Jim Murphy on tue 8 jul 03
For inquiring minds in search of an understanding of the processes involved
in slumping, warping, reducing firing defects, etc., checkout the following=
:
1. "Holistic Approach to Defect Reduction" (Presented at NCECA March 2002)
apparently applies to fast-firing schedules for porcelains - (URL link
below) - where we learn among other things:
(a) Porcelain Glass Phase Compositions (expressed in unity molecular
formula) proposed to be identical for all porcelains at any given
temperature. The glass phase compositions are (note the constant
alkali-to-alumina R2O:Al2O3 levels) - (Slide #30):
~Cone 1 ~Cone 15
(1150=B0C) (1400=B0C)
R2O 1.0 1.0
Al2O3 1.24 1.24
SiO2 11.3 19.0
(b) Amount of glass that forms dictates firing temperature. Optimum glass
levels appear to be between 50% and 65%. Excess glass leads to excessive
slumping - (Slide #32).
(c) Pyroplastic Deformation is proposed to be most favorable between
990-1150 C (Eutectic melt is formed at 990 C in the K2O-Al2O3-SiO2 System.
Mullite crystallization
is apparently complete by 1150 C) - (Slide #35).
=20
2. "Observations on the Glass Phase Compositions in Porcelains" (Presente=
d
at the 104th Annual Meeting of the American Ceramic Society, St, Louis, MO
April 28 - May 1, 2002) - (URL link below) - where we learn about:
(a) Glass Phase Compositions (for slow-cooled samples) - (Slide #23):
~Cone 1 ~Cone 15
(1150=B0C) (1400=B0C)
R2O 1.0 1.0
Al2O3 1.3 1.3
SiO2 11.3 19.0
(b) "The Big Picture" - (Slide #25) -
Mullite level dictated by alumina solubility in the glass phase;
Alumina level in the glass phase dictated by alkali level;
Silica level in the glass phase, and correspondingly, the quartz
dissolution level
is determined entirely by temperature and dwell time (necessary to
saturate the glass
phase with silica).
(c) Formation of "Quartz Dissolution Rims" - (Slide #32-34)
(d) Viscosity of the glass phase (Don't miss Slide #66 - xNa2O-SiO2)
(e) Cracking upon cooling must occur within the filler particles, not the
glass matrix (Slide #76)
>
Much to comprehend & discuss.
Best wishes,
Jim Murphy
| |
|
