Hydrogen is emitted by aluminum heated in a vacuum after high-temperature steam treatment. Wire samples are tested for this effect, showing dependence on surface area. Two different mechanisms of absorption are inferred, and reactions deduced

Andreev, L. A.

Gelman, B. G.

Zhukhovitskiy, A. A.

English

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NASA TECHNICAL MEMORANDUM 
 NASA TM-75360
 
HYDROGEN ABSORPTION IN SOLID ALUMINUM DURING
 
HIGH-TEMPERATURE STEAM OXIDATION
 
L.A. Andreev, B.G. Gel'man, A.A. Zhukhovitski
 
(NASA-TM-7536) HYDROGEN-ABSORPTION IN 
 N79-14191
 
SOLID ALUMINUM DURING HIGH-TEMPERATURE STEAM
 
OXIDATION (National Aeronautics, and Space
 
Aditinistration) 11 p HC A02/MF A01 CSCL 11F Unclas
 
.. . ..-.. .. 
_ LG3/26 41029
 
Translation of "Pogloshchenie Vodorova Tverdym Alyuminiem pri
Vysokotemperaturnom Okislenii v Parakh Vody," Fiziko-khimicheskie 
Issledovaniya Metallurgicheskikh Protsessov, VoL. 1, 1973, 
pp. 90 - 94. 
RECEIVED 
NASA STI FAOIUTy . 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
 
WASHINGTON, D.C. 20546 JANUARY 1979
 
https://ntrs.nasa.gov/search.jsp?R=19790006020 2020-03-22T00:16:32+00:00Z
STANDARD TITLE PAGE 
1. 	 Report No. 	 2. Government Accession No. 3. Recipient's Catalog No. 
NASA TI1-75360 I 
4. 	 Title and Sublitle 	 S. Report Date 
HYDROGEN ABSORPTION IN SOLID ALUMINUM Jan. 1979 
DURING HIGH-TEMPERATURE STEAM OXIDA- 6. Performing Organ,zation Coda 
TION


7. 	 Author(s) 	 8. Performing Organizotion Report No. 
L.A. Andreev, B.G. Gel'man,


A.A. 	 Zhukhovitski 9 10. Work Unit No­
(Moscow Instituteof Steel & Alloys)
 

11. Contract or Groat ^. 
9. 	 Performing Orgonizatio Name cad Address NASW-3199 
Leo Kanner Associates, 13. Type of Report and Period Covered 
Redwood City, CA 94063


Translation 
12. S onsorlng Agency Name and Address 
National Aeronautics and Space Admin­

istration, Washington, DC 20546 14. Sponsong Agency Codo 
15. Supplementary Notes 
Translation of "Pogloshchenie Vodorova Tverdym Alyuminiem


pri Vysokotemperaturndm Okislenii v Parakh Vody," Fiziko­

khimicheskie Issledovaniya Metallurgicheskikh Protsessov,


Vol. 1, 1973, p" 9o - 94. 
16. Abstract 
Hydrogen is emitted by aluminum heated in a vacuum after


high-temperature steam treatment. Wire samples are tested


for this effect, showing dependence on surface area. Two


different mechanisms of absorption are inferred, and


reactions deduced.


17. Key Words (Selected by Author(s)) 	 18. Distribution Statement 
Unclassified-unlimited


19. Socurif' Classif. (of this report) 20. Security Clossif. (of this page) 21- No. of Pages 22. Price 
Unclassified Unclassified


NASA-HO


HYDROGEN ABSORPTION IN SOLID ALUMINUM DURING


HIGH-TEMPERATRE STEAM OXIDATION
 

L.A. Andreev, B.G. Gel'man, A.A. Zhukovitskiy


(Moscow Institute of Steel and Alloys)I


During vacuum heating.after.high-temperature.steam treatment, /90*


samples of aluminum release.significant amounts of hydrogen.


The greater part of this emitted hydrogen-consists of the so­

called "surface" hydrogen. The-process of emission of "surface"


hydrogen during' vacuum heating is still little studied. In


particular., theIej i a lack of data characterizing the kinetic


development of this process, which among other things is extremely


important to the study of the oxidation of metals in aqneous steam.


The process of.metal oxidation.and the growth of a protective


oxide layer is not limited to the external "oxide-gas" boundary.


It also proceeds, although to a much smaller extent, at the


"metal-oxide" boundary. When.metal is oxidized in steam, this


process, can'cause the hydrogenation--of the metal.since the


hydrogen..releasedby the oxidation beneathan oxide layer a:t


the "oxide-metal" interface.may dissolve into themetal.


This paper studies the absorption and emission of different


fractions of.hydrogen after steam.treatment of hydrogen. It


considers the.dependence of these processes on the properties


of the oxide layer and external conditions.


Method of. Investigation


The experiment used cylindrical aluminum samples.of equiva­

lent volume, 0.8 and 0.2 mm in diameter and 200 and.3200 mm long,


Numbers.inthe margin indicatepagination in the foreign text.


:1 
respectively, of type ABOO0. The samples were cleaned and then


soaked for 3 minutes in a 10% NaOH solution, followed by 3 min­

utes in a 10% HN0 3 solution.. After three hours of preliminary


heating at 600'C in a vacuum, the quartz tube containing the


samples.was cut off from the vacuumpumps, and the samples were


subjected to isothermal steam heating. At the end of the steam


heating, the system was pumped out again, during which tine the


samples were placed in an oven. In this .way the condensation of


the steam onto the oxide layer was avoided. Finally, the samples


were drawn from the oven and allowed to cool.


The decomposition of the- steam at the cathode of the omega­

tron gauge led to the formation of -hydrogen. To eliminate this


side effect which introduced an uncontrollable error into the


analysis of the samples, we mounted two liquid nitrogen traps


in front of the RMO-45 gauge. These completely absorbed the


steam, even at-momeentryfemissi6hsloo times greater than


occurred during the annealing of the samples.


During analysis the samples.were inserted,in turn into the


oven and heated to the temperature necessary to extract the gas.


Any water vapor was caught by the traps, while the emitted


hydrogen was continuously pumped through the omegatron gauge.


The total amount of emitted.hydrogen was the area under the


curve drawn by the automatically recording pen [1].


Interaction.of Steam.and Aluminum


We determined the amount of hydrogen emitted by samples,of /91


aluminum wire during vacuum heating after their exposure to


steam at ,200, 400, 500, and 6000C for different periods of time.


In all cases when the duration of steam exposure was increased


above 30 minutes, the amount of hydrogen reached a certain lim­

iting value and was subsequently unchanged. Table 1 presents


these characteristic limiting values for a.steam partial pressure


2


TABLE 1. of 18 mm Hg. It follows 
HYDROGEN CONTENT, IN CM3/100 G, from the table that the


EMITTED BY ALUMINUM SAMPLES DURING VACUUM amount of hydrogen emitted


HEATING AFTER 30 MINUTES' EXPOSURE


TO STEAM AT 18 NM HG after exposure to steam at 
200 and 400 0 C is perhaps 
Surface 
area, cm 
Steam temperature, OC 
200 I 400 500 I600 
1.5 times greater from the 
samples of wire with the 
5 0.08 0.07 0.09 0.05 smaller area (when dia. = 
20 0.05 0.05 0.09 0.05 0..8 mm, a = 5 cm 2 ) than 
from the samples of larger 
surface area (when dia. = 0.2 mm,. = 20 cm2 ). On the other hand, 
the amount of hydrogen emitted after exposure to steam at 500 and


60,0°C is the same for samples of different surface area.


This circumstance prompts the hypbqthesis of different types


of hydrogen retention by aluminum interacting with water vapor.


It also points out the essential-difference in the characteristic


parameters of the emission of hydrogen from samples after steam


treatment at these two ranges of temperature. Since the diffu­

sion coefficient of hydrogen in aluminum in the range 200-4000 C


is extremely small, it is natural to assume that the accumulation


of hydrogen during interaction withwater proceeds mainly as a


result of a process of adsorption (,which is possible in the form
 

of an OH- group). At higher temperatures, the actual absorption


of hydrogenby the metallic samples becomes possible. Thus, the


mechanism of its emission during the subsequent heating in a


vacuum will be.different.


The. characteristic parameters of the kinetics of hydrogen


emission during vacuum heating were determined from the curves


of gas emission recorded by the automatic pen. The curve measur­

ing the partial pressure of hydrogen gas during the heating


typically contains a maximm;, it represents the result of two


processes, the emission of gas at the rate I and the pumping out


3 
of gas at the speed S. Thus-,


VdP=Idt
- SPdt, 
where P is the .partial pressure of hydrogen in the system;


V is the volume of the system.


After integrating (1) and assuming that I declines exponen­

tially with time, we use the .linear relation between the signal


of the omegatron gauge, h, and the.partial.pressure of hydrogen,


P = mh, to obtain:


;h-
 Cok [exp (-t) - exp (-At)], (2)

ml'(A-k) 
where Co is the initial concentration of hydrogen in the sample;


k is the gas emission constant;


A E S/V is. the pumping constant.


The experimental curves were treated in accordance with /9-2


equation (2). The values of the constants k and A,were obtained


from the straight line formed by the experimental curve h = h(t)


in the co-ordinates 
h- [exp (-ki)- exp (--At)].. 
The calibration,value of the pumping constant A was deter­

minedby a preliminary experiment .[l]. The error in,k determined


by this method does not exceed 20%. The values.of the.constant


obtainedin this manner are incorporated in Table 2.


Table 2 indicates that the coefficient k of.samples subjected


to steam treatment at 200-400C depends,neither on the geometric


surface area of the sample nor on the. duration of the steam treat­

ment (at least,, in the interval l-30.0.minutes-). The energy of


activation of hydrogen emission, which is .obtained from the


temperature dependence of k, is.about 21,000 cal/mole after


30 minutes' exposureto 4000,C steam at 18 mm Hg. On the other


4 
hand, in the temperature range 500-600°C, the rate of hydrogen


emission during subsequent vacuum heating,depends substantially


on the sample surface area and the length of exposure to the


steam. The ratio of the coefficients of gas emission for samples


of different surface area, ka=o0/k,= , is 3 to 3.5.


TABLE' 2. The hyrogen absorption 
DEPENDENCE OF THE RATE CONSTANT k(ain)' during steam treatment 
OF HYDROGEN-EMISSION: ON THE,TEMPERATURE


AND DURATION OF STEAM TREATMENT AT depends on the means used 
18 NM HG (-VACUUM HEATING AT 6000C) to prepare the sample. In 
Steam Sur- Exposure time, minutes particular, with a complete 
Steam face - surface treatment (etchingtemp., area, 2 [ISO1 300 ±42vacuum heating),
 
0-
­

oc aea 30 + absorbed 
hydrogen is observed in
200 5 - 0,8 0.8 - - ­
20 - 0.8 0.8 both temperature ranges 
400 5 - 0,8 0,70 - 0.70 ­
20 - 0:8 0.80 - o80 - only in thin wire samples 
500 5 0,37 - o30 0.20 - 0,10 (dia. of 0.2 and 0.8 mm),20 1:20 - 1.00 0,70 - 0,35 
600 5 0,35 - 0,-5 0)10 0,10 0.10 while thicker (4 mm dia.)
'20 1.00 - 0.50 0A35 0,35 0,352samples, 
 
also cold drawn,


do not display this effect.


Obviously, the crystallographic nature of the oxide layer on


aluminum does not depend on the diameter of the wire; conse­

quently, the observed effect is related to a certain type of


inhomogeneity in the structure of the surface. In the contrary


case, that is, assuming samples with homogeneous surfaces, we


would expect an effect to be observed in every trial.


The three types.of aluminum samples, naturally, differ-in


the extent of preliminary baking and structural peculiarities.


The thin samples were obtained by means of prolonged baking,


and they were characterized by a "bamboo" structure. The thick


samples (4 mm in dia.) were polycrystalline in structure. It


is quite natural to relate the observed phenomenon of hydrogen


5 
absorption by aluminum with the special structural feature of


the surface, the edges of the bamboo sections, which during


the prolonged.baking .cause the recrystallization of the material


in the stage of cold deformation. On these sections, which are /93


distinguished by an elevated corrosion activity, it is possible


for the corrosion products to accumulate, creating a surface
 

for development and an adsorption capacity. On the other hand,


the oxide layer is essentially disturbed near these section
 

edges, which reduces their resistance to further oxidation, and


this is probably the fundamental source of the volume hydrogena­

tion of the metal. This process can be expressed as the total


reaction


2AI +3/2HO=A1 20 3+3 [H]. 
As the dependence of the.coefficient k on the sample surface
 

area indicates, however, the entire surface takes part in the


emission of hydrogen during vacuum heating. The process possibly


involves a limited amount of penetration by hydrogen across the


oxide layer to the metal.


As a result of special surface treatment (in this case,


steam treatment at 600 0C and 10 mm Hg for one hour), the thick


cylindrical,samples also acquired an absorption capacity for


hydrogen during high-temperature steam oxidation. We obtained


the effect, to be specific, as a result of boiling the samples


in distilled water for 4 hours and heating them in a vacuum for


3 hours at 60O0 C. The experimental results were as follows:


Sample weight, g: ... ..... 	 0,250 0420 0,480 0,800 1,480


0,062 0,061 0,063 0,062 0,057
Hydrogen, cm 3/100 g: 
 .......
 
The proportional increase in the amount of hydrogen emitted,


during vacuum-heating at increasing sample weights,, is evidence


of volume absorption of the hydrogen by the mass of aluminum.


6 
Just as in the case of the samples of thin wire, we observe


local sections on the surface of the massive samples boiled


in water which, upon,subsequent high-temperature steam treatment,


developed intensive oxidation of the metal and simultaneous


volume hydrogenation.


The generation of "surface" hydrogen upon the .vacuumheating


of samples after preliminary steam treatment at comparatively


low (400 0C) temperatures is probably caused by OH- groups which


are strongly absorbed on the aluminum oxide in local sections


of the surface of the samples. The treatment of the oxidized


samples withsteam creates a layer of absorbed,ions, thus:


1.3H2 + 3 (e/A) -+ 3(OHAac+ 3/H 2 . 
During the subsequent vacuum heating, the following reactions

take place:
 Z11 	 kzno- I-j-6 (~e/Al1); 
-3. 3(e/AI)-42 (AIg)). 1-3 (OH-a c+ A!203+5 /2H41, 
where 	 (e/Al) are electrons in the conducting band of the metal;


(Al03+) are cations between TattiCe o8:es (internodal).


We must realize that the slowest stage of the oxidation of


Al is reaction 2, the process of dissolving cations into the


internodal layers of oxide 12]. This process must be assisted


by an electrostatic polarity, created as a result of the adsorp­

tion of negatively-charged particles on the exterior surface at


the "oxide-gas" interface. If E is the electric field strength,


no the number of ions per cm2 of the surface of the metal, D the


diffusion coefficient of the ions, then the cation current


across the.oxide layer,, according to [2], is equal to:


I=D~n0, 	 (3) 
Since in this case the oxidation proceeds due to an adsorbed


layer, to that extent, the process of depositing OH- groups on /94


7 
the surface.will slow down. Consequently, at E­

(where is the thickness,of the oxide layer;
, 
nOH_ is. the concentration-of hydroxide ions on the surface;


is the dielectric constant of the oxide)-,


then


tidt14x 2D.n 0 nH-I / 
The final .expression,for j, after the integration of (4), is


(5)


In this case, the gas emission constant, k, is essentially


independent of the sample surface area. There is an approximate


correspondence of the activation energy of the process (21,000


cal/mole) with that calculated earlier from the data on the


kinetics of oxidation [2]. This ,supports the.assumptions made


concerning the limited extent-of emission of hydrogen during


vacuum heating.


8 
REFERENCES


1. Andreev, L.A., and B.G. Gel'man, Zav. lab., 1971 (10).


2. Grimli, T., "Oxidation.of metals," in: Khimiya,Tverdogo


Kaostoyaniya 	 ("Solid State Chemistry"), Moscow, IIL,


1961, p. 479.


9 


Hydrogen absorption in solid aluminum during high-temperature steam oxidation

Abstract

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