Titanium, etching

S.A. Marzouk, Improved electrodeposited iridium oxide pH sensor fabricated on etched titanium substrates. Anal. Chem. 75, 1258—1266 (2003). 

Ir Ir02 electrodes (commercially available from Cypress Systems, Lawrence, KS) can measure pH in harsh environments or microscopic spaces [S. A. M. Marzouk, Improved Electrodeposited Iridium Oxide pH Sensor Fabricated on Etched Titanium Substrates, Anal. Chem. 2003, 75, 1258 A. N. Bezbaruah and T. C. Zhang, Fabrication of Anodically Electrodeposited Iridium Oxide Film pH Microelectrodes for Microenvironmental Studies, Anal. Chem. 2002, 74. 5726 D. O. Wipf. F. Ge, T. W. Spaine, and J. E. Baur, Microscopic Measurement of pH with Ir02 Microelectrodes, Anal. Chem. 2000, 72, 4921]. For pH measurement in nanoscopic spaces, see X. Zhang,... 

Figure 4.19 Comparison of the effect of acceleration voltage on topographic contrast of acid etched titanium specimen, (a) 20 kV, and (b) 5 kV.

The substrate is first coated, for instance, via electroless or physical vapor deposition with a thin (< 1 pm) metallic layer, which in turn is patterned by photolithography and wet etching. This layer serves two roles, as a plating base and as an electrically conducting layer for the finished structures. In the subsequent step a sacrificial layer, of about 5 pm in tliickness, is deposited on the substrate and also patterned by photolithography and wet etching. Titanium is used most often as the sacrificial material because it adheres well to the resist and to the electrodeposited layer and can be etched with hydrofluoric acid that does not attack other materials such as chromium, silver, nickel, copper, and which are usually used in the LIGA process. 

G. F. Zhang, X. Zheng, and Z. T. Liu, Nucleation and growth behaviour of diamond films deposited on chemically etched titanium alloy substrates, J. Cryst. Growth, 133(1-2) 117-122 (1993)... 

In the phosphate-fluoride process, the adherend is etched in 3% HF. The etched titanium is then immersed in an aqueous solution of the following composition for... 

Figure 20 SEM micrographs of Pasa Jell etched titanium alloy [25] (Courtesy Elsevier...

The Ruthenium dioxide-titanium dioxide based electrode is a new anodic material which has found an ever increasing application in chlorine electrolysis (see, for example, [336-341]). These anodes are known by their registered trade name DSA (dimensionally stable anodes). This material is a mixture of RUO2 and Ti02 mainly in the form of a solid solution deposited as a result of thermal decomposition of concentrated solution of salts on a cleaned and etched titanium substrate. 

Peripheral pitting and etching associated with the low current densities arising outside the main machining zone occur when higher current densities of 45-75 A/cm are appHed. This is a recurrent difficulty when high alloy, particularly those containing about 6% molybdenum, titanium alloys are electrochemicaHy machined. 

He concluded that for aluminium and titanium certain etching or anodization pretreatment processes produce oxide films on the metal surfaces, which because of their porosity and microscopic roughness, mechanically interlock with the polymer forming much stronger bonds than if the surface were smooth . 

Many applications of novolacs are found in the electronics industry. Examples include microchip module packaging, circuit board adhesives, and photoresists for microchip etching. These applications are very sensitive to trace metal contamination. Therefore the applicable novolacs have stringent metal-content specifications, often in the low ppb range. Low level restrictions may also be applied to free phenol, acid, moisture, and other monomers. There is often a strong interaction between the monomers and catalysts chosen and attainment of low metals levels. These requirements, in combination with the high temperature requirements mentioned above, often dictate special materials be used for reactor vessel construction. Whereas many resoles can be processed in mild steel reactors, novolacs require special alloys (e.g. Inconel ), titanium, or glass for contact surfaces. These materials are very expensive and most have associated maintenance problems as well. 

Fig. 12. Auger electron spectroscopy (AES) sputter-depth profile of CAA-treated titanium after various exposure.s in vacuum (a) as anodized, (b) 450°C for 1 h, and (c) 7(X)°C for 1 h. The sputter etch rate is 1.5 nm/min. The line indicates the original interface. The arrow denotes oxygen diffused into the substrate. Adapted from Ref. [51].

Surface cleaning/etches. As with aluminum and titanium, the most critical test for bonded steel joints is durability in hostile (i.e., humid) environments. The fact that the problem is a serious one for steel was illustrated in a study [117] that compared solvent cleaned (smooth) 1010 cold-rolled steel surfaces with FPL aluminum (microrough) substrates. Although the dry lap-shear strengths were not markedly different, stressed lap-shear joints of steel adherends that were exposed to a humid environment failed in less than 30 days, whereas the aluminum joints lasted for more than 3000 days. 

Etch priming is widely used on aluminium alloy, and is particularly effective on cadmium and zinc. The adhesion to stainless steel and titanium is good. It has also been used quite widely on bare steel and on magnesium alloy, but on these metals its performance is not, in the opinion of some investigators, always quite reliable. For best protection the etch primer coating is followed with a full paint scheme. 

Titanium can be etched in fluorine-, chlorine-, or bromine-containing gases, because all the halides are volatile. Chlorides and bromides have been studied to a great extent since they result in high selectivity over silicon- containing films, and do not promote staining on gold (77). 

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