Purchasing experience: acidic metal cleaning agent and alkaline metal cleaning agent which is good?

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There are various kinds of dirt on the metal surface, oil soluble, water soluble, metal rust, scale, dust and so on. Acid cleaning is mainly used to clean inorganic salt scale, alkaline oxides and hydroxides on metal surfaces. Commonly used acids are inorganic acids and organic acids, of which hydrochloric acid and sulfuric acid are the most widely used.

On the other hand, an acid radical ion of phosphoric acid, citric acid, or the like has a plurality of coordination atoms, and can be combined with a divalent metal ion to form a chelate. The effect of acid on metal rust is mainly through acid-base neutralization reaction to convert it into water-soluble salt. Because metal rust is mainly metal oxides and hydroxides. If the acid group has a complex effect on the metal ion, it is also beneficial to the dissolution of the metal oxide.

alkaline metal cleaner
Inmetal cleaning agentAlkaline cleaning agents are more widely used than acidic cleaning agents and can be used alone or alternately or mixed with other cleaning agents. Mainly used to remove grease scale, but also used to remove inorganic salts, metal oxides, organic coatings and protein dirt.
Alkaline metal cleaning agent has a strong ability to remove animal and vegetable oil, but it is difficult to remove mineral oil. In order to improve the detergency of alkaline cleaners, a small amount of surfactant is often added. The use of alkaline cleaning agent rust, descaling than the use of acid cleaning agent rust, descaling cost is high, the speed is slow. However, except for equipment for amphoteric metals (Al, Zn, Sn), alkaline cleaning will not cause severe corrosion of the metal and will not cause significant changes in the size of the workpiece.

Cleaning effect of alkaline metal detergent
(1) Animal and vegetable grease scale cleaning The use of alkali degreasing washing ability to remove oil on clothing, long before the emergence of soap has been applied by humans, such as using plant ash (the main component is potassium carbonate and other alkaline substances) laundry. Alkaline detergents are particularly effective in cleaning greasy soils. Because on the one hand, it can saponify fats and oils and turn them into water-soluble fatty acid soaps; on the other hand, animal and vegetable fats and oils often contain free fatty acids, which can be converted into fatty acid soaps. Fatty acid soap is a surfactant that can promote the emulsification and dispersion of oily soils.
The main chemical composition of animal and vegetable oils and fats is high-carbon fatty acid triglyceride, which also contains about 30% free fatty acids. The chemical equation of their interaction with alkali is as follows:

(2) the cleaning of mineral oil stains Mineral oil stains and animal and vegetable oils are called oil dirt, but their structure is completely different. The typical structure of mineral oil is saturated chain hydrocarbons, non-polar substances, no carboxyl, sulfonic acid and other polar groups exist in the molecule, so it also becomes colloidal particles, which have certain emulsification, dispersion and adsorption on oily dirt. Therefore, the addition of silicate and polyphosphate in the alkaline washing liquid can promote the removal of mineral oil.

It is worth noting that the metal surface has a certain affinity for alkali, which is easy to form a surface covering film of alkali and is not easy to be washed clean. Under necessary conditions, the object can be immersed in a dilute acid solution to neutralize the alkali, and then washed with water.

Composition of alkaline metal cleaner
Alkaline cleaning solution is mainly composed of alkaline substances, and often a variety of alkali and. Commonly used alkaline compounds are sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium silicate and various phosphates. Sodium hydroxide is a strong alkali, it can neutralize acidic dirt, can make vegetable oil saponification, can also make some insoluble salt conversion and easy pickling
However, due to its strong alkalinity, it has a strong corrosive effect on human body and metal, so it should be paid attention to when using it. Sodium carbonate is a strong alkali weak acid salt, which is alkaline after hydrolysis, and its alkalinity is weaker than sodium hydroxide. Sodium bicarbonate is the acid salt of sodium carbonate and is more weakly alkaline. They can loosen, disperse, emulsify and saponify the grease, thus playing the role of cleaning. After hydrolysis of sodium silicate alkaline close to sodium hydroxide solution, it can not only make the grease dirt saponification, and sodium silicate hydrolysis of silicic acid in the form of colloidal, the dirt has a certain dispersion and stability. The simplest phosphate is sodium phosphate, disodium hydrogen phosphate and sodium dihydrogen phosphate are acid salts of sodium phosphate. In addition, sodium tripolyphosphate and sodium pyrophosphate are commonly used. Their aqueous solutions are alkaline and have certain decontamination ability. More importantly, phosphate has significant dispersion effect and can well disperse large particles of dirt. In addition, phosphate has certain chelating effect on metal ions.

In addition to alkaline substances, alkaline cleaners often add small amounts of surfactants. The main function of surfactants is to reduce surface tension, emulsify and disperse dirt, thereby significantly improving cleaning efficiency. On the other hand, in the alkaline cleaner, a large amount of the inorganic salt component lowers the critical micelle concentration (cmc) of the surfactant, thereby increasing the surface activity thereof. Non-ionic surfactants (such as alkyl phenol polyoxyethylene ether, polyether, etc.) have good wetting and penetrating ability, adding a small amount of non-ionic surfactants can improve the wetting and penetrating ability of alkaline ingredients to oily dirt, scale and rust. In addition, a small amount of a chelating agent, an organic solvent, and the like are added. AlkalineCleaning agentThe formula varies with the type of material to be cleaned, the composition of the dirt, the requirements for cleaning quality and speed, and the cleaning conditions.