Effect of microstructure of a phase separated sodium-borosilicate glass on mechanical properties

Residual stress versus microstructural effects on the strength and toughness of phase‐separated PbO–B2O3–Al2O3 glasses

“…Regarding this topic of residual stresses and strength of LLPS glasses, an anonymous reviewer of this manuscript observed that: “Häßler and Rüssel 8 claimed that residual stresses are responsible for the increase in bending strength; however, there is no clear relationship between the Δ CTE and bending strength in their data. In fact, plotting of their bending strength versus Δ CTE seems to present a weak negative correlation”.…”

“…This discussion is not new, and the literature brings several studies on the mechanical properties of oxide glasses showing LLPS, such as the Li 2 O–B 2 O 3 –SiO 2 , 6 Na 2 O–B 2 O 3 –SiO 2 , 6–8 Na 2 O–CaO–SiO 2 , 9 B 2 O 3 –SiO 2 , 9,10 PbO–B 2 O 3 , 11–13 K 2 O–Li 2 O–SiO 2 , 14 and B 2 O 3 –SiO 2 –Al 2 O 3 –P 2 O 5 15 glasses. Recently, these studies have resurfaced in the field of computer simulations to predict the mechanical properties of phase‐separated glasses 16,17 .…”

“…Häßler and Rüssel 8 studied the mechanical properties of SiO 2 –B 2 O 3 –Na 2 O ternary LLPS glasses containing 60‐mol% SiO 2 –37‐mol% B 2 O 3 –3‐mol% Na 2 O treated at temperatures ranging from 500 to 680°C for 1–80 h to develop a phase‐separated microstructure consisting of droplets rich in Na 2 O and B 2 O 3 ( CTE = 6.5–8.5 × 10 −6 K −1 ) and an SiO 2 ‐rich matrix phase ( CTE = 3.0–4.0 × 10 −6 K −1 ). Interestingly, these LLPS glasses were transparent as a result of their small particle size, which ranged from 20 to 50 nm in samples treated at 540°C for 5 h and from 80 to 400 nm in those treated at 680°C for 80 h. The Vickers hardness and elastic modulus did not change within the measurement errors, but the bending strength showed a maximum for particle sizes around 70 nm (115 MPa) and 99–115 MPa for thermal treatments at 600, 620, and 640°C for 20 h. Very large (120–160 nm) or very small (30–50 nm) droplet diameters lead to significantly lower bending strength values.…”

Mechanisms of microstructural deformation governing Vickers hardness in phase‐separated calcium aluminosilicate glasses

“…Haßler and Rüssel also observed a similar softening in response to phase separation; however, their glasses consisted of soft particles embedded in a hard matrix. 14 The weakest link effect likely applies here too; however, the data necessary to calculate β from their microstructures is not available.…”

“…13 Haßler and Rüssel investigated the bending strength of phase-separated sodium borosilicate glasses and concluded that residual stress was responsible for increased strength. 14 Some amount of residual stress is formed during cooling in phase-separated glasses due to differences in each phase's thermal expansion coefficient. 15,16 This stress cannot be removed by annealing because it forms when the glass cools below the T g of either phase.…”