Introduction To Ceramic Materials PDF

INTRODUCTION TO CERAMIC MATERIALS DR NORFADHILAH BINTI IBRAHIM Ceramics  One of the largest groups of materials with the properties of nonmetals and all are made by firing or burning, often including silicates and metal oxides.  Greek...

INTRODUCTION TO CERAMIC MATERIALS DR NORFADHILAH BINTI IBRAHIM Ceramics  One of the largest groups of materials with the properties of nonmetals and all are made by firing or burning, often including silicates and metal oxides.  Greek term Keramos, meaning "a potter" or "pottery”. Ceramic materials are attractive for several reasons :  Cheap in terms of its starting materials.  Compared to metals, lightweight and retain their strength up to 1000˚C where metals tends to fail.  They have electrical, optical, and magnetic properties of value in the computer and electronic industries. History  The art of making pottery by forming and burning clay has been practiced from the earliest civilizations.  Burnt clayware has been found dating from about 15,000 B.C. and as well developed as an industrial product in Egypt by about 5000 B.C.  Formed glass dates from the period 7000-5000 B.C. and was a stable industry in Egypt by about 1500 B.C. Ceramics Industry  An important characteristic of the ceramics industry is that it is basic to the successful operation of many other industries.  In the Philippines, smuggled ceramics has cause severe effect on the ceramic industry locally. But exporting of ceramic materials is significantly increasing. *Classification of Ceramics based on APPLICATION Properties of Ceramic Materials  High hardness, electrical and thermal insulating, chemical stability, and high melting temperatures  Brittle, virtually no ductility - can cause problems in both processing and performance of ceramic products  Some ceramics are translucent, window glass (based on silica) being the clearest example Ceramic Products  Clay construction products - bricks, clay pipe, and building tile  Refractory ceramics ‑ capable of high temperature applications such as furnace walls, crucibles, and molds  Cement used in concrete - used for construction and roads  Whiteware products - pottery, stoneware, fine china, porcelain, and other tableware, based on mixtures of clay and other minerals Ceramic Products (continued)  Glass ‑ bottles, glasses, lenses, window pane, and light bulbs  Glass fibers - thermal insulating wool, reinforced plastics (fiberglass), and fiber optics communications lines  Abrasives - aluminum oxide and silicon carbide in grinding wheels  Cutting tool materials - tungsten carbide, aluminum oxide, and cubic boron nitride Ceramic Products (continued)  Ceramic insulators ‑ applications include electrical transmission components, spark plugs, and microelectronic chip substrates  Magnetic ceramics – computer memories  Nuclear fuels based on uranium oxide (UO2)  Bioceramics - artificial teeth and bones Three Basic Categories of Ceramics 1. Traditional ceramics ‑ clay products such as pottery, bricks, common abrasives, and cement 2. New ceramics ‑ more recently developed ceramics based on oxides, carbides, etc., with better mechanical or physical properties than traditional ceramics 3. Glasses ‑ based primarily on silica and distinguished by their noncrystalline structure Strength Properties of Ceramics  Theoretically, the strength of ceramics should be higher than metals because their covalent and ionic bonding types are stronger than metallic bonding  But metallic bonding allows for slip, the mechanism by which metals deform plastically when stressed  Bonding in ceramics is more rigid and does not permit slip under stress  The inability to slip makes it much more difficult for ceramics to absorb stresses Imperfections in Crystal Structure of Ceramics  Ceramics contain the same imperfections in their crystal structure as metals ‑ vacancies, displaced atoms, interstitialcies, and microscopic cracks  Internal flaws tend to concentrate stresses, especially tensile, bending, or impact  Hence, ceramics fail by brittle fracture much more readily than metals  Strength is much less predictable due to random imperfections and processing variations Compressive Strength of Ceramics  The frailties that limit the tensile strength of ceramic materials are not nearly so operative when compressive stresses are applied  Ceramics are substantially stronger in compression than in tension  For engineering and structural applications, designers have learned to use ceramic components so that they are loaded in compression rather than tension or bending  Methods to Strengthen Ceramic Materials  Make starting materials more uniform  Decrease grain size in polycrystalline ceramic products  Minimize porosity  Introduce compressive surface stresses  Use fiber reinforcement  Heat treat Physical Properties of Ceramics  Density – most ceramics are lighter than metals but heavier than polymers  Melting temperatures - higher than for most metals  Some ceramics decompose rather than melt  Electrical and thermal conductivities - lower than for metals; but the range of values is greater, so some ceramics are insulators while others are conductors  Thermal expansion - somewhat less than for metals, but effects are more damaging because of brittleness Traditional Ceramics  Based on mineral silicates, silica, and mineral oxides found in nature  Primary products are fired clay (pottery, tableware, brick, and tile), cement, and natural abrasives such as alumina  Products and the processes to make them date back thousands of years  Glass is also a silicate ceramic material and is sometimes included among traditional ceramics Raw Materials for Traditional Ceramics  Mineral silicates, such as clays and silica, are among the most abundant substances in nature and are the principal raw materials for traditional ceramics  Another important raw material for traditional ceramics is alumina  These solid crystalline compounds have been formed and mixed in the earth’s crust over billions of years by complex geological processes Clay as a Ceramic Raw Material  Clays consist of fine particles of hydrous aluminum silicate  Mostly based on kaolinite, (Al2Si2O5(OH)4)  Mixed with water, clay becomes a plastic substance that is formable and moldable  When heated to a sufficiently elevated temperature (firing), clay fuses into a dense, strong material  Thus, clay can be shaped while wet and soft, and then fired to obtain the final hard product  Silica as a Ceramic Raw Material  Available naturally in various forms, most important is quartz  Main source of quartz is sandstone  Low cost  Hard and chemically stable  Principal component in glass, and an important ingredient in other ceramic products including whiteware, refractories, and abrasives Alumina as a Ceramic Raw Material  Bauxite - most alumina is processed from this mineral, which is an impure mixture of hydrous aluminum oxide and aluminum hydroxide plus similar compounds of iron or manganese  Bauxite is also the principal source of aluminum  Corundum - a more pure but less common form of Al2O3, which contains alumina in massive amounts  Alumina ceramic is used as an abrasive in grinding wheels and as a refractory brick in furnaces Traditional Ceramic Products  Pottery and Tableware  Brick and tile  Refractories  Abrasives Abrasives  is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away  a material often means polishing it to gain a smooth, reflective surface which can also involve roughening as in satin, matte or beaded finishes Abrasives Refractories  is one that retains its strength at high temperature Example: o kiln linings o gas fire radiants o steel o glass making crucibles Refractories Gas fire radiants Used in winter season Refractories glass making crucibles Advanced Ceramics  Advanced ceramics are ideally suited for industrial applications that provide a physical interface between different components due to their ability to withstand high temperatures, vibration and mechanical shock. A type of ceramic exhibiting a high degree of industrial efficiency.  A type of ceramic used in specialized, recently developed applications.  Advanced ceramics often have simple chemical compositions, but they are difficult to manufacture. TYPES OF ADVANCED CERAMICS Oxide Ceramics  Most important oxide ceramic is alumina Al2O3  Although included among traditional ceramics, alumina is also produced synthetically from bauxite  Through control of particle size and impurities, refinements in processing methods, and blending with small amounts of other ceramic ingredients, strength and toughness of alumina are improved substantially compared to its natural counterpart  Alumina also has good hot hardness, low thermal conductivity, and good corrosion resistance Carbide Ceramics  Includes silicon carbide (SiC), tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), and chromium carbide (Cr3C2)  Production of SiC dates from a century ago, and it is generally included among traditional ceramics  WC, TiC, and TaC are hard and wear resistant and are used in applications such as cutting tools  WC, TiC, and TaC must be combined with a metallic binder such as cobalt or nickel in order to fabricate a useful solid product Nitrides Important nitride ceramics are silicon nitride (Si 3N4), boron nitride (BN), and titanium nitride (TiN)  Properties: hard, brittle, high melting temperatures, usually electrically insulating, TiN being an exception  Applications:  Siliconnitride: components for gas turbines, rocket engines, and melting crucibles  Boron nitride and titanium nitride: cutting tool materials and coatings Glass A state of matter as well as a type of ceramic  As a state of matter, the term refers to an amorphous (noncrystalline) structure of a solid material  The glassy state occurs when insufficient time is allowed during cooling from the molten state to form a crystalline structure  As a type of ceramic, glass is an inorganic, nonmetallic compound (or mixture of compounds) that cools to a rigid condition without crystallizing Why So Much SiO2 in Glass?  Because SiO2 is the best glass former  Silica is the main component in glass products, usually comprising 50% to 75% of total chemistry  It naturally transforms into a glassy state upon cooling from the liquid, whereas most ceramics crystallize upon solidification Functions of Other Ingredients in Glass  Act as flux (promoting fusion) during heating  Increase fluidity in molten glass for processing  Improve chemical resistance against attack by acids, basic substances, or water  Add color  Alter index of refraction for optics  Glass‑Ceramics A ceramic material produced by conversion of glass into a polycrystalline structure through heat treatment  Proportion of crystalline phase range = 90% to 98%, remainder vitreous material  Grain size significantly smaller than the conventional ceramics, which makes glass‑ceramics much stronger than the glasses from which they are made  Due to crystal structure, glass‑ceramics are opaque (usually grey or white), not clear a) pure, b) different amount of mole of cordierite Different melting temperature. This is caused by the existence of small amount of Electroceramics  is a class of ceramic materials used primarily for their electrical properties. Further classified to:  Dielectric ceramics  Fast ion conductor ceramics  Piezoelectric and ferroelectric ceramics  Dielectric Ceramics  are capable of storing large amounts of electrical charge in relatively small volumes.  Is an electrical insulator that can be polarized by an applied electric field.  Dielectric materials can be solids, liquids, or gases.  Solid dielectrics are perhaps the most commonly used dielectrics in electrical engineering, and many solids are very good insulators.  Fast Ion Conductor Ceramics  are solids in which ions are highly mobile. These materials are important in the area of solid-state ionics, and are also known as solid electrolytes and superionic conductors.  These materials are useful in batteries and various sensors. Fast ion conductors are used primarily in solid oxide fuel cells. Advance Structural Ceramics  ceramic materials that demonstrate enhanced mechanical properties under demanding conditions. Because they serve as structural members, often being subjected to mechanical loading, they are given the name structural ceramics. Ordinarily, for structural applications ceramics tend to be expensive replacements for other materials, such as metals, polymers, and composites. Advance Structural Ceramics Classified to: o Nuclear Ceramics o Bioceramics o Tribological Ceramics o Automotive Ceramics  Nuclear Ceramics  nuclear ceramics, ceramic materials employed in the generation of nuclear power and in the disposal of radioactive nuclear wastes.  In their nuclear-related functions, ceramics are of major importance. Since the beginning of nuclear power generation, oxide ceramics, based on the fissionable metals uranium and plutonium, have been made into highly reliable fuel pellets for both water-cooled and liquid-metal-cooled reactors. Ceramics also can be employed to immobilize and store nuclear wastes. Although vitrification (glass formation) is a favoured approach for waste disposal, wastes can be processed with other ceramics into a synthetic rock, or synroc, or they can be mixed with cement powder to make hardened cements. All these nuclear applications are extremely demanding. In addition to severe thermal and chemical driving forces, nuclear ceramics are continuously subjected to high radiation doses.  Nuclear Ceramics The image above shows a vitrification process or encapsulating nuclear waste in glass is a possible method of containing nuclear wastes  Bioceramics  ceramic products or components employed in medical and dental applications, mainly as implants and replacements.  Bioceramics range in biocompatibility from the ceramic oxides, which are inert in the body, to the other extreme of resorbable materials, which are eventually replaced by the materials which they were used to repair.  Bioceramic materials are commonly subdivided by their bioactivity. Bioinert materials, (such as Oxide ceramics, Silica ceramics, Carbon fiber) are non-toxic and non-inflammatory. These materials must be long lasting, structural failure resistant, and corrosion resistant. Bioceramics additionally must have a low Young's modulus to help prevent cracking of the material.  Bioceramics  Ceramics are now commonly used in the medical fields as dental, and bone implants. Artificial teeth, and bones are relatively commonplace. Surgical cermets are used regularly. Joint replacements are commonly coated with bioceramic materials to reduce wear and inflammatory response. Other examples of medical uses for bioceramics are in pacemakers, kidney dialysis machines, and respirators. Femoral Head of a Hip Prosthesis Hip Prosthesis  Tribological Ceramics  Tribological ceramics, also called wear-resistant ceramics, ceramic materials that are resistant to friction and wear. They are employed in a variety of industrial and domestic applications, including mineral processing and metallurgy.  Advanced structural ceramics offer unique capabilities as tribomaterials.  They are being used today in diverse applications such as tips for ball-point pens, precision instrument bearings, and cutting tool inserts.  Tribological applications of ceramics can be divided into several categories based on the properties of the ceramics. These include: resistance to abrasion and erosion; resistance to corrosive wear; wear resistance at elevated temperatures; low density; and electrical, thermal and magnetic properties.  Tribological Ceramics Tip of a ball Point Pen Ceramic Instrumental Bearing  Automotive Ceramics  Automotive ceramics, advanced ceramic materials that are made into components for automobiles. Examples include spark plug insulators, catalysts and catalyst supports for emission control devices, and sensors of various kinds. Its powerful Spark Plug Insulators physical, thermal and electrical properties make it a reliable, highly durable and cost- effective alternative to metal. As the industry faces continued pressure to deliver innovative design, improved safety features and environment-friendly vehicles (while also reducing production costs), use of this material looks set to grow. Catalytic Converter  Summary  The term "ceramic" once referred only to clay-based materials. However, new generations of ceramic materials have tremendously expanded the scope and number of possible applications.  Ceramic materials are inorganic compounds, usually oxides, nitrides, silicates or carbides. The bonding is very strong--either ionic or network covalent. Many adopt crystalline structures, but some form glasses. The properties of the materials are a result of the bonding and structure.  Summary  Ceramics can withstand high temperatures, are good thermal insulators, and do not expand greatly when heated.  Glasses are transparent, amorphous ceramics that are widely used in windows, lenses, and many other familiar applications. Light can induce an electrical response in some ceramics, called photoconductivity.  Ceramics are strong, hard, and durable. This makes them attractive structural materials  Ceramics vary in electrical properties from excellent insulators to superconductors. Thus, they are used in a wide range of applications.  Ceramics has advanced far beyond its beginnings in clay pottery. Ceramic tiles cover the space shuttle as well as our kitchen floors. Ceramic electronic devices make possible high-tech instruments for everything from medicine to entertainment. Clearly, ceramics are our window to the future.