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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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