Copper-zinc alloys electrical resistivity

Figure 18.39 Room-temperature electrical resistivity versus composition for copper-zinc alloys.

Table 16 illustrates the property enhancements and tradeoffs seen when tin is added to a copper—zinc brass base composition. The most commonly used alloys for electrical connectors are the Cu—10 Zn—Sn brasses, such as C411, C422, and C425. These lower level zinc—tin alloys offer good corrosion resistance along with the good formabiHty, conductivity, and strength levels of brass. 

Homogeneous alloys of metals with atoms of similar radius are substitutional alloys. For example, in brass, zinc atoms readily replace copper atoms in the crystalline lattice, because they are nearly the same size (Fig. 16.41). However, the presence of the substituted atoms changes the lattice parameters and distorts the local electronic structure. This distortion lowers the electrical and thermal conductivity of the host metal, but it also increases hardness and strength. Coinage alloys are usually substitutional alloys. They are selected for durability—a coin must last for at least 3 years—and electrical resistance so that genuine coins can be identified by vending machines. 

Metallic Pigments. These pigments are metal flakes of various sizes made up of aluminum, copper, zinc, and/or their alloys. The aluminum flakes develop the silver metallic colors, whereas the copper, zinc, and aluminum alloys produce the gold, copper, brass, and bronze colors. The metal effect is modified, not only by shape and size, but also by perticle size distribution within a given product. Since aluminum, in particular, as a fine dry powder, can form explosive mixtures with air, most of these materials are commercially available in paste or liquid concentrates. In addition, surface treatments of these materials enhance their appearance and performance. Flakes of other metals, such as stainless steel, are used for surface protection purposes such as corrosion resistance and electrical conductivity. 

The objective of this research work is to develop a highly conductive copper alloy based diffusion barrier for copper metallization. The criteria for selection was that minimal increase in resistivity resulted on addition of one atomic percent of second element to copper. The copper-1 at.% zinc alloy conforms to this criteria and hence was selected as a candidate material for further study. Pure copper can easily be electroplated from simple acid copper baths, but the alloys of copper are more difficult when the deposition potential of individual elements is widely separated as in the present case. A Cu-Zn alloy can be deposited from baths containing coordinating agents. Having established that a Cu-Zn alloy can be successfully electroplated, an alloy of composition Cu-3.5%Zn was sputter deposited to develop an MOS capacitor and electrical testing was performed on as-sputtered and annealed samples. The bias temperature stability tests indicate that the alloy possesses promising diffusion barrier properties. 

Zinc in acid conditions has a potential of about -1.1 V against a copper/copper sulphate cell. A.s passive steel has a potential of about -100 mV and active steel is usually -350 to -500 mV, a zinc anode has 0.5 to 1.0 V electromotive force (emf) to cathodically protect the steel, assuming that the zinc is kept active. The potential of the zinc will change in the same way as the steel does, with the corrosiveness of the environment. Alloys are used in some cases to reduce the formation of oxides that will increase the electrical resistance between the anode and the steel. This issue of passivation of the anode is a problem with anodes in alkaline environments such as concrete. 

Tungsten-copper-boron nitride pseudoalloy electrodes have been tested in electric discharge machining of hard alloys [101,102]. Alloys used in the manufacture of electric contacts are frequently composites of metals and a-BN, providing for increased heat durability [103]. Thus, silver cermet electrical contact material for circuit breakers is made by hot-pressing of the constituents [104 to 106]. Again, Ag/BN composite layers can also be prepared by electrodeposition [107]. Zinc alloys as used in coating sheet steel as anticorrosion layers may contain dipersed a-BN for increased weldability and corrosion resistance [108 to 111]. 

Copper has the highest electrical conductivity of all metals and is used in highly purified form when electrical conductivity is important. Metals that have high electrical conductivity also have high thermal conductivity since the same characteristic is responsible for both. Many alloys of copper and zinc are used. These are called brasses. Alloys of copper and tin are called bronzes. Like aluminum, copper is relatively corrosion resistant due to a protective oxide film that has an esthetic greenish color. 

Copper and nickel can be alloyed with zinc to form nickel silvers. Nickel silvers are ductile, easily formed and machined, have good corrosion resistance, can be worked to provide a range of mechanical properties, and have an attractive white color. These alloys are used for ornamental purposes, as sHverplated and uncoated tableware and flatware in the electrical iadustry as contacts, connections, and springs and as many formed and machined parts (see Electrical connectors). 

The outstanding properties of copper-base materials are high electrical and thermal conductivity, good durabihty in mildly corrosive chemical environments and excellent ductility for forming complex shapes. As a relatively weak material, copper is often alloyed with zinc (brasses), tin (bronzes), aluminum and nickel to improve its mechanical properties and corrosion resistance. 

Mankind has used copper throughoutrecorded history. People learned to refine it from copper ore near 5000 BC. It was used for pottery, tools, coins and jewelry. Because ofits softness, Cu was no t useful for weapons and tools until itwas hardened by alloying it with other metals brass is Cu and zinc bronze is Cu and tin. Modern alloys are copper-aluminum and copper-nickel. Copper is one of the best conductors of electricity, so that it is widely used commercially for wiring. Its resistance to tarnishing by oxidation makes it a popular but expensive roofing material. 

OTHER COMMENTS used in the manufacture of bronzes, brass, and other copper alloys useful in the manufacture of electric wiring, electrical conductors, switches, and ammunition electroplated protective coatings and undercoats for nickel, chromium, zinc, etc. used in corrosion-resistant piping has also been used in cement, food, drugs, metallurgy, nylon, paper products, pigments, and dyes use as a pollution control catalyst. 

Anodizing is an electrolytic passivation process that increases the thickness of natural oxide layers on the surface of metals [13]. It basically forms an anodic oxide finish on a metal s surface to increase corrosion resistance. For the anodizing process, the metal to be treated serves as the anode (positive electrode, where electrons are lost) of an electrical circuit. Anodized films are most often applied to protect aluminum alloys. An aluminum alloy is seen on the front bicycle wheel in Fig. 2 [14]. For these alloys, aluminum is the predominant metal. It typically forms an alloy with the following elements copper, magnesium, manganese, silicon, tin, and zinc [15]. Two main classifications for these alloys are casting alloys and wrought alloys, both of which can be either heat treatable or non-heat treatable. 

Brass is a non-ferrous alloy of copper and zinc which is easily cast. Because it is harder than copper or aluminium it is easily machined. It Is a good conductor and is highly resistant to corrosion. For these reasons it is often used in the electrical and plumbing trades. Taps, valves, pipes, electrical terminals, plug top pins and terminal glands for steel wire armour (SWA) and Ml cables are some of the many applications. 

---