Copper and its alloys

Copper and its alloys are often heated to temperatures within this midrange and above 

To compare heating (soak) times and production rates of copper alloys with those of steel, use equations 3.6 and 3.7, both based on the ratio of diffusivities. (See also eq. 3.2a and 3.2b and fig. 3.25.) Thermal diffusivity (see glossary), a = thermal conductivity divided by volume specific heat, k/c(p). 

Soak time for material b = (known soak time for material a) (aa)/(ab) (3.6) 

The productivity, weight heated-through per unit time, is directly proportional to 

Weight/time for material b = (weight/time) (abfoia) 

Copper is a soft ductile material which increases in hardness and strength when cold-worked, i.e. in bending, spinning and drawing. The main advantages of copper are its high thermal and electrical conductivities and excellent corrosion-resistance to chemicals, water and the atmosphere. 

The electrical and thermal conductivities of high-purity copper are greater than those of any other metal except silver. Many grades of commercial purity are available. 

Tough-pitch copper, of 99.85% purity, is used in chemical and general engineering applications where the highest conductivity is not 

Phosphorus deoxidised arsenical copper, of 99.2% purity with 0.3% to 0.5% arsenic, is widely used for copper tube and general engineering 

Brass is essentially an alloy of copper and zinc, but may also contain small amounts of other alloying elements to improve strength, corrosion-resistance and machining characteristics. 

This alloy contains 70% copper and 30% zinc and is highly ductile. It is often referred to as cartridge brass, due to its use in the manufacture of ammunition. Because of its ductility it can be used in pressing, spinning and drawing operations. 

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Lead azide tends to hydrolyze at high humidities or in the presence of materials evolving moisture. The hydrazoic acid formed reacts with copper and its alloys to produce the sensitive cupric azide [14215-30-6] Cu(N2)2- Appropriate protection must be provided by hermetic sealing and the use of noncopper or coated-copper metal. 

Copper Corrosion Inhibitors. The most effective corrosion inhibitors for copper and its alloys are the aromatic triazoles, such as benzotriazole (BZT) and tolyltriazole (TTA). These compounds bond direcdy with cuprous oxide (CU2O) at the metal surface, forming a "chemisorbed" film. The plane of the triazole Hes parallel to the metal surface, thus each molecule covers a relatively large surface area. The exact mechanism of inhibition is unknown. Various studies indicate anodic inhibition, cathodic inhibition, or a combination of the two. Other studies indicate the formation of an insulating layer between the water surface and the metal surface. A recent study supports the idea of an electronic stabilization mechanism. The protective cuprous oxide layer is prevented from oxidizing to the nonprotective cupric oxide. This is an anodic mechanism. However, the triazole film exhibits some cathodic properties as well. 

Chromium compounds are used in etching and bright-dipping of copper and its alloys. A typical composition for the removal of scale after heat-treating contains 30 g/L Na2Cr20y 2H2O and 240 mL/L concentrated H2SO4. It is used at 50—60°C. 

Copper and its alloys also have relatively good thermal conductivity, which accounts for thek appHcation where heat removal is important, such as for heat sinks, condensers, and heat exchanger tubes (see Heatexchangetechnology). Thermal conductivity and electrical conductivity depend similarly on composition primarily because the conduction electrons carry some of the thermal energy. 

Copper and Alloys Copper and its alloys are widely used in chemical processing, particulany when heat and electrical conductivity are important fac tors. The thermal conductivity of copper is twice that of aluminum and 90 percent that of silver. A large number of cop-... 

Copper and Alloys With few exceptions the tensile strength of copper and its alloys increases quite markedly as the temperature goes down. However, coppers low structural strength becomes a problem when constructing large-scale equipment. Therefore, alloy must be used. One of the most successful for low temperatures is sihcon bronze, which can be used to —I95°C (—320°F) with safety. 

Metals and alloys Iron and steels Aluminium and its alloys Copper and its alloys Nickel and its alloys Titanium and its alloys... 

Materials for metal tanks and installations include plain carbon steel, hot-dipped galvanized steel, stainless steel [e.g., steel No. 1.4571 (AISI 316Ti)], copper and its alloys. The corrosion resistance of these materials in water is very variable and can... 

Methyl vinyl ether F Most common metals Copper and its alloys... 

Copper and its alloys, rubber or any composition thereof, oil, grease or readily combustible material... 

Copper and its alloys in certain fresh waters give rise to a form of localised attack that is referred to as nodular pitting in which the attacked areas are covered by small mounds or nodules composed of corrosion products and of CaC03 precipitated from the water. This is a serious problem in view of the extensive use of copper pipes and tanks for water supplies, and in aggressive water these may perforate in a relatively short time. 

However, in this section emphasis is placed upon damp and wet atmospheric corrosion which are characterised by the presence of a thin, invisible film of electrolyte solution on the metal surface (damp type) or by visible deposits of dew, rain, sea-spray, etc. (wet type). In these categories may be placed the rusting of iron and steel (both types involved), white rusting of zinc (wet type) and the formation of patinae on copper and its alloys (both types). 

Secondly, absorbent particles such as charcoal and soot are intrinsically inert but have surfaces or infrastructures that adsorb SO, and by either coadsorption of water vapour or condensation of water within the structure, catalyse the formation of a corrosive acid electrolyte solution. Dirt with soot assists the formation of patinae on copper and its alloys by retaining soluble corrosion products long enough for them to be converted to protective, insoluble basic salts. 

Several books contain general summaries of the corrosion behaviour of copper and its alloy and the formation of copper corrosion products and methods for their identification have been described in a number of papers... 

When unusually rapid corrosion of copper and its alloys occurs during atmospheric exposure, it is likely to be for one of the following reasons ... 

Despite these qualifications copper and its alloys are used extensively and successfully in much chemical equipment. Uses include condensers and evaporators, pipelines, pumps, fans, vacuum pans, fractionating columns, etc. Tin-bronzes, aluminium-bronzes and silicon-bronzes are used in some circumstances because they present better corrosion resistance than copper or brasses. 

Remarkably little has been published on corrosion fatigue crack propagation in copper and its alloys. In general little or no influence of marine environments has been observed in crack propagation experiments on manganese and nickel-aluminium bronzes although the frequencies employed were quite high (> 2.5 Hz) ... 

Copper and its alloys are all cathodic to steel, therefore sprayed coatings of these materials are not used for protection, except for ornamentation work in the interior of buildings, or in conditions such as where there is a minimum humidity. 

It is not possible to plate rhodium directly on to reactive metals of the type mentioned above, in view of the acid nature of the electrolyte, but copper and its alloys, e.g. nickel-silver, brass, phosphor-bronze, beryllium-copper, which are of special importance in the electrical contact field, may be plated directly. Even in this case, however, an undercoat is generally desirable. 

Copper and its alloys can be cleaned and brightened by immersion in solutions of substantial quantities of dichromate with a little acid (see, for instance method Q of DEF STD 03-2/1). Such solutions impart some resistance to tarnishing, ascribed to the formation of very thin chromate films. 

Although this reaction may cause slight problems, the primary issue concerning ammonia is ammoniacal corrosion of CR system metals where oxygen is present and the pH is over 8.3. Under these circumstances, copper and its alloys and other nonferrous metals are attacked, and severe damage results due to the formation of a stable cupric ammonium complex ion. 

Whether ammonia arises from its use as a FW pH level adjuster or from adventitious provision as a result of DO scavenger breakdown, it should be recognized that any excess ammonia will clearly end up in the steam-condensate system. Although the benefit of carbon dioxide neutralization may be legitimately claimed, unfortunately, excess ammonia also may permit the corrosion of copper and its alloys, especially if some oxygen persists. 

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