Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Not available / text

Thesis (M.S.)--George Mason University, 2009. / Vita: p. 164. Thesis director: Daniel Anderson. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mathematics. Title from PDF t.p. (viewed Oct. 12, 2009). Includes bibliographical references (p. 163). Also issued in print.

M.Sc. / Alloying Cr with non-magnetic Ru, results in unusual magnetoelastic effects due to strong magnetic interactions with the lattice. In the low concentration region, Ru increases the Neél temperature TN due to the enhancement of the spin density wave (SDW). The temperature dependence of the thermal expansion coefficient (a) of Cr o.997Ru0.003 displays Invar behaviour within a small temperature region (7.-: 5 K) of the magnetic transition at TN 390 K). This alloy is of little practical use since the Invar behaviour is well above room temperature. Mo, which is isoelectronic with Cr, is known to vary the strength of the SDW in Cr without changing its basic nature. It reduces and broadens the magnetic transition at TN of Cr and its alloys. Therefore Mo seems to be suitable for tayloring the Cr 0.997R110.003 alloy system, reducing the temperature region, in which the Invar effects are observed, down to room temperature. The temperature dependence of the thermal expansion and of the elastic constants were measured for (Cr i _rMor )0.997Ruo.003 and (Cri _yMoy )0.995Ru0.005 in the temperature range between 77 K and 450 K so that the effects of Mo on the Invar behaviour of Cr 0.997Ru0.003 and on the magnetoelasticity in (Cr i„Moz )0.997Ru0.003 and (Cr i _yMoy )0.995Ru0.005 could be studied. From the Invar-study we learn that although the addition of Mo to Cro.997Rno.003 succesfully decreased the Neel temperature down to room temperature, it simultaneously increased the coefficient of thermal expansion to much larger values. We were therefore not successful in our effort to improve the Invar type properties of the Cr0.997R110.003 alloy by the addition of Mo. Although the study was mainly focussed on tayloring the antiferromagnetic Invar Cr o.997Ru0.003 alloy with Mo, we also theoretically analysed the effects on the magnetoelasticity of Cr0.997Ru0.003, in terms of the temperature dependences of the thermal expansion and elastic constants in (Cri_xMox)0.997Ruo.003 and (Cri— yMoy )o.99sRuo.00s alloy systems when some of Cr atoms are replaced by those of Mo. In both Cr-Ru-Mo alloy systems, a(T) showed well defined anomalies with a minimum at the commensurate (C) SDW to paramagnetic (P) phase transition at TN and a maximum in the incommensurate (I) SDW-CSDW transition at T IC for x < 0.015 and y = 0.01. For x > 0.015, the CSDW state is completely suppressed and only the ISDW-P phase transition at TN is observed. The temperature dependence of the elastic constants in (Cri,M0x)o.997Ruo.003 with x = 0.015 and 0.07 showed only the ISDW-P phase transition, while the alloy with x = 0.007 showed both the CSDW-P at TN and a very small ISDW-CSDW transition at Ti.c . In general: Mo decreases the magnetic contributions to the volume and to the bulk modulus of Cr0.997Ru0.003 below TN . Mo completely suppresses the CSDW state of Cr0.997R11 0.003. The (Cri„Mos )0.997Ruo .003 and (Cri _yMoy )0 .995Ru0.005 show a second order phase transition at TN . Hysteresis effects were observed in (Cri—xMox)o.997Ruo.003 at the ISDW-CSDW phase transition implying a first order phase transition at T1c.. The fact that the transitions at TN are of second order, together with the effect of Mo on Cr0.997R110.003 completely suppressing the CSDW state, make it possible to theoretically analyse the temperature dependence of the magnetic contributions to the thermal expansion and elastic constants of the (Cri_xMoz)o.997Ruo.003 samples showing only the ISDW-P phase transition. From the application of the theories we learn that: There is a mutual dependence between the reduced temperature dependences of the magnetic contribution to volume expansivity, A i3(t) and to the bulk modulus, AB(t). A phenomenological thermodynamic model is found to define the temperature dependence of the magnetic contribution to the volume and to the bulk modulus quite well, for the samples showing no ISDW-CSDW, but only the ISDW-P phase transition, with an increase in temperature. The Griineisen parameters are defined reasonably well within the framework of the phenomenological approach of Fawcett and Alberts. The Mo atomic concentration dependence of the magnetic transition temperature was studied from the magnetic phase diagram of (Cri—xMos)o.997Ruo.00s alloys in terms of the two-band imperfect nesting model of Machida and Fujita. From the magnetic phase diagram: A magnetic triple point where the ISDW, CSDW and P states coexist can clearly be observed. The ISDW-CSDW, CSDW-P and ISDW-P transition boundaries were calculated. The theoretical model describes the ISDW-CSDW and CSDW-P boundaries reasonably well, while there is a significant deviation in the ISDW-P phase line which can probably be ascribed to the fact that impurity scattering effects are not incorporated into the theory.

M.Sc. (Physics) / Please refer to full text to view abstract

Due to the aluminum industry demands, a large effort has recently been devoted to the development of special alloys to be used as inert anodes for a newly designed aluminum reduction cell. The implementation of this new technology aims at the replacement of the graphite anodes that have been used for over 100 years in aluminum smelting, which would reduce fossil carbon consumption, and eliminate the emission of carbon dioxide and of perfluorocarbons. Ternary alloys containing copper, nickel, and iron have been the subject of the research activities. The present research focused on the stability of the Cu-Ni-Fe alloys at high temperatures in oxidizing and fluoridating environments. The experimental methods included thermodynamic calculations of the phase diagram ('Thermocalc'), optical microscopy and microprobe microstructural and chemical investigations (EMIPA-WDS), small-angle neutron scattering (SANS), differential thermal analysis (DTA), and air-oxidation studies. The results have led to the optimization of the Cu-Ni-Fe ternary phase diagram and to an extensive study of the thermodynamics and kinetics of the spinodal decomposition and discontinuous reactions occurring during ageing as a function of alloy composition. The oxidizing reactions occurring in air at high temperatures at the surface of the alloys have been also discussed in terms of thermodynamic and kinetic laws. The phase formation in a fluorine containing environment as encountered in an aluminum electrolytic cell is predicted using principles of physical chemistry. / Graduation date: 2004 / Best scan available. Figures in original document are very dark and have a moray pattern.

Thesis (Ph. D.)--Lehigh University, 2001. / Includes vita. Includes bibliographical references (leaves 220-228).

Thesis (M.S.)--University of Texas at El Paso, 2007. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Dr. David S. Sholl; Committee Member: Dr. Andrei G. Fedorov; Committee Member: Dr. Ronald R. Chance; Committee Member: Dr. Victor Breedveld; Committee Member: Dr. William Koros. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.Sc. (Physics)) -- University of Limpopo, 2021 / First-principles density functional theory has been used to study the stabilities of binary TiPt, TiTa, TiNi and TiCo potential shape memory alloys. Furthermore, ternary alloys Ti50Pt50-xMx with V, Ta, Hf and quaternary Ti50(PtCo)50-xTax systems were also investigated. The structural, electronic and mechanical properties were deduced to mimic the stabilities of these alloys. Furthermore, their vibrational stability, x-ray diffraction and temperature dependence have been examined. The structures were subjected to full geometry optimization to obtain equilibrium lattice constants. It was found that the equilibrium lattice parameters for all the binary systems are in good agreement with experimental results to within 5%. The heats of formation (ΔHf) were calculated to determine the thermodynamic stability of the B2 TiM systems. It was revealed that TiPt is the most energetically favourable (most stable) whereas TiTa is the least favourable due to high ΔHf value (less stable). In addition, electronic properties suggest that TiPt, TiNi and TiCo systems are stable with TiTa being the least favourable consistent with the ΔHf. The elastic properties were also calculated to mimic the mechanical stability of these alloys. TiNi, TiCo and TiTa were found to be mechanical stable whereas TiPt is unstable. This behaviour is consistent with the phonon dispersion curves for TiPt and TiCo. TiCo structure, in particular is the most stable in line with the predicted phonon dispersion. The effect of alloying on Ti50Pt50-xMx (M = V, Ta, Hf) ternary system was carried out using the supercell approach. It was observed that the lattice parameters decrease minimally with an increase in V and increases with an increase in Ta and Hf content. The structures ii become thermodynamically less stable with an increase in V, Ta and Hf content, as depicted by heats of formation. The shear modulus (C′) of Ti50Pt50-xMx increases with an increase in M (V, Ta and Hf) concentration suggesting mechanical stability of these alloys. This has been confirmed from the phonon curves where the phonon soft modes are reduced and tend to disappear with increasing content of the alloying elements. Thus the results suggest that the V, Ta and Hf addition reduces the transformation temperatures of the TiPt alloy as indicated by its higher shear modulus C′. Furthermore, it was observed that the lattice parameters of the quaternary system decrease with an increase in Ta content in the system. Thus ΔHf of the B2 and B19 Ti50Pt43.75-xCo6.25Tax and B19 Ti50Pt31.25-xCo18.75Tax alloy system showed that the 6.25 at.% Ta addition is energetically most favourable (ΔHf<0). The DOS behaviour confirms that the 6.25 at.% Ta as least favourable whereas for B19, the 6.25 at.% Ta is most favourable. The elastic constants for B19 and B2 show the positive shear modulus (mechanical stability). Moreover, the phonon dispersions and phonon density of states for the B2 and B19 Ti50Pt43.75-xCo6.25Tax and Ti50Pt31.25-xCo18.75Tax were calculated and are consistent with the elastic constant. The LAMMPS code was employed to investigate the temperature dependence of the B19 Ti50Pt43.75-xCo6.25Tax and Ti50Pt31.25-xCo18.75Tax structures. The martensitic to austenite transformation temperature decreases with an increase in Ta concentration. Temperature variations of the XRD patterns for the B19 are in reasonable agreement with predicted lattice parameters. / National Research Foundation (NRF) and Titanium centre of competence (TiCoC)