3D Crystallographic Alignment of Alumina Ceramics by Application of Low Magnetic Fields

TL;DR

This paper introduces a novel magnetic alignment technique for alumina ceramics that achieves near-perfect crystallographic orientation, enabling the creation of ceramics with tailored anisotropic properties using very low magnetic fields.

Contribution

The study presents a new method combining magnetic alignment and colloidal processing to control grain orientation in ceramics with minimal magnetic fields, surpassing previous alignment techniques.

Findings

Crystallographic orientation exceeds 99% in alumina ceramics.

Magnetic fields below 10 millitesla effectively align grains.

The method enables complex-shaped ceramics with designed properties.

Abstract

Non-cubic crystals exhibit anisotropic physical and functional properties. Microscopic crystallites as constituents of polycrystalline materials are randomly oriented, thus polycrystalline ceramics lack the anisotropic properties of their monocrystalline counterparts. We propose a technology that exploits the synergy between magnetic alignment and colloidal ceramics processing, and enables to independently tune the orientation of grains in different sample regions by infinitesimal magnetic fields (<10 millitesla). The grain pivot mechanism enables the emulation of single crystals, as well as the creation of large complex-shaped ceramic elements with designed crystallographic landscapes and spatially and directionally tuned properties. Ultra-high magnetic response arises from magnetic shape anisotropy of platelet-shaped seed crystallites coated with small amounts of iron oxide nanoparticles. To control crystallographic growth directions during subsequent annealing procedures, the seeds are dispersed and aligned in a matrix of chemically identical, but much finer spherical particles. The degree of crystalline orientation in accordingly prepared aluminum oxide exceeds 99%. This technology opens an avenue to remarkably improve structural and functional properties of ceramic elements employed in numerous industrial applications.