Function Of Exposure Conditions Research Articles

The Influence of Water Concentration on High-Temperature Reactive Evaporation and Condensation of Cr in 800°C Air

Deleterious reactive evaporation of chromium from stainless steels commonly used in solid oxide electrochemical systems is well-documented; however, interactions between Cr vapor species and surrounding interfaces during complex and dynamic system exposures is poorly understood. Understanding the interactions between Cr vapor species and downstream components during operation is critical for improving system performance and safeguarding environmental, health and safety, as many condensed Cr compounds contain toxic and carcinogenic hexavalent chromium Cr(VI). Furthermore, the interactions between volatilized Cr species and surrounding interfaces are dependent upon dynamic chemical environments. The objective of this study is to systematically investigate and report on condensation pathways of Cr vapors within representative system environments with variable water concentrations. To accomplish this objective, an experimental platform was designed to generate Cr vapor species from the reactive evaporation of chromia (Cr2O3) powder with high-temperature (>1100 K) air/H2O mixtures, and expose downstream ceramic insulation materials (e.g., aluminosilicate fibers) at reduced temperatures (<600 K). Insulation material chemical compositions investigated include pure silica (SiO2) and alumina (Al2O3) to combinations thereof with and without inclusions of alkaline earth metals (e.g., Ca, Mg, Sr). Materials are studied as a function of exposure conditions using complementary materials characterization tools such as SEM-EDX, XPS, and diphenyl carbazide reactions to assess Cr(VI) concentrations. Reactive evaporation of Cr from chromia occurs in the presence of oxygen and/or water vapor to form various Cr-containing vapor species. Thermodynamic data reveals an equilibrium partial pressure increase of several orders of magnitude at elevated (>500 K) temperatures for all Cr vapor species. In the presence of water vapor, the partial pressure of Cr oxyhydroxide (CrO2(OH)2(g)) is greater by many several orders of magnitude and becomes the dominant species up to ~1500 K. The research objective is to explore effects of water vapor in air on Cr condensation and speciation on different ceramic insulation materials. The experimental setup thus far has exposed aluminosilicate fibers to volatilized Cr species from Cr oxide powder at 1100 K for 150 hours under varying water vapor conditions: 0 vol%(dry), 3 vol%, and 10 vol% H2O. Preliminary results show an increase in Cr(VI) formation on fibers exposed to volatile Cr species as water vapor content increases. See Figure 1 for an overview of the experimental concept, Cr(VI) test kit, and preliminary results for dependency on water vapor. Analyses of these results will be presented and discussed in context of potential implications for SOFC/SOEC systems. Figure 1

Electronic modification of wet-prepared Si surfaces by a dichlorosilane reaction at elevated temperature

Silicon growth using chemical vapor deposition (CVD) is omnipresent in electronic device technology. CVD reactions of different precursor molecules on Si have been the focus of research for decades. Renewed interest in the CVD growth of silicon films has been spurred by the need for high-quality, ultrathin films for fabrication of novel electronic devices. In this work, we have formulated an experimental nanoscale approach to analyze the modification of wet-prepared Si(001) surfaces by dichlorosilane (SiH2Cl2, DCS) reactions at low pressure and 500–650 °C performed in a thermal CVD reactor connected to a scanning tunneling microscopy and spectroscopy (STM/STS) system. The DCS dissociation reaction resulted in a decrease of the Si surface potential due to the creation of chlorine-induced electric dipoles. Employing the ability of the scanning tunneling spectroscopy (STS) to recognize specific adsorption sites, we have carried out a comparative analysis of the relative coverage by Cl and Si as a function of exposure conditions. The existence of an intermediate reaction state of the DCS molecule was confirmed by the STS spectra and further supported by Si XPS data and ab initio calculations. This experimental nanoscale approach shows great promise for the CVD growth of ultrathin films.

The effect of exposure condition on the degradation behavior of magnesium rich coatings

We evaluated magnesium rich epoxy polyamide primers under different environmental exposure conditions. The purpose was to highlight differences in deterioration of these types of coatings as a function of exposure condition. We compared data for samples under constant immersion in dilute Harrison's solution (DHS-CI) to identical samples exposed to 90% relative humidity (90% RH). EOCP, XPS and SEM analysis of the coatings supported our findings that the samples under DHS-CI undergo rapid dissolution and deterioration compared to the 90% RH samples. The difference was that the latter were able to form carbonate corrosion products, which are known to provide additional passivating protection.

Cascaded systems analysis of photon counting detectors.

Photon counting detectors (PCDs) are an emerging technology with applications in spectral and low-dose radiographic and tomographic imaging. This paper develops an analytical model of PCD imaging performance, including the system gain, modulation transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). A cascaded systems analysis model describing the propagation of quanta through the imaging chain was developed. The model was validated in comparison to the physical performance of a silicon-strip PCD implemented on an experimental imaging bench. The signal response, MTF, and NPS were measured and compared to theory as a function of exposure conditions (70 kVp, 1-7 mA), detector threshold, and readout mode (i.e., the option for coincidence detection). The model sheds new light on the dependence of spatial resolution, charge sharing, and additive noise effects on threshold selection and was used to investigate the factors governing PCD performance, including the fundamental advantages and limitations of PCDs in comparison to energy-integrating detectors (EIDs) in the linear regime for which pulse pileup can be ignored. The detector exhibited highly linear mean signal response across the system operating range and agreed well with theoretical prediction, as did the system MTF and NPS. The DQE analyzed as a function of kilovolt (peak), exposure, detector threshold, and readout mode revealed important considerations for system optimization. The model also demonstrated the important implications of false counts from both additive electronic noise and charge sharing and highlighted the system design and operational parameters that most affect detector performance in the presence of such factors: for example, increasing the detector threshold from 0 to 100 (arbitrary units of pulse height threshold roughly equivalent to 0.5 and 6 keV energy threshold, respectively), increased the f50 (spatial-frequency at which the MTF falls to a value of 0.50) by ∼30% with corresponding improvement in DQE. The range in exposure and additive noise for which PCDs yield intrinsically higher DQE was quantified, showing performance advantages under conditions of very low-dose, high additive noise, and high fidelity rejection of coincident photons. The model for PCD signal and noise performance agreed with measurements of detector signal, MTF, and NPS and provided a useful basis for understanding complex dependencies in PCD imaging performance and the potential advantages (and disadvantages) in comparison to EIDs as well as an important guide to task-based optimization in developing new PCD imaging systems.

Different uranium distribution patterns in cytosolic protein pool of zebrafish gills after chronic and acute waterborne exposures

The toxicity of uranium (U) to aquatic organisms depends notably on its compartmentalization in organs, tissues, cells as well as on its distribution among biomolecules. In order to contribute to the understanding of U accumulation and associated toxicity mechanisms in case of waterborne exposure, this study focused on U fate in the gills epithelia, uptake pathway, of the fish model Danio rerio (zebrafish). U distribution among cytosolic biomolecules was investigated after no addition (0μgL−1 (c0) for 3 and 30d), chronic (20μgL−1 (c20) for 30d) and acute (20μgL−1 (c20) and 250μgL−1 (c250) for 3d) exposures to depleted U. Cytosolic U accounted for an average of 24–32% of gills burden for c20 and c250, respectively. Size Exclusion Chromatography (SEC) coupled with Inductively Coupled Plasma-Sector Field Mass Spectrometry (ICP-SFMS) allowed identification of ecotoxicologically relevant U-containing fractions among cytosolic biomolecules as a function of exposure conditions. In c0 and c20 samples, most U (ca.80%) was found in the Low Molecular Weight fraction (LMW, <18kDa), often considered as a detoxifying fraction. In c250 exposed fish, U was equally distributed between LMW (40%) and High Molecular Weight (HMW, 150–670kDa; 40%) fractions, the latter including sensitive metalloproteins. Uranium-biomolecules were co-eluted with endogenous essential metal (Fe, Cu and Zn) species, however, no major influence on their cytosolic concentration and distribution pattern among cytosolic proteins was found.

Degradation of VX Surrogate Profenofos on Surfaces via in Situ Photo-oxidation

Surface degradation of profenofos (PF), a VX nerve gas surrogate, was investigated using in situ photo-oxidation that combines simple instrumentation and ambient gases (O2 and H2O) as a function of exposure conditions ([O3], [OH], UV light λ = 185 and/or 254 nm, relative humidity) and PF film surface density (0.38-3.8 g m(-2)). PF film 0.38 g m(-2) fully degraded after 60 min of exposure to both 254 and 185 nm UV light in humidified air and high ozone. The observed pseudo-first-order surface reaction rate constant (kobs = 0.075 ± 0.004 min(-1)) and calculated hydroxyl concentration near the film surface ([OH]g = (9 ± 2) × 10(7) molecules cm(-3)) were used to determine the second-order rate constant for heterogeneous reaction of PF and OH (k(OH)PF = (5 ± 1) × 10(-12) cm(3) molec(-1) s(-1)). PF degradation in the absence of 185 nm light or without humidity was lower (70% or 90% degradation, respectively). With denser PF films ranging from 2.3 to 3.8 g m(-2), only 80% degradation was achieved until the PF droplet was redissolved in acetonitrile which allowed >95% PF degradation. Surface product analysis indicated limited formation of the nontoxic phosphoric acid ester but the formation of nonvolatile chemicals with increased hydrophilicity and addition of OH.

Modelling of optical durability of enhanced aluminum solar reflectors

In order to reduce electricity generation costs of concentrating solar power (CSP) technologies, new low-cost reflector materials are being developed. These materials need to withstand harsh outdoor conditions without a significant loss in specular reflectance. In this work, samples of enhanced anodized aluminum reflectors protected by a sol–gel coating that have been exposed at different weathering sites were analyzed with an innovative specular reflectometer in order to monitor corrosion and scattering caused by surface roughness. A model to estimate the specular reflectance as a function of exposure conditions at different weathering sites has been developed.

Change in data marks and groove structures of compact recordable disks in response to a high power laser beam

Changes in data marks and groove structures are examined when a high power laser beam (>0.5 W) is focused on compact disk recordable (CD-R) data layers. Observations are recorded as a function of exposure condition and the type of dye used in the recording layer. All samples experience a decrease in the depths of data mark features and the pregroove modulations on exposure. Data marks on cyanine- and azo-dye disks become optically invisible after exposure, while data marks on phthalocyanine-dye disks remain visible, even after high-power exposure. Also, phthalocyanine-dye disks show interesting phenomena, including mixture of the dye and the substrate material during recording and contrast reversal of the marks.

A quantitative study of moisture adsorption in polyimide and its effect on the strength of the polyimide/silicon nitride interface

Polyimide films on silicon nitride substrates were exposed to moisture under varying conditions of relative humidity, time and temperature. The moisture content of the films was measured by FTIR spectroscopy, and the polyimide/silicon nitride interface strength was measured at room temperature by a laser spallation technique. The moisture adsorption by polyimide films was analyzed using a diffusion model. Under the experimental conditions of this study, it was found that the rate of moisture adsorption was controlled the surface exchange reaction. For samples exposed at 38 °C, the interface strength was found to decrease linearly with increasing interface moisture concentration. A critical interface moisture concentration was identified, where the strength is expected to go to zero. The interface strengths of all the measured samples were combined into one empirical equation that can be used as a basis to construct strength charts as a function of exposure conditions. Such strength charts should help in the development of more rational standards for handling packaged ICs during manufacturing and integration from the viewpoint of avoiding moisture-related failures.

Mg-rich coatings: A new paradigm for Cr-free corrosion protection of Al aerospace alloys

Environmentally acceptable alternative coatings to chromate pigments and pretreatments for the corrosion control of Al alloy 2024 T-3, commonly used in aircraft, were designed, formulated, and tested as primer coatings to provide protection using particulate Mg-rich pigmentation. The system was designed by analogy to pigmented Zn-rich primer coatings used for the protection of steel. In the current study, four coating polymer systems were examined as possible candidates as polymer matrices for Mg-rich cathodic protect coatings. Mg-rich primers were formulated with ∼50-micron average particle size magnesium powder, near to the critical pigment volume concentration (CPVC) for this system. Top-coated scribed coatings systems have been subjected to Prohesion™ exposure in dilute Harrison’s solution for up to 5000 hr. These coatings are the first nonchromated coatings to satisfy 3000 hr of such exposure and remain shiny and undamaged in the scribe area, only showing damage at about 4800 hr. The corrosion byproducts generated in the scribe areas during Prohesion exposure were examined by energy dispersive X-ray analysis (EDXA), and the local pH of the coating determined by the nature of the salt formed as a function of exposure conditions and time, did not cause Al corrosion.

Hydrophilic nature of silicate glass surfaces as a function of exposure condition

The work presented compares the hydrophilic nature of fused silica, BK-7 and soda lime silicate (SLS) glass surfaces as a function of exposure conditions. Oxygen (O 2) plasma, water (H 2O) plasma and a combination treatment of ultraviolet (UV) radiation (340 nm, 0.4 W/m 2) in an aqueous environment (UV/H 2O) were used as the exposure treatments. The hydrophilic character of the surfaces was based on Fourier transform infrared reflectance studies (4000–3000 cm −1 region) and contact angle analysis. It was found that the SLS glass was equally affected by all three exposure conditions, at least to the penetration depth of the IR reflection analysis (84° to the normal). A more hydrophilic behavior was achieved for fused silica and BK-7 using either the UV/H 2O treatment or the H 2O plasma treatment. It was confirmed by IR analysis that the O 2 plasma treatment of fused silica and BK-7 glass resulted in free silanol groups at the surface, which contributed to the lower hydrophilicity after treatment.

Dominant lethal studies in male mice after exposure to a 50‐Hz electric field

Male C3H/He mice were sham-exposed or exposed continuously for 2 weeks to a vertical, 50-Hz, electric field at 20 kV/m rms. Densities of currents induced in the testes are estimated to be near 100 microA/m2. After the exposure, each male was mated with two different female mice each week during a period of 8 weeks. By this schedule, female mice were impregnated with sperm that had been exposed to the electric field at different stages of the spermatogenic cycle. No significant differences as a function of exposure condition were observed in pregnancy rates or in survival of embryos before or after implantation. The absence of effects was not due to insensitivity of assays; other mice that were exposed to X-rays (dose to testes = 1.5 Gy) presented reliable evidence of mutagenesis.

Photo-stabilization and photo-degradation in organic coatings containing a hindered amine light stabilizer: Part IV—Photo-initiation rates and photo-oxidation rates in unstabilized coatings

The chemistries and rates of photo-oxidation have been studied in a series of acrylic melamine coatings as a function of exposure condition. Electron spin resonance (ESR) spectroscopy has been used to determine the photo-initiation rate (PIR) of free radicals using a nitroxide doping technique. Infrared spectroscopy has been used to follow changes in the relative concentrations of different functional groups. In particular, the rate of carbonyl group formation has been measured. This rate has been found to be proportional to the square root of the photo-initiation rate, confirming that the formation of carbonyl species in these coatings is a free radical induced photo-oxidation process. Infrared spectroscopic measurements of carbonyl formation can be used to evaluate the effectiveness of free-radical scavengers such as hindered amine light stabilizers in retarding photo-oxidation in polymer coatings.

Erosion-corrosion of materials at elevated temperatures

High-temperature corrosion and solid-particle erosion both involve the action of the environment on the near-surface region of materials. The interactions cause chemical, physical and mechanical changes in the material surfaces; as a result, life predictions for components exposed to such environments become difficult. Models are presented in this paper for the synergistic interaction of oxidation and erosion of metals and alloys. The models are based on an extension of earlier work on paralinear kinetics in which oxidation of metal is assumed to be diffusion-controlled and erosion is assumed to result in uniform removal of material. The models have been applied to oxidation-erosion data developed on pure metals such as nickel and cobalt and to burner-rig test data developed for a number of superalloys. The approach enables the identification of oxidation- or erosion-dominated regimes for future experiments, and aids in the prediction of metal consumption as a function of exposure conditions.

Photo-stabilisation and photo-degradation of organic coatings containing a hindered amine light stabiliser: Part III—Kinetics of stabilisation during free radical oxidation

The kinetics of nitroxide formation and decay and hindered amine light stabiliser consumption in organic coatings doped with bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate (HALS I) have been interpreted using a scheme based on conventional free radical oxidation. Rate constants have been determined by fitting experimental nitroxide kinetic data from coatings doped variously with HALS I- or a HALS-based nitroxide. Three rate constants are important to the understanding of the stabilisation kinetics of HALS I: the rate constant for the conversion of HALS I to nitroxide, the rate constant for the scavenging of free radicals by nitroxide to form aminoethers and the rate constant for the regeneration of nitroxide from aminoethers. These rate constants have been determined for both an acrylic/urethane and an acrylic/melamine coating as a function of exposure conditions. The rate constant for radical scavenging by nitroxide is independent of coating type. It is found that aminoethers are more easily converted to nitroxide than is HALS I. It is also found that the rate constants for the generation of nitroxide from HALS I are independent of humidity for the acrylic urethane coating but increase with increasing humidity in the acrylic/melamine coating. It is suggested that this is due to the influence of formaldehyde, released during hydrolysis of the acrylic/melamine coating, on the free radical chemistry.

Thin-Film Microwave Integrated Circuits

There has been an increase in the use of thin-film technology for the preparation of microwave circuits since it permits the realization of very complex circuitry with precision, reliability, and economy. The requirements for the realization of such circuits have made it necessary to extend the state of the art of the hybrid technology in many areas. Two new substrate types (fine-grain alumina and fused silica) and low-loss conductor systems that are both solderable and thermocompression (TC) bondable were introduced. Further complications which were overcome included bilevel patterns with laser-drilled plated via-holes, the control and measurement of the alumina substrates dielectric constant, and the use of laser trimming to adjust small geometries of tantalum nitride (Ta <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> N) termination resistors. Precise pattern delineation of conductors by laser machining, sputter etching, and selective plating was evaluated and the latter process was found to be the most economical and reliable, since the selective plating technique depends on good photoresist delineation, resist properties were evaluated with special attention given to the variation of linewidth as a function of exposure conditions and resist adhesion during the plating of the gold conductors to prevent underplating. The line shape of the resist was also determined as a function of exposure, development, mask-to-substrate distance, and postbake conditions. Linewidth tolerances such as ± 2.5 µm on fused silica and ±5.0 µm on alumina were routinely achieved. Microwave integrated circuits (an 18-GHz downconverter, a 1.7-GHz amplifier, a filter, and a demodulator) prepared by this technique are illustrated and their performances are discussed. These circuits are used in a digital transmission system currently under development.