SECTION 8 

 MISCELLANEOUS ALLOYS 



The miscellaneous alloys are those alloys or 

 metals which are "one of a kind" or do not belong to 

 any of the previous classes of alloys discussed. These 

 alloys would not be considered constructional 

 because of their price, mechanical properties, 

 scarcity, and, in some cases, poor corrosion resis- 

 tance. Many of them could be used advantageously in 

 specialty or unique applications. 



The chemical compositions of the miscellaneous 

 alloys are given in Table 85, and their corrosion rates 

 and types of corrosion in Table 86. 



Alloys columbium, gold, platinum, 90% 

 platinum-10% copper, 75% platinum- 25% copper, 

 tantalum, and tantalum-tungsten (Ta60) were 

 uncorroded during exposure both at depth and at the 

 surface. 



Alloy MP35N neither corroded nor was suscep- 

 tible to stress corrosion during 189 days of exposure 

 at the 6,000-foot depth. The MP35N bolts and nuts 

 were in a block of 6A1-4V titanium and were torqued 

 to 50 ft-lb. There was also no galvanic corrosion of 

 either member of the couple. 



The corrosion of the three magnesium alloys 

 (MIA, AZ31B, and HK31A) and beryllium was so 

 rapid that their use in seawater would be impractical. 



Platinum alloys containing 50 and 75% copper 

 were etched and pitted after 402 days of exposure at 

 the 2,500-foot depth. Such alloys are usually used for 

 contacts in electrical applications. These two alloys 

 would not be satisfactory for use in seawater. 



Silver was attacked by the uniform thinning type 

 of corrosion in seawater. The thin tarnish-like film is 

 an excellent insulator; hence, silver could not be used 

 as electrical contacts in seawater. 



8.1. DURATION OF EXPOSURE 



The effects of duration of exposure on some of 

 the miscellaneous alloys are shown in Figures 18, 19, 

 and 20. The corrosion rates of arsenical, chemical, 

 and tellurium lead, lead-tin solder, tin, and zinc 

 decreased with duration of exposure (Figures 18 and 



19), except for lead-tin solder and zinc at the 

 2,500-foot depth. The corrosion rates of these two 

 alloys increased with increasing time of exposure. At 

 the 6,000-foot depth the corrosion rate of tin 

 increased initially, and, thereafter, decreased with 

 increasing time of exposure. The extremely high 

 corrosion rate for tin after 751 days of exposure 

 (Table 86), obviously, is an error and must be dis- 



Only surface seawater data were available for 

 molybdenum and tungsten, and the effects of dura- 

 tion of exposure are shown in Figure 20. The 

 corrosion rate of molybdenum decreased, becoming 

 asymptotic with increasing time of exposure. The 

 corrosion rate of tungsten increased linearly with 

 time, at least during the first 760 days of exposure. 



8.2. EFFECT OF DEPTH 



The effects of depth on the corrosion of some of 

 the miscellaneous alloys after 1 year of exposure are 

 shown in Figure 21. The corrosion of lead, lead-tin 

 solder, molybdenum, tungsten, and tin was greater at 

 the surface than at depth in the Pacific Ocean. Only 

 the corrosion of zinc was greater at depth than at the 

 surface. 



8.3. EFFECT OF CONCENTRATION OF OXYGEN 



The effects of changes in the concentration of 

 oxygen in seawater are shown in Figure 22. The 

 corrosion rates of arsenical, chemical, and tellurium 

 lead, lead-tin solder, molybdenum, tungsten, and tin 

 were higher at the highest concentration of oxygen 

 than at the lowest, but the increases were not neces- 

 sarily proportional or linear. Only the corrosion of 

 zinc was not uniformly influenced by changes in the 

 concentration of oxygen in seawater between the 

 limits of 0.4 to 5.75 ml/1. 



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