Mass Spectrometric Study of the Noble Metal Oxides

8 Mass Spectrometric Study of the

Downloaded by NANYANG TECHNOLOGICAL UNIV on October 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch008

Noble Metal Oxides Ruthenium-Oxygen System

J.

H.

NORMAN,

H . G.

STALEY,

and W . E .

BELL

Gulf General Atomic Inc., John Jay Hopkins Laboratory for Pure and A p p l i e d Science, San Diego, Calif.

Mass spectrometric to

measure

RuO (g),

and RuO(g)

2

kcal./mole

at 1900°K.,

spectively.

Entropies

been determined tively,

Knudsen

4

of

as -17

the

kcal./mole

have been

species

temperature

was

ranges

also observed.

heats of formation

Noble

studied. metal

in the associated

A compilation

of Μ—Ο

metal oxides is

C t u d i e s (3, 29, 31, 33)

entropies

species

gaseous and

re have

respec

The

as measured in transpiration

discrepancies

28.4

at 1950°K.,

of these species

cell studies are found to be in good agreement

^

3

at 1250°K.,

and 85 kcal./mole of formation

used

RuO (g),

to be —20.8, —1.5, and 11.8 e.u.,

in the

RuO (g)

cell methods

heats of formation

oxide Knudsen

while

some

have been

noted.

bond energies for the gaseous

noble

presented.

of the r u t h e n i u m - o x y g e n s y s t e m i n the t e m p e r a -

t u r e r a n g e 1100° to 1800°K. a n d at o x y g e n pressures a r o u n d 1 a t m .

have shown R u 0

2

to b e the i m p o r t a n t c o n d e n s e d phase a n d R u 0

3

and

Ru0

4

to be i m p o r t a n t v a p o r species. D a t a o n the l o w e r gaseous oxides,

Ru0

2

a n d R u O , h a v e not b e e n a v a i l a b l e .

I n t h e present s t u d y , t h e r u t h e n i u m - o x y g e n system has b e e n i n v e s t i g a t e d b y mass s p e c t r o m e t r i c K n u d s e n c e l l m e t h o d s to d e t e r m i n e the i m p o r t a n t v a p o r species a n d associated t h e r m o d y n a m i c s at o x y g e n p r e s sures a r o u n d 1 0

- 4

a t m . b e t w e e n 1150° a n d 2050°K.

T h e r m o d y n a m i c values o b t a i n e d f r o m this s t u d y h a v e b e e n

com

p a r e d w i t h values f r o m t r a n s p i r a t i o n studies. I n a d d i t i o n , a r e v i e w of gaseous

n o b l e m e t a l o x i d e t h e r m o d y n a m i c s as m e a s u r e d u s i n g mass 101

Margrave; Mass Spectrometry in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

102

MASS SPECTROMETRY

spectrometric

K n u d s e n cell techniques

I N INORGANIC

is p r e s e n t e d .

these t h e r m o d y n a m i c s are also c o m p a r e d

CHEMISTRY

Where

possible

w i t h results o b t a i n e d u s i n g

t r a n s p i r a t i o n studies.


Experimental

Procedures

A C o n s o l i d a t e d E l e c t r o d y n a m i c s C o r p . M o d e l 21-703 ( 1 2 - i n c h r a d i u s , 6 0 ° s e c t o r ) mass s p e c t r o m e t e r m o d i f i e d for K n u d s e n c e l l e x p e r i ments w a s e m p l o y e d for this w o r k . T w o different cells w e r e u s e d i n the s t u d y . A t temperatures b e l o w 1500°K., a q u a r t z K n u d s e n c e l l h a v i n g a 0 . 7 - m m . - d i a m e t e r orifice w a s u s e d . T h e c e l l , fitted at the top w i t h a q u a r t z o x y g e n - f e e d t u b e , w a s h e l d i n a close-fitting m o l y b d e n u m c u p a n d w a s c o v e r e d w i t h three layers o f t a n t a l u m . A b o v e 1500°K., a n a l u m i n a c e l l of s i m i l a r d i m e n s i o n s was used. It w a s s i m i l a r i n g e o m e t r y except that the orifice was 1.4-mm. d i a m e t e r a n d the c e l l was f e d w i t h o x y g e n t h r o u g h a n a l u m i n a t u b e i n s e r t e d t h r o u g h the base of the c e l l . T h i s c e l l also w a s m o u n t e d i n s i d e a m o l y b d e n u m c e l l . T h e assemblies w e r e h e a t e d b y e l e c t r o n b o m b a r d m e n t u s i n g t u n g s t e n filaments m o u n t e d near the side of the c e l l a n d a b o v e the c e l l as i n the a u t h o r s ' other studies ( 2 2 ) . O x y g e n flowed into the c e l l t h r o u g h a v i s cous-flow i n l e t f r o m a l a r g e reservoir. O x y g e n pressure i n the c e l l was d e t e r m i n e d b y the pressure i n the r e s e r v o i r a n d the c e l l orifice size. T e m p e r a t u r e s b e l o w 1500°K. w e r e m e a s u r e d b y t w o P t / P t - 1 0 % R h t h e r m o c o u p l e s a t t a c h e d to the i n s i d e of the m o l y b d e n u m c e l l , one n e a r the t o p a n d the other near the b o t t o m . T e m p e r a t u r e s a b o v e 1500°K. w e r e m e a s u r e d b y m a k i n g o p t i c a l p y r o m e t e r sightings of the a l u m i n a c e l l t h r o u g h s m a l l holes i n the outer m o l y b d e n u m c e l l near the t o p a n d b o t t o m of the a l u m i n a c e l l . T e m p e r a t u r e s w e r e e q u a l i z e d b y a d j u s t i n g the p o t e n t i a l a p p l i e d across the t o p - m o u n t e d tungsten filaments. I n b o t h cases the cells w e r e c h a r g e d w i t h J o h n s o n M a t t h e y ( 9 9 . 9 9 5 % p u r i t y ) r u t h e n i u m metal. Results and

Discussion

M a s s peaks a t t r i b u t a b l e to effusate

f r o m the K n u d s e n cells

were

f o u n d to c o r r e s p o n d to 0 , R u \ 0 \ R u O , R u 0 \ R u O . , a n d R u O , a c +

2

+

2

{

+

t

+

c o r d i n g to masses a n d i s o t o p i c ratios. N o other R u - c o n t a i n i n g ions w e r e observed.

A p p e a r a n c e p o t e n t i a l s m e a s u r e d for the r u t h e n i u m - c o n t a i n i n g

ions w e r e 7.7, 8.7, 10.6, 11.2, a n d 12.8 e.v. for, r e s p e c t i v e l y , R u , R u O , +

Ru0

2

+

+

, R u O ; / , a n d R u O / . N e a r v o l t a g e i o n a p p e a r a n c e thresholds the

a b o v e - l i s t e d peaks w e r e b e l i e v e d to b e p a r e n t i o n peaks.

O x y g e n pres-

sure sensitivities p r e s e n t e d b e l o w g e n e r a l l y i n d i c a t e this to be the case. B r e a k s i n the a p p e a r a n c e p o t e n t i a l curves for R u a n d R u O +

+

from R u 0

2

w e r e m e a s u r e d to o c c u r at 13.0 a n d 12.8 e.v., r e s p e c t i v e l y . I n a n e x p e r i m e n t u s i n g the q u a r t z c e l l at 1240°K., the 0

pressure

2

w a s v a r i e d . F i g u r e 1, a p l o t o f the r e s u l t i n g l o g I ( ) + ( a n d I „ o + a n d RU

3

K

2

I R U O ) VS. l o g Io + d a t a , shows a 3 / 2 slope w i t h i n the u n c e r t a i n t y of the +

data.

2

T h i s suggests that the R u O . / i o n (at m/e

152)

is f o r m e d


from


8.

NORMAN ET AL.

Noble

Metal

103

Oxides

Figure 1. Metal oxide ion intensity dependence on 0 ion intensity +

2

R u 0 ( g ) since the m e t a l is the s o l i d state present u n d e r the e x p e r i m e n t a l 3

conditions ( 3 ) .

T h a t is, the i m p o r t a n t v a p o r i z a t i o n r e a c t i o n is Ru(«) + 3/2 0

2

= Ru0 (g).

(1)

3

A t 1190°K., the I o + vs. Io + i s o t h e r m , also i l l u s t r a t e d i n F i g u r e 1, shows R u

3

2

a slope close to 0.5. T h i s indicates that R u 0 ( s ) was the c o n d e n s e d phase 2

i n the 0

pressure r a n g e u s e d a n d that the i m p o r t a n t v a p o r i z a t i o n r e a c -

2

t i o n is R u 0 ( s ) + 1/2 0 2

T h e v a p o r pressure of R u 0 0

2

4

2

= RuOa(g).

over R u 0 ( s ) at 1140°

as d e t e r m i n e d b y B e l l a n d T a g a m i ( 3 )

The R u 0

4

+

2

(2) a n d 10"

4

atm.

s h o u l d b e a r o u n d 10"

8

atm.

i o n was o b s e r v e d i n this w o r k b u t was not intense e n o u g h to

p e r m i t s t u d y of its t h e r m a l b e h a v i o r .



104

MASS SPECTROMETRY

RECIPROCAL

Figure 2.

Dependence

I N INORGANIC

TEMPERATURE ( ° K

of Ru0

+

3

H

Χ

I0 ) 4

intensity functions on

temperature

L o g a r i t h m i c plots of the i o n currents of R u C V times T T~

i/2

CHEMISTRY

a n d times

, / 2

as a f u n c t i o n of r e c i p r o c a l t e m p e r a t u r e are s h o w n i n F i g u r e 2 .

In

t h e e x p e r i m e n t s f r o m w h i c h these d a t a w e r e o b t a i n e d , the i n t e n s i t y of the 0

2

+

f o r m e d f r o m the K n u d s e n c e l l effusate w a s set at a constant h i g h

l e v e l . U n d e r these c o n d i t i o n s , b e c a u s e of the ΖΓ p r o p o r t i o n a l i t y to p r e s sure, the q u a n t i t i e s Ι „ ο κ

3

+

Γ

1 Λ

a n d I R „ O T " , r e s p e c t i v e l y , are p r o p o r t i o n a l 3

+

,

, / 2

to t h e e q u i l i b r i u m constants for R e a c t i o n s 1 a n d 2 . F r o m slopes of lines d r a w n t h r o u g h the t w o sets of d a t a i n F i g u r e 2 , w e c a l c u l a t e ΔΗΙ Γ>« 2

5 4 k c a l . / m o l e for Reaction 2 and Δ Η

1 2 5

ο —

=

— 1 7 k c a l . / m o l e for R e a c t i o n

1. T h e s e v a l u e s are i n g o o d agreement w i t h ΔΗ »ο 12

values of + 5 4 . 7 a n d

— 1 3 . 9 k c a l . / m o l e c a l c u l a t e d for the r e s p e c t i v e reactions f r o m d a t a r e p o r t e d b y Schâfer, S c h n e i d e r e i t , a n d G e r h a r d t ( 3 1 ) , a n d Δ Η

1 2 Γ

» ο values

of + 5 1 . 6 a n d — 1 7 . 0 k c a l . / m o l e c a l c u l a t e d for the respective

reactions

from data reported b y Bell and T a g a m i ( 3 ) . U s i n g the a l u m i n a c e l l , t h e R u O ( g ) s

species c a n b e s u p p r e s s e d b y

g o i n g to h i g h e r t e m p e r a t u r e s , b u t m o r e i m p o r t a n t , the pressures of the


8.

NORMAN E T AL.

Noble

Metal

l o w e r oxides c a n b e increased.

105

Oxides

A t h i g h e r temperatures a n d a n o m i n a l

electron e n e r g y of 20 e.v., the i n t e n s i t y of the R u O / s i g n a l f r o m t h e K n u d s e n c e l l effusate was f o u n d to d e p e n d d i r e c t l y o n the square of t h a t p o r t i o n of the a t o m i c O " s i g n a l a t t r i b u t a b l e to K n u d s e n c e l l effusate. T h i s suggests t h a t R u 0

2

+

is a p a r e n t i o n a n d c a n b e u s e d i n d e s c r i b i n g

the v a p o r i z a t i o n of R u 0 ( g ) i n s t u d y i n g the r e a c t i o n 2

Ru(s) + 0 - ^ R u 0 ( g ) . Downloaded by NANYANG TECHNOLOGICAL UNIV on October 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch008

2

(3)

2

A t a n o m i n a l e l e c t r o n energy of 10 e.v., the R u O

+

signal intensity was

f o u n d to b e p r o p o r t i o n a l to the i n t e n s i t y of the s h u t t e r a b l e 0 ; therefore, +

RuO

+

Ru

w e r e f o u n d to h a v e the same 0

+

is a p a r e n t i o n at this electron energy. A t 20 e.v., the R u O a n d the +

1 3 6 ) , suggesting R u O ments of R u 0 ( g ) . 2

+

( a t m/e

d e p e n d e n c e as the R u 0

2

120) a n d R u

+

( a t m/e

+

2

( at

m/e

102) w e r e f r a g -

T h e v a p o r i z a t i o n r e a c t i o n for R u O ( g )

is

Ru(s) + l / 2 0 - > R u O ( g ) .

(4)

2

A t 10 e.v., the R u p e a k is f o u n d to be i n d e p e n d e n t of the 0 +

+

signal and

thus represents the d i r e c t v a p o r i z a t i o n of r u t h e n i u m m e t a l , Ru(s) - > R u ( g ) . O b s e r v a t i o n s of the v a r i a t i o n i n intensities of the R u 0 RuO

+

a n d R u at 10 e.v. w i t h 0 +

Figure 3.

+

(5) 2

+

at 20 e.v. a n d the

i n t e n s i t y are i l l u s t r a t e d i n F i g u r e 3.

Metal ion intensity dependence on 0 intensity at 2045° K.

+

ion



106

MASS SPECTROMETRY I N INORGANIC

4.8

5.0

52

5.4

5.6

CHEMISTRY

5.8

RECIPROCAL TEMPERATURE(°KxI0 ) 4

Figure 4.

Dependence

of ruthenium species ion intensity on temperature

I f the intensities of the R u , R u O , a n d R u 0 +

+

2

+

function

ions are s t u d i e d as a

f u n c t i o n of t e m p e r a t u r e at a p p r o p r i a t e electron energies a n d at a h i g h , constant flux of o x y g e n t h r o u g h the c e l l ( P o

2

>>

P o ) , the heats of

v a p o r i z a t i o n o f the p a r e n t species of these ions m a y b e d e t e r m i n e d f r o m the slopes of i o n i n t e n s i t y functions vs. r e c i p r o c a l t e m p e r a t u r e . E x a m p l e s of these d e t e r m i n a t i o n s are p r e s e n t e d i n F i g u r e 4. F o u r s u c h d e t e r m i n a tions w e r e m a d e f o r e a c h of these species, r e s u l t i n g i n values of 28.4 ± 1 . 0 , 85 ± 5 , a n d 152 ± 3 k c a l . / m o l e for R e a c t i o n s 3, 4, a n d 5, r e s p e c t i v e l y , i n the t e m p e r a t u r e ranges 1 7 4 0 ° - 2 0 4 0 ° K . , 1 8 7 0 ° - 2 0 2 0 ° K . , a n d

1900°-

2050°K. T o estimate the p a r t i a l pressures of the gaseous species R u O , R u 0 , 2

RuOs, R u 0 , O, and 0 4

2

present i n these systems, a pressure o f


Ru(g)

8.

Noble

NORMAN ET AL.

Metal

107

Oxides

w a s o b t a i n e d f r o m the studies of P a n i s h a n d R e i f (26) Walker and Plante ( β )

a n d of C a r r e r a ,

( t h e P a u l e a n d M a r g r a v e (27)

values differed

s l i g h t l y ) a n d u s e d as a s t a n d a r d i n the m e t h o d d e s c r i b e d b y I n g h r a m a n d D r o w a r t (13).

I n this m e t h o d , t o t a l i o n i z a t i o n cross sections a c c o r d

i n g to O t v o s a n d Stevenson (24)

were employed along w i t h multiplier

gains i n v e r s e l y p r o p o r t i o n a l to the square root of the m o l e c u l a r w e i g h t a n d the a p p e a r a n c e potentials r e p o r t e d i n this s t u d y a n d b y K i s e r

(16).


U s i n g these d a t a , e n t r o p y values for R e a c t i o n s 1, 3, a n d 4 w e r e c a l c u l a t e d to b e —20.8, —1.5, a n d 11.8 e.u., r e s p e c t i v e l y , i n the t e m p e r a t u r e ranges s t u d i e d . T h e heat of v a p o r i z a t i o n of R u 0 ( g ) ( —45.4 k c a l . / m o l e ) 4

f r o m the studies of B e l l a n d T a g a m i (3)

leads to a n e n t r o p y of

the

vaporization reaction, Ru(s) + 2 0 - » R u 0 ( g ) , 2

of —33.6 e.u. f r o m the e x p e r i m e n t a l R u 0 166 a n d a c o r r e s p o n d i n g 0

2

(6)

4

4

+

i n t e n s i t y m e a s u r e d at

m/e

i o n intensity.

+

Review of Noble Metal Oxide Vaporization

Data

O x i d e t r a n s p i r a t i o n studies h a v e b e e n m a d e b y A l c o c k a n d H o o p e r (2)

( A H ) , for the metals P t , P d , R h , I r , a n d R h . O t h e r n o b l e m e t a l oxide

t r a n s p i r a t i o n studies i n c l u d e a R u s t u d y b y B e l l a n d T a g a m i (3) a R u s t u d y b y Schâfer, T e b b e n , a n d G e r h a r d t (33) Schâfer a n d H e i t l a n d (30)

( S H ) , K u r i a k o s e a n d M a r g r a v e (17)

a n d C o r d f u n k e a n d M e y e r (8) T e b b e n (32)

(ST).

(BT);

( S T G ) ; I r studies b y

G r i m l e y , B u r n s , a n d I n g h r a m (10)

vestigated the gas phase O s 0

4

(KM),

( C M ) ; a n d a P t s t u d y b y Schâfer a n d —> O s 0

3

+

1/2 0

2

( G B I ) have i n -

equilibrium in a K n u d -

sen c e l l mass s p e c t r o m e t r i c a l l y , a n d N o r m a n , Staley, a n d B e l l (20, 21, 22, 23)

h a v e s t u d i e d the oxides of R u , I r , R h , P t , a n d P d u s i n g mass spec-

t r o m e t r i c K n u d s e n c e l l techniques. a n d N i k o l s k i i a n d R y a b o v (19) information.

Schâfer, T e b b e n , a n d G e r h a r d t

(33)

h a v e presented r e v i e w s of some of this

T h e heats of f o r m a t i o n f r o m these studies are g i v e n i n

T a b l e I., w h e r e the c o m p i l a t i o n of C o u g h l i n ( 9 )

(C)

w a s u s e d to d e -

scribe the heat of f o r m a t i o n of O s 0 ( g ) . I n T a b l e I a l l of the heats h a v e 4

b e e n e x t r a p o l a t e d to 1500°K. b y e m p l o y i n g , i n the absence of s t r u c t u r a l i n f o r m a t i o n o n the oxides, H - H o d a t a f r o m the J A N A F tables (14) T

the a p p r o p r i a t e gaseous tungsten oxide K e l l e y s (15)

Os0

4

except for

tetroxides,

for

where

heat c a p a c i t y f o r m u l a was e x t r a p o l a t e d to 1500°K.

T h e error m a d e b y u s i n g the heat capacities of these gaseous c o m p o u n d s to describe the same M O . , . ( g ) species for other metals at the

moderate

temperatures i n v o l v e d s h o u l d b e rather s m a l l , except w h e r e the q u e s t i o n of l i n e a r i t y of the M O » ( g ) molecules L

is i n v o l v e d — a 1

v a r i a n c e . A p p r o p r i a t e d a t a for the c o n d e n s e d

cal./deg.-mole

metals a n d o x y g e n


were

108


t a k e n f r o m the J A N A F tables (14), et al. (12).

The R u 0

2

CHEMISTRY

Stull and Sinke (35), and H u l t g r e n ,

d a t a of A l c o c k a n d H o o p e r (2)

were

corrected

to t a k e i n t o a c c o u n t that R u 0

2

their conditions.

was t a k e n as the gaseous r h o d i u m oxide

Also, R h 0

2

w a s the c o n d e n s e d phase present u n d e r

present i n t h e i r studies. T h e d a t a of K u r i a k o s e a n d M a r g r a v e (17) t a k e n to a p p l y to the r e a c t i o n I r ( s ) +


Table I.

Reference°

Os

GBI C NR Β

Ir

2

-»

were

IrO (g). s

Heats of Formation of the Gaseous Noble Metal Oxides at 1 5 0 0 ° K . (kcal./mole)

Element

Ru

3/2 0

NSB AH STG BT NR Β NSB AH CM SH KM Β

MO(g)

M0 (g) 2

b

M0 (g)

Present (46) (39 ± 20) 86.7 ± 5

29.7 ± 1

MO (g)

3

k

-11.8 ± 1 -81.5 (-25) -17.0 ± 2 -16.5 -13.5 -16.7 ± 2

(40) (47 ± 15) Present

49.7 ± 1.0

-42.8 -45.4 ± 3 -43.1 ± 2

6.2 ± 1.5 4.8 4.2 4.0 7.1 ± 1.9

(48 ± 15)

Rh

NSB AH Β

91 ± 5

42.0 ± 2.0 45.6 ± 0.6 (27 ± 20)

Pt

NSB AH ST Β

102.3 ± 5

37.8 ± 2.3 39.4 ± 0.3 39.9 (43 ± 8)

Pd

NSB Β

80.0 ± 1.0 (41 ± 25)

" Authors' initials indicate pertinent works. Values in parentheses are estimated. h

T h e agreement of the e x p e r i m e n t a l values r e p o r t e d i n T a b l e I is i n d e e d g r a t i f y i n g . It w o u l d seem to g i v e c r e d e n c e to a l l of the d a t a r e p o r t e d . T h e agreement b e t w e e n the mass s p e c t r o m e t r i c a n d the t r a n s p i r a t i o n results s t r o n g l y suggests t h a t the same species are b e i n g e x a m i n e d i n the t w o different m e t h o d s , a n d other e v i d e n c e substantiates


8.

NORMAN ET AL.

Noble

Metal

109

Oxides

this. T h a t is, the mass s p e c t r o m e t r i c studies h a v e not r e v e a l e d p o l y m e r s b u t i n d i c a t e t h e presence of the m o n o m e r species a s s u m e d i n the t r a n s p i r a t i o n studies. W h i l e the o x y g e n pressures u s e d i n these t w o types of studies are q u i t e different, this has little to d o w i t h the P M O / P M O J , ratios X

—i.e., i f Ρ Μ Ο Χ

V

w e r e i m p o r t a n t i n the t r a n s p i r a t i o n studies, this species

υ

p r o b a b l y w o u l d h a v e been d e t e c t e d mass s p e c t r o m e t r i c a l l y . It appears, t h e n , t h a t a l l these studies, w i t h the possible exception of the Ir studies Downloaded by NANYANG TECHNOLOGICAL UNIV on October 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch008

of K u r i a k o s e a n d M a r g r a v e (17),

i n d i c a t e o n l y the presence of

mono-

m e r i c v a p o r species of the n o b l e m e t a l oxides. O n e m i g h t q u e s t i o n w h e t h e r t r a n s p i r a t i o n studies are a p p r o p r i a t e for systems as c o m p l e x as these.

N o t e , h o w e v e r , that the possible p r e s

ence of several species i n the t r a n s p i r a t i o n studies does not seem to h a v e a d v e r s e l y affected the results. F o r instance, B e l l a n d T a g a m i o b t a i n e d thermodynamic information on both R u 0

8

and R u 0

4

by interpreting

r u t h e n i u m transport to b e c a u s e d b y b o t h species. Brewer (5) oxides at 0 ° K .

( B ) has e s t i m a t e d the dissociation energies for the d i I n T a b l e I., his values h a v e b e e n c o n v e r t e d into heats of

f o r m a t i o n at 1500°K. f o r c o m p a r i s o n w i t h the e x p e r i m e n t a l values, w h e r e a v a i l a b l e . W h i l e there are discrepancies u p to 20 k c a l . / m o l e , B r e w e r s estimates are w i t h i n his stated uncertainties. T h e heat of f o r m a t i o n d a t a g i v e n i n T a b l e I c a n b e c o n v e r t e d i n t o b o n d e n e r g y i n f o r m a t i o n . T a b l e I I presents the heats of f o r m a t i o n of the gaseous oxides p e r oxygen a t o m i c oxygen.

a t o m at 1500°K. f r o m gaseous m e t a l a n d

F o r self-consistency, the K n u d s e n c e l l values are u s e d

w h e r e a v a i l a b l e . D a t a u s e d i n c o n s t r u c t i n g this t a b l e i n c l u d e the heat of d i s s o c i a t i o n of o x y g e n molecules at 1500°K. as p r e s e n t e d i n the J A N A F tables (14)

a n d heats of v a p o r i z a t i o n of the n o b l e metals at 1500°K. as

g i v e n b y S t u l l a n d S i n k e ( 3 5 ) , H u l t g r e n , et al. (12), p e r i m e n t a l d e t e r m i n a t i o n s (6, 22, 25, 26, 27).

a n d / o r recent ex

T h e s e selected heats of

v a p o r i z a t i o n are also i n c l u d e d i n T a b l e I I . O n e n o t e w o r t h y o b s e r v a t i o n c o n c e r n i n g the b o n d energies p r e s e n t e d i n T a b l e I I is t h a t t h e y e x h i b i t a degree of agreement w i t h a n a d d i t i v i t y rule.

T h e system w i t h the most extensive p e r t i n e n t d a t a w o u l d b e the

r u t h e n i u m oxides. I n this case, 127 k c a l . are associated w i t h the b o n d i n g of the first g r a m a t o m of o x y g e n , w h i l e o n l y 89 k c a l . are associated w i t h the f o u r t h — 0 . 7 of the v a l u e for the first g r a m a t o m . W h i l e this does not i n d i c a t e c o m p l e t e agreement w i t h the a d d i t i v i t y r u l e , this decrease f r o m 1 to 0.7 of the first b o n d energy across the w h o l e series seems a r a t h e r s m a l l change

a n d indicates near a p p l i c a b i l i t y of the r u l e .

Observed

deviations for O s , R u , a n d I r are i n the o r d e r of d e c r e a s i n g b o n d strength w i t h a d d i t i o n a l b o n d s , w h i l e R h a n d P t seem to e x h i b i t a reverse t r e n d b y a c c e p t i n g a s e c o n d g r a m a t o m of o x y g e n s o m e w h a t m o r e e n e r g e t i c a l l y t h a n the

first.


110


T a b l e II.


Element Os Ru Ir Rh Pt Pd

CHEMISTRY

Heats of Formation per Oxygen A t o m of the Noble Metal Gaseous Oxides at 1 5 0 0 ° K . from Atomic Oxygen and M ( g ) (—kcal./mole) Reference

M(g)

(6, 26) This study {25,27) (12, 35) (12, 35) (22)

185 152 156 131 134 89

MOJ2

127

122 114 105 109

101 92 70

MOJ4

MOJ3

MO

127(C) 110

145 ( G B I ) 117 111

N i k o l s k i i a n d R y a b o v ( 19 ) q u e s t i o n the G r i m l e y , B u r n s , a n d I n g h r a m v a l u e u s e d b y Schâfer, T e b b e n , a n d G e r h a r d t (33)

(10)

c a l c u l a t e —66.2 k c a l . / m o l e for Δ Η °

2 9 8

of O s O n ( g ) .

i n t h e i r r e v i e w to

T h i s v a l u e is r e l a t e d

to the degree of d e p a r t u r e f r o m a d d i t i v i t y of O s — Ο b o n d s .

Indeed, the

G B I 1 8 - k c a l . / m o l e difference i n o x y g e n average b o n d energies for the t w o h i g h e r oxides of o s m i u m p r e s e n t e d i n T a b l e I I is l a r g e , b u t i t is diffi c u l t to s h o w that i t is too l a r g e , a n d i t seems u n n e c e s s a r i l y p r e c l u s i v e to argue this q u e s t i o n f r o m c o n d e n s e d state t h e r m o d y n a m i c s .

It seems

best to accept this a p p a r e n t l y excellent d e s c r i p t i o n of the O s O s — 0 — 2

Os0

4

e q u i l i b r i u m b y r e p o r t i n g the G B I heat of f o r m a t i o n of

m i n u s that of O s O ( g ) . s

Δ Η ° 2 9 8 for O s 0

2

N i k o l s k i i a n d R y a b o v (19)

Os0 (g) 4

h a v e also p r e d i c t e d

a n d R u 0 . T h e r e is no e x p e r i m e n t a l i n f o r m a t i o n c o n 2

cerning O s 0 , and their O s 0 2

difficulties as is t h e i r O s 0

3

2

estimate c e r t a i n l y is subject to the same

estimate. T h e i r R u 0

estimate, c o n v e r t e d to

2

1 5 0 0 ° C , w o u l d b e 9 k c a l . / m o l e h i g h e r t h a n the e x p e r i m e n t a l v a l u e . T h e n o b l e metals are p r e s e n t e d i n T a b l e s I a n d I I essentially i n the o r d e r of the s t a b i l i t y of t h e i r oxides a n d t h e i r heats of v a p o r i z a t i o n . T h e r e l a t i o n of these properties a n d t h e i r p o s i t i o n i n the p e r i o d i c t a b l e is evident. A l t h o u g h the n o b l e m e t a l o x i d e e x p e r i m e n t a l heats of

formation

f r o m the mass s p e c t r o m e t r i c a n d t r a n s p i r a t i o n t e c h n i q u e s are i n g o o d agreement, w h e r e t h e y c a n b e cross-checked, the v a p o r pressures deter m i n e d u s i n g the t w o m e t h o d s differ c o n s i d e r a b l y .

T o demonstrate this

p r o b l e m , a l l of the c o m p a r a b l e cases are p r e s e n t e d i n T a b l e I I I . W h i l e several of the values u s e d cannot b e c o n s i d e r e d w e l l e s t a b l i s h e d , t w o cases, I r O * a n d P t 0 , s t a n d o u t as reasonable tests. T h r e e t r a n s p i r a t i o n 2

studies, w h e n e x t r a p o l a t e d , g i v e 1.7 ( ± 0 . 2 ) pressure at 2033°K. a n d 1 a t m . 0

2

X 10" a t m . as the I r 0 3

3

vapor

pressure i n the presence of the m e t a l .

T h e c o r r e s p o n d i n g v a l u e f r o m the mass s p e c t r o m e t r i c m e t h o d is 3.5 10" , a factor of five l o w e r . 4

χ

I n the p l a t i n u m oxide t r a n s p i r a t i o n studies

c i t e d , the e x t r a p o l a t e d v a p o r pressure of P t 0 ( g ) 2

i n 1 a t m . o x y g e n over

the m e t a l at 2018°K. was d e t e r m i n e d to b e 1.0 ( ± 0 . 1 ) X 10" a t m . T h e 4


8.

Noble

NORMAN ET AL.

Metal

111

Oxides

mass s p e c t r o m e t r i c s t u d y leads to a v a l u e of 8.5 X 10" a t m . , a f a c t o r of 6

11 s m a l l e r . T h e R u 0

3

case is not q u i t e as clear. T h e t w o t r a n s p i r a t i o n

results at 1779°K. a n d 1 a t m . 0 c o m p a r e d w i t h 4.1 X

2

o v e r t h e m e t a l g i v e 4.8 (d=3)

χ

10"

2

10~ o b t a i n e d mass s p e c t r o m e t r i c a l l y i n this case, 3

a f a c t o r of f o u r to 20 l o w e r . I n the single c o m p a r i s o n of R h 0

2

pressures,

the mass s p e c t r o m e t r i c v a l u e is c o n s i d e r a b l y l o w e r t h a n i n t h e other cases. I n the P d O case, n o r e a l c o m p a r i s o n c a n b e m a d e except to say Downloaded by NANYANG TECHNOLOGICAL UNIV on October 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0072.ch008

t h a t A l c o c k a n d H o o p e r ( 2 ) b e l i e v e , b a s e d o n t h e i r t r a n s p i r a t i o n studies, that P d O pressures s h o u l d b e h i g h e r t h a n w e r e m e a s u r e d s p e c t r o m e t r i cally b y N o r m a n , Staley, a n d B e l l (22).

T h e one r e m a i n i n g c o m p a r i s o n

also is not w e l l e s t a b l i s h e d since, i n the case of R u 0 ( g ) , n o mass spectro 4

m e t r i c heats w e r e o b t a i n e d a n d the t r a n s p i r a t i o n results w e r e b a s e d o n a m i n o r species d e t e r m i n a t i o n . I n this s i n g l e case, h o w e v e r , t h e mass s p e c t r o m e t r i c pressures w e r e h i g h e r t h a n the t r a n s p i r a t i o n pressures. Table I I I .

Noble Metal Oxide Comparative Vapor Pressures (atm.)

Gaseous

Mass Spec. (NSB)

Species

T(°K.)

Ru0

1729

4

T JT ^ M0

0

Transpiration T

a

(2 Χ 10" ) max 2

M

0

J ?

0

^

Transpiration a

Mass Spec.

3.5 Χ 10" ( S T G ) 1.1 Χ 10~ ( B T )

(0.5-0.05)

6.9 X 10" ( S T G ) 2.7 Χ ΙΟ" ( B T )

20-5

1.6 Χ 10" ( A H ) 1.6 Χ ΙΟ" ( S H ) 1.9 X I O - ( C M )

5

1.4 Χ 10" ( A H )

50

8.9 Χ 10" ( A H ) 1.1 Χ 10" ( S T )

13-10

(4 X 10"«) ( A H )

(40)

3

3

RuO

1729

s

4.1 Χ 10"

3

2

2

Ir0

2033

3

3.5 Χ 10"

4

3

3

3

Rh0 Pt0

2

2

2000

3 Χ ΙΟ"

2018

8.5 X 10"

6

4

6

5

4

PdO

1900

1.0 X 10"

6

* Po = atm. 2

T h e s e results, t h e n , suggest that g e n e r a l l y a n u n d e r e s t i m a t i o n of m e t a l o x i d e pressures is m a d e i n the mass s p e c t r o m e t r i c studies or a n o v e r e s t i m a t i o n is m a d e i n the t r a n s p i r a t i o n studies. I t is difficult to b e l i e v e that i n the t r a n s p i r a t i o n m e t h o d mass t r a n s p o r t was grossly o v e r e s t i m a t e d or d i f f u s i o n a l effects w e r e not p r o p e r l y a c c o u n t e d for.

For

reasons m e n t i o n e d p r e v i o u s l y , i t is also difficult to b e l i e v e that p o l y m e r s cause the differences i n the t w o m e t h o d s , a l t h o u g h u n d e r u n u s u a l c i r cumstances M 0 x

2

c o u l d b e c o n s i d e r e d to b e M 0

s t u d y , g i v i n g excessively h i g h M 0

2

2

i n the t r a n s p i r a t i o n

pressures. It seems m u c h m o r e l i k e l y


112

MASS SPECTROMETRY

I N INORGANIC

CHEMISTRY

t h a t t h e c r u x of this p r o b l e m is i n c o n v e r t i n g mass s p e c t r o m e t r i c i o n i n tensities to c e l l species pressures. I n d e e d , questions c o n c e r n i n g the v a l i d i t y of e m p l o y i n g the cross sections of O t v o s a n d Stevenson (24)

and

t h e a d d i t i v i t y of these q u a n t i t i e s h a v e b e e n b r o u g h t u p ( 7 , 1 8 , 28). f o r d (34)

Staf

has p r o p o s e d u s i n g cross sections d e r i v e d f r o m G r y z i n s k i ' s

c a l c u l a t i o n a l scheme.

I n s e v e r a l studies ( I , 4, 36)

(11)

attempts w e r e m a d e

to a v o i d the use of c a l c u l a t e d cross sections.


S o m e p r o b l e m s are associated w i t h pressure e s t i m a t i o n u s e d i n the mass s p e c t r o m e t r i c m e t h o d .

M a s s s p e c t r o m e t r i c i o n intensities are c o n

v e r t e d to pressures or e q u i l i b r i u m constants b y e m p l o y i n g ratios of i n tensities. O n e e i t h e r considers a d i m e n s i o n l e s s pressure r a t i o as a n e q u i l i b r i u m constant o r establishes the pressure of a species of interest b y c o m p a r i s o n w i t h a n a v a i l a b l e pressure s t a n d a r d . F o r the n o b l e m e t a l M0

gaseous

2

=

PMO /PO 2

2

species,

ΚΙ*ιοζ/Ιθ2

it was

indeed

sionless reactions s u c h as M ( s ) + the 1 / 2 0

2

reasonable

to

use

the

K

P

=

r e l a t i o n s h i p . I n other cases, one c a n u t i l i z e d i m e n 2 0

2

-» M 0

3

+

Ο w h e r e , i n a sense,

- » Ο e q u i l i b r i u m is e m p l o y e d to c a l i b r a t e the system.

Often

the n o b l e m e t a l pressure m a y b e u s e d as a c a l i b r a t i n g agent, or s o m e a d d i t i v e to the s y s t e m , s u c h as silver, m a y be u s e d i n the c a l i b r a t i o n . W h i l e these p r o c e d u r e s a p p e a r s o u n d a n d b e y o n d q u e s t i o n , t h e y d o n o t c i r c u m v e n t the necessity of e s t i m a t i n g r e l a t i v e cross sections a n d detector sensitivities. O n e is often c o n f r o n t e d

w i t h the p r o b l e m of the e x p e r i m e n t a l l y

i n d e t e r m i n a t e q u e s t i o n of h o w efficiently ions of a p a r t i c u l a r t y p e c a n b e m a d e f r o m specific n e u t r a l species. and

D r o w a r t (13)

T h e method described by Inghram

for e s t i m a t i n g ratios of t o t a l i o n i z a t i o n efficiencies

accepts O t v o s a n d Stevenson's

(24)

t o t a l i o n i z a t i o n cross sections a n d

a d d i t i v i t y of these cross sections. T h e m e t h o d also accepts a l i n e a r r e l a t i o n s h i p b e t w e e n cross section a n d i o n i z i n g e n e r g y of the e x c i t i n g elec trons a b o v e a t h r e s h o l d v a l u e to p r o v i d e these ratios of t o t a l i o n i z i n g efficiencies.

S p e c i f i c c r i t i c i s m s o f the u n i v e r s a l i t y o f this f o r m u l a m a y

be directed at: 1. T h e t o t a l a t o m i c cross section values themselves. 2. A d d i t i v i t y of these values to get m o l e c u l a r cross sections. 3. T h e s i m p l i c i t y of the a s s u m e d a p p r o a c h t o w a r d the m a x i m u m cross s e c t i o n a l v a l u e s as a f u n c t i o n of e l e c t r o n energy. 4. T h e a p p l i c a t i o n of these values to cases w h e r e u n d e t e c t e d f r a g m e n t a t i o n m a y b e significant. Q u e s t i o n s of d i v i s i o n of t r a n s f e r r e d e n e r g y i n t o e x c i t a t i o n a n d i o n i z a t i o n , e l e c t r o n i c s t r u c t u r e of atoms a n d m o l e c u l e s , a n d other b a s i c p r o p erties are i n v o l v e d . F o r instance, Stafford's (34)

p r o p o s e d cross sections

differ i n m a n y cases f r o m n o r m a l i z e d O t v o s a n d Stevenson v a l u e s b y a factor of t w o or three.

H i s values s h o w d e v i a t i o n f r o m e x p e r i m e n t a l l y


8.

NORMAN ET AL.

Noble

Metal

113

Oxides

d e t e r m i n e d cross sections, a l t h o u g h not as often as d o the n o r m a l i z e d O t v o s a n d Stevenson values. L e t us c o n s i d e r the situation for the n o b l e m e t a l o x i d e measurements. I o n i z a t i o n cross sections for o x y g e n m o l e c u l e s as e m p l o y e d

i n these

studies seem to agree w i t h e x p e r i m e n t a l values—i.e., the r a t i o of 0

2

to M

cross sections at the voltages e m p l o y e d is i n l i n e w i t h e x p e r i m e n t a l cross section ratios of 0

2

a n d H g at the e m p l o y e d voltages. I f H g cross section


a g r e e m e n t c a n b e t a k e n as i n d i c a t i n g n o b l e m e t a l agreement, t h e n the pressure d i s c r e p a n c y p r o b l e m seems to b e c o n c e r n e d w i t h the i o n i z a t i o n cross section o f M O * c o m p a r e d w i t h M a n d / o r u n d e t e c t e d f r a g m e n t a t i o n of M O * .

O n e or b o t h m i g h t w e l l b e the root of the pressure d i s c r e p a n c i e s

p r e s e n t e d here. It appears that a l t h o u g h Stafford's (34)

a p p r o a c h c o u l d h e l p the

cross section p r o b l e m s o m e w h a t , c o n s i d e r a b l e d o u b t w i l l r e m a i n e v e n after s u c h a n analysis of cross sections of n o b l e m e t a l oxides. T h e o r e t i c a l l y , t h e f r a g m e n t a t i o n p r o b l e m s h o u l d not b e severe since one s h o u l d r e c o g n i z e fragments a n d account for t h e i r presence. H o w e v e r , i n the r e a l case, t h e p o s s i b i l i t y of t r a n s m i s s i o n p r o b l e m s o f ions b o r n w i t h h i g h k i n e t i c e n e r g y ( n o t c o n s i d e r e d i n this s t u d y ) a n d the i n a b i l i t y to r e c o g n i z e f r a g m e n t peaks b u r i e d u n d e r l a r g e system peaks cause c o n s i d e r a b l e u n c e r t a i n t y r e g a r d i n g the degree of f r a g m e n t a t i o n . A d d e d to this u n c e r t a i n t y , m u l t i p l i e r sensitivities are g e n e r a l l y e s t i m a t e d . A c c o r d i n g l y , t h e n , i t seems that mass s p e c t r o m e t r i c pressures u s i n g estimated values s h o u l d b e t r e a t e d w i t h some c a u t i o n . T h e p u r p o s e of this p o r t i o n of the p a p e r is not to i m p l y that mass s p e c t r o m e t r i c K n u d s e n c e l l studies p r o v i d e i n a d e q u a t e t h e r m o d y n a m i c s , b u t to p o i n t out that some c a u t i o n s h o u l d b e e m p l o y e d w h e n u s i n g mass s p e c t r o m e t r i c a l l y d e t e r m i n e d e q u i l i b r i u m constants b a s e d o n e s t i m a t e d cross sections, etc. T h e authors are c o n v i n c e d that, i n g e n e r a l , m e a s u r e ments of this t y p e p r o v i d e a n d w i l l c o n t i n u e to p r o v i d e the best a v a i l a b l e e x p e r i m e n t a l h i g h t e m p e r a t u r e gaseous system t h e r m o d y n a m i c s .

The

authors are also c o n v i n c e d , because of the uncertainties associated w i t h t h e e q u i l i b r i u m constant " e s t i m a t i o n , " that g o o d mass s p e c t r o m e t r i c a l l y d e t e r m i n e d second l a w heats h a v e c o n s i d e r a b l e m e r i t w h e n c o m p a r e d w i t h t h i r d l a w heats for c o m p l e x systems as r e p o r t e d here.

Literature

Cited

(1) Ackermann, R. J., Rauh, E. G., Thorn, R. J., Cannon, M. C., J. Phys. Chem. 67, 762 (1963). (2) Alcock, C. B., Hooper, G. W., Proc. Roy. Soc. (London) A254, 551 (1960). (3) Bell, W. E., Tagami, M., J. Phys. Chem. 67, 2432 (1963). (4) Berkowitz, J., Marquart, J. R.,J.Chem. Phys. 39, 275 (1963).



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MASS SPECTROMETRY IN INORGANIC CHEMISTRY

(5) Brewer, L., U. S. At. Energy Comm. Rept. UCRL-8356, Univ. of Calif. Radiation Lab., July 1958. (6) Carrera, Ν. J., Walker, R. F., Plante, Ε. R., J. Res. Natl. Bur. Std. 68A, 325 (1964). (7) Cooper, J. L., Pressley, G. Α., Stafford, F. E., J. Chem. Phys. 44, 3946 (1966). (8) Cordfunke, Ε. P. H., Meyer, G., Rec. Trav. Chim. 81, 495 (1962). (9) Coughlin, J. P., U. S. Bur. Mines Bull. 542 (1954). (10) Grimley, R. T., Burns, R. P., Inghram, M . G., J. Chem. Phys. 33, 308 (1960). (11) Gryzinski, M., Phys. Rev. 138, A305, A322, A336 (1965). (12) Hultgren, R., Orr, R. L., Anderson, P. D., Kelley, Κ. K., "Selected Values of Thermodynamic Properties of Metals and Alloys," John Wiley and Sons, New York, 1963. (13) Inghram, M. G., Drowart, J., in Proc. Intern. Symp. High Temp. Technol., Asilomar Conf. Grounds, Calif., October 1959 (1960). (14) JANAF Thermochemical Tables, The Dow Chemical Co., Midland, Mich., 1963. (15) Kelley, K. K., U. S. Bur. Mines, Bull. 584, U. S. Govt. Printing Office, 1960. (16) Kiser, R., U. S. At. Energy Comm. Rept. TID-6142, University of Kansas, June 20, 1960. (17) Kuriakose, A. K., Margrave, J. L., "Kinetics of Oxidation of Iridium at High Temperature," Summary Tech. Rept. No. 2, Rice University (no date). (18) Lampe, F. W., Franklin, J. L., Field, F. H., J. Am. Chem. Soc. 79, 6129 (1957). (19) Nikolskii, A. B., Ryabov, A. N., Zh. Neorgan. Khim. 10, 1 (1965). (20) Norman, J. H., Staley, H. G., Bell, W. E., J. Chem. Phys. 42, 1123 (1965). (21) Norman, J. H., Staley, H. G., Bell, W. E.,J.Phys. Chem. 68, 662 (1964). (22) Ibid., 69, 1373 (1965). (23) Ibid., 71, 3686 (1967). (24) Otvos, J. W., Stevenson, D. P.,J.Am. Chem. Soc. 78, 546 (1956). (25) Panish, M. B., Reif, L., J. Chem. Phys. 34, 1915 (1961). (26) Ibid., 37, 128 (1962). (27) Paule, R. C., Margrave, J. L., J. Phys. Chem. 67, 1896 (1963). (28) Pottie, R. F.,J.Chem. Phys. 44, 916 (1966). (29) Schäfer, H., Gerhardt, W., Tebben, Α., Angew. Chem. 73, 27, 115

(1961). (30) Schäfer, H., Heitland, H. J., Z. Anorg. Allgem. Chem. 304, 249 (1960). (31) Schäfer, H., Schneidereit, G., Gerhardt, W., Z. Anorg. Allgem. Chem. 319, 327 (1963). (32) Schäfer, H., Tebben, Α., Ζ. Anorg. Allgem. Chem. 304, 317 (1960). (33) Schäfer, H., Tebben, Α., Gerhardt, W., Z. Anorg. Allgem. Chem. 321, 41 (1963). (34) Stafford, F. E., J. Chem. Phys. 45, 859 (1966). (35) Stull, D. R., Sinke, G. C., ADVAN. C H E M . SER. 18, 1956.

(36) White, D., Seshadri, K. S., Dever, D. F., Mann, D. E., Linevsky, M. J., J. Chem. Phys. 39, 2463 (1963). RECEIVED October 24, 1966. Supported i n part by U . S. Atomic Energy C o m mission, Contract A T ( 0 4 - 3 ) - 1 6 4 .


Mass Spectrometric Study of the Noble Metal Oxides

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