Sodium-Sulfate/15NaS_0.4MPa_19Sep05

This run features an aqueous solution that is approximately
15.5 wt.% Na2SO4. Initially, the pressure was about 0.4 MPa.

05/09/19 17:15:52: The run starts around T = 294 K. There were still
some mirabilite crystals near the bottom of the screen left over from the
previous run. Upon initial cooling, those crystals grow from the bottom
of the window. (Gravity points down.) The temperature decreases,
but the volume slowly increases as the crystal grow. (Though the
crystals are more dense than the surrounding fluid, the remaining fluid
is significantly less dense, leading to an overall slight increase
in volume.) The light was initially dim, but was gradually increased
to make those crystals visible.

05/09/19 20:51:20: The remaining fluid suddenly freezes.
The screen goes dark. Since the Ice Ih expands upon freezing, the
volume increases dramatically, and the pressure goes up as well.

Next, the system will be warmed up to eventually reach the eutectic
temperature. Since the connecting tubing is also frozen, neither the
pressure nor volume transducer accurately reflects conditions in the
growth cell. The pressure inside is much higher.

05/09/20 11:19:20: Some crystals start to melt at T = 252.44, consistent
with what would be expected if the internal pressure were quite high —
around 190 MPa.

05/09/20: 14:43:20: As the solid melts and the material in the connecting
tubing softens, the pressure goes down somewhat, and there is even
some re-solidification. As the system is gradually warmed, this sort
of behavior happens again.

05/09/21 17:25:20: Enough material has melted so that the transducer
is finally free to move, and the pressure and volume readings are again
reflective of conditions inside the pressure cell. As the system is gradually
warmed, the mirabilite crystals at the bottom start to dissolve.

05/09/21 21:04:20: Upon cooling very slightly to T = 271.85, crystals
start growing rapidly again.

05/09/22 07:53:20: Upon warming, melting starts again around 271.99.
The tight volume/temperature loop shows that this is a reversible eutectic
melting transition.

05/09/22 08:17:38: A small air bubble is visible in the system.
At higher pressures, no such bubbles were observed.

05/09/22 16:08:20: The volume had been dropping steadily as Ice Ih
melted, but now the ice is all gone and the only remaining solids are
the mirabilite crystals at the bottom of the cell. These gradually
dissolve as the temperature is raised. As the crystals dissolve, the
volume goes down.

05/09/25 11:50:20: Eventually, all the solid is dissolved; the remaining
liquid undergoes modest thermal expansion as the temperature continues
to rise up through the end of the run. The lenses in the optical tube
eventually get covered with condensation and the image grows fainter.