Ultrastrong Translucent Glass Ceramic with Nanocrystalline, Biomimetic Structure

Transparent/translucent
glass ceramics (GCs) have broad applications
in biomedicine, armor, energy, and constructions. However, GCs with
improved optical properties typically suffer from impaired mechanical
properties, compared to traditional sintered full-ceramics. We present
a method of obtaining high-strength, translucent GCs by preparing
ZrO2–SiO2 nanocrystalline glass ceramics
(NCGCs) with a microstructure of monocrystalline ZrO2 nanoparticles
(NPs), embedded in an amorphous SiO2 matrix. The ZrO2–SiO2 NCGC with a composition of 65%ZrO/35%SiO2 (molar ratio, 65Zr) achieved an average flexural strength
of 1 GPa. This is one of the highest flexural strength values ever
reported for GCs. ZrO2 NPs bond strongly with SiO2 matrix due to the formation of a thin (2–3 nm) amorphous
Zr/Si interfacial layer between the ZrO2 NPs and SiO2 matrix. The diffusion of Si atoms into the ZrO2 NPs forms a ZrOSi superlattice. Electron tomography
results show that some of the ZrO2 NPs are connected in
one direction, forming in situ ZrO2 nanofibers (with length
of ∼500 nm), and that the ZrO2 nanofibers are stacked
in an ordered way in all three dimensions. The nanoarchitecture of
the ZrO2 nanofibers mimics the architecture of mineralized
collagen fibril in cortical bone. Strong interface bonding enables
efficient load transfer from the SiO2 matrix to the 3D
nanoarchitecture built by ZrO2 nanofibers and NPs, and
the 3D nanoarchitecture carries the majority of the external load.
These two factors synergistically contribute to the high strength
of the 65Zr NCGC. This study deepens our fundamental understanding
of the microstructure-mechanical strength relationship, which could
guide the design and manufacture of other high-strength, translucent
GCs.