Cite the main clay products application areas.

The use of clay created to meet the construction needs in areas without other building materials, such as wood or stone, but rich in clay. Archaeologists have found bricks in the Middle East dating 10,000 years ago. The ancient city of Ur (modern Iraq) was built with mud bricks around 4,000 B.C. Many ancient structures made of bricks, such as the Great Wall of China and remnants of Roman buildings, are still standing today. The Pyramid of the Sun was built of adobe bricks by the Aztecs in the fifteenth century and is still standing. From the Sumerians to the Babylonians, from the Assyrians to the Egyptians, from the Greeks to the Romans, terracotta bricks represent a material which has been used beyond every national boundary throughout history. There is considerable evidence of the rich medieval architecture in Europe.

25 - Define the terms: adobe bricks, kiln, terracotta, terra nigra.

The adobe brick is the oldest type of brick in the Western Hemisphere. An adobe brick is a composite material made of clay mixed with water and an organic material such as straw or dung, and baked in the sun. The soil composition typically contains clay and sand. Straw is useful in binding the brick together and allowing the brick to dry evenly. Dung offers the same advantage and is also added to repel insects. The mixture is roughly half sand (50%), one-third clay (35%), and one-sixth straw (15%). Adobe soil can be found in dry regions throughout the world, but most notably in Central America, Mexico, and the southwestern United States.

There are many differents types of kilns, the main are:

Rail kilns: In modern brickworks, this is usually done in a continuously fired tunnel kiln, in which the bricks move slowly through the kiln on conveyors, rails, or kiln cars to achieve consistency for all bricks.

The Trench Kiln method was developed in the late nineteenth century. An oval or circular trench, 6-9 meters wide, 2-2.5 meters deep, and 100-150 meters in circumference, is dug. Half or more of the trench is filled with unfired bricks which are stacked in an open lattice pattern to allow airflow. In operation, new bricks, along with roofing bricks, are stacked at one end of the brick pile; cooled finished bricks are removed from the other end for transport. In the middle the brick workers create a firing zone by dropping fuel through access holes in the roof above the trench. The advantage of this design is a much greater energy efficiency. The process is continuous.

Terracotta is a clay-based unglazed ceramic. Terracotta has been used for sculpture and pottery, as well as bricks and roof shingles. The first clay sculptures were dried in the sun after being formed. Later, they were placed in the ashes of open hearths to harden, and finally kilns were used, similar to those used for pottery today. Only after firing to high temperature would it be classed as a ceramic material. An appropriate refined clay is partially dried and cast, molded, or hand worked into the desired shape. After thorough drying it is placed in a kiln and then fired. When unglazed, the material will not be waterproof. Most other uses such as for table ware, sanitary piping, or building decoration in freezing environments require that the material be glazed. The unglazed color after firing can vary widely.

Terra nigra was a term for black glossed wares, most often plain, which were produced at various times and places, especially in Italy, during the Roman period. The fabrication of ceramic whose surface is covered by an intense black color. The black color actually comes about at temperatures as low as 250°C, through a migration of black organo-mineral complexes. The optimal relationship between curing temperature, strength and black color is obtained at 450-550°C in a simple garden wood fire.

26 - What is porcelain and how it produced?

Porcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, it is cooked in a kiln to temperatures between 1,200 oC and 1,400. The toughness, strength, and translucence of porcelain arise mainly from the formation of glass and the mineral mullite within the fired body at these high temperatures.

Date: 2016-01-03; view: 874