Electrical Resistivity, Copper Alloys

Electrical—Thermal Conductivities. Electrical conductivities of alloys (Table 5) are often expressed as a percentage relative to an International Annealed Copper Standard (lACS), ie, units of % lACS, where the value of 100 % lACS is assigned to pure copper having a measured resistivity value of 0.017241 Q mm /m. The measurement of resistivity and its conversion to % lACS is covered under ASTM B193 (8). 

Resistance welding has been successfully appHed to copper alloys in all of its various spot, seam, or butt joining modes. Because the process depends on ohmic (l R) heating at the interface to be joined, the abiHty to resistance weld is inversely related to electrical conductivity of the alloys being welded. 

Light, sandy, well-drained soil of high electrical resistivity is low in corrosivity and coated steel or bare stainless steels can be employed. It is unlikely that the whole pipe run would be in the same type of soil. In heavier or damp soils, or where the quality of back filling cannot be guaranteed, there are two major corrosion risks. Steel, copper alloys and most stainless steels are susceptible to sulfide attack brought about by the action of sulfate-reducing bacteria in the soil. SRB are ubiquitous but thrive particularly well in the anaerobic conditions which persist in compacted soil, especially clay. The mechanism of corrosion where SRB are involved is described in Section... 

Copper and copper alloys are amongst the earliest metals known to man, having been used from prehistoric times, and their present-day importance is greater than ever before. Their widespread use depends on a combination of good corrosion resistance in a variety of environments, excellent workability, high thermal and electrical conductivities, and attractive mechanical properties at low, normal and moderately elevated temperatures. 

Beryllium is obtained by electrolytic reduction of molten beryllium chloride. The element s low density makes it useful for the construction of missiles and satellites. Beryllium is also used as windows for x-ray tubes because Be atoms have so few electrons, thin sheets of the metal are transparent to x-rays and allow the rays to escape. Beryllium is added in small amounts to copper the small Be atoms pin the Cu atoms together in an interstitial alloy that is more rigid than pure copper but still conducts electricity well. These hard, electrically conducting alloys are formed into nonsparking tools for use in oil refineries and grain elevators, where there is a risk of explosion. Beryllium-copper alloys are also used in the electronics industry to form tiny nonmagnetic parts and contacts that resist deformation and corrosion. 

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. 

In principle, one could consider a number of metals and alloys to be used for the construction of the magnet but, considering their physical and electrical characteristics, copper and silver are undoubtedly the best choices. This assertion sounds obvious but the use of other metals with higher resistivity, such as aluminum alloys, is sometimes justified because of their negligible cost and mechanical properties which simplify the manufacturing process. The most important physical characteristics of the best conductors such as OF copper (Oxygen Free) and silver, are shown in Table I. 

Silver is employed for low resistance electrical contacts and conductors, and in silver cell batteries. Antimony is used in lead add storage batteries to improve the workability of the lead and lead oxides. Copper and copper alloy wires, connectors, cables, switches, printed drcuit boards, and transistor and rectifier bases are common throughout the industry. Nickel is used in high resistance heating elements, glass-to-metal seals, batteries, and spedalty steels for power generation equipment Household appliances employ stainless and electroplated steel containing nickel. 

It is well known that many important alloy combinations have properties that are not easy to predict, simply on the basis of knowledge of the constituent metals. For example, copper and nickel, both having good electrical conductivity, form solid-solution type alloys having very low conductivity, or high resistivity, making them useful as electrical resistance... 

The effect of long-range order on the electrical resistivity of copper-gold alloys is shown in Figure 8.6. The increased periodicity produced by ordering during annealing at 200 °C decreases the resistivity. 

Ordering lowers the electrical resistivity of copper-gold alloys. Adapted from C. S. Barrett, Structure of Metals and Alloys (New York McGraw-Hill, 1943), p. 244, figure 14. 

Rhodium melts at 1907° C.4 and boils at about 2500° C. It is less volatile than platinum,5 and when alloyed with that metal not only stiffens it, but, unlike iridium, reduces its volatility at all temperatures above 900° C. It has been suggested,6 therefore, that a useful alloy for best quality crucibles would consist of platinum 95 to 97 per cent., and rhodium 3 to 5 per cent., and containing no other detectable impurities. Below 900° C. the presence of rhodium appears to exert a negligible effect. When cooled to — 80° C. rhodium appears to undergo a molecular transformation of some kind, analogous to that evidenced by copper. At this temperature the electrical resistance is considerably below the calculated value.7 The most intense lines in the spectrum of rhodium are as follow 8 ... 

Copper, widely distributed in nature in ores containing sulfides, arsenides, chlorides, and carbonates, is valued for its high electrical conductivity and its resistance to corrosion. It is widely used for plumbing, and 50% of all copper produced annually is used for electrical applications. Copper is a major constituent in several well-known alloys (see Table 20.10). 

Platinum is a very expensive metal and therefore unsuitable for such mass-produced glass-to-metal seals as are found in radio valves and electric lamps. No other pure metal has a suitable coefficient of expansion or a suitable electrical resistance for sealing to lead or soda glasses. A composite wire has been developed as a substitute for platinum. It consists of a core of nickel-iron alloy (43% nickel) covered with a thin sheath of electrically deposited copper. The composite wire is drawn out to about 0.5 mm diameter, the copper sheath is then about 0.03 mm thick. This composite wire has a comparatively high electrical resistance and a short length, just sufficient for the seal, is butt welded to a nickel wire on the vacuum side of the seal and to a copper wire on the other side. 

Tellurium is also added to copper to improve machinability. Tellurium-copper alloys are also easier to work with than pure copper. And the essential ability of copper to conduct an electric current is not affected. Tellurium is also added to lead. Tellurium-lead alloys are more resistant to vibration and fatigue than pure lead. Metal fatigue is the tendency of a metal to wear out and eventually break down after long use. 

Use Alloys (low-alloy steels, stainless steel, copper and brass, permanent magnets, electrical resistance alloys), electroplated protective coatings, electro-formed coatings, alkaline storage battery, fuel cell electrodes, catalyst for methanation of fuel gases and hydrogenation of vegetable oils. 

Copper alloys consist of several families that have high electrical and thermal conductivity and corrosion resistance. See Figure 4-12. 

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. 

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