PRACTICE QUIZ Flashcards
Mechanical Properties, thermal properties
hardness,
brittleness, and high melting temperatures.
Ceramic pieces normally cannot be
fabricated using conventional metal forming
techniques
TRUE
are a familiar group of ceramics
glasses
What are the
applications of glasses
containers, lenses, and fiberglass
they are
noncrystalline silicates containing other oxides, notably
CaO, Na2O, K2O, and Al2O3, which influence the its
properties.
glasses
consists of
approximately 70 wt% SiO2, the balance being mainly
Na2O (soda) and CaO (lime).
soda–lime glass
two prime
assets of glasses
optical transparency
and the relative ease with which they may be
fabricated.
Most inorganic glasses can be made to
transform from a noncrystalline state to one that is
crystalline by the proper high-temperature heat
treatment.
Crystallization
The product of crystallization is a fine grained polycrystalline material
that is often called a
glass-ceramic.
the formation of
these small glass-ceramic grains is, in a sense, a
phase transformation, which involves
nucleation and
growth stages.
is
often added to the glass to promote crystallization
nucleating agent
exmaple of nucleating agent
titanium dioxide
Glass-ceramic materials have been designed to have relatively high mechanical strengths
true
Glass-ceramic materials have been designed to have high coefficients of thermal expansion (to avoid thermal
shock);
FALSE
Glass-ceramic materials have been designed to have relatively high temperature capabilities;
*good dielectric properties (for electronic packaging
applications);
TRUE
Glass-ceramic materials have been designed to have good biological compatibility
TRUE
Some glass-ceramics may be made optically
transparent;
others are opaque.
the most attractive attribute of GLASS CERAMICS
ease with which they may be
fabricated
used conveniently in the mass production of nearly pore-free
ware.
conventional glass-forming techniques
Glass-ceramics are manufactured
commercially under the trade names of
Pyrocem
CorningWare
Cercor
Vision
most common uses for glass ceramics
are ovenware, tableware, oven
windows, and range tops
ovenware,
tableware,
oven
windows, and
range tops
Why are glass ceramics used in thermal environment usage
strength
excellent resistance to thermal shock
serve as electrical insulators
substrates for printed circuit boards
architectural cladding
heat exchangers and
regenerators
most widely used ceramic raw
materials
Clay
inexpensive ingredient,
found naturally in great abundance
clay
is
used as mined without any upgrading of quality
clay
its popularity lies in the ease
with which they may be formed
clay
when
mixed in the proper proportions, clay and water
form
plastic mass
is very amenable to
shaping.
plastic mass
Most of the clay-based products fall within two
broad classifications
structural clay products and
the whitewares
include
building bricks, tiles, and sewer pipes—applications
in which structural integrity is important.
Structural clay products
become white after the high-
temperature firing. Included in this group are
porcelain, pottery, tableware, china, and plumbing
fixtures (sanitary ware).
Whiteware ceramics
Another important class of ceramics
that are used in large tonnages
refractory ceramics.
salient properties of refractory ceramics
withstand high temperatures without melting
or decomposing and the capacity to remain
unreactive and inert when exposed to
severe environments.
most common marketed form of refactory materails
bricks
The performance of a refractory ceramic
depends to a large degree on its
composition. On this basis, there are
several classifications
- Fireclay ref.
- Silica Ref.
- Basic Ref.
- Special ref.
The primary ingredients for the fireclay
refractories are
high-purity fireclays, alumina
and silica mixtures usually containing between
25 and 45 wt% alumina.
During refractory service use, the
presence of a small amount of a liquid phase
is not allowable so does compromising
mechanical integrity.
false
at this temperature, the fraction
of liquid phase present will depend on
refractory composition
above 1587 degree celscius
are used principally in
furnace construction, to confine hot
atmospheres, and to thermally insulate
structural members from excessive
temperatures.
fireclay bricks
strength is
not ordinarily an important consideration in this type of brick
fireclay
Its prime ingredient is silica and it is sometimes termed as acid refractories
Silica Ref.
These materials, well
known for their high-temperature load-
bearing capacity, are commonly used in the
arched roofs of steel- and glass-making
furnaces
Silica Ref.
slags that are rich in silica and is often used as
containment vessels for them.
acid slags
Since they are readily attacked by slags
composed of a high proportion of ________, and _________contact with
these oxide materials should be avoided.
CaO
and/or MgO (basic slugs)
refractories that are rich in
periclase, or magnesia (MgO), and may also contain calcium, chromium and iron compounds, are termed
Basic ref.
The
presence of this compound is deleterious to Basec ref’s high-
temperature performance
silica
are especially resistant to attack by slags
containing high concentrations of MgO and
CaO and find extensive use in some steel-
making open hearth furnaces
Basic refractories
are relatively high-purity
oxide materials, many of which may be produced with very little
porosity.
Special Refractories
Included in this group are alumina, silica, magnesia,
beryllia (BeO), zirconia (ZrO2), and mullite (3Al2O3–2SiO2)
speical ref.
has been used for electrical resistance
heating elements, as a crucible material, and in internal furnace
components.
Silicon carbide (SiC)
are very refractory, but find
limited application because they are susceptible to oxidation at
temperatures in excess of about 800°C (1470°F).
Carbon and graphite
Expected to be relatively expensive
spe. ref.
are used to wear, grind, or cut
away other material, which necessarily is softer.
abrasive ceramics
he prime requisite for this group of materials
is hardness or
wear resistance; in addition,
a high degree of toughness
abrasive ceramics
may be
produced from abrasive
frictional forces, so some
refractoriness is also desirable.
high temperatures
both
natural and synthetic, are
utilized as abrasives
diamond
are used in several forms—
bonded to grinding wheels, as coated
abrasives, and as loose grains
abrasives
the abrasive particles are
bonded to a wheel by means of a glassy
ceramic or an organic resin
bonded to form grinding wheels
The surface
structure should contain some porosity; a
continual flow of air currents or liquid coolants
within the pores that surround the refractory
grains prevents excessive heating
true
are those in which an
abrasive powder is coated on some type of
paper or cloth material
Coated abrasives
is probably
the most familiar example of coated abrasive
sandpaper
are all frequently ground
and polished using this form of abrasive
woods, metal, cermaics and plastics
are all frequently ground
and polished using this form of abrasive
loose abrasive grains
delivered in some type of oil- or water-based
vehicle
loose abrasive grains
Several familiar ceramic
materials are classified as
inorganic
cements
cement,
plaster of paris, and lime,
which, as a group, are produced
in extremely large quantities.
cements
materials act as a
bonding phase that chemically binds
particulate aggregates into a single cohesive
structure.
cements
glassy bonding phase that forms when clay
products and some refractory bricks are fired.
One important difference, however, is that the
cementitious bond develops at room
temperature
true
consumed in the largest
tonnages
Portland cement
