Boric Acid And Boron Oxide

Among the binary compounds of boron, the most common and most versatile is diboron trioxide. Diboron trioxide is a white powder. This powder has a strange property. Put it on a quartz plate , when heated to three or four hundred degrees, it will turn into a paste, and when this paste is cooled, another transparent substance will be obtained. This is because the molten boron trioxide is not formed into crystals after cooling, but a kind of glass. Such properties directly affect its preparation method.
Under normal circumstances, the preparation of oxides only needs to heat the elemental element in air or oxygen, but this method does not work on boron. Burning elemental boron in air will indeed change its surface. , but only the surface is slightly discolored, this is not because the chemical properties of elemental boron are stable at high temperatures, but because the formed boron trioxide turns into a layer of glass at high temperatures, covering the surface of boron, making The internal reaction cannot proceed.
In order to produce a large amount of boron oxide, the method of boric acid dehydration is usually used. In the laboratory, we put boric acid into a hard vacuum glass tube and heat it. Since then, boric acid has started a series of dehydration reactions, (H3BO3→HBO2→H2B4O7→B4O3) to first metaboric acid, then tetraboric acid, until After losing all the moisture, it melts again to become a glass body, and after cooling, it is crushed to become the familiar diboron trioxide.
Boron oxide is a standard acidic oxide, which is also one of the strong evidences that boron is listed as a non-metal. In a heated state, boron trioxide can react with many metal oxides to form colored and beautiful borates Glass. Take a refractory board, put a mixture of diboron trioxide, ferric chloride, chloroauric acid, and cobalt acetate on it in turn, after heating, as the boron oxide melts, the corresponding metal salt will react with it, and finally in Yellow, red and blue glass remains on the quartz plate.
This reaction has a very wide range of applications in the field of art. People can make special high-temperature pigments by sintering and crushing materials mixed with boron oxide, metal compounds and other materials. If this layer of pigments is covered on clay And other substrates are called glazes. The so-called glaze in porcelain technology, the bright layer on the surface of porcelain, is this kind of substance. The substrate can also be upgraded to metal. Early Europeans liked to use precious metals such as gold and silver, and painted these pigments on the surface and then sintered to obtain the famous gold wire enamel. In China, copper tires are generally used, and the products produced by burning are the well-known cloisonne. Later, Europeans invented the process of sintering glaze on the surface of iron tires. Because the sintering temperature is much lower, it is called "Italian cold enamel".