Aerospace Defense

Effect of Mechanical Activation of Andalusite on Mullitization and Sintering Behavior of Mullite-Based Ceramics for Aerospace and Advanced Thermal Applications

Document Type : Original Article

Author

Mohammad Dadegh Abdi Maghsoudlou

Department of Materials Engineering, Faculty of , Malayer University, Malayer, Iran

Abstract
Introduction: Mullite is a key high-temperature ceramic phase widely recognized for its outstanding properties in advanced refractory and structural applications.

Methods:This study investigates the synthesis and sintering behavior of mullite-based ceramics using mechanically activated Iranian andalusite. Raw andalusite powder was washed, characterized, and subjected to high-energy ball milling for up to ۶۰ h. The phase evolution, microstructural development, and sintering behavior of the milled powders were evaluated between ۸۰۰ °C and ۱۵۰۰ °C and compared with an unmilled reference sample.

Findings: XRD analysis showed that prolonged mechanical activation disrupted the crystalline structure of andalusite and lowered the onset of mullitization by approximately ۴۰۰ °C. The activated powder began forming mullite at ۸۰۰ °C and reached a predominantly single-phase mullite state above ۱۲۰۰ °C. Crystallite size calculated by the Scherrer equation remained in the nanocrystalline range (approximately ۸–۱۳ nm), while Williamson–Hall analysis indicated a progressive reduction of lattice microstrain with increasing temperature, approaching near-zero values at ۱۵۰۰ °C. SEM observations of samples sintered at ۱۵۰۰ °C revealed that mechanical activation produced finer, more elongated, and more uniformly distributed acicular mullite grains (aspect ratio ≈ ۸–۱۵) together with a denser microstructure, in contrast to the coarser and more porous structure of the unmilled sample.

Conclusion:Consequently, the activated powder exhibited more stable densification and higher relative density at lower firing temperatures. This work provides an efficient route for fabricating fine-grained, homogeneous mullite ceramics that are of significant interest for high-temperature aerospace and defense applications

Keywords

Andalusite
Mechanical activation
Mullitization
Phase evolution
Sintering behavior
High-temperature ceramics
Subjects
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Aerospace Defense
Volume 5, Issue 2
Summer 2026
Pages 28-49

  • Receive Date 22 February 2026
  • Revise Date 21 March 2025
  • Accept Date 28 April 2026

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