Corrosion rate copper

In addition to bonding with the metal surface, triazoles bond with copper ions in solution. Thus dissolved copper represents a "demand" for triazole, which must be satisfied before surface filming can occur. Although the surface demand for triazole filming is generally negligible, copper corrosion products can consume a considerable amount of treatment chemical. Excessive chlorination will deactivate the triazoles and significantly increase copper corrosion rates. Due to all of these factors, treatment with triazoles is a complex process. 

A copper bar of 300-cm total exposed area coupled to an iron bar 50-cm area is immersed in seawater. What minimum current must be applied to the couple in order to avoid corrosion of both iron and copper (Corrosion rate of uncoupled iron in seawater is 0.13 mm/y.)... 

Fluorine can be handled using a variety of materials (100—103). Table 4 shows the corrosion rates of some of these as a function of temperature. System cleanliness and passivation ate critical to success. Materials such as nickel, Monel, aluminum, magnesium, copper, brass, stainless steel, and carbon steel ate commonly used. Mote information is available in the Hterature (20,104). 

Corrosion. Copper-base alloys are seriously corroded by sodium thiosulfate (22) and ammonium thiosulfate [7783-18-8] (23). Corrosion rates exceed 10 kg/(m yr) at 100°C. High siUcon cast iron has reasonable corrosion resistance to thiosulfates, with a corrosion rate <4.4 kg/(m yr)) at 100°C. The preferred material of constmction for pumps, piping, reactors, and storage tanks is austenitic stainless steels such as 304, 316, or Alloy 20. The corrosion rate for stainless steels is <440 g/(m yr) at 100°C (see also Corrosion and corrosion control). 

Sa.tura.tion Index. Materials of constmction used in pools are subject to the corrosive effects of water, eg, iron and copper equipment can corrode whereas concrete and plaster can undergo dissolution, ie, etching. The corrosion rate of metallic surfaces has been shown to be a function of the concentrations of Cl ,, dissolved O2, alkalinity, and Ca hardness as well as buffer intensity, time, and the calcium carbonate saturation index (35). 

The main advantages of the Cosorb process over the older copper ammonium salt process are low corrosion rate, abiHty to work in carbon dioxide atmospheres, and low energy consumption. The active CuAlCl C H CH complex is considerably more stable than the cuprous ammonium salt, and solvent toluene losses are much lower than the ammonia losses of the older process (94). 

Hence, copper heat exchanger tubes handling acetic acid can he more seriously corroded at low temperatures than at high temperatures. Sulfuric acid at room temperature is handled routinely in carbon steel drums and tanks when water concentration is low, but it becomes extremely corrosive as water concentration increases. As ferric-ion concentration increases during acid cleaning of industrial systems, the corrosion rate of steel increases rapidly. 

Copper alloys are attacked at high pH. However, attack is usually caused not by elevated pH alone but because of copper complexation by ammonia or substituted ammonium compounds. In fact, copper resists corrosion in caustic solutions. For example, corrosion rates in hot caustic soda may be less than 1 mil/y (0.025 mm/y). 

Copper-alloy corrosion behavior depends on the alloying elements added. Alloying copper with zinc increases corrosion rates in caustic solutions whereas nickel additions decrease corrosion rates. Silicon bronzes containing between 95% and 98% copper have corrosion rates as low as 2 mil/y (0.051 mm/y) at 140°F (60°C) in 30% caustic solutions. Figure 8.2 shows the corrosion rate in a 50% caustic soda evaporator as a function of nickel content. As is obvious, the corrosion rate falls to even lower values as nickel concentration increases. Caustic solutions attack zinc brasses at rates of 2 to 20 mil/y (0.051 to 0.51 mm/y). 

Figure 8.2 Corrosion rates of copper and copper-nickel alloys in a 50% caustic soda evaporator (Courtesy ofF. L. LaQue, Corrosion 10 391 1954.)...

TABLE 8.1 Corrosion Rates of Several Copper Alloys in 0.8% Ammonia at 104°F (40°C)... 

Copper alloys are attacked hy ammonium hydroxide, but corrosion rates increase only moderately with caustic concentration. 

An interesting effect is sometimes observed when cupronickels are galvanically coupled to less noble materials. The corrosion rate of the active metal is increased and the corrosion rate of the cupronickel is diminished, as expected. The diminished corrosion rate of the cupronickel can, however, diminish its fouling resistance since reduced production of copper ions lowers toxicity to copper-ion-sensitive organisms. 

Galvanic corrosion is the enhanced corrosion of one metal by contact with a more noble metal. The two metals require only being in electrical contact with each other and exposing to the same electrolyte environment. By virtue of the potential difference that exists between the two metals, a current flows between them, as in the case of copper and zinc in a Daniell cell. This current dissolves the more reactive metal (zinc in this case), simultaneously reducing the corrosion rate of the less reactive metal. This principle is exploited in the cathodic protection (Section 53.7.2) of steel structures by the sacrificial loss of aluminum or zinc anodes. 

It is also of interest to note that Wranglen considers that the decrease in the corrosion rate of steel in the atmosphere and the pitting rate in acid and neutral solution brought about by small alloying additions of copper is due to the formation of CU2S, which reduces the activity of the HS and Scions to a very low value so that they do not catalyse anodic dissolution, and a similar mechanism was put forward by Fyfe etal. to explain the corrosion resistance of copper-containing steels when exposed to industrial atmospheres. 

A striking example of the interaction of solution velocity and concentration is given by Zembura who found that for copper in aerated 0-1 N H2SO4, the controlling process was the oxygen reduction reaction and that up to 50°C, the slow step is the activation process for that reaction. At 75 C the process is now controlled by diffiision, and increasing solution velocity has a large effect on the corrosion rate (Fig. 2.5), but little effect at temperatures below 50 C. This study shows how unwise it is to separate these various... 

Fig. 2.5 Corrosion rate of a copper rotating disc in air-saturated 0-1 n H2SO4 at various temperatures (after Zembura )...

Lead, aluminium and copper corrode initially but eventually form completely protective films". Nickel in urban atmospheres does not form a completely protective film, the corrosion/time curve being nearly parabolic". The corrosion rate of zinc appears to become linear after an initial period of decreasing corrosion rate". 

Alexander for corrosion rates of copper and aluminium in tropical waters compared with those obtained around the British Isles suggests that the corrosion rate increases by a factor of two for every 10° C rise in temperature. 

Oxidation-reduction potential Because of the interest in bacterial corrosion under anaerobic conditions, the oxidation-reduction situation in the soil was suggested as an indication of expected corrosion rates. The work of Starkey and Wight , McVey , and others led to the development and testing of the so-called redox probe. The probe with platinum electrodes and copper sulphate reference cells has been described as difficult to clean. Hence, results are difficult to reproduce. At the present time this procedure does not seem adapted to use in field tests. Of more importance is the fact that the data obtained by the redox method simply indicate anaerobic situations in the soil. Such data would be effective in predicting anaerobic corrosion by sulphate-reducing bacteria, but would fail to give any information regarding other types of corrosion. 

Low-alloy steels, which contain about 2-3% of alloying elements, commonly copper, chromium and nickel. These steels still rust, but under certain conditions in the atmosphere, the rust formed becomes adherent and protective so that the corrosion rate becomes several times less rapid than with the ordinary steels mentioned above. These steels are often termed weathering steels. 

Briefly, the addition of about 0-2% of copper results in a two to three-fold reduction in the corrosion rate in air compared with a copper-free steel ... 

The corrosion rates of wrought iron and mild steel when immersed in seawater or buried in soil are not significantly different when the copper contents are similar. 

---