Effect of High Cooling Rates on the Mineralogy and Hydraulic Properties of Stainless Steel Slags

This article investigates the effect of chemical composition and cooling rate during solidification on the mineralogy and hydraulic properties of synthetic stainless steel slags. Three synthetic slags, covering the range of typical chemical composition in industrial practice, were subjected to high cooling rates, by melt spinning granulation or quenching in water, and to low cooling rates, by cooling inside the furnace. Both methods of rapid cooling led to volumetrically stable slags unlike the slow cooling which resulted in a powder-like material. Stabilized slags consisted predominantly of lamellar β-dicalcium silicate (β-C₂S) and Mg, Ca-silicates (merwinite and bredigite); the latter form the matrix at low basicity and are segregated along the C₂S grain boundaries at high basicities. Slowly cooled slags consist of the γ-C₂S polymorph instead of the β-C₂S and of less Mg, Ca-silicates. Isothermal conduction calorimetry and thermogravimetric analysis indicate the occurrence of hydration reactions in the stabilized slags after mixing with water, while calcium silicate hydrates (C-S-H) of typical acicular morphology are identified by SEM. The present results demonstrate that the application of high cooling rates can result in a stable, environmental-friendly, hydraulic binder from stainless steel slags, rich in β-C₂S, without the necessity of introducing any additions to arrest the β polymorph.     

Towards treatment planning for the embolization of arteriovenous malformations of the brain: intranidal hemodynamics modeling

This paper presents a patient-derived model for the simulation of the hemodynamics of arteriovenous malformations of the brain (BAVM). This new approach is a step toward the simulation of the outcome of the embolization of the BAVM during treatment planning. More specifically, two aspects of the planning are pursued: simulation of the change of blood flow in the brain vasculature after the blocking of the malformation and simulation of the transport of the embolic liquid. The method we propose is tested on 3 BAVM cases of varying complexity. Twenty two out of 24 main BAVM flow paths have been identified well by simulation.     

Polynuclear aromatic hydrocarbon and particulate emissions from two-stage combustion of polystyrene: the effects of the secondary furnace (afterburner) temperature and soot filtration

Laboratory experiments were conducted in a two-stage horizontal muffle furnace in order to monitor emissions from batch combustion of polystyrene (PS) and identify conditions that minimize them. PS is a dominant component of municipal and hospital waste streams. Bench-scale combustion of small samples (0.5 g) of shredded styrofoam cups was conducted in air, using an electrically heated horizontal muffle furnace, kept at Tgas = 1000 degrees C. Upon devolatilization, combustion of the polymer took place in a diffusion flame over the sample. The gaseous combustion products were mixed with additional air in a venturi and were channeled to a secondary muffle furnace (afterburner) kept at Tgas = 900-1100 degrees C; residence time therein varied between 0.6 and 0.8 s. At the exits of the primary and the secondary furnace the emissions of CO, CO2, O2, NOx, particulates as well as volatile and semivolatile hydrocarbons, such as polycyclic aromatic hydrocarbons (PAH), were monitored. Online analyzers, gravimetric techniques, and gas chromatography coupled to mass spectrometry (GC-MS) were used. Experiments were also conducted with a high-temperature barrier filter, placed just before the exit of the primary furnace to prevent the particulates from entering into the secondary furnace. Results demonstrated the beneficial effect of the afterburner in reducing PAH concentrations, including those of mutagenic species such as benzo[a]pyrene. Concentrations of individual PAH exhibited a pronounced after burner temperature dependence, typically ranging from a small decrease at 900 degrees C to a larger degree of consumption at 1100 degrees C. Consumption of PAH was observed to be the dominant feature at 900 degrees C, while significant quantities of benzene and some of its derivatives, captured by means of carbosieve/Carbotrap adsorbents, were formed in the afterburner at a temperature of 1000 degrees C. In the primary furnace, about 30% of the mass of the initial polystyrene was converted into soot, while the total mass of PAH represented about 3% of the initial mass of combustible. The afterburner reduced the particulate (soot) emissions by only 20-30%, which indicates that once soot is formed its destruction is rather difficult because its oxidation kinetics are slow undertypical furnace conditions. Moreover, increasing the afterburnertemperature resulted in an increasing trend of soot emissions therefrom, which might indicate competition between soot oxidation and formation, with some additional formation occurring at the higher temperatures. Contrary to the limited effect of the afterburner, high-temperature filtration of the combustion effluent prior to the exit of the primary furnace allowed for effective soot oxidation inside of the ceramic filter. Filtration drastically reduced soot emissions, by more than 90%. Limited soot formation in the afterburner was again observed with increasing temperatures. The yields of both CO and CO2 were largely unaffected by the temperature of the afterburner but increased at the presence of the filter indicating oxidation therein. A previously developed kinetic model was used to identify major chemical reaction pathways involving PAH in the afterburner. The experimental data at the exit of the primary furnace was used as input to these model computations. A first evaluation of the predictive capability of the model was conducted for the case with ceramic filter and a temperature of 900 degrees C. The afterburner was approximated as a plug-flow reactor, and model predictions at a residence time of 0.8 s were compared to experimental data collected at its exit. In agreement with the experimental PAH concentration, only a minor impact of the afterburner treatment was observed for most species at 900 degrees C. OH was deduced to be the major reactant with a mole fraction about 4 orders of magnitudes higher than that of hydrogen radicals. Evidence for the need of further work on the quantitative assessment of oxidation of PAH and their radicals is given.     

Effects of dissolved carbonates and carboxylates on the sorption of thiuram disulfide pesticides on humic acids and model surfaces

The sorption of a hydrophobic pesticide, thiram, on humic acid (HA) occurs via a specific pH-dependent binding of thiram at the deprotonated carboxylates of humic acid, forming a species thiram-[HACOO-] with K = 0.69. Similarly, thiram was sorbed by two model polycarboxylate-{SiO2COOH} materials via the formation of a surface species thiram-{SiO2COO-} with K = 0.45 between thiram and the eprotonated carboxylates grafted on SiO2 particles. In all cases, allowance of presence of bicarbonate at natural concentration caused severe inhibition of thiram's sorption. Oxalate and formate mimic the inhibitive effect of bicarbonate. Theoretical fit of the data showed that the inhibitive effect of HCO3- is due to the formation of the anionic species [thiram-HCO3](-1) (with K = 0.90) which is water soluble and competes with the bound species thiram-{HACOO-}. The same phenomena were observed for the sorption of disulfiram. The specific interaction phenomena reported here bear relevance to the sorption properties of thiram and disulfiram on real soils and, therefore, may determine their environmental fate.     

A structured autopsy-based audit of 370 firearm fatalities: Contribution to inform policy decisions and the probability of the injured arriving alive at a hospital and receiving definitive care

The objectives of this autopsy-based audit of firearm-related fatalities were to acquire data to inform policy decisions and to assess the probability of the injured arriving alive at a hospital and receiving definitive care.