Engineering surfaces of metals

The importance of a clean surface for painting is paramount (see Engineering surfaces of metals). For metallic substrates, either mechanical or chemical surface treatment is almost always needed to remove surface contamination and promote adhesion. Chemical pre-treatment of metals prior to painting is an effective method of surface conversion that can provide both corrosion resistance and improved paint adhesion. For ferrous metals, the most common chemical pre-treatment is a phosphate for aluminium (and many other non-ferrous metals), the most effective pre-treatment is chromate. Metals must first be cleaned with an alkaline cleaner and then rinsed before they can be converted chemically in an immersion bath or by spray. 

Engineering surfaces of metals J F WATTS Practical metallic surfaces are oxidized, contaminated and rough pre-treatments adhesion... 

Microbiocides may be toxic to humans therefore, care must be taken when used. When selecting the microbiocide, the field engineer can obtain pertinent information on chemicals from the service company providing the chemicals. The microbiocide selected must be compatible with the system in which it is being used. Some chemicals such as quaternary amines have dual functions one as microbiocides and the other as film-forming corrosion inhibitors. Insufficient concentrations of this type of chemical may not be enough to coat the whole surface of metal and can cause pitting corrosion. The selection must also depend on chemicals that can produce the desired control in minimum time limits and... 

Poly(a-olefins) or PAOs, polyol esters and diesters are now used in automotive and marine engine oils. To understand how an ester lubricates, it is important to consider its behavior in the different lubrication regimes, especially boundary lubrication when the properties of the bulk lubricant (e.g. viscosity) are of minor importance. The chemical properties of the lubricant responses under extreme conditions will become increasingly important. The polar ester will preferentially stick to the surface of metal when a small amount of ester is added to a low viscosity nonpolar fluid (PAO), (Randles, 1999 Spikes, 1999). When the two metal surfaces come closer together, the polar ester molecules stay in the contact zone. The use of fully synthetic engine oil formulations has produced some improvement in viscosity control and engine cleanliness in the piston and valve train areas over petroleum-based oils (Boehringer, 1975 Frame et ah, 1989 Kennedy, 1995 Lohuis and Harlow, 1985). 

The structure of surfaces of metals and alloys used in engineering is never perfect (see Chapter 3). These surfaces reproduce structural features of the bulk metal such as phase boundaries, grain boundaries, emerging dislocations, non metallic inclusions of different composition and size, they exhibit roughness at different scales, and they are often plastically deformed due to machining or polishing. Thin passive oxide films are able to cover up many of these imperfections, but it is unlikely that locally their structure is not affected by them. Passive films on real metal surfaces therefore contain a variety of structural defects that can act as preferred sites for anodic depassivation and pit initiation. 

If the ECM of titanium is attempted in sodium chloride electrolyte, very low (10—20%) current efficiency is usually obtained. When this solution is replaced by some mixture of fluoride-based electrolytes, to achieve greater efficiencies (> 60%), a higher voltage (ca 60 V) is used. These conditions ate needed to break down the tenacious oxide film that forms on the surface of titanium. It is this film which accounts for the corrosion resistance of titanium, and together with its toughness and lightness, make this metal so useful in the aircraft engine industry. 

Little scientific examination of the deterioration of materials at depth has been undertaken except that by the US Naval Civil Engineering Laboratory and Naval Research, Laboratory. The results of this work were reported by Reinhart in 1966 and more recently the work has been reviewed by Kirk . Typical corrosion data for a selection of metals exposed in the Pacific Ocean at several sites and for different times are shown in Table 2.19 and are compared with results obtained in surface waters at Wrightsville Beach by International Nickel Inc. 

The CRC-Elsevier materials selector , 2nd edition, N.A. Waterman, and M.E Ashby CRC Press (1996) ISBN 0412615509. (Now, also available on CD-ROM). Basic reference work. Three-volume compilation of data for all materials includes selection and design guide. The Materials Selector is the most comprehensive and up-to-date comparative information system on engineering materials and related methods of component manufacture. It contains information on the properties, performance and processability of metals, plastics, ceramics, composites, surface treatments and the characteristics and comparative economics of the manufacturing routes which convert these materials into engineering components and products. 

Catalysts can be poisoned, or inactivated. A common cause of such poisoning is the adsorption of a molecule so tightly to the catalyst that it seals the surface of the catalyst against further reaction. Some heavy metals, especially lead, are very potent poisons for heterogeneous catalysts, which is why lead-free gasoline must be used in engines fitted with catalytic converters. The elimination of... 

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