http://hdl.handle.net/1721.1/7678 http://hdl.handle.net/1721.1/44825 Processing factors contributing to growth and decline in the steel industry Dufalla, Michele (Michele Helene) During the second half of the twentieth century, a technological shift occurred in the steel industry. A different mix of refining and melting furnaces were used, with increasing use being made of basic oxygen and electric arc furnaces as compared to the basic open hearth. Additionally, continuous casting began to replace ingot casting. Iron ore price, scrap steel price and electricity price were examined as predictor variables for these technological shifts. For the furnace shift, iron ore price and scrap steel price seemed to play a role, though much smaller than the role of time. For the casting shift, only time seemed to be correlated. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. Includes bibliographical references (p. 16-17). http://hdl.handle.net/1721.1/44821 Interdiffusivity in titanium-tantalum alloys processed at 1473 K Dibbern, Jennifer C Titanium-tantalum (Ti-Ta) alloys are likely to have a high biocompatibility and corrosion resistance that renders them novel materials of interest for biomedical applications[7, 14, 2]. With high strength and a low elastic modulus, Ti-Ta alloys have attracted attention as candidates for such uses as hip replacements[2]. A current challenge impeding use of these alloys is that, with a melting temperature of 3269 K, homogeneous alloys involving Ta are difficult to produce by conventional melting practice[3]. The objective of this work was to, as most structural changes occur via diffusion, gain insight into this matter through determination of the interdiffusivity in Ti-Ta alloys. A scanning electron microscope was utilized to perform energy dispersive x-ray analysis on Ti-Ta alloy samples in the range of 20 to 60 weight percent (wt %) Ta. A computational model that employed Fick's Second Law was used to extract interdiffusivity values from the data. Interdiffusivity values, which ranged from 4.0. 10-13-Tfor 20 wt % Ta to 3.0. 0-14- for 60 wt % Ta, exhibited a systematic variation with composition. The interdiffusion coefficient was seen to decrease with increasing weight fraction Ta. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. Includes bibliographical references (leaves 33-34). http://hdl.handle.net/1721.1/44819 Design of a CMOS compatible, athermal, optical waveguide Fernandez, Luis Enrique, S.B. Massachusetts Institute of Technology This paper explores a possible design for a CMOS compatible, athermal, optical waveguide. The design explored is a slot waveguide with light guided in the low index material. A design paradigm is proposed which shows the relationship between cross-sectional parameters and their impact on both the effective index of refraction and the thermo-optic coefficient of the device. Two materials choices were explored to serve as the low index material, poly(ether imide) (PI) and poly(methyl methacrylate) (PMMA). The slot waveguide with PI as the low index material had a simulated, device thermo-optic coefficient of -8.5 x 10-4K-1, and the slot waveguide with PMMA as the low index material had a simulated, device thermo-optic coefficient of 1.7 x 10-5K-1. Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. Includes bibliographical references (p. 49). http://hdl.handle.net/1721.1/44818 Fabrication of InGaP LEDs on a graded buffer substrate Martínez, Josué F Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. Includes bibliographical references (leaf 33).