A second stone age?

Ever imagine opening the hood of an automobile and not seeing a metal engine inside?

That day may be coming soon.

A firm in Japan has produced a diesel engine using fine ceramics in place of metal parts.

Instead of metal it looks like a glazed clay or porcelain material.

Perhaps it's not so surprising that a diesel engine can be built of new ceramics. These materials are already being used in the space industry. They are also playing a bigger and bigger role in the other advanced forms of technology. Such advanced forms of technology are called high technology. Computers and robots are good examples of high technology.

Fine ceramics, or new ceramics, is the term used to tell the difference between a new kind of ceramics that is becoming a very large modern industry and the older kind of ceramics, which you can find in your own home.

Ceramics comes from the Greek word keramos. It means ''potter'' or ''potter's clay.'' The term refers to the ancient use of clay to make vases and pots and urns. The early Greek and Etruscan civilizations were full of them. Yet ceramics is not linked to just that.

Bathroom floor and wall tiles, washbowls, some water and sewerage pipes, as well as bricks come under the heading of ceramics. Glass, even though it is made from sand and not clay, is regarded as part of the ceramics family.

New ceramics is really the term used to classify all new materials that are taking the place of metals. That diesel engine made in Japan is just such an example.

The new ceramics or fine ceramics as they are also called are not made out of clay only. They are formed by combining them with other materials such as bauxite, feldspar, and talc.

Whatever the combination, these ceramics have a lot of excellent properties or values that make them very useful to industry. They can take terrific temperatures without melting or changing their form. They are very tough and hard and can last a long time. Unlike the metals iron and steel they do not rust.

These factors help explain why the ceramics industry is becoming so valuable and important. In the coming years new ceramics could become as well known as plastics, also a very important man-made invention.

Already new ceramic materials are playing an impressive role in atomic energy and in the electronics industry.

Remember those heat-shielding tiles on the space shuttle Columbia? Unfortunately a few came off soon after blastoff. Those heat-shielding tiles are an example of the uses now being put to ceramics. They were used because they can withstand, that is to say take, a great deal of heat.

This is why ceramic materials are also used in the nose cones of rockets and missiles, where they must stand temperatures of up to 5,000 degrees F.

Some people have gone so far as to say that with ceramics the world may be entering a ''second stone age.'' The only difference is that the new ceramic tools are going to be a whole lot more sophisticated than those Stone Age tools wielded by cavemen.