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Composite Ceramics

Advanced ceramic materials have such interesting properties that mechanical engineers are becoming more and more interested in their use as structural parts.

Ceramic cutting tools have been in use for some time. However, it is only during the last twenty years that there has been rapid development in this field because of the development of new composite ceramics.

Composite materials are materials in which two or more different substances, such as metals, ceramics, glasses, or polymers are combined without chemical reaction. As a result one can produce a material with properties different from those of any of the individual constituents. The constituents of a composite would retain their individual charac­teristics.

Recently engineers have developed various kinds of composite ceramics which must combine an increased toughness with the same hardness and strength of usual ceramics. A promising recent development is the addition of a tiny quantity of metal to increase toughness and tool life. Thus, at room and high temperatures (1000°C) the composite ceramics for cutting tools should possess the following properties: high strength, high toughness, high hardness, high thermal shock resistance and high chemical inertness.

Where can materials with such properties be used?

 

6.19 Make a short presentation of a material widely used in the field you specialize in. Your presentation should include information about the following:

1. When people began using the material. If it is a synthetic material, who and when obtained it first.

2. Properties of the material relevant to the sphere of use described.

3. Uses of the material in the field of your specialization.

 

6.20 Read the sentences (1-3) below. What does the word smart mean in each one?

1. He wore a smartsuit to the meeting.

2. She's the smartestgirl in her class.

3. They stayed in a smarthotel in New York.

 

6.21 Look at the title of the text. Which of the meanings of the word smart is used? Read the text to check your answer.

Smart Materials

Smart – or shape memory – materials are an invention that has changed the world of engineering. There are two types: metal alloys and plastic polymers. The metal alloys were made first and they are usually an expensive mixture of titanium and nickel.

Shape memory materials are called 'smart' because they react to changes in their environment, for example:

• plastics that return to their original shape when the temperature changes. One use is in surgery where plastic threads 'remember' the shape of a knot, react to the patient's body temperature and make themselves into stitches.



• metal alloys that have a 'memory' and can return to their original shape. They are used in medical implants that are compressed so they can be put inside the patient's body through a small cut. The implant then expands back to its original shape. More everyday uses are for flexible spectacle frames and teeth braces, solids that darken in sunlight, like the lenses in some sunglasses.

• liquid crystals that change shape and colour. These have been used in climbing ropes that change colour if there is too much strain and weight on them.

The future of these materials and their possible uses is limited only by human imagination. One clever idea is that if cars were made of smart metal, a minor accident could be repaired by leaving the car in the sun!





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