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

A eutectic in La-rich La-Cu₀.₅Ni₀.₅-Al alloys was determined by studying the melting behaviors and the microstructure observations. The microstructures of the La-Cu-Ni-Al alloys prepared by Bridgman Solidification and copper mould casting were studied by using scanning electron microscope (SEM). The results show that La₆₆[Cu₀.₅Ni₀.₅]₂₀Al₁₄ alloy is very near to a pseudo-ternary eutectic. When the cooling rate is higher than 450 K/s, fully amorphous can be formed; when the cooling rate is within 15 K/s to 450 K/s, the alloy has a microstructure of dendrite plus amorphous, when the cooling rate is within 12 K/s to 1.5 K/s, the microstructures of the alloy are dendrite plus eutectic, and when the cooling rate is lower than 0.12 K/s, the morphology of the alloy is eutectic microstructure. The off eutectic alloy has better glass forming ability, the best glass forming alloy obtained at La₆₂[Cu₀.₅Ni₀.₅>]₂₄Al₁₄ along the composition line of La₈₆₋x[Cu₀.₅Ni₀.₅]xAl₁₄. It has a potential to form bulk metallic glassy rod samples with diameter larger than 12 mm. / Singapore-MIT Alliance (SMA)

Silver containing chalcogenide glasses have been extensively studied during the last few decades; the main interest in these materials being their electrical conductivity which changes by several orders of magnitude upon silver doping. Glassy chalcogenides doped with silver have applications in optical elements, gratings, micro-lenses, waveguides, bio & chemical sensors, solid electrolytes, batteries, etc. Chalcohalide glasses have become important in the recent times, from both scientific & technological points of view, due to the interesting properties exhibited by these glasses such as the transparency in the infrared region, the stability against devitrification, solubility of rare earth elements, etc. In this thesis work, the thermal properties and electrical switching behavior of certain silver and iodine doped chalcogenide glasses have been investigated The thesis contains five chapters: Chapter 1: This chapter is an introduction to the fundamental aspects of amorphous semiconductors with a particular reference to chalcogenide glasses. The advantages and applications of chalcogenide glasses are also described. Chapter 2: The methods of preparation and characterization of the glasses investigated are described in this chapter. Also, the details of the experiments undertaken, namely temperature modulated Alternating Differential Scanning Calorimetry (ADSC), electrical switching analysis, Photo-thermal Deflection Spectroscopy (PDS), etc, are outlined. Chapter 3: In this chapter, the thermal behavior and electrical switching of silver doped Ge-Se and As-Se chalcogenide glasses are described. Bulk, melt-quenched Se-rich Ge0.15Se0.85-xAgx glasses have been found to be microscopically phase separated and composed of Ag2Se clusters and GeSe2-Se network. When the silver concentration exceeds 10 atom %, the Ag2Se clusters embedded in the GeSe2-Se network percolate. The signature of this percolation threshold is clearly observed as the sudden appearance of two exothermic crystallization peaks in ADSC runs. Density, molar volume and micro hardness studies also strongly support the view of a percolation transition. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be connected with the silver phase percolation. It has been found that Ge0.15Se0.85-xAgx glasses of lower silver concentration (x = 0.07 and 0.08) do not exhibit electrical switching at voltages up to 1100 V. A negative resistance behavior and threshold type electrical switching is seen in Ge0.15Se0.85-xAgx samples with x 0.09. Also, fluctuations are observed in the I-V characteristics of these samples, which have been attributed to the difference in thermal conductivities between the Ag2Se inclusions and the Ge-Se base glass. A sharp drop has been observed in the switching voltage with Ag concentration which is due to the more metallic nature of silver and the presence of Ag+ ions. Further, the saturation in the decrease of VT around x = 0.10, is related to silver phase percolation in these glasses. Bulk As20Se80-xAgx glasses (0 x 15) have been found to exhibit two endothermic glass transitions and two exothermic crystallization reactions on heating. Based on which it is suggested that As20Se80-xAgx glasses are also microscopically phase separated, containing Ag2Se phases embedded in an As-Se backbone. The occurrence of microscopic phase separation in As20Se80-xAgx glasses is also confirmed by SEM studies. With increasing silver concentration, the Ag2Se phase percolates in the As-Se matrix, with a well-defined percolation threshold at x = 8. This silver phase percolation is exemplified by sudden jumps in the composition dependence of the second crystallization peak and non-reversible heat-flow, Hnr obtained at the second glass transition reaction of As20Se80-xAgx glasses. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be associated with the observed silver phase percolation. Like Ge0.15Se0.85-xAgx glasses, As20Se80-xAgx glasses also exhibit threshold type electrical switching with fluctuations in the I-V characteristics; these fluctuations have been attributed to the difference in thermal conductivities between the Ag2Se inclusions and the As-Se base glass. A sharp drop has been observed in the switching voltage with Ag concentration which is due to the more metallic nature of silver and the presence of Ag+ ions. Further, the saturation in the decrease of VT around x = 8, is found to be related to silver phase percolation in these glasses, which has been proposed on the basis of ADSC experiments. Chapter 4: The chapter 4 deals with thermal studies, electrical switching investigations and Photo-thermal Deflection Spectroscopic (PDS) measurements on certain Ge-Te-I and As-Te-I chalcohalide glasses. It has been found that the compositional variation of the glass transition temperature of Ge22Te78-xIx glasses, obtained by Alternating Differential Scanning Calorimetry (ADSC), exhibits a broad hump around 5 atom % of iodine. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy (Hnr) of Ge22Te78-xIx glasses at x = 5, which is suggestive of a thermally reversing window at this composition. Electrical switching studies on Ge22Te78-xIx glasses indicate that these glasses exhibit memory type electrical switching. At lower iodine concentrations, a decrease is seen in switching voltages with an increase in iodine content (in comparison with the base Ge22Te78 glass), which is due to the decrease in network connectivity. The increase seen in switching voltages of Ge22Te78-xIx glasses at higher iodine contents, suggests that the influence of the metallicity is stronger at higher iodine proportions. It is also interesting to note that the composition dependence of the threshold voltages shows a slope change at x = 5, the inverse rigidity percolation threshold of the Ge22Te78-xIx system. . Further, it is found that the thermal diffusivities ( D) of Ge22Te78-xIx glasses decrease with the increase in iodine content, which has been understood on the basis of fragmentation of the Ge-Te network with the addition of iodine. Also, a cusp is seen in the composition dependence of thermal diffusivity at the composition x = 5 (average coordination number, r = 2.39), which has been identified to be the inverse rigidity percolation threshold of the system at which the network connectivity is lost. ADSC studies on As45Te55-xIx chalcohalide glasses (3 x 10) reveal that there is not much variation in the glass transition temperature of As45Te55-xIx glasses, even though there is a wide variation in r . Based on this observation we suggest that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than the average coordination number. Further, the non-reversing enthalpy Hnr of As45Te55-xIx glasses is found to exhibit a sharp minimum at the composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range 5 x 7. These results indicate a narrow thermally reversing window in As45Te55-xIx glasses around the composition x = 6. As45Te55-xIx glasses have been found to exhibit a memory to threshold type change in switching behavior with iodine content (x 6), which has been understood on the basis of the sharp increase in thermal diffusivity above x = 6. It is also observed that the switching voltages do not change appreciably with composition/average coordination number. Though no pronounced signature of a stiffness transition is seen in the variation with composition of VT, fluctuations are seen in the switching voltages around x = 6, the composition corresponding to the sharp thermally revering window. PDS studies indicate that the thermal diffusivities () of As45Te55-xIx chalcohalide exhibit a sharp minimum at the composition x = 6. This result reasserts the presence of a sharp thermally reversing window in As45Te55-xIx glasses around the composition x = 6. Chapter 5: The significant results obtained in the present thesis work have been summarized in this chapter. Further, the scope for future work is also presented.

Amorphous Mg-Cu-Y metallic glasses are established by density functional theory and simulated annealing method in this study. The mechanical properties of amorphous Mg-Cu-Y metallic glasses are investigated by molecular statics simulations for the nano-indentation and the nano-scratch process. In this study, some potential energy parameters are obtained by fitting for describing the Mg-Cu-Y system. The bulk modulus, the Young¡¦s modulus and X-ray structure of the Mg-Cu-Y system are calculated. Our results are within 10% error compared with experimental values, which prove the correctness of fitted potential parameters. For the cases of nanoindentations, the indentation force-displacement and the influenced depth are calculated. The mechanical properties are obtained are close to experimental results. The both ¡§slip vector¡¨ and Honeycutt-Andemen index (HA index) parameters are also used to study the deformation behavior and bond-type of a group of atoms. Our results indicate that the influenced depths can be affected by the tip indentation and the gather of copper atoms. The gather of copper atoms can provide the resistance and strengthen the mechanical properties of Mg-Cu-Y material. On the other hand, our results indicate that the amorphous structure of Mg-Cu-Y metallic glasses cannot be transferred to crystal structure during nano-indentation process by analysis of HA index. For the cases of nano-scratch, two different scratch depth (5Å and 15Å) are investigated to understand the understand the depth effect. the scratch force-displacement curve is also obtained. As the same with nano-indentation results, the scratch force will increase because the gather of copper atoms and provide the resistance.

The objective of this research is to synthesize and characterize microstructures and some elastic properties of bioactive glasses subject to relaxation and/or devitrification treatments. We synthesize two kinds of bioglasses, i.e. P-richer 45S5 and P-poorer 55S4.3. After tempering, the as-prepared bioactive glasses are transparent, 55S4.3 being colorless while 45S5 pale pink in color. The thermal events in DTA analysis indicated that the crystallization of 45S5 and 55S4.3 starts at 620oC and 680oC, respectively. The two bioactive glasses became ivory upon heating at 715oC, and the degree of being opaque increases with dwelling time. The crystalline phase for 45S5 is Na2CaSiO4 -derived Na2Ca2Si3O9 or Na4CaSi3O9. By XRD traces and polarizing optical micrographs, we conclude that the crystal is based on simple cubic structure with a=7.5054Å and space group P213 (198). Due to poor crystallization rate, the crystal in P-poor 55S4.3 glass was not investigated in detail. However, according to the similarity of Raman spectra for devitrified 45S5 and 55S4.3, we suggest that the crystal is similar for the two devitrified glasses. Raman spectra indicated that the relaxed 45S5 has predominant Q2 and Q3 species and the Q3/Q2 ratio decreases with firing time at 715oC. As for relaxed 55S4.3, the major structural unit is Q3, and the intensity of Q3 is higher for 55S4.3 than 45S5. As the Na+/Si4+ ratio increases, the intensity of 946 (or 947) cm-1 increases while bands near 1100 cm-1 decrease. Based on the Raman spectra of devitrified 45S5 and 55S4.3, the crystals in the two glasses have a common structural unit of SiO32- (Q2). The elasticity measurement by Brillouin scattering indicated that the moduli for devitrified glass 45S5 are greater than undevitrified 45S5 and 55S4.3 glass. The elasticity of the present bioactive glasses is lower than hydroxyapatite and fluorapatite.

The mechanical properties of the amorphous bulk metallic glassy (BMG) alloy, Mg58Cu31Y11, are examined by a non-traditional analytic method - nanoindentation scratch test. This thesis will discuss the influences of friction force, and fracture surface geometry on the BMG surface for load, depth of scratch, scratch velocity, and test temperature of the nano-scratch process. In this study, experimental factors, including load, depth of scratch, scratch velocity, and test temperature, are taken into consideration to investigate the effects of the friction force. And then, this research utilizes regression analysis to establish BMG machining experience formula. The significant parameters of the friction force on nano-scratch and the reliability of the prediction model are investigated by statistical software. According to the results, the friction force is nearly proportional to power of the load. The friction force exhibits a slightly dependence on the test temperature. Besides, the nano-scratch results show that the friction coefficient also increases as the load and test temperature increases. The results associated with the analysis of the variance can be practiced to assess the prominence among experimental factors. The analysis indicates that the load, test temperature play significant factors on the friction force. The results of the regression analysis using a statistical software can be applied to model the mathematical relationship between machining factors and friction force. It anticipates that the model is able to predict friction force over a wide variety of scratching conditions. The model is also proved in good agreement with experimental results.

No description available.

Te2As3Se5 (TAS) fibers are often used in bio-sensing applications requiring direct contact between the fiber and live cells. However, the toxicity and stability of chalcogenide glasses typically used in such bio-sensing applications are not well known. The stability and toxicity of TAS glass fibers were therefore examined. The surface of TAS fibers stored for up to three years in air were analyzed using X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), and atomic force microscopy (AFM). It is shown that an oxide layer develops on the surface of TAS fibers stored in air. This oxide layer is highly soluble in water and therefore easily removed. Additional studies using cyclic voltammetry show that the fresh TAS glass surface is insoluble in water for at least a few days, and attenuation measurements show that oxidation does not affect the transmission properties of the glass fibers. It was also determined that old, oxidized fibers pose a toxic threat to cells, while washed and new fibers show no toxic effect. Therefore, it is concluded that a soluble oxide layer forms on the surface of TAS fibers stored in air and that this layer has a toxic effect on cells in an aqueous environment. However, through etching, the oxide layer and the toxicity can be easily removed.In other applications of telluride glasses, such as the search for possible signs of life on exoplanets, a glass transmitting further into the IR is required in order to detect molecules, such as CO2. A new family of Tellurium based glasses from the Ge-Te-I ternary system has therefore been investigated for use in space and bio-sensing applications. A systematic series of compositions has been synthesized in order to explore the ternary phase diagram in an attempt to optimize the glass composition for the fiber drawing and molding process. The resulting glass transition temperature range lies between 139°C and 174°C, with deltaT values between 64°C and 124°C. The most stable glass composition was found to be Ge20Te73I7. The Ge-Te-I glasses were found to have an effective transmission window between 2-20 microns, encompassing the region of interest for the identification of biologically relevant species such as carbon dioxide. Furthermore, the successful fibering and molding of the composition Ge20Te73I7 are shown. Lastly, an investigation into glass conductivity was completed resulting in a maximum conductivity value on the order of 10^-4 Ohm-1 cm-1 for the composition Ge20Te73I7.In an attempt to take advantage of the high conductivity of telluride glasses, a new approach to virus detection in an aqueous environment has been developed using the electrophoretic deposition of protein and viruses on the charged glass surface for in situ infrared characterization and identification. A proof of concept experiment has been completed using a germanium ATR plate and an indium tin oxide (ITO) plate as the experimental electrodes. Charged proteins and viruses were driven to the surface of the oppositely charged germanium ATR crystal, once a potential was applied to the system. FTIR/ATR spectroscopy was used before and throughout electro-deposition to enable the in situ observation of the deposition with time. This technique resulted in the successful deposition and removal of the protein Bovine Serum Albumin (BSA), and deposition of the virus MS2, a bacteriophage that infects only bacteria, with an applied voltage of only 1.1V. Furthermore, based on analysis of the ATR spectra, distinct spectral features were identified for the protein and virus showing the potential for identification and characterization of biological molecules in an aqueous environment. A Ge20Te73I7 ATR plate was synthesized but unsuccessfully applied as an electrode in these experiments, likely due to an inconsistent conductivity along the plate. A glass from the Ge-As-Te system with a lower but more consistent conductivity was thereafter synthesized and successfully used as an electrode and sensing element in the electro-deposition experiment.

The resistivity and thermopower of two series of amorphous alloys have been measured between 4 and 300K. The alloys studied are MgZn and CuZr, both in the largest concentration range available as amorphous materials. The alloys were measured in both the 'as made' and 'relaxed' states, as well as some partial or totally crystallized samples. The simple Ziman theory was found at variance with the experimental results in both cases (even for MgZn, proven to be free-electron like as required by the theory). A simple two component model is proposed as an extreme simplification of the Faber-Ziman theory of liquid metallic alloys. The excellent agreement obtained indicates that metallic glasses should be considered as the alloys they really are. A full Faber-Ziman calculation is performed for CuZr and from this follows the conclusion that the term containing the energy dependence of the pseudo-potential (r), usually assumed to be small, is probably of comparable magnitude to that of the disorder scattering (q). The suggested correlations between the electron-phonon mass-enhancement parameter (lamda) (determined from superconductivity experiments) and the thermopowers are studied and both found not to be valid for CuZr amorphous alloys.