The nature of ceramics

What is ceramics? Can this question be answered? Essentially it is defined as a combination of one or more definite metals with a non-metallic element, usually oxygen. The comparatively large oxygen atoms serve as a matrix with the small metal atoms. The main characteristics of the construction of ceramic crystals is that the atoms are linked by bonds that are primarily ionic but also to a significant extent covalent. These bonds are re­sponsible for the stability and strength of ceramic materials. In the combination of oxygen atoms with metal atoms the ionic bonds are particularly strong, ft should be noted that each oxy­gen atom with two electronic vacancies in its outer shell bor­rows two electrons from its metal neighbors, thus both kinds of atoms become highly ionized - one negatively, the other po­sitively.

As highly oxidized compounds the ceramics are strongly re­sistant to attack by nearly all chemicals. This accounts for many of their uses, even the making of steel depends an the use of ceramics.

A lot of analyses have been made by chemists. They found that the principal elements, for instance, in natural clays were oxy­gen, silicon, and aluminium. They form the compounds known as aluminosilicates.

But a giant step forward in ceramic science came when crys­tal structures were analyzed by means of X-ray diffraction. It has been found that in the construction of ceramic materials much depends on how the atoms are stacked.

Words to be remembered:

to define outer

definite resistant

bond neighbour

Significant silicon

to be responsible for to find cut

particularly

Notes on the texts

it should be noted - необходимо отметить

to account for - объяснять

№7

Construction materials

With few exceptions, construction materials are solid materials or hardened into solid materials. Solid materials can be grouped into three fundamental types: ceramics, metals and organics. The ceramic materials are rook or day minerals, or are compounded from such minerals. Examples are: sand, limestone, glass, brisk, cement, gypsum, etc. These are materials which are dug from the earth’s crust. Since they are extracted from the earth, they are relatively inexpensive as compared to me­tals or the organic materials. The ceramics have been used as building materials since ancient times.

Silicate materials include glass» porcelain, enamel and cement. Ordinary glass is a mixture of silicates in the form of su­percooled liquid. It is made by melting a mixture of sodium carbonate (or sodium sulphate), limestone and sand.

Ordinary glass contains about 10% sodium, 5%calcium, and 1% aluminium, the remainder is silicon and oxygen. It consists of an aluminosilicate tetrahedral framework, within which are embedded sodium ions and calcium ions.

Portland cement is an aluminosilicate powder which sets to a solid mass on treatment with water and consists of a mixture of calcium silicates and calcium aluminate. When treated with water the calcium aluminate hydrolyzes and forms calcium hydro­xide and aluminium hydroxide. These substances react further with the calcium silicates and produce calcium aluminosilicates in the form of crystals.

Words to be remembered:

exception limestone

solid porcelain

to harden enamel

rock sand

clay sodium

to extract hydroxide

Notes on the text:

tetrahedral – тетраэдрический

framework – каркас, конструкция, остов

portland cement - портланд-цемент

№8