A lot of different chemical substances are known in the worldconnections: 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,existing in the white light, are 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.
Carbides of metals, the formulas of which we quotebelow, 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 are references to the synthesissilicon carbide, but some of these attempts remain unrecognized. Large-scale production began in 1893 by an 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.
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 andinteract 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.
Almost all carbides react with water.Some - easily and without heating (for example, calcium carbide), but 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 will be 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 CaC2, we see that it contains the ion C22-. Hence, two hydrogen ions with a charge + can be attached to it. Thus, we obtain the compound C2X2 - Acetylene. In the same way, from a compound such as aluminum carbide, the formula of which Al4FROM3, we obtain CH4. Why not C3X12, 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 C3X8 (propane), and that ion with a charge of 12- decays into three ions with a charge of 4, which they give when they combine with the protons of the methane molecule.
Interesting are the oxidation reactionscarbides. They can occur both under the influence of strong oxidant mixtures, 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 consideredare 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.
It turns out that carbide, the formula of which, say, CaC2, substantially differs 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 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 typecarbides are 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: Fe3C) or cast iron. They have a chemical activity intermediate in their 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.
As we have already discussed, covalent carbides havethe largest range of practical applications. These include abrasive and cutting materials, and composite materials used in various areas (for example, as one of the materials included in body armor), and auto parts, electronic devices, heating elements, and nuclear power. And this is far from 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 the production of hydrocarbons. The way it happens, we already dismantled above.
Along with covalent, metal-like carbideshave the widest application in the 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 look at the process of obtaining them.
The first two types of carbides, which we examined,namely covalent and salt-like, are obtained most often in one simple manner: by reacting the elemental oxide and coke at a high temperature. At the same time, a part of the coke consisting of carbon is combined with the atom of the element 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 compoundsuse alternative reactions. 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.
Sodium carbide. The formula for this compound C2On2. This can be presented more like acetylide (thenis 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. It is a very active substance and, at any contact with water, interacts very actively with it to form acetylene and alkali.
Magnesium carbide. Formula: MgC2. Interesting ways of getting this enoughactive compound. 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.
Well, firstly, knowledge of chemical compoundscan 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.
Very simple. It's just a section of chemistry. And it should be studied according to the textbooks of chemistry. Begin with the school information and go to more in-depth, from the university textbooks and reference books.
This topic is not so simple and boring as it seems at first glance. Chemistry can always become interesting, if you find it's goal.
