Download to read offline
More Related Content
Ceramic
- 3. Ceramic Materials • Theterm ceramics has its origin in the Greek word 'keramos', meaning burnt matter. Probably associated with 'Cerami', an ancient district in Athens. • The term ceramics covers a wide variety of inorganic materials, which are generally non- metallic and frequently processed at high temperatures.
- 4. • Ceramic structureshave survived longer than any other works. • The great pyramids of Giza is solid ceramic (nearly 1,000,000 tonnes of it) and pottery from 5000 BC survives to the present day. • Ceramics may not be as tough as metals, but for resistance to corrosion, wear, decay, they are incomparable.
- 5. • In viewof the advances made in the last thirty years, it is convenient to categorize the ceramic materials into two classes: • a- Traditional ceramics • b- Engineering ceramics
- 6. Traditional Ceramics Traditional orconventional ceramics: These are generally in monolithic (uniform) form. These include bricks, pottery, tiles and variety of objects.
- 7. Feldspars is agroup of rock forming minerals (60%)
- 8. Engineering Ceramics Advanced, engineeringor high performance ceramics: these represent a new and improved class of ceramic materials where some sophisticated chemical processing route is used to obtain them. Generally their characteristics are a sensitive function of the high quality and purity of the raw materials used.
- 9. Classifications of Engineering Ceramics High-performanceceramics are classified into three groups oxides, nitrides and carbides of silicon, aluminium, titanium and zirconium.
- 10. The high-performance engineering ceramicscan replace, and greatly improve on metals in many very demanding applications.
- 11. • Comparison betweenthe service temperature of polymers, metals & ceramics.
- 12. Importance in someapplications • Cutting tools made of ‘sialons’ or of dense ‘alumina, can cut faster and last longer than the best metal tools. Engineering ceramics are highly wear- resistant: they are used to clad the leading edges of agricultural machinery like harrows, increasing the life by 10 times.
- 13. • They areinert and biocompatible, so they are good for making artificial joints (where wear is a big problem) and other implants. • A major attraction of ceramics is its relatively high mechanical strength at high temperatures.
- 14. Structure of ceramics •Aceramic, like a metal, has structure at the atomic scale: crystal structure (crystalline), or its amorphous structure (glassy).
- 15. Types of CeramicStructures Ceramics is classified into two main structure patterns: • 1- Ionic Ceramics • 2- Covalent Ceramics
- 16. Ionic Ceramics Ionic ceramicsare, typically, compounds of a metal with a non-metal; Examples of ionic ceramics: sodium chloride, NaCl; magnesium oxide, MgO; alumina Al2O3; zirconia ZrO2.
- 17. Bonding in Ionicceramics The metal and nonmetal have unlike electric charges. For example in sodium chloride, the sodium atoms have one positive charge and the chlorine atoms have one negative charge each.
- 18. The electrostatic attractionbetween the unlike charges gives most of the bonding. So the ions pack densely (to get as many plus and minus charges close to each other as possible), but with the constraint that ions of the same type (and so with the same charge) must not touch.
- 19. This leads tocertain basic ceramic structures, typified by: Rock salt, NaCl, or by alumina Al2O3
- 20. Cl - Na+ Unit Cellfor the rock salt (NaCl) structure
- 21.
- 22. Covalent Ceramics • Covalentceramics are different. • They are compounds of two non- metals (like silica SiO2), • or, some times, are just pure elements (like diamond, C, or silicon, Si).
- 23. • An atomin this class of ceramic (Covalent Ceramics) bonds by sharing electrons with its neighbours to give a fixed number of directional bonds.
- 24.
- 25.
- 26. Examples for CeramicMaterials Alumina Boron Carbide Chromium Carbide Graphite Magnesia Silicon Carbide Tungsten Carbide Zirconia Clay Brick Limestone Granite Silicon Nitride Boron Nitride
- 27. Properties of CeramicMaterials Crystalline and non-crystalline states High melting temperatures (varying from 3500 to 7000 o F) All ceramics are brittle at room temperatures Very low resistance to tensile loads. Very low fracture strengths. Microcracks are formed very easily under tensile stresses. Stronger under compressive loads and microcracks are not formed as easily as in tension.
- 28. Properties of CeramicMaterials (Cont’d) High hardness and good wear resistance. High toughness Low thermal and electrical conductivity. High creep resistance at elevated temperatures Un-reactive and inert when exposed to severe environments (chemically stable) Can be magnetized and demagnetized, some can be permanently magnetized
- 29. Fracture Properties At roomtemperature, ceramics almost fracture before plastic deformation occur in tensile loading. The measure of ceramic material’s ability to resist fracture when a crack is present is specified in terms of fracture toughness.
- 30. Material Material Fracture Toughness (psiinx103 ) Metals Alloy steel (4340 tempered) 46 Titanium alloy (Ti-6Al-4V) 40-60 Ceramics Aluminum Oxide 2 -5 Soda-lime glass 0.7 Polymers Polymethylmethacrylate (PMMA) 0.9 Polystyrene (PS) 0.7 -1.0 comparison between the toughness of ceramics and other materials.
- 31. Stress-Strain Behavior ofCeramics Instead of standard tensile test which is applied to metals, a transverse bending test (three-or four-point loading) is employed. In this test a rod specimen having either a circular or a rectangular cross section is bent until fracture. LOAD (F) L/2 L/2 SUPPORT
- 32. Stress-Strain Behavior ofCeramics The maximum stress, or stress at fracture is known as the Modulus of Rupture (mr), which is an important mechanical parameter for ceramics. Modulus of rupture is given by the following equations: 2 2 3 bd FL mr RECTANGULAR d b CIRCULAR 3 R FL mr 2R
- 33. MATERIAL Modulus of Rupture (Ksi) Modulusof Elasticity (Ksi) Aluminum Oxide 30-50 53 Silicon Carbide 25 68 Titanium Carbide 160 45 Glass 10 10 Table 2. Characteristic modulus of rupture and elastic modulus values for various ceramic materials.
- 34. 0.0002 0.0004 0.00060.0008 STRAIN 40,000 30,000 20,000 10,000 ALUMINUM OXIDE GLASS
- 35. GLASSES CLAY PRODUCTS ABRASIVES CEMENTS REFRACTORIES ADVANCED CERAMICS CERAMICMATERIALS STRUCTURAL WHITEWARES SPECIAL SILICA BASIC FIRECLAY (Classification based on application)
- 36. 1- Clay Products: Structuralproducts (Bricks, tiles, drain pipes) White-wares (Porcelain, pottery, tableware, china, bathroom fixtures) These products are composed of: Alumina (Al2O3) + Silica (SiO2)
- 37. 2- Refractories: Furnace linings Heattreatment equipment Power generation equipment Types of refractories: Old refractories (Fireclay & Silica) Special refractories (Zirconia, magnesia, alumina) Used as electrical resistance elements, crucible materials, internal furnace components.
- 38. 3- Abresives: Grinding wheels Polishingwheels Lapping wheels Types of abrasives: Diamond Silicon carbide Aluminum carbide Aluminum oxide Tungsten carbide
- 39. 4- Advanced Ceramics: Softmagnets Hard magnets Electrical insulators Semiconductor Internal combustion engine blocks Valves Rotors Electronic packaging (Boron nitride, aluminum nitride, silicon carbide) Composite materials (matrix or fiber)
- 40.
- 42. Ceramic Materials Drawback •Ceramics have high strength but low fracture toughness. • The low fracture toughness has its origin in the extreme sensitivity of ceramics to the presence of flaws in them.
- 43. Flaw types inceramics • Various flaw types can occur in ceramics. They could be categorized into three broad types • a- Processing induced flaws such as inclusions, pores, isolated large grains, laminations induced during pressing, machining induced necks and thermal stresses. • b- Design induced flaws like sharp corners, burrs, etc. c- Service induced flaws such as environmental degradation, thermal stresses, impact and wear.