Some of the important subjects covered are astronomy, meteorology, oceanography, new materials, immunology and biotechnology. Although many modern ceramics are not made from clay, their production involves heating to obtain the desired properties.
Materials - The Trio
Ceramics are formed by a combination of one or more metal elements with non-metals, the most common of which is '*ygen'. Plastics took over many of the human household duties previously performed by ceramics and metals.
The Variety
Biomedical ceramics are specially manufactured ceramic compounds that have both high strength and biocompatibility. The basic materials for structural ceramics are silicon nitride, silicon carbide and zirconium oxide.
Ordeal By Fire
Faint Footprints
Excavations at the ancient sites of Harappan Civilization B.C.) have led to the discovery of a variety of domestic pottery articles. This accidental discovery of the action of fire on mud was the starting point for the craft of pottery.
The Raw Materials
Stacking thousands and thousands of such plates on top of each other produces a tiny crystal of clay. When water is added, it fills the voids between the loosely fitting stacks of clay particles, allowing them to slide over each other without shattering.
Life Given by Fire
As mentioned earlier, clay contains various metal silicates in addition to the predominant aluminum silicate. Vitrification is essentially the formation of a dense impermeable material that fills some of the voids in the sintered clay and provides further strength by bonding the particles together. The development of pottery, then, represents the culminating influence of earth, water, sun, and fire—the four influential elements in early human life.
Turning
Because they do not absorb water, they do not lose anything when heated and therefore do not shrink. The water that escapes from the clay when heated leaves empty spaces that become filled with air, making the product porous. When the pottery is heated to 800-1000°C, they melt into a glassy liquid, which fills the pores between the individual clay particles and strengthens their contact points.
This is followed by drying and firing of the shaped article which stabilizes the shape.
The First Industry
Even in the more advanced countries of the West it is used for making individual art pieces of pottery. Over time, the mold absorbs water, leaving a thin layer of clay on the inside of the mold. The color of the product is usually buff to dark red or gray to black.
This fluid fills the pores in the object's otherwise porous body, leading to a non-porous or opaque body.
Making Them
For a space shuttle, the temperature can reach 1500°C, which will melt most metals. The frames of high-speed space vehicles must therefore withstand such very high temperatures. It has been found that the hotter an engine runs, the more efficient it is.
Heat-resistant silica tiles have been used as outer coverings for space shuttles, and ceramic car engines have already been successfully tested by motor com-.
Bearing the Heat
Eventually, they begin to swing so wildly that they cut ties with many of their neighbors and begin to move in small groups, leaving their regular positions. The secret to the heat resistant nature of ceramics lies in the strength of their interatomic bonds. So even if the individual atoms or ions vibrate violently as a result of heating the ceramic to very high temperatures, they will not separate.
All hold their assigned positions in the solid structure and do not easily break up into small groups.
The Strong and the Stiff and the Tough
An important measure of the nature of the material is the extent of stretching when pulled. If, even after applying a large force, the material stretches only a small amount, it would have a large tensile modulus. So when a material that is being pulled apart finally breaks, it is not because the bonding forces between the atoms are overcome, but because of the movement of the crack in the material.
Because ceramics are prepared by heating, a number of pores are left in the material when the heat expels water or any organic solvent used in shaping the material.
Why Metals are Tough
However, this glue is not very strong, and rows of atoms can slide past each other in metals. In the first case, the outermost or valence electrons of one atom are permanently transferred to another. In the case of covalent bonding, the outermost electrons of two different atoms are shared equally.
Neither atom allows its hold to be snatched away from the other and so the shared electrons act as a very strong glue.
Toughening the Ceramics
The two materials in the composite are very weakly bonded; one is embedded in the matrix or mass of the second. For example, when a crack approaches a fiber embedded in the matrix of ceramic, the weak bond between ceramic and fiber collapses. The crack is redirected along the length of the fiber because the weak bond between the fiber and the adjacent ceramic, along the length of the fiber, is easily broken and becomes the path of least resistance.
The Central Glass and Ceramics Research Institute (CGCRI), Kolkata, a unit of the Council of Scientific and Industrial Research (CSIR), is India's premier research and development center in the field of ceramics.
Measuring the Hardness
This deflects and widens the crack tip, thus providing an artificial way to harden the ceramic. He chose 10 minerals—talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, and diamond—as standards for measuring the hardness of materials. These were given the hardness values of 10, as each subsequent mineral in the series could scratch it earlier.
When Mohs wanted to know the hardness of any material, he scratched it with his standard minerals and gave it a hardness number depending on which of his standard minerals could scratch the sample.
Two is Tough
In one such method, the Vickers hardness test, a pyramid-shaped diamond is pushed with a constant force into the sample whose hardness is to be measured. The appearance of ceramic composites has largely solved the problem of fragility, and today, for all more demanding jobs, we first think of ceramics. Extremely hard ceramics and ceramic composites form the outermost protective layer or armor of modern combat vehicles such as tanks.
It is intended to be used as an easily malleable thermal insulator as a replacement for asbestos.
Crafting Novel Ceramics
It can be easily cut, folded and wrapped like asbestos, but unlike asbestos it is not a health hazard.
The Electrical
Chamel- Ions•
Conductors
Electrons can be thought of as individuals residing in rooms on different floors of a multi-story building. In good conductors, such as metals, the valence band is only partially full or the higher conduction band can be easily reached. In the case of insulators and semiconductors, like most ceramics, the valence band is full.
So there are virtually no electrons in the conduction band to carry the electrical charges.
Small is Big
The resistance of such a device depends on the thickness, width and length of the film used. The amount of heat generated depends on the resistance presented to the current flow. The operation of the iron, kettle and electric oven is based on the heat-producing effect of the electric current.
Normally, the amount of current flowing in a wire will depend on the difference in electrical potential between its ends.
Attractive Applications
The industrially important ferrites are mixed ferrites such as manganese-zinc or nickel-zinc ferrites, which are called soft ferrites. The interaction between ferrite magnetization and radio frequency signals, which are part magnetic and part electric, makes ferrites useful in microwave devices. These are mainly used as antenna rods and oscillators in the radio industry, as television parts and high frequency high power transformer cores in the telecommunications industry.
Super- conductors
Dnnes' Odyssey
Electrons Prefer Cold
The traditional ceramic preparation method is used in the production of these high temperature superconductors. A reaction occurring in the solid state converted the individual oxides into the mixed oxide compound. The traditional method of preparing ceramics usually produces a variety of other non-superconducting compounds, which also differ from the desired one only slightly in the ratio of the various atoms present in them.
Both problems were partially solved by a new preparation technique that depends on the reaction in the solution state.
Applications
Alkoxides are soluble in organic solvents and thus complete and uniform mixing can be achieved by stirring the mixture. If the coil is copper, a significant amount of electricity will be lost in transmission and the coil will also heat up. The squid is made of two very thin wires of the ceramic superconductor YBa2Cu3O,-y, which are joined together to form a loop.
These will be useful for researchers who need some superconductor capabilities in their labs.
Bony
Aids
The real progress came in the 1960s with the research of ceramics as a possible replacement for damaged bones. Bone consists of living cells embedded in a matrix or mass containing hydroxyapatite, a calcium phosphate ceramic, collagen (an insoluble fibrous protein), and water. Various channels and open spaces in the framework are inhabited by the bone cells, which regulate bone growth.
A Better Bite
The similarity between natural bone and calcium phosphate ceramics comes in handy when it comes to the success of dental implants. A natural tooth is able to form a "biological seal" between its root and the surrounding tissues. The first, which is similar to natural bone, provides the ability to bond with the bone and tissues in the jaw, while the second provides strength.
The bioceramic composition has a spongy structure that acts as a framework to stimulate natural bone growth and thus the implant can be directly attached to the natural bone.
Plugging the Holes
The Joint Effort
The metal head has a stem that can fit into a natural socket of the femur. Although the use of hip prostheses with ceramic heads has been commercialized in many Western countries, the exact method of preparation remains a closely guarded trade secret. The entire process was so carefully controlled that the density of the ceramic head matched the density of bone samples.
Tetragonal: A crystal with two of the three axes equal and all axes intersecting at right angles.
