EA-02

Effect of SnO2 addition on crystallization of
Li2O-Al2O3-SiO2 glass ceramic(Nippon Electric Glass Co., Ltd.) ○S. Nishida，K. Choju

SnO2 is adopted as an environmentally friendly fining agent instead of As2O3 or Sb2O3. Recently, it isreported SnO2 also works as a nucleating agent. SnO2 added Li2O-Al2O3-SiO2 glass was prepared and its
crystallization behavior was investigated using XRD and SEM. XRD intensity due to LAS crystalline ofLi2O-Al2O3-SiO2 glass-ceramics became higher as SnO2 content increased. This result suggests SnO2
promotes crystallization of Li2O-Al2O3-SiO2 glass-ceramic. Results were compared to Li2O-Al2O3-SiO2
glass ceramics containing nucleating agent such as ZrO2, TiO2 and P2O5. Effect of mixing SnO2 and ZrO2
was also investigated.
e-mail address of corresponding author: snishida@neg.co.jp
Introduction
Li2O-Al2O3-SiO2 glass ceramic, hereafter called LAS glass ceramic, has excellent characteristics such astransparency, heat resistance and thermal shock resistance, which is used for cooktop, cookware andfireplace window, etc. LAS glass ceramic is obtained through controlled two-step heat treatment consists ofnucleation and crystal growth. During heat treatment, β-quartz s. s. firstly crystallizes as a meta-stablephase and partly or completely transforms into β-spodumene s. s. as heat treatment temperature becomes
higher.
Glass for LAS glass ceramic mainly consists of LAS crystalline constituent, dissolvable constituent in
LAS crystalline, nucleating agent and fining agent.1 SnO2 is adopted as an environmentally friendly fining
agent instead of As2O3 or Sb2O3. Recently, it is reported SnO2 also works as a nucleating agent.2 However,detail of its effect is not understood well. Purpose of this work is understanding effect of SnO2 as anucleating agent in LAS glass ceramic. Results were compared to LAS glass ceramic containing
conventional nucleating agent such as ZrO2, TiO2 and P2O5. Effect of mixing SnO2 and ZrO2 was also
investigated.
Experimental
Glass with chemical composition of (76-x)SiO2-14Al2O3-1.5RO-8Li2O-0.5(Na2O+K2O)-xMyOz in mol%
was prepared using melt quenching method (where RO=MgO+CaO+SrO+BaO and MyOz=SnO2, ZrO2,TiO2 or P2O5). The melting temperature was 1650℃ and quenched glass was annealed at 700℃ and wascooled to RT. Prepared samples were heat treated and crystallized. Crystallization behaviors were analyzed
by XRD measurements and SEM observations.
Results and Discussion
Figure 1 shows XRD pattern of heat treated SnO2 free and SnO2 added sample changing crystal growthtemperature(nucleation 790℃-60min crystal growth 900～1100℃-20min). β-quartz s. s. was detected asfor SnO2 free sample. As for SnO2 added sample, β-spodumene was also detected, especially at high crystal
growth temperature. XRD intensity due to LAS crystalline becomes higher by SnO2 addition. These results
suggest SnO2 works as a nucleating agent and promotes crystallization of LAS glass ceramic.

Figure 1. XRD pattern of heat treated (a) SnO2 free and (b) SnO2 added samples.
To investigate the early stage of crystallization, SnO2 added sample after heat treatment only fornucleation was prepared. SnO2 crystalline was detected by XRD before LAS crystalline crystallization.
This result indicates SnO2 crystallize by itself at nucleation stage and promotes LAS crystalline nuclei

formation.
Crystallization behavior of SnO2 added sample was compared to those of ZrO2, TiO2 or P2O5 addedsamples. Figure 2 shows XRD intensity of each sample due to LAS crystalline changing crystal growthtemperature(nucleation 790℃-60min crystal growth 900～1100℃-20min). SnO2 or ZrO2 added samples
showed high XRD intensity compared to TiO2or P2O5 added samples. This result suggests
ZrO2andSnO2strongly
promotecrystallization compared to TiO2 and P2O5. At
early stage of crystallization, ZrO2 crystalline
was detected as for ZrO2 added sample.
However, no crystalline except for β-quartz s.
s. was detected as for TiO2 or P2O5 addedsamples.
SEM observation results indicated SnO2 andZrO2 promote bulk crystallization. As for TiO2
added sample, droplet like phase was observed,indicating phase separation. LAS crystalline
Figure 2. XRD intensity due to LAS crystalline chainging
selectively crystallized in droplet like phase.
nucleating agent.
According to TEM-EDX analysis, droplet like phase was Ti-Al rich phase. As for P2O5 added
sample, no crystalline was observed.
Figure 3 shows XRD intensity due to LAS crystalline of SnO2 and ZrO2 added samples changing
SnO2/(SnO2+ZrO2) (nucleation 790℃-60min crystal growth 900～1100℃-20min). SnO2 and ZrO2 added
samples showed high XRD intensity compared to that of SnO2 or ZrO2 added samples, especially
SnO2/(SnO2+ZrO2) is 0.25-0.5. This result indicates mixing SnO2 and ZrO2 promotes crystallization.
Figure 4 shows XRD intensity of SnO2 or ZrO2 added sample after heat treatment. After 2h heat treatment,
SnO2 was detected but ZrO2 was not detected. However, after 16h heat treatment, ZrO2 and LAS crystalline
were detected as for ZrO2 added sample whereas none of LAS crystalline was detected as for SnO2 addedsample.
With above results, crystallization mechanism of SnO2 and ZrO2 added sample could be proposed. As
glass is heat treated, SnO2 crystallizes first and acts as a nucleating agent for ZrO2 crystalline. As a result,crystallization of ZrO2 is promoted and that of LAS crystalline is promoted as well.

Figure 3. XRD intensity due to LAS
crystalline of SnO2 and ZrO2added samples.

Figure 4. XRD pattern of (a) SnO2 or (b) ZrO2 added samples.

Conclusion
Effect of SnO2 addition on crystallization of LAS glass ceramic was investigated. SnO2 promoted
crystallization of LAS glass ceramic and its effect was high compared to conventional nucleating agent
such as TiO2 and P2O5. Mixing SnO2 and ZrO2 promoted crystallization of LAS glass ceramic further. SnO2might work as a nucleating agent of ZrO2 crystalline. SnO2 can be used as a unique constituent which
enhances effect of nucleating agent such as ZrO2.
References
1. Z. Strnad, Glass-Ceramic Materials, 1986, p.96
2. M. Dressler, B. Rudinger, J. Deubener, Journal of Non-Crystalline Solids, Vol. 389, 2014, 60-65