4
Reaction of Platinum Dioxide with
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Some Metal Oxides
HENRY R. HOEKSTRA, STANLEY SIEGEL, and FRANCIS X. GALLAGHER Argonne National Laboratory, Argonne, Ill. 60439 The structure of platinum dioxide and its reactions with some di, tri, and tetravalent metal oxides have been investigated. Ternary platinum oxides were synthesized at high pressure (40 kilobars) and temperature (to 1600°C). Properties of the systems were studied by x-ray, thermal analysis, and infrared methods. Complete miscibility is observed in most PtO -rutile-type oxide systems, but no miscibility or compound formation is found with fluorite dioxides. Lead dioxide reacts with PtO to form cubic Pb Pt O . Several corundum-type sesquioxides exhibit measurable solubility in PtO . Two series of compounds are formed with metal monoxides: M PtO (where M is Mg, Zn, Cd) and MPt O (where M is Mg, Co, Ni, Cu, Zn, Cd, and Hg). 2
2
2
2
7
2
2
4
3
6
'Tphe literature on anhydrous binary or ternary platinum oxides is relatively limited. Muller and Roy (6) have reviewed the simple platinum oxides and were able to confirm the existence of only two oxides, P t 0 and Pt0 , with the dioxide existing in two crystal modifications. Shannon (13) has discussed the preparation and properties of orthorhombic Pt0 . Ternary oxides of platinum include several with the alkali metals (NaJPtsO^ Na Pt0 , L i P t 0 ) (12) and with the alkaline earths [Ba Pt 0 (18), Sr Pt 0 , and Sr PtO (10)]. More recent work has been reported on T l P t 0 (4) and the rare earth-platinum pyrochlores (3, 17), as well as the spinels Z n P t 0 and M g P t 0 (5). The investigations of platinum pyrochlores have demonstrated the effectiveness of high pressure techniques in the synthesis of anhydrous oxides when one or both reactants have limited thermal stability. The bulk of the work reported here represents a continuation of an exploration of metal oxide-platinum oxide systems at high pressure. 3
4
2
2
2
3
2
7
3
3
2
7
2
2
7
2
3
4
2
e
4
2
4
39 Rao; Platinum Group Metals and Compounds Advances in Chemistry; American Chemical Society: Washington, DC, 1971.
40
P L A T I N U M
G R O U P
M E T A L S
A N D
C O M P O U N D S
Equipment and Procedure T h e h i g h pressure a p p a r a t u s u s e d i n this w o r k is a t e t r a h e d r a l a n v i l apparatus. D e t a i l s of the e q u i p m e n t , the o p e r a t i n g p r o c e d u r e , a n d the sample assembly have been described previously (2) r e p e a t e d here.
B r i e f l y , the p o w d e r e d
and w i l l not
be
o x i d e samples are w r a p p e d i n
p l a t i n u m or i n g o l d f o i l to isolate t h e m , as m u c h as possible, f r o m r e a c t i o n w i t h m a t e r i a l s other t h a n the reactant m i x t u r e . W e s h a l l see t h a t o n Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 9, 2016 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0098.ch004
occasion the o x i d e samples w i l l react w i t h the p l a t i n u m f o i l c o n t a i n e r to g i v e l o w e r v a l e n c e p l a t i n u m oxides. A s a r u l e , three o x i d e samples, w h i c h h a v e b e e n w r a p p e d i n f o i l a n d pressed i n t o pellets, are l o a d e d i n t o the s a m p l e c a v i t y (•—1
cc v o l u m e ) of a p y r o p h y l l i t e t e t r a h e d r o n for e a c h
h i g h pressure r u n . I n a t y p i c a l e x p e r i m e n t , the t e t r a h e d r o n w i t h its three samples is c o m pressed to 40 k b pressure; the s a m p l e c a v i t y is h e a t e d to 1200 ° C a n d m a i n t a i n e d at that t e m p e r a t u r e for a n h o u r b e f o r e b e i n g q u e n c h e d room temperature.
F i n a l l y , pressure is released s l o w l y .
to
A l t h o u g h the
b u l k of o u r experiments h a v e b e e n r u n at 40 k b pressure, the range i n pressure a p p l i e d has v a r i e d f r o m 20 to 60 k b ; e x p e r i m e n t a l temperatures v a r i e d f r o m 500° to 1600 ° C . W e find that u n d e r these e x p e r i m e n t a l c o n d i t i o n s loss of a n a p p r e c i a b l e a m o u n t of o x y g e n f r o m the s a m p l e p e l l e t occurs v e r y r a r e l y , e v e n t h o u g h the oxides are h e a t e d to several h u n d r e d degrees a b o v e t h e i r d e c o m p o s i t i o n t e m p e r a t u r e at a t m o s p h e r i c pressure.
E x c e p t i o n s to this
r u l e o c c u r w i t h the f o r m a t i o n of a n y stable oxide phase w h i c h does not u t i l i z e a l l of the oxygen present i n the i n i t i a l reactant m i x t u r e . T h i s "excess" o x y g e n is lost r a t h e r r a p i d l y f r o m the s a m p l e enclosure. O u r i n v e s t i g a t i o n of the properties of the p l a t i n u m oxides i n c l u d e s x-ray, i n f r a r e d , a n d t h e r m a l analysis. P o w d e r x - r a y d a t a w e r e o b t a i n e d w i t h a P h i l i p s 114.59 m m c a m e r a , u s i n g either N i - f i l t e r e d C u r a d i a t i o n or V - f i l t e r e d C r r a d i a t i o n . C e l l parameters w e r e o b t a i n e d u s i n g a least squares refinement, a n d are b a s e d o n C u Κα = 2.2909. T h e dta-tga
1.5418 A a n d C r Κα —-
results w e r e o b t a i n e d o n a M e t t l e r r e c o r d i n g t h e r m o -
a n a l y z e r over the t e m p e r a t u r e i n t e r v a l 2 5 ° - 1 4 0 0 ° C , w i t h a h e a t i n g rate of 6 ° / m i n u t e a n d a s e n s i t i v i t y of 100 μΥ.
I n f r a r e d spectra to 200 c m "
w e r e t a k e n w i t h a B e c k m a n I R - 1 2 spectrophotometer.
1
N u j o l mulls were
s p r e a d o n p o l y e t h y l e n e disks for the l o w f r e q u e n c y p o r t i o n of the spec t r u m a n d o n K B r plates for the frequencies a b o v e 400 c m " .
Platinum
1
d i o x i d e w a s p r e p a r e d b y the r e a c t i o n of K P t C l 2
purity) with molten K N 0 s o l u t i o n of the K N 0 for several hours. than 0.2%
3
3
at 4 0 0 ° C .
4
or K P t C l 2
6
(99.9%
T h e dioxide was recovered
by
i n water and purified by heating i n aqua regia
S p e c t r o c h e m i c a l analysis of the p r o d u c t s h o w e d less
of a l k a l i metals, a n d no w a t e r or h y d r o x y l i o n w a s
Rao; Platinum Group Metals and Compounds Advances in Chemistry; American Chemical Society: Washington, DC, 1971.
detect-
4.
H O E K S T R A
E T
Reaction
A L .
Table I.
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41
Dioxide
X - r a y Powder Data for a - P t 0 a = 3.100(2)
Hexagonal
a
of Platinum
hkl
d
001 100 101 002 102 110 111 003 200 201 112 103 202 113 210 211 203 212 300 301 114 302
4.107 2.664 2.241 2.065 1.637 1.543 1.448 1.381 1.337 1.2734 1.2388 1.2287 1.1255 1.0309 1.0126 0.9841 0.9628 0.9111 0.8945 0.8752 0.8629 0.8218
c = 4.161(3)
2
A
I calcd
I obsd
a
100 100 170 15 100 50 70 10 25 50 40 50 50 40 40 90 45 115 30 60 80 75
60 100 90 10 60 90 70 1 45 50 30 15 35 5 55 55 20 60 35 40 20 100
Based on C d l - t y p e structure. 2
able b y i n f r a r e d analysis. M e t a l oxides u s e d i n the reactions w i t h P t 0
2
w e r e u s u a l l y reagent grade c h e m i c a l s ; exceptions i n c l u d e d oxides s u c h as F e O , C r 0 , M n O , M n 0 , V 0 , a n d M o 0 , w h i c h w e r e p r e p a r e d b y 2
accepted
2
procedures
3
2
2
f r o m reagent grade s t a r t i n g m a t e r i a l s . P u r i t y
of
these p r o d u c t s w a s c o n f i r m e d b y x-ray, t h e r m a l , a n d c h e m i c a l analysis.
Results «-Pt0 . 2
S e v e r a l proposals c o n c e r n i n g t h e structure of the a m b i e n t
pressure f o r m of P t 0
2
h a v e b e e n r e v i e w e d b y M u l l e r a n d R o y (6).
Diffi-
culties arise p r i n c i p a l l y f r o m the p o o r c r y s t a l l i n i t y w h i c h characterizes this phase, regardless of the h e a t i n g t i m e e m p l o y e d i n its p r e p a r a t i o n . D i s o r d e r is p a r t i c u l a r l y t r o u b l e s o m e i n the o d i r e e t i o n of the h e x a g o n a l structure since hkl lines w i t h 1 ^ 0
b e c o m e i n c r e a s i n g l y w e a k a n d diffuse
w i t h increase i n 1. O u r experience w i t h the synthesis of
