Development of plasma-sprayed molybdenum carbide-based anode layers with various metal oxides for SOFC.

Air plasma-sprayed (APS) coatings provide an ability to deposit a range of novel fuel cell materials at competitive costs. This work develops three separate types of composite anodes (Mo-Mo2C/Al2O3, Mo-Mo2C/ZrO2, Mo-Mo2C/TiO2) using a combination of APS process parameters on Hastelloy®X for application in intermediate temperature proton-conducting solid oxide fuel cells. Commercially available carbide of molybdenum powder catalyst (Mo-Mo2C) and three metal oxides (Al2O3, ZrO2, TiO2) was used to prepare three separate composite feedstock powders to fabricate three different anodes. Each of the modified composition anode feedstock powders included a stoichiometric weight ratio of 0.8:0.2. The coatings were characterized by scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction, nanoindentation, and conductivity. We report herein that three optimized anode layers of thicknesses between 200 and 300µm and porosity as high as 20% for Mo-Mo2C/Al2O3 (250-µm thick) and Mo-Mo2C/TiO2 (300µm thick) and 17% for Mo-Mo2C/ZrO2 (220-µm thick), controllable by a selection of the APS process parameters with no addition of sacrificial pore-forming material. The nanohardness results indicate the upper layers of the coatings have higher values than the subsurface layers in coatings with some effect of the deposition on the substrate. Mo-Mo2C/ZrO2 shows high electrical conductivity

Microstructural evaluation of suspension thermally sprayed WC-Co nanocomposite coatings.

Microstructural and sliding wear evaluations of nanostructured coatings deposited by Suspension High Velocity Oxy-Fuel (S-HVOF) spraying were conducted in as-sprayed and HIPed (Hot Isostatically Pressed) conditions. S-HVOF coatings were nanostructured via ball milling of the WC-12Co start powder, and deposited via an aqueous based suspension using modified HVOF (TopGun) spraying. Microstructural evaluations of these hardmetal coatings included TEM (Transmission Electron Microscopy), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that nanostructured features inherited from the start powder in S-HVOF spraying were retained in the resulting coatings. The decarburisation of WC due to a higher surface area to volume ratio was also observed in the S-HVOF coatings. Nanostructured and amorphous phases caused by the high cooling rates during thermal spraying crystallized into complex eta-phases after the HIPing treatment. Sliding wear performance indicated that the coating wear was lower for the HIPed coatings

Sliding wear investigation of suspension sprayed WC-Co nanocomposite coatings.

Sliding wear evaluation of nanostructured coatings deposited by Suspension High Velocity Oxy-Fuel (S-HVOF) and conventional HVOF (Jet Kote (HVOF-JK) and JP5000 (HVOF-JP)) spraying were evaluated. S-HVOF coatings were nanostructured and deposited via an aqueous based suspension of the WC-Co powder, using modified HVOF (TopGun) spraying. Microstructural evaluations of these hardmetal coatings included X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDX). Sliding wear tests on coatings were conducted using a ball-on-flat test rig against steel, silicon nitride (Si3N4) ceramic and WC-6Co balls. Results indicated that nanosized particles inherited from the starting powder in S-HVOF spraying were retained in the resulting coatings. Significant changes in the chemical and phase composition were observed in the S-HVOF coatings. Despite decarburization, the hardness and sliding wear resistance of the S-HVOF coatings was comparable to the HVOF-JK and HVOF-JP coatings. The sliding wear performance was dependent on the ball-coating test couple. In general a higher ball wear rate was observed with lower coating wear rate. Comparison of the total (ball and coating) wear rate indicated that for steel and ceramic balls, HVOF-JP coatings performed the best followed by the S-HVOF and HVOF-JK coatings. For the WC-Co ball tests, average performance of S-HVOF was better than that of HVOF-JK and HVOF-JP coatings. Changes in sliding wear behavior were attributed to the support of metal matrix due to relatively higher tungsten content, and uniform distribution of nanoparticles in the S-HVOF coating microstructure. The presence of tribofilm was also observed for all test couples

Comparison of wear performance of thermal sprayed cermet (WC-Co) coatings from suspension and feedstock powders.

WC-Co coatings were deposited using conventional High Velocity Oxy-Fuel Jet-Kote (HVOF-JK) and Suspension HVOF (S-HVOF) methods. Microstructural and mechanical properties along with the wear resistance of coatings were investigated. Reciprocating sliding wear tests were conducted against sintered Si3N4 counter-body with a normal load of 25N and total sliding distance of 500m following ASTM G133-2 standard. Coatings were characterised by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and nano-Indentation techniques. HVOF-JK coating showed good retention of WC whereas S-HVOF coating showed the presence of W, W2C and amorphous/nanocrystalline phases. Nano-indentation of HVOF-JK and S-HVOF showed that the relative hardness of the HVOF-JK coating was higher but their elastic modulus was lower. The lower total wear rate was exhibited by the HVOF-JK coating. This difference in wear performance is attributed to the difference in hardness of the coatings and decarburisation of WC particles

Influence of post-treatment on the microstructural and tribomechanical properties of suspension thermally sprayed WC-12 wt%Co nanocomposite coatings.

The potential to improve the tribomechanical performance of HVOF-sprayed WC-12Co coatings was studied by using aqueous WC-12Co suspensions as feed-stock. Both as-sprayed and hot-isostatic-pressed (HIPed) coatings were studied. Mathematical models of wear rate based on the structure property relationships, even for the conventionally sprayed WC-Co hardmetal coatings, are at best based on the semiempirical approach. This paper aims to develop these semiempirical mathematical models for suspension sprayed nanocomposite coatings in as-sprayed and heat-treated (HIPed) conditions. Microstructural evaluations included transmission electron microscopy, X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that the HIPing post-treatment resulted in crystallization of amorphous coating phases and increase in elastic modulus and hardness. Influence of these changes in the wear mechanisms and wear rate is discussed. Results are also compared with conventionally sprayed high-velocity oxy-fuel hardmetal WC-Co coatings

Effect of cyclic changes in temperature and pressure on permeation properties of composite polyamide seawater reverse osmosis membranes

The effects of cyclic changes in feed water temperature and pressure on permeate flux, solute rejection, and compaction in spiral wound composite polyamide seawater reverse osmosis membranes were examined with pure water and 4% NaCl solutions. A membrane permeability hysteresis or memory effect due to the up and down temperature and pressure sequences was only seen with the saline water studies. However, the observed changes appeared to be reversible and were consistent with the Spiegler-Kedem/ Film Theory and the Kimura-Sourirajan Analysis/ Film Theory models. The overall results suggest that the net effect on permeance and solute rejection is the consequence of several interactions with feed/operating temperatures affecting membrane porosity and water/solute cluster size, and transmembrane pressure influencing membrane compaction. \ua9 Taylor & Francis Group, LLC.Peer reviewed: YesNRC publication: Ye

Controlled release of testosterone and estradiol-17 β from biodegradable cylinders

A controlled release device for the hormones, testosterone and estradiol-17 β, was developed by coating a melt extruded hormone/poly (ϵ-caprolactone) cylinder with pure polylactide. Since testosterone and estradiol-17β have much higher permeabilities in poly (ϵ-caprolactone) than in polylactide, they primarily permeate through the open ends of the cylinder, with little release through the polylactide wall. By changing the cylinder length, the release rate and duration could be adjusted. The release followed Pick's diffusion equation for a drug loading below its solubility in poly (ϵ-caprolactone) or Higuchi's equation for a drug loading above the solubility. The diffusion coefficients of testosterone and estradiol-17β in poly (ϵ-caprolactone) were estimated as $(8.31 \pm 3.12) \times 10^{−18}$ and $(0.728 \pm 0.250) \times 10^{-18} cm^{2}/s$, respectively