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07- CERAMICS


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Ceramics
An inorganic compound with a crystalline structure consisting of metal or semi-metal, and one or more non metals. Has strong covalent and ionic bonding which accounts for high hardness and stiffness, and low conduction of heat and electricity. A clay pot, a brick, glass, tungsten-carbide tool are ceramics. Can be grouped into two groups: [1] TRADITIONAL CERAMICS - silicates used for bricks, clay pots, abrasives and cement. [2] NEW CERAMICS - non-silicate, oxide and carbide based ceramics with better mechanical properties. [3] GLASSES CERAMICS - glasses with crystalline structure due to heat treatment. >>> TRADITIONAL, COMMON POTS HOUSE SIMPLER CARBIDE BLADES AND SHINE WITH GLASSY FINISH.
Strengthening of ceramics
There are a few methods to that: [1] Uniformity of starting materials. [2] Smaller grain size. [3] minimization of porosity. [4] Compressive surface stresses - glazing that contracts. [5] Fiber reinforcement. [6] Heat treatments. >>> UNIFORM STRUCTURE, SMALL GRAINS, AND FIBER REINFORCED GLAZING COMPRESS POROSITY AFTER HEAT TREATMENT.
Structure and properties of ceramics
Ceramics have covalent and ionic bonding, bonding stronger than the one in metals which accounts for great stiffness and hardness of ceramics, yet makes them into poor conductors with low hardness and high brittleness. Can be in single crystal or polycrystalline form, the polycrystalline form is stronger if the crystal grains are small. >>> STIFF, BRITTLE INSULATOR BECOMES STRONGER WITH SMALL GRAINS.
Mechanical properties of ceramics
High hardness, brittleness (no slip mechanism), and no ductility.
Physical properties of ceramics
Electrical and thermal insulating, medium density (mostly below the density of metals), high melting temperatures, and thermal expansion usually less than metals. Ceramics with high thermal expansion and low conductivity can fail due to their properties, resulting in thermal cracking. >>> BRITTLE ISOLATOR CRACKS EASILY UNDER GRUELLING HEAT.
Thermal shock
OCCURS WHEN A THERMAL GRADIENT CAUSES DIFFERENT PARTS OF AN OBJECT TO EXPAND BY DIFFERENT AMOUNTS. This differential expansion can be understood in terms of stress or of strain, equivalently. At some point, this stress can exceed the strength of the material, causing a crack to form. If nothing stops this crack from propagating through the material, it will cause the object's structure to fail.
Difference between glass and ceramics
Glass is noncrystalline (amorphous), while most other ceramics assume a crystalline structure.
Traditional ceramics
Made out of silicates, clays, minerals which are very abundunt in nature. Used to make pottery, bricks, abrasives: grinding wheels, refractories: materials with high temperature resistance >>> TRANSITIONAL, ABRASIVE BRICKS MAKE GOOD, HEAT RESISTANT POTS.
New ceramics
Recent and synthetically developed ceramic materials that utilize a variety of techniques allowing for a better control over the material's structure. Can be separated into the following categories: [1] Oxides. [2] Carbides. [3] Nitrides.
Oxide ceramics
Allumina ceramics are the most important of those - due a better process it has better strength, toughness and possess hot hardness, low thermal conductivity, and good corrosion resistance. Used in abrasives (grinding wheel grit), bioceramics ( artificial bones and teeth), cutting tools, refractory brick. >>> SHARP, ABRASIVE TEETH TEAR APART TOUGH TIN MEN.
Carbides
Tungsten, titanium, chromium carbides (the most chemically stable) combined with metallic binders such as cobalt or nickel carbides form useful and very hard products, such as carbide cutting tools, hard drawing dies, rock drilling bits. >>> CARBIDE POWDER IN METAL FRAMEWORK CUTS THROUGH STEEL LIKE HOT KNIFE THROUGH BUTTER.
Nitrides
Nitride ceramics are hard and brittle, having a high melting point. Used for coating of cutting tools to prolong tool life. >>> THIN NITRIDE COATING PROLONGS TOOL LIFE.
Glass
INORGANIC, NONMETALLIC MATERIAL THAT COOLS TO A RIGID SOLID WITHOUT CRYSTALLIZATION. Glassy state can occur in a material when insufficient time is allowed during colling for a crystal structure to form. Glassy state can occur in ceramics, metals, and polymers. Glass used in a variety of products such as in WINDOW GLASS, LIGHT BULB, GLASSWARE, GLASS FIBERS.
Silica
The most common ingredient in glasses, occurs in quartz and in silica sand. One of the best glass formers out there - NATURALLY TRANSFORMS INTO A GLASSY STATE UPON COOLING.
Devitrification
Transformation from the glassy state into a polycrystalline state.
Glass ceramics
GLASS WITH A POLYCRYSTALLINE STRUCTURE, a structure of fine crystal grains achieved by adding nucleation agents and a heat treatment, a structure that accounts for good mechanical and physical properties, such as high strength (higher than glass), absence of porosity, low coefficient of thermal expansion, resistant to thermal shock. >>> STRONG PYROCERAM POT COOKS FRESH BABIES ON SLOW FIRE.
Elements related to ceramics
Elements such as carbon, silicon, and boron have some engineering importance. [1] CARBON - used as graphite or diamonds. [2] SILICON - used in electronics and alloying elements. [3] BORON - electroplating, nitrate for cutting tools. >>> INDUSTRIAL DIAMOND CUTS SILICON PROCESSOR ON A BORING, BORON ELECTROPLATE.
Ceramics processing
Ceramics are usually processed in two ways: [1] Glass-working. [2] Particulate - like sintering of powders