Effects of high pressure nitrogen on the thermal stability of SiC fibers

Polymer-derived SiC fibers were exposed to nitrogen gas pressures of 7 and 50 atm at temperatures up to 1800 C. The fiber weight loss, chemical composition, and tensile strength were then measured at room temperature in order to understand the effects of nitrogen exposure on fiber stability. High pressure nitrogen treatments limited weight loss to 3 percent or less for temperatures up to 1800 C. The bulk Si-C-O chemical composition of the fiber remained relatively constant up to 1800 C with only a slight increase in nitrogen content after treatment at 50 atm; however, fiber strength retention was significantly improved. To further understand the effects of the nitrogen atmosphere on the fiber stability, the results of previous high pressure argon treatments were compared to those of the high pressure nitrogen treatments. High pressure inert gas can temporarily maintain fiber strength by physically inhibiting the evolution of gaseous species which result from internal reactions. In addition to this physical effect, it would appear that high pressure nitrogen further improved fiber temperature capability by chemically reacting with the fiber surface, thereby reducing the rate of gas evolution. Subsequent low pressure argon treatments following the initial nitrogen treatments resulted in stronger fibers than after argon treatment alone, further supporting the chemical reaction mechanism and its beneficial effects on fiber strength

“Is it his Language?” A Neuroeducation Approach to Exploring the Connection Between Levels of Language Function and Prosocial Concepts for Elementary Students Identified with Emotional and Behavioral Disorders

Preparing students to acquire prosocial behaviors is of growing concern for educators. Although a connection between language structures and students struggling to acquire prosocial behaviors has been established, students identified with emotional and behavioral disorders (EBD) are not being consistently identified with language impairment (LI). Viewing language differently, the acquisition of language functions is theorized to play a role in the attainment of prosocial concepts resulting in prosocial behaviors. Currently, limited research exists that explores the connection between language functions and students struggling to acquire prosocial behaviors. The purpose of this study was to: (a) triangulate literature in the areas of cognitive psychology, neuroscience, and language to support a theoretical framework in neuroeducation to address the acquisition of prosocial behaviors; and, (b) apply this framework by exploring the connection between levels of language function and the acquisition of the underlying prosocial concepts through language function sampling analyses with elementary students identified with EBD and/or LI. Four methods of language sampling were used to address two main research questions: (a) What similarities and differences in language function levels and characteristics exist, if any, among varying educational levels of students with EBD, LI, and/or both? (b) Will students identified with EBD, LI and/or both make prosocial or antisocial relationships among the agents, their actions, and the context? This study of language sampling included nine participants identified with EBD and two identified with LI. Language samples were analyzed through deductive content analysis based off predefined codes from existing literature in language function. Key findings include: (a) Commensurate deficits of iv language function among participants with EBD and LI indicated by pre-language levels of language function; (b) a proclivity among the students with EBD to assign antisocial meaning to oral and cartooned responses to event-based pictures; and (c) limited production of prosocial responses from all participants to event-based pictures. The results of this study suggest the current structural methods of language assessment for educational eligibility may be inadequate among elementary students identified with EBD. The inclusion of language function measures is recommended for this student population. Additionally, this study suggests that (a) current behavioral curricula that do not factor in acquisition of language function may fail to provide the concepts necessary for acquisition of prosocial behaviors; and (b) a neuroeducation approach that considers the importance of prosocial concept acquisition may result in prosocial development

Pressure effects on the thermal stability of SiC fibers

Commercially available polymer derived SiC fibers were treated at temperatures from 1000 to 2200 C in vacuum and argon gas pressure of 1 and 1360 atm. Effects of gas pressure on the thermal stability of the fibers were determined through property comparison between the pressure treated fibers and vacuum treated fibers. Investigation of the thermal stability included studies of the fiber microstructure, weight loss, grain growth, and tensile strength. The 1360 atm argon gas treatment was found to shift the onset of fiber weight loss from 1200 to above 1500 C. Grain growth and tensile strength degradation were correlated with weight loss and were thus also inhibited by high pressure treatments. Additional heat treatment in 1 atm argon of the fibers initially treated at 1360 atm argon caused further weight loss and tensile strength degradation, thus indicating that high pressure inert gas conditions would be effective only in delaying fiber strength degradation. However, if the high gas pressure could be maintained throughout composite fabrication, then the composites could be processed at higher temperatures

Alternative Processing Method Leads to Stronger Sapphire-Reinforced Alumina Composites

The development of advanced engines for aerospace applications depends on the availability of strong, tough materials that can withstand increasingly higher temperatures under oxidizing conditions. The need for such materials led to the study of an oxide-based composite composed of an alumina matrix reinforced with zirconia-coated sapphire fibers. Because the nonbrittle behavior of this system depends on the interface and its ability to prevent fiber-to-matrix bonding and reduce interfacial shear stress, the microstructure of the zirconia must be carefully controlled during both coating application and composite processing. When it was both porous and unstabilized, zirconia (which does not react easily with alumina) was found to be the most effective material tested in reducing interfacial shear strength between the fiber and matrix

Advanced Ceramics for NASA's Current and Future Needs

Ceramic composites and monolithics are widely recognized by NASA as enabling materials for a variety of aerospace applications. Compared to traditional materials, ceramic materials offer higher specific strength which can enable lighter weight vehicle and engine concepts, increased payloads, and increased operational margins. Additionally, the higher temperature capabilities of these materials allows for increased operating temperatures within the engine and on the vehicle surfaces which can lead to improved engine efficiency and vehicle performance. To meet the requirements of the next generation of both rocket and air-breathing engines, NASA is actively pursuing the development and maturation of a variety of ceramic materials. Anticipated applications for carbide, nitride and oxide-based ceramics will be presented. The current status of these materials and needs for future goals will be outlined. NASA also understands the importance of teaming with other government agencies and industry to optimize these materials and advance them to the level of maturation needed for eventual vehicle and engine demonstrations. A number of successful partnering efforts with NASA and industry will be highlighted

Dr. Yaeger Contributes in Veterinary Diagnostic Laboratory

Seniors taking their diagnostic rotation have been seeing a new face in the Veterinary Diagnostic Laboratory. Dr. Michael Yaeger joined the Iowa State University faculty in July of 1996, has become a valued member of the diagnostic team, and has shown himself to be a talented instructor. Dr. Yaeger believes that hands-on experience enhances the learning of students and is essential for complete understanding. Students in his class spend a few hours in the morning in lecture and the rest of the day working in the necropsy lab investigating and correlating data, trying to come up with a diagnosis for specimens sent to Iowa State University

Subscale Testing of a Ceramic Composite Cooled Panel Led to Its Design and Fabrication for Scramjet Engine Testing

In a partnership between the NASA Glenn Research Center and Pratt & Whitney, a ceramic heat exchanger panel intended for use along the hot-flow-path walls of future reusable launch vehicles was designed, fabricated, and tested. These regeneratively cooled ceramic matrix composite (CMC) panels offer lighter weight, higher operating temperatures, and reduced coolant requirements in comparison to their more traditional metallic counterparts. A maintainable approach to the design was adopted which allowed the panel components to be assembled with high-temperature fasteners rather than by permanent bonding methods. With this approach, the CMC hot face sheet, the coolant containment system, and backside structure were all fabricated separately and could be replaced individually as the need occurred during use. This maintainable design leads to both ease of fabrication and reduced cost

Cooled Ceramic Composite Panel Tested Successfully in Rocket Combustion Facility

Regeneratively cooled ceramic matrix composite (CMC) structures are being considered for use along the walls of the hot-flow paths of rocket-based or turbine-based combined-cycle propulsion systems. They offer the combined benefits of substantial weight savings, higher operating temperatures, and reduced coolant requirements in comparison to components designed with traditional metals. These cooled structures, which use the fuel as the coolant, require materials that can survive aggressive thermal, mechanical, acoustic, and aerodynamic loads while acting as heat exchangers, which can improve the efficiency of the engine. A team effort between the NASA Glenn Research Center, the NASA Marshall Space Flight Center, and various industrial partners has led to the design, development, and fabrication of several types of regeneratively cooled panels. The concepts for these panels range from ultra-lightweight designs that rely only on CMC tubes for coolant containment to more maintainable designs that incorporate metal coolant containment tubes to allow for the rapid assembly or disassembly of the heat exchanger. One of the cooled panels based on an all-CMC design was successfully tested in the rocket combustion facility at Glenn. Testing of the remaining four panels is underway

Ceramic Fiber Structures for Cryogenic Load-Bearing Applications

This invention is intended for use as a load-bearing device under cryogenic temperatures and/or abrasive conditions (i.e., during missions to the Moon). The innovation consists of small-diameter, ceramic fibers that are woven or braided into devices like ropes, belts, tracks, or cables. The fibers can be formed from a variety of ceramic materials like silicon carbide, carbon, aluminosilicate, or aluminum oxide. The fiber architecture of the weave or braid is determined by both the fiber properties and the mechanical requirements of the application. A variety of weave or braid architectures is possible for this application. Thickness of load-bearing devices can be achieved by using either a 3D woven structure, or a layered, 2D structure. For the prototype device, a belt approximately 0.10 in. (0.25 cm) thick, and 3.0 in. (7.6 cm) wide was formed by layering and stitching a 2D aluminosilicate fiber weave