Methods of using phosphoric acid against rust

A common “disease” of metal (steel and steel alloys) is rust. It is formed under the influence of oxygen, carbon dioxide and water. In scientific terms, this is a chemical reaction that produces hydroxides and iron oxides. When rust first appears, it is necessary to clean the surface of the metal product and protect it, because, unlike patina on bronze, rust on steel does not create a protective film.

You can clean oxides or hydroxides (oxides) in several ways:

• mechanical;
• chemical;
• using sandblasting equipment.

Orthophosphoric acid is suitable for the chemical purification of oxides, although mechanical and chemical treatments are most often combined.

What is phosphoric acid?

Phosphoric (phosphoric) acid - a water-soluble product of inorganic origin, is produced in the form of an 85% aqueous solution of a syrup-like colorless consistency. Use it in various industries, including food. It is one of the main components in the production of phosphate chemical fertilizers, and is also used in dentistry.

In the production of household chemicals, this acid is also used quite actively - it is present in almost all factory rust control agents. But it is based on a primer for metal, and the rust converter contains it as the main ingredient.

Precautionary measures

If it is necessary to remove rust by chemical means, first of all, you need to take care of your safety - prepare a respirator and rubber gloves. Phosphoric acid is an aggressive substance that can cause burns to the skin, and its vapor - burns of the respiratory tract and acute poisoning. In addition, it is fire and explosive.
All work must be carried out in well-ventilated areas, and the substance must not be allowed to get on the skin. If this happens, rinse the affected area under running water. With a chemical burn on a large area, you must immediately contact a medical institution.

Rust removal

The advantage of using phosphoric acid for chemical cleaning of rust is that it not only removes the loose mass of oxides, but also creates a thin protective film. The mechanism for creating such protection is that the acid, corroding and absorbing iron oxide, phosphates the surface. Those who worked with this substance could observe that after processing the metal and drying on its surface, in place of a red coating, a grayish film is formed, oil to the touch.

Depending on the degree of corrosion and the size of the part or product being cleaned, you can choose different methods for removing oxides:

• etching a part with complete immersion in a solution;
• single or multiple acid treatment of the surface with a roller or spray;
• drawing on metal with preliminary mechanical cleaning.

Full Dip Etching

If there is a sufficient amount of phosphoric acid and the required capacity, it is easiest to remove completely by immersion. To do this, follow these steps:

• degrease the part with any detergent and rinse it;
• fill the container with a solution with the ratio: 100-150 g of 85% acid per 1 liter of water;
• immerse the part in a container and leave for 60 minutes, stirring the solution from time to time;
• remove and rinse;
• prepare a neutralizing solution in the following proportions: 50% water, 48% alcohol, 2% ammonia;
• rinse the part with the prepared solution, and then with clean water and dry immediately.

You can not skip any of the above steps, since they are all interconnected. For example, if the degreaser treatment is not performed, the etching will be uneven, since this acid does not corrode organic contaminants, and problem areas will have to be further cleaned. This method is suitable for parts with any degree of corrosion, however, the larger the rust layer, the more time it takes to clean.

Tip

If, after the final washing, the surface is not immediately dried, then hydroxide immediately forms on it. Drying can be performed in any way, including convection.

Surface Acid

If the dimensions of the part are large, there is no suitable capacity or not enough acid, you can apply it on a metal surface using a spray gun, roller or brush with natural pile. At the same time, the degree of corrosion must be taken into account. If the rust layer is large, you will have to use the combined method and first remove the surface layer of the loose mass by mechanical means. This can be done manually or with the help of a grinder, on which the nozzle is put on - a metal brush or a petal circle.

After mechanical cleaning, degrease and apply an aqueous acid solution, being careful not to skip. Two hours after application, you can rinse with a neutralizing solution, and then finish wash and dry. With little corrosion, mechanical devices can be dispensed with, although this may require repeated use.

Tip

In a solution with acid, you can add an inhibitor - catapine, which inhibits the chemical process and prevents the reaction with non-oxidized metal. It is added in an amount of 1-2 g per liter of water.

Removal of rust from the surface of bathtubs, toilets and washbasins

Phosphoric acid can also be used as household chemicals. She copes with cleaning traces of rusty water in toilets and enameled baths. This product is not suitable only for acrylic bathtubs.

Application for faience and enameled surfaces:

• 100 g of 85% acid should be added to 500 ml of water;
• degrease the surface with any detergent;
• brush with a natural pile to treat the contaminated surface;
• after a few hours (from 1 to 12 - depends on the accumulation of oxides) wash off the acid with a solution of soda - 1 tbsp. spoon per liter of water.

The advantages of this method of cleaning rust - you do not have to rub anything, so the enamel is not broken. Information for housewives who use Coca-Cola to clean up red plaque: it is orthophosphoric acid present in small quantities in this drink that gives such a result. It is much more effective to use the active substance in the right proportion, and use the drinks as intended.

Tip

When working with acid, do not forget about safety rules. Do not allow the chemical to come into contact with the skin, and if this still happened, wash immediately with warm water and soap.

Rust converter

The rust converter (rust modifier) ​​is a solution of the same phosphoric acid, but with special additives. Depending on the additives, these drugs are divided into several groups:

• primers
• stabilizer modifiers
• rust converters.

As an example of the first group, the primer EVA-0112, consisting of two components - the base and 85% acid. It is used as a base for paint for steel products. The Tsinkar converter also incorporates phosphoric acid with the addition of zinc and manganese salts.Thanks to these additives, transformed rust results in a hardened protective layer (metal alloying effect). Before using the converter, it is necessary to familiarize yourself with the instructions, and the composition can be used only in accordance with the manufacturer's recommendations.

Which is better to choose?

Choosing a tool for removing rust, you need to focus on the place of its application. To clean parts by complete immersion, a large volume of acid is required. Here, the acquisition of orthophosphoric acid of 85% concentration will be justified both from a practical and economic point of view. If you need not only to remove rust, but also to create a protective layer for the paintwork, then a independently made solution will not work. In this case, it is better to buy a factory converter with all the necessary additives.

You also need to consider whether a primer coat will be applied or not. Modifier converters increase the water-repellent and inhibitory properties of the primer, but are not primers in themselves. But after processing the converter primer, you can immediately paint the metal with paint.

In conclusion, I want to focus on the fact that phosphoric acid creates a protective layer for the interoperational period. That is, without coating LKM metal will be susceptible to corrosion.