Optimisation of the performance characteristics of Cu-Al-Mo thin film resistors

This thesis presents a novel approach to the manufacture of thin film resistors using a new low resistivity material of copper, aluminium and molybdenum, which under industrially achievable optimised process conditions, is shown to be capable of producing excellent temperature coefficient of resistance (TCR) and long term stability properties. Previous developments in the field of thin film resistors have mainly centred around the well established resistive materials such as nickel-chromium, tantalum-nitride and chromium-silicon-monoxide. However recent market demands for lower value resistors have been difficult to satisfy with these materials due to their inherent high resistivity properties. This work focuses on the development and processing of a thin film resistor material system having lower resistivity and equal performance characteristics to that of the well established materials. An in depth review of thin film resistor materials and manufacturing processes was undertaken before the electrical properties of a binary thin film system of copper and aluminium were assessed. These properties were further enhanced through the incorporation of a third doping element, molybdenum, which was used to reduce the TCR and improve the electrical stability of the film. Once the desired chemical composition was established, the performance of the film was then fine tuned through optimisation of critical manufacturing process stages such as sputter deposition, heat treatment and laser adjustment. The results of these investigations were then analysed and used to generate a set of optimum process conditions, suitable for repeatedly producing thin film resistors in the 1 to 10? resistance range, to tolerances of less than ±0.25% and TCR values better than ±15ppm/oC

Joining of steel to aluminium alloys for advanced structural applications

When joining steel to aluminium there is a reaction between iron and aluminium which results in the formation of brittle intermetallic compounds (IMC). These compounds are usually the reason for the poor mechanical strength of the dissimilar metallic joints. The research on dissimilar metal joining is vast but is mainly focused on the automotive industry and therefore, the material in use is very thin, usually less than 1 mm. For materials with thicker sections the present solution is a transition joint made by explosion welding which permits joining of steel to aluminium and avoids the formation of IMCs. However, this solution brings additional costs and extra processing time to join the materials. The main goals of this project are to understand the mechanism of formation of the IMCs, control the formation of the IMCs, and understand their effects on the mechanical properties of the dissimilar Fe-Al joints during laser welding. Laser welding permits accurate and precise control of the welding thermal cycle and thereby the underpinning mechanism of IMC formation can be easily understood along with the factors which control the strength of the joints. The further goal of this project is to find an appropriate interlayer to restrict the Fe-Al reaction. The first stage of the work was focused on the formation and growth of the Fe-Al IMCs during laser welding. The understanding of how the processing conditions affect the IMC growth provides an opportunity to act and avoid its formation and thereby, to optimize the strength of the dissimilar metal joints. The results showed that even with a negligible amount of energy it was not possible to prevent the IMC formation which was composed of both Fe2Al5 and FeAl3 phases. The IMC growth increases exponentially with the applied specific point energy. However, for higher power densities the growth is more accentuated. The strength of the Fe-Al lap-joints was found to be not only dependent on the IMC layer thickness but also on the bonding area. In order to obtain sound joints it is necessary to achieve a balance between these two factors. The thermal model developed for the laser welding process in this joint configuration showed that for the same level of energy it is more efficient to use higher power densities than longer interaction iv times. Even though a thicker IMC layer is formed under this condition due to higher temperature there is also more melting of aluminium which creates a larger bonding area between the steel and the aluminium. The joint strength is thus improved ... [cont.]

Modification and Utilization of Nanoporous Gold for Loading and Release of Drugs

Nanoporous gold (np-Au) is a sponge-like structure of gold, which can be created by removing the less noble element from the precursor alloy, most typically silver or copper, using different chemical or electrochemical methods. It consists of interconnected ligaments and gaps between the ligaments, whose width can range from a few nanometers to a few hundreds of nanometers, creating a high surface area-to-volume ratio. Due to its many important properties (e.g., conductivity, high surface area-to-volume ratio, plasmonic response, biocompatibility, chemically inertness, and physically robustness), np-Au is suitable for different types of applications, including as a transducer for biosensors, in catalysis, for biomolecule separation, as a substrate for enzyme immobilization, and in drug delivery. The widths of the ligaments and gaps of np-Au can be easily tuned by varying conditions during the pre- or post-production process, for example, time kept in an acid bath and post-annealing (e.g. thermal, chemical, and electrochemical), depending on the requirement of the study. Thermal annealing is a commonly used process for tuning the ligaments and pore size of np-Au. However, the effects of thermal annealing on modification of ligaments and gaps sizes are not completely understood and more research needs to be done. Herein, we have explored the effect of annealing time and thickness of the np-Au sample on modification of ligaments and gaps. Furthermore, we used the electroless plating method to cover the pores or gaps partially on the surface without modifying the interior of np-Au. As-prepared np-Au was then studied as a platform for molecular loading and releasing kinetics for the possible use in drug delivery. We have found that simply applying the electroless deposition for 2 to 5 min can drastically decrease the rate of release of the molecules, and flow cell-based loading is the preferred way to load the molecules inside np-Au compared to the static method. The structure of the np-Au monoliths before and after the modification was characterized using Energy-Dispersive X-ray Spectroscopy (EDS) and scanning electron microscopy (SEM), whereas the molecular loading and releasing studies were performed using UV-Vis spectrophotometer

Dealloying of Al-based alloys and their mechanisms

Metal based anodes, like tin (Sn), are promising candidate anodes for lithium ion batteries (LIBs) due to their higher specific capacities than traditional graphite electrodes. However, their dramatic volume expansion during lithiation and delithiation could lead to pulverization of the material as well as inadequate cycle life. Materials with nano/microporosity hold promise to accommodate the volume change. This thesis focuses on preparing porous metallic materials for batteries through a dealloying approach. Dealloying is a selective dissolution process, during which one or more active components dissolve from a binary or multicomponent alloy, leaving behind a (nano)porous-structured material enriched in the nobler or less active alloy component(s). In this thesis, porous Sn and nanoporous Cu-Sn composites, which can be used as anodes, and bimodal porous Cu, which can be used as current collector, have been fabricated by dealloying immiscible Al-Sn alloys, ternary Al-Cu-Sn alloy and two-phase Al-Cu alloy, respectively. The dealloying mechanisms of these precursor alloys have been systematically investigated by a variety of means including both ex-situ and in-situ synchrotron X-ray diffraction (XRD). The following findings are most notable. 1) Micro-sized porous Sn (anode material) can be fabricated by dealloying of immiscible Al-Sn alloys. 2) Nanoporous Cu-Sn composite structures (anode material) can be fabricated by concurrent dealloying and realloying of a ternary Al-Cu-Sn alloy. 3) Bimodal porous Cu materials (current collector) can be fabricated from annealing-electrochemical dealloying of Al-Cu alloys. 4) The dealloying of Al2Cu (first dealloyed) and AlCu occurred in sequence and resulted in a hierarchical nanoporous structure. 5)The temperature sensitivity of intermetallic formation in the Cu-Sn system was confirmed by synchrotron studies of the Al67Cu18Sn15 alloy subjected to dealloying at different temperatures (55 °C, 70 °C and 90 °C). The following findings are most notable

Al62Cu25Fe12 and Quasicrystalline Phases and Their Influence on Oxidation

In this article, we will cover a study of the formation of icosahedral and decagonal phases two quasicrystals Al62Cu25Fe12 and Al65Ni15Co20 oxidation of influence in this alloy. For this purpose, research used the diffraction of X-ray, scanning electron microscopy/energy dispersive spectroscopy, differential scanning calorimetry and thermogravimetric analysis. The results displayed found aspects of morphological structural as well as the surface of the two compositions of quasicrystals, these were prepared and obtained in electric arc furnaces and induction and arc. Oxidation of Al62Cu25Fe12 alloy, intermetallic phases presented with combinations of alloying elements and above 675 °C it was observed that the crystalline phase is stable. In icosahedral phase oxidation of aluminum forms a dense layer on the passivating outer most surface of the quasicrystal which causes depletion in both copper and iron. In Al65Ni15Co20 nominal composition of oxygen interaction occurs on the surface of symmetry 10 times plane perpendicular vector. The formation of a thin film of aluminum oxide having well-ordered hexagonal structure and with the opposition area decagonal phase with the lateral size of approximately 35Å. DOI: http://dx.doi.org/10.17807/orbital.v9i1.87

原子分解能その場電子線照射観察による純AlとAl-Cu合金中の格子欠陥挙動に関する研究

Tohoku University永井康介課

Experimental Study of Oxidation, Ignition and Combustion of Aluminum Based Nanomaterials

PhdAluminum based reactive nanomaterials have extensive applications in many fields including solid propellants, pyrotechnics, and catalytic reactions. One recent example is the novel concept of using nanostructured energetic particles for energy storage where the controlled exothermic reaction is the key to control the energy release process. It is of primary interest to understand the thermodynamics, kinetics, morphological and structural properties of these particles during the exothermic reaction. While the physiochemical properties of the monometallic powders are determined only by their size, the properties of bimetallic nanoalloys can be also engineered by their constituent compositions. This thesis conducts a systematic experimental investigation of the oxidation, ignition, and combustion of nano aluminum particles (nAl) and nanoalloys such as nanoscale aluminium-copper (n-AlCu) and aluminium-zinc (n-AlZn). The oxidation experiments are conducted by a TGA/DSC system with detailed characterisation of particles before and after the experiments by scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Nanosizer, Brunauer–Emmett–Teller (BET), energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffractionmetry (XRD). In the TGA/DSC analysis, nanomaterials are oxidized either at constant temperature or under different heating rates in the controlled atmosphere of air or nitrogen. A unique early ignition reaction is observed at the high heating rates for nAl and n-AlCu, which is associated with the effect of polymorphic phase transformation of the alumina shell and the early melting of the aluminum core. Different to the conventional shrink-core concept, hollow structures, i.e. nanoholes, in the central regions of nAl are observed and a phenomenal model is proposed. The comparison of the thermal-chemical characteristics of different nanomaterials reveals some unique 5 features related to nano-alloys such as increased reactivity. A preliminary combustion experiment on feeding nanoparticles in a methane stream is performed with a Bunsen burner setup, where the burning characteristics of different nanoparticles are analysed.University of Engineering and Technology Lahore, Pakista

Microstructual and Thermal Analysis of Aluminum-Silicon and Magnesium-Aluminum Alloys Subjected to High Cooling Rates

This thesis is an examination of the effects of varying cooling rate on the solidification properties of AlSi and MgAl alloys. Rapid cooling accessories for the Universal Metallurgical Simulator and Analyzer Technology Platform (UMSA) were developed that enabled quenching up to peak rates of 520°C/s. Samples from four automotive production alloys (aluminum A356 and a Sr-modified Al-20wt.%-Si alloy as well as magnesium AM60B and AE44) were resolidified under a range of cooling rates. Resultant micrographs revealed improvements to the microstructure, especially for the modified hypereutectic alloy. The AM60B microstructure also indicated invariance to cooling rate. Thermal data from the magnesium alloys was used in the development of baseline and fraction solid calculations that are extensible to higher cooling rates. Though these techniques cannot yet be applied to the highest cooling rates, excellent phase composition data for the AM60B alloy was generated for cooling rates of approximately 20°C/s (peak)