A lot of different chemical compounds are known in the world: about hundreds of millions. And all of them, like people, are individual. It is impossible to find two substances that would have the same chemical and physical properties with different composition.
One of the most interesting inorganic substances that exist in the world are carbides. In this article, we will discuss their structure, physical and chemical properties, applications and analyze the intricacies of their production. But first, a little about the history of the 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 decompose when interacting with water. Therefore, it is worth talking about the first attempts to synthesize carbides here.
From 1849 there are 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 process that was later named after him.
The history of the synthesis of calcium carbide also does not differ in a large amount of information. In 1862, the German chemist Friedrich Wöhler obtained it by heating alloyed zinc and calcium with coal.
Now let's move on to more interesting sections: chemical andphysical properties. After all, it is in them that the whole essence of the use of this class of substances lies.
Physical properties
Absolutely all carbides are distinguished by their hardness. For example, one of the hardest 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 insoluble in any solvents. However, dissolution can be considered interaction with water with the destruction of bonds and the formation of metal hydroxide and hydrocarbon.
We will talk about the last reaction and many other interesting chemical transformations involving carbides in the next section.
Chemical properties
Almost all carbides interact with water. Some - easily and without heating (for example, calcium carbide), and some (for example, silicon carbide) - by heating water vapor to 1800 degrees. The reactivity in this case depends on the nature of the bond in the compound, which we will discuss later. In the reaction with water, various hydrocarbons are formed. This happens because the hydrogen contained in the water combines with the carbon in the carbide. It is possible to understand which hydrocarbon will turn out (and both saturated and unsaturated compounds can turn out) based on the valency of the carbon contained in the original substance. For example, if uwe have calcium carbide, the formula of which is CaC2, we see that it contains the ion C22-. This means that two hydrogen ions with a + charge can be attached to it. Thus, we get the compound C2H2 - acetylene. In the same way, from a compound such as aluminum carbide, the formula of which is Al4C3, we get CH4. Why not C3H12, 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. This means that only a compound with the formula C3H8 (propane) can exist, and that ion with a charge of 12- decays into three ions with a charge of 4-, which give methane molecules when combined with protons.
Oxidation reactions of carbides are interesting. They can occur both when exposed to strong mixtures of oxidizing agents, and during ordinary combustion in an oxygen atmosphere. If everything is clear with oxygen: two oxides are obtained, then with other oxidizing agents it is more interesting. It all depends on the nature of the metal that is part of the carbide, as well as on the nature of the oxidizing agent. For example, silicon carbide, the formula of which is SiC, when interacting with a mixture of nitric and hydrofluoric acids, forms hexafluorosilicic acid with the release of carbon dioxide. And when carrying out the same reaction, but with only nitric acid, we get silicon oxide and carbon dioxide. Halogens and chalcogens can also be referred to as oxidizing agents. Any carbide interacts with them, the reaction formula depends only on its structure.
Metal carbides, the formulas of which we have considered, are far from the only representatives of this class of compounds. Now we will take a closer look at each of the industrially important compounds of this class and then talk about their application in our lives.
What are carbides?
It turns out that carbide, whose formula, say, CaC2, differs significantly in structure from SiC. And the difference is primarily in the nature of the bond between atoms. In the first case, we are dealing with s alt-like carbide. This class of compounds is named so because it actually behaves like a s alt, that is, it is able to dissociate into ions. Such an ionic bond is very weak, which makes it easy to carry out the hydrolysis reaction and many other transformations, including interactions between ions.
Another, perhaps more industrially important, type of carbide is the covalent carbide, such as SiC or WC. They are characterized by high density and strength. Also 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, one can distinguish, for example, cementite (iron carbide, the formula of which varies, but on average it is approximately the following: Fe3C) or cast iron. They have a chemical activity intermediate in degree between ionic and covalent carbides.
Each of these subspecies of the class of chemical compounds we are discussing has its own practical application. How and where to applyeach one, we'll talk about in the next section.
Practical application of carbides
As we have already discussed, covalent carbides have the widest range of practical applications. These are abrasive and cutting materials, and composite materials used in various fields (for example, as one of the materials that make up body armor), and auto parts, and electronic devices, and heating elements, and nuclear energy. And this is not a complete list of applications for these superhard carbides.
S alt-forming carbides have the narrowest application. Their reaction with water is used as a laboratory method for producing hydrocarbons. We have already discussed how this happens 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 metal compounds interspersed with carbon. As a rule, the metal found in such substances belongs to the class of d-metals. That is why it is inclined to form not covalent bonds, but, as it were, to be introduced into the structure of the metal.
In our opinion, the above compounds have more than enough practical applications. Now let's take a look at the process of obtaining them.
Production of carbides
The first two types of carbides that we examined, namely covalent and s alt-like, are most often obtained in one simple way: by the reaction of the oxide of the element and coke at high temperature. At the same time, partcoke, consisting of carbon, combines with an atom of an element in the composition of the oxide, and forms a carbide. The other part "takes" oxygen and forms carbon monoxide. This method is very energy-consuming, as it requires maintaining a high temperature (about 1600-2500 degrees) in the reaction zone.
Alternative reactions are used to obtain certain types of compounds. For example, the decomposition of the compound, which ultimately gives the carbide. The reaction formula depends on the specific compound, so we will not discuss it.
Before we conclude our article, let's discuss some interesting carbides and talk about them in more detail.
Interesting compounds
Sodium carbide. The formula for this compound is C2Na2. This can be thought of more as an acetylenide (i.e., the product of the replacement of hydrogen atoms in acetylene by sodium atoms), rather than a 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 it very actively interacts with it with the formation of acetylene and alkali.
Magnesium carbide. Formula: MgC2. Methods for obtaining this sufficiently active compound are of interest. One of them involves the sintering of magnesium fluoride with calcium carbide at high temperature. As a result of this, two products are obtained: calcium fluoride and the carbide we need. The formula for this reaction is quite simple, and you can read it in the specialized literature if you wish.
If you are not sure about the usefulness of the material presented in the article, then the followingsection for you.
How can this be useful in life?
Well, first of all, knowledge of chemical compounds can never be superfluous. It is always better to be armed with knowledge than to be left 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 proceeding to the end, I would like to give some recommendations for the study of this material.
How to study it?
Very simple. It's just a branch of chemistry. And it should be studied in chemistry textbooks. Start with school information and move on to more in-depth information from university textbooks and reference books.
Conclusion
This topic is not as simple and boring as it seems at first glance. Chemistry can always be interesting if you find your purpose in it.
