Chapter 13 Flashcards
crystallization
most inorganic glasses can be made to transform from a noncrystalline state into one that is crystalline by the proper high-temperature heat treatment
glass–ceramic
product is a fine-grained polycrystalline material
glass–ceramic materials
characteristics: relatively high mechanical strengths, low coefficients of thermal expansion, good high-temperature capabilities, good dielectric properties, and good biological compatibility
structural clay products
building bricks, tiles, and sewer pipes—applications in which structural integrity is important
firing
a high-temperature heat treatment that increases the
density and strength of a ceramic piece
whiteware
ceramics that turn white after firing
refractory ceramics
a metal or ceramic that may be exposed to extremely
high temperatures without deteriorating rapidly or
without melting
basic refractories
refractories that are rich in periclase or magnesia (MgO)
abrasive ceramics
used to wear, grind, or cut away other material, which necessarily is softer
cements
when mixed with water, they form a paste that subsequently sets and hardens
calcination,
- grinding and intimately mixing clay and lime-bearing minerals in the proper proportions and then heating the mixture to about 1400”C (2550”F) in a rotary kiln
- produces physical and chemical changes in the raw materials
hydraulic cement
hardness develops by chemical reactions with water
graphitic carbon fibers
graphene layers assume the ordered structure of graphite—planes are parallel to one another having relatively weak van der Waals interplanar bonds
turbostratic carbon
graphene sheets become randomly folded, tilted, and crumpled
microelectromechanical systems
miniature “smart” systems consisting of a multitude of mechanical devices that are integrated with large numbers of electrical elements on a substrate of silicon
nanocarbons,
-a particle having a size of less than about 100 nm
composed of carbon atoms that are bonded together with sp2 hybridized electron orbitals
-three nanocarbon types: fullerenes, carbon nanotubes, and graphene
single-walled carbon nanotube
a single sheet of graphite (i.e., graphene) that is rolled into a tube
glass transition temperature
below this temperature, the material is considered to be a glass; above it, the material is first a supercooled liquid and, finally, a liquid
melting point (527)
temperature at which the viscosity is 10 Pa-s (100 P); the glass is fluid enough to be considered a liquid
working point (527)
temperature at which the viscosity is 103 Pa-s (104 P); the glass is easily deformed at this viscosity
softening point (527)
maximum temperature at which a glass piece may be handled without causing significant dimensional alterations
annealing point (527)
at this temperature, atomic diffusion is sufficiently rapid that any residual stresses may be removed within about 15 min
strain point (527)
-for temperatures below the strain point, fracture will
occur before the onset of plastic deformation
-glass transition temperature will be above the strain point
five different forming methods are used to fabricate glass products (528)
pressing, blowing, drawing, and sheet and fiber forming
pressing (528)
glass piece is formed by pressure application in a graphite-coated cast iron mold having the desired shape; the mold is typically heated to ensure an even surface
parison (528)
temporary shape from a raw gob of glass is formed by mechanical pressing in a mold
blowing (528)
- from a raw gob of glass a temporary shape is formed by mechanical pressing in a mold
- piece is inserted into a finishing or blow mold and forced to conform to the mold contours by the pressure created from a blast of air
drawing (528)
used to form long glass pieces that have a constant cross section, such as sheet, rod, tubing, and fibers
float process (529)
- with this technique, the molten glass passes (on rollers) from one furnace onto a bath of liquid tin located in a second furnace
- as glass ribbon “floats” on the surface of the molten tin, gravitational and surface tension forces cause the faces to become perfectly flat and parallel and the resulting sheet to be of uniform thickness
- sheet next passes into an annealing furnace (lehr), and is finally cut into sections
thermal stresses (529)
stresses introduced as a result of the difference in cooling rate and thermal contraction between the surface and interior regions when a ceramic material is cooled from an elevated temperature
thermal shock (529)
the fracture of a brittle material as a result of
stresses introduced by a rapid temperature change
thermal tempering (530)
- strength of a glass piece enhanced by intentionally inducing compressive residual surface stresses
- glassware is heated to a temperature above the glass transition region yet below the softening point
- then cooled to room temperature in a jet of air or, in some cases, an oil bath
- residual stresses arise from differences in cooling rates for surface and interior regions
hydroplasticity (531)
when water is added to clay minerals, they become very plastic
hydroplastic forming (532)
the molding or shaping of clay-based
ceramics that have been made plastic and pliable by adding water
slip casting (532)
a forming technique used for some ceramic materials.
A slip, or suspension of solid particles in water, is poured into a porous mold. A solid layer forms on the inside wall as water is absorbed by the mold, leaving a shell (or ultimately a solid piece) having the shape of the mold
extrusion (532)
- type of hydroplastic forming
- a stiff plastic ceramic mass is forced through a die orifice having the desired cross-sectional geometry
slip (532)
suspension of clay and/or other nonplastic materials in water
drain casting (532)
- when poured into a porous mold, water from the slip is absorbed into the mold, leaving behind a solid layer on the mold wall, the thickness of which depends on the time
- process is terminated when the solid shell wall reaches the desired thickness, by inverting the mold and pouring out the excess slip
green (533)
body that has been formed and dried but not fired
vitrification (534)
- gradual formation of a liquid glass that flows into and fills some of the pore volume
- degree of vitrification depends on firing temperature and time, as well as on the composition of the body
powder pressing (535)
used to fabricate both clay and nonclay compositions,
including electronic and magnetic ceramics, as well as some refractory brick products
three basic powder-pressing procedures (536)
uniaxial, isostatic (or hydrostatic), and hot pressing
uniaxial pressing (536)
powder is compacted in a metal die by pressure that is applied in a single direction
isostatic pressing (536)
powdered material is contained in a rubber envelope and the pressure is applied isostatically by a fluid (i.e., it has the same magnitude in all directions)
sintering (536)
-coalescence of the powder particles into a denser
mass
-carried out below the melting temperature,
hot pressing (537)
-powder pressing and heat treatment are performed
simultaneously—the powder aggregate is compacted at an elevated temperature
-costly in terms of time, because both mold and die must be heated and cooled during each cycle
tape casting (537)
thin sheets of a flexible tape are produced by means of a casting process
isomers
have same chemical formula but different properties and groups are in different locations
