Metal joining, gold

Certain properties of gold are used to advantage in metal joining. In particular,... 

Gold, platinum, palladium, and silver are the principal components of most of the solders used for joining both noble and base metal alloys. Some solders for base metal alloys also contain nickel, chromium, and/or cobalt as primary ingredients. 

The contact between the aluminium layers and the ceramic substrate requires a joining material which will wet both metal and ceramic, and solders such as the conventional Pb-Sn alloy have been used which are molten during the annealing process. The contact between the solder and the aluminium layer is frequently unsatisfactoty because of the intervention of the AI2O3 layer, and a practical solution appears to be to place drree layers of metal clrromium in contact widr the aluminium, copper in contact with the clrromium, and gold between the copper layer and the solder. 

Typically, coatings most often in use as intermediate layers are silver, nickel, copper, and gold however, silver is used by far the most often. This is so because of the low dissociation temperature of silver oxide, making it relatively easy to obtain clean surfaces. Also, the typical thickness range of electroplates used, in practice, for diffusion welding is about 15 to 40/rm, but thicknesses as great as 130 )um must sometimes be used. A considerable variety of steel types as well as aluminum and a host of other difficult-to-join metals and even beryllium have been and continue to be diffusion bonded with the use of electroplated intermediate layers. 

Joshua mentioned the iron chariots of the Canaanites (Josh. 17, 16). In the days of Saul and Jonathan, there was no smith in all Israel (I Sam. 13, 19) (92). When David was preparing material for the Temple, iron was abundant. And David prepared iron in abundance for the nails for the doors of the gates, and for the joinings.. . . Now, behold, in my trouble I have prepared for the house of the Lord an hundred thousand talents of gold, and a thousand thousand talents of silver and of brass and iron without weight for it is in abundance. . . (I Chron. 22, 3, 14). Saws, harrows, and axes of this metal were also used in the time of David (II Sam. 12, 31). 

Gold, like all metals, is shiny, malleable, ductile, and a good conductor of electricity and heat. Unlike most metals and other elements, however, gold is found in nature in its pure form, as an element. Most elements are chemically combined in the form of compounds. Why is this so Why do atoms of some elements join together as compounds, while others do not In this chapter, you will use the periodic trends you examined in Chapter 2 to help you answer these questions. You will learn about the bonds that hold elements together in compounds. At the same time, you will learn how to write chemical formulas and how to name compounds. 

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