Silicate Industry

Silicate industry is the industry processing the natural compounds of silicon. *It embraces the production of cement, glass, and ceramics1.

The production of ceramic goods is based on the property of clay when mixed with water to form putty, from which various articles can easily be moulded. When these are dried and then for easily moulding baked, that is, ignited at a high temperature, they become hard and retain their shape, no longer being softened by water.

In this way clay, mixed water and sand is moulded into bricks, which are then dried and baked. The materials used to make silicate bricks are white sand and slaked lime.

Cement Production. Cement is made from limestone and clay, or from their natural mixture, marls. The materials roasted in cylindrical rotary kilns are charged into a slowly rotating kiln at its upper end and travel, mixing continuously, towards the lower end, while a current of hot gases, the products of the burning of fuel, flows in the opposite direction. During the period of their movement through the kiln the clay and the limestone react chemically, and the material emerging from the kiln in lumps of a caked mass is cement, which is then grounded.

When cement is mixed with water, it forms mortar, which hard­ens, binding various objects, such as bricks or stones, very firmly. It is for this reason that cement is used widely as a binding materials in large-scale construction, including underwater construction.

Cement is often mixed with sand or gravel, in which case we get concrete. Concrete has roughly the same coefficient of thermal ex­pansion as iron.

Glass Production. The initial materials for the production of or­dinary glass are mainly soda, limestone, and sand. A mixture of these substances is heated in a bath-shaped furnace.

When it cools, the liquid mass of glass *does not become hard at once2. At first it becomes viscous and readily assumes any shape. This property of glass is used in making various articles out of it. Definite portions of the cooling semiliquid mass are taken from the bath, and these are blown or pressed to make various glassware. By machine methods glass sheets, tubes, etc., can be drawn continuous­ly from the molten mass.

Sand is the chief material used as a fine aggregate. It is required in mortar or concrete for economy and to prevent the excessive crack­ing. Mortar made without sand would be expensive.

The word "sand" is applied to any finely divided material which will not injuriously affect the cement or lime and * which is not sub­ject to disintegration or decay. Sand is almost the only material which is sufficiently cheap and which can fulfil these requirements.

A mixture of coarse and fine grains is very satisfactory, as it makes a denser and stronger concrete with a less amount of cement than when only fine-grained sand is used.

The following sands are used for mortars: pit or quarry sand, river sand and sea sand.

Lime is a calcium oxide. It is used in great quantities for mortar and plaster. Lime (quicklime) is a white solid that reacts violently with water to form calcium hydroxide. It is made by heating lime­stone in a special kind of furnace called a "kiln". Lime must be stored in a dry place, otherwise it will absorb moisture.

Limes may be divided into three distinct classes:

1. Rich limes that contain not more than 6 percent of impurities, slake very rapidly, and are entirely dependent *on external agents for setting power4. These are widely used for interior plasterer's works.

2. Poor limes that contain from 15 percent to 30 percent of use­less impurities and possess the general properties of rich limes, only to a lesser degree.

3. Hydraulic limes that contain certain proportions of impurities, which when calcinated, combine with the lime and endow it with the valuable property of setting under water or without external agents.

Lime is a basic building material extensively used all over the world, but it was not until the later years of the 19th century that a greater appreciation of the fuel-burning problems involved became apparent. Until this time the requirement for lime was largely agri­cultural and it was produced by farmers or by small builders who used it for making mortar and plaster.

As industrial requirements increased "running" kilns were devel­oped. These were lined with firebrick and charged at regular inter­vals with stone and fuel.

Around the world there are many different types of kilns and variations in lime-burning practice.

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