Effect of additive ZrO2 on spinodal phase separation and pore distributionof borosilicate glasses

Sodium borosilicate porous glasses arising from spinodal phase separation a re promising functional materials for separation membranes, enzyme and cata lyst supports, and photonic materials. The present paper studied the effect of the additive of ZrO2 on the spinodal phase separation and pore distribu tion of the sodium borosilicate glasses using B-11 nuclear magnetic resonan ce spectrum, Si-29 nuclear magnetic resonance spectrum, mercury measurement , and nitrogen adsorption techniques. The experimental results showed that ZrO2 inhibited both the initiation process in early stage and the coarsenin g process in later stage of the spinodal phase separation. The pore volume was found to decrease slightly with the addition of ZrO2 at the beginning. However, when ZrO2 content > 7 mass%, the pore volume decreases dramaticall y with further addition of ZrO2. 65% of the pore volume in the sample witho ut addition of ZrO2 will be lost when the addition amount of ZrO2 increases from 0 to 10 mass%. The inhibition effect on the pore volume is due to the structural change of boron network by the introduction of ZrO2. The oxygen defects, such as oxygen vacancy, which initiates the spinodal phase separa tion, are reduced during the transformation process from four-coordinated b oron to three-coordinated boron by the introduction of ZrO2. The growth of the pore size of the sample, which is controlled by the dynamic process of coarsening in the later stage of the spinodal phase separation, is also inh ibited by the introduction of ZrO2. With the addition of zirconia, the thre e-coordinated boron with stronger bond energy increases. This may reduce th e movement of the oxygen-contained boron groups during mass transfer of the coarsening process of the spinodal phase separation, and consequently inhi bit the growth of the pore size.