IMECE2002-39368 DEPOSITION OF YSZ THIN FILMS BY LIQUID FUEL COMBUSTION CHEMICAL VAPOR DEPOSITION

ABSTRACT Thin film of YSZ electrolyte is highly desired to reduce the electrical resistance in SOFCs. YSZ thin Films have been successfully produced using liquid fuel combustion chemical vapor deposition (CCVD) technique. Nucleation of the YSZ particles were investigated based on two processing parameters, i.e., substrate temperature and total-metal-concentration in the liquid fuel. An optimum substrate temperature was found for highest the nucleation density. The nucleation density was increased with the total-metal-concentration. Microstructure evolution of the YSZ particles in the early stage in film growth was also studied. It was found that the particle growth rate was linear with processing time, and the particle orientation was varying with the time in the early stage of the film processing. To enhance the film growth rate, the effect of thermophoresis was studied. By increase the temperature gradient towards substrate, the effect of thermophoresis was enhanced and the film growth is also increased

IMECE2004-61012 PROCESSING OF COMPOSITE CATHODE AND YSZ COATINGS FOR SOLID OXIDE FUEL CELLS

ABSTRACT In our research, composite cathodes of strontium-doped lanthanum manganite (LSM) and yttria-stabilized zirconia (YSZ) were produced by using slurry casting and sintering procedures. The slurry was prepared using ball milling. The time of ball milling was studied in terms of particle size and homogeneity of the powder in the slurry. The effect of the composition of the slurry on the microstructure was studied to obtain cathodes with desired porosity. The sintering process was also optimized to compromise the porosity, grain size, and strength of the cathodes. The YSZ coating was implemented using electrophoretic deposition in liquid phase. Different charging methods of the YSZ powder in the suspension was used and their results were compared. The microstructures of cathodes and YSZ coatings were characterized using scanning electron microscope (SEM). INTRODUCTION Among the various kinds of fuel cells, the energy conversion efficiency of the solid oxide fuel cells (SOFC) is particularly high due to the high operation temperature. Furthermore, SOFCs have several advantages, such as the high power density, fuel flexibility, and unprecedented reliability. However, the application of the SOFC is slowed down by the current high manufacturing cost. The development of low cost processing techniques for the cell components is highly desired. Yttria stabilized zirconia (YSZ) and porous strontium doped lanthanum manganese oxide (LSM) are commonly used as electrolyte and cathode, respectively, for SOFCs. Composites of LSM and YSZ have been widely used [1-3] to increase catalytic activity for oxygen reduction of the cathode. The composite cathode has demonstrated to improve its performance at medium temperatures. A variety of techniques, such as tape castin

IMECE2005-79967 EFFECT OF PROCESSING PARAMETERS ON THE CONDUCTIVITY OF THE SOLID OXIDE ANODE FOR FUEL CELLS

ABSTRACT Good electrical conductivity is highly desirable in Ni / YSZ cermet anodes for solid oxide fuel cells (SOFCs), that operate at temperatures typically around 700 -900 °C. The conductivity of the cell controls the polarization loss of the cell which affects the overall efficiency of the fuel cell. In the current study, the effect of processing parameters on the conductivity of the anode cermet at room temperature is studied. The cermet is prepared with two different NiO vol. % and also sintered at two different temperatures. Different sintering temperatures lead to different microstructure and overall pore volume. The dependency of the conductivity on the microstructure, pore volume, sintering temperature and also the Ni content in the cermet are analyzed. The current analysis shows that the conductivity of the anode cermet strongly depends on the overall pore volume. Increase in sintering temperature reduces the pore volume and also reduces the active electrical conduction path. Increased density also decreases the active diffusion path which eventually means that there is a reduction in electrochemically active sites. These changes directly affect the efficiency of the cell. The Ni content in the cermet also influences the conductivity. The conductivity of the cermet varies with the Ni volume present in the cermet

Magnesium incorporated chitosan based scaffolds for tissue engineering applications

Chitosan based porous scaffolds are of great interest in biomedical applications especially in tissue engineering because of their excellent biocompatibility in vivo, controllable degradation rate and tailorable mechanical properties. This paper presents a study of the fabrication and characterization of bioactive scaffolds made of chitosan (CS), carboxymethyl chitosan (CMC) and magnesium gluconate (MgG). Scaffolds were fabricated by subsequent freezing-induced phase separation and lyophilization of polyelectrolyte complexes of CS, CMC and MgG. The scaffolds possess uniform porosity with highly interconnected pores of 50–250 μm size range. Compressive strengths up to 400 kPa, and elastic moduli up to 5 MPa were obtained. The scaffolds were found to remain intact, retaining their original three-dimensional frameworks while testing in in-vitro conditions. These scaffolds exhibited no cytotoxicity to 3T3 fibroblast and osteoblast cells. These observations demonstrate the efficacy of this new approach to preparing scaffold materials suitable for tissue engineering applications

Structural, mechanical and tribological investigations of sputter deposited CrN–WS2 nanocomposite solid lubricant coatings

Nanocomposite coatings of CrN–WS2 were prepared at different Cr contents (approximately 8–39 at%)using an unbalanced magnetron sputtering system. Structural changes in CrN–WS2 coatings with variation in Cr content were studied using X-ray diffraction. CrN–WS2 coatings displayed a dense, compact microstructure with reduced columnar growth in the field emission scanning electron microscopy data. Nanoindentation and nanoscratch data showed that CrN–WS2 coatings exhibited improved mechanical and adhesive properties, respectively. Micro-tribometer tests at a load of 2 N indicated that CrN–WS2 coatings prepared at 31 at% Cr exhibited a stable friction coefficient of 0.20–0.24 even after 8 h

Mechanical and tribological properties of sputter deposited nanostructured Cr-WS2 solid lubricant coatings

Solid lubricant coatings of WS2 and Cr–WS2 (15–50 at.% Cr) prepared using an unbalanced magnetron sputtering system were evaluated for their mechanical and tribological properties. Nanoindentation results indicated that addition of Cr helped in improving the mechanical properties and the elastic recovery ability of Cr–WS2 coatings. The adhesive strengths of Cr–WS2 coatings were evaluated using a nanoscratch tester and from the nanoscratch profiles, critical load values and optical images, it was evident that the adhesion of Cr–WS2 coatings increased with an increase in the Cr content. Further analysis of the nanoscratch data indicated that WS2 coatings exhibited large amount of plastic deformation compared to Cr–WS2 coatings which showed a combination of elastic–plastic deformation. However, micro-tribometer measurements at a load of 2 N showed that the tribological properties of Cr–WS2 coatings deteriorated with an increase in the Cr content. For example, Cr–WS2 coatings prepared at Cr content ≥33 at.% failed after a sliding distance of 1 m. On the other hand, WS2 and Cr–WS2 coatings prepared at low Cr contents (15–23 at.% Cr) exhibited a stable friction coefficient (50–60% relative humidity) in the range of 0.10–0.13 for a sliding distance of 14 m. Micro-Raman spectroscopy data of the worn films taken after a sliding distance of 14 m indicated the presence of WS2 transfer films for WS2 and Cr–WS2 coatings prepared at low Cr contents. For Cr–WS2 coatings with Cr content ≥33 at.%, the worn films consisted predominantly of WO3. After an extended sliding distance of 50 m, Cr–WS2 coatings (15–23 at.% Cr) outperformed WS2 coating which failed after 20 m. Further, the coatings prepared at low Cr contents did not show any failure even after a sliding distance of 200 m. At ahigher load of 7 N, Cr–WS2 coating with 15 at.% Cr exhibited the best performance with a friction coefficient of 0.07 up to a sliding distance of 72 m. These results indicate that the amount of Cr in the WS2 matrix needsto be controlled judiciously to obtain improved mechanical and tribological properties in Cr–WS2 solid lubricant coatings

Directional-Tribological Investigation of Magnesium Alloys Under As-Cast and Hot Extrusion Conditions

ABSTRACT In recent years, magnesium (Mg) and its alloy are being studied for their potential use in orthopedic implants with the novel ability to biodegrade after the implant serves its therapeutic function. Pure Mg, by itself, would not be suitable for use in a load-bearing implant application, due to its high corrosion rate and poor tribological properties. However, through proper alloying, this degradable metal is capable of achieving good mechanical properties reasonably similar to bone, a retarded rate of corrosion and enhanced biocompatibility. Previous studies have shown that alloying Mg with aluminum, lithium, rare earth (RE), zinc (Zn), and calcium (Ca) result in lower corrosion rates and enhanced mechanical properties. Despite the growing popularity of Mg and it alloys, there is relatively little information in the literature on their wear performance. In this paper, we report on an investigation of the directional tribological properties of Mg and Mg-Zn-Ca-RE alloy fabricated via two different manufacturing processing routes: as-cast and hot-extruded after casting, with extrusion ratios of 10 and 50. Pure Mg was cast 350°C. After casting, MgZn-Ca-RE alloy was heat-treated at 510°C. Another Mg-Zn-Ca-RE alloy was hot-extruded at 400°C. Dry sliding wear tests were performed on as-cast and hot-extruded pure Mg and Mg-Zn-Ca-RE alloys using a reciprocating test configuration. Wear rate, coefficient of friction and wear coefficient were measured under applied loads ranging from 0.5 -2.5N at sliding frequency of 0.2 Hz for 120 cycles, using microtribometery. Wear properties of the extruded specimen were measured in cross-section and longitudinal section. In the longitudinal section studies, wear properties were investigated along the extrusion direction and the transverse direction. Hardness properties were evaluated using microindentation. Cross-section and longitudinal section were indented with a Vickers indenter under applied load of 2.94 N. Alloying and extrusion enhanced the mechanical properties significantly, increased hardness by 80% and wear resistance by 50% compared to pure Mg. Despite the low hardness in both Mg and the Mg alloy cross-sections, the cross-sections for both displayed higher wear resistance compared to the longitudinal section. In the longitudinal section, wear resistance was higher along the transverse direction of the longitudinal section for both Mg and the Mg alloy. The wear coefficient was used to evaluate how the wear behavior of the material varied with respect to alloying, fabrication process, and direction of wear. The wear coefficient of pure Mg decreased as the extrusion ratio increased, thus, increasing the specific wear rate. The opposite behavior was found in the Mg alloy: as the wear coefficient increases, the specific wear rate decreases. The active wear mechanisms observed on the worn surface of Mg were fatigue, abrasive, adhesive and delamination wear. The same wear mechanisms were observed in the Mg alloy except for fatigue wear. Surface microstructure and topographical characterization were conducted using optical microscopy, scanning electron microscopy mechanical stylus profilometry, and optical profilometry

Structure, morphology and chemical composition of sputter deposited nanostructured Cr-WS2 solid lubricant coatings

WS2 and Cr–WS2 nanocomposite coatings were deposited at different Cr contents (approximately 15–50 at. %) on silicon and mild steel substrates using an unbalanced magnetron sputtering system. X-ray diffraction (XRD) was used to study the structure of Cr–WS2 coatings and the bonding structure of the coatings was studied using X-ray photoelectron spectroscopy (XPS). The characterization of different phases present in Cr–WS2 coatings was carried out using micro-Raman spectroscopy. The XPS and Raman data indicated the formation of a thin layer of WO3 on the surface of Cr–WS2 coatings and the intensity of the oxide phase decreased with an increase in the Cr content, which was also confirmed using energy-dispersive X-ray analysis results. The surface morphologies of WS2 and Cr–WS2 coatings were examined using field emission scanning electron microscopy (FESEM) and atomic force microscopy. It has been demonstrated that incorporation of Cr in WS2 strongly influences the structure and morphology of Cr–WS2 coatings. The XRD and FESEM results suggested that increase in the Cr content of Cr–WS2 coatings resulted in a structural transition from a mixture of nanocrystalline and amorphous phases to a complete amorphous phase. The cross-sectional FESEM data of WS2 coating showed a porous and columnar microstructure. For the Cr–WS2 coatings, a mixture of columnar and featureless microstructure was observed at low Cr ontents (≤23 at.%),whereas, a dense and featureless microstructure was observed at high Cr contents. Detailed cross-sectional transmission electron microscopy (TEM) studies of Cr–WS2 coatings prepared at Cr content ≤23 at.% indicated the presence of both nanocrystalline (near the interface) and amorphous phases (near the surface). Furthermore, high-resolution TEM data obtained from the nanocrystalline region showed inclusion of traces of amorphous phase in the nanocrystalline WS2 phase. Potentiodynamic polarization measurements indicated that the corrosion resistance of Cr–WS2 coatings was superior to that of the uncoated mild steel substrate and the corrosion rate decreased with an increase in the Cr content

Performance evaluation of TiAlCrYN nanocomposite coatings deposited using four-cathode reactive unbalanced pulsed direct current magnetron sputtering system

Approximately 1.5e2.5 mm thick nanocomposite coatings of TiAlCrYN were deposited using a fourcathode reactive unbalanced pulsed direct current magnetron sputtering system from the sputtering of Ti, Al, Cr, and Y targets in Ar þ N2 plasma. The TiAlCrYN nanocomposite coatings were deposited on various substrates such as high speed steel (HSS) drill bits, mild steel and silicon. TiAlCrYN coatings with almost similar mechanical properties but with different Ti, Al, Cr and Y contents were prepared to study their thermal stability and machining performance. The structural and mechanical properties of the coatings were characterized using X-ray diffraction and nanoindentation technique, respectively. The elemental composition, bonding structure, surface morphology and cross-sectional data were studied using energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy, respectively. Nanoscratch tests were performed to determine the adhesive strength of the coatings. The corrosion behavior of TiAlCrYN nanocomposite coatings on mild steel substrate was studied using potentiodynamic polarization in a 3.5% NaCl solution. Micro-Raman pectroscopy was used to characterize the structural changes as a result of heating of the nanocomposite coatings in air (600e 1000 �C). TiAlCrYN coatings prepared at 17 at.% Ti, 13 at.% Al, 21 at.% Cr and 1 at.% Y exhibited thermal stability as high as 900 �C in air (denoted as Sample 3). For the performance evaluation, the TiAlCrYN coated HSS drill bits were tested under accelerated machining conditions. With a drill speed of 800 rpm and a feed rate of 0.08 mm/rev the TiAlCrYN coated HSS drill bits (Sample 3) averaged 657 holes, while drilling a 12 mm thick 304 stainless steel plate under dry conditions, before failure. Whereas, the uncoated drill bits failed after drilling 50 holes under the same machining conditions. Results indicated that for the HSS drill bits coated with TiAlCrYN, the tool life increased by a factor of more than 12