Titanium corrosion rate

Titanium Corrosion Rate Data- Commercially Pure Grades... 

The titanium oxide film consists of mtile or anatase (31) and is typically 250-A thick. It is insoluble, repairable, and nonporous in many chemical media and provides excellent corrosion resistance. The oxide is fully stable in aqueous environments over a range of pH, from highly oxidizing to mildly reducing. However, when this oxide film is broken, the corrosion rate is very rapid. Usually the presence of a small amount of water is sufficient to repair the damaged oxide film. In a seawater solution, this film is maintained in the passive region from ca 0.2 to 10 V versus the saturated calomel electrode (32,33). 

Titanium, HasteUoy (grades C22 and C276), and 316 stainless steel all exhibit corrosion rates of less than 0.08 mm/yr at room temperature in 35 wt % chloric acid solutions (2). 

Steel is the most common constructional material, and is used wherever corrosion rates are acceptable and product contamination by iron pick-up is not important. For processes at low or high pH, where iron pick-up must be avoided or where corrosive species such as dissolved gases are present, stainless steels are often employed. Stainless steels suffer various forms of corrosion, as described in Section 53.5.2. As the corrosivity of the environment increases, the more alloyed grades of stainless steel can be selected. At temperatures in excess of 60°C, in the presence of chloride ions, stress corrosion cracking presents the most serious threat to austenitic stainless steels. Duplex stainless steels, ferritic stainless steels and nickel alloys are very resistant to this form of attack. For more corrosive environments, titanium and ultimately nickel-molybdenum alloys are used. 

The successful clinical use of titanium and cobalt-chromium alloy combinations has been reported Lucas etal. also investigated this combination using electrochemical studies based on mixed potential and protection potential theories. Verification of these studies was made by direct coupling experiments. The electrochemical studies predicted coupled corrosion potentials of -0.22 V and low coupled corrosion rates of 0.02 ft A/cm. Direct coupling experiments verified these results. The cobalt-titanium interfaces on the implants were macroscopically examined and no instances of extensive corrosion were found. Overall, the in-vitro corrosion studies and the examination of retrieved prostheses predicted no exaggerated in-vivo corrosion due to the coupling of these cobalt and titanium alloys. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

Other alloys of molybdenum which have been investigated for their corrosion resistance contain 10-50% Ta and were found to have excellent resistance to hydrochloric acid. Ti-Mo alloys were found to resist chemicals that attack titanium and Ti-Pd alloys, notably strong reducing acids such as hot concentrated hydrochloric, sulphuric, phosphoric, oxalic, formic and trichloroacetic. For example, a Ti-30Mo alloy has the following corrosion rates in boiling 20% hydrochloric acid, 0-127-0-254 mm/y in 10% oxalic acid at 100°C, 0-038 mm/y, which compares favourably with the respective rates of 19-5 and 122 mm/y for the Ti-0-2Pd alloy. 

The addition of 0-2% palladium to titanium decreases the corrosion rate in boiling 5% sulphuric acid by a factor of 500, and in boiling 5% hydrochloric acid by a factor of 1 500, in relation to the rates obtained with unalloyed titanium. The addition of palladium in these quantities thus provides an adequate measure of resistance to relatively weak concentrations of the acids mentioned. ... 

Furthermore, the restrictions on operating voltage that apply to titanium in a marine enviroment are not always relevant to titanium in soils free of chloride contamination. Coke breeze is, however, an integral part of the groundbed construction and ensures a lower platinum consumption rate. However, for some borehole groundbeds, platinised niobium is preferred, particularly in the absence of carbonaceous backfill or in situations where the water chemistry within a borehole can be complex and may, in certain circumstances, contain contaminants which favour breakdown of the anodic Ti02 film on titanium. In particular, the pH of a chloride solution in a confined space will tend to decrease owing to the formation of HOCl and HCl, and this will result in an increase in the corrosion rate of the platinum. 

SCWO testing was conducted using energetic hydrolysate slurried with shredded and micronized dunnage. The tests showed very low corrosion rates with an inexpensive titanium liner and excellent organic destruction efficiency. The committee concluded that these tests were successful. 

Titanium liner showed corrosion rates compatible with 500 hr of operational life. Other test data indicated that a platinum liner (per Configuration 5 in Table 5-2) would be sufficiently corrosion resistant to not need change-out during HD hydrolysate disposal at Blue Grass. 

Figures 16.8 and 16.9 show only the anodic polarization curves for corrosion cells. The important question is, where do these curves intersect with the polarization curves for likely cathodic reactions, such as hydrogen evolution or oxygen absorption The intersection point defines the corrosion current density icorr and hence the corrosion rate per unit surface area. As an example, let us consider the corrosion of titanium (which passivates at negative Eh) by aqueous acid. In Fig. 16.10, the polarization curves for H2 evolution on Ti and for the Ti/Ti3+ couple intersect in the active region of the Ti anode. To make the intersection occur in the passive region (as in Fig. 16.11), we must either move the H+/H2 polarization curve bodily...

The direct electrochemical measurement of such low corrosion rates is difficult and limited in accuracy. However, electrochemical techniques can be used to establish a database against which to validate rates determined by more conventional methods (such as weight change measurements) applied after long exposure times. Blackwood et al. (29) used a combination of anodic polarization scans and open circuit potential measurements to determine the dissolution rates of passive films on titanium in acidic and alkaline solutions. An oxide film was first grown by applying an anodic potential scan to a preset anodic limit (generally 3.0 V), Fig. 24, curve 1. Subsequently, the electrode was switched to open-circuit and a portion of the oxide allowed to chemically dissolve. Then a second anodic... 

Moderate resistance general corrosion rate varies with the type of acid, concentration and temperature High corrosion rates, used for pickling, etching Pd, Ru, Mo, Ni render the titanium to be more resistant to corrosion... 

The corrosion resistance of steel can be greatly increased by alloying with chromium to form the stainless steels. Figure 12 shows the effect of increasing chromium content on the corrosion rate of steel. At 12-14% Cr there is a dramatic decrease in corrosion rate. The corrosion resistance is due to the formation of a thin adherent layer of chromium oxide on the steel surface [23]. The steel will remain stainless provided the oxide layer remains intact or can be rapidly repaired, i.e. the steel is exposed to oxidising conditions. The precipitation of chromium carbide at grain boundaries will cause disruption of this oxide film (See Sect. 3.2.5) and hence localised corrosion. Precipitation of chromium carbide can be reduced by alloying with elements which form carbides more readily than chromium, e.g. titanium, niobium, and tantalum. 

The corrosion rates of the titanium casing under cathodical conditions were smaller than that of stainless steel in nitric acid ( 0,05 mm Ti/y). This value as well as the corrosion rate of the platinized tantalum anode is within the expected order of magnitude (< 0,005 mm/y). 

Alloy B-3 can tolerate quite high concentrations of hydrochloric acid without severe corrosion, provided the solution is free of oxidizing ions such as Fe, Cu" ", Ni" " Mo" " , and Ti" ". In contrast, hydrochloric acid solutions containing these ions can be easily handled in vessels made of titanium, which would quickly corrode in pure hydrochloric acid. Even low concentrations (<30 ppm) of ferric ion in hydrochloric acid have been demonstrated to greatly reduce the corrosion rate of titanium. ... 

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