Surface roughness cleaning

One of the biggest challenges in this industry is the wide variety of substrates that can be encountered for any given application. Not only can the materials be substantially different in their chemical make up, but they may also be quite different in surface roughness, surface curvature and thermal expansion behavior. To help adhesion to these substrates, preparation of the surface to be bonded may be critical. This preparation may be as simple as a cleaning step, but may also include chemical priming and sanding of the surface. 

Blast-cleaning produces a roughened surface and the profile of that surface is important. The size and nature of the profile is largely determined by the type and size of the abrasive used. To identify and control surface roughness, comparators are available conforming to ISO 8503/1 specifica-... 

Welds on steelwork need special attention because of the different composition of weld metal and adjacent steelwork, the rough surface and spatter caused by welding and the presence of welding flux. The latter is often alkaline and destructive to many paints. It is necessary to clean thoroughly, preferably by reblasting for 25-50 mm each side of the weld, fare the rough metal and wash off residual flux. The cleaned surface should then be stripe coated with the primer used on the remainder of the surface. 

Figures 30 and 31 are representative of the results. It is obvious that a rough, clean surface is better for boiling heat transfer than is a smooth, clean one. In fact, for a given AT1 the heat transfer rate shown for the coarse polish is well over double that for the smooth metal.

As indicated above, the goal in recent years in the ultra-large-scale integrated-circuit (ULSI) industry was to reduce contamination on surfaces to below the level detectable with state-of-the-art equipment. For economic and environmental reasons, this had to be replaced by one referred to as just clean enough. This requires that action-reaction-type relationships be identified between contaminants and their influence on a given surface in order to be able to fix acceptable levels of organic and metallic contamination, surface roughness, and other surface characteristics. 

The structure of clean surfaces of polyatomic solids (alloys, halides, oxides, sulfides, etc.) should be explored along with molecular solid surfaces (organic systems). More open, rough surfaces with high Miller indices should be investigated, including the structure of atoms and molecules bonded to steps and kinks on surfaces. Such sites are known to be key for some important surface chemical processes, but little is known of their structure. 

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