Contributions to the Data on Theoretical Metallurgy: [Part] 3. The Free Energies of Vaporization and Vapor Pressures of Inorganic Substances Page: 92

                                
92    CONTRIBUTIONS TO DATA ON THEORETICAL METALLURGY
Trifluoro-chloro-monosilane.-The vapor pressure of this substance,
SiF3C1, was measured by Schumb and Gamble (356) (187-2160).
Their results are very concordant, and the following equations are
obtained if AC , is neglected.
Liquid--, Gas (SiF3C1)
AH= 4,460,
AFO = 4,460 - 21.97 T,
B. P. = 203.00; AS203.0- 22.0.
The above authors give 1350 for the melting point.
Difluoro-dichloro-monosilane.-Schumb and Gamble (356) (195-
2570) also have given a very consistent set of vapor-pressure measure-
ments for the compound, SiF2C12, in the liquid state. They report
the melting point at 1290. Again AC, is neglected.
Liquid-+ Gas (SiF2C12)
AH= 5,080,
AFO = 5,080 - 21.03 T,
B. P.= 241.60; AS241.6= 21.0,
AF298.1 =- 1,189.
Disilane. - Stock and Somieski (392) (155-2580) and Stock,
Somieski, and Wintgen (402) (163-2580) have measured the vapor
pressure of disilane, Si2H6. The results obtained are very concordant,
and AC---4 has been assumed in deriving the following equations.
These investigators find 140.60 for the melting point.
Liquid-- Gas (Si2H6)
AC, = - 4,
AH= 6,140-4 T,
AFO = 6,140 + 9.2 T log T-45.92 T,
B. P..=258.80; AH258.8= 5,105; AS258.8 --19.7,
AH298.1 = 4,948; AF0298.1 - 763.
Hexachloro-disilane.-Martin (240) (313-4180) has measured the
vapor pressure of this substance, Si2C16, in the liquid state and reports
2720 for the melting point. The data are too erratic to warrant
anything but an approximate vapor-pressure equation.
Liquid-+ Gas (Si2Cl6)
2,404
log P (at.)--    +5.838,
B. P. 4120.
Hexafluoro-disilane.-The vapor pressures of solid and liquid hexa-
fluoro-disilane, Si2F,, were measured by Schumb and Gamble (354,
355) (194-2700) and the melting point is given as 254.60. The vapor-
pressure results are consistent. AC, is neglected.
Solid-* Gas (Si2F6)
AH= 10,400,
AFo -10,400-40.92 T,
S. P. = 254.20; S254.2= 40.9,
AF0298.1=  - 1,798.
Liquid--> Gas (Si2F6)
AH= 6,500,
AFo = 6,500- 25.60 T,
AFo298.1- - 1,139.
The solid vaporizes at 1 atmosphere pressure just below the melt-
ing point. The heat of fusion deduced from these equations is 3,900
calories per gram formula weight.