How to remove traces of phosphoric acid?

Cleaning metal from corrosion and old paint layers can be done in three ways:

chemical;
mechanical;
thermal.

Mechanical method

This method, considered the most effective, involves removing rust and paint manually or using a power tool. Processing can be performed:

wire brushes;
grinding discs;
using a sandblasting unit;
by waterjet method (performed only in industrial enterprises).

Chemical treatment

Chemical treatment is based on the effect of chemical substances sprayed on the surface or applied with a brush to rust.

Rust removing compounds are divided into two types:

washable;
indelible.

The disadvantage of wash-off products is the likelihood of new foci of corrosion appearing on the metal, therefore after treatment the surface must be immediately dried and treated with anti-corrosion compounds.

When treating rust with indelible compounds, a chemical reaction results in the formation of a kind of primer layer on the metal surface that cannot be washed off with water.

Processing of metal structures is most often performed:

a solution of sulfuric or hydrochloric acid (5%) with the addition of a corrosion inhibitor;
orthophosphoric acid (15-30% essence), which converts rust into a protective coating;
mixture 50 gr. hydroxypropionic acid per 100 ml of petroleum jelly, under the influence of which rust turns into salt and is easily cleaned from the surface with a rag.

Thermal method

Removing paint from metal surfaces using the thermal method involves using a blowtorch. The metal is heated until the paint coating gradually peels off, which can be easily removed with a spatula or a metal brush.

The main advantage of this method is significant time savings, but the main disadvantage is a fire hazard and some restrictions on the types of surfaces. It is impossible to process sheet and galvanized material, cast iron using this method - the surface is deformed and the integrity of the structures is compromised.

Removing rust with phosphoric acid

Possible in three ways:

Complete immersion of the element being processed in a solution of orthophosphoric acid;
A combination of chemical and mechanical rust removal methods (mechanical cleaning plus treatment with phosphoric acid);
Treating the problematic surface with orthophosphoric acid using a spray gun or roller (one or more times).

How to remove rust from metal

On an industrial scale, when it is necessary to remove corrosion from a large area, sandblasting or shot blasting is often used. But the most common method is still cleaning rust from metal using a converter. This is a composition based on orthophosphoric acid, thanks to which rust is converted into stable iron phosphates. There are alternative options for removing corrosive changes. In particular, this is tannin, which is tannic acid (under its influence, rust is transformed into iron tanate, which tightly adheres to iron (steel)). There are also compounds that convert rust into iron oxide pigment. Remove rust from metal using a rust converter step by step. The first step is to remove the upper exfoliating part of the loose substance mechanically: with a metal brush, scraper, sandpaper. After the initial cleaning, apply a rust converter and leave it for at least two hours - so that the reaction of the rust with the substance is as complete as possible. Remains of the converter that has not come into contact should be washed off with plain water. After the surface has dried, it can be primed and painted. We remind you that this procedure is not required if you are going to paint the metal with paints that already contain all the necessary components.

Rust removal methods

Rust is treated and removed using several successful methods. The required method can be determined based on the degree of surface destruction the corrosion has reached and the extent of the damage caused by it. How to treat a surface in need of improvement? It all depends on what available material is within reach.

Painting, applying varnish or another protective layer is the best way to protect metal from corrosion, which is available at home without the use of industrial products.

There are several common methods for treating metal before painting:

remove rust using chemicals;
remove rust from metal by mechanical means (using a wire brush, scraper, sandpaper);
remove rust from metal using a grinding device;
treat the product thermally (with an oxygen-acetylene torch you can burn a layer of scale, old paint and rust).

There are also industrial ways to get rid of corrosion scourge - for this, sandblasting or shot blasting using special equipment is used.

In industrial production, rust can be removed by treating the surface with a converter. For these purposes the following is used:

oxidation (creating a protective film on metal using oxides);
phosphating (phosphate films under the influence of orthophosphoric acid);
nitriding (saturation of the steel surface with nitrogen);
cementation (combination of metal with carbon using a chemical reaction);
bluing (combination with organic substances);
changing the composition of the metal by introducing anti-corrosion additives into it.

Rules for storing orthophosphoric acid

Phosphoric acid is a rather aggressive chemical compound, and this should never be neglected. When dry, the acid must be placed in a completely sealed container. To ensure that the powder produces a high-quality acid solution, all containers used must be dry and clean.

The ingress of impurities can render the solution useless or lead to extraneous chemical reactions leading to the formation of gases hazardous to health. Acid should be stored in a dry place where condensation cannot form. The temperature should be room temperature, without changes. There is no need to change the container in which the substance was initially stored. The acid must be stored in the same container until the end of packaging.

It is possible to transport orthophosphoric acid over long distances only if you have the necessary accompanying documentation, since this cargo is considered dangerous.

You can buy phosphoric acid for your own needs at car dealerships and radio parts stores. The price for this reagent is very affordable, although a small volume will cost more per liter than when purchasing a large container.

Phosphoric acid and its properties

Being a relatively weak acid compared to its counterparts from the table of chemical elements, phosphoric acid is an inorganic substance. Usually it looks like a scattering of small transparent crystals. By themselves, under normal conditions, they show virtually no chemical activity. But as soon as these crystals are heated to temperatures exceeding 42 degrees Celsius, their basic chemical properties begin to appear.

Crystals of orthophosphoric acid will begin to melt under the influence of high temperature, due to which they will turn into a liquid substance, which is used in everyday life. It is also worth noting that the concentration of chemically active components in orthophosphoric acid usually does not exceed 85%.

The most important property of this acid is its solubility, thanks to which you can independently obtain solutions of varying concentrations depending on the scope of application of this substance. Also, the acid is odorless and, importantly, reacts well with other chemicals.

How to remove rust?

Removing rust with phosphoric acid

Simply painting over the rust will not work. Or rather, it will work out, only the iron oxide remaining under the paint, like a virus, will infect another, “healthy” metal. Therefore, the first stage of restoring a car’s paintwork is removing existing rust. There are several ways.

In this article we will pay attention to the chemical, which is based on the use of phosphoric acid. Its use against rust is widespread.

Where to buy phosphoric acid?

In auto chemical goods, electronics, radio equipment stores, you can find it at construction markets, and, of course, order it on the Internet. Phosphoric acid is sold where other acids, paints, solders, and various reagents are also sold. It is rarely found in its pure form; more often it can be found as part of a rust converter based on orthophosphoric acid (almost all).

What is orthophosphoric acid?

This is an inorganic compound that is highly soluble in water. It is used in the food industry (as part of chemical phosphate fertilizers), in medicine (dentistry), in the production of household chemicals (as the main component for rust converters and primers for metal).

Expert advice

You need to clean areas of rust very carefully so that no holes appear and the metal does not become too thin. It is not recommended to use discs with very large abrasive particles during work, as instead of removing rust, they can cause more harm than good.

Before starting all repair work to remove rust, you must remember that this product is very powerful and strong. After all, it can remove not only the rust itself, but also the decorative coating: chrome, zinc. Therefore, it is necessary to process car parts very carefully and carefully so that you do not have to spend money on new spare parts in the future.

If all work to remove rust using phosphoric acid was carried out in accordance with all standards, then the resulting surface will be durable and reliable. And although the use of converters is considered the most popular method for body work, we should not forget about other options known to craftsmen.

In order for the work to lead to the expected results, and not a trace of rust remains, all instructions must be strictly followed.

A little converter is applied to a surface cleaned of a thick layer of rust and left for a couple of minutes or hours, depending on the concentration of the solution, and then further repair work begins.

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