Seal Coat Research Articles

Oxidation of SiC Fiber-Reinforced SiC Matrix Composites with a BN Interphase

The oxidation kinetics of SiC fiber-reinforced SiC matrix composites with a BN interphase (SiC/BN/SiC) and the constituent fibers was characterized by thermogravimetric analysis and microstructural characterization at temperatures (816-1538°C) and oxygen partial pressures (0.1% to 5% O2) relevant to the hypersonic flight and re-entry environments. TGA of the SiC fibers showed that oxidation of the thin BN surface layer led to initially rapid oxidation kinetics and formation of a relatively thick silica scale at very short times under most test conditions. At longer times the fiber oxidation kinetics were representative of silica formation on pure SiC. Oxidation of the composites was conducted on coupons with the SiC seal coat removed on one edge to simulate damage to the composite, allowing ingress of oxygen to the fiber tows. Microscopy was conducted to determine the distance of oxygen ingress into the coupon. At the lower temperatures and oxygen partial pressures the exposed edge did not seal off by silica formation, yet the BN interphase areas were only minimally oxidized. At the intermediate temperatures silica formed at the exposed surface limiting further oxidation of the exposed fibers and BN interphase areas. Finally at the highest temperature and lowest oxygen partial pressure, active oxidation of SiC occurred for both the fibers and coupons resulting in irregular material attack. Implications for use of SiC/BN/SiC materials for hypersonic vehicle thermal protection systems are summarized.

Analysis of Mechanical Behavior of Fine Sand Filling Embankment

It is serious problem of the deficiency of high quality embankment filling in the expressway construction in shanghai, the Yangtze estuary fine sand has been extensive applied as the substitute filling material to avoid destroying the cultivated land and cropland. It is signality of the fine sand filling embankment technique popularization and application to the improvement of highway construction level, the protection of the cultivated land and the protection of the eco-environment. For the natural sand is no-viscous bulk solid material with great variation on mechanical properties to traditional embankment filling, now there are some problems on the application of fine sand filling embankment engineering haven’t been analyzed such as the highway performance of fine sand filling embankment. In the paper, it analyzed the fine sand filling embankment stability by considering with the shape of landslide and safety factor by using the combination method of the strength reduction method and Fast Lagrange method. The analysis included geometrical and material properties of the slope ratio, the subgrade height, the presence or absence of the surrounding soil and the thickness of it, the top seal coat, pavement structure etc. and proposed the design suggestions of the optimum fine sand filling embankment based on the analysis above[5].

Electrical Conductivity of 2D-SiCf/CVI-SiC

Electrical conductivity (EC) data for several plate forms of two-dimensional, silicon carbide composite made with chemical vapor infiltration matrix and with Hi NicalonTM type S fibers (2D-SiCf/CVI-SiC) were acquired. The composite fibers were coated with pyrocarbon (PyC) of various thicknesses (50 to 310 nm) and an outer thin (˜60 μm) SiC “seal coat” was applied by CVD to the infiltrated plates.The EC was highly anisotropic in the transverse and in-plane directions. In-plane EC ranged from ˜150 to 1600 S/m, increased slowly with increasing temperature, and depended primarily on the total PyC thickness. High in-plane EC-values occur because it is dominated by conduction along the numerous, continuous PyC fiber coating pathways. Transverse EC ranged from ˜1 to 60 S/m, and increased strongly with increasing temperature up to 800°C. The transverse EC is controlled by conduction through the interconnections of the carbon-coating network within and between fiber bundles, especially at moderate temperatures (˜300 to 700°C). Below ˜300°C, the electrical resistance of the pure SiC seal coat becomes increasingly more important as temperatures are further lowered.Importantly, a “3-layer series” model predicts that transverse EC-values for a standard seal-coated 2D-SiCf/CVI-SiC with a monolayer PyC fiber coating of ˜50-nm thickness will be <20 S/m for all temperatures up to 800°C, as desired for a flow channel insert in a fusion reactor blanket component.

Investigation on the Permeability of Electric Arc Spraying Sealing Coat with Nano-Sized TiO&lt;sub&gt;2&lt;/sub&gt;,SiO&lt;sub&gt;2&lt;/sub&gt; of Steel Structures

In this dissertation, the electric arc spraying coatings on steel structure were sealed over with the organic coatings addition with nano-sized TiO2, SiO2. Some means as light microscope, SEM, energy spectrum and binding force tests were adopted for research the permeability of the sealer. The mechanism for permeable closeness of the sealer was mainly discussed. The results indicated that homogeneous nanofillers can improvement the runnability and permeability of the epikote, stiffen the adhesion between the coatings and the metal substrate. The coating can seal the metal substrate effectively; enhance the protective property of the tectonic systems with electric arc spraying coatings and organic coatings.

Characterization of laser sealed coatings of yttria partially stabilized zirconia

Abstract The present paper reports an experimental investigation based on X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and wavelength dispersive spectroscopy (WDS) analyses of phases formed after laser sealing of plasma sprayed coatings of 8.5 wt% yttria partially stabilized zirconia (YPSZ). X-ray diffraction and X-ray step-scanning analyses showed that the plasma sprayed and sealed coatings consisted mainly of t ′ phase with a very small amount of monoclinic phase ( m phase) in the plasma sprayed coatings. It was also found that the small amounts of m and cubic phases ( c phase) present in the sealed coatings were dependent on laser processing specific energies (specific energy is equal to laser power/traverse speed x beam diameter). It was also found that rhombohedral ( r ) phase formed after laser sealing of coatings at higher specific energies. A direct relationship between c / a ratio of transformable tetragonal phase ( t phase) produced by thermal treatment of sealed coatings and nontransformable tetragonal phase ( t ′ phase) and the amount of Yttria was obtained. A new equation was derived, which describes the relationship between Yttria concentration and the c / a ratio of tetragonal phases ( t or t ′).

Mitigating seal coat damage due to superheavy load moves in Texas low volume roads

Over the past few years, the number of Super Heavy Load (SHL) moves on the Texas highways has drastically increased, resulting in severe damage, particularly on low volume roads. One of the major failure modes on these low volume roads is peeling the fresh seal coats that have been employed as a primary maintenance option by the Texas Department of Transportation (TxDOT). In this paper, a mechanistic-empirical (M-E) guideline that incorporates a Microsoft Excel spreadsheet program was developed to aid in the evaluation and characterization of the damage (peel-off) potential of seal coats when subjected to SHL vehicle loading. Field validations were conducted to validate and calibrate the guideline. It was observed that the pavement surface temperature is the most critical factor along with pavement slope in travel direction, combination of aggregate and binder types, and curing period. Additionally, the texture depth that was measured using the sand patch test method was found to play a significant role in characterizing and controlling seal coat damage. Overall, the developed M-E guideline exhibits great promising potential to serve as an aid for evaluating and mitigating seal coat damage due to SHL vehicle loading on low volume roads in Texas.

Sealing HVOF Thermally Sprayed WC-CoCr Coatings by Sol-Gel Methods

The offshore industry faces challenges with corrosion resistance in hydraulic cylinders used in marine environments. Thermal spray coating appears to be a promising technique for replacing electroplated coating in many applications, but the performance of thermal spray coatings in highly corrosive environments must be improved. In the present work, a new sealing method for HVOF WC-CoCr coatings for their application on hydraulic cylinders for marine environments has been tested. The method consists of applying sol-gel solution that can penetrate, fill, and thus seal the pores and cracks in the coating. The sealed coatings have been tested with and without posttreatment and compared with as-sprayed coatings. Open-circuit potential (OCP) and tribocorrosion tests in 3.4% NaCl were performed to evaluate the performance of the sealing method. Both tests showed that the sealed coatings had the best performance.

Oxidation of Carbon Fiber‐Reinforced Silicon Carbide Matrix Composites at Reduced Oxygen Partial Pressures

Carbon fibers (Polyacrylonitrile‐derived T‐300) and T‐300 carbon fiber‐reinforced silicon carbide composites (C/SiC) were oxidized in flowing 0.1 MPa reduced oxygen partial pressure environments (50% O2, 5% O2, 0.5% O2, and 0.1% O2 in argon). Experiments were conducted at temperatures of 816°, 1149°, 1343°, and 1538°C. The oxidation kinetics were monitored using thermogravimetric analysis. T‐300 fibers were completely oxidized for times between 0.6 and 325 h. C/SiC coupons were oxidized for either 25 or 100 h. Fiber oxidation rates had an oxygen partial pressure dependence with a power‐law exponent close to one but were only weakly dependent on temperature. Fiber oxidation kinetics were consistent with gas‐phase diffusion control at these temperatures. The C/SiC coupon oxidation kinetics showed some variability, attributed to differences in the number and width of cracks in the SiC seal coat. Oxidation of the carbon fibers dominated the coupon oxidation behavior. For C/SiC coupons, low temperatures and high oxygen pressures resulted in the most rapid consumption of the carbon fibers. At higher temperatures, the lower oxidation rates were attributed to crack closure due to SiC thermal expansion, rather than oxidation of SiC. At the highest temperature and lowest oxygen partial pressure, active oxidation of SiC was observed.

Synthesis of tailored 2D SiCf/SiC ceramic matrix composites with BN/C interphase through ICVI

Synthesis of 2D SiCf /SiC composites for applications in fusion reactors is a challenging task due to the stringent specification requirements on various mechanical and thermo-mechanical properties, chemical compatibility (with Pb–Li), oxidation resistance and irradiation resistance. Three types of SiCf/SiC composites with C interface and BN interface, with and without intermediate heat treatment are prepared through isothermal and isobaric chemical vapor infiltration process. Dense SiC seal coat applied to the composites has improved their oxidation resistance. The tensile, flexural and fracture toughness values of composite with BN interface were found to be improved by stabilizing the BN interface through thermal treatment. The electrical and thermal conductivity values obtained for composites with C interface are in the range of 10–29S/m and 2.5–3.25W/mK for the temperature range 500–900°C as required for fusion reactor applications.

Fabrication of Si&lt;SUB align="right"&gt;3N&lt;SUB align="right"&gt;4-based seal coating on porous Si&lt;SUB align="right"&gt;3N&lt;SUB align="right"&gt;4 ceramics

In this study, Si3N4–based seal coatings using MgO, Al2O3 and SiO2 as the sintering additives were prepared on the porous Si3N4 substrates by room temperature spraying and pressureless sintering. The composition of the Si3N4–based seal coatings was well designed, in order to both match the coefficient of thermal expansion with that of the porous Si3N4 substrate and form the liquid phase at a relative low temperature. During the sintering process, the liquid phases promote the densification and homogenisation of the Si3N4–based seal coatings. A good combination between Si3N4–based seal coatings and substrate is achieved, as a result of the liquid–phase penetration into the pores in the porous Si3N4 substrate.

Development of ultrananocrystalline diamond (UNCD) coatings for multipurpose mechanical pump seals

The reliability and performance of silicon carbide (SiC) shaft seals on multipurpose mechanical pumps are improved by applying a protective coating of ultrananocrystalline diamond (UNCD). UNCD exhibits extreme hardness (97 GPa), low friction (0.1 in air) and outstanding chemical resistance. Consequently, the application of UNCD coatings to multipurpose mechanical pump seals can reduce frictional energy losses and eliminate the downtime and hazardous emissions from seal failure and leakage. In this study, UNCD films were prepared by microwave plasma chemical vapor deposition utilizing an argon/methane gas mixture. Prior to coating, the SiC seals were subjected to mechanical polishing using different grades of micron-sized diamond powder to produce different starting surfaces with well-controlled surface roughnesses. Following this roughening process, the seals were seeded by mechanical abrasion with diamond nanopowder, and subsequently coated with UNCD. The coated seals were subjected to dynamic wear testing performed at 3600 RPM and 100 psi for up to 10 days during which the seals were periodically removed and inspected. The UNCD-coated seals were examined using Raman microanalysis, scanning electron microscopy, optical profilometry, and adhesion testing before and after the wear testing. These analyses revealed that delamination of the UNCD films was prevented when the initial SiC seal surface had an initial roughness >0.1 μm. In addition, the UNCD surfaces showed no measurable wear as compared to approximately 0.2 μm of wear for the untreated SiC surfaces.

Erosion–corrosion of thermally sprayed coatings in simulated splash zone

The damage of marine steel structures in the splash zone is very severe. Applying thermally sprayed metal coatings is among the most important protective technologies, but the service life of current coatings is limited. In this paper, arc spray was used to prepare four types of metal coatings, that is, aluminum (Al), zinc bottom coating combined with aluminum topcoat (Zn+Al), aluminum–zinc pseudo alloy (Al/Zn) and aluminum–titanium pseudo alloy (Al/Ti) coatings. These metal coatings were sealed with epoxy priming and aliphatic polyurethane topcoat. Erosion–corrosion experiments were carried out on self-made device by simulating the splash zone working environment of steel structures and protective coatings. The results show that all the sealed coatings could improve the steel resistance to erosion–corrosion, and the aluminum–zinc pseudo alloy is the most excellent coating. In the coating failure process, mechanical erosion rather than corrosion is the key factor causing coating erosion–corrosion in splash zone. Improving the anti-cutting properties could help to prolong the coating life.

Influence of post-treatment on the corrosion resistance of PEO coated AM50B and AM60B Mg alloys

Magnesium alloys are highly reactive and require protection for their successful applications. In this work, coatings of 10 μm and 25 μm nominal thicknesses were prepared by Plasma Electrolytic Oxidation on AM50B and AM60B alloys. The effect of subsequent post-PEO treatments such as alkaline phosphate, alkaline silicate and sol–gel sealing was studied on coatings with 10 μm thickness. The microstructure and composition of the PEO coatings and post-treated coatings were analysed by Scanning Electron Microscope and Energy Dispersive X-ray Spectroscopy. Phase analysis of the coatings was carried out using X-ray Diffraction method. Potentiodynamic polarization method was used to evaluate the corrosion behaviour of these coatings in 3.5% NaCl solution. Electrochemical corrosion results indicated that the sealed PEO coatings of 10 μm thickness showed better corrosion resistance than the unsealed PEO coatings of 25 μm thickness. The structural surface defects of the PEO coatings were sealed by post-treatments resulting in decreases in surface roughness and open pores. Sol–gel post-treatment provided the most effective sealing to the PEO coatings.

Toxicity of coal–tar and asphalt sealants to eastern newts, Notophthalmus viridescens

Between 1970 and 2000 the concentration of total polycyclic aromatic hydrocarbons (TPAH) in several lakes across the country increased whereas those of other persistent organic pollutants (POPs) tended to remain stable or declined. Urbanized watersheds experienced greater rises in TPAH concentration compared to non-urban lakes. Sources for urban PAHs include industrial wastes, vehicular exhausts and oil leaks and sealants from pavement surfaces. Both coal–tar and asphalt sealants are used to protect surfaces but runoff from surfaces coated with coal–tar can have mean concentrations of 3500 mg TPAHs kg −1, much higher than runoff from asphalt-sealed or cement surfaces. Unaltered parent compounds of PAHs can have many lethal and sublethal toxic effects, but oxidation and UV radiation can alter the toxicity of these compounds, sometimes creating degradates that are many times more toxic than parent compounds. The purposes of this study were to determine if coal–tar sealants can be toxic to adult eastern newts ( Notophthalmus viridescens) and to compare the toxicity of coal–tar sealant to that of asphalt sealant. Newts were exposed to sediments containing dried sealants ranging from 0 mg kg −1 to 1500 mg kg −1 under simultaneous exposure to UV radiation and visible light to determine concentration/response relationships. No significant mortality occurred with any treatment. Significant effects due to sealants included decreased righting ability and diminished liver enzyme activities. Coal–tar sealant was more effective in inducing these changes than was asphalt sealant.

Characteristics of sealed plasma electrolytic oxidation coatings with electrochemical impedance spectroscopy

Plasma electrolytic oxidation (PEO) coatings are prepared on aluminium with graphite powders added into the electrolyte. The scanning electron microscopy (SEM) coupled with an energy dispersive x-ray analysis system (EDX) is used to characterize the surface and the cross-section morphologies of the coatings. The electrochemical impedance spectroscopy (EIS) is used not only to evaluate the corrosion resistance but also to analyse the structure of the coating. Results show that graphite powders are embedded in the PEO coating. The corrosion resistances of both the inner barrier and the outer porous layer are greatly improved, and the EIS could give some valuable detailed information about the coating structure.

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Estimating demographic parameters for capture–recapture data in the presence of multiple mark types

In mark-recapture studies, various techniques can be used to uniquely identify individual animals, such as ringing, tagging or photo-identification using natural markings. In some long-term studies more than one type of marking procedure may be implemented during the study period. In these circumstances, ignoring the different mark types can produce biased survival estimates since the assumption that the different mark types are equally catchable (homogeneous capture probability across mark types) may be incorrect. We implement an integrated approach where we simultaneously analyse data obtained using three different marking techniques, assuming that animals can be cross-classified across the different mark types. We discriminate between competing models using the AIC statistic. This technique also allows us to estimate both relative mark-loss probabilities and relative recapture efficiency rates for the different marking methods. We initially perform a simulation study to explore the different biases that can be introduced if we assume a homogeneous recapture probability over mark type, before applying the method to a real dataset. We make use of data obtained from an intensive long-term observational study of UK female grey seals (Halichoerus grypus) at a single breeding colony, where three different methods are used to identify individuals within a single study: branding, tagging and photo-identification based on seal coat pattern or pelage.

Costs and Benefits of Thin Surface Treatments on Bituminous Pavements in Kansas

This study investigated the benefits and costs of commonly used thin surface treatments for maintenance of bituminous pavements in Kansas. Cost and performance data were collected from the Kansas Pavement Management Information System for all treatments applied from 1992 to 2006. Results show that seal coats have a short average service life on Interstate highways. The average life on non-Interstate highways is about 4 years. This life is slightly lower than that for other thin surface treatments, including hot-mix asphalt (HMA) overlays. Seal coats also have a significantly lower equivalent uniform annual cost than do all other thin surface treatments in Kansas. A comparison of pavement benefit values before and after application showed that seal coat could not mitigate distresses better than other methods, especially thin HMA overlays. However, its performance is quite similar to that of the modified slurry seal.

Verificación del diseño de tratamientos superficiales mediante el método MODOT T 72 y la sección 409 del Estado de Missouri y su posible incorporación a la normativa argentina

El presente artículo tiene por objeto observar la relación entre las especificaciones citadas en el Departamento de Transporte de Materiales de Construcción del Estado de Missouri, Estados Unidos “Test Method MoDOT T 72 Sweep Test of Bituminous Surface Treatment Simple” y la Sección 409 “Seal Coat” con las especificaciones establecidas en el Pliego de la Dirección Nacional de Vialidad de la República Argentina, considerando además adecuaciones surgidas en el LEMaC, a efectos de lograr mayor representatividad en relación a la obra. Para llevar a cabo la correlación de lo citado, se diseñó un tratamiento superficial simple con el método de dosificación propuesto por el Ing. Tagle, conocido como la Regla de 9-5-3 y una capa de sello con arena de trituración. Al tratamiento se lo somete al ensayo de barrido, y teniendo en cuenta los valores citados en la Sección 409 del MoDOT, se desea valorar la eficiencia del método de dosificación optado. Se analizaron los resultados obtenidos y se comparó si el método de dosificación con lo estipulado por la Sección 409 de acuerdo a la granulometría de la capa de sellado y las pérdidas derivadas del ensayo. En las Especificaciones Nacionales no existe una restricción numérica de dichas pérdidas sino solo la experiencia de obra y los resultados de ensayos cuando el tratamiento ya está colocado como lisura superficial, rugosidad y coeficiente de fricción, además de los parámetros de los materiales separadamente. Se ha logrado con la experimentación analizada, establecer una recomendación para su posible incorporación a los Pliegos citados.

Performance modeling of Deep Burn TRISO fuel using ZrC as a load-bearing layer and an oxygen getter

The effects of design choices for the TRISO particle fuel were explored in order to determine their contribution to attaining high-burnup in Deep Burn modular helium reactor fuels containing transuranics from light water reactor spent fuel. The new design features were: (1) ZrC coating substituted for the SiC, allowing the fuel to survive higher accident temperatures; (2) pyrocarbon/SiC “alloy” substituted for the inner pyrocarbon coating to reduce layer failure and (3) pyrocarbon seal coat and thin ZrC oxygen getter coating on the kernel to eliminate CO. Fuel performance was evaluated using General Atomics Company’s PISA code. The only acceptable design has a 200-μm kernel diameter coupled with at least 150-μm thick, 50% porosity buffer, a 15-μm ZrC getter over a 10-μm pyrocarbon seal coat on the kernel, an alloy inner pyrocarbon, and ZrC substituted for SiC. The code predicted that during a 1600°C postulated accident at 70% FIMA, the ZrC failure probability is <10−4.