environmental release at the end of lamp life. This work characterizes the time-resolved release of mercury vapor from broken CFLs and from underlying substrates after removal of glass fragments to simulate cleanup. In new lamps, mercury vapor is released gradually in amounts that reach 1.3 mg or 30% of the total lamp inventory after four days. Similar time profiles but smaller amounts are released from spent lamps or from underlying substrates. Nanoscale formulations of S, Se, Cu, Ni, Zn, Ag, and WS2 are evaluated for capture of Hg vapor under these conditions and compared to conventional microscale formulations. Adsorption capacities range over 7 orders of magnitude, from 0.005 (Zn micropowder) to 188 000 μg/g (unstabilized nano-Se), depending on sorbent chemistry and particle size. Nanosynthesis offers clear advantages for most sorbent chemistries. Unstabilized nano-selenium in two forms (dry powder and impregnated cloth) was successfully used in a proof-of-principle test for the in situ, real-time suppression of Hg vapor escape following CFL fracture.

Improvement of photocatalytic activity of titanium (IV) oxide by dispersion of Au on TiO2

Abstract TiO2 samples were prepared by two procedures and their catalytic activities were compared to samples of commercial TiO2 (P25). The addition of gold to all of these samples increased their photocatalytic activity.

Preparation and characterization of Titanium(IV) oxide photocatalysts

Abstract Titanium(IV) oxide samples were prepared by two techniques, namely, ultrasonic nebulization and flame hydrolysis, and the ultrasonic nebulization and furnace pyrolysis. Titanium(IV) chloride and diisopropoxy-titanium(IV)-bis-(acetylacetonate) were employed for the preparation of titanium(IV) oxide samples. The photocatalytic activities of the prepared samples were evaluated by measuring the degradation of 1,4-dichlorobenzene and compared with that of Degussa P25 titanium(IV) oxide. The ultrasonic nebulization and flame hydrolysis method was more efficient than nebulization and furnace pyrolysis. Products obtained using this method gave photocatalytic activities similar to that of P25.

Preparation and photocatalytic properties of titanium(IV) oxide films

Films of titanium(IV) oxide were deposited on a variety of substrates by a simple nebulization and pyrolysis technique. Good uniformity and adhesion was obtained in all cases. The films showed appreciable photocatalytic activity toward the degradation of salicylic acid. The observed activity was increased by the deposition of elemental gold on the TiO2 films.

Growth and characterization of zinc sulfide films by conversion of zinc oxide films with H2S

Abstract Zinc sulfide films were prepared by conversion of zinc oxide films in the presence of hydrogen sulfide. The films which contained both the hexagonal and cubic forms of zinc sulfide were shown to be uniform and gave a measured band gap of 3.65 eV.

Photocatalytic properties of titanium (IV) oxide thin films prepared by spin coating and spray pyrolysis

Abstract TiO2 thin films were prepared by spin coating and spray pyrolysis techniques. The observed photocatalytic activity is the same for films prepared by both techniques. The photocatalytic activity increases as film thickness increases but remains constant after the thickness reaches 0.60 μm. These films are shown to be capable of photodecomposing organic impurities in water.

Ozonation for the chemical modification of carbon surfaces in fly ash

1 Brown University, Providence RI, 2 Electric Power Research Institute, 3 PCI-WedecoKEYWORDS: concrete, beneficiation, LOI, air entrainmentINTRODUCTIONA practical problem with fly ash concrete is the tendency of residual carbon in ash tointerfere with the air entrainment process. Porous carbon adsorbs the chemicalsurfactants (air entraining admixtures, or AEAs) used to generate and stabilize a micro-void system in concrete pastes, as shown by Helmuth (1987), Freeman et al. (1997),and Hill et al. (1997). Without a sufficient network of sub-millimeter air bubbles,concrete fails under internal pressure generated by the freezing and expansion oftrapped residual water. About two-thirds of the concrete in North America is airentrained (Dolch, 1995), and this surfactant adsorption phenomenon is the primarydriving force for national and regional regulations limiting the carbon content of ashused in concrete. Recent work by Freeman et al. (1997), Gao et al. (1998), and Yu etal. (2000) clearly demonstrate great variability in the extent to which field ash samplesadsorb AEAs. This recent work has identified the following four primary factorsgoverning ash adsorptivity:1. the mass fraction carbon2. the total surface area of the carbon3. the accessibility of that surface, as governed by particle size and pore size distribution4. the carbon surface chemistry.The inorganic fraction of ash is found to play a minor role in AEA adsorption.The role of carbon surface chemistry is particularly apparent from the behavior of ashduring thermal oxidation in air. Introduction of surface oxides by exposure to air at 350-450 C has been observed by Hachmann et al (1998) to significantly reduce subsequentAEA adsorption without consuming a measurable amount of carbon. In contrast,treatment in inert gas at temperatures sufficient to drive-off many pre-existing surfaceoxides (900 o C) has been observed to

Growth and Characterization of Gallium (III) Oxide Films

Abstract A simple spray pyrolysis technique has been applied to the formation of dense, homogeneous gallium(III) oxide thin films on both silicon and silica substrates. The high quality of these films has been established by transmission electron microscopy, x-ray diffraction, optical spectra, and current-voltage measurements.