This article will focus on the analysis of the phenomenon of metal oxidation. Here we will consider a general idea of \u200b\u200bthis phenomenon, get acquainted with some varieties and study them using the example of steel. The reader will also learn how to do this process yourself.
Definition of oxidation
To begin with, we will focus on the concept of oxidation itself. This is a 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 the redox reactions. Most often, such measures are used in the oxidation of metals, decorative elements and in order to form a dielectric layer. Among the main varieties are the following: thermal, plasma, chemical and electrochemical form.
Species diversity
Dwelling on the description of the above listed species, about each of them we can say that:
- Thermal form of oxidation can be carried out during the heating of a certain product orinstrument in atmospheres of water vapor or oxygen. When metals such as iron and low alloy steel are oxidized, the process is called bluing.
- 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 in order to give the product protection against corrosion processes.
- Oxidation of the electrochemical type is characterized by what takes place inside the electrolytes. It is also called micro-arc oxidation.
- Plasma form of oxidation can be realized only in the presence of low temperature plasma. It must contain O2. The second condition is the presence of a DC discharge, as well as RF and / or microwave.
General concept of oxidation
To better understand what this is - the oxidation of metals, it would also be desirable to familiarize yourself with the general, brief characteristics of oxidation.
Oxidation is a process of a chemical nature, which is accompanied by an increase in the degree of atomic oxidation of a substance that undergoes this phenomenon. This happens through the transfer of negatively charged particles - electrons, from the atom, which is the reducing agent. It may also be called a donor. The transfer of electrons is done with respect to the oxidizing atom, the electron acceptor.
Sometimes, during oxidation, the molecules of the original compounds can become unstable and break up into smaller constituent fragments. Whereinsome of the atoms formed by the molecular particles will have a higher degree of oxidation than the same types of atoms, but in their original, original state.
On the example of steel oxidation
What is metal oxidation? The answer to this question will be better considered with an example for which we will use this process with steel.
Under the chemical oxidation of metal - steel, we understand the process of doing work, during which the metal surface will be covered with an oxide film. This operation is carried out, most often, to form a protective coating or give a new feature to the decor element; they also do it in order to create dielectric layers on steel products.
Speaking of chemical oxidation, it is important to know: first, the product is treated with some alloy or solution of chromate, nitrate, or a number of other oxidizing agents. This will give the metal protection against the effects of corrosion. The procedure can also be carried out using compositions of an alkaline or acidic nature.
The chemical form of oxidation, carried out by using alkalis, must be carried out at a temperature of 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 rinsed very thoroughly and then dried. Sometimes a workpiece that has already gone through the oxidation procedure can be additionally oiled.
Details of 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, orthophosphoric and nitric acids. A small amount of manganese compounds and others are added to them. The variation in temperature indicators in which oxidation of metal - steel can occur, by using the acid method, lies in the range from 30 to 100 ° С.
Chemical oxidation, described for two methods, gives a person the opportunity to obtain, both in production and at home, a film that causes a sufficiently 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 advantages of electrochemical. method over chemical oxidation, the latter is used less frequently for steel objects.
Anodic form of oxidation
Oxidation of metals can take place using the anodic 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 you to apply a high quality film to the object:
- The thickness of the thin layer coating ranges from 0.1 to 0.4 micrometers.
- Electrical insulating and wear-resistant properties are possible if the thickness isfluctuate from two to three to three hundred microns.
- Protective coating=0.3 – 15 microns.
- Layers with properties similar to enamel can be applied. Specialists often call such a film enamel coating.
The characteristic of the product that has been anodized is the presence of a positive potential. This procedure is recommended in order to protect the elements of integrated circuits, as well as to create a dielectric coating on the surface of semiconductors, alloys and steels.
The process of oxidation of anodized type metals can, if desired, be performed by any person at home, 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 special cases of anodizing is the method of microarc oxidation. It allows a person to obtain a number of unique coatings with high parameters of a 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 that have a slightly alkaline character. The method under consideration makes it possible to obtain a coating thickness from two hundred to two hundred and fifty microns. After the operation, the surface will become similar to ceramics.
Bluing process
Oxidation of ferrous metals in professional terminology is calledbluing.
When talking about blueing of steel, such as oxidizing, blackening or bluing, we can say that this is a process during which a layer of iron oxide is formed on cast iron or low alloy steel. As a rule, the thickness of such a film lies in the range from one to ten microns. The thickness of the layer also determines the presence of a certain tint color. Depending on the increase in the thickness of the film layer, the colors can be: yellow, brown, cherry, purple, blue and gray.
Currently there are several types of bluing:
- 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.
- Acid type bluing 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 thickness of the atmosphere of superheated water vapor. If an ammonia-alcohol mixture is used, then the temperature requirements increase to 880 °C, and in molten s alts - from 400 to 600 °C. The use of an air atmosphere requires pre-coating the surface of the part with a thin layer of varnish, which should be asph alt or oil.
Introduction to Thermal Oxidation
Thermal oxidation of metals is a technique in which an oxide film is applied to steel inspace of the water vapor atmosphere. Other oxygen-containing media with sufficiently high temperatures can also be used. It is quite difficult to carry out heat treatment at home, and therefore, as a rule, it is not performed. Speaking of the plasma type of oxidation, it is important to know that it is almost impossible to do this at home.
Self-operation
Oxidation of metal at home can be done independently. The easiest way is to subject steel products to such processing. To do this, you first 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 five percent H2SO4 (sulfuric acid). The product must be kept in the liquid for sixty seconds.
Next steps
After the stage of placing the part in the acid bath has passed, it should be washed under warm water and passivated or, in other words, boiled 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 carried out all these actions, we have come to the end of oxidation. To implement the procedure, you must:
- Use containers that are enameled and do not have chips or scratches on the inside.
- Fill the container with water and dilute with the appropriate amount of grams of caustic soda (per 1 liter=50 grams).
- Move the vessel fromwater on the stove and place the product on top.
- Heat the mixture to about 135-150°C.
After 90 minutes, you can pull out the part and contemplate your own work.
Some data
The reader will know that if such an operation is needed, 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 performed both by specialists in various fields of services, and at home, by people. Some types of such means of imparting protection to the 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 object. To find specialists in such a case, it is enough to type in a Google search query, for example: "performing chemical oxidation in … (a certain city or region)", or something similar.
