Vapour pressure at high temperature

Provided that the temperature is high enough for the relation hVi kT to be satisfied, even for the highest lattice frequencies, the Helmholtz free energy of the crystal is given by equation (13 46)  

X For further discussion see, for example, Fowler and Guggenheim, Statistical Thermodynamics (Cambridge, 1049), Chapter iv. 

It was shown in equation (12 65) that the chemical potential of a perfect gas may be expressed in the form 

The quantity pvc + w is very nearly the negative of the latent heat of evaporation Lq at the absolute zero.f The last equation can therefore be rearranged to give 

In the special case where the substance is monatomic the factor / /Wo may be expected to be unity. Therefore 

---

Silica exhibits a comparatively high vapour pressure at high temperatures. Molecules of Si02 and SiO were identified in gaseous phase, while SiO predominated under oxidizing conditions. Ackermann and Thorn (1961) record a value of 10 for the equilibrium constant of the reaction SiO (g) + 1/2 O2 (g) - S1O2 (g) at 1800 °C this means that under an oxygen pressure of 1 atm, the partial pressure of SiOa is ten times that of SiO,... 

The Knudsen effusion method is the most popular method for determination of vapour pressures at high temperatures. In this a specimen is contained in a small cell which is heated in a vacuum. Vapour in equilibrium with the specimen effuses through an orifice in the lid of the cell. If m is the mass of material effusing in time t and at temperature T, from an orifice of area A, then the vapour pressure is given by the expression ... 

They remain liquid under normal, ambient operating conditions (moderate temperature, atmospheric pressure). Safety in storage and handling should also be considered. A storable liquid propellant should not have an excessively high vapour pressure at ambient temperature. The leading storable propellant uses dinitrogen tetroxide as oxidizer and a 50/50 mixture of hydrazine-unsymmetrical dimethylhydrazine (UDMH) as fuel [71], Nitrogen tetroxide and UDMH is another storable propellant mixture in use [73],... 

Very High Temperatures The commoner oils and greases are limited to maximum temperatures in air of perhaps 160 to 180°C for any extended operation, and to 240 C for very brief periods. More exotic (and expensive) liquids such as silicones, polyphenylethers and perfluoropolyethers can be used in turn up to about 350 - 400 C, but they are poor lubricants in boundary conditions. In inert atmospheres they can be used to higher temperatures, but in vacuum or eventually in inert gases they are limited by high vapour pressure. At higher temperatures still it is theoretically possible to use liquid metals or liquid... 

From this table it will be seen that bromine has a high vapour pressure at ordinary temperatures. ... 

If the analyte has a high vapour pressure at room temperature then reduction of liquid volumes is more difficult, as losses of analyte may occur when evaporating the solvent. For volatile compounds, gas chromatography rather than HPLC is normally the method of choice. 

Since the gas phase data of ER, which does not have sufficient vapour pressure at accessible temperatures, is not available, it is difficult to say definitely, but from the pictorial representation of APS-ER given in Fig.1 the ER moiety of APS-ER may well be expected to be partially in the gas phase. Consequently, a high collision frequency of oxygen may be responsible for the shortened fluorescence lifetime of APS-ER in the air. 

Colourless liquid with high vapour pressure at room temperature. Exposure can occur during electroplating and nickel refining. Vapour is insoluble in water and penetrates deep into the lung, causing pulmonary oedema and cancer. 

---