Metal deposits cleaning

Electroless reactions must be autocatalytic. Some metals are autocatalytic, such as iron, in electroless nickel. The initial deposition site on other surfaces serves as a catalyst, usually palladium on noncatalytic metals or a palladium—tin mixture on dielectrics, which is a good hydrogenation catalyst (20,21). The catalyst is quickly covered by a monolayer of electroless metal film which as a fresh, continuously renewed clean metal surface continues to function as a dehydrogenation catalyst. Silver is a borderline material, being so weakly catalytic that only very thin films form unless the surface is repeatedly cataly2ed newly developed baths are truly autocatalytic (22). In contrast, electroless copper is relatively easy to maintain in an active state commercial film thicknesses vary from <0.25 to 35 p.m or more. 

Eitch indented into the tube. Tube 48 was a clean copper tube that ad 50 longitudinal flutes pressed into the wall (Gener Electric double-flute profile, Diedrich, U.S. Patent 3,244,601, Apr. 5, 1966). Tubes 47 and 39 had a specially patterned porous sintered-metal deposit on the boihng side to promote nucleate boiling (Minton, U.S. 

Alter the environment to render it less eorrosive. This approach may be as simple as maintaining clean metal surfaces. It is well known that the chemistry of the environment beneath deposits can become substantially different than that of the bulk environment. This difference can lead to localized, underdeposit corrosion (see Chap. 4, Underdeposit Corrosion ). The pit sites produced may then induce corrosion fatigue when cyclic stresses are present. The specific steps taken to reduce corrosivity vary with the metal under consideration. In general, appropriate adjustments to pH and reduction or elimination of aggressive ions should be considered. 

At least as important, however, is the need to ensure clean metal surfaces because, as stated earlier, concentration cell corrosion mechanisms commonly occur under boiler section sludges and deposits. 

Inadequate acid cleaning procedures also may introduce traces of copper into the boiler (typically originally present as copper-containing deposits), which can plate out onto clean metal surfaces and cause localized, anodic area pitting corrosion. 

Fig. 2 Infrared spectra taken after metal deposition and exposure to increasing amounts of CO at a constant temperature a 0.02 ML Rh, 60 K b 0.013 ML Pd, 60 K c 0.2ML V, 90 K. CO bands present on nominally clean surfaces are due to CO adsorption from the background during sample preparation...

Focusing on selected aspects, a few reviews have covered SAM-controlled electrometallization [29], [30, 183]. Reviewing work published over the past 15 years, the following sections summarize the current state-of-the-art and discuss the different routes currently pursued. For this purpose we first start with a brief account of metal deposition on a clean metal substrate [29]... 

Cyanide Baths. Cyanide zincs have excellent covering power and throwing power, good cleaning ability, deposit relatively pure zinc, are capable of thick deposits, and require litde control. Zinc deposits from cyanide baths are purer than from the other baths, but still contain traces of the metal contaminants, bTightener components, sulfur, hydrogen, and other gases. Pure, sulfur-free zinc is resistant to hydrochloric acid (141,142). 

Because of the ability of glucoheptonates to chelate calcium and iron and dissolve rust films without attacking the bare metal, they are very useful as metal surface cleaners. They are often considered a ferrous corrosion inhibitor, but the real function of these chelants is their ability to dissolve iron- and calcium-rich deposits on the metal surface, within a pH range of 5 to 9, and to provide clean metal surfaces. Thus they permit access by other true corrosion inhibitors and help to minimize differential aeration and under-deposit corrosion mechanisms. 

The deposition of crystalline scales, air-borne contaminants, biofilms, etc. tends to be higher on previously fouled or corroded surfaces than on clean surfaces. Also, deposition and fouling affect both the rates and mechanisms of corrosion on a clean metal surface. It can therefore be useful to obtain subjective information on deposition and fouling tendencies in a cooling system, provided that the methods are simple and produce results quickly. The use of blank coupons inserted in a bypass corrosion rack can often provide this support information. 

Copper 18 mm diameter discs were utilized as substrates for glucose detection. After cleaning, approximately 10 lL of the nanosphere suspension (4% solids, 390 nm diameter) was drop coated onto each copper substrate and allowed to dry in ambient conditions.58 The substrates were then mounted into an electron beam deposition system for metal deposition (Kurt J. Lesker, Clairton, PA). Silver metal films (dm = 200 nm) were deposited over and through the sphere masks on the substrates.58 59... 

Sodium or rubidium atoms were deposited in much the same way as Al- and Ca-atoms, with the exception that the atoms were obtained from SAES getter sources (zeolites), which could be mounted, one at a time, into a heated glass shield (to maintain a stream of atoms in the correct direction in the UHV chamber), then opened in UHV and maintained clean during the course of the measurements1. Spectroscopically clean metal films could be prepared from these sources, as a check on source purity. 

It is perhaps obvious that the nature of the interface between a molecular solid (polymer) and a (clean) metal surface is not necessarily equivalent to the interface formed when a metal is vapor-deposited (essentially atom-by-atom ) on to the (clean) surface of the polymer or molecular solid. Atoms of all metals are active in the form of individual atoms , even gold atoms. In the context of the new polymer LEDs, some of the works discussed in chapter 7 involve the study of the early stages of formation of the interface in the latter configuration (metal-on-polymer interfaces). Very little has been reported on conjugated polymer-on-metal interfaces, however, primarily because of the difficulties in preparing monolayers of polymer materials on well defined metal substrates appropriate for study (via PES or any other surface sensitive spectroscopy). The issues discussed below are based upon information accumulated over two decades of involvement with the surfaces of condensed molecular solids and conjugated polymers in ultra-thin form, represented by the examples in the previous chapter. 

SAMs can be formed by exposing a clean metal surface to a solution of the surface active molecule or complex at room temperature, followed by rinsing with a solvent. The bulk concentration has a significant influence over the quality of the monolayer formed. Very low, i.e. micromolar, concentrations result in slow self-assembly and favor the production of large crystalline domains. It is possible for the deposition solvent to become entrapped in the monolayer and this entrapped solvent may not be removed in the subsequent washing cycle. 

---