Sapphire reinforced alumina matrix composites

Unidirectionally reinforced A1203 matrix composites have been fabricated by hot pressing. Approximately 30 volume % of either coated or uncoated sapphire fiber was used as reinforcement. Unstabilized ZrO2 was applied as the fiber coating. Composite mechanical behavior was analyzed both after fabrication and after additional heat treatment. The results of composite tensile tests were correlated with fiber-matrix interfacial shear strengths determined from fiber push-out tests. Substantially higher strength and greater fiber pull-out were observed for the coated fiber composites for all processing conditions studied. The coated fiber composites retained up to 95% and 87% of their as-fabricated strength when heat treated at 14000C for 8 or 24 hours, respectively. Electron microscopy analysis of the fracture surfaces revealed extensive fiber pull-out both before and after heat treatment

Generation of High Pressure Oxygen via Electrochemical Pumping in a Multi-Stage Electrolysis Stack

An oxygen pump can produce high-purity high-pressure oxygen. Oxygen ions (O(2-)) are electrochemically pumped through a multi-stage electrolysis stack of cells. Each cell includes an oxygen-ion conducting solid-state electrolyte between cathode and anode sides. Oxygen dissociates into the ions at the cathode side. The ions migrate across the electrolyte and recombine at the anode side. An insulator is between adjacent cells to electrically isolate each individual cell. Each cell receives a similar volt potential. Recombined oxygen from a previous stage can diffuse through the insulator to reach the cathode side of the next stage. Each successive stage similarly incrementally pressurizes the oxygen to produce a final elevated pressure

Preparation and Evaluation of Multi-Layer Anodes of Solid Oxide Fuel Cell

The development of an energy device with abundant energy generation, ultra-high specific power density, high stability and long life is critical for enabling longer missions and for reducing mission costs. Of all different types of fuel cells, the solid oxide fuel cells (SOFC) is a promising high temperature device that can generate electricity as a byproduct of a chemical reaction in a clean way and produce high quality heat that can be used for other purposes. For aerospace applications, a power-to-weight of (is) greater than 1.0 kW/kg is required. NASA has a patented fuel cell technology under development, capable of achieving the 1.0 kW/kg figure of merit. The first step toward achieving these goals is increasing anode durability. The catalyst plays an important role in the fuel cells for power generation, stability, efficiency and long life. Not only the anode composition, but its preparation and reduction are key to achieving better cell performance. In this research, multi-layer anodes were prepared varying the chemistry of each layer to optimize the performance of the cells. Microstructure analyses were done to the new anodes before and after fuel cell operation. The cells' durability and performance were evaluated in 200 hrs life tests in hydrogen at 850 C. The chemistry of the standard nickel anode was modified successfully reducing the anode degradation from 40% to 8.4% in 1000 hrs and retaining its microstructure

Method for Making a Fuel Cell

The invention is a novel solid oxide fuel cell (SOFC) stack comprising individual bi-electrode supported fuel cells in which an electrolyte layer is supported between porous electrodes. The porous electrodes may be made from graded pore ceramic tape that has been created by the freeze cast method followed by freeze-drying. Each piece of graded pore tape later becomes a graded pore electrode scaffold that, subsequent to sintering, is made into either an anode or a cathode. The electrode scaffold comprising the anode includes a layer of liquid metal. The pores of the electrode scaffolds gradually increase in diameter as the layer extends away from the electrolyte layer. As a result of this diameter increase, any forces that would tend to pull the liquid metal away from the electrolyte are reduced while maintaining a diffusion path for the fuel. Advantageously, the fuel cell of the invention may utilize a hydrocarbon fuel without pre-processing to remove sulfur

Freeze-cast yttria-stabilized zirconia pore networks: Effects of alcohol additives

Freeze casting yttria-stabilized zirconia (YSZ) can be useful in making electrodes for solid oxide fuel cells (SOFCs) by introducing hierarchical porosity to increase triple-phase boundary (TPB) area while maintaining adequate fuel flow. In this study the influence of alcohol additives on pore structure of aqueous YSZ freeze-cast samples was investigated. Slurries with ethanol, iso-propyl alcohol, or methanol as additives were compared to a control sample. Pore characteristics along sample lengths were measured using X-ray computed tomography reconstructions. The control sample showed significant changes in pore size along sample length, whereas pore size of the alcohol additive samples remained similar, indicating that freezing rates of the additive samples remained constant during solidification. Ice lens formation and interactions between alcohols and slurry functional additives (dispersant, surfactant, and binder) resulted in complex pore structures which show promise in increasing SOFC TPB area

Regenerative Performance of the NASA Symmetrical Solid Oxide Fuel Cell Design

The NASA Glenn Research Center is developing both a novel cell design (BSC) and a novel ceramic fabrication technique to produce fuel cells predicted to exceed a specific power density of 1.0 kW/kg. The NASA Glenn cell design has taken a completely different approach among planar designs by removing the metal interconnect and returning to the use of a thin, doped LaCrO3 interconnect. The cell is structurally symmetrical. Both electrodes support the thin electrolyte and contain micro-channels for gas flow-- a geometry referred to as a bi-electrode supported cell or BSC. The cell characteristics have been demonstrated under both SOFC and SOE conditions. Electrolysis tests verify that this cell design operates at very high electrochemical voltage efficiencies (EVE) and high H2O conversion percentages, even at the low flow rates predicted for closed loop systems encountered in unmanned aerial vehicle (UAV) applications. For UAVs the volume, weight and the efficiency are critical as they determine the size of the water tank, the solar panel size, and other system requirements. For UAVs, regenerative solid oxide fuel cell stacks (RSOFC) use solar panels during daylight to generate power for electrolysis and then operate in fuel cell mode during the night to power the UAV and electronics. Recent studies, performed by NASA for a more electric commercial aircraft, evaluated SOFCs for auxiliary power units (APUs). System studies were also conducted for regenerative RSOFC systems. One common requirement for aerospace SOFCs and RSOFCs, determined independently in each application study, was the need for high specific power density and volume density, on the order of 1.0 kW/kg and greater than 1.0 kW/L. Until recently the best reported performance for SOFCs was 0.2 kW/kg or less for stacks. NASA Glenn is working to prototype the light weight, low volume BSC design for such high specific power aerospace applications

NASA Glenn high temperature EB-coated CVI SiC/SiC minicomposite testing and characterization

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Mechanical Behavior of Sapphire Reinforced Alumina Matrix Composites at Elevated Temperatures

Zirconia coated sapphire reinforced alumina matrix composites have been tested both after heat treatment to 1400 C and at temperatures ranging from 800 C to 1200 C in. air. Interfacial shear stress has also been measured with fiber pushout tests performed in air at room temperature, 800 C and 1OOO C. Matrix crack spacing was measured for the tensile tested composites and used to estimate interfacial shear stress up to 1200 C. Electron microscopy was used to determine the source of fiber fracture and to study interfacial failure within the composite

Cultural difference and adaptation of communication styles in computer-mediated group brainstorming

Supporting creativity via collaborative group brainstorming is a prevalent practice in organizations. Today’s technology makes it easy for international and intercultural group members to brainstorm together remotely, but surprisingly little is known about how culture and medium shape the underlying brainstorming process. In a laboratory study, we examined the influences of individual cultural background (American versus Chinese), group cultural composition (same- versus mixed-culture groups), and communication medium (text-only versus video-enabled chatrooms) on group brainstorming conversations. Cultural differences and adaptation in conversational talkativeness and responsiveness were identified. The text-only medium reduced cultural differences in talkativeness. Working in a mixed-culture group led to cultural adaptation in the communication style of Chinese but not American participants. We discuss implications for international group brainstorming. Author Keywords Cross-cultural communication, group brainstorming

Freeze-cast yttria-stabilized zirconia pore networks: Effects of alcohol additives

Freeze casting yttria-stabilized zirconia (YSZ) can be useful in making electrodes for solid oxide fuel cells (SOFCs) by introducing hierarchical porosity to increase triple-phase boundary (TPB) area while maintaining adequate fuel flow. In this study the influence of alcohol additives on pore structure of aqueous YSZ freeze-cast samples was investigated. Slurries with ethanol, iso-propyl alcohol, or methanol as additives were compared to a control sample. Pore characteristics along sample lengths were measured using X-ray computed tomography reconstructions. The control sample showed significant changes in pore size along sample length, whereas pore size of the alcohol additive samples remained similar, indicating that freezing rates of the additive samples remained constant during solidification. Ice lens formation and interactions between alcohols and slurry functional additives (dispersant, surfactant, and binder) resulted in complex pore structures which show promise in increasing SOFC TPB area