Preparation of refractory cermet structures for lithium compatibility testing

High-purity nitride and carbide cermets were synthesized for compatability testing in liquid lithium. A process was developed for the preparation of high-purity hafnium nitride powder, which was subsequently blended with tungsten powder or tantalum nitride and tungsten powders and fabricated into 3 in diameter billets by uniaxial hot pressing. Specimens were then cut from the billets for compatability testing. Similar processing techniques were applied to produce hafnium carbide and zirconium carbide cermets for use in the testing program. All billets produced were characterized with respect to chemistry, structure, density, and strength properties

Petrologic and microstructural constraints on focused melt transport in dunites and the rheology of the shallow mantle

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2004Observations at mid-ocean ridges indicate that magmas are focused to the ridge axis by a network of porous dunites in near chemical isolation. This thesis investigates several of the outstanding questions regarding the mechanisms of melt transport and its effects on the shallow mantle. Chapter 1 details the current understanding of melt migration from observations at mid-ocean ridges and ophiolites. Chapter 2 uses the size distribution and abundance of dunites measured in the Oman ophiolite to place limits on the potential mechanisms by which dunites form and subsequently estimate the flux of chemically unequilbrated melt which a network of dunites can supply. Chapter 3 characterizes the chemical composition of dunites and harzburgites from Oman to further constrain the process by which dunites form and relates the observed trends within dunites to variations in the time-integrated meltrock ratio. Chapter 4 examines the microstructures of peridotites in Oman to constrain the deformation mechanisms which determine the viscosity of shallow mantle. Chapter 5 is a numerical investigation of advection beneath ridges incorporating the rheology inferred from the observed microstructures. Chapter 6 integrates the conclusions of the previous chapters, reevaluating the potential melt flux through dunites and constraining the permeabilty of the shallow mantle.Funding for my research was provided by The National Science Foundation through a Graduate Research Fellowship 2277600 and grants OCE-0118572, OCE- 9819666, EAR-0230267, EAR-9405845, OCE-9521113. Additional support was generously provided by the Woods Hole Oceanographic Institution through the Office of Academic Programs and the Deep Ocean Exploration Institute

Structure and Function of Food Products: A Review

A proper understanding of the behavior of food products requires knowledge of its structure, i.e., the spatial arrangement of the various structural elements and their interactions. The structure can properly be studied by visual observation techniques. In products such as fat spreads, creams, dressings, cheese, bread , milk , yoghurt , whipped cream, and ice cream , different structural elements can be distinguished. A number of those elements a re discussed, viz. , water droplets, oil droplets, gas cell s, particles, fat crystals and strand s. In addition examples of interactions between structural element s are presented, viz., oil droplets/matrix, protein/ protein, protein carbohydrate, and fat crystal/ fat crystal interactions. Finally, it is indicated how these elements cooperate in the formation of structure and contribute to function and macroscopic behavior of food products. Particular attention is given to fat spreads, processed cheese, protein gelation, and examples of the mutual interaction of milk proteins and of carbohydrates with milk proteins. It is expected that a proper understanding of the relation between structure and function will help us to design new ways of structuring in our continuing efforts to manufacture high quality, healthy and tasty food products

Fractal Analysis of Microstructural and Fractograpghic Images for Evaluation of Materials

Materials have hierarchically organized complex structures at different length scales. Quantitative description of material behaviour is dependent on four fundamental length scales [1], which are of concern to materials scientists. These are (1) nano scale, 1-103 nm, (2)micro scale, 1-10 3 μm, (3) macro scale, 1-103mm, and (4) global size scale, 1-106 m. While the nano scale corresponds to, often, highly ordered atomic structures, the global size scale relates geophysical phenomena and large man made engineering structures. Micro scale and macro scale correspond to size of material samples used in laboratories, for designing and for fabrication of miniature to small machineries