Crystal Nucleation and Growth Rates, Time-Temperature Transformation Diagram, and Mechanical Properties of a SiO2-Al2O3-CaO-MgO-(R2O) Glass in the Presence of Cr2O3, Fe2O3, and TiO2 Nucleants

Abstract

The crystallization of a SiO2–Al2O3–CaO–MgO–(R2O) glass in the presence of Cr2O3, Fe2O3, and TiO2 nucleants was investigated utilizing differential thermal analyses, X‐ray diffraction, and scanning electron microscope. The optimum nucleation and growth rates of aluminian diopside crystals was determined for the most promising glass specimen containing all three nucleants as 1018 m3/s and 6.17 ± 0.55 × 10−9 m/s, respectively. A time–temperature transformation (TTT) diagram was also constructed for 82 wt% crystallization for the above glass sample and a nose time of ≈55 min was obtained. The bending strength of some heat‐treated specimens were also determined and were related to crystallization behavior and microstructures. The highest strength value obtained was 166 ± 6 MPa.

The effect of TiO2 additions on CaO–MgO–Al2O3–SiO2 (CMAS) crystallization behavior from the melt

“…Previous studies on the effect of TiO 2 as a nucleating agent in similar glass compositions suggest that additions around 5‐10 wt% (3.6‐7.2 mol%; Table ) will likely not aid crystallization of CMAS. Indeed, in the current study, significant crystallization was not detected until about 12.5‐15 wt% TiO 2 was added to the glass.…”

Caustic-Stable, Controlled-Pore Glass-Ceramics

“…In the case of CPGC developed here, nucleating agents were added as per Table , using lower quantities, but keeping the same ratios (1:1:0.6) as was suggested by Rezvani and co-workers . The DSC curves for this glass displayed a sharp exothermic peak at 850 °C which was largely independent of the particle size, as shown in Figure (top three curves), indicative of bulk crystallization.…”

“…Rezvani et al suggested that bulk nucleation can occur synergistically when a combination of Cr 2 O 3 , Fe 2 O 3 , and TiO 2 are used, with 5, 5, and 3 wt % respectively, reported as optimal. 31 During nucleation, it is believed that Cr 3+ precipitates from the glass matrix and interacts with Mg 2+ and Fe 2+ ions, forming the (Mg)(Fe,Cr) 2 O 4 spinel, with these spinel acting as nuclei for the final precipitation of diopside crystals through epitaxial growth.…”

“…In fact, the individual diopside and nepheline glass systems are well known for their surface crystallization characteristics. − Several studies have been conducted to investigate the addition of various nucleating agents including chromium oxide, , iron oxide, and silver nanoparticles to the SiO 2 –Al 2 O 3 –CaO–MgO (R 2 O, where R = Na, K) glass system in order to promote bulk crystallization. Rezvani et al suggested that bulk nucleation can occur synergistically when a combination of Cr 2 O 3 , Fe 2 O 3 , and TiO 2 are used, with 5, 5, and 3 wt % respectively, reported as optimal . During nucleation, it is believed that Cr 3+ precipitates from the glass matrix and interacts with Mg 2+ and Fe 2+ ions, forming the (Mg)­(Fe,Cr) 2 O 4 spinel, with these spinel acting as nuclei for the final precipitation of diopside crystals through epitaxial growth.…”

Growth of diopside crystals in CMAS glass‐ceramics using Cr2O3 as a nucleating agent

“…To facilitate the crystallization, effective nucleation agents are normally added to reduce the crystallization activation energy through heterogeneous nucleation on the proper nuclei, such as P 2 O 5 , TiO 2, ZrO 2 , CaF 2 , and Cr 2 O 3. Ma and Hsiang considered that addition of TiO 2 and ZrO 2 into the CAMS‐based glass‐ceramics led to phase separation during annealing process, because Ti 4+ and Zr 4+ are ions with high electric field strength. As a result, small droplets with different chemical composition precipitated in the glass matrix.…”