Carbide: formula, application and properties

A lot of different chemical compounds are known in the world: about hundreds of millions. And all of them, like people, are individual. You can not find two substances that have the same chemical and physical properties for different compositions.

One of the most interesting inorganic substances that exist in the world is carbides. In this article, we will discuss their structure, physical and chemical properties, application and analyze the details of their production. But first, a little about the history of discovery.

History

Metal carbides, the formulas of which we will give below, are not natural compounds. This is due to the fact that their molecules tend to disintegrate when interacting with water. Therefore, here it is worth talking about the first attempts to synthesize carbides.

Since 1849, there have been references to the synthesis of silicon carbide, but some of these attempts remain unrecognized. Large-scale production began in 1893 by the American chemist Edward Acheson in a way that was later named after him.

The history of the synthesis of calcium carbide is also not very different. In 1862, he received a German chemist, Friedrich Wöhler, heating fused zinc and calcium with coal.

Now let's move on to more interesting sections: chemical and physical properties. After all, they are the essence of the application of this class of substances.

Physical properties

Absolutely all carbides differ in their hardness. For example, one of the most solid substances on the Mohs scale is tungsten carbide (9 out of 10 possible points). In addition, these substances are very refractory: the melting point of some of them reaches two thousand degrees.

Most carbides are chemically inert and interact with a small amount of substances. They are not soluble in any solvents. However, the interaction with water can be regarded as dissolution, with the destruction of bonds and the formation of a hydroxide of a metal and a hydrocarbon.

The last reaction and many other interesting chemical transformations involving carbides will be discussed in the next section.

Chemical properties

Almost all carbides react with water. Some are easy and without heating (for example, calcium carbide), and some (for example, silicon carbide) - when water vapor is heated to 1800 degrees. Reactivity in this case depends on the nature of the bond in the compound, which we will talk about later. In the reaction with water, different hydrocarbons are formed. This happens because the hydrogen contained in the water is connected to the carbon in the carbide. To understand what kind of hydrocarbon is obtained (or both the limiting and the unsaturated compound can be obtained), one can proceed from the valency of the carbon contained in the initial substance. For example, if we have calcium carbide, the formula of which is CaC ₂ , we see that it contains the ion C ₂ ^2- . This means that two hydrogen ions with a charge + can be attached to it. Thus, we obtain the compound C ₂ H ₂ -acetylene. In the same way, from a compound such as aluminum carbide, the formula of which is Al ₄ C ₃ , we get CH ₄ . Why not C ₃ H ₁₂ , you ask? After all, the ion has a charge of 12-. The fact is that the maximum number of hydrogen atoms is determined by the formula 2n + 2, where n is the number of carbon atoms. Hence, there can only exist a compound with the formula C ₃ H ₈ (propane), and that ion with a charge of 12- decays into three ions with a charge of 4, which they give when combined with protons of the methane molecule.

Interesting are the oxidation reactions of carbides. They can occur both under the influence of strong mixtures of oxidants, and in ordinary combustion in an oxygen atmosphere. If with oxygen everything is clear: two oxides are obtained, then with other oxidizers it is more interesting. Everything depends on the nature of the metal that is part of the carbide, and also on the nature of the oxidant. For example, silicon carbide, the formula of which SiC, when interacting with a mixture of nitric and hydrofluoric acids, forms hexafluorosilicic acid with the emission of carbon dioxide. And when carrying out the same reaction, but with nitric acid alone, we get silicon oxide and carbon dioxide. Oxidizers can also include halogens and chalcogenes. With them, any carbide interacts, the reaction formula depends only on its structure.

Metal carbides, the formulas of which we have considered, are by no means the only representatives of this class of compounds. Now we will take a closer look at each industrially important combination of this class and then talk about their application in our life.

What are carbides?

It turns out that carbide, the formula of which, say, CaC _2, differs in structure from SiC. And the difference is primarily in the nature of the bond between the atoms. In the first case, we are dealing with a salt-like carbide. This class of compounds is named so because it behaves in fact as a salt, that is, it is capable of dissociating into ions. Such an ionic bond is very weak, which makes it easy to carry out the hydrolysis reaction and many other transformations involving interactions between ions.

Another, probably more industrially important type of carbide is covalent carbides: such as, for example, SiC or WC. They are characterized by high density and strength. As well as refractory and inert to dilute chemicals.

There are also metal-like carbides. They can rather be considered as alloys of metals with carbon. Among these, we can distinguish, for example, cementite (iron carbide, the formula of which varies, but on average it is approximately the same: Fe ₃ C) or cast iron. They have chemical activity, intermediate in its degree between ionic and covalent carbides.

Each of these subspecies of the class of chemical compounds we are discussing has its practical application. About how and where each of them applies, we'll talk in the next section.

Practical application of carbides

As we have already discussed, covalent carbides have the largest range of practical applications. These include abrasive and cutting materials, and composite materials used in various fields (for example, as one of the materials included in body armor), and auto parts, electronic devices, heating elements, and nuclear power. And this is not a complete list of applications of these superhard carbides.

The narrowest use is made of salt-forming carbides. Their reaction with water is used as a laboratory method for obtaining hydrocarbons. How this happens, we have already disassembled above.

Along with covalent, metal-like carbides have the widest application in industry. As we have already said, such a metal-like type of the compounds we are discussing are steels, cast irons and other compounds of metals with carbon impregnations. As a rule, the metal contained in such substances belongs to the class of d-metals. That is why he is inclined to form not covalent bonds, but as it were to penetrate into the structure of the metal.

In our opinion, there are more than enough practical applications for the above-mentioned compounds. Now let's take a look at the process of obtaining them.

Production of carbides

The first two types of carbides that we have considered, namely covalent and salt-like, are most often obtained in one simple way: by reaction of elemental oxide and coke at high temperature. At the same time, a part of the coke consisting of carbon is combined with the element atom in the oxide and forms carbide. The other part "takes" oxygen and forms carbon monoxide. This method is very energy-intensive, since it requires maintaining a high temperature (about 1600-2500 degrees) in the reaction zone.

To obtain some types of compounds, alternative reactions are used. For example, decomposition of the compound, which eventually gives carbide. The reaction formula depends on the specific compound, so we will not discuss it.

Before completing our article, we will discuss some interesting carbides and talk about them in more detail.

Interesting compounds

Sodium carbide. The formula for this compound is C ₂ Na ₂ . This can be more likely represented as acetylide (that is, the product of substitution of hydrogen atoms in acetylene for sodium atoms), and not carbide. The chemical formula does not fully reflect these subtleties, so they must be sought in the structure. This is a very active substance and, in any contact with water, reacts very actively with it to form acetylene and alkali.

Magnesium carbide. Formula: MgC ₂ . Methods of obtaining this sufficiently active compound are interesting. One of them suggests sintering of magnesium fluoride with calcium carbide at high temperature. As a result, two products are obtained: calcium fluoride and the carbide we need. The formula for this reaction is quite simple, and you can, if you want, read it in specialized literature.

If you are not sure about the usefulness of the material in the article, then the next section is for you.

How can this be useful in life?

Well, first, knowledge of chemical compounds can never be superfluous. It is always better to be armed with knowledge than to remain without it. Secondly, the more you know about the existence of certain compounds, the better you understand the mechanism of their formation and the laws that allow them to exist.

Before going to the end, I would like to give some recommendations on the study of this material.

How to study this?

Very simple. This is just a section of chemistry. And it should be studied according to the textbooks of chemistry. Begin with school information and go on to more in-depth, from university textbooks and reference books.

Conclusion

This topic is not so simple and boring as it seems at first glance. Chemistry can always become interesting if you find your goal in it.