WADD-TR-eO-782 V/^ PART XXV
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VAPORIZATION OF COMPOUNDS AND ALLOYS AT HIGH TEMPERATURES
PART XXV. MASS SPECTROMETRIC STUDY OF THE VAPORIZATION OF THE TIN OXIDES THE
DISSOCIATION ENERGY OF SnO
TECHNICAL DOCUMENTARY REPORT No. VVADD-TR-eO-782. PART XXV
JANUARY 1965
AIR FORCE MATERIALS LABORATORY RESEARCH AND TECHNOLOGY DIVISION
AIR FORCE SYSTEMS COMMAND WRIGHT-PATTERSON AIR FORCE BASE. OHIO
Project No. 7350, Task No. 735001
(Prepared under Contract No AF 61(052)-764 by the (PXersite Libre de Bn.xelles Brussels, Belgmm;
R. Colin, J. Drowart and C. Verhaegen)
/Alftf^i^ m;: r:rrv[D
PORBMORD
Thia xttport was prepared by the Uhlversity of Brussels,
Belgium, under USAP Contract No. AF61(052)-764. The contract
was initiated under Project No. 7350, "Refractory Inorganic
Non-Metallic Materials," Task No. 735001, "Non-graphitic."
The work was adainistered under the direction of the Air Porce
Materials Laboratory, Research and Technology Division, Air
Porce Systems Goaaand, Wright-Patterson Air Porce Base, Ohio.
Mr. P. W. Vahldiek was the project engineer.
TIM authors aeknowlsdg« Professor P. Goldfinger'a interest in
this work. They thanüc Mr. J« Mlehelet for assistance with the ezperinents.
ABSTRACT
The evaporation of tin oxide SnC^ and mixtures of tin
and tin oxide was studied* The vaporization reactions are
SnO, 1iSnO) ♦ 1 0. (n« 1,2) n n 2 2
Sn ♦ Sn02 l(SnO}n (n« 1,2,3,4,) n
The dissociation energy of SnO ist D£el26#0+l«C
kcal/aole; the poljmerisation energies are HjggSÖÖ.e*^,
136.S+S, 207.6+5 kcal/aole for (SnO)2, (SnO)3 and (Sn0)4
respectively.
A reinterpretation of the total vapor pressures given
in the literature was made.
This technical documentary report has been reviewed and is
approved.
lUY^l W. G. RAMKB Chief, Ceramics and Graphite Branch Metals and Ceramics Division Air Force Materials Laboratory
ill
TiBLE OF CONTSfTS
sEoncMf PAGa
INTRODUCTION 1
EXPERIMENTAL 2
RESULTS 3
!• Coapo»ltlon of |hg Yaiw 3
2, Pr«««ir— 4
3. Thittodynaalc Propcrtie» of th» Sn 0 .
J 3 aB,Tj*4
DISCUSSION 10
REFHRENCES 13
IT
iwrRODUcrioN
The aass spectronetric study of the vaporization beha-
vior of a number of Group IVB-Group VIB coopounds has shown
the presence of polyaeric oolecules in the vapor of aost of
these l1**9'. The aeasurenents^' 'showed these to be present
in increasing aaounts in going froa QeOl ' to SnO and PbO.
Manuscript rslsasad toy authors Dsesnbsr 1964 for publloatios as an
RID Technical Report«
It was therefore of interest to investigate and analyse in detail the evaporation behavior of both SnO^ and SnO.tSn not only to »derive the thermodynamic properties of these mole- cules, but also to take their presence into account in the calculation of the dissociation energy of the molecule SnO from total pressure determination * , Doing so made it possible to explain the discrepancy between the previously generally accepted thermochemical value of the dissociation energy D0(SnO)s 13M1 kcal • and the spectroscopic data,
0 (13) which lead to an upper limit of 130.9 kcal/mole • The com- parison of the data furthermore enable one to show independently that also in SnO the electronically excited E state disso-
3 ciates to atomic products in their P, sublevels, the more
(lU) likely possibility implied by rotational analyses for CnO ,
SnS(15), Pb0(16> and PbSa7).
EXPERIMENTAL.
The mass spectrometer used is a single focussing, 60°
sector, 20cm radius of curvature instrument described pre- cis 1** y (20) (21) viously • ', The experimental set-up and the principle
of the thermodynamic study of vaporisation processes was also
given previously.
The commercial SnO samples were used as such. On the (11 22)
basis of the literature data * , it was considered that
in the temperature interval of interest here (1030-1200WK),
this compound has disproportionatcd to Sn ♦ Sn02. The Sn02
samples were heated at 1000UK under one atmosphere of oxygen
for 2U hours prior to evaporation. Several crucible materials
tried gave rise to reaction with both SnO and SnO.. Quartz
was found to be a satisfactory container for SnO, while molyb-
denum and platinum crucibles were used for SnO.
Temperatures were measured both with a Pt-Pt 10% Rh thermocouple and with an optical pyrometer.
RESULTS.
1. Composition of the Vapors.
The ions characteristic of this system, identified
by their mass and isotopic distribution and shown to be pro*
duced from neutral species originating from the cell by
use of a movable beam defining slit are: 0 , 0. , Sn , SnO ,
Sn70 and Sn909 . Their approximate appearance potentials are
given in table 1. From these it was concluded that 0 , Sn
and Sn^O are fragment ions whereas SnO , 0. and Sn^O-
are parent ions. The relative intensitie« of the different
ions further indicate that SnO-(s) vaporizes according to the
reaction
Sn02(s) •* SnO(g) ♦ 1/202(R) (I)
and to a lesser extent accoroing to
Sn02(s) - l/2Sn202(p) ♦ l/202(g) (II)
b) S^stem^SnOCs2i(Sn(1 )_*_Sn02(s)J.
The ionic species characteristic of this system iden- tified as above are: Sn , SnO , Sn-0 , Sn202 , Sn-O, and
Sn^O^ . Appearance potentials niven in table I, showed again Sn and Sn20 to be fragment ions and SnO , Sn-O^ , Sn30.
and Sn^O^ to be parent ions. The vaporization processes for SnO^s) ♦ Sn(l) are thus n/2(Sn0o(s) ♦ Sn(l)j -► Sn^O , i y 2 ' n n n= 1 to •♦. In the molybdenum crucibles low ion intensities attributed to SnO.MoO,, (SnOK.MoO. and (SnO)3.Mo03 were also measured . Low intensities at even higher masses were detected but due to the reduced separation at these
higher masses, it was not possible to identify the correspon-
ding ions as due to polymers of SnO or other gaseous molub-
dates. When a sample of SnO.Cs) + Sn(l) was studied in a
tungsten crucible it also gave rise to the formation of several (23) complex molecules . Among the ions formed by electron impact
from these are SnO.WO, , SnO, (WO,) , (SnOK.WO, , SnO.(W02)2 ,
(£nO)2.(W03)2* and (SnO)3.(W02 )2 .
2. Pressures,
The pressureaover Sn02(s) (table 2,), were calculated
from the Hertz Knudsen relation. Samples of known weight were
vaporized completely to do so, the intensities of the major
species (SnO and 0,) bein^ monitored and integrated with time.
In the Sn(s,l) ♦ Sn02(s) system, the SnO partial pres- sures were derived from the calculated energy of vaporization
based on the following cycle, in which the value of the disso-
ciation energy of SnO is that to be discussed later,
Sn02(s) - SnO(g) ♦ 1/2 02 AH298= 1U2*6*2»0
1/2 02 ♦ 1/2 Sn(s) ■♦ 1/2 Sn02(s) -1/2AH° 298=-69.1«0.8 J
l/2Sn02(s) ♦ l/2Sn(s) -^ SnO(p) AH°g8= 73.5*2.1
The numeric values for the thermodynamic functions
required in this calculatioü were taken from the literature
The heat of formation of Sn02 adopted, AM? 2g8= -138.1*0.5
kcal/mole will be justified in the discussion.
The partial pressures P of the polymers (table 3)
were obtained from the relation
Pn n
1 0nYn
where I is the intensity, a the relative ionization cross section and y the relative multiplier efficiency. The a
valueswere estimated on the basis that the ionization cross section for a dimer is 1.6 times that of the mono-
to h (30)
(27-29) mer as was shown to hold for several diatomic "' and dimeric molecules section were taken from Otvos and Stevenson
Values of atomic ionization cross (31). Multiplier
efficiencies were -ead from the calibration curve of a
multiplier (32) similar to the one used in this work; mole- (33) cuiar effects on the first dynode were taken into account
The numeric values used are o « 1, 1.6, 2.1 anu 2.6, y s 1.0, 0.7, 0.6 and 0.7 for SnO, Sn202, SnjO- and Sn.O^ respectively
%
O
3
3 O
NJ 0)
3
to
»
a»
ro
O
U)
O 3
>
r n
w O
(A)
I»
o •r
• oc •» O •
• oc t*
O
tr
•
•» C •
•* o en
C •» c en
ao >» c cr
M 3 O
3
C
v. 3
o
3
U)
CO 3
o
>
0»
3 o
3 rt H- 0» M
H 3
A <
TABLE 2. Vaporization of Sn02(s)
Pressures and Enthalpy for the Reaction
Sn02(s) * SnO(R) ♦ 1/2 02
T0K
SnO
-log P(a
02
tm)
Sn202
* GT"H298 AH298
125'* 7.1B(*0, 15) 8.00( *0. 15) - 6M.33 mu.7 1269 6.88 7.63 - 6U.28 m3.8
1290 6.53 7.31 - 6U.21 1U3.0
1321 6.23 6.92 - 6U.11 m3.3
1367 5.71 6.33 - 63.95 m2.8
1«»03 5.12 5.80 7.0000.30)63.83 1H1,0
im3 5.07 5.69 6.79 63.73 mi.a 1531 U.IO «♦.67 5.67 63.39 m2.2
1538 3.90 »♦.53 5.39
standard
63.73
deviation
1U0.9
1U2.6
total uncertainty *1.3
TABLE 3. Partial Pressures over SnO-Cs) ♦ Sn(l)
Exp.n0 T0K - log p(a tm)
SnO Sn202 Sn303 S%0-
0901 1153 5.2U(*0, .U) 5.17(»0 .5) 5.36(*0.5) 5.15(»0.5)
119M »♦.78 »♦.29 5.03- »♦.88
0913 1188 i».8U »♦.»♦0 »♦.92 »♦.79
0922 1080 6.09 5.91 6.«♦2 6.»^2
1095 5.92 5.68 6.»+l 6.19
1091 5.96 5.73 6.2U 6.22
1117 5.63 5.27 5.8U 5.57
1116 5.66 5.»^U 6.05 5.98
1171 5.02 «♦.83 5.US 5.46
8
3. Thermodvnamic Properties of the SruCU, .Sn^Oj and
Sn, o^ Polymeric Molecules.
The equilibrium constants for the reaction (SnO)n(R) * nSnO(g) (n=2,3,U)
are piven in fipure 1, For Sn-O«, equilibrium constants measured at the higher temperatures above SnO- were also included. The reaction enthalpies derived calculated by a least square treatment are
Sn202(f;) ■*■ 2 SnO(p) AH1218= 6l4*5t3 kcal/mole
Sn303(p) * 3 SnO(R) AHii32= 131-7t3 " Snu0u(P!) - «4 SnO(p) AHj132 = 200. 9 i3
By combining» these with the free energies for the corres- pondinp reactions the entropies S1218= 103.6t5, S,132=131.6»6 and S° 32= 168.6*6 e.u. for (Sn0)2, (Sn0)3 and (SnO)^ respec- tively, were calculated. By estimating hiph temperature entropies
and heat contents by analogy with a number of tetra, hexa- and octa-atomic molecules , the polymerization energies and entropies at 2980K were calculated to be AH2g8 = 66.8»»*(Sn202), 136.5*5 (Sn303), 207.6*5 kcal/mole (Sn^0u) and S2g8= 75.0*6 (Sn202), 90.7*8 (Sn303) and 108.1*8 e.u. (Sn,^).
\
DISCUSSION.
Different thermochemical values for the dissociation energy of SnO, calculated both from the present data for the vaporization of SnO« and from literature 'iata for the
vaporization of Sn02 ♦ Sn » or Sn ♦ Ga203(35) mixtures
and for the reactions Sn(l) ♦ CO, ♦ SnO(p) ♦ CO and SnO,(s)+ (11) CO * SnO(ß) ♦ CO« are summarized in table U.
These were based on cycles analogous to I, in which
the dissociation energy of 0, or the heat of sublimation of tin, AHfSp= 72.0 kcal/mole require no further comments.
The other data are briefly discussed now. The heat of formation for SnOjCs), AH°g8(Sn02(s))= -138.1t0.5 kcal/
mole is the; average value calculated from the equilibria:
1/2 Sn(8) ♦ C02(g) * l/2Sn02(s) ♦ C0(R) (11»36'39)
1/2 Sn(8) ♦ H20(g) ♦ l/2Sn02(s) ♦ H2(g) (,|0",*2)
which were both measured by several authors and treated here (2U 25) by a thir*! law procedure using the free energy functions *
and heats of formation , AH298 f^C02^= -9,♦•1 kcal/mole, AH298 f(co)s -26•,♦ kcal/mole and AH2g8 f(H20)= -57.8 kcal/ mole, given in the literature and from
the calorimetric value of Humphrey and O1Brian , AH2q8 f
(Sn02)= -138.7*0.15 kcal/mole.
Enthalpies for reaction 1 were recalculated from the apparent pressures measured by Veselowski and Platteeuw and Meyer who applied the Knudsen and flow methods respec- tively and both assumed the vapor over Sn07(s) ♦ Sn(l) to
contain only the molecule SnO. Taking into account the presence of the polymers by use of the relations
Pj= p(SnO) ♦ /7 pCSn^.)* /I pCSnjO-)* A pCSn^OJ
s p(SnO)> £ p(Sn0r ♦ ^ p(Sn0r ♦ £ p(SnO) (Knudsen) ^2 3 H
10
P*= p(SnO) ♦ 2p(Sn202) ♦ 3p(Sn303) ♦ •♦p(SnM0|4)
= p(SnO) = w- p(SnO)2= i- p(SnO)35 Ä- pCSnO)** (transport) K2 ^3 NU
where K are the eouilibrium constants for the reactions n Sn 0n(R) * SnO(p), the partial pressure of SnO were recal- culated. They are summarized in table U together with the heats of vaporization of the molecule SnO based thereoo.
Platteeuw and Meyer also measured th*» equilibria
SnO,(s) ♦ C0(R) -► SnO(j») + CO,(R) 2 and * l
Sn(l) ♦ C02(g) * SnO(R) ♦ CO(R) 3
by the flow method. The partial pressure of the monomeric
molecule calculated in a similar manner as above from the
apparent SnO pressures are also given in table U, together
with the corrected enthalpy chanpe for reactions 2 and 3. (35) Cochram and Förster on the other hand studied the
reaction 2Sn(l) ♦ Ga203(s) ■► 2 SnO(p) ♦ Ga20(g) U
by the Knudsen technique for which they obtained AH^.s
2U9.1 kcal/mole compared to the value AH° 8= 236.3 kcal/
mole expected on the basis of the previously accepted disso-
ciation energy of SnO (D0(SnO)s 13«» kcal/mole). The latter
authors therefore suggest that equilibrium was not established.
In fact, reaction 1 leads to a value D0(SnO)= 126.3 kcal/ * o mole if -to correction is made for the presence of small
amounts of polymers and to D0(SnO)= 126.U kcal/mole when such
correction is made in the same way as above. In the calcu-
lation of the dissociation energy from reaction U, the free
energy function of Ga~0(g) used was the same as that adopted (35) by Cochram and Foster . The heat of formation of Ga20(g)f
AH?gg= -20.7 kcal/mole was calculated from the reactions
11
MpO(s) ♦ 2Ga(8) -► Ga20(R) ♦ Mfr((»)(35) 5
Si02(s) ♦ 2Ga(8) * Ga20(R) ♦ SiO(p^(35) 6
l/2Ga203 ♦ «4/3Ga(s) * Ga20(R)(U5) 7
which, with ^g8>f(Si02)= .217.5(M6), <ubl.298(MR) = 35 6(26>.
AII298 f(Si0R)s ♦26»1 t AH°98 f(Ga203)= -261.05*0.3
lH/;
kcal/mole and the hi^h temperature entropy of Gao0, recently (•♦ 8)
determined by Pankratz and Kelley , pive respectively AH298 fi.Ga20(R^r -20.0, -20.3 and -21.9 kcal/mole. The
average AH2Q8 f(Ga20(R))s -20.7*1.0 kcal/mole was used in
the thermochemical cycle:
AH298
Sn(l)*l/2Ga203(s) * Sn0(K)*l/2Ga20(p) ♦125.3*1,5
l/2Ga20(B> -► Ga(s)*l/M 02(R) ♦ 10.U*0.5
3/H 02(g)^Ga(8) * l/2Ga203(s) -130.5*0.2
Sn(R) * Sn(8) - 72.0«0.5
0(R) ♦ Sn(R) * Sn0(*) -126.»»*1.6
The average thermochemical value, Do(Sn0)= 125.2*1 kcal/
mole is in good agreement with two spectroscopic values. o
One is based on a continuous absorption at 1931*6 A,
attributed to dissociation into Sn (1D0) ♦ 0(3P)(13), which gives Do(Sn0)s 12»».0 kcal/mole . The other is obtained
o from the accurately known convergence limit of the Estate
(13) at 130.9 kcal/mole . Rotational analysis for SnO, as well
as for the analogous molecules, SnS , PbO and PbS
have shown the latter to correlate most presumably with the 3 P. sublevels of both Sn and 0. On substracting the corres-
ponding excitation energies from the converpence limit, one
obtains Do(Sn0)= 125.6 kcal/mole. The agreement between this o
value and the thermochemical one confirms, as in the case
of SnS and PbS that the excited E states of these molecules
12
correlate most probably with the P, sublevels of the corres-
ponding atoms.
As appears in Table 3 the polymer molecules Sn-Oj,
Sn.O. and Sn^O. are all of comparable importance in the pressure
range investigated here. As discussed above, their presence
markedly influences the thermochemical value of the dissociation
enerpy of the monomer calculated from total pressure measurements,
In these polymers, the average SnO-SnO bond as well as
the energy required to abstract one monomer from a given polymer
are all very close to one another (Table IV). The abstraction
energy tends further, as in the other Group IVu-Group VID (3578) polymers » » » towards the heat of sublimation of the monomer,
especially if the latter is calculated for the metastable com-
pound SnO for whicn AH0 .K 000= 71.9 kcal/mole (AH? OftO(Sn0,s)s /UQ\ sub,298 f,298
-67.6 kcal/molev 3').
TABLE «♦, Bond Ctrenghts in the (SnO) Polymers (kcal/mole).
Reaction
Sn202(g) ♦ 2SnO(s)
Sn303(g) ♦ Sn202(g) ♦ SnO(g)
Sn^O^g) -► Sn303(g) ♦ SnO(g)
SnO(s) ♦ SnO(g)
AH298
66.8'<4
69.7tU
71.1tu
71.9t2.5
i
13
^
a o er o»
3 3 3 y O O O H-
W *" MJQ <• * 3*
O 3 fs> 01 r+
Pt rf Qi 3 ft 3 » a CT a 3
M a ^J A tu M
g. CJ H- O 3 « 3 C
(I ft »i r* » » (• » rt
H» H» »♦ A M A «
M •
3 35 M3
* 5* i A r* H«
9Q A rf A a
*1 O O O A O r> 3* Ä
2
a
IS> C/) W 3 3 ^-» <^ M 3Q >^ ««^ ♦ ♦ O cn o A rs>
fsJ ^■N
O *» U) ««•
*^ ♦ A W w 3 ♦ O N> ^"S
w ]q 3 >-/ O ♦ ^N o TQ o \^ s^ ♦ 3Q O ^ A
•O o ^* n %*
H» M H» H» fO U) u> u» -o w >l O u> u> CJ o>
3 30 A
en
to *r
tn r *■ u» • • • • u* ■>! Is» » ro W» H» o»
K» Kl N* ro tr V* tn *■
O ¥- O u> • • • • w CO ^i »-•
M N> O» •
* O
ISJ
I < A
»< A A A rf A »1 f+ M ^ A 0 }-> A J: 00 C (0 wC X
H«
s a to
cn •-• M 3 >«. ^ O IS) ls>
N» to C/J ^s 3 3 A O O >^ rs» NJ ♦ ^^ <-\ O A A O >^ w* o-s ♦ ♦ 30 M »-• v-* ^ ^ i IS» ro M C/> M 3 3 3 O ^s ^■N
^s M M 30 ^x w *^ ♦ 4 ♦ OJ M O 3 3 o O O
ro ^N /"s ^s OQ 30 30 ^* ^x >-«'
»-• M *-> M 1- Ui t*> ■c IS» M U> O O o 00 a> u> a» a» o o a> a»
^> ^N *\ <-» ^N ^>
cr A A ***
A <*•
A
u> IS) *-> N> jr a> • • • • • • m Ul tn U> »-• K) at> N> O OD !-• tr»
«• U» »o Ut l/i ^i • • • • • • M cn 00 •«1 o H" ^1 (O »-' a» ISJ tP
H"4 «J >J ^1 ^j >j ^1 -J
bl U» b> NJ >s> IS» U) u> is» • • • • • • • • • 00|(O oi ^J 00 a» O IS) «J
*-> M M M N» is» ^1 ^1 a» • • • Ck> OD -si I» •» •»
• IS* • •
tn tn U»
3 >
H- rt A 3*
0 < 1 o T X
CO 3 o is»
(0
CO 3 o
30
is» O
N» ^s
CO
c
cr
> 03 r n
A A A
rf A cr
H o
O JO
I »-' o
JO •a ^> CO 3
rt 0 A Hi 1
A rf •+ 3^ C A »1
A
? o H A A rf O A C H M| A 0
1
3 rf O 3*
A
O H« A A 0 O H- Ik rf H- 0 3
o w s«^ 3 A 1
^ «0 ><
IS» ISJ© • (O a» 0O
H» O is» O O <n ^"^ • CO •-• 3 ■» o
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15
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