1. Ultra-hard glasses and glass-ceramics
Ashutosh Goel
Assistant Professor
Department of Materials Science and Engineering
Rutgers, The State University of New Jersey
Spring 2016 Industrial Advisory Board Meeting

2. Aluminosilicate glasses
Na2O-Al2O3-SiO2
Glass forming region in Na2O-Al2O3 SiO2 system (mol.%)
[Ref: Mysen and Richet, Silicate Glasses and Melts, Elsevier]
Vicker’s hardness: 4 – 6 GPa
Young’s modulus: 60 – 85 GPa
Fracture toughness: ~0.7 – 1 MPa m1/2
[Yoshida et al., J. Non-Cryst. Solids, 344 (2004) 37-43]
40 SiO2 – 60 Al2O3 (mol.%)
Vicker’s hardness: 8.07 GPa
Young’s modulus: GPa
[Rosales-Sosa et al., Sci. Rep., 6 (2016) 23620]

3. Aluminosilicate glasses
CaO-Al2O3-SiO2
Glass forming region in the CaO-Al2O3-SiO2 system. The liquidus temperature of 1600 °C is indicated by heavy solid lines. [Shelby, J. Am. Ceram. Soc. 68 (1985) ].
Density: 2.4 – 2.8 g/cm3
Vicker’s hardness: 6.3 – 7.3 GPa
Young’s modulus: 83 – 103 GPa
Fracture toughness: ~1.18 – 1.55 MPa m1/2
[Ponitzsch et al., J. Non-Cryst. Solids, 434 (2016) 1-12]
Young’s modulus: 107 GPa
[Foy., Ph.D. dissertation, Rutgers University, 2008]
40.8 Al2O3 – 49 CaO – 4.1 MgO – 6.1 SiO2

4. Our Goal
To synthesize glasses/glass-ceramics with elastic and mechanical properties higher than the conventional silicate/aluminosilicate glasses
Background
Bulk rare-earth aluminate glass-ceramics 76 79 82 85 88 97
Al2O3
mol.%
1800
1850
2000
1950
Phase diagram of the alumina- rich La2O3-Al2O3 system
[Fritsche and Tensmeyer, J. Am. Ceram. Soc. 50 (1967) 167]
Example
La2O3-Al2O3 glasses
Vicker’s microhardness
Glass: >10 GPa
Glass-ceramic: >15 GPa
Al2O3-rich glasses near eutectic of La2O3–Al2O3 have been synthesized.
[Rosenflanz et al., Nature, 430 (2004) 761]

5. Background Example La2O3-Al2O3 glasses Two major challenges76 79 82 85 88 97
Al2O3
mol.%
1800
1850
2000
1950
Phase diagram of the alumina- rich La2O3-Al2O3 system
[Fritsche and Tensmeyer, J. Am. Ceram. Soc. 50 (1967) 167]
Example
La2O3-Al2O3 glasses
Two major challenges
High melting and processing temperatures – not amenable for synthesis in conventional glass melting furnaces
Small glass forming region – high tendency towards crystallization
Processing temperature: >1800 °C
Small glass forming region
Synthesized either by flame spray method or aero-levitation technique
Difficult to obtain monolith glasses for practical applications.

6. Aim
Our aim is to design and develop ultra-hard glass/glass-ceramic compositions that can be produced in the form of monoliths without multiple processing steps
Approach
We plan to follow a two pronged approach.
Designing SiO2 based glass compositions with elastic and mechanical properties superior than conventional aluminosilicate or borosilicate glasses.
We have recently synthesized a rare-earth containing alkaline-earth aluminosilicate glass composition that exhibits Vicker’s microhardness of ~8 GPa at 200 g load. The glass can be melted at 1650 °C. These are preliminary results and require more systematic studies before they can be reported.
We plan to study the compositional dependence of elastic and mechanical properties in these glasses.
Design and synthesis of Al2O3-based multicomponent glasses which can be processed into monoliths at temperatures ≤1700 °C.
We have been successful in synthesizing a glass with composition 43.5 CaO – 56.5 Al2O3 (wt.%) at 1600 °C. The glass melt required rapid quenching as it is prone to crystallization. We plan to use this system as baseline and introduce compositional complexity in order to (i) minimize the tendency towards devitrification, (ii) increase Al2O3 concentration without increasing its processing temperatures.

7. Thank you