Suggest an appropriate characterisation technique which could be used to follow the progress of the crystallisation of a
Posted: Tue May 24, 2022 11:20 am
Suggest an appropriate characterisation technique which could be
used to follow the progress of the crystallisation of a glass,
assuming spherical crystals form, and briefly explain how this
could be used to determine the fraction crystallised as a function
of time. [2 marks] (c) Isothermal crystallisation experiments on a
lithium disilicate glass sample at 510oC gave the following
results: Time, t / h Fraction Crystallised, f 0 0.000 24 0.002 48
0.033 60 0.079 73 0.165 87 0.305 100 0.470 112 0.632 123 0.766 140
0.913 By plotting a suitable graph, verify that the crystallisation
process obeys the Johnson-Mehl-Avrami equation with a value of the
Avrami exponent, n = 4, and determine the rate constant, (d)
What can you deduce about the mechanism of crystallisation and the
morphology of the crystallites from this value of n?
used to follow the progress of the crystallisation of a glass,
assuming spherical crystals form, and briefly explain how this
could be used to determine the fraction crystallised as a function
of time. [2 marks] (c) Isothermal crystallisation experiments on a
lithium disilicate glass sample at 510oC gave the following
results: Time, t / h Fraction Crystallised, f 0 0.000 24 0.002 48
0.033 60 0.079 73 0.165 87 0.305 100 0.470 112 0.632 123 0.766 140
0.913 By plotting a suitable graph, verify that the crystallisation
process obeys the Johnson-Mehl-Avrami equation with a value of the
Avrami exponent, n = 4, and determine the rate constant, (d)
What can you deduce about the mechanism of crystallisation and the
morphology of the crystallites from this value of n?