Hence, the word Karakas as to infer ‘burned substance’ or ‘burned earth’. Ceramics are things made from clay, the basic material for all ceramic creations. The clay is created as a result of the decomposition of igneous rock, which makes up the entire earth’s crust. Everything you will do with clay involves the interplay of these 3 variables: Moisture Plasticity Heat History Ceramics is one of the most ancient industries on the planet. Once humans discovered that clay could be dug up and formed into objects by first mixing with water and then firing, the industry was born.
As early as 24,000 BC, animal and unman figurines were made from clay and other materials, then fired in kilns partially dug into the ground. Almost 10,000 years later, as settled communities were established, tiles were manufactured in Mesopotamia and India. The first use of functional pottery vessels for storing water and food is thought to be around 9000 or 10,000 BC. Clay bricks were also made around the same time. Glass was believed to be discovered in Egypt around 8000 BC, when overheating of kilns produced a colored glaze on the pottery.
Experts estimate that it was not until 1 500 BC that glass was produced independently of ceramics and fashioned into prepare items. Fast forward to the Middle Ages, when the metal industry was in its infancy. Furnaces at that time for melting the metal were constructed of natural materials. When synthetic materials with better resistance to high temperatures (called refractoriness) were developed in the 16th century, the industrial revolution was born. These refractoriness created the necessary conditions for melting metals and glass on an industrial scale, as well as for the manufacture of coke, cement, chemicals, and ceramics.
Another major development occurred in the second half of the 19th century, when reamer materials for electrical insulation were developed. As other inventions came on the scene-including automobiles, radios, televisions, computers-ceramic and glass materials were needed to help these become a reality, as shown in the following timeline. As Ceramics are made of earthen materials, they are the most compatible products with the nature. Ceramics are the only materials which are nature friendly and therefore they are free from decays due to gradual natural impacts like corrosion, erosion, abrasion, thermal shocks, etc.
Even though Ceramics are brittle; they are the only materials which subsist to see the races to come. Hence, we may call them a strong-fragile part of human life. Timeline of Selected Ceramic and Glass Developments Year Development 24,000 B. C. Ceramic figurines used for ceremonial purposes 14,000 B. C. First tiles made in Mesopotamia and India 9000-10,000 B. C. Pottery making begins 5000-8000 B. C. Glazes discovered in Egypt 1500 B. C. Glass objects first made 1550 A. D.
Synthetic refractoriness (temperature resistant) for furnaces used to make steel, glass, ceramics, cement Mid sass’s Porcelain electrical insulation Incandescent light bulb ass’s High-strength quartz-enriched porcelain for insulators Alumina spark plugs Glass windows for automobiles sass’s Capacitors and magnetic ferrite’s sass’s Alumina insulators for voltages over 220 xv Application of carbides and nitrides sass’s Introduction to nigh-performance cellular ceramic substrates tort catalytic converters and particulate filters for diesel engines sass’s High temperature superconductors Properties of Ceramics The properties of ceramic materials, like all materials, are dictated by the types of atoms present, the types of bonding between the atoms, and the way the atoms are jacked together. The type of bonding and structure helps determine what type of properties a material will have. Ceramics usually have a combination of stronger bonds called ionic (occurs between a metal and non-metal and involves the attraction of opposite charges when electrons are transferred from the metal to the non-metal); and covalent (occurs between two non-metals and involves sharing of atoms). The strength of an ionic bond depends on the size of the charge on each ion and on the radius of each ion.
The greater the number of electrons being shared, is the greater he force of attraction, or the stronger the covalent bond. These types of bonds result in high elastic modulus and hardness, high melting points, low thermal expansion, and good chemical resistance. On the other hand, ceramics are also hard and often brittle (unless the material is toughened by reinforcements or other means), which leads to fracture. In general, metals have weaker bonds than ceramics, which allows the electrons to move freely between atoms. Think of a box containing marbles surrounded by water. The marbles can be pushed anywhere within the box and the water will follow them, always surrounding he marbles.
This type of bond results in the property called ductility, where the metal can be easily bent without breaking, allowing it to be drawn into wire. The free movement of electrons also explains why metals tend to be conductors of electricity and heat. Plastics or polymers of the organic type consist of long chains of molecules which are either tangled or ordered at room temperature. Because the forces (known as van deer Walls) between the molecules are very weak, polymers are very elastic (like a rubber band), can be easily melted, and have low strength. Like ceramics, polymers eave good chemical resistance, electrical and thermal insulation properties.
They are also brittle at low temperatures. The following table provides a general comparison of the properties between the three types of materials. General Comparison of Materials Property Ceramic Metal Polymer Hardness Very High Low Very Low Elastic modulus High High temperature strength Thermal expansion Ductility Corrosion resistance Wear resistance Electrical conductivity Depends on material Density Thermal conductivity Magnetic Note: For general comparison only; specific properties depend on the material’s pacific composition and how it is made. These three material types can also be combined in various ways to form composites to take advantage of each material’s properties.
For instance, ceramic particles or fibers can be added to a ceramic or metal matrix to improve the mechanical properties and/or produce a special property the matrix by itself generally would not have. Polymers are also reinforced with glass fibers for a wide range of construction and structural applications. Mechanical properties Mechanical properties are important in structural and building materials as well as excite fabrics. They include the many properties used to describe the strength of materials such as: elasticity / plasticity, tensile strength, compressive strength, shear strength, fracture toughness& ductility (low in brittle materials), and indentation hardness. Fracture mechanics is the field of mechanics concerned with the study of the formation and subsequent propagation of microcosmic in materials.
It uses methods of analytical solid mechanics to calculate the thermodynamic driving force on a crack and the methods of experimental solid mechanics to characterize the trial’s resistance to fracture and catastrophic failure. In modern materials science, fracture mechanics is an important tool in improving the mechanical performance of materials and components. It applies the physics of stress and strain, in particular the theories of elasticity and plasticity, to the microscopic crystallographic defects found in real materials in order to predict the macroscopic mechanical failure of bodies. Pornography is widely used with fracture mechanics to understand the causes of failures and also verify the theoretical failure predictions with real life failures.
Thus, since cracks and other macrostructure defects can lower the strength of a structure beyond that which might be predicted by the theory of crystalline objects, a different property of the material�above and beyond conventional strength�is needed to describe the fracture resistance of engineering materials. This is the reason for the need for fracture mechanics: the evaluation of the strength of flawed structures. Ceramic materials are usually ionic or covalent bonded materials, and can be crystalline or amorphous. A material held together by either type of bond will tend to fracture before any plastic formation takes place, which results in poor toughness in these materials.
Additionally, because these materials tend to be porous, the pores and other microscopic imperfections act as stress concentrators, decreasing the toughness further, and reducing the tensile strength. These combine to give catastrophic failures, as opposed to the normally much more gentle failure modes of metals. These materials do show plastic deformation. However, due to the rigid structure of the crystalline materials, there are very tee available slip systems tort dislocations to move, and so they deform very slowly. With the non-crystalline (glassy) trials, viscous flow is the dominant source of plastic deformation, and is also very slow. It is therefore neglected in many applications of ceramic materials.
To overcome the brittle behavior, ceramic material development has introduced the class of ceramic matrix composite materials, in which ceramic fibers are embedded and with specific coatings are forming fiber bridges across any crack. This mechanism substantially increases the fracture toughness of such ceramics. The ceramic disc brakes are, for example using a ceramic matrix composite material manufactured with a specific process. Electrical properties Semiconductors Some ceramics are semiconductors. Most of these are transition metal oxides that are II-VI semiconductors, such as zinc oxide. While there are prospects of mass- producing blue Leeds from zinc oxide, ceramicists are most interested in the electrical properties that show grain boundary effects. One of the most widely used of these is the variations.
These are devices that exhibit the property that resistance drops sharply at a certain threshold voltage. Once the voltage across the device reaches the threshold, there is a breakdown of the electrical structure in the vicinity of the grain mandarins, which results in its electrical resistance dropping from several ohms down to a few hundred ohms. The major advantage of these is that they can dissipate a lot of energy, and they self-reset – after the voltage across the device drops below the threshold, its resistance returns to being high. This makes them ideal for surge-protection applications; as there is control over the threshold voltage and energy tolerance, they find use in all sorts of applications.
The best demonstration of their ability can be found in electrical substations, where they are employed to protect the infrastructure from lightning strikes. They have rapid response, are low maintenance, and do not appreciably degrade from use, making them virtually ideal devices for this application. Semiconductors ceramics are also employed as gas sensors. When various gases are passed over a polycrystalline ceramic, its electrical resistance changes. With tuning to the possible gas mixtures, very inexpensive devices can be produced. Superconductivity Under some conditions, such as extremely low temperature, some ceramics exhibit high temperature superconductivity. The exact reason for this is not known, but there are two major families of superconducting ceramics.
Ferroelectric and supersets Piezoelectricity, a link between electrical and mechanical response, is exhibited by a large number of ceramic materials, including the quartz used to measure time in watches and other electronics. Such devices use both properties of piezoelectric, using electricity to produce a mechanical motion (powering the device) and then using this mechanical motion to produce electricity (generating a signal). The unit of time measured is the natural interval required for electricity to be converted into mechanical energy and back again. The piezoelectric detect is generally stronger in materials that also exhibit perfectibility, and all ferroelectric materials are also piezoelectric.
These materials can be used to inter convert between thermal, mechanical, or electrical energy; for instance, after synthesis in a furnace, a ferroelectric crystal allowed to cool under no applied stress generally builds up a static charge of thousands of volts. Such materials are used in motion sensors, where the tiny rise in temperature from a warm body entering the room is enough to produce a measurable voltage in the crystal. In turn, perfectibility is seen most strongly in materials which also display he ferroelectric effect, in which a stable electric dipole can be oriented or reversed by applying an electrostatic field. Perfectibility is also a necessary consequence of ferroelectric. This can be used to store information in ferroelectric capacitors, elements of ferroelectric RAM. The most common such materials are lead coronate iodinate and barium iodinate.
Aside from the uses mentioned above, their strong piezoelectric response is exploited in the design of high-frequency loudspeakers, transducers for sonar, and actuators for atomic force and scanning tunneling microscopes. Positive thermal coefficient Increases in temperature can cause grain boundaries to suddenly become insulating in some semiconductors ceramic materials, mostly mixtures of heavy metal dominates. The critical transition temperature can be adjusted over a wide range by variations in chemistry. In such materials, current will pass through the material until Joule heating brings it to the transition temperature, at which point the circuit will be broken and current flow will cease. Such ceramics are used as self-controlled heating elements in, for example, the rear-window defrost circuits of automobiles.
At the transition temperature, the material’s dielectric response becomes theoretically infinite. While a lack of temperature control would rule out any practical use of the material near its critical temperature, the dielectric effect remains exceptionally strong even at much higher temperatures. Dominates with critical temperatures far below room temperature have become synonymous with “ceramic” in the context of ceramic capacitors for Just this reason. Optical properties Optically transparent materials focus on the response of a material to incoming lightfaces of a range of wavelengths. Frequency selective optical filters can be utilized to alter or enhance the brightness and contrast of a digital image.
Guided lightface transmission via frequency selective waveguides involves the emerging field of fiber optics and the ability of certain glassy compositions as a transmission medium for a range of frequencies simultaneously (multi-mode optical fiber) with little or no interference between competing wavelengths or frequencies. This resonant mode energy and data transmission via electromagnetic (light) wave propagation, though low powered, is virtually lossless. Optical waveguides are seed as components in Integrated optical circuits (e. G. Light-emitting diodes, Leeds) or as the transmission medium in local and long haul optical communication systems. Also of value to the emerging materials scientist is the sensitivity of materials to radiation in the thermal interred (IR portion to the electromagnetic spectrum. T heat-seeking ability is responsible for such diverse optical phenomena as Night- vision and IR luminescence.
Thus, there is an increasing need in the military sector for high-strength, robust materials which have the capability to transmit light (electromagnetic waves) in the visible (0. – 0. 7 micrometers) and mid-infrared (1 – 5 micrometers) regions of the spectrum. These materials are needed for applications requiring transparent armor, including next-generation high- speed missiles and pods, as well as protection against improvised explosive devices (DE). In the sass, scientists at General Electric (GE) discovered that under the right manufacturing conditions, some ceramics, especially aluminum oxide (alumina), could be understatement. These translucent materials were transparent enough to be used for containing the electrical plasma generated in high- pressure sodium street lamps.
During the past two decades, additional types of transparent ceramics have been developed for applications such as nose cones for heat-seeking missiles, windows for fighter aircraft, indiscrimination counters for computed tomography scanners. In the early sass, Thomas Joules pioneered computer modeling of light transmission through translucent ceramic alumina. His model showed that microscopic pores in ceramic, mainly trapped at the Junctions of microelectronics grains, caused light to scatter and prevented true transparency. The volume fraction of these microscopic pores had to be less than 1% for high-quality optical transmission. This is basically a particle size effect. Opacity results from the incoherent scattering of light at surfaces and interfaces.
In addition to pores, most of the interfaces in a typical metal or ceramic object are in the form of grain boundaries which separate tiny regions of crystalline order. When the size of the scattering center (or grain boundary) is reduced below the size of the wavelength of the light being scattered, the scattering no longer occurs to any significant extent. In the formation of polycrystalline materials (metals and ceramics) the size of he crystalline grains is determined largely by the size of the crystalline particles present in the raw material during formation (or pressing) of the object. Moreover, the size of the grain boundaries scales directly with particle size.
Thus a reduction of the original particle size below the wavelength of visible light (� 0. 5 micrometers for shortwave violet) eliminates any light scattering, resulting in a transparent material. Types of Ceramics ALUMINA Alumina is the most widely used advanced ceramic material. It offers very good performance in terms of wear resistance, corrosion resistance and strength at a seasonable price. Its high dielectric properties are beneficial in electronic products. Applications include armor, semiconductor processing equipment parts, faucet disc valves, seals, electronic substrates and industrial machine components. SILICON NITRIDE Silicon nitride exceeds other ceramic materials in thermal shock resistance.
It also offers an excellent combination of low density, high strength, low thermal expansion and good corrosion resistance and fracture toughness. Applications include various aerospace and automotive engine components, printmaking machine wear surfaces, armor, burner nozzles and molten metal recessing parts. SILICON CARBIDE Silicon carbide has the highest corrosion resistance of all the advanced ceramic materials. It also retains its strength at temperatures as high as 14000C and offers excellent wear resistance and thermal shock resistance. Applications include armor, mechanical seals, nozzles, silicon wafer polishing plates and pump parts. ZIRCON Zircon has the highest strength and toughness at room temperature of all the advanced ceramic materials.
The fine grain size allows for extremely smooth surfaces and sharp edges. Applications include scissors, knifes, slitters, pump shafts, metal-forming tools, sutures, tweezers, wire drawing rings, bearing sleeves and valves. SAPPHIRE Single crystal sapphire offers superior mechanical properties and chemical stability coupled with light transmission. Applications include Gas carrier plates, POS scanner window, microwave plasma tubes and windows, fixtures for high temperature equipment and blue LED. Example of Ceramics materials Until the sass, the most important ceramic materials were (1) pottery, bricks and tiles, (2) cements and (3) glass. A composite material of ceramic and metal is known as cermets.
Barium iodinate (often mixed with strontium iodinate) splays ferroelectric, meaning that its mechanical, electrical, and thermal responses are coupled to one another and also history-dependent. It is widely used in electromechanical transducers, ceramic capacitors, and data estrangements. Grain boundary conditions can create OPT effects in heating elements. Bismuth strontium calcium copper oxide, a high-temperature superconductor Boron nitride is structurally collections to carbon and takes on similar physical forms: a graphite-like one used as a lubricant, and a diamond-like one used as an abrasive. Earthenware used for domestic ware such as plates and USGS.
Ferrite is used in the magnetic cores of electrical transformers and magnetic core memory. Lead coronate iodinate (PAST) was developed at the United States National Bureau of Standards in 1954. PAST is used as an ultrasonic transducer, as its piezoelectric properties greatly exceed those of Rockwell salt. [3] Magnesium debrief (MGM) is an unconventional superconductor. Porcelain is used for a wide range of household and industrial products. Salon (Silicon Aluminum Contrived) has high strength; resistance to thermal shock, chemical and wear resistance, and low density. These ceramics are used in non-ferrous molten metal handling, weld pins and the chemical industry.
Silicon carbide (SIC) is used as a support in microwave terraces, a commonly used abrasive, and as a retractors material. Silicon nitride (Signs) is used as an abrasive powder. Estimate (magnesium silicates) is used as an electrical insulator. Titanium carbide Used in space shuttle re-entry shields and scratchpad’s watches. Uranium oxide (1302), used as fuel in nuclear reactors. Yttrium barium copper oxide (YBa2Cu307-x), another high temperature superconductor. Zinc oxide (Zoon), which is a semiconductor, and used n the construction of variations. Zirconium dioxide (zircon), which in pure form undergoes many phase changes between room temperature and practical sintering temperatures, can be chemically “stabilized” in several different forms.
Its high oxygen ion conductivity recommends it for use in fuel cells and automotive oxygen sensors. In another variant, metastases structures can impart transformation toughening for mechanical applications; most ceramic knife blades are made of this material. Partially stabilized zircon (ASS) is much less brittle than other ceramics and is used for metal forming tools, valves and liners, abrasive slurries, kitchen knives and bearings subject to severe abrasion. Conclusion Today, ceramic as an artistic form of expression thrives alongside its importance in various technical industries. Ceramics have received major media attention in recent years, particularly for use as parts in a future ceramic heat engine.
However, corrosion resistance, chemical inertness, thermal shock resistance, and other properties that materials scientists and engineers can design into ceramic materials make both traditional and advanced ceramics highly attractive in a large number of applications. The combination of properties mentioned above make ceramics good candidates for wear-resistance applications. Electrical properties place ceramics in great demand as solid electrolytes in experimental batteries and fuel cells. Other uses include automotive sensors, packaging for integrated circuits, electronic/optical devices, fiber optics, microchips, and magnetic head. In the marriage of the computer and communications technologies, ceramics play a major role. The chemical inertness of ceramics is finding many uses in the medical field, where contact with body fluids is less of a problem than with most other materials.
Finally, ceramics play a big role in the machine-tool industry. Their thermal and mechanical stability allows them to retain their smooth, accurate cutting surfaces longer than metals do. Coated cutting tools and insert, some with as many as 12 extremely thin coatings, each designed to serve a special function, can run productively at faster cutting speeds and at fast feed rates than any metal-alloy tool in the machining of hand steels, superfluous, and ceramics. What is remarkable about these multifaceted carbide inserts is the fact that, 3 with slightly over a dozen thin ceramic layers, the total thickness of the coatings is only 10 to mm.
