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Mass spectrometric studies at high temperatures—XIII
J. inorg, nucl. Chem., 1967, Vol. 29, pp. 59 to 63. Pergamon Press Ltd. Printed in Northern Ireland
MASS SPECTROMETRIC STUDIES AT HIGH TEMPERATURES--XIII STABILITIES OF SAMARIUM, EUROPIUM AND GADOLINIUM MONO- AND DIFLUORIDES K. F. ZMBOV* and J. L. MARGRAVE Department of Chemistry, Rice University, Houston, Texas
(Received21 May 1966) Abstract---Gaseous subfluorides of Sm, Eu and Gd were produced in a Knudsen cell and the equilibria among them studied with a mass spectrometer. Dissociation energies and heats of atomization were determined. INTRODUCTION
DATA regarding the stabilities of various transition metal and rare earth fluorides have been reported previouslym and lead to correlations between the removal energies of fluorine in MF(g), MF~(g) and MF3(g). This paper presents further experimental results obtained by mass spectrometric analysis of the thermodynamic equilibria involving various fluorides of Sm, Eu and Gd. EXPERIMENTAL A detailed description of the apparatus and the techniques used in this experiment has been published, m The subfluorides of Sm and Eu were produced by evaporating mixtures of the trifluorides of these elements and Ho metal in a Ta Knudsen cell. For studies of the Ho-Gd-F system, a mixture of Gd-metal and HoFa was used. RESULTS
W h e n the S m F 3 + H o and E u F 3 + H o mixtures were heated in the temperature ranges 1140-1240°K and 1238-1423°K respectively, the important ions showing a shutter effect were: Sm +, S m F +, H o +, H o F +, Eu + and E u F +. I n the G d - H o F 3 system which was studied in a higher temperature range, 1358-1514°K, the M +, M F + and MF2 + ions o f both elements were observed. I n Table 1 are given the appearance potentials and the suggested neutral precursors o f the observed ions. The intensities o f the ions were measured at different temperatures, using lowenergy electrons, with voltages 5 eV above thresholds. The G d + / G d ion intensity was too low to allow precise measurements and was not used in the calculations. The GdF2+/GdF3 ion current was calculated f r o m the measured GdF2 + ion intensity at 18 eV after introducing the correction for dissociative ionization processes. The ion intensities were used to calculate the ion-current analogs o f the equilibrium constants, (Ki), for the reactions. F r o m the variation o f log K s with liT the heats of the reactions were derived by a second-law procedure. Plots o f log K s vs. liT for various reactions are presented * On leave from the Boris Kidrich Institute of Nuclear Science, Belgrade, Yugoslavia. m K. F. ZMBovand J. L. MARGRAW,jr. chem. Phys. 45 (1966). 59
60
K . F . ZMBOVand J. L. MARGRAVE TABLE 1.--APPEARANCEPOTENTIALSAND NEUTRALPRECURSORSOF IONS OBSERVE.DOVER Trm Ho-Sm-F, Ho-Eu-F AND Ho-Gd-F SYSTEMS
Ion Ho + Sm+ Eu + Gd + HoF + SmF ÷ EuF + GdF + HoF, + GdF, +
Appearance potential (eV)
Neutral precursor
5"9 -4- 0"1 5"2 4- 0.1 5.5 4- 0"1 6"0 + 0"1 6'1 4- 0"3 5"7 4- 0"3 5"9 4- 0"3 6'2 4- 0"3 6"9 4- 0"3 13"3 4- 0"5 6"5 4- 0"3 12"2 4- 0'5
Ho Sm Eu Gd HoF SmF EuF GdF HoFz HoFs GdFz GdF3
in Figs. 1 and 2, and heats o f reaction as evaluated f r o m the least-square analysis o f the plots are given in Table 2. The isomolecular exchange reactions
and
Ho(g) + SmF(g) = H o F ( g ) + Sm(g)
(1)
Ho(g) + EuF(g) = H o F ( g ) + Eu(g)
(2)
were used to calculate dissociation energies o f S m F and EuF. The heats o f the reactions (1) and (2) represent the difference a m o n g the dissociation energies o f H o F and the dissociation energies o f S m F and EuF, respectively, and no corrections to 298°K were applied. F r o m the heats o f reactions (1) and (2), AH1 ° = --2.7 4- 1.4 and AH2 ° = --3.5 4- 1.1 kcal. mole -1, and the previously determined ~2) dissociation energy o f H o F , D~9s ( H o F ) = 129'.6 4- 3 kcal. mole -1, one obtains D~9s (SmF) = 126.9 4- 4.4 kcal. mole -1, and D~0s (EuF) = 126.1 + 4.4 kcal. mole -1. The second-law plots for the heterogeneous reactions o f the type 3MF(g) = 2M(g) + MFa(s )
(3)
for Ho, Sm and Eu are shown on Fig. 2. The Ho-curve, representing Equation (3) was studied for c o m p a r i s o n with previous results32) The heat o f the reaction, - - 126.2 4- 2.0 kcal. mole -1, is in g o o d agreement with the earlier value, 127.6 4- 2.0 kcal. mole -1. By employing the differences in the heats o f the reactions (3) and (4), and (3) and (5) f r o m Table 2 and using the literature data: AH~gs,subl.(Ho) ca) = 70.6 kcal. m o l e - l ; AH~0s.subL(Sm) (a) = 48.6 kcal. m o l e - l ; A/-/~29s,sub1.(Eu)ta) = 41.9 kcal. m o l e - l ; A H I ° [HoFa(s)] (4) ---- --405.8 -+- 0.4 kcal. m o l e - l ; D~gs(HoF)tZ~ = 129.6 + 3.0 kcal. mole-X; D:gs(SmF ) : 126.9 4- 4.4 kcal. m o l e - l ; D:gs(EuF) = 126.1 ± 4.1 kcal. mole -1, one can obtain A H I ° [SmF3(s)] : --427 4- 10 kcal. mole-1 a n d A H l ° [EuFs(s)] : --413 4- 10 kcal. mole -1. t2~ K. F. ZMBOVand J. L. MARGRAVE,J. phys. Chem. 70 (1966). ts~ C. F. HABERMANand A. H. DAANE,J. chem. Phys. 41, 2818 (1964). m E. RUDZlTISand E. VANDEVENTER,Private communication, January (1965).
0.1
I0
I00
67
6. el
---o-------o-
61.9
0
j-O
o
1
Gd F2111+ HoF(g)" Gd F~II)+Ho(gl
2 HoF(01+GdFIgl-2Ho(ol ~1" ,GdF3(g)
---O
,!.
~ - -
,/~
O
,!3
0-
®
,HoF(g) + Sin(g)
O-----O----O ®
HO(gl+SmF(g)
74'
I0 IT
, ,0t
-0--
(K "t)
0
,!6
O
GO
,',
O
,!.
Ho(g)+EuF(e)-HoF(ll + iru(i)
1.--Second-law plots for various homogeneous exchange reactions.
l 7.0
0
GdF(I)+ HoF2{~) "GdF;~ (g)+ HoF{t)
FIG.
--
j
719
I
8.0
o0
t
I::
C:
W
62
K . F . ZMnov and J. L. MARORAW
---28.0 I0-
....
8.2 ,
84
8.6
9.0 f
S,.2 r
11.4
10-3
D i0 -4
3 MF'(g)=2M(I~*MF= (.) Sm .,,, F u
i0 -~
o Ho
10. 6
68
¢.4
¢o
7'6
82
104/T (K -~)
Fie. 2.--Second-law plots for various heterogeneous equilibria. (Upper scale for Smdata; lower scale for Eu and Ho-data.)
TABLE 2 . - - H E A T S OF REACTIONS IN THE
Ho--Sm-F, H o - E u - F
AND H o - G d - F
SYSTEMS
Number
Average T(°K)
Reaction
AH~° (kcal. mole-a)
AH~ga (kcal. mole-a)
1 2 3 4 5 6 7 8
1401 1321 1401 1187 1321 1428 1428 1428
Ho(g) d- SmF(g)= HoF(g) + Sin(g) Ho(g) + EuF(g) = HoF(g) + Eu(g) 3HoF(g) = 2Ho(g) + HoFs(s) 3SmF(g) 2Sin(g) + SmFs(s) 3EuF(g) = 2Eu(g) -}- EuFs(s) 2HoF(g) + GdF(g) + 2Ho(g) = GdFs(g) GdF=(g)+ HoF(g) = GdFs(g) + Ho(g) GdF(g) + HoF=(g) = GdF=(g) + HoF(g)
--2"7 4- 1"4 --3"5 4- 1"1 --126-2 4- 2 --133.4 4- 3 --115.6 4- 3 --32.6 4- 2 --22.1 4- 4 --6"1 4- 1-1
--2-7 4- 1"4 --3"5 4- 1"1
=
--41.8 4- 3"3 --30 4- 6 --6"1 4- 2
Mass spectrometric studies at high temperatures--XIII
63
The recently measured m) heats of sublimation of SmF a and EuFa, AHs(SmFa) = 107.2 4- 1"0 kcal. mole -1 and AHs(EuFa) = 101-0 -1- 1.2 kcal. mole -1 and the dissociation energy of fluorine, t6~ yielded AHatom [SmFa(g)] = 424"3 kcal. mole -x and AHatom [EuF3(g)] : 408"5 kcal. mole -1. EXPERIMENTS WITH GADOLINIUM SUBFLUORIDES The small intensities of Gd+/Gd ion current in the used temperature range made impossible the determination of the dissociation energies of gadolinium subfluorides from direct exchange reactions with holmium subfluorides. An alternative is to employ the known tT) value of the heat of formation of G d F 3 and consider only reactions which do not include G d atoms as reactants. With reaction (6) and data for D~gs(HoF),t~) AH~(GdF3),(5) AHI[GdFa(s)] and AH~(Gd), (3) one obtains D~gs(GdF ) = 140.5-q-6.5 kcal. mole-L The same procedure applied for reaction (7) yielded AHatom[GdF~(g)] ---- 283"6 4- 9"2 kcal. mole-L This value, along with the heat of the exchange reaction (8) and the data for H o F and HoF2 (2) leads to an independent value for D ( G d F ) = 141.7 4- 3.4, in excellent agreement with that from reaction (6). The heat of atomization of GdFa(g ) can be calculated from the heat of formation of GdFa(s) and the data for AH~(Gd), AH~(GdFa) and D(F2). This gives AHatom [GdF3(g)] = 443"0 4- 10 kcal. mole-L Table 3 lists various thermodynamic properties of Sm, Eu and Gd subfluorides. TABLE 3.--DISSOCIATION ENERGIES A N D HEATS OF FORMATION OF Sm, Eu AND G d FLUORIDES M
Sm
Eu
Gd
(a) Dissociation energies (in kcal. mole-x) D(Fa-M-F) D(F-M-F) D(M-F) AH;,~0a[MF3(s)] AH~°,ggs[MFs(g)] AH;.2aa[MF~(g)] AHt°,sgs[MF(g)]
(160 4- 10) (138 4- 10) 126.9 ± 4.4
(160 4- 10) (138 4- 10) 126.1 -4-4.1
(b) Heats of formation (in kcal. mole-t) --425 ± 10 --411 4- 10 --318 4- 10 --310 -t- 10 (--160 4- 1) (--160 4- 10) --64 4- 6 --58 ± 6
150 4- 10 143 4- 9 141.1 4- 4.0 --406"5 -4- 0'3 --310 ± 10 --162 -4- 10 --40 4- 6
Acknowledgements--This work was supported by the United States Atomic Energy Commission
under Contract No. AT-(40-1)-2907. c5~K. F. ZMBOV,G. BESENBRUCH,T. V. CHARLUand J. L. MARGRAVE,to be published (1966). t6~J A N A F Thermochemical Tables (Edited by D. R. STtrLL),Clearinghouse for Federal Scientific and Technical Information, Springfield, Va., August (1965). No. PB-168-370. t~ E. Rtrozrrts and E. VAN DEVENTER, Private communication.
MASS SPECTROMETRIC STUDIES AT HIGH TEMPERATURES--XIII STABILITIES OF SAMARIUM, EUROPIUM AND GADOLINIUM MONO- AND DIFLUORIDES K. F. ZMBOV* and J. L. MARGRAVE Department of Chemistry, Rice University, Houston, Texas
(Received21 May 1966) Abstract---Gaseous subfluorides of Sm, Eu and Gd were produced in a Knudsen cell and the equilibria among them studied with a mass spectrometer. Dissociation energies and heats of atomization were determined. INTRODUCTION
DATA regarding the stabilities of various transition metal and rare earth fluorides have been reported previouslym and lead to correlations between the removal energies of fluorine in MF(g), MF~(g) and MF3(g). This paper presents further experimental results obtained by mass spectrometric analysis of the thermodynamic equilibria involving various fluorides of Sm, Eu and Gd. EXPERIMENTAL A detailed description of the apparatus and the techniques used in this experiment has been published, m The subfluorides of Sm and Eu were produced by evaporating mixtures of the trifluorides of these elements and Ho metal in a Ta Knudsen cell. For studies of the Ho-Gd-F system, a mixture of Gd-metal and HoFa was used. RESULTS
W h e n the S m F 3 + H o and E u F 3 + H o mixtures were heated in the temperature ranges 1140-1240°K and 1238-1423°K respectively, the important ions showing a shutter effect were: Sm +, S m F +, H o +, H o F +, Eu + and E u F +. I n the G d - H o F 3 system which was studied in a higher temperature range, 1358-1514°K, the M +, M F + and MF2 + ions o f both elements were observed. I n Table 1 are given the appearance potentials and the suggested neutral precursors o f the observed ions. The intensities o f the ions were measured at different temperatures, using lowenergy electrons, with voltages 5 eV above thresholds. The G d + / G d ion intensity was too low to allow precise measurements and was not used in the calculations. The GdF2+/GdF3 ion current was calculated f r o m the measured GdF2 + ion intensity at 18 eV after introducing the correction for dissociative ionization processes. The ion intensities were used to calculate the ion-current analogs o f the equilibrium constants, (Ki), for the reactions. F r o m the variation o f log K s with liT the heats of the reactions were derived by a second-law procedure. Plots o f log K s vs. liT for various reactions are presented * On leave from the Boris Kidrich Institute of Nuclear Science, Belgrade, Yugoslavia. m K. F. ZMBovand J. L. MARGRAW,jr. chem. Phys. 45 (1966). 59
60
K . F . ZMBOVand J. L. MARGRAVE TABLE 1.--APPEARANCEPOTENTIALSAND NEUTRALPRECURSORSOF IONS OBSERVE.DOVER Trm Ho-Sm-F, Ho-Eu-F AND Ho-Gd-F SYSTEMS
Ion Ho + Sm+ Eu + Gd + HoF + SmF ÷ EuF + GdF + HoF, + GdF, +
Appearance potential (eV)
Neutral precursor
5"9 -4- 0"1 5"2 4- 0.1 5.5 4- 0"1 6"0 + 0"1 6'1 4- 0"3 5"7 4- 0"3 5"9 4- 0"3 6'2 4- 0"3 6"9 4- 0"3 13"3 4- 0"5 6"5 4- 0"3 12"2 4- 0'5
Ho Sm Eu Gd HoF SmF EuF GdF HoFz HoFs GdFz GdF3
in Figs. 1 and 2, and heats o f reaction as evaluated f r o m the least-square analysis o f the plots are given in Table 2. The isomolecular exchange reactions
and
Ho(g) + SmF(g) = H o F ( g ) + Sm(g)
(1)
Ho(g) + EuF(g) = H o F ( g ) + Eu(g)
(2)
were used to calculate dissociation energies o f S m F and EuF. The heats o f the reactions (1) and (2) represent the difference a m o n g the dissociation energies o f H o F and the dissociation energies o f S m F and EuF, respectively, and no corrections to 298°K were applied. F r o m the heats o f reactions (1) and (2), AH1 ° = --2.7 4- 1.4 and AH2 ° = --3.5 4- 1.1 kcal. mole -1, and the previously determined ~2) dissociation energy o f H o F , D~9s ( H o F ) = 129'.6 4- 3 kcal. mole -1, one obtains D~9s (SmF) = 126.9 4- 4.4 kcal. mole -1, and D~0s (EuF) = 126.1 + 4.4 kcal. mole -1. The second-law plots for the heterogeneous reactions o f the type 3MF(g) = 2M(g) + MFa(s )
(3)
for Ho, Sm and Eu are shown on Fig. 2. The Ho-curve, representing Equation (3) was studied for c o m p a r i s o n with previous results32) The heat o f the reaction, - - 126.2 4- 2.0 kcal. mole -1, is in g o o d agreement with the earlier value, 127.6 4- 2.0 kcal. mole -1. By employing the differences in the heats o f the reactions (3) and (4), and (3) and (5) f r o m Table 2 and using the literature data: AH~gs,subl.(Ho) ca) = 70.6 kcal. m o l e - l ; AH~0s.subL(Sm) (a) = 48.6 kcal. m o l e - l ; A/-/~29s,sub1.(Eu)ta) = 41.9 kcal. m o l e - l ; A H I ° [HoFa(s)] (4) ---- --405.8 -+- 0.4 kcal. m o l e - l ; D~gs(HoF)tZ~ = 129.6 + 3.0 kcal. mole-X; D:gs(SmF ) : 126.9 4- 4.4 kcal. m o l e - l ; D:gs(EuF) = 126.1 ± 4.1 kcal. mole -1, one can obtain A H I ° [SmF3(s)] : --427 4- 10 kcal. mole-1 a n d A H l ° [EuFs(s)] : --413 4- 10 kcal. mole -1. t2~ K. F. ZMBOVand J. L. MARGRAVE,J. phys. Chem. 70 (1966). ts~ C. F. HABERMANand A. H. DAANE,J. chem. Phys. 41, 2818 (1964). m E. RUDZlTISand E. VANDEVENTER,Private communication, January (1965).
0.1
I0
I00
67
6. el
---o-------o-
61.9
0
j-O
o
1
Gd F2111+ HoF(g)" Gd F~II)+Ho(gl
2 HoF(01+GdFIgl-2Ho(ol ~1" ,GdF3(g)
---O
,!.
~ - -
,/~
O
,!3
0-
®
,HoF(g) + Sin(g)
O-----O----O ®
HO(gl+SmF(g)
74'
I0 IT
, ,0t
-0--
(K "t)
0
,!6
O
GO
,',
O
,!.
Ho(g)+EuF(e)-HoF(ll + iru(i)
1.--Second-law plots for various homogeneous exchange reactions.
l 7.0
0
GdF(I)+ HoF2{~) "GdF;~ (g)+ HoF{t)
FIG.
--
j
719
I
8.0
o0
t
I::
C:
W
62
K . F . ZMnov and J. L. MARORAW
---28.0 I0-
....
8.2 ,
84
8.6
9.0 f
S,.2 r
11.4
10-3
D i0 -4
3 MF'(g)=2M(I~*MF= (.) Sm .,,, F u
i0 -~
o Ho
10. 6
68
¢.4
¢o
7'6
82
104/T (K -~)
Fie. 2.--Second-law plots for various heterogeneous equilibria. (Upper scale for Smdata; lower scale for Eu and Ho-data.)
TABLE 2 . - - H E A T S OF REACTIONS IN THE
Ho--Sm-F, H o - E u - F
AND H o - G d - F
SYSTEMS
Number
Average T(°K)
Reaction
AH~° (kcal. mole-a)
AH~ga (kcal. mole-a)
1 2 3 4 5 6 7 8
1401 1321 1401 1187 1321 1428 1428 1428
Ho(g) d- SmF(g)= HoF(g) + Sin(g) Ho(g) + EuF(g) = HoF(g) + Eu(g) 3HoF(g) = 2Ho(g) + HoFs(s) 3SmF(g) 2Sin(g) + SmFs(s) 3EuF(g) = 2Eu(g) -}- EuFs(s) 2HoF(g) + GdF(g) + 2Ho(g) = GdFs(g) GdF=(g)+ HoF(g) = GdFs(g) + Ho(g) GdF(g) + HoF=(g) = GdF=(g) + HoF(g)
--2"7 4- 1"4 --3"5 4- 1"1 --126-2 4- 2 --133.4 4- 3 --115.6 4- 3 --32.6 4- 2 --22.1 4- 4 --6"1 4- 1-1
--2-7 4- 1"4 --3"5 4- 1"1
=
--41.8 4- 3"3 --30 4- 6 --6"1 4- 2
Mass spectrometric studies at high temperatures--XIII
63
The recently measured m) heats of sublimation of SmF a and EuFa, AHs(SmFa) = 107.2 4- 1"0 kcal. mole -1 and AHs(EuFa) = 101-0 -1- 1.2 kcal. mole -1 and the dissociation energy of fluorine, t6~ yielded AHatom [SmFa(g)] = 424"3 kcal. mole -x and AHatom [EuF3(g)] : 408"5 kcal. mole -1. EXPERIMENTS WITH GADOLINIUM SUBFLUORIDES The small intensities of Gd+/Gd ion current in the used temperature range made impossible the determination of the dissociation energies of gadolinium subfluorides from direct exchange reactions with holmium subfluorides. An alternative is to employ the known tT) value of the heat of formation of G d F 3 and consider only reactions which do not include G d atoms as reactants. With reaction (6) and data for D~gs(HoF),t~) AH~(GdF3),(5) AHI[GdFa(s)] and AH~(Gd), (3) one obtains D~gs(GdF ) = 140.5-q-6.5 kcal. mole-L The same procedure applied for reaction (7) yielded AHatom[GdF~(g)] ---- 283"6 4- 9"2 kcal. mole-L This value, along with the heat of the exchange reaction (8) and the data for H o F and HoF2 (2) leads to an independent value for D ( G d F ) = 141.7 4- 3.4, in excellent agreement with that from reaction (6). The heat of atomization of GdFa(g ) can be calculated from the heat of formation of GdFa(s) and the data for AH~(Gd), AH~(GdFa) and D(F2). This gives AHatom [GdF3(g)] = 443"0 4- 10 kcal. mole-L Table 3 lists various thermodynamic properties of Sm, Eu and Gd subfluorides. TABLE 3.--DISSOCIATION ENERGIES A N D HEATS OF FORMATION OF Sm, Eu AND G d FLUORIDES M
Sm
Eu
Gd
(a) Dissociation energies (in kcal. mole-x) D(Fa-M-F) D(F-M-F) D(M-F) AH;,~0a[MF3(s)] AH~°,ggs[MFs(g)] AH;.2aa[MF~(g)] AHt°,sgs[MF(g)]
(160 4- 10) (138 4- 10) 126.9 ± 4.4
(160 4- 10) (138 4- 10) 126.1 -4-4.1
(b) Heats of formation (in kcal. mole-t) --425 ± 10 --411 4- 10 --318 4- 10 --310 -t- 10 (--160 4- 1) (--160 4- 10) --64 4- 6 --58 ± 6
150 4- 10 143 4- 9 141.1 4- 4.0 --406"5 -4- 0'3 --310 ± 10 --162 -4- 10 --40 4- 6
Acknowledgements--This work was supported by the United States Atomic Energy Commission
under Contract No. AT-(40-1)-2907. c5~K. F. ZMBOV,G. BESENBRUCH,T. V. CHARLUand J. L. MARGRAVE,to be published (1966). t6~J A N A F Thermochemical Tables (Edited by D. R. STtrLL),Clearinghouse for Federal Scientific and Technical Information, Springfield, Va., August (1965). No. PB-168-370. t~ E. Rtrozrrts and E. VAN DEVENTER, Private communication.