The earliest application of gold as a therapeutic agent was in China, and it was widely used by physicians and surgeons. For example, pure gold was used to treat furuncles, smallpox and skin ulcers and to remove mercury from skin and flesh; some ancient references noted that gold drugs can cure joint disease and disease in lungs. There were also prescriptions containing gold for curing measles and other diseases. Plant and animal medicines were used in ancient prescriptions and many of these contain gold as a trace element. Ancient China had remarkable achievements in the pharmacology of gold. The evolution of "medicinal gold" and "potable gold" also promoted the development of preparation techniques using gold foil and gold powder, and refining and separation techniques for gold and gold-silver. The scientific benefits gave a worldwide lead at that time and still have relevance in contemporary pharmacology, chemistry and metallurgy of gold.
IntroductionAs we know, gold is soft and can be strengthened through alloying. The conventional alloying elements typically used include silver (Ag), copper (Cu), nickel (Ni), platinum (Pt), palladium (Pd), manganese (Mn) and chromium (Cr). Of these, Ag, Cu and Ni are the main strengthening elements, and Mn and Cr are used mainly as resistance-sensitive elements. Gold can also be strengthened by microalloying (1). Of the possible microalloying elements, rare earth (RE) metals are very effective strengthening agents for both pure gold and gold alloys (2). In the present paper, the influence of RE additions on some properties of gold and gold alloys, such as Au-Ni, Au-Ni-Cr, Au-Ag-Cu and Au-Ag-Cu-Mn, have been studied and applications of such RE-modified gold alloys are reported.
A sketch map of simplified phase diagrams for Au-RE systems has been plotted and the interactions and the alloying behaviour between gold and the rare earth (RE) metals are summarized in this paper. The solid solubilities of the rare earth metals in gold increase as their atomic number increases. The solid solubilities and alloying behaviour of yttrium and scandium are dose to and similar to those of dysprosium and lutetium, respectively. The factors influencing the solid solubility are discussed. Hume-Rothery and Darken-Gurry proposed that the relationship between atomic size and electronegativity was a criterion for solid solubility. This can be revised for the alloying behaviour between gold and RE metals. The maximum solubility of RE metals in gold is greater than 1.0 at% RE when the difference in atomic size is less than 25% and that of the electronegativity is less than 0.7 units. The.relationship between the way in which the intermediate phases that exist in the various Au-RE systems areformed and their respective crystal structures .are also summarized. The changes in transformation temperatures of eutectic reactions and the various intermediate phases, expressed as ratios with the melting points of gold or the RE metals, have been studied in relation to the atomic sizes and atomic numbers of the RE metals. These temperature ratios decrease as the atomic numbers of the RE metals increase although those for cerium and ytterbium have anomalously high values. The trends in the distribution and strengthening effect of RE metals present as trace or dilute solute in gold are discussed.
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