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

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: 134.2 GPa [Rosales-Sosa et al., Sci. Rep., 6 (2016) 23620]

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) 155-158]. 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

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]

Background Example La2O3-Al2O3 glasses Two major challenges 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 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.

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.

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