Titanium copper-based

Recently P. CHABARDES has proposed new titanium / copper based catalysts. [6] which allow a simple, efficient and selective isomerisation of a-acetylenic alcohols in liquid phase. 

Titanium in contact with other metals In most environments the potentials of passive titanium. Monel and stainless steel, are similar, so that galvanic effects are not likely to occur when these metals are connected. On the other hand, titanium usually functions as an efficient cathode, and thus while contact with dissimilar metals is not likely to lead to any significant attack upon titanium, there may well be adverse galvanic effects upon the other metal. The extent and degree of such galvanic attack will depend upon the relative areas of the titanium and the other metal where the area of the second metal is small in relation to that of titanium severe corrosion of the former will occur, while less corrosion will be evident where the proportions are reversedMetals such as stainless steel, which, like titanium, polarise easily, are much less affected in these circumstances than copper-base alloys and mild steel. 

Copper-base alloys will corrode in aerated conditions. It is, therefore, sometimes appropriate to consider cathodic protection. It becomes particularly relevant when the flow rates are high or when the design of an item causes the copper to be an anode in a galvanic cell (e.g. a copper alloy tube plate in a titanium-tubed heat exchanger). Corrosion can be controlled by polarisation to approximately — 0-6V (vs. CU/CUSO4) and may be achieved using soft iron sacrificial anodes. 

Both metals are applied to copper-base alloys, stainless steels and titanium to stop bimetallic corrosion at contacts between these metals and aluminium and magnesium alloys, and their application to non-stainless steel can serve this purpose as well as protecting the steel. In spite of their different potentials, zinc and cadmium appear to be equally effective for this purpose, even for contacts with magnesium alloys Choice between the two metals will therefore be made on the other grounds previously discussed. 

The use of shape-memory alloys as actuators depends on their use in the plastic martensitic phase that has been constrained within the structural device. Shape-memory alloys (SMAs) can be divided into three functional groups one-way SMAs, tw o-vvav SMAs, and magnetically controlled SMAs. The magnetically controlled SMAs show great potential as actuator materials for smart structures because they could provide rapid strokes with large amplitudes under precise control. The most extensively used conventional shape-memory alloys are the nickel-titanium- and copper-based alloys (see Shape-Memory Alloys). 

Titanium. Unlike other metals, titanium normally does not pit, is not susceptible to stress corrosion, is free from local corrosion under fouling organisms, is free from impingement and cavitation attack at velocities which attack copper-base alloys, and is not susceptible to sulfide attack in contaminated sea water. Experiments with water velocities at 20 to 50 feet per second show no attack on titanium. 

A large number of copper-base and nickel-base alloys (such as cupro-nickels, Monel, and aluminum brass) have been used in sea-water service with success. Special materials such as Hastelloy C, Illium, and titanium are available for extremely corrosive situations. The evidence, so far, indicates titanium to be outstanding and to rank above other commercially available metals in corrosion resistance under conditions involving high temperature, velocity, and other adverse environmental conditions. 

For use in heat exchangers, the thermal conductivity is of interest. In titanium it is at the same level as in austenitic stainless steels, but much lower than in copper-based alloys. Here, it must also be taken into account that the wall thickness of titanium can be less, partly because of higher strength and partly due to superior corrosion properties compared with Cu alloys. 

Anodizing is the process of forming a surface oxide film by electrochemical oxidation. It is used as a surface finishing technique particularly for aluminium but also for titanium, copper and steel, and for the manufacture of electrolytic capacitors based on aluminium, tantalum and niobium. 

The major workhorse of the diaphragm-cell electrolysis is the ELTECH electrolyzer, H-4 and MDC-55. There are several conunon features in these cell designs, as can be seen in Fig. 5.17. The base of the cell is a copper plate with spot faced holes to anchor the anodes (Fig. 5.18). It also acts as a current conductor. Either a sheet rubber cover or a titanium base cover using rubber rings around the anode posts protects the copper base. 

Alloys having litde or no sensitivity are claimed to be 7075-T6 aluminum Haynes 188 (cobalt-base) beryllium copper (copper-base) Types 304, 316, and 310 austenitic stainless steels Type 430 high-hardness ferritic steel and age-hardened austenitic A286 steel. Titanium-base alloy T1-6A1-4V exhibits moderate sensitivity. Alloys with high sensitivity are Haynes 25 (cobalt-base) and iron-base alloys, including medium- and high-strength steels. 

Besides nickel, cobalt, and copper-based alloys, there are other industrial non-ferrous corrosion-resistant metals such as the reactive metals zirconium, titanium, niobium, and tantalum. Table 2-18 shows the chemical composition and UNS designations of the reactive metals alloys. 

Titanium is immune to corrosion in all natural waters, including highly polluted seawater, at temperatures up to the boiling point. Titanium has replaced copper-based alloys that were corroding in the presence of sulfides, as well as stainless steels that were suffering from pitting and SCC caused by chlorides. 

BRUSH ALLOY 25, a heat-treatable beryllium copper product contains 1.80 to 2.00% beryllium. BRUSH ALLOY 25 is resistant to hydrogen embrittlement, and not susceptible to either sulfide stress cracking or chloride stress cracking. Moreover, in marine and certain industrial environments this alloy outperforms stainless steel, titanium, and most copper based alloys. Beryllium copper is available in a wide range of forms, including strip, tube, rod, bar, extrusions, casting and master alloy, and forging billet. 

Where corrosion of copper-based alloys by sulfides in the hydrocarbon stream is excessive, consideration should be given to either providing a greater corrosion allowance than normal or to the use of materials such as nickel-based alloys (such as Monel, Incoloy 801), aluminum alloys (such as Alclad), and titanium alloys. 

SMAs include copper-zinc-aluminum, copper-aluminum-nickel, and nickel-titanium (NiTi) alloys. NiTi alloys exhibit better mechanical properties than copper-based SMAs which were first developed in the early 1960s. SMAs have been widely used in retrofit and strengthening projects in the field of damping, active vibration control, and prestressing or posttensioning of structures with fibers and tendons, while recently, iron-based SMAs were developed that can reduce the cost. 

---