Hydrogen and oxygen effects on nickel surface, ammonia catalysis on tungsten surface, and work function measurements on tungsten crystal plane

Germer, L. H.

English

NASA Technical Reports Server

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Annual Progress Report for 1967 - 1968 
t o  the 
National Aeronautical and Space Administration 
by- 
Lester H a  Germer 
"CHEMICAL REACTIONS AT METAL SURFACES" 
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May 1, 1967 to April 30, 1968 
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1 Research Contract NGR 33-010-029 
Principal Investigator: Lester H. Germer 
Department of Applied Physics 
Cornel1 University 
Ithaca, New York 14850 
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(ACCESSION NUMBER) (THRU) - 8 d I I 
(PAOESJ (CODE) 
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https://ntrs.nasa.gov/search.jsp?R=19680012732 2020-03-12T09:01:39+00:00Z
During the year from May 1, 1 9 6 7  to April 30,  1968 ,  the 
following people have worked on this project: 
L. H. Germer Principal Investigator 
J. W. May Postdoctoral Fellow 
R .  J. Szostak Postdoctoral Fellow, on leave from 
Fritz-Haber Institute, Berlin, 
Germany. He returned to Germany 
in December 1 9 6 7 .  
C. C. Chang Graduate Student: received Ph.D. 
degree and is no longer here. 
J. C. Tracy Graduate Student 
We have published during the year: 
"Thermally Ordered Oxygen on a Nickel Surface", 
L. H. Germer, J. W. May and R. J. Szostak, Surface 
Science - 7, 430-447 ( 1 9 6 7 ) .  
"Oxidation of the (112) Face of Tungsten", 
C. C. Chang and L. H. Germer, Surface Science 
8, 1 1 5 - 1 2 9  ( 1 9 6 7 ) .  
The reprints of each of these two papers were sent to NASA. 
do not review them here. 
We 
We have now in press the following papers: 
"Incipient Oxidation sf (110) Nickel", 
J. W. May and L. H. Germer, accepted for 
publication in Surface Science, 
Five copies of the manuscript of this paper were furnished to 
NASA in February 1 9 6 8 .  Reprints will be sent as soon as avail- 
able. 
"Temperature Controller for LEED Experiments", 
J. C. Tracy, submitted to Review of Scientific 
Instruments, March 28,  1 9 6 8 ,  
Five copies of the manuscript of this paper are attached to this 
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report, It is not reviewed here. 
We have completed the manuscript of a paper: 
"Hydrogen and Oxygen on a (110) Nickel Surface", 
J. W. May and L o  H. Germer 
This will be presented at the Fourth International Materials 
Symposium to be held at Berkeley, California June 17-21, 1968. 
It will be published in the book of the Conference. The work 
will be reviewed only briefly below, Five copies of the manu- 
script are attached. 
The manuscript of another paper will be ready for publi- 
cation in a few more weeks: 
"Ammonia Adsorption and Decomposition on a Tungsten 
(211) Surface'', J. W, May, R ,  J. Szostak and L. H. 
Germer e 
This will be sent to the Journal of Chemical Physics or to Sur- 
face Science. Five copies of the manuscript will be sent to,NASA 
as soon as available. This work is reviewed briefly below. 
The following additional projects are under way: 
"Work Function and Surface Structure Corre- 
lations in the Adsorption of Oxygen on Single 
Crystal Planes of Tungsten", J. C, Tracy and 
J. M. Blakely (J- M e  Blakely is Associate 
Professor, working on LEED investigations 
but not supported by this contract), 
This paper will be presented at the Fourth International Mater- 
ials Symposium to be held at Berkeley, California June 17-21, 
1968. This paper is reviewed very briefly below. 
Additional research work by J, C .  Tracy, not covered 
above, is also reviewed briefly below. 
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BRIEF REVIEWS OF ACCOMPLISHMENTS 
The paper, "Incipient Oxidation of a SllOP Nickel Surface", 
which is in press,represents, in the opinion of the Principal 
Investigator, a major contribution to the understanding of 
corrosion processes, It presents and establishes new and basic 
views about corrosion of potentially great importance. But, 
because copies of the manuscript are already in the hands of 
NASA, this work is not reviewed here. 
"Hydrogen and Oxygen on a (110) Nickel Surface" 
This paper is divided into three parts. In the first part, 
evidence is brought forward that the nickel atoms on this single 
crystal surface are rearranged at room temperature when the sur- 
face is exposed to hydrogen. This alters previous views about 
adsorption and, in the opinion of the Principal Investigator, is 
one of the most important results ever found in the study of sur- 
faces. 
evidence presented here is the most conclusive so far found. The 
This conclusion has been promulgated before but the new 
second part of t h i s  paper describes the reaction at room tempera- 
ture of oxygen with a surface previously covered by hydrogen. 
The stronger adsorption of oxygen is found to dominate the situa- 
tion and most of the adsorption of oxygen takes place just as if 
the hydrogen were not present, 
described the reaction of hydrogen with an oxygen covered surface. 
In the third part of the paper is 
The efficiency of Fernoval of oxygen varies between 10 -5 at 400°K 
to the highest measured value of O r 0 2  at 800°K, At intermediate 
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templeratures the growth of islands of clean metal modifies greatly 
the course of the reaction. 
rather well known increase of rate of reduction of oxide with 
time. This was described in Langmuir in 1922 (and by others) 
but heretofore has not been understood. 
It leads to an understanding of the 
"Catalytic Decomposition of Ammonia on a Single Crystal Tungsten 
Surf ace" 
Ammonia is adsorbed upon a tungsten surface without decompo- 
sition. 
evolved at 500°K leaving NH2 radicals on the surface. 
come well ordered at about 800'K into a rather simple structure 
in which the nitrogen atoms are bound to each other by hydrogen 
When a surface covered by ammonia is heated, hydrogen is 
These be- 
bonds in a single monolayer lying upon the surface. 
above this temperature some hydrogen and nitrogen are evplved with 
continuous stretching of the hydrogen bonds and expansion of the 
structure in the [llO] surface direction. 
about 12 percent the bonds break and the NH2 radicals are held 
independently to the surface with an arrangement which is not 
detectably influenced by the presence of attached hydrogen, i.e. 
the arrangement seems to be same as that of pure nitrogen. 
1200°K this NH2 is vaporized from the surface in the form of N2 
and atomic hydrogen. This work represents, in the opinion of 
the Principal Investigator, a major advance in underetanding 
catalytic processes. 
With heating 
At an expansion of 
At 
"Work Function and Surface Structure Correlation in the Adsorption 
of Oxygen on Single Crystal Planes of Tungsten" 
Work function changes have been measured by the Kelvin 
method. Work function has been found to increase on all tungsten 
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crystal planes with oxygen coverage. 
one monolayer coverage on the (1121 plane, interpreted as depol- 
arization between surface dipoles, but on other planes alteration 
is monotonically increasing. 
A minimum develop$ at about 
Other Research.of J. C. Tracy 
The tungsten crystal planes (112) and (100) develop (110) 
faaets when covered by oxygen aKd heated. Under the same condi- 
tions, the (111) planes develop first (112) facets and then 
(110) facets upon the already formed (112) facets, After oxygen 
and heat treatment all of these surfaces have the same work 
function, as one might expect from the fact that the final sur- 
face facets are crystallographically identical. 
constituting the Tracy Ph.D- thesis, is nearly completed. 
This work, 
A Few Closinq Comments 
The Principal Investigator has pbblished twenty-five ( 2 5 )  
papers in this field since coming to Cornel1 in December 1961. 
The LEED technique was originally developed by the Prin- 
cipal Investigator. Commercial equipment is being built now by 
at least a half dozen manufacturers in at least three different 
countries. These are being used in about 100 laboratories in 
at least 8 different countries. (U.S,A,, England, Japan, France, 
Germany, Netherlands, Russia and Sweden,) Because of his 
beginning work in the field of this proposal, a very considerable 
fraction of the best work published up to this time has been 
carried out by the Principal Investigator, His positleon in the 
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field is still dominant, 
The experimental procedures in has laboratory at Cornel1 
University have n o t  yet been so well developed in any other 
laboratory in the world. The equipment is in excellent oper- 
ating condition. Its replacement value is greatly in excess of 
$60,000. 
Proposals 
The work on ammonia decomposition has been planned and 
carried out by Dr. J. W e  May and Dr. R. J. Szostak. Dr. May 
goes to the Bartol Research Foundation of the Franklin Institute 
on September 1, 1968. Up to this time he hopes to extend the 
work to cover a few features which are not yet clear. 
formulated plans for experiments on ammonia synthesis to be 
carried out during the coming year. 
We have 
The Principal Investigafior will also extend the investi- 
gation of oxidation to develop models of how individual oxygen 
and metal atoms move upon a surface under the driving force 
resulting from the energy of oxygen adsorption. 
Lester H e  Germer 


Chemical reactions at metal surfaces Annual progress report, May 1, 1967 - Apr. 30, 1968

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