2 . The main component of ceramics is silicate.
3 . Most ceramics contain silicon,Si,oxygen,O and aluminium, Al.
4 . Ceramics cannot be recycled. ceramics that have been solidified cannot be melted again as they are extremely heat resistant.
Composition of Ceramic
1 . Ceramics are made from clay that has been heated at a very high temperature.
2 . The main component of ceramics is silicate.
3 . Most ceramics contain silicon,Si,oxygen,O and aluminium, Al.
4 . Ceramics cannot be recycled. ceramics that have been solidified cannot be melted again as they are extremely heat resistant.
2 . The main component of ceramics is silicate.
3 . Most ceramics contain silicon,Si,oxygen,O and aluminium, Al.
4 . Ceramics cannot be recycled. ceramics that have been solidified cannot be melted again as they are extremely heat resistant.
Types of Ceramics .
ALUMINA
Alumina is the most widely used advanced ceramic material . It pffers very good performance in terms of wear resistance , corrosion resistance and strength at a reasonable 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 offerts 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 , papermaking machine wear surfaces , armor , burner nozzles and molten metal processing parts .
SILICON CARBIDE
Silicon carbide has the highest corrosion resistance of all the advanced ceramic materials . It also retains its strength at temperature as high as 1400 Celcius and offers excellent wear resistance and thermal shock resistance .
Applications include armor , mechanical seals , nozles , silicon wafer polishing plates and pump parts .
ZIRCONIA
Zirconia has the highest strength and toughness at room temperature of all he advanced ceramic materials . The fine grain size allows for extremely smooth surfaces and sharp edges .
Applications include scissors , knifes , slitters , pump shaftd , metal-forming tools , fixtures , tweezers , wire drawing rings , bearing sleeves and valves .
SAPPHIRE
Single crystal sapphire offers superior mechanical properties and chemical stability coupled with light transmission .
Application include GaAs carrier plates , POS scanner window , microwave plasma tubes and windows , fixtures for high temperature equipment and blue LED .
Alumina is the most widely used advanced ceramic material . It pffers very good performance in terms of wear resistance , corrosion resistance and strength at a reasonable 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 offerts 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 , papermaking machine wear surfaces , armor , burner nozzles and molten metal processing parts .
SILICON CARBIDE
Silicon carbide has the highest corrosion resistance of all the advanced ceramic materials . It also retains its strength at temperature as high as 1400 Celcius and offers excellent wear resistance and thermal shock resistance .Applications include armor , mechanical seals , nozles , silicon wafer polishing plates and pump parts .
ZIRCONIA
Zirconia has the highest strength and toughness at room temperature of all he advanced ceramic materials . The fine grain size allows for extremely smooth surfaces and sharp edges .Applications include scissors , knifes , slitters , pump shaftd , metal-forming tools , fixtures , tweezers , wire drawing rings , bearing sleeves and valves .
SAPPHIRE
Single crystal sapphire offers superior mechanical properties and chemical stability coupled with light transmission .Application include GaAs carrier plates , POS scanner window , microwave plasma tubes and windows , fixtures for high temperature equipment and blue LED .
Classification of Ceramics
They ar classified as non-crystalline and crytalline ceramics . The non-crystalline ceramics are formed from melts and are called glass ceramic . They are produced after a great range of processing whereas the crystalline ceramics do nor require much doling out . Apart from the ones discussed above , ceramics have a wide range of usage .
- It is used in making knives and ceramic knives are sharper than steel knives . Though they are brittle , their blades are more durable .
- Ceramics like alumina and boron carbide are used as "Small Arms Protective Inserts"
- Steel can be replaced by ceramic ball bearings . Due to their hardness they have a longer lifetime . Their electrical insulating capacities are also valuable in bearings but a major drawback is their high cost .
- Ceramic engines can be used in laboratories due to their high fuel efficiency and they do not need any cooling system . However mass production is not possible becaouse cracks can easily develop in ceramics which may result in dangerous equipment failue .
- Nowadays bio-ceramics are made which include synthetic bone and dental implants .
- High tech ceramic is also employed in making watch cases .
Uses Of Ceramics .
Ceramics offer many advantages compared to other materials. They are harder and stiffer than steel; more heat and corrosion resistant than metals or polymers; less dense than most metals and their alloys; and their raw materials are both plentiful and inexpensive. Ceramic materials display a wide range of properties which facilitate their use in many different product areas.
- Aerospace: space shuttle tiles, thermal barriers, high temperature glass windows, fuel cells
- Consumer Uses: glassware, windows, pottery, Corning¨ ware, magnets, dinnerware, ceramic tiles, lenses, home electronics, microwave transducers
- Automotive: catalytic converters, ceramic filters, airbag sensors, ceramic rotors, valves, spark plugs, pressure sensors, thermistors, vibration sensors, oxygen sensors, safety glass windshields, piston rings
- Medical (Bioceramics): orthopedic joint replacement, prosthesis, dental restoration, bone implants
- Military: structural components for ground, air and naval vehicles, missiles, sensors
- Computers: insulators, resistors, superconductors, capacitors, ferroelectric components, microelectronic packaging
- Other Industries: bricks, cement, membranes and filters, lab equipment
- Communications: fiber optic/laser communications, TV and radio components, microphones
Ceramic Structures
Crystal Structures
Ceramic bonds are mixed , ionic and covalent , with a proportion that depends on the particular ceramics . The ionic character is given by the difference of electronegativity between the cations (+) and anions (-) . Covalent bonds involve sharing of valence electrons. Very ionic crystals usually involve cations which are alkalis or alkaline-earths (first two columns of the periodic table) and oxygen or halogens as anions .
The building criteria for the crystal structure are two :
- maintain neutrality
- charge balance dictates chemical formula
- achieve closest packing
the condition for minimum energy implies maximum attraction and minimum repulsion . This leads to contact , configurations where anions have the highest number of cation neighbors and viceversa .
The parameter that is important in determining contact is the ratio of cation to anion radii , rC/rA. Table 13.2 gives the coordination number and geometry as a function of rC/rA. For example , in the NaCl structure (Fig. 13.2) , rC = rNa = 0.102 nm, rA =rCl. = 0.181 nm , so rC/rA.= 0.56 . From table 13.2 this implies coordination number = 6 , as observed for this rock-salt structure .
Other structures were shown in class, but will not be included in the test .
Silicate Ceramics
Oxygen and Silicon are the most abundant elements in Earth’s crust . Their combination (silicates) occur in rocks , soils , clays and sand . The bond is weekly ionic , with Si4+ as the cation and O2- as the anion . rSi = 0.04 nm , rO.= 0.14 nm , so rC/rA = 0.286. From table 13.2 this implies coordination number = 4, that is tetrahedral coordination .
The tetrahedron is charged : Si4+ + 4 O2- Þ (Si O4) 4- . Silicates differ on how the tetrahedra are arranged. In silica , ( SiO2 ) , every oxygen atom is shared by adjacent tetrahedra . Silica can be crystalline (e.g., quartz) or amorphous , as in glass .
Soda glasses melt at lower temperature than amorphous SiO2 because the addition of Na2O (soda) breaks the tetrahedral network . A lower melting point makes it easy to form glass to make , for instance , bottles .
Ceramic Properties
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 packed together . This is known as the atomic scale structure . Most ceramics are made up of two or more elements . This is called a compound . For example , alumina (Al2O3) , is a compound made up of aluminum atoms and oxygen atoms .
The atoms in ceramic materials are held together by a chemical bond . The two most common chemical bonds for ceramic materials are covalent and ionic . For metals , the chemical bond is called the metallic bond . The bonding of atoms together is much stronger in covalent and ionic bonding than in metallic . That is why , generally speaking , metals are ductile and ceramics are brittle . Due to ceramic materials wide range of properties , they are used for a multitude of applications . In general , most ceramics are :
The atoms in ceramic materials are held together by a chemical bond . The two most common chemical bonds for ceramic materials are covalent and ionic . For metals , the chemical bond is called the metallic bond . The bonding of atoms together is much stronger in covalent and ionic bonding than in metallic . That is why , generally speaking , metals are ductile and ceramics are brittle . Due to ceramic materials wide range of properties , they are used for a multitude of applications . In general , most ceramics are :
- Hard
- Wear-resistant
- Brittle
- refractory
- Thermal insulators
- Electrical insulators
- non magnetic
- oxidation resistant
- Prone to thermal shock
- Chemically stable
Ceramics for engineering applications can be broadly into "traditional" and "new" materials . We define traditional materials as those produced from materials mined directly from the earth . The newer ceramic materials , those with well defined and controlled properties are produced from nearly chemically and phase pure starting materials . Accuratus is capable of working with most these material types .
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