Alkaline Aqueous General Information Alkaline aqueous solutions are the most common form of aqueous cleaning chemistry. Alkaline materials are those with pH above 7. Most alkaline cleaners have pH's from 9 to 14. Cleaning solutions may consist of water, an alkali, a sequestrant, a surfactant of some type, and possibly a corrosion inhibitor. (See glossary for definitions.) Cleaners may by anionic, cationic, or neutral. Nonionic cleaners are lower foaming and may be more suitable for applications using agitation or sprays. The ionic cleaners will probably need more rinsing than nonionic types. Emulsifiers may be added to keep oils/greases dispersed in the solution. Aqueous processes may require rinse and dry stages. Alkaline cleaners have been used to remove: Cutting oils and coolants Salts Cosmolene Lubricating oils Grease Waxes Fingerprints Drawing compounds Shop dirt Oily particles Polishing and buffing compounds Rust and scale Alkaline cleaners may be designed to allow good separation between the water and contaminant such as oil. This allows control of the waste stream produced during cleaning. By allowing the contaminated liquid to separate, the aqueous solution can be recycled back to the process and the contaminant can be trapped and removed. High pH values do not automatically mean that a cleaner will etch susceptible metals. Inhibitors can reduce etch rates while maintaining cleaning capabilities. Silicates may be used as inhibiting agents. These materials must be thoroughly rinsed off to avoid problems with coating or plating operations. Alkaline cleaners used to clean aluminum must be very low alkaline or contain inhibitors, usually sodium silicate or chromate. Alkaline aqueous cleaners have been successfully used to clean mild and stainless steels and irons. Flash corrosion may be a problem with some materials. Strongly alkaline cleaners may tarnish brass; however inhibitors can be used. Magnesium can be affected by weakly alkaline, neutral, or slightly acidic cleaners but is not sensitive to strong alkalies or pH 10.6+. Silicates may offer some protection at lower pH. Acid chromate is also used. Tin is sensitive to strong alkalies. Both silicate and chromate are effective inhibitors and are more effective when combined. Lead and terneplate are sensitive to hot alkaline cleaners, especially those containing sequestrants or chlorides. Silicates have an inhibiting effect. Titanium is not attacked by strong alkaline cleaners unless chelating agents are present. Sodium zincate is an effective inhibitor in strongly alkaline cleaners used on glass and ceramic. Certain silicates have also been used. Alkaline cleaners may be used at a very broad range of temperatures. This may increase its suitability for general-purpose cleaning. Aqueous systems can be designed as closed-loop systems. Various filtration technologies can be used to separate the water from the contaminant. Cleaners of low alkalinity reduce saponification of fats thus reducing foaming if the soil is fatty. But high alkalinity may be necessary to obtain good bath life in the same situation. State Information | Glossary | Conversion Checklist | Comments Home | Process Advisor | Alternatives | Links | Search All SAGE material, Copyright© 1992, Research Triangle Institute Last Update: 06 May 1997 sage@rti.org http://clean.rti.org/alt.cfm?id=alk&cat=gi