Callister - An introduction - 8th edition

13.12 Compare the softening points for 96% silica,
borosilicate, and soda–lime glasses.
13.13 The viscosity of a glass varies with temperature
according to the relationship
where Q vis is the energy of activation for viscous
flow, A is a temperature-independent
constant, and R and T are, respectively, the gas
constant and the absolute temperature.A plot
of ln versus l/T should be nearly linear, and
with a slope of Q vis /R. Using the data in Figure
13.7, (a) make such a plot for the borosilicate
glass, and (b) determine the activation
energy between temperatures of 500 and
900C.
13.14 For many viscous materials, the viscosity
may be defined in terms of the expression
h
s
dP/dt
where and d/dt are, respectively, the tensile
stress and the strain rate. A cylindrical
specimen of a soda–lime glass of diameter 5
mm (0.2 in.) and length 100 mm (4 in.) is subjected
to a tensile force of 1 N (0.224 lb f ) along
its axis. If its deformation is to be less than
1 mm (0.04 in.) over a week’s time, using
Figure 13.7, determine the maximum temperature
to which the specimen may be heated.
13.15 (a) Explain why residual thermal stresses are
introduced into a glass piece when it is cooled.
(b) Are thermal stresses introduced upon
heating? Why or why not?
13.16 Borosilicate glasses and fused silica are resistant
to thermal shock. Why is this so?
13.17 In your own words, briefly describe what happens
as a glass piece is thermally tempered.
Design Problem • 531
13.18 Glass pieces may also be strengthened by
chemical tempering.With this procedure, the
glass surface is put in a state of compression
by exchanging some of the cations near the
surface with other cations having a larger di-
A exp a Q vis
RT b
ameter. Suggest one type of cation that, by
replacing Na , will induce chemical tempering
in a soda–lime glass.
Fabrication and Processing of Clay Products
13.19 Cite the two desirable characteristics of clay
minerals relative to fabrication processes.
13.20 From a molecular perspective, briefly explain
the mechanism by which clay minerals
become hydroplastic when water is added.
13.21 (a) What are the three main components of
a whiteware ceramic such as porcelain?
(b) What role does each component play in
the forming and firing procedures?
13.22 (a) Why is it so important to control the rate
of drying of a ceramic body that has been
hydroplastically formed or slip cast?
(b) Cite three factors that influence the rate of
drying, and explain how each affects the rate.
13.23 Cite one reason why drying shrinkage is
greater for slip cast or hydroplastic products
that have smaller clay particles.
13.24 (a) Name three factors that influence the degree
to which vitrification occurs in claybased
ceramic wares.
(b) Explain how density, firing distortion,
strength, corrosion resistance, and thermal
conductivity are affected by the extent of
vitrification.
Powder Pressing
13.25 Some ceramic materials are fabricated by
hot isostatic pressing. Cite some of the limitations
and difficulties associated with this
technique.
DESIGN PROBLEM
13.D1 Some of our modern kitchen cookware is
made of ceramic materials.
(a) List at least three important characteristics
required of a material to be used for
this application.
(b) Compare the relative properties and
cost of three ceramic materials.
(c) On the basis of this comparison, select
the material most suitable for the cookware.