Knowledge of the structural arrangement of the atoms in a solid is an important prerequisite to a detailed understanding of physical and chemical properties. In this work, structural investigations of phosphate (Ca-P-O) and aluminofluorophosphate (Na/Ba-Al-P-O-F) glasses with and without nitridation were performed. Nitrogen was introduced via metal nitrides (AlN, Ba₃N₂, or Ca₃N₂) or ammonia gas treatment of the melt. These glasses were characterized by chemical, thermal and optical techniques. Infrared, Raman, and MASS NMR spectroscopies were used to determine the local coordination and atomic structure of these glasses. The presence of peaks corresponding to P-O-P and PO₂ molecular vibrations in Ca-P-O glasses provided a basis for proposing a calcium metaphosphate glass structure comprised of long chains. As calcium oxide is added to calcium metaphosphate glasses, the long chains are broken up into shorter pyrophosphate units, as indicated by the presence of PO₃²⁻ terminal groups. MASS NMR of Ba-Al-P-O glasses showed that Al occurs as Al(4), Al(6), and either Al(5) or Al(6) linked through Al-O-Al bonds (such as in α-Al₂O₃). The addition of F in both the Ba-Al-P-O-F and Na-Al-P-O-F systems increases the relative abundance of Al(6). The ³¹P peak maxima in the MASS NMR spectra at about -5 to -10 ppm for Ba-Al-P-O-F-N glasses and -9 to -17 for Na-Al-P-O-F-N glass, indicate that pyrophosphate units dominate the structure of these glassy solids. Raman spectroscopy of a series of Al(PO₃)₃-NaF glasses showed that an increase in NaF content causes a shortening of the P-O-P chains and a more disrupted structural network. The presence of P-O-F units were observed only at the higher (>80 mole %) NaF contents. While the complexity of the Raman spectra make it difficult to confirm the presence of P-N bonding, glasses prepared in an ammonia atmosphere (nitrogen content of 1.6 wt%) suggest the possibility of P-N bonding on the basis of a vibrational peak at 826 cm⁻¹.

The aim of this study was to investigate the electrochemical and electrocatalytic properties of a selection of glassy alloys for the hydrogen evolution reaction in base. The glassy alloy compositions tested included the known alloys Fe67Co18B14Si1, Co66Fe4Si16B12Mo2, Fe40Ni40B20 and Fe40Ni40P14B6 and an entirely new alloy Zr74Ti19Cu2Fe5. The electrochemical techniques employed were cyclic voltammetry and slow sweep polarisation. Electrochemical techniques were used in conjunction with the surface analysis techniques of scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDS) to gain insight into the morphology and chemical compositions of the electrode surfaces after various treatments. The aims included: 1) To obtain an understanding of the field of electrochemistry of glassy alloys. 2) To develop systems, techniques and procedures to enable the testing of a new alloy to be performed with confidence. 3) To this end, techniques were firstly developed and then compared with published data on the known alloys. Once the handling techniques were satisfactory the new and previously untested Zr74Ti19Cu2Fe5 glassy alloy was characterised, in particular its catalytic properties and its corrosion resistant properties were investigated. The physical properties of the Zr74Ti19Cu2Fe5 alloy are under investigation by another group in the School of Physics. My findings are presented here. The corrosion resistance of the alloys was determined in their as-polished state and after surface pretreatment from slow sweep anodic polarisation studies and cyclic voltammetry. Glassy Fe67Co18Bl4Si1 and Co66Fe4Si16B12Mo2 displayed the poorest corrosion resistance of the alloy compositions tested. The anodic polarisation curve of the Zr74Ti19Cu2Fe5 alloy produced no active region and displayed potentially excellent anticorrosive properties in the basic media which was attributed to highly passivating Zr oxide and Ti oxide surface films. The electrocatalytic activity of the glassy alloys for hydrogen evolution was evaluated in 1MKOH. Cathodic polarisation curves were used to construct Tafel plots from which the kinetic Tafel parameters, i0 and b, were calculated. The least corrosion resistant glassy alloy compositions, Fe67Co18B14Sil and Co66Fe4Si16B12Mo2, displayed the highest catalytic activity for hydrogen evolution in the as-polished state. The most corrosion resistant alloy, Zr74Ti19Cu2Fe5, showed the poorest catalytic activity for the reaction in the as-polished state and only a slight improvement was obtained by increasing the electrolyte temperature in comparison to the other alloys tested. This was again attributed to passivating Zr oxide and Ti oxide surface layers that inhibited the HER. It was found that the Zr-based alloy displayed no substantial advantages over the other glassy alloys or more expensive noble metal surfaces in basic media, unless pre-treated as described in this thesis. The influence of ex situ chemical pretreatment on the electrocataytic activity of the glassy alloys for the HER was determined using pure HF and HF/HNo3 mixtures. Acid pretreatment of glassy C066Fe4SiI6B12M02 and Fe40Ni40Pl4B6 with IM HF/lM HN03 (10 minutes) and Zr74Til9Cu2Fe5 with 1M HF (10 seconds) resulted in a significant improvement in the activity of the alloys in comparison to their as-polished state. SEM/EDS analysis indicated that preferential dissolution of a P-enriched surface region on the Fe40Ni40P14B6 electrode created a porous structure with a greatly enlarged surface area at which the HER could occur. In comparison, the P-free, Fe40Ni40B20, composition displayed a much lower improvement in activity after acid pretreatment with only slight surface roughening observed. The Zr component of glassy Zr74Ti19Cu2Fes was selectively leached by acid pretreatment to produce a porous surface, however, the corrosion resistance of the alloy was also reduced, as indicated from anodic polarisation curve that showed an active and passive region of greater current density than the as-polished electrode. Hence the beneficial effect of acid pretreatment in activating the alloy surface for the HER was countered by a reduction in the general corrosion resistance of the alloy. In view of the dramatic effect on the HER shown by prior ex situ (acidic) oxidation of the glassy alloy surface, the influence of in situ (anodic) oxidation in the basic medium was investigated for comparison. For all the glassy alloy compositions tested, anodic activation was found to be less effective than acidic activation. Anodic pretreatment of glassy Zr74Ti19Cu2Fe5 (3000µA.cm-2) resulted in the greatest improvement in activity in comparison to the as-polished state out of the alloy compositions tested. In addition, the corrosion resistance of the alloy was not reduced by anodic pretreatment and consequently formed a less destructive activation procedure than acidic pretreatment. In this regard, anodic pretreatment would produce a more durable electrocatalyst and is the preferred technique for activating the glassy alloy surfaces for the HER. Initial characterisation of the surface deposits formed by anodic oxidation, using SEM and EDS techniques, indicates that the composition of these deposits and the mechanism by which anodic activation activates the glassy alloy surfaces requires further investigation. / Thesis (M.Sc.)-University of Natal, Durban, 1999.

by Tong Kwok Wang. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1990. / Bibliography: leaves 71-74. / Acknowledgement / Abstract / Chapter 1. --- Introduction / Chapter 1.1 --- General Introduction --- p.1 / Chapter 1.2 --- Properties --- p.5 / Chapter 1.3 --- Background of this research --- p.10 / Chapter 1.4 --- The Present Experiment --- p.11 / Chapter 2. --- Theory / Chapter 2.1 --- Conduction Mechanism --- p.15 / Chapter 2.2 --- Temperature Dependence of Thermal Conductivity --- p.16 / Chapter 2.3 --- Phonon Conductivity and phonon mean free path --- p.20 / Chapter 3. --- Experimental / Chapter 3.1 --- Thermal Diffusivity by Laser Photothermal Radiometry --- p.22 / Chapter 3.2 --- Resistivity Measurement --- p.30 / Chapter 3.3 --- Sample Preparation --- p.36 / Chapter 3.4 --- Data Analysis --- p.37 / Chapter 4. --- Results and Discussion / Chapter 4.1 --- Thermal Conductivity --- p.41 / Chapter 4.2 --- Electronic Thermal Conductivity --- p.47 / Chapter 4.3 --- Phonon Thermal Conductivity --- p.52 / Chapter 4.4 --- Phonon Mean Free Path --- p.58 / Chapter 5. --- Conclusion and Suggestions for Further Work --- p.68 / References --- p.71 / Appendixes --- p.75

by Chua Lai Fei Joseph. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references. / by Chua Lai Fei Joseph. / ACKNOWLEDGMENTS --- p.2 / ABSTRACT --- p.3 / Chapter CHAPTER 1: --- INTRODUCTION --- p.5 / Chapter 1.1 --- METALLIC GLASS --- p.5 / Chapter 1.2 --- SOLIDIFICATION PROCESS OF AN ALLOY --- p.7 / Chapter 1.2.1 --- COOLING PATH --- p.7 / Chapter 1.2.2 --- FREE VOLUME MODEL --- p.8 / Chapter 1.2.3 --- NUCLEATION --- p.9 / Chapter 1.2.4 --- LIQUID PHASE SEPARATION --- p.10 / Chapter 1.3 --- IDEAS ON SOME CHARACTERISTIC PARAMETER OF GLASS AND GLASS FORMING ABILITY OF AN METALLIC ALLOY --- p.11 / Chapter 1.3.1 --- CORRELATION FOR THE EXPANSION COEFFICIENT AND THE GLASS TRANSITION TEMPERATURE --- p.11 / Chapter 1.3.2 --- CORRELATION FOR THE GLASS FORMING ABILITY WITH CRYSTALLINE COMPOUNDS/SOLID-SOLUTIONS --- p.12 / REFERENCES --- p.13 / Chapter CHAPTER 2: --- EXPERIMENTAL --- p.17 / Chapter 2.1 --- SAMPLE PREPARATION --- p.17 / Chapter 2.2 --- EXPERIMENTAL DETAILS FOR ALPHA MEASUREMENT --- p.17 / Chapter 2.3 --- EXPERIMENTAL DETAILS FOR FINDING EQUILIBRIUM PHASES AND GLASS FORMING ABILITY OF AN ALLOY --- p.20 / Chapter 2.3.1 --- FINDING EQUILIBRIUM PHASES --- p.20 / Chapter 2.3.2 --- FINDING GLASS FORMING ABILITY --- p.21 / Chapter CHAPTER 3: --- CORRELATION FOR THERMAL EXPANSION COEFFICIENTS OF MOLTEN GLASS FORMING SYSTEMS --- p.28 / REFERENCES --- p.37 / Chapter CHAPTER 4: --- CORRELATION FOR THE GLASS FORMING ABILITY OF PD83.5-XCUXSI16.5 WITH CRYSTALLINE COMPOUNDS/SOLID- SOLUTIONS --- p.38 / Chapter 4.1 --- INTRODUCTION --- p.39 / Chapter 4.2 --- EXPERIMENTAL --- p.39 / Chapter 4.3 --- RESULTS --- p.41 / Chapter 4.4 --- DISCUSSION --- p.43 / REFERENCES --- p.54 / Chapter CHAPTER 5: --- CONCLUSION --- p.55

Graduation date: 2005

Graduation date: 2004

Graduation date: 2004

This paper documents the investigation into injection molding, or die casting, a bulk metallic glass (BMG). A BMG is an amorphous metal of a thickness greater than 25 ��m, according to leading researchers in the field. This critical thickness differentiates a normal metallic glass from a "bulk" metallic glass. The impetus for studying the ability to process lies in the material properties of the BMG, which has twice the strength of steel and the ability to be formed much like a thermoplastic. An initial discussion of processing options and history precedes a detailed description of the machine concept and design, including the governing parameters placed on the design. An account of methods and materials used has been included, along with problems encountered and resultant remedies. The initial results consist of the verification of the machine concept and the ability to replicate nanometer-sized surface features from a mold. Design issues are addressed and the corresponding revisions described. The final machine revision shows an increase in process repeatability. A presentation of photographs, which show results of forming the BMG against both copper and stainless steel, is offered as a qualitative assessment of the processing capability. A discussion of considerations and paths forward has been included for future research using the machine that was developed, but these processing theories could also be carried over to other experiments. In the end, this study proves the ability to form extremely small surface features in cast BMG parts and makes suggestions on research avenues that may give a better understanding of the variables involved in processing BMG from the molten state. / Graduation date: 2003

By the investigation of the bulk metallic glass-forming liquids that have very low critical cooling rates, the thermodynamics of metallic glasses can be clarified. For studying thermodynamic properties, such as the specific heat capacity, calorimetry (DSC) is utilized and one of the most used instruments is the differential scanning calorimeter. In this study calorimetry was used to investigate the thermodynamics of the Pd������Ni������Cu������P������ alloy. The specific heat capacity of the liquid and crystalline state, enthalpy, entropy, as well as Gibbs free energy difference between the liquid and crystalline state were measured and evaluated in comparison with previous studies of the alloy. The Pd������Ni������Cu������P������ alloy is known as a metallic glass-forming alloy that has high ability for vitrification without crystallization. By observing the onset of heat flux of the exothermic reactions in the DSC, the time-temperature-transformation diagram can be constructed, and the diagram confirms the high ability for the vitrification for the sample. In addition, the effect of fluxing by B���O��� to reduce heterogeneous nucleation is determined by the TTT-diagram. The enthalpy change during the crystallization was directly measured in experiments in which the sample was held isothermally in the DSC. Both enthalpies, calculated from the specific heat capacity measurements and direct measured enthalpy exactly match each other. The very interesting effect in these experiments is an effect of heat treatment in the samples. Two glass transition temperatures can be noticeably recognized by scanning the exothermic event of the sample with the DSC. The material separates into two undercooled liquids. The two phases that are separated during heat treatment can be described by two different fragility parameters. / Graduation date: 2001

This paper summarizes a recently developed continuum theory for the elastic-viscoplastic deformation of amorphous solids such as polymeric and metallic glasses. Introducing an internal-state variable that represents the local free-volume associated with certain metastable states, we are able to capture the highly non-linear stress-strain behavior that precedes the yield-peak and gives rise to post-yield strain-softening. Our theory explicitly accounts for the dependence of the Helmholtz free energy on the plastic deformation in a thermodynamically consistent manner. This dependence leads directly to a backstress in the underlying flow rule, and allows us to model the rapid strain-hardening response after the initial yield-drop in monotonic deformations, as well as the Bauschinger-type reverse-yielding phenomena typically observed in amorphous polymeric solids upon unloading after large plastic deformations. We have implemented a special set of constitutive equations resulting from the general theory in a finite-element computer program. Using this finite-element program, we apply the specialized equations to model the large-deformation response of the amorphous polymeric solid polycarbonate, at ambient temperature and pressure. We show numerical results to some representative problems, and compare them against corresponding results from physical experiments. / Singapore-MIT Alliance (SMA)