Cast iron anodes

Pyrometa.llurgica.1 Processes. Nickel oxide ores are processed by pyrometaHurgical or hydrometaHurgical methods. In the former, oxide ores are smelted with a sulfiding material, eg, gypsum, to produce an iron—nickel matte that can be treated similarly to the matte obtained from sulfide ores. The iron—nickel matte may be processed in a converter to eliminate iron. The nickel matte then can be cast into anodes and refined electrolyticaHy.  [c.3]

Piebaked anodes aie produced by molding petroleum coke and coal tar pitch binder into blocks typically 70 cm x 125 cm x 50 cm, and baking to 1000—1200°C. Petroleum coke is used because of its low impurity (ash) content. The more noble impurities, such as iron and siUcon, deposit in the aluminum whereas less noble ones such as calcium and magnesium, accumulate as fluorides in the bath. Coal-based coke could be used, but extensive and expensive prepurification would be required. Steel stubs seated in the anode using cast iron support the anodes (via anode rods) in the electrolyte and conduct electric current into the anodes (Fig. 3). Electrical resistivity of prebaked anodes ranges from 5-6 Hm anode current density ranges from 0.65 to 1.3 A/crn.  [c.98]

Bhster copper is fire-refined in reverberatory or rotary furnaces similar to converters. Both types have capacities of 100—600 t. Most plants fire-refine and cast the anodes or fire-refined ingots within the smelter building so that the fire-refining furnace is supphed with molten bhster copper. Sohdifted bhster must be melted first. Next, air is blown into the copper through iron pipes or tuyeres to oxidize some impurities and remove volatile impurities. Sodium carbonate flux may be added to remove arsenic and antimony, and finally the copper is reduced by poling with green wood poles or by feeding a reducing gas such as ammonia, reformed gas, or natural gas. The degrees of oxidation and reduction ate deterrnined by removing and casting small samples of copper. An experienced operator knows whether the copper has the proper oxygen and sulfur content by the appearance of the samples.  [c.201]

Inorganic coatings are also used to provide a barrier between the environment and the metal (1,2,39). Inorganic coatings include chemical conversion coatings, glass (qv) linings, enamels (see Enamels, PORCELAIN ORVITREOUS), and cement (qv). Chemical conversion coatings are produced by intentionally corroding the metal surface in a controUed manner. This is done so as to produce an adherent corrosion product that protects the metal from further corrosion. Anodization of aluminum produces a protective aluminum oxide film on the aluminum metal. Other examples of chemical conversion coatings include phosphatizing for the protection of automobile bodies and chromatizing for the protection of zinc and magnesium. Porcelain enamel coatings which are inert in water and resistant to most weather are routinely appHed to steel, cast iron, and aluminum. They are commonly seen on appHances and plumbing fixtures. Glass-lined metals are used in process industries where there is concern over corrosion or contamination of the product. Glass-lined steels are used in the pharmaceutical industry, breweries, and food plants. Pordand cement coatings have been used to protect steel and cast-Hon water pipes and have an exceUent performance record.  [c.283]

The first anode installation for the cathodic protection of gas pipelines in New Orleans consisted of a 5-m-long horizontal cast-iron tube. Later old tramway lines were used. Since in downtown New Orleans there was no suitable place to install impressed current anodes and to avoid detrimental effects on other pipelines, Kuhn recommended the use of deep anodes which were first installed in 1952 at a depth  [c.17]

The assessment for nonalloyed ferrous materials (e.g., mild steel, cast iron) can also be applied generally to hot-dipped galvanized steel. Surface films of corrosion products act favorably in limiting corrosion of the zinc. This strongly retards the development of anodic areas. Surface film formation can also be assessed from the sum of rating numbers [3, 14].  [c.148]

Galvanic anodes of cast iron were already in use in 1824 for protecting the copper cladding on wooden ships (see Section 1.3). Even today iron anodes are still used for objects with a relatively positive protection potential, especially if only a small reduction in potential is desired, e.g., by the presence of limiting values U" (see Section 2.4). In such cases, anodes of pure iron (Armco iron) are mostly used. The most important data are shown in Table 6-1.  [c.185]

Usually all cast galvanic anodes have specially shaped feeder appendages as anode supports by which the anodes are fixed by screws, brazing or welding. This guarantees a very low resistance for current flowing from the anode to the object to be protected. Anode supports usually consist of mild steel. Supports of nonmagnetic steels or bronze are used on warships. Wire anodes of zinc can have an aluminum core. Sheet iron supports 20 to 40 mm in breadth and 3 to 6 mm thick are used for plate anodes, and cast iron rods 8 to 15 mm in diameter for rod anodes. For larger anodes such as those used, for example, in the offshore field (see Chapter 16), heavier supports are necessary. Here pipes of suitable diameter are used as appendages and section steel as core material.  [c.198]

Since the anodic dissolution of iron takes place with almost 100% current efficiency through the formation of Fe(II) compounds, 1 kg of iron gives about 960 A h. This high weight loss requires the use of a large amount of scrap iron [1]. For a protection system that requires 10 A, at least 2 tons of scrap iron are necessary for 20 years of service life. Iron anodes in the ground are always embedded in coke. Low cost and good stability during transport make up for the high material consumption.  [c.210]

Cylindrical anodes with a construction similar to those in Section 7.5.1 are also suitable for use in water to protect steel-water constmctions and offshore installations, and for the inner protection of tanks. In addition to graphite, magnetite and high-silicon iron, anodes of lead-silver alloys are used as well as titanium, niobium or tantalum coated with platinum or lithium ferrite. These anodes are not usually solid, but are produced in tube form. In the case of lead-silver anodes, the reason is their heavy weight and relatively low anode current density with coated valve metals, only the coating suffers any loss. Finally, the tubular shape gives larger surfaces and therefore higher anode currents. The same types of connection apply to lead-silver anodes as those given in Section 7.5.1. The cable can be directly soft soldered onto the anode if a reduction in the tensile load is required. This is not possible with titanium. Such anodes are therefore provided with a screw connection welded on where appropriate, which is also of titanium. The complete connection is finally coated with cast resin or the whole tube is filled with a suitable sealing compound. Because of the poor electrical conductivity of titanium, with long and highly loaded anodes it is advisable to provide current connections at both ends.  [c.221]

Underground railways in large cities are being extended or newly constructed as are tunnels for tramways. Based on the permitted anodic potential change of up to 0.1 V in installations affected by stray currents [1], the limiting value for the voltage drop in a tunnel within an individual feeder section and over the whole of the tunnel length is specified as 0.1 V. In all tunnels with walls of reinforced concrete, or steel or cast iron, as well as combinations of steel and reinforced concrete (e.g., steel sheet linings and steel tubings), the following requirements given in Ref. 4 must be met  [c.352]

Sulfuric acid Plain carbon steel is used at strengths in the range 70-100% at temperatures up to 80°C. In flowing conditions the corrosion rate increases, thereby rendering steels unsuitable for pumps. Storage tanks for sulfuric acid require care in design to prevent the possible ingress of water vapor. This creates a layer of dilute acid on top of the bulk acid, creating rapid attack at the fill line. At strengths below 70°C chemical lead is the preferred material for tanks but at temperatures above 120°C corrosion becomes significant. For castings such as pumps, valves, fittings and some heat exchangers cast iron containing 15% silicon is used at strengths up to 100%, at temperatures up to the boiling point. Where iron pick-up must be avoided, conventional stainless steels can be used in certain ranges of strength and temperature. Anodically protected titanium is used at 70% (60°C) and 40% (up to 90°C). For higher temperatures and strengths above 100%, nickel-based alloys were molybdenum is used. Glass, gold and platinum are required for specific combinations of acid strength and temperature.  [c.898]

The operating principle of CP is shown in Figure 53.9. For buried pipelines, the power source is most frequently D.C. voltage derived from a rectified mains power supply, or in suitable climates such as Australia and the Middle East, solar cells. Such systems operate by impressed current and suitable anodes are platinized titanium or niobium wire, cast iron, and graphite. They are not consumed, but can be damaged by the chlorine generated in seawater CP systems. Reinforcing steel in concrete jetties, bridge and car park decks and some offshore structures are generally protected by means of impressed current systems.  [c.909]

It is interesting that the first large-scale application of cathodic protection by Davy was directed at protecting copper rather than steel. It is also a measure of Davy s grasp of the topic that he was able to consider the use of two techniques of cathodic protection, viz. sacrificial anodes and impressed current, and two types of sacrificial anode, viz. zinc and cast iron.  [c.110]

Plate and compact anodes with cast-on supports are predominantly used for the external protection of ships, for steel-water structures and for the internal protection of large storage tanks. This form of anode is not suitable in soils due to the large grounding resistance. Compact anodes are supplied with either square, rectangular or round cross-sections, often with iron tubes cast into them for fixing them with bolts (see Fig. 6-12a). Such anodes are usually magnesium alloys. They also comprise compact anodes for the internal protection of storage tanks (see Fig. 6-12b). Plate anodes are primarily used where the flow resistance should be as low as possible, e.g., the external protection of ships. They are more or less long anodes and have a teardrop-shaped contour with flat iron holders sticking out at the ends or are lateral  [c.200]

Offshore anodes are similar in shape to tank anodes. They are, however, much larger and weigh about 0.5 t. They are predominantly manufactured from aluminum alloys. On the basis of strength, most of them are cast onto pipes or profile iron as supports on which lateral protruding shackles are welded. The cross-section is usually trapezoidal (see Fig. 6-15).  [c.202]

The anodes most suitable for burying in soil are cylindrical anodes of high-silicon iron of 1 to 80 kg and with diameters from 30 to 110 mm and lengths from 250 to 1500 mm. The anodes are slightly conical and have at the thicker end for the current lead an iron connector cast into the anode material, to which the cable connection is joined by brazing or wedging. This anode connection is usually sealed with cast resin and forms the anode head (see Fig. 7-2). Ninety percent of premature anode failures occur at the anode head, i.e., at the cable connection to the anode [29], Since installation and assembly costs are the main components of the total cost of an  [c.219]

In addition to anodes with a simple connecting head, there are cylindrical double anodes that have cable connectors cast on at both ends and that can be used in the construction of horizontal or vertical anode chains. Anodes of graphite or magnetite are more compact than anodes of high-silicon iron because of the danger of fracture.  [c.220]

Pipelines in seawater are usually covered with a thick coating. For weighting and for mechanical protection, a 5-cm-thick concrete casing is applied which is reinforced with 2- to 3- mm-diameter galvanized wire mesh. This wire mesh should not be in electrical contact with either the pipe or the anode. The pipes should be partly water jetted into the seabed to protect them from movement and damage from deep drag nets or anchors. The soil removed by water jetting is used to fill the trench or the trench is filled with rubble. The pipelines have to be anchored where the seabed is stony or rocky. Zinc anodes for offshore pipelines can consist of two half-shells. These are cast into sheet iron that protrudes at the ends these are welded together and connected to the pipeline by copper cables. There are also bracelets made from individual blocks of anodes which are welded onto sheet iron around the pipelines (see Section 6.5.4).  [c.384]

The first full-hull installation on a vessel in service was applied to the frigate HMS Samarang in 1824. Four groups of cast iron anodes were fitted and virtually perfect protection of the copper was achieved. So effective was the system that the prevention of corrosion of the copper resulted in the loss of the copper ions required to act as a toxicide for marine growth leading to increased marine fouling of the hull. Since this led to some loss of performance from the vessel, interest in cathodic protection waned. The beneficial action of the copper ions in preventing fouling was judged to be more important than preventing deterioration of the sheathing. Cathodic protection was therefore neglected for 100 years after which it began to be used successfully by oil companies in the United States to protect underground pipelines  [c.110]

The copper ore from the mine, often containing less than 1% copper, is transported to the concentrator, where it is emshed and then ground with water. The ground-ore slurry enters dotation cells, where copper minerals are collected as a froth known as concentrate (see Flotation). Following dewatering (qv) by filtration (qv), the minerals are shipped to the smelter. In the smelter the sulfide minerals react with oxygen and duxes to produce impure copper metal, sulfur dioxide [7446-09-5] SO2, and slag. Smelting occurs in two steps. In the smelting furnace, the copper concentrate reacts with air and oxygen, it is melted to produce matte, the mixed sulfides of copper and iron, sulfur dioxide gas, and a slag containing much of the iron and all of the siheates in the concentrates. In the next step, converting air is blown through the matte, producing impure copper, more sulfur dioxide gas, plus a slag containing the remaining iron. The impure copper is further fire-refined to adjust the oxygen and sulfur content, then cast into anodes, and purified by plating onto pure copper in an electrolytic tank house. Figure 1 illustrates these steps.  [c.195]

After Davy communicated these results to the Royal Society and the British Admiralty, he obtained permission in 1824 to begin practical experiments on the copper eladding of warships. These experiments were carried out at the Portsmouth naval base. Davy attached zinc and cast-iron plates to the copper-clad ships to protect against corrosion. He established that cast-iron was the most economical material. Cast-iron plates 5 cm thick and 60 cm long gave veiy satisfactoiy results on nine ships. On ships hulls where rivets and nails were already rusted, the corrosion protection was only effective in the immediate vicinity of the anodes. To explain this, Davy carried out further experiments on the warship Sammarang (Fig. 1-8). The ship had been eovered with new copper sheet in India in 1821. Cast-iron metal plates constituting 1.2% of the total copper surface of the ship s hull were fixed to the bow and the stern. The ship then made a voyage to Nova Scotia (Canada) and returned in January 1825. Apart from some attack at the stem which was attributed to water vortices, there was no corrosion damage to the rest of the ship. Equally good results were achieved with the Earl of Damley s yacht Elizabeth and the 650-ton  [c.11]

The matte from the furnace is charged to converters, where the molten material is oxidized in the presence of air to remove the iron and sulfur impurities (as converter slag) and to form blister copper. Blister copper is further refined as either fire-refmed copper or anode copper (99.5% pure copper), which is used in subsequent electrolytic refining. In fire refining, molten blister copper is placed in a fire-refining furnace, a flux may be added, and air is blown through the molten mixture to remove residual sulfur. Air blowing results in residual oxygen, which is removed by the addition of natural gas, propane, ammonia, or wood. The fire-refined copper is then cast into anodes for further refining by electrolytic processes or is cast into shapes for sale.  [c.142]

Condenser water-boxes were hitherto usually made of unprotected (or poorly protected) cast iron and these afforded a measure of cathodic protection to the tube-plates and tube ends. This beneficial effect has been lost with the general adoption of water-boxes completely coated with rubber or some other impervious layer, or of water-boxes made from resistant materials such as gunmetal, aluminium-bronze or cupro-nickel, or steel clad with cupronickel or Monel. To prevent attack on tube-plates and tube-ends in these circumstances, it is highly desirable to install either a suitable applied-current cathodic-protection systems , or sacrificial soft-iron or mild-steel anodes. Ferrous wastage plates have the additional advantage that the iron corrosion products introduced into the cooling water assist in the development of good protective films throughout the length of the tubes. This is particularly important in the case of aluminium-brass tubes indeed, with such tubes it may be desirable, as an additional preventive measure, to add a suitable soluble iron salt (such as ferrous sulphate) regularly to the cooling water. Cases of the success of such treatment in power station condensers have been described by Bostwick and Lockhartand other workershave since studied the effects of ferrous sulphate treatment on tube behaviour.  [c.699]

The high cost of platinised materials for use in borehole groundbeds as opposed to conventional silicon-iron anodes may also be offset by the reduction in required borehole diameter, hence lower installation cost, with the relative economics between the different systems dependent upon a combination of both material and installation costs.  [c.169]

Silicon-iron Silicon-iron anodes are again generally supplied in standard sizes, e.g. 2-0in (approx. 50mm) dia. x 4 ft (1 2 m) long and 3 in (75 mm) X 5 ft (l-5m) long and are complete with a cable tail. These anodes are made from cast iron with a high silicon content of 14-15%, together with small percentages of alloying elements such as chromium. The main disadvantage is their extreme brittleness, resulting in transport problems from the foundry to the cathodic protection site, especially if this is overseas.  [c.209]

Skold and Larson" in studies of the corrosion of steel and cast iron in natural water found that a linear relationship existed between potential and the applied anodic and cathodic current densities, providing the values of the latter were low. However, the recognition of the importance of these observations is due to Stern and his co-workerswho used the term linear polarisation to describe the linearity of the rj — i curve in the region of E o , the corrosion potential. The slope of this linear curve, AE — AJ or Af - A/, is termed the polarisation resistance, / p, since it has dimensions of ohms, and this term is synonymous with linear polarisation in  [c.1011]

Electroplating. Metal fluoroborate electroplatiag (qv) baths (27,110,111) are employed where speed and quaUty of deposition are important. High current densities can be used for fast deposition and near 100% anode and cathode efficiencies can be expected. Because the salts are very soluble, highly concentrated solutions can be used without any crystallization. The high conductivity of these solutions reduces the power costs. The metal content of the bath is also easily maintained and the pH is adjusted with HBF or aqueous ammonia. The disadvantages of usiag fluoroborate baths are treeiag, lack of throwing power, and high initial cost. Treeing and throwing power can be controlled by additives grain size of the deposits can also be changed. As of this writing, metals being plated from fluoroborate baths are Cd, Co, Cu, Fe, In, Ni, Pb, Sb, and Zn. Studies on Fe (112,113), Ni (113), and Co (113) fluoroborate baths describe the compositions and conditions of operation as well as the properties of the coatings. Iron foils electrodeposited from fluoroborate baths and properly annealed have exceptionally high tensile strength (113).  [c.168]

Atmospheric corrosion is electrochemical ia nature and depends on the flow of current between anodic and cathodic areas. The resulting attack is generally localized to particular features of the metallurgical stmcture. Features that contribute to differences ia potential iaclude the iatermetaUic particles and the electrode potentials of the matrix. The electrode potentials of some soHd solutions and iatermetaUic particles are shown ia Table 26. Iron and sUicon impurities ia commercially pure aluminum form iatermetaUic coastitueat particles that are cathodic to alumiaum. Because the oxide film over these coastitueats may be weak, they can promote electrochemical attack of the surrounding aluminum matrix. The superior resistance to corrosion of high purity aluminum is attributed to the small number of these constituents.  [c.125]

The main appHcation of zinc is to protect iron and other metals from corrosion. Zinc in contact with iron and other metals, as a coating or attached anode, corrodes sacrificiaHy and protects the iron. Most commonly, zinc is appHed in the molten state, ie, galvanizing, but is also appHed either by electro deposition or by various mechanical procedures using zinc dust or powder (see Metallic COATINGS Metal surface treatments). Zinc dust paints are growing in importance (2). Another important use is in alloys for die casting. These alloys are used extensively because of their high quaUty and low cost. Brass and bronze products account for the third largest usage.  [c.396]

Acryflc coatings of fairly similar composition can also be applied as top coats directly on metal by anionic electro deposition. Some iron is dissolved at the anode however, and anionic electro deposition coatings tend to become discolored. Cationic electro deposition top coats can be made, using for example, 2-(dimethylamino)ethy1 acrylate as a comonomer and a blocked aliphatic diisocyanate as the cross-linking agent for hydroxy-functional groups. Electro deposition top coats are particularly useflil where it is difficult to achieve fliU, uniform coverage by other means such as on articles having sharp edges, eg, finned heat exchange units. The highly automated electro deposition process can lead to significant cost reduction. It has been reported for cationic electro deposition coating of air conditioners that replacing a former system of flow-coated primer and spray-applied top coat required only one operator. In the former system, 50 people, including those doing the required touch up and repair were needed (159).  [c.354]

Magnetite, Fe304, conducts electrons because of its defect structure. The resistivity of pure magnetite lies between 5.2 x 10 cm [2] and as high as 10 X 10 cm. Magnetite occurs as the mineral (kirunavara and gellivare) in northern Sweden and is mined in large amounts as iron ore. The melting point can be lowered by adding small amounts of other minerals. Cast magnetite is glass hard and free of pores. Formerly only cylindrical compact anodes were produced because of the difficulty of casting this material. According to production data [3], the anode consumption is 1.5 g A a calculated from an anode current density of 90 to 100 A m". Consumption increases with increasing anode current density but it is still very low even at 160 A m , giving 2.5 g A a l Magnetite anodes can be used in soils and aqueous environments, including seawater. They endure high voltages and are insensitive to residual ripple. Their disadvantage is their brittleness, the difficulty in casting, and the relatively high electrical resistance of the material.  [c.210]

The installation costs for a single impressed current anode of high-silicon iron can be taken as Kj = DM 975 (S550). This involves about 5 m of cable trench between anodes so that the costs for horizontal or vertical anodes or for anodes in a common continuous coke bed are almost the same. To calculate the total costs, the annuity factor for a trouble-free service life of 20 years (a = 0.11, given in Fig. 22-2) should be used. For the cost of current, an industrial power tariff of 0.188 DM/kWh should be assumed for t = 8750 hours of use per year, and for the rectifier an efficiency of w = 0.5. The annual basic charge of about DM 152 for 0.5 kW gives about 0.0174 DM/kWh for the calculated hours of use, so that the total current cost comes to  [c.254]

See pages that mention the term Cast iron anodes : [c.164]    [c.164]    [c.225]    [c.560]    [c.269]    [c.235]    [c.1146]    [c.152]   
Corrosion, Volume 2 (2000) -- [ c.10 , c.68 , c.69 ]