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In the operation of thermoelectric power plants, fossil fuels are burned, generating air pollutants such as carbon monoxide (CO), nitrogen oxide (NOX), particulate matter (PM), sulfur dioxide (SO2), and volatile organic compounds (VOCs). Accordingly, the objective of this study was to simulate the dispersion of atmospheric pollutants from the Borborema S.A thermal power plant, using the Aermod View program as a tool to evaluate the concentrations resulting from the simulation and to make comparisons with allowable levels according to current law. Thus, the emission sources of chimney air pollutants of a thermal power plant in 2016 were evaluated using the Aermod View, Aermet View, and WRPLOT View software. Regarding the pollutants generated, NOx values at 1 h showed NO2 concentration over the primary and secondary standards allowed by law, with a maximum concentration of 1680 μg/m3, about five times higher than the primary standard and eight times the secondary. The simulation indices for the concentrations of PM, SOx, NOx, and CO, even though they are appeared very low, except NO2 at 1 h, it was observed that these pollutants can affect the health of the local population, fauna and flora, in view of the process of bioaccumulation, which is inherent to organisms, which directly or indirectly absorb substances or chemical compounds.

In this paper, we present a numerical model to study pollutant dispersion in the atmospheric boundary layer (ABL). The model accounts for the mechanisms of advection by the mean wind in the horizontal direction, turbulent diffusion in the vertical direction to ground surface, dry deposition, and radioactive decay. More importantly, the model is capable of accounting for the evolution of the ABL structure over a diurnal cycle by considering parameterizations for the wind-speed and eddy-diffusivity profiles that depend on the atmospheric stability condition, which in turn undergoes dramatic changes throughout the day. To solve the resulting advection–diffusion equation, we propose a numerical method based on a stabilized finite element formulation. After validating the numerical model by simulating classical experiments and comparing its predictions with those available in literature, we study the dispersion of a pollutant during a full diurnal ABL cycle with the meteorological parameters generated by AERMET for a 24-h period on a 1-h basis.

In this research we aim to present a fast and semi-quantitative electrochemical method – based on cyclic voltammetry (CV) – to easily screen the H uptake of materials. We used Aermet 100, an ultrahigh-strength steel, in its as-quenched (martensitic) state and an aged state to investigate the H-desorption properties of different microstructures. The CV-based method clearly shows the influence of the alloying elements, the microstructure and the effect of hydrogen recombination poisons on the H uptake. The experiments indicate that a significant part of the uptake of hydrogen is due to (i) the presence of Ni as an alloying element and (ii) the presence of austenite that forms during the heat treatment.

This paper investigates grinding force and grinding temperature of ultra-high strength steel Aermet 100 in conventional surface grinding using a single alumina wheel, a white alumina wheel and a cubic boron nitride wheel. First, mathematical models of grinding force and grinding temperature for three wheels were established. Then, the role of chip formation force and friction force in grinding force was investigated and thermal distribution in contact zone between workpiece and wheel was analyzed based on the mathematical model. The experimental result indicated that the minimum grinding force and the maximum grinding force ratio under the same grinding parameters can be achieved when using a CBN wheel and a single alumina wheel, respectively. When the phenomenon of large grinding force and high grinding temperature appeared, the workpiece material would adhere locally to the single alumina wheel. Grinding temperature was in a high state under the effect of two main aspects: poor thermal properties of grinding wheel and low coolant efficiency. The predicted value of grinding force and grinding temperature were compared with those experimentally obtained and the results show a reasonable agreement.

Monitoring campaigns from different locations have recently shown how air concentrations of persistent semivolatile contaminants such as polychlorinated biphenyls (PCBs) often exhibit short-term (less than 24 h) variations. The observed patterns have been ascribed to different factors, such as temperature-mediated air-surface exchange and variability of planetary boundary layer (PBL) height and dynamics. Here, we present a new modeling approach developed in order to investigate the short-term variability in air concentrations of organic pollutants at a local scale. A new dynamic multimedia box model is supplied by a meteorological preprocessor (AERMET) with hourly values of air compartment height and wind speed. The resulting model is tested against an existing dataset of PCB air concentrations measured in Zurich, Switzerland. Results show the importance of such modeling approach in elucidating the short- and long-term behavior of semivolatile contaminants in the air/soil system.

Fluid catalytic cracking unit is of great importance in petroleum refining industries as it treats heavy fractions from various process units to produce light ends (valuable products). FCC unit feedstock consists of heavy hydrocarbon with high sulfur contents, and the catalyst in use is zeolite impregnated with rare earth metals, i.e., lanthanum and cerium. Catalytic cracking reaction takes place at elevated temperature in fluidized bed reactor generating sulfur-contaminated coke on the catalyst with large quantity of attrited catalyst fines. In the regenerator, coke is completely burnt producing SO2, PM emissions. The impact of the FCC unit is assessed in the immediate neighborhood of the refinery. Year-long emission inventories for both SO2 and PM have been prepared for one of the major petroleum refining industry in Kuwait. The corresponding comprehensive meteorological data are obtained and preprocessed using Aermet (Aermod preprocessor). US EPA approved dispersion model, Aermod, is used to predict ground level concentrations of both pollutants in the selected study area. Model output is validated with measured values at discrete receptors, and an extensive parametric study has been conducted using three scenarios, stack diameter, stack height, and emission rate. It is noticed that stack diameter has no effect on ground level concentration, as stack exit velocity is a function of stack diameter. With the increase in stack height, the predicted concentrations decrease showing an inverse relation. The influence of the emission rate is linearly related to the computed ground level concentrations.

The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.

Modern precipitation-hardened ultra-high-strength AERMET 100 steel (Fe-Co-Ni-Cr-Mo-C) is susceptible to severe transgranular hydrogen environment–assisted cracking (HEAC) in neutral 3.5 pct NaCl solution. The threshold stress intensity for HEAC, K TH , is reduced to as low as 10 pct of K IC , and the stage II subcritical crack growth rate, da/dt II, is up to 0.5 μm/s. Low K TH and high da/dt II are produced at potentials substantially cathodic, as well as mildly anodic, to free corrosion. However, a range exists at slightly cathodic potentials (–0.625 to –0.700 VSCE), where the crack growth rate is greatly reduced, consistent with reduced crack-tip acidification and low cathodic overpotential for limited H uptake. Short crack size (250 to 1000 μm) does not promote unexpectedly severe HEAC. High-purity AERMET 100 is susceptible to HEAC because martensite boundary trapping and high crack-tip stresses strongly enhance H segregation to sites that form a transgranular crack path. The stage II da/dt is H diffusion rate limited for all potentials examined. A semiquantitative model predicts the applied potential dependence of da/dt II using reasonable input parameters, particularly crack-tip H uptake reverse calculated from measured K TH and a realistic critical distance. Modeling challenges remain.

Hydrogen (H) trap states and binding energies were determined for AERMET 100 (Fe-13.4Co-11Ni-3Cr-1.2Mo-0.2C), an ultrahigh-strength steel using thermal desorption methods. Three major H desorption peaks were identified in the precipitation-hardened microstructure, associated with three distinct metallurgical trap states, and apparent activation energies for desorption were determined for each. The lattice diffusivity (D L ) associated with interstitial H was measured experimentally and verified through trapping theory to yield H-trap binding energies (E b ). Solid-solution elements in AERMET 100 reduce D L by decreasing the pre-exponential diffusion coefficient, while the activation energy for migration is similar to that of pure iron. M2C precipitates are the major reversible trap states, with E b of 11.4 to 11.6 kJ/mol and confirmed by heat treatment that eliminated these precipitates and the associated H-desorption peak. A strong trap state with E b of 61.3 to 62.2 kJ/mol is likely associated with martensite interfaces, austenite grain boundaries, and mixed dislocation cores. Undissolved metal carbides and highly misoriented grain boundaries trap H with a binding energy of 89.1 to 89.9 kJ/mol. Severe transgranular hydrogen embrittlement in peak-aged AERMET 100 at a low threshold-stress intensity is due to H repartitioning from a high density of homogeneously distributed and reversible M2C traps to the crack tip under the influence of high hydrostatic tensile stress.

The diffusivity of hydrogen at room temperature in an ultra high strength steel Aermet® 100 was studied using a variety of techniques, such as an electrochemical method, sub-surface microhardness profiling, quantitative depth profiling using nuclear reaction analysis (NRA) and nanohardness profiling. Aermet® 100 samples were cathodically charged under a galvanostatic condition at a current density of 10 A/m2. The electrochemical technique was used to determine the diffusivity of hydrogen in the Aermet® 100 cathode by monitoring the potential as a function of time. These results were compared with diffusivity data extracted from sub-surface microhardness profiling. Independently, nanohardness depth profiling was carried out to validate the hardness data near the surface. Excellent correlations were obtained in the data for hydrogen diffusivity from each of these techniques. The room temperature hydrogen diffusivity in Aermet® 100 was measured at approximately 2.91×10−13 m2/s. NRA indicated that the near-surface concentration of hydrogen under the electrolytic charging conditions utilized was about 5 at.%.

The hydrogen-uptake capacity and mobility in ultrahigh-strength AERMET 100 are characterized for various electrochemical charging and baking conditions. From thermal desorption spectroscopy, the apparent hydrogen diffusivity (D H < 3 × 10−8 cm2/s at 23 °C) is over tenfold less than the values typical of tempered martensitic steels such as AISI 4130. The value of D H decreases with decreasing temperature below 200 °C, with a relatively high apparent activation energy for diffusion of 17.7 to 18.8 ± 0.2 kJ/mol at the 95 pct confidence level. The value of D H also decreases with decreasing diffusible H concentration from less-severe charging or increased baking. Potentiostatic charging in saturated Ca(OH)2 produced total and diffusible H concentrations in AERMET 100 which increase with (H+/H) overpotential and are significantly higher than results for AISI 4130 steel under the same conditions. A significant H concentration was produced by zero overpotential deposition. These characteristics are explained by extensive reversible and irreversible H trapping involving at least three unique trap states in the ultrafine AERMET 100 microstructure. The former likely include coherent M2C carbides, soluble Ni, or precipitated austenite, and the latter include larger incoherent M x C y or martensite lathed-packet interfaces. Baking at 23 °C and 200 °C removes H from the lowest binding-energy sites, but results in reduced D H levels to prolong outgassing time. Additionally, substantial H was retained in stronger trap states. These trapping effects are pertinent to hydrogen embrittlement of AERMET 100 steel.

Non-proportional torsion–tension and biaxial-compressive experimental results are presented on tantalum, tantalum alloy with 2.5% tungsten, and AerMet 100 steel. These test results form a comprehensive set of data to show the material behaviors at finite strain and wide strain-rate range. Using the parameter set determined from uniaxial constant strain-rate compressive and tensile tests, the capability of a new constitutive model (Khan, A.S., Liang, R., 1999. Behaviors of three BCC metal over a wide range of strain rates and temperatures: experiments and modeling. International Journal of Plasticity 15, 1089–1109) is shown to accurately predict complex loading paths of current experimental results. Using von Mises equivalent strain, stress, and strain rate, the constitutive model gives excellent predictions of these non-proportional experimental results.

Summary We performed a series of depth-of-penetration experiments using 7.11-mm-diameter, 71.12-mm-long, ogive-nose steel projectiles and 254-mm-diameter, 6061-T6511 aluminum targets. The projectiles were made from vacuum-arc remelted (VAR) 4340 steel (Rc 38) and AerMet 100 steel (Rc 53), had a nominal mass of 0.021 kg, and were launched using a powder gun or a two-stage, light gas gun to striking velocities between 0.5 and 3.0 km/s. Since the tensile yield strength of AerMet 100 (Rc 53) steel is about 1.5 times greater than VAR 4340 (Rc 38) steel, we were able to demonstrate the effect of projectile strength on ballistic performance. Post-test radiographs of the targets showed three different regions of penetrator response as the striking velocity increased: (1) the projectiles remained rigid and visibly undeformed; (2) the projectiles deformed during penetration without nose erosion, deviated from the target centerline, and exited the side of the target or turned severely within the target; and (3) the projectiles eroded during penetration and lost mass. To show the effect of projectile strength, we present depth-of-penetration data as a function of striking velocity for both types of steel projectiles at striking velocities ranging from 0.5 and 3.0 km/s. In addition, we show good agreement between the rigid-projectile penetration data and a cavityexpansion model.

The elastic–plastic behaviors of three body-centered cubic metals, tantalum, tantalum alloy with 2.5% tungsten, and AerMet 100 steel, are presented over a wide range of strains (15%), strain rates (10−6–104 s−1) and temperatures (77–600°F). Johnson-Cook and Zerilli-Armstrong models were found inadequate to describe the observations. A new viscoplastic model is proposed based on these experimental results. The proposed constitutive model gives good correlations with these experimental results and strain-rate jump experiments. In the next paper (Liang, R., Khan A.S., 2000. Behaviors of three BCC metals during non-proportional multi-axial loadings and predictions using a recently proposed model. International Journal of Plasticity, in press), multi-axial loading results on these materials and comparison with the proposed model will be presented.

Hydrogen trapping in three high-strength steels—AerMet 100 and AISI 4340 and H11—was studied using a potentiostatic pulse technique. Irreversible trapping constants ( k ) and hydrogen entry fluxes were determined for these alloys in 1 mol/l acetic acid/1 mol/l sodium acetate. The order of the k values for the three steels and two 18Ni maraging steels previously studied inversely parallels their threshold stress intensities for stress corrosion cracking ( K ISCC ). Irreversible trapping in AerMet 100 varies with aging temperature and appears to depend on the type of carbide (Fe 3 C or M 2 C) present. For 4340 steel, k can be correlated with K ISCC over a range of yield strengths. The change in k is consistent with a change in the principal type of irreversible trap from matrix boundaries to incoherent Fe 3 C. The principal irreversible traps in H11 at high yield strengths are thought to be similar to those in 4340 steel.

The variation in strength and Charpy impact toughness as a function of tempering temperature in the range of 200 ‡C to 650 ‡C was investigated in AF 1410 and AF 1410 + 1 pct Cr steels produced in a laboratory-scale, and a commercially produced AerMet 100 steel. The tensile test results showed that AF 1410 + 1 pct Cr had lower strength compared to AF 1410, while AerMet 100 had the highest strength of the three steels examined. Transmission electron microscopy (TEM) studies demonstrated that the strength variations among the steels can be attributed to differences in the matrix/carbide coherency strain and the volume fraction of the strengthening M2C carbides. The toughness values of the three steels were comparable when tempered up to 424 ‡C. Tempering at and above 454 ‡C resulted in a relative enhancement of toughness in AF 1410 + 1 pct Cr steel compared to AF 1410. This toughening was attributed to the destabilization of cementite at lath and prior austenite boundaries and the formation of reverted austenite.

The effect of tempering on the microstructure and mechanical properties of ultrahigh strength Aermet 100 steel was examined. In the as-quenched condition, the steel contained a dispersion of relatively fine, undissolved, (CrTiFeMo)C and (CrFeMo)23C6 carbides in a martensitic matrix. Upon tempering at 427 °C, the martensite decomposed to form a high density of cementite particles concomitant with a significant drop in toughness. Tempering at 454 °C resulted in peak strength (yield strength ∼ 1756 MPa) due to the precipitation of coherent zones of fine carbides. The peak in toughness (170 MPa√m), attained at a tempering temperature of 482 °C, was attributed to both the absence of cementite and the formation of reverted, stable austenite. Tempering at higher temperatures resulted in loss of both strength and toughness, which was suggested to be the result of precipitate coarsening and formation of unstable austenite, respectively. The details of the electron microscopy studies and mechanism of strengthening and toughening are discussed in light of the current understanding of this subject.

The goal of this research is to extend the potential region of high toughness in an ultra-high strength steel (UHSS) to anodic and cathodic potentials where hydrogen environment embrittlement (HEE) is normally observed due to hydrogen uptake in the absence of inhibitors. This is being explored through the investigation of several selected chemical inhibitors (anodic inhibitors and cathodic blocking agents). The research is conducted in three stages. The effect of inhibition on lowering hydrogen production and ingress (absorption) is determined using planar coupons under conditions representative of crack tips. Studies are then extended to rescaled crevices that model occluded sites of much smaller dimensions (will not be discussed in this paper). Finally, verification of chemical inhibition of HEE susceptibility, in fracture experiments, is exhibited by a restoration in toughness and/or a reduction in crack growth rate on fatigue pre-cracked specimen. Fracture experiments are performed at various applied potentials in a marine environment. This research is part of an overall scheme to combine the study of inhibition with the control of metallurgical purity and hydrogen trap states, as well as tailored cathodic protection to optimize the fracture toughness of UHSS in marine environments. The long term goal is to provide a coupled strategy to mitigate HEE of modem high strength steels.

The role of corrosion preventive compound (CPC) in corrosion specifically general corrosion and a localized corrosion: stress corrosion cracking (SCC) and hydrogen embrittlement of AerMet 100 steel was investigated in 3.5% NaCi solution. Eighteen CPCs were evaluated for the effectiveness and persistency in corrosion prevention/mitigation, determining the essential parameters: open circuit potential, effective period, and threshold stress intensity for stress corrosion cracking (Kiscc). It was found that: (1) CPC ZC-OlO is most effective and persistent in prevention/mitigation of general corrosion, respectively, (2) Carwell AR500 and Omega 2775 are best in that of SCC, and (3) Break Free SMX is optimum in that of hydrogen embrittlement.

Samples of four modern steels were implanted with 120 keV N2+ ions at doses ranging from 5 X 1015 to 1.2 X 1017 ions/cm2 at room temperature. The sample surfaces were studied for their tribological properties. The Knoop microhardnesses increased by 9 percent to 30 percent after ion implantation. A heat treatment study from 200 degrees C to 600 degrees C on AerMet 100 and Sverker 21 following implantation with 8 X 1016 ions/cm2 of nitrogen comparing implanted to unimplanted samples shows that the hardness reduction arising for the heat treatment was lower for the implanted samples. The projected ranges for the implanted specimens were obtained using the TRIM program. The microhardness of the implanted layers alone was calculated by the Hoensson-Hogmark model. The residual stress of the Orvar Supreme surface after 60 keV nitrogen ion implantation at a dose of 8 X 1016 ions/cm2 was also measured by x-ray diffraction. The friction and wear test was obtained using an Optimol SRV friction and wear tester. After nitrogen implantation and heat treatment, samples were depth profiled by AES and XPS.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.