[AdiDex]

I knew Tungesten is the metal which has lowest vapour pressure and  highest melting point .
But I got amazed when i read this statement in the University Chemistry , Bruce H. Mahan

"It has been calculated  that about one gaseous of Tungesten is all that is necessary to form an equilibrium system with solid Tungesten at room temperature in a volume almost  the size of the known universe."

I tried to calculate its vapour pressure , but its quite old book , 1960s or 1970s book . So i don't know what was that "size of known universe " .
I assumed that it should be atleast size of our galaxy , which has diameter of 10²¹ meters .and volume is near about 10⁶¹ m³ .

I am getting the vapour pressure of order 10^-80 Pascals using Perfect gas law. I don't know ,whether it is correct .
Tungesten has 1 Pa vapour pressure at 3427 K .
Isn't it doubtful such huge decreasement in vapor pressure from 3427 K to 298 K ??

[Enthalpy]

Appended is a diagram with the vapour pressure of W (and Ta, Nb, Mo) between 1500°C and 3000°C. Extracted from a doc by Plansee about molybdenum, but their doc about tungsten contains it too.

• You can observe 9 magnitudes variation from 2940°C to 1700°C, so 70 magnitudes to 298K look much, but the law isn't a simple exponential.
• You can (after conversion from °C to K) extract a heat of sublimation and, if this heat looks constant enough, use it to extrapolate a vapour pressure at 298K. No experiment will contradict you anyway.
• 0.17Pa @3273K and 10^-10Pa @1973K make a (constant?) activation energy of 105580K. Misusing the same activation energy towards 298K gives a vapour pressure 4×10¹³⁰ times smaller, or 2.4×10^-141Pa.

In the 1970s, the expansion and horizon were known
https://en.wikipedia.org/wiki/Edwin_Hubble
so I'd take 15Gly=1.4×10²⁶m as a radius, or 1.2×10⁸⁰m³.

One atom at 298K in this volume would imply a pressure of 1.8×10^-82Pa, so tungsten evaporates less than one atom at 298K.

In this particular case, impurities make all the vapour pressure. Trace metals will provide more vapour pressure than tungsten, and adsorbed gases even more.

[AdiDex]

By the way from this graph at 1900K vapor pressure is of order 10^-7 . You have written 10^-10 . This was done intentionally or by mistake ??
 
Another question came to my mind . Why it has lowest Vapor pressure ?? High packing efficiency ??

[Enthalpy]

The graph's scale is in °C. 1700°C=1973K.

Why the low vapour pressure: huh, I dunno. I'm a dumb engineer, you know: I check datasheets and experimental data. Metals better then ceramics were a surprize to me.

I vaguely suppose that transition elements sharing many electrons makes the metallic bond stronger per atom.
https://www.webelements.com/periodicity/boiling_point/
There would be a correlation with the molar volume
https://www.webelements.com/periodicity/molar_volume/
interesting, but insufficient, if you consider Be, B, C versus W, Re.

[AdiDex]

No, you are not dumb ( atleast for me  ) . I am that dumb who didn't see that Temperature scale is in Celsius