Indium corrosion resistant alloys

Solders. In spite of the wide use and development of solders for millennia, as of the mid-1990s most principal solders are lead- or tin-based alloys to which a small amount of silver, zinc, antimony, bismuth, and indium or a combination thereof are added. The principal criterion for choosing a certain solder is its melting characteristics, ie, soHdus and Hquidus temperatures and the temperature spread or pasty range between them. Other criteria are mechanical properties such as strength and creep resistance, physical properties such as electrical and thermal conductivity, and corrosion resistance. 

Of the elements commonly found in lead alloys, zinc and bismuth aggravate corrosion in most circumstances, while additions of copper, tellurium, antimony, nickel, silver, tin, arsenic and calcium may reduce corrosion resistance only slightly, or even improve it depending on the service conditions. Alloying elements that are of increasing importance are calcium especially in maintenance-free battery alloys and selenium, or sulphur combined with copper as nucleants in low antimony battery alloys. Other elements of interest are indium in anodesaluminium in batteries and selenium in chemical lead as a grain refiner ". 

Uses. Indium finds application in making low melting alloys the eutectic alloy indium-gallium (14.2 at.% In, 21.4 mass% In) melts at 15.3°C. In is used as an additive to solder alloys to improve malleability at low temperature and corrosion resistance it is also used in dental alloys, in the preparation of semiconductors, etc. 

Antimony alloys have many commercial applications. The metal makes its alloys hard and stiff and imparts resistance to corrosion. Such alloys are used in battery grids and parts, tank linings, pipes and pumps. The lead plates in the lead storage batteries constitute 94% lead and 6% antimony. Babbit metal, an alloy of antimony, tin, and copper is used to make antifriction machine bearings. Alloys made from very high purity grade antimony with indium, gallium and bismuth are used as infrared detectors, diodes, hall effect devices and thermoelectric coolers. 

The solder and alloy market, including low melting or fusible alloys, is a principal user of indium (see Solders AND BRAZING alloys). The addition of indium results in unique properties of solders such as improved corrosion and fatigue resistance, increased hardness, and compatibility with gold substrates. To facilitate use in various applications, indium and its alloys can be easily fabricated into wire, ribbon, foil, spheres, preforms, solder paste, and powder. 

Soldered joints present their own characteristic corrosion problems usually in the form of dissimilar metal attack often aided by inadequate flux removal after soldering. Such joints have always been a source of concern to the electrical industry - . Lead-containing solders must be used with caution for some types of electrical connection since Pb(OH)j.PbCOj may be found as a corrosion product and can interrupt current flow. Indium has been found to be a useful addition to Sn-Pb solders to improve their corrosion resistance . However, in view of the toxicity of lead and its alloys, the use of lead solders, particularly in contact with potable waters and foodstuffs, is likely to decline. 

In overlay bearings operating above about 140°C, the tin or indium in the overlay diffuses towards, and alloys with, the underlying copper, depleting the overlay and reducing its resistance to corrosion. This depletion by diffusion can be combatted by the use of a diffusion barrier or dam , e.g. a nickel-rich layer between the bearing alloy and, the overlay . 

The history of these intriguing materials goes back to 1938, when A. Oleander observed the shape memory ability of An—Cd and Cu—Zn alloys (Wayman and Harrison, 1989). Later on other materials such as indium-, nickel-, titanium-, and iron-based alloys were shown to have similar behaviour (Reardon, 2011). Unlike other shape memory alloys, Ni—Ti in particular was found to be very resistant to corrosion and/or degradation and hence ideally suited to implantation in a range of applications, including the human body, albeit more expensive than its other counterparts. Hence the very first temperature-dependent shape memory alloys to be commercialised were nickel—titanium (Bogue, 2009). 

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