This article will devote its attention to the analysis of the phenomenon of metal oxidation. Here we will consider the general idea of this phenomenon, get acquainted with some varieties and study them using steel as an example. The reader will also learn how to complete this process on their own.
Oxidation determination
First, we will focus on the concept of oxidation itself. This is the process during which an oxide film is created on the surface area of the product, as well as on the workpiece. It becomes possible due to redox reactions. Most often, such measures are used in the oxidation of metals, decor elements and in order to form a dielectric layer. Among the main varieties, the following are distinguished: thermal, plasma, chemical and electrochemical forms.
Species diversity
Dwelling on the description of the above types, about each of them we can say that:
- The thermal form of oxidation can be carried out during the heating of a particular product or tool in atmospheres of water vapor or oxygen. If metal oxidation occurs, for example, iron and low alloy steel, then the process is called burnishing.
- The chemical form of oxidation characterizes itself, as a processing process, through the use of melts or solutions of oxidizing agents. These can be representatives of chromates, nitrates, etc. Most often this is done to give the product protection against corrosion processes.
- Oxidation of the electrochemical type is characterized by what occurs inside electrolytes. It is also called microarc oxidation.
- The plasma form of oxidation can only be realized in the presence of plasma with a low temperature. It should contain O2. The second condition is the presence of a direct current discharge, as well as RF and / or microwave.
The general concept of oxidation
In order to better understand that this is metal oxidation, it would also be advisable to familiarize yourself with the general, brief description of the oxidation.
Oxidation is a process of a chemical nature, which is accompanied by an increase in the degree of atomic oxidation of a substance, which undergoes this phenomenon. This occurs by sending negatively charged particles - electrons, from the atom, which is the reducing agent. He may also be called a donor. The transfer of electrons takes place in relation to the oxidizing atom, an electronic acceptor.
Sometimes during oxidation, the molecules of the starting compounds can become unstable and break up into smaller composite fragments. In this case, some of the atoms formed by molecular particles will have a greater degree of oxidation than the same types of atoms, but in their original, initial state.
On the example of steel oxidation
What is metal oxidation? The answer to this question will be better considered using an example for which we will use this process with steel.
By chemical oxidation of metal - steel, they understand the process of performing work, during which the metal surface is covered with an oxide film. This operation is carried out, most often, to form a protective coating or to give a new touch to the decor element; they also do this in order to create dielectric layers on steel products.
Speaking about chemical oxidation, it is important to know: first, the product is subjected to treatment with any alloy or solution of chromate, nitrate or some other oxidizing agents. This will give the metal protection against corrosion. The procedure can also be carried out using compositions of an alkaline or acidic nature.
The chemical form of oxidation, carried out through the use of alkalis, should be carried out at a temperature of from 30 to 180 ° C. For such procedures, it is necessary to use alkalis with an admixture of a small amount of oxidizing agents. After the part has been treated with an alkaline compound, it must be washed very carefully, and then dried. Sometimes a preform that has already gone through an oxidation procedure can be oiled further.
More on the Acid Method
To apply the method of acid operations, it is necessary to use several acids, more often it is two or three. The main substances of this type are hydrochloric, phosphoric and nitric acids. A small amount of manganese compounds and others are added to them. The variation in temperature indices in which metal-steel oxidation can occur, using the acid method, ranges from 30 to 100 ° .
Chemical oxidation, described for the two methods, gives a person the opportunity to get a film, both in production and at home, which causes a fairly strong protection of the product. However, it will be important to know that the protection of steel and other metals will be more reliable if an electrochemical procedure is used. It is because of the benefits of electrochem. chemical oxidation method, the latter is used less frequently in relation to steel objects.
Anodic Oxidation Form
Oxidation of metals can take place using the anode process. Most often, the electrochemical oxidation process is called anodic. It is carried out in the thickness of electrolytes of a solid or liquid state of aggregation. Also, the use of this method will allow applying a high-quality film to the object:
- The thickness of the thin layer coating ranges from 0.1 to 0.4 micrometers.
- Providing electrical insulating and wear-resistant properties is possible if the thickness varies from two to three to three hundred microns.
- Protective coating = 0.3 - 15 microns.
- Layers with properties similar to enamel may be applied. Specialists often call such a film an enamel coating.
A characteristic of an anodized product is its positive potential. This procedure is recommended in order to protect the elements of integrated circuits, as well as when creating a dielectric coating on the surface of semiconductors, alloys and steels.
The process of oxidation of metals of the anodized type can, if desired, be performed by any person in a domestic environment, at home. However, it will be very important to comply with all safety conditions, and this must be done unconditionally. This is due to the use of very aggressive compounds in this method.
One of the particular cases of anodizing is considered to be the method of microarc oxidation. It allows a person to receive a number of unique coatings with high parameters of decorative, heat-resistant, protective, insulating and anti-corrosion type. The microarc form of the process can be carried out only under the influence of alternating or pulsed current in the thickness of electrolytes with a slightly alkaline nature. The considered method allows to obtain a coating thickness from two hundred to two hundred and fifty microns. After the operation is completed, the surface will look like ceramic.
Burnishing process
Oxidation of ferrous metals in professional terminology is called burnishing.
If we talk about steel bluing, for example, oxidation, blackening or blueing, we can say that this is a process during which a layer of iron oxide is formed on cast iron or low alloy steel. Typically, the thickness of such a film ranges from one to ten microns. The thickness of the layer determines the presence of a certain color tint. Depending on the increase in the thickness of the film layer, the colors can be: yellow, brown, cherry, violet, blue and gray.
There are currently several types of burnishing:
- The alkaline type is characterized by the use of appropriate solutions, with the addition of oxidizing agents, under conditions of temperature from 135 to 150 degrees Celsius.
- The acid type of burnishing uses acidic solutions and chemical or electrochemical methods.
- The thermal form of processing is characterized by the use of sufficiently high temperatures (from 200 to 400 ° C). The process takes place in the atmosphere of superheated water vapor. If you use an ammonia-alcohol mixture, the temperature requirements increase to 880 ° C, and in molten salts from 400 to 600 ° C. The use of an air atmosphere requires preliminary coating of the surface of the spare part with a thin layer of varnish, which should be asphalt or oil.
Introduction to Thermal Oxidation
Thermal oxidation of metals is a technique in which an oxide film is applied to steel in the atmosphere of water vapor. Other oxygen-containing media with sufficiently high temperatures can also be used. It is quite difficult to conduct heat treatment at home, and therefore, as a rule, it is not performed. Mentioning the plasma type of oxidation, it is important to know that it is almost impossible to do this at home.
Independent operation
Metal oxidation at home can be done independently. The easiest way to do this is to process steel products. To do this, first you need to polish or clean the part on which the oxidation work will be carried out. Next, oxides should be removed from the surface by using solutions of 5% H2SO4 (sulfuric acid). The product must be kept in fluid for sixty seconds.
Further actions
After the stage of placing the part in the acid bath passes, it should be washed under warm water and passivated, or, in other words, boil the object for five minutes. To do this, use a solution of water from the water supply with fifty grams of simple laundry soap. Here the calculation is for 1 liter of liquid. Having completed all these actions, we have come to the end of oxidation. To implement the procedure, you must:
- Use containers subject to enameling and free from chips or scratches on the inside.
- Fill the container with water and dilute with the appropriate number of grams of caustic soda (calculated per 1 liter = 50 grams).
- Transfer the vessel with water to the stove and place the product on top.
- Heat the mixture to approximately 135-150 ° C.
After 90 minutes, the part can be pulled out and contemplate your own work.
Some data
The reader will know that if there is a need for such an operation, but in the absence of skill or desire, such a request can be addressed to various specialists. Oxidation of metals in Moscow, for example, can be carried out both by specialists in various services, and at home, by people. Some types of such a means of imparting protection to a part can be quite expensive. In the capital of the Russian Federation, the anodized type of oxidation will be quite expensive, but it will give a high reliability indicator to the facility. To find specialists in a similar matter, it’s enough to type Google in a search query, for example: “performing chemical oxidation in ... (a certain city or region)”, or something similar.