Study of gold-based alloy phase diagrams

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The partial constitutions of the Au-Ge-X and Au-Pb-X ternary alloys have been investigated, where X is a metallic element, selected from the sub-groups period 1m and rrm of the periodic table (In, Ga, Zn, or Cd), which forms one or more stable compounds with gold, but which forms no stable compound with Ge and Pb. The Smith Thermal Analysis Method, supplemented by metallographic and X-ray techniques, was used to determine the constitutions of the ternary systems. Eutectiferous, pseudobinary systems were found between Ge and the stable congruent intermediate compounds, AuIn, Auln2' AuGa, AuGa2' AuZn and AuCd. The solubility of Ge in the AuX compounds was not determined directly. However, it was 1.3 at.% Ge for Zn and Cd containing alloys and less than 1.0 at. % Ge for In and Ga containing alloys at the eutectic temperatures, which is in accordance with the Hume-Rothery rule. Ternary eutectic points were also determined in the Auln-AuIn2-Ge, Auln2-In-Ge and AuGa-AuGa2-Ge partial ternary systems. No evidence of liquid immiscibility was found in any of these ternary systems. The experimental results obtained were in good agreement with computed features of the diagrams. However, pseudobinary systems were not found between Pb and the stable congruent melting intermediate compounds, AuGa, AuGa2, AuZn and AuCd (the AuIn-Pb and AuIn2-Pb sections had already been investigated). The evidence of an extensive liquid immiscibility was found in each of these systems. The miscibility in the liquid state was found to decrease progressively down group IV when the elements of this group react with AuX compounds, which can be attributed to the progressive increase of the atomic size and decrease in electronegativities and solubility parameters of the elements, down this group. Two rules were derived to relate the liquid immiscibility/miscibility of ternary systems. One of the rules based upon the atomic sizes and melting points of the constituent elements showed a fair agreement with many systems. However, the other rule based upon the solubility parameter and electronegativities of the constituent elements showed good agreement with immiscible systems, but gave a poor predictability for miscible systems. The lower temperature equilibria of the Au-rich portion of the Au-Sn binary phase diagram are not well defined. So, long term heat treatment of samples at appropriate temperatures and compositions was carried out. Optical microscopy and SEMIEDAX techniques were employed and hence the low temperature equilibria of the Au-Sn binary system have been amended.This study is partly funded by the Ministry of Science and Technology, Government of Pakistan for the S & T scholarship award and Punjab University, Lahore

Corrosion trends of Ti based Shape Memory Alloys having biomedical applications: A perspective study

Ti-based shape memory alloys (SMAs) have been investigated as materials for medical devices and as a biomaterial that can be implanted in a living system as an alternative of any part. The behavior of such materials is evaluated by its activity, corrosion resistance, stability and compatibility with the living body. The direction of this paper is to deliver a brief description of the trends of corrosion in these materials. Titanium (Ti) shows satisfactory resistance to corrosion in natural and acidic environment but it has a trend toward corrosion in reducing acids. The shape memory alloys based on Ti are much favorable corrosion resistant materials to use in reducing acids. Normally human body fluid is analogous to a solution of about 0.9% NaCl which has a pH value 7.4. During surgery this value can be changed, with an increase of 7.8 and then dropping it to 5.5. Later some days the standard pH value of 7.4 can be re-gained. To evaluate corrosion rate of Ti based shape memory alloys in human body fluid, 0.9% NaCl solution was used as a medium. The basics of the shape memory material i.e. the mechanisms for shape memory, the shape memory effect and characterization of the evaluation of corrosion in systems based on Ti shape memory alloy is also reviewed in this article

A COMPARATIVE STUDY OF MECHANICAL PROPERTIES AND MICROSTRUCTURES OF DEFORMED BARS (GRADE-60) LOCALLY MANUFACTURED IN PAKISTAN

The MS deformed bars are widely used in construction, housing, bridges, flyovers, dams etc. And often the properties claimed by the industries may or may not be compatible with ASTM Standards. In order to check their compatibility with ASTM standards, MS deformed bar samples of Grade 60 of one inch (25 mm) diameter of five different companies were taken from open market. As One of Pakistan's popular examples of consistent business success has been the stainless steel and mild steel production. The hypothesis explored in this paper is that meeting such standards requires greater properties, both among producers as well as mechanical properties obtained by Tensometer and Universal Hydralic Tensile Machine. The study draws on qualitative data to examine either how much difference or similarity is drawn within samples of various industries. And these samples were coded as S-1, S-2, S-3, S-4 and S-5. First of all composition was determined by using Optical Spectrometer then Tensile performed at universal hydraulic Testing Machine and time load graphs were taken as this test is commercially used, and also Tensile was performed on Tensometer at laboratory level and Stress-Strain graph was obtained and calculated. It was concluded that the experimental results of most of the industries were in good agreement with ASTM but only a few did not show compatibility with ASTM standards

Injection Moulding and Heat Treatment of Ni-Cr-Si-B Alloy Powder

Injection moulding, debinding, sintering and heat treatment of Ni-Cr-Si-B alloy powder of high hardness value have been studied. A binder system comprised of two polymers, a major component of water soluble polyethylene glycols (PEGs) and a minor component of very finely dispersed polymethyl methacrylate (PMMA) derived from an emulsion was employed. Mixing of a number of different feedstocks was carried out manually. Following the identification of the optimum binder composition (20 wt. % PMMA, 80 wt. % PEGs) and solid loading (65 Vol. %), several test specimens were injection moulded for further processing. The PEGs were removed by leaching with water. The PMMA was removed by pyrolysis, prior to the sintering stage. Samples were sintered to ~ 99 % of theoretical density. With careful control of the various processing parameters, including sintering temperature and time, cooling rate and heat treatment conditions, good mechanical properties including high hardness of HRC ~57 were attained. In an attempt to reduce the process cycle time, the sintering ramp was modified to include solutionising and oil-quenching in a single sintering cycle. The hardened samples were tempered at temperatures from 250 to 350 °C for 2 hours. Scanning electron microscopy was used to reveal the micro-structural changes during various sintering and heat-treatment stages

A Study on Injection Moulding of Two Different Pottery Bodies

Injection moulding of a conventional high clay pottery body and an unconventional low clay pottery body has been described. The Sheffield Binder System comprising of a major component of PEG and a minor component of PMMA was used. The behavior of these pottery bodies during various stages of injection moulding has been analyzed. Optical and scanning electron microscopy was used to examine the structure of green and sintered specimens

Production of Tin Powder Using Gas Atomization Process

Gas atomization process is widely used for the production of various metal and pre-alloyed powders. The process involves the disintegration of a liquid stream of molten metal into liquid metal droplets by the impingement of high pressure gas jets. The liquid metal droplets subsequently cool and solidify into metal powder particles, which can typically range from 1 to 150 µm. After a detailed study of various atomizing processes, the cross jet gas atomizing scheme was selected for the present research work. Experiments were carried out using air and argon gas as atomizing media. Particle shape was observed using Scanning Electron Microscope. The particle size distribution was measured using the Laser Particle Size Analyzer. XRD analysis of different powder samples was carried out to measure the oxygen contents. Spherical shape particles ranging from 1 µm to 60 µm sizes were produced

Evaluating the Biocompatibility of materials: Routes and strategies of exploring the host response

A Biomaterial is a synthetic material which is used in living body as replacement of any part and its evaluation and performance is measured by its activity, stability and compatibility with living system. Usually in the field of biomaterial characterization its performance is based upon Biocompatibility. The aim of the present research is to describe the parameters and standards for evaluation of biocompatibility of biomaterials. In this study various techniques of biocompatibility testing have been described such as  Cytotoxicity Testing, Genotoxicology / Mutagenicity Testing, Hemocompatibility Testing, Implantation Testing, Irritation/Intracutaneous Reactivity Testing, Pyrogenicity Testing (In Vivo), Sensitization Testing, Subacute/Subchronic Toxicity Testing, Systemic (Acute) Toxicity Testing, Chronic Toxicity and Carcinogenicity Testing, Immunogenicity testing, Pharmacokinetics and Pharmacodynamics testing, Cell Culture Test, Mucosal damage and Mucosa usage tests, Periapical tissue damage and endodontic usage test, Intraosseous Implant test, Diagnostic tests on patients, Patch test, Prick Test, Radio allegro sorbent test (RAST) and Corrosion testing. The description of the basics of these techniques along with evaluation standards is also the fundamental objective of this work

Viscosity of lead bismuth gallate glasses containing minor addition of silica and germania

Heavy metal oxide glasses with and without minor additions of Silica and Germania in the system PbO-Bi203-Ga203 have been prepared which have potential applications for infrared fibers. Viscosity measurements using penetration viscometry were first carried out on sample of glass No. 711 provided by National Bureau of Standards (NBS) over a range of 107 to 1010 Pa.s and showed good agreement with NBS data with a mean error of 1.35% using modified-Nemilov equation. The viscosity of glasses studied fell sharply about three orders of magnitude in a temperature interval of less than 45 degrees (on Celsius scale). The results have been discussed in relation to activation energy for viscous flow and the fragility of the melts has been compared

Hyperbranched polyethyleneimine induced polycationic membranes for improved fouling resistance and high RO performance

The study shows a new method for hyperbranched polyethyleneimine (HPEI) induced polycation membranes with an objective of achieving better fouling resistance and high reverse osmosis (RO) performance. Chemically crosslinked composite membrane (CCCM) was prepared with polyvinyl alcohol (PVA), maleic acid (MA) and Pluronic F127 via chemical crosslinking methodology. Polycation induced membranes were fabricated by surface coating of HPEI onto the CCCM (PVA/MA/PluronicF127) RO membranes. Functional group analysis, morphology and surface roughness of CCCM and HPEI-RO membranes were analyzed by Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy respectively. The hydrophilicity and water permeability of CCCM and HPEI-RO were examined with water contact angle measurement and RO performance test. Optimum RO performance was obtained for HPEI-RO3 membrane with NaCl and MgSO4, as for RNaCl = 96.1%, JNaCl = 58.2 L m�2 h�1 and RMgSO4 = 99.6%, JMgSO4 = 15.8 L m�2 h�1 (testing with 3.28 wt.% aqueous NaCl and MgSO4 solution at 25 �C and 55 bar). Moreover, cetyl trimethylammonium bromide (CTAB) as standard foulants presented a smaller fouling tendency for the modified HPEI-RO3 membrane. HPEI-RO3 compared to the unmodified membrane, was able to decrease the stickiness of charged bacteria, Gram negative Escherichia coli and Gram positive Staphylococcus epidermidis. Therefore, the permeation flux, salt rejection and fouling resistant property of membrane (HPEI-RO3) were significantly improved with polycation induction into the membranes