Density maxima in high-pressure supercooled water and liquid silicon dioxide

With glass capillary pressure vessels it has been possible to study the effect of pressure on the temperature of maximum density (TMD) and on the "sharpness" of the density maximum in liquid H₂O and D ₂O in the important but little-studied supercooled regime. A pressure of 1200 bars produces a 33°C depression of the TMD in these liquids and a considerable reduction in sharpness. Comparison with the ratherflat density maximum for liquid SiO₂ supports the notion that the presence or absence of density anomalies in "tetrahedral" liquids depends on the average bridge-bond angle, which is evidently unusually large in water at normal pressure.