Advanced ceramics

During the past five years, ceramics has undergone a revolution almost as dramatic as the more familiar one in electronics. Novel approaches to preparing and processing ceramic solids have been developed, ingenious ways of circumventing the age-old problem of brittleness have been introduced, and new markets have begun to open up in such areas as sensors, orthopaedics, photonics, and heat engines.

We are now entering the initial growth phase of the advanced ceramics industry, in which scientific understanding and developments are exploited in diverse areas, completely new applications are appearing, and companies are beginning to compete for market share. Field of ceramics has influenced, or been influenced by, other technical fields, especially chemistry, physics, metallurgy, medicine, and mechanical engineering.
Here are some pictures of ceramics:

CERAMICS AND CHEMISTRY: CERAMIC SYNTHESIS

Traditionally, ceramics have been used in chemistry as catalysts. Today, ceramics are beginning to be used as chemical-specific sensors for the detection of oxygen, hydrogen, carbon monoxide, and more complex organic species such as propane or isobutane.10 They also are being used as durable containers for active chemical and nuclear wastes, the new lead-iron phosphate glasses being a thousand times more resistant to leaching than standard borosilicate glasses.

From figure above.Improved resistance of lead-iron phosphate glass to aqueous corrosion (90°C for 30 days) over conventional borosilicate glass.

Conventional chemical approaches for making fine particulate solids involve colloidal suspension followed by removal of the solvent. But if the suspension is simply dried by heating or evaporation, coarse crystals or agglomerates usually result. An alternative route is through sol-gel chemistry, first used in 1864 by Thomas Graham to make silica gel. It involves three steps: (1) producing a concentrated solution of a metallic salt in a dilute acid (the sol); (2) adjusting the pH, adding a gelling agent, and evaporating the liquid to produce a gel; and (3) calcining the gel under carefully controlled atmospheric conditions to produce fine particles of the requisite ceramic. This approach is especially useful for oxide-based ceramics such as Al2O3, ZrO2, and TiO2. Sol-gel processes have been used to produce a variety of glass and ceramic fibres. Another route particularly appropriate for the production of such ceramic fibers as SiC and Si3N4 involves the thermal degradation of polymers.Other routes for producing ceramic particles involve vapor-phase reactions.

THE FUTURE

This chapter has reviewed the progress made in ceramics over the past 25 years. What of the next 25 years? Predictions are always difficult and usually err on the conservative side because they underestimate scientific ingenuity, capitalist entrepreneurism, and the breakthroughs in understanding or processing capability that open up completely unexpected paths of development. By 2010, photonics will have become a dominant technology based on integrated ceramic devices. Coated-fiber sensors will translate electrical, magnetic, and pressure variations into optical signals for real-time processing.

Ceramics material

Properties: High hardness, strength and wear resistance. Very good insulator. Hard and brittle. Good resistance to corrosion. Good refractoriness.

Examples: Porcelain, Glass, Silicon nitride, pottery, tiles, bricks, abrasive cutting tools, high temperature jet engines components.