Titanium surface corrosion products

It should be noted that titanium aUo5 are generally not susceptible to sulfide stress cracking (SSC) in HjS-rich, sulfides, and/or sulfur containing environments (e.g., sour gas/oil well fluids). This inherent SSC resistance stems from the fact that formation of titanium sulfide corrosion products is not thermodynamically favored, such that stability of titanium s protective oxide surface film wiU prevail even at higher service temperatures. In these hot sour brine service environments, resistance to chloride-induced SCC is a more relevemt issue for titanium alloys. 

Although most metals display an active or activation controlled region, when polarised anodically from the equilibrium potential, many metals and perhaps even more so alloys developed for engineering applications, produce a solid corrosion product. In many examples the solid is an oxide that is the stable phase rather than the ion in solution. If this solid product is formed at the metal surface and has good intimate contact with the metal, and features low ion-conductivity, the dissolution rate of the metal is limited to the rate at which metal ions can migrate through the film. The layer of corrosion product acts as a barrier to further ion movement across the interface. The resistance afforded by this corrosion layer is generally referred to as the passivity. Alloys such as the stainless steels, nickel alloys and metals like titanium owe their corrosion resistance to this passive layer. 

Reasonably, the corrosion form is typical at relatively high velocities between the material surface and flie fluid, and it is particularly intensive in cases of two-phase or multiphase flow, i.e. hquid-gas and liquid-solid particle flow. Components often liable to erosion corrosion are propellers, pumps, turbine parts, valves, heat exchanger tubes, nozzles, bends, and equipment exposed to liquid sputter or jets. Most sensitive materials are those normally protected by corrosion products with inferior strength and adhesion to flie substrate, e.g. lead, copper and its alloys, steel, and under some conditions aluminium/aluminium alloys. Stainless steel, titanium... 

If the critical shear stress that acts on the layer of corrosion products present at a surface is exceeded, mechanical film damage leads to a strong increase in the rate of corrosion. According to this view, stainless steel and titanium are not susceptible to flow accelerated corrosion because the thin passive oxide films formed on these metals are more resistant to shear stresses than the corrosion product layers found on copper and its alloys [16]. 

For more than a century, a number of different aluminum alloys have been commonly used in the aircraft industry These substrates mainly contain several alloying elements, such as copper, chromium, iron, nickel, cobalt, magnesium, manganese, silicon, titanium and zinc. It is known that these metals and alloys can be dissolved as oxides or other compounds in an aqueous medium due to the chemical or electrochemical reactions between their metal surfaces and the environment (solution). The rate of the dissolution from anode to cathode phases at the metal surfaces can be influenced by the electrical conductivity of electrolytic solutions. Thus, anodic and cathodic electron transfer reactions readily exist with bulk electrolytes in water and, hence, produce corrosive products and ions. It is known that pure water has poor electrical conductivity, which in turn lowers the corrosion rate of materials however, natural environmental solutions (e g. sea water, acid rains, emissions or pollutants, chemical products and industrial waste) are highly corrosive and the environment s temperature, humidity, UV light and pressure continuously vary depending on time and the type of process involved. ... 

This is a clear liquid that vaporizes and, on contact with damp air, combines with w ater to produce a dense acid mist. Titanium tetrachloride can be painted on to surfaces, such as fume cupboard sills, from which it will evaporate over a period of several seconds showing the airflow patterns close to the surface. (Airflow patterns close to a surface could also be visualized by fastening short filaments of wool or cotton to the surface). Titanium tetrachloride can also be used, when soaked onto a cotton swab, in a similar way to a smoke tube. It is a simple and inexpensive method but the production of smoke, which is toxic and corrosive, is uncontrollable. 

The production of corrosion-resistant materials hy alloying is well established, hut the mechanisms are noi lull) understood. It is known, of course, that elements like chromium, mckcl. titanium, and aluminum depend for their corrosion resistance upon a tenacious surface oxide layer (passive film). Alloying elements added for the purpose of passivation must be in solid solution. The potential of ion implantation is promising because restrictions deriving from equilibrium phase diagrams frequently do not applv li e., concentrations of elements beyond tile limits of equilibrium solid solubility might he incorporated). This can lead to heretofore unknown alloyed surfact-s which are very corrosion resistant... 

Titanium dioxide (Ti02) is one of the most widely used semiconductors for heterogeneous photocatalysis. This is mainly due to its activity, photostabihty, non-toxicity and commercial availability. It is found in nature and can exist in three crystal modifications rutile, anatase and brookite (Kirk-Othmer, 1996). Its composition is temperature dependent at calcination temperatures above 900 K, the anatase modification is transformed into rutile. Ti02 is insoluble in water and in diluted acids, but it dissolves slowly in hot sulfuric acid (Remy, 1973). It has a high surface activity and corrosion stabihty. The commercial production of this white pigment has been known since the early 1900s. 

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