A good alkaline cleaning material must be soluble in water and its solution must possess superior ability to:
- Wet the surface of the metal being cleaned.
- Wet and penetrate the soil being removed.
- Dissolved or saponify animal and vegetable oils and greases or temporarily emulsify or suspend the insoluble or nonsaponifiable oils and solid dirt particles.
- Soften water to prevent formation of insoluble calcium and magnesium soaps.
- Rinse freely.
- Prevent attack on or tarnish of the metal surface.
- Neutralize acidic substances introduced with the soiled metal without change of pH.
- Remove the dirt effectively in a reasonable time in average equipment.
- Producing a metal surface that will plate satisfactorily.
- Form no excessive foam or suds in the cleaning and rinsing operations.
The chemical use for compounding alkaline cleaners may be listed, but no single alkali makes a good all-round cleaner. If takes a combination of alkalis with the proper soaps or surfactants, chelating agents, and other chemicals to get maximum metal cleaning effectiveness.
Soda ash sodium carbonate, Na2CO3, is one of the most widely used alkalis. It provides good buffering capacity, alkalinity, and water softening and has good compounding properties. It is an excellent carrier for liquid surface active agents in dry mix compounds.
Sodium hydroxide or caustic soda (NaOH) is the most important alkali for metal cleaning. Caustic soda has the property of saponifying fats and oils to make water soluble soaps, reacting with the amphoteric metals and their oxides to form soluble salts, splitting esters, attacking organics, and reacting vigorously. It has the highest conductivity of all the alkalis and is important for heavy duty metal cleaning compounds, alkaline dusters, alkaline permanganate scale conditioners, and many plating baths.