CZ38678U1 - A preparation to pickle carbon steels, stainless steels and aluminium alloys - Google Patents

Description

Pickling agent for carbon steels, stainless steels and aluminum alloys

Technical field

The field of technology relates to a combined three-functional preparation for pickling or pickling of metals in the form of a solution, which creates a process of treating the surface of a metal material, sometimes also called descaling. While pickling is effective in removing heavy oxide layers - iron oxide, etc., on the other hand, it does not fully restore the corrosion-resistant properties of e.g. stainless steel. To achieve a truly passive corrosion-resistant surface, additional treatment with a so-called passivation preparation is required.

The subject of the technical field is therefore metal pickling, which is a common method of treating metals, i.e. pickling carbon steel (low alloy), stainless steel (high alloy) with a higher proportion of alloying elements, as well as pickling aluminum alloys, which aims to prepare materials for subsequent passivation treatments.

State of the art

Pickling of carbon steels and stainless steels is used to remove impurities, rust and scaling from the surface of a material composed of an alloy of iron with carbon - in combination with manganese (Mn), silicon (Si), nickel (Ni), molybdenum (Mo), etc. During hot working processes, a so-called oxide layer (referred to as "scale" - scalability or extensibility) develops on the surface of metals. Pickling is aimed at removing oxide layers, rust, or scale (scale: oxidized flakes of metal - iron oxides), which are formed during the thermal forming of iron-based metal alloys due to the influence of atmospheric oxygen and other impurities on the surface of stainless steels, etc. Stainless steels (highly alloyed), which contain a higher percentage of alloying elements than carbon steels, can also undergo a two-phase pickling process.

Before pickling, the steel must be cleaned of grease, oil and other contaminants to ensure that everything works effectively. Common methods include degreasing with solvents or alkaline solutions. After pickling, the steel/aluminium alloys are rinsed with pressurized water to remove any remaining acid, including subsequent drying. Pickling as such has a significant impact on the mechanical properties of carbon and stainless steels, including aluminium alloys. This is essential, for example, for steels requiring high stress resistance or so-called deformation tolerance. Pickling not only prepares the surface for passivation, but also removes oxides, chips, rust or other residues from previous production phases. During the production process, the surface of aluminium alloys, carbon and stainless steels is contaminated with grease, oil, etc., or initial corrosion (aluminium oxides, iron oxides, depending on the material). These contaminants must be removed.

Pickling removes the damaged layer of metal, oxides, rust, and also removes impurities from these metal surfaces, etc. These residues mostly come from previous manufacturing, welding processes, mechanical work such as cutting and bending, but also simple contact with surfaces and this is enough to infect clean metal surfaces. This is the reason for removing impurities that can also weaken welds or interfere with the adhesion of the protective molecular layer on the surface of the above metals.

Pickling of carbon steels and stainless steels is used to remove dirt, rust and scaling from the surface of these materials. This pre-treatment is aimed at removing various oxide layers, rust or scale (scale is a mixture of iron oxides that are formed, for example, during its processing on rolling mills).

Pickling of aluminum alloys - this process involves etching the surface and subsequently chemically removing corrosion and scale from the surface of aluminum alloys, with the aim of improving its resistance to

- 1 CZ 38678 U1 corrosion in the given environment, etc. The effect of the solution must be strong and relatively fast (1 to 10 min.).

In the pickling of 5 cast aluminum (combination, for example, with copper, magnesium, manganese, silicon and zinc), this process chemically removes the coating from the aluminum, which is formed, for example, during rolling and casting. Compared to iron, aluminum is a base metal. Shiny aluminum surfaces are very quickly covered with a very thin oxide layer, which protects the aluminum very well against further oxidation. However, this natural protective layer causes the applied wet or powder coatings to not be anchored to the base material, but often causes them to peel off. In order to eliminate this undesirable phenomenon, it is necessary to remove this disturbing oxide layer by so-called pickling, for example using strong acids and releasing (dissolving) aluminum ions into the bath. Pickling of aluminum results in etching of the surface and consequently in the chemical removal of corrosion and scale from the aluminum surface.

In general - the purpose of pickling is to restore the appearance and corrosion-resistant properties of metals after the manufacturing process (i.e. removal of iron contamination, etc.). Pickling of carbon steel, stainless steel and aluminum alloys is also intended to prepare these materials for subsequent treatments such as passivation and anodizing. Pickling not only prepares the surface for the passivation process, but also removes oxides, chips, rust or other residues from previous manufacturing stages.

Defects in metals also occur when steel is heated, e.g. by welding or other means, to the extent that the heat shade is visible, with e.g. the layer in the weld, its surroundings and below it being depleted of chromium, making the steel less resistant to corrosion. Pickling is the process of applying a special solution to remove heat-affected zones, etc. For example, pickled steel should not contain surface carbon steel - contamination and deposited iron particles. Simply put, pickling removes the heat-affected layer of stainless steel and prepares the surface for the next passivation process.

After the pickling process, the surface of the treated material must be rinsed with pressurized water and dried properly. Insufficient rinsing and drying may cause further corrosion of the material.

This means that pickling serves as a preparatory step for passivation - cleaning steels, aluminum alloys, etc. And passivation, as a further step, serves to increase the corrosion resistance of steels, aluminum alloys, etc.

Older techniques are currently used for pickling steel, etc., using, for example, hydrochloric acid (HCl), also sulfuric acid, and especially mixtures of nitric acid and hydrofluoric acid, which are dangerous acids and therefore expensive (disposal of these acids, employee health, etc.).

These are strong and dangerous acids (listed below) to remove metal surface layers, while passivation uses acids to create a protective oxide layer. In pickling, the acid penetrates the pores and cracks of the rust and scale layer, disrupting and dissolving it.

To treat the surface, a mordant - a solution is commonly used for pickling, where the treatment of metals with aggressive acids that are commonly used today is listed below:

- phosphoric acid (also suitable for phosphating or rust removal);

- hydrochloric acid (e.g. for carbon steel);

- sulfuric acid (especially pickling of copper alloys);

- hydrofluoric acid (titanium pickling);

- phosphoric, nitric or hydrofluoric acid (e.g. high-alloy steels);

- mixtures of the above acids.

The above-mentioned acids are dangerous and aggressive for work processes and especially for the health of employees. At the same time, they are associated with a relatively high purchase price and an even higher price for disposal. Although the traditional mixture of nitric acid and other acids is effective for pickling, this (and other dangerous) poses significant safety risks. The strong acid with corrosive effects can cause serious injuries on contact, inhalation, etc. These hazards require strict handling protocols, which makes it difficult to manage traditional solutions for collection and disposal, in the given

- 2 CZ 38678 U1 environments.

Pickling is regulated by the European standard - EN ISO 8504-4:2024 (Surface preparation methods Acid pickling).

Pickling is also defined quite precisely in the American standard ASTM A380:20217, and is a more aggressive chemical cleaning process used on stainless steels and other engineering alloys. ASTM A380/A380M-13 is the standard practice for cleaning.

Pickling of components - some industrial examples of use

Oil and gas industry:

Pickled steel is also used in the manufacture of piping systems used in the oil, gas and water sectors. The removal of surface oxides ensures the integrity and performance of piping systems, ensuring the smooth transport of oil, gas and other fluids.

Automotive industry:

Pickled steel plays a vital role in the automotive industry, e.g. for chassis and structural parts. The clean surface of the material ensures excellent paint adhesion and corrosion resistance, which are essential for both durability and aesthetic appeal. The increased functionality of the material is important for automotive and other lightweight structures.

Construction:

In the construction industry, pickled steel is used to make beams, pipes, various types of panels and other structural components. The clean surface ensures better welding and surface performance, making it ideal for structures that support heavy loads. Applications also include bridges, high-rise buildings, etc.

Production of molded components:

Removing surface contaminants ensures accuracy during the stamping of various parts and reduces tool wear, leading to cost-effective manufacturing processes. The smooth surface also supports high-quality finishes and coatings.

[Literature 1]

Crude glycerol as an innovative corrosion inhibitor

Isam Al Zubaidi, Robert Jones, Mohammed Alzughaibi, Moayed Albayyadhi, Farzad Darzi and Hussameldin Ibrahim

Industrial Systems Engineering, Faculty of Engineering and Applied Sciences, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada

Application Syst. Innovation 2018, 1(2), 12; https://doi.org/10.3390/asi1020012

Submission received: February 12, 2018 // Revised: April 25, 2018 // Accepted: April 25, 2018 // Published: April 29, 2018

Source: https://www.mdpi.com/2571-5577/1/2/12

Abstract

Crude glycerol, a by-product of biodiesel production, was evaluated as a potential green inhibitor for steel corrosion in acidic environments. The study was conducted using steel samples placed in hydrochloric acid solution (0.5M), at constant room temperature (25 °C) and crude glycerol concentrations ranging from 0.1% to 1.0% w/w. The method used to evaluate the extent of corrosion was weight loss and corrosion. In addition, fresh and used samples were characterized using scanning electron microscopy and potentiodynamic polarization measurements. It was found that in general, corrosion inhibition increased with inhibitor concentration. The results also showed that the maximum inhibition efficiency was achieved at 70 h of residence, after which the inhibition efficiency at a given concentration either remained unchanged or slightly decreased. In addition, the overall maximum inhibition efficiency (98%) was observed at 70 h in solution and a concentration of 1% inhibitor.

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Introduction

Corrosion is the surface breakdown of metals and non-metallic materials, including ceramics, plastics, rubber, and wood, due to exposure to certain combinations of liquids or gases. The mechanism and rate of corrosion depend on the exact nature of the atmosphere in which corrosion occurs. Corrosion of metals includes rusting of iron, oxidation of silver, dissolution of metals in acidic solutions, and the growth of patina on copper. Corrosion occurs in public infrastructures such as bridges, pipelines, vehicles, utilities (electrical, water, telecommunications, and nuclear power plants), engineering and manufacturing, the chemical industry, and the oil and gas industry. Acid solutions are widely used in the process industry as corrosion inhibitors by preventing metal parts from rusting. The application of corrosion inhibitors has been widely adopted as an acceptable engineering practice due to their protective nature against acid attack.

Hydrochloric acid (HCl) is widely used for pickling, cleaning, dewatering and etching of metals. However, HCl is known to be responsible for corrosion of metal surfaces through acid attack mechanisms, resulting in millions of dollars spent on maintenance each year. It is reported that 25 to 30% of maintenance costs can be avoided with proper corrosion prevention techniques.

The use of corrosion inhibitors, even in small amounts, is one of the most economical and environmentally friendly solutions to the corrosion problem. Several factors are considered when selecting a suitable corrosion inhibitor. These include cost, efficacy and the amount to be used, availability and stability, toxicity and environmental impact. It has been found that several organic inhibitors could be used during acid collection with reportable inhibition. For example, a mixture of benzotriazole, chitosan, polyacrylic acid and zinc salt has been used as a corrosion and scale inhibitor for carbon steel in cooling towers. Since this organic corrosion inhibitor is phosphate-free, it does not tend to cause eutrophication. In terms of product performance and environmental impact, a phosphate-free corrosion and scale inhibitor is superior to the traditional one.

In addition, the application of natural Jatropha curcas oil as a steel corrosion inhibitor was recently investigated in the presence of hydrochloric acid using mass loss, electrochemical and electrochemical impedance spectroscopy (EIS) techniques. It was found that the corrosion efficiency increased with the concentration of inhibitors. In addition, potentiodynamic polarization technique revealed that the presence of natural Jatropha curcas oil did not change the mechanism of the hydrogen evolution reaction and instead acted as a surface protection inhibitor.

Corrosion inhibition data were implemented on the adsorption isotherm model. Dithiocarboxylic acid derivatives were also studied as corrosion inhibitors for steel in 0.5M hydrochloric acid solution. Langmuir isotherms were used to fit these inhibitory adsorption data with sufficient accuracy. However, the common denominator of the most used corrosion inhibitors is their toxicity and negative impact on the environment. Replacing toxic inhibitors with more environmentally friendly inhibitors for the protection of metals in acidic media has been the subject of many studies in recent years. Monads and vegetable oil have been used as corrosion inhibitors for steel sheets in acidic solutions. Recently, several studies have focused on the inhibitory effect of various environmentally friendly materials as corrosion inhibitors for stainless steel corrosion and mild steel corrosion in HCl media.

While organic corrosion inhibitors are toxic in nature, green inhibitors are biodegradable and do not contain any heavy metals or other toxic compounds.

The used organic and inorganic inhibitors are released into the environment as aqueous wastes, causing harmful effects on living organisms. In offshore operations, corrosion inhibitors are used to create a barrier layer between the oil and the water phase.

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[Literature 2]

Corrosion resistance of low-alloy steel S355MC in raw Glycerol Mariána Palcutová, Žaneta Gerhátová, Patrik Šulhánek and Petr Gogola Faculty of Materials Science and Technology, Slovak University of Technology, J. Bottu 25, 91724 Trnava, Slovakia

Technologies 2023, 11(3), 69; https://doi.org/10.3390/technologies11030069

Submission received: March 27, 2023 // Revised: May 5, 2023 // Accepted: May 16, 2023

Source: https://www.mdpi.Com/2227-7080/11/3/69

Abstract

Corrosion is the degradation of materials in an oxidizing environment. In aqueous solutions, it is initiated by the surface reaction of a metallic material with the surrounding electrolyte. The corrosion rate of metals can be significantly reduced by the presence of organic compounds. Crude glycerol is an organic by-product of biodiesel, soap and fatty acid production. It is produced in significant quantities by transesterification. Crude glycerol contains several impurities and has low economic value. Its disposal in the environment is undesirable and potential applications need to be explored. In the present short communication, steel corrosion in crude glycerol was investigated for the first time. The corrosion behavior of low-alloy structural steel S355MC in untreated crude glycerol was studied by electrochemical methods. The results were compared with the use of tap water. The open circuit potential (OCP) of S355MC in crude glycerol was more negative compared to the tap water potential (OAP). The OCP was stable over time, indicating rapid passivation of the steel substrate. Corrosion resistance was further investigated by electrode polarization. A wide passivation region was found on the polarization curve of S355MC in crude glycerol. In addition, the corrosion rate was 2.2 times lower compared to tap water. The surface exposed to water was significantly degraded by red rose. On the contrary, the surface of S355MC after exposure to crude glycerol was less affected by corrosion and covered with a protective layer. The results show a significant activity of crude glycerol, which could be used in various technologies.

Conclusions

In the present communication, the corrosion behavior of S355MC structural steel in crude glycerol was investigated by electrochemical methods. The results were compared with those using tap water. Glycerol reduced the corrosion rate of the steel. The corrosion rate of S355MC steel in glycerol was 2.06 x 10 ^-2 mm/year. This value was approximately 2.2 times lower compared to drinking water. The surface of the steel exposed to the glycerol solution was covered with a layer of corrosion products. This study suggests that crude glycerol can reduce the corrosion of structural steel in aqueous solutions. The inhibitory effect is probably related to the adsorption of glycerol on the metal surface.

[Literature 3]

Inhibitory protection of low carbon steel in citric acid solution

Jaroslav Avdeev 1, Maria Tyurina 1, Vladimir Rabinkov 2, Andrei Luchkin 1

1-A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, Moscow, 119071 Russian Federation

2-Moscow state university of civil engineering, Yaroslavskoye shosse, 26, Moscow, Russia, 129337

DOI: 10.1051/, 00143 (2017) 71170014117

MATEC Web of Conferences matecconf/201 XXVI R-S-P Seminar 2017, Theoretical Foundation of Civil Engineering

Source: https://www.matec-conferences.org/articles/matecconf/pdf/2017/31/matecconf rsp2017 00143.pdf

Introduction

Thermal power equipment is chemically cleaned with citric acid solutions (CLH^) before start-up (pre-operational chemical cleaning) to remove rust, scale and other deposits and during operation (operational cleaning) to remove iron oxide and carbonate (crust) formations. These solutions have low aggressiveness towards steel equipment and are effective in removing scale, magnetite

- 5 CZ 38678 UI sediments and crusts, including their complexing properties. Treatment with citrate solutions is quite often carried out at temperatures (t) close to 100 °C. Solutions of other organic acids (adipic, maleic, oxalic, succinic) are less effective cleaning agents in thermal power plants than citric acid solutions. Mixtures containing toxic pyridine derivatives - Catapin K and inhibitor I-l-A, benzotriazole, cinnamic aldehyde and various plant extracts are recommended as additives to inhibit corrosion of steels in citric acid solutions. In this case, benzotriazole, cinnamic aldehyde and plant extracts do not allow obtaining a degree of metal protection of 90%. Recently, 1,2,4-triazole derivatives are gaining importance for the protection of metals and alloys in mineral and organic acid solutions. The inhibitor of this class, IFKhAN-92, which we have developed, allows protecting low-carbon steel in mineral acids, as well as in acetic and formic acid environments. As its main advantage, IFKhAN-92 is stable in hot acid solutions. It turned out to be expedient to develop an inhibitor based on IFKhAN-92, which is a substituted triazole, to protect low-carbon steel in hot citric acid solutions (up to 95 °C).

The essence of the technical solution

The essence of the technical solution is a pickling preparation for metals, which contains:

- citric acid (citric acid);

- ammonium bifluoride (ABF);

- glycerol (glycerin);

- the balance up to 100% of the weight of this pickling (mildly passivating) preparation consists of water.

According to the table of examples, the optimal composition was selected from column no. 4.

Raw material (g/1000 g water) 1 2 3 4 Citric acid (monohydrate) 49 grams 63 126 189 Ammonium bifluoride (etching) 1.9 grams 2.1 4.2 6.3 Glycerol (polymer) 1.08 grams 1.3 grams 2.6 3.9 Water (filtered) up to 1000 g up to 1000 g up to 1000 g up to 1000 g

For pickling ferritic and high-speed steels, hydrochloric acid (HC1) and sulfuric acid (H2SO4) are currently used, while for austenitic steels and alloys, mixtures of nitric acid (HNO3) with hydrofluoric acid (HF), or hydrogen peroxide (H2O2), are used, which are dangerous acids.

These acids have been replaced with other, safer ones - i.e. citric acid, ammonium bifluoride (ABF) and glycerol.

The chemical pickling process of steel and aluminum alloys offers a proposed solution for ensuring corrosion resistance, by developing or restoring its protective layer to the preferred quality and, in particular, a less hazardous metal pickling process (impacts on employees and the environment) and of course, economically cheaper, due to the composition of substances used and the use - dilution of the preparation.

In this case, it's about finding a safer and, above all, cheaper alternative:

- pickling with dangerous acids is replaced with citric acid (the main active ingredient) - a safe natural substance;

- citric acid is also a so-called green corrosion inhibitor;

- highly hazardous etching chemicals are replaced with milder ammonium bifluoride (ABF);

- the technology of the product is further supplemented with another green corrosion inhibitor, glycerol, i.e. an inhibitory-corrosion, anodic substance, which also creates crosslinking - protection of metal surfaces;

- pickling with this product can be carried out with sufficient efficiency even at a normal temperature of around 20 °C.

-6CZ 38678 U1

The pickling process with citric acid in solution form is, compared to, for example, nitric acid: - more cost-effective - cheaper, due to lower risks of handling the material;

- reduction in the cost of purchasing raw materials - cheaper raw materials;

- reduction of waste disposal costs (one of the highest items for hazardous acids);

- increased worker safety (one of the most important health protection items).

Forms of pickling with this product - or types of pickling that are used to remove, in particular, unwanted oxide layers from stainless steel surfaces, decarburize and further eliminate impurities:

- pickling in an immersion bath;

- spray pickling - a newer method;

- Circulation pickling - is used in pipelines and industrial equipment where the pickling agent flows through the system in a closed circuit (a newer method).

1. Citric acid is non-toxic (also used in the food industry) and biodegradable. In addition, it simplifies compliance with environmental regulations and, in particular, protects the health and safety of employees. The effect of this corrosion inhibitor is more pronounced where (in pickling) the surface of the material is irregularly oxidized and where the clean surface is exposed to pickling baths.

Not only does citric acid effectively remove aluminum oxides from aluminum alloys and Fe oxides from carbon and stainless steels, but it is also needed in lower concentrations, in a pickling solution diluted in given proportions, which is economically quite different in terms of the volume of funds (against dangerous acids), as well as in the volume by weight, in this preparation.

2. Ammonium bifluoride (ABF) is a less toxic colorless salt (white crystalline solid) and when added to water, ABF becomes a less aggressive version of hydrofluoric acid. Ammonium bifluoride (NH4HF2) is a versatile chemical widely used in metal processing, glass etching and industrial cleaning. Due to its nature, it is very common in truck wash soaps and other cleaning products. Ammonium bifluoride (ABF) replaces the traditional but dangerous material - hydrofluoric acid, which is very aggressive (causes e.g. severe burns) and releases pollutants into the air (especially when inhaled). The use of ammonium bifluoride is safer for use, storage and transportation and reduces costs by about 15%, it is non-flammable - not subject to ADR during transportation. ABF is extremely soluble in cold water (ABF is also recently used in passivation and simultaneous anodizing of aluminum and in a gel preparation).

2.1. Surfaces with ammonium bifluoride increase the durability and longevity of steels. It is also used in manufacturing, semiconductor cleaning and anodizing. It is also used for:

- metal surface treatment - to remove iron stains (in the pickling process);

- building protection (as part of cleaning products);

- boiler and rust cleaning - removal of silica in boilers and evaporators;

- wood preservative;

- ammonium bifluoride successfully replaces wood preservatives.

3. We also specialized in the effects of glycerol, a green corrosion inhibitor, on improving the efficiency of the pickling process. It is esterification - which is a reaction to crosslink the surface of materials on a molecular basis - this leads to polymerization, which can distribute metal ions through polymer networks. It is about crosslinking surfaces and thus protecting metals, see more detailed description below.

4. Disposal of the used mixture is much easier and, above all, cheaper. This also applies to the purchase of chemicals and, in particular, to the protection of employee health.

5. We also focused on ensuring a more optimal process and, in particular, use at a lower ambient temperature range (approx. 20 °C), which is economically advantageous from an energy point of view compared to higher temperatures.

This pickling mixture, which forms the essence of the technical solution, reduces the risk of material corrosion, while

- 7 CZ 38678 U1 maintaining the effectiveness of the substances used, and at the same time being a less aggressive and, in particular, cheaper alternative to the current pickling chemicals of the above-mentioned acids, with the benefits listed below.

• Benefits of citric acid: it is generally recognized as safe (GRAS). Green corrosion inhibitor - it is much less dangerous than, for example, nitric acid, etc. Its properties also reduce the likelihood of excessive effect, which could otherwise severely etch the surface of, for example, stainless steel (see very strong and dangerous acids).

• Citric acid offers a number of other benefits, including increased personnel safety, reduced environmental impact and, in particular, reduced operating costs in purchasing substances and, in particular, subsequent disposal, which is the biggest problem with hazardous acids.

• Citric acid provides pickling of carbon and stainless steel as well as aluminum alloys. It is also about ease of use and less maintenance of the equipment.

• Benefits of ammonium bifluoride (ABF): dry fluoride compound (etching agent) with low weight content (in diluted form) in the preparation. It is less hazardous than hydrofluoric acid (currently widely used), easier to transport (non-flammable - not subject to ADR) and especially mixes better than e.g. nitric (or sulfuric) acid.

• Benefits of glycerol: safe and innovative corrosion inhibitor - phosphate-free, so-called green corrosion inhibitor (synergist), against steel corrosion in acidic environments. This green inhibitor is biodegradable and does not contain any heavy metals. The esterification reaction between citric acid and glycerol leads to polymerization, which can distribute metal ions, i.e. by crosslinking the metal surface - molecular crosslinking of metal surfaces, which is used as an additive that also facilitates mixing with water, etc.

• When using this solution in the form of pickling, pickling can be widely used even at ambient (room) temperature of approx. 20 °C. The pickling temperature can be adjusted and also the time of approx. 1 min. to 60 min., even according to the contamination of the surfaces in the form of an operational test.

Overall, this solution combines higher safety, lower cost and ease of use. Citric acid, ammonium bifluoride (ABF) and glycerol offer a number of benefits, including increased personnel safety, reduced environmental impact and reduced operational costs for purchasing chemicals and then disposing of them.

1. Citric acid - pickling/pickling based on citric acid is a newer technical solution (including other substances) e.g. against nitric acid, sulfuric acid, etc.:

Citric acid, like other carboxylic acids, is soluble in water and serves as an organic reducing agent that prevents the formation of oxides on the surface of steels. In our case, it also acts as a buffer (buffer solution) and also as a cleaning agent. For example, soluble aluminum oxyhydroxides and insoluble aluminum-containing particles form a complex with citric acid under conditions of high hydrolysis. Organic substances can protect existing particle surfaces from dissolution or maintain the solubility of cations.

1.1. When using e.g. nitric or sulfuric acid, approx. 15 to 20% and hydrofluoric acid 3 to 5% are used in pickling. The present diluted pickling solution ranges from 4 to 7% citric acid and 2.1% bifluoride by weight in the diluted pickling solution (which is economically interesting).

1.2. Citric acid is a good chelating agent, which means it can bind to metal ions and form soluble complexes. It can be used on multiple types of steel alloys and aluminum alloys, so it can be used for systems composed of different metal alloys.

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1.3. Environmentally friendly: citric acid is low in toxicity, biodegradable and therefore less harmful to the environment compared to, for example, nitric acid.

1.4. Since it is used as a food additive and is on the GRAS (generally recognized as safe) list, it is also suitable for use in processing, e.g. in the food industry.

1.5. Citric acid is safe (like glycerol), with low toxicity and fumes, which reduces risks to worker safety (e.g. against nitric acid, sulfuric acid, etc.).

1.6. Based on the above, the preparation is non-flammable (does not fall under the ADR regime).

In addition to the above advantages, citric acid is a modern solution for pickling and passivation of steels and aluminum alloys. It is safer, easier to handle (e.g. against nitric acid and hydrofluoric acid, etc.).

2. Ammonium bifluoride (abbreviation ABF):

Ammonium bifluoride is an etchant (etching agent) that should be considered as an example of soluble fluoride salts suitable for the purpose of pickling. Also known as ammonium hydrogen difluoride, an industrial chemical with various applications. It is available in two main grades: Industrial Grade and Electronic Grade, each of which serves specific industrial needs.

2.1. In this case, ABF effectively removes oxides, etc., ensuring that the metal surfaces are cleaned and ready for subsequent treatment (passivation).

2.2. Ammonium bifluoride (etching agent) is a less toxic colorless salt and when added to water becomes a less aggressive version of hydrofluoric acid used in pickling. That is why ABF is very common, for example, in truck wash soaps and other cleaning products.

2.3. Industrial grade ammonium bifluoride (ABF) is widely used in various applications such as a cleaning agent for food processing equipment, in chemical analysis and for electroplating. It is also used as an etching agent in the ceramic industry. In this case, it provides a means for creating specific textures - surface finishes on steels, etc. The substance itself is non-flammable.

In addition, it is used in the manufacture of detergents and as an auxiliary agent in petroleum production. Industrial grade is recognized for its effectiveness in these applications due to its ability to react and form new compounds, thereby improving the efficiency and results of various processes.

3. Glycerol:

Glycerol or glycerin, systematic name propane-1,2,3-triol, is a hygroscopic colorless viscous liquid with a density of 1.26 g/cm3, odorless, sweet taste. The so-called green inhibitor of corrosion of steels and aluminum alloys, in acidic environments. It is a hygroscopic colorless viscous liquid. This green inhibitor is biodegradable and does not contain any heavy metals. The presence of glycerol during pickling increases corrosion resistance and supports the formation of more compact applied coatings by the so-called polymerization of metal surfaces.

3.1. Glycerol can reduce corrosion of structural steels in aqueous solutions. The inhibitory effect is related to the so-called adsorption of glycerol on the metal surface (adsorption is the so-called accumulation of particles - atoms, molecules) of a gas, liquid or solid on the surface (phase interface) by the effect of interfacial attractive forces.

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3.2. Esterification reaction of glycerol - in which an ester is formed from an organic or inorganic oxygen acid and an alcohol. Esterification is mainly understood as the reaction of a carboxylic acid and an alcohol, with the formation of an ester of a carboxylic acid (citric acid) and water, where this reaction between citric acid and glycerol leads to the so-called polymerization, which can distribute metal ions in the form of polymer networks. That is, polymerization occurs between citric acid and glycerol, which can distribute metal ions through polymer networks (so-called crosslinking of metal surfaces).

3.3. Glycerol is a highly viscous polyhydric alcohol with three OH groups, which results in better polymerization (so-called higher branched network). This pickling synergist for steels and aluminum alloys is particularly suitable for adding to the pickling solution to promote the cleaning of compact oxide scales formed on the surface of various steel strips and profiles. It can also improve the surface quality of steels after pickling, shorten the pickling time, reduce acid consumption, and thus improve the pickling environment (see scientific studies).

3.4. That is, glycerin and citric acid are green corrosion inhibitors that include protection of metals in the form of coatings, including crosslinking of surfaces by polymerization.

• Glycerol influences mechanical, barrier and thermal properties in the form of bio-stress polymers.

• Efficient use of glycerol is essential to prevent environmental pollution.

• Glycerol is an emerging additive for today's polymer industry.

Green corrosion inhibitors (citric acid and glycerin, together with a weaker ABF) are currently, in our opinion, a very cost-effective method for pickling, passivation, anodizing of metals, including descaling by the so-called circulation method, which is easily proven by basic indicators - the price of purchasing raw materials, disposal of raw materials and low hazard to employees.

The use of corrosion inhibitors, even in small (yet very functional) quantities, is one of the most economical and environmentally friendly solutions to corrosion problems, which is scientifically proven.

Pickling ensures uniform surface quality, where there is no longer a high risk of contamination, using green inhibitors (citric acid, glycerol), which have shown the suitability of the selected pickling preparation, including the ABF element.

The metal pickling process, based on the above facts, is overall cost-effective, due to lower material handling risks, lower raw material and waste disposal costs, including increased worker safety. Furthermore, its low-toxicity nature simplifies compliance with environmental regulations and, in particular, saves employee health.

Forms of application of preparations for pickling steels and aluminum alloys, depending on use and equipment:

1. Pickling in a bath - immersion pickling in small-volume and large-volume baths:

It is still the most widely used pickling method, which involves immersing the object in a large tank, where the acid comes into contact with the metal surface, triggering a chemical reaction that dissolves harmful oxides resulting from the production processes of the treated material, thereby decontaminating the surface.

2. Spray pickling (for large-area objects that cannot be pickled in an immersion bath due to their size):

This is the pickling of oversized objects by spraying, where this technique allows the process to be carried out efficiently and according to the given possibilities. This newer pickling technique has been made possible by extensive research at more established companies, aimed at improving and simplifying pickling processes. The advantages of this technique also lie in the reduction of the volume of liquid used and the possibility of using a smaller amount of pickling agents than when using pickling baths. Spray pickling is applied to the surface of metal parts and after an appropriate reaction time the surface is blasted with high-pressure water.

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3. Circulation pickling (little known and practiced):

The circulation method for already installed piping systems (implementation by hydraulic system) can effectively remove oxides, sludge, etc. from the inner wall of the piping, which prevents not only corrosion on the inner wall of the piping, but also the occurrence of residual chemical reaction deposits (biofilms, sludge, etc.). A pickling process is simultaneously created in the piping. After circulation, the process is introduced - acid collection by hydraulic system. The requirements for the operating process are: piping circulation approx. 30 min. to 2 hrs. Then flushing the piping with clean pressurized water (after pipe passivation).

4. CPL - continuous pickling line - this is how large volumes of metals (sheet metal coils, etc.) are pickled: Pickling is, in addition to metal passivation, one of the most important forms of so-called cleaning of steels and aluminum alloys, etc., and has many applications in a wide range of industries. Last but not least, pickling is an important operation in the production of rolled or drawn metal material - sheets (coils), etc., on so-called CPL - continuous pickling lines.

These include, among others, industrial plants that have automatic (continuous) lines, e.g. for sheet metal coils with significant volumes of pickling material. The system includes evaporator stations, drying, etc. (the automotive industry also uses a similar, so-called continuous method of continuous passivation by immersion of parts in smaller continuous baths, which are much smaller than for pickling coils, this is not CPL).

4.1. CPL-continuous pickling line for steel etc. (mainly coils etc.). These are conventional horizontal structures with coil inlet, welder, preheating water tanks, acid tanks, pressure water rinsing, dryer, looper, side cutter, winder, lubrication device etc. This is an alternative pickling method which is very cost effective, especially when used for pickling/cleaning simple products such as sheets etc. on these continuous pickling lines.

4.2. Advantages of CPL technology - continuous pickling line:

• avoiding more complicated manipulations with materials and especially with chemicals;

• improved efficiency and productivity (very high capacity of processed material);

• cost-effective, high performance (comprehensive automation, economical operation);

• CPLs may include modular designs to optimize operational activities;

• on-line acid management for analysis accuracy and control of acids, waste and fumes;

• increased environmental sustainability (when using the product);

• customized form of pickling solution for different steel grades, etc.;

• integration with Industry 4.0 technologies (a designation for upcoming innovations and transformations of production processes).

CPL lines must be prepared and optimized to process many different steel grades, etc. They also provide precise control of strip tension and its precise guidance, high-quality pickling control and, above all, fast, stable and safe processes. For example, the welding device in a CPL connects/welds the individual coils of sheet metal into an endless strip when the material enters the continuous line, while the horizontal loops ensure a continuously high speed in the processing section. This means that high speeds can be achieved in this way without interrupting the production cycle, at a very high capacity of the plant.

Another example of advanced CPL technology is the nozzle racks that continuously spray acid into a shallow storage channel, generating high turbulence. This ensures maximum contact between the acid and the strip surface by continuously penetrating the microscopic cracks in the pickling metal layer.

Description - adsorption reaction and polymer crosslinking of metals, our pickling agent for various types of carbon steels, stainless steels and aluminum alloys:

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In addition to pickling/cleaning capabilities, this product also has the ability to perform the so-called anodic-cathode reaction - adsorption reaction, based on citric acid (tricarboxylic acid).

In another green corrosion inhibitor, glycerol, which provides polymeric crosslinking of metals (so-called esterification). The esterification reaction takes place between citric acid and glycerol, leading to polymerization, which can distribute metal ions, i.e. crosslinking of metal surfaces - or molecular crosslinking of metal surfaces (more detailed description above - for glycerol).

Adsorption is a process whose principle is the accumulation of particles (atoms, molecules) of a gas, liquid or solid on a surface (phase interface) by the effect of interfacial attractive forces. Thanks to chemical and physical bonds, the substance firmly adheres to the metal, creating a protective molecular layer on it and thus preventing moisture from reaching the metal.

These are mainly substances that inhibit the corrosion reaction by removing the corrosive agent, so-called anodic inhibitors, which create on the metal surface, thanks to chemical and physical bonds (at the phase interface), a proactive oxide film about 30 to 200 Å thick (the angstrom unit Å is equal to 100 pm or 0.1 nm or 10 ^ θ m), which prevents the corrosive substance from reaching the material. These protective films are tough and tend to repair themselves in case of damage, so these substances can be used in economical concentrations (citric acid and glycerol).

This process removes surface contaminants (e.g. iron compounds) by chemical dissolution. These inhibitors form a so-called adsorbed protective film. An effective adsorption method is protection with a preparation that prevents corrosion by creating an electrochemical cell from the metal surface.

Comparison table of preparations based on: nitric acid and citric acid.

Nitric acid fAcidum nitricum) Citric acid) Manipulation Very dangerous. Much less dangerous to use. Flexibility Time, temperature and concentration must be carefully monitored. Less risk to the user, equipment or product in case of excessively long application or high concentration. Temperatures High temperature is required for most applications. Ambient (room) for many applications. Cost High costs of disposal of used mixtures High costs of equipment maintenance. Lower costs for disposal of used mixtures. Lower costs for equipment maintenance.

Technical data of the pickling agent / physical properties:

The product is intended for professional use only.

The product is non-flammable (does not fall under the ADR regime).

The product meets or exceeds industry standards for cleanliness and protection of metals against corrosion.

Plastic - HDPE, or stainless steel should be used to store this product.

The product has negative effects on mucous membrane and upper respiratory tract tissues, eyes and skin.

The product causes damage to zinc and galvanized steel surfaces.

Citric acid and glycerol have been shown to have many benefits, including that pickled (and also passivated) surfaces of steel and aluminum alloys perform well, passing all required tests. Surface chemistry of stainless steel shows that citric acid pickling eliminates contaminants from the surface and helps create, together with ammonium bifluoride and glycerol, a sufficiently treated material by pickling steels and aluminum alloys.

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Using a professional pickling agent:

The product is intended for pickling - carbon steels, stainless steels and aluminum alloys.

The product is intended for professional use only.

Dilute and mix thoroughly before use.

Ambient (room) temperature may be adequate (approx. 20°C), depending on the end use. Use at a range of 20 to 70°C, especially for heavily oxidized surfaces a higher temperature is appropriate. Stainless steels (high alloy) with a higher proportion of alloying elements can also be pickled in two phases. Always test the products before using the product at 20°C and above.

Forms of use of the pickling agent:

- pickling of metals - pickling in a bath;

- spray pickling, a technique for pickling metals by spraying;

- circulating pickling of metals is used in pipelines and industrial equipment - piping systems where the pickling agent flows through the hydraulic system in a closed circuit (lesser known method);

- CPL continuous pickling line.

Approximate times - pickling and passivation for carbon steels, stainless steels and aluminum alloys:

1. Pickling of stainless steels, high alloy - approximately from 15 minutes to 2 hours, depending on the temperatures used. Stainless steels with a higher proportion of alloying elements are usually pickled for a longer period of time. Stainless steels that contain a higher percentage of alloying elements than carbon steels often require a two-phase pickling process.

2. Pickling of carbon steels, low alloy steels - approximately from 10 minutes to 1 hour, depending on the temperatures used, in a shorter period of time than stainless steels.

3. Pickling of aluminum alloys - be careful 1 to 15 minutes, depending on the temperatures used, if the surface of the aluminum alloy is heavily soiled, a longer time can be used - according to points 1, 2 and 3, it is necessary to test the effect on a given sample in advance.

4. Time testing is always carried out before the production process (recommendations according to ATSM, etc.), for carbon steels, stainless steels and aluminum alloys before mass use of the product in the production cycle, first at an ambient temperature of approx. 20 °C and, depending on the result, at a higher temperature - approx. up to 70 °C, or for a longer time.

5. Warning:

5.1. Aluminum alloys are highly reactive with acidic preparations (citric acid). On the other hand, high-alloy steels can be pickled in two phases (and in a longer time cycle).

5.2. Carbon steel is often confused with the term stainless steel - although they have the same basic composition of iron and carbon, different types of steel tend to have different alloying elements. Carbon steel usually has less than 10.5% chromium, but stainless steel must contain at least 10.5% chromium to be considered stainless.

Procedure for applying pickling agent - carbon steel, stainless steel and aluminum alloys:

• Mix or shake the product thoroughly before use.

• All equipment (dilution canisters, applicators, etc.) should be clean and dry before use. Only HDPE - polypropylene or other durable plastic or stainless steel containers should be used to hold or store this product.

• Time, temperature and concentration of the product should always be tested before use in the production process. The product can also be applied to surfaces by sprayer. Coverage is approx. 35 m ² per 5 liters at ambient temperature.

• Products are tested before using the product at a temperature of 20 °C and above. Pickling time - testing is used to time the minutes in subsequent production conditions.

- 13 CZ 38678 U1 • The temperature and concentration of the product should be tested before use in production. It is possible to use an ambient temperature (ambient temperature) of 20° C - with low etching of the base material. Then testing can take place up to approx. 70° C.

• When testing the material, wait for the application test, then rinse the product with pressurized water and dry thoroughly. Repeat the process if necessary to obtain the desired results.

• Please note that increasing the pickling temperature by 10 °C increases the pickling speed by approximately 100% and vice versa. A higher temperature is particularly suitable for heavily oxidized surfaces.

• When using this product, pickling can be widely used even at an ambient temperature of approx. 20 °C. The pickling temperature can be adjusted to 20 to 70 °C. At ambient temperatures, the pickling time is usually longer.

• The pickling procedure is followed by blasting with pressurized water. The recommended pressure is 18 MPa.

• Drying is the final and absolutely necessary stage of the pickling process for the above materials. It is very necessary to prevent possible corrosion by removing any moisture.

Warning: The product contains a small amount of ammonium bifluoride (ABF) - may be harmful if swallowed or inhaled. It has negative effects on mucous membranes and upper respiratory tract tissues, eyes and skin. Before using this product, it is necessary to use eye protection, reinforced rubber gloves and a rubber apron, including protective clothing.

Further warnings can be found in the Safety Data Sheet. Concentrated ammonium bifluoride can also irritate and burn the skin and eyes with possible eye damage. Inhalation of ammonium bifluoride can irritate and burn the nose, throat and lungs, causing nosebleeds, coughing, wheezing and shortness of breath.

Storage and disposal of the product:

The product should be stored at temperatures between 5°C and 28°C in stainless steel or approved plastic containers (HDPE).

Warranty period: 18 months from the date of manufacture. Disposal - according to regulations.

Overview of pickling, passivation and gel preparations, a comprehensive coordinated product line:

1. Pickling agent for carbon, stainless steel and aluminum alloys (pickling, solution): The agent is diluted 1 part:4 parts water for aluminum alloys (with water - water lines). The agent is diluted 1 part:3 parts water for carbon steels (with water - water lines). The agent is diluted 1 part:2 parts water for stainless steels (with water - water lines). The proportions can be adjusted by one part water according to tests, depending on surface contamination, etc.

Pickling of carbon steels, stainless steels and aluminum alloys. This is a chemical cleaning or pickling process that serves to remove surface layers of oxides, etc.

Pickling of carbon steels, stainless steels and aluminum alloys results in etching of the surface and subsequent chemical removal of corrosion, scale and other impurities from the surface of these alloys.

It is advisable to perform time and temperature testing of the material at a solution temperature of approx. 20 °C, or higher. To achieve a better result, the test procedure is repeated.

2. Passivation, anodizing/anodization and polymerization of metals, for steels and aluminum alloys, solution: The product is diluted 1 part:3 parts water for aluminum alloys (with water - water lines). The product is diluted 1 part:2 parts water for carbon steels (with water - water lines). The product is diluted 1 part:1 part water for stainless steels (with water - water lines).

The proportions can be adjusted by one part water according to tests, surface contamination, etc.

Passivation, simultaneous anodization and ion polymerization of carbon steels, stainless steels and aluminum alloys, the purpose of which is to create a protective film that effectively extends the life of the products.

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Anodizing (or anodizing) is often synonymous with aluminum, which is new information for many experts that this is not the case, according to new scientific findings. Stainless steel is also able to benefit from this preparation from the anodizing transformation process (or anodizing).

Passivation, anodization/anodization and ion polymerization of carbon and stainless steels with this product not only optimizes their appearance, but also improves corrosion and wear resistance.

Passivation, anodization/anodization and ionic polymerization of aluminum alloys (anodic oxidation) is an electrochemical process that creates a uniformly compact layer of aluminum oxide on the aluminum surface.

It is advisable to perform time and temperature testing of the material, at approx. 20 °C, or higher. To achieve a better result, the test procedure is repeated.

2.1. Preparation (see point 2): Passivation, anodization, polymerization of piping systems:

Dilution according to point 2 - removal of rust, scale, sludge, biofilms and impurities.

I.e. anti-corrosion cleaning and polymerization of carbon and stainless steels (except aluminum alloys) by the circulation method (hydraulic system) on already installed piping systems (only for carbon steel and stainless steel. The product is not intended for aluminum alloy pipes.

The product works by - removing rust, scale, sludge and biofilms, while simultaneously passivating and anodizing the internal parts of steel piping systems - it applies to already installed piping systems, including - ionic polymerization of the metal surface. This treatment method does not require dismantling the piping systems, which significantly reduces costs.

The product provides protection against corrosive influences (against subsequent perforation of the pipe - pitting, surface corrosion, etc.) and also removes mineral deposits, etc.

3. Pickling gel for carbon steel, stainless steel and aluminum alloys (viscous gel):

The product is not diluted, to achieve a better result, the effect time is extended from 15 to 120 minutes depending on the material: for aluminum materials the shortest time, for stainless steel the longest time, according to time tests.

Pickling of welds, parts, etc. This involves changing the color of welds and their surroundings, especially on small and large or complex welds, as well as removing various abrasions after contact with non-precious materials and other iron contamination, by applying with a brush/spray, etc. Depending on the type of material, weld and ambient temperature, it is left to act, then the surface must be blasted with pressurized water and dried properly.

It is advisable to perform time and temperature testing of the material at approx. 20 °C, or higher. To achieve a better result, the test procedure is repeated.

Examples of implementing a technical solution

It is a pickling agent that acts in the form of chemicals on carbon steel, stainless steel and aluminum alloys, so-called pickling. Pickled steels then do not contain so-called surface contamination and deposited iron particles, the same applies to aluminum alloys - oxide layers.

Composition: citric acid is very soluble in water (59.2 g/100 ml at 20 °C), as is ammonium bifluoride, the so-called etching agent. Another substance is glycerol, a synergist for citric acid (the so-called green corrosion inhibitor).

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This product is presented in four examples of technical solutions.

Example 1

Preparation with subsequent composition of a pickling agent with a cleaning and anti-corrosion effect, for the treatment of carbon steels, stainless steels and aluminum alloys, i.e. on various technological equipment, parts, etc. All of the listed substances (chemicals) have a liquid/solid form and are soluble in cold water. The substances listed below were mixed at temperatures between 19 and 23 °C.

The raw materials (chemicals) listed in the table of examples were dissolved at laboratory temperature in water, forming a pickling solution. The tested samples are considered 100% and were diluted with water (filtered, with a 3-stage pre-filtration system for chlorine and chlorine derivatives, lead, heavy metals, organic compounds and other deposits) to the desired concentrations.

The pickling agent is prepared by dissolving complexing agents:

- citric acid (monohydrate) - 49 g/1000 g;

- ammonium bifluoride (inorganic etching compound) - 1.9 g/1000 g;

- glycerol (propane-1,2,3-triol) - 1.08 g/1000 g;

in filtered water, see table of examples below.

The balance of up to 100% of the weight of this pickling preparation is water. The result of this process is a clear, homogeneous solution.

Example 2

Preparation with subsequent composition of a pickling agent with a cleaning and anti-corrosion effect, for the treatment of carbon steels, stainless steels and aluminum alloys, i.e. on various technological equipment, parts, etc. All of the listed substances (chemicals) have a liquid/solid form and are soluble in cold water. The substances listed below were mixed at temperatures between 19 and 23 °C.

The raw materials (chemicals) listed in the table of examples were dissolved at laboratory temperature in water, forming a pickling solution. The tested samples are considered 100% and were diluted with water (filtered, with a 3-stage pre-filtration system for chlorine and chlorine derivatives, lead, heavy metals, organic compounds and other deposits) to the desired concentrations.

The pickling agent is prepared by dissolving complexing agents:

- citric acid (monohydrate) - 63 g/1000 g;

- ammonium bifluoride (inorganic etching compound) - 2.1 g/1000 g;

- glycerol (propane-1,2,3-triol) - 1.3 g/1000 g;

in filtered water, see table of examples below.

The balance of up to 100% of the weight of this pickling preparation is water. The result of this process is a clear, homogeneous solution.

Example 3

Preparation with subsequent composition of a pickling agent with a cleaning and anti-corrosion effect, for the treatment of carbon steels, stainless steels and aluminum alloys, i.e. on various technological equipment, parts, etc. All of the listed substances (chemicals) have a liquid/solid form and are soluble in cold water. The substances listed below were mixed at temperatures between 19 and 23 °C.

The raw materials (chemicals) listed in the table of examples were dissolved at laboratory temperature in water, forming a pickling solution. The tested samples are considered 100% and were diluted with water (filtered, with a 3-stage pre-filtration system for chlorine and chlorine derivatives, lead, heavy metals, organic compounds and other deposits) to the desired concentrations.

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The pickling agent is prepared by dissolving complexing agents:

- citric acid (monohydrate) - 126 g/1000 g;

- ammonium bifluoride (inorganic etching compound) - 4.2 g/1000 g;

- glycerol (propane-1,2,3-triol) - 2.6 g/1000 g;

in filtered water, see table of examples below.

The balance of up to 100% of the weight of this pickling preparation is water. The result of this process is a clear, homogeneous solution.

Example 4

Preparation with subsequent composition of a pickling agent with a cleaning and anti-corrosion effect, for the treatment of carbon steels, stainless steels and aluminum alloys, i.e. on various technological equipment, parts, etc. All of the listed substances (chemicals) have a liquid/solid form and are soluble in cold water. The substances listed below were mixed at temperatures between 19 and 23 °C.

The raw materials (chemicals) listed in the table of examples were dissolved at laboratory temperature in water, forming a pickling solution. The tested samples are considered 100% and were diluted with water (filtered, with a 3-stage pre-filtration system for chlorine and chlorine derivatives, lead, heavy metals, organic compounds and other deposits) to the desired concentrations.

The pickling agent is prepared by dissolving complexing agents:

- citric acid (monohydrate) - 189 g/1000 g;

- ammonium bifluoride (inorganic etching compound) - 6.3 g/1000 g;

- glycerol (propane-1,2,3-triol) - 3.9 g/1000 g;

in filtered water, see table of examples below.

The balance of up to 100% of the weight of this pickling preparation is water. The result of this process is a clear, homogeneous solution.

According to the table of examples, the optimal composition was selected from column no. 4.

Raw material (g/1000 g water) 1 2 3 4 Citric acid (monohydrate) 49 grams 63 126 189 Ammonium bifluoride (etching) 1.9 grams 2.1 4.2 6.3 Glycerol (polymer) 1.08 grams 1.3 grams 2.6 3.9 Water (filtered) up to 1000 g up to 1000 g up to 1000 g up to 1000 g

Industrial applicability

The preparation for pickling metals with our solution has the following forms of use:

- metal pickling - immersion system;

- pickling by spraying metals - with a spray gun (newer method);

- Circulation pickling of metals is used in steel pipe industrial equipment - the pickling agent flows through a hydraulic system in a closed pipe circuit (newer method).

Claims (2)

1. A preparation for pickling carbon steels, stainless steels and aluminum alloys, characterized in that it contains citric acid in an amount of from 0.6% to 39.6% by weight of the preparation, ammonium bifluoride in an amount of from 0.3% to 25.6% by weight of the preparation, glycerol in an amount of from 0.3% to 22.8% by weight of the preparation and the balance up to 100% by weight of this preparation consists of water. 2. The preparation according to claim 1, characterized in that it is in the form of a solution.