Investigation of solid-liquid interactions in high temperature metal-ceramic systems

Studio delle interazioni solido-liquido in sistemi metallo-ceramico testati ad alta temperatur

Microgravity Science and Applications. Program Tasks and Bibliography for FY 1993

An annual report published by the Microgravity Science and Applications Division (MSAD) of NASA is presented. It represents a compilation of the Division's currently-funded ground, flight and Advanced Technology Development tasks. An overview and progress report for these tasks, including progress reports by principal investigators selected from the academic, industry and government communities, are provided. The document includes a listing of new bibliographic data provided by the principal investigators to reflect the dissemination of research data during FY 1993 via publications and presentations. The document also includes division research metrics and an index of the funded investigators. The document contains three sections and three appendices: Section 1 includes an introduction and metrics data, Section 2 is a compilation of the task reports in an order representative of its ground, flight or ATD status and the science discipline it represents, and Section 3 is the bibliography. The three appendices, in the order of presentation, are: Appendix A - a microgravity science acronym list, Appendix B - a list of guest investigators associated with a biotechnology task, and Appendix C - an index of the currently funded principal investigators

Wet chemical synthesis of nano and submicron Al particles for the preparation of Ni and Ru aluminides

Aufgrund ihrer großen Oberfläche besitzen Nanopartikel eine im Vergleich zu Mikropartikeln stark erhöhte Reaktivität. Während diese beispielsweise bei Thermiten in Form von Nanothermiten bereits ausgenutzt wird, ist ihre Verwendung zur Herstellung von Aluminiden unüblich. Zur Herstellung von Nanopartikeln haben sich unter anderem nasschemische Methoden etabliert. Diese Arbeit soll daher die Eignung nasschemisch hergestellter Nanopartikel zur Synthese von binären Ni and Ru Aluminiden untersuchen. Dazu wurde zunächst die nasschemische Synthese von Al Partikeln untersucht. Es wurde eine Methode zur Synthese von Al-Partikeln mit Größen von 100 – 150 nm mittels thermischer Zersetzung von Triisobutylaluminium entwickelt. Bei der Synthese mittels katalytischer Zersetzung von Alanen wurde der Einfluss der Reaktionsparameter auf die die Größe und Morphologie der Partikel systematisch untersucht. Um eine gute Durchmischung und einen guten Partikelkontakt zu erreichen wurde zur Synthese von binären Aluminiden eine Eintopfsynthese entwickelt. Dabei erfolgte zunächst die Synthese von Al Partikeln mittels Zersetzung von Triisobutylaluminium, bevor das zweite Metall durch Zersetzung einer geeigneten Vorstufe, wie Bis(cycloocta-1,5-dien)nickel(0) oder Ru3(CO)12, eingebracht wurde. Verglichen mit Systemen aus getrennt hergestellten Partikeln konnten diese Gemische durch thermische Behandlung mit höheren Umsätzen und niedrigeren Onsettemperaturen zu den jeweiligen Aluminiden umgesetzt werden.Due to their large surface, nanoparticles are exhibiting a highly increased reactivity compared to microparticles. While this is for example already exploited in the field of thermites in the form of nanothermites, their application for the preparation of aluminides is uncommon. Amongst others, wet chemical methods have been established for the preparation of nanoparticles. Thus, this work studies the suitability of wet chemically prepared nanoparticles for the preparation of binary Ni and Ru aluminides. The wet chemical synthesis of Al particles was studied. A method for the preparation of Al particles with sizes of 100 – 150 nm via a thermal decomposition of triisobutylaluminum was developed. Within the catalytic decomposition approach, the influence of the reaction parameters on the size and morphology of the resulting particles was systematically studied. To ensure a good intermixing and a good particle contact, a one-pot synthesis protocol was developed for the preparation of binary aluminides. Within this protocol, Al particles were prepared via a decomposition of triisobutylaluminum followed by the decomposition of a suitable precursor of the additional metal, such as bis(cycloocta-1,5-diene)nickel(0) or Ru3(CO)12. Compared to samples prepared from separately synthesized particles, these mixtures were reacted with increased yields as well as lower onset temperatures to the respective aluminides by a thermal treatment

Microgravity Science and Applications Program Tasks, 1984 Revision

This report is a compilation of the active research tasks as of the end of the fiscal year 1984 of the Microgravity Science and Applications Program, NASA-Office of Space Science and Applications, involving several NASA centers and other organizations. The purpose of the document is to provide an overview of the program scope for managers and scientists in industry, university, and government communities. The report is structured to include an introductory description of the program, strategy and overall goal; identification of the organizational structures and people involved; and a description of each research task, together with a list of recent publications. The tasks are grouped into six categories: (1) electronic materials; (2) solidification of metals, alloys, and composites; (3) fluid dynamics and transports; (4) biotechnology; (5) glasses and ceramics; and (6) combustion

Reconfigurable Periodic Porous Membranes & Nanoparticle Assemblies

The thesis here will cover two parts of my research. The focus of the first part of the thesis will be using responsive hydrogel materials to manipulate the pattern transformation at microscale (Chapter 3-5), and meanwhile using the finite element method (FEM) to guide new designs of the periodic porous structures that can undergo controlled pattern transformation processes (Chapter 6). In beginning, I design fabrication methods of micro-structures from responsive hydrogel materials via micro-/nano- imprinting. The responsiveness of the hydrogels is introduced by incorporating responsive monomers into the hydrogel precursors. Here, the responsiveness of the hydrogel leads to the tunable swelling ratio of the hydrogel under external stimuli, e.g. pH, temperature, and variation of humidity, so that the imprinted nano-/micro- structures can be dynamically controlled. Later, upon using FEM simulation, we design and experimentally test the deformation and mechanical properties of the periodic porous membranes based on different collapsing modes of kagome lattices. The experiments are performed at macroscopic scale taking advantage of powerful 3D printing prototyping. As the deformation phenomenon is scale independent, the observed phenomenon is applicable to predict the deformation of the micro-structures. In the second part of the thesis, we investigate two colloidal assembly systems. First (Chapter 7-8), we utilize the new form of silica nanoparticles with chain-like morphology to generate sharp nanostructures on the coating surface that minimize the contact between liquid and solid phase, and thus improve dramatically the water repellency on the coating surfaces. The stability test of the superhydrophobicity against hydrodynamic/hydrostatic pressure, low surface tension liquid, and vapor phase condensation, are also investigated for a complete interpretation of the wetting behavior. Secondly (Chapter 9), I design colloidal suspensions matching the inter-particle interactions with those used in theoretical study of colloidal assembly within the confined the space. The beauty of the system is that the colloidal suspension can be cross-linked and lock the assembled structures, so that the assembled structure can be observed under electron microscope and compare to theory and simulation. So far, a good consistence has been observed, indicating a validated design of the systems

ICCG-10: Tenth International Conference on Crystal Growth. Oral presentation abstracts

Oral presentation abstracts from the tenth International Conference on Crystal Growth (ICCG) (Aug. 16-21, 1992) are provided. Topics discussed at the conference include superconductors, semiconductors, nucleation, crystal growth mechanisms, and laser materials. Organizing committees, ICCG advisory board and officers, and sponsors of the conference are also included

Molten Core Fabrication of Bismuth-Containing Optical Fibers

Glass optical fibers have generated significant commercial and research interest in the fields of communications, lasers and sensors since their successful development in the 1970s. Since then, higher performing optical fibers have arisen due to new and evolving demands necessitating the community to occasionally rethink the materials from which optical fibers are made. Although chemical vapor deposition (CVD)-based methods dominate due to their ability to make extremely low loss optical fiber, it is limited in the range of materials, hence properties, that can be brought to bear on modern problems. Accordingly, the method for fiber fabrication has proven to be a very useful technology from which fruitful knowledge and fiber performance has emerged. Not only does this technique allow the study of new and unusual glass optical fibers but it has also provided the opportunity of fabricating crystalline core analogs as well. Crystals, because of their regular structure, are very attractive fiber waveguide materials; particularly for electro-optic functionalities. The fabrication of crystalline oxide core phases using the molten core method is further intriguing because of the high quench speed (~m/min compared to mm/h for standard conventional crystal fiber growth techniques), which usually leads to amorphous phases. The possibility of fabricating both phases (crystals and glasses) whilst using conventional optical fiber drawing techniques is thus an attractive feature of the molten core method. The thermodynamic-kinetic interplay offered by said method is the central topic of this dissertation. The questions of where does the thermodynamic takes over the kinetics when one draws fibers using the molten core method? and can one control crystal formation during fiber draw? will be investigated. For that purpose, the bismuth germanate and bismuth silicate system will be explored for their interesting electro-optic and nonlinear optic phases (Bi4Ge3O12/Bi4Si3O12 crystals and bismuth oxide glass). Chapter I provides a background on optical fiber history and the principal optical fiber fabrication techniques. Additionally, the fundamental origin of nonlinearities in materials are described as are a few nonlinear applications. Chapter II investigates the fabrication of Bi4Ge3O12 (BGO) crystalline core fibers in borosilicate glass cladding. Phase pure BGO crystalline core fibers were demonstrated. It is shown that one needs to control the inherent core-clad interaction, which incorporates glass cladding compounds and prevents one to retain a stoichiometric melt in order to obtain a single phase. Nonetheless, the glass cladding compounds (SiO2 notably) are found incorporated into the crystal structure and do not prevent the crystallization processes from taking place. Chapter III explores the understanding of eulytine crystal formation during fiber draw in borosilicate and soda-lime silicate glass claddings. Homogeneous nucleation is investigated and refuted as a crystallization mechanism. Instead, heterogeneous nucleation is demonstrated as a pathway for crystal growth. The reaction 2Bi2SiO5 + SiO2 → Bi4Si3O12 for crystal growth is also considered but could not be identified as the mechanism. Chapter IV studies the necessary processing conditions using the molten core method in order to fabricate bismuth-containing glass optical fibers. The materials’ processing conditions are shown to affect the fiber core structure, where a low density precursor powder is necessary to achieve a glass core phase as a result of a volume expansion effect. Furthermore, it is found that fibers fabricated from a borosilicate glass cladding are impractical due to cracks as a result of the CTE mismatch between core and cladding, and, soda-lime silicate glass cladding provides a better match. Finally, the thermo-reduction behavior of bismuth oxide is studied and it is shown that bismuth metallic nanoparticles are formed during fiber draw. The use of an oxidizing agent such as CeO2 is shown to have no relevant impact on the formation of these nanoparticles

Microgravity Science and Applications: Program Tasks and Bibliography for Fiscal Year 1996

NASA's Microgravity Science and Applications Division (MSAD) sponsors a program that expands the use of space as a laboratory for the study of important physical, chemical, and biochemical processes. The primary objective of the program is to broaden the value and capabilities of human presence in space by exploiting the unique characteristics of the space environment for research. However, since flight opportunities are rare and flight research development is expensive, a vigorous ground-based research program, from which only the best experiments evolve, is critical to the continuing strength of the program. The microgravity environment affords unique characteristics that allow the investigation of phenomena and processes that are difficult or impossible to study an Earth. The ability to control gravitational effects such as buoyancy driven convection, sedimentation, and hydrostatic pressures make it possible to isolate phenomena and make measurements that have significantly greater accuracy than can be achieved in normal gravity. Space flight gives scientists the opportunity to study the fundamental states of physical matter-solids, liquids and gasses-and the forces that affect those states. Because the orbital environment allows the treatment of gravity as a variable, research in microgravity leads to a greater fundamental understanding of the influence of gravity on the world around us. With appropriate emphasis, the results of space experiments lead to both knowledge and technological advances that have direct applications on Earth. Microgravity research also provides the practical knowledge essential to the development of future space systems. The Office of Life and Microgravity Sciences and Applications (OLMSA) is responsible for planning and executing research stimulated by the Agency's broad scientific goals. OLMSA's Microgravity Science and Applications Division (MSAD) is responsible for guiding and focusing a comprehensive program, and currently manages its research and development tasks through five major scientific areas: biotechnology, combustion science, fluid physics, fundamental physics, and materials science. FY 1996 was an important year for MSAD. NASA continued to build a solid research community for the coming space station era. During FY 1996, the NASA Microgravity Research Program continued investigations selected from the 1994 combustion science, fluid physics, and materials science NRAS. MSAD also released a NASA Research Announcement in microgravity biotechnology, with more than 130 proposals received in response. Selection of research for funding is expected in early 1997. The principal investigators chosen from these NRAs will form the core of the MSAD research program at the beginning of the space station era. The third United States Microgravity Payload (USMP-3) and the Life and Microgravity Spacelab (LMS) missions yielded a wealth of microgravity data in FY 1996. The USMP-3 mission included a fluids facility and three solidification furnaces, each designed to examine a different type of crystal growth