- •Chemistry
- •Introduction
- •Some facts about chemistry
- •Some facts about atoms (I)
- •Some facts about atoms (II)
- •The atomic model
- •The nature of ceramics
- •Construction materials
- •The measurements in chemistry
- •The metric system
- •Isotopes
- •Liquids (I)
- •Words to be remembered:
- •Liquids (II)
- •Words to be remembered:
- •Solid state (I)
- •Words to be remembered:
- •Solid state (II)
- •Words to be remembered:
- •Properties of solids
- •Notes on the texts:
- •Words to be remembered:
- •Organic chemistry
- •Word to be remembered:
- •Elementary carbon
- •Words to be remembered:
- •Notes on the texts:
- •Carbon dioxide
- •Words to be remembered:
- •Words to be remembered:
- •Hydrogen
- •Words to be remembered):
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. It should be noted that each oxygen atom with two electronic vacancies in its outer shell borrows two electrons from its metal neighbours, 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 on 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 rock or clay 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 - портландцемент
№8