Chapter 13 (Applications and Processing of Ceramics)
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what are die blanks made of
polycrystalline diamond particles
why do is polycrystalline diamond used?
helps control fracture and gives a uniform hardness in all directions
list the advantages of using ceramics for automobile engines
high operating temperatures low frictional losses operate without a cooling system lower weights than current engines
list the disadvantages
ceramics are brittle difficult to remove internal voids ceramic parts are difficult to form and machine
what are bottles windows and lenses all made from?
silica based glass
what are the main properties of glass
optical transparency easy manufacturing and shaping of objects hard vaccum tight chemically resistant
what is particular about glasses in comparison to crystalline materials
• they don’t solidify at particular temperature • they increase in viscocity as temperature drops • they don’t show sudden change in volume upon solidifying.
what can be said about the change in volume for glasses as temperature decreases
they gradullly shrink
what is the basic structure of glass
(SiO4)4- tetrahedron
what do impurities do for glass
they interfere with the formation of crystalline structure, which then causes non-crystlline strucutre (amorphous)
describe the behaviour of crystalline materials as they are cooled
they crystallize at melting temperature an have and abrupt change in specific volume at melting temp.
describe the behaviour of glasses as they are cooled
they don’t crystallize. And the specific volume varies smoothly with temperature
what is the glass viscosity
the temp at which glass is fluid enough to be considered a liquid
what is the working point
the temp at which the glass is easily deformed
what is the softening point
the maximum temp at which a glass piece may be handled without causing significant dimensional alterations
what is the annealing point
temp at which atomic diffusion is sufficiently rapid that any residual stresses may be removed within 15 mins
what are the units of viscosity?
Pa-s
what is the relationship between viscosity and temperature
as temp increases, viscosity decreases
which is the most common type of glass
soda-lime
what is sheet forming
continuous casting: sheets are formed by floating the molten glass on a pool of molten tin
What can happen during annealing
internal stresses build up during the cooling phase, can cause spontaneous fracture
how can you avoid spontaneous fracture
slow cooling
what is glass tempering
deliberate introduction of residual stresses by rapid surface cooling of hot glass
what are the benefits of glass tempering
it suppresses the growth of cracks from surface scratches