ENTHALPIES OF ATOMIZATION OF AlO(g), Al2O(g), AND Al2O2(g)

A.D. Chervonnyi

Institute of Problems of Chemical Physics RAS, Russia,
Chernogolovka, Moscow oblast, 142432 Russia, e-mail: chad@icp.ac.ru

Earlier, Chervonnyi at al. [1] measured ion currents of species effusing from an tungsten cell under heating alumina in it at temperatures of 2300-2600 K. Three sets of ionization cross-sections (i) for ion currents of O+, Al+, AlO+, Al2O+, Al2O2+, WO2+, and WO3+ registered in [1] were used for conversion of mass spectral ion intensity data for individual species at specified temperatures to absolute partial pressures (see Table 1).
Table 1 Ionization cross-sections (in Ǻ2) at energies a 5 eV above the ionization threshold

Set	O	Al	AlO	Al2O	Al2O2	WO2	WO3	
1 a	0.115	1.235	0.385	2.106	0.616	1.729	2.000	
2	0.186 [2]	6.88 [3]	0.95 [4] b	4.00 [4] b	1.19 d	1.15 [4] b	0.70 [4] b	
3	0.186 [2]	6.88 [3]	4.18 [4] c	12.90 [4] c	5.22 d	2.55 [4] c	2.23 [4] c	
Remarks: a  (O), (Al), and (W) from ref [5]; (Al2O), (WO2), and (WO3) were calculated as i = 0.75[n(M)+m(O)], where M=Al or W, and m, n  corresponding stoichiometric coefficients; (AlO) = (Al)/3 according to conclusion in ref [4] that (AlO) < (Al); (Al2O2) = 1.25(AlO); b  data from ref [4] (DM formalism); c  data from ref [4] (MAR formalism), d  (Al2O2) = 1.25(AlO), where (AlO) from ref [4].	
Third law enthalpies of atomization were evaluated from partial pressures in vapor over alunina and compared with the referenced data [6] and data [7] (see Table 2). It is seen that the values obtained by using i from set 1 are in best agreement with data [6,7].
Table 2 Enthalpies of atomization (in kJ·mol)

	[6]	[7]	i(Set 1)	i(Set 2)	i(Set 3)	
atHo0(AlО, gas)	507.0	510.0	510.7	514.2	491.5	
atHo0(Al2О, gas)	1050.0	1065.7	1067.2	1088.2	1079.1	
atHo0(Al2О2, gas)	1550.0	1572.9	1556.7	1564.3	1556.3	
Free energy functions used in evaluation were from ref [6].	

REFERENCES

[1] A.D. Chervonnyi et al. High Temp. Sci. 9 (1977) 99.
[2] W.R. Thompson, M.B. Shah, H.B. Gilbody. J. Phys. B28 (1995) 1321.
[3] R.S. Freund, R.C. Wetzel, R.S. Shul, T.R. Hayes. Phys. Rev. A 41 (1990) 3575.
[4] H. Deutsch, K. Hilpert, K. Becker et al. J. Appl. Phys. 89 (2001) 1915.
[5] J.B. Mann. in Recent Developments in Mass Spectroscopy, Proceed. of the Conf. on Mass Spectroscopy, Tokyo, 814, Univ. Park Press, Baltimore, MD (1970).
[6] Thermodynamic Properties of Individual Substances: in Bank dannykh “IVTANTERMO” (Moscow: Termotsentr Ross. Akad. Nauk im. V.P. Glushko, 2002).
[7] M.I. Milushin, A.M. Emelyanov, L.N. Gorokhov. High Temp. 25 (1987) 46.