Shrinkage for the Z-axis leveled off at 39.68 percent and
39.69 percent, for firing temperatures of 746 and 7608C,
respectively, slow-axis shrinkage decreased from 30.48 percent
to 28.08 percent at 746 and 7608C, respectively, showing a
small expansion. This expansion was likely due to the
slumping effect that occurs when glass reaches a threshold
temperature known as the glass transition temperature TGand
begins to flow (Scholes, 1951; Zarzycki, 1991). Glass
transition temperatures are typically within the range of 530
to 1,3308C, depending on the type of glass (Le Bourhis,
2008). fast-axis shrinkage increased from 15.79 percent to
16.59 percent at 746 and 7608C, respectively, showing a trend
towards asymptotic behavior. In addition, Z-axis shrinkage
was by far the most profound, exhibiting 6-11 percent and
15-23 percent more shrinkage over the range of firing
temperatures than the slow- and fast-Axes, respectively. The
average shrinkage ratios for the slow- and fast-axis to the
Z-axis were 1:1.37 and 1:2.74, respectively. These extreme
differences can be attributed to the layer-by-layer production
method, binder burn-off, and inconsistencies in the recycled
glass stock.