Ceramics ~ Chapter 7
Recognize characteristics of old and new ceramics
Distinguish material property trends between ceramics and other materials
What are ceramics?
An inorganic compound consisting of a metal (or semi-metal) and one or more nonmetal
What are some examples?
Silica (SiO2)- silicon dioxide is the main ingredient in most glass products
Alumina (Al2O3)- aluminum oxide, used in various applications form abrasives to artificial bones
Hydrous aluminum silicate (Al2Si2O5(OH)4)- a complex that is the main ingredient in most clay products
What are some properties?
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 is the clearest example
Strength properties of ceramics?
Theoretically, why should the strength of ceramics be higher than metals? Covalent and ionic bonding types are stronger than metallic bonding
What is slip and why is it important in metals? A basic mechanism by which allows metals to deform when subjected to high stresses. Metallic bonding allows for slip.
Why are ceramics weaker than metals? Bonding in ceramics is much more rigid and does permit slip under stress. Therefore, the inability to slip makes it much more difficult for ceramics to absorb stresses.
What is compressive strength?
The resistance of material to breaking under compression
Compressive strength in ceramics?
Ceramics are substantially stronger in compression than in tension. Therefore, when it comers to engineering and structural applications, designers have learned that it is much more better to use ceramics so they load in compression, rather than in tension or bending.
What are some physical properties of ceramics?
Density- most ceramics are lighter than metals but heavier than polymers
Melting temperatures- higher than most metals *some ceramics decompose rather than melt
Electrical and thermal conductivity- lower than for metals but ceramics are much more spread in perspective; some ceramics are insulators while other are conductors
Thermal expansion- somewhat less than for metals, but the effects are much more damaging because of brittleness
Major types of ceramics?
Traditional, New, Glass
Traditional? Some ceramic products?
Clay products such as pottery bricks, common abrasives and cement
Clay construction- bricks, clay pipe, and building tile
Refractory ceramics- capable of higher temperature applications (i.e. furnace walls, crucibles, and molds
Cement used in concrete- construction and roads
Whiteware products- pottery, stoneware, fine china, and other tableware based on mixtures of clay and other minerals
Raw materials?
Mineral silicates- clays of various compositions and silica, such as quartz (are among the most abundant substances in nature and constitute the principal raw materials for traditional ceramics)
Alumina is also an important raw material
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?
Commonly made up of a mineral called kauolinite (Al2Si2O5(OH)4)
When mixed with water, clay becomes a plastic substance that is formable and moldable
Firing- heating to a sufficiently elevated temperature
Firing is used to fuse class into a dense strong material
Clay can be shaped while wet and soft, and then fired to obtain the final hard product
Silica as RM?
Available naturally in various forms, most important is quartz *main source is sandstone
Lost cost
Hard and chemically stable
Principal component in glass
Important when it comes to other ceramic products: whitewall, refractories, and abrasives
Alumina as RM?
Bauxite (impure mixture)- most alumina is processed from this mineral *the principal source of metallic aluminum
Corundum (more pure)- contains alumina in massive amounts
Alumina- abrasive (grinding wheels) and refractory brick (furnaces)
What are new ceramics?
more recently developed ceramics based on oxides carbides, etc., with better mechanical or physical properties than traditional ceramics
New Products?
Glass- bottles, glasses, lenses, window panes, and light bulbs
Glass fiber- 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
Ceramics insulators- electrical transmission components, spark plugs, and microelectronic chip substrates
Magnetic ceramics- computer memories
Nuclear fuels on uranium oxide (UO2)
Bioceramics- artificial teeth and bones
How were they developed?
Ceramic materials developed synthetically over the several decades
Improvements in processing techniques that provide greater control over structures and properties of ceramics materials
Based on compounds other than variations of aluminum silicate *aluminum silicate form most of the traditional ceramic materials
Usually simpler chemically than traditional ceramics *i.e. oxides, carbides, nitrides, and borides
Products of oxide?
abrasives (grinding wheel grit)
bioceramics (artificial bones and teeth)
electrical insulators and electronic components
refractory bricks
cutting tool inserts
spark plug barrels
engineering components
Products of carbide?
silicon carbide(SiC), tungsten carbide(WC), titanium carbide(TiC), tantalum carbide (TaC), and chromium carbide (Cr3C2)
Production methods for SiC were developed a century ago
WC, TiC, TaC are valued for their hardness and wear resistance in application
WC, TiC, TaC must be combined with a metallic binder such as cobalt or nickel in order to fabricate a useful solid product
What is glass?
What kind of structure does glass?
Why is so much SIO2 in glass?
Explain the glassy state of glass?
Other ingredients in the glass?
What are glass ceramics?
Other Related Material?
Graphite?
Diamond?
Silicon?
Applications and Significance of Silicon?
Boron?